NPTEL - Biomass refinery book.pdf

INDEX
S.NO TOPICS PAGE.NO
Week 1
1 Lec 1 : Energy and Environment scenario 3
2 Lec 2 : Need for biomass based industries 41
Week 2
3 Lec 3 : Biomass basics 72
4 Lec 4 : Dedicated energy crops 112
5 Lec 5 : Oil cropns and microalgae 156
6 Lec 6 : Enhancing biomass properties 198
Week 3
7 Lec 7 : Basic concepts and types 242
8 Lec 8 : Feedstocks and properties 269
9 Lec 9 : Economics and LCA 308
Week 4
10 Lec 10 : Barriers and Types 342
11 Lec 11 : Dilute acid, alkali, ozone 378
12 Lec 12 : Hybrid methods 422
Week 5
13 Lec 13 : Physical Processes 453
14 Lec 14 : Gasification and Pyrolysis 499
15 Lec 15 : Products and Commercial Success Stories 550
Week 6
16 Lec 16 : Types, fundamentals, equipments, applications 594
17 Lec 17 : Details of various processes 637
18 Lec 18 : Products and Commercial Success Stories 673
Week 7
19 Lec 19 : Diesel from vegetable oils, microalgae and syngas 696
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20 Lec 20 : Transesterification; FT process, catalysts 738
21 Lec 21 : Biodiesel purification, fuel properties 774
Week 8
22 Lec 22 : Biooil and biochar production, reactors 824
23
Lec 23 : Factors affecting biooil, biochar production, fuel properties
characterization 867
24 Lec 24 : Biooil upgradation technologies 909
Week 9
25
Lec 25 : Microorganisms, current industrial ethanol production
technology 953
26 Lec 26 : Cellulase production, SSF and CBP 989
27
Lec 27 : ABE fermentation pathway and kinetics, product recovery
technologies 1020
Week 10
28 Lec 28 : Biohydrogen production, metabolics, microorganisms 1060
29 Lec 29 : Biogas technology, fermenter designs, biogas purification 1092
30 Lec 30 : Methanol production and utilization 1126
Week 11
31
Lec 31 : Biomass as feedstock for synthetic organic chemicals, lactic
acid, polylactic acid 1154
32 Lec 32 : Succinic acid, propionic acid, acetic acid, butyric acid 1195
33 Lec 33 : 1,3-propanediol, 2,3-butanedioil, PHA 1225
Week 12
34 Lec 34 : Concept, lignocellulosic biorefinery 1250
35 Lec 35 : Aquaculture and algal biorefinery, waste biorefinery 1288
36 Lec 36 : Techno-economic evaluation 1326
37 Lec 37 : Life-cycle assessment 1359
2

Biomass Conversion and Biorefinery
Prof. Kaustubha Mohanty
Department of Chemical Engineering
Indian Institute of Technology – Guwahati
Lecture 01
Energy and Environment scenario
Good morning students. As you know, today is the first lecture of Biomass conversion and
Biorefinery. As I told you in our introduction slide, we will be covering two lectures basically
dedicated to introduction. So, today is the first one in which we will be covering world
energy scenario, consumption pattern, fossil fuel depletion and environmental issues. A bit
more elaborately I will tell you, how the fossil fuel depletion is taking place, what is the
energy requirement, how renewables are taking shape into big component in the next few
years of energy consumption as well as production and how the climate mitigation problems
are also taking shape with respect to global carbon dioxide sequestration.
(Refer Slide Time: 01:27)
So, as you know, there are institutions such as the International Energy Agency (IEA), the US
Energy Information Administration (EIA) and the European Environment Agency (EEA).
These are the three Agencies which record and publish energy data periodically. You will get
all these data, and, even whatever I am discussing today, mostly has been taken from their
records. Improved data and understanding of world energy consumption may reveal systemic
trends and patterns, which could help frame current energy issues and encourage movement
towards collectively useful solutions. The current policies scenario shows what happens if the
world continues along its present path, without any additional changes in policy. In this
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scenario energy demand will rise by 1.3 % each year till year 2040. So, basically this is how
it is being predicted.
This scenario charts a path fully aligned with the Paris agreement by holding the rise in
global temperatures to well below 2 °C. That is what the Paris agreement says about that
temperature rise should not be more than 2 °C. And they are still pursuing efforts and
convincing all the signatories of this agreement to limit it to 1.5 °C.
Electrification is emerging as the key solution for reducing emission. Now, you know that in
many developing countries and rather underdeveloped countries, electrification is still a big
issue; including India and most of the so-called Asian giants or giant/big economies. This is
however taking shape in a very nice way and increasingly it can be sourced at the lowest cost
from renewable energy. So, basically electricity from renewable energy; that is how it is
being envisaged.
There is something called tonne of oil equivalent (toe) which is a unit of energy and basically
defined as the amount of energy released by burning 1 tonne of crude oil.
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So let us understand the energy classification or how energy is being classified. So, primary
and secondary energy, commercial and non commercial energy, renewable and non-
renewable energy. Primary energy sources are those that are either found or scored in nature,
e.g. coal, oil, natural gas, biomass, nuclear energy etc. Secondary energy is mostly converted
in industrial utilities from other sources of energy (such as) coal and oil, all these things.
So when you talk about commercial and non-commercial energy, in commercial energy it is
electricity, lignite, coal which are commercially available. Non-commercial energy is
basically fire wood, cattle dung, agricultural waste, biogas etc. It also includes wind energy.
Then comes renewable or non-renewable sources. The renewable sources are essential
inexhaustible. E.g. wind power, solar power, geothermal, tidal, biomass and hydroelectric
power. Non-renewable energy are conventional fossil fuels such as coal, oil, gas which are
basically depleting with respect to time.
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So, if you look at the energy mix of world and India, I will be showing so many of these
statistics which are taken from these environmental energy associations and other societies.
This is from Niti Aayog. So, you can see in the energy mix of the world how much is actually
being consumed in the entire world in the form of oil and coal. So they are the most
important.
So if you look at India, 58.1 % comes from the coal and it is a very big number. The rest is
from oil and very few from hydroelectric and other sources. Now, renewables as you can see
is 2.2% and it is slowly increasing. We project that around 2035-2040 it will be more than 10
to 12%.
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Now let us understand the world total primary energy supply, consumption and demand by
source and region.
This is the world primary energy supply from 1971 to 2017 by source. If you see that round 1
(pie chart), you can see that in 2017 coal is 27%, oil is 32%. These two are more than 50%.
Rest are natural gas, bio-fuel wastes and other sources such as hydro and nuclear sources.
Similarly, if you see by source, again you can see that oil is the major one. This is the
consumption pattern by source. So oil is the major followed by natural gas, electricity and
bio-fuel.
So this is the supply in terms of region. You will see that there is something interesting. You
can see from the round 1 (pie chart) that only China accounts for 22% and OECD countries
for 38%, India actually lies in the red zone, which is non-OECD Asia. It accounts for 13.5%
out of which India is almost more than 50% which is a very significant number.
So China and India together are supplying a huge amount of energy required in the total
Global energy supply.
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So if you talk about the final consumption, again OECD is followed by China and the non-
OECD countries, the same pattern. The energy consumption pattern as well as the energy
supplied pattern is almost same.
So if you look at this particular slide, this talks about the top five countries total primary
energy supply. So, if you go by sector then you can see that the People's Republic of China
stands first followed by United States of America, India, Russian Federation and Japan. Now
if you look at the second plot that side, you can see that China’s steel consumption is actually
hugely dependent on coal followed by oil, natural gas and renewables.
And India almost follows the same pattern. However, you can see that in India the
renewables are increasing day by day. That is very interesting and that is because the
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Government of India has so much of thrust and excellent policies on actually renewables. So
if you look at this again, top 5 countries total primary energy consumption, you will see that
China’s iron and steel is followed by chemical and petrochemical, followed by non-metallic
minerals. These are basically industry based consumption patterns. And India also is
following the same trend except that the chemical and petrochemical is a very small one and
in non-specific industries it is more. Because of these non-specific, under that basically
small-scale industries comes up and you know in Indian economy small scale industries play
a very big and crucial role.
So, what if the world continues on its current path with no additional changes? So, what if we
reflect today's policy intentions and targets? This is the Stated Policies Scenario (STEPS) or
the New Policies Scenario (NPS); what we are going to adapt basically, the NPS. There is
something called the SDS, which is basically meeting the sustainable development goals. We
call it the sustainable development scenario. So, whether it is NPS and SDS or both, this is
how actually now things are being decided.
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So, if you look at the Global total primary energy demand, that is going to have a plateau
after 2035 (projection basically), even if there is a strong population expansion as well as
economic growth. So, if you look at this, the Global total energy demand will have a
plateauing effect at 2035 or beyond 2035, primarily driven by the penetration of the
renewable energy sources into the energy mix.
As more renewables are coming into picture, they are taking a big thrust of the entire energy
supply as well as consumption pattern. So, you can understand, that is why actually there will
be a plateauing effect after 2035. So, also falling energy intensity offsets the effects of a
growing population with increasing income levels, leading to a slowdown in the energy
demand growth.
So, energy intensity actually falls as service industries take up large share of the global
economy. That is what is happening in most of the developing countries, where the service
industries are playing a big role in the economy as well as in Energy consumption basically.
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So, if we look at how the projection looks actually; so you can see that there is something
interesting here; despite a doubling of global GDP between 2016 and 2050, the global
primary energy demand actually grows by 14%. So this is a projection towards 2050, which
you can see here. So, it is the first time in history that growth in energy demand and
economic growth are decoupled. So, this is very interesting. The first uptake of renewables is
a key driver as they often substitute for fossil fuel based generation technologies with low
efficiency.
So, renewables complemented by nuclear, nuclear power, basically, will almost double their
share in the overall energy mix (from 19% to 34%) and will provide more than half of the
electricity by 2035. So, what we understand from this particular slide is that, renewables
along with nuclear power is going to substitute almost 50% of the total energy supply after
2035 in most of the countries.
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So if you have an understanding of the total primary energy supply by 2040; this is a
prediction. You can see that, if you look at this slide, coal is continuously getting depleted.
And similarly, the natural gas though it is taking a shift after 2035. It will slowly it will come
down. Similarly, there are other sectors also.
And if you look at the sector wise, so we will understand that in a sustainable development
scenario, industry, transport, building and agriculture, these are the major shares. And if we
look at the new policies scenario, it is all the same thing; only the net amount or the net
percentage varies a little. Otherwise they easily complement each other.
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So this is the global energy demand in stated policy scenario. So you can see that, there is
something interesting, how the wood is getting decreased. Initially, long back when we
started 19th
or early 18th
century, so you can see that the wood was the primary source of
energy. Slowly it gets depleted and the use of coal has increased. Then oil has come into
picture and now slowly fossil fuels are depleting. So we have to depend more on the nuclear
and modern renewables. And those are taking the major amount of the energy supply and of
course demand also.
Global energy demand per fuel, if you look at, you see that in this particular plot, you see that
renewables and other fuels after 2035, here, every other thing, whether it is gas, oil or coal, it
is getting depleted or getting a plateauing effect after 2035. But renewables are increasing.
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So, this is what it tells us that due to the policy intervention by most of the governments
across the world, there is more focus on the development of renewables.
So that is why renewables and other fuels are taking a steady curve or the curve is increasing
and not depleting.
So this is interesting. If you look at this, it is about electricity. So, if you look at this
particular slide, this and this, you just understand that 36% of oil, 14% coal, 16% of natural
gas and only 19% electricity. As you move beyond 2016, this is up to 2016. And as projected
up to 2050, you can see electricity is going to take the centre stage with 49%. See it is 50%.
Half of the main energy source will be by electricity. Followed by the modern bio-mass, bio-
energy, what we are going to discuss in our lecture, basically in this course. So you can
understand how the policies are actually driving all the Global major economies, including
the small economies also across the world to focus on the renewables and including
electricity. So mostly it will be electricity. And again, electricity can be hydropower, it can be
nuclear power and it can be from other renewables also.
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So, this particular slide tells us that India along with China emerges as the key driver for
global energy market. Another interesting observation is about Africa; the entire African
countries, in the last one (bar graph) as you can see here. You can see here, how China and
India are taking shape in 2040 (this is a projection till 2040). This is total population by
region. So in China, India and Africa (Africa means African continent and not South Africa),
you see their projected oil demand, see their natural gas demand. India is falling in the natural
gas demand because we are not yet moving into the gas natural gas. However, China has
surpassed all of us. And if you look at the renewables, you see that India is playing an
interesting role, a very big role. And of course Africa also.
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So, we will see different energy sources, their supply, consumption and demand by source
and region. We will just quickly glance through it. So the first one is crude oil.
So you can see the world oil crude oil production from 1971 to 2018 by region. And you can
see that, OECD is of course 26.8% and Middle East (33.2%). So OECD and Middle East is
close to almost 60%. The rest is non-OECD Europe and Eurasia, then China, Asia and other
countries.
So mostly it is coming from the Gulf countries and OECD countries. If you see the final
consumption from 1971 to 2017 by sector, you can see that road, or the transportation sector
basically is almost 49.2%, followed by navigation, aviation and non-energy use sector.
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So, similarly if you see the refinery output, you can see that mostly it is coming from the
middle distillate, followed by the motor gasoline, fuel oil and then LPG, ethane, naphtha and
other products.
Let us now understand the oil demand growth, how it looks like beyond 2030-35 and till
2050. So you can see that oil demand has grown more than 1% per annum for over the last
three decades. But, this growth is expected to slow down significantly from 2020 onwards.
So from the current year onwards. The reason is due to the (fact that) more and more recent
development of the electric based systems or we are depending more on the electricity rather
than other sources of energy.
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So there is a projection of a peak in 2033. Beyond 2033 there will be a plateauing effect
again. So, by 2050 demand is projected at almost 30 million barrels per day (bpd), which is
one-third (times) below today's demand as of now. So, the chemical sector which is an
important engine of growth for the oil demand shows a slow down with respect to post 2030
projection.
Why? The reason is that, there is an increased rate of plastic recycling. That is also very
interesting now. So you know that more and more plastic recycling is happening. So that is
why there will be a plateauing effect after 2030 specially in the chemical sector.
Now when you talk about the chemical sector, more than half of the oil demand growth will
be for the next 15 years. Until 2035 chemicals is the biggest demand growth sector, and then
there will plateauing effect. So, oil use in power is the largest declining sector beyond 2030-
35. So the decline in oil demand for the road transport is modest as the EV is coming into
picture.
There are 2 things, first is EV (the electric vehicles basically). Mostly it is a huge transition in
the OECD countries. They are almost going for EV (they are already doing it). And China is
partially offset by continued use of the ICE vehicles. Though the OECD countries are going
more into the EV; however, China being one of the largest economy in Asia as well as by
population or by energy use and as well as by consumption, still China is going to continue
the ICE (that means the internal combustion engine) vehicles. So that is why in Asia it will be
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little less. Aviation growth is most prominent in non-OECD Asia and hub countries such as
Dubai.
Then, let us understand coal. So, if you look at the total final consumption from 1971 to 2017
by sector, you will see that oil is 41%, followed by electricity, natural gas and interestingly
you see biofuel, 10.7% (it’s a big one). So it is up to 2017. So understand that, beyond that
how the biomass based industries, bio-fuels that are coming from (different) other sources
(waste sources) is going to shape up our economy.
So, the world production of coal by 2018, if you look at this round one (pie chart), you can
see that China is almost half (45.6%). India comes under the non-OECD Asia (this red
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portion) (almost 30% to 35% under that is from India) and of course followed by the OECD
and other countries.
So here, if you look at this particular slide, you can understand that 40% decline in coal
demand happens despite the substantial growth of coal use in India as well as other non-
OECD Asian countries. This is basically driven by China’s decline in coal use. So that is also
very interesting right; with the decline of 53 million TJ, this is equal to two thirds of today's
total demand in China. So, all these things have driven our focus towards renewable.
Then again, we will quickly understand natural gas, the way we have discussed about coal
and oil. So Natural gas supply, consumption and demand.
20

So, here you can see that natural gas production. So, mostly it is by the non-OECD European
countries and OECD countries (close to 60%). And India has a very minimal role to play
here.
So, for the final consumption; of course industry is the most important one, followed by the
residential areas and then commercial and public services.
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Then, when you talk about natural gas, so it is the only fossil fuel which grows its share of
total energy demand. You must understand that, among all the fossil fuels this is the only
fossil fuel (natural gas) whose demand is continuously growing for the various advantages it
has over other fossil fuels. So, particularly in short-term till 2025 and mid-term (2035) gas
demand continues to grow across all sectors led by industrial demand.
The plateauing of demand which is happening after 2035, as we can see here, almost there is
a plateauing of demand here. So, it is driven largely by the increasing competition from the
renewables. So, the Oil and Gas Industries’ own use of gas is expected to remain in line with
the total gas demand.
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So these are certain things (points to be noted on) how the gas demand is going to take shape
up to 2035. So in the power sectors China’s gas demand growth is much higher than any
other countries (including the US). In the Middle East (previously the growth region) gas
demand peaks before 2030. Then there is chemical sector and there is transport sector.
The next (topic) is World electricity supply, consumption and demand by source and region.
So, this is the world electricity generation from 1971 to 2017 (by fuel). So, mostly it is from
coal; just like in India, it is the National Thermal Power Plant, they supply a major portion of
the electricity followed by hydro, natural gas and nuclear. In India also nuclear is slowly
taking shape.
23

And (for) the electricity generation by region: if you look at (this slide), OECD is the major
(contributor) (43%), followed by China. So OECD countries and China is almost (accounts
for) more than 60%. India comes under the non-OECD Asian countries.
This is the total electricity consumption by sector. So the industry of course (consumes) close
to 42% and rest almost 50% is (consumed by) residential, commercial and public services
(sectors).
So if we talk about nuclear electricity production, you can see that close to 75% is by OECD
countries, i.e., mostly the European countries including the United Kingdom, France and
other countries and as well as the United States also. And non OECD Europe is almost 12%.
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Asia is lagging behind in this nuclear power sector, but slowly China, India and other
countries are developing their nuclear power sector.
So this is hydroelectricity (power production). Here also, you can see that OECD and China
takes the centre stage, followed by the non-OECD Asia, in which India comes into picture
and other American and African countries too.
So this is wind electricity. Again here also, OECD takes the major share. Now, what we
understand from these few slides is, basically, when we talk about renewable electricity, the
OECD countries have already taken the lead. Now China is following them and India is also
following them. And we are sure that beyond 2035 you will see a huge change in the total
energy consumption pattern as well as source.
25

So this is solar PV (photo voltaic electricity). This is one sector in which the government of
India is giving a lot of emphasis. There are a lot of subsidies available to set up a solar PV
system, including the small ones in the household sector too. Awareness is also increasing
and the Government of India is playing a big role in shaping up that particular sector.
Then, let us understand about the electrification areas across the key end uses. If you see this
particular slide, you can understand that electricity demand doubles until 2050 (this is how it
has been projected) and the policies are also like that. And it (electricity demand) grows its
(share in) total (final) energy consumption from 19% today to 29% by 2050 as demand for
other fuels are flattening (other fuels means the fossil fuels).
So, the increasing adaptation of the electric vehicles is also leading to this particular surge in
electricity demand.
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So, in transport sector electrification is driven by strong improvements in economics of the
electrical vehicles, reaching cost parity with conventional fuel vehicles in the early 2020s.
This is what, is the actual aim of the OECD countries. They want some sort of trade mark or
cut off with the cost in comparison to adaptation of EV’s or electric vehicles. So, you can see
that, for future improvement in battery Technology, (that is that is also very important) huge
amount of research is still going on. This will enable the electrification of the heavy-duty
segments which are currently the hardest to electrify. So renewables will become cheaper
than existing coal and gas in most regions before 2030. Then you will be forced to switch
over to renewables even if you are not ready to adapt. So, that is going to happen by 2030. So
a majority of the countries will reach this tipping point in the next 5 years including India.
But anyway; in India we are already into renewables and our renewable production is also
much higher than other developing countries.
27

So as a consequence, by 2035, nearly half of the Global total capacity will be in solar and
wind, with China and India both taking the centre stage or they will become the main
contributor (that is very interesting). So solar and wind account for close to half of the Global
capacity by 2035. China, India and OECD countries are the major contributors.
Natural gas sees further capacity additions, particularly in North America and China. So
Global net additions of ~675 GW until 2035. So coal capacity declines, because in most of
the countries there is a decline in production of course, (that is true) as well as a decline in
adaptation or use. In India, the role of coal to supply and the rapid uptake in demand is much
smaller than in the earlier projections.
So that is actually good as solar in particular becomes more attractive alternative. As I told
you, that Government of India has given (emphasis on) the use of this policy as well as (the
government) giving so much of subsidies to setup solar PV systems, including the rooftop
solar PV systems for use in the households also.
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So, renewable generation accounts for more than 50% of the power supply post 2035. This is
where the NPS and SDS both complement each other. So in this particular slide, you can see,
how from 2030 onwards there is a huge increase in the Solar. You can see that yellow ones
(yellow part of the bar graphs) are the Solar and how it is increasing followed by the wind
and hydro. So this is how we are going to focus, including India. The major focus will be
mostly on the Solar PV systems. Then of course solar thermal is also there, wind energy,
hydro energy and nuclear energy. So all renewable sources.
Now let us just quickly understand (since this is introductory class) about the global
environmental issues. So we will talk about only the carbon dioxide emissions and climate
change.
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So the trend in long-term global warming continued in 2018, which also happened to be the
fourth warmest year on record. So, you know, since the last ten or twenty years the warmest
years basically occurred in the past 22 years. And the top four were in the last four years
alone. So that is very bad. This is according to the WMO or the World Meteorological
Organisation.
The IPCC special report on the impacts of global warming of 1.5 °C reports that, for the
decade, 2006 to 2015, the average Global temperature was 0.86 °C above the pre-industrial
baseline. For the most recent decade, i.e., 2009 to 2018, the average temperature was 0.93 °C.
So it is almost going to be 1 °C.
And for the last five years 2014 to 2018 it is 1.04 °C (above the baseline). So the last four
years consecutively 2019, 2018, 2017 and 2016 are the hottest or warmest years till date. So
as a result of this, there is a huge increase in the number of cyclones that is affecting the
entire northern hemisphere and north east Pacific basins as well as Indian Ocean sides also.
So in July and August of 2018, north of Arctic circle, many record high temperatures were
registered, as well as record long periods of high temperatures. Japan and Republic of Korea
saw new national heat records 41.1 °C and 41.0 °C. These are huge temperatures; they have
never witnessed in their entire life span, (I mean) the people (of) who are currently in Japan
and Korea. Eastern Australia also experience significant drought during 2018. Severe drought
affected Uruguay and northern and central Argentina in late 2017 and early 2018 leading to
heavy agricultural losses.
30

Now British Columbia, Canada broke its record for the most area burned in the fire season
for the second successive year. The US State of California also suffered devastating wildfires.
These are the things we already know, right. These have all been reported in the news and we
know all these things. So these examples show that climate change is not a distant or future
problem, rather it is happening (now), since almost 2 to 3 decades.
And now this is the peak time that we are facing and so much of global climate change is
taking place.
Now, this slide will basically tell you the environmental impacts of various sources of
electricity generation. So coal, natural gas, nuclear, wind, solar, water (basically the reservoir
hydro power) and then again water (that is the streaming hydropower). So what are the
Environmental effects? If you look at wind, there is a potential of bird kills, the wind turbines
are highly visible and noise issue is also there.
Similarly, if you talk about solar, though it is very good, but there are issues regarding high
energy used in the manufacturing process when you make solar PV and then there is a toxic
Silicon tetrachloride waste. Similarly, flooding is a problem in hydropower dams; but you
know, all these so-called environmental impacts also can be properly minimised (mitigated)
if we take sufficient precautions. That is what is being done now-a-days by most of the
countries and they adapting the safety measures and latest technologies so that the impact on
the environment will be very minimal.
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If you look at the world carbon dioxide emission, you will see that oil and coal are the major
emitting sectors followed by natural gas. And China and OECD again (because they are the
largest consumers of course) are the largest emitters.
So (now), if you look at the heavy industries sector, the projection from 2019 to 2060; (let us
see the from the first one 2019, 2030, 2040, 2050 and 2060), you can see that the industries
which are unlocked emissions that is increasing. See that these are all Industries which are
emitting hugely. Slowly it (emissions) is decreasing and unlocked emissions are increasing.
Then all (only) unlock emission increased (remains). And in 2050 all (other emissions) this is
gone and 2060 that is also gone (all emissions are reduced). This is how it is projected.
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So if you look at this particular slide, it says that Global carbon emissions peak in 2024 and
there is a fall by ~20% by 2050, primarily driven by the reduction in the emission from the
coal. So coal emission is gone. Once that is gone, almost 20% to 30% of the Global carbon
dioxide emission will drop immediately. So there will be an excellent balance of the carbon
dioxide that is actually being emitted by the developed and the developing countries.
So if you look at the developing economies in Asia, there is a huge percentage (statistics
wise), other developing economies and advanced economies. So these coal based plants
basically.
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And solar is becoming the star. So you can see, this very interesting to see the how the curve
is actually increasing from 2000 to 2040 (it is prediction basically, which is going to be
absolutely true as it is). There will be absolute, the unit values may differ, but the curve will
remain so. And apart from this there are others such as wind, hydro and nuclear. Here, the
biggest problem in nuclear are the safety issues as well as the installation cost. It is a very
costly technology. But once established it is very good.
So, a carbon neutral Europe puts offshore wind in front. So this is about Europe. You see
here, in Europe there is something interesting about this bio-energy. From 2018 you see how
it is slowly increasing till 2050. Though, not a very significant jump, but the adaptation and
maintaining it is also very important. So, in Europe, the offshore wind is going to take a
major role. Solar will be less, because in Europe, you know that availability of the solar
34

power or the sunlight is much lesser than other countries, especially, with respect to the Asian
countries.
Having said that, there is no single or simple solution to reach a sustainable energy goal.
Every country is putting their efforts. A host of policies and technologies are required and it
is already there. Policies are there, technologies are also there. So to keep the climate change
targets within reach, and further technology innovation will be essential so that we do not go
beyond 1.5 °C. Though the Paris agreement says 2 °C, however most countries have agreed
that will they will try to keep it not more than 1.5 °C.
So before we end up our lecture we will quickly understand the focus of our course, i.e., the
biomass energy or the bio-energy. Let us understand what is the bio energy potential across
35

world. So, you can see that in 1980 what it was, 2015 what it was, and 2050 what it will be.
This is the worlds’ primary energy demand. And this is the bio-energy demand (its
projected). 2050c
and 2050d
, c is based on the upper limit of the amount of biomass that can
come available as a primary energy supply without affecting the supply for food crops
(basically from agricultural residues and all).
And d (which is this one) is based on the source where a typical type of agricultural
management applied is similar to the best available technology in the industrialized regions.
So, you can understand that there is a huge upsurge in the biofuels and bioenergy based
supply.
So this is the contribution of each Biomass resource category to the Global potential of
biomass for energy use in 2050. What are these different types of feedstock. We can talk
about feedstock. So, biomass production on surplus agricultural land, bio-materials, biomass
production on degraded land, agricultural residues, animal manure (dung, where you go for
biogas basically), forest residues, tertiary residues (organic waste).
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Then you can see that energy used in the transport sector, non-fossil globally. So bio fuel is
going to take almost 73% beyond 2050. Similarly, heat production also 96% (it is a huge
number) from renewables; this is 2017 data.
Domestic supply of biomass globally; so you can see how it is. So, primary solid bio-fuel is
86%, still it is same. Slowly bio-gas and liquid bio-fuels are coming into picture. So, liquid
bio-fuels are gaining more importance because of its availability. Actually availabilities can
be round the year rather (when compared to) than Biogas. Biogas, during winter has a
depleting supply.
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So biopower generation globally; you can see that this is till 2017. You can understand that
the components that are being considered are municipal waste, industrial waste, solid bio
fuels, biogas and liquid bio fuel. You see, solid bio fuel is taking the centre stage. Now
slowly liquid bio fuel will also be coming into the picture, especially in the European
countries. Whereas, in Asia it is very less, however, slowly the Asian countries also will
catch up.
Use of biomass in electricity only plants in continents in 2017. You can see that in Asia for
solid bio-fuels again there is a huge surge. And heat generation globally.
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With this we will wind up. This is liquid bio fuel production globally. So you can see bio
ethanol, bio diesel other biofuels. So this is bio ethanol, this is biodiesel. And then other
biofuels. Other biofuels can be bio oil, it can be bio ethanol, it can be bio butanol and other
bio fuels. So what we understand from today's lecture is that, no single or simple solution
exist to reach the sustainable energy goals.
So, energy policies and adjusting to new pressure and imperatives, but the overall response is
still far from adequate to meet the energy security and environmental threats the world now
faces. The oil and gas landscape is being profoundly reshaped by shale, ushering in a period
of intense competition among suppliers and adding impetus to the rethink of company
business models and strategies.
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Solar, wind, biomass technologies are transforming the electricity sector, but an inclusive and
deep transition also means tackling Legacy issue from existing infrastructure. Energy is vital
for the developing countries, and their Energy future is increasingly influential for global
trends as it undergoes the largest urbanisation the world has ever seen. One classic example
are the African countries. The way the urbanisation has taken place in African countries after
2000 is phenomenal.
And, all have a part to play but the governments must take the lead in writing the next chapter
in energy history and steering us on to a more secure and sustainable course.
So, thank you students. Thank you for listening. So the next class will be again introduction.
In the next class we will understand about Biomass, what is actually Biomass and what
actually bio mass based Industries looks like and bio-refinery concept. I will explain the bio-
refinery concept.
Thank you very much. In case you have anything to ask please feel free to write to me at
kmohanty@iitg.ac.in or please post your questions in the NPTEL Swayam portal. I will be
happy to answer that. So thank you very much.
40

Indian Institute of Technology – Guwahati
Lecture 02
Need for Biomass based industries
Good morning students. This is lecture 2 our course. So, in this lecture, today we will discuss
about the need for the Biomass based industries under a biorefinery concept. Before
discussing (about) the biorefinery, we will try to understand the basics of biomass.
So, you know Biomass is a renewable organic material, usually which comes from plants and
animals. So, some of the important or most common (or you can say may be promising)
Biomass feedstock are: grains and starch crops such as sugarcane, corn, wheat, sugar beets
and sweet potatoes etc.; agricultural residues (such as) corn stover, wheat straw, rice straw
and all these things. Then there are food wastes, basically, coming from the food processing
industries; Forestry materials (such as) logging residues, forest thinnings; then we have
animal by-products (such as) Tallow soil, fish oil, manure etc.
Then we have dedicated energy crops, (which are specific energy crops); some of them are
switchgrass, miscanthus then we have a poplar, willow etc and of course Algae. Then, Urban
and Suburban wastes. Under this MSW comes (Municipal solid waste), lawn waste,
wastewater treatment sludge and there are many other things also.
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So what is actually the importance of the biomass energy and why we were discussing. Last
class (during our introduction) we have understood that what is the importance of biomass
based energy and Biomass based industries. So, the Global energy picture is changing rapidly
in favour of renewable energy. So, according to IRENA’s global renewable energy road map,
which is called REmap 2030 - if the realizable potential of all renewable energy technologies
beyond the business as usual implement then renewable energy will be accounting for almost
36% of the total Global energy mix by 2030. So if all the governments, according to their
policies implement it then this is going to happen. So this would be equal to a doubling of the
Global renewable energy share with compared to 2010 levels.
So then biomass has an auspicious future. So by 2030 Biomass could account for 60% of
total final renewable energy used as Biomass has potential in all sectors. So Biomass based
energy and other value added chemicals or value added products can be used across all
sectors. So that is the beauty of biomass actually. So most Biomass demand today is its
traditional used for cooking and heating.
As of now also (today) whatever Biomass is being utilised, it is basically (used) for the
traditional use (for cooking as well as heating). So in 2010 more than 60% of the total Global
Biomass demand of 53 exajoules was used in residential and commercial building sectors.
Much of this was related to traditional use of biomass for cooking and heating. Biomass
demand in the manufacturing industry is almost 15%, transport sector is 9% and the power in
district heating actually it is 8%. So this is almost about one third.
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So, Biomass applications could change over time. So, global biomass demand could double
to 108 exajoules by 2030; if all its potential beyond the business as well as usual is
implemented. So, that means nearly a third of its total will be consumed to produce power
and direct heat generation. About 30% would be utilised in biofuel production (mostly for the
transport sector) and the remainder would be halved between heating applications in the
manufacturing industry and building sectors.
So Biomass use in the combined heat and power generation (CHP technology basically) will
be key to raise its share in the manufacturing industry and power sectors. Then, estimated
Global Biomass demand according to the REmap 2030, the United States, China, India,
Brazil and Indonesia (these are the five countries, which are also five big economies of the
world) are going to account for 56% of the total Biomass demand by 2030.
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Global biomass supply in 2030 is estimated to range from 97 EJ (exajoules) to 147 exajoules
per year. Approximately 40% of this will originate from the agricultural residues. So there
lies a very important information about the agricultural and forest residues and waste
materials basically. The remaining supply potential is shared between energy crops (33 to 39
exajoules) and forest products including forest residues.
So, the largest supply potential exists in Europe and Asia (including Russia). So this is
another interesting thing that, these countries are blessed with huge biomass reserves. So that
is why they will be the potential feedstock suppliers basically. International trade of biomass
would play an important role in meeting the increasing Global demand. Trade (could)
account for between 20 to 40% of the total Global demand by 2030.
Domestic supply costs of biomass is estimated to range from as low as USD 3 for agricultural
residues to as high as USD 17 GJ for the energy crops.
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There are many challenges to be addressed in the Biomass demand and supply. Having said
that, the biomass and biomass energy is everything it’s good for the economy as a biorefinery
concept and all; everything is fine, but having said that, we need to understand that there are
many challenges that need to be addressed for the Biomass demand and supply. That is the
most important bottleneck actually.
So, its international trade as well as substitution of its traditional uses in realising such high
growth rates. So, if you keep on using Biomass for cooking purposes and heating purposes,
then this is not going to help us in a roadmap; basically if you think about the 2030-2035 road
map, which most of the countries have agreed to. So what we have to do is, basically the
bioenergy demand is estimated to be doubled between 2010 and 2030, ensuring that
sustainability of biomass will gain even more importance including environmental, economic
and societal aspects.
Now, for a sustainable and affordable bioenergy system, existing National and international
initiatives and partnerships as well as energy and resource policies need to be expanded to
address the challenges across the Biomass use and supply chain. Now, while biomass
represents an important stepping stone in doubling the Global Renewable Energy share,
potential of other renewable energy sources basically should be or must be expanded.
It should be an integrated approach rather than only Biomass and Biomass; that is not going
to help in a sustainable way, right. So for that we need to expand our work on our
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government policies including subsidising many of the installation facilities, transportation
and of course, the tax will also come into picture.
Biomass energy has rapidly become a vital part of the Global renewable energy mix and
account for an ever growing share of the electric capacity added worldwide. So, now most
importantly (last class also we have discussed that) Biomass based electricity generation is
directly feeding into the grid. So these are the upcoming things that has happened. It is
happening in many countries and will happen in India too very soon.
So, traditional Biomass primarily for cooking and heating represents about 13% and is
growing slowly or even declining. The declining is a good thing for it, but declining in the
traditional uses as well as their use in more sophisticated modern Biomass based industries, is
going to help us. So, some of the recent predictions suggest that biomass energy is likely to
make up one third of the total world energy mix by 2050.
In fact, bio fuel will provide right now almost 3% of the world's total fuel for Transport
(liquid fuel basically or maybe some gaseous fuels). So, biomass energy sources and readily
available in rural and urban areas of all countries. Biomass based industries can foster rural
development, provide employment opportunities and promote biomass regrowth through
sustainable land management practices.
This is another important thing. Let us understand, that we talked about dedicated energy
crops like as I told you maybe poplar, it may be switch grass, miscanthus, whatever it is. For
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that, when I need to cultivate them, I need to grow them, I need to plant them; so where do I
plant? So, the available land for agriculture is decreasing day by day across the world due to
more and more urbanisation. We know this. It is happening in the in India also. But we need
to understand that when I wish to grow this type of energy crops, I should not use our prime
agricultural lands, rather, I will use such land which are barren or not suitable for growing the
food crops. We can use (those lands) with a little modification, upgrade them and use for
these energy crops.
Then things will be very nice. Otherwise, sustainable Land management issue will come into
picture.
So, the negative aspects of traditional Biomass utilisation in developing countries can be
mitigated by promotion of modern waste to energy technologies which provide solid, liquid
and gaseous fuels as well as well as electricity. Another hot topic nowadays, is about
conversion of the waste to energy. You might have heard about this waste-to-energy many
times. There is another term is called water energy Nexus that also is very upcoming.
So let us talk about waste to energy. So most of the wastes of Biological nature can be
converted into energy. Now, having said that, there is one technology (of course we will
discuss in detail in one of our lectures later when we discuss about the thermochemical
aspects). So I will just tell you in a nutshell. Thermochemical conversion technologies; one
such is gasification, then we have pyrolysis. These are beautiful Technologies. If we adapt
that, we get three different types of bio fuels. One is the liquid bio fuel, one is solid bio fuel
and other is a gaseous biofuel. So these technologies are available. Only we need to upgrade
ourselves to suit a particular feedstock or rather, I can say that technology should be
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developed in such a way that they can process multiple feedstock. That is the challenge
basically. So the most common technique for producing both heat and electrical energy from
Biomass wastes is direct combustion.
Thermal efficiencies as high as 80 to 90% can be achieved by advanced gasification
technology with greatly reduced atmospheric emissions. Then of course CHP is there (the
combined heat and power system) ranging from small scale technology to large scale grid
connected facility. This is what I was telling you; just technologies are available. And now
what is the emphasis is given on? Emphasis is mostly given on how to generate electricity
from Biomass and connect it to the grid.
So, biochemical processes like anaerobic digestion and sanitary landfills can also produce
Clean Energy in the form of biogas and producer gas, which can be converted to power and
heat using a gas engine.
Now let us talk about what are the advantages of biomass energy. So, bioenergy systems
offer significant possibilities for reducing greenhouse gas emissions due to their immense
potential to replace fossil fuels in energy production. Biomass reduces emissions and
enhances carbon sequestration, since short rotation crops or forest established on abandoned
agricultural land accumulate carbon in the soil.
So this is also very interesting. That is because we know that biomass is carbon negative. The
reason is that, let us say, whatever carbon dioxide we generate by burning fuel even if it is a
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biofuel, that goes to the atmosphere. Again, we say that this carbon dioxide will be utilised by
the same feedstock materials when you are growing them. Basically it can be any energy
dedicated energy crops or any plants or maybe forest as a whole.
So, that is how the carbon cycle is supposed to be managed. And bioenergy usually provides
an irreversible mitigation effect by reducing carbon dioxide at source, but it may emit more
carbon per unit of energy than fossil fuels, unless, Biomass fuels are produced unsustainably.
So this is what we again need to understand that unless and until we produce Biomass based
fuel in a huge quantity, what will happen is that, we will be end up in producing more carbon
dioxide than we are consuming.
So biomass can play a major role in reducing the reliance on fossil fuels by making use of
thermochemical conversion Technology. I just mentioned about it (of course we will discuss
more in our subsequent lectures). So in addition, the increased utilisation of biomass based
fuel will be instrumental in safeguarding the environment, generation of new job
opportunities, sustainable development and health improvements in rural areas.
The development of efficient Biomass handling technology, improvement of agro-forestry
systems and establishment of small and large scale Biomass based power plants can play a
major role in rural development. So another important thing we need to understand is that, the
collection of such agricultural and forest wastes for the Biomass based industries is not that
easy. So rural people can be engaged for doing that. And there are many concerns about the
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transportation of such wastes to a plant where we will convert them basically to liquid and
gaseous fuels or generate electricity.
So, if we can locate the plants very near to the rural areas or the forests where these materials
are being collected, then it will be a win-win situation. So, we will save a lot of money in
transportation as well as the rural people will get some jobs and there will be some
community development also. So when compared with wind and Solar Energy, Biomass
power plant cell able to provide crucial, reliable based load generation.
This is more important. This is basically when we are talking about connecting to the grid.
There should be a proper sustainable supply. Otherwise, what will happen, today where you
are supplying one particular rate, tomorrow it will fall; that is not going to help in a
sustainable way when we talk about grid connectivity. So biomass plays a better role with
respect to wind and solar. So a large amount of energy is expended in the cultivation and
processing of crops like sugarcane, coconut and rice, which can be met by utilising energy
rich residues for electricity production.
So some of these processing, you know, use huge energy; sugarcane, coconut, rice mills (all
these things). So what is being suggested is that, there is a sugarcane waste, which is called
bagasse, then there is coconut waste, there is rice straw (all these wastes), if these wastes
which are generated at the site can be converted using suitable technologies to heat or energy,
or any such thing and maybe electricity or may be a small scale gasification plant; it can save
a lot of money basically.
So basically, it is an integrated approach. So, the waste generated at the source and treated
and converted in the same source to a value added product or you can say that, maybe to
energy. That approach will help us a lot. The integration of biomass-fueled gasifiers in coal
fired power stations would be advantages in terms of improved flexibility in response to
fluctuations in Biomass availability and lower investment costs.
So if you couple Biomass fueled gasifiers along with coal fired power station; it will help us
with 2 things; first is that, it will address the (issue of) availability of the Biomass around the
year, because coal is available to generate power. Second thing is that, we will reduce use of
coal thereby reducing the carbon dioxide generation.
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So, look at this particular biomass demand plot. This is extrapolated till 2030. Just look at the
last; look at these studies: Indonesia, then Russia, Brazil, India, China and United States. So,
these six countries mostly, even if you can consider Canada also, but I am counting these 4 to
5 countries. So just look at this particular plot. You can see that United States, China, India
and Brazil, these are the four major contributors or let us say that their demand for Biomass is
more compared to the rest of the world.
Because these countries have huge biomass reserve, as well as, they have realised the
potential of the biomass based fuels and energy and of course industries also.
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So, this is (breakdown of biomass supply) by region. Again you see Asia, the huge one here.
Basically, the contribution is coming mostly from China, India and Indonesia; then Europe
North America (in North America United States only) and then Latin America is also there.
So mostly it is coming from harvesting residues here in Asia (in which India falls). Then we
have processing residues, and of course we have fuel wood, wood residues as well as wood
waste.
Energy crops (share) is very less in Asia. However, it is so high in Europe, America and other
countries because they have started cultivating the dedicated energy crops. We are slowly
adopting it.
Then, having said about the Biomass based industries, the advantages of bioenergy and all
these things; let us now understand what are the challenges related to Biomass. So the
existing challenges of biomass supply chain related to different feedstock can be broadly
classified into four things or five things. First is operational, then economical challenge, then
social and policy and then regulatory challenges.
We will see one by one. What are operational challenges? So, feedstock unavailability;
Inefficient Resource Management and the government non-intervention approach are the key
factors hindering the expansion of the Biomass industry. Feedstock of biomass should be in
such a way that it should be available in a sustainable way throughout the year, but, can we
ensure that? Let us understand that; I am talking about rice straw or say bagasse. These are
seasonal crops. Any such crops that are seasonal, we need to understand that, of course their
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generation of waste is also seasonal. So, can we produce so much of waste, so that we can
keep it or store it for round the year application? The answer right now is, no. At least for the
Indian context, but, we need to work on that. There are policy matters, government should
interfere and make policies in such a way. And there should be Technologies, developed in
such a way that we can store these wastes for long-term use (right now that is not happening).
So, regional and seasonal availability of biomass and storage problem; this is what I already
told you. Then, pressure on transport section. Because biomass contains a huge amount of
moisture, that is why transporting waste biomass from the plantation to the production site
becomes energetically unfavourable and costly with the increase in distance. Basically
distance between the collection side and the plant.
So then, inefficiency of conversion facility, core technology and equipment shortage; now
technical barriers were resulted from the lack of standards on bioenergy systems and
equipment, especially where the energy sources are so diverse. Appropriate pre-treatment
required to prevent biodegradation and loss of heating value not only increases the production
cost, but also in equipment’s investment. So there is something called pre-treatment which
we will discuss in our subsequent lectures, what is pre-treatment and what is the importance
of it. So, we need to pre-treat the biomass according to where they are going to be used,
whether it is going to be in the thermal conversion technology or biological conversion
technology. So, depending on that we need to pre-treat the biomass. Basically fractionation
and size reduction and there are other things also.
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So then, immature industry chain; so, it is virtually impossible to get long term contracts for
consistent feedstock supply in reasonable price. So, industry will only be interested, if I am
going to supply them throughout the year in a sustainable way (the particular feedstock;
everybody is interested in a particular feedstock). So, that is not going to happen, right? But
policies should be framed and it should be implemented in such a way that industry are
favoured by implementing such techniques.
Then economic challenges; so feedstock acquisition cost; the Biomass resources are scattered
and in order to reduce the cost of transportation, biomass projects are eager to occupy land
close to the source, leading to centralisation of biomass projects. Then, limiting financing
channels and high investment and capital cost; as of now, the industries which are
implementing them, I can tell you that, there is a huge cost which is required basically for the
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capital investment; for procuring the equipment, installation, the land cost (forget about the
running cost and manpower cost). So here, the government has to intervene and make
policies in such a way that there will be GST credit, and there will be less tax on procuring
equipment. And of course there are other things apart from the subsidies.
Then social challenges; so, under social challenges there are a few things. First one is the
conflicting decision: so, decision making on selection of supplier, location, routes and
technologies is crucial and needs proper communication. So basically, which supplier you are
going to choose, whether it is reliable or not, where it is located, where is my plant located,
what are the routes or distance, how much it is going to cover for the transportation of the
feedstock from the procurement site to my plant and technologies.
So, we need to have a proper decision making system for that. So, land use issues: land use
issues lead to the loss of ecosystem preservation and the homes of indigenous people. That is
why I was just mentioning that, we should use such lands which are not at all used for the
dedicated food crops.
Then; impact on the environment: The Biomass plantation depletes nutrients from the soil,
promote aesthetic degradation, increase the loss of biodiversity. Other social impacts will
result from installation of energy farms within rural areas, like increased need of services
increased traffic etc. The potential negative social impacts appear strong enough to ignore
the benefit of new and permanent employment generation. So, if we try to develop a rural
based bio economy, then most of these issues will (should) be addressed.
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Then let us talk about the policy and regulatory challenges. At present the government is
subsidizing the domestic fuel prices which in turn makes the electricity generating cost from
conventional sources lower than the power production cost from Renewable Sources. This is
exactly what is expected from the governments. Not only from the Government of India but
from the governments of the all other countries also; that they are doing it.
So, there are no specific rules to regulate the work of utilisation of biomass resources and
there are no specific penalties for not using behaviour that should be comprehensively used.
So basically policy guidelines should be there. Governments should come up with clear cut
policies and guidelines; what is to be done and what is not to be done. If you are doing
something which is not expected, it will result in Environmental concerns on social concerns.
Then, you need to be penalized. As such, now such policies are not available. But I know that
there are coming. Soon it will be implemented in India as well as other countries also. There
is no special mechanism to manage the development of the Biomass resources industry and
there is no specialist department to manage the implementation of relevant national standards
and policies.
So all these things come under the government. These are governments’ job, basically. So I
know the government actually is coming up with so much of policies for the Biomass based
industries and there are already some existing policies, but, more needs to be done and it is
being done actually.
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Let us now understand the supply and demand framework of bio energy. You can see this
particular slide, how it is being actually depicted here. So, the land demand, land use and
energy production. So, land demand in all countries is basically based on the food demand;
for growing the food crops and of course (also) for wood demand; that means it is for either
the industrial demand for forests.
So when we talk about (land) use; so the domestic production is basically for the food and
industrial firewood and all these things plus international trade. And then, the remaining land
should be utilised for the energy crops and surplus firewood. And the energy production from
the Biomass residue, harvesting residue, processing residue, animal waste, household waste
etc.
Then primary bio energy will come from these dedicated energy crops such as sugarcane,
starch, oil crops and other cellulosic crops.
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So, if you look at the current land use and suitable area for agriculture. So this is the land use
in 2010 and that one is the potential for the crop production. So you can see that, right now
the forest is 4 billion hectares, then crop production is going on in 1.5 billion hectares. And
here, we were talking about the projection, suitable and available area that will be basically
for the dedicated energy crop production or biomass production; it will be almost around 2.7
billion hectares. So there will be a 1.4 billion hectares of surplus available land that can be
utilised.
So let us understand the relationship between the players along the value chain. This is very
interesting and very important, where you can understand that every one of us has a role to
play in this business. So all the policy makers, they will decide the policies. They may give
financial support and all these things. Then there is something called a researcher. Where
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people like me and some of you are coming into picture. What they do is, they are involved
or integrated into various sectors, whether it is a supplier, whether it is the manufacturer,
whether it is a customer.
Researcher has a big role to play in every sector. So then there is Logistics for raw Biomass
storage and transportation, and there is Logistic which is related to the bio products,
(processed products basically) for transportation and to take them to the reach of the common
people or the customers. So the researcher has a lot of role to play in the entire system; this
Biomass based industry and processing industries sector.
Let us talk about the life cycle of biomass industry. Please see where we are heading, we are
now here in the current status. You see the red one here. So that is between the initialisation
phase and the growth phase (I am talking especially about India). So we have started from the
fuel from the thermal energy sources (and) electricity. Electricity has been implemented
hugely in our country. Still there are many villages in rural areas where the electricity has not
reached.
It is going to be implemented very soon. Government of India is doing that. So then, we
move to the growth phase. In growth phase what is available? So basically there will be
increasing demand (of electricity or you can say energy) due to urbanization and
industrialization and there will be low to high value added products that will come into
picture when we pass from the initialisation phase to this particular growth phase.
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So, those products can be fertilizers, fibres, platform chemicals or other value added
products. Then we go to the maturity and decline stage. When you go to the maturity stage,
we have a constant demand. Now our demand is basically increasing. The moment you reach
here, there will be a plateauing effect and we will have a constant demand because you have
reached a mature stage.
And more or less our industrialisation or let us say the urbanisation has saturated. So, we go
for very high value added products like biochemical. Then after that there may come a
decline stage where there will be a reducing demand. And there will be no more product
innovations happening.
So here, this is the stakeholders’ interaction and role in commercialization of biomass
conversion technologies. So, in one of the slides; just 2 slides back we have discussed how
researchers are playing a role. Here also, you can see that the researchers in the top one you
see there. How they have integrated themselves into various other people basically the
supplier, customer, industry and the government.
They have completely integrated themselves along with all other stakeholders. So what do
they do? Researchers will resolve the upstream issues or harvesting issues basically. They
will provide strategies to meet the national goals as mentioned by their governments. They
provide strategies to satisfy the customer needs. And they will provide technical know-how
and expert. Then the supplier; what the supplier is supposed to do? The supplier will provide
raw material and share information.
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They provide services that meet customer need. They will obey the Regulation and policy set
and it is the long term collaboration. So, when I talk about long term collaboration that means
it’s the consistent supply. And what the government will do? The governments’ job is to
provide research funding. Governments’ job is to regulate the Biomass pricing and legal
enforcement. Then, a government must promote the importance of Sustainable development
and a government should go for financial support, whether it is an incentive, subsidy, tax
exemption like GST credit and all these things will be there.
Then there will be customer. So, the customer; what is their job? So, publicity and provide
data that (basically feedback, they should give a feedback), support green suppliers, support
green products and provide feedback on this (what I already told). And then there is the
industry, the most important. So, adapt research innovative ideas and share information, they
should have a long-term collaboration (looking for a consistent demand basically), they
should be able to beat that demand, they should generate products that meet customer needs
and obey the Regulation and policy set. So, you can understand in this particular slide, how
all the stakeholders, all of us, you, me, government, the suppliers, the industry people. So, all
of us have a role to play as a stakeholder in this particular Biomass conversion business.
Let us understand the problems of biomass large scale supply. So one of the biggest problems
related to Biomass large scale supply is the energy density. Briefly if Biomass moisture of
conventional wood is 30%, what it means? It means that every one 1 ton of wood or the
Biomass that I transport, I am transporting almost 300 kg of water. So it is huge, it is waste
basically and I am paying a heavy price for the transportation.
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So additionally, Biomass feedstock shape; so it is also very important. So whether it is
chipped, pelletized, rounded, baled, all these things will strongly influence the bulk density
and affect transportation economics. So we should also look into that. Then, in addition to the
bulk and energy density, large-scale Biomass supply is affected by a wide range of
bottlenecks, including raw material initial cost, biomass producers’ involvement and
environmental regulation and sustainability.
Now, finding solutions for all these problems means finding the solution for the creation of
the future biomass commodity in worldwide.
So are there are problems (of course), but there are solutions also. So, let us understand what
are the problems and what can be the solution. So, high quality Biomass is considerable but
limited expensive not always sustainable. So what can be the solution? Utilisation of Agro-
forestry residue; that can be a sustainable solution. High availability is there and fully
environmentally sustainable.
What is the other problem? Agro-forestry residues have lower quality and higher Micro
elements (that is true actually), calcium, magnesium and all these mineral compounds
basically. So what can be the solution? The blending of different Biomass feedstock to
arrange suitable average composition. So, do not go for a single stock. It is not going to help
us in a sustainable way. We should always go for multiple feedstock.
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So that is why, the technology should be developed in such a way that, basically our process
or equipment or let us say the process itself is capable enough to take (utilize) multiple
feedstock. So, because multiple feedstock will have different composition. So you can play
around and mix the composition in such a way that we will have an average composition that
is good enough for producing the energy or let us say, other value added products.
Availability is mainly reduced to forest areas. Now, residues have much lower costs and
dispersed and available almost everywhere. So, if you talk about the municipal solid waste,
food processing waste, industrial waste, then the dependence on only forest waste will come
down. Now; low energy density and bulk volume of fresh biomass affect storage cost and
transportation. This is what we just discussed in the previous slide.
So the activities, what we need to do is that, you go for chipping, enhance biomass storage
density, dry them, but again energy is coming into picture. So it is always advisable to reduce
the transportation cost. So how do you do that? Locate the biomass industries in such areas
where there is a huge biomass reserve. Then biomass degradability affect large distance
transport activities, long term storage.
Agro pellets production; you produce pellets from the Biomass and then it is easy to
transport, the density will come down (with low moisture and high energy density), avoiding
degradation and transportation issues. These are some of the major problems which are
associated with the Biomass and what we can and how we can address them suitably.
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So let us now understand what is a biorefinery? So I will show you 2, 3 slides to understand
what is biorefinery, then we will discuss about the Biomass based biorefinery things
(concept). So facility that integrates Biomass conversion processes and equipment to produce
fuels, power and Chemicals from Biomass is called a biorefinery. So it can be classified by
several categories: by feedstock materials, by resulting products, by technologies utilised or a
combination of all these three.
So, biomass feedstock; categorised by: chemical composition; maybe carbohydrates, lipids,
proteins, lignocellulosic materials.
So the resulting product categories may be biofuels, chemicals, biogas, electricity and heat
and technologies and unit operations employed include fermentation, gasification, pyrolysis,
hydrothermal liquefaction (It is very upcoming technology actually), hydrogenation,
hydrothermolysis and oxidation and hydrodeoxygenation.
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So some of the feedstock that has been tested (and I have just listed few there are many and
list is endless basically) are cultivated crops, agricultural waste, forest resources, urban and
industrial waste and micro algae. Algae is something interesting. We will discuss about algae
letter on; so microalgae have a great potential as a feedstock for the production of a wide
range of end products under the broad concept of biorefinery.
Algae can be used for the production of biofuels and a variety of value-added chemicals,
since they possess high amount of lipids, proteins, carbohydrates, vitamins, pigments and
enzymes.
So the importance of bio refinery for bio based industries: The International Energy Agency
Bioenergy Task 42 defined biorefining as the sustainable processing of biomass into a
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spectrum of bio based products. So it can be food, feed, chemicals and materials, as well as
bio energy that means bio fuels, power and/or heat. As refineries, biorefineries also can
provide multiple chemicals by fractioning an initial raw material (which is biomass in this
case) into multiple intermediates (so it can be Carbohydrate, protein, triglycerides) that can
be further converted into value added products. Each refining phase is also referred to as a
cascading phase. Now, biorefinery involves the enabling Technologies to make this possible,
as it allows for optimal utilisation as well as value creation of biomass. Development of
integrated closed-loop biorefineries that ensure their sustainability and economical viability
through a complete use of biomass, minimise waste, and generate the greatest possible added
value from the available sources.
What is this integrated close bio refinery? Let us say, it is a bio mass based refinery, I am
going to use one or two feedstock. I process them. Then I produce electricity or maybe liquid
bio fuels or maybe steam (if I am going for some steam based power generation) or some
other commodity products or value added products. Now thereby, I also produce a huge
amount wastewater because water is required in every stage of processing.
So having said that, you know, the fresh water availability is reducing day by day across the
globe in various places. We know that in India also, it is a huge problem in a few areas. So,
what is the need of the hour? It is that you have to treat and recycle this waste water in a
closed loop system. That means if you do that, we will be depending less on our freshwater
resources (that is what is the need of the hour).
Because a time will come when there will be very scarce water available. So how will we run
a refining process? Refining process, whether it is a bio refining or Petroleum crude based
refining, it consumes huge amount of freshwater. So we should look for an integrated closed
loop biorefinery. That means whatever waste we are generating it can be solid waste also. I
am not just talking about liquid waste (basically the wastewater), let us not talk about only
the liquid. Let us do something about the solid waste also. Whatever solid waste we generate
can we further process them to get fuels out of that, or, can we further process them to get
some value added products from that? If you do that in a closed to biorefinery circle, then the
biorefinery will become economically sustainable and will be a viable option.
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So the new you biorefinery concept overcomes the problems arising from the generation of
residues by giving them new value. This is how a significant increasee in profitability and
competitiveness over petrochemical equivalents will be achieved. Otherwise petrochemical
based fuels and products will always be low cost than whatever we produce from the
biomass. So Profitability and Competitiveness has to be taken care of also.
So we go for multiple products. What is the answer for that? We go for multiple products. Do
not aim only for the fuels or energy, but you please look for other products also. So,
biorefining is the main element in the framework of the emerging bio economy as a broad
spectrum of biomass resources offers great opportunities for a wide-ranging product portfolio
to satisfy the different needs of society.
So, as I told you, unless and until we go for multiple products, unless until we work for a
waste to energy or water energy nexus and how do we convert in-house generated waste from
the refining process, whether it is solid or liquid and get some value added products out of
that, we are not going to have a sustainable and economically viable biorefinery.
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So currently some biorefineries are operating on a commercial scale. Pulp and Paper
Industry, biofuel industry and food industry. Furthermore, many different newly advanced
biorefineries are under development. So the main characteristics of a biorefinery are: there
should be coupled generation of energy (gaseous and liquid bio fuels) as well as materials (it
can be Chemicals, food and feed). A combination of several process steps; it can be
mechanical processes, it can be thermochemical processes, it can be biochemical processes
also.
Use different raw materials; from both virgin and residual sources (that is also very
important). A common hurdle in the commercialization of biorefineries it is economic
viability. The economic hurdle starts from procuring Biomass and its logistics, technology
maturity and policy support. This is what we have already discussed.
So, the rate of commercialization of biorefineries is slow primarily due to the lack of policy
support. This I have already mentioned that the government has or should come up with
policies which will support the establishment of biorefineries. So biorefineries have to
compete with well-established petrochemical products. Policy support can drive innovation,
help technology to mature, create competitiveness to a market which in turn could reduce the
cost thus making the economic viability of biorefineries a reality. Government as a big role to
play.
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This is how it looks like basically. You have a biomass here, you process in the biorefinery,
you have downstream processing, you have separation technology. It can be catalytic
conversion or it may not be. Then we get this type of products: fuels, solvents, bulk
Chemicals, plastics, fibres, fine Chemicals and oils and what not? You can just see what not
we are getting from the biorefinery.
But again, one particular feedstock will not give me like this. So I should go for multiple
feedstock. And as well as not only virgin feedstock, but also processing feedstock, processing
with.
So before I wind up, I just quickly show you. We will glance through the different bio based
industries that are actually established and running successfully. Blue Marble Energy, so that
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is in Odessa and the Missoula. Canada's first integrated biorefinery, developed on anaerobic
digestion technology by Himark BioGas that is in Alberta, then Chemrec’s technology for
Black Liquor gasification and production of second generation of biofuels such as
biomethanol and bioDME. That is integrated with the host pulp mill and utilizes a major
sulphate or sulphite process waste product as the feedstock (completely waste product based
biorefinery).
Then Novamont has converted old petrol chemical factories into biorefinery. This is a very
interesting thing. So by just changing some of the processing things, some equipment, they
are running this refinery in a sustainable way.
C16 Biosciences they produce synthetic palm oil from carbon containing waste. Then there is
MacroCascade that aims to refine seaweed into food and fodder, and product for health care,
cosmetics, fine chemical industries and they have processed other things also. FUMI
Ingredients that produces foaming agents, heat set gels and emulsifiers from microalgae with
the help of microorganisms such as yeast and brewer’s yeast.
BIOCON, it is an Indian company. So they a processing the wood into various products.
More precisely, their researchers are looking at transforming Lignin and cellulose into
various products. Lignin based biorefineries are also there. Lignin for example can be
transformed into phenolic components which can be used to make glue, plastics and
agricultural products (crop protection). Cellulose can be transformed into clothes and
packaging.
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Now, in South Africa there is a company called Numbitrax LLC. They have bought a Bloom
biorefinery system for producing bioethanol as well as additional high return offtake products
from local and readily available resources such as prickly pear cactus plant basically. Then;
BiteBack Insect that makes insect cooking oil, insect butter and all these things.
Then there is a company called Circular Organics (it is a part of Kempen insect Valley) that
grows black soldier fly larvae on waste from the agricultural and Food Industry. So Fruit and
Vegetables surplus, remaining waste fruit juice and jam production (basically the solid
waste). These larvae are used to produce protein, grease and chitin. So, the grease is usable in
the pharmaceutical industries for cosmetics, surfactant for shower gel thereby replacing other
vegetable oil such as palm oil or it can be used as fodder also.
So with this I complete my lecture today. So thank you very much. And in the next lecture we
will start module 2. The module 2 is focused on biomass. So, we will be discussing the
availability and abundance of biomass, photosynthesis, composition and energy potential,
virgin Biomass production, agricultural, forestry waste and all these things. Their availability
and potential.
So thank you very much once again, and if you have any query, please write to me at
kmohanty@iitg.ac.in or you can also write to me in the Swayam portal. Thank you.
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Indian Institute of Technology-Guwahati
Module-02
Lecture-03
Biomass Basics
Good morning students. This is module 2 and lecture 1.
So, in this entire module, basically we will be discussing about biomass and biomass
structure, its availability, then composition, their energy potential, what type of biomass are
available, what type of land requirements are there; all these things slowly we will be
discussing.
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So, let us start our lecture today. So, as you know, biomass has always been an important
energy source, considering the benefits it offers. It is renewable, widely available and carbon
neutral and has the potential to provide significant employment in the rural areas. This is
what I discussed (in the) last class also; that how biomass based industry is going to effect the
economics of the rural people.
About 32% of the total primary energy use in India is still derived from biomass. More than
70% of the country's population depends upon it for their energy needs. The current
availability of biomass in India is estimated at about 500 million metric tons per year.
So, biomass is defined as the bio residue available by water based vegetation, forest or
organic waste, by product of crop production, agro or food industries waste. Various biomass
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resources are available in India in different form. They can be classified simply in the way
they are available in nature as: grasses, woody plants, fruits, vegetables, manures and aquatic
plants.
Algae and Jatropha are also now used for manufacturing biodiesel (we will be discussing
about them in detail later on). Core distinct sources of biomass energy can be classified as
residue of agricultural crop, energy plantation and municipal and industrial waste.
So, let us have a look at this particular slide. So, (first) you can see energy crops; plants
exclusively grown to derive energy. Basically it can be fuel, liquid fuel, solid fuel as well as
gaseous fuel. So, here there are some examples, bamboo, prosopis, leuceana, then we have
miscanthus, elephant grass, switch grass etc.
Then we have agro industrial wastes. So wastes from paper mills, molasses from sugar
refineries, pulp wastes from wood processing industries, textile fibre waste etc. Then we have
agricultural waste. So, waste that is coming from farming; such as straws of cereals and
pulses, stalks of fiber crops, seed coats of oil seed (basically de-oiled cake), then crop waste
like sugar cane trash, rice husk, coconut shell etc.
Then we have MSW, which we call municipal solid waste. So, mostly they are
biodegradable, such as food and kitchen waste, green waste, paper, inert waste, like fabrics,
clothes come under that (needs to be separated basically). Forest waste; so, basically logs,
chips, barks, leaves, forest industry waste products like sawdust.
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Now, bioenergy is the largest renewable energy source globally. In 2016, total primary
energy supply of biomass resources was 56.5 Exajoules, constituting almost 70% of the share
among all renewable energy sources. So, this table will give you an idea about, what is the
total energy that is available and the biomass based energy. So, you can see that in 2016
(latest figures), if you see 80.5 is the available energy of the renewables and out of that 56.5
comes from the biomass.
In continents, the role of biomass is very prominent. In Africa more than 90% of the total
primary energy supply of renewable energy sources comes from biomass. In every other
continent, biomass is the largest renewable energy source in terms of supply and accounting
from between 40% (Oceania) to almost 96% in Africa. So, this particular table shows you
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what is the biomass fraction, basically from various continents, Africa, Americas and Asia.
The biomass is huge almost everywhere. It is more in Asia, okay followed by Africa.
So, understanding photosynthesis is the most important thing related to biomass. So,
understanding the photosynthesis of biomass began long back, in 1772 by the English
scientist, Joseph Priestley. So, he discovered that, green plants expire a life-sustaining
substance (that is basically oxygen) to the atmosphere, while a live mouse or a burning candle
removes the same substance from the atmosphere (removed meaning it is consumed
basically).
So, in 1804, the Swiss scientist Nicolas Theodore de Sausseure showed that the amount of
carbon dioxide absorbed by green plants is the molecular equivalent of the oxygen expired.
That means, he found out that, how much carbon dioxide is being consumed, is almost
equivalent (on a molecular level) to the oxygen that the plants expire. So, in this way, the
stoichiometry of the process was developed and major advancements were made to detail the
chemistry of photosynthesis, and how the assimilation of carbon dioxide takes place. About
75% of the energy in solar radiation is contained in light of wavelengths between the visible
and near infrared portions of the electromagnetic spectrum. So, that is almost in the range of
400 to 1100 nanometers.
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The light absorbing pigments effective in photosynthesis have absorption bands in this range,
particularly in that 400 to 1100 range. So, chlorophyll a and chlorophyll b, which strongly
absorb wavelengths in the red and blue regions of the spectrum, and accessory carotenoid and
phycobilin pigments participate in the process. So, photosynthesis is a biological conversion
of solar energy into sugars and starches, which are energy rich compounds.
So, in photosynthesis reaction, water and carbon dioxide molecules break down and a
carbohydrate is formed with the release of pure oxygen.
CO2 + H2O + light + Chlorophyll → C6H12O6 (Glucose) + O2
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Now, there are two reactions, light reaction and dark reaction in photosynthesis. So, in the
light reaction, the splitting of water molecule into hydrogen and oxygen is happening under
the influence of chlorophyll and sunlight. So it is a photochemical phase reaction. Under the
dark reaction hydrogen is transferred to carbon dioxide to form starch or sugar, and it is a
biochemical phase reaction.
So, let us now understand the biomass composition. I can tell you that biomass composition
is a significant property that has so much to do with biomass processing and further their
value added product generation. So, what type of composition it has? If we talk about the
lignocellulosic biomass, these basically consists of 3 primary components, first one is
cellulose, then hemicellulose, and then lignin.
Apart from that there are other components also. So, how much cellulose and how much
lignin and how much the hemicellulose is present. So, this has to be calculated a priori. So,
this comes under the physicochemical characterization of the biomass. So, you need to
characterize it and you need to find out what is the crystallinity of the cellulose.
So, there is a process called delignification in which you basically remove the lignin from the
lignocellulosic biomass, to make them more amorphous and you will get the cellulose in a
pure form. So, that can be further processed and made into sugars. So, the chemical
composition of biomass, whether it is lignocellulosic or herbaceous, can be characterized by
5 primary components: cellulose, hemicellulose, lignin, extractives/volatiles and ash. So,
these are the components which are present in almost all biomass. But, what varies, is their
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amount from biomass to biomass. In some biomass, like hard woody biomass lignin presence
will be more, the amount of lignin will be very high. And in some soft biomass like creeps
and leaves the lignin presence will be very less okay.
So, the most abundant biopolymer on the earth is cellulose. It is a polysaccharide of glucose
monomers held together by β (1 → 4) linkages (it is a bond, a glycosidic bond basically). So,
these β (1 → 4) linkages are what makes cellulose resistant to hydrolysis. That means it’s all
about the crystallinity of the cellulose. So, if it is more crystalline, then you need to process it
further, you need more energy to break it. So, if we remove lignin, then the crystallinity will
also come down (reduce).
The second major component of the biomass is hemicellulose. It is an amorphous
heteropolymer comprised of several different carbohydrates including xylose, mannose and
glucose, among others. Due to its amorphous structure hemicellulose is significantly more
susceptible to hydrolysis than crystalline cellulose. So, cellulose and hemicellulose combined
with the third major component of the biomass, that is lignin, make up about 90% of
lignocellulosic biomass and 80% of herbaceous biomass.
So, lignin is an intricate array of aromatic alcohols and it is intertwined with the cellulose and
hemicellulose fraction of the biomass structure. So, this interwoven nature of the lignin helps
provide rigidity to lignocellulosic materials such as trees. So, lignin is bound along with
cellulose and hemicellulose in a very intertwined manner. So, that is why there is a need to
de-lignify (basically remove lignin) so, that cellulose and hemicellulose may be released from
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the interlinking bond that was present previously. So, that cellulose will be more accessible
for hydrolysis purposes. The other minor components of the biomass are extractives/volatiles
and ash. While these components make up a smaller portion of the biomass composition, they
can still have a major influence on what ends up being the optimal conversion process.
So, please again note that the amount of volatiles/extractives present and the amount of ash
present plays a significant role. If there is huge ash present in the biomass, then they are not
good for certain particular processing, whether it is the thermochemical or biochemical. So,
every component has a role to play and will somehow effect the conversion technology or
conversion process.
The components comprising the extractives/volatiles include both water and ethanol solubles.
So, water soluble compounds include non-structural, sugars and proteins and ethanol soluble
compounds are typically represented by chlorophyll and waxes. Ash, which comprises the
inorganic content in biomass can be intrinsic to the biomass or added anthropogenically.
Anthropogenically means man-made (basically during the processing), so it is getting added
from the outside, it is not present inside the biomass. So, intrinsic ash includes material like
calcium and potassium ions, while anthropogenic ash is mostly silica. Silica is basically
coming from the dirt. When you are processing it in the field, it is getting dumped on the
field. So, you are taking it out. So, silica is coming into picture, that is how it is getting added
anthropogenically during harvesting.
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So, let us talk about biomass energy potential. So, biomass for energy originates from a
variety of sources classified into forestry, agricultural and waste streams. Some of the
potential sources include: crops for biofuels (dedicated crops), energy grass, short rotation
forests, woody biomass and residues, herbaceous by-products and municipal solid waste.
Globally, in 2012, the biggest share of biomass for energy came from the forests- almost 49
Exajoule out of a total supply of 56.2 Exajoule. So, the current global energy supply is about
560 Exajoule.
So, a conservative estimate of the energy potential of biomass from agriculture, forestry and
waste sectors is totalling to almost 150 Exajoule in the next 20 years. It is a huge energy
potential. About 43% coming from agricultural (so, that is residues by-products and energy
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crops), 52% from the forest (which is wood fuel, forest residues and by-products of the forest
industry like sawdust) and 5% from waste streams. Now, biomass can play an important role
in the transformation to a new energy system based on renewable energies.
Let us now understand virgin biomass production and selection, how the biomass is getting
produced, the land requirements, etc, and how do we select them. So, virgin biomass includes
all naturally occurring terrestrial plants, such as trees, bushes and grass. The manufacture of
synfuels or synthetic fuels or energy products from virgin biomass requires that suitable
quantities of biomass chosen for use as energy crops be grown, harvested and transported to
the end user or to the conversion plant.
Since at least 2,50,000 botanical species of which only about 300 are cash crops are known in
the world, which indicates that biomass selection for energy could be achieved rather easily.
Because it is a narrowed loop, it is not a very big loop. And compared to the total known
botanical species, a relatively small number are suitable for the manufacture of synfuels and
other energy products.
The selection is not easily accomplished in some cases, because of the discontinuous nature
of the growing season and the compositional changes that sometimes occur on biomass
storage.
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Many parameters must be studied in great detail to choose the proper biomass species or
combination of species for operation of the system. Some of them are growth area
availability, soil type, quality and topography, propagation and planting procedures, growth
cycles, fertilizer, herbicide, pesticide and other chemical needs, disease resistance of the
monocultures, insolation, temperature, precipitation and irrigation needs.
And there is pre harvest management, crop management and harvesting methods, storage
stability of the harvest, solar drying in the field versus in-plant drying in connection with
conversion requirements, growth area competition for food, feed, fiber and other end uses,
the possibilities and potential benefits of simultaneous or sequential growth of two or more
biomass species for synthetic fuels and foodstuffs, multiple end uses and transport to the
conversion plant gate or end-use site.
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Biomass chosen for energy applications, in the ideal case should be a high-yield, low-cash-
value species, that have short growth cycles and that grow well in the area in which biomass
energy system is located. Now, again, I am telling you, last class also we have discussed,
apart from these listed things (there are so many), one of the major costs usually comes from
the transportation of the biomass.
Now, we discussed in the last class about the biomass chipping and all, basically, the shape of
biomass and the moisture content of the biomass. So, if the moisture content is very high
almost 30% (let us say in most of the biomasses), then I am transporting almost 300 kgs of
water along with the transport of 1 tonne of biomass.
So, it is a huge thing and it is of no use, because even if you go for a thermo chemical process
or a biochemical or any other process, you need to have a dry biomass. If it is not 100%
moisture free, some moisture is okay, but you need to dry it. So, you cannot have 30%
moisture. So, you have to reduce it almost to a 5% or even less than that. Certain conversion
technologies require not more than 1%, 2% or 3% moisture.
So, then shape also plays a very important role. So, I was telling you in the last class if you
recall, that it is better for the policymakers, the implementers, industry people who are going
to set up such plants, that they must choose the location of their plant in such a way that
transportation cost should be reduced, it should be as less as possible.
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So, fertilization requirements should be low and possibly nil if the species selected fix
ambient nitrogen, thereby minimizing the amount of external chemical nutrients that have to
be supplied to the growth areas. In areas having low annual rainfall, the species grown should
have low consumptive water uses and be able to utilize available precipitation at high
efficiencies.
For terrestrial energy crops the requirements should be such that they can grow well in low
grade soils so, that the best classes of agricultural or forestry lands are not needed. After
harvesting, growth should commence again without need for replanting by vegetative or
coppice growth. So, what do we understand basically is that, lands should be chosen in such a
way to grow the dedicated energy crops, which are not been used for our traditional crops.
So, agricultural fields basically. So, most of the agricultural fields which are being utilized in
India to grow crops, cereals, pulses etc., even for vegetables production are extremely fertile.
So, in no way we are going to use those land for biomass production or let us say, for
growing energy crops or some other biomasses.
So, you must look for such lands which are either barren or are not fertile enough to grow the
energy crops. So, those types of lands are sufficiently available. So, this is one point. Second
thing is that, we should go for short rotation species. So, that means in another way I can tell
a fast growing species. There are certain species of softer bamboo which grow very fast.
So, those are being utilized or can be utilized for making bioethanol or other biomass based
products from bamboo. So, like that there are many other species which are having fastest
growth rate. And you should also take care that such species should be planted, which
required minimum attention.
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So, then let us talk about climatic and environmental factors. So, the biomass species selected
as energy crops and the climate must be compatible to sustain operation of the energy or fuel
under human controlled conditions. So, the compatibility of biomass and climate is
nevertheless essential to ensure that these systems can ultimately be operated at a profit on a
commercial scale.
The 3 primary climatic factors that have most influence on the productivity and yields of an
indigenous or transplanted biomass species are insolation (that is the solar radiation),
precipitation (rainfall & moisture), and temperature. So, we will discuss one by one.
So, natural fluctuations of these factors remove them from human control. But the
information compiled over the years in meteorological records and from agricultural and
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forestry practice, supplies a valuable database from which biomass energy system can be
conceptualized and developed. That means all these records are going to help us in choosing
and selecting a particular biomass as well as the area or land for growing this biomass.
Of these three factors, precipitation has the greatest impact, because droughts can wreak
havoc on biomass growth. And that is not only true for biomass, that is true for any plantation
or any crop. So fluctuations in insolation and temperature during normal growing seasons do
not adversely affect the biomass growth as much as insufficient water. So, ambient carbon
dioxide concentration and the availability of macronutrients and micronutrients are important
factors in the biomass production.
Having said that, we may look for such lands which are not highly fertile. But we need to
again remember that we need to supply certain nutrients (micro or macro) for the biomass
growth. However, that can be supplied in limited quantity throughout the year, in a sequential
manner so that the growth of the biomass does not get hindered.
So, let us understand insolation. So, the intensity of the incident solar radiation at the Earth's
surface is one of the key factors in photosynthesis. Except in a few rare cases, natural
biomass growth will not occur without solar energy. Insolation varies with geographical
location, time of day and season of the year, and as is well known, it is high in the tropics and
near the equator. At a given latitude, the incident radiation is not constant and often exhibits
large changes over relatively short distances.
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Although several environmental factors influence biomass productivity, there is usually a
relatively good correlation between the annual yields of the dry biomass per unit area and the
average insolation value (there is a correlation that exists).
All other factors being equal, it is generally true that the higher the insolation, the higher the
annual yield of a particular energy crop provided it is adapted to the local environment. The
approximate changes of insolation with latitude are illustrated in this table. You can have a
look in this table and you can understand that location wise what is the maximum, minimum
and average insolation at these places.
So, the next is precipitation. Precipitation as rain or in the form of snow, sleet or hail,
depending on atmospheric temperature and other conditions is governed by the movement of
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air and is generally abundant wherever air currents are predominantly upward. So, the
greatest precipitation should therefore, almost occur near the equator. The annual
requirements for good growth have been found for many biomass species to be in the range
50 centimeter to 76 centimeter.
Some crops such as wheat, exhibit good growth with much less water, but they are in the
minority (minority means when we compare with other cereals or pulses on a global scale,
they are less; that is why it is being mentioned as minority). Without irrigation, water is
supplied during the growing season by the water in the soil at the beginning of the season and
by rainfall.
So, it should be realized, though, that rainfall alone is not quantitatively related to the
productivity of terrestrial biomass, because of the differences in soil characteristics, water
evaporation rates and infiltration. The transpiration of water to the atmosphere through
biomass stomata is proportional to the vapour pressure difference between the atmosphere
and the saturated vapour present inside the leaves.
Now, having said that, we must understand that, the vapour pressure inside the leaves and the
pressure outside or the ambient pressure do play a role on controlling that stomata opening.
Transpiration is obviously affected by atmospheric temperature and humidity. The internal
water is essential for biomass growth. The efficiency of utilizing this water (we call it water
use efficiency or WUE) has been defined as the ratio of biomass accumulation to the water
consumed, expressed as transpiration or total water input to the system.
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Analysis of the transpiration phenomena and the possibilities for manipulation of WUE have
led some researchers to conclude that biomass production is inextricably linked to the
biomass transpiration. Agronomic methods that minimize surface runoff and soil evaporation
and biochemical alterations that reduce transpiration in C3 plants have the potential to
increase the WUE.
But for water limited regions fact remains that without additional water the research results
indicate that these areas cannot be expected to become regions of high biomass yields.
Irrigation and full exploitation of humid climates are of the highest priority in attempting to
increase biomass yield in these areas. So, basically in India, you know, most of our
agricultural lands till date depends on the natural rain fall. We will always be looking towards
a better monsoon this year or that year (and so on). So, as we do not have lift irrigation
system in most of the agricultural lands. Though in many areas it is there, but almost I can
say about 50% or 40% has been covered (if I am correct, according to the statistics), but still
almost 50% people completely depend upon the rainfall. Rainfall during the monsoon season
and during other season also. So, irrigation has to be done properly whether it is for the
biomass production in a large scale for the dedicated energy crops or for our usual
agricultural purposes also.
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Now, let us understand the effect of temperature. Most biomass species grow well at
temperatures between 15.6 and 32.3 degrees centigrade. Typical examples are corn, kenaf
and napier grass. So, kenaf is basically in the African continent, it is being planted for years
together for food and fiber purposes. Napier grass is another plant in grass family which is
being used for fuel production.
So, tropical grasses and certain warm season biomass have optimum growth temperatures in
the range of 35 to 40 degrees centigrade, but minimum growth temperature is still near 15
degrees. So, cool weather biomass such as wheat may show favourable growth below 15
degrees centigrade and certain marine biomass such as the giant brown kelp only survive in
water at temperature below 20 to 22 (degree centigrade).
Giant brown kelp is an algae. So, it is a big algae (which) basically looks like plant inside the
sea. So, it cannot survive at a temperature more than 22 degrees centigrade. The effect of
temperature fluctuations on net carbon dioxide uptake is a very important factor to be
considered. Ideally, the biomass species grown in an area should have a maximum rate of net
photosynthesis as close as possible to the average temperature during the growing season in
that particular area.
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So, now let us understand about different wastes one by one. So, waste biomass, municipal,
industrial, agricultural and forestry, their availability, abundance and potential. So, up to the
mid 1990s only a few commercial virgin biomass energy systems in which dedicated biomass
is grown for use as an energy resource were in operation in industrialized countries (basically
Europe and America).
So, the technology is available or under development and is slowly being incorporated into
regional, national and world energy markets. Most of the contribution of biomass to primary
energy demand in the late 1990s comes from waste biomass. Now, waste biomass is energy
containing materials that are discarded or disposed of and that are mainly derived from or
have their origin in the virgin biomass.
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So, they are lower in cost than the virgin biomass and often have negative costs, because they
are being just thrown away. So, some are quite abundant and some can be disposed of in a
manner that provides economic benefits to reduce disposal costs. So, having said that, another
most important thing we must understand and we are slowly getting aware of the fact is
segregation of the wastes. Whether segregation of the wastes is at home or in offices, whether
it is in plants where we are processing biomass, or whether it is in hotels and restaurants and
canteens. So, it is having a very big effect on the further downstream processing. So waste
biomass is generated by anthropological activities and some natural events also. So, it
includes municipal solid waste, basically urban refuse, municipal bio-solids (sewage), wood
wastes and related wastes produced in the forest and logging and forestry operations,
agricultural waste such as crop residues produced in farming, ranching and related operations,
the wastes produced by certain industries such as the pulp and paper industry and those
involved with processing of foodstuffs.
Now let us understand municipal wastes. So, there are basically two types of municipal
wastes that offer opportunities for a combined waste disposal and energy recovery. First is
the municipal solid waste that is MSW, the garbage, urban refuse and then the bio-solids, that
is coming from the sludge and sewage. So, each has its own distinctive set of characteristics
as a biomass energy resource. There are huge works already reported in literature. So, you
can refer to those.
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MSW is collected for disposal by urban communities in all industrialized countries. So, there
is no question regarding its physical availability as a waste biomass feedstock in centralized
location in these countries. The question is how best to utilize this material if it is regarded as
an “urban ore” rather than urban waste. A large portion of the MSW generated is available as
feedstock for additional energy recovery processing.
Landfilled MSW can provide energy as fuel gas for heat, steam and electric power production
over a long period of time. Surface processing of MSW can also provide energy for the same
end uses when MSW is being used as a fuel or feedstock. So, basically what we need to
understand is, how best we are going to use. Please understand that technologies are available
to process MSW, there is nothing new to be done. Available technologies are already
available.
But segregation of waste is the most important thing. Then another important thing is
basically how you are going to utilize it and where. Again you are collecting the municipal
solid waste from the entire municipal area, city, townships or even the rural areas; then you
have to transport it. Again transportation cost is a big thing. Where your plant is located, the
location of the land plant is again important thing.
So, we need to have an integrated approach thereby understanding the value of the MSW
what type of value it is. Now, please do not think that every MSWs economic value, let us
say, with respect to energy production is same. It is not so. So, the MSW from Bombay will
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have certain value, the MSW from Guwahati maybe something else. So, component wise it
may vary.
So, we have to see which MSW is best suited for what technology; that is also to be seen. So,
we need an integrated approach where MSW can be properly utilized, converted for energy
purposes as well as for other value addition also.
So, the world generates almost 2.01 billion tonnes of municipal solid waste annually with at
least 33% of that conservatively not managed in an environmentally safe manner. I am sure
this percentage 33% may be very high in Asian and African countries. So, worldwide waste
generated per person per day averages almost 0.74 kilogram, but ranges widely from 0.11 to
4.54 kilograms.
The waste generated per person from the developed countries is much, much higher than that
generated from the underdeveloped or developing countries. So, when looking forward,
global waste is expected to grow to 3.4 billion tonnes by 2050, more than double population
growth over the same period.
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Let us talk about India. Urban India about 377 million people generates 62 million tonnes of
municipal solid waste each year. Of this about 43 million tonnes (amounting to almost 70%)
is collected and 11.9 million tonnes is treated. About 31 million tonnes is dumped in landfill
sites. Now when we dump MSW in landfill sites, many a times it produces many different
types of gases, including methane and some toxic gases, thereby polluting the nearby
environment.
So, if it is not properly landfilled, then it is going to affect two things. First is the
environment in the form of leakages of gases. Second is, leaching of the components to the
groundwater sources (toxic components). Average waste is about 450 grams per person per
day (this is an Indian figure). However, there is much variability in per capita: daily
household municipal solid waste generation ranges from 170 grams per person in small towns
to 620 grams per person in large cities.
So, the trend is same; the urbanized people living in the large cities, produce more waste than
the people those are staying in the rural areas. So, waste generation will most likely increase
from 62 million tonnes to about 165 million tonnes in 2030. The associated difficulties of
MSW disposal have become a serious problem that do not bode well for the future
generations of city dwellers and the areas that have high population densities.
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So, governments often mandate the use of more environmentally acceptable methods of
MSW disposal by limiting and sometimes phasing out some of the more traditional disposal
methods. The collection and disposal costs increase and proper disposal becomes more
difficult to achieve with the passage of time. And talking about the energy potential; the
global energy potential of waste can be estimated at 8 to 18 Exajoule per year in 2010, which
could increase to 13 to 30 in 2025, if a heating value of municipal waste ranging from 6 to 14
mega joules per kg.
So, with the best estimate moving from 12 Exajoule in 2010 to 20 Exajoule in 2025, for an
average heating value of 9 mega joules per kg for waste. Some sort of estimation basically;
exact figures may vary depending upon the type of waste we are dealing with.
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So, now, let us talk about industrial wastes. So, the food industry produces large number of
residues and by-products that can be used as biomass energy sources. These waste materials
are generated from all sectors of the food industry, with everything from meat production to
confectionery producing waste that can be utilized as an energy source. Solid wastes include
peelings and scraps from fruit and vegetables, food that do not meet quality control standards,
pulp and fiber from sugar and starch extraction, filter sludges and coffee grounds. These
wastes are usually disposed of in the landfill dumps.
Now, there are liquid wastes too. So, liquid wastes are generated by washing meat, fruit and
vegetables, blanching fruit and vegetables, pre cooking meats, poultry and fish, cleaning and
processing operation as well as wine making. These wastewaters contain sugars, starches and
other dissolved and solid organic matter. The potential exists for these industrial wastes to be
anaerobically digested to produce biogas or fermented to produce ethanol (bio-ethanol), and
several commercial examples of waste to energy conversion already exist. Pulp and paper
industry is considered to be one of the highly polluting industries and consumes large amount
of energy and water in various unit operations.
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The wastewater discharged by this industry is highly heterogeneous as it contains compounds
from wood and other raw materials, processed chemicals as well as compound formed during
processing. Black liquor can be judiciously utilized for production of biogas using anaerobic
UASB technology. We will discuss about that technology later on in one of our class. So, if
you look at this particular table, you can see that this gives the domestic supply of municipal
and industrial waste. So, it is the total value and how much the industrial waste is
contributing (that is almost close to 50%).
So, this is again continent wise and understanding of the industrial waste and their energy
values. So, again, almost close to 40% here, if you look at the global data.
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Now, we are discussing about the agricultural wastes. So, out of all the wastes, my
understanding is that, agricultural waste has the greatest potential that can be utilized for
energy production or the bioenergy production, whether it is pyrolysis, whether it is
gasification, whether it is producing ethanol or use the ABE fermentation to get butanol,
biogas. Any such thing can be done using the agricultural residues, because they are very
clean and are produced in very large quantities. So, there is certainly a sustainable issue for
throughout the year getting this one (availability), but we do not have to segregate things.
Rather, technologies are now developed, where we can mix more than one type of
agricultural waste including forest waste to produce and convert them to value added
products and of course fuels.
So, the main source for energy from agricultural land is in the form of crops for biofuels and
residues for biogas, as well as use in the form of heating and cooking. In terms of area
harvested, cereal food crops, such as maize, rice and wheat, together account for more than
580 million hectares of the land use and together account for more than 80% of the area
harvested for major crops.
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So, a major indication of the significant development in agricultural practices is visible in the
increasing yield of crops around the world. Most of the major crops including cereals, oil
crops and sugar crops have shown double digit growth in yield globally, while at the same
time the area harvested for these crops has not shown similar growth. Now, some crops such
as sugar beet, barley, sorghum, etc., have reduced area harvested while at the same time
increasing yields.
So, globally, now, more food is being produced efficiently from the same area of land than
before. Thanks to the development in agricultural sector. So, high yield crops are now being
planted, which gives better yield and they are also pest resistant, thereby increasing their
overall yield.
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Crops which show a tremendous growth in area harvested include maize 45%, soybean 66%
and cassava 55%. Now, it is important to note that the use of crops for biofuels is a very
small share of the overall use of crops for food production. In terms of actual production
major crops such as maize, rice and wheat dominate the crop production globally due to their
increasing use in America (maize) and Asia (rice and wheat).
Although a minor share of maize is used for biofuel production, the potential for energy from
crops such as rice and wheat lie in their efficient use of residues such as the husk and straw,
which are currently unutilized and sometimes cause environmental concerns. In India you
know that every year there is a big problem near Delhi; from the Punjab and Haryana side the
agricultural crop residues are being burnt up. So, in huge quantities the entire polluted air
affects the National Capital Region, and breathing also becomes a problem. So, it is a very
serious problem. Now, many farmers have understood the bioenergy potential of the residues
or wastes that is generated from their crops to produce some value added products and they
have started making small plants near their agricultural lands and farms, to produce energy.
So, there are certain reports that farmers are producing energy from gasification unit and even
pyrolysis unit (small scale). So, things are happening in a very positive way, in India, as well
as in other developing and developed countries.
So, although a minor share of maize used for biofuels production, the potential for energy
from crops such as rice and wheat lie in their efficient use of residues such as husk and straw,
which are currently unutilized and sometimes cause environmental concerns. So, now, let us
talk about the oil crops. Both soybean and rapeseed production has almost doubled globally
because of their huge demand - mainly due to the extensive production of soybean in South
America (Americas itself account for 90% of the soybean production globally) and of
rapeseed in America, Asia and Europe.
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This will make you understand region wise the areas that is being utilized for harvesting
certain crops, (this is in 2017). In the worldwide figure if you see, out of all these crops,
maize, rice, wheat and soybeans constitute more than 80% (75 to 80%).
So, similarly, this will tell us, continent wise crop yield globally. Again, you can see here,
that the sugar beet and the sugarcane are the highest in yields because they are produced in an
extremely large scale in the Americas. So, this is production quantity of crops globally in
2017. Again you can see that sugarcane, maize, rice and wheat, they constitute almost more
than 75%.
So, let us talk about energy potential. Now one of the most promising sectors for growth in
bioenergy production is in the form of residues from agriculture sector. Currently, that sector
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contributes less than 3% to the total bioenergy production. However, due to the increasing
demand for replacing fossil fuels in power plants for heat and electricity with sustainable,
renewable and dispatchable energy sources, agricultural residues such as straw and husk can
form a major share of the bioenergy generation. Now, apart from replacing fossil fuels and
reducing emissions, agricultural residues also solve the environmental challenge, which can
occur due to the annual burning of harvested residues in major countries such as China and
India. This is what I just mentioned about; burning of the crop residues.
Considering the fact that 50% of the residues have to be left on the field for soil quality
purposes (basically to enhance the soil quality), the theoretical potential for utilizing
agricultural residue is still enormous. Data shows that utilizing the residues from all major
crops for energy can generate approximately 4.3 billion tonnes to 9.4 billion tonnes annually
around the world.
Utilizing standard energy conversion factors for residues by conservative moisture content
and energy content of the fuels, the theoretical energy potential from residues can be in the
range of 17.8 Exajoule to 82.3 Exajoule. The major contribution is coming from the cereals,
mainly maize, rice and wheat. So energy generation from agricultural residues could meet
about 3 to 14% of the total energy supply globally. So, this is an estimated figure for around
2030.
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So, this is the theoretical potential of the agricultural residues globally. You can see that the
first column is giving you the different types of crops, then the residues in million tonnes and
then the residues’ energy potential. You can see that maize, rice, wheat and soybean is
constituting more than 80% of the total production. And if you look at the corresponding
energy values, they are actually excellent. So, they are better and higher than other crops like
barley, oats, sorghum, olive etc.
Now, let us understand the importance of the forestry wastes. The forestry sector is the
largest contributor to the bioenergy mix globally. Forestry products, including charcoal, fuel,
pellets and wood chips account for more than 85% of the biomass used for energy purposes.
Most of the use of the forestry product is in the form of residues from pulp, paper and
sawmill industries while a significant percentage also the use of fuelwood for cooking and
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heating purposes in Africa and Asia - so called traditional fuelwood or biomass. Globally,
3.99 billion hectares of the land is classified as forest land. Most of the forest land is in the
form of other naturally regenerated forest (almost 61%), while primary forest accounted for
one third of the all forest land.
Recently, planted forests have been increasing, leading to an increasing forest land globally,
although they account for a minor share (7%). Globally, forest land has been decreasing since
2000. The decrease in forest area is noticeable in Africa (almost -7.7%), followed by America
(-3.1%) while the decrease has been compensated noticeably due to the increasing forestland
in Asia (+ 5.1%) and Europe (+ 1.4%). I can tell you that India played a significant role in
afforestation adding up to this number. So, you can see in this particular table, the forest land
area that is globally available.
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So, among continents, majority of the forest land occurs in the Americas (40%), followed by
Europe (25%) and equal share in Africa and Asia (15% each).
So, this is due to the enormous area of primary forest in the Amazon in South America,
which accounts for almost half of all primary forests globally. These primary forests are
naturally regenerated forests of native species with no visible indications of human
intervention.
So, due to significant afforestation efforts in the major economies like India and China, the
global planted forest area has increased by more than 30% during 2000 to 2017 even though
planted forests account for a minor share of the overall forest land. China and India are
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engaged in huge afforestation. So, as a result, there is a huge upsurge in the total amount of
forest area that is available, but these are basically manmade forest.
So, Asian continent accounts for 45% of all the planted forests globally. Planted forests
include those forests where the trees are predominantly of introduced species and mainly due
to human intervention.
Americas also account for the highest share of other naturally regenerated forest (34%)
globally, which are tree species that are predominately non native and do not require human
intervention to reproduce/maintain population over time. So, this particular table will tell you
about the primary forest, other naturally regenerated forest and the planted forest that is
available.
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Now, let us understand their energy potential. So, one of the primary products from forests
that are used for bioenergy production is wood fuel. Most of the wood fuel is used for
traditional cooking and heating in developing countries in Asia and Africa. Globally 1.9
billion meter cube of wood fuel was used for energy purposes - for example, fuel wood and
charcoal production.
Now, the volume includes wood removed from felling of forest or from trees killed or
damaged by natural causes. We are not supposed to cut the trees, for making any fuel. So, it
is important to note that wood fuel does not include the use of wood residues from industrial
processing of round wood, which forms a major share of the bioenergy in Europe. Among
continents, both Asia and Africa together account for three fourths of all wood fuel
production globally. India and China both adding a larger share. And the share has remained
constant in the last past 17 years, which is a good thing.
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So, woody biomass is an important source of energy and is currently the most important
source of renewable energy in the world. In 2010, global use of woody biomass for energy
was about 3.80 Gm3
/year, which consisted of 1.90 Gm3
/year for households fuel wood and
the similar number for large scale industrial use. During the same period, world primary
energy consumption was 541 Exajoule per year and world renewable primary energy
consumption was 71 Exajoule per year. Hence in 2010, woody biomass formed roughly 9%
of the world primary energy consumption and 65% of the world's renewable primary energy
consumption.
So, I wind up with this today and in our next class, we are going to discuss about the biomass
as energy resources. We will be discussing about the dedicated energy crops that I talked
about in today's lecture and even last lecture. So, some of those crops we’ll understand in a
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better way. How they are being grown, what are their properties and how best they can be
utilized, like maize, sorghum, sugar beet, etc. And some perennial crops such as sugar cane,
switch grass, miscanthus, etc.
So, thank you very much. And in case you have any query, please drop a mail to me at
kmohanty@iitg.ac.in or feel free to log into the Swayam portal and post your query there. I
will be happy to address those. Thank you.
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Module-02
Lecture-04
Good morning students. This is lecture 2 of module 2.
And in today's lecture we will be discussing about dedicated energy crops, including some of
the annual crops like maize, sorghum, sugar, beet, hemp, etc. And then perennial herbaceous
crops like sugarcane, switchgrass, miscanthus and short rotation woody crops, like poplar,
willow, etc. Basically how they can be grown for bioenergy purposes and what is their
potential, the land availability, the energy content, all these things we will discuss.
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So, let us see this particular slide. You can see that biomass have been basically categorized
into two groups; Dedicated energy crops and Residues/Wastes. So, under dedicated energy
crops, we have the fuel wood which is basically hardwood and softwood (different traditional
fuel woods) and then herbaceous. So, there (under herbaceous) we have grain and oil crops,
and perennial grasses.
So, under residue and wastes (this we have discussed in one of our classes, this is a very large
scale quantity) we have agricultural residues, we have municipal discards, we have wood
residues. So a crop & livestock derived (under agricultural residues), wastewater/landfill and
food processing waste (under municipal discards), then urban wood waste (and primary and
secondary milling residues) (under wood residue category). So, we will discuss a few of
these.
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So, coming to the dedicated crops. Dedicated energy crops have been proposed as a strategy
to produce energy without impacting food security or the environment. As I told you in one
of the classes, one of the aims of the biofuel production is to depend on such crops or waste
materials which will not interfere, the food versus feed problem. So, it should be outside of
the food chain. Otherwise in a country like India, having huge population and huge food
demand, we are not supposed to use sugarcane directly, or let us say beet roots (sugar beet),
sorghum, corn for the bio ethanol or biofuel production. We cannot afford to do that, whereas
the same is being done in some of the developed Western countries.
So, they are grown specifically for their utilization in energy conversion processes in ways
that do not displace food production. So, they are beneficial in providing certain ecosystem
services, including carbon sequestration, biodiversity enhancement, salinity mitigation, and
enhancement of soil and water quality. So, they provide a source for the production of
renewable energy, chemicals and materials due to their composition of sugars, lipids, proteins
and fibers.
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So, crop residues and dedicated bioenergy crops together constitute 3 to 9 Exajoule of the
bioenergy potential. In general, energy crops with a larger fraction of fibrous material (the
lignocellulosic part) contain the highest calorific value making it advantageous to maximize
the yield of this plant fraction for the production of energy and fuels.
That is why I already mentioned in our previous lecture, that currently lignocellulosic
biomass are being utilized for the biofuel or bioenergy production, because of the huge
energy content in them. So, fuel wood (dedicated energy crop) produces usable heat for the
residential, commercial and power in the electric utility sector. Not all residues are available
for bioenergy production because they are needed for livestock feed and to maintain soil
fertility. So, everything cannot be converted to biofuels.
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So, they (dedicated crops) are a potentially significant source of low carbon biofuel in India.
And they have low ILUC (which is called indirect land use change, basically related to
unintended consequence of release of carbon) emissions. So, depending on where and how
they are cultivated, energy crops can be grown without creating pressure on the food market.
India supported the deployment of Jatropha, an oilseed crop, capable of being grown on
degraded lands unsuitable for conventional agriculture. The expansion of Jatropha failed to
live up to its potential for a variety of reasons, particularly its low yields.
So, I will show you this Jatropha cycle. You see these are the seeds, then they are being made
to seedlings. Then it is planted that is a (to grow into a) mature plant; then you can see plant
bearing fruits; then fruit getting dried up or ripened, and then you collect the seeds. Now from
the seed we get Jatropha oil, which is being converted to biodiesel. Now please understand
that why the Jatropha failed; it is because of this life cycle.
When you start with this seed and seedling, you plant it and you keep waiting for years
together for the Jatropha to bear fruits and ripen; then you will harvest. This is one of the
things – it is a huge time that you need to spend or you need to wait, before you get these
Jatropha seeds. And then, as I already mentioned in the previous slide, the low oil yield is one
of the major reasons why Jatropha has failed. Now nobody's talking about Jatropha anymore.
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So, the switch grass is another one (which) may offer better potential as they can often
survive under adverse conditions with little labor input and can support biodiversity and soil
carbon sequestration. With India's growing population, all currently utilized agricultural land
will likely need to be maintained or expanded by 2030 to supply sufficient food. That means
in a nutshell, we can understand that, India is no more in a position to provide its prime land
or the agricultural land for such bioenergy dedicated crops.
So, the need is to look for lands which are not cultivable. The reported yields for switch grass
and Eucalyptus, for example, range from 8 to 13 and 14 to 51 dry tonnes, respectively, per
hectare on agricultural land, but only 3 to 9 and 0 to 17 dry tonnes per hectare on marginal
land. Of course, in agricultural land the production will be very high, but the aim is not to use
the agricultural land, because that will be utilized for growing the crops. So, an estimation of
maximum of 39 million tonnes of biomass could be produced from cellulosic energy crops
grown on wastelands in India in 2030. This is a projection.
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So, if you see the biomass energy produced till 2015 percentagewise, you will see that
Finland, followed by Sweden, Austria is there, then Europe then United States. So, in the
Asian countries actually it is very less. From an energy point of view that total biomass in the
world has a potential production capacity of 33,000 Exajoule. However, currently, biomass is
partially exploited, accounting for only 14% of the primary energy in the world, standing at
approximately 56 million Terra joule per year.
Now we will discuss about the annual crops. Energy crops include plants intended for energy
production. One of their main strengths is stable production, which can ensure a large scale
long term raw material supply. In particular, new crops have significantly higher yields per
unit area than conventional ones. Now traditional crops whose final product is used to
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produce energy and biofuels are also considered as energy crops such as wheat, barley,
maize, sugar beet, sunflower, etc.
Let us understand maize. So, maize is a member of the Poaceae family. It is one of the most
popular cultivations around the world, such as in the United States, China, India and Brazil
and these 4 countries produces the largest quantities. Maize is the annual plant, wind
pollinated, both self and cross pollinated. Maize is mainly used for two reasons: (i) for the
starchy raw material content in the seeds and the material from which bio ethanol is mainly
produced; (ii) for the biomass (the crop residues) resulting from the removal of the seeds and
consisting of leaf, stems and cone of the blade.
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Maize stands out among the agricultural species with the potential to supply biomass for
energy production because it has a large acreage of approximately 177 million acres
worldwide and grain production of nearly 989.3 million tons in 2015 and 16. Now the maize
is a kharif crop and is majorly harvested from September to December. The maize Rabi is
majorly harvested in January and May.
So, in India we do twice and in other places also. So, here you can see in the left side is the
crop calendar. This is about India and in which month it is being actually planted and
harvested. So, it gives an idea about that. So, it is sowing, growing and harvesting, three
things, three phases are being shown here.
So, maize production is influenced by nitrogen application (increasing in nitrogen increases
the potential for energy generation) and inter-row spacing (very little influence). So, this
biomass presents an energy potential of 11,050 kilowatt hour per hectare. So, considering the
use of only husks and cobs it is possible to generate 2712 kilowatt hour per hectare
bioenergy. The high calorific value ranges from 15.6 to 18.3 mega joule per kg. Because of
the different energy contents and amounts of biomass produced by distinct parts of the maize
plant its potential to generate energy varies significantly.
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Then corn cobs. So, corn cobs must not be too crumbled, that is, the percentage of particles
smaller than 2 mm must be lower than 5% in which case they would be suitable for
controlled combustion. The length of corncob should be equal to 0.667 times its diameter. It
is advisable to use simple high effective chippers in order to facilitate transport of corncob
from the grinding mill to the warehouse and from the warehouse to the firebox.
You can see here; the general composition of the corn cob given in table 1; starch, cellulose,
proteins, fat and ash. You can see the starch is the highest followed by cellulose. So, this
cellulose can be basically exploited for bioenergy purposes.
Then dry corn cob. So, due to ash melting, the temperatures of ash combustion in the
fireboxes must not exceed 900 degrees centigrade. Insignificant quantity of NOX compounds
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is produced at high temperatures. You can see the proximate and ultimate analysis. So, the
moisture content is around 9.6%, the volatile matter is 80% and remaining is ash 2.16. And in
the element analysis you can see the carbon content is very high; it is almost close to 50%.
Now, the melting temperatures of ash produced from corncob combustion are: during the
early stages of sintering at 760 degrees centigrade, during the early stages of softening at 970
degrees centigrade, during the softening stage of ash at 1100 degrees centigrade, and finally,
during the melting stage of ash at 1325 degrees centigrade. So, these parameters, are very
important when somebody is going to design a particular bioenergy unit or a system or a
process.
Now, let us understand how corn is being converted to ethanol. You can see here. So, the
corn stock gets separated into flower, stem, cob and husk and leaf. All these are having
excellent bioenergy potential as it is. So, we can combine them and see what is their
bioenergy potential (that also can be done). So what you do basically, once you take it out, of
course, remove the corn, all other parts will remain. So, then you go for different
pretreatment technologies to break the recalcitrant nature of the materials. So, you can go for
dilute acid (there are many technologies), dilute acid is very common. And it is less costly,
less time consuming also. So, let us assume that we go for dilute acid pretreatment. Then
once it is done, solid residues are left. So, then you can go for the enzymatic hydrolysis, then
whatever sugar you got, it goes for the fermentation.
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So, (next is) ethanol fermentation and you get that lignocellulosic ethanol or bioethanol.
Here, in a nutshell, you can understand about the schematic of the ethanol production from
the corn stock.
Let us understand about another annual crop which is sweet sorghum. So, sorghum is the
second most important feed grain grown in the United States in terms of planting acreage,
and is also planted in India and countries of Africa. So, it contains two things, both soluble
and insoluble carbohydrate. So, in soluble we have glucose and sucrose and in insoluble we
have cellulose and hemicellulose, in almost the same quantity (soluble and insoluble in
almost same quantity) and is thus considered a good substrate for bioethanol production.
However, currently, there is only one species of sorghum that is called Sorghum bicolour,
that has the potential to mass produce ethanol. Sorghum bicolour, better known as the sweet
sorghum, has three different components which can be used for ethanol production, the grain,
the bagasse and the juice.
Now the juice extracted from plant stalks contains plenty of sugar such as sucrose, glucose
and fructose, which can be directly converted via biological fermentation process into
ethanol.
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So, approximately 50 to 85 tons per hectare of sweet sorghum stalks yields 39.7 to 42.5 ton of
juice per hectare, which upon fermentation yield 3450 to 4132 litres of ethanol per hectare.
Please note that it is a very good yield. And sweet sorghum exhibits several better
characteristics over the other energy crops. For example, drought and salt tolerance, has a
short period of growth (almost within 4 months you can take it out) and requires less water
and fertilizer leading to a low cost of production.
So, these are all very interesting features when we are thinking of growing sweet sorghum
with an aim for bio energy potential or bioenergy purposes. Now the three of the most
important traits of sweet sorghum are high biomass yield, high sugar to ethanol yield and the
ability to grow on marginal land areas. Other important traits of sweet sorghum are high
conversion efficiency of light into biomass energy, high water use efficiency and a relatively
high tolerance to soil constraints, such as salinity and water concentration.
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Sweet sorghum juice is rich in minerals, like calcium, magnesium, zinc, iron etc. After juice
extraction from sweet sorghum stalks, pulp or dry refuse left is the bagasse; and that has also
enormous potential towards bioenergy or biofuel production. So, the proximate and elemental
composition of sweet sorghum bagasse clearly indicates that it has a high carbon to nitrogen
ratio, but low amounts of nutrients.
Now, the ash consists of calcium oxide, magnesium oxide, sodium oxide, potassium oxide,
silicon oxide as well as traces of chlorine. Pretreatment, enzymatic hydrolysis and
fermentation are the essential processes (required for its) processing to ethanol.
So, you can see the composition. Basically, this is the biochemical composition of the
sorghum. You can see 35 to 50% is cellulose, 15 to 25% is hemicellulose and then rest is
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lignin. So, here the ultimate and proximate analysis is given. Fixed carbon is 16.6%, carbon is
35.5%, hydrogen, nitrogen sulfur ash is very less and volatile matter is 65.5% (huge volatile
matter content basically).
So, this scheme will make you understand, how sweet sorghum can be made into various
value added products. So, if you look about the whole plant, and then here is the plant parts;
if you look at the whole plant → make into chips; then you go for combustion, and then you
get ash for fertilizer, then you go for the pyrolysis (another thermochemical conversion
process), silage, ethanol second generation, lignin.
So, you get so many different types of products. It can be converted further into electricity
and fertilizer, some platform chemicals also. Then bagasse, leaves, sugar juice (of course, it
will go to the food and feed purposes), then the seeds will be there (that also goes for food
and feed purposes), other than that parts of juice, leaves will be converted to fertilizer and
transport fuel. So, this will make us understand about the different uses of the sweet sorghum.
And you can see that apart from other uses, it has enormous energy potential or bioenergy
potential.
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So, in India, the major factor which determines sweet sorghum as a feedstock is its likelihood
of cultivation and processing for ethanol during the non-crushing season. The Government of
India has started the Ethanol Blended Petrol Program (EBPP) in 9 states and 4 union
territories in January 2003. Now, this program encourages the blending of gasoline with
ethanol and the utilization of biodiesel obtained from non edible oils for blending with diesel
(5% blending).
Now, however, regardless of efforts, the EBPP has not taken off effectively due to unfeasible
ethanol production from molasses as well as other sources. So, though the government is
mandating that we should have almost 10% ethanol blending, however, it is not happening
due to inadequate supply, because we do not have such plants as it is. And I am happy to tell
you that Numaligarh refinery Ltd. located in Numaligarh, Assam (Indian Oil Corporation), is
basically establishing a state-of-the-art bioethanol plant. So, within 2 years, the production
will start, it is under the process now.
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So, the techno economic feasibility (carried out in India) of ethanol from sweet sorghum is
slightly lower compared to that of ethanol (from sugarcane molasses). So, sweet sorghum is
around 13 rupees, sugar cane molasses is close to 15 rupees. So, the net income from sweet
sorghum is 38% more compared to that of the sugar beets. Now, the global fuel ethanol
production in 2016 is presented in this pie chart. You can see that United States is the huge
amount (has a production of about) 57% and India is contributing only 1%. But please note
that, India is working on this particular crop and soon within three to four years or maybe
down 5 years, we will most likely double our bioethanol capacity or production capacity.
So, now understand about the sugar beet as a bioenergy crop. Now sugar beet is a man made
crop with its origin in the 19th century from table and fodder beets. Sugar beet provides an
abundance of sucrose which is easily fermented by many microbes. The amount of sucrose
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extracted per hectare is dependent on three factors. The weight of the beets harvested, the
percentage sucrose in these beets, and the amount of sucrose that is extractable.
The root of the sugar beet may contain almost 20% sucrose by fresh weight. Pulp or marc
remains after the sucrose and molasses have been extracted from the crop. The pulp
represents the 22 to 28% of the dry mass of the sugar beet root that is not solubilized during
the sugar beet extraction process. However, the amount extracted is less (if you compare that
is almost 15.3% average from the United States crop data) because some cations like sodium
and potassium or some amino nitrogen compounds like betaine and glutamine, interfere with
the extraction of the sucrose. So, thereby making the sucrose extraction a bit complicated.
So, after the sucrose has been extracted, the remaining juice is the molasses. Today, more
than 25% of the world's sugar requirement is made from sugar beet and beet sugar industry is
now well established in 45 countries spread over 4 continents of the world. For farmers, sugar
beet is important for three main reasons. First, it is a dependable cash crop. Second, it
ameliorates salt affected soils with promoting soil fertility through sound farming practices.
And third, the by-products provide nutritious cattle feed during the hot months of the year,
when green fodder is not readily available. So, this is a win, win situation for the farmers
basically. So, among sugar beet and sugar cane sugar beet accounts for only 16 to 20% area
of the world, whereas production accounts for only 11 to 13% of the world. This is a 2014
data.
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You can see this table 4, the chemical composition analysis of the sugar beet pulp. You can
see that the lignocellulosic part, that is basically hemicellulose, cellulose and lignin; they are
the highest. And when you go for sugar analysis you will see that glucose is the highest and
followed by arabinose and xylose and very minor quantity of galactose, mannose and
rhamnose.
So, the obtained values for the degree of methylation and degree of acetylation were 42.5%
and 56% respectively, which are characteristics features of the SBP (that sugar beet pulp).
The density of the sugar beet pulp is 0.596 grams per liter and the pH of 100 grams per liter
water slurry has a value of 5.14.
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So, we can further discuss little about this chemical composition analysis. The first one, table
5, tells you the chemical composition analysis of sugar beet root (dry matter basically). Then
table 6 will give you the same for sugar beet pulp and table 7 will give you that of the sugar
beet molasses. So, you can see the ash, protein, ether extracts, crude fiber and sucrose
content. You can see that the root is having the highest sucrose content, almost close to 70%.
So, sucrose is the main constituent of the sugar beet root dry matter. Protein and lipid
contents of beet pulp products are usually low. In addition, beet protein contains mainly non
essential amino acids. So, then minor carbohydrates are glucose, fructose, raffinose and some
other oligo or polysaccharides, their concentration is below 1% and it depends to a significant
extent on the manufacturing process.
And now let us understand another annual crop which is known as hemp. Hemp is Cannabis
sativa. So, there are many other species also. It is grown for various purposes of using the
fibre and seeds. It is one of the oldest non food crops in the world. Now, it is considered as an
interesting industrial plant with great uses that can be grown under a wide range of agro
ecological conditions and is more efficient compared to many other plants.
Hemp as a species also has one major drawback. It is associated with the production of illegal
drugs. So, that means you can understand that there is a controlled growing basically. So, as a
consequence, only registered hemp cultivators that are reported for the cultivation can be the
source of this valuable raw material.
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So, the main problem may be establishing a crop, because hemp is very sensitive to poor soil
structure and water shortage or excess during the early stages of growth. In terms of its
energy use, it is important that the green crop yield from hemp is on average 14.5 ton per
hectare of which 70 to 75% are hemp shives (the byproduct of the hemp processing), which
are usually left in the field constituting organic fertilizer.
Now at the same time, hemp biomass shows a significant variation in fuel properties
(calorific value, heat of combustion, ash content, ash softening temperature etc.) depending
on the season in which the harvest takes place. The heat of combustion of hemp biomass
collected in August - December is on average 18.4 mega joule per kg versus that collected in
January, April is 19.1 mega joule per kg. You can say that there is no significant or very huge
dip in that, but still there is a difference.
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So, grinding the hemp to a particle diameter of 8 mm requires an energy consumption of 117
kilowatt hour per tonne, which is about 50% smaller than the briquetting capacity of fruit
biomass at 25 kg per hour. However, compaction itself requires an energy demand of about
110 kilowatt hour per tonne, which is almost 40% more energy intensive than that of the fruit
wood.
At the same time problems related to cutting the hemp biomass are the subject of research on
reducing its energy consumption and optimizing the efficiency of this process. Literature
show that hemp has high dry matter content and good energy concentration per hectare.
Moreover, hemp is a good ratio of energy efficiency to input and is therefore an above-
average energy crop.
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So, particularly noteworthy here is the content of volatiles at the level of 69%. Please have a
look at this proximate analysis of hemp biomass, you can see that the highest constituent or
component is basically the volatile matter and if you see the ultimate analysis, the carbon is
43.36% followed by hydrogen and then of course nitrogen and sulfur, sulfur is very small
quantity.
So, you can see that by comparing this data with the possibility of growing hemp in 2019 in
the Lublin province, one can dispose of just over 100,000 tons of biomass which contains (if
you take into account its heat of combustion as per the tabulated) 1.7 PJ of energy which is
equivalent to approximately 85,000 tons of hard coal with the calorific value of 20 mega
joule per kg.
So, having said that the inherent meaning of this table data is saying that hemp is having huge
potential for bioenergy production. So, if you compared to even the hard wood also. So, since
this is outside, it is a non-food crop, and can be grown at marginal lands with little care, then
we can certainly look for such a beautiful crop for a dedicated bioenergy potential or
purposes.
So, you can see this particular slide; it will tell you about the hemp plant basically; these are
the various parts and this particular figure or the scheme will tell you what are the different
usages of hemp plant. So, you can see that there are industrial textiles and consumer textiles
fibers, agricultural benefits are there, then we can make paper, building materials okay THC,
all these things from the leafs and the bast fibers, then the hemp seed oil.
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So, seed is being used for food purposes, seed cake can go for the animal feed, the oil can go
for the personal hygienic products, for industrial products, and even for the foods also. So, it
is so much use.
So, now let us understand another crop which is called a herbaceous crop towards this energy
potential. So, herbaceous crops have the highest ranking for bioenergy production due to their
high biomass yield, high net energy gain and biomass quality that renders them suitable for
both biochemical and thermochemical conversion. Now, please understand one more thing,
among all these, whatever we were discussing, the different biomasses; biomasses are not
suitable for both biochemical and thermochemical conversion.
Some are pretty good for biochemical conversion that means fermentation to get bio alcohols,
ethanol or butanol; and some are pretty good for thermo chemical conversion, for using in
gasification, pyrolysis etc. However, there are only few noteworthy biomasses which can be
used for both the purposes and herbaceous crops are one among them.
Perennial herbaceous crops have a greater biomass production compared to woody crops,
relatively better biomass quality, low lignin content and high digestibility render herbaceous
biomass crops suitable for second generation biofuel production. Some of the native grasses
that are being developed as biomass feedstocks are big bluestem and Indian grass. So, the
first one you can see is big bluestem and the second picture is that of the Indian grass.
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Then let us discuss one of the most important crop in India and apart from India in other
countries also, i.e., sugar cane. Now sugar cane belonging to the family Poaceae is a tropical
perennial grass widely used for the sugar production. Now, the sugars extracted from sugar
cane can be easily fermented to produce ethanol. But having said that, please note that in
India we cannot afford to do that. It can be produced that is true, but, in India we are not
doing that. So, in addition the bagasse (biomass remaining after the juice is extracted from
the stalks) can be further used by sugar mills to generate steam and electricity. In India, what
we are doing is we are doing with the bagasse. Now, this bagasse is being traditionally
utilized to produce steam. And in the boilers (basically we are burning it in the boilers). And
then gasification process to generate steam and of course, feed it to the boiler and you get
electricity also. In small scale also this is being implemented in various sugar producing
industries. So, its high photosynthetic efficiency and tillering and ratooning ability make this
crop extremely attractive to be used as an energy crop. Now being a source of 70% of world's
sugar production, it is very important cash crop for cane growing countries.
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Worldwide it is grown on an area of 26.8 million hectare and its total production is 1.9 billion
tons with a fresh cane yield of 70.9 tons per hectare. Sugarcane is a C4 for plant and as a C4
for plant, sugar cane yields higher biomass than maize, miscanthus and switch grass.
Sugarcane as a feedstock has potential to become a major bioenergy source, as it has highest
yield per unit area among the agricultural commodities, thus offering possibility of excellent
energy balance than other bioenergy options.
Sugarcane and energy cane have good potential for cultivation on non fertile agricultural
lands as well. Please understand, you may be wondering what is energy cane. Energy cane is
nothing but a genetically modified version of the sugarcane and that is modified with an aim
to increase its bioenergy potential.
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So, sugarcane’s fibrous stalks are rich in sucrose, which is accumulated in its internodes.
Sugarcane industry and distilleries extract this sugar and subject it to fermentation to generate
ethanol. Now, cane derived ethanol is being used as a first generation biofuel predominantly
in Brazil where half of the total crop is used to produce ethanol. Now in Brazil, they can
afford to do so but that is not possible in India or other developing countries including most
of the Asia.
So, worldwide sugarcane is source of 21 million m3
ethanol. And average sugarcane varieties
yield 85 to 100 kg sugar and 35 to 45 kg molasses (that is the byproduct) from 1 ton of cane
biomass, whereas, 22 to 25% ethanol recovery is obtained from molasses through
fermentation. Again, I am telling you that fermentation of molasses to produce bio-ethanol,
we are not going to use the sucrose part to produce bio ethanol.
Though it is being done in Brazil and some of the developed countries, because, for them the
availability is huge with respect to their consumption. But in other countries like India and
Asian countries, that is not possible. So, we look for basically the bagasse and molasses.
So, bagasse the other major byproduct of the sugarcane processing is mainly used as a source
of bioelectricity and also for paper, board and xylitol production purposes. So, xylitol is a
very high demand compound or component you can say. So, it’s a sugar, which is being used
mostly in the chewing gums. So, xylitol will be fermented from xylose, which is one of the
sugars present in the bagasse.
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So, presently, first generation, bioethanol is being produced from sugarcane, which involves
sucrose concentration and extraction from juice, followed by fermentation and distillation.
Now, this ethanol fraction corresponds to only a third of the cane energy and the other plant
residues corresponding to the remaining two thirds. So, by utilizing bagasse, straw, trash and
tops the other portion (that is 66%) of the sugarcane biomass, production of bioenergy from
this group can be enhanced.
Having said that, the meaning is literally that: forget about the sucrose part, that will go
basically for the production of the sugar; rest everything which is amounting to almost 66%,
every part of this, whether it is bagasse, whether it is the top, trash, straw, these all can be
converted into bioenergy or biofuels.
However, recently, focus has also been shifted to “high-fibre/high-biomass” energy cane
varieties for the production of second generation bioethanol. These are genetically modified
sugarcane which is known as energy cane. Now such cultivars are further classified into two
types. So, type one contains sugar greater than 13% and has fiber content of greater than
17%.
Whereas type two energy cane is exclusively developed for higher biomass and contains low
sugar and high fiber. Now, please understand that this energy cane, especially the type two, is
exclusively grown for bioenergy purposes because the sugar content is very less. So, we can
just use that part also as it is, if it is possible, directly to produce ethanol.
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So, energy cane also contains marginally higher lignin than the conventional type. The total
biomass and fiber contents of energy cane are significantly higher, almost 138% and 235%
more than the conventional cultivars. Such cane type easily meets all the requirements of a
renewable biomass resource.
Now, if you look at the typical features of sugarcane biomass, then table 11 will tell you the
chemical composition of the biomass and energy cane. So, you can see that basically the total
fiber content is almost 26.7 in the energy cane, cellulose is 41.6 and 43.3 in both bagasse and
energy cane. So, they are comparatively complementing each other. Lignin by percentage dry
weight is also comparable (20.3 and 21.7). And table 10 will give you the typical features of
the sugarcane biomass, the properties and the yield, the brix, fibre and fertilizer requirement
and NPK basically.
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So, table 12 will tell you about the average sugarcane energy content mostly used in
commercial sugarcane varieties; the juice, then fiber residues, sugar agricultural residue
(which is called a SCAR); and that will tell you about their mass per 1 ton of sugarcane and
the corresponding energy value.
It is very interesting; all these values they are all complementing each other. That means,
whether it is juice, whether it is fiber residue bagasse or it is SCAR, every component is
having huge bioenergy potential. So, you can see that juice is having almost 15.89 mega joule
per kg energy obtained from the sugarcane, from fiber residues it is 15.67, from sugar
agricultural residues that is SCAR, it is 15.6; all are almost complementing each other.
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So, here you can see the sugarcane production in different countries. So, you can see that
India stands here, India produces huge amount of sugarcane (a little lesser than Brazil). And
far more than that of the mainland China and other Asian countries like Thailand and
Pakistan.
So, these are the application of sugarcane biomass. You go for sugar, then filtered mud (that
is organic fertilizer), molasses (that can be converted into ethanol and animal feed), then we
have the juice (that can be converted to biofuels, pharma based products), we have bagasse
(that can be converted to ethanol), we have other renewable energy.
So, let us understand another interesting herbaceous crop, which is called switch grass. Now,
switch grass is a native warm season perennial grass indigenous, to the central and North
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American tall grass prairie into Canada. So, the plant is an immense biomass producer that
can reach heights of 10 feet or more. Its high cellulosic content makes switch grass a
candidate for ethanol production as well as, as a combustion fuel source for power
production. The use of switch grass relative to other annual row crops leads to a 95%
reduction in soil erosion and a 90% reduction in pesticide usage. So, all switch grass contains
a number of different inorganic elements, which are not useful in the conversion of this
bioresource to biofuels. And please also understand that there are different species of this
particular switch grass. There are many different varieties that are grown in India and other
countries also.
So, these elements must be treated as a side stream during the processing and conversion of
biomass to biofuels, and in order to minimize and understand their effect, it is necessary to
determine the amount of these species in the switch grass sample. Now, it can be seen that the
production of fuels from the biomass is dependent on the content and structure of the
structural components in the cell wall, as well as the inorganic constituents.
Yields of switchgrass in a study performed in Iowa state showed that they varied from 6.9 to
13.1 metric tons per hectare, with an average yield of 9 metric tons per hectare. The lowland
varieties are characterized by tall, thick stems and are generally found in heavier soils and
wetter regions.
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The upland cultivars preferred drier soils and grow better in semi-arid regions, they are also
shorter and thin-stemmed. The upland varieties of switch grass include Trailblazer,
Blackwell, Cave in Rock, Pathfinder and Caddo. These are some varieties of switch grasses.
Common low land varieties are Alamo and Kanlow. Now the elemental analysis for
switchgrass cultivars was found to be comparable to that of the hybrid poplar, another
potential biofuel feedstock.
The HHV/ the heating values are comparable to that obtained from the hybrid poplar which is
around 19 mega joules per kg and to other grasses such as the reed canary grass which has
been reported to have a value of 18 mega joules per kg.
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You can see the elemental analysis of different types of switchgrass grown in the Iowa state
in the United States. The elemental composition of biomass is a basic chemical property that
is useful in determining the potential of a given bioresource for biofuels and biopower
application. Elemental analyses for switch grass cultivars were found to be comparable to that
of the hybrid poplar and other potential biofuel feedstock.
So, this is the lignocellulosic composition of switch grass from the Iowa State. So, different
species you can see listed here. So, literature showed that the dried biomass of switch grass
contained 3400 to 4200 milligrams per kg of phosphorous and 8100 to 10900 milligrams per
kg of potassium. In general, the results show that the relative concentration of the elements in
the switch grass samples was Silicon=potassium > phosphate=calcium > chlorine > Sulphur >
Aluminium. So, the results from Kanlow do indicate that there are differences in these
components dependent on plant constituents (basically whether it is leaves, whether it is a
stem, or other parts).
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So, this particular scheme will tell you the residual biomass production for unit fuel in
different countries. So, you can see the United States top among all that followed by the rest
of Asia.
And this is the flow of biofuel production from switch grass. This is interesting, I will just
explain. So, you can see that solar energy being utilized to grow the switchgrass. So, then you
get the feedstock, then it goes for the fodder part or lignocellulosic part you just differentiate
them, then go for acid treatment, you get cellulose and hemicellulose. That is cellulose and
hemicellulose can be sccharified to sugars, hexoses and pentoses, now then can be fermented
to get biofuels. Now you can have simultaneous scarification and fermentation which is
called co-fermentation. So, that also can be possible. This is a biochemical part, now here the
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cellulose, hemicellulosic part including the lignin part can be pyrolyzed which is a
thermochemical conversion part.
Pyrolysis to what; usually highest yield is the bio-oil or you can call it pyrolytic oil and you
get some gases also. Those gases can be converted to methanol and again it can be blended,
then from bio oil we can make diesel and we can get some other co-product. It is very
interesting to note that this bio-oil, basically from pyrolysis what we get, from any
lignocellulosic biomass when you settle it, is easily settle able to 2 different phases.
One phase which is rich in the organic components, and that is the oil part, and the other part
is the aqueous part. Now, that aqueous part also contains very useful chemicals and which, if
they are present in a particular amount or in a good amount, then that can be purified to get
some platform chemicals; some value added products, nothing is waste basically.
So, then let us talk about the short rotation woody crops. The short rotation woody crops are
ideal for woody biomass production and management system because they are renewable
energy feedstocks for biofuels, bioenergy and bioproducts, that can be strategically placed in
the landscape to conserve soil and water, recycle nutrients and sequester carbon. Wood
biomass is a preferred feedstock for the pyrolytic production of bio oils because high lignin,
with its greater energy density is a desired characteristic.
The selection of species and the genetic improvement for use as a feedstock will have to take
different approaches to serve the two biofuel platforms. So, either you can go for the
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biochemical conversion using the sugars or you go for the thermochemical conversion using
the pyrolysis.
So for the biochemical platform for fuel production trees have been seen by some as a less
desirable feedstock because of the high lignin content and recalcitrance to digestion. So,
lignin has less oxygen than carbohydrates (so there is less to remove) and high energy density
meaning more energy content per ton of biomass that is processed. The first one you can see
here on the left hand side the top one is the hybrid poplar plant. And the below one is the P
deltoides. Improved woody biomass production and management systems and needed to
maintain healthy forests and ecosystem, create high paying manufacturing jobs and meet
local and regional energy demands. And these short rotation woody crops fulfill all these
criteria. So, P. deltoides has a very high growth rate (mean annual increment of 20 to 25
metre cube per hectare per year) in India.
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The genus Populus comprises (let us understand about poplar plant) 25 to 35 species of
deciduous plants native to the Northern Hemisphere. Common names used for the different
species include poplar, aspen and cottonwood. Poplar breeding mainly focuses on three
native species: Populus deltoides, Populus balsamifera and Populus trichocarpa; and two
non-native species: Populus maximowiczii and Populus nigra. So, hybrid poplars are among
fast growing trees in North America and are well suited for a variety of applications such as
biofuel production, pulp and paper applications and other bio based products such as
chemicals and adhesives.
The nominal yield of hybrid poplar species in North America is estimated to be 14 Mg per
hectare per year. The heating values for hybrid popular species are 19 megajoules per kg. The
heating values for P. deltoids species are around 16 megajoules per kg. Soil productivity
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requirements may necessitate that this valuable inorganic resource be returned to the soils.
Also, some inorganic elements, such as phosphorus, calcium, magnesium are present. So,
they have their different roles during thermochemical or biochemical conversion.
So, non structural material is often removed from biomass prior to chemical analysis. We
have solvent soluble and non-volatile compounds such as fatty acid, resins, chlorophylls and
usually that comprises a minor proportion of the biomass. For large-scale biorefinery
operation extractives can be a potential source of value added co-products. The compounds
present in the extractive fraction are a function of the solvent, which is usually ethanol,
acetone, dichloromethane or a mixture of ethanol/benzene.
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So, ethanol extractives include waxes and chlorophyll, whereas ethanol/benzene extractives
also include low-molecular-weight carbohydrates. To avoid the use of large amounts of
organic solvents on an industrial scale the extractive fraction can be effectively isolated by
using supercritical carbon dioxide or steam as the solvent. So, the ethanol extractives content
of poplar species is similar to corn stover and pine, but is much lower compared to that of the
switchgrass.
The extractive content of P. deltoides is 1.4% (the extractive content from corn is 3.9% and
switchgrass is 15.5%). So, this is very less in case of P. deltoides.
Interest in the use of willows as a feedstock for bioenergy and bioproduct has developed over
the past few decades because of the multiple environmental and rural development benefits
associated with their production and use. Depending on different estimates between 350 to
500 species of willow, basically the Salix species, are found worldwide and predominate in
the Northern hemisphere.
Although the India Himalayan region is home to 24 willow species only 10 are reported from
the Lahaul valley itself. The yield of dry oven biomass amounted on average 14.1 Mg per
hectare per year and its gain of energy is equal to 242.3 GJ per hectare per year.
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It is relatively fast growth rate and low agro-chemical requirement. It is a commercially
grown crop. You can go for the CHP, that is combined heat and power production. There are
2 potential sources of high value products from the willows. The first is the component
polymers of biomass and second is the extractives in the bark and heartwood. So, a common
misconception about willow biomass is that it makes a poor choice for the production of
different forms of energy because its energy content is lower than other woody biomass and
has higher ash content. While the energy content of willow on a volume basis is lower than
the hardwoods, due to willow’s lower specific gravity however, on the weight basis willow is
almost similar to other hardwoods.
So, the energy content of a three-year-old willow stems averaged almost 19.4 mega joule per
kg. The mean specific gravity of three-year-old stems for a different willow varieties ranges
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from 0.4 to 0.43 gram per cm3
. So, this willow biomass crops are grown using coppice
management that utilizes the willows natural ability to resprout. So, this results in biomass
being produced and distributed across several stems.
The number of stems produced and maintained in this production system varies among
varieties and has ranged from 4.6 to 13.7 stems per stool after three years of regrowth
following coppicing. After the first growing season the willow is coppiced and material is
typically left in the field since first year production is very low, typically between 0.4 and 1.0
tons per hector.
So, this you can have a look. The ultimate analysis of the willow biomass; proximate analysis
and the lignocellulosic composition; you can see that the cellulose content is 42%
hemicellulose is 33% and lignin is 25%. That means it can be utilized under various
platforms to produce bioenergy, whether it is thermochemical or biochemical. So, a
significant amount of moisture is present during the time of harvest (50%), which is not good
when you go for a thermochemical conversion process. So, the high heating value of willow
biomass shows that it can be effectively used as an alternate biomass.
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So, you can see this; if you compare it with the usual petro, Naphtha (crude oil basically), the
same sort of things (products) you can get it from the biorefinery way using the willow. So,
in petrochemical way one raw material and you get diverse chemical products, whereas, in a
biorefinery way you have many raw materials and you get many different products. This is
the beauty of the biorefinery concept.
So, this will tell you about the type of solid fuels and their origin. So, from the agricultural
biomass, forest biomass and fossil fuels.
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And moisture content of different biomass varies from agricultural biomass (where it is
highest), followed by the forest and the fossil fuel. So, the moisture content in fuel causes
significant problems during ignition and combustion process. A high amount of generated
heat is lost to heating and evaporation of water which leads to a decrease in the useful energy.
So, before you process for the thermochemical conversion especially, you need to reduce the
moisture content of the biomasses.
So, with this I wind up and in the next lecture we will be discussing about the dedicated oil
crops and their biorefinery potential. Then we will also discuss about the microalgae as
feedstock for biochemicals and biofuel production. So, thank you very much and if you have
any query please feel free to write to me at kmohanty@iitg.ac.in, thank you.
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Module 02
Lecture-05
Oil Crops and Microalgae
Good morning students, this is lecture 3 under module 2.
In today's lecture we will discuss about the dedicated oil crops and their biorefinery potential one
by one. And then later we will discuss about microalgae. How micro algae can be used as a
feedstock for biofuels and biochemicals under a bio refinery platform.
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So, interest in the use of biofuels worldwide has grown strongly in recent years due to the limited
oil reserves, concerns about climate change from greenhouse gas emissions and desire to
promote domestic rural economies. The term biofuel is as such referred to solid, liquid or
gaseous fuels that are produced from plant matter and residues, agricultural crops, municipal
wastes and agricultural as well as forestry by-products.
Biodiesel can be derived from a variety of sources, including vegetable oils, animal fats and
waste cooking oil. So, waste cooking oil has been tried for biodiesel production since almost a
decade and it has been quite successful. Vegetable oils, also known as triglycerides, are
chemically an ester in which three fatty acid groups are attached to one glycerol molecule.
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Vegetable oils from renewable oil seeds can be used as alternate to diesel fuels. The advantages
of vegetable oils as diesel fuel are their portability, ready availability, renewability, higher heat
content (almost about 88% of number 2 diesel fuel), lower sulfur content, lower aromatic content
and biodegradability. However, the main disadvantages are the higher viscosity, higher cost,
lower volatility and the reactivity of unsaturated hydrocarbon chains.
The vegetable oils are all extremely viscous, with viscosities ranging almost 10 to 20 times
greater than number 2 diesel fuel. Blending of vegetable oils with diesel, however, reduces the
viscosity drastically. And the fuel handling system of the engine can handle vegetable oil - diesel
blends, without any problem. Initially when the blending was started, it was almost 5%. Then
gradually it can be increased. So, now government is desiring for a 10% blend in number 2 diesel
as well as in our petroleum, gasoline.
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So, over the last 30 years, the oil crop production in the world increased by 240%, while the
increase in area and in the yield was 82% and 48% respectively. The main oilseed produced in
the world is soybean whereby it represents more than 50% of total oil crop production in the
entire world. A 40% increase of growing area and an over 100% increase in total crop yield was
observed from 1989 to 2008.
The expansion was brought about by a 150% increase in oil palm acreage and additional
increases in rapeseed, soybean and sunflower acreages by 75%, 65% and 64% respectively.
Now, these data or statistics basically indicate that, there has been a huge upsurge in the
plantation as well as production of the different vegetable oils; whether it is sunflower, whether it
is soybean, whether it is rapeseed. In India mustard has also taken a significant space.
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Now annual as well as perennial oil crops was grown on a worldwide acreage of over 261
million hectares of agricultural land in total. The overall yield achieved from oil crop production
was about 72 million tons for the 2008 season; due to high difference in oil concentration
between the various crop species this translates into an estimated vegetable oil yield of 157
million tons. So, on the level of plant species, 38% of the total oil crops acreage is planted with
soybean, whereas, cottonseed and oilseed rape are grown on 12% each, followed by groundnuts
and sunflower and later on comes the oil palm (6%).
So, in terms of production, 32% of total crop yield is made up by soybean, whereas, about 28%
is from oil palm which is due to the high annual fruit of that perennial species. In the past,
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vegetable oils and fats were predominantly used for food and livestock feeding purposes,
whereas, nonfood utilization of vegetable oils in oleochemistry applications mainly focused on
particular crop species such as oilseed rape, such as canola, linseed, cotton or castor.
So, you can see these are the four pictures or images of these crops. The first one is the canola,
the second one is the linseed, third one is the cotton and fourth is the Castor. So, this situation is
currently changing due to the growing need of oil as biofuel feedstocks. Between marketing
years of 2005 and 2007, biofuel use of vegetable oils increased from 4.1% to 8.5% (almost
double) and by the year 2017, over 15% of the worldwide vegetable oil production was used as
biofuel feedstock.
So, let us look for the traditional oil crops. Most of the biodiesel is currently made from soybean,
rapeseed, sunflower and palm oils. Now having said that, kindly note that in India we are not
doing so. As I told you in the last class that whether it is in India or developing countries, when
we talk about vegetable oil to biodiesel, it comes directly under the food versus feed problem, so
we are not doing so. But having said that you have to understand that these are being done in
some of the countries in which the production is huge. And they have a huge problem of storing
the oils. So, new plant oils that are under consideration include mustard seed, peanut, sunflower
and cottonseed. Soybean oil is commonly used in the United States and rapeseed oil is used in
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many European countries for biodiesel production, whereas coconut oil and palm oils are used in
Malaysia and Indonesia for biodiesel production.
So, it is all about the supply and the production; basically, how much we are producing and how
much we are consuming. If the production of any such crops is much higher than the requirement
of a particular country, then, they can think of converting those to biofuels otherwise it is not
possible.
So, about 80% of the European Union's total biofuel production is comprised of biodiesel
produced from rapeseed and sunflower seeds (because they can afford to do that). So, soybean
oil accounts for approximately 90% of the biodiesel produced in the United States, rapeseed oil
has a 59% of total global biodiesel raw material sources followed by soybean, palm oil,
sunflower and others.
Now another thing I want you to know, that whenever we are directly showing this type of
statistics 59% of these or 28% of that, please understand that it is not only the oil that is getting
produced from that particular species but also its waste. So, let us say bagasse, the stalk, the
kernels, the husk etc. So, those are also being added to that particular statistics to produce
different types of biofuels not only biodiesel but also bio alcohols.
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So, this table will make you understand different fuel related properties of the selected vegetable
oils. So, you can see that, the first one is the different types of oil, A. indica is Azadirachta
indica, that is neem’s oil, then Jatropha, then Mahua that is Madhuca indica, then Pongamia
pinnata that is karanja and then there are other seeds. So, you can see that iodine values are very
good. However, you can (also) see that the viscosity of these oils are very high.
Especially the R. communis is extremely high, thereby, making its direct use in an engine more
difficult. And you can see there are other properties like cetane number, cloud point, pour point,
flash point all these details.
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So, the major obstacle for commercialization of biodiesel is it is cost as approximately 70% to
90% of the biodiesel production cost arises from the cost of the raw materials. Therefore,
biodiesel produced from edible vegetable oils is currently not economically feasible. Now that is
what I was just mentioning to you about, that whether it is a developing countries or developed
countries let us tell it in a sustainable way.
So, in a sustainable way producing this is not so feasible. Let us understand that in a particular
year, sunflower has been produced so large in quantities, that storing is a big problem. Now
please understand, that may not happen in the next year or next to next year. Because most of the
countries are still depending upon the season or the climate for the agricultural purposes whether
it is in India, or it is any developing countries.
And there are other factors which also govern the yield and the mass production of the crops. So,
in a sustainable way, it is very difficult to do that; whether it is in developing countries or
developed countries. So, now later has moved from the edible to non edible oil seeds. So, non
edible oil plants are easily available in all the countries and are very economical compared to the
edible plant oils.
Now the biggest thing about this non edible oil plants is that this do not come under the food
versus feed problem. And then extensive use of edible oils may cause other significant problems
such as starvation in developing countries (this is what I was mentioning). There are concerns
that biodiesel feedstock may compete with food supply in the long term. So, the sustainability
always comes into picture and economics also has to be taken care of. So, biodiesel produced
from non edible vegetable oil has a good potential as an alternative diesel fuel.
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The use of non-edible plant oils when compared with edible plant oils is very significant because
of the tremendous demand for the edible oils for food and they are far too expensive to be used
as fuel at present. Now non edible oil plants can be grown in waste lands (that is another biggest
advantage) that are not suitable for food crops and the cost of cultivation is also much lower
because these plants can still sustain reasonably high yield without intensive care. So, there are
many examples of non-edible oilseed crops such as Jatropha, Mahua, karanja, castor, neem,
rubber seed, tobacco seed, rice bran etc.
So, now we will see one by one, what are their properties and how they can contribute to this
biodiesel production. So, the first one Jatropha curcas; we have discussed about Jatropha, I
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showed you the Jatropha lifecycle in last class. So, it is a tall bush or small tree up to 5 to 7 meter
tall, belonging to the Euphorbiaceae family. Originally from Central America, Jatropha curcas
is found throughout the tropics including much of African and Asia.
So, a research study showed that one hectare of Jatropha curcas could capture up to 25 tons of
carbon dioxide from the atmosphere every year (that is a significant number of course). So,
Jatropha curcas seeds have an oil content ranging between 30% and 40%. Jatropha curcas oil
contains approximately 24.6% of crude protein, 47.25% of crude fat and 5.54% of moisture
content.
So, most of the non edible oils including Jatropha carry a high level of the free fatty acids. The
oil fraction of Jatropha consists of both saturated and unsaturated fatty acids.
So, the next one is Pongamia pinnata, which is commonly known as karanja. It is a medium
sized glabrous, perennial tree that grows in the littoral regions of South Eastern Asia and
Australia. India is full of these plants; you can see in many places. The yield of oil seed per tree
is between 8 and 24 kg.
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And the seeds of Pongamia pinnata content about 30 to 40% of oil. The oil is considered to be
less toxic and cheaper than Jatropha curcas oil, so it has become the subject of biodiesel
research.
Most of the physical and chemical properties of the Pongamia pinnata oil as similar to those of
the diesel fuel, however, this oil is more viscous and produce higher carbon residue. So,
Pongamia pinnata oil contents oleic acid (51.8%) as the major fatty acid followed by linoleic,
palmitic and stearic acid.
So, the next is also very famous tree in India which is called Madhuca indica. It is commonly
known as Mahua or butternut tree. It is a middle sized large deciduous tree which grows to a
height of 10 to 15 meter. The tree starts producing seeds after 10 years and continues for up to 60
years. An average yield of 800 kg per hectare can be expected in a mahua plantation after a
decade. So, each tree yields about 20 to 40 kg of seeds per year, mahua seed contains 35% of oil
and 16% of protein.
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Fresh Mahua oil from properly stored seeds is yellow, while commercial oils are generally
greenish yellow with an offensive odour and disagreeable taste. Mahua oil contains the high
level of free fatty acids (almost up to 20%) and a proper procedure for converting this oil to
biodiesel is very much required.
The next is Ricinus communis, which is popularly known as castor oil plant and belongs to the
family Euphorbiaceae. It originates in Africa but it is found in both wild and cultivated states in
all the tropical and subtropical countries of the world. In India also we have huge castor oil
plantation. It is a small wooden tree that can reach a height of about 6 meters. The comparitive
advantage of this plant is that, its growing period is much shorter than that of the Jatropha and
pongamia.
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So, Castor seed is an ideal candidate for production of high value industrial oil feedstocks
because of the very high oil content (almost 48 to 60% of the seed) depending upon the species,
and the extremely high levels of potential oil production (500 to 1000 liters of oil per acre) which
is a very good yield. So, the main constituent of castor oil is ricinoleic acid (which is 90%),
which contains 18 carbon atoms with a hydroxyl group position at 12.
Castor oil contains more oxygen than other oils and therefore castor oil and it is derivatives are
more soluble in alcohols during the transesterification reaction, thereby yielding a higher
biodiesel, after the reaction. So, the main disadvantage of castor oil is it is high viscosity, the
high viscosity of this oil leads to its poor atomization of the fuel, incomplete combustion,
choking of the fuel injectors and ring carbonization.
So, in India we have huge plantations of all such things, whether it is Castor, whether it is
Jatropha, whether it is Mahua. You will see Mahua and Castor especially in the eastern side of
the country. So, huge plantation is there in Odisha, Jharkhand, Bengal and Bihar. Jatropha was
planted in huge quantities. But as I told you in the last class, its sustainability has become a big
problem. Therefore, most of the Jatropha plantation has been discontinued.
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So, next is Azadirachta indica which is the neem tree. It is a member of the family Meliaceae. It
is a majestic, evergreen, tropical forest tree with a broad crown and a height of approximately 25
meters. So, it is a well established plant in at least 30 countries worldwide in Asia, Africa and
Central and South America. India is full of these trees, anywhere you go; and due to it is
environmental benefits such as purifying oxygen/air, it has been deliberately planted in the
roadsides.
So, neem seeds contain about 45% of the brownish yellow fixed soil, mainly constituted by the
oleic acid, palmitic acid and stearic acid followed by linoleic acid. Traditionally, neem oil has
been used as a fuel in lamps for lighting purposes in rural areas. And it is used on an industrial
scale for manufacturing of soaps, cosmetics, pharmaceuticals and some non edible products. And
one more important thing is that neem oil also has certain medicinal properties.
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So, next is Hevea brasiliensis, commonly known as the rubber tree. It is a fast growing tree that
belongs to the family Euphorbiaceae. It is the major source of natural rubber and is native to the
Amazon forests and is now widely cultivated in tropics across the world. In India also we have
huge rubber plantation in states like Kerala, Karnataka and many southern states.
So, normal seed production yields vary from 70 to 500 kg per hectare per year, while the annual
seed production potential in India is about 150 kg per hectare. Rubber seed contain
approximately about 40% of kernel with 20% to 25% of moisture. Apart from it is use in latex
production for foreign exchange, rubber tree produces oil bearing seed whose oil content in dried
kernel varies from 35% to 45%. Now rubber oil does not contain any unusual fatty acids and its
rich source of essential fatty acids, C18:2 and C18:3, that makes up almost 52% of it is total free
fatty acid composition.
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So, the next is Nicotiana tabacum, so it is the tobacco plant. It is an annually grown herbaceous
plant belonging to the Solanaceae family, widespread in North and South America commonly
grown for the collection of the leaves. So, the highest seed production is found in Nicotiana
tabacum varieties used to obtain the chewing tobacco, reaching 1171 kg seeds per hectare, which
corresponds to 432.9 kg oil per hectare. Now the seed oil content ranges between 33 and 40 wt%.
The major fatty acids in seed triacylglycerols are linoleic acid, followed by oleic acid, palmitic
acid and stearic acid.
The next is rice bran. Rice is the main cultivation in subtropical Southern Asia, and it is a staple
food for a large part of the world's human population especially in East, South and South Eastern
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Asia, making it the most consumed cereal grain. Rice bran is the low value co product of rice
milling which contains approximately 15 to 23% of oil. The oil fraction of rice bran consists of
both saturated and unsaturated fatty acids, cultivated in countries like China and India.
Very little research has been done to utilize this oil as a replacement for the mineral diesel. I used
to tell you that the CSIR Institute of Chemical Technology or CSIR IICT, Hyderabad. So, they
have developed an excellent process for converting this rice bran to the vegetable oil for the
human consumption. And it is in the market and has been consumed by a big number of people
in India as well as in the world.
So, the next is Moringa oleifera which is also called as drumstick tree. So, its fruit has been
consumed in India in huge quantities in South India as well as East and West India. So, Moringa
is most commonly cultivated in South India, Ethiopia, Philippines, Sudan and has been grown in
West, East and South Africa, tropical Asia, Latin America, Caribbean, Florida and Pacific
Islands.
So, Moringa seed has an oil content of between 30% to 40% depending upon the plant variety
and climate. Moringa oil contains oleic acid as the major fatty acid followed by stearic acid,
behenic acid, arachidic acid, palmitic acid, linoleic and eicosenoic acid.
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The next is Calophyllum inophyllum. It is commonly known as polanga or hone; it is a large
evergreen tree and belongs to the Clusiaceae family, widespread in East Africa, India, Southeast
Asia and Australia. So, it is a medium and large sized evergreen sub maritime tree that averages
8 to 20 meter in height, with a broad spreading crown of irregular branches. The nut kernel
contains 50% to 70% of oil and the mature tree may produce 1 to 10 kg of oil per year depending
upon the productivity of the tree as well as the efficiency of the extraction process.
Traditionally, polanga oil has been used in medicinal applications, soap, lamp oil, hair grease and
cosmetics in different parts of the world.
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Then Simmondsia chinensis; so this is commonly known as jojoba. It is a perennial shrub
belonging to the familiar Simmondsiaceae. This plant is native to Mojave and Sonoran deserts of
Mexico, California and Arizona. A 10-year-old tree yields on an average of 1 kg seeds per year.
It is unique among plants in the fact that it is seeds content about 50% of oil by weight, which is
more than the amount in soybean and somewhat more than in most of the oil seed crops.
Jojoba oil is practically colorless and odorless and it is composed mainly of straight chain
monoesters of C20 and C22 acids and alcohols with two double bonds.
The next is Sapindus mukorossi; so Sapindus mukorossi is a well known as soap nut tree. It is a
perennial tree belonging to the family Sapindaceae, indigenious to northern India. Now this plant
grows very well in deep loamy soils and leached soils. So, cultivation of Sapindus mukorossi in
such soil avoids potential soil erosion; it has been deliberately planted in most of the places to
restrict the soil erosion.
This tree can be used for rural building construction, oil and sugar presses, agricultural
implements. Sapindus mukorossi seed contains about 23% of oil out of which 92% is
triglycerides.
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Then Melia azedarach; so Melia azedarach which is also known as syringa, is a deciduous tree
that grows between 7 to 12 meter in height in the mahogany family of Meliaceae that is native to
India, Southeast Asia and Australia. The oil content of dried syringa berries is around 10 wt%.
Melia azedarach oil is characterized by a high percentage of unsaturated fatty acids, such as
oleic and linoleic acids. Other constituents that are present in greater than 1% are saturated
species such as palmitic and stearic acid.
Vernicia fordii, it is commonly known as tung tree, is an oil bearing woody plant belonging to
Euphorbecaeae family that is native to China, Burma and Vietnam. The oil content of tung seeds
and the whole nuts is approximately 21 and 41 wt% respectively and the average oil yield is
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about 450 to 600 kg per hectare. It is a good oil yield basically from this species. Its seed oil had
been conventionally used in lamps for lighting, as well as an ingredient for wood paints and
varnish. Tung oil principally contains unusual conjugated fatty acids, eleostearic acid,
octadecatrienoic acid; with linoleic, oleic, behenic acids also present in significant quantities.
Then Schleichera oleosa, it is also known as kusum. So, it is a medium sized up to almost 40
meter in height, deciduous or nearly evergreen tree belonging to the Sapindaceae family that is
native to South and South-East Asia. So, the fruits, seeds and young leaves of this plant are
edible and used for medicinal and dye purposes. The oil content of kusum seeds is 51% to 62%
but the yields are 25% to 27% in village ghanis (the oil mills) and about 36% in the expellers.
So, of course when you do a better processing or extraction technology, the yield of oil that will
come from the same seed will be much higher. Iodine value of the oil is almost 215 to 220 and it
is total fatty acid content is 91.6%.
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So, this table will make you understand the oil content in seeds and kernels of some of the non-
edible plants. So, you can see the listed neem, polanga, rubber, mahua, syringa, drumstick,
tobacco, karanja, castor, soap nut, jojoba. All those what we have actually discussed, you can
see, in most of trees (these are plants and some are shrubs), you can see this wt% seed and wt%
kernels. Let us focus on the seed only. You see that mostly they are comparative or
complementing each other (almost 20 to 30 to 40% in that range), which emphasizes that most of
these seeds can produce a huge amount of oil. And again I am telling you that extraction of oil is
a tedious job. If you are going for the traditional extraction then you may end up in getting
almost 60 to 70% or even less than that.
When you talk about chemical based or some other supercritical based extraction, then you may
go up to 80% yield. Depending upon seed, oil and in which type of soil it has been grown and
under what climatic conditions it has been grown; so many things actually affect the final yield
of the oil.
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So, this table will again make you understand the yields of various non edible feedstocks. It is
given in kg per hectare. You can see that polanga, followed by drumstick, then jatropha and
neem, so these are high yield varieties.
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Now we will discuss about microalgae. So microalgae as a feedstock for biofuels production, not
only biodiesel but how we can use microalgae in a bio refinery concept, to produce various other
biofuels apart from biodiesel as well as other platform chemicals.
Although oil crops are renewable resources, biodiesel production from oil crops in large
quantities has been deemed unsustainable. Production of crop derived biodiesel will require large
amount of arable land, which has to compete with the cultivation of food crops. Now this has led
to the controversy of “food versus fuel”. The increasing criticism of the sustainability of many
first generation biofuels has stimulated the interest in developing second generation biofuels
which are being produced from non-food feedstocks such as lignocellulosic biomass.
Now microalgae as a feedstock for biofuels has received considerable attention due to their
advantages over higher plants and other organisms. Although long term research and
development in this field have been carried out, commercial implementation of microalgal
biodiesel is still in it is infancy (there are various reasons for that). Many key technologies need
to be developed and optimized at almost all stages of microalgal biodiesel pipeline, from
screening of suitable microbial strains to downstream processing.
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So, microalgae appear to be the only promising alternative to biofuel crop plants because of the
following facts:
(a) it grows rapidly and many species contain high amounts of lipids (basically the oils) which
can provide sufficient feedstock for large scale biodiesel production;
(b) Non-requirement of arable land for microalgal culture makes their growth without conflict
with the food production.
 According to an estimate, meeting only half of the existing U.S transport fuel needs by
biodiesel would require 24% of the total cropland to grow oil palm with the highest oil
productivity. (So, you can see these are some of the algal blooms or green algal blooms).
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(A brown algal bloom is being shown here)
 On the other hand, only 2.5% of existing cropping area would be required for cultivation
of microalgae with 30% oil in biomass, which can also produce equivalent biodiesel.
 The percentage of cropping area required can still be lower, because 30% oil content in
the biomass can be achieved easily for many oleaginous microalgae.
(c) The next advantage is that, microalgal cells have photosynthetic mechanism similar to those
of higher plants to fix carbon dioxide in air and convert the carbon to carbohydrates and lipids,
with some species accumulating large amounts of triacylglycerides (TAGs - these are also
triglycerides), which are suitable for biodiesel production.
 The photosynthetic mechanism of microalgae is cost effective compared with oil
producing heterotrophic microorganisms that utilize glucose and other organic carbon
sources.
(d) So, the next advantage is that microalgae can remove large amounts of carbon dioxide
emitted by power plants and other industrial sources contributing significantly to the greenhouse
gas mitigation.
(e) From an environmental standpoint, some microalgae can efficiently treat highly polluted
municipal and agricultural wastewater that contain excess nitrogen and phosphorus nutrients.
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(f) As an attractive bioreactor system, microalgae can produce useful byproducts including long-
chain polyunsaturated fatty acids, carotenoids for foodstuffs, and other compounds used in the
cosmetic and pharmaceutical industries.
 Integrated utilization of these byproducts will make an important contribution to the
reduction of overall production costs. Now this is what I will just explain you briefly.
Now please note that, microalgae is something, each and every part of that particular
organism is being useful, it is just like a banana plant. So, the fruits we eat, the flowers
are also being eaten in India and many parts of the South East Asia. The leaves are being
used traditionally for various purposes, the trunk is also eatable. So, it is an endless thing.
Similarly, for algae also every part is being utilized. What we are talking about in these
particular slides, is about the biodiesel from microalgae; but, it is not the end of the story.
See, once you extract the biodiesel, that means the oil is extracted or lipid is extracted and
there is something left out solid, which is called lipid extracted biomass, microalgal
biomass. This will have so many other valuable things present such as a huge amount of
carbohydrates. It may have pigments, it may have other important valuable products,
such as astaxanthin, vitamins so on. So, what I mean to say is that once you extract the
lipid from the microalgae, it is not the end of the story. So, then we are going to work on
the leftover part, the solid part. So, depending upon its component analysis we can
convert it; if there is huge carbohydrate, we can go for hydrolysis followed by
fermentation thereby producing bio alcohol. We can also produce bio butanol, following
the Abe fermentation. If we see that, it has good chlorophyll content, we can extract that
chlorophyll; if it has good astaxanthin content or some different pigments, that can also
be extracted. So, vitamins also can be extracted, so we can play with it depending upon
what species it is and what is that component analysis after the oil is being extracted. So,
if we look into that perspective, in a complete biorefinery perspective, then it will become
sustainable. Otherwise, if you only talk about microalgae to biodiesel, it is not going to be
a sustainable process.
 Microalgae also produce other fuels such as alkanes, ethanol, butanol and hydrogen in a
more bio refinery platform.
(g) The use of biodiesel from microalgae results in minimal release of sulfur dioxide, nitrous
oxide and other contaminants when compared to petroleum derived diesel.
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Now let us understand the biodiversity of microalgal lipid properties. Please look at this
particular slide; you can see there are so many different types of species that has been shown
here. The picture has been taken from the European algae biomass association, you can see the
different types of algae, please do understand that algae is only green, it is not so. There are blue
green algae, there is brown algae (it is just like a plant).
So, you do not usually understand if you see with the naked eye that it is an algae. So, it is very
diverse basically. Microalgae comprise several groups of unicellular, colonial or filamentous,
photosynthetic and heterotrophic microorganisms containing chlorophyll and other pigments. So,
microalgae can grow autotrophically or heterotopically with a wide range of tolerance to
different temperature, salinity, pH and nutrient availabilities.
More than 40,000 microalgal species have been classified as prokaryotes (cyanobacteria) and
several eukaryotes including green algae, diatoms, yellow green algae, golden algae, red algae,
brown algae, dinoflagellates and others.
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Many different classes of lipids can be produced in microalgal cells. Based on chemical
structures and polarity, these lipids are divided into polar and neutral liquids. In most cases, polar
lipids function as a membrane structure component, which commonly include phospholipids and
glycolipids. So, neutral lipids include tri, di and mono acyl glycerols, waxes, isoprenoid type
lipids (for example, carotenoids), among which triacylglycerols (TAGs) are frequently found to
be accumulated as energy storage under various stress condition. These TAGs will be eventually
converted to biodiesel by the transesterification pathway.
So, although almost all types of microalgal lipids can be extracted, only TAGs are easily
transesterified into biodiesel by traditional methods. Analysis of thousands of microalgal species
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have shown tremendous difference in lipid content among different strains ranging from 1%
approximately to 85% of that dry cell weight. Microalgae produce a wide variety of fatty acids
with chain length from C10 to C24 depending on species or strains.
For example, the filamentous cyanobacterium, that is the Trichodesmium erythraeum can
synthesize C10 fatty acid accounting for almost 50% of total fatty acids. Whereas dinoflagellate
Crypthecodinium cohnii can produce docosahexaenoic acid (DHA) as high as 30 to 50% of the
total fatty acids. Moreover, for any one microalgal strain the lipid content, lipid class and fatty
acid composition fluctuate under different culture conditions.
Screening of oleaginous microalgae; due to the variation and diversity of microalgal lipids,
selection of oleaginous microalgal strains suitable for biodiesel production will require screening
large number of microalgal strains. The first large scale collection and screening of oleaginous
algae dates back to 1978, when the Aquatic Species Program was launched by the U.S National
Renewable Energy Laboratory for production of biodiesel from high lipid content algae.
With 8 years of effort about 3000 strains were collected and eventually around 300 species were
identified as oil rich algae. The main indexes determining the potential of microalgal strains as
biodiesel feedstock are growth rate, lipid content and lipid productivity.
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This table will make you understand about different microalgal species with relatively high lipid
content and productivity. So, you see that these are some of the microalgal species, here the lipid
content is given and that is the lipid productivity. You can see mostly they are complementing to
each other whereas this Pavlova lutheri giving us the highest in this particular species that is
being reported here, so followed by Neochloris sp. as well as Nannochloropsis oculata.
Both microalgae and cyanobacteria are considered as potential source of high value nutrients,
such as pigments, proteins, carbohydrate and lipid molecules. And this is what I was mentioning
about in the broad bio-refinery concept. It is not only about the lipid molecules that is being
getting extracted for biodiesel but we can play with all these things pigments, proteins,
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carbohydrates, there are vitamins and there are certain other chemicals which also can be
purified and made into the platform chemicals.
So, industrial scale production of microalgae has evolved worldwide due to human consumption
of microalgae as nutritional supplements. Apart from biomass, microalgae produce variety of
pigment molecules like chlorophyll, carotenoids, beta carotene, that are used as colorants in
cosmetic and food industry. Algae strains Chlorella sp., Dunaliella sp., Scenedesmus sp. and
cyanobacterial strains such as Spirulina sp. and Nostoc sp. are used as sources of fine chemicals
and nutrient rich foods supplements.
Further pigments; pigments are interesting class of chemicals, which can be purified from the
microalgal species. So, they are used in cosmetic industry as anti-ageing cream, refreshing or
regenerating care products for healing and repairing of damaged skin with nourishments. The
microalgae Haematococcus pluvialis (which is shown in this particular slide you can see), is
known as the natural source for the keto-carotenoid astaxanthin. Astaxanthin is one such pigment
which is of course having a lot of commercial value. Red pigment astaxanthin is the precursor
molecule for vitamin A and this pigment play important role in embryo development and cell
production in poultry as well as aquaculture firms. Moreover, astaxanthin has superior
antioxidant properties compared to those of beta carotene, alpha carotene, lutein, lycopene,
canthaxanthin and vitamin E, and therefore is becoming as popular as a human dietary
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supplement. That is what I was just mentioning about; that there is a huge commercial value of
this particular pigment.
Consequently, a number of industries such as Cyanotech, Seambiotic, Mera Pharmaceuticals and
Fuji chemical, are the producers of microalgae biomass for high value added products in
cosmetics, nutritious feed and pharmaceuticals. Selection of suitable process for pigment
extraction from the microalgae depend on several factors like biochemical features of pigments,
choice of solvents for extraction, extraction yield, duration of extraction, reproducibility,
denaturation and degradation of molecules, cost and easy operation. Now all these factors will
eventually determine how much pigments we are able to extract from a particular microalgal
species.
So, a number of processes like ultra high pressure extraction, use of supercritical carbon dioxide
for extraction, combination of techniques such as soaking in liquid nitrogen followed by buffer
extraction are currently being exploited and under research for further development to establish
energy efficient, low cost extraction technique for the pigments.
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So, microalgae are also considered as reliable rich source of the vegetable protein. Nutritional
studies on different microalgae has demonstrated that microalgae produced high amount and
high quality proteins which are the source of essential amino acids. You can see there is a
particular picture there, that picture is of the red algae Rhodophyta. These Rhodophyta and other
cyanobacterial strains produce a group of accessory photosynthetic pigment protein complexes,
for light harvesting purpose are also called phyco-billiproteins, these are high value products.
So, these proteins have a high demand in pharmaceutical industries and specific application in
the biological field as fluorophores. So, fluorophore are chemical compounds, which are
essentially responsible for emitting light. So, protein extraction from microalgae is done using
aqueous, acidic and alkaline methods followed by centrifugation, ultrafiltration, precipitation,
chromatography techniques for the recovery of the protein molecules.
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So, industrial scale extraction and purification of proteins from microalgae is not studied widely
and scalable downstream processes of microalgae for efficient extraction of proteins are still in
very high demand. So, diversity in microalgal species, variation in the cell structure, variation in
the intracellular protein content, release of protein degrading enzymes (proteases) from the cells
are major obstructions for up-scaling of the protein extraction process.
Some novel extraction techniques such as pulsed electric field, microwave assisted extraction
and ultrasound assisted extraction are employed for successful extraction of proteins from
microalgae. So, please note that the downstream processing cost usually constitute almost 40 to
50% of the entire product cost. So, that particular cost has to be brought down to a certain level,
so that the cost of the product eventually decreases.
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So, manipulation in growth conditions can enrich microalgae with high amount of carbohydrate
or polysaccharide molecules. Major components of the cell wall of algae are cellulose and
hemicellulose. Other than the cell wall algae also store polysaccharide molecules in the
cytoplasm. Marine algae produce complex sulfated cell wall polysaccharides, which have many
biomedical applications.
Some cyanobacterial strains (you see some of these are shown in this slide), are surrounded by a
matrix of polymeric substance mainly constituted by polysaccharides, which form a protective
layer between the cell and the intermediate environment.
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Biotechnological potential of the cyanobacterial extracellular polymeric matrix are attracting
increasing attention to the pharmaceutical, bio-plastic as well as food industries. Novel extraction
technologies such as enzyme assisted extraction, microwave assisted extraction, ultrasound
assisted extraction, supercritical fluid extraction and pressurized liquid extraction are currently
being applied for the extraction of bioactive molecules from microalgae.
These extraction technologies are attracting interest from the industries because of it is
advantages (such as higher yield, reduced treatment time and lower cost) compare to that of the
conventional solvent extraction techniques. A huge scope is still available for developing the
downstream processing part.
So, we will quickly go through some of the industrial products from microalgae, please see this
pigment. The product name is beta carotene, chlorophyll (chlorophyll is from green algae); this is
the structure, it is being used in the food industries, it is a natural pigment ingredient. Similarly,
beta carotene from Spirulina and, Caulerpa species; that is the structure of beta carotene and it is
found to be useful in the prevention against certain type of cancer and heart diseases.
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The next is protein; so protein powder or tablets is the form. There are different species such as
Chlorella and other cyanobacteria species such as Anthrospira. And this is the Spirulina powder
how it looks likes, this is a SEM image. It has so much of nutritional benefits, used as a
feedstock for animal and poultry. Then carbohydrate; the product name is agar, so Rhodophyta
and red algae and there are many other species.
This is how it almost consist of 70% of agarose and 30% of the agaropectin, so this is the
structure of agaropectin and agarose. So, best known application of agar is the preparation of
culture media and in petri dishes, huge application in the research lab for the growth of the
microorganisms.
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The next is carbohydrate again, Carrageenan, Fucoidan. So Carageenan can comes from the red
seaweeds. Now these are the structures, it is common food additives due to their thickening,
gelling and emulsion stabilizing properties. Fucoidan, this is the structure; it exhibits
anticoagulant abilities by enhancing the heparin cofactor II. So, they may become an alternative
to heparin due to their herbal origin.
So, the next is Alginate, carbohydrate in the form of Alginate. Different species such as
Macrocystis pyrifera, Ascophyllum nodosum, these are the structures. Alginate is a linear
polysaccharide consisting of two types of monomers. It is widely applied as a stabilizing,
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thickening or emulsifying agent in the food, cosmetic, paper and dye industries, it has so much of
medicinal applications also.
And the last one is the organic plastic, in the form of biopolymers (PLA or poly lactic acid, bio
polyethylene etc.). So, Nostoc sp., Phormidium mucicola, then Chlorella stigmaaphora and then
Chlorella vulgaris. Chlorella vulgaris is a well-known species. This is the structure, it is a
monomer and the repeating unit. So thickening agents for mobility control in water flood oil
recovery, food additive, flocculants useful in the wastewater treatment, soil conditioning, drilling
mud extenders, pet food and farm feed stabilizers. So, this is all about microalgae and I windup
today’s lecture.
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So, in the next lecture we will discuss about how to enhance the biomass properties for biofuels
and what are the challenges in conversion. So, thank you very much for listening; if you have
any query please feel free to drop mail to me at kmohanty@iitg.ac.in also post your query in the
Swayam portal, thank you.
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Module 02
Lecture-06
Enhancing Biomass Properties
Good morning students, this is lecture 4 of module 2.
In today's lecture, we will be discussing about the biomass properties, how we can enhance some of these
properties and what are the challenges in conversion of the biomass into biofuels?
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So, let us begin by discussing about physical properties of biomasses. So, some of the physical properties
of biomass affect it is pyrolysis and gasification behavior (basically the thermochemical conversion). For
example, permeability is an important factor in pyrolysis. High permeability will allow the pyrolysis
gases to be trapped in the pores, increasing their residence time in the reaction zone.
Thus, it increases the potential for secondary cracking to produce char. The pores in wood are generally
oriented longitudinally. As a result, the thermal conductivity and diffusivity in the longitudinal direction
are different from those in the lateral direction. This anisotropic behavior of wood can affect its
thermochemical conversion. A densification process such as torrefaction can reduce the anisotropic
behavior and therefore change the permeability of biomass. Hence permeability is an important property
with respect to the pyrolysis.
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Density is an important design parameter for any biomass conversion system. For a granular biomass we
can define four characteristic densities: true density, apparent density, bulk density and biomass (growth)
density. Now true density is the weight per unit volume occupied by the solid constituent of biomass. So,
it is given by total mass of biomass divided by solid volume in biomass.
The cell walls constitute the major solid content of a biomass. For common wood the density of the cell
wall is typically 1530 kg per meter cube and it is constant for most of the wood cells. The measurement of
true density of a biomass is as difficult as the measurement of a true solid volume. So, it can either be
measured with a pycnometer or maybe estimated using ultimate analysis and true density of the
constituent elements.
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Next is apparent density; so it is based on the apparent or external volume of the biomass. This includes
its pore volume or you can say the volume of all the cell cavities. For a regular shaped biomass,
mechanical means such as micrometers can be used to measure different sides of a particle to obtain its
apparent volume. An alternative is the use of volume displacement in water. The apparent density
considered the internal pores of a biomass particle but not the interstitial volume between the biomass
packed together. So this is the equation for the apparent density.
The pore volume of a biomass expressed as a fraction of it is total volume is known as it is porosity.
Apparent density is most commonly used for design calculations because it is the easiest to measure and it
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gives the actual volume occupied by a particle in a system. So, you can see the table 1 has given apparent
density of some of the wood species.
Then the bulk density; So bulk density is based on the overall space occupied by an amount or a group of
biomass particles. Bulk volume includes interstitial volume between the particles and as such it depends
on how the biomass is packed. For example, after pouring the biomass particles into a vessel, if the vessel
is tapped, the volume occupied by the particles settles to a lower value. The interstitial volume expressed
as a function of the total packed volume is known as bulk porosity.
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So, this is the bulk density equation.
So to determine the biomass bulk density, we can use standard like the American Society for testing
materials, E-873-06 standard. So, this process involves pouring the biomass into a standard sized box of a
particular size (given here), from a height of 610 millimeters. The box is then dropped from a height of
150 millimeters three times for settlement and refilling. The final weight of the biomass in the box is
divided by the box volume which gives its bulk density. This is how we can measure bulk density of the
biomass.
The total mass of the biomass may contain the green moisture of a living plant, external moisture
collected during storage and moisture inherent in the biomass. So, once the biomass is dried in a standard
oven, its mass reduces. Thus, the density can be based on either green or oven-dry depending on whether
its weight includes surface moisture or not. The external moisture depends on the degree of wetness of the
received biomass. To avoid this issue, we can completely saturate the biomass in deionized water,
measure its maximum moisture density, and specify it is bulk density accordingly.
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So, there is a relation between these three densities as given here.
Where, epsilon p is the void fraction or voidage in a biomass particle and epsilon b is the voidage of
particle packing.
So, then the next is the biomass growth density. It is specifically for biomass not for other materials. So,
the term biomass growth density is used in bioresource industries to express how much biomass is
available per unit area of land.
So, it is defined as the total amount of above-ground living organic matter in trees expressed as oven-dry
tons per unit area (that is basically the tons per hectare) and includes all organic materials: whether it is
leaves, twigs, branches, main bole, bark and the trees.
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Then we will see some of the thermodynamic properties. When we talk about gasification, which is a
thermo chemical conversion process, the thermodynamic properties of biomass heavily influence its
gasification properties (so do for pyrolysis also). So, the three important thermodynamic properties are
thermal conductivity, specific heat and heat of formation. Now what is thermal conductivity: biomass
particles are subject to heat conduction along and across their fibre which in turn influences the pyrolysis
behavior, and/or gasification behavior of course. Thus the thermal conductivity of the biomass is an
important parameter in this context. It changes with density and moisture.
So, how it changes? We will see. So based on a large number of samples, MacLean in 1941, developed
the following correlations (which is adopted from this Kitani and Hall 1989, a book is given in the page
number 877). So, K effective watts per meter Kelvin, is specific gravity in bracket 0.2 + 0.004 into m d +
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0.00238. So, this particular correlation, as you know correlations are valid for certain range, so for this
particular correlation it is only valid when your m d is greater than 40%. Now another equation which is
given by this, you can see that equation also (I am not reading it). So that is valid when m d is less than
40%.
So, two equations or correlations were proposed, the first one is when the m d is greater than 40% and the
second one is when the m d is less than 40%. So, m d is the moisture percentage of the biomass on a dry
basis. So, unlike metal and other solids biomass is highly anisotropic. Conductivity also depends on the
biomass’s moisture content, porosity as well as temperature.
Some of these depend on the degree of conversion as the biomass undergoes combustion or gasification.
Thunman and Leckner in 2002 wrote the effective thermal conductivity parallel to the direction of wood
fibre as a sum of contributions from fibres, moisture and gas in it. It is a good equation which many of us
working on the biomass sector they use it. So, K effective in watts per meter Kelvin, is G K s + F K + H
into K g + K rad for a parallel fiber.
Where, G x, F x and H x are the functions of the cell structure and it is dimensionless length; K s, K w
and K g are thermal conductivities of the dry solid (that is fibre wall), moisture and gas respectively; And
K rad represents the contribution of radiation to conductivity; it is a very nice or excellent equation which
is being adopted universally.
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So, we will see few more equations. So these components are given by the following empirical relations,
which are to be used to calculate the directional values of the thermal conductivities. Here all the thermal
conductivities are measured in watts per meter Kelvin. So, Kw is given by this equation - 0.487 + 5.887
into 10 rise of - 3 into T - 7.39 into 10 power of - 6 T square. Now K z is given by this long equation, K w
is 0.52 in perpendicular direction and K rad, so which is coming from the radiation is 5.33 e of radiation
then sigma d pore and T cube.
So, E rad is the emissivity of the pores having diameter d pore and sigma is the Stefan Boltzmann
constant, and T is the temperature in Kelvin. The contribution of gas radiation in the pores K rad, to
conductivity is important only at high temperatures.
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Now we will talk about specific heat, another important thermodynamic property. So, specific heat of
biomass is often required for thermodynamic calculations. So, it is an indication of the heat capacity of a
substance. Both moisture and temperature affect the specific heat of biomass. But density of wood species
do not have much effect on the specific heat. So, the specific heat changes much with temperature it also
depends on to some extent on the type and source of the biomass.
So, please look at this particular figure. So, you can see there are three (specific heat of a softwood
species parts) species temperature versus specific heat has been given here. So, the below one that is the
wood char, the red one is the wood bark and the blue one is the wood. So, this figure shows the increase
in specific heat of a softwood species with temperature. It also shows that bark of the wood has higher
specific heat, when it is compared to the other two species.
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Char produced from this wood has interestingly much lower specific heat. Some experimental correlation
of specific heat with temperature and moisture content is given as this Ragland et al equation 1.39 +
0.00036 T for the wood char, Gupta et al suggested for the softwood fuel 0.00546 into T - 0.524 and for
the hardwood fuel 0.0038 into 10 power of - 3 T square + 0.00598 T - 0.795.
Ragland et al., (1991): 1.39 + 0.00036 T for Wood char
Gupta et al., (2003): For softwood fuel: 0.00546T – 0.524
For hardwood fuel: 0.0038 * 10-3
T2
+ 0.00598T – 0.795
Now I want to say something about this so called relations; please note I do not know whether most of
you are aware of the fact or not regarding these correlations. So, let us understand what is the meaning of
correlation; why suddenly some particular number of 0.003, some x square some T square is coming into
picture. Now please understand that any correlation is an equation which is developed by doing certain
fixed number of experiments; it is all based on the experimental results.
That is why they have some specificity or limitation, like we are showing m d in the last equation. I told
you that these particular two equations, one equation is valid when the moisture content is greater than
40%, another equation is valid when the moisture content is less than 40%. So, that the reason is that this
is how the experiments are being done and this is how the equation has come from different experiments
and mostly they are average values, there is a particular way to do it. So, you need to understand that any
correlation are experimentally derived equations and has some limitations.
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So, then let us understand the heat of formation; heat of formation also known as the enthalpy of
formation is the enthalpy change when one mole of compound is formed at standard state, that is 25
degrees centigrade and 1 atmosphere from its constituting elements in their standard state. Now for
example, hydrogen and oxygen are stable in their elemental form, so their enthalpy of formation is always
zero, in elemental form.
Now however an amount of energy 241.5 kilojoules is released per mole when they are combined to form
steam, that means hydrogen and oxygen. So, the heat of formation of steam is thus - 2241.5 kilojoules per
mole that is in the gaseous form. So, this amount of energy is taken out of the system and is therefore
given a negative sign in the equation to indicate that it is an exothermic reaction. If the compound is
formed through multiple steps, the heat of formation is the sum of the enthalpy change in each process
step.
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So, gases like hydrogen, oxygen, nitrogen and chlorine are not compounds and the heat of formation for
them is zero. Values for heat of formationn for some of the compounds are given, you can see it later
water is - 241, carbon dioxide is - 393, right there are a few were given just for your understanding.
Now this is a small example problem, you can just go through it. So, find that heat of formation of
sawdust, the heating value of which is given as 476 kilojoules per mole, assume its chemical formula to
be CH 1.35 O 0.617. Now stoichiometry has to be written. The conversion of SW can be written in the
simplest term as CHO + 1.029 Oxygen will give C carbon dioxide + water 0.6575 water - 476 kilojoules
per mole of sawdust is the isothermic reaction.
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So, heat of reaction you can calculate like this, HF of carbon dioxide + 0.675 HF of water - HF of
sawdust - 1.029 HF of oxygen. So, consider the values of HF of heat of formation of carbon dioxide,
oxygen and water and substitute. So, you will get heat of reaction for the above combustion reaction -
476, it is given. So, you will calculate the heating value to be - 80.5 kilojoules per mole.
Consider the values of HF of CO2, O2, H2O (g):
The HR for the above combustion reaction is -476 kJ/mol. So,
So, the heat of reaction is the amount of heat released or absorbed in a chemical reaction with no change
in temperature. In the context of combustion reactions, heat of reaction is called the heat of combustion.
deltaH comb submits a combination, which can be calculated from the heat of formation as: methane plus
oxygen gives you 2 water plus carbon dioxide, so heat of combination will be 2 of deltaH water + deltaH
carbon dioxide - deltaH methane - deltaH oxygen.
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So, the deltaH comb, the heat of combustion of the combination for the entire fuel, can be defined as the
enthalpy change for the combustion reaction when it is a balance. So, fuel plus oxygen will give you
water plus carbon dioxide minus heat of reaction.
So, the heating value of biomass is the amount of energy biomass releases when it is completely burnt in
adequate oxygen. So, it is one of the most important properties of biomass as far as energy conversion is
concerned. Compared to most fossil fuels, the heating value of biomass is low especially on a volume
basis because its density is very low and it is high oxygen containing fuel. Higher heating value, what is
higher heating value? This is also very important to understand. So, it is defined as the amount of heat
released by the unit mass or volume of fuel, initially at 25 degrees centigrade, once it is combusted, and
the products have returned to a temperature of 25 degrees centigrade.
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It includes the latent heat of vaporization of water. HHV is also called as the gross calorific value. In
North America, the thermal efficiency of a system is usually expressed in terms of HHV, so it is
important to know the HHV of the design fuel. Then there is something called LHV or lower heating
value, so LHV is also known as net calorific value. HHV is gross calorific value and LHV is the net
calorific value.
So, the lower heating value is defined is the amount of heat released by fully combusting a specified
quantity less the heat of vaporization of the water in the combustion product, so this is the equation you
can refer to.
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So, then the next thermodynamic property is ignition temperature. So, ignition temperature is an
important property of any fuel because the combustion reaction of the fuel becomes self sustaining only
above this temperature. So, above only this temperature it will ignite basically. So in a typical gasifier a
certain amount of combustion is necessary to provide the energy required for drying and pyrolysis and
finally for the endothermic gasification reaction.
Exothermic chemical reaction can take place even at room temperature but the reaction rate being an
exponential function of temperature is very slow at low temperatures. So, when the fuel is heated by some
external means, the rate of exothermic reaction increases with a corresponding increase in the heat
generation rate.
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So, above a certain temperature the rate of heat generation matches or exceeds the rate of heat loss. When
this happens the process becomes self sustaining and that minimum temperature is called the ignition
temperature. So, the ignition temperature is generally lower for higher volatile matter content fuel because
biomass particles have a higher volatile metal content than coal. So, usually they have significantly lower
ignition temperature.
So, the inherent meaning is that, so biomass particles will ignite very fast compared to the coal. So, for
example the wheat straw has a volatile matter of 72% (daf basis, so daf is the dry ash free basis). The
ignition temperature is 220 degrees centigrade while the volatile matter of anthracite is only 7.3% but the
ignition temperature is 927 degrees centigrade.
Now we will try to understand how we will enhance the primary raw materials for the biofuels and what
are the different types of techniques that exist, including some of the genetic engineering aspects. Now
the use of plant cell wall as major energy sources would establish a virtuous industrial cycle and thus help
mitigate global warming problems as plant cell walls constitute the natural carbon dioxide sinks.
Unfortunately plant cell walls are extremely resistant to enzymatic degradation and so are difficult to
degrade into fermentable sugars. Now that is the reason why as it is mentioned here; there is a need for
the pretreatment of the biomass, (we will also discuss in our subsequent slides today itself). And due to
this recalcitrant nature of the cell wall, huge amount of energy and effort is required to make it amorphous
thus releasing the sugars which is responsible for producing alcohol.
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As a result, current dynamic area of research is the transformation and harvesting of plants. So, the
cellulose microfibrils which could be easily hydrolyzed by cellulose preparations or which could self
degrade their cellulose microfibrils by expressing a cocktail of hydrolytic enzymes. On the other hand,
now it is clear that such genetic modifications capable of conferring these novel characteristics would be
feasible only if the resultant genetically modified plants could achieve adequate public acceptance and
were able to strive in natural cropping system.
Now here I wish to tell you something very interesting. So, many of you will be knowing about this
genetic modified crops. You remember few years back in India there is a lot of hue and cry regarding the
genetic or transgenic brinjal. So, public perception about genetic modification till date is not so good. So,
they feel that if a particular species is genetically modified and being consumed, by the humans or the
animals it may have some bad effect, which I cannot give a right straightaway answer to that; we need to
do more study on that actually, I cannot say whether it is good or bad in this platform. But we need to
understand one thing, that the public perception is not so good and acceptability of such genetic crops
actually needs more public awareness and you need to convince the public about what is the importance
of this and whether there is any adverse effect if it is being consumed by the humans and/or animals. This
is first thing.
Second thing; this so called genetically modified species, plants, crops, whatever it is, they must have the
capacity of naturally cropping systems, that is one thing. There should also be able to withstand the usual
natural environment as well as the climatic conditions. So, these are some of the challenges which still
remain in the development of so called genetic engineering or genetic engineered species, crops or
transgenic plants, you can call them.
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So, the current technologies for biofuel production typically involve the pretreatment of lignocellulose
before hydrolysis with cellulase preparations. Cellulase is the enzyme which will degrade the cellulose to
glucose. So, an alternative concept is to either upregulate or downregulate hydrolases by introducing and
programming their genes in order to achieve in situ modification of the plant cell wall polysaccharides.
So, we can do in situ modification inside the plant cell itself by doing some genetic modifications by over
expressing either certain genes or certain proteins which is responsible for a particular, let us say, either
increasing the cellulose yield or carbohydrate yield or making it resistant to certain types of pathogens
attack. There are many things. It is not that genetic engineering is being done only to have a higher yield
of the biomass or have higher yield of cellulose, it is not so.
So, in principle the introduction and programming of such genes should not decrease cellulose production
levels in plants otherwise it will have an adverse effect, so our main aim is not going to be achieved.
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So, as such genetic engineering could promote the degradability of cell walls in plants bred for use as
biofuels. Although the degradative gene products in bacteria and fungi are more effective in digesting
polysaccharides than those present in plants, so plants sometimes produce pathogen related proteins such
as antibodies. So, thus it is necessary to create and improve a technical barrier to plant engineering using
trans-kingdom genes, I hope you all understand what is genes.
So, you can browse little more about these particular few slides and few of the particular words which
you may not be aware of; please read it from literature.
So, we will discuss how we can do this genetic engineering technique using the In-Fibril modification.
Now cellulose is most abundant biopolymer on the earth. An important characteristic of this biological
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polymer is that, it has a strong tendency to self-associate into microfibrils that: are not easily hydrolyzed
either chemically or biologically and that accumulate primarily in the walls of the plant cells. Now since
individual strands of cellulose are intrinsically less hydrophilic than other soluble polysaccharides,
cellulose crystals tend to form extensive intra and intermolecular hydrogen bonds with complex 3
dimensional structures. In natural crystals, for example cellulose I, the cellulose strands are parallel and
form triclinic cellulose, and monoclinic cellulose in varying proportions depending on their origins.
So, the microfibril is drawn with its chain axis as a monoclinic structure corresponding to the native
cellulose of higher plants. After strong alkaline denaturation, cellulose I forms a thermodynamically more
stable structure than that of the cellulose II with an anti parallel arrangement of strands. Therefore,
cellulose II is artificially generated from cellulose I by two industrial processes, first is called regeneration
and second is called the mercerization.
Each microfibril consist of repeated crystalline and non crystalline regions, each of which might be
relatively short (almost around 10 to 100 glucosyl residues that it contains). The microfibrils are too rigid
for cellulases to attack both the crystalline and the non crystalline regions. Lignin (another component, a
very high class compound) may bind to hemicelluloses mainly xylan, thereby associating with cellulose
microfibrils and further rigidifying them.
So, in a lignocellulosic biomass (next sometimes I will show you a structure), cellulose, hemicellulose
and lignin are bound together in a very intricate manner. So, thereby making it more rigid to the cellulase
attack, cellulase is the enzyme which we want to use for degrading the cellulose whatever is available. So,
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that is the reason why we talk about this delignification process, the pretreatment is mostly about
delignification. Not always it is delignification; but mostly, it is roughly understood as delignification.
That means removing the lignin or separating lignin from cellulose and hemicellulose. Cellulose is C 6
sugar and hemicelluloses are C 5 sugars, pentose sugars basically.
Pretreatment for decomposition of lignocellulose could represent a critical step in the conversion of
lignocellulosic biomass, as their function comprises increasing the susceptibility of plant microfibrils to
cellulase action. A noteworthy strategy for cellulose hydrolysis is not only to promote decrystallization
between the so called 1, 4 beta glucans in the crystalline regions, but also to loosen the association
between 1, 4 beta glucan and hemicellulose in the non-crystalline regions.
So, that is very important, this particular sentence is very important. So, the cellulose hydrolysis is not
only doing the decrystallization between this 1, 4 beta glucans, but it is also losing the association
between this 1, 4 beta glucan as well as others hemicelluloses in the non-crystalline regions. So, the use of
transglucosylase, such as xyloglucan endotransglucosylase (which is known as XET), is yet another
potential method for transferring glucosyl residues of 1, 4 beta glucan to another chain.
Now this can be exemplified by the action of barley XET, which catalyses the transfer of cellulose
molecules to xyloglucan and thereby forms a link between cellulose and xyloglucan.
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It is well known that the removal of lignin results in an increased level of saccharification of plant cell
walls, and this method is commonly used to facilitate the process of bioethanol production. Lignin occurs
in close association with cellulose microfibrils, it is always expected that a decrease in lignin content
would in turn increase the accessibility of the cellulose microfibrils to degradative enzymes. Lignin is an
important cell wall components, in the plants not only for water transport in xylem but also for stem
straightness and protection against pathogen attack.
So, lignin provides some sort of mechanical support also, you can say that. Therefore, it seems likely that
a dramatic reduction of the lignin content in the growing plants would result in a detrimental effects of the
plant growth, so you need to balance it. So, consequently reducing the lignin content of lignocellulosic
biofuel crops appears to be that of (little) practical use.
Let us understand that, if we want to reduce the lignin content of a dedicated energy crop in which the
lignin content is already less (let us say miscanthus, switch grass, elephant grass - they are bush type of
plants, they are grasses), then it is not going to have a much higher effect on the mechanical stability of
the plants or these bushes (because they are grasses and bush basically).
But having said that, if we are drastically reducing the in-fibril lignin, for the hardwood or softwood trees,
then we need to be careful about whether the plant can grow properly and erect and stand on the soil by
itself, by having a good mechanical stability. So that is the question basically. That is how the genetic
engineering or the engineers must ensure that there is no adverse effect on the growth of the plant.
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So, the transgenic Populus tremula overexpressing Arabidopsis cellulase (that is cell1) exhibits longer
internodes and longer fibre cells; remarkably, those characteristics translate into immediate gains in
bioconversion productivity. In addition, the enzymatic trimming of amorphous regions in the microfibrils
leads to the solubilization of some xyloglucan that is intercalated with disordered para-crystalline
domains of the microfibrils.
Xyloglucan is a key polysaccharide that is used by the plants to control the assembly of cellulose
microfibrils through cross linking. So, therefore the degradation and reconnection of xyloglucans could
induce the modification of cell wall polysaccharides in such a way, so as to further facilitate industrial
saccharification. Since adjacent cellulose microfibrils could be crosslinked to xyloglucans, the separation
of microfibrils during elongation is thought to require enzymes that solubilize xyloglucan or loosen its
binding to microfibrils.
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An additional enzyme that is an important target for plants genetic engineering is xyloglucanase, which is
called XEG, which catalyses the endo-hydrolysis of the xyloglucan backbones and exhibits xyloglucan
specific endo-1, 4-beta glucanase activity. XEG is widely distributed in nature, being present not only in
plants but also in fungi and bacteria. So, the overexpression of XEG in poplar (poplar is a plant which we
have discussed in our last class - a dedicated energy crop) resulted in the cleavage of xyloglucans
crosslinked with cellulose microfibrils, and in an acceleration of stem elongation by loosening of the wall.
The overexpression of this enzyme also causes an increase in wall density and cellulose content. So, I will
tell you in a crude way, what is the meaning of overexpression. These are genetic engineering terms. So,
as I told you please go back and read a little more about certain terms which you are not very clear about.
So, in this particular class, it is very difficult to make you understand each and every bit of the genetic
engineering aspects, so that is not the scope of this course also. So, I will be telling in a nutshell;
overexpression means making more copies of the parent protein, or gene. So, for example if cellulose
formation in wild type poplar is restricted by the entanglement with xyloglucan, the relaxation resulting
from the cleavage of crosslinking xyloglucans in the modified poplar may accelerate cellulose
biosynthesis and deposition. So, the meaning of this particular sentence is that, when we overexpress
XEG in the poplar, it has helped in cleavage of the xyloglucans which is cross-linked to the cellulose
microfibrils.
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So, by these mechanisms, the expression of XEG would promote not only cellulose degradation, but also
the production of cellulose in plants. So, the observation that overexpression of XEG in poplar results in
the acceleration of cellulose degradation by cellulase preparations is consistent with this hypothesis. Now
it is also noteworthy that the reconnection between xyloglucan molecules in the walls can be catalysed by
xyloglucan endotransglucosylase, which is called the XET, an enzyme encoded by the gene of XTH gene
family. However, XEH present in plant cell walls has not been well characterized (another class of
enzyme). So, there is possibility of some relationship and/or interaction might exist between XTH and
cellulose synthase gene expressions; it is possible that this mechanism might be leveraged to facilitate
biomass processing. More work is currently being done on whatever we have written in this last sentence
here.
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So, French bean cells habituated to grow in the presence of 2, 6 dichlorobenzonitrile formed large
amounts of soluble beta glucan and evoked the XET activity. Such inhibition of cellulose biosynthesis
would apparently not only cause the occurrence of soluble 1, 4 beta glucan but also decrease the plant
growth. While the cellulose biosynthesis pathway in plants remain unclear, there is convincing evidence
that a relationship exists between cellulose synthase, cellulase the enzyme, and the XET.
One line of research and development to facilitate the implementation of lignocellulosic biomass at a
large scale is thus to make the use of this relationship to weaken the cellulose polymers in vivo, which can
be achieved by appropriately altering the genetic makeup of biofuel crops. It is hoped that this might be
achieved in such a way that the industrial saccharification of lignocellulosic biomass could be performed
under optimal economic conditions without affecting the natural ability of these crops to grow in a natural
cropping system.
Again this is what we have already discussed in one of the slides, as I told that everything is so good
about the genetic engineering things. It has to be done in a proper way and proper understanding that if I
am decreasing the lignin content, then it should not affect the growth of the plant. This is one of the
foremost important thing.
Let us learn what is In-Planta modification. Like another genetic engineering technique. A two-pronged
strategy is required to improve lignocellulosic crops for optimal biofuel yield. So, the first one, it is
necessary to increase the yield of the cellulose production based on the plant mass, while on the other
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hand, it is also necessary to increase the conversion of cellulose into glucose. There are two things, first
you increase the yield of cellulose, by means of the genetic engineering aspect.
Second thing is that, you increase cellulose; but cellulose is bound in such an intricate fashion with
hemicellulose and lignin and their rigidity so high they are crystalline. So, that crystallinity has to be
overcome so that the cellulose can be transformed into glucose. So, improvements in the post harvest
processing in-planta were originally attempted in transgenic tobacco which constitutively produced
hyperthermophilic a-glucosidase and b-glucosidase (two different types of enzymes) from the
hyperthermophile Sulfolobus solfataricus.
So, this is one particular unicellular organism from which these two enzymes have been derived.
Transgenic plant means genetically modified plant. So, the transgene glucosidases began to accumulate in
the tobacco plant after a certain delay and were inactivate at plant growth temperature. After harvest,
however glucose could be produced from endogenous polysaccharide upon incubation at high
temperature.
I would like to say that transgenic tobacco is being farmed in many of the Western countries, because not
for the consumption of the tobacco leaves, but to purify one particular monoclonal antibody which is
present in the transgenic tobacco. Usually it is present in a very small quantity, about 6 to 7% not more
than that. Sometimes it is less than that depending upon the species, so it is a very high class antibody,
needs to be purified, for that purpose this transgenic tobacco plants are been cultivated.
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So Oraby et al in 2007, showed that cellulase expressed in rice can effectively convert the cellulose of
ammonia-fibre-explosion-pretreated rice and maize biomass into glucose. Now ammonia fibre explosion
pretreated rice, so ammonia fibre explosion is one of the pretreatment technique, we will read about more
pretreatment techniques later in our subsequent lectures. We will discuss about ammonia fibre explosion
als. So, these authors suggested that such a method of expression could be used as an environmentally
friendly technology for the hydrolysis of wasteful rice straw.
So, next genetic engineering technique is In-CRES-T modification. So, CRES-T means chimeric
REpressor silencing technology; it was developed as a novel method to silence the target genes of
transcriptional activators in plants. Transcription factor is a protein; and what is transcription? So,
transcription means in a nutshell, transferring one particular information from the DNA to the messenger
RNA or mRNA. So that process is called transcription.
You can read little more about these terminologies from the literature, so that things will be more clear. In
CRES-T, a fused gene encoding a transcriptional activator and a repression domain named as SRDX at
the carboxy terminus is expressed as an artificial chimeric repressor. The SRDX is a modified short
amphiphilic peptide of 12 amino acids derived from the plant specific transcriptional repressor known as
SUPERMAN.
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This strategy has the following advantages over the conventional genetic manipulations, such as RNAi or
gene knockout particularly in many horticultural plants which have high polyploidy and only limited
sequence information: (You know polyploidy; there is something called diploid, what is the meaning of
that? So, when an offspring is actually born, it usually carries one set of chromosomes, in their genes
from each of the parents. In polyploids, they will have two sets of genes, two from one parent and two
form another parent. You can understand in a crude way.)
i) So, chimeric repressor can dominantly suppress the expression of target genes and induce loss-of-
function phenotype, even if the endogenous paralogous genes function redundantly.
ii) Plasmid construction is very easy, what is plasmid? Plasmid is a small extra chromosomal DNA, i.e.,
not present in the chromosome itself.
iii) Cloning of the gene encoding the target transcription factor from each plant species is not necessarily
required because the construct of the model plant can be effective in other plant species.
To this date various traits of several floricultural plants have been successfully modified by the CRES-T
technique.
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Because lignin content and fermentable sugar yields are reversibly correlated, the enzymatic
saccharification rate of plants without secondary walls in their stem may be higher than that of the plants
enriched in the secondary walls. Some additional modifications may be required to utilize plants lacking
secondary walls because their total amount of cellulose is decreased, thus preventing the plants from
standing erect and making them very fragile.
Further analysis of each plant species is required to evaluate whether these disadvantages could be
compensated by the positive attributes exhibited by plants that lack secondary walls. It is particularly
worth noting that a reduced lignin content in secondary walls improves the glucose yield. That is what we
have already understood.
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Since lignin and cellulose - the major components of secondary walls - are polymers of completely
different molecular classes and result from unrelated biosynthetic mechanisms, each component of the
cell wall is likely to be independently regulated by different transcription factors downstream of the NST
genes. I am leaving it as it is, you please read this later on, if you have any query, please ask me. This
little more detail about the genetic engineering aspect, though is not so much important for this course but
I felt that I will basically write it, so you can later on read it. So, I am just moving ahead with the other
material.
So, this also the same thing, I am just leaving it to you to read. In case you have any query, please feel
free to write to me, I will be definitely happy to address those.
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Now we will try to understand what are the challenges in conversion of biomass to biofuels. There are
only few challenges. But that needs to be addressed suitably, so that we will have no problem in the
conversion. The first one is the moisture content; we have discussed it in a nutshell earlier. So, biomass
materials with high moisture content is not suitable feedstock for conventional thermochemical
conversion technologies such as gasification, pyrolysis.
High moisture can reduce the effectiveness of conversion processes. Moisture in raw biomass materials is
also undesired because fuel wood produced from these materials can contain more moisture. The fuels,
which have high moisture contents cannot burn easily. Some part of the energy in the fuel are always
consumed for the vaporization of water, which is present in the fuel. In order to maximize the heating
value of the fuel produced from these materials the moisture content biomass should be always less than
20%.
Drying the materials before being used in the conversion process is not preferable because of high cost
(because it is an energy intensive process). On the other hand, some biomass conversion processes use
biomass with high moisture content. The first one is hydrothermal conversion process. This is a beautiful
technology; it is currently being adopted in many industrial practices. So, in this particular technology, in
a high pressure high temperature system, you are going to convert the high moisture content feedstock (it
can be anything, any biomass or anything) to crude oil (basically biocrude). And in certain biological
processes such as alcohol production from carbohydrates by biomass, high moisture content does not
create any problem. So, in these processes, moisture in the biomass play an important role in the
conversion either as a major reactant or as a reaction environment.
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For example, high moisture content in biomass causes biological degradation, mold formation and losses
in the organic content during storage, that could reduce the yield of the fuel wood from these materials.
Storing biomass at less than 10% can extend the conservation time of the materials and reduce major
losses (that means losses of the sugars) during the storage period. The drawbacks of high moisture content
can be mostly solved by compressing the biomass material for more uniform properties and that process is
called densification.
So, you must have heard about densification of biomass. So increasing bulk density of biomass materials
by densification reduces transportation cost and storage volume. However, this process adds an extra cost,
densification is an added process basically. So for any added process there is a cost to it and hence the
overall cost increases.
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Then density; bulk density of lignocellulosic biomass materials is generally low. This creates difficulties
to handle such large quantities of feedstocks and increases the transportation and storage cost. The bulk
density of biomass should be between 190 to 240 kg per meter cube for efficient transport in various sizes
of trucks with approximately 25 ton loads. The size, shape, moisture content, particle density and surface
characteristics are the factors affecting the bulk density of a material. The challenge for low density and
different size and shapes of biomass can be overcome by densification process.
So, biomass in densification process; biomass materials are mechanically compressed to increase their
density and convert them into uniform shapes and sizes. You can see, how these have been converted into
particular shapes. These are powder, these are some sort of briquettes, these are some sort of rolls. You
can briquette them, pelletizing them, cubing them. So, then density of biomass can be increased ten-fold
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depending upon the biomass type, moisture content and processing condition. The costs of handling,
transportation and storage of resulted densified materials can be considerably reduced. Now because of
uniform size and shape the materials can be easily handled.
So, the next is complexity and diversity. Lignocellulosic biomass materials is mainly composed of three
components lignin, cellulose and hemicellulose. These polymers are organized in the complex non
uniform three dimensional structures and each one has different polymerization degrees. Polymerization
degree and/or structures of these biopolymers can vary among the biomass species. Cellulose is a linear
structure composite of beta 1-4 linked glucose subunits. Cellulose molecules determine the cell wall
framework.
The inter and intra chain hydrogen bonding in the structure makes the cellulose to be crystalline and this
portion of cellulose does not hydrolyze easily compared to the amorphous cellulose structure. And that is
what we have understood during the genetic modification steps that we have discussed. How the cellulose
can be available or more amenable to degradation, either by removing lignin, decrease the lignin content
or overexpressing certain cellulases (enzymes basically). So, that whatever we want that will be fulfilled.
Hemicellulose has a random and amorphous structure which is composed of several heteropolymers such
as xylan, galactomannan, arabinoxylan, glucomannan and xyloglucan.
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Phenylpropanoid monomeric units in the lignin polymer are identified as p-hydroxyphenyl, guaiacyl and
syringyl units. Composition of lignin, cellulose and hemicellulose in biomass materials significantly
differ among biomass species. For instance, some biomass materials such as hardwoods contain more
cellulose in their structures while others such as straws have more hemicellulose. Hemicellulose fractions
of softwoods mainly have D-mannose derived structures such as galactoglucomannans while
hemicelluloses in hardwoods have D-xylose derived structures.
Now this diversity among biomass material can significantly affect the conversion process for production
of biofuel and other useful products from the biomass materials.
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So, the next is recalcitrance and dissolution difficulties. Success of using lignocellulosic biomass for
biofuels and other useful chemical productions depends largely upon the physical and chemical properties
of the biomass, on pretreatment methods and optimization of the processing conditions. The
compositional changes in plant cell wall and the differences in ultra structure greatly influence the
pretreatment and hydrolysis efficiency of the biomass.
Hydrolysis is a chemical reaction that releases sugars from biomass structures. Biomass dissolution
involves both physical, chemical and/or thermochemical treatment processes. We will read more about
these techniques later on in our subsequent lectures. So, things will be clearer that time. So the
crystallinity of cellulose, hydrophobicity of lignin, and embedding the cellulose in lignin-hemicellulose
matrix and difficulties in cleavage of some linkages (for example hydrogen bonding, ether linkages
between phenyl propane units) make biomass materials resistant to hydrolysis.
Hydrolysates from biomass can be used for producing a wide range of value added products, including
biofuels (it can be ethanol, hydrogen, butanol any such things), industrially important chemicals (for
example some of the solvents) and food products (sugar and sugar alcohols).
Significant existing challenges for hydrolysis of lignocellulosic biomaterials include the following. So,
first is that existing hydrolysis methods are expensive and time consuming. Most of them are not
environmental friendly. Second is that additional steps are required, just like here pretreatment,
neutralization etc. Then third is, released carbohydrates decompose in harsh hydrolysis conditions which
is prevalent during the hydrolysis process. So these are some of the challenges that needs to be tackled.
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The major hydrolysis processes typically used for solubilization of biomass require either use of toxic,
corrosive and hazardous chemicals (for example acids, alkali) or longer retention time (for example
during enzymatic hydrolysis), which collectively make the process environmentally unsafe and/or
expensive. That is why there is a huge work right now going on across the globe to develop different pre-
treatment techniques. Basically different pre-treatment techniques; I’d rather say that efficient and
sustainable pre-treatment techniques in which the yield will be more. The techniques should be
environmentally benign. It should be a green approach.
So, huge work is going on. There are developments of hybrid techniques. We will discuss something;
hybrid means basically combining more than one unit operations together. Because in one single unit
operation, you may not achieve the yield which you are looking for; so you combine two processes. But
having said all these, three things we should note with respect to the pre-treatment:
First is that, it should be a low-cost technique and it should be done at a very faster rate. So, time is
directly related to money in industry. Second, it should result in a higher yield of the cellulose. Third is
that, it should be a greener process.
So, concentrated acid hydrolysis has been applied, but the problem with concentrated acid hydrolysis are
several. So, though they provide higher conversion, but, there are environmental concerns, corrosion and
so many other things. So, due to all these things some of these are listed here, please refer later on. Since
almost two decades’ researchers have focused their attention to dilute acid pre-treatment rather than
concentrated acid pre-treatment.
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At dilute acid pre-treatment you will see hundreds and hundreds of literature reported by various
researchers who have worked with so many different types of species and studied the pre-treatment using
the dilute acid method. So, we will of course discuss more about that.
So, subcritical water is an alternative way to hydrolyze lignocellulosic biomass but please not that when
you talk subcritical, supercritical the reactor in which we are going to achieve it, the initial investment is
very high and you are going to again use higher energy to achieve that. Now this table will make you
understand about certain breakdown methods, pre-treatment methods, alkali, acidic, enzymatic,
subcritical water and their various advantages and disadvantages. So, please refer to it later on.
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So, the presence of a weak acid in subcritical water media can also improve hydrolysis of biomass
materials. The use of carbon dioxide as a pressurizing gas also caused formation of carbonic acid that
plays catalytic role in effective solubilization of biomass. Some studies have indicated that the addition of
small amounts of hydrogen peroxide can enhance lignin removal. The differences in the content and
composition of resulted hydrolysates can change the yield of the biofuel, that is another concern again.
So, for maximum usability, biomass components in hydrolysates should be further broken down into
smaller molecular weight components with a suitable method.
So, there are other challenges also, we will just quickly go through it. So, although energy demands are
continuous, biomass materials are seasonal. So some biomass feedstocks have advantages in terms of
production, harvesting, storage and transportation compared to others. So, perennial energy crops such as
switch grass and miscanthus do not need to be replanted each year and they do not require special care
and high maintenance to grow.
On the other hand, agricultural biomass residues, whether it is a corn stover, wheat straw, rice husk, crop
peels, pulps etc. are promising low-cost feedstocks since they do not need additional land for biomass
growth and the land used for agriculture belongs to these type of biomass materials. However, high cost
of their harvesting and transportation limit their use. In addition to the advantages and disadvantages
listed above, different sources of biomass feedstocks do not have the same composition, uniform size and
shape etc. that considerably affect the efficiency of the conversion process for a specific product.
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So, there are so many things that needs to be taken care of while you go and design for a particular
conversion technology. Therefore, biomass feedstocks for a bio-refinery needs to be standardized, this is
the ultimate thing and has to be done.
So, with this I windup. So thank you very much. In the next class that will be module 3, we will start
discussing on bio-refinery. We will try to understand what is the concept of bio-refinery though in a
nutshell I have covered it in the introduction class and what are the types of bio-refinery. So, thank you
very much, if you have any query please drop a mail to me at kmohanty@iitg.ac.in or please drop your
query in the swayam portal, thank you.
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Indian Institute of Science – Guwahati
Lecture 07
Basic Concepts and Types
Good morning students. This is module 3 and lecture 1. Under this module we will be
discussing about the biorefineries. And in today's class we will discuss about basic concept.
What is definition of biorefinery, how biorefinery functions, and what are the different types
of biorefineries?
Let us start. Please have a close look at this particular slide. I have deliberately added (this
slide) to make you understand the difference between Traditional oil refinery and biorefinery.
So, this is the traditional oil refinery, in which petroleum or petro crude is being processed to
fuels and energy and some platform Chemicals. The core is here; the petroleum in the core is
the crude oil.
Here the core feedstock is the Biomass. So you will have so many different types of products
from here. Fuels and energy so it can be bio-ethanol, biodiesel, biogas, hydrogen and all sorts
of liquid and gaseous fuels and even some solid fuels also. Then there can be some material
utilisation, like your basic and fine chemicals (which we call many times platform
chemicals), then Polymers and plastics. So the basic difference between Traditional refinery
and biorefineries is that, in biorefinery Biomass is the feed stock.
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There are so many different types of biomasses that can be utilised. So the feedstock can be
of n number of types. Not like in the petroleum refinery where only petro crude is being
processed. And the processes are more or less similar in the sense of their principle, whether
it is thermo chemical or sometimes bio-chemical also, and then we will have a number of
different types of products.
So the concept of the biorefinery evolved during the late 1990s. Various definitions of
biorefinery evolved by different stakeholders. Biorefinery is the separation of biomass into
distinct components which can be individually brought to the market either directly after
separation or after further (biological, thermochemical or chemical) treatment/s. Bio-refining
is the transfer of the efficiency and logic of fossil-based chemistry and substantial converting
industry as well as the production of energy on to the Biomass industries. So, these are few;
there are hundreds of such definitions provided by various stakeholders.
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Biorefinery is an overall concept of a promising plant where Biomass feedstocks are
converted and extracted into a spectrum of valuable products (this is what the US department
of energy has defined). NREL says that, biorefinery integrates Biomass conversion processes
and equipment to produce fuels, power and value-added chemical from Biomass. Then
International Energy Agency’s Bioenergy Task 42, they defined biorefining as the sustainable
processing of biomass into a spectrum of marketable bio-based products (it can be food, feed,
chemical materials) and bioenergy (biofuels, power and/or heat). And this is what is being
widely accepted by the scientists.
So, this particular definition, this NREL definition, includes the following keywords and we
will try to understand what are those:
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 Biorefinery: So here the concepts, facilities, processes and clusters of industries come
into picture.
 When you talk about sustainable; that means maximizing the economics, minimising
environmental aspects, fossil fuel replacement, socio economic aspects taken into
account.
 Then processing: upstream processing, transformation, fractionation, thermochemical
and/or biochemical conversion, extraction, separation and downstream processing.
 Then Biomass: what biomass means (with biorefining perspective). So, it can be
crops, organic Residues, agro residues, forest residues, wood, aquatic Biomass (such
as algae and all).
 Then spectrum, spectrum means more than one.
 Then marketable: A market (having an acceptable volume and prices) already exists
or is expected to become available in the near future.
 Then products: both intermediate and final products, i.e., food, feed, chemicals and
materials.
 Then energy: energy means fuels, power and heat.
So, biorefinery involves the enabling Technologies to make this possible as it allows for
optimal utilisation as well as value creation of biomass. Development of integrated closed
loop biorefineries that ensure their sustainability and economical viability through a complete
use of biomass, minimise waste and generate the greatest possible added value from the
available resources. The new biorefinery concept overcomes problems arising from the
generation of residues by giving them new value.
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This is how a significant increase in profitability and competitiveness over petrochemical
equivalents will be achieved - due to a greater efficiency derived from generating multiple
products. So biorefinery always targets for multiple products because we have to understand
that the feedstock is of low commercial value that we are going to utilise. Though its initial
value will be low. However, due to the densification and transportation cost, the cost of the
feed stock from procuring and to that of the plant will increase enormously basically.
Another thing I have already discussed and again I am telling you; feedstock sustainability is
it always a big question because most of the feedstock are seasonal. Unless and until we
standardize them for a particular biorefinery with multiple feedstocks, we cannot have a
sustainable biorefinery. And to do that, we should aim for more number of value added
products or co-products.
So, please have a look on this particular slide. Let us see what it means actually. It is a
concept. Here you can see that sustainable biomass supply. This is what I was just
mentioning; biomass supply should be sustainable. The inherent meaning of that; because
they are seasonal, so we should look for different types of biomass basically or multiple
feedstocks, so that their procurement will not face any problem throughout the year.
Then Sustainable Pre-treatment Technology. So pre-treatment technologies should be
developed in such a way that they are, efficient in handling almost all the feedstock.
Whatever maybe it? Some may be high lignin content; some may be less lignin content. How
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the pretreatment technology is going to address these issues low lignin content or high lignin
content, will depend upon what type of pretreatment technology is, being developed and
adopted.
Then you can get for different platforms: protein, Sugars, lignin, oils and fats and fibres. And
then you convert into various materials.
So separation technology is an integrated part of any refinery; whether it is a petrochemical
refinery or a biorefinery. And based on my understanding, it cost almost about 40%
(sometimes little higher than that of the entire product cost). So, you can understand that
unless and until you have a very good and low-cost separation technology, our final end-
product will be always very costly.
So, then you get so many different types of products. This already I have shown you long
back also. So, we will just quickly glance through.
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Then now there is so much of talk about circular bio economy. Meaning of circular bio
economy is that whatever we are actually producing as a final product, once they are
consumed, some waste is coming out of that. The by-products and the waste that is getting
generated during the processing should be recycled and reused in such a way that it almost
becomes a circular economy.
And also the economy of the rural people and other people who are engaged in these
industries are also being taken care of. You can see this: recycle, resources, nutrients, water
and carbon. Then renewable sources. This is the core of the circular bio economy, which is
your biorefinery. Then you get array of different products, services; use them and you
generate waste. And these wastes should also be recycled back.
I mean it should be processed into some valuable products. In one class I have given an
example of the wastewater and how water and wastewater that is being used in the Refineries
must be treated and recycled back. So, that we have to depend less on the freshwater because
freshwater resources are also depleting year by year. So then you have to recycle materials
bulk chemicals. So, it takes into account all these recycle and reuse of the materials basically.
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Let us now understand the different types of biorefinery. Two main previous attempts to
classify biorefinery systems are recognised in the literature. This is by Kamm and Kamm and
Ree and Annevelink. The corresponding citation I have given in some other slides; it will
come actually in the subsequent slides. So, several other papers mention classification
schemes for individual biorefinery set-ups such as the liquid phase catalytic processing
biorefinery and the forest based biorefinery.
So, previous classifications are based on: Raw material input (either it can be a green
refinery, it can be a whole crop biorefinery, it can be lignocellulosic feedstock biorefinery, it
can be a Marine biorefinery); Status of technology (either it is conventional or advanced
biorefinery, first and second generation biorefinery); then main (intermediate) products
produced (Syngas platform, sugar platform, Lignin platform). So slowly we will see all these
things.
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So please have a look at this particular slide where you can see that there are different types
of biorefineries listed. 9 different types and their features. So, the conventional biorefinery;
based on the existing industries such as the sugar and starch industry. The whole crop
biorefinery; it uses raw material such as cereals or maize. The green biorefinery; it uses
nature-wet biomasses, such as green grass, alfalfa, clover or immature cereals. Then 2
platform concept biorefinery; this includes sugar and syngas platforms. Lignocellulosic
feedstock biorefinery; uses nature dry raw material such as cellulose containing Biomass and
wastes. Then thermochemical biorefinery; so this is based on a mix of several Technologies,
it can be gasification, it can be pyrolysis. Then the Marine biorefinery; So that is based on the
Marine biomass (basically micro and macroalgae). Then liquid phase catalytic processing
biorefinery; this is based on the production of functionalized Hydrocarbons from biomass-
derived intermediates. Then forest based biorefinery; based on the full integration of biomass
and other feedstocks (including energy) for simultaneous production of pulp, paper, fibres,
chemicals and energy. This is all about the different types.
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We will just the conventional biorefinery what it means actually. So, many existing industries
are in fact already a sort of conventional biorefinery. So, either the sugar industry, starch
industry, vegetable oil industry, feed industry, food industry, Pulp and Paper, chemical
industry, conventional biofuel industries. Now these industries use conversion and upgrading
Technologies to separate Biomass into some main products and their residual materials.
And these Industries like the food industry already try to add some value by supplying their
by-products to other sectors. As for example, to the feed industry. However, their main
emphasis is still on producing their main products and no large efforts are made yet to
produce a broad spectrum of other value-added products like bio chemical or biofuels. That is
not happening in a large scale.
So, most of the focus is always on the main product development. However, the focus should
now be shifted to how you can generate the by-products and other wastes and convert them
into value added products. So that biorefinery will become both sustainable and economical.
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Please have a close look at this one. This is the whole crop biorefinery. In the whole crop
biorefinery this is based on dry or wet milling of biomass such as cereals: whether it is rye,
whether it is wheat, or whether it is maize. So what is being done in the first step is the
mechanical separation into grain and straw fractions, so you get a grain fraction here, so you
get a straw fraction here.
Now this grain and straw fractions will be converted. Approximately 20% is the grain
fraction and the straw is almost 80%. So both streams will be further processed separately.
The grain will deliver starch (so that is the starch platform). Then the straw (which is a
mixture of chaff, nodes, ears and leaves) represent the lignocellulosic feedstocks and may be
further processed in a lignocellulosic feedstock biorefinery.
So here, what we understand in the whole crop biorefinery is that, initially crop will be
processed into starch platform and a lignocellulosic based platform. Now that lignocellulosic
based, whatever we are getting generated, the straw basically, can be further processed in a
lignocellulosic biorefinery to other value-added chemicals and products.
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Next is Green biorefinery: Now the green biorefinery is based on the pressurization of wet
biomass such as green grasses and green Crops resulting in a fibre rich press cake and
nutrient rich press juice. The first initial step is that whatever the mechanical processing is
being done, so we will get a juice which is almost 25% and the rest 70% - 75% is the press
cake or the solid part. Now this biorefinery concept differs from others because fresh
biomasses processed here.
Advantage is that: rapid primary processing, high biomass profit per hectare and a good link
with the agricultural production. All agricultural production residues can be process here.
So this is an actual image of a pilot plant green biorefinery. So, you can see that the things are
getting processed here. So we get a protein platform, we get a fibre platform, we have a grass
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juice platform. The grass juice concentrate is here. Then this is a pilot plant biorefinery
scheme actually. And here we can get so many products like construction materials, paper,
polymer extrusions. There we get green grass protein and white grass protein. Now there are
other so many things that is happening here.
So let us understand the two platform concept biorefinery. This is based on fractionation of
biomass into mainly a sugar (basically cellulose and hemicellulose, the C6 and C5 sugar) and
a lignin fraction. Now, what is being done here is that, the Biomass, whatever it is coming, it
is converted into two things (or fractionated). One, we get a sugar platform, where sugar is
the raw material. Then it can be further processed to fuels, chemicals, polymer and raw
material.
And then you have a platform which is the Lignin platform. That lignin platform can go to
gasification (basically the thermal conversion) and you get a syngas here. Then we can have a
co-generation (CHP basically) of heat and power; and we will also get fuels and chemicals
and polymers from this platform.
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The next is lignocellulosic feedstock biorefinery. And this is most interesting because most of
the biorefineries are now looking for lignocellulosic based feedstocks. This is based on the
fractionation of lignocellulosic-rich biomass into the intermediate output streams cellulose,
hemicellulose and lignin, which can then be further processed into a portfolio of bio-based
end-products, materials, chemicals, fuels and/or heat.
Lignocellulosic-rich biomass is expected to become the most important biomass source of the
future because it will become widely available at moderate costs, and its cultivation and use
compete less with the food and feed crops. So that means, there is no food versus feed
problem here. Please understand the difference between this and the earlier one. Here we are
getting a sugar platform and then a syngas platform which is based on Lignin.
But Lignin can be converted into other things also. But in the lignocellulosic, we get
cellulosic platform and we get a lignin platform here. Now, lignin is not producing syngas
directly. It can produce whatever lignin can be used as a raw material. It is a very high value
product or it can be used for the cogeneration, which was present in the earlier this one
(Biorefinery) also. And there is a hemicellulose part also which needs to be taken care of
also.
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So then, thermochemical biorefinery. So in a thermochemical biorefinery, several
technologies could be applied such as: torrefaction, pyrolysis, gasification and HTU or HTL
(Hydrothermal upgrading or hydrothermal liquefaction). So, raw biomass and/or biomass-
derived intermediates (as for example char, pyrolysis, oil, torrefaction pellets, syngas HTU-
derived biocrude) could be conditioned and then could be introduced into these existing
capital-intensive infrastructures, substituting fossil fuels and raw materials for the sustainable
production of a spectrum of conventional petrochemical products.
Now have a close look at this particular slide. You can understand how this particular
refinery works; starting from the very source of the lignocellulosic materials, goes through
torrefaction, gasification, you remove tar, go for a scrubbing, and whatever you scrubbed out
(solid part) can be used as a fertilizer. Then you can remove carbon dioxide. You can
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concentrate carbon dioxide also. Then you can go for cryogenic distillation where we can get
acetylene and ethylene. Then we can have syngas, gaseous fuel and then the cycle goes on.
Then marine or algae biorefinery: That is more interesting now-a-days, because lot of work is
being done on this particular aspect of the algal refineries. So this is based on aquatic,
basically micro or macroalgae biomass. So microalgae can be cultivated on fresh wastewater
as well as marine water while macroalgae can only be cultivated on marine water. Here what
is happening actually; so you see this aquatic biomass that is getting cultivated here, it can be
microalgae, seaweeds, macroalgae, whatever it is. Then you go for the initial cell disruption,
product extraction (like remove the lipid content or oil whatever it is). Then, you can go for
the oil fractionation. There basically you extract oil. Then it goes to chemicals, value-added
products. You transesterify it to biodiesel. This is one of the most important aspect. Then
there are so many things left, like minerals. It can go to fertilizers and nutrients. Whatever left
out, the solid Biomass, I told you one in one of the class that it contains huge amount of
carbohydrates. Of course, the exact amount will depend upon what species we’re dealing
with. Apart from that, there will be pigments, there will be vitamins, there will be some other
important Chemicals also. The carbohydrate part can go to fermentation after hydrolysis. So
you can get alcohol based fuels, either butanol or ethanol; and other value added products like
pigments such as astaxanthin, beta-carotene; then you can also remove chlorophyll, it is a
very important class of chemicals.
So, what not we are getting from a single component or single feedstock. Now the refinery
should again be developed in such a way that you can a process different types of algae,
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whether it is microalgae, macroalgae. There are hundreds and thousands of species. So the
processes’ technology should be developed in such a way that all sorts of different species
can be converted in a single platform.
Let us now talk about, what the new biorefinery classification approach is, provided by the
International Energy Agency (IEA). So, it says that the new classification relies on the four
main features: first is the Platform; second is Products; third is Feedstock; fourth is Processes.
So, based on these four things the biorefinery has been classified. A Biorefinery system is
described as a conversion pathway from feedstock to Products via different platforms and
processes.
Now first we will see the platforms. So, the platforms are intermediates from which final
products are derived. They are the most important feature in specifying the type of
biorefinery. Platforms are intermediates which link feedstocks and final products. These
platforms are recognised as the main pillars of this biorefinery classification, since they might
be reached via different conversion processes applied to various raw materials.
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Let us see some of the platforms. The most important platforms which can be recognised in
energy driven biorefineries are the following: Biogas (A mixture of mainly methane and
carbon dioxide), it comes from anaerobic digestion; Syngas (a mixture of carbon monoxide
and hydrogen), it comes from gasification; Hydrogen from water shift gas reaction, steam
reforming, water electrolysis and fermentation (So, hydrogen come from various sources); C6
sugars (glucose, Fructose, galactose), from hydrolysis of sucrose, starch, cellulose and
hemicellulose; C5 sugars (Xylose, arabinose etc.), from hydrolysis of hemicellulose and food
and feed side streams; Lignin (phenylpropane building blocks), from the processing of
lignocellulosic biomass; pyrolysis liquid or we call it pyrolytic liquid people call it bio oil
also (So it is multi-component mixture of different size molecules), it comes from pyrolysis;
Then oil (basically triglycerides which to convert to your biodiesel), comes from the oilseed
crops, Algae and oil-based residues; then organic juice (made of different chemicals), which
is the liquid phase extracted after pressing of wet biomasses (for example grass); Then the
final one is electricity and heat, which can be internally used to meet the energy needs of the
biorefinery or sold to the grid depending upon how much you are generating basically.
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So the next is products. So biorefineries produce both energetic and non-energetic products
and can be broadly grouped into two main classes: first is energy driven biorefinery system
and the second is material driven biorefinery system.
So in energy driven biorefinery system, biomass is primarily used for the production of
secondary energy carriers. So, secondary energy carriers are basically transportation fuels,
power and/or heat. The products as feed are sold and even better can be upgraded to added-
value bio-based products, to optimise economic and ecological performance of the full
biomass supply chain. Besides electricity and heat, the energy products include the most
promising transportation biofuels until 2020: bio-ethanol, biodiesel, synthetic biofuels (FT
fuels or Fischer–Tropsch fuels and others) and maybe biomethane.
And in the material driven biorefinery systems, which primarily generate bio-based products
(like biomaterial, lubricants, Chemicals, food and feed) and process residues that can be
further processed and used to produce energy (It can be for internal use or for the outside sale
also).
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So, material products include fine Chemicals (such as amino acids, organic acids and
extracts) used in the food, chemical, pharmaceutical industry and animal feed and fibre
products among others. The selected subgroups of material products are: fertilizers; bio-
hydrogen, glycerine (it can be from transesterification of triglycerides basically); Chemicals
and building blocks (refer to the corresponding slide for examples); then we can have
Polymers and resins; we have food; animal feed; and bio materials. So, different types of
materials-based platform.
So the next is feedstock. Feedstock is the renewable raw material that is converted into
marketable products in a biorefinery. The Biomass feedstock can be subdivided into primary,
secondary or tertiary. Today renewable carbon-based feedstocks for biorefinery are typically
provided from four different sectors: (1) Agriculture (which is dedicated crops and crop
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residues); (2) Forestry (that is wood, short rotation poplar, logging residues); (3) Industry
(process residues and waste) and Domestic activities; and (4) Aquaculture (which is algae
and seaweed).
Now Biomass feedstocks, vary composition with different shares of basic components
(cellulose, hemicellulose, lignin, starch, triglycerides and proteins) and three chemical
elements: carbon, oxygen and hydrogen (plus smaller percentage of sulphur, nitrogen and
ashes). Other important characteristics are the water content, heating value, specific volume.
This is the most important thing here: different shares of basic components. This is what
doesn’t happen in the petroleum refineries. The crude which we process in petroleum
refineries, they are almost similar in composition. Of course they vary slightly depending on
from where it is; is it Indian crude, gulf crude (from where it is coming depending upon that
it varies). But not so much like Biomass. So that is why, biorefinery is extremely challenging.
So, in this classification approach, the following subgroups of biomass feedstocks are
assumed: First one is dedicated feedstock: it can be sugar crop, starch crops, lignocellulosic
crops, oil-based crops, grasses, marine biomass (like algae); The seconds is residues: oil-
based residues (It can be animal fat from the food processing industries or used cooking oil -
many times it is called waste cooking oil), then lignocellulosic residue, organic residue and
others.
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Then let us understand the processes. So, in order to produce biofuels, biochemicals,
biomaterials, food and/or feed, the feedstock is transformed into final products using different
conversion processes. Dependent on their products biorefineries can be divided in systems
where operations like fractionation/separation into polymeric products are the main processes
and systems for biofuels and biochemicals in which depolymerisation and chemical,
thermochemical and/or biochemical conversion are the major processes.
Apart from this there is an important process, which is called deoxygenation. Now
deoxygenation is important especially for those processes which are producing transportation
biofuels because the presence of oxygen may reduce the heat content of the molecules and
usually gives them higher polarity, thus decreasing blending possibilities with the existing
fossil fuels. So for the transportation sector you need to deoxygenate the liquid fuel.
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So in the biorefinery systems, several technological processes can be applied to convert
Biomass feedstock into marketable products. This classification approach identifies main
subgroups of processes such as: mechanical and physical, biochemical, chemical processes
and thermochemical. This is what we have already discussed in some of our slides of this
particular lecture.
So, you can quickly have a glance through all the things. So basically, again in a single slide
you can see the biorefinery classification based on platforms, products, feedstocks and
processes. Now you can see there are n number of processes. All these processes are not
mandatory to be present in all biorefineries; it is not so. What are the components (processes),
this will basically depend upon what is your feedstock, what products you want and what are
the platforms you are going to adapt.
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So how these 4 features with their subgroups are used for classification of biorefinery system.
This is one classical example, just have a look at this particular image. So, this is one
particular stream we can say that. It starts from feedstock, it goes for mechanical processing,
then chemical processing, platform, then biochemical processes and then we get either energy
or material products.
And if I take an example of corn, please have a look at (b), the starch crop. Corn is the
feedstock there. Then I process it, mechanically process it, basically the pre-treatment part,
then I hydrolyse it. What I will get? I will get in this platform; I will get C6 sugars. So, it is
now a sugar-based platform. The platform becomes C6 sugar platform. Then it goes to the
biochemical processing. Here the biochemical processing is fermentation and we get two or
more than two products. Bio-ethanol the most important product and then whatever other
things, for example, I have seen animal feed; there can be other products also.
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So, this is the application of new classification approach to selected biorefinery system. This
is based on the product. So, the name, one platform C6 sugars, one platform biorefinery for
biodiesel (oil based), syngas based, biogas and organic juice based, C6/C5 both and
Lignin/syngas. Please have a look later on.
So, we continue with that actually, so again coming to different platforms here. So, this is a
2-platform system (C5/C6 sugars both it is processing). Then again one-platform based on the
pyrolytic liquid. And then oil based platform and we get different types of products and the
source of other energy like heat and power whether it can be possible or not. Whether it can
be integrated into grid or not.
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So, this is based on products. I again leave it to you, please go through it later on when you
actually go through these slides. So, you can see what are the different types of platforms that
we’re using, basically sugar based. And then what are the energy output we are getting
whether it is alcohol based liquid fuel or it is electricity, heat, or it is the gaseous like bio-
methane.
So, this is a classical example, this looks very complicated, but it is not so complicated. We
can try to understand and follow actually what is actually happening. This is a network where
the individual biorefinery systems are combined. So, it is a biogas platform, we are getting
organic juice platform, syngas, hydrogen, we have C5 sugars, C6 sugars, lignin, we have
pyrolytic liquid and oil-based platform.
So, all these have been integrated. How they are integrated? This particular slide is making
you clear and make you understand. Please have a look, what are the products we are getting;
n number of products: biomethane, biomaterials, fertilizer, biohydrogen, chemicals, ethanol,
glycerine, Polymers and resins, food, feed, electricity and heat and biodiesel. This is how the
different types of materials, all the top, the green ones, they are basically the feedstock. So,
feedstock can be on organic residues here, grasses, starch crops, sugar crops, lignocellulosic
crops, then lignocellulosic residues, then oil crops, Marine Biomass, oil-based residues and
what not. Everything has been put and they have been integrated. So, it looks complicated
because of the processes here, but you can understand in a nutshell that all these different
types of feedstocks can be processed in an integrated biorefinery approach where we target
basically for not only biofuels or bioenergy but also for multiple value added end products.
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This is another example a little more simplified based on the biomass here and their
precursors. So, the Biomass and their precursors; carbohydrates, starch, hemicellulose,
cellulose, Lignin, lipid and protein which are extracted from the Biomass depending upon
what type of biomass you are using; and is the platform syngas, sugar, lignin, lipid.
And this is arranged in a little simpler way than the earliest slide. The flow is little easy to
understand here. So, you can see how they are integrated here. That means, one particular
process or feedstock is being used by different platforms as well as it is being resulted into
different end products which are again being integrated with each other to give some end-
product of high commercial value.
I think with this I will stop today's lecture. So, if you have any questions please feel free to
write to me kmohanty@iitg.ac.in or do post your queries in the Swayam portal. And in the
next class the module 2 of the biorefinery module we will be discussing about the different
feedstocks, their properties and integrated biorefinery concept. Thank you very much.
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Lecture 08
Feedstocks and properties
Good morning students. This is lecture 2 under module 3 in which were discussing
biorefinery. So, in today's class we will be basically discuss about the biorefinery feedstocks,
their properties and integrated biorefinery. So, we have almost discussed feedstocks when we
discussed about the Biomass and types and all these things. But here in a biorefinery
perspective we will discuss about the different types of feedstocks that can be used, and their
properties and what it means by an integrated biorefinery.
Let us talk about the chemical composition and characterization of biomass. So, there are
various things. The first one is the elemental composition. So, plant Biomass is mostly
composed of three elements. So, it is 42 to 47% of carbon, 40 - 44% of Oxygen and around
6% of hydrogen. So, all percentages are in dry matter. This elemental composition of biomass
is followed by the so-called macronutrients which are essential for Biomass production.
So, they are and nitrogen, Phosphorus, potassium, calcium, magnesium and Sulphur.
Moreover, plants also need some additional elements in lower quantities which are known as
micronutrients and many times mentioned as trace elements. So some of them are sodium,
chlorine, iron, manganese, copper, zinc, molybdenum, nickel, Selenium and silicon. So, all
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summing together up to almost 4%. Biomass also contains, namely in the ashes, some
different elements like aluminium, arsenic, barium, cadmium, chromium, Mercury, lead,
antimony, Titanium, thallium, vanadium, tungsten. So, these are some of the heavy metals.
So, this is a classical representation of how the elemental composition of plant Biomass looks
like if you have a pictorial presentation. We will take into account the corresponding amount
of that particular element in the composition of biomass. As already mentioned you can see
the highest is of course carbon, followed by oxygen and then hydrogen, then of course
nitrogen, calcium and potassium, silicon all these things.
Then comes organic matter. Organic components can be classified into four major groups:
Carbohydrates, proteins, lipids and nucleic acids (we will see one by one). So, the first one is
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carbohydrate. These are compounds from the combination of carbon, hydrogen and oxygen to
form soluble Sugars. For example, all the monosaccharides and disaccharides and polymeric
carbohydrates such as polysaccharides.
Among the most important monosaccharides, glucose and Fructose should be mentioned.
These are the two most important monosaccharides which we’ll derive from the Biomass and
when they combine, they constitute something called sucrose, which is a disaccharide. So,
polysaccharides are formed through the aggregation of different monosaccharides which are
then used for either reserve or structural function.
Apart from that, starch and inulin (which are also starchy compound basically) are the most
important reserve polysaccharides from an energy point of view. The former is a glucose
polymer present in many seeds such a cereal grain and tubers such as potato and roots as for
example parsnip. While inulin is composed of fructose and glucose and typically found in
roots and tubers.
So, in the bioenergy context both carbohydrates can be hydrolysed into monomers and then
fermented to produce ethanol or even directly fermented with specific microorganisms.
Structural polysaccharides are used to build the cell walls and consists of four organic
compounds: cellulose, hemicellulose, pectins and Lignin. Cellulose is a polysaccharide made
up of 200 to 5000 molecules of glucose, aggregated in linear chains or bundles to build the
microfibers or we called it cellulose microfibrils and of course fibres. So, the hemicellulose
consists of polymers of pentoses and hexoses entangled among the cellulose fibres. Both
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polymers, cellulose and hemicellulose as relatively easy to hydrolyse and represent two thirds
of the lignocellulosic Biomass (they are the major component). Lignin is another major
component; is a high molecular weight insoluble plant polymer, which have complex and
variable structures made from phenylpropanoid alcohols.
Lignin is a complicated structure and it is very rigid. It requires strong acids or bases or other
hydrothermal treatments to be hydrolysed and make cellulose and hemicelluloses accessible.
That is delignification of course partly we discussed it.
This is how Cellulose, Lignin, pectins and hemicelluloses are bound to each other in a very
intricate and complex manner. So, by seeing the structure you can understand that the
cellulose and hemicellulose are very much amenable to hydrolysis, but due to this recalcitrant
nature and intricate structure, you need to remove the lignin. Once you remove the lignin or
delignify it by doing some pre-treatment methods, lignin will be removed, cellulose and
hemicellulose also becomes separated and then you can purify them and take it out for
various purposes. The feasibility and energy demand for hydrolyzing the structural
polysaccharides are essential parameters for the development of second-generation biofuels.
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Then protein: Proteins are made up of Chains of amino acids, organic compounds containing
amine (that is a -NH2 group) and a carboxyl (-COOH) group which provides plants with
enzymatic and structural functions. The production of proteins by plants require high
quantities of energy in comparison with other organic compounds. So, considering the higher
heating value of protein and cellulose the energy yield is almost 52.5% and 96.5%
respectively from protein and cellulose.
Therefore, protein rich biomasses are more interesting for food and feed production rather
than for energy uses. And for energy uses we always concentrate on celluloses and
sometimes of course hemicelluloses also.
Lipids: Lipids are heterogeneous and hydrophobic organic compounds that make up the
building blocks of the structure and function of living cells. The main lipid contained in
Biomass feedstocks are fats, oils phospholipids and waxes.
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Major components of fats or oils are tri-esters of fatty acids and glycerol which are called
triacylglycerols. According to the saturation level of fatty acids whether the containing
carbon is saturated by hydrogen atoms, double or triple bonds, they are classified as saturated
or unsaturated fats. Saturated fatty acids as contained in animal fats have a higher melting
point and thus they are solids at room temperature.
So, you must have heard many times about the saturated, unsaturated, trans fat and all these
things. So saturated fats as it is mentioned that it has the higher melting point so it is not good
to be taken in the food items. Then there are unsaturated fatty acids; vegetable lipids usually
have lower melting point because they contain fatty acids of longer chains and higher
proportions of unsaturated fatty acid and hence they are also called as oils. So, all the nuts
and all contains so much of these unsaturated fatty acids.
Waxes are esters made from the union of long chain of alcohols and acids with the aim of
acting as water proof layers and avoiding water loss in certain parts of the plants.
Phospholipids are composed of glycerol and fatty acid and a phosphate molecule to provide
structure and protection to cells.
From an energy point of view, the production of fats entails an energy demand of almost 50.5
kilojoules per gram with an energy yield of 77.2 %, if you consider a high heating value of
38.93 kilo joules.
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The next one is Nucleic acids. So, the Nucleic acids are composed of nucleotides which are
monomers made up of three components. First is a pentose group, then a phosphate group
and then a nitrogenous base. Now according to their containing sugars, there are two types of
nucleic acid: DNA (which is called deoxyribonucleic acid) and RNA (which is called
Ribonucleic acid). And they are responsible for the encoding and transcription of proteins.
Then water content and the heating value of biomass. The moisture content of biomass is the
quantity of water existing within the Biomass expressed as a percentage of the total materials’
mass. Moisture content of Biomass in natural conditions without any further processing
varies enormously depending upon the type of biomass ranging from less than 15% in cereals
straw to more than 90% as in algae biomass.
So, this is a critical parameter when using Biomass for energy purposes since it has a marked
effect on the conversion efficiency and heating value. So, in no case any Biomass is preferred
for conversion whether it is a thermochemical conversion or biochemical conversion, if it has
more than 20 to 25% or 30% of moisture, that is not desirable. It is true that last class I was
telling you that a certain high moisture containing Biomass can be converted suitably in a
biochemical platform. That is true. But more moisture containing also do create problems
while processing.
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Moreover, high moisture content entails logistic issues since it increases the tendency to
decompose that means resulting in energy loss during storage and reduces the energy and cost
balances. The heating value of biomass feedstock represents the energy amount per unit mass
or volume released on complete combustion. The heating value is referenced into different
ways: the higher or gross heating value HHB and the lower or net heating value LHV.
And we have already discussed in one of the class that LHV is the one, which is appropriate
value to assess the energy available for the subsequent use in case of bio refinery concept or
let us say if you are talking about Biomass to biofuels.
Then inorganic compounds and ash composition: Many elements are present in the Biomass
feedstocks such as Silicon, Calcium, Magnesium and there are many. As well as certain
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heavy metals such as Copper, Zinc, Cobalt, molybdenum etc. The presence of these inorganic
elements has a strong influence in the combustion process by forming gaseous and solid
emissions as well as influencing the ash melting behaviour which may add on to the
corrosion process.
While Sodium and potassium could lead to ash vitrification, high content of chlorine entails
emission of dioxins and material corrosion. The oxidation of S produces sulphur oxides
mainly Sulphur Dioxide which in combination with steam generates sulphuric acid
contributing to acid rain formation. The presence of elements such as Arsenic, barium
cadmium all these heavy metals allows the use of the generated ashes as fertilizers which
improve the environmental performance of the use of biomass for energy purpose and
additional use basically.
Then we will discuss the classification of biomass types with respect to biorefinery. So, if we
classify them according to their chemical composition. So, they can be classified as:
lignocellulosic Biomass, sugar rich biomass, starch rich biomass, oil rich biomass, protein
rich basically these types. So, lignocellulosic we have already discussed many times so it is
containing mostly the plant fibres which contains cellulose, hemicellulose and Lignin. So,
wood, starch, straw and energy grasses all this comes under lignocellulosic Biomass and this
type of Biomass is intrinsically linked to the classification of Biomass into herbaceous
Biomass and woody biomass.
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Under sugar rich biomasses, so there enriched with carbohydrates in the form of
monosaccharides mainly glucose and Fructose and disaccharides sucrose. Such as sugar beet
and sugar cane.
Then if you talk about starch rich biomasses, they have a high proportion of reserve
polysaccharides, basically starch and inulin (Inulin is a starchy compound again), such as
found in the grain cereals whether it is wheat, corn etc. or tubers, potato, artichoke etc.
Oil rich biomasses; so they have high lipid content especially in some specific parts such as
rapeseed and some micro and macro algae.
Then protein rich biomasses. So, from plant Biomass such as oil seed as for example
soybean, sunflower and legumes. As for example peas and also from animal biomasses. Pig
meat, fish and this so called this meat and fish processing industries.
Then agricultural Biomass, forest Biomass, by-products residues and waste, and aquatic
biomass. So, biomass grown in agricultural land, which includes all kinds of Agricultural
produce regardless of chemical composition, whether it is lignocellulosic, starch, oil crops
etcetera and whether it is edible or not.
So then forest biomass; wood from forest including tree plantation in forest land for energy
and woody biomass from forest management. So basically, pruning activities and thinning
activities all these things. Nobody is going to cut the healthy plants to make biofuel. So, that
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is not allowed in any country and should not be done also. So, anything that is because falling
from the tree or when we are doing this pruning and thinning business that time whatever we
are producing the wood or woody products so those can be coupled under the so-called forest
biomass.
Then by-products, residues and waste: This can be defined as biomass from well-defined
side-streams from either agricultural forestry or related industrial operations. It also includes
organic residues from Municipal solid waste, MSW.
Then comes the aquatic biomass, so it refers to any plant or animal material that has formed
in water such as algae, seaweed and aquatic plants.
Now let us talk about the biorefinery feedstocks. Broadly we can classify them as either: (1)
dedicated or non-waste feedstock; (b) residual or waste as feedstock. So, further distinction
can be made for the feedstocks according to their source of origin such as agriculture,
forestry, industry and aquaculture we have just seen that.
So (1) dedicated crops as feedstock involve a fresh carbon-based feedstock which is actually
developed for biorefinery use or purpose from the agricultural, aquaculture and forestry
sectors. This is known as primary feedstocks which is solely used for the biorefinery
purposes and are also well known as energy crops. So, they are only planted for the bio-
refinery or energy purposes. So then (2) residual feedstock involves the carbon-based
feedstocks in the form of waste or by-products or residues from the agricultural, aquaculture,
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forestry, household, organic residues and industrial sector. This is known as secondary
feedstock which is the by-product of primary processing and needed proper dispose or reuse.
So, both these are carbon-based feedstocks that are generally varied/having slight variation in
their original basic composition (of hydrogen, carbon, oxygen and other trace elements)
depending on the geographical location or position, species type, and the environment.
Moreover, they may also differ in the percentage amount of sulphur, nitrogen, phosphorous,
moisture content, micro-inorganic constituents and ashes.
They may also differ in the calorific value, heating value or specific heat, specific volume
and actual weight content. However, carbon is the main constituent of any kind of feedstock
utilised for the carbon based biorefinery.
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So, the dedicated feedstock basically involves the following types of crops: lignocellulosic
Biomasses, that is the energy crops such as forest hardwood, softwood, pine and miscanthus;
Grasses such as green plant materials, grass silage, immature cereals, herbs, bushes, plant
shoots and switch grass; Algal, or Marine Biomass such as seaweeds, sea plants and Marine
micro and macro algae; Oil crops such as rapeseed oil, coconut oil, soybean oil, palm oil,
jatropha oil and cottonseed oil and then many others; starch crops such wheat, corn, ray,
barely and maize; Then sugar crops such as sugar beet, Sorghum, potato, sweet corn, rice and
sugar cane.
The residual feedstock generally involves the following carbon-based waste or bio-products:
Residue from lignocellulosic Biomass treatment such as field crop residues, saw mill residues
such as saw dust, nonedible part of the crop and the forestry residues (which are basically left
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out after the processing); Then organic residues and by-products such as organic urban waste,
domestic waste, waste paper, food waste, compost, fruit peels, vegetable residues, cattle dung
and Swine manure; Industrial organic waste; Oil based residues such as animal fats from food
Industries, slaughterhouse waste, tanning waste, leather waste, oil cake, oil ghee waste, soap
industry waste and used cooking oil from restaurants households and others; Grass residues
and waste such as green plant materials, grass silages, silage leachate immature cereals and
plant shoot.
This is the conventional classification of feedstock. I am just telling you again. We have
discussed about the biorefinery classification. Again, the feedstock has been also classified in
the same way as the biorefineries has been classified: (1) lignocellulosic feedstock for
biorefinery; (2) whole crop feedstock for biorefinery; (3) green feedstock for biorefinery; (4)
the two platform (the two platform we have already we discussed, please understand and
don’t get confused. Again, I am repeating that this is the name here whatever listed here you
are seeing, all these has been classified as it is for the biorefinery. The types of biorefineries
we have discussed in the last class. Now the feedstock for the biorefineries are also classified
in the same manner); (5) Oleochemical feedstock for biorefinery; (6) Algal feedstock; and (7)
Organic waste feedstock. We will just quickly see what are these types of feedstocks. What
are the advantages and disadvantages and how do we process these feedstocks one by one
will quickly see.
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Lignocellulosic feedstock; Most successful, primitive, primary, and potential biorefinery
feedstock among all the biorefinery feedstock. So, it involves the nature dry lignocellulosic
feedstock such as wood material, straw, corn stover other agricultural residues, energy crops
and Municipal lignocellulosic wastes. Now this involves three major interior constituents
such as hemicellulose, cellulose and Lignin.
So, how do we process these feedstocks? So, pretreatment and dissolution of lignocellulosic
biomass (that is the first thing) using a suitable solvent. Then you separate the lignocellulosic
feedstocks into basic three components cellulose, hemicellulose, and Lignin. Once that is
done, so you take out the cellulose and then you hydrolyse the cellulose. So, you hydrolyse it
to what? To fermentable sugars or fermentable glucose.
That can be converted into sugar to biofuels or chemical intermediates like alcohol -
basically, it is an alcohol platform (whether it is methanol, ethanol and butanol) and organic
acid (succinic acid, lactic acid, levulinic acid etc.) either by chemical and biochemical
methodology. Then hydrolysis of the hemicellulose polysaccharides into the xylose sugar that
can be converted into biofuels or Chemicals like xylitol and furfurals by using chemicals and
biochemical methodology.
Lignin can be converted into value added polyphenolic aromatic compounds, bioil and value-
added Chemicals by various catalytic and thermocatalytic transformation. Lignocellulosic
Biomass feedstocks and residues can be used for co-generation of the heat and energy that
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can be used for internal processing. After complete treatment residual cake can be used as
animal feed.
Now the advantages are: they’re easily available and are of course lower cost if compared to
any other raw materials and feedstock; several product varieties - that means we get a wide
array of formation of products - can be possible from lignocellulosic Biomass by various
thermochemical and biochemical platforms. And some of these products are well marketed in
the society; So, the biorefinery products are well replaceable by the petrochemical refinery;
and natural structures of the lignocellulosic feedstock derived/extracted polyphenols are very
well preserved; And simultaneous co-generation of heat and energy is also possible from the
last cake or residual part. After processing whatever solid residues is left over that can go to
co-generation of heat and energy.
However, there are certain disadvantages also; So, dissolution is the difficult task due to the
reluctant nature of the interior complex cell wall. This we have discussed in the slide also I
have shown you have noticed how Lignin, hemicellulose, cellulose and pectins are packed
together. So, breaking it is a big job or tough job. So, you need huge amount of energy and
sometimes Chemicals. So the cost of the process is very high and sometimes it may be time
taking process also. So then costly and tedious pre-treatments are necessarily required. The
development of separation technology to separate primary components is required.
Degradation and conversion of the lignin into respective valuable polyphenolic compounds is
a very difficult task and unless and until you have achieved a proper efficiency, we cannot
have a sustainable biorefinery that functioning basically.
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So, yes in a nutshell, please have a look at this particular slide. Where it is lignocellulosic
feedstock biorefinery. LCF biorefinery we call it. So various types of feedstock; basically
first you divide them, or segregate them, or dissolve them into lignin fraction, hemicellulose
fractions and cellulose fraction. So the lignin fraction, lignin is a high value compound so it
can be used as a natural binder and adhesives. It can go as a substitute for a sub-bituminous
coal and sulphur free solid fuel. Then hemicellulose, if you hydrolyse hemicellulose, such
pentoses and hexoses (C5 sugars), so, you get Xylose, Xylite and furfural and then so many
other things, some platform Chemicals also. So you can have plant gum, can be used as
thickeners, adhesive, protective colloids, emulsifiers and stabilizers.
Now let us look to the cellulose platform. This is the cellulose platform, entire cellulose
platform. If you hydrolyse cellulose, we get glucose that is C6 sugars. So it can be fermented
and you get fuels the like ethanol, butanol and all these things and some other organic acids.
So, you also get HMF hydroxymethyl furfural, Levulinic acid (so these are very high value
component) (And HMF is also fuel additive), so then we can also get lubricants, some sort of
chemicals and Polymers and some softening agents and solvents. From this we can
understand that the lignocellulolytic biorefinery gives us a wide range of products.
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So, the next is whole crop feedstock for biorefinery: So various kinds of the cereal crops like
rye, wheat, triticale, stover, Maize and corn and these entire crops as used as sole feedstock
material. Initially seeds and grains which is amounting to 30 to 40% of what is harvested, will
be mechanically separated from the straw which is 60 to 70% of the total in the weight basis
basically.
The straw generally involves the mixture of chaff, stalk, nodes and leaves) and of course then
these seeds are processed to produce the starch and different value-added products such as
oil, biofuel, biopolymer, bio-oil, lipids and Chemicals. Whereas the straw part that can be
used to generate various value-added products. Similar to those of those of the lignocellulosic
feedstock biorefinery.
It involves dry or wet milling processes depending on the dry or wet feedstock to give the
basic fractionation, hence, feedstock is further divided into two subparts: (1) whole crop dry
mill feedstock; (2) whole crop wet mill feedstock. So the dry mill feedstock is basically entire
cereal plants as harvested. And this harvested plant Biomass is preserved, dried and stored for
long time up to their reuse in biorefinery. And the wet mill feedstock involves swelling and
soaking of the feedstock before it is processed for biorefinery purposes.
So how do you process this whole crop feedstock? So first you go for mechanical segregation
of the seeds and grains from the straw, you remove them. So, for the dry milling entire
harvested feedstock is preserved, dried and stored for long time. While wet milling involves
the primary swelling and soaking of the feedstock.
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The starch present in the cereal is then hydrolysed into glucose via chemical or biochemical
methodology to generate bioethanol or any other alcohol also and other value added side
products such as succinic and lactic acid. Further extraction of the remaining grain
components provides the polysaccharide-based bio Polymers, some drug intermediate, animal
feed and certain other value-added products.
That treated residues or agricultural residues of crops are allowed for the fractionation just
similar to that of the lignocellulosic biorefinery. Moreover, it can also be used for the
generation of the heat and electricity in the CHP platform.
So, please have a look at this particular platform. You can see that from the feeds that grains
such as cereals, corn and maize are actually procured or harvested. Then we segregate them
into the seed, this is the seed platform. And this is the straw platform. You can see the straw
when you decompose then you get the Lignin and hemicellulose and cellulose after the
pretreatment.
So then this all can go to subsequent further processing. You go for elevated gasification.
You get syngas, methanol all these things. Then seed portion can directly go to meal and can
be directly used. Then we can get starch from the seed which can also be extruded and co-
extruded go for Making bioplastics and certain other Polymers basically.
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Then if you go for a biotechnological conversion. So you get glucose, then the glucose will
go for the alcohol platform - fermentation, ethanol. So, you can also have other things also.
So then, when you go for a chemical conversion and modification, so you go for
hydrogenation, you go for some other esterification and other processes and you get you get
many different types of products.
So, in a nutshell we can understand that almost similar type of product also you are getting in
this whole crop biorefinery as we get from the lignocellulosic biorefinery. However, in case
of the lignocellulosic biorefinery the area of such value-added products that is getting
generated or produced is very large compared to other feedstocks.
The advantages are the preservation of the natural elements and structural composition is at a
greater extent and the entire whole crop is utilised for the biorefinery purpose without
creating further waste. So this is one beautiful thing. This entire thing whatever is being
harvested is being used for the biorefinery purposes. Nothing is being wasted.
So, the disadvantage is that utilisation of the expensive and specific energy crop that is
generally not economically viable. Second, this may cause increment in the prices of the
manufactured products in the market. This will happen this thing along with the agricultural
land that may be utilised to grow the energy crops. It may happen as in when this so-called
biorefinery concept is being applied and there are so many biorefineries are getting set up
whether it is in India or other countries. So, people including even the farmers will have a
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tendency to grow such energy crops which takes less time to produce and which also needs
little care during plantation.
And the yield per hectare as well as the energy value and economical value is much much
higher than that of the certain agricultural crops. That is some sort of a threat. So thats the
disadvantage. However, government should help, I have told you in one of our introduction
classes. Again, I am repeating; here comes the government which will play a big role to make
a policy so that no dedicated agricultural lands which are having high value land basically or
fertile lands, should not be utilised for growing dedicated energy crops.
So that should be the government policy because in a country like India where you have huge
population and we need a huge amount of food supply, we cannot do this.
Then green feedstock for biorefinery. So, this involves the feedstock green plant matter and
more specifically green grasses that are naturally wet to produce the variety of products. It
can include the closure fields; nature conservative grassland; Some Green crops, like lucerne
or alfalfa, clover, humid-based organic waste/compost and some immature cereals. Now
these feeds stocks are relativity of lower cost and potentially available in larger quantities.
This naturally wet green Biomass or green feedstock can be successfully converted into the
useful non-feed products such as energy, organochemicals, bioplastics and even feed
products such as animal feed by applying different chemical or biotechnological processing.
So once to do that there is something called a press cake or the leftover solid biomass. So that
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majorly consists of the cellulose, starch along with some small content of essential
components such as dyes, pigments, crude drugs and other organic compounds.
So, this press/green cake is a wide resource for the fibre production and can be used for the
production of animal feed pellets. So, it acts as a raw material for the production of wide
variety of chemicals such as monosaccharide units, organic Chemicals, acids such as
Levulinic or succinic acid and synthetic biofuels. So, press cake can be used for the insulation
material, construction panels and bio-composite materials synthesis.
This is again you please have a look to this particular slide. You can see that from the fields
we get the green wet raw material grass, lucerne whatever it is and then it can; if you are
drying it so you can get a drying material. So, then you can have so many things here. Here
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you have the press that can goes to the juice platform. We have discussed in the biorefinery
concept in the last class.
And whatever left out after the juice is getting extracted is the press cake or the solid part
which is carbohydrate rich. So, the juice can go for different platforms such as this valuable
products and enzymes, dyes all these things. And press cake can go for so many different
types of value-added material, including your biogas, syngas and fibres and solid fuels also.
And whole crops such as straw, seeds, starch etc. you pre-treat them get a carbohydrate
source then ferment you may get whatever left out and convert them to biogas and energy
generation. So integrated way, it can be operated.
So, how do you process this? So, the green biorefinery involves the primary processing
pretreatment of green feedstock or the humid organic waste. Biomass is fractionated into
fibre rich press cake and organic rich green juice. Press cake is allowed to treat for the
hydrothermal and thermochemical processing to obtain the variety of chemicals or
biomaterials. Green juice is treated by the biochemical techniques or the extraction process to
obtain the variety of miscellaneous organic compound and natural extracts.
The residue streams from the above processing can be used in anaerobic digestion for the
production of biogas to generate the heat and power for the internal use.
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Let us understand the advantages and disadvantages of this particular feedstock.
(Advantages) Multi productive system: that is a beautiful thing about this particular feedstock
and low price. And these are available in large quantities. So, grassy green feedstock is more
easily pre-treated and fractionated (the reason is because it has its contents low amount of
Lignin), so it can be fractionated into basic constituents for biorefinery processing that
ultimately reduces costing of the end product formulation when you compare it to the woody
lignocellulosic feedstock. A large variety of the secondary products can be extracted, isolated
and synthesized. Organic waste such as agricultural and forestry waste can be considered and
utilised as a green feedstock.
(Disadvantages) And if you talk about disadvantages: Isolation and separation of natural
compounds by the extraction technique needs further improvement in advanced technologies
and process economics. If you talk about the downstream processing part. Then isolation of
the natural pigments and components or constituents from the press juice is a tedious process.
Tedious process means it is time consuming and the technology also whatever it is there, the
yield is very low. Basically, we need research and more development in the downstream and
processing part.
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Now let us discuss about the Two platform feedstock for the biorefinery. So, this concept has
been implemented by the NREL (National Renewable Energy Laboratory) of the United
States. The feedstocks are separated into two different kinds of platforms, one is sugar
flatform, another is the syngas platform. Now both these platforms can offer energy and
value-added products such as Chemicals, biomaterials, biopolymers and animal food.
Use the initial complete conversion of the carbohydrate materials and then to perform further
conversion process for the syngas production and additional products. The sugar platform
biorefinery involves the production of C5 and C6 sugars from the lignocellulosic Biomass
feedstock via biochemical conversion or fermentation processes.
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The syngas platform biorefinery involves the thermochemical conversion processes that are
basically focused on the gasification reactions of the Biomass feedstock. Other processes
such as pyrolysis, hydrothermolysis, thermolysis, combusting and burning are also carried out
simultaneously. This syngas platform offers the synthesis gas and its consequent production
of fuels, power, electricity and some speciality chemicals.
So how do you process this feedstock? So initially we have to fractionate them to two
platforms basically. So, this fractionated feedstock is then biochemically applied for the
production of the C5 and C6 sugar platforms that can further be transferred into the value-
added products. So, it is a pentose and hexose platform. Then later on whatever the residual
feedstock is left out that is thermochemically treated for the syngas production or using the
gasification reactions at the higher temperatures which can be able to produce the synthetic
fuels and other speciality Chemicals.
The last remaining residues can be used for the production of biogas to generate heat and
electricity for the internal use and animal feed cake.
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If you talk about advantages and disadvantages; (Advantages) the combination of two
different platforms in one biorefinery concept offers a wide array for the production of value-
added products from the single feedstock. So, this kind of bio refinery produces the biofuels
and synthetic fuel. This biorefinery offer the complete use of the feedstock with minimum
process economics.
(Disadvantage) is that, the development of the two-platform binary refinery system and
processing is a challenging task by the means of technological development aspect. The two
platform biorefinery is specifically a sugar-based biorefinery that generally avoids the use of
the higher nitrogen and sulphur containing Biomass compounds.
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You can see this particular slide. So, this is one typical example from the wood chips. It is a
biorefinery plant concept. So the wood chips goes to the steam gasification. So, you get
syngas. So, syngas you catalytically convert using the Fischer Tropsch (FT synthesis
basically). Then when it goes to combustion, we get electricity and heat. So you further
process it (hydroprocessing basically). So, you get the Fischer Tropsch diesel and you get the
Fischer Tropsch gasoline, fractionate them.
And then whatever is left out solid part that is basically the wax. This is one of the simplest
platforms.
Then let us understand the oleochemical feedstock for the biorefinery. So, an oleochemical
biorefinery consists of the oil-rich feedstocks such as long fatty acids and esters, glycerol, oil
seed and vegetable oil crops (There are many, rapeseeds, castor seed, cotton seed we have
seen it in one of the class) which tend to produce primary speciality Chemicals such as
functional monomer, grease, lubricants and surfactants. These speciality chemicals are also
widely used in cosmetics, detergent, drug, Pharmaceuticals and household products.
Saturated C12 and C14 fatty acids are called the laurics, which are made up of the coconut,
palm kernel oil and worked as feedstock for surfactants. Then the unsaturated C16 and C18
fatty acids are called as oleics, which is worked as feedstock for the production of the
biodiesel, lubricants and certain oleochemical Polymers.
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How do you process them? So seed and lignocellulosic Biomass is separated from the oil
seed plants. The seed is allowed to extract the fatty acid ester oil content by extraction while
the lignocellulosic materials which is left of the solid parts (so basically, the oil and removed
part), is fractionated into the Sugars platform. And of course, the Lignin is generated, so the
lignin goes to various end use.
So, the seed oil is then biochemically treated for the production of the biofuel. The
fractionated lignocellulosic material is then utilised for the production of various value-added
material or products. The oil cake residues can be used as a feed for the animals. The treated
lignocellulosic residues can be used as a feedstock for the biogas plant and the generation of
the heat and electricity.
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So, if we talk about the advantages and disadvantages of this particular feedstocks.
(Advantages) It is a long chain fatty acid, so it’s a better resource to convert the raw
feedstock into biodiesel and biofuel (yield will be basically very high if we compared to other
biomasses). So, it can employ the various hydrolytic enzymes for the direct conversion of the
fatty acid esters into the biodiesel and biofuel. It will directly offer the simple fatty acid
methyl and ethyl esters by chemical and biocatalytic conversion routes that is nothing but
biodiesel.
(Disadvantages) So, disadvantages are, the extraction of the oil is a difficult task that
produces the lower yield (because of this extraction technology - need to work more on that).
So, it requires the large amount of organic solvents for the extraction process, which
increases the distillation and recovery cost. The cost of oil-based plants is much higher as
compared to that of the other lignocellulosic plants. All these oil-rich crops are edible plants
that may compete with the human food chain.
The next one is the Marine feedstock for biorefinery. So, the marine feedstock is a widely
available feeds stock in nature that can be efficiently use for the biorefinery purposes. Since it
involves the phytoplanktons which are the largest representative biomass present on the earth.
It basically involves the macro or micro algae. So more than 1 million of the species are well-
known and these algae maybe autotrophic and heterotrophic or mixotrophic.
However, species to species and according to environmental condition, the Algae are varied
in their content such as oil, carbohydrate, starch, minerals, salts and vitamins. So, they are
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recognised as the possible biggest source of the oil and carbohydrate for biofuel production.
Moreover, these aquatic plants are the major source of carbon dioxide sequestration. This is
the most interesting part of the so-called algal business macro or micro algae whatever it is,
as I told you in one of the introduction classes; why so much people are talking about algae
and algal biorefinery nowadays? Why many people across the globe working on algae? The
reason is that, it is its carbon dioxide sequestration or Carbon dioxide uptake capacity which
is almost ten times or even more than that of the Terrestrial plants. So that is one of the most
important aspect of this algal business.
So, you are growing algae, and then you are taking the biomass and you are doing the bio-
processing to get the biofuels, value added products and what not. At the same time, you are
also doing the carbon dioxide sequestration.
So how do you process them? So initially the biomass is separated or harvested from the
aquatic media. The harvesting of algal biomass is itself is very, very time taking and again
whatever (harvesting) methods are available, they are not so efficient. So, people still
working on that. So, the algal Biomass is then allowed for the filtration, centrifugation and
drying.
Then you do the cell disruption. So, you do cell disruption by so many different methods.
You can go for mechanical methods like milling, you go for autoclaving, you go for
ultrasound assisted methods, microwave radiation methods. So, (cell disruption is done) to
remove the components which are present inside the cell of the algae and take it out basically.
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So, the oil that is obtained from the algal Biomass is then treated by biochemical conversion
to obtain the biofuel and biodiesel. The algal residual cakes are a rich source of various
nutrients, like essential minerals, carbohydrates and pigments that can be efficiently isolated.
Also, this residual cake can be used as animal feed or feedstock for the biogas plant.
So, advantages are: of course the cultivation of algae is more advantages to the terrestrial
Biomass. Carbon dioxide sequestration is a biggest advantage. Then Algae are very well
known to adjust to the climatic conditions harsh or mild. So lignocellulosic biomass
possesses the complex cell wall structure while algae have simple structure. And so, you can
easily basically pre-treat them. So like terrestrial biomass, deforestation is not a problem in
case of aquatic biomass.
Algae cultivated in the lakes and oceans do not compete with the basic needs of the terrestrial
life/animals for food crops, land and freshwater for their growth. Another important aspect.
So, the growth rate of the aquatic plants or algae is much higher than the terrestrial plants.
Also, products derived from the algal biorefinery are unique since the carbohydrate sources
produced by the macroalgae are more diverse than that of the conventional plants. This is
another important aspect. Now this aquatic biomass can also be used to produce the
bioenergy products such as biofuel, bioethanol and bio-oil and treated cake can also be
utilised as a rich source for the biogas plant.
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Of course, having said that there are certain disadvantages like the high cultivation cost. So,
you know algae be needs a growth medium. It is not only water. You need to supply food to
them and apart from that they also need the macro and micronutrients. So, the existing
commercial growth media, which is available, which is BG11 or there are many others such
commercial growth media, they are very costly.
So, if you go for a raceway pond culturing and any such photobioreactor in a large scale,
then the entire cost of this cultivation becomes too much. And ultimately your product cost
will be so high that it cannot be commercially viable. So that is why the people are still
working on how to produce algae on waste water streams? Many people are working and my
group is also currently working on this particular aspect that how do we grow algae on low
cost media and different wastewaters, whether it is domestic wastewater or Industrial waste
water.
Some complicated conditions are needed for the successful and resourceful cultivation such
as high exposure of Sunlight, volume to surface area ratio, gas mixing, aeration/ventilation
etc. Economics also not so favourable right now, but so much of work has been going on and
I am sure that in the next decade algal biorefinery will take a centre stage in the entire
biorefinery business.
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So, then the last one is waste based feedstock for biorefinery. So, the waste generated is a
severe problem of the current Civilization since the rate of waste generation is much, much
greater than its actual disposal. That is why you will find waste everywhere. So, the
Civilization waste is most general a carbon based or organic waste which is ideally a nutrient
rich source for the microorganism-based biotransformation.
So, to accomplish the efficient utilisation, the renewable organic waste residues is being
categorised into the following four sectors:
(a) Organic waste from agricultural residue; (b) Organic waste from industrial residue; (c)
Organic waste from the forestry residue and; (d) Organic waste from the urban residue or
Municipal waste.
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Again, the processing is similar type: separated physically, to maintain the homogeneity of
the feedstock. You pre-treat them by various physicochemical techniques. Fractionate the
pre-treated waste into fibre rich press cake and organic content rich green juice. Then you
follow the extraction technique and other hydrothermal and thermochemical processing to get
various platform Chemicals, fuels, heat and other Polymers.
So, advantage is that: You are generally talking about waste, which is already waste. So, you
have to basically collect it, segregate it and then of course use it. So, waste biorefinery assist
to clean our society by converting the waste into value added products such as Chemicals and
energy. Hence, civilization organic waste is considered as the renewable feedstock that can
be reused for gaining several value-added products.
Having said that there is a disadvantage also, that this is available regularly in huge amount
and it needs to segregate properly according to their basic types and chemical composition
before processing. So, this segregation is a big task. The municipal solid waste contains so
many things. It contains metals, it contains plastic, polythene and all these things, food waste
then organic waste, then waste from industries and there are so many things.
So, everything together cannot be dumped to a thermochemical or biochemical platform, you
cannot do that. So, you need to segregate it. So that segregation itself is a big task and if we
educate people to segregate that at source, which is the best possible method to do that when
we generate it, then is good. Otherwise, it is very difficult.
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So, let us talk in a glance how the integrated biorefinery looks like. So have a look at this. So,
Biomass feedstock is coming (any biomass feedstock). It is pre-treated - you do the
extraction, separation and whatever it is. Then it goes for thermochemical conversion using
either combustion, gasification, or pyrolysis. You get steam, gas, bio-oil etc. and you further
get these things.
Then you basically convert it in the biochemical conversion platform using either anaerobic
digestion or fermentation. So, you get biogas and the alcohol platform (this is bioethanol,
biobutanol all these things). And all these things can be combined together to produce the
CHP or the combined heat and power and further electricity generation. So this is an
integrated approach.
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Another one, this is a biorefinery general scheme for precursor containing biomass with
preference for a carbohydrate line. So basically, with more emphasis on carbohydrate. So you
can see this soft wood, cereals, maize, sugar beet all these things, mostly carbohydrate rich;
you fractionate them. Lignin, carbohydrates, fats and protein. So, lignin part can come to
syngas and syngas can be converted to methanol, gasoline and all these things.
Some of the Biomass precursors like straw, bagasse etc. can be converted to energy by
gasification, pyrolysis. Then the carbohydrate platform goes to glucose, then ethanol, ethene
all these things. Certain organic acids will come here. Fats, proteins will also go for so many
other products like enzymes, some animal feed etc.
So, another one. This is an integrated biorefinery emerged from a paper mill: basic product
and their applications. So, this is an example of a thousand kilogram of wood. So, wood yard,
then it is digester, then there is a Bleaching Plant, and it is going to drying machine. Then the
ethanol plant, where we are getting almost 50 kg of ethanol per 1000 kg of the wood
processed. Then Vanillin, it is a very high value product. Three kg vanillin, so it’s a very
small amount with respect to 1000 kg of the wood that is processed and the Lignin. You see
the amount of the Lignin. So for hard wood the Lignin content is very high. Its almost 40%
straight away; for 1000 kg wood processed we get 400 kg of Lignin. And remember, this is a
huge amount of lignin and if we can have a lignin biorefinery here further that side, then this
entire concept of this integrated biorefinery along with this Pulp and Paper Mill will be a
sustainable biorefinery process. You get so many products of course.
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This is one last slide I wish to show you. So, this is the system integration for a waste
biorefinery concept combining biochemical and thermochemical processes to produce
platforms for biofuels and chemical products. So, have a look at the organic waste and
biomass, if it is having algae, it goes to hydrothermal liquefaction, one of the most important
technique will learn about this later on.
So, you get the biocrude. This crude if I process and distil I will get the similar cuts I get in a
traditional refinery - petroleum, diesel, naphtha all these things. Beautiful technique, please
try to understand, you will be wondering where did the plastic emerge from? So, this plastic
is an add-on thing. So, if I can mix plastics with these algae (We have also done some work
on that), it will produce excellent quality of biocrude and the quality of the fuel that will
come from this biocrude will be much, much better than the “only algal” biocrude. And in
this way we are also taking care of the plastic utilisation or waste plastic utilisation. So, then,
the high lignin materials will go to pre-treatment. Then lignin, this is the lignin platform, then
whatever solid that is left out, you can anaerobically digest it.
So, you get basically the volatile fatty acid (VFAs). So then yeast fermentation - you get oil.
Esterification and hydrogenation we get ethanol, butanol, propanol. Again, this is the alcohol
platform. Now anaerobic digestion - we get biogas, biogas can be converted into energy
generation. It can be directly integrated to the grid also, by adopting proper technology. Heat
and electricity from the biorefinery.
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Now, whatever hydrothermal liquefaction residues will be there (very less) that can also be
combined with this anaerobic digestion process to produce electricity. So, do you understand
it is a beautiful process and a complete integrated refinery concept in which a particular waste
can be segregated and another waste like plastics also can be integrated to take care of the
solid waste management or plastic waste management problem. And so as to get a better fuel
quality also.
So, another one just quickly will go through. It is an integrated 4-platform (biogas, green
juice, green fibres and electricity and heat) biorefinery using grass silage and food residues
for bioplastic, insulation material, fertilizer and electricity. So, the grass silage - process it
and separate, you get green juice. And then green juice can be anaerobically fermented.
Separate, you get fertilizer, biogas platform this is you get heat and electricity. Natural gas
also can be combined with this. This is another integrated four platform bio refinery concept.
With this I conclude and thank you very much. If you have any query, please write a mail to
me at kmohanty@iitg.ac.in. You can also drop your query in the Swayam portal. And in the
next class which is module 3 and lecture 3 we will discuss about the economics and life cycle
assessment of the biorefineries. Thank you very much.
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Lecture 09
Economics and LCA
Good morning students, today is lecture 3 under module 3 and you know that we are
discussing about biorefinery and concepts under this module. So today we will be discussing
about the economics and the life cycle assessment of biorefineries. So, let us begin.
The development of a new bio refinery, its design and construction, requires huge
investments; cost estimation are often Paramount for deciding the economic viability of
biorefineries and must be performed on a case-by-case basis. However, it is possible to make
a rough estimation based and data from demo plants, process Modelling and/or literature at
various stages of the biorefinery development. A Biorefinery system include the harvesting,
storage and transport of the products as well as the biorefinery itself. Innovative new
conversion Technologies usually follow a development pathway from the lab, to piloting,
then demonstration and finally the construction of a commercial plant. The number of years
for a bio-based product to reach commercialisation depends heavily on the economics and
hence on drop-in versus non-drop-in (which means existing demand and infrastructure), type
of conversion technology and supply chain integration.
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Total cost can be divided into two things: one is a capital expenditure, which is called as
CAPEX and then the other one is the operating expenditure, which is called OPEX. CAPEX
can be subdivided into mainly two things, one is plant cost and off-site cost and another cost
also we can add on which is called engineering cost. So, the plant cost represents the capital
necessary for the installed process equipment with all the auxiliary and accessories that are
needed for the complete process operations. So, including from the piping, instrumentation,
insulation, foundations, site preparation everything. Whereas off-site costs are not directly
related to the process operation. They rather include costs of the addition of the site
infrastructure, for example power generation units, boilers, pipelines, offices etc. OPEX
consists of fixed and variable cost. Variable costs comprise cost of feedstock and supplies,
waste management, product packaging, finished and semi-finished products in stock etc.
Fixed cost comprises salaries, taxes, licence fees, interest payments, marketing cost etc. This
gives us a rough idea about what are the different types of costs involved in a biorefinery.
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So, if you represent it in a schematic, we can understand in a better way, please have a look.
You can see that 20% to 30% of the cost comes under the capital costs, which are investment
cost basically. Equity, interest rate, life time etc. Then the major cost, 40% to 70%, is the
consumption related cost. So, these are feedstock cost, auxiliaries (like electricity requirement
- energy basically, chemicals), disposal cost etc.
Then the next is 10% to 25% is the operation related cost, which takes into account the
manpower cost, insurance cost, cost of services etc. All these things, these three are basically
the cost of the entire biorefinery process. So minus if you do the revenue, then that will
become your profit.
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So, estimations for the cost of biorefinery products are affected by a range of drivers that
could change in direction and importance over time. So, some of these include: supply cost,
market price and demand, competing, non-energy markets for Biomass, preferences of
farmers and Woodland owners, Success of alternative waste recovery and recycling,
production cost, storage costs, distribution cost, access to market.
The first one, supply cost is basically feedstock supply cost. So how the feedstock is getting
procured from the source and getting transported and all these things will come into that.
Then again, the market price of the feedstock and market price of the product that you are
eventually going to sell off all these things comes under that, with respect to demand for that
particular product.
Then the second is, competing non-energy markets for the biomass. One of the most
important thing that we need to understand at this point also that these bio-based products’
acceptability has to be increased. So, a public awareness and campaigning is required to do
that. So, right now even when somebody going to install a biorefinery, it is of paramount
importance that they should also work on increasing the awareness of the bio-based products.
Then preferences of farmers and Woodland owners. So this is for both the things: one, is that
feedstock procurement and all these things; then second, to whom you are selling the
products. So, in both the cases farmers are of course stakeholders and the Woodland owners.
The next one is about the success of alternative waste recovery and recycling. As I told you in
one of our class that recycle and reuse is one of the most important factors that is associated
with the so-called bio refinery concept. So, unless and until we are looking for a value-based
product from the waste that is getting generated from the biorefinery itself, we cannot have a
sustainable economy. So that needs to be done. For that you have to develop the process
technologies also. Production cost is of course very important that has to be taken care of, so
then storage cost also important cost. You are you are going to store 2 things. First is that
storing of the feedstocks; second is that storing of the finished products. And apart from that
in between also storing of this waste and all, till they get recycled and converted. So then
distribution cost and access to markets, all these will impact the entire costing of the
biorefinery system.
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So, main economic factors are capital cost, Plant capacity, process technology, raw material
cost and chemical costs. The major economic factor to consider for input cost of biodiesel
production is the feedstock, which is about 75 to 80% of the total operating cost. This is for
an example that let us understand that if biodiesel is a prime product or the main product
from a particular bio refinery, then what is the situation.
So, other important costs of course labour, methanol and catalyst which must be added to the
feedstock with respect to biodiesel. Using an estimated process cost exclusive of feedstock
cost US dollar 0.158 per litre for biodiesel production and estimating a feedstock cost of US
dollar 0.539 per litre for the refined soy oil and overall cost of US dollar 0.70 litre for the
production of soy-based biodiesel was estimated. So, I have given the reference at the bottom
you can refer to it later on.
Palm oil is the main option that is traded internationally and with potential for import in the
short-term basis.
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So, the oil in vegetable seeds is converted into biodiesel through oil extraction, oil refining
and transesterification. And as I told you in last class even last to last class, we have
discussed that extraction technology should be developed in such a way that they are very
efficient as well as they are low cost. And the cost of biodiesel can be lowered by increasing
feedstock yields, developing novel technologies and increasing economic return on glycerol.
Please understand that glycerine is one of the most important by product from the
transesterification reaction or biodiesel production. Glycerol is a very high value product but
the problem right now is that the amount of glycerol that is produced across the globe and
that is converted into useful products, there is a disparity. So you have huge surplus of
glycerol. Unless and until we develop technologies to convert glycerine to other value added
products rather than what is right now being used commercially then the sustainability of a
bio diesel a based biorefinery is still in question.
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Let us look at Biomass cost which is one of the most significant cost associated with the
biorefinery. The biological fraction from waste generated in developing countries is 50%
higher when compared with developed nations. So, waste based biorefineries play a vital role
in the economy of developing countries. In India the most common feedstock for bioethanol
biorefineries is molasses.
Because there is a huge by-product that is coming from the sugar processing industries,
mostly based on sugarcane. So, the market price of molasses fluctuated from 18 to 92 US
dollar per tonne in the last decade. And market price fluctuated between US dollar per tonne
for rice straw is between 11 to 13, bagasse 12 to 14 and rice husk is 22 to 30. Now in India
food grain straw is mainly used as a cattle feed, followed by its use in industry as a packaging
material, construction materials, straw board and paper and hardboard units. Cost of
Agricultural and Forestry Residue is dependent on various parameters such as biomass
production, pre-processing, handling and transportation. So, when you talk about biomass
cost, all these costs are coming into picture.
Cost of residues fluctuated between 14 to 34 US dollar per tonne, minimum being for the
bajra straw and the maximum for the arhar stalks. In another scenario when the travel
distance was 100 KM from the farms cost fluctuated from US Dollar 36 to 55 per tonne for
bajra straw and arhar stalks respectively highlighting the influence of transportation on
market price of the residues.
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We have discussed about this travel cost in one of our lectures previously that the
transportation cost is a significant cost with respect to the Biomass procurement cost. The
cost of the Biomass as it is will be very low because any way when it is getting procured
from forest resources, agricultural field or anywhere, municipal waste also, its price or cost is
very less. But when we keep on transporting it the transportation cost increases significantly
due two things.
First is, where is the Plant located, how far it is from the source, that is source of procurement
and what is the density and shape and size of this biomasses. If it is low dense, then it is
basically very high-volume and transportation becomes difficult as well as it becomes costly.
So, India is known for its biomass diversity which can be categorised as grasses, woody
plants, fruits, vegetables, manures, aquatic plants and what not there are so many. So,
biodiesel manufacturers have also started using algae as feedstock. These available biomass
sources can be broadly divided into three categories: energy crops, agricultural crop residues,
municipal and industrial wastes. And we have already discussed this significantly in a few of
our classes.
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So, let us now understand what contributes to the logistics cost. So, one of the bottlenecks
involved in commercialization of biorefinery is the cost involved in logistics, which include
several discreet processes. Harvesting and collection of biomass and site that is from the
cultivation field or forest. Storage of biomass is a significant cost, so proper storage of
biomass is of paramount importance to ensure round the year availability even though they
are harvested at different times of the year. Because most of the crops are seasonal. Location
of the storage space can be at the collection site, biorefinery, or at any place in between the
two sites. So the location will eventually decide about the transportation. Then biomass
storage at the collection site is a low-cost option, but that is not always a Win-Win situation
because there are certain disadvantages associated with it such as the loss of biomass material
due to degradation; uncontrolled moisture content of biomass leading to processing
difficulties; chances of contamination due to spore formation or fungal infection; and finally
low storage period as the farmers need the land for cultivation of next crop. So, biomass
storage is a critical stage in the biomass supply chain, hence, the location and facilities should
be decided based on the holistic analysis of respective storage unit.
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Processing of biomass: So, low energy content of Biomass in comparison to fossil fuels
coupled with low density means that comparatively large amount of biomass is required to
obtain a similar amount of energy. So, this poses severe handling and transportation
problems. Compacting of biomass through several processing or pretreatment steps is
advantageous as it reduces the volume of biomass as well as improve the storage, handling
and transportation efficiency.
Though densification techniques (we have discussed that how do you densify this, you make
into briquettes, pellets and all these things) the harvested biomass can be processed into bales,
pellets, cubes, pucks, briquettes and wood chips. Technically processing can be undertaken at
any stage. However, the advantages are maximized if it is done after harvesting or collection
stage.
Transfer of biomass from the collection point to a common point from where the
transportation can be initiated is also very important. It also involves loading of biomass into
the transportation vehicles and unloading them once the Biomass reaches the biorefineries; so
for each and every step there is a cost associated.
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Transportation: biomass feedstocks have geographically varied locations, low energy content
and density, which makes transportation the cost-intensive step of the entire supply chain.
Cost input during transportation is dependent on travel distance, travel time and bio mass
density. Travel distance affects the cost involved in the fuel purchased for vehicles and also
the travel time involved. Then travel time in turn affects the cost involved in hiring
manpower, maintenance of the vehicles and insurance. Manpower is required for basically
loading and unloading the Biomass in the transportation vehicles. So, travel time includes the
time spent on a round trip and the waiting time during the loading and unloading of biomass
at the site and biorefinery respectively. Hence, the larger the distance between the two sites,
larger the travel time and higher is the capital allocation and manpower and maintenance; so
these things needs to be optimised.
Another factor affecting the transportation cost is the Biomass density. The low density of
biomass means a large volume of biomass needed to be transported, hence more number of
vehicles required or multiple trips to be undertaken by limited number of vehicles.
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Economic viability of biorefinery system. So in economic viability of biorefinery systems, we
will see a case study of bioethanol. Bioethanol plants and sugar cane mills are well
established processes, where the biorefinery concept can be implemented little easily since
sugarcane bagasse is a feasible feedstock to produce fuels as well as certain chemicals.
Techno economic analysis of Ethanol production using mild liquefaction of bagasse plus
simultaneous saccharification and co-fermentation shows a minimum selling price between
50.38 and 62.72 US cents per litre which is comparable with the market price.
The production of xylitol, citric acid and glutamic acid from sugarcane lignocellulose that
includes bagasse and harvesting residues each in combination with electricity have been
evaluated. The three biorefinery systems were simulated to be annexed to an existing sugar
mill in South Africa. The case study is there, please read the references that have been given
at the bottom. You can please refer to those and read in details from the manuscripts.
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The production of xylitol and glutamic acid has shown economic feasibility with an internal
rate of return of almost 12.3% and 31.5% exceeding the internal rate of return of the base
case which is 10.3%. Likewise, the production of ethanol, lactic acid or methanol and
ethanol-lactic acid from sugarcane bagasse have been studied. Lactic acid demonstrated to be
economically attractive by showing the greatest net present value almost it ranges from 476
to 1276 million dollars.
In the same way the production of ethanol and lactic acid as co-product was found to be a
favourable scenario. Since this acid has applications in pharmaceutical, cosmetic, chemical,
and food industry.
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Let us now understand the biodiesel. So as for biodiesel production this industry also has the
potential to integrate bio refinery system to convert residual biomasses and waste into
biofuel, heat, electricity and bio-based green products. Glycerol is the main co-product in
biodiesel production and can be transferred into valuable products through chemo catalytic
technologies.
The valorization of glycerol for the production of lactic acid, acrylic acid, allyl alcohol
propanediols and glycerol carbonate has been evaluated; all glycerol valorization routes
shown to be profitable, being the most attractive the manufacture of glycerol carbonate. Palm
empty fruit bunches are abundant lignocellulosic residues from the palm oil biodiesel
industry. The conversion of this residue into ethanol, heat and power, and cattle feed were
evaluated according to the techno economic principles.
So, the economic feasibility of bio oil production from the EFB via fast pyrolysis using a
fluidized bed technology was studied. Crude bio oil can potentially be produced from the
EFB at a product value of 0.47 dollar per kg with a payback period and return on investment
of 3.2 years and 21.9% respectively, which is considered as almost a moderate range. So, the
integration of microalgae and Jatropha as viable route for the production of biofuels and
biochemical has also been analysed in the United Arab Emirates context.
Three scenarios were examined; in all of them, biodiesel and glycerol is produced; in the first
scenario biogas and organic fertilizer is produced by anaerobic fermentation of Jatropha fruit
cake and seedcake. And in the second scenario the production of lipids from Jatropha and
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microalgae to produce biodiesel was evaluated and the production of animal feed, biogas and
organic fertilizer was also integrated. In the third scenario that involves the production of
lipids from microalgae for the production of biodiesel, as well as hydrogen and animal feed
as final product (from the lipid extracted from algae basically); so this is the first scenario
which was almost profitable compared to other scenarios.
So now we will understand about the life cycle assessment. Now, whenever we are going to
develop a process technology or let us say refinery, biorefinery or any industry whether it is a
waste biomass-based industry or any other feedstock-based industry we need to carry out a
life cycle assessment plus the techno economic evaluation. So, we have discussed about the
cost, in a nutshell we understand what are the different types of cost that are associated in
setting up a biorefinery. Now we will try to understand what is the meaning of a life cycle
assessment (LCA).
LCA provides a quantitative estimation of the potential environmental problems of an
examined system in terms of environmental indicators proposing concurrently ways to
overcome the environmental burdens thus addressing thoroughly the issue of sustainability.
The LCA results could provide the basis for decision to support establishing new
technologies, processes or products for industrial applications and policy-making for
mitigation of Climate Change or fossils resources dependency.
Based on the biorefinery system the assessment of parameters related to its implementation
potentials (for example feedstock availability), feasibility and stability add valuable aspects
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of the new products and production Technologies. Moreover, these results constitute the
cornerstone of robust conclusions and future oriented recommendations for the industries.
So, let us understand how it happens actually. So in step 1, we have to define the goals. So in
the step 2 we will talk about the inventory data collection. In step 3 it is the impact
assessment and in step 4 it is the results interpretation. So, the method of choice for deriving
environmental indicators for biorefinery is life cycle assessment based on the ISO 14040
methodology encompassing the 4 steps as mentioned here (refer slide).
So, if all necessary input and output streams cannot be collected within the framework of life
cycle inventory due to a lack of valid data, this can result in a retroactive redefinition of the
system boundaries. The sensitivity analysis can also show the necessity to refine the system
boundaries.
When you define the goal in the step 1 basically you are talking about the system boundaries.
You define the system boundaries, functional units, and what are the environmental impacts,
that is going to arise from the processing of the feedstocks, handling them and when you
convert them to value added products. In the second step it is about inventory Data Collection
where experimental and literature data will be collected and stored, then databases will be
accessed and you have to take the help of certain LCA software.
In the third step, it is impact assessment, where the data processing for the environmental
impact will be basically carried out to understand whether there are any environmental effects
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at all from the biorefinery perspective when you are processing the Biomass and converting
them to the value-added products. And in the final step, that is the result interpretation, you
basically elaborate what are the results we have actually received. Then, based on that, what
are the recommendations for reducing the environmental impact and/or mitigation. So, these
are the essential 4 steps which are required to carry out the basic LCA study. There are so
many other things also but, in a nutshell, let us try to understand what is LCA.
So, in the course of evaluation and interpretation, it can be determined that additional data
must be generated in order to arrive at a representative result. Therefore, the data required for
the life cycle inventory is of particular importance within the LCA. The representativeness of
data and factors needs to be verified in a case specific way for every biorefinery pathway
assessment.
The life cycle steps are implemented in different modules of the assessment - From the
feedstock generation to the standardized products. Furthermore, the modules gather the
input’s consumption and calculate the emissions of the three main greenhouse gases - carbon
dioxide, Methane and Nitrous oxide and primary energy demand. So, the parameters that are
considered for each production step of the biorefinery as input factors for the assessment are:
agro inputs, field work, field emission, use of the Fossil energy resources, conversion inputs
transport efficiencies, emissions from steam production, Electricity production, multi product
outputs and the residues.
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So, two categories of input parameters: emission driving parameters and process parameters.
For example, the input of the field emission needs the process parameter of the field work to
calculate the exact amount of emissions. So, you have to basically collect so much of field
data and then analyse them to understand the value of emission. The emission driving
parameters are linked to emission coefficients. Applying representative emission factors is a
significant challenge and application of default values and non-specific data, for example on
energy-mixes, can impose strong divergences concerning the representativeness of results.
The use and disposal phase can only be partly covered as operators and developers have only
limited data and influence on the use and disposal of products. Based on these limitations, the
results can only be interpreted as estimates. Further, the overall emissions of the different
biorefinery operations and process steps can be calculated, and a second step the emissions
are converted to a specific value with regard to the functional units like for example the
annual product quantity.
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The handling of cut-off rules must also be very carefully considered as these lead to
considerable uncertainties in the result if too many material and energy flows are excluded
from the LCA. So non-relevant life cycle stages, including the associated material and energy
flows are excluded based on these cut-off rules. Cut-off criteria should ensure that this
procedure is not purely arbitrary.
Life cycle thinking is referring to a maximum balancing scope, for example cradle-to-grave
(the meaning of cradle to grave here is basically you start from the feedstock and end up in
the finished goods or finished product. The entire lifecycle, so that is basically from cradle-
to-grave. That’s what it means.), as bio-based products strongly reveal their positive
environmental potential especially in the use phase by substituting Fossil-based reference
products and services or end of life phase related to the biogenic origin of product bound
carbon.
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So, let us look at this, particular generalized system boundaries of a biorefinery LCA
approach. This is a complete system boundary that is defined for a particular value-added
biofuel based biorefinery. So, you start with the Biomass production chain basically, inputs,
energy, fertilizer etc. to grow biomass, procure, transport, process. Then in that case there
will be emissions and that will be the residues.
Now to make a sustainable biorefinery we also should convert these residues into value added
products that is basically the recycling of the waste. Then the biomass goes to the Processing
Unit, the plant, in which you are processing into value added products. So, when you are
doing that there is an enormous amount of emissions that is coming out. And of course, again
another set of by-product.
That by-product also should be taken into consideration to convert to value added products
and basically minimise the waste and recycle them. Inputs are energy, Chemicals, nutrients
and enzymes and there may be many things and the biofuels and other value-added products
in terms of energy, electricity, and platform chemical. So, this is the complete system
boundary and it’s an entire system.
Now I can take some small boundaries here also (refer to the corresponding slide for
explanation @time 28:05 min). This is a generalized one. So, I can take one by one
processes, one system boundaries, find out what are the emissions and also, we can do the
techno economic assessment also by defining the system boundaries. So, this is how actually
the boundaries have been defined for a biorefinery LCA approach.
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Let us now understand the current challenges of assessing biorefineries. Considering life
cycle assessment as an established method, to assess the environmental impacts of a product,
based on the ISO 10400 criteria, the choice of allocation is one of the most discussed issues.
Additionally, the choice of functional unit, system boundaries and whether the LCA is
accounting or consequential are the key issues for the LCAs of biorefineries.
So, functional unit and allocation: Let us understand what it means. So, the functional unit is
often reflected by reference material flows (for example, the amount of output) rather than
the function (for example, the heat value). Biorefineries producing multiple outputs increases
the difficulty of identifying one main function. The importance of the choice of functional
unit for comparing and interpret results is unquestionable. Multifunctionality of biorefinery
concepts are also leading to the common challenge of allocating the environmental impacts to
various outputs.
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Different outputs from a biorefinery can actually have different functional units and physical
attributes leading to a core question in the LCA for biorefineries. The partitioning method is
an ideal choice for biorefinery which is based on artificial splitting up of multifunctional
processes into a number of independently operating monofunctional process. So, it is easier
to assess basically if you do like that. It is necessary to distinguish between processes with or
without an underlying physical relationship between the outputs and the emissions.
Now, let us understand system boundaries. So, the choice of system boundaries or balancing
the scope strongly influences the result of value based biorefinery quality evaluation. So, you
can go for an entire cradle to grave life cycle. However, from a practical point view due to
limitations in data availability especially in terms of the use and the end of life phase, the
assessments of one follow cradle-to-gate or gate-to-gate approach. So these are midsegment
approaches.
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The considered life cycle stages include: Biomass cultivation; process steps upstream and
inside the biorefinery; consumer use of biorefinery products; and product disposal. Although
there is a distinction between bio based and non-bio-based value chains, it is worth noting
that a purely bio-based value chain may have connections and interactions in common with
non-bio-based value chain. The system boundaries of the case studies in the reports are
mostly cradle-to-gate.
The use and disposal phase is often not covered as operators and developers of biorefineries
have only limited data and influence on the use and disposal of products.
This is an interesting slide where we can understand, what is this cradle-to-Grave, cradle-to-
gate and gate-to-gate system boundaries under LCA concept. Look at the Cradle-to-Grave, so
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it starts from the Biomass cultivation and extraction everything to recycling and disposal you
get it? So it is the entire bio refinery system. Now let us understand cradle-to-gate which is
intermediate boundary. It starts from Biomass cultivation and extraction, let us go to the
production, processing, intermediate product and let us say till production or processing. It is
not sacrosanctly defined like this. You can either take it that side or you can bring it this side
also. You can end anywhere. It depends upon what type of data is available with you and how
easily you can proceed with the availability of the data basically. Then, if you understand
about gate-to-gate it is basically a single process. Let us see this. Production and processing
of the biomass. This is one gate-to-gate approach. It can be production and processing of the
intermediate product. Again, gate-to-gate approach. So, this is how the system boundaries has
been defined for LCA analysis. So, the second one is a non-bio-based value chain and top one
is the bio-based value chain.
So, now let us take a case study of the technical, economic and environmental assessment of
a biorefinery. So, we are talking about a 2-platform biorefinery, where there is a C5 and C6
sugar platform to convert it to bioethanol and the Biomass is corn stover. So, the raw material
is corn stover, the platform is the sugar platform, both C5 and C6, the process is a
lignocellulosic biomass conversion.
The product and the major end material is ethanol. There may be the other by-products also.
Product energy is electricity and heat. Concept according to the VDI 6310 is the
lignocellulosic biorefinery and the balancing scope is cradle-to-gate.
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This case study is characterizing a lignocellulosic biorefinery using residual corn stover to
produce ethanol as fossil fuels substitute. So, it has on-site process energy generation via
Lignin combustion in a boiler and Electricity production with steam from combustor. So, the
inherent meaning of this particular sentence is that whatever lignin is getting generated
during the pretreatment or delignification of the Biomass is getting burnt to produce
electricity.
Additionally, biogas is generated on-site by the anaerobic digestion of wastewater. No
external energy supply is needed, every energy that is required for the biorefinery is getting
generated on-site. So, the lignocellulosic bio refinery has on-site cellulase enzyme production
facility also. So, the bio refinery process described is designed for a capacity of
approximately 104 tonne corn stover operating 24 hours 6 days a week. This corresponds to
approximately 7,500 plant operating hours per annum.
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So, this is the overview of the techno economical assessment: the process pathways of
ethanol synthesis from corn stover. So, these are the agrochemicals requirement. How much
it is required it is written there. The energy, how much it is getting consumed in the form of
electricity, steam and how much electricity credit you are generating. Then the operating
materials like cost of the corn steep liquor, sulphuric acid, diammonium phosphate, some
other solvents all these things and of course, the water (it is a huge requirement and a huge
cost).
So, then it goes to the cultivation of the corn stover, you get let us say 3883 kilograms per
hectare per year and it goes to the lignocellulosic biorefinery (biomass productivity), comes
to the biorefinery and you get almost 834 kilograms per hectare per year of the ethanol. Then
of course there are other things. So you can refer it and get an understanding that how that
TEE looks like.
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So then lignocellulosic ethanol biorefinery pathway. Ethanol is produced based on corn
stover. The milled corn stover is pre-treated in a dilute acid pretreatment process. So, 18
milligrams of sulphuric acid per gram of dry mass is optimised requirement. Enzymatic
Hydrolysis is used to convert the hemicellulose and cellulose into monomeric C5 and C6
Sugars and lignin which are the platform inside the described ethanol biorefinery.
Cellulase is produced on site. The C5 and C6 sugars are fed into fermentation tanks. The
fermentation uses metabolically engineered strains of the Saccharomyces cerevisiae
microorganisms that are capable of co-fermenting xylose and glucose to ethanol. So, this
particular Saccharomyces cerevisiae, which is the engineered strain, can co-ferment both C5
and C6 Sugars to ethanol whereas, a separate hydrolysis and fermentation processes applied,
SHF process.
So finally, the fermentation broth is fed into a distillation process. Distillation columns and
Molecular sieves are used to produce 99.5% ethanol. It is a very great purity. So again, you
can see here, whatever Lignin is coming from this hydrolysis after the delignification step, is
being fed to the boiler. So, lignin is burnt basically and you generate electricity and heat in a
CHP platform.
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So, this is the biorefinery and reference system – a value chain case study with reference to
cradle-to-gate approach. So, the Biomass - corn stover – transport - biorefinery - we get
ethanol, Lignin - converted to energy, whatever left out can be converted to fertilizer. It is not
that fertilizer is the only thing, it can be any other things also. So crude oil – extraction –
transport – refinery - gasoline, naphtha, aromatic etc. This is your general refinery. This is a
bio refinery.
So, the key characteristics of the case study based on the 2 platform C5, C6 sugars and Lignin
bio refinery to produce bioethanol, electricity and heat from corn stover is that; so, the state
of technology is almost commercial. Country is United States; the main data source is from
literature. The products are ethanol and Electricity, these are the costs given in a million
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Euros - investment, feedstock, operating, labour and all these costs and then auxiliaries,
feedstock, conversion rates are also given.
So, if you look the mass balance case study; so you can see, these are the different things -
waste water, conversion loss, Lignin (converted to CHP), ethanol, water, corn stover, and
Chemicals. Have a look here, the input - the major input cost is of course that of the water,
followed by the Biomass that is corn stover, and the small amount is due to the Chemicals.
Now, if you talk about the output, so the major cost is wastewater.
So, this was what I was mentioning that waste water needs to be treated. Recycle in-house so
that our dependency of freshwater will come down. Followed by the conversion losses, huge
amount of conversion that is getting lost and then this yellow (z)one you can see, that is the
lignin - of course it is value added because it is getting converted to electricity and heat;
followed by this brown (z)one, which is the ethanol production. See the cost in terms of the
mass balance.
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So, when you talk about the sharing of the cost, it is again in the same manner - raw material
supply, followed by auxiliary and operating material, followed by the imputed interest, then
the next is the write-off cost and there are some other costs like insurance and auxiliary and
operating material.
So, if you look at the sensitivity analysis of the cost structure in a case study, you can see this
red one is the raw material supply and the blue one is the total investment (the entire
investment cost) and the line which is horizontal you can see that is the other costs. So, based
on the self-sustained energy supply within the biorefinery, especially no effect on the
sensitivity of the overall cost structure is related to the energy cost. So that is what is
understood from this particular slide.
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So, value chain environmental assessment in case study. So, this is an overview of the TEE
assessment results cases study. So, the greenhouse gas emissions. This was estimated after
the LCA study or TEE study. Raw material sourcing corn stover is almost 2651 tons of
carbon dioxide equivalent; so the biorefinery 35017, reference system 368751 tonnes and
savings is 331083 tonnes. Then this is the cumulated energy demand in terms of the terra-
joule, then these are the other costs in terms of the million euros.
If we talk about the greenhouse gas emissions of biorefinery compared to reference case
study, you see, this is the second-generation ethanol biorefinery. And this is the greenhouse
gas emission. You see the gas (emission), this is nothing when you compared to the fossil
reference. So, this is quite understood from this particular slide, when you talk about
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biorefinery concept that Greenhouse gas emissions is far less compared to the Fossil fuel
emissions.
So, the next is cumulative energy demand of biorefinery compared to reference. So again you
can see that the energy demand for biorefinery compared to the fossil fuel reference, with
respect to renewables, it is little higher. But then you have to understand, what is the output in
terms of every aspect including the environmental aspect. It is not about only the energy
demand or energy requirement.
This is the cost and revenue, the final one. You can see, this is the input cost basically and
this is the final value of the ethanol selling price. So, you can see that it is marginally higher
than all the input cost and everything is being accounted here, whether it is water supply,
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disposal, raw material, insurance, maintenance, everything. So, we can understand from this
particular slide that, the ethanol cost (the annual selling price) of the total amount that is
produced is higher than the input cost or the production costs. That means we are in profit.
So, let us conclude this LCA discussion. So, today's biorefinery processes still show
significant optimisation potential while the production processes of fossils-based products are
technically mature and optimised. Technical developments in the biorefinery sector continue
to generate new knowledge and as they are commercialized and deployed, these are likely to
lead to further improvements via economies of scale. As a result, it is expected that the
production cost for bio refinery products will decline in the near future and that the product
will become more competitive over time. Until this is achieved, bio refinery pathways will
continue to rely on targeted policy measures and public transport programs to drive the
development.
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The wide implementation of biorefinery technologies requires that a large number of possible
products meet the quality and price requirement of the market. So, basically price is one
factor, another is the awareness of the bio based products and their acceptability by the end
users. So in addition it is necessary to identify and optimise the site-adapted biorefinery
technologies and recycling paths from the multitude of potentially available raw materials
and conversion paths.
So, with this I wind up today's lecture; in case you have any query, please feel free to write to
me at kmohanty@iitg.ac.in or post your query in the Swayam portal itself I will definitely
answer those. In the next module we will be discussing about the biomass pre-treatment
technologies. What are the different types of biomass pretreatment techniques that is
available? What are their pros and cons and how they can be carried out? So, thank you very
much.
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Lecture 10
Barriers and Types
Good morning students. Today's class is lecture 1 under module 4 and in this module we will
be discussing about the Biomass pretreatment. So, this is one of the most important aspect of
the entire Biomass conversion or biorefinery concept. So, in today's class we will discuss
about what are the barriers that exist for the lignocellulosic Biomass conversion and what are
the different types of pretreatment technologies that are commercially adapted one by one.
Lignocellulose is the most abundantly available, inexpensive and renewable raw material.
Lignocellulosic Biomass is being investigated as a promising feedstock for the production of
alternative fuels, Chemicals and materials. The production of commercially valuable
Chemicals and biofuels using lignocellulose based processes has the potential to decrease
Greenhouse gas emissions, bring benefits to rural economy, and promote energy security.
The composition of lignocellulosic biomass varies with biomass source. So hard wood, soft
wood, agriculture residue, energy crops, municipal solid waste all these things and is affected
by the origin, age, climatic conditions, harvesting and storage processes. Some of these things
we already know; during our subsequent classes we have discussed this.
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Now, please have a look at this particular table, where the chemical composition of various
lignocellulosic Biomass has been listed and the source has also been given. You can later on
see. It is basically listed under three different categories: cellulose, hemicellulose and Lignin.
Please understand that, apart from these there are some other materials also, there are
proteins, there are volatile materials, ash all these things.
The main chemical building blocks of lignocellulosic biomass that includes actually cellulose
- almost about 35 to 50%, hemicellulose - 20 to 35% and Lignin which vary from 15 to 20%.
Now the composition varies and depends on cultivation conditions, geographical location and
the age of plants. Now let us see, this corn straw or oat straw. You see this it is almost 39-42
in that range is the cellulose, and hemicellulose is from 27-21 in that range, and Lignin is 10
to 20 in that range.
Now, you come to bagasse, here the cellulose little more. Now you come to Aspen (this
forestry residues) cellulose amount is increased basically, there are so many things. Now if
you come to solid cattle manure, you can see the cellulose, hemicellulose and lignin all the
three major components are very less. There are other components which are more
predominantly in that particular material.
So likewise, the understanding is that, the cellulose, hemicellulose and Lignin varies apart
from other materials. And the process or the technologies for converting this Biomass,
including of course, the pre-treatment technologies, should be developed in such a way that
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any process can consider or can take the various multiple feedstocks rather than developing a
process for a single or two feedstocks.
Please have a look at this particular slide. You see that, one class long back I think we have
discussed how the cellulose, hemicellulose and Lignin actually intricately bind together. This
again it is telling, you please see that the cellulose is the blue part. Lignin is the green part,
and the hemicellulose is the red part or the orange whatever it is will be visible from your
side. So these are intricately bound together. So that is the reason why we are talking about in
today's class pre-treatment.
Why the pre-treatment is required? Because I want or we want this cellulose and
hemicellulose to be disintegrated. Because it is bound together - cellulose, hemicellulose and
Lignin all are bound together and you need to disintegrate them. Then you need to take out
the cellulose and hemicellulose part. We will go for hydrolysis, we will get C6 and C5 sugar,
then that will be fermented to Bioethanol, alcohol platforms and other chemicals.
Now lignocellulosic Biomass is composed of cellulose and hemicellulose, tightly packed and
protected by phenol aldehyde Lignin polymer. And the polysaccharide fractions of
lignocellulosic biomass, including cellulose and hemicellulose can be broken down into sugar
monomers. They are then converted into biofuels, biogas and biochemicals through
biotechnological platforms such as anaerobic digestion and fermentation.
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Lignocellulosic Biomass consists of carbohydrate fraction such as cellulose and
hemicellulose and non-carbohydrate functions like lignin, protein and other extractives or
volatile matters. So, cellulose and hemicellulose which are polysaccharides in the biomass
can be converted to bioethanol, biobutanol and other fermentation products through various
biological pathways. They can also be transformed into furan based chemicals and other
organic acids by thermochemical pathways. Either it is pyrolysis and gasification or any such
processes.
For effective conversion of these carbohydrates, it is necessary to overcome and/or reduce the
recalcitrance of biomass prior to the conversion process. Bio recalcitrance is defined as the
natural resistance of plant cell walls for its biological conversion mainly caused by the
complexity and heterogeneity of biomass.
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The recalcitrant nature of lignocellulosic biomass presents a technical challenge for releasing
fermentable sugars from the Biomass and a major hurdle in its use in biorefinery. Several
phenotypes of biomass have been evaluated as recalcitrance factors. So, some of these are
listed here. First is the chemical composition and second is the molecular weight of lignin,
lignin syringyl or guaiacyl unit (we will discuss about this later on little), Cellulose
crystallinity, then degree of polymerization of cellulose and cellulose accessibility.
Let us talk about cellulose. So we will try to understand what are the various components,
and their composition, and their role in the recalcitrant nature of the lignocellulosic biomass.
Now you know cellulose is one of the most abundantly available material on the earth
(natural material). So, the composition of lignocellulosic biomass varies with plant species,
age, stage of growth and season; this is well understood.
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Cellulose is a linear polymer composed of D-glucose units linked together by the β-(1-4)
glycosidic bonds. This is a classical structure of the single cellulose molecule. The degree of
polymerization is approximately 4000 to 6000 glucose in Woody Biomass. Polymers of
cellulose are interlinked through hydrogen and van der Waals bond to form a microfibril and
present in crystalline and amorphous form. These microfibrils are covered by hemicellulose
and Lignin and intricately actually pegged.
So, crystalline cellulose fibre parts attached to each other by non-covalent hydrogen bonding,
which provides 3 to 30 times lower degradability as compared to the amorphous part. Now
cellulase, that is the enzyme which will degrade cellulose, is readily able to hydrolyse more
accessible amorphous cellulose but it is not effective at degrading the less accessible
crystalline portion. That is the reason why we are going for pre-treatment.
Now, let us understand hemicellulose. So, this is a classical structure of hemicellulose
molecule. So, hemicellulose, the second most abundant heterogeneously branched polymer, is
composed of pentoses (D-xylose and L-arabinose), hexoses (such as D-Glucose, D-mannose
and D-galactose), apart from these sugar units, there are certain acetyl groups and uronic
acids.
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So, the degree of polymerization is as high as 50 - 300 monosaccharide units. Hemicellulose
lacks a crystalline structure owing to its branched structure and the presence of acetyl group
and is easily degradable owing to its amorphous nature. This is the basic structural difference
between cellulose and hemicellulose. Where cellulose is more recalcitrant in nature and
hemicellulose is little less than cellulose in recalcitrance.
So, the composition of hemicellulose varies with plant species. Soft wood hemicellulose
components are galactoglucomannan and arabinoglucuronoxylan, while glucuronoxylan is
the main component of hemicellulose in hardwood. Hemicellulose acts as a physical barrier
and restricts the accessibility of cellulase to cellulose. Removal of hemicellulose with
pretreatment methods such as acid or steam hydrolysis and the addition of enzymes increases
the cellulose hydrolysis.
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So then Lignin. Lignin is the most complex amorphous polyphenolic polymer composed of
three o-methoxylated p-hydroxypenyl propanoid units (which are known as a monolignols as
for example of p-coumaryl, coniferyl and sinapyl alcohol). So, you can see the structure of
the p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol and that of the lignin. So, these
monomer units give rise to p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) subunits
when incorporated into a lignin polymer.
So, this H, G and S they are intricately bound together and linked together to form the
complex lignin molecular structure. So, depending on the biomass source, lignin composition
varies with the change in the ratio of different monomer units. So, gymnosperms or you can
say that soft wood plants and Fern Lignin are generally composed of G as the main
component followed by a small amount of H unit.
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Now contrastingly in angiosperm that is hard plants, Lignin is mainly composed of S units
followed by G units. So more of S followed by less of G. So, the main lignin components of
herbaceous crops are G followed by H and S. So, from this statement we will understand
basically that this H, S and G, depending up on how much amount they are present, the
softness or hardness is basically decided.
So various monomer units are linked through this β-O-4 aryl ether bonds and lignin acts as
glue around the cellulose and hemicellulose fibres. And its main function is to provide
mechanical strength and support for the formation of vascular tissue for the transport of
nutrients and to promote resistance against microbial attack. This is the main function of
Lignin in plants. And Lignin makes Biomass recalcitrant by restricting the accessibility of
cellulase enzyme to cellulose and by preventing the deactivation of enzymes by various
lignin derived compounds.
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This is the figure which will tell about this main component of lignocellulosic biomass, how
intricately they are actually bound together. So, the Biomass, this is a typical plant cell
microscopic image. This is the Macro fibril and this is the microfibrils. In the microfibril you
can see that how Lignin, which is this rod shaped green shown here, then cellulose and
hemicellulose (this brown portion), so you can understand that, that looks like scattered but
they are intricately bound together with each other.
So, we need to actually disintegrate this entire structure. So that we get cellulose and of
course hemicellulose also.
Lignocellulosic biomass recalcitrance is the natural resistance of plant cells against microbial,
degradation, animal attacks and other environmental conditions. Now along with the
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structural components, there are other factors that influence recalcitrance. So, some of them
are acetyl groups and proteins and the porosity of the biomass. In table 2 we will learn more
about that. So acetyl groups bind hemicellulose via covalent ester bonds and deacetylation of
biomass may increase lignocellulose degradation by 5 to 7 times.
This recalcitrance property is a bottleneck in industrial utilisation of lignocellulosic biomass
and various pre-treatments are required to overcome this issue. Proteins also have negative
and positive influences on recalcitrance.
Some proteins help to break hydrogen bonds between polysaccharides which improves
degradation while some proteins inhibit the activity of various hydrolases. So, hydrolases are
the enzymes that are responsible for doing the hydrolysis. So, to overcome the inhibitory
effects of various proteins, usually dried lignocellulosic materials are used in the bio refinery,
as drying and storage of biomass denature protein.
So, the physical structure which includes the accessible surface area (We call it ASA),
particle size and pore volume of the material plays an important role in the biomass
recalcitrance. Higher ASA provides more surface area for enzymes during hydrolysis.
Ultrafine grinding leads to smaller particle sizes leading to changes in polymerization and
porosity and enhances enzymatic hydrolysis. When you are grinding them to finer particle
size, basically you are increasing the surface area and thereby resulting in more degradation.
The pore size of the Biomass also has an important role, as enzymes which can only enter the
pore of specific size, because enzyme has a certain size.
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So, this is the table 2. Let us understand what is being given here and this is the reference of
this particular table. So, effect of lignocellulosic biomass composition and physical structure
and recalcitrance. So, this is the pre-treatment method: chemical method and physical
method. So the components are Lignin, hemicellulose, acetyl group, proteins. Then under
physical we will be talking about crystallinity, degree of polymerization, particle size, pore
size and surface area. This is what we have already discussed.
So, in a nutshell whatever we have discussed is represented in this particular table. So please
refer to it later on; we will just quickly glance through it. So, lignin acts as a physical barrier
and restricts accessibility to cellulose. Lignin derived compounds have inhibitory effects on
hydrolysis. That is very important. So, when you do this hydrolysis, and there are certain by-
products that will be created which are not required at all and which are many times are toxic
to the entire process.
We need to get rid of them. So lignin plays a very important role in making such or
generating such by-product. That is why lignin has to be removed completely. Hemicellulose
acts the physical barrier and restrict the accessibility of cellulase enzyme to cellulose. Acetyl
group interferes with enzymes recognition. Proteins will have both positive and negative
effects on hydrolysis.
Crystallinity tells us that hydrolysis rate of amorphous cellulose is almost 30 times higher
than the crystalline cellulose. That is why more crystalline the cellulose, we need to have a
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better pre-treatment technology and we need to spend the more energy, Chemicals and all
these things to make the higher crystalline cellulose amenable to hydrolysis; and other things
please go through it later on.
Now, we will discuss about the pre-treatment of lignocellulosic biomass, the different
methods. The conversion of lignocellulosic biomass requires pre-treatment to transform the
Biomass for the fermentation process. Pretreatment is also needed to break the rigid structure
of Lignin and hemicellulose and to release cellulose for the enzymatic hydrolysis.
Pretreatment will cause changes in both micro and macro structure of lignocelluloses and
initiate modifications in the chemical composition of lignocelluloses.
The pre-treatment methods aid in the alteration of the natural structure of lignocellulose for
the microbial attack in the decomposition process. Pretreatment process helps breakdown
Lignin and hemicellulose that surround cellulose to release cellulose from the cell.
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The process involves the removal of Lignin and the degradation of hemicelluloses which
causes the alteration in cellulose crystalline structure and subsequently it releases cellulose.
This process helps the interaction of enzyme and substrate which enhances the hydrolysis
process. The pretreatment process ought to be straightforward, environmental friendly,
economical and efficient. It has to be like that. Otherwise it will not be a sustainable process
and cannot be a part of the biorefinery.
Additionally, the pretreatment method must not cause in the rise of inhibitory compounds.
This is what I was just mentioning. So, these inhibitory compounds formation should be
restricted by choosing a particular pre-treatment method which will not create a greater
amount of such inhibitory compounds.
Up to date, no synchronised pre-treatment approach that matches the whole variety of
lignocellulosic biomass, and the process of pre-treatment varies according to the type of
lignocellulosic biomass and preferred products. This is what I was mentioned in the
beginning of the class. You have to note; it is a very serious thing actually. When we are
talking about these pre-treatment processes or when we are talking about the entire
biorefinery concept, we need to understand that the pretreatment cost is almost 40%, if you
talk about the entire cost of the product. Now, why it is 40% right now or almost in that
range? The reason is that; first thing is that whatever pre-treatment techniques are available,
these are suitable for certain particular types of biomass. So no pretreatment technology, not a
single one or hybrid Technology has been developed which will take into account so many
different types of multiple feedstocks; because different feedstocks will have different
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components. Some will have higher cellulose, and some will have very low amount of
hemicellulose, some will have high amount of lignin; so it all depends. That is the reason why
we need to work more to develop more efficient pre-treatment technologies, which will be
economical, which will also take less time, which will not be energy-intensive and then
which will be sustainable. And which will again, I am telling you that, must be able to take
into account multiple feedstocks or it will be able to process multiple feedstocks, that is very
important.
So, the following criteria lead to an improvement in the enzymatic hydrolysis of
lignocellulosic materials: The first is increasing the surface area and porosity which can be
done by doing the mechanical processing; modification of the lignin structure (modification
of the lignin structure can be done by genetic engineering - in one of our class we have
discussed that); you have to remove Lignin, so this is a delignification process (you call this
one pretreatment also); partial depolymerization of the hemicellulose (So, you have to release
hemicellulose also or depolymerize so that hemicellulose which is bound to cellulose will be
disintegrated); then remove hemicellulose, because hemicellulose also can be hydrolysed and
converted to the sugar; and then reducing the crystallinity of the cellulose.
So, once you do the pre-treatment (you can see how it is intricately bound); so, this is the
lignin, green one is cellulose and this thread type whatever it is being shown here is
hemicellulose. You disintegrate, that means you treat it, delignify it and it will be
disintegrated into something like this: hemicellulose pure, lignin in the purest form and
cellulose in the purest form.
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Let us understand the pretreatment methods. So we have two different broad categories of
pretreatment methods: first one is biological and second is a non-biological. So, in the
biological we have fungi based pretreatment methods, we can have bacteria based or Archae
based. And under non biological we have varieties of pretreatment methods: some are
physical, some are chemical and some are physico chemical. So in today's class we will
discuss few of them and some we will discussion in our next class.
These are some of the methods I have listed, there are many which are not listed here also.
Physical: under physical it can be milling, microwave, ultrasound, pyrolysis. Under chemical
it is acid treatment, alkali treatment, ozonolysis, organosolvent process and ionic liquids. And
ionic liquids are excellent class of green solvents. And then physico-chemical: hot water
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treatment, steam explosion, Ammonia based treatment, wet oxidation and carbon dioxide
explosion.
Some of these physico chemical treatment and chemical treatments are of course, they are
costly.
Now this particular slide will show you whatever I have just told you in the earlier slide. It is
presented in a better way here. So, classification of the lignocellulosic Biomass pre-treatment
methods in detail. Physical: extrusion, pulsed electric energy based, liquid hot water,
pyrolysis, irradiation (basically the microwave treatment), Mechanical milling, grinding,
chipping.
When you come to chemical: It is again acid, alkali, solvolysis (that means using organic
solvents), oxidative (using either oxygen, ozone, hydrogen peroxide), then ionic liquid -
different types of ionic liquids are there, and hydrotropes like sodium benzoate and salts -
certain metal salts.
Then we have physico-chemical. So, steam explosion, Ammonia fibre explosion (AFEX) - It
is a very interesting and very efficient technique. But you have to do it in a proper way.
Otherwise there are risks associated with that - anyway will discuss later on. Ultrasound-
assisted chemical pre-treatment - this is one of the most efficient processes. But however, it
has its own limitation. Now beyond certain limit, it cannot work and it’s a low-cost
technology though a certain amount of energy is required. Then microwave-assisted chemical
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treatment. Not only microwave, but microwave assisted chemical pre-treatment. Then
microwave-assisted pyrolysis. Then combined pre-treatment. So, this is called hybrid - more
work is being done here. So, it is a combination of one or two different pre-treatment
methods. Then biological; based on enzymes, microorganisms and development of suitable
microbial consortium to take care of the pretreatment.
So, this is the bioconversion of lignocellulosic biomass into value added products with the
inclusion of the pretreatment steps. So this is your biomass and this is the structure. So you
pre-treat here. Biological, chemical, physical, physico-chemical, anything we get and that
will result in something, the disintegration of the structure of the Lignin, cellulose and
hemicellulose.
Then you convert them: cellulose and hemicellulose will be basically purified. So, you
hydrolyse them. So, then you can (subject to) any bio chemical or bio technological platform
such as fermentation, anaerobic digestion, so you get alcohol platform. It can be bio-ethanol.
It can be bio butanol. Then we can get biogas also. Next is lignin, so lignin either it can go for
pyrolysis, gasification with or without the presence of catalysis.
So, we can get biopolymers, we will get aromatic hydrocarbons and other value-added
chemicals.
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So, physical methods of biomass pre-treatment we will discuss. So, in general physical pre-
treatment is responsible for the changes in specific surface area, particle sizes, crystallinity
index and polymerization degree of biomass. Physical pre-treatment avoids the use of
chemicals thus reducing the generation of waste and inhibitors for subsequent reaction. Now
mechanical, microwave or ultrasound pretreatments are the most common techniques carried
out in order to improve the efficiency of the main steps in biomass processing.
So, let us understand mechanical pretreatment. The advantages of mechanical pretreatment of
lignocellulosic materials are: reduction of particle size, increase of specific surface area and
bulk density and reduction of the amount of chemical waste. So higher bulk density helps
with handling of biomass after harvesting, storage and transport. In turn lower particle sizes
as well as an increase in the specific surface area makes the chemical or physical processing
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easier due to: (1) development of a phase boundary between lignocellulosic material and
chemicals and; (2) elimination of heat transfer limitation. So, the main disadvantage of
mechanical pre-treatment is the high energy consumption which contributes to high
processing cost of lignocellulosic materials.
These are some of the schematic representation of the mechanical pre-treatment processes.
This is a hammer mill where milling is done. This is an extruder for the extrusion process.
That is a ball mill where small balls are present to disintegrate or reduce the size of the
Biomass. This is an Air mill and that is a roll mill. All are mechanical operation process
basically.
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So, where do we apply this actually. So the effectiveness of milling, chipping and mashing of
pre-treatments of Norway spruce (it’s an example here) were compared for enzymatic
hydrolysis of this feedstock into when it is being converted into biobutanol. So pre-treatment
with ball milling gave the lowest particle size of the spruce in comparison to mashing or
chipping but resulted in low hydrolysis efficiency.
Now application of extrusion has a large potential in the pretreatment of lignocellulosic
materials for biogas production. Researchers have applied twin screw extruder in vine
trimming shoots pre-treatment for Methane production in anaerobic digestion. Now treated
samples generated around almost 15 to 21% of more biogas compared to untreated material.
So, it is a very good finding with physical treatment.
So, it was observed that an extrusion reduces the amount of hemicellulose fraction by around
50% simultaneously increasing the fraction of soluble Chemicals like carbohydrates proteins,
lipids, minerals and vitamins which are rapidly converted by methanogenic microorganisms
hence, increasing Methane production. However, this investigation proved that use of ball
milling has only a small impact on the process efficiency.
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This is the selected examples of the studies concerning mechanical pretreatment. So, I leave it
to you. Please have a look later on. So, you can see that there are different types of biomasses
are listed here, different types of pretreatment methods are listed here, a mechanical one.
Then pretreatment conditions. How much time and all these things are given here. And what
is the efficiency of the process?
So, we will just see the first one. The Douglas fir residues. So, the hammer milling, air
classifier milling, ball milling, chipped, mashed all these things has been compared. So, the
time of residence inside the mill is basically 7 to 30 minutes. The result is that, highest yield
of glucose and xylose/mannose and was obtained after 30 minutes of ball milling. So ball
milling decreases the cellulose crystal from 40.73% to 11.7% which is a significant decrease.
Please have a look later on.
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Now the next one Microwave and its application. So, Microwave is a type of electromagnetic
non-ionizing radiation with frequency between the infrared and radio waves. Microwave
radiation absorbed by matter has appropriate energy to excite the vibration of molecules, but
its energy is too low to break chemical bonds. The electric field of microwave transfer their
energy to molecules which leads to the generation of thermal energy.
The main advantages of microwave heating versus conventional heating are: lower energy
consumption, shorter reaction time and avoided contact with the feedstock. On the other
hand, the prolonged time of microwave treatment increases degradation of polysaccharides.
So researchers have demonstrated advantages of the application of microwave in the increase
of the yield of biogas in biomethanation of organic matter.
This is just one of the researches which I have listed here, there are many works. So,
Microwave generated heat increases the solubility of Lignin, released soluble compounds and
improved the rate of hydrolysis due to cellular disruption. However, the effectiveness of
biogas production depended on the time of exposure and power of irradiation. A longer
exposure time can lead to fractional degradation of reducing Sugars and the generation of
inhibitors negatively affecting the biogas formation.
Nevertheless, appropriate time of microwave irradiation of biomass increased cell frangibility
and improved enzymatic hydrolysis by disruption of biomass complex structure. It is a good
process, it is easy to operate and not too energy-intensive also.
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So, let us talk about one of its application for converting the switchgrass and miscanthus into
alcohol platform. So, microwave pretreatment was effectively applied to reduce the
recalcitrance of complex biomass feedstock structure of switchgrass and miscanthus to
enhance their solubility in subcritical water in the hydrogen production in aqueous phase
reforming. It was the done for the hydrogen production process.
So, this was possible owing to the action of microwaves on oxygenated polar functional
groups present in the biomass structure. Additionally, the temperature pretreatment above
200 degrees centigrade accelerated the deconstruction of polymer complexes leading to
delignification as well as partial removal of hemicellulose. It enhances solubilisation
switchgrass and miscanthus however this negatively affected the gasification efficiency.
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So, this table will again let us understand what are the different types of studies that concerns
about the application of microwaves. You can see again switchgrass, is there and miscanthus,
and then Cauliflower and cabbage is also mentioned here. So there are direct pre-treatment
and then domestic microwave oven at different microwave power. This is a domestic
microwave oven which is being used here. Time of residence is 15 to 30 min. You can see
that highest increase in biogas production emerged in microwave power of 350 watts in 25
minutes.
And another in very interesting fact about microwave treatment is that, it is a very faster
process. So, time is money in industries. So, we should choose such processes which are
faster. So please have a look later on.
The next one is ultrasound and its application. Application of ultrasound as a green
Technology plays a positive role in the efficient production of added value Chemicals or
biofuels by effective decomposition of recalcitrant lignocellulosic materials. The main
advantages of ultrasound pre-treatment are: shorter processing time, lower operation
temperature and finally a lower amount of chemicals used during further valorization.
Additionally, it has potential to be combined with other technologies.
However, the effect of the ultrasound treatment differs depending on the type of
lignocellulosic material.
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One example of grape pomace has been listed here. So, the influence of ultrasound pre-
treatment on the efficiency of biomass processing was tested for Methane production from
grape pomace among others. So, increases of Methane yield and kinetic constant of the
hydrolysis after the application of ultrasound by all most 10% and 35% respectively were
observed in comparison to untreated material.
Moreover, pretreatment of grape pomace reduced the amount of hemicellulose and Lignin
and slightly increased the content of soluble ingredients compared to control samples. It is
almost by 13%, 6% and 5% respectively. So, the positive effects of ultrasounds on both
chemical composition and yield to Methane were explained by the presence of the formed
Cavitation bubbles which mechanically disrupted the cell wall structure of the lignocellulosic
material.
So, it is an interesting technology actually technique. So simple one, where the Cavitation
actually happens by the formation of bubbles and it will do the disruption of the cellular
structure.
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So, we will see one of the applications on the Agava leaves. So, researchers, showed the
effect of ultrasound pretreatment on the physico chemical properties of the Agava leaves. The
use of ultrasound for 30 minutes resulted in an increase in the content of holocellulose and
Lignin and a reduction of extractives and ash in the analysed material. Now holocellulose is
the amount of water non-soluble carbohydrates basically.
So, moreover the agava leaves treated for 30 minutes showed enlarged pores and damaged
cellular structure. As a result, Polymers were more accessible for further processing. The use
of ultrasound resulted in mechanical breaking down of the complex structure of leaves which
led to fracturing of bonds binding Lignin and cellulose and hemicellulose. An increase in the
sonication time to 60 minutes, caused the decrease in the amount of holocellulose and Lignin
which was related to the fractionation or breaking down of Lignin and hemicellulose
molecules.
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So this particular table has given examples of studies concerning the application of
ultrasound. You can see again that grape pomace and Agava leaves are being ultra sound
treated and the different pretreatment conditions are given. You can see the efficiency of the
process. So, the first one in case of grape pomace less than 25 degree centigrade almost 40 to
70 minutes is the time of Residence. So, ultrasound treatment reduced yield of hemicellulose
and Lignin by 13.3 and 6.3% respectively. Ultrasound pre-treatment provided increase in
Methane production compared to untreated sample. Moreover, pre-treatment of grape pomace
slightly increased the amount of soluble ingredients compared to the control sample.
Similarly, in case of the Agava leaves pre-treatment resulted in the production of inulinases
and cellulases and a reduction in the amount of extractives and ash; these are the enzymes.
So, ultrasound pre-treatment for 30 minutes, results in 1.5 to 2 times higher specific
enzymatic activity which is known as SEA of inulinases, but reduces SEA for other enzymes.
So, these are some of the classical findings from the ultrasound-based treatment.
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So now we will discuss the biological approaches to hydrolyse lignocellulosic structures.
Biological pretreatment using microorganisms is a promising approach to degrade
lignocellulose structure extracellularly thus increasing the sugar conversion rate of the
biomass. Now they have several attractive traits such as eco-friendly and simple operation,
low capital cost, low energy requirement and almost no chemical requirement.
However, the major drawback are the long pre-treatment time and strict microbial growth
conditions. So, the extraction of Lignin degrading enzymes from microorganisms to be used
directly on the Biomass emerges as an alternative approach to eliminate the above problems.
However, efforts in reducing the cost of enzyme extraction are necessary to make it a viable
process.
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So, this is the schematic representation. So, here the lignocellulosic Biomass. Any such
lignocellulosic Biomass, treat it with microorganisms. It can be a single strain
microorganism. It can be a microbial consortium also; depends on what you are deciding
actually. Then again actually it goes for the Lignin degradation, and the cellulose
decrystallization.
So, from cellulose to reducing sugars using the cellulase enzyme. So then of course you can
further ferment them to alcohol platforms.
So, cellulolytic and ligninolytic microorganisms. So, the commonly used microorganisms are
bacteria and filamentous fungi (for example Ascomycetes, Basidiomycetes), which are found
ubiquitous in soil, living plants and lignocellulosic waste material. The fungi can be classified
into brown rot, white rot and soft rot fungi. These microorganisms secrete enzymes that are
capable of selectively degrading Lignin (they are known as the ligninolytic fungi) or
hydrolyse cellulose (they are known as the cellulolytic bacteria). Now biological pretreatment
using microorganisms and enzymes extracted from them also offer a great opportunity to
produce various high value-added Chemicals from the waste-by-product lignin. Among the
microorganisms, white rot fungi have been extensively studied and proven to be one of the
most effective lignin degrading species. However again I am telling you that it is a time-
consuming process.
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Let us talk about the applications. So during their growth most white rot fungi, whether it is
Pleurotus ostreatus, whether it is Trametes versicolor, whether it is Phanerochaete
chrysosporium, produce extracellular Lignin modifying enzymes including laccase, Lignin
peroxidase (which are known as LiPs) and manganese peroxidases (which are known as
MnPs). Now these are enzymes.
Now these enzymes exhibit specificity for Lignin and catalyse enzymatic cleavage of Lignin
aromatic rings through oxidation processes. And these are all slow processes. So, as a result
the linkages between polysaccharides and Lignin are broken down thus liberating the
cellulose component and enhancing the hydrolysis of lignocellulose. In addition, some of the
white rot fungi as mentioned here, for example the Phanerochaete chrysosporium, secrete
cellulolytic enzymes known to hydrolyse cellulose thus increasing its enzymatic digestibility.
So, it is happening simultaneously basically you can say in that spirit.
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So, some of the different types of fungus and bacteria and the feedstock and the operating
conditions and what has happened after the pre-treatment process. So we will see one thing;
the white rot fungus T. versicolor. Cow manure and selected cereal crops were being
considered. Operation condition is 25 degrees centigrade, 135 RPM rotations per minute, 6
days, 75% MC. and pH is 4.2. So, the result is 80% increase in cellulose degradation. It is an
excellent result.
But it has taken time, you can understand that it is 6 days’ time. So, 10 to 18% increase in
methane yield. So if you look at this particular table in a proper way you will understand that
efficiency is not an issue. The only issue is that it is very time consuming and then since we
are dealing with live organisms, we have to ensure each and every day that their growth
conditions are maintained.
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So ligninolytic enzymes. In an alternative approach to microorganism incubation, ligninolytic
enzymes extracted from the fungal and bacterial cultures can be purified and used directly on
the biomass as pre-treatment. Here what we are talking about that, instead of using the
microorganisms directly we extract the enzymes which is responsible for this pre-treatment,
delignification or disintegration, can be extracted and purified and then it will be used.
So now in this case, we are done away with the growth condition of the microorganisms.
Only we have to maintain proper conditions for the enzymatic attack on to the plant cell or
the biomass cells basically. But please understand that, it is a better technique. However,
extracting and purifying enzymes from microorganisms is a very tedious job and is time-
consuming as well as it is a high cost matter.
So, these ligninolytic enzymes are capable of catalysing various biochemical reactions to
degrade selectively Lignin with minimal cellulose consumption. The direct application of
enzymes on the Biomass eliminates the long growing period of microorganisms thus
significantly reducing the pretreatment time. So, 15 to 40 days to almost 6 to 24 hours. That
is fine, but again, the cost has a bigger role to play.
So as a result, enzymatic pre-treatment can accelerate bioenergy production at minimal
environmental impacts, no chemical addition and lower energy.
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Modified Lignin after enzymatic pretreatment can also be recovered for effective uses in fast
pyrolysis to produce biooil. This is one of the significant works. So, common enzymes used
for prre-treating lignocellulosic Biomass are mostly commercialized products from leading
companies such as DuPont, Novozymes and DSM. So these are some of the companies, the
enzyme making companies basically and very well known.
The capability to identify microorganisms and growth conditions to cost-effectively produce
and purify high amount of stable ligninolytic enzymes is critical for this pretreatment to be
commercially viable.
So major ligninolytic enzymes such laccase, LiPs which is called Lignin peroxidase and
MnPs - Manganese peroxidase have been evaluated for their efficiency in delignifying
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lignocellulosic biomass. Up to 50% lignin removal was attained by pre-treatment with P.
ostreatus laccases for high Lignin content biomass (29% and 33% for coffee silverskin and
potato peel respectively).
The pre-treatment of wheat straw using a P. cinnabarinus laccase achieved 37% Lignin
removal, leading to an increase of 60% in glucose yield after the enzymatic hydrolysis.
Sugarcane bagasse pre-treated with ligninolytic enzyme extracted from P. ostreatus IBL-02
strain containing laccase, LiPs and MnPs also reported 34% delignification and ethanol
production of 16 grams per litre after the fermentation process.
This table lists some of the properties of the important ligninolytic enzymes. So, you can see
three enzymes are listed here: laccase, LiPs and MnPs. And different types of plant materials.
What are the characteristic features, and what is the substrate specificity. So, you please go
through it later on when you go through the lecture note. So, with this I conclude today's
lecture.
And tomorrow we will be discussing dilute acid, alkali hydrolysis and Ozone treatment
pretreatment methods. If you have any query, please feel free to write to me at
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kmohanty@iitg.ac.in or please register your query in the Swayam portal. So, thank you very
much.
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Lecture 11
Dilute Acid, Alkali, Ozone
Good morning students. Today is lecture 2 under module 4 and as you know that this module
is dedicated to our Biomass pretreatment and we have discussed basics in the last class.
Today we will discuss some of the most important pre-treatment processes such as dilute
acid, alkali based pre-treatment, auto hydrolysis, Ozone based pre-treatment and few others.
Let us start. As you know that pre-treatment of lignocellulosic biomasses can be carried out
by various methods: chemical, physical, combined and physico-chemical. So, some of these
we have discussed; some we’re going to discuss today. So, under chemical: it is acid pre-
treatment, alkaline, organosolv, ionic liquids, deep eutectic solvents. All these things we will
be discussing today; physical we have already discussed.
So, in the combined pre-treatment it is actually with Microwave based pre-treatment, then
Microwave with the alkali, Microwave with deep eutectic solvents, then ultrasound with ionic
liquids, like this, basically a combination of two pre-treatment technologies. And then
physicochemical: steam explosion, Ammonia fibre explosion, liquid hot water these things
also we’re going to discuss today.
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So, the goal is again the same as we have already discussed; it is to release or defragment
cellulose, Lignin and hemicellulose. So, remove Lignin and purify cellulose and
hemicellulose so that they can be converted into various value-added products.
Let us talk about chemical pre-treatment. This particular image is a beautiful image from the
perspective that it can tell us how different types of chemical pre-treatment are there and how
they overlap each other in a doing a particular job. Now, let us look at this particular green
one. The green boundary here. You can see, that is almost taking into everything except little
part of the acid pre-treatment.
With this green boundary pertains to the lignin removal. All these processes under this green
they will do Lignin removal more efficiently than other processes. Similarly, if you see this
red one, so that one is for the cellulose removal, whether ionic liquid or deep eutectic
solvents, alkaline pretreatment, even part of little organosolv pretreatment also. Similarly,
oxidative, acid pretreatment and alkaline. This takes care of the hemicellulose removal.
This type of pretreatment uses chemical reactions to change the recalcitrant structure of
lignocellulosic materials. Most commonly used are acid, alkaline, ionic liquids, oxidizing
agents and organosolv pretreatment. Now depending upon the chemical substances used
during pretreatment various mechanisms of the Biomass decomposition can occur.
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Let us understand acidic pretreatment: So, pretreatment of lignocelluloses with acids is one of
the most effective method of solubilizing the hemicellulose making cellulose more
accessible. Now acid pretreatment involves the use of concentrated and dilute acid both, to
break the rigid structure of the lignocellulosic materials. The main reactions during acid
pretreatment at the hydrolysis of hemicellulose and condensation and precipitation of the
solubilized Lignin.
The most commonly used acid is the dilute sulphuric acid which has been commercially used
to pre-treat a wide variety of biomass types whether it is switchgrass, cronstover, Spruce and
poplar. So, this list is basically endless. If you see just type dilute acid pretreatment of
lignocellulosic biomass there are hundreds and hundreds of excellent research papers
available.
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Dilute sulphuric acid has traditionally been used to manufacture furfurals by hydrolysing the
hemicellulose to simple sugars such as xylose which continues to convert into furfurals.
Other acids have also been studied such as hydrochloric acid, then Phosphoric acid and nitric
acid. Due to its ability to remove hemicellulose acid pretreatment has been used as part of
overall processes in fractionating the components of lignocellulosic biomass.
Acid pretreatment followed by alkali pretreatment results in relativity pure cellulose. Now,
please give little more emphasis on this particular sentence, which I have highlighted in blue
colour. So, acid pretreatment which basically talking about the removal of hemicellulose in a
more efficient manner than that of cellulose and Lignin followed by alkalis. Alkali is more
predominantly will be doing the role to remove lignin.
So, if you combine this it becomes a hybrid process. Dilute acid followed by Alkali so both
hemicellulose and Lignin will be removed and whatever left out is cellulose. So, the
disadvantages of acid pretreatment are corrosive environment of reaction and possible
formation of inhibitors like HMF (hydroxymethylfurfural) and acetic acid during further
processing. Now when you talk about corrosive environment of the reaction that means you
have to use a very sophisticated reactor of a particular material so that it can deal with the
corrosive environment. So, glass is better. But you know that glass you cannot makeup in
very big size reactors. It is very difficult to do that. This basically adds on to extra additional
cost to the entire process. HMF is a very high value material or solvent. So, it is a fuel
additive also.
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So, it was reported that the concentration of 2 grams per litre of HMF and 3 grams per litre of
Acetic Acid formed during acidic pretreatment of lignocellulosic feedstock can result in the
loss of the efficiency of further fermentation process. The meaning of this particular sentence
is that for certain cases as for example dilute acid pretreatment of few biomasses, it has been
noticed that beyond 2 grams of HMF and 3 grams per litre of Acetic Acid the process and the
fermentation is not proceeding in a proper direction because this HMF and acetic acid is
becoming toxic for the fermentation to proceed.
Strong acid treatment allows to obtain high sugar yield at mild temperatures during
hydrolysis of cellulose. Although strong acid hydrolysis is very efficient and independent
from the feedstock source the reaction medium is highly toxic and corrosive which requires
the design of resistant and robust reactors; that affects the cost of biomass processing. So that
means adding additional cost.
So, the solution that reduces cost while maintaining the high process efficiency is the
application of the dilute acid. If you talk about dilute acid also, the problem of corrosiveness
also comes down to a lesser extent. So, the advantages of dilute acid treatment are: high
reaction rates of hemicellulose and cellulose hydrolysis and limited formation of inhibitors.
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See few examples. The first one is application of dilute acid pretreatment in enzymatic
hydrolysis of Bananas pseudostem. Shimizu et al studied the effect of sulfuric acid
concentration on the chemical composition of products and glucose yield in enzymatic
hydrolysis of Banana pseudostem so this the image. So, the sulphuric acid in concentration up
to 25% broke glycosidic bond which resulted in random and effective removal of
hemicellulose and an increase in the cellulose and Lignin content in comparison to the
untreated material.
Removal of hemicellulose from the studied feedstock was accompanied by growth in both
external and internal surface area of the treated biomass which exposes the cellulose fraction.
On the other hand, aggressive acidic environment that means sulphuric acid with the
concentration of above 25% completely remove hemicellulose from the banana pseudostem
and lead to cellulose degradation.
And that is what also we do not want. So as a result, lower glucose yield in enzymatic
hydrolysis was obtained; because cellulose was degraded. Now, for all such a processes
whether it is dilute acid pretreatment, then enzymatic hydrolysis, fermentation you need to
optimise the process parameters so that you get a proper yield of the cellulose and then it gets
converted to glucose.
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So, another application on Elephant grass. The effect of sulphuric acid treatment on
crystallinity index, solid recovery and chemical composition of elephant grass was studied by
Santos et al. It was demonstrated that acid effectiveness during the pretreatment depended on
the part of the plant that has been treated. Acid pretreatment removed hemicellulose from
samples proportional to the acid concentration used additional increasing the amount of
glucan and Lignin.
Moreover, the pretreatment resulted in the removal of a higher amount of solid from leaf and
whole plant rather than from the stem. The yield of enzymatic hydrolysis decreases in the
following order: Leaves, whole plant and stem fraction.
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So, another one application on the Agava leaves. Effect of the type of acid whether sulfuric
acid or hydrochloric acid on the yield of reducing Sugars obtained from Agava leaves was
tested by Avila-Gaxiola et al in 2018. So, you can refer that reference has been given. A
slightly higher yield of reducing Sugars was observed after pretreatment in the presence of
oxoacids. An increase concentration of acids regardless of the type led to a reduction in the
amount of sugar produced which is associated with their degradation to furfurals or
hydroxymethylfurfural.
The best results of the treatments applied in the lignocellulosic materials were sulphuric acid
at only 0.5% volume by volume basis, very diluted concentration. Sugars released is 68
grams of reducing sugar per 100 grams of Agava powder, which is actually very good yield.
No inhibitory compounds were detected; that’s because the concentration of the sulphuric
acid is very low.
So, another application on green landscaping waste. Dilute phosphoric acid was used for
obtaining high quality value-added cellulose Acetate from Green landscaping waste. So, the
performed investigation showed that wood structure after exposition to phosphoric acid
degrades in lower temperature than untreated sample. And the crystalline fraction of the
cellulose increased, while the amorphous one decreased after the use of the phosphoric acid.
Such treatment improves the separation of hemicellulose from the feedstock degrading the
bonding of Lignin and cellulose. As a result, the yield of cellulose acetate obtained from the
solid fraction increased.
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This particular table, please refer to this one. So here it is given that selected samples of the
studies concerning acid pretreatment. This list is only a representative in nature. There are
many. This has been taken from a particular reference which is listed here. You can refer to it
later there are many. I just quickly explain to you. Banana pseudostem we have already seen.
Let us see this Sisal fibre. So different concentration, say 0.5 to 1.5%, so different
concentrations of sulphuric acid has been tested.
The condition is; temperature is around 100 degrees to 120 degrees’ centigrade; time of
residence is of course not mentioned and the efficiency is that the highest xylose
concentration of 0.132 gram per litre of the fibre was obtained at 120 degrees centigrade with
2.5 % volume by volume of sulphuric acid. Like similarly, I do not want to read out all these
things you can refer it later on and I deliberately added all these things so that those (of you)
who will be working on Biomass related topics for their academic interest or otherwise for
doing some research, it will be helpful for them to get some first-hand information about the
different effects of the dilute acid pretreatment. Similarly, this is continuing, so you can see
the Agava plant which we have discussed, this is cornstover dilute phosphoric acid 50 degree
centigrade, 10 hours. So you can see that it substantially decreases the gaseous product
formation, but increase the amount of liquid fraction in the pyrolysis process. This is
particularly done, pre-treated cornstover with an aim to pyrolyze it.
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The next one is alkaline pretreatment: Alkaline pretreatment involves the use of bases such as
Sodium, Potassium, calcium and ammonium Hydroxide for the pretreatment of
lignocellulosic biomass. The use of an alkali causes the degradation of Ester and glycosidic
side chains resulting in structural alteration of Lignin and cellulose swelling, partially de-
crystallization of cellulose and partial solvation of hemicellulose.
Sodium hydroxide has been used extensively by researchers for many years and it has been
shown to disrupt the lignin structure of the Biomass increasing the accessibility of enzyme to
cellulose and hemicellulose. Another alkali that has been used for the pretreatment of
biomass is the lime. Lignocellulosic feedstocks that have been shown to benefit from this
method of pretreatment are cornstover, switchgrass, bagasse, wheat, rice straw and the list is
actually end less there are many other. Just a few are listed here.
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So, pretreatment of biomass with the use of bases can be carried out at room temperature and
its yield depends on the lignin content. Pretreatment is most efficient for lignocellulosic
materials characterized by low lignin content. The advantages of this particular alkaline
treatment are: (a) use of cheap chemicals: actually that means the low-cost chemicals; (b)
mild reaction conditions; (c) Effective removal of Lignin and xylan and (d) possibility of
biomass fractionation. However, the biggest disadvantage of that particular process is the
long process time it requires and difficulties in neutralization of the post treatment mixture.
So that means you have to neutralize after the processes is over. There will be still so much of
Alkaline content in the reaction mixture.
So, you need to take out your Lignin and cellulose, hemicellulose. So, you need to neutralize
it. So that neutralization also adds some another cost. So, you have to add some acid to
neutralize it. The most important thing is of course the long process time. So that is the
disadvantage and in commercial or industrial applications we have to have the processes
which are faster and as well as low cost.
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This is an excellent slide. You see this is a flowchart of a pretreatment process using the
alkalis. What it does. This is a representative one. It is not true for every biomass. So let us
just understand. A biomass - so, you give alkalis to pre-treat it, so whatever you get is
(subjected to) a filtration. So, it is a solid residue - you wash it - then whatever the solid
residue that is obtained is nothing but the cellulose enriched residues.
So, you can further process it to get pure cellulose out of that. So, the brown liquor after the
alkali pretreatment. So, alkali pretreatment will result into two things. One is this solid rich
leftover mass. So that is basically Cellulose rich and another is a brown liquor liquid. So that
brown liquor when you do the further processing by adjusting its pH and all these things it
goes for precipitation – centrifugation - then again, you will get a solid part - wash it - you get
hemicellulose. And from here this particular process whatever the solid part is come down as
hemicellulose whatever liquid part remain it has become by the time colourless liquid. That
goes to further processing of evaporation - centrifugation - washer - lyophilization and you
get lignin. Here actually during this evaporation what is evaporated is this alcohol.
So this alcohol or in this case ethanol will be again recycled back to this particular space.
Now you can see and understand that from this particular process that in three subsequent
steps we are getting cellulose rich residue, then hemicelluloses and Lignin by alkali
pretreatment.
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So, few applications we will see, application on bamboo. Yuan et al investigated in detail the
effect of sodium hydroxide concentration on the chemical composition of bamboo which can
be used as a potential feedstock for the production of Sugars and alcohol. Additionally, they
showed that post treatment liquor can be a source of high-value Lignin and silica. It was
demonstrated that severe conditions can lead to degradation of cellulose and hemicellulose
monomer hence decreasing the sugar yield.
And effective removal of sugar from the solid fraction resulted in their larger share in the
liquid fraction. Furfural and hydroxymethylfurfural potential inhibiter for further processing
were not detected in liquid fraction. So that is a good thing actually. So we will get more
bioethanol.
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Application on banana pseudostem. So, by again Shimizu et al. Influence of sodium
hydroxide in the range of 5 to 30% was studied for the yield of glucose. Alkaline
pretreatment in the range of 5 to 25% concentration of sodium hydroxide gradually removed
hemicellulose and Lignin from the Biomass structure. However higher alkaline concentration,
that is 30% and above led to a decrease in the cellulose content as compared to 25% Sodium
Hydroxide suggesting cellulose degradation.
So, this is what is I was talking about optimisation. So, you have to take different
concentrations and to see at what concentration of sodium hydroxide or alkali, you are getting
the best result, the higher yield of reducing sugar. So, glucose yield is increased gradually
with increasing concentration of sodium hydroxide achieving the highest value after
treatment by 25% sodium hydroxide.
So, high glucose yield resulted from solubilization of Lignin and hemicellulose fractions
caused by the alkali pretreatment; this is the reason for high yield.
So then application on commercials Xylan. An important issue in the alkali pretreatment is
the presence of impurities like potassium, sodium, calcium and magnesium ions that affect
the initial decomposition of the organic Biomass components. Giudicianni et al in 2018
investigated the effect of the presence of calcium and sodium ions in commercials Xylan on
the composition of gaseous and liquid products formed during its pyrolysis.
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So, a comparison of the chemical composition of the demineralized and raw Xylan prove that
incorporation of the metal ions into the Xylan structure affect the mechanism of its
decomposition. Metal ions decrease the initial decomposition temperature of Xylan. The
presence of metals results also in the reduction in the amount of furfural (being a product of
depolymerization of Xylan chain, rearrangement and dehydration reactions) and an increase
in the content of furfuryl alcohol and other low molecular weight products.
So, this is again another table which gives selected examples of studies concerning alkaline
pretreatment. So, you can see so many are mentioned here actually if you look at literature,
there are hundreds of papers on alkali pretreatment of different Biomass. So here we have
listed Banana pseudostem, wheat straw, Zizania latifolia, commercial Bamboo chips, peach
tree, miscanthus and giganteus and then many. So, you please refer to it later on, I am not
going to read this table.
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And we will move into the next pretreatment method which is a very important class of
pretreatment methods known as organosolv method. The organosolv is a method of biomass
pretreatment that uses various organic and aqueous organic solvent mixture to solubilize
hemicellulose and extract Lignin. Please understand acids are out of this; no acids and alkalis
are covered under this.
So organic solvent such as methanol, ethanol and Acetone, ethylene glycol, Triethylene
glycol and tetrahedrofurfuryl alcohol are the most commonly used solvent for the organosolv
pretreatment process. Organic acids such as Oxalic, salicylic and acetylsalicylic acid are
catalyst to organosolv solvation process. So, they act as catalyst, they are not the main
solvents. So the organosolv pretreatment of lignocellulosic materials with the use of alcohol
leads to the hydrolysis of the internal bonds of Lignin and hemicellulose as well as hydrolysis
of ether and Ester interpolymer bond between them resulting in lignin removal and almost
complete solubilisation of the hemicellulose.
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The presence of organic acids in the organosolv process leads to the formation of hydrogen
ions, which facilitate delignification of biomass and dissolution of Lignin. So, this the
mechanism. So, the optimal temperature of the process is in the range 100 degree to 250
degree centigrade and depends on the type of biomass. However, the use of a catalyst (so that
includes any organic or inorganic acids) allows the process to be run effectively at lower
temperature.
So, you use catalyst the temperature will come down. Then addition of an inorganic acid to
the reaction mixture causes hydrolysis of hemicellulose which significantly increases the
availability of cellulose for further process. The solvents used in the process are open
inhibitors for further reactions of fermentation or enzymatic hydrolysis, so they must be
removed after the pretreatment process.
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The advantages of the organosolv pretreatment are: high efficiency, mild conditions, easy
solvent recovery, and the possibility of its recycling and relatively high purity of biomass
fractions and the possibility of their separation. The disadvantages are: high cost of solvent
and their recovery but also, the cost of a process related to the specific requirement of the
used equipment due to the use of volatile solvents.
So again, you need specific type of sophisticated equipment to carry out this particular
pretreatment.
So, we will see alcohol pretreatment under organosolv. Alcohol, especially the lower
molecular weight aliphatic alcohols are the most frequently used solvents in the organosolv
pretreatment. Regarding the type of alcohol, it was found that normal primary alcohols were
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better agent than the secondary or tertiary alcohols for delignification. Although the mixtures
of n-butyl alcohol water appeared to be the most efficient in removing Lignin from the wood.
However, due to the low cost and ease recovery methanol and ethanol seems to be the most
favoured alcohol for alcohol based organosolv pretreatment.
On the other hand, some polyhydric alcohol also can be employed for the pre-treating
Biomass under atmospheric pressure with or without catalyst.
So, let us see this process flowchart for methanol and ethanol pretreatment. So the
lignocellulosic Biomass, you use either ethanol or methanol water. You pre-treat it, so
whatever you get is basically the unwashed pulp. So that you filter it then again go for warm
solvent washing so you get the solvent washes, again it goes to the solvent recovery process.
You need to recover the solvent because solvents are costly.
Then again, followed by a warm water washing, solid fraction, you will be getting and this
goes to the enzymatic hydrolysis or SSF. So, whatever spent liquor you are getting here that
goes to the solvent recovery process and the solvent is again feed back into the pretreatment
process. So, this is from here again, you can see that. From the solvent recovery you will get
something a concentrated Black Liquor.
So that is rich in lignin fraction. So, you need to recover Lignin. So, you go for the different
processes such as dilution with water followed by precipitation filtration. So then again, you
see water washing, drying and you get organosolv lignin fraction. And then here again the
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water washing and filter again recovery and the reuse of this process. This is one simple
system where you can see that we are getting the solid fraction which can be processed for
the enzymatic hydrolysis or SSF. And then we get a lignin there apart from that some other
solvents.
So, the main products from pretreatment are the following. First one is the cellulosic fibres.
So which contain the original cellulose component and varying amounts of hemicellulose and
little residual Lignin which could not be taken out. The second part, solid Lignin obtained
after removal of the volatile solvent from the black liquor by distillation. It may contain
lipophilic extractives from the original lignocellulosic feedstock. And the third one is an
aqueous solution of the hemicellulose sugars, which consists mainly of xylose in the case of
hard wood or agricultural residues. You do not get xylose every time. It depends which
Biomass you are using. This solution is the filtrate of the previous solvent-evaporated liquor
in which the lignin fraction was precipitated.
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So, we will see 1 or 2 applications. So, application on wheat straw. An ethanol treatment of
straw remove both lignin 14% and hemicellulose 51%. Partial delignification and significant
loss of hemicellulose fraction resulted in a 15% increase in cumulative biogas production
compared to the untreated sample.
Another application on bagasse, para rubber wood sawdust, Palm and cassava fibre. So, the
studies of Inkrod et al of the extraction of Lignin from Bagasse, para rubber wood sawdust,
palm and cassava fibres in the presence of a solvent mixture of methyl isobutyl ketone,
ethanol, water, and sulfuric acid showed that the highest efficiency in Lignin removal was
obtained for the bagasse sample that is 88% in 160 degree centigrade.
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Other lignocellulosic materials revealed a similar yield of Lignin in the range of 67 to 71%.
The Lignins extracted from bagasse and para rubber wood sawdust had the highest purity of
89% and 87% respectively while purity of Lignin present in other samples was in the range of
64 to 78%. And it is a good process and quite efficient.
Another application of this process on Pinu radiate. So, in another work it was demonstrated
that the conditions of the organosolv process have a strong impact on the thermal stability of
Lignin extracted from Pinu radiate. It was observed that severe process conditions like high
temperature or to a lesser extent process time lead to a decrease in the thermal stability of
Lignin due to the degradation of its macromolecular structure. Lignin is a very complex
molecule. So, we have seen the structure. Though it is a very rigid structure, however too
harsh treatment will result in the lignin degradation.
So, this is selected examples of some of the studies concerning the organosolv method. You
can see that some of the Biomasses like sugarcane, barley, straw, oak sawdust, wheat, pinus
all these things are there and different pretreatment processes. Ethanol 50% volume by
volume here acetone and water is mixed in 50-50 ratio, and sulfuric acid concentration of 10
to 35 moles per dm cube.
That is very small amount. It acts as catalyst. As I mentioned that in the alcohol adding acid,
acid is actually working as a catalyst. So then ethanol 50% and then again ethanol 60% by
weight 40 to 60% of Ethanol in water. There are so many different types of pretreatment
processes and then followed by their conditions. Again, I am telling you for your
understanding whatever you are seeing here; let us say the time of residence to 50 to 60
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minutes, temperature 130 to 670 degree, these are the range and they have varied, like 15, 20,
30, 40, 50, 60 like that they might have varied. I am just telling you for your understanding.
That you will understand how to optimise the process. Temperature again, 130, 140, 150,
200, 300, 500 up to 670. So this is the range they have varied and they might have got an
optimised condition. And let us see the optimised condition he has given here for one
particular optimal condition; 160 degrees centigrade, 10 minutes and 0.5% concentration of
sulphuric acid for 50% ethanol water mixture.
This is what is called the optimised process condition for the most efficient or the highest
reducing sugar yield you can say.
So, the next class of solvents are ionic liquids. Ionic liquids are considered as the green
solvents owing to their unique solvation properties. So Ionic liquids shows high thermal
stability and low toxicity and required low vapour pressure. This ionic liquid selectively
remove the Lignin and hemicellulose part of biomass to provide pure cellulose for further
hydrolysis. The IL pretreatment process can be operated more efficiently in continuous mode
with high biomass input.
However, the main challenges are IL toxicity, pH compatibility, costliness - Ionic liquid still
whatever it is commercially available most of them are very costly - and process complexity.
Low cost and environmentally friendly IL’s have been synthesized using Lignin and
hemicellulose derived compounds. The reduced amination of Lignin monomers, furfural,
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vanillin, and P-anisaldehyde followed by treatment with phosphoric acid has generated ionic
liquids including this.
So, these are some of the ionic liquids which are actually being generated from Lignin and
lignin derived products.
How do you prepare ionic liquids? It is very simple, mix this and this; representative am
telling you. what is that? These 4 on the top are all cations. These 4 on the bottom are all
anions. So, any cation and any anion you fuse them together you get an ionic liquid. It is not
so easy to do that. It can be done in the lab scale but you need further processing. Fusing
together at certain conditions is fine.
But then the purity comes into picture. So, it may be 50%, 60%, 70% pure but then you need
to purify to 80% 85% 90% it is again a challenge. So, these are different types of ionic liquids
cations and anions; imidazolium based, pyrrolidinium based, Piperidinium based and based
on ammonium. And these are some of the anions; hexafluorophosphate, dicyanamide, tetra
chloroaluminate and ammonium.
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So, there are 2 ways you can do. The path one is fractional dissolution of lignocellulose or
pulping and path 2 is dissolution and reconstruction of cellulose.
Which is being explained in more detail in such a nice schematic representation, but let us
first understand what is Path 1. So, ionic liquids are used as solvents in the process owing to
their good solubilizing power and Ultra low Vapour pressure and therefore negligible loss
into the environment. Moreover, used IL’s like N222 HSO4, BMIM HSO4, BMIM Cl are
quite cheap. I can tell you, see let us look at this, BMIM is your cation and HSO4 is anion,
like that you can understand.
So that BMIM is the cation and Cl is the anion. So high degree of Lignin removal leaves
behind the cellulose with quite porous structure that can easily be transformed into hexoses in
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high yield. Further fermentation can afford bioethanol is fuels. Alternatively, chemical
pretreatment that can also be done in ionic liquid can transform sugar into platform chemical
such as a HMF or Levulinic acid.
Part 2 is dissolution and reconstruction of cellulose. So, some ionic liquids like EMIM OAc,
EMIM DEP are good solvent for the dissolution of wood - hardwoods basically - dissolving
all of the wood constituents whether it is cellulose, hemicellulose and Lignin. Now, this
dissolved cellulose can be reconstructed in amorphous state by addition of water, spun into
fibres, transformed into composites, films, nanoparticles or chemically modified for further
use.
So how these two things have been done here, we will try to understand. So, this is the
lignocellulosic Biomass. So, you add ionic liquid to it. Then follow the proper protocol how
to do it. There are steps and process conditions. Now the first one use EMIM DEP or EMIM
OAc, you got, this is the part 2 basically which we have discussed, dissolved cellulose. Now
this dissolved cellulose can be purified into cellulose.
It goes for further processing like cellulose derivatives, HMF, Levulinic acid and
fermentation to Sugars, ethanol, this is alcohol or biofuel platform. So, then this dissolved
cellulose can be further spun into fibres, nanoparticles, films and composite and you can use
them. Now in the part 1 which discussed if you use N222 HSO4 and similar other ionic
liquids so you are getting for a fractionalization.
So, you pre-treat and pretreatment process, then you get cellulose and further processing and
whatever precipitation is remaining that is rich in Lignin basically, deep brown in colour.
You can see the colour is also been shown here. Again, you further process it so you get 2
things hemicellulose rich fraction to be purified to get hemicellulose and lignin rich fraction
you get lignin. So, you are getting cellulose, hemicellulose and Lignin in ionic liquid
pretreatment process and all are in a better yield.
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So, this table is showing you selected examples of the studies concerning application of the
ionic liquids. So again, I am not going to read out this. So please refer to it later. So, the
temperature, residence time, efficiency of the process, what are the Chemicals, what are the
different types of ionic liquids being used and these are the different types of biomass.
Similar table with different Biomass again.
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So next class of solvent is Deep Eutectic Solvents. So deep eutectic solvents come in the
picture as a result of certain disadvantages of the ionic liquids. So, DES, these are two or
more components mixture in which one is a hydrogen bond acceptor, which is known as
HBA, another is a hydrogen bond donor (HBD). So, you fuse together a hydrogen bond
acceptor like ChCl or hydrogen bond donor like urea in a molar ratio that you decide.
So, you will get ChCl urea, which is the deep eutectic solvent. It is just like ionic liquid you
are fusing one cation and anion. Here we are talking in terms of hydrogen bond acceptor and
hydrogen donor. So, an application of the DES for pretreatment of biomass is an alternative
to conventional IL’s especially due to their lower cost. In comparison to the IL’s the synthesis
of DES is easier and DES can be obtained from widely available and inexpensive ingredients.
So, for example your quaternary ammonium salt and metal chloride; these are less costly than
the ionic liquids.
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The other advantages of DES are low-volatility, wide liquid range, low toxicity
biodegradability and enzyme compatibility. Biodegradability is very important feature for a
solvent to be extraordinarily green solvent. So, the ability to remove Lignin and
hemicellulose from Biomass structure during pretreatment is determined by the capacity of
the dissociation of protons by this DES.
Strong electron withdrawing groups of HBD’s - hydrogen bond donors - can enhance process
performance while hydroxyl or amino groups of the hydrogen bond donors negatively
influence the process efficiency. So, strong acidic DES can effectively remove Xylan from
rice straw structure. As a result, cellulose is more available for enzyme despite the presence
of Lignin in the structure of biomass.
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So, we will see one application in Sago waste. So 3 types of DES differing in HBD choline
chloride that is ChCl urea and ChCl citric acid and ChCl glycerol was synthesized and used
for the pretreatment of sago waste in the enzymatic hydrolysis into sugar. So, basically three
different types of Deep eutectic solvents are prepared. A more acidic or alkaline character of
the hydrogen bond donor increases sugar yield due to more efficient disrupting of the
lignocellulosic structure.
The neutral HBD in ChCl glycerol pretreatment resulted in low glucose yield. Moreover,
ChCl urea DES deep eutectic solvent behaves like a conventional alkaline reagent that breaks
down the Lignin and facilitate excess of enzymes to the Biomass.
So, another application on rice straw. Xing et al presented a novel type of DES that uses the
dihydrogen bonding donors, a mixture of formic acid and acetic acid with ChCl, which
effectively removes Lignin and hemicellulose increasing the amount of cellulose.
Pretreatment of rice straw with a dihydrogen bonding DES showed significant abrasion and
splitting of fibres as well as some delamination and peeling as a result of partial
decomposition of hemicellulose.
This increased the total sugar yield in comparison to the use of DES containing single
hydrogen bond donor. This is a very good work. I have given you the reference. It is a
published work in chemical engineering journal. Those who are interested please refer to this.
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And again, one more table in which listed are the studies concerning application of the
different Deep eutectic solvents with respect to different Biomass like say rice straw, Sago
waste, herbal residues, what are the Chemicals and HDB’s all that is being used, what is the
temperature, time of residence and what is the efficiency. So please refer to this later on.
Again, this is continuing with switchgrass and rice straw.
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So will move to the next class of treatment which is called oxidative pretreatment. The
oxidative pretreatment is based on the treatment of lignocellulosic materials with oxidizing
agent. So, what are those? Those can be Ozone, hydrogen peroxide, oxygen or even air. The
processes mainly involve removal of Lignin from the Biomass structure and increase the
accessibility of cellulose. Unfortunately, Biomass oxidation is not a selective process and the
removal of Lignin is often accompanied by the loss of hemicellulose and Cellulose.
The effectiveness of the delignification process is the result of the oxidation of the aromatic
rings in the presence of an oxidizing agent to Carboxylic acids. Other reactions of the
delignification process that take part during oxidative pretreatment include electrophilic
substitution, displacement of sides chains, and cleavage of alkylaryl linkage. So, these are the
other type of reactions.
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Let us understand the Ozone oxidation to promote delignification. Ozone is a promising
reagent for the oxidation of lignocellulosic biomass due to its selective reactivity lignin. Its
powerful oxidising property target compounds with functional groups with high electron
density such as Lignin and overlook cellulose and hemicellulose. Thus, no significant losses
of Carbohydrates occur and the Sugars’ accessibility to enzymes and microbes is increased
due to the destruction of lignocellulosic biomass structure.
Advantages include: no production of toxic residues, mild operating conditions - basically
room temperature and pressure, easy onsite production - that is reduced transport cost,
chemical supply and storage problems. On the contrary Ozone production requires high
energy inputs (36 megajoule per kg of Ozone) and high doses for pretreatment (example, 9kg
Ozone per tonne of dry biomass to produce 63 kg of ethanol).
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This is a schematic of the Ozone oxidation process. So, basically you have an Oxygen gas
tank here - then by flowmeter it goes to a unit, which is basically Ozone generator. So, you
maintain standard temperature and pressure. Now this ozone will be fed to a packed bed type
of column which is having this lignocellulosic Biomass.
And you have a micro bubble diffuser - so the Ozone will be diffused and it will come in
contact with the lignocellulosic Biomass, then whatever the Ozone is getting or moving out
of this column has to be passed through an Ozone destructor. So again, convert Ozone to
oxygen. So, this is very simplest way - this can be done in a large scale very easily. No harsh
pretreatment condition and no requirement of sophisticated instrumentation only you need a
Ozone generator and oxygen cylinder.
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So, studies have been conducted to explore the application of Ozone oxidation in
lignocellulosic bio-refinery. It has been used to pretreat a wide range of lignocellulosic
biomass to generate biogas, bioethanol and biohydrogen. This table again list out selected
examples of biofuel production from lignocellulosic Biomass pre-treated with Ozone
oxidation. So, MC is moisture content. So you can see it is written 45% w/w MC that is
moisture content.
So, it is biogas. The target is biogas production, bioethanol production, biohydrogen
production. So, please refer to the slide later on.
So, we will talk about the physicochemical pretreatment methods. This category of
pretreatment includes methods that combine physical changes and chemical reactions during
the processing hence the name physicochemical. Generally, lignocellulosic Biomass is treated
at high temperature and under pressure with an inorganic compound which leads to
disruption of its recalcitrant structure. As a result the basic components of biomass are
fractionated, which facilitates further processing.
We will see one example, one such pre-treatment method which is steam explosion method
or auto hydrolysis. So, Steam explosion is one of the most commonly used methods of
physicochemical pretreatment of lignocellulosic biomass. So, this method is based on the
treatment of the biomass by high pressure saturated steam, which is rapidly lowered. That is
why it is causing explosion. Causing the explosive decompression.
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So typical conditions of the steam explosion process are temperature 160 to 240 degree and a
pressure of 0.7 to 4.8 Mega Pascal. The purpose of the vapour explosion is to solubilize
hemicellulose and improve the accessibility of cellulose while avoiding formation of
inhibitors for further enzymatic processes. The steam explosion pretreatment results in partial
hydrolysis of hemicellulose by released acetic acid.
Lignin is removed only to a limited extent, but melting, depolymerization and
repolymerization reaction causes its redistribution on the surface of the fibre. The main
advantages of the steam explosive pretreatment are residence time is very short - so, it is
good for commercial application, low energy consumption and lack of chemicals used. So the
entire process is very economically justified.
However, there are certain issues, like poor lignin removal, deconstruction of Xylan into
hemicellulose and possible generation of inhibitors affecting further processing. Again this
HMF and acetic acid and all this. So, if you go for a high temperature application.
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So, we will see one application on bagasse. So, steam explosion was used in the pretreatment
of bagasse in the extraction of cellulose nanofibrils. The pretreatment result in partial removal
of hemicellulose from Biomass increasing the crystallinity index. In addition, the processing
stripped middle lamella and primary wall separated the closely packed fibres in the bagasse
structure.
Another application on hardwood, soft wood and agricultural residues. Priyanto et al, this is a
very good study published in ACS Sustainable Chemistry engineering. So, what they did
actually they used moisture from Biomass as a source of steam in order to improve properties
of feedstock pretreatment. This is very interesting study. Hardwood, softwood and
agricultural residues with different moisture content from 45% to 75% were treated in a
specially designed reactor.
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The process called self-steam explosion effectively reduced the grain size (almost average
below 1 mm) of feedstock increasing the heating values and hydrophobicity. It was suggested
that such a type of pretreatment can be economically efficient reducing processing cost more
than half compared to the conventional milling.
This table is giving you selected examples of some of the studies concerning application of
the steam explosion method. Various types of biomass, their pretreatment conditions and the
efficiency has been listed, please refer to it later on.
So, we move ahead to one of the again more studied method which is called AFEX that is
Ammonia fibre explosion method. So here, it is similar to the steam explosion. So here it is
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based in the pretreatment of lignocellulose with liquid Ammonia at elevated temperature.
With the pressure around 0.7 to 2.7 mega pascal. The process conditions and the presence of
ammonia causes the swelling of the biomass, increasing the available surface area, the
degradation of hemicellulose to oligomeric sugars and the change of the lignin structure.
Basically, the mechanism is that, the ammonia is swelling the Biomass making it more
porous and they will be more accessible to the enzyme. So an important disadvantage of this
AFEX process is the low efficiency of the process as in the case of acid pretreatment, the
corrosive reaction and environment also.
So, for this reason the process requires the use of appropriate reactors and hence again
additional cost come into the picture.
We will see some of these AFEX study. So the AFEX process was used as a pretreatment
method of Corn stover, prairie cord grass and switchgrass before the pyrolysis process. All
this has been used for pyrolysis but before that they are pre-treated with AFEX to increase the
pyrolytic product yield. The impact of the treatment was negligible and did not significantly
improved the properties of tested materials.
Parameters such as moisture content, volatile matter, ash content or heating values were
almost the same before and after pretreatment. However, the AFEX process increased pellet
durability and decrease the temperature of the sample degradation, not much effect has been
actually reported. During the pyrolysis process the yield just increased for biochar from 22 to
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25% and for the bio-oil it is 46 to 48% after the AFEX pretreatment which is very, very
marginal actually not significant.
This is again selected examples of the studies concerning application of the AFEX method.
Various biomass is like cornstover, grass, switchgrass, which we just saw. Agava, bagasse
and leaf, Agava salmiana bagasse. So please see the different chemical that is listed. The
conditions, time of residence and the efficiency of the process, please refer to it later.
And we will see one of the most important class of this pretreatment process, which is called
liquid hot water and hydrothermal liquefaction methods. In hydrothermal process water is
used for the pretreatment of lignocellulosic biomass. No catalyst or chemicals other than
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water are used. So that it is called hydrothermal method. So, depending on the process
temperature hydrothermal processes are divided into 5 types.
(a) The first one is the hot water extraction; (b) second one is pressurised hot water
extraction; (c) Third one is the liquid hot water pretreatment; (d) forth one is hydrothermal
carbonization or HTC; and, (e) hydrothermal liquefaction or HTL. HTC and HCL are widely
studied since last decade and have lot of applications and excellent studies have been
reported. So, the low-temperature process in which the process temperature is below the
boiling point of the water (less than hundred degree centigrade) is used to extract some of the
water-soluble Biomass components such as pectin and tannin.
Due to the temperature range of the process, the target of each is different. So that we need to
understand. Here whatever is being listed you’re seeing, everything has a certain different
temperature. The temperature, temperature range depending upon their product whatever
coming out will also be different. We will see. So in the pressurized hot water extraction, it is
carried out in the 150 to 180 degree centigrade in that range and can be used as a pretreatment
of the pulp dissolving process and for the reduction of hemicellulose content in the forest bio
refineries samples.
In the liquid hot water process the applied temperature is 140 to 230 degree centigrade is little
or a we can say slightly higher than the PHWE. So this process leads to partial dissolution of
hemicellulose and Lignin and reduction of the durability of the structure. In turn in the HTC
or the hydrothermal carbonization, which is carried out at 180 to 250 degree centigrade is
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used to convert Biomass into modern carbon materials with specific physicochemical
properties.
High quality carbon can be prepared that is why the name is actually hydrothermal
carbonization. Then during the HTC process hydrolysis, dehydration, decarboxylation,
polymerization, aromatization and condensation reaction takes place. As a result of the high-
temperature starting from 280 degree centigrade in the HTL process, a biocrude that is oil
like product can be obtained. We will discuss HTL later on, its a very good process actually.
Whatever we have discussed this has been given in this particular some sort of schematic
representation of graphical abstract type you can see. Biomass, the treatment method. You
can see this. The first one is the hydrothermal liquefaction HTL which was discussed at the
end. So that converts, you will get Carbon, you get bio-oil and you get water soluble
degradation products.
Apart from that you get carbon dioxide, carbon monoxide, hydrogen and methane. When you
go for the liquid hot water pretreatment, you get hemicellulose and extracted biomass here.
The solid biomass can be fractionated again into valuable products. For hot water extraction,
which is below 100 degree centigrade we get extracted biomass which can be for the
processed to again value-added products and we get the polysaccharides and polyphenolic
compounds.
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So, this is the lowest in the lowest range of the hydrothermal processes and HTL is the
highest range in terms of the temperature and the uses.
So, a table line gives you the studies concerning application of the hydrothermal method. So
again, I am telling you that you please refer to it later on. So different Biomass are listed,
different pretreatment conditions and their efficiency of the process has been listed. So, this
will help you if at all going to do some work on Biomass fractionation or biomass
pretreatment.
We will see this the characteristics of the lignocellulosic pretreatment techniques. This is an
overall idea. So, you can see this, different pre-treatment methods like microorganisms - the
biological one, followed by ligninolytic enzymes, alkali method, acids or dilute acids method,
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Ozone oxidation, ionic liquids and deep eutectic solvents, you have mechanical - this is a
mechanical and physical method milling and grinding, then irradiation using using
microwave, ultrasound, hydrothermal - like hot liquid and steam explosion. So, I will leave it
to you for read and referred to it later on. There is not much to again describe or there is no
much point in reading. Whatever being listed here we have already discussed throughout our
today's lecture. This in a single table is this has been compared. So, you can understand what
are the advantages, disadvantages of a particular process for a particular biomass.
So, with this I conclude my today's lecture. So please feel free to post your query in the
Swayam portal as well as drop a mail to me at kmohanty@iitg.ac.in. I shall be happy to
answer and in the next class that is the third of the module 4 we will be discussing about
hybrid methods and the role of pretreatment in a biorefinery concept. Thank you very much.
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Lecture 12
Hybrid Methods
Good morning students. Today is lecture 3 under module 4. In this module as you know that
we are discussing about the Biomass pre-treatment. Today we will discuss about the hybrid
methods of pre-treatment and what is the importance of pre-treatment in a biorefinery
concept.
So, based on the drawbacks of single pre-treatment methods researchers have been trying to
combine these methods to overcome the problems and increase efficiency. If you recall one
of my class, I emphasized that why do we basically need a hybrid system; because you know
any process has its own limitations in terms of the efficiency, yield or such parameters,
restricted to maybe 70 to 80% depending upon the type of technology or process it is.
So, in any single step process it is very difficult to achieve a very higher yield and that is the
reason why there are many operations or processes that can be combined together with the
sole aim to increase the yield. So that is how actually the hybrid methods came into picture.
Since many years ago many studies have been carried out by a combination of various pre-
treatment methods.
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Combinations of one or more pre-treatment methods to improve the pre-treatment process
may be a possibility to find process designs that will be suitable for enhanced fractionation of
the raw material. This could be for instance, to yield process streams which are optimised for
hemicellulose while others streams are optimised for other compounds.
The implementation of several different pre-treatment methods comes with an additional cost
if the methods are dissimilar. So cost is a very important aspect when you talk about
commercialization. So that also need to be taken care of. So, it would not be advisable to
apply widely different pre-treatment methods. Nevertheless, pre-treatment is commonly
preceded by size reduction step which can be regarded as a mechanical pre-treatment. If the
size reduction is Thorough.
The reverse operational procedure is also a possibility. Now Microwave and Ultrasound
technique in combination with other pre-treatment techniques such as pre-treatment using the
deep eutectic solvents, acids, alkalis (these are all that we have discussed in our last class)
have been widely used as a part of the hybrid process of pre-treatment. Please understand that
this is whatever written here, the hybrid is not only restricted to this. There are many numbers
of studies. We will just discuss few of them to get an idea about actually a how and why this
hybrid processes have been adopted.
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So, we will see the microwave-assisted method, which is one of the most common and a low-
cost method and faster process also we will discuss that. So microwave technology can be
combined with other pre-treatment technologies to increase the efficiency of the process. So,
Microwave Technology has been successfully applied along with deep eutectic solvents pre-
treatment, DES, Alkali pre-treatment and acid pre-treatment usually dilute acid pre-treatment.
Let us have a look at this hybrid technology application in the switchgrass, corn stover and
miscanthus feedstocks. Microwave technology combined with the use of DES pre-treatment
was applied to ultrafast fractionation of switchgrass, corn stover and miscanthus feedstocks.
The combination of Microwave irradiation and ChCl and lactic acid over only 45 seconds
resulted in a highly effective lignin and hemicellulose removal and left the cellulose intact.
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Please understand it is very faster process 45 seconds only. Now this kind of pre-treatment
allowed the removal of more hemicellulose than lignin. Additionally, microwave
significantly improve the efficiency of the pre-treatment by DES. So overall we can say that
it is an excellent hybrid system.
So, the electromagnetic field of microwaves led to the breakdown of the biomass structure
mainly due to molecular collision caused by dielectric polarization. In addition, microwave
radiation increases the molecular polarity of DES which enhance the efficiency of the pre-
treatment. Pre-treated biomass showed a 2 to 5, fold increase in digestibility during
enzymatic hydrolysis in comparison to the untreated feedstock.
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Now, please have a look at this particular schematic of the microwave assisted DES pre-
treatment. So, this is the lignocellulosic Biomass whatever it can be miscanthus, corn stover
whatever we have discussed, switch grass. So, then it has been put it under a microwave
reactor. Along with that DES in different concentrations of course because you need to
optimise it, the process parameters.
So, you can see within 45 seconds they have degraded and result into 2 two different
fractions. So, one fraction is basically pre-treatment liquor which is thick, viscous and brown
in colour this colour. And then another one is the solid residue. That solid residue basically
contain glucose and Xylan; basically you can say that it contains your carbohydrates. And
this part which is dark in colour it contains lignin mostly.
But depending upon the efficiency of the process. It will always happen that some of the
carbohydrates remains here and some of the Lignin also remains there.
So, microwave technology combined with acid pre-treatment. So, one application is in with
Jabon tree Biomass. So, Microwave with the presence of the acid, intensified the
decomposition of biomass during the Jabon tree pre-treatment which allowed obtaining
higher yield of sugars. Despite the increased efficiency in removal of Lignin with the time of
irradiation the formation of side products occurs, which affected further processing.
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Then a microwave combined with alkali pre-treatment. Application in brewers’ spent grains
(BSG). So, microwave assisted alkali was found as the most effective pre-treatment among
others studied techniques such as your steam explosion, Ammonia fibre explosion, then dilute
acid, organosolv used for reducing sugar production by enzymatic hydrolysis of brewers
spent grains that is called BSG.
After treatment with the combination of Microwave and alkali the surface of the BSG
increase due to disruption of the structure of the investigated material which resulted in larger
sugar yield in comparison to the use of the other pre-treatment methods.
So, the process is described here in brief. So, a domestic Microwave with the maximum
output power of 800 watts was employed for this purpose. 1% weight by volume biomass
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was loaded to 0.5% Sodium Hydroxide weight by volume in a stoppered flask and subjected
to microwave irradiation at varying power settings of 400 watts, 560 watts and 800 watts for
different residence times varying from 30 second, 60 seconds and 120 seconds.
Please understand again I am telling you that the microwave techniques at superfast
techniques. It is very faster than any other pre-treatment processes, even if you are combining
two processes or talking about a single process also. After pre-treatment the Biomass
thoroughly washed with distilled water till pH 6 and dried in air. The dried solid Residue was
used for enzymatic hydrolysis and composition analysis because the that dried solid residue
contains most of the carbohydrates.
Comprehensive studies on the effect of microwave alkali pre-treatment on the crystallinity
index, specific surface area and morphology of BSG were also performed by Kan et al. This
particular publication has been referred here. So, it is an interesting work. So those who wish
to read more can please refer to this particular citation, which is given below. So, it was
shown that the pre-treatment of BSG caused removal of Lignin from the feedstock structure
and significant growth of the specific surface area from 9 m2
/g for raw Biomass to 162 m2
/g
for treated samples. A huge surface area increase.
The treatment of the investigated samples with alkali in the presence of microwave assures
effective removal of hemicellulose and Lignin from the lignocellulosic materials. However,
the presence of a large amount of sodium hydroxide resulted in degradation of the crystalline
and part of cellulose, while the high microwave power and extended treatment time led to
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degradation of the organic fraction of cellulose which reduced the efficiency of further
processing.
So, we will see the systems this hybrid process application in Cassava stem hydrolysis. So,
similar observations were noted for combined microwave alkali pre-treatment of cassava
stem for sugar production which depended on reaction time, base concentration, solid to
liquid ratio and microwave frequency. So, microwave frequency was found to be the most
significant factor affecting the sugar yield.
And the importance of other parameters decreases in the following order, reaction time, solid
to liquid ratio, base content. So, the authors have varied basically the 4 different types of
parameter. The first one is of course the microwave frequency which was found to be the
most important parameter that is affecting the sugar yield followed by the others like reaction
time, solid to liquid ratio and the base content. So, Microwave with alkali treatment increases
the crystallinity index of cassava stem removing all its amorphous parts.
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And now we can discuss the comparison of acid and alkali assisted microwave pre-treatment
in cassava bioconversion. So, you have seen the individual processes clubbed with
Microwave. Now, we will discuss about the comparison. So, the methods of microwave pre-
treatment with alkali and Microwave with acid were compared for efficiency in cassava
bioconversion. In both methods the microwave power and the process time were indicated as
the main factors providing high efficiency of the initial treatment.
It was exhibited that the yield of Sugars during enzymatic cassava hydrolysis was 52% higher
after microwave-assisted Sodium Hydroxide treatment in comparison to the microwave
assisted sulphuric acid treatment. Differences in the performance of two types of pre-
treatment results from the presence of inhibitors of enzymatic hydrolysis, which are
generated during the microwave acidic method.
In general, the acid solubilizes the hemicellulose whereas the base solubilizes lignin. So, this
the mechanism. And the application of microwave is only intensifying the chemical
processing.
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Now we will discuss about the ultrasound assisted methods. So, ultrasound technology can be
combined with other pre-treatment technologies to increase the efficiency of the process.
Now Ultrasound Technology has been successfully applied with ionic liquids pre-treatment,
alkali pre-treatment and enzymatic pre-treatment. For your information I am telling you can
read little more about ultrasonication processes. In a nutshell I am telling you that this is also
one of the very good technology or the process which is also a faster process compared to
other such pre-treatment processes. And it is also low cost.
We will see the ultrasound Technology combined with IL’s treatment in its application in the
sugarcane bagasse and wheat straw. So, ultrasound combined with the ionic liquids
effectively improve the process of saccharification of sugarcane bagasse as well as wheat
straw. Ionic liquids by forming hydrogen bonds with cellulose disrupted its crystalline
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structure while ultrasound treatment through the mechanical effect opened the biomass
structure and intensified the chemical interaction of the ionic liquids.
The combined method significantly improves the efficiency of enzymatic reduction of Sugars
compared to Biomass treated only with ionic liquid.
So, we will see in brief the process how it was carried out. So, 1 gram of biomass anything
either bagasse or wheat straw was dispersed in 20 grams of ionic liquids (so, in this case the
[Bmim] Cl or [Bmim] OAc) in a double jacketed beaker. Sonication was performed by a
single frequency counter current flow ultrasound reactor. The sonication system was operated
at 5 frequencies 20, 28, 35, 40 and 50 kilo hertz.
Five different probes with diameters of 1.34, 3.61, 3.05, 2.03 and 1.05 (cm) were used for the
frequencies of 20, 28, 35, 40 and 50 kilo hertz respectively. After completion of the reaction
2 volumes of deionized water were added to the reaction mixture. The mixture was stirred at
600 RPM by using a magnetic stirrer and filter under suction to remove as much liquid as
possible. The filtered biomass was soaked in ethanol, filtered again, washed 3 times with
deionized water, dried to a constant weight and kept further analysis.
So, this is a nut shell I just told you about the process how ultrasound-assisted ionic liquid
pre-treatment method was carried out. So, one beautiful thing about the entire hybrid system
is that as you know that there are so many different types of ionic liquids available or one can
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tailor make ionic liquid in the lab. So, as I told you in the last class you need to take a cation
and you need to take anion and fuse them together to obtain a ionic liquid.
So, if you can study the chemistry little more - chemistry of the Biomass, its structure and all,
so then we can understand that what type of ionic liquid will be better suited for that
particular biomass. So, with that type of study we can include those for doing the
experimentation with ultrasound-assisted ionic liquid pre-treatment.
Now, the next one is ultrasound Technology combined with enzymatic hydrolysis. So we will
discuss its application in peanuts shells, coconut shells and pistachio shells. The mechanical
effect of ultrasound treatment on the Biomass structure and intensify the Sodium Hydroxide
performance during the combined pre-treatment of peanut shells, coconut shells and pistachio
shells before enzymatic hydrolysis to sugars.
Ultrasound enhance the rate of the delignification by morphological changes caused by
intense turbulence and shear effects. In addition, ultrasound created free radicals in water
taking part in the cleavage of Lignin and Xylan structure. The use of this combined process
besides intensified delignification reduce the time of the process and the amount of alkali
leading to the higher sugar yield.
As such this was proved to be a very good hybrid process. It has resulted in a more
delignification. It has reduced the time of the entire process and the amount of alkali that is
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being used earlier, or if you compared to the single alkali pre-treatment process so thereby
resulting in a higher sugar yield.
This is the experimental setup for ultrasound assisted alkaline pre-treatment in 100 ml batch
reactor. This is a reactor simple reactor chemical reactor. So, this is the ultrasound generator,
and this is the ultrasound gun or probe whatever you can say. This is the reactor and this is a
jacketed reactor - you need to cool it in case the heat is evolving, and it is a stirred reactor.
Stirring will further enhance the mass transfer or the rate of reaction. And it is a simple
system and can be done in lab easily.
Now we will discuss about the comparison of the ionic liquid and alkali assisted ultrasound
pre-treatment for eucalyptus. Wang et al compared the effect of the ultrasound-assisted ionic
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liquid and alkaline pre-treatment methods on the structure and chemical composition of
eucalyptus and the yield of its enzymatic saccharification. It was found that ultrasound in
combination with ionic liquid was much more efficient in the delignification process while
ultrasound in combination with alkaline was a more efficient in removal of the hemicellulose
from the eucalyptus structure.
So, in addition ultrasound combined with ionic liquids remove the amorphous fraction during
the pre-treatment more effectively than alkali combined with ultrasound. As a consequence,
higher yield of Sugars could be obtained in the first case that means ultrasound followed by
ionic liquids.
So, we will see some of these results which are reported in Literature and I have tabulated
here. The reference is given here from where this table have been taken. These are some
selected examples where studies concerning the applications of the combined methods or
hybrid method. So, all type of biomass, the different treatment method, the chemicals that are
being used, then the predetermined conditions very important - this last class also I discussed,
again I am telling so this is actually very important. You need to optimise the process
parameters. You need to vary the range of reaction time or residence time, the temperature -
if at all it is there, the amount of chemicals you’re using, the amount of energy, the type of
solvents, all these things are there and the efficiency of the processor. Let us see one thing we
have not discussed about this one Jabon tree craft pulp.
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So, it is a microwave of almost 1000 watts plus acid, in which they have used only 1%
sulphuric acid and the conditions are - temperature 180 degrees centigrade, 190 and 200
degrees, that is what they have varied, three different sets of temperature and three different
sets of residence time 5 minutes, 7 minutes and 10 minutes. So, the result is very interesting.
So optimal temperature they found it is 190 degrees centigrade and reducing sugar yield
increases of around 40 grams per 100 gram of dry pulp, which is a good yield.
Please understand the yield of sugar is directly related to type of biomass because first of all
every Biomass are distinct in their composition. So, if the carbohydrate fraction is more, then
we are going to get more sugar. And if the lignin is more, compared to carbohydrates, the
reducing sugar yield will be of course less. Let us move ahead.
There are many I have listed here. So, if you see this sugarcane bagasse, wheat straw which
was ultrasound with ionic liquids. So, they have used 20 - 50 kilo hertz, in that range they
have varied. 1-Butyl-3-methylimidazolium chloride (Bmim Cl basically) and they have used
also Bmim Acetate (OAc) and the temperature is 80 degrees centigrade, time of residence is
30 minutes. So that is again in this case that are optimised.
So, they have put that optimal condition 30 minutes, 80 degrees centigrade, 20 kilohertz and
with the glucose yield of 40% and 53% for bagasse and wheat straw respectively, which is
again very good in terms of glucose yield. So similarly, there are so many things as listed
here. So, what I request is that you can please go through all these things.
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We are still continuing; these are some of the more different types of hybrid treatments given
here. So, corn stover Biomass alkaline oxidative treatment (AlkOx it is called). So the
chemical used is 10 molar sodium hydroxide, along with the hydrogen peroxide. Temperature
is 60 degrees centigrade, time of residence is 5 hours; so it takes long time. So, it was found
that combined method dissolves 93.4% and 83.5% of Lignin and hemicellulose respectively,
which is a very good result.
Now then ultrasound followed by AlkOx (sugarcane bagasse), then steam alkali pre-treatment
(debarked white birch chips), then steam and hydrogen peroxide combined (sugarcane
bagasse). Now we have discussed certain hybrid pre-treatment technology in today's class.
There are many, everything it is not possible to discuss in a single class and is also out of the
scope of this particular course. So the idea is to make you understand that how the hybrid
processes works and it is always not true that you can just combined two any different
processes and a look for that.
You can do some experiment to find out which is good or which is bad but there should be
some theoretical understanding that which particular two different pre-treatment methods
should be combined and why and how they will be combined. So, I hope you get an
understanding about the different hybrid processes.
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So, we will just discuss briefly about other combined treatment methods. So, alkaline pre-
treatment combined with mechanical extrusion. So, as mentioned earlier the alkaline pre-
treatment method is one of the most commonly used methods for pre-treatment of
lignocellulosic materials. However, alkaline treatment combined with mechanical extrusion
enhance noticeably the removal of Lignin and hemicellulose from the corn stover structure.
The use of a combined mechanical alkaline method increases the yield of Sugars by about
25% in comparison to the yield obtained after alkaline treatments only.
Both methods ensure destruction of the corn stover structure. The combination of mechanical
and alkaline treatment allows for not only disruption of the recalcitrance of the Biomass
structure, but can also be useful in further processing.
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Alkaline pre-treatment in the presence of hydrogen peroxide. It is called AHP. So AHP is an
oxidative pre-treatment process. It acts in the delignification of the lignocellulosic Biomass
which allows a greater efficiency to be achieved in the recovery of Sugars in the liquid phase
of enzymatic hydrolysis since the presence of Lignin makes it difficult for the enzymes to
attack the substrate.
The hydrogen peroxide is very unstable in alkaline conditions and decomposes very fast. So
that generate hydroxyl radicals and superoxide it can result in an increase in the efficiency of
delignification of biomass. The effectiveness of the alkaline pre-treatment with hydrogen
peroxide depends on the reaction conditions such as the amount of biomass to be treated,
time, temperature and concentration of peroxide and base.
This type of pre-treatment has low energy consumption and does not generate inhibitors like
hydroxymethylfurfural and furfurals. So, this is one of the best take-home-message from this
particular AHP study, that, they do not generate the inhibitors; because this inhibitors HMF
and furfurals and then some other intermediates they have a very bad effect on the further
fermentation process.
So, we will see its application in corn straw and gooseweed. The use of a combined sodium
hydroxide and hydrogen peroxide pre-treatment (the AHP pre-treatment) of corn straw result
in the removal of 93% of Lignin and 83% of hemicellulose from the structure of the raw
material. Effective treatment of the main components of lignocellulose during the enzymatic
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hydrolysis allowed the achievement of 61% conversion of cellulose to glucose and 69%
conversion of hemicellulose to xylose.
And on the other hand, alkali and hydrogen peroxide did not make any difference to sugar
yield obtained in Gooseweed pre-treatment before bioethanol production. Combined sodium
hydroxide and hydrogen peroxide treatment released an equal amount of sugar in comparison
to the use of the alkaline pre-treatment method. Therefore, the researchers have indicated that
it is more economically justified to use only an alkaline pre-treatment method.
So, the next combined method is sequential acid and alkaline pre-treatment. This is a very
interesting study reported in Bioresource technology, the reference is given if you are
interested to learn more in detail, please refer and read. So, a combination of dilute acid pre-
treatment with alkaline pre-treatment makes the removal of hemicellulosic Sugars and Lignin
from the lignocellulosic Biomass possible in order to enhance their enzymatic digestibility
and fermentability.
Most processes involve the use of dilute sulphuric acid pre-treatment with subsequent
alkaline Lignin extraction using Sodium Hydroxide followed by further enzymatic digestion
and fermentation. Besides sulphuric acid and sodium hydroxide, sequential hydrochloric acid
and lime pre-treatment has also been applied to corn stover achieving maximum glucose and
xylose yields of 89.5% and 97% respectively with the cellulase doses of 10 filter paper units
per gram of substrate.
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So, the solid material that is resulting out of the sequential pre-treatment shows a higher
crystallinity index, as the amorphous contributions from hemicellulose and Lignin were
removed. In addition, depending on the severity of the alkaline treatment cellulose
crystallinity is decreased due to the polymorphic transformation of cellulose from type 1 to
type 2. This phenomenon results in higher enzymatic digestibility of cellulose rich material.
So, these are the process conditions and the schematic. So Biomass is (subjected to) a process
standard acid hydrolysis. So, you get pentoses or the C5 sugars. Then the acid treated bio
masses is being send to a alkaline extraction system where you get actually Lignin as the
bottom or the product which are there in the liquid fraction and you get the crude cellulose in
the solid fraction. So, this is the different process condition.
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So here the authors actually have studied four different types of biomass. First one is soybean
husk, second one is oil palm empty fruit bunches, third is Pinus species straw and the fourth
one is Eucalyptus straw. Now a different process conditions both for Acid hydrolysis and
alkaline conditions are given here. So, you can have a look later on.
So, the applications of this particular technology and its result we will discuss. Some
investigation evaluated sequential alkaline acid pre-treatment. The sequential alkaline and
acid pre-treatment using a 14.49% solid to liquid this yield was applied to corncobs. The
maximum reducing sugar yield obtained after enzymatic hydrolysis of the cellulose rich
material was 0.99 gram per gram.
In another study on cotton stalks first applied on alkaline pre-treatment removing 52.48% of
the lignin with sugar loss of 3.5 %. A subsequent 2 stage dilute acid treatment using sulphuric
acid of the delignified Biomass release 29.4 grams per litre of sugar, 63.5% Hollocellulose
hydrolysis in the hydrolysate along with 2.18 and 1.32 grams per litre of phenolics and
furfurals respectively.
Again, you see that there are some inhabitance and that is being resulted which is actually not
warranted. We are always supposed to develop pre-treatment processes in such a way that
one of the aims is to get rid of these inhibitors.
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So finally, detoxification of the hydrolysate by over liming and adsorption with activated
charcoal reduce the furfurals and phenolics. To remove the formation or to reduce the
formation of this inhibitory compounds like these furfurals, activated charcoal adsorption was
used and it resulted in a good removal of this furfurals and phenolics. However, in sequential
alkaline acid process, considerable amount of hemicellulose is removed together with lignin,
resulting in a loss of fermentable sugars as the Lignin present in the Black Liquor inhibits
microbial metabolism and Xylose consumption.
So, 2 different references have been listed here. So those who are interested to read more
these are classic studies and very good results, so please refer to them.
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So, finally we will see the comparison of an acid, alkali and hybrid acid alkali what we have
discussed in a nutshell. So, you can see this mild acid biomass pre-treatment, Alkaline
industrial pulping process, and Sequential acid and alkaline based pre-treatment. So, these are
the advantages given here and these are certain disadvantages. So, in the case of mild acid
biomass pre-treatment the advantages are high recovery yields of each Biomass production,
possibility to use all Biomass fractions, low energy demand, low chemical cost, low
concentration of toxic compounds. And there are certain disadvantages long processing time,
two processing steps required to recover the three main biomass constituents, and greater
equipment requirement to handle the corrosive environment, and more research demands to
enhance the whole process, more research also demanded to enhance the utilisation of the
Biomass constituents.
Then let us talk about the alkaline industrial pulping process. So short processing time,
simple processing steps, efficiency in obtaining cellulose pulp and defined processing
technology are some of the advantages. Now if you talk about the disadvantages, then it is
highly concentrated processing media, low yields of cellulose, high volumes of liquid
residue, generation of polluting residues and high production of toxic compounds.
Now let us understand the sequential acid and alkaline biomass pre-treatment. So, recovery of
hemicellulose, Sugars, Lignin and cellulose with greater efficiency is one of the advantages.
Then enhanced enzymatic digestibility, and fermentability. But there are few disadvantages
also which are additional processing steps, more research demands to enhance the entire
process and more research also demands to enhance the utilisation of biomass constituents.
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Now will discuss about the role of pre-treatment in the biorefinery concept. We have already
discussed in a nutshell, that how the pre-treatment and why the pre-treatment is required, we
will discuss in a biorefinery concept. A biorefinery can be defined as the renewable
equivalent of a petroleum refinery. The main differences being raw material. In the
biorefinery biomass can be converted into a wide range of chemicals and energy carriers.
And it can also contribute to the development of a circular economy. The concept is based on
the model that lignocellulosic materials which were used to generate bio-based products can
be recovered to a certain degree and be recovered and recycled. The International Energy
Agency, Bioenergy Task42 defines biorefining as the sustainable processing of biomass into
a spectrum of marketable bio-based products, Chemicals, material etc and bioenergy. So, it
can be biofuels, power and heat.
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So, if you see in a nutshell that this is a schematic representation of a biorefinery for
production of energy carriers and chemicals. So, you see that lignocellulosic crops or
lignocellulosic waste, it can be Municipal solid waste also are pre-treated, followed by
hydrolysis. So, we get 3 different fractions. So, the first fraction is rich in Lignin content, the
second is rich in C6 sugars, third is rich in C5 sugars.
So, they can be further processed and fed to different reactors, or let us say further processed
either thermochemically or biochemically or physico-chemically to get different products
such as biodiesel, Methane and hydrogen, ethanol certain chemical building blocks, food and
feed, Polymers and resins and other biomaterials.
So, some important considerations have been suggested for the biorefinery concept to
become a path forward towards a less Fossil dependent society. The development of
biorefineries is a vital key for integration of food, feed, Chemicals, fuels and energy
production in the future. Combinations of physical and biotechnological processes for the
production of proteins but also for platform chemicals such as lactic acid will be of
importance in the future.
That is most important thing. We have been discussing this during our many lectures that a
biorefinery will become sustainable if at all we will recycle and reuse the waste that is getting
generated. Second, most of the by-products when they are converted into some valuable
products must be marketable. And there should be acceptability by the people also. There are
so many things we have discussed during biorefinery.
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So, Biomass can mitigate to some extent the high atmospheric levels of carbon dioxide by
replacing fossil fuels. So, this precisely is telling that Biomass sources are carbon dioxide
sequesters. So, they help in carbon dioxide sequestration. In addition, in many countries
around the world the concept may be important to secure domestic energy carriers and the
supply of chemicals. Most lignocellulosic feedstock is generally much more Complex and
recalcitrant than the currently used starchy materials, for example, the ethanol industry,
which poses a great challenge.
One of the major challenges that the biorefinery concept faces to become successful is to find
suitable raw material. It is likely that second grade or waste material will be the main raw
material supply in a biorefinery. When we discussed about the Biomasses for biorefinery we
have discussed about the waste material and different lignocellulosic materials. So this
includes straw, bagasse, tree root, branches, forest thinning etc. to name few, there are many
more.
However, large part of the published research that deals with Woody materials are often
based on wood chips of high quality. Now this wood chips even including the wood sawdust
also having a huge commercial value. So, when you talk about using them for converting in
Biorefinery perspective to other valuable products. So, there is a challenge to it. So, this is in
direct competition with, e.g., the interests of the pulp producers. This is what I was just
mentioning because the pulp producers need more than in a biorefinery.
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Because it has a direct commercial value, well-established marketable end product. So, on the
other hand the residue from agricultural operations are in so many cases available for
conversion to other valuable products and are not at all in high demand. So thus, it calls for
very robust and versatile production methods to be able to handle raw materials of different
origin. It is not likely that a biorefinery will be capable of processing all sorts of
lignocellulosic materials.
Now till today. We understand that a single biorefinery, unless and until fitted properly with
robust and versatile production method and technologies, it cannot process multiple
feedstocks. And unless and until multiple feedstocks are processed a biorefinery cannot be
sustainable.
So, the purpose of the Biomass pre-treatment step somewhat shifted during the last decades.
Previously the main interest was to use lignocellulosic materials mainly for bioethanol
production. If you go back to some 10-15 years back researches, you will see that whatever
pre-treatment methods were being studied and reported all are aimed to get C5 and C6
Sugars. Mostly C6 sugars convert them to glucose, then convert them to and then process
them in a ethanol platform to get bioethanol or sometimes may be biobutanol.
Now since few years there is a change in this attitude that researchers have looked for pre-
treating the Biomass for other thermochemical conversion processes, whether it is a pyrolysis
or whether it is gasification. So today it is of great importance to find ways to maximize the
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overall yield of the valuable compounds that make up lignocellulosic materials. Pre-treatment
methods that enable efficient recovery of Carbohydrates as well as lignin are desired.
However, this all depends on the situation and the final product. The energy requirement in
the production processes must be met under any circumstances either by internal or external
integration of high energy streams, such as in a mill producing pulp where the excess Lignin
is the main process energy supply.
So pre-treatment is a step that is included as one of the first steps in the process to elevate
access to the raw material. It is difficult to define the best pre-treatment for all situations and
raw materials. However, it is vital that some important features of the pre-treatment methods
are fulfilled, such as high recovery of the individual Polymers and other compounds in the
lignocellulosic materials. In addition, the formation of toxic or inhibiting compounds must be
low (as low as possible) to decrease the risk of negative effects in the enzymatic hydrolysis
and fermentation steps if they are part of the process.
It is not true that always they will be a part of the process. If you are talking about
thermochemical conversion after the first treatment, then you do not have to worry about this
particular formation of toxic inhibiting compound. It is well known that too severe condition
during pre-treatment because greater degradation of hemicellulosic sugars which can cause
formation of highly toxic compounds such as furfural, HMF and other organic acids.
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The energy requirement is another most important aspect of the entire pre-treatment process.
It must be as low as possible. So, it is also an advantage if energy integration between the
pre-treatment step and other parts of the production facility can be implemented, such as
utilisation of a low-grade steam for distillation purposes. It has also been established that
economic success of a biorefinery is heavily dependent on the solid content of the pre-treated
materials.
So, if too dilute solutions are produced, the energy cost for purification may be prohibitively
very high which can cause an otherwise well-functioning treatment method to be discarded.
So, it is very important that if your pre-treatment processes have resulted in a too much of
dilute solution, then that dilute solutions will be full of aqueous part or water rich part. You
need to purify your sugar.
So that is the downstream processing part, that part will take on almost 40% of the entire
product cost (40 to 45%). So, you need to decrease that. So that is why if the solid content is
more in the resultant product then it is always good.
So effective pre-treatment of available lignocellulosic Biomass contribute to the generation of
sustainable biorefineries and the decrease in Environmental impacts caused by organic waste
disposal. The polysaccharide fractions of lignocellulosic biomass, including cellulose and
hemicellulose can be broken down into sugar monomers. They are then converted into
biofuels, biogas and biochemicals through bio technologies such as an anaerobic digestion
and fermentation.
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Efficiency and cost effectiveness of the bio conversion process depend on the transformation
of polysaccharides to monomers sugars. Commercial applications of lignocellulosic biomass
are hindered by the resistance of polysaccharides into hydrolysis, and the presence of
recalcitrant Lignin.
So, a range of pre-treatment methods have been developed and employed to increase
conversion efficiency. The pre-treatment of lignocellulosic biomass aims to decrystallise
cellulose structure through lignin removal, increase the cellulose and hemicellulose solubility,
increases accessible surface area to enzymes and Chemicals and minimises the loss of sugars.
So, the anticipated end products also determine the choice of pre-treatment method as each
method induces different effects on different types of lignocellulosic biomass.
Various by-products generated through this processes can be recovered and utilised for other
by biochemical productions. The success in identifying and applying effective pre-treatment
to lignocellulosic Biomass can increase the socio-economic impacts and resolve the global
problems involving sustainable energy and development.
So, with this I conclude today's lecture. So, we have completed this module 4 in which we
have discussed about the pre-treatment methods. The next module this module 5 we will be
dealing with physical and thermal conversion processes and the class 1 and lecture 1 of
module 5 will discuss about the types, the fundamental principles, equipment and
applications of thermochemical conversion processes. So, thank you very much if you have
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any query, please register your query in the Swayam portal or drop a mail to me at
kmohanty@iitg.ac.in, thank you.
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Module 05
Lecture-13
Physical Processes
Good morning students, today is lecture 1 under module 5. And under module 5 we will be
discussing about the physical and thermal conversion processes. In today's lecture, we will
discuss about the physical conversion of biomass. So, let us begin.
There are numerous aquatic and terrestrial virgin biomass species and many types of waste
biomass that are potential fuels or feedstocks. With the exception of microalgae and some high
moisture content biomass, essentially all are solid materials. Now some of the compositional
differences already exist and we have discussed that also in some of our earlier classes.
So, the aquatics, municipal bio-solids, and animal manures are high in moisture content. The
terrestrial species contain relatively small amounts of moisture. On a moisture and ash free basis
the heating value of most biomass is in the same range, but on a dry basis, these materials can
exhibit wide variation. Because of these broad differences, many of the possible feedstock
process energy product combinations are not feasible.
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So, such feedstocks do not support self sustained combustion under conventional conditions
unless the moisture is reduced by a considerable amount, a high cost process in wastewater
treatment plants. Bio-solids are more suited for microbial conversion in aqueous systems, where
a liquid water medium is essential. In contrast, woody biomass is often suitable for direct use as
a solid fuel or as a feedstock for thermochemical conversion (such as pyrolysis, gasification
which we are going to discuss under this module). The physical processes are employed to
prepare biomass for use as a fuel or as feedstock for a conversion process. The processes
examined are dewatering and drying, size reduction, densification and separation. So, these are
the things which we are going to discuss under the physical conversion of biomass today.
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So, first let us understand about the dewatering and drying. So, dewatering and drying the basic
difference between these 2 is that in the first case that is in dewatering, it is basically the removal
of all or part of the contained moisture from biomass as a liquid. And while drying, it is the same
thing except that the moisture that is getting removed is removed as vapour. So, open air solar
drying is the one which is very much in practice in most of the countries to process biomass.
So, that is the low cost drying method and can be used. So, raw materials that are not sufficiently
stable to be dried by solar methods can be dried more rapidly using industrial dryers, such as
spray dryers, drum dryers and convection ovens if cost permits. Here the cost is basically the
equipments are not so costly, the cost is the energy costs. The key biomass property that should
be obviously examined in addition to conversion process requirement is the moisture content of
the fresh biomass.
The method available for its partial or total removal and the effects, if any on the properties of
the remaining biomass. So, moisture content, the amount of moisture present in the initial phase
of the biomass when it is getting procured is of utmost important. Because that is finally going to
decide about which conversion process you are going to use, and what will be the resultant
product.
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So, the moisture content of biomass is as variable as the multitude of biomass species available
as potential feedstocks.
The water content in the untreated municipal bio-solids is high because of the nature of the
collection system. That is dilution with water to facilitate localized disposal and transport in
municipal lines to wastewater treatment plants that is what is being practiced in all municipalities
across the world. So, in the table 1, some of the species are mentioned along with their water
content.
Aquatic plants, you can see almost 95%, untreated municipal bio-solids also 95, farm animal
waste 80%, terrestrial biomass 40 to 60%, agricultural crop residues 15%, municipal solid waste
30%. The terrestrial biomass is considered as a potential biomass and it includes most
herbaceous species, softwoods and hardwoods. The agricultural residue that have been exposed
to open air solar drying contain less moisture content. Straws are good example of this particular
process. These potential feedstocks include most herbaceous species, softwoods as well as
hardwoods.
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About one half of the solar energy falling on the leaves supplies the energy to facilitate
transpiration which is necessary for the photosynthesis to occur. Wood also absorbs moisture
from humid air and is equivalent of an elastic gel that exhibits limited swelling as water vapor is
taken up from the air. Two different mechanisms are operative: one is adsorption; another is
absorption.
In adsorption moisture is transferred from air to the wood surfaces and results from the attraction
between polar water molecules and the negatively charged surfaces of the wood. The negative
charges involve functional groups on the surface that can carry full or partial negative charges or
organic molecules that can exist as dipoles with the negative ends clustered on the surface. The
amount of moisture adsorbed on wood surface is relatively small, it ranges up to about 5 to 6
weight percentage of that wood at 20 degrees centigrade and 100% relative humidity.
So, I was talking about this here you can see that functional groups. Now functional groups are a
certain type of groups that are present on any surface. So, any material you can say whether it is
a living material, nonliving material and in most of the applications. Now I can tell you a
classical example of a membrane or even a catalyst. So, I can make a membrane - tailor make
basically - So, that means for a particular intended application, so let us say I want to remove
some cations or anions from a particular aqueous stream. So, I will use a membrane which is
doped with or let us say which is fused or topped with certain functional groups of negatively
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charged ions. So, if I want to remove cations, I can have anions, if I want to remove anions I can
have cations, in that way.
So, basically it will attract negative charges attracts and then it will be retained on the surface of
the membrane, other low molecular weight compounds and solvents will pass through it.
Similarly, to make a intended and a particular synthesis, chemical reaction or a better yield we
can sometimes dope different functional groups on the surface of a catalyst, so as to increase its
catalytic activity.
So, functional groups can be easily found out by FTIR technique - the Fourier transform infrared
techniques, spectroscopic technique and there are many other analytical techniques also
available.
So, in absorption, water molecules are drawn into the permeable pores of the wood by sponge
like processes due to diffusional and osmotic forces followed by capillary condensation. So, a
large number of fine capillaries in the wood fibres facilitate this. So, you can read a little more
about capillary condensation. So, I can say in a nutshell that how and what happens? So, it is
very predominant when you talk about porous materials - it can be catalyst, it can be membrane,
it can be similar type of materials which contains distinct pores.
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So, let us say, something is getting, adsorbent basically, here we are talking about adsorption and
absorption. So what is happening? Suppose, you are adsorbing some gaseous component on the
surface of the adsorbent let us say, I am just giving an example to understand capillary
condensation. So, it will adsorb on the surface then when you decrease the pressure it can go
inside the pore of the catalyst or adsorbent whatever it is.
So, after the adsorption, you do desorption the reverse of the process, so you decrease the
pressure. Once you decrease the pressure what will happen whatever the material or gaseous
molecules are inside the pore they will try to move out. So, when they will try to move out, so
they will form a meniscus on the surface of the pore, something like this and that is due to
resultant capillary condensation or capillary forces.
So, due to this the rate of adsorption and rate of desorption are quite different, they do not fall on
the same line though ideally they should have; and this is due to capillary condensation
phenomena, so and this process in adsorption is called hysteresis. And so you can read little more
about capillary condensation if you are more interested from any mass transfers books.
So, the amount of moisture absorbed within the woody structure depends upon the pore
diameters and distribution of the capillaries. In spruce wood pulps, for example, the amount of
water vapor absorbed at 20 degrees centigrade and 100% relative humidity is almost about 25
weight percentage. The maximum total amount of water taken up from air at ambient conditions
by absorption and adsorption is about 30 wt% of the wood but can reach almost 200 weight
percentage if the woody is soaked liquid water.
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Dry biomass burns at higher temperatures and have higher thermal efficiencies than wet biomass.
For example, the flame temperatures of greenwood containing 50 weight percentage moisture
and dry wood in conventional combustor that supply boiler heat are about 980 degrees centigrade
and 1260 to 1370 degrees centigrade respectively. Flame temperature is directly related to the
amount of heat necessary to evaporate the moisture content in the wood.
The lower the moisture content, the lower the amount of energy needed to remove the water and
the higher the boiler efficiency. With the exception of suspension firing units for which the
moisture content of the fuel is usually in the 20 weight percentage range, the maximum moisture
content range is 55 to 65 weight percentage.
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Indeed, combustion of biomass containing 65 weight percentage moisture in conventional grate
type systems can result in lowering the adiabatic flame temperature to the point where self
sustained combustion does not occur. Many of the large scale biomass combustion systems for
producing heat, hot water or steam accept biomass fuels containing relatively large amount of
moisture and are operated without much apparent concern for the effects of moisture content of
the fuel on the combustion process itself.
One of the largest biomass fuel power plants equipped with travelling grates operates very well
with the wood chips containing an average of 50 weight percentage moisture. Although a few
initial handling and storage problems caused by high moisture fuel supplies had to be solved.
The fluid bed combustors are excellent systems which are designed to operate with the fuel
having a variable moisture content up to about 50 weight percentage, so they are excellent. So,
they are fluidized bed combustors basically.
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So pre-drying of biomass has sometimes been justified in the past only for the large scale
operations, or where low cost energy is available as waste heat. It is important to realize
however, that the absence of any capability to pre dry feedstock for thermochemical conversion
has sometimes caused severe operating problems, particularly for gasification processes. In one
of the early fluid bed gasification plants fueled with wood chips and sawdust to produce low
energy gas as an onsite boiler fuel, it was very difficult to control combustion.
The industrial gas burners installed in the plant did not function satisfactorily with the product
gas. These problems were attributed to large variations in the quality of the gas caused by
accepting wood feedstock at any moisture content up to 50 weight percentage which in turn
resulted in large swings in gas heating values from about 3 to 8 mega joule per meter cube.
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So, let us now understand the drying methods. The mechanism of water uptake by trees suggests
several methods of drying terrestrial biomass. The most obvious method is to expose biomass to
circulating low humidity air that is heated. So, the final moisture content of the air dried biomass
is usually in the 35 weight percentage range or less. The advantage of this partial drying method
is that it is low in cost, so mostly it is adopted even in commercial scale.
So, that disadvantages are however several, the process is slow and it depends on the local
climate. Some labor is required to arrange the freshly harvested biomass in suitable piles or
windrows to facilitate exposure to sunlight and air circulation and then if there is rain then there
is a big problem. So, forage crops have traditionally been partially dried in open air to this
moisture level. So, they can be removed from the field and stored without significant
deterioration and loss of nutrient value. Solar drying also facilitates densification of hay by
baling.
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There is another technology which is also adopted in large scale in industry, it is called Kiln
drying. So, under this kiln drying controlled conditions is commonly employed to improve the
stability and physical characteristics of lumber products used as materials of construction or for
manufacturing furniture, whereas open air drying is traditionally employed for the curing or
seasoning of tree parts and round woods to be used as fuel.
A kiln drying promotes the removal of moisture by circulating heated air by natural draft or with
fans or blowers through the wood, which is carefully piled in the kiln to promote the drying
process. Heat is transferred from hot air, heated by steam coil supplied by a boiler or from hot
stack gases heated by the burning of waste biomass or other fuels through manifolds. Kiln drying
is rapid compared to the rate of open air solar drying, but it is too slow for some continuous
thermo chemical conversion processes, unless the dryers and storage facilities are sized to handle
the demand for pre dried feedstock. So, essentially the meaning is that when we are preparing a
feedstock for a thermo chemical conversion like biomass pyrolysis, which are large in scale. So,
unless until we have such a similar scale kiln drying, so you cannot supply a biomass to
thermochemical conversion process, the quantity it is required using the Kiln dryer.
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So, this is one image of the kiln drying system or dryer. So, it is rapid compared to the rate of
open air solar drying but too slow for some continuous processes. So, the use of superheated
steam for drying other than burning of some of feedstock as heat source may allow further
improvement in efficiency. The direct heat systems are generally lower in cost than the indirect
heat systems, if commercial drying units are used and these are not very expensive systems also.
So, thermochemical conversion reactors can also be designed, so that incoming fresh feed is
dried to the desired level by heat transfer from the hot reaction products. So, that means this is
essentially talking about the heat that is getting generated from the thermochemical conversion
processes and are basically getting wasted, so some sort of waste heat recovery.
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So, that heat can be used to dry the feedstock which is going to be used in the thermochemical
conversion systems. The simple addition of enclosed drying tunnels for passages of hot air or
stack gases over and through incoming fresh feed can sometimes suffice to reduce moisture to
the desired level and preheat the feed without the need to install the industrial driers.
Note, however, that stack gases from biomass fired boilers contain about 15 weight percentage of
moisture and that temperatures below 250 degrees centigrade only a small amount of additional
moisture can be absorbed before the gas becomes fully saturated. So, this is the equation WG
equals to 2940M by T i minus T 0, where WG is the drying gas weight in kilograms per hour, M
is the water evaporated in kilograms per hour, T i is the temperature of drying gas that is entering
in degrees centigrade and T 0 is the temperature of the drying gas leaving in degrees centigrade.
Now this equation indicates that large fans and motors are required for circulation of the drying
gases when low temperature gas is used as the drying medium. To obtain sufficient heat for
drying purposes, some of the stack gas may have to be extracted upstream of the boiler heat
recovery equipment, which can have an adverse effect on the steam generation. For most
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thermochemical conversion system that process green biomass, a balance is usually struck
among the optimum moisture range that is needed for the conversion, the feedstock demand rate,
the drying requirements, the size of the feedstock storage facility, feedstock stability on storage
and the cost of supplying pre dried feedstock. Whenever it is necessary to remove moisture from
virgin or waste biomass feedstocks, air drying, mechanical dewatering and drying with waste
heat or stack gases should be evaluated first.
So, the entire idea of this discussion is that when you talk about a sustainable bio refinery
perspective, basically whatever the heat that is getting generated from one or the other processes
and are being wasted. So, should not be wasted basically that is what is the message. So, you
need to go for the waste heat recovery systems. There are excellent waste heat recovery systems
that are being designed and are being implemented in most of the petroleum refineries, where the
process streams that comes out is at very elevated temperature and we basically use some
selective heat exchanger type of units to recover the heat. And that heat can again be used for
drying purposes or for something else where the heat and/or energy is being required. Energy is
very important in any process industries that takes the major amount of the cost, one of the major
amount of the cost. So, it is always important that energy whatever it is being getting into wastes
should be recovered and reused.
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So, now let us discuss about size reduction. So, we have understood little about size reduction
during in some of our earlier classes, that we need to reduce size to increase it is surface area and
all. So, let us just quickly glance through the same thing once again in a little elaborate manner.
So, reduction in physical size is often required before biomass is used as a fuel or feedstock.
Size reduction techniques are employed to prepare biomass for direct fuel use, fabrication into
fuel pellets, cubes, briquettes and/or conversion. Now smaller particles and pieces of biomass,
reduce its storage volume, facilitate handling of the material in the solid state and transport of the
material as a slurry or pneumatically and sometimes permit ready separation of components such
as bark and whitewood.
The size of the pieces or particles can be critical when drying is used. Because the exposed
surface area which is a function of physical size, can determine drying time and the methods and
conditions needed to remove moisture. There are a few exceptions where size reduction is not
needed, such as in whole tree burning, but nobody is doing all these things nowadays so, because
that takes more amount of energy to start the burning.
So, particle size should satisfy the requirements of supplying feedstocks to the conversion reactor
and of the conversion process itself. For combustion systems, the combustion chamber and heat
exchanger designs, the operating conditions and the methods of delivering solid fuel and
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removing the ash, determine the optimum size characteristics of the fuel. For thermal gasification
and liquefaction processes, particle size and size reduction can influence the rate of conversion,
the operating conditions of the process and product yields and distributions. Biological processes
are also affected by the physical size of the feedstock. In general, the smaller the substrate
particles the higher the reaction rate because more surface area is exposed to the enzymes and
microorganisms that promote the process.
So, this is one of the application size reduction machine basically, so it is the hammer mill. So,
dry shredders are commercially used for reducing the size of biomass. The most common types
of machines are vertical and horizontal shaft hammer mills. Metal hammers on rotating shafts or
drums reduced particle size by impacting the feed material until the particles are small enough to
drop through the grate openings.
So, hammer mills are commonly used in the MSW, MSW means here municipal solid waste,
MSW processing systems to reduce the size of the components before separation of RDF, RDF is
the refuse-derived fuel or you can say that combustible fraction of the municipal solid waste.
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So, there is another machine which is called a hydro pulper. So, hydro pulpers are wet shredders
in which a high speed cutting blade pulverizes a water suspension of the feed over a perforated
plate. So, you can see this is a tank and which is holding this, this is the extraction plate and
extraction box here, then air plunged seal here, there is a gearbox motor that is rotating actually.
So, the pulped material passes through the plate and then non pulping materials are rejected.
Anything that is mostly you can say that semi-solid form or in a paste form or basically the pulp
that will pass through smoothly through that extraction plate and rest everything will be retained
on the surface of the plate and will be rejected. The action is similar to that of a kitchen waste
disposal unit.
So, the hydro pulpers can also be used for the simultaneous size reduction and separation of the
combustible fraction of the municipal solid waste from the inorganic materials. Experimental
studies have shown that hydro pulpers can also supply good feedstocks for microbial processing
from other biomass. Maintenance cost wet shredders are lower than those for the dry shredders.
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Chipping has been the traditional mechanical method of size reduction to prepare wood fuels for
direct combustion. It is an energy intensive operation, but it does improve bulk density, handling
and transportation cost. So, it is a good technique, now also being widely used. Disc chipping
and hogging at the 2 preferred means of preparing the wood fuels. A hammer hogs with free
swing hammers break the feed into small pieces, whereas knife hogs cut the feed with blades.
So, the 2 way basically either you cut it otherwise you just hammer it. So, the least desirable
option seems to be chipping in the field at the time of harvest, which requires that a power
chipper accompanying the harvester through the field. So, this particular thing is very interesting,
we have discussed this when we discussed about this bio refinery details. So it is always
important that whatever processing of the biomass you are doing you please do at the source, it is
always not possible but it is important for more sustainability. If you do the processing in the
field, then the transportation cost also reduces significantly. Among the other options that can be
considered for producing wood or chunking, billeting and crushing. Crushing is carried out by
passing the stems between 2 or more metal rolls of varying size, at different rotational speed and
the different types of surfaces.
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So, the crushing and brunching of wood may offer significant advantages over chipping, this is a
biomass crusher grinder. So, this technique is flexible and is able to process lengthy stems to
yield bolts of crushed wood that exhibit relatively rapid drying. For reactor feeding purposes,
however further size reduction would be necessary. The feedstock characteristics required for the
combustion or conversion process used determine which of these methods of size reduction
maybe applicable.
Next is the size reduction in using steam explosion. See, we have understood steam explosion in
detail in our one of the last module classes when we discussed pretreatment processes
physiochemical pretreatment processes. So, the treatment of wood chips with steam at elevated
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pressures and temperatures for shorter time periods followed by rapid decompression, this is
what is the principle of steam explosion, changes the physical state of the woody structure by
defibration.
Although some chemical changes occur with the hemicelluloses and lignin in this process, the
particle sizes are reduced and surface areas and pore volume is increased. The commercial
process involves pressurization with saturated steam at pressure to about 7 megapascals. The
process has also been proposed for the pretreatment of lignocellulosic feedstock in the
production of fermentation ethanol because of the large increase in accessibility of the cellulosic
fraction to enzymatic hydrolysis. So, studies on steam explosion suggests that the technique can
be used for several different biomass applications, ranging from modifying the fibrous structure
and particle sizes alone at the low temperatures to a combination of physical and chemical
changes at the higher temperatures.
Next is densification, so baling has long been used to densify hays, straws and other agricultural
crops such as cotton to simplify removal from the field and to reduce storage space and
transportation costs. Baled straw has a density of 70 to 90 kilograms per meter cube at 10 to 50
weight percent moisture content, whereas bulk density of piled straw is about 5 to 15% of this
density range.
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When straws are compressed to form pellets, briquettes or cubes in specially designed dies and
presses the density can be increased to 350 to 1200 kilograms per meter cube. In contrast, dried
wood has a density of 600 to 700 kg per meter cube and a bulk density of about 350 to 450 kg
per meter cube, whereas the bulk densities and densities of wood briquettes are 700 to 800
kilograms per meter cube and up to 1400 kilograms per meter cube respectively.
Biomass densification appears to have the greatest use for upgrading agricultural and forestry
residues that might otherwise be lost, or that require disposal at additional cost. High Density
fabricated biomass shapes simplify the logistics of handling and storage, improve biomass
stability, facilitate the feeding of solid biomass fuels to furnaces, and feedstocks to reactors, and
offer higher energy density, cleaner burning solid fuels that in some cases can approach the
heating value of coals.
The heating value depends on the moisture and ash contents of the densified material, and is
usually in the range of 15 to 17 mega joules per kg. Numerous commercial processes for
production of densified fuels in the form of logs, briquettes, and pellets from a wide range of
biomass provide domestic fuels for space heating, industry uses the pellets and briquettes as
boiler fuels.
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Numerous devices and methods of fabricating solid fuel pellets and briquettes from a variety of
biomass, especially RDF, wood and wood and agricultural residues have been developed and
patented. The pellets and briquettes are manufactured by extrusion and other techniques. A
binding agent such as a thermoplastic resin may sometimes be incorporated during the
fabrication.
A ring die extrusion or a die and roller mill is the most widely used machine type in wood
pelleting, although punch and die technology has been developed. Other types of pelleting
machines include disk pelletizers, drum and rotary cylindrical pelletizers, tablet presses,
compacting and briquetting rolls, piston type briquetters, cubers and screw extruders. There are
so many different types of units are available for doing this densification.
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An exemplary method for production of pellets was developed in 1977. A raw material of
random particle size such as sawdust or wood residue from which rocks, tramp metal and other
foreign materials are removed is conveyed to a hammer mill where particle sizes is adjusted to a
uniform maximum dimension that is about 85% or less of the minimum thickness of the pellets
desired.
The milled product is then dried in a rotary drum dryer to a moisture content of about 14 to 22
weight percent and fed through a ring shaped die capable of generating pressure between 55 to
275 megapascals to afford the desired shape and diameter. The pellet mill die and roller
assembly must be capable of producing sufficient compression within the die to raise the
temperature of the material to about 162 to 177 degree centigrade.
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The products from the mill have a low uniform moisture content, a maximum cross sectional
dimension of 13 mm, a density of 400 kilograms per meter cube and a heating of 19.8 to 20.9
mega joules per kg. It is not necessary to add a binder to the particles, providing the pressure
during the pelleting produces the necessary temperature increase. During extrusion, the lignin in
biomass migrate to the pellet surface and form a skin on cooling that protects the pellet from
shattering and from any rapid change in the moisture content before use. Briquettes are formed
by similar procedures, except the products are usually larger in diameter and length then the
pellets.
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These are images of some of the briquettes. So briquetting is described to consist of subjecting
wood residues containing 8 to 15 weight percent of moisture at a maximum particle size of 0.5 to
1 centimeter to a pressure of about 200 megapascals, which increases the temperature about 100
to 150 degrees centigrade. The major machine types used to manufacture briquettes are impact,
extrusion, hydraulic, pneumatic and double roll presses and die presses that can also be used for
pellet production.
Briquette production rates are 200 to 1500 kilograms per hour for impact presses, but some
models can produce 2000 to 6000 kilograms per hour, 500 to 2500 kilograms per hour for
extrusion presses and up to 5000 kilograms per hour for hydraulic and pneumatic presses.
There is something called a Biotruck 2000, so this is the image of biotruck 2000, so what is this?
This is a unique commercially available system, it is a truck , transportation vehicle, so what it
does? So, it is a moving vehicle of special design, so that continuously perform all the operations
in the field, so it has to be taken to the field. So, from harvesting agricultural virgin biomass to
pellet production.
So, what it will do is that, it will do the harvesting of the agricultural crops as well as at the same
time after harvesting of the cereals and grains whatever the left out biomass straw or whatever it
is , it will convert on the field itself to pellets. So, the operating sequence consists of the
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integration into one machine of continuous crop harvesting, size reduction of about 0.6 mm
pieces, heating the pieces to a temperature between 80 to 120 degrees centigrade using the waste
heat of the engine, and compressing the heated pieces in a toothed wheel pelleting press.
Now this is again very interesting, you can see this using the waste heat of the engine, what
about the heat that is getting generated when the engine is running, that heat is being captured to
do the process. So, no binder is used. The production rate of the pelletized cereal crops is about
8000 kilograms per hour, it is a huge amount. And the bulk density is about 500 to 700 kilograms
per meter cube, so the transportation becomes easy.
So, another unique example of densification is the production of high density, moisture resistant
briquettes from wet wood residues without pre drying or the use of binders. The briquettes do not
disintegrate when wet and retain a maximum of about 40 weight percent moisture after
immersion in water. They are made from wood and bark alone and from mixtures in the pilot
extruder at operating pressures typically ranging from 30 to 50 megapascals at a maximum
surface temperature about around 210 degrees centigrade.
Moisture resistant briquettes were made in tests from the Western hemlock sawdust, a mixture of
50:50 Western hemlock and red cedar sawdust and Western hemlock bark hog fuel, this is just an
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example. So, the feed contains up to about 65 weight percent moisture and must be sized, so that
maximum size is less than 80% of the barrel diameter.
So, let us understand the economical factors or economic factors of the densification process.
The wholesale cost in the United States of wood waste pellets is in the range of 85 to 140 dollars
per ton, so that was in mid 1997. Now this cost range effectively precludes their use as a
feedstock for most conversion processes, and it limits residential fuel applications. The
production cost exclusive of biomass cost is estimated to be about 30 to 60% of the wholesale
cost, and depends on production rates and the amount of processing needed.
For example, in Spain the increase in electric energy consumption required to mill wood waste to
5 to 8 mm sizes is almost totally compensated for by the decrease in electrical energy
consumption during the densification process itself.
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Exclusive of wood cost, the cost of manufacturing densified wood residues in small units
operated by one person is about 22 dollar per ton at a production rate of 1250 tons per year.
Smaller particles in the 2 mm size range can increase production rates by 50% or more, but the
energy cost is excessive. Industrial manufacturing cost in Spain of densified wood wastes
exclusive of wet wood costs are about 30 to 200 dollars per ton at a production rates of one ton
per hour.
So, in Finland the cost of producing straw fuel pellets on farms in small portable pelletizers is
estimated to be about 54 to 84 dollar per ton. Biotruck 2000, described as earlier for producing
pellets or briquettes from agricultural waste in Europe has a production rate of about 8 ton per
hours in the field and cost about 400,000 dollar.
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Now we will discuss about the separation. It is sometimes desirable to physically separate
potential biomass feedstocks into 2 or more components of different applications. So, the subject
is quite broad in scope because of the wide range of biomass types processed and the variety of
separation methods that are used. Examples are the separation of agricultural biomass into
foodstuffs and residues that may serve as fuel or as a raw material for synfuel manufacture.
The separation of marine biomass to isolate various chemicals and the separation of oils from
oilseeds. Now common operations such as screening, air classification, magnetic separation,
extraction, mechanical expression under pressure, distillation, filtration, and crystallization are
often used, as well as industry specific methods characteristic of farming, forest products, and
specialized industries - depending upon your biomass, you need to choose a particular separation
process.
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So MSW, the municipal solid waste, is a complex mixture of inorganic and organic materials.
Efficient separation and economic recovery of the RDF - the refuse derived fuel and the
components that can be recycled is the ultimate challenge to engineers who specialize in
designing resource recovery equipment for the large scale processing of solid waste generated by
urban communities.
One of the first comprehensive resource recovery plants in the world was built in Dade County,
Florida in United States. A brief description of this facility when it was in full scale operation to
recover recyclables and RDF is very, very informative. You can read more by Google searching
the name of the place. The plant was designed to process 2720 tons per day of MSW, but it
frequently processed over more than that, close to 4000 tons per day. And it could process up to
5000 tons per day if only household garbage were received.
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So, it was designed to accept in addition to household garbage, a wide variety of solid wastes,
including trash, garden clipping, trees, tires, plastics, pathological wastes, white goods - As for
example stoves, refrigerators, air conditioners, and industrial, commercial and demolition wastes.
RDF and shredded tires approximately 1000 per day were burned for onsite power generation in
a 77 megawatt power plant and glass, aluminum, ferrous metals as well as materials including
the ash and fly ash were recovered and sold.
The plant achieved a 97% volumetric reduction compared to as received MSW. Only about 6%
of the total incoming MSW remained as unsalable residue and was disposed of in a proper
manner using landfill technology. The plant also conformed to all effluent, leachate, emissions,
noise and odor requirements, so the environmental clearance basically from the environmental
agencies. So, impressive results such as this dependent on the availability and reliability of the
efficient separation methods, this is an very good, classic success story of the MSW treatment.
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Simplified description of the first comprehensive materials recovery facility of its type in the
United States illustrates how one plant was designed to accomplish some of these separations.
The plant called Recovery 1 was built in New Orleans, Louisiana to process 590 tons per day of
municipal solid waste.
The waste was delivered and unloaded at one of the 2 receiving pit conveyers and transported by
conveyers to the first separation unit, a 13.7-meter-long by 3-meter diameter rotating trommel
that contained circular holes 12 centimeter in diameter. So it is a perforated trommel, rotating
trommel. So, plastic and paper bags tumbling in the trommel were broken upon by the lifters.
The smaller and heavier objects such as heavy metal, glass bottles, even some of the plastics, that
fell through the holes were transported directly to a magnetic ferrous recovery station and an air
classifier. So, air classifier is a unit in which air is being used to fluidize the MSW. So, based
upon their density, so they will be separated. The larger and light materials such as paper, textiles
and aluminum containers that pass through the trommel were conveyed to a 746 kilowatt primary
shredder.
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This shredded material was then conveyed to the ferrous recovery station and the air classifier. In
the air classifier a high speed air current blows the light materials out of the top of the classifier.
This fraction RDF which is the refuse fuel consist of shredded paper, plastic, wood, yard waste
and food wastes. The heavy fraction is essentially glass, aluminum and other non-ferrous metals
and some organic material, it was routed to the recovery building for further processing.
A secondary 746 kilowatt shredder system handled oversized bulky wastes without passage
through the trommel. The output was also conveyed to the air classifier where RDF was obtained
as the overhead and the heavy fraction was conveyed to the recovery building. Each shredder
was sized to process around 590 ton of the MSW in about 12 hour to ensure operating reliability.
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Three modules were located in the recovery building, the first module consisted of a vibrating
screen to separate the shredded material by particle size, a drum magnet to separate residual
ferrous material, an eddy current separator to remove the non magnetic aluminum and other
nonferrous metals, and a small hammer mill to further shred the aluminum fraction to increase it
is bulk density.
The output from the first module consisted of the ferrous fraction, the aluminum fraction and a
fraction that contained primarily glass and some non ferrous metals. The glass fraction,
containing some residual non ferrous metal was conveyed to the secondary recovery module
which consisted of a crusher, another vibrating screen, a rod mill and a two-deck, fine mesh
vibrating screen. The glass fraction was then crushed and screened in the second module.
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The smaller fraction was treated with a pulsed water stream that separated the light fraction
which was discarded. The heavier glass fraction was pumped as slurries to the bottom deck of
the fine mesh second screen to separate the larger particles for crushing in the rod mill.
Recycling of the milled material back to the top deck of the fine mesh screen yielded a glass
cullet fraction for further treatment in the third module, and a non ferrous metal fraction which
was removed from the second screen.
In the third module contained a hydro cyclone, a froth floatation tank and a glass dryer. The glass
cullet fraction from the second module was mixed with clean water in the pre float tank to
remove any remaining organic particles, separated from the slurry through centrifugal separation
and froth flotation and conveyed to the loadout building for shipment.
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So, you can have a close look at this MSW processing. Municipal solid waste. So, three things it
has been shown here, first one is the thermal conversion process, second is the biological
conversion, third one is the landfilling. So, look at this thermal conversion process, this is what
we are going to discuss in this module. So, different types of process, incineration, pyrolysis,
gasification and RDF the refused derived fuel.
So, what it gives us, heat and power, gas, oil, charcoal, syngas, heat and power everything is
energy. Then biological fractions, basically 2 things anaerobic digestion which gives us biogas,
methane rich biogas maybe sometimes hydrogen also in more quantity depending upon what is
the feedstock and composting, so you get compost. Again we are talking about energy, then
landfill with gas recovery and that landfill gas can also be collected and can be converted to the
energy systems and landfill without gas recovery.
So, RDF was recovered from the air classifier and the ferrous, aluminum and glass fractions
were recovered from the bottom of the classifier, this is a simplified description of how MSW is
separated into recyclables and fuel. There are many refinements of these operations, this is just a
simple understanding that what processes can be used to convert municipal solid waste into
energy.
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Now we will understand the separation of the virgin biomass. The production of virgin biomass
for food and feed has progressed from the very labour-intensive, low-efficiency agricultural
practices over the 1800s and 1900s to what some now consider to be a modern miracle. Now the
invention of numerous agricultural machines in the late 1800s that can seed the earth and reap
the harvest with minimum labour and energy inputs made it possible to continuously produce
biomass in quantity to help meet the massive demand for foodstuffs and other farm products
caused by the growing population.
Eli Whitney’s cotton gin, so this is the Eli Whitney’s cotton gin machine it is a classic example
of this type of machine which will do the virgin biomass separation. And the Cyrus
McCormick’s reaper, you can see this, it is a reaper which is being used in the field. And these
are the 2 devices that helped mechanize agriculture and change the course of history by
providing non labour intensive methods of physically separating the desired products - cotton
and grain for these particular inventions from biomass, these units actually made history. So,
earlier everything was completely labour-dependent, after these discoveries less labour-
dependent processing of the entire agricultural product was possible basically.
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Simultaneously with the advancement of agriculture, although not via the same pathway, new
hardware and improved methodologies were developed for the planting, managing and
harvesting of trees that made large scale commercial forestry operations more economic and less
dependent on labour. Better methods of land clearing, thinning and growth management and
improved hardware for harvesting such as feller bunchers which were first used in the early
1970s, resulted in modern forest products industry that supplies commercial and industrial needs
for the wood and wood products. As the use of trees for energy and feedstock expands, it is
expected that much of the existing commercial hardware and improvements will be applied to
meet these needs.
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A few of the non manual separation methods used for woody biomass processing that have use in
energy applications are briefly described. Delimbing and debarking of trees is an old technology.
For the smaller trees where fibre in the form of white wood chips is the desired product, the trees
can be debarked and delimbed by the use of chain flails which will remove the outer bark layer,
leaving the white wood behind. Hammer milling then yields a homogenous product. Basically
white board, white chip whatever it is.
So in most thermochemical energy applications however, separation of the bark and wood is not
necessary. But where it is necessary to remove the bark, some efforts have been made to recover
the residues for fuel from flail machines by using them together with tub grinders.
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A tub grinder operating simultaneously with a chain flail was successfully used to comminute the
residues. The green weight of the fuel residues was about one-fourth to one-third of the total
clean chip plus fuel weight. In a few installations that burn hogged wood, disc and shaker screens
have been employed to separate preselected, oversized pieces for subsequent size reduction and
return to the fuel stream.
Finely divided wood fuels such as sawdust and sander dust are sometimes screened to remove
the larger pieces. By-product hulls from the production of rice, cotton, peanuts, soybean and
similar crops that have outer shells covering small seed of fruit are sometimes used directly as
fuels or feedstocks.
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So, you can see this is the virgin biomass processing actually, so the biomass that is getting
generated by the use of solar energy and the carbon dioxide that is getting used during the
photosynthesis are being collected and chipped and processed into various by-products. Then it
goes to the biomass power plant where it is basically converted into energy.
And after the shells are fractured most of the hulls can be separated with vibrating screens or
rotating trommels having appropriately sized openings. The by-product hulls that have high ash
content and bulk density present a few difficulties on direct combustion or gasification, but
specially designed systems are available to eliminate these problems.
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So, now we will discuss about the extraction. Solvent extraction is the age old technique and it is
still in practice whether it is in the lab scale or in the commercial scale. So, solvent extraction of
biomass, its derived ash or biomass parts such as the seeds has been or being currently used
commercially to isolate and separate certain chemicals or group of related compounds that are
present. Inorganic salts are found in some biomass species at concentrations that may justify
extraction and purification.
Aqueous extraction of the ash from giant brown kelp and the spent pulp of sugar beet and
fractional crystallization of the extract, for example, were commercial processes for the
manufacture of potassium compounds in the early 1900s. Examples of the some of the organic
compounds that are extracted with solvents are trigycerides, terpenes and lignins. Water and
water in mixtures with polar solvents have been used for extraction of several of the low
molecular weight water soluble sugars.
Aqueous organic solvents are effective for the selective extraction of lignins in biomass. Lignins
can also be extracted from biomass by the use of dilute aqueous alkali under mild conditions but
aqueous alcohols alone such as 50% ehanol solubilize lignins in wood leaving relatively pure
undecomposed cellulose. Deciduous trees are delignified by aqueous ethanol extraction to a
greater extent than conifers.
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Lignin is also readily extracted by mixtures of butanol or amyl or isoamyl alcohols with water.
Separation of the lignins from the extracts yields tarlike substances that become brittle on
cooling.
Since one of the prime objective of producing chemical pulps from wood is delignification,
without changing the cellulosic fibres the data accumulated on the solvent extraction of wood
suggests that high quality paper pulps could be manufactured by solvent extraction of hardwoods
and softwoods as well as other biomass species. The lignins in the extracts might provide the
starting point for the production of new lignin derivatives and polymers. As you have understood
that lignin is a by-product and having high commercial value. Solvent extraction of biomass
under relatively mild conditions to remove lignins by a strictly physical process without the
addition of other chemicals would seem to offer several advantages of a chemical pulping
methods.
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Solvent recoveries approaching 100% should permit solvent recycling with minimal losses. A
continuous process for the pulping of wood with aqueous n-butanol which was found to be the
most effective solvent has been proposed for the pulping of wood and the separation of lignins.
So, this type of process which would be expected to be environmentally benign, does not seem to
have been commercialized to any extent by the pulp industry.
So, with this I windup today, so today we have discussed about the physical conversion of the
biomasses and tried to learn how this happens basically. In the next class we will be discussing
about the gasification and pyrolysis process, the fundamentals and how gasification and
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pyrolysis actually can be conducted. So, thank you very much, in case you have any query please
submit it in the swayam portal or drop a mail to me at kmohanty@iitg.ac.in.
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Module 05
Lecture-14
Gasification and Pyrolysis
Good morning students this is lecture 2 under module 5. And as you know that we are discussing
biomass physicochemical and thermochemical conversion in this module. And today's class is an
important one in which we will be discussing about 2 most important thermochemical
conversion processes, one is gasification and another is pyrolysis, so let us begin.
So, gasification is a partial oxidation process that converts biomass into carbon monoxide and
hydrogen with less amount of carbon dioxide and water. Now this process occurs at high
temperatures (above 700 degrees centigrade) without combustion, with a controlled amount of
oxygen and/or steam. Gasification typically uses only 25 to 40% of the theoretical oxidant - it
can be either pure oxygen or air - to generate enough heat to gasify the remaining unoxidized
fuel producing syngas or producer gas which are used as fuels.
Gasification generates lower amounts of some pollutants such as SOx and NOx in comparison to
combustion. Now basically combustion is a full oxidation process in which all the biomass is
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completely oxidized, whereas in gasification, we use less than theoretical oxygen that is required,
for the partial oxidation process.
So, biomass gasification processes are generally designed to produce low or medium energy fuel
gases for the manufacturer of chemicals or hydrogen. More than one million small scale, air
blown gasifiers for wood and biomass derived charcoal feedstocks were built during World War
II to manufacture low energy gas to power vehicles and to generate steam and electric power.
A significant number of biomass gasification plants have been built but many have been closed
down and dismantled or mothballed. The pyrolytic gasification of biomass has been interpreted
to involve the decomposition of carbohydrates by depolymerization and dehydration followed by
steam carbon or steam carbon fragmentation reactions. So, pyrolytic gasification is a type of
gasification process.
I would like to say during this discussion is that, pyrolysis, though it is a separate
thermochemical conversion process, but whenever gasification is actually happening, so the
second step is the pyrolysis reaction. So, before the gasification reaction really begins, so
pyrolysis happens. We will discuss in our subsequent discussion today, when we will talk about
the reaction mechanisms, then it will be a little more clear.
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So, some of the coal gasification processes are also suitable for biomass feedstocks. Since the
conditions required for coal gasification are more severe than those needed for biomass, some
coal gasifiers can be operated on biomass or biomass-coal feedstock blends. Indeed, some
gasifiers that were originally designed for coal gasification are currently in commercial use with
biomass feedstock because coal is being depleting day by day.
The chemistries of coal and biomass gasification are quite similar in terms of the steam carbon
chemistry, and are essentially identical after a certain point is reached in the gasification process.
Note, however, that biomass is much more reactive than most of the coals. Biomass contains
more volatile matter than coal, and the pyrolytic chars from biomass are more reactive than
pyrolytic coal chars.
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The thermodynamic equilibrium concentrations of specific gases in the mixture depend on the
abundance of carbon, hydrogen and oxygen, the temperature, as well as the pressure. Biomass is
gasified at lower temperatures than coal because its main constituents, the high-oxygen cellulose
and hemicellulose, have higher reactivity than oxygen-deficient carbonaceous materials in the
coal.
In addition of co-reactants to the biomass system, such as oxygen and steam, can result in large
changes in reaction rates, product gas compositions and yields and selectivity as in coal
conversion. Biomass feedstocks contain a high proportion of volatile materials 70 to 90% for
wood, compared to 30 to 45% for typical coals.
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A relatively large fraction of most biomass feedstocks can be devolatilized rapidly at low to
moderate temperatures, and the organic volatiles can be rapidly converted to gaseous products.
The chars formed on pyrolytic gasification of most biomass feedstocks have high reactivity and
they gasify very rapidly. For biomass and waste biomass, steam gasification generally starts at a
temperature near to 300 to 375 degrees centigrade, again depending upon the type of feedstock.
Undesirable emissions and byproducts from the thermal gasification of biomass can include
particulates, alkali and heavy metals oils, tars and some aqueous condensates.
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It is important to avoid gas turbine blade corrosion and corrosion by removing undesirable
particulates that maybe present. The removal of tars and condensable gases may also be
necessary. Furthermore, utilization of the sensible heat in the product gas improves the overall
thermal operating efficiencies. Non turbine applications of the gas may also be able to take
advantages of the process that provide clean, pressurized hot gas such, as certain downstream
chemical syntheses and fuel uses.
So, what happens, basically when the gasification is happening in a gasifier any type of gasifier
we will also discuss in our class today, what are the different types of gasifiers available and of
course, pyrolysis reactors are pyrolysers. So, there are many obnoxious byproducts that actually
getting formed including some of the tar also. So, these needs to be removed frequently
otherwise it will create a problem inside the reactor.
So, the reactor vessel will corrode if there are some corroding elements present and if you do not
take it out from for a prolonged time and they keep on presenting then there cannot be a proper
reaction will proceed basically. So, research on thermal biomass gasification in North America
has tended to concentrate on medium energy gas production, scale-up of advanced process
concepts that have been evaluated at the PDU scale, and the problems that need to be solved to
permit large scale thermal biomass gasifiers to be operated in a reliable fashion for power
production, especially for advanced power cycles. So, PDU means the power distribution unit.
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So, this is a typical scheme please have a look. The first one here, it talks about the gasification
routes, the second one is about the gasification reactions, we will discuss that in detail in our next
slide. So, let us understand this is what I was telling you that pyrolysis is a part of the entire
gasification process if you stop here and do only pyrolysis then it becomes a pyrolysis reaction
and then subsequent products.
But then if you go on for the next step, that step is basically the gasification process, let us
understand. So, biomass needs to be dried for any thermochemical conversion process, we have
discussed last class in one of the pretreatment classes, we have discussed that biomass needs to
be dried to a particular moisture level otherwise the reaction may not proceed in a proper
direction, so it is dried then it goes for pyrolysis.
So, after pyrolysis there may be so many different types of things you can see that gases, liquids,
oxygenated compounds and solid is basically the char. So, if you go for a gas phase reactions
like cracking, reforming, combustion, water gas shift reactions, you get carbon monoxide,
hydrogen, methane, water, carbon dioxide and some other smaller components. If you go for the
char gasification reactions, so you get carbon monoxide, hydrogen, methane, water carbon
dioxide, residual carbon.
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So, if you talk about the product, the product from the gasification is mostly the syngas/synthesis
gas or maybe producer guess. So, these are the some of the reactions that happens actually the
carbonation reaction, oxidation reaction, water gas shift reaction - water gas shift reaction takes
place at very high temperature, then methanation and steam reforming. So, this is given in detail
we will see in the next slide the reactions.
So, 4 to 5 different types of reactions happen. The first one is the dehydration or the drying
process as I have shown you here, the drying process. So, that occurs at around 100 degrees
centigrade, so the resulted steam is then mixed into the gaseous flow and maybe involved with
subsequent chemical reactions predominantly the water gas reaction if high temperature actually
exists.
So, after that the biomass or whatever the vapor that is getting generated actually that goes to the
pyrolysis step, which is called as devolatilization state. So that occurs between 200 to 300
degrees centigrade, sometimes up to 350 degrees also. This process releases the volatiles, thereby
producing char as an effect almost 70% weight loss. So, char is getting produced because there is
severe weight loss almost approximately up to 70%.
The process is, however dependent on the properties of the biomass which eventually determines
the structure and composition of the char. Then in the next step it goes to the combustion
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reaction. So, the char then undergoes the combustion reactions to primarily form carbon dioxide
and small amounts of carbon monoxide that provides heat for the subsequent gasification
reactions.
So, you can see that here the fuel, let us understand it is a dry fuel or after the drying fuel, then
when the devolatilization or the pyrolysis reaction is proceeding we get char. And some of the
tars and hydrogen, some methane, some gases - you can trap it or you can leave it depending
upon how much you are producing. Then this char subsequently goes for the combustion
reaction and gasification reactions.
So, the gasification process occurs as the char reacts with steam and carbon dioxide to produce
carbon monoxide and hydrogen. Now there is a reversible gas phase water shift reaction which
we talked in the step one also. And this happens at very high temperatures, and this reaction,
water gas shift reaction reaches equilibrium very fast when the temperature is very high thereby
balancing the concentrations of carbon monoxide, steam, carbon dioxide and hydrogen.
The major product of syngas or synthesis gas is of course carbon monoxide and hydrogen, and if
certain amount of carbon comes into contact with a proper amount of oxygen and get combusted
then it will result in some amount of carbon dioxide.
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So, let us understand the different types of gasification process variations. So, the primary
products of biomass pyrolysis under conventional pyrolysis conditions are gas, oil, char and
water. As the reaction temperature increases, gas yield increases. That means what
predominantly it means, when you stop during pyrolysis - at the pyrolysis reaction that the entire
thermochemical conversion process becomes pyrolysis process.
Then you will get gas, oil, char and water, that is what we get from the pyrolysis reaction. But
when we are proceeding in a gasifier and doing the gasification reactions, so then we will get the
gases - there will be more gaseous product yield. So, it is important to note that pyrolysis may
involve green or pre dried biomass and that product water is formed in both cases.
Water is released as the biomass dries in the gasifier and is also a product of a chemical reaction
that occur even with bone dry biomass, even if the dry biomass is almost close to 95, 98% or
close to 99% dry. So, unless it is rapidly removed from the reactor, this water would be expected
to participate in the process along with any added feed water or steam. One or one of the more
innovative pyrolytic gasification process is an indirectly heated fluid bed system, we will discuss
about that later.
Now this system uses two fluid bed reactors containing sand as a heat transfer medium. Now
sand holds the heat for a long time and it is a good medium for doing the heat transfer. So, that is
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why it is being used and it is low cost readily available can be recycled back. So, combustion of
char formed in the pyrolysis reactor takes place with air within the combustion reactor. The heat
released supplies the energy of pyrolysis of the combustible fraction in the pyrolysis reactor.
Heat transfer is then accomplished by flow of hot sand from the combustion reactor at 950
degrees centigrade to the pyrolysis reactor at 800 degree centigrade and then the sand can be
returned back or recycled back to the combustion reactor. So, this configuration separates the
combustion and pyrolysis reactions, that means predominantly instead of a single gasifier under
which drying pyrolysis, gasification, combustion everything is happening you have 2 different
reactors.
In which in one reactor pyrolysis is happening and another reactor combustion is happening. And
it yields a pyrolysis gas that can be upgraded to a high energy gas, which is a substitute natural
gas is called SNG by shifting, scrubbing and methanation with regard to nitrogen separation. So,
there are certain the shifting, scrubbing, methanation are the polishing steps.
So, let us have a look at this particular 2 bed fluidized reactor system which is being used to
produce methane. So, you can see this, this is the fluidized bed combustion process, this is the
fluidized bed pyrolysis process, both are using the sand. The sand is as a heating medium and the
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sand is getting interchanged or recycled between these 2 beds. So, when the air is supplied to
combustion reactor, whatever you get is the combustible products.
Then this one, under the pyrolysis reaction, the shredded feed organics are being actually fed
your feedstock, so and whatever you get is basically the gas and char. Now under there is a
separator, the separator actually separates that char and the gas phase, so the gas phase means the
pyrolysis gas phase. Then it goes to the some shifting reactions, carbon monoxides, scrubbing to
remove carbon dioxide, then methanation reaction to get methane, pure methane, you have to
purify it and part of the pyrolysis gas is being recycled to maintain the reaction conditions inside
the pyrolysis reactor. And the char is getting fed to the combustion reactor where it is undergoing
the gasification reaction. So, the pyrolysis gas with hybrid popular feedstocks typically contains
about 38% carbon monoxide, 15% carbon dioxide, 15% methane, 26 mole percent of hydrogen
and 6% of C2S.
Now this is a medium energy gas having a higher heating value of about 19.4 mega joule per
meter cube. The projected gas yields are about 670 meter cube of pyrolysis gas or about 200
meter cube meter of methane per dry ton of feed is SNG is produced, substitute natural gas. It is
a very nice process.
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So, many thermal conversion processes can be classified as partial oxidation processes in which
the biomass is supplied with less than the stoichiometric amount of oxygen needed for complete
combustion. When the oxygen is supplied by air, low energy gases are formed that contain
higher concentrations of hydrogen, carbon monoxide and carbon dioxide than medium energy
gases.
When we use pure oxygen or oxygen enriched air or even air also gases with higher energy
values can be obtained. In some or certain partial oxidation processes, the various chemical
reactions may occur simultaneously in the same reactor zone. Most of the time you will
understand that the gasification process is being done in a single gasifier, in a single reactor let us
called it single reactor all sorts of reactions are happening there are different zones.
But what we have discussed is just before this last slide about the 2 fluidized bed systems that
has essentially done to produce when you look for 2 different things, one is this syngas, producer
gas whatever it is and one is the pure methane. So, that was particularly aimed to produce
methane as well as the usual syngas, so then you go for a 2 bed systems.
Otherwise if you are looking for a syngas whether high quality energy carrier or low energy
carrier gas whatever it is depending upon the feedstock and other process conditions a single
gasifier is more than enough. So, in others the reactor maybe divided into zones that is what I
was just telling - a combustion zone that supplies the heat to promote the pyrolysis in a second
zone, and perhaps a third zone for drying, the overall result of which is partial oxidation.
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So, this is another example of the partial oxidation process, so here the production of synthesis
gas in a three zone shaft reactor furnace. Please understand that it is a three zone shaft reactor,
but it is a single reactor. Now let us understand, so the three zone, so here you feed the biomass.
So, the biomass is being feed, this is that zone which is responsible for the first reaction that is
that drying zone.
Then comes the second zone that is the pyrolysis zone, then it comes to the third zone where
oxygen or air enriched with oxygen is being fed to do the combustion process in a of course less
than theoretical demand. So, whatever you get is basically the molten slag, then it goes to feed
quenching and the gas will be recovered here on the top of the reactor.
Then it goes to water scrubbing and you get a downstream part of that or the bottom product is
being separated and recycled. So, this is the fine liquid that is getting recycled, the wastewater is
again treated and then discharged. And whatever is coming here is the almost pure gas after the
water scrubbing, then it goes to electrostatic precipitation to remove fly ash and other certain
components.
Then you cool it and you get product gas and whatever during the cooling process certain
amount of moisture whatever it is actually still remains in the gas phase will condense and then
that can be fed back to the separation unit. So, in this process, coarsely shredded feed is fed to
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the top of the furnace. As it descends to the first zone the charge is dried by the ascending hot
gases which are partially cleaned by the feed.
So, please try to understand what is happening here, you feed it, so when you feed initially here
drying is happening. So, the drying is happening then pyrolysis combustion, when the pyrolysis
and combustion reaction is happening at the bottom portion, the gas is moving upward. So, this
gas is also doing the drying process, correct, do you understand this? So, that means in a single
thing you do not have to supply extra energy or heat to take care of the drying process.
The product gas whatever is producing that is doing the drying. So, the gas is reduced in
temperature from about 315 degrees centigrade to the range of 40 to 200 degrees centigrade. The
dried feed then enters the pyrolytic zone in which temperature ranges from 315 to 1000 degrees
centigrade. Again depending on what feed you are using, for different feedstocks the temperature
may vary.
So, the resulting char and ash then descend to the hearth zone, where the char is partially
oxidized with pure oxygen, the hearth is that the bottom zone basically. Slagging temperatures
near 1650 degrees centigrade occur in this zone, and the resulting molten slag of metal oxide
forms a liquid pool at the bottom of the hearth. Continuous withdrawal of the pool and
quenching forms a sterile granular frit.
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The product gas is processed to remove fly ash and liquids, which are recycled to the reactor. A
typical gas analysis is almost 40 mole percent of carbon monoxide, 23 mole percent of carbon
dioxide, 5 mole percent of methane, 5 tool percent of C2S and 20 mole percent of hydrogen. This
gas has higher heating value of about 14.5 mega joule per meter cube.
An example of the gasification of biomass by partial oxidation in which air is supplied without
zone separation in the gasifier is the molten salt process. In this process, shredded biomass and
air are continuously introduced beneath the surface of a sodium carbonate containing melt which
is maintained at about 1000 degrees centigrade. As the resulting gas passes through the melt the
acid gases are absorbed by the alkaline media and the ash is also retained in the melt.
The melt is continuously withdrawn for processing to remove the ash and is then returned to the
gasifier. No tars or liquid products are formed in this process. Thus, with about 20, 15, 75% of
the theoretical air needed for complete oxidation, the respective higher heating values of the gas
are about 9, 4.3, 2.2 mega joules per meter cube.
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Basically, biomass gasifiers can be categorized into several reactor design groups. A descending
bed of biomass often referred to as a moving or fixed bed with counter current gas flow updraft
and a descending bed of biomass with counter current gas flow that is called downdraft. A
descending bed of biomass with crossflow gas, a fluidized bed of biomass with rising gas and
entrained flow circulating bed of biomass and a tumbling beds, there are various types of
arrangements can be possible.
So, some of the designs that are being tested and are commercialized are fixed bed, moving beds,
suspended bed, fluid bed reactors, entrained feed solid reactor, stationary vertical shaft reactors,
inclined rotating kilns, horizontal shaft kilns, high temperature electrically heated reactors with
gas blanketed walls, single and multi hearth reactors, ablative, ultrafast and flash pyrolysis
reactors and several other designs.
You can see that there are so many different types of designs of the reactors that is already been
tested. There are clearly numerous reactor designs and configurations for biomass gasification
probably more than in the case of coal gasification systems because of the relative ease of
thermal biomass conversion.
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So, let us now understand the different biomass gasifier design, we will just try to understand in
a glance, how this looks like. This you can see in this particular diagram, I have shown 2
different type of fixed bed gasifiers. One is the updraft gasifier another is the downdraft gasifier.
Now a fixed bed gasifier can be either updraft, that means what is happening in the updraft.
The fuel is getting dropped from the top, gasifying agent from the bottom. And the downdraft, so
both fuel and gasification agents occurs from the top, it is a co-current flow, here the flow is
counter current. In updraft gasification, the char at the bottom of the bed meets the gasifying
agent first and complete combustion occurs producing hydrogen and carbon dioxide and raising
the temperature to almost 1000 degrees centigrade.
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So, the hot gases percolate upwards through the bed driving endothermic reactions with
unreacted char to form hydrogen and carbon monoxide with consequent cooling to 750 degrees
centigrade. The gases pyrolyze the dry biomass which is descending and also of course near the
top of the reactor and also dry the incoming biomass. Updraft gasifiers typically produced
between 10 to 20 weight percent tar in the produced gas which is far too high for many advanced
applications, it is not a good thing of course.
The allowable tar levels depend on the downstream application. These are around 0.05 grams
normal per meter cube, 0.005 gram normal per meter cube 0.001 gram normal per meter cube,
for gas engines, gas turbines and fuel cells applications respectively. In contrast to an updraft
gasifier in a downdraft gasifier which is the closed loop, the gas flows co-currently with the fuel.
A throated gasifier has a restriction partway down the gasifier where air or oxygen is added and
when the temperature rises to 1200 degree to 1400 degree centigrade, and the fuel feedstock is
either burned or pyrolyses.
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The combustion gases then pass down over the hot char at the bottom of the bed where they are
reduced to hydrogen and carbon monoxide. The high temperature within the throat ensures that
the tar formed during pyrolysis are significantly cracked, that is the homogeneous cracking with
further cracking occurring as the gas meets the hot char on the way out of the bed, heterogeneous
cracking leading to a less tarry off-gas.
Some disadvantages of a throated gasifiers are, the constriction at the throat affects the type of
biomass that can be successfully gasified, a low moisture content is required almost 25 weight
percent. Ash and dust are significantly present in the exhaust; tar can still be up to 5 grams
normal per meter cube needing further cleanup.
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Biomass gasifier designs. So this is a bubbling fluidized bed system. So, the biomass is fed from
the side, you can see this is the main bubbling fluidized bed. Here the biomass is being fed using
a hopper and a feeding screw, there is a screw system which is slowly actually feed in a
particular rate. There are grids here, this is the fluidized bed, then whatever the gasification
product is going basis the gas phase, that needs to be separated from the fly ash and other
components. So, that will be done using a cyclone separator, then you get the hot product gas and
whatever it is remain the solid fractions will again come down to the bottom of the reactor. So,
either they will be burned again or they can be collected from the bottom. So, the biomass is feed
from the side and/or below the bottom of the bed and the gasifying agent’s velocity is controlled
so, that it is just greater than the minimum fluidization velocity of the bed material, the product
gas exits from the top of the gasifier and ash is either removed from the bottom or from the
product gas using a cyclone.
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So, next design is a circulating fluidized bed. So, circulating fluidized bed known as CFB
systems use 2 different integrated units. In the first unit, there are 2 systems you can see, this is
one column there is another column here. So, the first unit is called the riser the second unit is
called the downcomer. Now in the first unit, which is known as the riser the bed material is kept
fluidized.
So, this is the main reactor where the fluidization is happening by the gasifying agent. So, you
see that we feed the biofuel feed or the feedstock is being fed here somewhere and from the
bottom you collect the ash. And then when the gas goes out and there is a downcomer here, here
you basically do some processing some other things are also there, you collect the product gas
here.
So, there is air pre heater and then part of that gas is also being recycled back. So, in the riser, the
biomass is fluidized by the gasifying agent with a higher velocity that then found in the bubbling
fluidized bed the BFB, which we discussed. Now this allows the bed material to be fluidized to a
greater extent than the BFB and the overall residence time is higher due to the circulation, which
is effected by passing the product gas and entrained bed material through a cyclone which
separates the product gas from the bed material which is re-circulated back to the riser.
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So, we will now discuss about a special gasification technique which is called supercritical water
gasification. Water above it is critical point which is 374.12 degree centigrade and a 221.2 bar is
termed as supercritical. Now under these settings, the liquid and gas phase do not exist, it is a
phase between a liquid and gas phase, it is called supercritical phase. And in that phase
particularly the water shows distinctive reactivity and solvency characteristics.
So, the water in supercritical phase will have both the properties of a gas phase as well as a liquid
phase. Solubilities of organic materials and gases which are normally insoluble are enhanced
with a decrease in solubility for inorganics. So, supercritical water gasification has been applied
to wet biomass without the need for pre drying. So, this technology is being actually developed
to take care of the wet biomasses.
Please understand that when the biomasses are highly wet or has high moisture content, then you
need a significant amount of energy to basically dry them before you feed them to a gasifier or a
pyrolysers. So, if you go for a supercritical water gasification system, then whatever the water or
moisture is present inside the biomass will actually behave like a reactant? So, this is the major
advantage and this is the aim of developing the supercritical water gasification system.
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So, product gas from this SCWG is mainly comprises hydrogen, carbon dioxide, methane and
carbon monoxide. The carbon monoxide yield is comparatively low as carbon monoxide
transforms into carbon dioxide through the water gas shift reaction.
So, this is the unit. So, this supercritical water gasification the main reactor is of course very
costly, you can think about the high temperature and high pressure required to make the water
into the supercritical stage. So, here the main reaction is happening then whatever you are getting
here the product it goes through some heat exchanger and there is a phase separator, you get
clean water and you get the product gas.
And whatever portion from this is a combustion air and methane is recycled and being collected
as a flue gas or maybe used for other purposes. So, by employing the supercritical water
gasification process, even liquid biomass such as olive mill water can be utilized with the
production of low tar hydrogen gas. It is a very nice technology, the only problem is the cost and
special types of reactors of course, and that is why it leads to the extra or additional cost.
Tar and coke formation are curtailed by rapid dissolution of product gas components in
supercritical water. Wet biomass treatment without pre drying, liquid biomass treatments such as
olive mill wastewater, high hydrogen yield, high gasification efficiency and low tar formation
are the main advantages of this particular technology.
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We are just further discussing about that particular technology only. If you look at this particular
slide, you can see that hydrogen, this is the blue one is the hydrogen production. You can see that
it enhances exponentially after the 600 degrees centigrade. So, up to 600 degrees centigrade it is
almost in a saturated stage the production is happening. The moment we cross 600 degrees
centigrade, there is an exponential increase in the hydrogen gas production.
While the carbon monoxide, the carbon monoxide is the red one, it decreases after 600 degrees
centigrade, it is almost after 660 or 650 you can say that. So, methane decreases to 540 degrees
centigrade and then remains almost constant when even the temperature is increased. Major
limitations include requirements of high pressure, high temperature resistance and rust resistant
materials, consequently increasing the investment cost and high energy requirements.
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The major motivation behind biomass gasification is to exploit a large variety of waste materials
as feedstock, to increase resource efficiency and to reduce adverse climate change via carbon
dioxide mitigation. Although gasification is a key technology to utilize biomass waste, it poses
many potential kinds of risks, which have a significant impact on society and the environment at
large.
One of the main problems is the potential emissions of particulates. Some are dioxins, PAH,
carbon monoxide, SOx, NOx, and some volatile organics. These pollutants can interact with
humans through inhalation, ingestion, and dermal contact and thus pose a grave threat to human
health. Ash and tars are noteworthy elements which have potential for environmental
contamination, should be properly disposed off.
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So, gasification is a system which has an inherent risk for fire and explosion vulnerability,
especially since the gasifiers operate at high temperature and pressure. This probability enhances
significantly when hydrogen is the desired product; it is highly flammable and therefore
necessitates a great amount of caution. The waste streams formed require a suitable disposal
system to be implemented that meets all the legislative guidelines, especially these
environmental guidelines.
Techniques like low temperature circulating fluidized bed, which can produce ash with
negligible PAH impurity pose little threat to the environment, meaning that this ash can also be
used as a fertilizer or soil enhancer basically.
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So, next is we will discuss about pyrolysis. So, biomass pyrolysis can be described as the direct
thermal decomposition of the organic components in biomass in the absence of oxygen to yield
an array of useful products, liquid or solid derivatives and fuel gases. Eventually, pyrolysis
processes were utilized for the commercial production of a wide range of fuels, solvents,
chemicals and other products from biomass feedstocks.
Knowledge of the effects of various independent parameters such as biomass feedstock type,
composition, reaction temperature and pressure, residence time and catalyst on reaction rates,
product selectivities and product yields has led to the development of advanced biomass
pyrolysis processes.
The accumulation of considerable experimental data on these parameters has resulted in
advanced pyrolysis methods for the direct thermal conversion of biomass to liquid fuels and
various chemicals in higher yields than those obtained by the traditional long residence time
pyrolysis methods.
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So, the main product from pyrolysis, there is I already told you in the beginning of the class that
pyrolysis is a step inside the gasification. However, when you only go for pyrolysis reaction, our
main aim is mostly to produce the bio oil or pyrolytic oil, which can be further processed and can
be blended as a transportation fuel and it can have several other users also.
So, let us understand pyrolysis with different types of reaction conditions. So, a biomass is
mainly composed of long polymeric chain of cellulose, hemicellulose and pectin and some other
components - volatiles. Now the proportion of each end product depends on the temperature,
time - residence time, heating rate and pressure, types of precursors that we are using, and the
reactor design and configurations.
We can see how the reactions proceeds. So less than 200 degrees centigrade what is happening,
that is called as dehydration, drying or removal of the moisture, we call it dehydration. The
moment you proceed beyond 200 and within that 200 to 280 degrees centigrade you can see this
first hemicellulose will start degrading, so hemicellulose decomposes. So, it will result in some
amount of syngas and a minor quantity of bio oil, then we proceed further to beyond 280 degrees
centigrade and in the range of almost 300 degrees centigrade.
The broad range of 240 to 350 degrees centigrade, the cellulose degrades, when the cellulose
decomposes, it again produces some amount of syngas some more amount of bio oil, and minor
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amount of the bio char, that is the solid residue that will be left out. You proceed further beyond
350 degrees centigrade up to 400 or 500 degrees centigrade here lignin decomposes, lignin
decomposes mostly to the bio char and certain less amount of bio oil, so this is how the pyrolysis
reaction happens.
So, this is the yield of the pyrolytic products, you can see the yield of the bio char this decreases
as and when we proceed with the pyrolysis reaction or we increase the temperature. So, this is
the yield of bio oil, you can see that the most amount of the highest yield is about this 500
degrees centigrade you beyond that it decreases. Because beyond that lignin is decomposed,
lignin is not resulting more into bio oil, it is getting converted more into your bio char.
Then there is gas and water also. So, a modern technology was developed to extract maximum
possible energy from biomass using combustion, which is exothermic reaction, gasification
which is another exothermic reaction and pyrolysis which an endothermic reaction. Pyrolysis can
be considered as part of gasification and combustion, this is what I already mentioned you.
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So, these are some of the end products and the temperature and the type of reactions. So, less
than 350 moisture loss, depolymerization we get carbonyl and carboxyl group production, this is
what I have already described, but this is given in a tabular format for a better understanding. So,
between 350 to 450, you get breaking up glycosides chain of polysaccharides. So, tar production
begins that contains levoglucosan, anhydrides and oligosaccharides. Above 450 dehydration
rearrangement and fission of sugar units happens, you get acetaldehyde, glyoxalin, acrolein
production and some other components. Above 500 degree centigrade a mixture of all the
processes reactions that is happening and mixture of all the above products also being produced.
So then condensation reaction happens. So, unsaturated products condense and cleave to the
char, a highly reactive char residue containing trapped free radicals is the end product.
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So, conventional pyrolysis consists of the slow irreversible thermal degradation of the organic
components in biomass, most of which are lignocellulosic polymers, in the absence of oxygen.
So, pyrolysis is happening without oxygen, whereas gasification is happening which happens
after the pyrolysis with a less amount of theoretical oxygen, which is required for the combustion
process.
So, slow pyrolysis has traditionally been used for the production of charcoal. Short residence
time pyrolysis which are flash pyrolysis, ultra pyrolysis of biomass at moderate temperatures can
afford up to 70 weight percent yields of the liquid products. So, they are very good in producing
higher amount of bio oil. Pyrolysis conditions can be used, that provides high yields of gas or
liquid products and char yields of less than 5%.
One configuration of an advanced biomass pyrolysis system, for example, involves an ablative
vortex reactor for pyrolysis at biomass residence times of fractions of a second coupled to a
downstream vapor cracker.
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Overall, the pyrolysis process can be classified as slow and fast depending upon the heating rate.
In slow pyrolysis process, the time of heating the biomass substrate to pyrolysis temperature is
longer than the time of retention of the substrate at characteristic pyrolysis reaction temperature.
However, in fast pyrolysis, the initial heating time of the precursor is smaller than the final
retention time at pyrolysis peak temperature.
Based on medium, pyrolysis can be another 2 types namely hydrous pyrolysis and hydro
pyrolysis, what medium is being used. So, a slow and fast pyrolysis is usually carried out in inert
atmosphere, whereas hydrous pyrolysis is carried out in the presence of water and hydro
pyrolysis occurred in the presence of hydrogen.
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So, this table gives you the types of pyrolysis process with resultant products. So, a fast pyrolysis
the retention time is extremely low, less than 2 seconds, rate of heating is very high, final
temperature is around 500 degrees centigrade and the major product that you get is the bio oil.
The highest yield is of course bio oil. Flash pyrolysis less than one second extremely fast, high
rate of heating less than around 650 degrees centigrade. And again the major product is bio oil
and certain chemicals and maybe gas - less amount of gas. Ultra-rapid - less than 0.5 second,
very high rate of heating; the temperature required is 1000 degrees centigrade, you get chemicals
and gases. Vacuum pyrolysis, you get bio oil. Hydro pyrolysis less than 10 seconds, high rate of
heating, temperature required is less than 500 and the major product is bio oil.
And carbonization - this is the slow pyrolysis which was initially used so many years before to
produce that char - charcoal. So, the resultant product is charcoal and less than 400 degrees
centigrade. Conventional is about 5 to 30 minutes, (heating rate) low, many times we can call it
as an intermediate pyrolysis, so the maximum temperature we can go depending upon the type of
feedstock is 600, you get so many different types of products in a certain proportion - char, bio
oil and gas. However, again depending upon the type of feedstock, maximum yield is of course
of the bio oil.
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So, fast pyrolysis. So, during the fast pyrolysis process, biomass residues are heated in absence
of oxygen at high temperature using higher heating rate. Based on the initial weight of the
biomass fast pyrolysis can provide 60 to 75% of the liquid bio fuels with 15 to 25% of the
biochar residues. So, the process is characterized by small vapor retention time, however quick
chilling of vapors and aerosol can ensure higher bio oil yield, so this is another further step.
So, you get a pyrolysis oil here, non condensable gases - can be processed through the gas
burner. And you get the heat - again that heat can be used in the pyrolysis here. So, the pyrolysis
oil you can see that so many different types of processing here, synthesis and extraction to
biobased chemicals. I can tell you again we have already discussed once, the major product from
the fast pyrolysis or any pyrolysis of course, is the oil, that is the major aim.
Whenever we generate oil, so you just leave it or settle it under gravity, allow it for some time,
you see that 2 distinct phases, one top phase and bottom phase, there is phase separation. The one
phase is containing the oil rich phase that is the organic components and that is if we decant it
properly and take it out and further process that is the bio oil.
And there are other portion which is aquatic phase, that aquatic phase contains so many different
types of chemicals and some of these chemicals can be of very high value depending upon what
is the feedstock you are using, that can be processed. You get that type of platform chemicals
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here. Upgrade you get advanced bio fuels, if you can go for some sort of distillation process.
Feed to turbine engine you get a clean power here.
Boiler you get heat and whatever the biochar that leaves, it can either be burnt in a boiler to
produce the heat - maybe steam at certain cases or if the quality of the char is poor it can be used
as a soil enhancer.
Fast pyrolysis technology is getting implausible acceptance for producing liquid fuels due to
certain technical advantages, so some of them are listed here. So, it can ensure preliminary
disintegration of the simple oligomer and lignin portions from the lignocellulosic biomass with
successive upgrading. The scaling up of this process is economically feasible. It can utilize
second generation bio oil feedstock such as forest residues, municipal and industrial wastes.
It provides easy storability and transportability of liquid fuels. It can ensure secondary
transformation of motor fuels, additives or special chemicals.
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Then is flash pyrolysis. So this is a flash pyrolyser or flash pyrolysis reactor. So, flash pyrolysis
process of biomass can give solid, liquid and gaseous products. The bio oil production can go up
to 75% if you use this particular technology. This procedure is carried out by speedy
devolatilization under inert atmosphere using higher heating rate with high pyrolysis temperature
around 450 to 1000 degree centigrade.
So, in this process, the gas residence time is less than 1 second - is too little. Nevertheless, the
process has poor thermal stability. Due to catalytic effect of the char, the oil becomes viscous
and sometimes it contains some solid residues also which is not desirable but you can further
process it to take out the solid part.
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Then slow pyrolysis. Slow pyrolysis can yield good quality charcoal using low temperature as
well as low heating rates. The vapour residence time can be around 5 to 30 minutes in this
process. The volatile organic fractions present in vapor phase continue to react with each other to
yield char and some liquid fractions. The quality of bio oil produce in this process is very low.
So, if your aim is to produce bio oil it is recommended not to use slow pyrolysis, you can better
go for an intermediate pyrolysis where you get a good amount of bio oil. And if you only want
higher bio-oil yield then you can go for the fast pyrolysis or flash pyrolysis. So, the longer
residence time in slow pyrolysis initiates further cracking to reduce the yield of bio oil.
The process suffers from low heat transfer values with longer retention time leading to enhance
the expenditure by higher input of energy. The stoichiometric equation for a production of
charcoal is shown by this equation :
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Then let us understand catalytic pyrolysis. A mixture of hydrocarbon was produced earlier from
methanol over zeolites like ZSM-5. Another patent suggested passing the vapors from pyrolyzer
over a bed of zeolite ZSM-5 to produce short chain hydrocarbons. It was reported that the
catalyst of ZSM-5 can convert bio oils generated from the pyrolyzer to alkylated benzene. The
disadvantage of using ZSM-5 as catalyst was coke formation.
However, these disadvantages can be overcome by using a circulating fluidized bed technology,
where the fluidized bed can be prepared using different types of catalyst instead of sand. So, this
CFB whatever we have discussed under the gasification, the same reactor can be used. Catalyst
can be mixed with lignocellulosic substrate earlier to pyrolysis process or separately with the
gaseous reactants to obtain desired products.
So, this statement you will see many times. You will come across 2 different terminologies, one
is called ex-situ catalytic pyrolysis, one is called in-situ catalytic pyrolysis; where the in-situ
catalytic pyrolysis the catalyst is physically mixed with the biomass, then we go for the pyrolysis
reaction. In ex-situ pyrolysis reaction what happens that there is a fixed bed type of reactor, it
can be fluidized bed also. There the biomass is not mixed with the catalyst, so the catalyst is kept
in a separate section and the when the vapour is getting generated after the pyrolysis reaction
from the feed biomass, that passes through a bed of catalyst. So, the catalytic cracking is
happening for the vapor phase, so you can call it vapor phase catalytic cracking.
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That is better because this catalyst can be regenerated and reused. Whereas, if you mix with the
feedstock then you cannot separate the catalyst from the biomass and it will be waste basically.
And you know the catalysts are extremely costly, most of the catalyst or commercial catalyst. So,
it was revealed that parting of the catalyst and biomass was more operative for the
transformation of the required products.
So, catalytic hydro pyrolysis. So catalytic hydro pyrolysis is a kind of catalytic pyrolysis where
pyrolysis is carried out using fluidized bed reactor under the flow of hydrogen. In this process
the fluidized bed is replaced by a transition metal catalyst. It was reported that the replacement
inert sand with nickel based catalyst under atmospheric pressure can convert the bio oil into low
molecular weight hydrocarbons within short contact time.
Recently, Gas Technology Institute in Illinois, United States reported a new process where the
overall process is carried out under 7 to 34 bar pressure. Due to high pressure C1 and C3 gases
are evolved which after reforming produce large amount of hydrogen. However, the system is
also very complex as it is a combination of hydro-pyrolysis and reforming. Overall the
establishment of this process is very costly.
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So, we will see certain types of reactors. The first is the fixed bed reactor. So, this is a very
simple technology that gives priority to the production of bio oils which are relatively uniform in
size with low fines content. So, it is made up of 2 basic components; that is the gas cooling
compartment and the cleaning system by filtering through the cyclone, wet scrubbers and dry
filters.
So, here this is a gas distributor which is distributing the sweeping gas, here you feed your
biomass through a feeder and it is a fixed bed pyrolysis reaction happens; the heat is being
supplied and whatever the resultant is the vapor, gas and aerosol.
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So, during reaction, the solid sample is allowed to pass through a vertical shaft where it
encounters an upwardly moving counter current gas stream product. This reactor can be made
using either steel, firebricks or concrete and composed of the feeding unit, a unit for removing
the ash and the gas escape unit.
The reactor, which has it is priority for applications involving small scale heat and power, has
high ability to conserve carbon and can operate for long time for solid residence, low gas
velocity and of course with a low ash carry-over. It has it is own limitation in the problem is
usually encountered during the tar removal.
Then fluidized bed system, the unit looks like similar - it is a schematic. Here it can be little
something conical like shape maybe, there are different designs available. But the bed is
fluidized it is not a fixed bed, the remaining things are same, so this reactor consist of a mixture
of 2 phases the solid and the liquid and usually accomplished by passing a pressurized fluid
through the solid material.
Now there are different types of fluidized bed reactors which include bubbling fluidized,
circulating fluidized, ablative reactor, vortex reactor, rotating disk reactor, vacuum pyrolysis
reactor and rotating cone reactor, there are many different designs are available and this is the
simplest schematic.
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So, the advantages of fluidized bed are: The provision of heat transfer is very rapid. It has a good
grip of pyrolysis reaction and vapor holding time control. It has sufficiently high surface area for
contact between the 2 phases in the mixture, because, the biomass is in suspended medium. The
heat transfer in the system is exemplary and the relative velocity between the phases is very high.
So, then the next is bubbling fluidized bed reactor. So, the high presence of solid density in the
bed ensures a better temperature control, smooth contact between gas and solid, good transfer of
heat and excellent storage capacity. The biomass is heated in an environment devoid of oxygen
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and decomposed into gas, vapor, aerosols and char and these components are finally collected
from the reactor.
While the charcoal is collected using the cyclone separator and stored, the vapour is cooled
rapidly and condensed into high quality bio oil and stored with about almost 70% yield of the
biomass weight - dry weight basically.
Then next is the circulating fluidized bed. So you can have a close look at the image, you can see
that there are 2 different sections. The first one is the fluidized bed here, the main reactor here
and this is the combustor. So the features of this reactor is similar to that of a bubbling fluidized
bed reactor described above except the fact that residence time for the vapors and char is shorter.
This makes the gas velocity and the content of char in the bio oil to be higher. However, it has a
large throughputs advantage, single and double type of these reactors are also available.
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Then next is vacuum pyrolysis reactor. This is a slow pyrolysis reactor with heat transfer rate
very low. This results in a lower bio oil yield usually in the range of 35 to 50 weight percent. The
design is highly complicated and requirement for investment and maintenance is always high
thereby making the technology uneconomically suitable. The biomass is conveyed into the
vacuum chamber with a high temperature with the aid of a conveyor metal belt with periodical
stirring of the biomass by mechanical agitation.
The heat carrier is usually made of a burner while the biomass is melted by heating inductively
using molten salts. So, it has the ability to process larger particle size biomass but requires
special solid feeds, special discharging devices in order to have an effective seal all the time.
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Then rotating cone reactor. Unlike the fluidized bed reactor the rotating cone reactor requires the
mixing of biomass and hot sand mechanically and does not require the use of inert gas. The feed
and the hot sand are fed in from the bottom of the cone while they are transported to the lip of
the cone during spinning using a centrifugal force and as they get up to the tip, the vapour
generated is condensed by the condenser and then you can collect the condensable part.
The char and the sand are combusted with the sand being heated up again and reintroduced to
mix the fresh feedstock at the bottom of the cone. So you take out the char. And char if it is
getting converted and fully combusted, so you basically end up with a certain ash and the ash is
having a low density and it can be easily separated. And the sand which is already containing
high amount of heat can be recycled back. Though the design of this reactor might be complex,
its high bio oil yield makes it extremely desirable.
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So, the 2 different designs which we have already discussed - this is the vacuum pyrolysis
reactor and that is the rotating cone reactor. So, you can have more different stages in the
vacuum pyrolysis reactor, you can have a single stage also, you can have multiple stages also.
Then whatever it is coming out - biomass is usually fed from the top or if it has different distinct
stages, so you can feed from this side also.
There is a condenser which condenses the liquid and you get the liquid here and the char can be
collected from the bottom. Again in the rotating cone reactor also biomass as well as the hot sand
which is carrying the heat is being fed from the top and the cone is rotating.
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So, we will just summarize. So advantages and disadvantages of different pyrolysis reactor. If
you look at fixed bed reactor, the advantages are simplicity in design, reliable results and
biomass size is independent, no fixed biomass size is required. However, the disadvantages are
high carbon conservation, long solid residence time, low ash carry-over and difficult to remove
the char.
If you talk about bubbling fluidized bed, the advantages are the design is simple and easy
operational procedures. However, it suffers from good temperature control and suitable for large
scale application, small particle sizes are needed. There is a small mistake here actually the good
temperature control will come to the advantages.
And for the circulating fluidized bed, the advantages are: well understood technology, better
thermal control, large particle sizes can be processed, disadvantages large scale production
difficulty, complex hydrodynamics and char is very, very fine. So, that char cannot be utilized
for any better purposes you can restrict itself to only soil amendment.
Rotating cone, advantages are: centrifugal force circulates hot sand and biomass substrate, no
carrier gas is required. Difficulty is that: operational processes are (difficult) having
disadvantageous position, smaller particle sizes needed - otherwise you cannot circulate them
and they will deposit on the bottom, large scale application is difficult.
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If you talk about vacuum pyrolysis, the advantages are that: the oil that you get from this
particular reactor is very clean. Can process larger particles of 3 to 5 centimeter, no carrier gas
required, lower temperature required, condensation of liquid product is very easier. The
disadvantages are that: it is a slow process, solid residence time is too high, requires large scale
equipment, poor heat and mass transfer rate and it generates more water.
So, we will talk about the pyrolysis mechanisms. Many dehydration, cracking, isomerization,
dehydrogenation, aromatization, coking and condensation reactions and rearrangements happen
during the pyrolysis reaction. So, the pyrolysis reactions are very complex and predicting them
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for a particular biomass is too difficult. The products are water, carbon oxides, other gases,
charcoal, organic compounds, tar and polymer.
When cellulose is slowly heated at about 250 to 270 degree centigrade, a large quantity of gas is
produced consisting chiefly of carbon dioxide and carbon monoxide. Initially, small amounts of
hydrogen and hydro carbon gases and large amount carbon oxides are emitted. The hydrocarbon
in the product gas then increase with further temperature increases until hydrogen is the main
product. The carbon oxide and most other products owe their formation to the secondary and
further reactions.
(Refer Slide Time: 1:00:10)
Pyrolysis of cellulose yields the best known of the 1, 6-anhydrohexoses, β-glucosan or
levoglucosan, in reasonably good yields. A novel technique based on flash devolatilization of
biomass and direct molecular-beam, mass spectrometric analysis has shown that levoglucosan is
a primary product of the pyrolysis of pure cellulose. However, the yield of levoglucosan on
pyrolysis of most biomass is low even though the cellulose content is about 50 weight percent.
Also, when pure cellulose is treated with only small amount of alkali, levoglucosan formation is
inhibited and a different product slate composed of furan derivatives are produced.
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So, this is the reaction you can see of the β-glucosan formation during pyrolysis. This is from the
β-D-glucose, it’s a mixture, here it can be from cellulose or starch. So, levoglucosan is also
obtained directly on pyrolysis of glucose and starch. The compound has the same empirical
formula as the monomeric building block of the cellulosic polymers.
So, with this I wind up and thank you very much, so in the next class we will be discussing about
the thermal conversion products, what are the different types of products, their composition, their
applications and some certain commercial success stories about the gasification and pyrolysis,
thank you very much. If you have any query please feel free to register it in the swayam portal or
drop a mail to me at kmohanty@iitg.ac.in, thank you.
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Module 05
Lecture-15
Products and Commercial Success Stories
Good morning students, this is lecture 3 of module 5. And in this lecture as you know that we are
discussing about the thermochemical processes. Today we will discuss about the thermal
conversion products and some commercial successful stories. So, let us begin.
Food waste can be classified into four major groups by source generation as residential,
institutional, commercial and industrial. So, we have discussed about different types of
biomasses which includes this type of wastes also. And we will try to understand that how this
food waste has been commercially used to generate different types of value added products
including the biofuels.
Now from these type of food waste, commercial (which takes into account agricultural waste,
supermarket waste), and industrial (for example, food processing industry). So, these food wastes
can be classified as pre-consumption food waste, and whereas residential and institutional like
cafeteria, hospital etc, these wastes are considered to be the post-consumption food waste.
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So, mixed food waste sources from post consumer groups are characterized by high moisture
content almost 60 to 90% very, very high moisture content, including also high organic content
almost 95% dry matter. Along with that there is high salt content and rich nutrition which are
very valuable for recycling and valorization.
The mixed characteristics of postconsumer waste make it more challenging to convert into
energy, bio based materials and high value chemicals. In addition, post consumer institutional
waste generation from cafeterias and hospitals is often contaminated by plastic utensils, because
you know that we have a habit of carrying all these materials in plastic. So, when we consume
the food, we just dump it along with the rest of food waste, so that creates a big problem.
So, by comparison pre consumer food waste is more homogeneous than post consumer mixed
waste. So, post consumer waste is always a mixed waste, so it comes with mixing up
polyethylenes that means plastics as well as paper and some other materials also. So, literature
reports that commercial and industrial food waste are less susceptible to quick deterioration
compared to mixed food waste from residential and institutional waste.
Now food waste conversion into power, heat, fuels and bio-products varies based on the specific
feedstock and is generally categorized into 2 major conversion pathways either biochemical or
thermochemical.
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So, let us understand the thermochemical conversion products of the food waste. Now this
schematic will make you understand that how the different food waste can be converted by both
the routes, one is biochemical as well as thermochemical. So, let us see the first one, biological
one. So, you can go for anaerobic digestion, which will yield me biogas enriched with methane,
you can ferment it.
So, after taking the carbohydrate parts and again do hydrolysis to get glucose. We will get an
ethanol platform, so bio-ethanol apart from small carbon dioxide. So, then coming to
thermochemical, so we can have incineration, incineration will give me heat and electricity. If
you go for pyrolysis and gasification it gives me bio oil, char which is coming from the pyrolysis
and syngas which is a product from gasification, this we have discussed in our last class.
So, another important thing is hydrothermal carbonization. So, that will give me hydrochar or
char and some gases. Now this makes an understanding that food waste having enormous
potential to be converted into so many different types of value added products apart from the
energy either using the biological route or your thermochemical route.
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Let us understand the thermal conversion of post consumer mixed food waste by gasification. So,
postconsumer food waste from residential, institutional and some commercial sectors is
represented by heterogeneous chemical characteristics. So, because they include carbohydrates,
lipid, amino acids, phosphates, vitamins and carbon, but also containing other substances. In
addition, postconsumer mixed waste may have a high moisture content.
Now it has been reported that average proximate analysis of food waste is 80% volatile matter,
50% fixed carbon, 5% ash. So, this is just a generalized statistic for most of the so called
postconsumer mixed waste. However, research on thermal decomposition of mixed food waste
suggests that with a moisture content higher than 45%, a steam gasification approach would be
viable because the water vapor liberated in the pyrolysis test can be used in the gasification stage
and therefore, the energy consumed to evaporate moisture can be recovered.
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Generally, the char gasification stage is slower than the prior pyrolysis stage and that is why it is
the rate limiting step. And understanding the catalytic effect of char on the overall efficiency of
gasification is essential. Because of the presence of inorganic constituents in the food waste, char
from the initial pyrolysis step was found to have a catalytic effect. If you recall our last lecture,
then I precisely told you that when you talk about pyrolysis and gasification, please understand
that pyrolysis is also a part of gasification.
This is what we are talking about here also. So, when gasification proceeds or starts, so the initial
step is your dehydration or let us we can say that removal of the moisture around up to 150, 200
degrees centigrade beyond that your pyrolysis reaction starts in, so in the pyrolysis we will get a
char. So, the resultant is char and very small amount of gas and other materials will come into
picture.
Now this char with the help of either steam or air will be converted or let us say will be gasified
with less than a theoretical amount of oxygen that is required to do combustion is required for
the gasification process. So, that much amount of oxygen will gasify either it can be oxygen or it
can be a steam. So, another important thing which here also we are mentioning that the char may
contain several different types of inorganic materials.
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So, these inorganic materials have a vital role to play during the gasification process. So, they
may act as a catalyst during the gasification process thereby enhancing the rate of reaction and
also increasing the yield. So, char reactivity increased with the degree of conversion. Research
on post-consumer mixed food waste considered pre-processing the food waste by dehydrating,
grinding and palletizing due to the heterogeneous properties of the waste.
Comparison of simulated gasification results with direct combustion indicated that, although
combustion of pelletized food waste is energetically comparable to wood combustion,
gasification results are also in agreement with other biomass gasification literature.
So, this is the schematic of the thermal conversion of post consumer mixed food waste through
gasification. So, unprepared food, so this is the food preparation, so you can see the spoilage,
unserved excess, so this is pre consumer waste. So, then of course water is hugely consumed
during the processing of the food.
So, then prepared food, that goes to the food service, so you get consumed food and whatever
served excess plate waste all these different types of wastes are being mixed. Plastics, then some
cutlery things, your paper napkins all these things come into this, so that is post consumer waste.
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Now let us talk about the another very important product of the gasification that is, the syngas.
So, the immediate near-term opportunities for lignocellulosic biorefineries use lignin for the
process heat, power and steam. However, there are other opportunities to consider for lignin that
would be implemented in the 3 to 10 years’ timeframe. Although these opportunities have
technical challenges, they have few technology barrier, and R & D support can be largely limited
to process engineering, recovery and integration refinements.
Lignin combustion is practiced today in paper mills to produce process heat, power, steam and to
recover pulping chemicals. For lignocellulosic biorefineries, there will be technical challenges
around material handling, and overall heat balance and integration.
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Lignin gasification produces syngas which is enriched with carbon monoxide and hydrogen. The
addition of a second step employing water gas shift technology allows production of a pure
hydrogen steam with co formation of carbon dioxide. Now hydrogen can be used to make
electricity, for example in fuel cell applications or for hydrogenation and hydrogenolysis
applications.
Now syngas can be used in different ways; technologies to produce DME that is the methanol/
dimethyl ether is well established. The products can be used directly or maybe converted to
green gasoline via the methanol to gasoline that is called MTG process or to olefins via the
methanol to olefin process which is known as MTO. So, these processes are very well
established and commercially adapted also.
Now because of the high degree of technology development in the methanol DME catalysts and
processes, the use of lignin derived syngas could be readily implemented. Now the technology
needs include the economic purification of syngas and demonstration that gasification can
proceed smoothly with biorefinery lignin.
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The FT technology, the Fischer Tropsch technology to produce green diesel represents another
use of lignin derived syngas. For example, Sasol has a extensive technology in this area. The
technical needs for the FT include economical purification of syngas streams and catalysts and
process improvements to reduce unwanted products such as methane and higher molecular
weight compounds such as waxes.
So, there are a lot of technology development has happened since last 2 decades for the FT
technology. So, that all these, such drawbacks which has been mentioned would be overcome.
The conversion of syngas to mixed alcohols has not been commercialized, it would allow the
production of ethanol and other fuel alcohols or high value alcohol chemicals. A major challenge
for this technology is catalyst and process improvements to increase space time yields.
So, the catalysts are lacking in selectivity and rate and that is the reason so many academicians
and scientists are working day and night on developing different types of catalysts, which will
have a better selectivity as well as rate for different processes, it is not about FT also, there are
many other processes. In chemical reaction engineering, in energy production in other
environmental application, in so many different areas.
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Although syngas production via gasification is a well developed technology for coal and natural
gas, there is continuing controversy over gasification economics at the scale anticipated for the
lignocellulosic biorefinery. Because see if you remember we have discussed all these things, one
of the most important aspect of the entire biorefinery or if you precisely talk about
lignocellulosic biorefinery is that unless until we aim and get or we produce, let us say we
produce different high value products which comes out or derived from the byproducts as well as
from the waste, then the lignocellulosic biorefinery cannot be sustainable. And one more
important part lignocellulosic biorefinery aspect is that, the different types of feedstocks that
required to be treated in a single biorefinery without changing the equipments, process streams
or maybe with a little modification or less interference in the process dynamics.
So, these are the challenges already exist, and people are working day and night to overcome
this. So, a better understanding of this issue is needed which may lead to identification of
specific improvements needed in overall gasification technology. Gasification of different lignin
sources may also differ; this is what I was just mentioning. For example, gasification a black
liquor a byproduct of pulping has been problematic within industry, that has due to the
concentration as well as also the viscosity also played a big role during conversion.
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So, this is a thermochemcial standalone gasifier, where it fits into a biorefinery in numerous
ways. For example, this is a standalone process where the biomass residues would be fed directly
into the gasifier, the resultant syngas would then be converted to products such as FT liquids.
That means we can call it green fuels, methanol or mixed alcohols.
So in another example, the gasifier is integrated into a biochemical lignocellulosic biorefinery.
Now in this particular example, the biochemical or thermochemical integrated biorefinery, the
lignin rich residues from lignocellulosic feedstock are fed into the gasifier. Now sugars are
primarily converted to ethanol while the lignin is primarily converted into the syngas products.
So, this is also very simplified and highly adapted technology across various biorefineries.
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So, now let us understand the pyrolysis products. So, among all the different types of pyrolysis
which we have discussed in last class, fast pyrolysis is readily adaptable by most of the
industries, because of it is high yield of bio oil or pyrolysis oil. So, fast pyrolysis is a method that
converts dry biomass to a liquid product known as pyrolysis oil or bio oil.
As produced bio oils are generally quite unstable to viscosity changes and oxidation, which
makes their use for chemicals and fuels problematic. So, pyrolysis oils could be incorporated into
various petroleum refinery processes provided they are appropriately pretreated and stabilized.
So, the outcome, would be displacement of a fraction of imported petroleum and the production
of green fuels and chemicals.
Now technology needs include preconditioning, the pyrolysis oil before stabilization, then
catalyst and process development to stabilize the pyrolysis oil for storage and transport from a
bio refinery to a petroleum refinery. Then validation of the stabilized pyrolysis oil compatibility
with current petroleum conversion catalysts and processes.
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Now let us look at this particular pyrolysis integrated with gasification technology process. So,
the pyrolysis technology could be the basis for a standalone biorefinery, that is integrated into a
biochemical or thermochemical refinery. So, you can see here, so the forest residue is pyrolyzed,
this is a pyrolysis technology here. So, whatever the pyrolytic lignin is left out that goes to the
hydrotreating or hydrocracking, where we get green gasoline, green diesel, this type of fractions.
Then water soluble pyrolysis oil, because I told you and again I am repeating, that whenever we
talk about bio oil, pyrolytic oil, pyrolysis oil, please understand that it has a huge amount of
aqueous fraction and that needs to be decanted, because the oil is the only organic phase that is
useful for us. So, that goes to reforming, then syngas, then alcohol synthesis, then we get a
ethanol or we may get methanol, n- propanol, n-butanol and n-pentanol.
So, the fast pyrolysis needs a dry precursor, absolutely dry precursor, dry feedstock, 0.5 second,
500 degrees centigrade, 1 atm - very fast process and it needs inert atmosphere and solid particle
heat carrier, so this is what is required. So, products are pyrolysis oil, aqueous phase. So aqueous
phase as I told you, again I am telling you that it may contain different types of valuable
chemicals, now depending upon what is the feedstock.
And if their concentration in this aqueous phase is good enough, and it is a high value product
then it should be purified. But please again note that purification that is the downstream
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processing part is a very costly affair. So in commercial applications are liquid, smoke, resins,
mixtures, there are so many applications.
So, this is the biochemical thermochemical pyrolysis biorefinery. So, here the feedstock is corn
stover. So, the corn stover is being processed into the ethanol platform where ethanol is being
produced as one of the product whatever left out is the lignin residues goes to pyrolysis. Then it
again another stage where we are hydrotreating or hydrocracking it to get green gasoline. And
the coal also can be used to do the steam generation and steam as well as power and it is a
integrated part of the entire biorefinery system, where both gasification and pyrolysis are taking
place .
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So, the next example is the bio oil derived products’ selective hydro deoxygenation. Now mild
hydro deoxygenation is of interest to remove oxygen functional groups and produce olefins as
reactive hydrocarbon feedstock. Now please note that, bio oil usually contains a huge amount of
oxygen which are not desirable, if we are going to use in any engines, where the fuel is getting
burnt, so it has to be removed. So, to do that hydro deoxygenation is one of the technology.
So, for example, mild hydro deoxygenation of acetone can produce propylene that can be used to
produce valuable C3 chemicals. As for example acrylic acid and acrylates, acrylonitrile, pyridine
propylene oxide and 1, 2-propane diol, and the most consumed polymer is polypropylene.
Aliphatic and cyclic ketones are common oxygenate compounds found in bio oil and a lot more
in upgrading of the bio oil by ketonization process. The direct reduction usually leads to
formation of paraffin and alcohol when drastic and/or mild condition is used respectively.
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A catalytic system designed for mild hydro deoxygenation of ketone to olefin was investigated.
Hydrogenation of ketone to alcohol was accomplished over metal catalyst, various types of
metals has been studied - nickel, copper, iron, cobalt, platinum and their alloys - at low
temperature. The alcohol produced was then dehydrated over acidic catalyst. Hydrogenation and
dehydration were separately studied in order to understand the role of each catalytic function.
Now that integrated hydrogenation-dehydration over double bed, physical mixed bed and bi-
functional catalyst bed were then optimized to allow only essential amount of hydrogen
consumption in the first stage.
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This is one schematic of how selective HDO ketone is being carried out. So, this is the reference
of this particular paper has been given here, you can go through it later, Catalysts science and
technology; it is a very nice interesting work. So, what is happening here you can see this is
ketonization. So, your bio oil is getting impregnated over the catalyst surface here it is copper.
So, resulting in a corresponding alcohol, now that alcohol will be dehydrated using another
catalyst which are basically acidic catalyst. So, a rapid dehydration synergistically prevents
reversible dehydrogenation of alcohol while excessive olefin hydrogenation can be limited over
selected metal. So, you can read a little more and about this particular work.
So, let us now discuss about furfural, which is one of the most important platform chemicals
from such biorefineries. Now furfural identified as one of the top 30 platform chemicals derived
from biomass is an important fuel precursor, which can be converted to hydrocarbon fuels and
fuel intermediates. With current global production greater than 200,000 tonnes annually it is
currently a high value commercial commodity chemical produced primarily from agricultural
waste, such as oat hulls, corn cobs and sugarcane bagasse.
Industrial processes for furfural production were developed as early as 1921 when the Quaker
Oats batch process was developed to produce furfural from oat hulls. Since then many alternative
batch and continuous processes have been developed, with most of the batch operations
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primarily using sulfuric acid as a homogeneous acid catalyst, and temperatures ranging between
160 to 200 degrees centigrade.
High operating costs and low energy efficiency coupled with low furfural yield, on the order of
less than 50% resulted in the closure of batch plants in 1990s. So, another significant industrial
continuous process for furfural production was developed by Quaker Oats which was operated
for 40 years in Belle Glade in Florida until 1997. Now the continuous process utilized a
traditional horizontal screw style reactor similar to the 1 ton per day horizontal reactor system
which was installed in Metso, used at the NREL laboratory for diluted acid pretreatment. A
slightly improved furfural yield of about 55% was obtained in the continuous process developed
by the Quaker Oats using a residence time of one hour. While this process was technically
successful, the plant ultimately shut down due to the high maintenance cost of the continuous
reactor system. So, with this you can understand it is not about only the technology, the
processing cost is very important.
The yield is important, the entire cost whatever you are actually going to have it during the
processing of this any product is very much important. So, in industrial parlance the most
important thing to decide is about the cost. The cost means several different types of costs, which
we have already discussed.
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So, improving furfural yield beyond 55% in industrial production has been the subject of much
research since last 100 years. This is a difficult task because furfural once produced, rapidly
degrades through resinification and condensation reactions. So, furfural resinification is a
reaction in which furfural reacts with itself, while condensation reactions occur when furfural
reacts with xylose or one of the intermediates of xylose to furfural conversion to form furfural
pentose or di-furfural pentose.
Now resinification is, you can say some sort of autonomous process. The loss of furfural by
condensation is significantly greater than those by resinification. Much research has been
conducted in recent decades to try to minimize degradation and improve furfural yield.
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The main focus of the process improvements to achieve higher furfural yield can be categorized
into three ways. First is by improving furfural removal efficiency using steam or an inert gas, for
example the Suprayield process which uses nitrogen stripping. Second is that by extracting
furfural using a secondary organic phase in a biphasic reaction, for example using cyclopentyl
methyl ether CPME 26, o-nitortoluene, tetrahydrofuran, and/or γ-valerolactone.
So, another technique is by using different homogeneous or heterogeneous solid catalyst, for
example maleic acid27, formic acid21, metal salts and or Amberlyst70.
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Now production value of added chemical furfural from biomass you can understand, this is just a
schematic. A corn stover has been shown, it has to be pretreated, pretreated is very important we
have discussed how it has been carried out in one of our module exclusively that dedicated to
this. Then it will give us pentose sugars, now this pentose sugar under dehydration will give me
furfural.
The first furfural production plant was a batch process originally developed by Quaker Oats in
1920s in the United States. In this process, biomass was treated with acid, aqueous sulfuric acid
or phosphoric acid and steam at 153 degrees centigrade in a hydrolysis step, which could convert
the pentosans in the biomass to pentoses. The generated pentoses were then converted into
furfural in a subsequent stage, and then furfural was recovered by steam stripping from solution.
However, the drawback of this process was very low yield - less than 50% based on mono
sugars, substantial steam requirements, steam is a very costly product in any process industries,
then high effluent production. High effluent in this case is very acidic wastewater and high
operating costs which lead to the closure of the plants in developed countries till 1990s.
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The rather low yield of this process was attributed to the fact that the first step that was the
hydrolysis reaction was 50 times faster than the second step that is the dehydration. So, there is a
mismatch about the rate of reaction of both the steps. So consequently a significant number of
side reactions occurred because of the high availability of mono sugars in the process, which
ultimately reduce the quantity of mono sugars available for furfural production.
Recently, Westpro has modified the Quaker Oats technology process in China into a continuous
process, and it has been quite successful process. Now this method uses fixed bed reactors and a
continuous dynamic azeotropic distillation refining process, which led to a 4 to 12% production
yield with respect to the initial weight of dry biomass used, corn cobs, rice hulls, flax dregs,
cotton hulls, sugarcane bagasse, wood, so many different types of feedstock has been tried.
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SupraYield is another modification of the Quaker Oats technology process introduced in the late
1990s. In this technology lignocelluloses are hydrolyzed in one stage and then pentoses are
converted into furfural in the aqueous solution at it is boiling point with or without phosphoric
acid as a catalyst. The solution containing furfural is then adiabatically flash distilled, which
facilitates the transfer of the furfural formed from the aqueous phase to the vapor purpose. This
process has a production yield of 50 to 70% and is less expensive than the traditional process
described above.
So, now we will see some of the commercial success stories. First in the world biorefinery
producing wood based renewable biodiesel is the UPM biofuels. So, UPM biofuels is a big
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company in Finland, has developed an innovative production process from the crude tall oil, a
natural wood extract and a residue of pulp making process, to biofuel for transportation. So, their
product is known as UPM BioVerno, is a unique wood based renewable diesel resembling
almost the fossil diesel, suitable for current distribution systems and all diesel engines without
any modification. The greenhouse gas emissions are reduced significantly over 80%, it is a very
significant result. And in addition, tailpipe emissions such as NOx and other particles are
reduced significantly. Converting that crude tall oil - many times called Talal also - to biofuel is
an innovative way to use an own process residue without changing the main process that is the
pulp production.
So, this bio refinery has been integrated to the original pulp production unit, where you are using
the pulp production waste and converting it to diesel.
So, the key success factor is certified sustainability, it is very interesting. So, feedstock is wood
based non food origin with no increase in harvesting or land use. So, no question of any food
versus feed problem, and the greenhouse gas emission reduction is significant. Distributors value
the high stability of this high quality oxygen free hydrocarbon fuel as it functions as direct
replacement for fossil diesel.
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There are no blending limitations like in the first generation bio diesels. As a result UPM
produces a cost competitive high quality transport fuel that truly decreases emissions. During
2017, production efficiency has increased significantly and energy consumption was reduced by
25%. Another significant improvement in that entire integrated biorefinery technology.
Currently, UPM biofuels is evaluating growth opportunities for a possible second biorefinery in
Mussalo, that is in Kotka, in southeastern Finland with a planned capacity of 500,000 tons.
This is a photo of actually the UPM Biorefinery, UPM Biorefinery is also an excellent example
of innovation in the forest industry, as it utilizes the residue of pulp production, does not increase
harvesting of forest, but provides an environmentally friendly option for the transport. In
addition, tailpipe emissions such as NOx and particles are reduced significantly, so it is a win-
win story basically.
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So, this is their refinery production process, let us quickly glance through it and understand, this
is being given in a nutshell. So, this is the crude tall oil, a residue of chemical pulping process
containing the natural extractive components of the wood which they have used as a feedstock.
Now this goes to that pretreatment. So, crude tall oil is purified, so the salts, impurities, solid
particles and water are removed.
And this is a quite energy intensive and cost intensive process, then it goes to the hydro
treatment. So, in the hydro treatment pretreated crude tall oil is fed together with makeup and
recycled hydrogen to the reactor where the chemical structure is modified. So, the reaction water
is separated and directed to wastewater treatment plant. They have a very good in-house and very
efficient wastewater treatment plan also, where they recycle water.
Then it goes to the fractionation, so here the remaining hydrogen sulfide and uncondensable
gases are removed, the remaining liquid is distilled to separate renewable diesel. Then you get
the renewable diesel and otherwise renewable naphtha both way they produce. So, fantastic
technology and a very nice integrated biorefinery.
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So, next is our own Indian success story. So that DBT-ICT, 2G Ethanol Technology, so DBT is
the Department of biotechnology, Government of India and ICT, the Institute of Chemical
Technology mostly, many of few may be knowing it as a UDCT it is in Mumbai, India. So,
DBT-ICT 2G Ethanol Technology has been validated and demonstrated at a scale of 10 ton
biomass per day at India Glycols limited site at Kashipur, Uttarakhand.
The technology and plant designed at feedstock flexible that is the beauty of this technology, any
biomass feedstock from hardwood chips and cotton stock to soft bagasse and rice straw can be
processed and has been processed. The technology employs continuous processing from biomass
size reduction to fermentation and converts biomass feed to alcohol within 24 hours compared to
other technologies that take anywhere from 3 to 5 days, another significant milestone achieved.
So, the plant design with a low footprint also has unique features such as advanced reactor
design and separation technologies with slurry flow rapid reaction regime operations.
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So, this is what in a nutshell we can describe it. The process outline, lignocellulosic biomass as I
told any biomass soft, hard does not matter. It will be pretreated, the first step is always
pretreatment, then it will goes to saccharification, that separation, fermentation and purification,
you get sugars, lignin, alcohol can further be processed into other products.
So, fractionation to sugars, lignin, rapid and efficient process less than 24 hours, high
conversion, enzyme and chemical that is whatever being used are recycled. So, zero waste
almost zero waste technology we can say and silica and inorganic recovery is also being carried
out, especially when you are using this rice husk and other bagasses which contains some
amount of silica in it, so excellent technology.
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So, this is how they have processed, this you see lab scale process 1 kg per day, 2009 it was
developed in the lab scale in ICT. So, then it goes to a pilot scale 1 ton per day in 2010 to 13 that
they have tested. And then it goes to a pre commercial scale 10 ton per day in March 2016, now
it is a full scale plant.
So, the achievements, if you talk about achievements, that technology has several novel features
and achievements, that marks it apart from other globally promoted technologies. The first is 2
steps alkali soda-nitric acid fractionation. Second, slurry flow systems with recycle and reuse of
water, alkali and acid. Then next feedstock agnostic technology, this is the most beautiful part of
this entire technology. Any biomass feedstock from hardwood chips and cotton stalk to soft
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bagasse and rice straw can be processed. Lowest enzyme dosage on account of enzyme reuse
over weeks. No fancy metallurgy hence low capital expenditure.
Low cost of production with recycling of enzymes, chemicals and water, low consumption of
power and water. And demonstration plant ran smoothly from the first run without any problem
related to solid handling and other issues that plague other technologies, so excellent technology.
So, challenges that this technology addressed are scalable technology to a wide range from 100
tons biomass per day to 500 ton per day as the technology can find decentralized deployment in
the Indian agricultural heartland not only providing biofuel options for India, but positively
impacting farm revenues for farmers. Creation of jobs, net reduction in import of crude oil and
reduction in carbon emissions, thereby fuelling India's green economic growth engine, so it is a
fantastic technology.
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So, based on the data generated at the 10 tons per day plant basic and detailed engineering has
been carried out for a 450 ton per day rice straw processing plant to produce 100 kilo liter per
day fuel grade ethanol. This plant shall come up and start operations in 2020. The 10-ton
biomass per day plant was scaled up in one go from a 1-ton biomass per day plant. The scale up
went without any hitch and the plant could be operated end to end from size reduction to
fermentation, including all the continuous flow system in a single week.
So, DBT-ICT technology is feedstock agnostic, however as per the biomass availability survey
in Bathinda region rice straw and cotton stalk will be used as raw material in their Bathinda
plant. So, feedstock capacity is 450 tons biomass processing per day.
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Next such commercial adaptation is the biomass technology group BTG. So, here the pyrolysis
has been adapted. Pyrolysis offers the possibility of decoupling, time, place and scale, easy
handling of the liquids and a more consistent quality compared to any solid biomass. With fast
pyrolysis a clean liquid is produced as an intermediate suitable for a wide variety of applications.
BTG's fast pyrolysis process is based on the rotating cone reactor developed by the University of
Twente in Netherlands.
Biomass particles at room temperature and hot sand particles are introduced near the bottom of
the cone where the solids are mixed and transported upwards by the rotating action of the cone.
In this type of reactor rapid heating, and a short gas phase residence time can be realized. The
initial work of the University of Twente has been the basis for BTG to further develop pyrolysis
reactor and the overall process. Since 1993, BTG has been involved in numerous projects on fast
pyrolysis.
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Biomass particles are fed near the bottom of the pyrolysis reactor together with an excess flow of
hot heat carrier material such as sand where it is being pyrolyzed. We have already seen that how
sand can be used as a heat carrier. So, the produced vapors pass through several cyclones before
entering the condenser, in which the vapors are quenched by re-circulated oil.
The pyrolysis reactor is integrated in a circulating sand system composed of a riser, a fluidized
bed char combustor, the pyrolysis reactor and a down-comer. So, these are the parts of the unit.
Now in this concept char is burned with air to provide the heat required for the pyrolysis process.
Oil is the main product, non condensable pyrolysis gases are combusted and can be used as for
example to generate additional steam. Now excess heat can be used for drying the feedstock.
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Two test facilities are available in BTG’s lab, a small unit 2 to 3 kg per hour to enable rapid
screening of potential feedstock and a 100 to 200 kg per hour pilot plant. Due to large amounts
of oxygenated compounds present the oil has a polar nature and does not mix readily with
hydrocarbons. The degradation products from the biomass constituents include organic acids like
formic acid, acetic acid, giving the oil its low pH.
Water is an integral part of the single phase chemical solution. The hydrophilic bio oils have a
water content of typically 15 to 35 weight percent. Again as you know that this depends upon
what feedstock you are using and how much initial moisture content that feedstock is having. So,
typically phase separation does occur when the water content is higher than that of the 30 to
45%.
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So, BTG’s full scale plant takes into account 2 tons per hour fast pyrolysis process and it was
constructed, designed and delivered to Malaysia. In the factory located closely to an existing
palm mill where what they are using actually the empty fruit bunches or you can say the empty
palm fruit bunches are converted into the pyrolysis oil. Usually the wet EFB where the moisture
is about 65% are combusted on-site yielding only ash which can be recycled to the plantations.
The palm mill produces about 6 ton per hour of this wet EFB, empty fruit bunches. So, the empty
fruit bunches can be converted into pyrolysis oil using BTG’s fast pyrolysis technology. Prior to
feeding it to the pyrolysis plant the EFB is further sized and dried. In a dryer the moisture
content is reduced down to about 5 to 10%. In this way, all the wet EFB from the palm is
converted into approximately 1.2 ton per hour pyrolysis oil.
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This is their technology, very simple technology, but nicely integrated, so that the yield of the
pyrolytic oil is very high. You can see this biomass is fed to this circulated sand based reactor
where actually the pyrolysis is happening here. So, the gas or the vapors, what is coming out of
the pyrolysis is being feed to a tower which is basically cooler , where it is the condensable part
is condensed and you get the oil here.
Now what about non condensable gases - that can be collected and burnt. Similarly you can see
that the sand along with the char whatever left out is from the pyrolysis reactor is being fed to
another unit where the sand has been recovered and again can be processed or fed back to the
main pyrolyzer or the pyrolysis reactor. And whatever the gas is still left out that can be fed to
another cyclone, where the ash can be collected. Because of the due to the density difference and
that gas can go to steam production. So, you can see this is a very nice integrated approach.
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So, in Hengelo, the Netherlands a 5 tons per hour pyrolysis plant is planned. This unit will
convert wood into pyrolysis oil, process steam and electricity. The main advantages for the BTG-
BTL’s technology in comparison to other pyrolysis technologies are: high biomass throughput
per reactor volume resulting in compact reactor design. Absence of inert carrier gas resulting in
minimum downstream equipment size.
Maximum calorific value of pyrolysis gas actually, very simple process, no gas cycle required.
High flexibility for feedstocks, so waste material, large particle size, all these feedstocks can be
actually processed. Low amount of solids in the oil.
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The compact design of the modified rotating cone reactor makes scaling up straight forward to
capacities larger than 5 tons per hour. Now BTL standard design includes recovery of excess
heat in the form of steam which can be used for the industrial or local heating applications and
electricity production. Now depending on local conditions, energy efficiencies of 85 to 90% can
be achieved, so that is based on biomass and oil, heat, electricity out.
So, because of the feed flexibility, BTL’s technology can also handle biomasses with low ash
melting temperature, such as palm derived EFB’s. Now BTL’s technology can process particles
with a thickness of up to 3 mm. So, 2 beautiful things about this particular technology is that it
can just like our DBT-ICT 2G ethanol technology. Now this technology also can process
different types of feedstock materials not only different types of feedstock also different size of
feedstock also.
Fluid bed technologies may use similar sized particles, while CFB technology must use smaller
ones as a residence times are limited, CFB with the circulating fluidized bed technology.
So, this is the BTG-BTL plant process flow diagram. So, you can see that wet biomass right
now, once it comes it is being fed to some sort of dryer where air is being used and the moisture
is taken out. So, the biomass is getting dried then it is collected somewhere. Now here there is a
587

conveyer system you can see that which is basically taking the biomass up and put it in the
somewhere in the top where there is the feeder.
From here the biomass is slowly fed to the main reactor, here the pyrolysis is happening. Now
from the main reactor, it goes to the separator and air is being fed also here. So, what it is
separating is the sand and char, the solid part. So, the sand and char is being separated and char is
being fed to the char combustor, where the flue gas is being taken away from the top and is being
used for steam generation and some other purposes.
And the oil whatever it is getting converted from here the condensable part that goes straight to
the condenser, where the oil is getting condensed and collected and further processed. So, this is
a simple and nicely integrated technology by the BTG-BTL technology, and the yield is very
high. And as we have already discussed that it can process any type of feedstock as well as
different sizes of the feedstock particles also.
So, the next is again an Indian success story it is about the Praj biorefinery, so Praj second
generation biomass to bioethanol technology which is named as enfinity and biomethanation of
stillage to biogas and renewable CNG, is a beautiful technology which is actually being praised
by most of the western countries also. So, it is located in Pune, Maharashtra, and the plant’s
capacity is 1 million liters per annum.
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The principle feedstocks are rice straw, sugar cane bagasse, wheat straw, corn cobs, corn stover,
cotton stalk and saw dust, and please understand there are many more also, these are the
principle feedstock of course. The feedstock capacity is more than 4000 metric tons per year on a
bone dry basis. So, feedstock supply arranged through local farmers and biomass suppliers from
different parts of India.
Praj’s state of the art second generation ethanol pilot plant facility is operational since 2009. This
facility has tested more than 450 metric ton of biomass such as corn cob, cane bagasse and other
things. Empty fruit bunches, rice straw also has been processed. Rigorous testing and 800,000
man hours of technology development efforts enabled Praj to scale the Enfinity to 1 million liters
per annum capacity.
Multi-product, so the plant is designed to produce bio-ethanol, bio-gas or bioCNG, bio-fertilizer
and there is also provision for production of biochemicals, Iso-butanol to jet fuel. End to end
technology demonstration from feedstock processing till end product and wastewater treatment.
Zero process liquid discharge, that is very interesting actually. Process integration for
optimization of energy and water consumption.
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Efficient pretreatment technology developed after extensive screening, enzymatic hydrolysis
optimized after numerous cocktails. Behavior of different feedstocks were studied by applying
different process treatment. Enzymatic hydrolysis reactor based on CFD modeling studies, the
fermentation process using robust co-fermenting yeast strain was developed. Strain development
involved both classical and targeted techniques for improved yields and titer. Residue which is
rich in lignin used as fuel for boiler to generate steam and electricity.
So, this is Praj’s smart biorefinery concept, so the first generation and second generation it has
both it is taking to account. Molasses, juice, grain, lignocellulosic, municipal solid waste. So, it
goes to the smart biorefinery processing where we get this multiple products such as fuel grade
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ethanol, pharma grade ethanol also, then iso-butanol, biochemicals and bio jet fuel. And left out
can be used as biofertilizers, biogas it can be converted to biogas, bio CNG and lignin cake,
lignin cake can be further pyrolysed also.
So, this is the entire schematic process, this is the business model for their energy production
from biomass. So, the biomass pretreated, pretreated slurry coming to enzymatic hydrolysis, it is
getting fermented, you get purification distillation process, dehydration you get the ethanol,
ethanol is stored here. So, the lignin cake from here the liquid solid separation process can be
processed in this platform. It is a co-generation platform where you can use gasification,
pyrolysis any other things to again generate the power, in a CHP platform module. And that is
you can see the utility of the existing distillery process and the 2G bolt on moduler, here it is
pretreatment, enzymatic hydrolysis. This is hydrolyzed slurry that goes to fermentation process,
so this is a very nice and beautiful technology which was developed by Praj.
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So, the Praj process actually it ensures healthy lives and promote well-being of all at all ages:
Smoke produced due to the burning of the agricultural crop residue deteriorated the human
health, by using residue in the process to produce bioethanol will avoid the burning of crop
residue, resulting in improving air quality and human health, one of the most important aspect.
Second is, they ensure a sustainable consumption and production patterns. It ensures the
sustainable crop production and economical development of the society. Crop residue generated
is going to be consumed by such projects, it assures crop production and its utilization pattern.
Ethanol produced from such projects will also help to meet the demand of ethanol blending
target of the said state.
So, it further ensures access to affordable, reliable, sustainable and modern energy for all. So,
production of ethanol from crop residues and making it available for transport fuel ensures
affordability reliability to the society.
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So, with this I end my today’s lecture. So, if you have any queries please feel free to register
your query in the swayam portal or else you can drop a mail to me at kmohanty@iitg.ac.in. So,
in the next module that is module 6 we will discuss the microbial conversion process, so thank
you very much.
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Module 06
Lecture-16
Types, Fundamentals, Equipments, Applications
Good morning students. Today we are starting module 6, and under module 6 we will be
discussing about the various microbial conversion processes. So, in today’s lecture we will be
discussing different types of microbial conversion processes, then the fundamentals basically
and what are the equipments that are being used for the microbial conversion processes and
few applications. So, let us begin.
So, biochemical conversion processes allow the decomposition of biomass to available
carbohydrates, which could be converted into liquid fuels and biogas as well as different
types of bioproducts using biological agents such as bacteria and enzymes etc. Now, in this
process, various soluble and gaseous metabolites including alcohols, volatile fatty acids,
methane, carbon dioxide and hydrogen can be produced through pure and complex
microorganisms.
Some of the processes that are having tremendous commercial application are anaerobic
digestion, fermentation, microbial fuel cell or microbial electrochemical systems and
composting.
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So, we will see all of these briefly. So, first one is anaerobic digestion. Now, anaerobic
digestion is a multi-step biological process that is useful not only for proper waste
management, but also for generating renewable energy. It consists of 4 basic stages:
hydrolysis, acidogenesis, acetogenesis and methanogenesis. Now, during the whole process,
there are a series of chemical reactions occurring through natural metabolic pathways enabled
by microorganisms in an oxygen free environment.
So, anaerobic digestion means basically, the entire process is happening without oxygen.
Now, these reactions break down the organic macromolecules into simpler molecules,
leading to the generation of biogas. So, biogas basically here, it is a mixture of methane and
carbon dioxide, as well as traces of other gases and digestate.
Now, the feedstocks commonly used for this type of processes include sewage sludge,
agricultural residues, the municipal solid residue and animal manure. Anaerobic digestion can
be carried out at the mesophiclic which is basically from 20 to 45 degrees centigrade, or
thermophilic range from 45 to 60 degrees centigrade conditions.
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Many factors including hydraulic retention time, organic loading rate and substrates can also
affect the fermentation performance. Now, substrates containing excessive inhibitors such as
ammonia, sulphide, metals and organics may make the fermentation process more instable
resulting in a low yield of bio-methane.
Actually, what happens during an anaerobic digestion process? So, when the process is
happening, there are many byproducts that are produced. Now, some of these are actually not
required for that particular environment. So, we can call them that, they are inhibitors or toxic
compounds. Now, what way they are inhibiting basically? So beyond certain limit, if they are
getting produced and again let us say produced and remained in the environment or in the
process equipment itself, then they will hamper the growth of the microorganisms and their
metabolic activities. Now, so, that is not good. So, in any such fermentation process,
including anaerobic digestion, when such type of inhibitory compounds are getting formed, it
is required that these compounds needs to be removed frequently. So, as to maintain their
concentration inside the equipment, at a very small level, so that they are not going to inhibit
the metabolic activity of the microorganisms.
Apart from that, if we go for a short hydraulic retention time, so that might lead to the risk of
wash out of microbial communities. So, retention time basically means how much time the
feed is going to be spent or going to be processed inside a particular reactor. So, a high OLR
that means organic loading rate will boost the acidogenesis stage. So, that means the
feedstock is very much enriched with the organic compound.
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So, if you have a high OLR, so it will boost the acidogenesis stage of easily degradable
substrates and the excessive accumulation of volatile fatty acids may further inhibit the
activity of microorganisms. So, precisely this means that if you have a high organic loading
so there will be faster degradation of the easily degradable substrates, basically during the
acidogenesis stage, which usually results into the volatile fatty acids.
And even though volatile fatty acids are important, but beyond certain limit again, they will
inhibit the activity of the microorganisms. The biogas produced possesses an energy content
of 20 to 40% lower than the heating value of the raw material. Now, the process is ideal for
organic waste with a moisture content ranging between 80 to 90%. One of the advantages of
the process lies in the potential of the final biogas to be used directly in ignition gas engines
and gas turbines.
The overall conversion efficiency of the process is 21%. Residual heat from the engines and
turbines can be recovered through an exchange. So, I told you in the last class or even last to
last class when we were discussing about thermochemical conversion process, I told you that
when any such conversion processes whether it is thermochemical, biochemical or any other
unit operations are going on, so, usually there is some heat generation. Now, that heat
generation even if it is not so high also, if we can harness that heat generation by some waste
heat recovery process and recycle back it to some other unit which requires the heat, maybe
for steam generation, maybe for drying the biomass, then it will be a very good thing or we
can say it will help us in a sustainable bio-refinery approach.
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We will see the reaction steps. The first one is hydrolysis. So, hydrolysis represents the initial
phase of the process. Biomass that consists of very large organic polymers such as fats,
carbohydrates and proteins are converted into smaller molecules such as fatty acids, simple
sugars and amino acids. It should be noted that most of the large molecules are further
decomposed in the acidogenesis stage. On the other hand, other by-products resulting from
the hydrolysis stage including hydrogen and acetate are used in the final stage of the process
that is methanogenesis.
The second step is acidogenesis. Acidogenesis is the second stage of the anaerobic digestion
through which acidogenic microorganisms basically fermentative bacteria, further decompose
the products of the hydrolysis stage producing ammonia, carbon dioxide, hydrogen, hydrogen
sulphide, alcohols, lighter volatile fatty acids, carbonic acid and certain alcohols.
Acidogenesis process only partially decomposes the biomass, therefore for the final
production of methane, the acetogenesis process is required.
Now acetogenesis, this step employs acetogenic microorganisms catabolizing the products
created in a acidogenesis phases into acetic acid CH3COOH, carbon dioxide and hydrogen.
Now acetogens finalize the breakdown process of the biomass facilitating the action of the
methanogenic archaea to produce methane as biofuel.
Then the last step is the methanogenesis. And now this is the final stage of anaerobic
digestion during which as mentioned earlier, methane is generated from the main products of
acetogenesis that is acetic acid and carbon dioxide through hydrogenotrophic methanogenesis
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and/or acetoclastic methanogenesis as given below. So, 2 different types of reactions take
place:
Have a look at this particular slide, this is the basic concept and steps for the anaerobic
digestion process. So, whatever we have discussed it is given in a schematic representation
here. So, the 4 degradation steps that what we just discussed - hydrolysis, acidogenesis,
acetogenesis, methanogenesis. So, doubling time is 1 to 48 hour. This is again the second step
is 1 to 48 hour. Acetogenesis takes more time 9 to 120 hours and methanogenesis is 18 to 120
hours.
So, the polysaccharides, proteins, fats. So, that gets converted to monomers, that again get
converted to fatty acids, lactate, alcohols, acetate, hydrogen, carbon dioxide, formate. So, this
is the methanation step, that is the hydrolysis steps. So, ultimately, we get methane and
carbon dioxide by the final 2 reactions, which we just discussed in the previous slide.
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So, the next is fermentation. So, fermentation is an enzyme catalyzed metabolic process
whereby organisms convert starch or sugar to alcohol or an acid or hydrogen, anaerobically,
releasing energy. Now, fermentation is an anaerobic biochemical process. In fermentation the
first process is the same as cellular respiration, which is the formation of pyruvic acid by
glycolysis where 2 net ATP molecules are synthesized.
So, you can see this scheme, here nicely it is represented. So, that glucose goes through that
glycolysis step and it provides the pyruvic acid, so this is the same as the respiratory cycle.
And here 2 net ATP molecules are synthesized. Now then in the next step pyruvate is reduced
to lactic acid. So, in this step, so pyruvate to lactic acid and ethanol plus carbon dioxide and
other products.
So, here NAD+ is formed which is reutilized back in the glycolysis process. So, you can see
the reaction here and NADH + H+ it gives us NAD+. Now, this NAD+ is again goes back
here that means, whatever it is getting produced here will be consumed in that glycolysis
step.
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So, on the basis of the end product formed, fermentation can be categorized as acid
fermentation, alcohol fermentation and hydrogen fermentation. So, we will see one by one
what are those. Let us first discuss about the acid fermentation. So under acid fermentation
lactic acid fermentation. So, lactic acid is formed from pyruvate produced in glycolysis.
NAD+ is generated from NADH. Enzyme lactate dehydrogenase catalyze this reaction. So,
lactate dehydrogenase is the enzyme that catalyzes this reaction. Lactobacillus bacteria
prepare curd from milk via this type of lactic acid fermentation. Now, during intense exercise
when oxygen supply is inadequate muscles derive energy by producing lactic acid, which
gets accumulated in the cells causing fatigue and all of us have noticed this when we get
stressed up.
So, the muscles basically pain and if you go for a this one some sort of we can say intense
exercise, most of us have felt this lactic acid production and this lactic acid production inside
the muscles actually causes the fatigue and sometimes pain also. So, when we go for a
massage for the muscles, so, it basically it removes or disperses this lactic acid which is
stored in a particular area of the muscles, thereby reducing the fatigue and pain.
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So, the next one is acetic acid fermentation. Vinegar, which is one of the most widely used
product, in the food and beverage and this one restaurant industries is produced by this
process. So, this is a 2 step process. The first step is the formation of ethyl alcohol from sugar
anaerobically using yeast and in the second step ethyl alcohol is further oxidized to form
acetic acid using acetobacter bacteria. Now microbial oxidation of alcohol to acid is an
aerobic process.
So, the next one butyric acid fermentation. Now, this type of fermentation is characteristics of
obligate anaerobic bacteria, genus Clostridium. This occurs in retting of jute fiber, rancid
butter, tobacco processing and tanning of leather. Butyric acid is produced in human colon as
a product of dietary fiber fermentation, it is an important source of energy for colorectal
epithelium.
Sugar is first oxidized to pyruvate by the process of glycolysis. And then pyruvate is further
oxidized to form acetyl coenzyme A by the oxidoreductase enzyme with the production of
hydrogen and carbon dioxide. Now, this acetyl coenzyme A is further reduced to form butyric
acid, this type of fermentation leads to a relatively higher yield of energy, a 3 ATP. We have
seen that in glycolysis, it is 2 ATP, here in this case it is 3 ATP.
602

So, the next is alcohol fermentation. So, we have discussed about acid fermentation. So, we
will now discuss about alcohol fermentation. So, this is used in the industrial production of
wine, beer, biofuel etc. The end product is alcohol and carbon dioxide. Pyruvic acid breaks
down into acetaldehyde and carbon dioxide is released. In the next step ethanol is formed
from acetaldehyde.
NAD+ is also formed from NADH utilized in glycolysis. Enzyme pyruvic acid decarboxylase
and alcohol dehydrogenase catalyzes these reactions. So, these are 2 enzymes which are
responsible for doing these reactions. Now, microorganisms commonly used to carry out the
process are Saccharomyces cerevisiae, while the feedstock used for this type of process are
categorized into 3 different classes, sugars, starch and lignocellulosic structures.
In detail the theoretical yield of the processes is 51.14 gram of ethanol and 48.86 grams of
carbon dioxide from 100 gram of hexoses or pentoses. So, this is the reaction:
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So, in addition to ethanol and carbon dioxide glycerol and carboxylic acids are also produced
as by-products. The quality and yields of the process depends on various factors such as
feedstock, temperature, pH, inoculum and fermentation time. The conversion of sugars into
ethanol could take place through different metabolic pathways depending on the starting
substrate.
More specifically from hexoses such as glucose through glycolysis or EMP pathway - the
Embden-Meyerhof pathway and from pentoses through a pentose phosphate pathway, which
is known as PPP pathway. So, the conversion reactions of the hexoses are faster than those of
the pentoses. At the end of the conversion process ethanol is distilled and dehydrated in order
to obtain concentrated alcohol while the solid residues can be used as fuel in boilers for the
production of gas or can be used as feed for livestock.
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So, you can see this particular schematic representation how glucose is getting converted to
pyruvic acid. Pyruvic acid is getting converted to different types of these are here the
different types of organisms are written. And here the fermentation products are written, you
can see the pyruvic acid depending upon the different types of organisms are going to give us
different types of products.
If you are using the Escherichia or Acetobacter we will get acetic acid, that is vinegar.
Pyruvic acid will be converted to lactic acid, Cheese, yogurt, soya sauce further processing, if
we use as Aspergillus, Lactobacillus, Streptococcus, all these organisms. So, pyruvic acid can
be converted to propionic acid, if we use Propionibacterium. So, further if you use
Saccharomyces you will get ethanol plus carbon dioxide, if you use Clostridium, you will get
acetone , isopropanol and butyric acid.
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The next is hydrogen fermentation. Now, hydrogen is a potential alternative energy source
due to its cleanliness and high energy density by mass. It can be produced by various routes
through using different types of microorganisms, including dark fermentation via hydrogen
producing bacteria, photo fermentation via photosynthetic bacteria and direct bio-photolysis
using green microalgae or indirect bio-photolysis using cyanobacteria.
Now, dark fermentation can be considered as a sub process derived from anaerobic digestion,
in which the methanogenesis stage is hindered by the inactivation of the methanogenic
archaea. Now in terms of photo-fermentation and this photosynthetic bacteria, the
photosynthetic bacteria can degrade low molecular weight organics, including sugars,
alcohols and volatile fatty acids to hydrogen and carbon monoxide under an anaerobic
environment.
So, this is more or less similar to the anaerobic digestion process, this particular step. So, the
hydrogen production is a natural response of the cellular need for the releasing of the excess
of electrons and is always coupled with volatile fatty acids and/or alcohol production.
606

The stoichiometric yields are 4 moles of hydrogen for each mole of glucose, when acetic acid
is the co-product and 2 moles of hydrogen if butyric acid is produced. So, many times what
happens if you are looking for pure hydrogen production, then you have to suppress the path
to produce butyric acid, we will always go for the acetic acid pathway where we will get
more hydrogen yield per mole of glucose.
In practice the hydrogen yields are within the range of 10 to 20% of the COD the chemical
oxygen demand, which is equivalent to 1.17 to 2.3 moles hydrogen per mole of glucose.
Now, production of dark fermentative hydrogen is a ubiquitous phenomenon that occurs in
most of the anaerobic natural environments. It consists in an obligate cascade of reduction
oxidation or redox reactions that must be kept in balance.
Now dark fermentation can involve any type of organic molecules, glucose being the most
common substructure investigated in literature. Many biological pathways have been
proposed using glucose as model substrate. I will show you the next figure. And photo
fermentative hydrogen production involves the conversion of organic compounds into carbon
dioxide and hydrogen in the presence of light as an energy source with no oxygen evolution.
Photo fermentation can completely convert organic compounds into hydrogen even with a
relatively high hydrogen partial pressure.
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So, this is the pathways for the hydrogen production by dark fermentation from glucose under
anaerobic conditions using mixed cultures. So, let us try to understand, so the glucose that is
getting degraded to this PEP using NAD + and NADH that cycle. So, then it gives to
fumarate and succinate. Now when it comes in the glycolysis pathway, this straight forward
here, so, 2 ATPs are being produced.
So, it is getting converted to pyruvate. Now this pyruvate can be converted to lactate and
again propionate, this is another pathway. Now when we come down here and we go for this
acetyl coenzyme A production. Now this acetyl coenzyme A can further be converted to
acetate to ethanol or butyryl coenzyme A via different, different pathways.
Now Pyruvate formate lyase, which is known as PFL, is the common pathway in the
facultative anaerobes. So, pyruvate-ferredoxin oxidoreductase, which is known as PFOR, is
the common pathway in strict anaerobes. Additional hydrogen production by hydrogenases at
low hydrogen partial pressure less than 60 Pascal is also happens.
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So, next is we will try to understand the basic concepts about the microbial fuel cell or
microbial electrochemical systems. Now, microbial electrochemical systems exploit the
metabolism of microorganisms to bio-electrochemically convert low grade chemical energy
stored in biodegradable substrates to high grade energy, that is electricity and value added
chemicals like hydrogen and methane.
As a rapidly evolving technology, this microbial electrolytic electrochemical system has been
successfully implemented to treat wastewater for electricity generation using microbial fuel
cells, and in bio-refinery facilities using microbial electrolysis cells and microbial
electrosynthesis. Now, specific applications include wastewater treatment, power sources for
remote sensors, research platforms for electrode-bacteria interaction and value added
component production.
Compared with other biological processes, this MES show higher versatility and lower sludge
production making them very promising in practical applications. In many other applications,
if there is a high rate of sludge production, then sludge disposal is an another issue which
needs to be tackled because that sludge has to be properly disposed, otherwise where you will
keep the sludge.
So, that is of course, there are many applications of the sludge nowadays. So, many value
added products are being produced, depending upon of course, the quality of the sludge. The
substrates used in MES can vary greatly from glucose, acetate, lactate and dyes to domestic
wastewater containing complex species.
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Typically, these biodegradable substances are electro-oxidized at the anode via bacterial
metabolism to produce electrons and protons. Then the electrons are conducted to the cathode
and are accepted by oxygen nitrate and metal ions. After decades of research and
development, the performance and stability of MES have approached industry standards. It is
predicted that MFCs can potentially produce 23.3 and 40 terawatt hour of electricity from
wastewater in India by 2025 and 2050 respectively.
So, this is a projection or prediction you can say. The long term operational stability has also
been verified. So Zhang et al installed and operated 2 microbial fuel cells in a municipal
wastewater treatment plant for about 400 days. These 2 microbial fuel cells showed great
durability in the COD removal and fluctuation tolerance, demonstrating the long term
effectiveness of this technology outside the laboratory.
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So, the next important microbial conversion process is composting. Composting is a preferred
and environmentally sound method whereby organic waste is reduced to organic fertilizer and
soil conditioners through biological processes. It involves 3 phases, and uses diverse
microflora such as bacteria, fungi and mesophiclic and as well as thermophilic eventually
converting organic waste to humus.
During the first phase there is an increase in carbon dioxide along with the temperature, the
substrate is reduced due to the degradation of sugar and proteins by the action of mesophiclic
organisms. The second phase leads to an increase of the temperature in the compost piles
from 45 degrees centigrade to approximately 70 degrees centigrade and the mesophiles are
replaced by thermophiles.
Large number of pathogenic individuals are degraded during this time; the third phage begins
with the decrease of the temperature of the compost pile. Various parameters including the
carbon nitrogen ratio, composting temperature, pH of the finished product, moisture content
are important during the composting process.
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Now, let us understand the different equipments, those are essentially required to accomplish
the microbial conversion processes. So, bioreactors, especially are closed bioreactors can
provide the ideal milieu for the microbial growth and metabolism, because why we are
talking about closed bioreactors, because we can easily control all the parameters in a closed
system.
A bioreactor represents the equipment in which biological reactions and microbial cell
reproduction occur using enzymes or living cell as bio-catalyst. Microbial biofuel conversion
is mainly divided into an upstream treatment process that includes fermentation for microbial
growth and product generation and a downstream treatment process that includes product
purification, isolation and collection.
In order to improve energy conversion efficiency, the specifications of the bioreactor should
integrate not only the correct structural configuration, but also precise operational control for
optimized multiphase flow as well as heat and mass transfer in the reaction solution.
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Due to their adaptable operating conditions, bioreactors are widely used in different types of
microbial biofuel conversion processes, such as biogas production by anaerobic digestion,
hydrogen production by photo-fermentation or dark fermentation, alcohol production by
fermentation and fatty acid production by microalgae. During the microbial conversion
processes, microbial cells are sensitive to variations in their surroundings and any instability
is detrimental to their growth and product synthesis.
In bioreactors the environmental parameters there are many. So, some of these are noted here
like temperature, pH, medium composition, retention time, mass and heat transfer rate. So,
this can be maintained at near optimal ranges to enhance microorganism growth and product
accumulation. So, whenever we are going to start a process using a bioreactor and a particular
microorganism, a single strain or a mixed strain and the different types of substrates, you
need to optimize the various process parameters which are written here in the last sentence
and we have just discussed. So, this optimization is required because at that particular
optimized conditions probably will get the highest yield of the product which is your desired
product.
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So, let us now discuss about the bioreactors for anaerobic digestion and their configurations.
Bioreactor design is usually conducted on an experimental basis considering influencing
factors like gas-liquid-gas multiphase flow, mass and heat transfer balance and energy
conversion efficiency. A bioreactor with superior performance requires a watertight structure,
high heat and mass transfer efficiency, good mixing performance, low energy investment and
high product output.
The most commonly used configurations are: convectional anaerobic reactor, such as the
anaerobic sequencing batch reactor, the continuous stirred tank reactor and the anaerobic plug
flow reactor. Then, in the second category it is the sludge retention reactor, such as anaerobic
contact reactor, the up-flow anaerobic sludge bed reactor, the up-flow anaerobic solid state
reactor, the anaerobic baffled reactor and the internal circulation reactor.
And in the third category it’s an anaerobic membrane reactor, such as the anaerobic filter
reactor, the anaerobic fluidized bed reactor and the expanded granular sludge blanket.
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The conventional anaerobic reactor is a single-tank system that utilizes the same tank for
substrate treatment and fermentation. It is the single equipment or the single reactor in which
all sorts of reactions are happening. All steps of microbial biofuels conversion take place in a
single tank, which means that downstream treatment process as well as the intermediate
byproducts can have significant negative influences on the upstream treatment processes
because in a single reactor it is happening.
So, when there is product formation that the amount of product as well as the inhibitory
compounds that form due to certain secondary reactions, they are all retaining in the same
reactor. So, it will further inhibit the growth of the microorganism and even stop the further
reactions. Thus, efficient approaches to avoid the interactive effects of different reactions are
essential to enhance bioreactor performance.
The configuration of sludge retention reactors is relatively complex compared to the
conventional reactors, sludge retention reactors usually contain 2 main components, the
liquid phase reaction module and the solid phase recycling or gathering module.
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Anaerobic membrane reactors are constructed with a supporting membrane to enhance
contact between wastewater and the bacterial microorganism. Now when there is the growth
of this bacterial biofilm. So, it grows on the supporting membrane causing a separation
between the bacterial biomass and the wastewater in the reactor. So, in the anaerobic
fluidized bed reactor inert particles like fine sand and alumina are provided for the thin
bacterial biofilm to grow on. The configurations of anaerobic membrane reactor enhance the
resistance of the microbes to inhibitors, thereby improving biofuel production.
We will see the bioreactor functions. So, in that microbial conversion process bioreactors
provide fine control of operating conditions for microorganisms’ growth, metabolism and
product synthesis thus improving the biofuel production. For example, the pH can be
maintained at suitable levels by adding buffer solutions and the temperature can be controlled
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by a thermostatic water bath or the hydraulic retention time of wastewater can be controlled
by regulating the inward feeding rate.
Now, different structural characteristics are required for different applications of a bioreactor,
for example the leakage resistance of a bioreactor is critical when applied to biogas
production. The function of conventional anaerobic reactors is to supply relatively stable
operating conditions in an established temporal sequence. Owing to its simple structure the
sequencing anaerobic reactor has the advantages of operational simplicity and low cost. The
major function of sludge retention reactor is the recycling of microbial biomass thus,
avoiding biomass washout.
Some configurations of sludge retention reactors can have special functions. For example, in
the anaerobic baffled reactor, the flow patterns of waste influents can be regulated by
arranging the baffles, serving to separate acidogenesis and methanogenesis along the vertical
axis of the reactor and allowing different bacterial communities to develop under
independently suited conditions.
The function of the anaerobic membrane reactor is based on the supporting membrane
material used for microbial biofilm formation, which serves to separate influents from the
microbial biomass. By generating this microbial biofilm biomass washout can be avoided.
So, this is one of the greatest advantage of using a solid membranes. And the microbes have a
longer retention time than hydraulic retention time.
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As a result the mechanical mixing and sludge settling that occur in sludge retention reactors
can be avoided in anaerobic membrane reactors. So, these are very important class of
membrane reactors.
Now, let us understand the influencing factors for the bioreactors for anaerobic digestion.
Reactor size and shape usually influence biofuel output capacity increasing the size of the
container can improve biofuel production to some extent, but can also cause biomass
concentration gradients in the reactors, which further hinders the biofuel production.
Bioreactors operated at low temperature are less prone to thermal instability and degradation.
However, since some thermophilic bacteria prefer high ambient temperatures of up to 65
degrees centigrade, bioreactors must maintain the standard of thermotolerance. Generated
byproducts can dissolve and accumulate in the bioreactor over time inhibiting microbial
growth and metabolism. Thus, in order to maximize the efficiency of microbial biofuel
conversion, bioreactor design must incorporate some mechanism to quickly remove such
byproducts.
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Let us understand the bioreactors for fermentation. So, their configuration. So, bioreactors for
fermentation process are also termed as fermenters. Two types of fermenter vessels are used.
So, the small scales are usually made up of glass and for the industrial purposes, we use
stainless steel. So, glass is non toxic and corrosion proof, it is easy to examine the interior
reaction what is happening inside the vessel.
Sterilization is easily done with the autoclaves. So, these are very small fermenters with a
diameter of around 60 centimeter. Then stainless steel is mostly used for large scale
fermentations, these vessels have the potential to resist pressure and corrosion, the
sterilization is achieved in situ. So, heat in the fermenter vessel is produced due to microbial
activity and agitation.
Temperature in the vessel is maintained by either adding or removing heat from the system.
So, we can have jacketed system. I will show you one of the figure in which we can
understand this. So, thermostatically controlled baths or internal coils of generally used to
provide heat while silicon jackets are used to remove excess heat.
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So, it has doubled silicon mat with heating wires sandwiched between the mats. Now, if the
size is exceeded, resulting in covering the surface by the jacket heat removal is tedious and
then in the internal coils cold water has to be circulated to maintain the exact temperature, it
is always easy if you have an outside temperature control. Now, that is possible only when
you have a smaller reactors or fermenters.
If we have large reactors or fermenters then some inside internal coiling facility has to be
integrated, but that again creates problem for the proper mixing of the fermentation broth.
Then next is sealing assembly. So, it is used for sealing of the stirrer shaft to offer proper
agitation and it can function for a longer period aseptically. There are 3 types of sealing
assembly in the fermenter.
Packed gland seal: so in this the shaft has been sealed with several packing rings of asbestos,
pushed by gland against the shaft. To prevent insufficient heat penetration packing rings have
been regularly checked and replaced. The second one is mechanical seal and the third one is
magnetic drives. So, in the mechanical seal it consists of 2 portion, stationary portion in the
bearing and rotating portion for the shaft. Two parts are pushed together with the help of
springs. Under the magnetic drives, these are again of 2 types of magnets that is driving and
driven magnet, the driving magnet will be seized on the external part of the head plate in
bearing and associated to the drive shaft and another that driven magnet will be located at the
end of the impeller shaft and seized in the bearings on the head plates’ inner surface.
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Now, let us see this particular schematic representation of a usual fermenter, it can be a lab
scale fermenter, it can be industrial scale fermenter. Let us see. So, you can see that this is the
reactor: there is a motor and this is the impeller. This is the impeller; you can see these are the
small plates which are there. So, please understand that impellers there are so many different
types of impeller designs are available, it is not that only this has to be used, this is a
particular design.
Now, what impeller design you will choose that is the job of the engineer or the scientist who
are basically designing the fermenters, that based on what type of substrate you are going to
use inside the fermenter. So, this is about impeller. So, this whatever you were seeing here,
this is an external jacket. So, that job is to remove the heat that is produced inside the
fermenter.
So, how do you do that? So you can send in the cooling water - ice cold water and it will take
away the excess heat what is being produced in the fermenter and not required and you will
get the cooling water out here. So, it will have elevated temperature depending upon what
temperature is there. Now, there is a sparger that is provided. Again I am telling you sparger
there are so many different types of sparger designs are there.
You can use a single nozzle sparger, you can use 10 perforated whole plates, you can use 100
perforated whole plates or you can have different types of designs. Again you have to decide
what is your requirement and whatever you are seeing this is a culture broth then we can have
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baffles. Now baffles are not mandated everywhere, the necessity arises that if baffles are
there the mixing will be good inside this.
So, impeller will be there, it is very slow, it will move very slowly. But if it moves too slow
then the microorganisms will start depositing on the surface of the impeller plates. So, that is
also not correct. So, there are so many other things are there you can see that steam can be
put here. So, that the reason the steam is required to sterilize one particular batch is over, then
you need to sterilize it in the big systems.
Or if it is a small fermenter that glass type, you can take it out remove the heads shaft, motor
and everything and all accessories, take it and put it in autoclave where we can go for
sterilization there. So, baffles are there, impellers, disc turbines, variable pitch open turbine. I
have already told what is the job of baffles and impellers. So, let us move ahead.
So, sparger provides proper aeration in the vessels so that sufficient oxygen is supplied to the
microorganisms for metabolic process. Three types of spargers are used porous spargers,
nozzle spargers and combined spargers and agitator. In the porous spargers these are made up
of ceramic or sintered glass and used in non-agitated vessel on the laboratory scale. Nozzle
sparger has opened or partially open single pipe.
Now, this type of sparger is generally used because they do not get blocked and provide
lower pressure. So, in case of combined sparger and agitator they introduce air by hollow
agitator shaft and release it from the holes of the drill disc to connect to the base of the main
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shaft. When the agitator is operated at the range of RPM, the deliver good aeration in a
baffled vessel.
Then there are feed ports, which are tubes made up of silicon. They are used to add nutrients
and acid/alkali in the fermenter, in situ sterilization is performed before removal or addition
of the product. Then, another very important thing for the fermenters are foam controller.
Now they have 2 units foam sensing and control unit. In the fermenter a probe has been
inserted through the top and set at a distinct level above the broth surface.
Now when the form level rises and touches this probe tip a current will be passed through the
circuit. So, this current will activate the pump and antifoam will immediately be released to
combat that situation, because foaming is not beneficial for the fermentation.
Then different types of valves are used in the fermenter to control the movement of liquid in
the vessel, like globe valve, butterfly valve, ball valve and diaphragm value. Now globe
valves are suitable for general purposes but they do not regulate flow. Butterfly valves are not
suitable for aseptic conditions and are used for large diameter pipes which operate under low
pressure. Ball valves are essentially suitable for aseptic conditions. They handle mycelial
broths and are operated under high temperature. Diaphragm valves help in flow adjustment.
Then apart from that we have safety valves. So, they are built-in in air and pipe layout to
operate under pressure. With the help of these valves the pressure is maintained within the
safe limits.
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Now let us discuss about the types of fermenters. We will quickly discuss about the basics of
the few fermenters which are essentially adapted in the lab scale as well as commercial scale.
There are many types. So, the first one is the continuous stirred tank reactor, then we have
airlift reactor, we have fluidized bed reactor, we have packed bed reactors, we have
photobioreactors, membrane fermenters and bubble column fermemter.
So, we will see quickly all these reactors in a glance. So, the first one you can see the image.
So, that is the stirred tank fermenter the simplest one. So, one of the most conventional
bioreactors is the stirred tank bioreactor used in the lab scale as well as in the commercial
scale also. The core component of the stirred tank bioreactor is the agitator or impeller which
performs a wide range of functions.
So, it does the heat and mass transfer functions that means it helps in enhancing the heat and
mass transfer rate, it does aeration also and it does mixing of the fermentation broth.
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Second one is airlift fermenters. So, these are classic fermenters and are being used in
industrial scale as well in the lab scale also. So, airlift reactor is generally for the gas liquid or
gas liquid solid contacting devices. They have different fluid circulation, which is a definite
cyclic pattern via built channels. Stream of air or other gases provides agitation to the content
inside channels.
The gas stream helps swap over the material between the gas phase and the medium, oxygen
is usually transferred to the liquid. Products formed after the reactions are excreted when the
gas phase is inserted. Two types of airlift reactors are there: one is called the internal loop
you can see the first image and then there is a second one which is called external loop. Now
in the internal loop and in both the systems we have there are 2 things.
First one is called riser column, another is called downcomer. See this riser and downcomer
differentiation you can easily understand in the external loop reactor where the downcomer is
outside the main reactor. And here it is inside. So, you can you can see 2 pipes, big pipes.
One big diameter pipe inside that a small diameter pipe if it is placed like that.
So, the inside one will be the riser through which the flow is basically happening like this and
then it is coming. It is a circulating flow like this. And when it is in outside that is the external
loop airlift reactor, most of the reactions are happening in the riser section and this is what
helps in a proper heat and mass transfer rate as well as to maintain the microorganism
growth. And some other activities like that you can talk about the HRT, OLR and all these
things.
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So, the next is bubble column fermenter. So, these are very classical reactors, which are used
in many chemical, petrochemical and biochemical industries. Now, these reactors are simple
in construction, they are easy to maintain and they have low operating costs. So, these are
cylindrical in shape with a ratio of 4 is to 6 : height to diameter ratio basically and at the base
of the column air or gas is introduced via perforated pipes or plates or metal microporous
sparger.
So, you can see that, so, this is a column it is a big column, it can be made up of a glass, it
can be made up of perspex, it can be any other material also. So, here there is a sparger that is
provided – multiperforated/multiple hole sparger you can see, you can use different types of
sparger also. So, gas is being passed through like this and through this particular sparger the
gas will be pushed through and when it will come in contact with the fermentation broth, it
will result in small, small bubbles.
Now, the concept in the entire the bubble column is that how the bubbles are getting created.
The size that matters, and how they are getting coalesced with each other because bubbles has
a tendency to coalesce with each other, so they will form a small to big bubbles. Now these
big bubbles under agitation, mechanical agitation or any sorts of agitation inside the
fermentation broth will again be ruptured into smaller bubbles.
So, what is the idea is that it is a continuous generation of bubbles, coalescence and again
break down into smaller bubbles will create high mass transfer area. So, that is the basic
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concept in the bubble column reactor. So, flow rate of air or gas is maintained accurately so
that the proper oxygen transfer or mixing is achieved. Perforated plates are attached in the
fermenter to improve the performance of the reactor.
So, the next is packed bed fermenter. Now, packed bed fermenter reactors are also called as
fixed bed reactors, which are used in many chemical processing applications like absorption,
distillation, stripping, separation processes and catalytic reactions. It consists of partition like
tube or channel which has catalytic particles of pellets on to which liquid flows through the
catalyst.
Chemical composition of the substance gets altered when the liquid reacts with the catalyst.
This reactor has many advantages as its conversion rate is high for the catalyst, easy to
manage and build, more efficient contact between reactant and catalyst is made compared to
other types of reactors, product formation is more due to the increased contact of
reactant/catalyst. Please understand, if this is only one of the reactor in which there is
intimate contact between the reactant and the catalyst.
So, the entire amount of the catalytic surface will be covered with the reactants, so, that there
will be more product formation. So, these reactors work effectively even on high
temperatures and pressures.
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So, the next is another class of fermenters which are also industrially used and adapted. So,
are called fluidized bed fermenters. Now, design of the reactor must be proper so that fluid
flow rate is sufficient to suspend the catalyst particles. So, catalyst is laid on the bottom of the
reactor and the reactants are pumped into reactor via distributor pump to make the bed
fluidized.
If the reactant is liquid then bed expands uniformly and make homogeneous fluidization and
if it is gas then bed expands non uniformally to make aggregative fluidization. During this
whole process the reaction between the reactant and catalyst led to the formation of new
products which are retrieved continuously during the course of time.
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So, the next is photobioreactors. So, the main application of photobioreactors are in
photosynthetic processes involving vegetable biomass growth or microalgae growth under
restricted conditions. Now, the introduction of more complicated cultivating methods of
microalgae with higher production value and capable of providing sterile conditions which is
accessible by different types of close photobioreactors applied outdoors.
So, here whatever you are seeing now. So, in general, if you talk about the laboratory scale
photobioreactors they are artificially illuminated because we need to provide light for the
photosynthesis. So, here whatever you are seeing, so, this is an image of a (open/outdoor)
raceway pond. These raceway ponds can also be constructed in-house where we can supply
this one artificial lighting.
But this is an open to atmosphere and open to sunlight raceway pond. Now, these are plate
type algal photobioreactor, these are tubular photobioreactors. Now, here this, this and this,
these 3 are closed systems. So, as I told you that during this discussion this closed systems
are always good because we can easily control the different process parameters inside a
closed system and they are not susceptible to any other infectious bacteria, virus or this such
environmental problems.
Whereas this type of raceway pond are always susceptible to environmental conditions -
sometimes rains, let us say the rain happens it will immediately increase the amount of the
broth inside the reactor. So, everything gets diluted, which is not happening here and here and
here. Now, this is easy to maintain, the cost is low. However, these are initially very costly
processes, but once you have this, so then you can maintain it easily and control it easily. So,
that the yield will be better.
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So, next is these are latest development in the environmental and energy sites actually the
membrane bioreactors. So, it basically combines traditional treatment with filtration via
membranes, resulting in the removal of organic and suspended solid matters that are also
removes high level of nutrients. Now, membrane bioreactor systems are submerged in an
aerated biological reactor. The pore size of the membrane ranges from 0.035 microns to 0.4
microns.
Membrane bioreactor system is widely used in treatment of wastewater from several sources.
However, membrane fouling is a chief obstacle to the extensive application of membranes.
So, you can see here 2 different images are there. So, here what is happening the membrane is
outside. So, this is the bioreactor. So, membrane is used as separate. This is a 2 different unit
operations; bioreactors, here everything is happening all the reactions, product formation,
then you need to remove product and other value added products or inhibitory compounds
use a membrane reactor. So, it will remove the effluent and the retentate can be recycled.
This is one system.
In another system where we have this activated sludge ponds and such type of units the
membrane bioreactors can be directly placed inside the aerobic ponds. So, it has its own
advantages and disadvantages, this has its own advantages disadvantages. This is easy to
control. Here the clogging and concentration polarization can be an issue, if we are putting it
directly inside - because microorganisms will start growing on the surface of the membrane.
So, there are issues into that but both are used.
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So, then we will talk about the bioreactors for microbial fuel cell and microbial electrolysis
systems their configurations. At the heart of an MES lies the bioreactor where biodegradable
substrates are converted to electrical current. The current is utilized directly in the MFCs or
conducted to the cathode for further reaction in case of the MECs.
Now, therefore, the performance of an MES is dictated by the performance of the bioreactor
within where scientific disciplines like microorganism ecology, biomaterial science,
mechanical engineering and control strategy meet multiphysics phenomena like biofilm
formation, multiphase flow, heat and mass transfer and bioelectrochemical conversion
complicated systems.
So, many different types of parameters needs to be controlled and taken care of. A typical
MES consists of 2 chambers the anode chamber for electron production and the cathode
chamber to close the circuit and the yield of the final products. MES have evolved from
typical 2 chamber configurations to single chamber and hybrid designs. Novel modes of
operation like the up-flow mode have also been developed.
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In a 2 chamber MES aqueous and gaseous substrates are bioelectrochemically degraded to
produce electrons in the anode, these electrons are transferred to the cathode resulting in
electricity production or product generation. Liu et al demonstrated the first single chamber
MFC in which atmospheric oxygen can passively diffuse into and react with the porous
hydrophobic cathode.
Plain anode and cathode can also be used to form a single chamber MES bioreactor. Single
chamber MFCs are capable of treating wastewater with a high concentration of nitrogen,
although ammonia inhibition was still observed. So, ammonia whatever is getting produced,
if it is again produced a certain amount which is beyond a tolerable amount then it will
suppress all the metabolic activities.
So, the maximum power density decreased from 6.1 to 1.4 watts per meter cube when TAN
concentration increased from 3500 to 10,000 milligrams per liter. So, TAN is the total
ammonia nitrogen. So, one concern for the single chamber MFC is that a large percentage of
the organic substrate is lost without contributing to the electricity production.
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From a geometric perspective, both the single and double-chamber MESs can be engineered
to form a tubular configuration. Now, this configuration is considered very promising due to
increased sludge rentention time and reduced hydraulic retention time. Tubular MESs can be
readily integrated to fit into existing facilities. Ye et al developed tubular 2 chamber MFCs
using PMMA (polymethyl Methacrylate) tubes of different diameters; the inner tube and
interspace served as the anode and cathodic chambers (respectively).
Five of these MFCs were integrated into a sink drainpipe for kitchen wastewater treatments.
It is a very nice work. I have referred it down. Please read if you wish to read and learn more
on this particular technology.
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So, these are the configurations of the microbial electrolytic systems. So, the first one
whatever you are seeing, this this schematic and prototype of the first single chamber MFC.
So, it is a very simple system. And the second one, where it says a single chamber MFC with
a plain anode and a cathode. So, this is the cathode here, Air cathode this is the anode here,
you can see the organic matter and microorganisms start depositing on the surface of the
anode.
In the third one so, it is a tublar 2 chamber MFC. Here in this case the 5 MFCs were
connected to form a stack and integrated into a sink drain pipe. You can set the cascading
basically or multistging.
Now, let us understand the system integration of the bioreactors for MFCs and MES. So, the
output of a single bioreactor is usually insufficient for most of the applications. One
promising approach to this problem is to combine several bioreactors to form a stack, which
improves productivity and efficiency. For example, several MFCs can be hydraulically and
electrically connected to form an MFC stack.
This approach does not affect the columbic efficiency of individual fuel cells, but can
increase the total power output and COD removal efficiency. Ledezma et al demonstrated the
first self sustained MFC stack that is not only self sufficient in terms of feeding, hydration,
sensing and reporting, but can also produce sufficient net power output to run peristaltic
pumps.
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So, peristaltic pumps are required to feed different types of materials, whether it can be your
substrate, whether it can be different types of nutrients, even supplying buffers also. MFC
configuration as well as the hydraulic and electric connections in stacked MFCs have to be
properly engineered to avoid short circuiting and to fulfill the requirements of the desired
application.
One major challenge for MFC stacks is voltage reversal. When one or more MFCs reverse
polarity. So, this results in severe deterioration of the MFC system as a whole. Capacitors can
be integrated into a serially connected MFC stack to accumulate charge, which should
prevent voltage reversal and enhance power output. So, bioreactors do not serve as stand-
alone devices, they need to be integrated with other MES and even other energy systems for
maximum performance and energy efficiency.
In a classical study Liu et al proposed an integrated MFC-SBR (SBR is sequencing batch
reactor) for the activated sludge process. The MFC was submerged inside this SBR, synthetic
wastewater was fed to the MFC first and the resulting effluent was processed by the SBR.
The oxygen for the aeration process was shared by the MFC biocathode to further recover
electrical energy and reduce the cost of operation.
MESs can also be coupled to renewable energy sources like solar, wind and geothermal
energy to maximize the energy production of the entire system.
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With this I conclude today's lecture. In our next lecture, we will be discussing about the
details of the various microbial conversion processes. So, if you have any query regarding
this lecture, please feel free to post your query in Swayam portal or drop a mail to me at
kmohanty@iitg.ac.in. Thank you.
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Module 06
Lecture-17
Details of Various Processes
Good morning students, today is lecture 2 under module 6. As you know that we are
discussing various microbial conversion processes and in the last class we have discussed in
brief the different processes and different types of equipments and the products under that
lecture. So, in today's class we will be basically discussing about the processes in little detail
- anaerobic digestion and fermentation. So, let us begin anaerobic digestion.
Anaerobic digestion is a series of biological processes in which complex organic materials
are broken down into their simpler chemical components by various microorganisms without
the presence of oxygen. It is a multi-step biological process that is useful not only for proper
waste management but also for generating renewable energy like various types of biofuels. It
consists of 4 basic stages hydrolysis, acidogenesis, acetogenesis and methanogenesis.
During the entire process there are series of chemical reactions occurring through natural
metabolic pathways enabled by microorganisms in an oxygen free environment. Now these
reactions break down the organic macromolecules into simpler molecules leading to the
generation of biogas which is a mixture of methane, carbon dioxide and traces of other gases
like hydrogen and carbon monoxide.
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And apart from that the digestate or the solid part. So, the feedstocks that are commonly used
in this type process include sewage sludge, agricultural residues, municipal solid residue,
animal manure and there can be many other feedstocks also.
Now the process is ideal for organic waste with a moisture content ranging between 80 to
90%. One of the advantages of the process lies in the potential of the final biogas to be used
directly in ignition gas engines and gas turbines. The overall conversion efficiency of this
process is 21%, residual heat from the engines and turbines can be recovered through an
exchanger. Now the process can be summarized in 4 main stages.
First is hydrolysis. So, in hydrolysis the complex organic materials for example proteins,
lipids and carbohydrates - they are broken down into low molecular weight compounds such
as amino acids, fatty acids and simple sugars. Under acidogenesis the acidic bacteria promote
a process of fermentation producing the volatile fatty acids. Apart from volatile fatty acids
there are alcohols, hydrogen and carbon dioxide also get produced. Then acetogenesis, here
acetic acid, carbon dioxide and hydrogen are formed from the volatile fatty acids by acid
forming bacteria, they are known as also acetogens. And in the last which is the most
important step is the methanogenesis, here the methanogenic bacteria continue the
consumption of the volatile fatty acids and produce the methane gas.
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We will try to see in a nutshell - if you recall last class I have shown you one sketch, here this
is little in an elaborate way it is being presented. So, let us quickly glance through it. So, the
first step is hydrolysis here. The organic materials you can call them, group them and term
them as biopolymers - they are getting converted under lipids, carbohydrates and proteins to
various routes.
If you look at the first route the lipids are getting converted to LCVFA- the low carbon
volatile fatty acids and glycerine. Now that can be converted to organic intermediates and
alcohols, lactic acid - further to acetic acid by the step 2 and step 3. So, up to this. Now
carbohydrates can be converted into mono and disaccharides and then they also can be
converted either into organic intermediates or inorganic intermediates.
Similarly, the proteins get converted to polypeptides and again peptides and then again these
peptides can be converted to either organic intermediates or inorganic intermediates. Now
please understand that when I am telling that this conversion is happening it depends upon
what type of microorganism is being present and what they are converting. So, that is the
most important thing apart from other things.
Now before you come to the last one which is called the methanogenesis. So, you can see that
methanogenesis can happen via 2 different routes, one is this acetate route - acetic acid route,
another is the carbon dioxide and hydrogen route. So, either acetic acid can convert to
methane and carbon dioxide via this reaction or the carbon dioxide plus hydrogen can be
converted to methane plus water.
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So, please understand that the final reaction again proceeds mostly by the methanogens via 2
different routes. Now if we use the acetotropic methanogens - so mostly this is for the 70% of
the methane that is getting produced, this is the route, then we get the acetate route. And if we
are using the hydrotropic methanogens then the next 30% of the entire methane that is being
produced is coming from this particular route. So, the entire scheme is again presented there
in a very a brief way.
So, now we will try to understand the microbiology of the entire anaerobic digestion process.
So, let us first talk about the general scheme. So, 3 different forms of bacteria are active
during the AD process. So, they are fermentative bacteria, they are acetogens and
methanogens. So, these are the main microflora which are responsible for the entire anaerobic
digestion process for different reactions.
Now the hydrolyzing and fermenting microorganisms are responsible for the initial attack on
polymers and monomers found in the waste material and produce mainly acetate and
hydrogen, but also varying amounts of volatile fatty acids such as propionate and butyrate as
well as some alcohols. Now the obligate hydrogen-producing acetogenic bacteria convert this
propionate and butyrate into again acetate and hydrogen. So, 2 groups of methanogenic
archaea produce methane from the acetate or hydrogen respectively.
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So, this is again we will try to understand. This is a schematic representation of how the
carbon is flowing in the anaerobic environment with methanogen. So, this is for with
methanogens and this is without methanogen. So, let us try to understand what is happening
with the methanogens. So, when the complex organic materials are getting degraded in the
presence of methanogens then 3 things will happen.
So, usually if you see this particular route from this side the left side, you can see 51% is
getting converted through this route. So, the organic materials are degraded to acetate, acetate
is degrading to methane. So, as I told you 2 slides before that the 70% of the methane that is
produced from the anaerobic digestion comes via this route - acetate. Apart from that 51%,
30% is again converted to propionate and butyrate, which are further again converted to
either acetate or hydrogen and carbon dioxide depending upon the process condition as well
as depending upon the type of microorganisms present. And the next 19% is directly getting
converted to hydrogen and carbon monoxide and this 30% of the entire methane that is
getting produced coming via hydrogen plus carbon dioxide reaction. Now this entire scheme
is when the methanogens is present.
Now when methanogens are not present then what is happening to the carbon cycle? So, here
the complex material are getting converted to acetate, intermediates and hydrogen and carbon
dioxide in various of course percentage and further processing is not happening because there
are no methanogens available which will degrade these compounds into methane and carbon
monoxide.
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Now this scheme we have understood; now we will go ahead and try to understand in a gist
that what the scheme is all about. So, the major part of the carbon flow in a well operating
anaerobic reactor occurs between the fermentative microorganisms and the methanogens.
Only between 20 to 30% of the carbon is transferred into intermediary products before these
are metabolized into methane and carbon.
So, this is what I have shown you - the intermediate products are propionate, butyrate etc.
Now again these will be converted either to acetate or hydrogen and carbon dioxide route.
Before finally being converted to methane. Now a balanced anaerobic digestion process
demands that, the products from the first 2 groups of microbes responsible for hydrolyzing
and fermenting the material to hydrogen and acetate, simultaneously are used by the third
group of microbes for the production of methane and carbon dioxide. So, this is very
important. Now the first group of microorganisms can survive without the presence of
methanogens but will under these conditions form an increased amount of the reduced
products such as volatile fatty acids. The second group does however rely on the activity of
methanogens for removing hydrogen to make their metabolism thermodynamically possible
as their reactions are endergonic under standard conditions and only occurs when the
hydrogen is kept below a certain concentration. Now endergonic reactions are such reactions
in which the heat is actually absorbed. So, the net change of free energy is always positive.
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The relationship between the volatile fatty acid degrading bacteria and the hydrogen utilizing
methanogens is defined as syntrophic due to the dependent nature of this relationship and the
process is called interspecies hydrogen transport. Now syntrophic is a process or we can say
that it is a technique by which even the microorganisms especially in such anaerobic
digestion process coexist.
So, in this process let us say there are 2 different types of microorganisms are present in a
syntrophic relationship; then basically they are syntrophic because they are co-feeding each
other. So, the products are generated by one microorganism is being consumed by the other
microorganisms. So, they are interdependent on each other, they are not actually parasite,
they are interdependent and both are actually feeding on the products of each other. So, the
interspecies hydrogen transfer actually affects the entire carbon cycle - I have mentioned
here.
So, methanogens can participate in the interspecies hydrogen transfer combining hydrogen
and carbon dioxide to produce methane. So, besides methanogens, acetogens and sulphate
reducing bacteria can also participate in the IHT. So, the lower the hydrogen concentration,
better are the thermodynamics of the volatile fatty acid degradation. So, the distance between
the VFA degrader and the hydrogen utilizer that eventually affects the thermodynamics of the
process.
Therefore, the conversion is improved in granules and flocks compared to a situation where
the microbes are distributed freely in liquid solution. Essentially what is the meaning of that?
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Microorganisms are grown in granules and flocks and when they are suspended freely in the
liquid solution without forming flocks, the entire thermodynamics inside the process and the
hydrogen utilization, actually the IHT is getting affected.
Two partners have to share a very small amount of energy and the conditions for ensuring
energy for both microbes is very strict and can only be met within a narrow range of
hydrogen concentrations.
So, this is a schematic representation of the biomass anaerobic digestion scheme. It is a
general representation. So, you can see just we will quickly glance. So the biomass, it has to
be pre-processed - so you may have to sometimes chop it - mechanical pre-processing, then
you can go for some slight thermal pre-processing where you remove moisture and all.
Bring them to a desired particle size and bring them to a desired moisture content before you
feed them to the digester. Then they are made into slurry. Now you do not dump the entire
solid biomass under the digester. So, you usually make them into a slurry. This slurry goes to
the digester. Now here the anaerobic digestion is happening, so you have to give inoculum, if
required, you have to supply certain other micro nutrients or nutrients and maintain the
proper temperature inside the digester so that the anaerobic digestion happens. And it’s
strictly anaerobic process - dark fermentation. Now once the process starts happening, slowly
you will see that day 3, day 4, day 5 and after that so biogas will start coming. Now this
biogas whatever will come will be collected in a biogas storage vessel. From here you can
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either convert it to liquid fuels by compressing it or you can send it to the gas turbine system
where you can generate electricity directly.
And whatever left out here - the digestate or semi solid type of with having some moisture in
that - it can go to a separator where you get the filtrate liquid, this also can be converted to
some other value added products and then the fiber or solid again we can process it under
thermochemical conversion process or you can use as cattle feed and some other value added
products.
The second thing is that, this is what we talked about with the general scheme. Now we are
discussing about the syntrophic acetate conversion process. Now the syntrophic relationships
have also been found to be importance for the conversion of acetate when the acetate
degrading methanogens are inhibited by concentrations of ammonia or sulfite. So, we
discussed syntrophic for the IHT - interspecies hydrogen transfer.
Now we are discussing that, syntrophic relationship also having some importance when we
talk about acetate conversion. Now under these conditions the acetate utilizing methanogens
are inhibited and other groups of microbes replace them to obtain energy from the oxidation
of acetate to hydrogen and carbon dioxide. Due to thermodynamic constants this reaction
proceeds much better at increased temperatures and is the way of acetate transformation
when the temperature is usually higher than the 60 degree centigrade.
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So, that is the upper limit of the thermophilic acetate utilizing methanogens. So, in
accordance to this, the population of Methanosarcina species which is one of the methanogen
species disappeared more or less instantaneously from a biogas reactor operated on manure
when the temperature was increased from 55 to 65 degree centigrade. Now concurrently the
acetate concentration first increased and then stabilized at a level somewhat higher than that
found in the 60 degree centigrade.
So, clearly telling us that beyond 60 degree centigrade some of these thermophilic activities
are happening and the acetate utilizing methanogens are inhibited.
So, this coincided with a significant increase in the population of hydrogen utilizing
methanogens indicating that this group had become dominant in the overall conversion. So,
there will be more hydrogen production. When the concentration of acetate is low, syntrophic
acetate conversion is the major process for acetate transformation. However, when the
concentration of acetate is above the threshold level for the specific population of acetate
utilizing methanogens in the reactor, these will be the major group active in the system.
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The next is enzymatic ability to degrade substrate. Now bacteria degrade substrate through
the use of enzymes. Enzymes are proteinaceous molecules that catalyze biochemical
reactions. Two types of enzymes are involved in the substrate degradation: endoenzymes and
exoenzymes. Now a large and diverse community of bacteria is needed to ensure that proper
types of exoenzymes and endoenzymes are available for the degradation of the substrates
present.
The relative abundance of bacteria within an aerobic digester often is greater than 1016
cells
per millilitre. This population consists of a saccharolytic bacteria, proteolytic bacteria,
lipolytic bacteria and methane-forming bacteria. So, the table below gives an understanding
about that substrates to be degraded, different types of exoenzyme that is required and
examples.
Now we can see one case. Let us see the first one, the polysaccharides. So, this is the
substrate that is getting degraded and the exoenzyme you need to degrade this substrate is
saccharolytic exoenzyme. An example is cellulase. Cellulase is exactly it is the enzyme, that
will do the degradation and the bacterium that is required is the Bacillus species, the
Cellulomonas species and the product will be the simple sugar. So, similarly it is there for
proteins and lipids which will be converted into amino acids and fatty acids by Bacillus and
Mycobacterium species.
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Next is acetate forming bacteria. Acetate forming bacteria or acetogenic bacteria grows in a
symbiotic relationship with methane forming bacteria. Acetate serves as a substrate for
methane forming bacteria. For example, when ethanol is converted to acetate, carbon dioxide
is used and acetate and hydrogen are produced. So, this is the reaction:
When acetate forming bacteria produce acetate hydrogen is also produced. If the hydrogen
accumulates and significant hydrogen pressure occurs, the pressure results in the termination
of activity of acetate forming bacteria and loss of acetate production. So, this has to be
controlled in the fermenters. However, methane forming bacteria utilize hydrogen in the
production of methane and significant hydrogen pressure does not occur:
Acetate forming bacteria are obligate hydrogen producers and survive only at very low
concentrations of hydrogen in the environment, they can only survive if their metabolic waste
that is hydrogen is continuously removed or consumed by other microflora. Now this is
achieved in their symbiotic relationship with hydrogen utilizing bacteria and/or methane
forming bacteria.
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So, the next is sulphate reducing bacteria. So, SRB are also found in anaerobic digesters
along with acetate forming bacteria and methane forming bacteria. If sulphates are present,
then SRB such as Desulfovibrio disulfuricans multiply. So, this is one type of sulfate
reducing bacteria. Their multiplication or reproduction often requires the use of hydrogen and
acetate the same substrates used by the methane forming bacteria methanogens.
When sulfate is used to degrade an organic compound, sulphate is reduced to hydrogen
sulfide. Hydrogen is needed to reduce sulfate to hydrogen sulphide. The need for hydrogen
results in competition for hydrogen between 2 bacterial groups SRB and MFB. When SRB
and MFB compete for hydrogen and acetate, SRB obtain hydrogen and acetate more easily
than MFB under low acetate concentrations.
At substrate-to-sulfate ratios less than 2, SRB out compete MFB for acetate and at substrate-
to-sulfate ratios between 2 and 3, competition is very intense between the 2 groups and when
substrate-to-sulfate ratio is greater than 3, the methanogens are favoured.
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So, the hydrogen sulfide produced by SRB has a greater inhibitory effect at low
concentrations on MFB and acetate forming bacteria than acid forming bacteria. This is one
of the simple representation scheme that how the sulphate reducing bacteria and methane
forming bacteria are surviving in a synergistic relationship between them - symbiotic. So, you
can see that the sulphate is being reduced by the sulphate reducing bacteria to hydrogen
sulfide.
And they are also consuming the hydrogen and acetate that is getting produced from the
methane forming bacteria, as we have understood, then beyond certain limits of the hydrogen
inside the fermenter or anaerobic digester the methane forming bacteria will cease to do their
methanogenic activities. So, the hydrogen has to be continuously removed. Now in this
symbiotic relationship the hydrogen is getting consumed by the sulphate reducing bacteria to
hydrogen sulfide and the level of hydrogen is maintained in such a way that the
methanogenesis reaction is getting favoured.
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So, next is methane forming bacteria. MFB are some of the oldest bacteria and are grouped in
the domain Archaeabacteria. MFB are oxygen sensitive, fastidious anaerobes and are free
living terrestrial and aquatic organisms. Coenzymes that are unique to MFB are coenzyme M
and the nickel containing coenzymes F 420 and F 430. Coenzyme M is used to reduce carbon
dioxide to methane.
The nickel containing coenzymes are important hydrogen carriers in the methanogens. So,
MFB obtain energy by reducing simplistic compounds or substrates such as carbon dioxide
and acetate. MFB grow as microbial consortia, tolerate high concentrations of salt and are
obligate anaerobes. MFB grow well in aquatic environments in which strict anaerobic
condition exists.
The anaerobic condition of an aquatic environment is expressed in terms of it ORP or which
is called the oxidation reduction potential. MFB grow best in an environment with an ORP of
less than - 300 millivolt. Most facultative anaerobes do well in aquatic environments with
ORP between + 200 and - 200 millivolt. So, facultative anaerobes are a group of
microorganisms which do actually their metabolic activity in the presence of oxygen.
But when we deplete oxygen and they can also go for their metabolic activity without the
presence of oxygen also. So, they are that is why called facultative anaerobes.
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The reproductive times or generation times for MFB range from 3 days at 35 degrees
centigrade to 50 days at 10 degree centigrade. Because of the long generation time of MFB
high retention times are required in an anaerobic digester to ensure the growth of a large
population of MFB for the degradation of organic compounds. At least 12 days are required
to obtain a large population of MFB.
MFB obtain their energy for reproduction and cellular activity from the degradation of a
relatively small number of simple substrates including hydrogen, 1 carbon compounds and
acetate as the 2 carbon compound. 1 carbon compounds include formate, methanol, carbon
dioxide, carbon monoxide and methylamine. Other one carbon compounds that can be
converted to substrate for MFB include dimethyl sulfide, dimethylamine and trimethylamine.
Several alcohols including 2-propanol and 2-butanol as well as propanol and butanol may be
used in the reduction of carbon dioxide to methane.
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The most familiar and frequently acknowledged substrates of MFB are acetate and hydrogen.
Acetate is commonly split to form methane while hydrogen is combined with carbon dioxide
to form methane. So, these reactions we have seen many times, again it has been just reported
here for the easy understanding and to maintain the flow.
So, each methane forming bacterium has a specific substrate or group of substrates that it can
degrade. So, you can see here there are only 5 methanogens are being listed, there are many
others. So, if you see the first one the Methanobacterium formicicum. So, what it does, its
substrate is carbon dioxide, formate and hydrogen. If you talk about the last one
Methanosarcina bakerii, so for it the substrate is acetate, carbon dioxide, hydrogen, methanol
and methylamine.
Now there are 3 principal groups of methane-forming bacteria. So, these groups are
hydrogenotrophic methanogens, acetotrophic methanogens and methylotrophic methanogens.
Broadly grouped into 3 different types.
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Let us see the hydrogenotrophic methanogens. The hydrogenotrophic methanogens use
hydrogen to convert carbon dioxide to methane. By converting carbon dioxide to methane
these organisms help to maintain a low partial hydrogen pressure in an anaerobic digester that
is required for the acetogenic bacteria to do this reaction:
Now the acetotropic methanogens split acetate into methane and carbon dioxide. The carbon
dioxide produced from acetate may be converted by hydrogenotrophic methanogens to
methane. Some hydrogenotrophic methanogens use carbon monoxide also to produce
methane. So, this is the reaction:
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So, the acetotropic methanogens reproduce more slowly than the hydrogenotrophic
methanogens and are adversely affected by the accumulation of hydrogen. Therefore, the
maintenance of a low partial hydrogen pressure in an anaerobic digester is favourable for the
activity of not only acetate-forming bacteria, but also acetotrophic methanogens. Under a
relatively high hydrogen partial pressure acetate and methane production are reduced.
Now let us talk about the methylotrophic methanogens. The methylotrophic methanogens
grow on substrates that contain the methyl group CH3. Examples of these substrates include
methanol and methylamines. Group 1 and group 2 methanogens produce methane from
carbon dioxide and hydrogen, whereas group 3 methanogens produce methane directly from
the methyl groups and not from the carbon dioxide.
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So, the use of different substrates by MFB results in different energy gains by the bacteria.
For example hydrogen consuming methane production results in more energy gain for
methane-forming bacteria than acetate degradation. Although methane production using
hydrogen is the more effective process for energy captured by methane forming bacteria, less
than 30% of the methane produced in anaerobic digester is by this method only.
Approximately 70% of the methane produced in an anaerobic digester is directly derived
from the acetate pathway. The reason for this is the limited supply of hydrogen in an
anaerobic digester. So, the majority of the methane obtained from acetate is produced by 2
genera of acetotrophic methanogens that is Methanosarcina and Methanothrix.
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Now we will discuss about the fermentation process in a bit more detail than what we
discussed in our last lecture.
So, the term fermentation was first used by Louis Pasteur to define respiration in the absence
of free molecular oxygen. Fermentation can be broadly defined as respiration that occurs in
the dark and not involve the use of free molecular oxygen or nitrite ions as the final electron
acceptors of the degraded organic compounds. Therefore, respiration may occur through
several fermentative pathways including sulfate reduction, mixed acid production and
methane production.
Fermentation is a form of anaerobic respiration. The bacteria that perform fermentation are
facultative anaerobes. So, I have already explained what is facultative anaerobes.
Fermentation involves the transformation of organic compounds to various inorganic and
organic products. During fermentation a portion of an organic compound may be oxidized
while another portion is reduced.
It is from this oxidation-reduction of organic compounds that fermenting bacteria obtain their
energy and produce numerous simplistic and soluble organic compounds.
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Fermentative bacteria are capable of performing a variety of oxidation-reduction reactions
involving the organic carbon dioxide, carbon monoxide, molecular hydrogen and sulfur
compounds. Fermentative bacteria include facultative anaerobes, aerotolerant anaerobes and
strict anaerobes. Some fermentative bacteria such as Clostridia and Escherichia coli produce
a large variety of products, whereas other fermentative bacteria such as Acetobacterium
produce a very small number of products.
As environmental and operational conditions change for example the pH and temperature the
bacteria that are active and inactive also change, because the environment has a huge effect
on the different types of microorganisms. These changes in activity are responsible for
changes in the types and quantities of compounds that are produced through fermentation. Let
us see these 2 small tables are listed here.
The first one is the fermentative products of Clostridium species. You can see that organic
products like acetate, acetone, butanol, inorganic carbon dioxide and hydrogen. And this one
the second one is the fermentative products from E. coli or Escherichia coli, acetate, ethanol,
formate everything under organic and under inorganic carbon dioxide and hydrogen.
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So, we can have a look at the different types of fermentation, this is presented in a nice
scheme. So, different pathways are when you degrade hexoses, for example, glucose and
fructose through different fermentative pathways. So, these are the different paths. So, when
you go for the lactate fermentation you get lactate, ethanol and carbon dioxide. When you go
for the alcohol fermentation it is ethanol and carbon dioxide, when you go for butyrate
fermentation you get butyrate, butanol, isopropanol, ethanol, carbon dioxide and when you go
for this butanediol fermentation you get butanediol and carbon dioxide.
Similarly, the propionate fermentation will give you propionate, acetate and carbon dioxide.
And mixed acid fermentation will give you acetate, ethanol and carbon dioxide along with
some formate, formic acid. Now there are several types of fermentation which are classified
according to the major end products obtained in the fermentation process. Now these types of
fermentation include acetate, alcohol or basically ethanol, butyrate, lactate, mixed acid,
mixed acid and butanediol, propionate and succinate, sulfide and methane. So, these are
different types of fermentation pathways we will see one by one.
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So, the first is acetate fermentation. Acetate is produced in several fermentative pathways. A
large diversity of bacteria collectively known as acetogenic or acetate forming bacteria
produces non gaseous acetate. These organisms include bacteria in the genera
Acetobacterium, Clostridium and Sporomusa. Some acetogenic bacteria are of course
thermophilic, but not all.
Several biochemical reactions are used by acetogenic bacteria to produce acetate. Most
acetogenic bacteria produce acetate from hydrogen and carbon monoxide while some
produce acetate from water and carbon monoxide by this particular reaction:
Some acidogenic bacteria produce acetate from carbon dioxide and methanol and often 6
carbon sugars or hexoses are degraded to acetone. Even propionate is converted to acetate.
So, these are the reactions:
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Then we will talk about the butyrate fermentation. Butyrate is a major fermentative product
of many bacteria. Strict anaerobes in the genera of Clostridium and Butyrivibrio ferment a
variety of sugars to produce butyrate. Under low pH values almost less than 4.5 several
clostridia species produce small amounts of acetone and n-Butanol. Now n-Butanol is highly
toxic to bacteria because of its interference with the cellular membrane functions. So, the
hexose that is getting converted to butyrate:
The next is lactate fermentation. A common product of many fermentative reaction is lactate.
The production of lactate is achieved by the aerotolerant, strictly fermentative lactate forming
bacteria and they are highly saccharolytic.
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There are 3 biochemical reactions for lactate production from sugar such as glucose:
The above reactions depend on what type of bacterial species it is being used. So, these are
some of the bacterial species are being shown in the other side of the slide. So, in addition to
the glucose other sugars fermented by lactate forming bacteria include fructose, galactose,
mannose, saccharose, lactose, maltose and some pentoses.
The next is propionate and succinate fermentation. Anaerobic Propionibacterium or
propionate-forming bacteria ferment glucose and lactate. Lactate the major end product of the
lactate fermentation is the preferred substrate for the propionate forming bacteria. Although
succinate usually is an intermediate product of the fermentation some succinate is produced
as an end product.
The above reactions depend upon which species is converting it or degrading it. These are
some of the species responsible for doing these conversions of glucose and lactate to
propionate is being listed there. So, propionate is a major substrate for acid fermentation that
can be converted to acetate and then used in methane production. Propionate increases the
relatively high concentrations under adverse operational conditions.
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Then the next is mixed acid fermentation and it is sometimes combined with that of the
butanediol production. Now a large variety of bacteria in the genera Enterobacter,
Escherichia, Erwinia, Salmonella, Serratia and Shigella are responsible for the mixed acid
fermentation. These organisms ferment sugars to a mixture of acids such as acetate, formate,
lactate and succinate.
Carbon dioxide, hydrogen and ethanol are also being produced. The prevalence of acids
among the products of mixed acid fermentation account for the name of the fermentation
process. Bacteria in the genera Enterobacter and Erwinia also produce 2, 3 butanediol in
addition to acids. The production of butanediol increases when the pH is decrease that means
less than 6.
So, in anaerobic digester acid production takes place simultaneously with methane
production. Although several acids are produced during acid fermentation, acetate is the
primary substrate used for methane production in an anaerobic digester.
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We will see the next one which is the methane fermentation. Three types of methane-forming
bacteria achieve methane for production, 2 groups of obligate chemolithotrophic
methanogens and one group of methylotrophic methanogens. Chemolithotrophic
methanogens produce methane from carbon dioxide and hydrogen or formate by this
reaction:
Now carbon monoxide also may be used by some chemolithotropic methanogens in the
production of methane, by this reaction:
Now methylotrophic methanogens produce methane by using methyl group containing
substrates such as methanol, methylamine and acetic and these organisms produce methane
directly from the methyl group and not via carbon dioxide by these 2 following reactions:
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Then next is sulfide fermentation. Sulfate is reduced to sulfide by bacteria for 2 purposes. So,
first is that bacteria use sulfate as the principal sulfur nutrient. Now this is done by enzyme
systems that reduce sulfate to sulfide. The reduction of sulfate to sulfide and its incorporation
as a nutrient into cellular material is termed as a assimilatory sulfate reduction. Second is that
during sulfide fermentation or desulfurification, sulfate is reduced to sulfide as organic
compounds are oxidized.
Because the sulfide produced through fermentation is released to the environment and not
incorporated into the cellular material, sulfide fermentation is also known as dissimilatory
sulfate reduction. There are 2 groups of sulfate reducing bacteria first group is called
incomplete oxidizers and the second are complete oxidizers.
Incomplete oxidizers degrade organic compounds to new bacterial cells, carbon dioxide and
acetate, ethanol, formate, lactate and propionate, whereas complete oxidizers degrade organic
compounds to new bacterial cells and carbon dioxide. So, you can see that the incomplete
oxidizers actually produce so many different types of products.
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So, the table list actually genera of sulfate reducing bacteria. So, you can see different genus
of sulfate reducing bacteria there and it is mentioned whether they are the species of
incomplete oxidizers or they fall under the species of complete oxidizer. So, the
Desulfobacter the first one. This is a complete oxidizer. The second one is Desulfobulbus, it
is a incomplete oxidizer. Like similarly there are others also mentioned.
So, the next fermentation type is the alcohol or ethanol fermentation. Though alcohol
fermentation is the domain of yeast, so mostly the Saccharomyces, alcohol is also produced
by several species of bacteria in the genera of Erwinia, Sarcina and Zymomonas. Now these
organisms produce ethanol from the anaerobic degradation of hexoses such as glucose.
At relatively low pH value less than 4.5, alcohol is produced by the bacteria in the genera
Enterobacter and Serratia, by this reaction:
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So, now we will quickly understand and the different methods of fermentation. Now
fermentation has been classified into liquid fermentation, submerged fermentation or solid-
state fermentation mainly based on the level of water used during the fermentation. So, SmF
which is the submerged fermentation exploits or utilizes free flowing liquid substrate broths
and molasses.
The bioactive compounds are secreted into the fermentation broth. The substrates are utilized
quite rapidly and hence need to be constantly replaced or supplemented with nutrients. This
fermentation method is suitable for microorganisms such as bacteria that need high moisture
content. An additional choice of this technique/method is that purification and refining of
products is easier. SmF is mainly used in the extraction of secondary metabolites that
necessitate to be used in the liquid form.
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In contrast, SSF utilizes the solid substrate like bran, bagasse and paper pulp. The main
interest and advantage of using this substrate is that nutrient-rich waste materials can be
easily or efficiently recycled as substrate. In this fermentation method or technique, the same
substrate can be used for a long fermentation period and can be utilized very slowly and
steadily.
Henceforth, this technique supports controlled release of nutrients. SSF is best suited or
adapted for fermentation techniques including fungi and microorganisms that depend on
limited moisture content. Nevertheless, it cannot be used in fermentation process involving
organisms they require a very high aw value (aw is the water activity value) such as most of
the bacteria. So, bacteria and yeasts are equally involved in SmF and SSF, whereas fungi are
mostly concerned with the SSF processes.
The roles of bacteria and yeast in SMF are mostly related to food and beverage processing
industries. Filamentous fungi are best suited for SSF owing to their physiological,
biochemical and enzymological properties and dominate in oriental foods, ensiling and
composting processes.
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So, this is a table which gives us information about the different factors, the liquid substrate
fermentation and the solid substrate fermentation. So, if you see the second one under aseptic
condition; so the liquid substrate fermentation, there will be heat sterilization and aseptic
control and the solid substrate fermentation, vapour treatment and non-sterile conditions.
So, when you talk about let us say the inoculation here - so easy inoculation and continuous
process under the liquid substrate fermentation and under solid state fermentation spore
inoculation and it is a batch process. Because mostly it is being done by the fungi. So, you
can go through the table later on.
So, I am moving ahead. So, we will try to understand what are the different fermentation
modes, how it can be done? Essentially there are 3, one is the batch one which is very much
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is being practiced in most of the lab scales, then the fed-batch and then the continuous
culture. Now what is batch? Now here you can see nicely I have depicted this particular
figure - given this particular figure, from here you can directly understand what is a batch,
what is the fed-batch and what is a continuous process from this. There is an inlet, there is
outlet, you can see that under batch inlet and outlet both are strike down, what does it mean?
So, this means that no extra feeding is used from the beginning to the end of the process.
Once the substrate is fed to the batch reactor and the microorganisms and other necessary
things are being supplied it is being closed and reaction will proceed. Once the reaction stops
the products are formed you will open the reactor. So, this is what is batch.
Now what is fed-batch? So, you can see that outlet, there is no outlet, but there is intermittent
inlet. So, once you supply the feed then you can intermittently also supply the feed. What
does it mean? So, fed-batch is a process where feeding with substrate and supplements can
extend the duration of a culture for higher cell densities or to switch metabolism to produce a
recombinant protein for example. So, intermittently you are feeding.
The next is the continuous culture where inlet and outlet both are open throughout the
process. That is why it is a continuous process. Continuous feeding and continuous taking out
of the reaction products. So, it is mostly adapted in the industries. So, continuous culture
where either the feed rate of a growth limiting substance keeps cell density constant (that
reactor is called a chemostat) or cell density determines the fed rate of the substrate (That
reactor is called a turbidostat). Now cell retention can offer another very productive option,
that is called perfusion. The incoming feed rate matches the rate of the removal of the
harvest. The balanced nature of the feeding allows a steady state to be achieved which can
last for days to months. This state is good for studying microbial metabolism or long-term
production.
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Now this is again described nicely under this particular schematic representation which tells
us the salient features of various fermentative modes. We will quickly go through it. The
batch, fed-batch and continuous. Let us see the batch. So, it is commonly used, relatively
slow substrate utilization rate and low risk of contamination and strain mutation because it is
a closed system. There is no feeding, there is no taking out of the products.
In the fed-batch it is best during substrate inhibition. When there is substrate inhibition you
feed little more again the dilution factor actually increases inside the fermentation and it will
dilute the inhibitory products. So, that inhibitory products under dilution will not more serve
as inhibitory substances (the inhibitory effect will be diminished) and it has prolonged log and
stationary phase of the microorganisms (growth phase we are talking about). So, when you
compare fed-batch, we can say the effectiveness of fed-batch over batch due to concentrated
substrate utilization and large metabolites production during stationary phase. Now this is the
advantages of fed-batch with batch respectively.
Now let us talk about the continuous system. Now here less sterilization and re-inoculation is
required because we are continuously feeding the substrate as well as continuously taking out
the substrate. Less maintenance cost and fastest substrate utilization rate. Now if you
compare continuous with fed-batch or batch we can say that it is more effective due to high
productivity and reduce product inhibition. So, this is all about fermentation and how we can
do the fermentation via various types of reactors or the various types of mode.
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So, with this today I conclude my lecture and in our next lecture under this module we will be
discussing about the various products of the microbial conversion processes and their utilities
and some of the commercial success stories. So, thank you very much and if you have any
query please register it under the Swayam portal or drop a mail to me at kmohanty.iitg.ac.in.
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Module 06
Lecture-18
Products and Commercial Success Stories
Good morning students. This is lecture 3 of module 6. As you know that in this module we are
discussing about the microbial conversion processes. In today's lecture, we will discuss about the
different types of microbial conversion products and few commercial success stories related to these
products. So, let us begin.
So, the first and foremost important microbial conversion product is of course, biogas which is
coming from the anaerobic digestion. So, AD of municipal sludges results in the production of a
mixture of gases. Collectively these are referred as either digester gas or biogas. The only gas of
economic value that is produced in an anaerobic digester is methane. Now, methane can be used as a
source of fuel.
It is a natural flammable gas, methane is odourless and burns cleanly. Pure methane has a heat value
of around 1000 British thermal unit per feet cube. Typically, biogas production in municipal
anaerobic digesters is between 10 to 25 feet cube per pound of volatile solids degraded or 0.75 to 1
meter cube per kg of volatile solids. The heat value of biogas is approximately 500 to 600 Btu per feet
cube, much lower than that of the methane because of the dilution of the methane by carbon dioxide.
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Now, with an increase in the quantity of carbon dioxide in the biogas, its heat value will be
decreasing. So, if the carbon dioxide content of the biogas becomes too large, biogas will not allow
for a self sustained burn and supplemental fuel will be required. So, that means if carbon dioxide will
be too much, then biogas will not ignite and you need to have some secondary fuel to do the ignition.
So, if the carbon dioxide fraction in the biogas increases above 30%, the acid concentration in the
sludge increases and the pH drops below 7. And at pH values below 7 significant acid fermentation
occurs. Now that is not good for the anaerobic digestion, when we are talking about biogas or
methane formation. Now numerous gases are produced in an anaerobic digester. The gases produced
in largest quantities are methane and carbon dioxide by volume methane is about 60 to 65% and
carbon dioxide is 35 to 40%.
Most of the municipal wastewater treatment plants use biogas to heat digesters to around 32 to 35
degrees centigrade. The biogas may also be used to heat buildings. Biogas not used to heat digesters is
simply flamed up. So, the organic compounds include methane and volatile organic compounds. The
VOC contains different types of other components such as volatile fatty acids, nitrogen containing
compounds and volatile sulfur compound VSC.
The production of nitrogen containing VOC and VSC is usually due to the degradation of
proteinaceous wastes that is present in different types of wastes like municipal solid waste. Now of
the inorganic gases produced in an anaerobic digester, hydrogen sulfide is the most undesirable. The
reason is that if the biogas contents too much of hydrogen sulfide, the gas may damage the digester
equipment, this is basically due to the corrosion.
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So, hydrogen sulfide can be scrubbed from biogas, but the scrubbing process is expensive, usually,
you go for a chemical scrubbing. So, means you are adding more cost to the entire process.
So, let us look at this particular slide where I have given the organic gases that is produced through
microbial activity. So, this particular table gives the different types of organic gases. And here we
have different types of inorganic gases. So, you can see that inorganic gases are basically ammonia,
carbon dioxide, carbon disulfide, carbon monoxide, hydrogen sulfide, nitrogen and nitrous oxide. And
organic gases are so many - acetate, butyrate, caproic acid, formate, propionate, succinate and there is
a big list basically.
So, the inorganic gases like molecular nitrogen and nitrous oxide are produced through anoxic
respiration, the process is called denitrification in the anaerobic digester. Now, anoxic respiration can
occur with the transfer of nitrate ions, to the digester with sludges or the addition of nitrate containing
compounds, such as sodium nitrate to increase the digester alkalinity.
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So, the next product is lactic acid. So, lactic acid is an organic acid. It has molecular formula
CH3CH(OH)COOH. It is white in solid state and is miscible with water. While in liquid state that
means in the dissolved form, it is a colourless solution. Fermentation has virtually waived chemical
synthesis of lactic acid. The lactic acid is produced anaerobically with a 95% w/w yield based on
carbohydrate, a titer of over 100 grams per liter and a productivity of over 2 grams per liter. Now, this
is comparable to process employing the lactic acid bacteria.
Lactobacilli produce mixed isomers, whereas Rhizopus forms L –(+)- LA exclusively, lactic acid
exclusively. So, Rhizopus oryzae is favoured for formation since it makes only the stereochemically
pure L plus lactic acid. In a homolactic fermentation, one mole of glucose is ultimately converted to 2
moles of lactic acid and under a heterolactic fermentation yields we get carbon dioxide and ethanol in
addition to lactic acid in a process called the phosphoketolase pathway.
Now, lactate dehydrogenase that is the enzyme responsible for lactic acid formation, catalyzes the
interconversion of pyruvate and lactate with concomitant interconversion of NADH and NAD +. So,
if you are interested, you can read a little more on the phosphoketolase pathway to understand the
entire process in a better way.
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So, here we are trying to understand in brief what are the different types of products and of course,
their end uses and other necessary things ascribed to these products. So, Griffith and Compere these 2
scientists in 1977 described a fixed film system for continuous lactic acid production from the
wastewaters which contained readily recoverable sugar polymers from the pulp, paper and fibreboard
industries.
Now their fixed film unit (it is 2 inches x 6 inches small one), was seeded with Lactobacilli and
lactose fermenting yeast. So, usually the kefir culture we many times called it kephir. So, kephir. So,
kefir culture is a symbiotic mesophilic mixed culture, where bacteria and yeast are both present in
symbiosis. Now the wood molasses substrate wastewater concentrate was pre-treated with cellulase,
diastase and hemicellulases. So, these are the enzymes.
Now with a continuous feed rate of 60 gram per gram wood molasses over the seed(ed) fixed film
unit, 31 to 32 grams per gram per lactic acid yield was obtained, which is pretty good. So, the
production of calcium lactate from molasses by Lactobacillus delbrueckii has also been reported by
Tewari and Vyas in 1971. So, 2 of the most common applications of lactic acid fermentation is
production of yogurt, and sauerkraut.
Now, yogurt all of us know and sauerkraut is a cabbage based product which is fermented - the
cabbage is basically sliced into very thin strips and then fermented using the lactic acid bacteria. So,
lactic acid is found primarily in sour milk products such as koumiss, laban, yogurt, kefir and some
cottage cheeses. The casein in fermented milk is coagulated (curdled) by lactic acid. Lactic acid is
also responsible for the sour flavour of the sourdough bread.
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So, then acetic acid. Acetic acid can be produced by biomass fermentation in 5 different well known
methods. So we will see one by one. The first one is anaerobic gasification of biopolymers to methane
and carbon dioxide, followed by methanolic carbonylation to acetic acid. Now, this method
essentially involves an anaerobic digestion to produce methane, followed by introduction of the
methane gas into a standard methanol carbonylation facility.
So, the second one is anaerobic yeast fermentation of hydrolyzed biopolymers to ethanol followed by
oxidation to acetaldehyde and then to produce acetic acid from acetaldehyde. Now, in this case,
oxygen enriched air and acetaldehyde are fed into a reactor at around 66 degrees centigrade and 101.3
kilo Pascal, where they undergo a 3 step chain reaction. Now, this process is about 95% efficient with
very few byproducts.
The next process is anaerobic yeast fermentation of hydrolyzed biopolymers to ethanol followed by
aerobic bacterial fermentation to acetic acid. So, in this single process both aerobic and anaerobic
processes are used. This is the third method, and the process is currently used for vinegar production,
it is very widely adapted process for vinegar production. We will just discuss in a little more detail.
So, in this process molasses, nutrients and 1% ethanol are used to start a submerged aerobic
fermentation. That is the seed you can say, first, the primary feedstock.
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Now, the concentration of ethanol is kept about 1% until the acetic acid concentration nears to 10 to
11%. Now this mixture of extractant and acetic acid is then put through a distillation chain to recover
both. A major drawback to this process for acetic acid production is the energy intensive distillation
step, which adds substantially to the cost of acetic acid production.
Then the fourth process is anaerobic bacterial homo-fermentation of biopolymers. So, that has
generated much interest in recent years. In this fermentation, hydrogen is oxidized and carbon dioxide
is reduced to acetic acid.
In the next method that is an anaerobic bacterial hetero-fermentation of biopolymers with
simultaneous production of ethanol and other acids. Now hetero-fermentation of carbohydrates to
acetic acids present several purification problems. Now these problems are multiplied in hetero-
fermentation by the presence of other organic products and the concomitant lower yield of acetic acid
is usually reported.
So, we understand that there are 5 different processes through which we can produce acetic acid. So,
we have discussed in a brief about this 5 different processes and their pros and cons.
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So, the next important class of product from the microbial conversion is alcohol - so ethyl alcohol. So,
ethyl alcohol is a primary metabolite that can be formed from fermentation of a carbohydrate or sugar
or a polysaccharide that can be depolymerized to a fermentable sugar. Now it has lower toxicity and is
easily biodegradable. It is soluble in water, harmless to the environment and does not generate
greenhouse gases.
Mostly, yeasts are preferred for these fermentation. Saccharomyces cerevisiae is the well known yeast
to do alcohol fermentation. But the species used depends on the substrate employed. Again, I am
telling you, it is very important, which species you are going to use, Saccharomyces different strains
are available. Now, that will depend on what is your substrate. For example, Saccharomyces
cerevisiae is used for the fermentation of hexose, whereas Candida species or Kluyveromyces fragilis
species may be employed if pentose or lactose is used as a substrate for the ethanol production.
Now, ethanol is produced in Brazil from cane sugar at 12.5 billion litres per year and is used as 25%
fuel blend or as a pure fuel. With regard to beverage ethanol, some 60 million tons of beer and 30
million tons of wine are produced each year. Now, having said that, please understand that we are
talking about Brazil here, sugar production from the sugar, sugar to ethanol in Brazil and various
other countries.
Now, this we have already discussed when we discuss about bio-refinery fundamentals and concepts,
we have discussed that we cannot do it in India and other developing countries because there is a food
versus feed problem. So, in India, we cannot talk about or think about producing ethanol from this but
certainly we can think about producing it from the waste, whether it is lignocellulosic waste from our
agricultural product forest tellings and all or even molasses and other wastes.
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Now, the uses of ethanol are many, including the use as a solvent in beverages, in food and feed via
single cell protein - which is very well known as a SCP, hydrocarbon synthesis via ethylene, as a
gasoline dilutant as gasohol. So, gasohol is almost 10% ethanol plus 90% gasoline. And for biological
energy generation, that is ATP and that happens during the metabolic pathway. So, the basic steps for
ethanol production from grain, cellulose or waste materials consists of 3 steps.
The first one is the conversion of the gram starch or cellulose to fermentable sugar. So, then, this
fermentable sugar is fermented to alcohol. And the third and one most important step is the separation
of the resulting fermentation beer, which contains 6 to 12% ethanol into substantially water-free
ethanol. So, sugars for ethanol production may be obtained from any feedstocks, such as grains,
watermelon, and fruits, sugar beets, sugar cane, sweet sorghum, and potatoes and from cellulosic
residues of corn, small grain straws, wastepaper, sawdust, wood chips, grasses or forages and
cellulose containing municipal waste.
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So, the next product is or we can say that, many times say it is a byproduct, is glycerol. So, we have
discussed about glycerol earlier that glycerol is one of the most important byproduct having lots of
commercial application from the biodiesel industries. But glycerol does produce during the microbial
conversion process also. So, glycerol is used in almost all chemical industries due to its particular
combination of physical and chemical properties.
The majority goes into the manufacturing of synthetic resins and ester gums, drugs, cosmetics and
toothpastes because glycerol is a good solvent for many compounds. So, one of the biochemical
processes that produce glycerol is aerobic fermentation with osmophilic yeast. Glycerol is
accumulated in the yeast as a compatible solute during the adaptation to high osmotic pressures or
high sugar concentrations.
Saccharomyces cerevisiae uses glycerol as its sole compatible osmolyte. The process usually
decreases the specific growth rate because of the limited oxygen transfer rates of industrial
bioreactors. Candida krusei is another osmophilic yeast which can ferment glucose into glycerol.
DuPont corporate and Genencor these are the 2 important industries which work on producing
different types of enzymes and enzyme producing microorganisms.
So, they have different cocktails of enzymes also. So, these 2 companies have engineered biosynthetic
pathways into an industrial strain of E. Coli to directly convert glucose to 1-3 propanediol, a route not
previously available in a single microorganism. So, this is an important breakthrough in enzyme
technology you can say.
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So, the next class of products are polymers and biodegradable plastics. So, a lot of emphasis is being
laid on biodegradable plastics due to various reasons of the plastic pollution and has been in market
since almost a decade, the biodegradable plastics. So, bio based polymers include various synthetic
polymers derived from renewable sources. So, biopolymers it can be nucleic acids, polyamides,
polysaccharides, polyesters and polyphenols and their derivatives and their blends and composites.
So, they are applied in the food, pharmaceutical, chemical and petroleum industries and are used as a
emulsifying agent, stabilizing agent and flocculating agents. Lactic acid produced from fermentation
has been used to synthesize biodegradable plastics. So, that is polylactic acid - PLA. Biodegradable
plastics have a high demand because they are thermoplastic and environmentally degradable and help
to reduce the disposal problem of the non degradable plastics.
Several polyesters with properties comparable to conventional plastics such as polybutylene
succinate, polyester carbonate, poly-D-3-hydroxybutyrate, polypropiolactone - PPL and poly-L-lactic
acid (actually polylactic acid – PLA) are used as biodegradable plastics.
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Many of these bio polymers such as polylactic acid and polyglycolic acid, have been accepted for use
in the medical industry as medical devices or cell culture matrices. Poly-glutamic acid produced by
genus Bacillus can be used as the basis in drug delivery applications for cancer therapy. Now PGA
conjugation can provide more stable and water soluble drugs, which control drugs’ exposure to
tumour cells. Polyhydroxyalkanoate, is one of the largest group of thermoplastic polyesters
synthesized by numerous bacteria as an intracellular carbon and energy storage compound and
accumulated as granules in the cytoplasm.
PHA is regarded as a potentially useful alternative to petroleum derived thermoplastics because it is
biodegradable and biocompatible. PHA has been industrially produced by pure cultures of Alcaligenes
latus, Azotobacter vinelandii, Pseudomonas oleovorans, Ralstonia eutropha, recombinant Alcaligenes
eutrophus and recombinant E. Coli.
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So, apart from all these products that we have discussed, which are actually the major products, there
are other various products which are being produced in very small or minor quantities. So, some of
these are having high industrial and commercial value, like microbial polysaccharides. So, xanthan
gum, Dextrans, Mannans, Pullulan, and Cellulose. Then amino acids - L-Alanine, L-Aspartic acid,
then L-Lysine, L-Phenylalanine, and L-Threonine.
Antibiotics such as Aminoglycosides, then Bacteriocin, β-Lactam, Nisin, Tetracyclines. Enzymes
such as alkaline proteases, α-Amylases, and there are many others and few vitamins like beta-
carotene, Provitamin D 2, vitamin B 12 and Riboflavin.
So, we will now see and discuss the different commercial success stories, how the microbial
conversion process has been commercially adapted to produce different products. So we will see 2 or
3.
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So, the first one is that Solrod biogas plant in Denmark. So, the Solrod biogas plant was taken into
operation in 2015 - very recently started. The plant was established and is operated by Solrod biogas
company founded in May 28, 2014 with Solrod Municipality as the shareholder. The idea is to build a
biogas plant in Solrod emerged from the need to find a sustainable solution to the community’s odour
problem, which is basically caused by the seaweed fouling the beach.
So, what happens in this particular province or the town of Solrod is that this huge amount of
seaweeds is coming and getting deposited on the sea shore. Now, slowly, they are degrading under the
attack of sunlight and of course water and they are getting degraded. So, when they are getting
degraded, they started producing obnoxious gases, I am not telling it is toxic, but they are creating
huge odour nuisance.
So, the people in the municipality of Solrod, they wanted to get rid of this odour in a permanent way.
So, then this idea has started that how to convert these seaweeds into valuable products, so that they
can get rid of this odour as well as they can produce some valuable products. So, then the story begins
actually. So, simultaneously the Solrod Municipality also wish to take concrete action concerning
climate change challenges by producing green energy.
So, the biogas plant has a treatment capacity of 200,000 tonnes feedstock per year, the biogas
produced is used directly for the CHP generation in a large gas engine - combined heat generation
system/cycle. So, the power is sold to the grid and the heat is supplied to the local district heating
system, which is operated by a particular company like Vestegnens and owned by 12 municipalities as
stakeholders.
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So, if you look at that input output system of the particular plant, so the treatment capacity is 200,000
tons per year, methane that is getting produced is 6 million meter cube per year, electricity production
is 23 gigawatts hour per year, heat production is basically the district heating is again at 28 gigawatts
hour per year. Now, if we talk about biomass feedstocks, the major feedstock is of course, the
seaweed which was the initial target actually.
So, seaweed contains various types of Zostera maritima, Pilayella littoralis and Ectocarpus sp. So,
usually 7400 tons, the share of biogas is about 0.5%. So, contribution to the value of the project is
nutrient supply and improved sea water quality. So, this is very interesting the last column and then
manure is being added of course, CP Kelco - that is a pectin, then Chr Hansen. So, altogether adds on
to 200,000 tons, but if you see the shares so you can see that from the pectin the share of biogas is
huge.
Seaweed, is not the major contributor however, in this way, they got rid of the entire odour creating
problem and simultaneously produced fuels. So, if you talk about manure so it is contribution to the
value of project is terms of gas production and process stability. Pectin, major contribution to the gas
production booster and Hansen actually, again, nutrient supply and gas production booster.
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So, if you talk about investment and economy, the Solrod biogas has a share capital of 16 million
Danish kroner consisting of a cash contribution of 6.08 million Danish kroner and 9.92 million Danish
kroner as assets, other than the cash. So, investment is 85 million DKK which is excluding the CHP
unit. Then the European Union grant is 0.5 million euro and the annual revenue that is coming right
now is around 30 million Danish kroner. So, this is quite a success story, and it is been recently
implemented.
So, if you talk about the estimated benefits related to the Solrod biogas plant, so it is 60 gigawatt hour
per year in renewable energy production, which is a very good amount, 104 local jobs are being
created out of which 14 are permanent jobs, 40,100 tons of carbon dioxide equivalent is almost saved
per year, which is almost 51% of the municipality target for the 2025. The next is sustainable waste
treatment and lower cost of the waste transport, production of digestate as bio-fertilizer for farmers.
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So, this is another success story from this particular biogas plant, where the digestate or the solid part
left out after the fermentation is being used as the biofertilizers and it is sold to different farmers. So,
reduced leaching of nitrogen to aquatic environment by almost 62 tons per year - So, 70%
requirement for the Koge Bay and reduced leaching of phosphate to the aquatic environment by 9 tons
per year - 100% of requirement of the Koge Bay. So, reduced odour nuisance from the beach and
seaweed which was their major target, then improved sea water quality and higher recreational value
of the maritime coastal area.
So, the next success story that we are going to discuss is about the Lantmannen Agroetanol, Sweden.
So, Lantmannen is a Swedish agricultural cooperative owned by 25,000 Swedish farmers, providing
food, feed and fuel nationally and internationally. Now since 2001 Lantmannen has produced fuel
ethanol at a facility in a Norrkoping in the South-Eastern Sweden, based on wheat and other grains as
well as residues from the food industry.
The plant was initiated to develop new markets for agricultural products. Thanks to the efficient
processes, the use of renewable process energy from adjacent biomass fuel CHP and important co-
products in the form of protein rich feed and biogas, the fuel ethanol produced reduces the greenhouse
gas emissions by more than 90% compared to the fossil fuels. Now this is the major outcome of this
entire project.
So, from 2015 onwards Lantmannen is also marketing a renewable ethanol fuel for the diesel engines
known as Agro Cleanpower 95, that is the trade mark which reduces the greenhouse gas emissions by
up to 90% compared to the fossil diesel. A noteworthy co-product here is the biobased carbon dioxide
that is sold as an industrial raw material to customers in the food processing and packaging industry,
that is an example of the biobased carbon capture and use.
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Yet the ethanol production at the Lantmannen plant has had significant problems in terms of business
performance. However, beginning in the second half of 2015, the plant has become profitable as a
result of increased ethanol volumes exported instead of used within the Sweden. So, actually what
happened when they were using whatever the ethanol that is being produced inside the Sweden in the
initial years, then they are not making profit.
Because of the policy problems that was there or existed that particular duration in the Sweden. Now,
so they decided to sell it off. So, export it to various other countries. So, once they started doing that,
their revenues have jumped like anything. Now, later on the Swedish government has also changed its
policy so that this Lantmannen ethanol was being again now marketed inside Sweden.
So, this was actually as I told that there was policy problem. So, in Germany, the policy measures
towards renewable fuels depending on the greenhouse gas emission reduction potential, whereas the
Swedish policy currently do not. But this has made Lantmannen’s ethanol highly competitive in other
European markets and has resulted in substantial profits. However, in 2018 Sweden introduced similar
policy measures as Germany.
So, Agroetanol has an annual capacity to convert 600,000 tons of grains to 230,000 meter cube of
ethanol with 200,000 tons of protein feed as co-product mainly for cattle and 200,000 tons of carbon
dioxide which is collected, liquefied and turned into green carbonic acid. So, that mainly goes for the
beverage production.
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So, this is all about the Lantmannen biorefinery which is located at the Norrkoping in Sweden. So,
this is the plant top aerial view. So, the grains residues from the food industries, then cellulose from
agricultural and forest tailings and forest residues are processed. So, they are into 3 distinct streams,
the one is starch rich stream, another is a protein and fiber rich stream another is a carbon dioxide, the
gas basically which is coming from the pre-processing.
Now, the starch goes to the ethanol platform, which gives us biofuels, green chemicals and packaging,
again the solid whatever is left out. Then the protein and fiber goes to the DDGS platform where it is
converted to feed and food. Then carbon dioxide, it goes to the carbic acid platform where it produced
food, industrial applications and of course carbon dioxide also goes for this greenhouse gas emission.
It is a bio based carbon dioxide capture and sequestration cycle basically you talk about.
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Then the year of implementation of this plant is 2005. But again, it is updated in or upgraded in 2015.
Location is of course Norrkoping in Sweden. The technology is ethanol biorefinery. So, the location
of ethanol plant close to biomass based CHP ensures deliveries of renewable electricity and process
heat. So, this is one of the most important take home message from this particular plant. Principle
feedstocks are wheat and other grains as well as starch rich residues from the food industry.
If you talk about Products and markets, then fuel ethanol and co-products in the form of protein rich
feed. A further co-product here is the biobased carbon dioxide that is captured and sold as industrial
raw material to customers in the food processing and packaging industry. So, if you talk about the
TRL the technology readiness level: it is TRL 9 - So, that is the actual system proven in operational
environment and it is quite a success story.
So, the next one is Biowert grass biorefinery, that is for the biobased plastics located in Germany. So,
Biowert industries was founded by Michael Gass in 2000 as a Swiss-German company. The first
Biowert grass refinery is started operation in 2007 and is located in Brensbach, Germany on an 18,000
m2
site. The main products based on grass from permanent pastureland and arable land for crop
production are grass fibre insulation (AgriCellBW
is the trademark name), natural fibre reinforced
plastic (AgriPlastBW
is the trademark name) and fertilizer made from digestate (AgriFerBW
that is the
trademark name). So, the facility has an annual throughput of about 2000 tons dry matter equivalent
to 8000 tons grass per year at 25 to 30% dry matter content. The integrated biogas plant produces
13,40,000 m3
of biogas annually, which is used in combined heat and power facilities, which in 2012
produced 5.2 gigawatt hour (GWhel) electricity.
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Now, the first step after ensiling includes mechanical treatment of the grass silage and isolation of
grass fibres through pulping, drying and pressing processes. The grass fibres are further processed
into AgriCellBW
and AgriPlastBW
synthetic granules. AgriPlastBW
contains 30 to 50% grass fibres and
50 to 70% recycled polyolefine and is used for injection moulding for a range of uses.
The grass juice remaining from the mechanical pretreatment of grass silage is used as a substrate in
the biogas plant together with local co-substrate such as food waste and slurry. The heat and
electricity derived from the biogas facility is used to satisfy the energy in the biorefinery and excess
electricity is exported to the electricity grid. Wastewater that is arising from the process is reused for
pretreatment of the grass silage. Digestate from the biogas plant is further processed to a concentrated
and a liquid biofertilizer used by the local farmers. Now, this closes the nutrient cycle in the circular
economy.
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So, if you closely look at this particular plant and how it happens, this is the aerial view of the
Biowert plant, these are the different types of agri-based products. Now, let us have a look here this is
interesting actually. This is a cycle which is Biower cycle, which talks about the circular economy.
So, there is a complete nutrient recycle here in this. If you start from the grass - Meadow grass, it is
harvested, then it is delivered, processed in the grass factory.
So, the solid parts go to the fibre production in a name of AgriCell, then whatever the other products
that comes here is again processed and granule into different products named as AgriPlast. Then the
slurry - grass slurry, that goes to the biogas reactor - basically for the anaerobic digestion. Here the
different other biomass also can be co-feeded. So, the co-feedstock process here. So, whatever comes
out is nothing but your green power.
Then whatever left out this can be used as AgriFerBW
agri fertilizer basically the slurry it can be
concentrated and made into your solid fertilizer also. Now, you can see that fertilizer is being again
used as fertilizer in plantation to grow Meadow grass. So, thereby the nutrients which are present in
the grass are getting recycled again. So, it is a complete nutrient recycle and circular economic
concept.
So, if you look at the input and output for this particular plant, - the input is biomass and then
electricity demand. So, biomass is about 8000 tons per year. And electricity demand is 2.5 to 3
gigawatt hour per year. And the biogas and CHP plant that produce actually grass juices - 1942 ton
per year - that is required as a feedstock to be fed to the digester and then the co-substrates in biogas
facility around 15,260 tons per year.
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So what is the output? Outputs are this actually: AgriCellBW
and AgriPlastBW
, the solid by-products
which are being converted into 2 different trade names and being marketed - and then biogas
(approximately 13,40,000 m3
per year of the methane concentration). And then of course, there is 5.2
gigawatt hour electricity generation. Now, please understand that - whatever it is getting produced
here, the electricity, almost 50 to 60% of that is being utilized in the entire plant and the rest either is
being sold or directly fed to the electricity grid.
So, with this, I conclude today's lecture. So, in the next module, that is module 7, we will be
discussing about bio-diesel. So, thank you very much in case you have any query please feel free to
register your query in the Swayam portal or you can drop a mail to me at kmohanty@iitg.ac.in, Thank
you.
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Module-07
Lecture-19
Diesel from Vegetable Oils, Microalgae and Syngas
Good morning students, today is lecture 1 of module 7. And this particular module is dedicated
to biodiesel. So, in today's class we will understand diesel from different vegetable oils,
microalgae as well as syngas. So let us begin.
The depleting trend of conventional, non-renewable, fossil based fuel has triggered research and
development of an alternative energy. So, biodiesel is one of the most promising renewable
energy in this century. In addition, biodiesel has many superior properties as compared to
petroleum diesel such as lower exhaust emissions, it is biodegradable, non-toxic, renewable, and
it is almost free of sulfur.
Since biodiesel is renewable and environmentally friendly, the use of this fuel is a shift towards
the sustainable energy. So, in the figure 1 here, you can see the different types of oils and their
yield per hectare. So, you can see soybean oil, then cameline oil, safflower, sunflower, rapeseed,
castor oil, jatropha, palm oil and algae oil. So, you can see that among all, algae, per hectare
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yield is very high. So, anyway we will be discussing about most of these oil sources and what are
the major composition of all these oils.
So, let us again, go to that. So, the history of biodiesel is as long as that of diesel engine itself.
The use of vegetable oils was investigated as early as the era when diesel engine was developed
by Rudolf Diesel - who has actually invented the diesel engine. So, when he invented and tested
the diesel engine; he used peanut oil as a fuel for his engine. So, many vegetable oils were
investigated during the historic times, which include palm oil, soybean oil, cottonseed oil and
castor oil etc.
The feedstock for biodiesel production can be categorized as lipid feedstock and alcohol
feedstock. Now lipid feedstock includes vegetable oils, animal fats, and more recently other plant
like organisms such as the cyanobacteria and algae. The vegetable oils used as lipid feedstock for
biodiesel production are highly dependent on regional climate. So, some of them are rapeseed oil
in European countries and Canada, Soybean oil predominantly in the United States, and palm oil
predominantly in the tropical countries such as Malaysia and Indonesia.
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Coconut oil is another lipid feedstock used for synthesis of biodiesel in coastal areas. Potential
non edible oils used as lipid feedstock in India include Jatropha oil and karanja oil. Now this
table will give you an understanding about the different oil seed plants, their oil content, their oil
seed production and average oil seed price and average oil price - given in US dollars and the
yield per kg per hectare per year.
So, you can see that rapeseeds, soybean, sunflower seed, palm, cottonseed, peanut, copra and
coconut all are listed. So, this gives us an understanding about that we have plenty options of oil
seeds available in the world. And most of these here listed are almost the vegetable oils which
can be used for the cooking purposes, but not all. Now that is why if you recall our discussion
during biorefinery, I have been telling you many times that in India and other developing
countries we cannot use such vegetable oils, or say anything, any feedstock that comes under
food. So, that is why in India our focus is initially when this biodiesel has started, our focus was
completely shifted to the Jatropha, Jatropha curcas. And in one of our class I have told you that
why Jatropha is not become sustainable, it could not fit to the sustainable; then moreover
economy is also a problem with such Jatropha based biodiesel.
So then, we have shifted our attention to other non food based seed oils, we can call them as non
edible oil seeds and in our lecture perhaps 5, we have discussed about various types of non edible
oil seeds, whether it is mahuya, karanja, neem and there are many.
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Soybean oil dominates the world oil seed production while rapeseed production is second only to
soybean oil. The oil content in soybean and rapeseed is 21% and 35% respectively. Despite the
lesser availability, palm oil is an interesting source for biodiesel production due to it is lower
price and relatively high oil content, it is almost 40%. So, oil seeds contain droplets of lipid
which can be extracted as vegetable oils.
But extraction, many times, is an energy intensive as well as a cost intensive process. So, the
major component of vegetable oil is triacylglycerol - which is called as TAG, or triglyceride,
which is called as TG - which is a molecule composed of three esters of fatty acid chain attached
to the glycerol backbone, so basically the glycerol group. So, when 1 and 2 acyl groups are
replaced by hydroxyl groups, it is called diacylglycerol – DAG, or diglycerides – DG; or
monoacylglycerol – MAG, or monoglyceride - MG respectively.
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Now this table will give you the understanding about the molecular structure of the triglyceride,
diglycerides and monoglyceride. So, the fatty acid chains usually range from 10 to 24 carbon
atoms. These fatty acids are frequently represented by a symbol such as C18:1, which indicates
that a fraction consists of 18 carbon atoms and 1 double bond. So, typical fatty acids attached to
TAG found in vegetable oils are presented in the table 3.
That means this table; so you can have a glance through this. So, it tells us about the structures of
common fatty acids found in vegetable oils. So, three different groups are presented here. The
first one is saturated, second is mono-unsaturated and third one is polyunsaturated. So, this is
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their common name and then this is the symbol and then the formula and double bond position -
where the double bond is located, which carbon atom basically.
So, naturally occurring fatty acids in vegetable oils have a cis-formation whereas, unnatural
trans-isomers occur due to partial hydrogenation process. And in cis-isomer, hydrogen atoms are
attached on the same side causing a “V” shape of the fatty acid chain. Now when two hydrogen
atoms are attached on the other side of each other, trans-isomer is formed and the molecular
structure is linear.
So, the shape of the configuration determines stacking of TAG molecules, proximity between
molecules and intermolecular forces between the molecules. Now all these factors are key
parameters for determining properties of various vegetable oils, such as crystallization and
melting temperature. The major difference between various vegetable oils is the type of fatty
acids attached in the triglyceride molecule.
Fatty acid composition is of utmost importance, as it determines fuel properties of biodiesel
derived from corresponding vegetable oils. Fatty acid composition also determines degree of
saturation, unsaturation and the molecular weight of vegetable oils. Fatty acid compositions of
various vegetable oils are shown in table 4. So, in the next table I will show you.
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So, this table gives us the fatty acid composition of vegetable oil. So, the vegetable oils common
name, species is given, and then fatty acid composition by weight percentage. So, we can see
one; let us see the soybean; the usual soybean or Glycine max. So, you can see that 10 weight
percent is to 0 fatty acid composition, so 16 carbon atoms and no double bond basically.
Then if you proceed again, you will see that 18 carbon atoms no double bond is 4.3 weight
percent. Then 18 carbon atoms and 1 double bond is 22.3%. So, similarly so many other
vegetable oils and their fatty acid composition has been listed, so you can go through it later.
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So, we will move ahead. So, the degree of saturation/unsaturation and molecular weight of
vegetable oils can be calculated by two things, first is something called an iodine value and
second is called saponification value (respectively). Now higher iodine value and saponification
value indicates higher degree of unsaturation and lower molecular weight of the corresponding
vegetable oils. Iodine and saponification values of selected vegetable oils are shown in the table
5.
So, you can see few oils are being listed, so rapeseed oil, soybean, palm, and sunflower
cottonseed, linseed, rice bran and their corresponding saponification value and iodine values
have been listed.
Now we will quickly glance through the different types of vegetable oils that has been used in
many places to produce biodiesel. So the first one is soybean oil; soybean or soya is referred to
as Glycine max which is found only under cultivation and is a member of the Papilionaceae
family. The origin of soybean is not very clear, for the genus Glycine has two major gene
centers; Eastern Africa and Australia.
So, many literatures will tell us that this soybean has been originated from Eastern Asia, but
there is no proper proof for that. So, based on historical and geographical evidence, north eastern
China has been considered as the region of origin of soybean domestication. So, today soybean is
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world's largest oil seed in terms of total production and in international trades. The oil content in
soybean seed ranges from 15 to 22%, depending on environmental conditions during the seeds
maturity. The major fatty acids are oleic acid, which is C18:1, we can say that 18 carbon atoms
and 1 double bond and linoleic which is having two double bonds.
The next is rapeseed oil, mustard, oil and canola oil. So, the word “rape” is originated from the
Latin world “rapum” which means turnip. Now this belongs to Brassica family including turnips,
mustard, cabbage, rutabagas, broccoli and kale. Now these seeds have oil content over 40%, in
which the dominant fatty acids include oleic acid, linoleic acid and erucic acid. Now when
rapeseed has erucic acid content higher than 5%, it is called HEAR, it is called high erucic acid
rapeseed. While a low erucic acid rapeseed which is known as LEAR is referred to as rapseed
having erucic acid concentration less than 5%. Now under Canadian Agricultural Product
Standards (CAPS) Act, canola oil is defined as oil extracted from rapeseeds of B. napus and B.
campestris species with low level in both erucic acid and glucosinolate content. The erucic acid
content in canola oil shall not exceed 5%, that is weight by weight.
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The next is palm oil. The origin of palm oil is believed to be in Africa, but most productive
regions are located in Southeast Asia especially Malaysia and Indonesia, which together account
for around 80% of the world production. There are generally two types of oil derived from the
palm, so palm oil from the mesocarp and then the palm kernel oil from the kernel inside the seed.
Palm oil is more saturated than soybean oil and rapeseed oil, as it is major fatty acids include
palmitic, stearic, oleic, and linoleic acids.
Now palm oil can be fractionated at ambient temperatures in Palm olein or oleic-rich oil and
palm stearin or stearic-rich oil. So, that is the solid fraction and the earlier one that is the oleic
rich oil is the liquid fraction. Now due to the saturated fatty acids contained in this oil, it has
superior oxidation stability as compared to other vegetable oils.
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The next is sunflower oil. So, Helianthus annuus is the botanical name of the common sunflower
species for which it is a member of the Compositae of flower plants growing throughout the
world. The name stems from Greek word helios meaning sun, and anthos meaning flower.
Sunflower originated in South-West United States and Mexico areas. Sunflower seeds are edible
and often crushed for oil extraction. The major fatty acids in sunflower oil are oleic and linoleic.
Sunflower is considered as one of the most ancient oil seed species as it is cultivation can be
traced back to 3000 B.C. Sunflower was once the world top rank oil producing plant prior to the
advent of soybean boom after World War II.
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The next is rice bran oil. So, rice bran is the main source of the rice oil. Lipid droplets can be
extracted from the rice bran using extruder, expander and expeller to form a bran flake or pallet
followed by solvent - usually hexane is being used for the extraction process in the extraction
bed. The majority of the oil components are triacylglyceride with palmitic, oleic and linoleic as
the major fatty acid present in the rice bran oil.
Diacylglyceride, monoacylglyceride and sterols may be present in minor amounts in rice bran
oil. Rice bran oil is used widely in Asian countries due to it is delicate flavour and odor. It is
recently gaining interest as healthy oil since it helps in reducing serum cholesterol. Recently rice
bran has been widely adopted in India and sub continents. And one of our premier research labs
in India which is CSIR Indian Institute of Chemical Technology has formulated an excellent rice
bran oil and that has been commercially produced now.
The next is Jatropha, now we are coming to the non-edible oils. Jatropha curcas is the member
of the Euphorbiaceae family. It originated in America but is harvested mainly in Asian countries
especially in India. Jatropha is well adapted to arid and semi arid conditions and it shreds it is
leaves in order to survive during the drought seasons. So, it can be grown on non cultivated and
degraded wasteland, and therefore is considered as one of the most promising feedstock for
biodiesel production.
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Oil derived from Jatropha is non edible due to curcin, a toxic compound that is found in the
seeds. The oil content ranges from 35 to 40% in the seed and 50 to 60% in the kernel with oleic
and linoleic as it is major fatty acid content. Having said that, you know we have already
discussed that why again in India, let us talk about Indian context. Now you do not see Jatropha
plantation anywhere in India because of the sustainable problem which we have already
discussed when we discussed about the Jatropha curcas cycle.
The next is karanja oil. So, karanja is a member of the Leguminaceae family with Pongamia
pinnata as it is botanical name. It is an oil seed bearing tree native to humid and subtropical
environments, such as those in Philippines, Indonesia, Malaysia, Myanmar, Australia, India and
the United States. It is highly tolerant to salinity and can be cultivated on degraded wasteland on
a variety of soil types, ranging from clay to sandy or stony.
The oil droplets extracted from Karanja appear yellowish orange to brown and are not edible due
to the presence of toxic flavonoids. Oil content varies from 9% to 46% with oleic and linoleic
acids major fatty acids.
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So, let us talk about biodiesel production. So under this module, in our next class that is a lecture
2 of module 7, we will be discussing in detail how do you produce biodiesel by
transesterification process, the reaction mechanism - how the reaction happens, how you conduct
it in a lab scale - All these things we will be discussing in our next class. Today in a gist we will
just go through and in detail we will discuss in our next class.
So, transesterification is the most common method used to reduce viscosity of vegetable oils and
produce biodiesel. In addition to transesterification of TAG biodiesel can be produced from free
fatty acids through esterification. Since ester is characterized by RCOOR group (R = alkyl group,
R is alkyl group), TAG is a type of ester and reaction that converts TAG into biodiesel is
therefore known as transesterification, that means transforming the ester.
In contrast, free fatty acid is not an ester and therefore the reaction to produce biodiesel from free
fatty acids is called esterification, that means making ester. Transesterification is the reaction
between glycerides with short chain alcohols and is comprised of three consecutive reactions
starting from TAG to DAG, DAG to MAG and from MAG to glycerol. We will discuss this in
detail in our next class.
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In each step, the reaction consumes one mole of alcohol and produces one mole of ester. In total,
one mole of TAG reacts with three moles of alcohol to produce three moles of ester that is
biodiesel and one mole of glycerol. So, glycerol is one of the most important byproducts having
a lot of commercial value and application from the biodiesel industries. So, in general the
reaction performance is influenced by various parameters such as type of alcohol, alcohol to oil
molar ratio, free fatty acid content, water content, reaction temperature, reaction duration and the
type of catalysts that you are using.
Now let us talk about the diesel that is coming out from microalgae. We have discussed about
microalgae in one of our previous classes that why microalgae suddenly become a big bloom and
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of research interest for many of the scientists and academicians across the globe. So, today we
will discuss how diesel can be produced from microalgae. So many microalgae, in particular the
green algae and diatoms can accumulate significant quantities of neutral lipids primarily as
triacylglycerols - TAGs.
Now these lipids can then be extracted from the biomass and converted into biodiesel or green
diesel as substitutes for petroleum derived transportation fuels. So, having said that, I am telling
you that, once you produce biodiesel, it needs some further processing, which we are going to
discuss in our subsequent lectures under this module, maybe in the lecture 3 under module 7. So,
you need to purify it, it is not that you produce and directly it can be used in the engines, it is not
so. We will discuss how this will eventually happen.
So the lipid content is the significant prerequisite determining the aptness of the microalgae for
commercial biofuel production. In general, microalgae cell contains 30 to 80% lipid. Lipids are
in general soluble in non-polar solvents but insoluble in polar solvents due to the presence of
hydrophobic chain. Therefore, they are easily extractable using organic solvent extraction
method. They are further categorized into neutral and polar type.
So, this particular table will make you understand or give you some information about some of
the typical microalgal species with relatively high lipid content and productivities which can be
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used or has been used for the biodiesel production. Please understand that we have more than
200,000 species of microalgae and out of that almost 50,000 might have been tested.
Please note that all species do not contain a huge amount of lipid which can be grown and
harvested for the biodiesel production, it cannot be. So, these are some of the already well tested
microalgal species which are having very high lipid content. So like C. protothecoides, then
Chlorococcum, Chlorella sorokiniana, D. salina all these things, there are so many different
types of species, even the Scenedesmus species also.
You can see that the first one, it comes under the Chlorophyceae genus; it has a lipid content
about 15 to 58% again depending upon the species (w/w). And the lipid productivity, if you talk
about the productivity in milligrams per litre per day, so it is the highest almost among those are
listed 1214. And one of the most important species is the Scenedesmus species; it can be grown
easily, it is very widely adapted, climatically adapted species along with even Chlorella vulgaris
and all other. So, it has also a good lipid content and a very nice lipid productivity.
So, during the last decade considerable attention is drawn towards algae for the economic
possibilities in their mass growth. It is not about only biodiesel, but there are various other
applications of the microalgae which I have already told you - what are the different types of
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components or the value added products that can be extracted from microalgae or further process
to make directly commercial products.
So, the biofuel synthesis from algae proceeds through the following 5 steps. First is that you need
to culture the algae; second is harvesting the algae or dewatering algae. So, this is right now also
this is one of the most important steps, because it consumes energy and it takes time also. So,
when you have huge amount of algae that needs to be dewatered and harvested; so, you have to
have a proper technology, which should be faster as well as it should be low in cost.
The third is the extraction of algae from oil (oil from algae). So, you can either go for this
chemical based extraction or physical extraction, it depends on what type of species it is, what is
the oil content. So, there are so many other parameters to be thought of, but again extraction is
also a cost intensive process. Then purification of the algal oil, so the downstream purification
you need to remove whatever water content, glycerol and any other components which are not
the fuel components needs to be removed. And the last one is the processing of oil into biofuels.
So, please have a look at this particular flowchart. This is the flowchart for biofuel production
from the microalgae. So, it starts from the strain selection - the first and foremost important thing
that which strain you are going to use for the biofuel production. So, now let us say I am in
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Guwahati, in Guwahati in my group alone we have strain, we have almost more than 100
different strains which we have screened for different purposes.
It is not only for the biodiesel production; we have used it for different purposes. And we have
seen that certain strains are naturally having very high lipid content. So, we can use those strains
for the biodiesel production. So the strain selection is very important. So, after that you have to
go for cultivation strategy, what type of cultivation strategy was going to add up? Suspended
cultures, immobilized cultures, hybrid systems, how we are growing them?
In raceway ponds, photobioreactors, open, closed so many things are coming into picture. Then
the sitting options, so wastewater treatment, aquaculture, carbon dioxide sources; it is again some
sort of hybrid digestion you can tell that. If you talk about wastewater treatment - in one of the
class I have already told you that if we can grow algae in wastewaters, then it is a win-win
situation.
Because it will purify the wastewater or let us say it will treat the wastewater, as well as the
microalgal growth will be there, so of course, you can harvest it. So, two things are happening in
a single thing, and you will be depending less on the amount of freshwater. So, thereby you can
recycle the harvested water after maybe some minor treatment back to the raceway pond or
bioreactors.
Then resources like of course, this is capital cost that is coming into picture. Then cultivation,
different factors will be there growing medium, light, carbon dioxide, nutrients. Then harvesting,
then it goes for the conversion process, what type of conversion process you are looking for?
Fractionation extraction technology, lipid extraction, extraction of carbohydrate, other things,
proteins; then conversion, photobiological, fermentation, anaerobic digestion, gasification,
pyrolysis, liquefaction and the last transesterification for the biodiesel production.
Then, once you do that, so you get majorly 2 different types of products - the biofuels, like solid
also dry biomass - that de-oiled cake you can say, charcoal. Under liquid we may get ethanol
from the carbohydrate platform, then butanol also from the carbohydrate platform, diesel coming
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from the lipid. Then jet fuel and gaseous if you talk about hydrogen, methane, syngas maybe
from anaerobic digestion and FTA and other processes. Then other various bio products like
cosmetic, fertilizers, bio plastics, antibiotics, vitamins and so many other things.
So, culturing up algae or algaculture. So, algal culture refers to the growth of algae similar to that
of aquaculture. The growth expectation of algae is very simple and affordable, that is, sufficient
light, naturally available dissolved nutrients and carbon dioxide is what the algae needs to grow.
Unialgal growth without contamination of other eukaryotic or prokaryotic organisms and axenic
culture (that means bacteria free) is challenging, especially when you are growing it openly.
So, the growth rate of algae is spectacularly high, it is almost doubling in 24 hours, unlike plants
as their energy is not spent on the growth of their parts. There are two kinds of algae culture
classified based on the growth characteristics are either batch culture or continuous flow culture,
BC and CFC.
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Now let us see the BC. The inoculation of algal cell in a container when the abundant resource is
available, follows the sigmoidal curve in the batch culture. The loss of medium slays the culture
and this could be subdued by introducing small volumes of fresh medium into the existing
culture. Then comes the continuous flow culture, CFC. The regulated addition of adequate
volume of fresh medium rich in nutrients to the culture medium to attain steady state is
performed in the CFC method.
A steady state is the uniform cell density where the birth rate is equal to the death rate. This is
the definition of steady state with respect to the CFC. Now this is done proportional to the
growth of algae in special culture technique known as Turbidostat culture or Chemostat culture.
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Now Turbidostat culture is the fresh addition of medium to the culture when the growth reaches
a certain limit, whereas, chemostat culture is the introduction of fresh medium to the culture at a
predetermined rate. So, let us now understand the major physical parameters that affects the
growth of the algae. The first and foremost important thing is pH, I have told you many times
whenever you deal anything with the aqueous medium pH always plays a big role.
The total collapse of algal cell wall occurs with the un-optimized pH level; so you have to be
very careful of the pH. And the proper cell growth happens in the pH range of 8.2 to 8.7 and
supplement of carbon dioxide into the medium enables the attainment of the optimized pH. Then
illumination, another important factor. Illumination needs to be concentrated in adequate
photoperiod and intensity.
These depend on the density of the culture and depth of the vessel in use. The important
strategies with respect to illumination are:
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Fluorescent lamps, photoperiod and light intensity. So, in fluorescent lamps the radiation in 380
to 500 nanometer usually the blue light and 600 to 700 nanometer usually the red light is
preferred for the algal growth. Photoperiod, the illumination period is expected to be around 16
to 18 hour for the appropriate culture maintenance. Again these so many things which we are
discussing all the parameters that also depends on a particular species.
Light intensity; algae growth differs with the intensity of light ranging from 5% to 10%. Mostly
the light and dark cycles are followed as the cells do not grow in continuous illumination. The
next is temperature, temperature of the culture medium varies with respect to the temperature
zone of the regions. Algaculture in countries like India and United States (basically temperate
zones) operates at 10 degree centigrade to 25 degrees centigrade.
And in tropical countries, especially Brazil and Singapore the temperature of action is below 20
degrees centigrade. The temperature beyond 35 degree centigrade leads to destructive algal
growth.
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Then the medium of culture; the medium is responsible for the contamination of culture and it
creates a hindrance in the sterilization also. The quality of water used in media has significance
and sea water with unpredictable contaminant is a serious issue in culturing medium. So,
seawater may contain vitamins, chelating agents, buffers, soil extract etc. and sometimes it needs
to be purified.
So, three major types of culturing are practiced worldwide and are discussed in this section, we
will try to understand in a nutshell. So, open pond system: algae usually grow in lakes and
copying this similar pattern is known as the open pond system for algal culturing. The ponds are
of one-foot depth and alga cultivation could be from one acre to several acres. The types of open
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pond system are raceway ponds (which are the most common), natural ponds (so they are the
shallow lagoons and shallow ponds), mixed ponds, circular open ponds mixed with center pivot
mixer. In raceway ponds, a closed loop with recirculation channel is designed with paddles for
better mixing, laminar flow and circulation of carbon dioxide. But it also has a high peril of
contamination with low rates of production due to it is sensitivity to the environmental
fluctuation.
The next are photobioreactors or closed loop culturing. Intensive research on algae production
compelled the idea of the closed loop reactor systems. Photobioreactor is a worth substitute for
OPS for it is massive productivity rate and high quality of algae. So, everything is good in
photobioreactors, that is because it is a closed system, it is very easy to control all the parameters
and there is no problem of this contamination also.
Now researchers have created many versions like tubular, bubble, christmas, plate, horizontal,
foil and porous photobioreactors. The tubular bioreactor is the common photobioreactor type
used in the algal culture and it comprises of tubular solar arrays, biomass unit, exchange column
to exchange gas and pump. The tubular solar arrays basically mean the tubular photobioreactors
which are placed under the sunlight in open atmosphere.
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The vertical column tubular photobioreactor offers good gas exchange while the horizontal
column tubular photobioreactor gets better access of light and also possess higher surface area.
However, the negatives of the vertical tubular photobioreactor is the low surface to volume ratio,
and horizontal column tubular photobioreactor is the low mass transfer leading to difficulty in
carbon dioxide elimination and excessive heat generation.
So, this is the closed photobioreactor - actually a schematic. So, the algae, carbon dioxide, then
water or wastewater whatever, the nutrients are all mixed in the feeding vessel, then it goes to the
photobioreactor where it is cultured; proper amount of carbon dioxide and light is being given.
And a proper light and dark cycle has been maintained, then you see that it goes for the
harvesting, the separator where the algal slurry has been separated.
And the secondary water can be used - treated and fed back to the photobioreactor or the
raceway pond whatever it is. Then the slurry is being centrifuged, so you will get the biomass,
the solid biomass which can be further processed, you can extract the lipid, make it biodiesel and
other parts also whatever left out in the solid residue can be used for various other platform
chemicals or other value added products.
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Disappointingly, in general photobioreactors suffer from their high capital cost (this is one of the
most important thing actually which hinders its application in large commercial sector) which
exceeds the output due to it is complexity and exclusive erection materials. Further, it suffers
from improper carbon dioxide and oxygen balance, control in temperature and biofilm formation
- fouling.
So, the next is hybrid systems. Synergizing the effectiveness of the open pond system and
photobioreactor can be achieved by the hybridization of both the systems. The two stage hybrid
cultivation system is the advanced version of the alga culture, where the cell medium is
transferred from the open pond system to the raceway pond system when the nutrients are found
to decline.
The feasible separation of biomass from the lipid accumulation and least possibility of
contamination strike the positive note. The hybrid system can be of small PBRs with big ponds
or ponds with large PBRs, anyone of these combinations.
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The hybrid system comprises of two stages. Stage I: PBRs are chosen as phase I to reduce the
lipid accumulation and contamination in the culture. The density of biomass can be increased in
the closed PBR system; once it is done you transfer it to the raceway ponds. In second, stage II:
the selection of OPS in the stage II increase the economic compatibility of the process. The two
most significant at the phase II after the completion of I phase helps to promote rich
carbohydrates and lipids in the algae.
So, then we will talk about increase of lipid content by alternative nitrogen supply. The trial of
reducing the nitrogen environment retards the growth of the culture. The latest research shows
the supply of nitrogen at the beginning of the culture growth and then deprive it after the
723

considerable dense biomass raises the lipid production, this is called nitrogen starvation, or
nitrogen shock. So, the nitrogen starvation disrupts the cell and directs the carbon towards
carbohydrate and lipid production. Nannochloropsis gaditana and Chlorella protothecoides are
the few algal species that produced good results in the switch over of nitrogen sources. So, this is
one of the widely studied problem or we can say the aspect of the microalgal culture and growth.
So, then brine condition; now this methodology is reverse to the nitrogen supply mechanism.
Better products are produced only with two stage cultivation process compared to single stage
cultivation.
Enhancement of algal growth is observed with saline condition and the gradual increase of
salinity lowers the metabolism. The lower salinity level improves the lipid and carbohydrate
generation in algae. Chlorophyceae species indicates the effect of salinity in their growth in stage
II cultivation.
724

Then harvesting or dewatering of algae. The cultured algae needs to be dewatered in order to
access the lipid profile. The dewatered algae looks like an interim of solid-liquid medium instead
of a liquid which flows easily. The experiments prove that only 0.1% of dry matter is available in
1 litre of the culture media. Filtration and centrifugation are the processes involved in removing
water from algae.
Many advanced mechanics are explored under these categories. Flocculation and membrane
filtration is effective in drying the algae. Methods involved in filtration are pressure, vacuum,
deepbed sand, cross flow and magnetic filtration. Huge amount of work is still going on, on this
particular harvesting technology.
725

So, then algal oil through lipid extraction from dry algal mass. The biological micro species has
multilayered cell wall made up of polysaccharides and cellulose synthesized from silicic acid.
The cell wall envelopes the lipid or fatty acids and the removal of algal oil is known as that lipid
extraction. The specific extraction of lipids is also performed by solvent extraction using
methanol and chloroform.
Interest is on microwave, grinding, bead beating and ultrasound mechanical methods for
extraction. This method does not require extra chemicals and the subsequent extraction step
becomes easier. Mostly, bead baiting is done to disturb the cell walls of microbes in small scale
level with beads made up of ceramics or glass.
726

In recent years, research is directed towards extraction free from solvents. The supercritical fluid
technique accomplishes the demand by producing safe and good quality end products. The
efficacy of this method in extracting specific components from a complex biological species is
worth enough. The oil extracted using n-heptane by Soxhlet extraction method is much lower
than that of the supercritical fluid extraction.
But please understand that supercritical fluid extraction is a costly process because of the huge
capital investment, it requires. So, lipid extracted from various microalgae and the method of
application is given in this particular table. You can see the different types of microalgal species
here, Chlorella vulgaris, Cyanobacteria, Scenesdemus, again Chlorella and Chlorophyta.
Different types of extraction technologies: Ultrasonification, microwave, using a virus, then
Soxhlet extraction. So you can see the type of algal oil it is given there, 16%, somewhere it is
49%, then almost 10 to 11%, and the last one it is 18%.
727

So, now we will discuss biofuel synthesis from algae by transesterification process. So, algae
competes the fellow contestants in the biodiesel synthesis market which gives an insight for the
future oil demand. Algal oil displays a remarkable tendency to get converted into diesel range
esters. Transesterification is the reaction between one mole of triglyceride molecule which is a
complex ester and 3 to 4 moles of alcohol to produce simple esters, that is called biodiesel.
The transesterification technique is often catalyzed by several acid catalysts, namely sulphonic
acid and sulfuric acid and base catalysts such as sodium hydroxide, potassium hydroxide, sodium
methoxide, sodium ethoxide and K2CO3. Now with several classes of catalyst in action, porous
catalyst Hβ and mixed oxide of nickel and molybdenum turns to be veracious materials. The
biodiesel yield in the presence of these catalysts almost reaches 100%.
So, that is excellent yield using this particular catalyst. Lot of research is still going on in
developing low cost and high yielding catalyst, which will basically lower the final product cost
of the biodiesel.
728

Potential of nano carbon particles is also being used to convert lipids onto biodiesel. The
conventional transesterification uses inorganic catalyst and has the demerit of polluting the
environment due to it is disposal hitches. Therefore, green substitutes like enzymes can act as a
better auxiliary. Biological catalysts, which are treated for the biodiesel formation and out of
them lipases have created a niche in the industry.
Immobilized lipases on metal oxide nanoparticles have fine thermal stability, corresponds to
good selectivity and also can be easily separated. Biodiesel yield was as high as 90% with
enzyme concentration of only 1 to 3.5%.
729

Now we will discuss about diesel from syngas. So, in today's class, as I told you in the beginning
we are discussing diesel from three various sources. First is vegetable oil, that we have discussed
and understood. Second is from the algae, we have understood in detail how algae can be grown,
how it can be cultured, what are the parameters that affect? And the third and last one is the
diesel from a syngas.
So, diesel powered heavy duty trucks and more efficient diesel cars have been widely used in
industrialized nations, especially in the European countries with the number of diesel engines
being increased to 1.1 billion by the year 2020. Increasingly stringent environmental regulations,
however dictate the need for a super clean diesel that is a carbon neutral fuel with low emissions
and a high internal combustion efficiency.
As an alternative fuel to the conventional crude oil based diesel, the FT diesel which is called the
Fischer-Tropsch diesel, has a high cetane number and almost zero sulfur content, has been
proven to be effective dramatically reducing the emission of sulfur dioxide, nitrous oxides,
nitrogen oxides and particulate matter - all the Sox and NOx all these things - as compared to the
conventional fossil fuel diesels.
Now consequently automobile manufacturers worldwide are increasingly viewing Fischer
Tropsch diesel as a feasible alternative diesel engine fuel given its two primary differentiating
attributes. The first: high fuel efficiency and the second: a low impact on the existing distribution
infrastructure. That means you do not have to modify the engines for the biodiesel or the FTD.
730

So, FT diesel can be obtained from syngas via the Fischer Tropsch synthesis process which
industrially usually consist of 3 steps. The first is the gasification or reforming into syngas of the
carbon containing materials such coal, natural gas or sustainable biomass. Second is the catalytic
Fischer Tropsch synthesis. The third: a product work-up, usually involves a mild hydrocracking
step.
So, this is a classical syngas biorefinery schematic presentation, let us understand. So, it can be
natural gas, coal, biomass, mostly since we are talking about biodiesel, so it is biomass.
However, coal and natural gas also can be co-feeded. Then we produce hydrogen and carbon
731

monoxide - the syngas. So, when you talk about the Fischer Tropsch synthesis if you go for the
FT synthesis then further refining will give us gases, LPG, naptha, kerosene, diesel all the cuts.
Then finally lubes and waxes. And, as it is also we can use hydrogen and methane. Then if you
go for the methanol synthesis route - we get DME or the dimethyl ether; so it can further be
converted to propylene, ethylene, gasoline, acrylic acid and further some oxygenating
compounds.
So, the FT synthesis converts syngas into hydrocarbons mainly alkane and alkene through
catalytic hydrogenation; the process can in principle be expressed by the following chemical
reactions in their simplified forms:
The hydrocarbon formation reaction:
The water-gas shift (WGS):
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Now, in these equations the CH2 group represent the chain type hydrocarbons ranging from
methane to heavier waxes. These reactions are in principle, very important due to their
applications in converting syngas derived from coal, natural gas or biomass based carbon
containing materials into several of the useful hydrocarbons that has served as the backbone of
modern motor fuels and the feedstock of chemical plants.
The hydrocarbons produced from the FT synthesis are mainly straight chain alkanes and alkenes,
although small amounts of isomers and oxygenates are also produced in addition to the primary
byproducts, water and secondary carbon dioxide.
733

So, this is an interesting process flow schematic for the biodiesel production from the syngas. So,
the raw gas from the gasification unit that is coming - it goes to the water gas shift reaction. Then
it goes to the acidic gas removal where carbon dioxide has been removed and you can have the
sulfur recovery coupled with that carbon dioxide removal process. And part of the carbon
dioxide also can be recycled back to other processes like this tail gas treatment.
Then this purified syngas which is having a sulfur content of almost less than 50 PPB goes to the
Fischer Tropsch synthesis loop. So, where the FTS is being after the process is over, we will get
the FTS crude. So, which will further be processed or maybe we can say that upgraded to give us
diesel almost 70% and naphtha 20%. Then the dry gas part of that FT gas can be sent back to the
tail gas treatment unit and again the lighter hydrocarbons can be recycled back.
And whatever is coming out from the tail gas treatment unit is nothing but the LPG - 6% around.
And from the water treatment plant also which is coming from the FTS loop the water based
actually. So, it will get oxygenating compounds almost 4%. So, this is the usual process
schematic for the biodiesel production from the syngas.
So, we will try to understand the process in a better way. Let us go through it. So, a simplified
flowchart of the Fischer Tropsch process that is what we have already seen it. From this diagram,
it is clear that the FT synthesis process for processing syngas is rather very straightforward
734

irrespective of the syngas source. Within the process boundary limits assumed here, part of the
inlet raw syngas stream from the gasification unit is first shifted in a water gas shift reactor to
adjust the hydrogen carbon monoxide ratio to approximately 1.6 to 2.
It is very important to do that otherwise your reaction will not proceed in the proper direction.
The raw syngas is subsequently subjected to a purification process to remove contaminants in
order to maintain sulfur concentration below 50 ppb - parts per billion. So, the acid gas stream
with high concentrations of hydrogen sulfide and other sulfur compounds exiting from the gas
purification unit is sent to a sulfur recovery unit to collect the elemental sulfur.
So, this is the sulfur recovery unit, just I was mentioning about that, it is also very important part.
Because you anyway you are recovering the sulfur out of that even if it is a small amount of
sulfur that is present in the entire process streams, you can understand that the amount of
feedstock the plant is processing per day. So, it is a quite significant amount of sulfur that is
needs to be recovered. So, in order to meet the quality specification, purified syngas must have a
hydrogen + carbon dioxide volumetric content above 98%.
735

So, once this level of purity has been reached, the syngas thus generated is fed to the FT
synthesis reactor to produce the hydrocarbons, so gaseous, liquid, wax and of course water. Since
a significant amount of reaction water is generated which usually dissolves the FT synthesis
oxygenates, a dedicated water treatment unit in the FT synthesis process is therefore required.
So, this is the water treatment unit which we are right now talking about which is directly
coming from the FTS loop the Fischer Tropsch synthesis loop.
The light condensate recovered is then combined with the major wax and condensate stream
from the FT synthesis reactor and subsequently sent to the product processing unit for upgrading
into end products such as diesel, naphtha and liquid petroleum gas.
736

So, students, with this I windup today’s lecture. So, in the next lecture we will discuss about
transesterification, the FT process and catalysts. So, basically we will understand the
transesterification reactions including the esterification reaction in detail. And we will also
understand what is the importance of catalyst and what are the various types catalyst that are
being used for transesterification and FT processes including the homogeneous and
heterogeneous catalyst all.
So, thank you, and in case you have any query please register your query in the swayam portal or
you can drop me a mail directly at kmohanty@iitg.ac.in.
737

Module-07
Lecture-20
Transesterification FT Process, Catalysts
Good morning students, this is lecture 2 under module 7. As you know that we are discussing
biodiesel under this particular module. Today we will discuss about transesterification reaction in
detail, the various reaction mechanisms basically. As well as the Fischer-Tropsch process and we
also discuss about the catalyst and the reactors which are required to carry out such reactions. So,
let us begin.
So, transesterification gained much acceptance in recent years for the conversion of the vegetable
oils into products with technically more compatible fuel properties. Transesterification is an
imperative process for biodiesel production, as it can reduce the viscosity of the feedstock
vegetable oils to a level closer to the conventional fossil based diesel oil. It represents an
important group of organic reactions during which interchange of the alkoxy moiety results in
the transformation of one ester to another as per this particular scheme.
738

You can see this, this is the simplest reaction glyceride + alcohol with a presence of a catalyst, it
can be any acid type catalyst, basic type catalyst or homogeneous, heterogeneous anything. So, it
will result us ester + glycerol, this is the general reaction scheme. So, we will learn about the
detailed mechanism later.
So, transesterification is an equilibrium reaction describing the alcoholysis of carboxylic esters
usually performed in the presence of a conventional catalyst (sodium hydroxide, potassium
hydroxide) for valuable acceleration of the equilibrium adjustment to achieve a higher yield of
esters. Chemically vegetable oils are triglyceride molecules with structural differences in their
glycerol bound alkyl moiety.
739

Now transesterification of these triglyceride molecules with short chain alcohols in the presence
of suitable catalyst results in fatty acid methyl esters and glycerol. Now these fatty acids (FAME)
are your biodiesel. Now a sequence of 3 consecutive reverse reactions illustrates the overall
transesterification process.
So, this is how it happens actually, this is the overall reaction mechanism of a biodiesel
formation. Now we have a triglyceride that reacts with methanol to give us diglyceride and one
methyl ester. Now what you see that, we are getting series of methyl ester R 1, R 2, R 3 different
R groups and a series of methyl esters. So, these reactions are happening simultaneously.
740

Now that diglyceride is again reacting with another methanol molecule to give us a
monoglyceride and another methyl ester. This monoglyceride is further reacting with methanol
to give as another methyl ester and glycerol. So, glycerol is the final byproduct of
transesterification reaction.
741

So, let us understand the chemical transesterification reactions. Chemically biodiesel can be
synthesized either by acid catalyzed or base catalyzed transesterification of the feedstock. Now
we will discuss both. So, acid catalyzed transesterification reactions: acid catalyzed
transesterification reactions are mostly carried out by Bronsted acids, preferentially sulfuric,
hydrochloric and sulfonic acids.
So, this name bronsted acid, bronsted base many times you will come across in such type of
reactions. So, bronsted acid is something which actually is ready to give a proton, and bronsted
base is one which is ready to accept a proton. So, this is the general understanding of bronsted
acid and base. So, the mechanism of acid esterification is described in scheme 3, so in the next
slide it is there.
742

So, let us see what is this reaction, I will try to make you understand. So, here you can see there
is one catalyst is there, so H+ is a protonated catalyst. So, here carbocation reaction II results
from the carbonyl group protonation of the ester as a first step followed by a nucleophilic attack
of an alcohol producing a tetrahedral intermediate. So, let me make you understand this reaction
mechanism.
So, here this is first getting protonated, now this protonated is going to make as a carbocation
molecule. Now what is a carbocation molecule? So, this is a carbocation molecule. So a
743

carbocation molecule is something in which the carbon atom is positively charged. So, it is a
carbon cation basically. The carbon atom here is positively charged, and it has 3 bonds, you can
see 1, 2, 3. Now this carbocation group is reacting with the alcohol to give as an intermediate
complex.
Now this intermediate complex, when we remove glycerol molecule from this intermediate
complex, then we will get the methyl ester. And the catalyst will be again further deprotonated.
So the deprotonated catalyst will have more active surface areas to further carryout the reaction.
So, this is an overall simplified understanding of how the esterification of the monoglyceride can
be extended to diglyceride and triglycerides, so this is a series of reactions.
Now, the presence of water may decrease the alkyl ester yield due to the formation of the
carboxylic acids by reaction with carbocation II; therefore, competitive carboxylic acid
formation can be avoided using water free feedstock. Although high yields of alkyl esters can be
achieved using acid esterification, certain disadvantages, that is slow reaction speed, high
temperature requirement and difficult glycerol recovery render it unfit for use.
Mostly acid esterification is recommended as a pre step for biodiesel production via base
catalyzed transesterification where an acid value lesser than 2 to 4 milligrams potassium
hydroxide per gram is required which can be easily achieved by acid transesterification of the
744

feedstock. Now chemical transesterification reactions catalyzed by acids are highly beneficial for
the feedstock with higher free fatty acid content. So, those, feedstock which have a very high
free FFA content they can go for the acid catalyzed reaction.
So, acid catalyzed reaction results in better yield, although the reaction is time consuming, slow
and requires higher temperature conditions. Acid esterification is well accepted as a pre step for
the base catalyzed transesterification reactions to esterify free fatty acids if higher than 2%, if
they are present higher than 2%. The acid catalyzed transesterification therefore helps in
reducing the levels of the free fatty acids to a level compatible with alkaline transesterification.
For acid esterification of feedstock with higher free fatty acids, sulfuric acid is a more effective
catalyst compared with others including hydrochloric acid, formic acid, nitric acid and acetic
acid. Inadequacy of base catalyzed transesterification reactions for the vegetable oils with high
free fatty acid content is also reported by various researchers.
745

Now we will discuss about the base catalyzed transesterification reaction. So, alkaline catalyzed
transesterification reactions are much faster than acid catalyzed esterification reactions and have
gained much attention. Substantially anhydrous feedstock with the least free fatty acid content
gives the best results regarding ester yield using base catalyzed transesterification. Now because
of the less corrosive nature of the alkaline catalyst compared with acid catalyst, at industrial scale
alkaline catalyzed transesterification is usually preferred, because it is anyway a faster reaction.
Now the most commonly employed alkaline catalyst are sodium and potassium hydroxides and
alkoxides. These catalysts are well accepted for industrial scale biodiesel production, because
these are low cost and easy to transport and store. Comparatively, sodium and potassium
methoxides are preferably being used to catalyze continuous flow processes for the production of
the biodiesel.
746

The only disadvantage associated with the base catalyzed transesterification is the additional
purification requirements of biodiesel and glycerol for the removal of the base catalyst. To avoid
this drawback, researchers have investigated heterogeneous catalyst for their potential to catalyze
transesterification. Simple filtration can separate heterogeneous catalyst from the end products
and thus can be reused.
Now some important heterogeneous catalyst investigated by scientific community to catalyze
transesterification reactions include Hb-zeolite, zinc oxide, titanium dioxide, zirconium dioxide,
zeolites, alkaline earth oxides, then ion exchange resins, dolomites, sodium aluminate, then
calcium oxide and magnesium oxide. So, there are many more; I have just listed a few. More or
less these are tested, gave high selectivity and also readily available and many of them are also
low cost.
747

So, now let us understand the mechanism for the base catalyzed transesterification reactions.
Now, base catalyzed transesterification of vegetable oil starts with the reaction of alcohol with
alkaline catalyst resulting in the generation of alkoxide along with the protonated catalyst. A
tetrahedral intermediate is then formed as a result of nucleophilic attack of alkoxide on carbonyl
moiety of the triglyceride. Let us see how; actually in the next slide it is there.
So, there are 4 steps being shown here. The first one, the alcohol is reacting with the catalyst, B
is the catalyst. So, the B is getting protonated, so BH and we will get a carbonyl moiety of the
triglyceride. So, here you can get a carbonyl moiety, so when it is again reacted, so we get
another intermediate product. Now that intermediate product is again decomposed into 1 anion,
748

this is 1 anionic group and plus here ester. Now this anionic group is further reacted with the
protonated catalyst to give as a methyl ester and deprotonated catalyst. Now this deprotonated
catalyst is having free or active more surface area which can carry out further reactions, so
simple reaction mechanism.
749

So, we will try to understand the experimental steps for biodiesel synthesis. Two step synthesis
of biodiesel from feed with high free fatty acid. Different steps of the process include: First is
that mixing of appropriate amount of oil, methanol and catalyst in a reaction vessel. Catalyst can
be homogeneous or heterogeneous acidic catalyst. Heterogeneous catalysts are preferred over
homogeneous as the later one is associated with disadvantage such as reactor corrosion and
difficulty in separation.
Now second, raising the temperature of the reaction mixture to the desired reaction temperature
and stirring the mixture for the desired reaction time at that temperature. Once the reaction is
finished and the desired free fatty acid level is reached, the mixture can be centrifuged to
separate the catalyst from it. That is why you can use the heterogeneous catalyst, so you can
remove is using centrifugation and filtration.
750

The separated esterified product can then be directly used for the transesterification process or
after removing the excess solvent from the product at reduced pressure in a rotary evaporator.
For the transesterification process the esterified product is mixed with appropriate amount of an
alcohol and a suitable base catalyst. The temperature of the mixture is then raised to the desired
reaction temperature at which it is mixed for the desired reaction time.
After completion of the reaction the excess solvent either methanol or ethanol is then separated
at reduced pressure by using a rotary evaporator. The solid catalyst is separated from liquid
product by centrifugation. The liquid mixture is then kept in a separating funnel where the
byproduct glycerol is separated as the bottom product. So, I hope you understand and I have
listed entirely the experimental procedure how to produce biodiesel.
751

So, this is the direct transesterification of the feed with low free fatty acid content. So, we can
see that, so vegetable oil or animal fat less than 2.5% free fatty acid, so you can add catalyst and
alcohol, so you can go for the transesterification. Here the vegetable oil and animal fat which are
having greater than 2.5 weight percent of free fatty acid will be esterified first.
So, try to understand the two different processes. Here if the free fatty acid content is less than
2.5 weight percent then you can directly add a catalyst and alcohol and you go for the
transesterification. Now if the free fatty acid content is higher than if you remember we have just
discussed that when the free fatty acid content is higher we usually go by the acid catalyzed
reaction. So, that is a pre step before the base catalyzed reaction so then you are just going to do
that.
So, esterification by the acid catalyst, then you get oil with free fatty acid content which is less
than 2.5 weight percent then you go for the usual transesterification route. Then you go for the
solvent recovery, catalyst separation, crude biodiesel and remove the glycerol. So, glycerol can
be further purified by base neutralization and you get the biodiesel. So, this is the schematic or
flow chart you can say of the biodiesel production.
752

Then we will try to also understand the biochemical or enzymatic transesterification reactions.
So much of work has already been done and reported (you can see the literature) on enzymatic
transesterification reactions. Now compared with the use of acids or alkalis to catalyze
transesterification reactions for biodiesel production, enzymes with significant advantages are
attracting the researchers.
The advantages associated with enzymes are: they have huge specificity, reuse ability, mild
reaction conditions requirement, and efficiency improvement by genetic engineering, whole cell
immobilization, capacity to accept multiple substrates, they are natural and their thermal stability
to catalyze green reactions. Now enzyme based catalyst reaction system is time consuming as
compared to the conventional catalyst reaction process.
We have learnt that basic catalyzed reactions are extremely fast, so they are industrially being
adapted. So, lipases extracted from different microbial strains have been utilized as biocatalyst
for the production of biodiesel by researchers.
753

High stability and repeated use of immobilized lipases were revealed to be the superior
characteristics compared to the free lipase for biodiesel production. Anyway in one class we
have discussed about the importance of immobilization. So, immobilized lipases can be reused
for many times rather than free lipases, and they have other advantages also. So, different
immobilization methods have been reported by different researchers but of these the most
appropriate method was found to be lipase entrapment on sol-gel matrices with hydrophobic
nature and lipase adsorption on hydrophobic carriers such as polypropylene.
Whereas lyophilized powders and immobilized preparations are the recognized commercially
available lipases. In the recent years, researchers have investigated different reaction systems for
conducting the best lipase catalyzed transesterification reactions. Solvent free system, organic
solvent medium with hydrophobic nature, hydrophilic reaction medium and ionic liquid medium
are among the well considered reaction systems for biodiesel productions.
754

So much of work has already been reported and some of them are fantastic works. So, this is I
am trying to show you the process flow schematic for the biodiesel production from the
vegetable oils. So, what you are going to do is that, you are adding methanol and catalyst to the
vegetable oil feed to the reactor. So, here the reaction is happening then you go for the separator,
so here you remove basically the glycerol.
So, almost close to 50% yield. So then you go for acidulation and separation, you are just adding
acid. So, you get the free fatty acid whatever unconverted free fatty acids here, then again you go
for your methanol removal here, so you get the methanol removal method, so you get the crude
glycerol which is almost 85% yield. So, the methanol can also be recovered and goes to the
methanol water rectification unit, so you can basically recover the methanol.
So, from here the methyl ester, your biodiesel part, goes to the methanol removal part, here
methanol is removed and again fed back to the rectification unit. Then it goes to the
neutralization and washing step which are just the finishing steps. So, you go for drying then you
get the finished biodiesel. So, you may need acid, water and all these things to do that in this
process.
755

So, please understand that this is the simplified schematic representation of the biodiesel
production from vegetable oils. There are many small unit operations and many small operations
are there which are not being shown here in industrial scale what is being required actually.
So, let us understand the process; alcohol catalyst and oil are combined in the reactor and
agitated for approximately an hour at 60 degree centigrade. Smaller plants often use batch
reactors but most, larger plants greater than 4 more million liters per year production, use
continuous flow processes involving continuous stirred tank reactors CSTR or plug flow
reactors.
Now let us understand the glycerol separation; following the reaction glycerol is removed from
the methyl esters. Due to the low solubility of glycerol in the esters this separation generally
occurs quickly and maybe accomplished with either a settling tank or a centrifuge. So, when you
talk about a huge amount of feedstock you are dealing with that, you cannot go for a centrifuge,
so you have to go for settling tank.
Now the excess methanol tends to act as a solubilizer and can slow the separation. However, this
excess methanol is usually not removed from the reaction stream until after the glycerol and
methyl esters are separated because the transesterification reaction is reversible and the methyl
756

esters may recombine with glycerin to form the monoglycerides. So, that is one of the biggest
disadvantage and you have to take care of that.
So, the glycerol stream leaving the separator is only about 50% glycerol, it contains some of the
excess methanol and most of the catalyst and soap. The first step in refining the glycerol is
usually to add acid to split the soaps into free fatty acid and salts. The free fatty acids are not
soluble in the glycerol and will rise to the top and where they can be removed and recycled. The
salts remain with the glycerol although depending upon the chemical compounds present some
may precipitate out.
After acidulation and separation of the free fatty acids the methanol in the glycerol is removed by
a vacuum flash process or another type of evaporator. The glycerol refining process takes the
purity up to 99.5% to 99.7% using vacuum distillation or ion exchange processes.
757

Then methanol separation; after separation from the glycerol the methyl esters pass through a
methanol stripper usually a vacuum flash process or a falling film evaporator before entering the
neutralization step and water washing. Acid is added to the biodiesel to neutralize any residual
catalyst and to split any soap that may have formed during the reaction. Soaps will react with the
acid to form water soluble salts and free fatty acids. The salts will be removed during the water
washing step and the free fatty acids will stay in the biodiesel.
Then washing the biodiesel; a water washing step is intended to remove any remaining catalyst,
soap, salts, methanol or free glycerol from the biodiesel. Neutralization before washing reduces
the water required and minimizes the potential for emulsions to form when the wash water is
758

added to the biodiesel. Following the wash process, any remaining water is removed from the
biodiesel by a vacuum flash process.
Now let us understand the FT synthesis, the Fischer Tropsch synthesis, though we have
discussed about Fischer Tropsch earlier also. We will again see the reactions and other process
conditions and reactors in detail. So, in FTS syngas, that is carbon monoxide and hydrogen is
catalytically converted into a spectrum of hydrocarbon chains, so this is the reaction, this we
have already discussed earlier.
But again to maintain the reading properly, so I have again given these reactions. So, the 4 main
metals considered for Fischer Tropsch synthesis are iron, cobalt, ruthenium and nickel.
Ruthenium the most active is impractical due to it is high cost and low abundance, it is a very
costly metal. Nickel although inexpensive is plagued by coking and typically considered a
methanation catalyst.
759

Thus cobalt and iron are the essential active industrial metals for the Fischer Tropsch synthesis.
The cost of iron based FT catalyst is estimated to be 10 to 40 dollar per pound, whereas cobalt
based FT catalyst can cost about 60 to 100 dollar per pound. And are more susceptible to the;
marketplace due to increasing demands in the aerospace and batteries. Each FT catalyst
developed to date has their, own yield structure.
Cobalt based catalyst produces more water and water cleanup is required whereas iron based
catalyst active for the WGS produces even carbon dioxide which can be sent to a (WGS is the
water gas shift reaction) shift reactor. So, iron catalyst can be used in a wider variety of
feedstocks compared to cobalt catalyst, however, economics still is the driving source and
finding the cheapest available feedstock. Another advantage of iron, spent cobalt catalyst needs
to be reclaimed whereas iron catalyst can be land filled.
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This is just a schematic understanding of the sources for the synthesis gas for the Fischer
Tropsch synthesis process. So, it can be coal, it can be biomass, it can be natural gas, now those
can be converted to syngas, carbon monoxide and hydrogen and further go for the Fischer
Tropsch process and you get your fuel. Similarly, carbon dioxide from the atmosphere or from
the flue gas and electricity also can help to produce carbon dioxide and hydrogen. And this also
can be further processed by the Fischer Tropsch process to generate fuel.
Now let us understand little more about the FTS catalysts. Structural and chemical promoters are
usually added on iron based catalyst. Binders such as silica are usually added to improve the
structural rigidity of iron catalyst. Alkali metals are electronic promoters that facilitate
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carburization, increase the FTS activity and improve the selectivity to high molecular weight
hydrocarbons.
Promoters such as copper are added in part to facilitate the reduction of iron oxides. Because
cobalt is expensive, to increase the number of cobalt atoms exposed at the surface, cobalt nano-
particles are dispersed on carriers such as metal oxides, zeolites, carbon materials, manganese,
ceria, silica carbide, and various other number of materials. Many of these supports originally
thought to be inert, are now being used to promote a specific selectivity.
Unlike iron, promoters used for cobalt do not significantly increase the turnover frequency;
rather these metals aid in increasing the percentage of reduction of cobalt oxides to cobalt metal.
Whether it promotes methanation depends on the nature of the promoter. Lastly, unlike cobalt
and ruthenium where the metallic surface is deemed active for the Fischer Tropsch synthesis,
several species of iron carbide exhibit Fischer Tropsch synthesis activity.
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So, we will try to understand the mechanism now. So, ninety years have passed since discovery
of the Fischer Tropsch synthesis process. However, many details regarding the mechanism
remains speculative. Interactions between the active metals with carbon monoxide or hydrogen
are still being investigated to elucidate specific dissociation pathways, and their kinetic effect on
hydrocarbon chain growth.
Carbon monoxide may dissociate directly or with assistance of hydrogen in a concerted manner.
Two different mechanistic families have been proposed to explain initiation and chain growth
steps during the Fischer Tropsch synthesis, first is carbide mechanism, second is carbon
monoxide insertion mechanism.
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So, in carbide mechanism first proposed by Fischer and Tropsch, carbon monoxide dissociatively
adsorbs to form carbide and surface oxygen. Carbide species are partially hydrogenated to CHx
intermediates which serve as a chain growth monomer. Termination occurs by abstraction of
hydrogen to form olefins or by addition of CH3 species or hydrogen to form paraffins. Whereas
in carbon monoxide insertion mechanism; carbon monoxide directly inserts into the growing
hydrocarbon chain prior to carbon oxygen scission manner.
Micro kinetic models, isotope tracer studies and steady state and transient kinetic investigations
lend support to this mechanistic scheme, where C-O scission is the key step.
764

So, tuning; since both carbon monoxide and vinylic intermediates are π-accepting based ligands,
both are susceptible to electronic back donation from the catalyst surface.
So, we will see a mechanism here. So, this is FTS mechanism, it is a balancing act controlled by
the localized electron donating capability of the active surface. So, you can see this, you can see
that carbon monoxide dissociation rate. Here this side it is decreasing where the electrons are
withdrawing, here it is increasing where the electrons are donating. Various catalyst like nickel,
cobalt, ruthenium, iron carbide, iron, all these are being used.
And different catalyst depending upon the different dissociation rate and what is the active
surface and what type of bonding is happening, you will get different types of products. Let us
go back; so this, whatever I have shown, is a Dewar-Chatt-Duncanson model and is a base model
used to describe how localized back donation from the metal will specifically affect how these
species will interact.
So, if the localized sp2 character is retained, both carbon monoxide and C2 will be weakly bound
to the surface and the C = C will be observed in the IR is remarkably similar to the free C = C.
So, it is specifically talking about this and the position is also very important. Now in contrast to
weak back donation, if too strong carbon takes one more sp3 character as a metallocyclopropane
species.
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Vibrational observations then reveal that C-C bond weakened to resemble a single bond X2, this
one. So, you can see here it is a double bond, here the bond is weakened, it is a single bond here.
So, vibrational observations reveal that C-C bond we can to resemble a single bond marked by
the X2 in the image. Thus, a balance for the back donation of FTS is of great importance and if
not held could lead to inferior and pore catalyst.
Now in general based upon the figure 3, different major scenarios can be identified. So, we will
discuss what are the 3 different scenarios that can happen while this carbon monoxide
dissociation is happening?
The first one is route A, weak back donation. So, carbon monoxide is adsorbed molecularly as
the scission of carbon bond with H+ is not kinetically favored. If carbon monoxide is weakly
adsorbed then the vinylic intermediate species will be an L configuration weakly bound to the
surface, this one. They will be in this type of configuration L configuration.
Thus the intermediate is susceptible to hydrogenation reactions and high selectivity to methane
and light hydrocarbons are observed. As carbon monoxide dissociation is difficult, carbon
growth from the weakly bound L configured vinylic intermediate could be through the carbon
766

monoxide insertion. Moreover, the carbons of the vinylic intermediate exhibit sp2 hybridization,
that is electrophilic in nature because of the weak back donation from the metal.
Now consequently, chain growth can occur at either C position, resulting in internal olefins,
branched paraffins, and oxygenated materials through a pseudo hydroformylation series of steps.
This configuration has been proposed for the un-promoted iron carbide. So, basically we
discussed about this, we can see the n-paraffins, branched olefins, 1-olefin, 2-olefin, acids,
ketones and esters all these things will be produced in this route weak back donation.
Now route B is the semi strong back donation. Now carbon monoxide adsorbs in an associative
manner followed by H dissociation on the active side. As adsorbed carbon monoxide is stable, so
is the vinylic intermediate as an X2 configuration. Now we are talking about this configuration,
we can call this as a semi strong back donation happening here, thus this is the metallic surface
of the catalyst.
So, these species are suitably stabilized on the active surface to favor chain growth solely at the
Cx position, resulting in a fingerprint of primarily linear paraffins and 1-olefins as observed for
cobalt and ruthenium catalyst, usually cobalt and ruthenium based catalyst are being used.
Potassium promoted iron catalyst can also be included in this configuration.
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Now route C, the last one is the strong back donation. Now as carbon monoxide rapidly
dissociates the vinylic intermediate, that is the π-acceptor, will also easily dissociate forming a
carbidic phase. The X2 configuration though present will not possess sufficient stability and will
dissociate to an active carbidic phase which will convert to methane or inactive graphite carbon.
Now this usually happens with nickel catalyst. So, you can see that the same X2 configuration,
with the nickel catalyst will result as methane and coke formation will happen, so due to the
strong back donation scheme. After carbon monoxide was decomposed on further surface of the
nickel or silicon dioxide immediately after hydrogen and unlabeled carbon monoxide produced
methane and carbon dioxide, suggesting that methanation involves a Cs intermediate, which
basically happens due to the strong back donation.
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So, we will try to understand now and learn about the different reactors that are essential for the
FT synthesis reaction. So, slurry bubble column reactor, the SBCR. The development of a low
temperature slurry phase FTS process began in 1938 by Kolbel and Ackermann and the
technology attained a production rate of 11.5 tons of hydrocarbons per day. In a typical slurry
bubble column reactor synthesis gas enters from the bottom of the reactor and thoroughly mixes
with the liquid phase containing the catalyst.
The reaction takes place on the catalyst surface and the product gas exits from the top with
heavier hydrocarbons being recovered from the bottom using an appropriately sized metal filter.
Cooling tubes remove the heat produced by the reaction; the major issue with the slurry phase
reactor was product separation from the catalyst. Since some breakthrough of the catalyst occurs
activity declined.
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A problem with the conventional SBCRs is the scale up. In most cases the initial reactor design
is solely based on the reactor results from the laboratory and/or pilots plant scale studies.
Assumptions made based on preliminary testing of the slurry bubble column reactors at small
scale may not apply at the industrial scale due to the differences in the reactor hydrodynamics.
So, SBCR technology has been adopted by both industry as well as academia because of the
simplicity of the operation compared to the fixed bed reactors. Exxon and Sasol have
independently developed SBCRs as shown in figure 4 a and 4 b.
We will see these 2 reactors. So, the A design is done by the Exxon company and B design is by
the Sasol. So, you can see that there is little difference between the design. So basically you can
770

see that in the B you have cooling coils that is inserted inside the reactors. So, that the cooling
can be done very fast, if you have it outside the reactor, so it will take time and cooling effect
may not be so good.
But if you put it inside the reaction, but there are problems also maintenance and all these things
is a big issue, so but the cooling can be faster. So, here you can see the reaction, this is the main
reaction zone and there are integrities given here. Mostly both the designs have been well
adapted by industrial sector, and are still in practice.
Then is the fluidized bed reactors which are also very common. Sasol has employed circulating
fluidized bed reactors commercially for many years. One drawback is that high temperature
operation is required to achieve high productivity. Now this precludes the use of typical high
surface area catalyst which would otherwise undergo attrition under such harsh conditions, thus
lower surface area, attrition resistance, catalysts are used.
Other problems include an energy requirement to circulate the catalyst and the pressure drop.
The Sasol fixed fluidized bed reactors have replaced circulating based reactors. So, this is a
typical circulating fluidized bed reactor.
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So, then we will discuss about the fixed bed and compact bed reactors. Now the fixed bed reactor
configuration offers high throughput with plug flow behavior, lower maintenance cost and
reduced losses due to attrition and wear. Moreover, they are easily tested at small scale using a
single tube. So, you can see that there are many tubular tubes are here, so you can have single
tube, you can have multiple tubes.
It is basically a design how much feed you are processing, that is very important. So, multi-
channel fixed bed reactors are much smaller in size as they are complicated to fabricate, but they
are more mobile useful for reaching standard resources. You can carry it them and install it any
other places. So, the catalytic activity in micro channel reactor can certainly be higher because of
the better heat transfer. However, there is also the reactor cost which is part of the capital cost
and has less impact on the economics unless the difference is huge.
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So, with this I wind up today's lecture. So, in the next lecture which is again under module 7
lecture 3 under biodiesel, we will discuss about the techniques to purify biodiesel and we will
also discuss about the biodiesel fuel properties. So, thank you very much, in case you have any
query, please register, it on the swayam portal or you can drop a mail to me at
kmohanty@iitg.ac.in.
773

Module-07
Lecture-21
Biodiesel Purification Fuel Properties
Good morning students. Today is lecture 3 under module 7 and as you know that we are
discussing biodiesel under module 7. Today we will be discussing about the biodiesel
purification and fuel property. So, let us begin.
Transesterification of triglycerides with short chain alcohols, that is either methanol or ethanol in
the presence of an alkali catalyst has been most widely used to obtain biodiesel or essentially we
can say that fatty acid alkyl esters. So, glycerol is an important byproduct of the
transesterification reaction which needs to be separated from the biodiesel phase.
So, if you recall in our last class, we have discussed extensively how transesterification reactions
happen, what are the different types of reactions, acid catalyzed, base catalyze and everything.
So, depending upon the regional regulation biodiesel needs to meet certain characterization prior
to reaching the market. Regional regulations essentially means every country has their own
regulations and fuel standards, so that you have to meet.
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So, even though the densities are biodiesel and glycerol are distinct enough from one another to
be separated via gravitational settling and centrifugation, further purification is required to
remove impurities? So what are those impurities? Now the remaining vegetable oil, alcohol,
catalyst, a little bit quantity of the soap and the free fatty acids which are not purified and meet
the standard specification introduced in the ASTM D6571 or EN 14214. So, ASTM is the
American Society for testing and materials, and EN is the European standards, any one of these.
Low quality biodiesel due to impurities cannot only compromise the engine performance, but
also complicate the storage and transportation of the fuel. Biodiesel purification techniques
include wet washing using water, you can use acidified water also, some organic solvents or
ionic liquids, the ionic liquids are a bit costly. Or else you can use dry washing via adsorption or
ion exchange and membrane separation.
Now biodiesel purification method has been characterized based on the nature of the process
such as either equilibrium based, affinity based, membrane based, solid-liquid or reaction
separation based.
775

So, as shown in the figure. So, this figure I will explain you. You can see this, this is the classical
representation of how the biodiesel can be purified, so as to get high purity biodiesel. So, 4
things have been shown here, 4 different types or distinct separation processes equilibrium
based, so it is distillation. You can see that crude biodiesel, impurities are present, so the
biodiesel mixed with solvent, then it will be purified.
Then affinity based is basically adsorption, so AD. So, here you will use different types of
adsorbents to remove the impurities. So, all the impurities will be adsorbed either in the surface
of the adsorbent or it may get inside the pores also. So, then you or you can have ion exchange
also. So, either you can have cation exchange bed, you can have anion exchange bed, so it is a
packed bed system, where the impurities will be attached to the ion exchange resins and
biodiesel will be purified.
Then membrane based: Membrane has often taken a very important role in most of the process
industries using chemicals, pharmaceuticals, then food and beverage industries. Now in this case
also biodiesel also can be purified using different types of membrane system maybe
ultrafiltration, nanofiltration and others where the beauty of the membrane separation is that you
can tailor make membrane to target a specific separation.
776

So, either you can retain them on the top, all the impurities, or you can pass them to the permeate
side depending upon the pore size. Then the last one is reaction based which is called reactive
distillation. So, reactive distillation is a distillation process where reaction and distillation both
are happening in the same chamber or the same unit, we will discuss this in detail later on or we
can have membrane bioreactor.
So, here feed is being processed, feed is being fed to the membrane bioreactor where the
biodiesel is getting produced as well as getting purified in a single system. So, we will discuss
one by one.
So, let us discuss the first one which is equilibrium based separation process. So, absorption and
distillation as well as supercritical fluid extraction and liquid-liquid extraction are some of the
most common equilibrium based separation processes. Absorption is commonly utilized for
separating particles and impurities from a gaseous mixture, therefore it does not have a major
application in the biodiesel separation which is a liquid phase process.
Let us talk about distillation. So, distillation is the most common method for separation of more
volatile compounds from heavier substances in a liquid mixture. There are different distillation
techniques including conventional distillation, which are ordinary, vacuum or steam distillation
777

or azeotropic distillation - if at all the feed streams have formed azeotropes (close boiling point
mixtures basically) or you can go for extractive distillation or molecular distillation.
Now conventional distillation and evaporation are perhaps by far the most common methods
used in biodiesel purification to remove the remaining alcohol or water from the crude biodiesel.
Typically, the unreacted alcohol is separated from biodiesel prior to further purification. In
molecular distillation carried out under high vacuum the molecules’ free path is longer than the
evaporation and condenser surface distance; therefore, most of the evaporated molecules reach
the condensing surface without being deflected on collision with foreign gas molecules resulting
in a higher separation yield. Literature reported that molecular distillation was used to purify
biodiesel obtained from waste cooking oil to achieve a 98% separation yield at the evaporator
temperature of 120 degree. So, if you look at the literature, you will find there are plenty of
works when biodiesel has been purified.
Basically the glycerol has been removed. Glycerol is already removed, when you are talking
about purification stuff we are just removing the unconverted vegetable oils, some free fatty
acids, then alcohol - very important. So, all these things are being very successfully removed by
distillation process. Now in certain cases, it has been also observed that distillation followed by
another unit operation where it can be treated as a last polishing step to further sometimes you
778

may have to dehydrate it and some other polishing steps are necessary, so as to get a purified
biodiesel.
So, then is LLE which is called liquid-liquid extraction. So, it is also known as the solvent
extraction - is a well-established separation technique to extract desirable components from a
liquid feed to a specific solvent. So, this process is the most common method used for biodiesel
purification that encompasses all the techniques developed for wet washing. The use of
deionized water to remove soap, catalyst, alcohol and other contaminants of biodiesel is one of
the most common biodiesel purification methods.
So, water temperature and volume are the key factors in improving purification of the biodiesel
phase. So, I will show you one table where we will see the negative effects of contaminants on
biodiesel and engines and why we are talking about purifying it?
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So, you can see that the methanol remains in a quantity which is more than that is desirable. Of
course, it is desirable that you remove all methanol, water, any catalyst, free fatty acids
everything. So, if methanol is present, then the deterioration of the natural rubber seals and
gaskets, lower flash points, problem in storage basically corrosion of pieces of alumina and zinc,
all these things will happen.
If water will remain in more quantity, then it will reduce the heat of combustion, corrosion of
system components, formation of ice crystals, bacteriological growth will also happen if water is
present. Then if the catalyst or soap remains then it will damage the injectors, it will pose
corrosion problems in engines, plugging up filters and weakening of the engines. If free fatty
acids are present then it will reduce the oxidation stability, it will also create corrosion problem
in the vital engine components.
Similarly, glycerides and glycerols, so all these things will lead to crystallization, decantation,
storage problems and has to be removed.
780

So, let us now understand the wet washing technologies. So, production of biodiesel is usually
followed with soaps formation and water production especially when low quality feedstock and
alkaline catalysts are used as shown in the figure. So, this is a fatty acid, so you are using sodium
hydroxide as the catalyst, you get the sodium soap and then water.
So, feedstocks would be dried to control water content, which causes hydrolysis of fats and oils
to free fatty acids. The presence of free fatty acids leads to soap formation, thus interfering in the
products purification process.
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Consequently, feedstocks with high amount of water and free fatty acids molecules could easily
interfere with the transesterification reaction, resulting in soaps formation thereby affecting the
purification of crude biodiesel and lowering the yield of the alkyl esters. The commonest
effective technique to remove glycerol and methanol from biodiesel production mixture is by
water washing, since both glycerol and methanol are highly soluble in water.
Biodiesel wet washing technique involves addition of certain amount of water to crude biodiesel
and then agitating it gently to avoid formation of emulsion, you have to be very careful beyond
certain rpm or rotations per minute. If you do that, then there will be a emulsion formation
because it is oil and water will mix with each other and it will form an emulsion. You can
observe in the naked eye also, some whitish or milky color formation will start, so that is not
actually required.
So, you have to be very careful about the agitation speed. So, the process is repeated until
colorless wash water is obtained, indicating complete removal of the impurities.
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So, wet washing process usually requires a lot of water approximately water wash solution at the
rate of 28% by volume of oil, and 1 gram of tannic acid per litre of water. The use of large
quantity of water generates huge amount of wastewater and incur high energy cost, because
again you need to process this wastewater. So, wet washing is mostly conducted through
washing with deionized water, washing with acid (5% usually phosphoric acid) and water and
washing with organic solvent and water.
Anyone you can do, either with pure deionized water or with the 5% phosphoric acid mixed
water or organic solvent and water mixture. So, let us talk about that deionized water washing
technology. Water washing has been traditionally used to purify crude biodiesel after its
separation from glycerol. It was reported that air was continuously introduced into the aqueous
layer, while gently stirring the mixture of crude biodiesel and water. In one of the significant
work for which the reference has been given here.
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So, this process was continued until the ester layer becomes clear. In addition, after settling the
aqueous solution was drained and water alone was added at 28% by volume of oil for the final
washing process. Water washing is the most problematic step in biodiesel production, although
water washing involves heated, softened water, wastewater treatment and water methanol
separation, but the process of water application provides an avenue for the addition of acid to
neutralize the remaining catalyst and remove the salts formed.
Though it has certain drawbacks as we have mentioned, but it is still preferred because of the low
cost and it is efficiency, it is a benign process, it is easy to carry out. So, if you talk about
applications, literature reported that after transesterification crude biodiesel and glycerol can be
phase separated within the first 10 minute, and a complete separation could be achieved in 2
hours after stirring is stopped.
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Also alcohol can be removed through distillation and evaporation and that care must be taken to
ensure zero water accumulation in the recovered alcohol stream. Authors reported that after
phase separation deionized water is added to crude biodiesel at the rate of 5.5% by volume of the
feedstock and the mixture is stirred for a period of 5 minutes and allow to settle for glycerol
removal.
This is the procedure which is reported in this particular reference which is given here. The
removal of complete glycerol is an indication of high quality biodiesel production. Also literature
noted that washing two times is enough to get rid of impurities from the methyl esters. The crude
methyl ester produced was washed and distilled under vacuum at 30 to 80 degrees centigrade and
133 Pascal.
The product was then dried at 80 degrees centigrade for 10 minute to remove traces of moisture
and the methyl ester yield was found to be 97 to 99% which is an excellent yield. So, you can
please refer to this particular reference, which is reported in the industrial engineering chemistry
research journal in 1998, long back but it is a classic study.
785

So, then acids and deionized water washing technology. Acids such as phosphoric acid, sulfuric
acid and hydrochloric acid are mostly used in the purification of crude biodiesel. This process is
followed with the use of distilled water to completely remove biodiesel impurities. For the
purpose of immediate use on diesel engines and long term storage purified biodiesel is properly
dried.
If you talk about applications, then literature noted that after one-step transesterification reaction,
the crude methyl esters produced was purified with hot water at 70 degrees centigrade and 5%
phosphoric acid at 50 degrees centigrade. The authors dried the methyl ester layer in a vacuum
and checked with ceric ammonium nitrate reagent for glycerol removal and the reference has
been given here. It is also a very interesting work reported in the fuel processing technology
journal in 2008.
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Another work stated that water have to be reduced to a limit of 0.05% volume by volume to meet
the ASTM D6751 standard specification. The authors washed biodiesel with water at a pH 4.5,
the process helped in neutralizing the catalyst and converting the soap formed to free fatty acids,
thus reducing it is emulsifying tendencies. So, one of the major aim of this work is to reduce the
emulsification.
So, further vacuum dryer wash used to reduce the residual water from initial value of 2.4% to a
final value of 0.045%. The water removed via drying was recycled into washing operation. As
well, to reduce the cost of production, the glycerol produced was also refined to a concentration
level suitable to the market value, that is approximately 80 weight by weight percent.
787

So, the next is organic solvent washing technology. Organic solvents such as petroleum ether has
been used to purify crude biodiesel. Now this process is usually followed with the use of the
large amount of demineralized water to remove residual soap and catalyst. So, let us talk about
some applications. The fatty acid methyl esters was distilled under vacuum at 180 degrees
centigrade, when the temperature reached 240 degrees centigrade, that distillation was assumed
to be completed.
The crude FAME was separated after acidic transesterification and then purified with petroleum
ether and washed with hot water until the washing reached a neutral pH. n-Hexane was also used
for the extraction of crude biodiesel at 1 : 1 ratio at room temperature, the mixture was washed
three times using distilled water and the final yield obtained was 93 weight percent. So, the
references also been given, it is also an excellent work published in energy conversion
management journal in 2007.
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So, let us go ahead and talk about other separation processes. We will talk about affinity based
separation process. So, adsorption and ion exchange are the most common affinity based
separation processes, also known as that dry washing methods for biodiesel purification. In these
processes an appropriate adsorbent is used to selectively adsorb certain impurities from the liquid
phase onto it is surface.
As you know that adsorption is a very selective process and you can also make certain
adsorbents, so as to target a specific impurity. Dry washing offers several advantages over wet
washing which includes the ease of integration into an existing plant, shorter purification time,
no water consumption and wastewater production and smaller unit sizes. The absence of water in
purification of biodiesel during dry washing results in biodiesel with acceptable water content,
which is less than 500 ppm that is based on the ASTM D675 standard.
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This is a simple schematic diagram of the biodiesel by dry washing technology. So, you can see
this unrefined biodiesel which is produced. So, then it goes to the residual alcohol, removal.
Initially you will remove alcohol, most probably this will be a distillation unit. Then you mix it
and goes for a mixing unit, so at 65 degrees centigrade for 20 to 30 minutes with a certain
agitation speed which should also take care that emulsification should not happen, so the speed
should be less than that.
Then you can add the adsorbent here, basically it can be magnesol ion exchange resins, activated
carbon. It can be in a suspended mode, in the liquid phase or you can go for a packed bed.
Usually many commercial scale applications are all packed bed units. Then whatever it is
coming out from the stream that goes to a filter section where you get the refined biodiesel, and
here spent adsorbent can be recovered and regenerated and can be reused back.
So, it is the simplfied system again, as I told you many times that whenever I am showing any
sketches, so there in between so many small, small unit operations and steps, which are not
usually shown in that schematic diagram because it is easy to understand in nutshell if the
schematic representation is concentrated only the major unit operations.
790

So, let us talk about adsorption. Adsorption is the process by which atoms, ions or molecules
known as adsorbate, from a substance mostly liquid or gas adhere to a solid surface called as
adsorbent. Adsorbents are natural or synthetic materials of amorphous or micro crystalline
structures, owning basic and acidic adsorption sites, where polar substances such as glycerol and
methanol can be adsorbed and filtered out of the biodiesel.
Adsorption loading, selectivity, regenerability, kinetics, compatibility and cost are the most
important criteria that need to be considered for adsorbent selection. Silica based adsorbents such
as Magnesol and Trisyl, bio-based adsorbents such as lignocellulosic substrates and activated
compounds, including the famous activated carbon, then you have activated fiber and activated
clay are among the most common adsorbents for this process.
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So, silica based adsorbents. So, silica is one of the key elements in different types of industrially
available adsorbents including silica gel, zeolites and molecular sieves. It is an amorphous
inorganic mesoporous adsorbent produced via polymerization of the silicic acid. Silica gel owns
a hydrophilic surface due to the presence of hydroxyl group, which makes it a proper adsorbent
for water, alcohol and other polar molecules.
Silica showed a great potential for removal of glycerol from biodiesel synthesized from waste
cooking oil. Silica gel could effectively remove glycerol and monoglycerides from biodiesel, and
the presence of small amounts of water and soaps does not influence that adsorption of glycerol.
792

Silica gel could effectively remove glycerol and monoglycerides from biodiesel and the presence
of small amounts of water and soap does not influence the adsorption of glycerol. However, the
presence of alcohol usually methanol negatively affects glycerol adsorption and decrease the
effective saturation capacity by about half due to the affinity effect of the methanol on silica
surface and glycerol in liquid phase.
One of the most important thing let me tell you about this entire adsorption phenomena is that
whenever we talk about adsorption and a system or a process that we are carrying out where
there are more number of impurities to be removed - It is not a single one or two there are many
then these impurities will try to adsorb on the surface of the adsorbent which is known as a
competitive adsorption, due to their inherent physiochemical properties as well as the
physiochemical properties of the adsorbent.
So, in this case, let us say if the methanol is trying to get adsorbed on the surface of the adsorbent
more than that of glycerol, so then that creates a problem. So, we have to choose adsorbent
selectively in such a way that initially either glycerol will be adsorbed or methanol or some other
impurities, then we can have successive columns. So, one will remove that glycerol completely
another will remove methanol completely - like that. But please understand that this also adds on
cost, as an as more unit operations you are adding that means you are increasing the cost of the
final product, so that also has to be taken care of.
So, the presence of water at severe conditions results in vegetable oil and glycerol hydrolysis to
free fatty acids which need to be separated during the biodiesel refining process. Magnesol is one
of the common commercially available silica based adsorbents used for biodiesel purification.
It is in fact an inorganic matrix of magnesium silicate and anhydrous sodium sulfate offering a
great potential for selective adsorption of hydrophilic impurities of the crude biodiesel.
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Similar to other adsorbents, biodiesel needs to be thoroughly mixed with the magnesol powder
for a certain period of time. The mixture is then subjected to filtration to separate magnesol from
the final Fuel. Faccini et al in one of the very important work, so they have evaluated different
types of adsorbents for biodiesel purification, where 1% magnesol and 2% silica salt showed
promising results.
The soap, methanol and water content of the crude biodiesel were about 1670 ppm, 2.13% and
1300 milligrams per kg, respectively. Those values correspondingly decreased to 60.85, 0.19%
and 500 milligrams per kg after purification by 1% magnesol which is good purification result.
So, this adsorbent also successfully decrease the free and total glycerol from 0.71 and 0.26 to
0.28 to 0.02 respectively, the reference has been listed below.
794

We will talk about biomass based adsorbents; so cellulosic and lignocellulosic substrates were
also found to be effective adsorbents for the biodiesel purification due to the enormous cost of
most of the synthetic adsorbents focus has been more on developing low cost or readily
available, renewable biomass based adsorbent. So, people have concentrated more and more on
lignocellulosic substrates.
These materials are abundant and inexpensive in addition to their advantages as renewable,
biocompatible and non toxic materials. This method is widely and simply used in small scale
biodiesel plants, and the biomass that adsorbs the impurities is burned for heating after saturation
and refilled with a fresh biomass. Gomes et al in 2015 use different types of starch with various
morphologies along with cellulose as a natural adsorbent for biodiesel purification.
Corn starch and rice starch own a polyhedral structure while potato starch and cassava starch
have ellipsoidal and semi spherical structures respectively.
795

The eucalyptus bleached kraft cellulose with a tape format was also used for biodiesel
purification. The dry washing was performed via admixing, 1 to 10% of the adsorbent in
biodiesel for 10 minutes at room temperature and 150 rpm followed by filtration using a filter
paper. Regardless of the adsorbent type and content the acidity index decreased after purification
with the aforementioned biomasses.
The free glycerol content of the biodiesel was about 0.13% which was completely removed using
the following substrates - 5% potato starch, 1 to 2% cassava starch and 1% rice starch. The
purified biodiesel with 2% corn starch could also meet the standard specification for free
glycerol. Turbidity, showing the presence of impurities in the biodiesel was also significantly
decreased in the case of using 5% potato starch or 1 to 2% cassava starch.
796

Rice husk ash showed promising performance in biodiesel purification up to 5% dose. The
adsorption capability of the rice husk ash is attributed to it is high silica content and the presence
of meso and macropores in its structure, so it is a very good adsorbent. Although the water
content of the purified biodiesel with RHA was still above the acceptable value, it was
significantly lower than that of the purified biodiesel using acidified water, 1% phosphoric acid
actually and magnesol using 1% magnesol.
Then activated compounds: So, activated carbon activated fiber which is known as carbon fiber
and activated alumina are among the most common adsorbents in industrial applications.
Activated carbon which owns a large porous volume and high surface area can be manufactured
797

from any carbonaceous organics. As for example, sawdust, petroleum coke, wood, charcoal,
peat, fruit nuts, bituminous coal, lignite and coconut shells.
The porous structure is activated through either steam or chemical activation. Two types of
activation usually done, steam activation is also called as physical activation. And chemical
activation use some sort of chemicals, either acids or bases to do the activation. So, in the case of
steam activation, the substrate is heated to 400 to 500 degree centigrade in an oxygen free
atmosphere to remove the volatile components, that step is called the carbonization step.
That is followed by the oxidization step using the steam or carbon dioxide at 800 to 1000 degree
centigrade. So, the chemical activation is performed via impregnation of the substrate with a
strong dehydrating agent, usually phosphoric acid or zinc chloride. But many times zinc chloride
is being not considered because it is little toxic. So, followed by heating to 500 to 800 degree
centigrade, then followed by washing, drying and grinding.
Thermal dehydration of hydrated alumina and recrystallization is the most common method used
to produce activated alumina. The presence of Lewis acids sites on the surface of activated
alumina makes it suitable adsorbent for polar compounds and oxygenates such as alcohols,
aldehydes, ketones and carboxylic acids. You know Lewis acid are the acids which are ready to
give electrons, they are ready to donate electrons, electron pairs you can say.
798

And Fadhil and Dheyab in one of the significant work - the references given here below -
compared the performance of activated carbon prior to and after acid treatment either with
sulfuric acid or hydrochloric acid for purifying biodiesel synthesized from spent cooking oil and
spent fish frying oil. So, the activated carbon purifications led to a better biodiesel yield usually
91.5 to 93.75%. It is a significant yield actually with respect to water washed product which is 86
to 89% on both of the feedstock.
In case of the spent fish frying oil, the modification of activated carbon with acids, improved its
performance especially in the case of activated carbon modified by sulfuric acid, which resulted
in a biodiesel yield of 93.75%. On the other hand, the untreated activated carbon led to the best
purification result for the spent cooking oil biodiesel, so almost you get 93.4% yield.
799

So, the next category is ion exchange. So, ion exchange is the process of exchanging the ions
between the solution and a proper solid phase due to a stronger affinity, basically the electrostatic
force between the target species and the functional groups on the surface. Ion exchangers consist
of a matrix with excess charges localized in specific sites of the structure. Ion exchangers resins
are one of the most common types of exchangers typically produced via fictionalization of the
polymer obtained from copolymerization of styrene crosslinked with divinylbenzene.
The ion exchange resins are categorized based on the functionality and yet divided according to
their strength (basically density of the charge) to strongly acidic cation, weakly acidic cations,
strongly basic anion and weakly basic anion exchange resins. So, basically 4 distinct types of
resins.
800

The presence of sulfonic acid groups (sulfonated polystyrene basically) in the matrix leads to the
formation of strong cation exchange resin as the protons can easily be exchanged with other
cations. On the other hand, carboxylic groups are usually incorporated in the exchanger’s matrix
to produce a weak cation exchange resin. The strong anion exchange resins are usually obtained
by insertion of the quaternary ammonium species into the matrix structure while the presence of
radicals of secondary or tertiary amines leads to the formation of weak anion exchangers.
The structural properties, that is degree of crosslinking, porosity and particle size exchange
capacity, stability, type and density of the charges need to be considered in order to choose a
proper ion exchange resin.
801

Let us discuss about applications. So, Boris and Skelton studied the performance of PD206 and
BD10 dry ion exchange resins which are strong acid cation resins for purification of biodiesel
produced from used cooking oil and rapeseed oil. Although the resins showed promising
performance for soap and glycerol removal, the methanol removal was not satisfactory. Lewatit
GF202, on the other hand showed a great potential for the methanol removal, along with it is
capability to decrease the soap and glycerol content in the purified biodiesel.
The reusability of this resin was an additional advantage. Now again, as I told you just few
minutes before, again I am telling you that in case of whether it is adsorption, ion exchange, ion
exchange resins or absorbent, no single species will purify the entire amount of different types of
impurities that we used to remove - that is not possible. Therefore, there is a need that we
develop different systems with higher efficiency to remove one particular component, either
glycerol, then followed by methanol, followed by water, soap and free fatty acids like that. So,
you need to fine tune and optimize your process in such a way that we will have minimum
number of columns to achieve that in a stage wise separation also can be done. So, this is where
the design engineers play a vital role in designing a low cost purification step otherwise the final
product cost will be too high.
802

So, now let us talk about the membrane based separation technologies in biodiesel purification.
So, these are the latest developments; some of these are also been commercialized. By stark
contrast to the high water content involved in typical water washing methods, membrane
technology has emerged as a low or no water alternative in the purification of crude biodiesel.
So, as well as the cost advantages associated with the lack of wastewater, this method avoids
potential emulsion in the product facilitating two phase separation.
Since we are not using water, so there is no question of any emulsion formation. So, micro
filtration which is basically 0.1 to 10 micron in that range, ultrafiltration between 1 to 20
nanometer and nanofiltration maximum pore size is of almost 1 nanometer. So, all these types of
membranes are all used depending on the characteristics of the feedstock. So, in the next figure, I
will show you a schematic of the micro and ultrafiltration experimental unit which was used by a
Atadashi et al and published in 2015 in a very good work.
803

So, it’s a simplified membrane based biodiesel purification unit. So, this is a feed tank, from here
the feed is getting pumped, these are rotameters and all and this is your membrane unit M1. So,
M1 is the membrane module, it is a hollow fiber membrane module here. So, it can be
ultrafiltration, it can be any other membrane separation, nanofiltration and all. So, whatever you
get the concentrate that concentrate goes back to feed tank again.
And the permeate can be recovered and the membrane separation units are very easy to handle.
And they are simple to design also, not much unit operations and much other accessories are
required. And energy requirement is also very, very low compared to other energy intensive
processes. Here whatever the energy is required is just the pumping cost, the membrane itself
does not need any energy to do the purification. You can refer particular work in this particular
journal which is published in 2015, it is a nice work.
804

Then we will talk about organic and polymeric membranes. The organic membranes employed in
biodiesel purification include Polysulfone, polyamide, and polycarbonate, regenerated celluloses,
polyvinylidene fluoride which is known as PVDF and polyacrylonitrile with varying success.
These organic membranes can be sorted according to their hydrophilicity and corresponding
hydrophobicity.
A hydrophilic membrane is less susceptible to fouling from a variety of biorefinery feeds due to
the water content but is more susceptible to deformation due to pH and temperature swings. A
hydrophobic material is more useful for the separation of oils. So, based upon the hydrophobicity
you can choose actually what is your intention and what you are going to remove? Are you going
to remove alcohol, are you going to remove glycerol and where you want to remove?
You want to pass them to the permeate side or you want to retain them on the surface of the
membrane? All these things has to be pre decided before you go for designing of a membrane
unit.
805

So, let us talk about applications. He et al directly compared polysulfone and polyacrylonitrile
membranes in obtaining high purity biodiesel as well as using water and acid washing for
comparison. While all methods were able to produce high purity biodiesel (almost 97.5%), only
the membrane extraction method was successful in decreasing ester losses, endemic to water and
acid washing methods.
So, 10.1 weight percent esters were lost even at the optimum temperature of 50 degrees
centigrade with distilled water due to emulsification. The polysulfone and polyacrylonitrile
membranes by contrast, were able to purify biodiesel with only 8.1 weight percent and 10.3
weight percent ester losses. However, the poly acrylonitrile membrane allowed for higher water
content in the final biodiesel product than any other methods making it perhaps unsuitable for the
biodiesel refining.
806

The polysulfone membrane additionally led to the highest purity of biodiesel at roughly 99%
without additional steps. Comparisons conducted between ultrafiltration poly ether-sulfone and
microfiltration cellulose ester membrane demonstrated successful separation of glycerol from the
final biodiesel product. This particular work reference is also given below it was published in
Renewable Energy.
And with nominal molecular weight cutoff of 10 kilo Dalton, the ultrafiltration poly ether-
sulfone membrane alone could reach 0.02% weight percent glycerol in the permeate, meeting
international standards. Additional success with ultrafiltration polyacrylonitrile membranes have
been experienced for glycerol separation from a biodiesel product. Saleh et al found a 63%
reduction in glycerol content in the permeate upon adding 1 weight percent water by mass
reaching a level of 0.013 weight percent glycerol in the permeate side.
807

So, we will talk about inorganic and ceramic membranes. So, there is a substantially less variety
in inorganic membranes versus their organic counterparts. Because they are generally focused on
either alpha alumina support structure, usually with titanium oxides or zirconium oxides, we are
talking about commercially available ceramic membranes. Now these membranes have
numerous positive qualities over organic membranes, such as increased fouling, temperature, pH
fluctuation resistance, a longer time on stream.
This allows inorganic membranes to deal more effectively with the base catalyst used in the
transesterification reactions endemic to the biodiesel production. Now these increased resistances
additionally lend to usefulness in a continuous process in which a FAME rich permeate flow is
separated from an unreacted retentate as transesterification occurs down the length of a
membrane bioreactor.
With a 0.05 micron ceramic membrane at 25 degrees centigrade, Saleh et al successfully met
ASTM standard for glycerol in the final biodiesel product. So, less than 0.02 weight percent - the
reference has been given here.
808

And this is the schematic representation of the ceramic membrane unit for biodiesel purification
process. So you can see that the crude acid alkyl esters - the biodiesel, it goes to the inorganic
membrane, then whatever is coming to the permeate side, that is nothing but the removal of the
glycerol, alcohol and other contaminants. Alcohol can be stored for further processing, you get
the recovered catalyst, you get purified glycerol for sale to other industries.
Please understand, again I am telling this is not a single unit, there are multiple units here but it
was shown to simplify the process. And from the inorganic membrane, you get the purified
biodiesel mostly in the retentate side and which can go for further drying and further processing
some polishing step before it is getting stored.
809

So, this table will give you a comparison of polymeric and different inorganic membranes. So, if
you talk about inorganic membranes, the advantages are - they having long term durability, you
can use them for many months and years. High thermal stability, they can withstand more than
200 degrees centigrade temperature which the polymeric membrane cannot. Chemical stability in
wide pH range they can handle; they can handle high structural integrity also.
Disadvantage is that they are very brittle. So, you have to be very careful otherwise it will break
very easily. It is expensive, that is one of the most or you can say the biggest disadvantage right
now and as some ceramic membranes have low hydrothermal stability. So, if you talk about
current status, so some small scale applications are already going on, and surface modifications
to improve hydrothermal stability is also being undertaken.
So, let us talk about polymeric membranes the advantages are that cheap or low cost. You can
produce them in mass larger scale productions. So, usually available in large quantities and they
have good quality control. However, the disadvantage is that they are structurally weak, not
stable, so we are talking about the mechanical stability. And temperature is also they cannot
withstand more than 100 - 120 degrees centigrade.
810

Prone to denature and be contaminated separation and they have a short lifespan; you have to
replace them frequently. The current status is that wide applications in aqueous phase and some
gaseous phase.
So, if you look at this particular table, here the advantages and disadvantages of the different
refining technologies which we have discussed till now. So, basically the three, one the first one
is the wet washing, then the dry washing and the membrane purification. Of course membrane
also a part of your dry washing you can say that because you are not using water. So, all the
advantages and disadvantages which we have already discussed have been given in a single
slide, so you can refer to it later on. So, we will go ahead.
811

So, now we will talk about the reaction based separation processes in biodiesel purification. In
the case of reversible reactions, the process yield is limited by the equilibrium. To overcome this
limitation a separation process that should be integrated with the reaction to separate the
substrate, that is basically product and keep it is concentration from the equilibrium
concentration. Hybrid reaction, membrane separation as for example, membrane bioreactor,
reactive distillation and adsorptive distillation are some of the common reaction based separation
methods.
So, let us talk about reactive distillation. The integration of chemical reaction and a product
separation that is the purification step in a single multifunctional process is known as the reactive
distillation. That means, in a single column you are doing the reaction as well as the separation.
So, this integration declines the chemical equilibrium limitations, avoids the potential necessity
of auxiliary solvent and increases the selectivity.
812

Therefore, reactive distillation has the potential to improve the efficiency of the process, while it
needs a lower capital investment, operation cost and energy consumption. However, this process
also has it is own operational challenges and economic limitations, especially in case of the gas
liquid reactions at severe operating conditions of very slow reactions. In fact, a large column is
required to provide a reasonable residence time in case of very slow reaction which compromises
the feasibility of the process. And again, it will increase the operational and fixed cost.
So, if you talk about applications Wang et al in a classical work reported that 10% saving in
energy consumption along with 50% higher productivity for methyl acetate hydrolysis using
reactive distillation compared with the conventional process using fixed bed reactor followed by
a distillation process. So, it is a significant work that reported 10% energy saving as well as 50%
higher productivity in a single unit where reaction as well as purification has been carried out.
813

Reactive distillation using acid catalyst has a potential to be used for biodiesel production or
pretreatment of feedstock with a very high free fatty acid content. Various designs have been
studied to maximize the reaction rate and biodiesel yield. It is noteworthy that the downstream
alcohol recovery step can be avoided in the case of biodiesel production using reactive
distillation.
So, let us talk about membrane bioreactors for biodiesel processing. In optimizing the inorganic
membrane for bioreactor technology three factors have thus far been studied. First is the amount
of catalyst, second is the appropriate residence time for the complete conversion and third is the
methanol to oil ratio. Baroutian et al in 2011 tested potassium hydroxide catalyst loadings up to
814

250 milligram per centimeter cube at temperatures of 50 and 70 degree centigrade in a packed
bed reactor system using activated carbon as the adsorbent.
So, for loading of 37.5 milligram per centimeter cube the conversion reached no higher than
89.3% at 70 degree centigrade - further increases to 143.75 milligrams per centimeter cube
yielded conversions up to 93.5% at same temperature 70 degree centigrade. Now beyond this the
conversion dropped slightly to a maximum of 91.5% at 250 milligram per centimeter cube and
70 degree centigrade due to soap formation. The reference has been listed down, it is a very good
work published in bioresource technology in 2011.
So, let us talk about biofuel properties. So, this particular table will give you the free fatty acid
composition of vegetable oils. I think we have discussed this when we discussed about vegetable
oils and all. But I have again added, so that you can understand while we are discussing about the
biodiesel purification, so the properties of the fuel, biodiesel as a fuel. So, you can see the fatty
acids different types of fatty acids are listed here, lauric, mysteric, palmitic, palmioleic, stearic,
oleic, linoleic all these things and this is the formula C by D ratio.
And this is the different sources - algae, soybean, sunflower, corn, cotton seed, canola, olive,
safflower, hazelnut and rapeseed. So, this is nothing to discuss here, so I leave it to you to refer it
815

later on when you go through the video, so you please see this and the reference has also been
given here.
In the next table the properties of the biodiesel from all vegetable oils are listed here. So, the
properties like the ester content, flash point, water and sediment, kinematic viscosity, density,
cetane number, CFPP, carbon residue, free glycerine, acid number, distillation temperature,
everything all the fuel properties. So, please have a close look here all different types of
feedstocks are been listed like algae, soybean, safflower, corn, cotton seed, all the vegetable oils.
So, you can understand that which particular feedstock has is having better fuel properties.
816

So, let us talk about the cetane number, it is one of the most important fuel property. The cetane
number which is an indicator of a diesel fuel self ignition quality, allows the fuel to be easily
ignited and burn quickly. It can be defined as the measure of knock tendency of a diesel fuel. The
cetane number is related to the ignition delay time which is the time interval between the start of
injection and the start of combustion.
As the cetane number increases the ignition delay decreases and the main combustion phase that
is the diffusion control combustion increases. Similar to low cetane number high cetane number
too is inconvenience as well. If the cetane number of diesel fuel is too high this fuel may ignite in
a short distance to a injector nozzle and causes excessive heating of the injector which is not at
all desirable.
817

As a result of the intense heating, cooked fuel properties inside the injector may plug the injector
nozzle. Because of this the cetane number of diesel fuel should not be higher than 65. The cetane
number of all biodiesel fuels are measured and their relation with the degree of unsaturation
levels of their feedstocks is depicted. So, this particular figure you can see how the cetane
number is changing with respect to the degree of unsaturation of the particular base oil.
Where it is olive oil, hazelnut oil, this red one is algae basically you can see the cetane number is
highest for the algal oil because of the very good amount of free fatty acids that is available with
the algal oil. The quality is actually good compared to other oils.
818

So, we will talk about cold filter plugging point CFPP. So, in the literature three main
characteristics are generally defined to characterize the cold flow properties of the fuel. First is
the cloud point, second is the pour point hence third is the cold filter plugging point CFPP. Cloud
point can be defined as the first temperature at which the cloud layer which is the indicator of the
onset of crystallization on the fuel surface is seen when the fuel is cooled.
The pour point can be expressed as the lowest temperature at which the fuel still maintains it is
fluidity. At temperatures lower than this value the fuel is no longer in a liquid state due to
excessive gelling. These two definitions are insufficient for automotive fuels, because the fuel
that can be pumped by the fuel pump (namely not yet reached to it is pour point) may plug the
fuel filter and therefore the vehicle may not start.
Because of this, the use of the CFPP value is more useful for determining the cold flow quality
of an automotive fuel. CFPP is the lowest temperature at which the fuel can pass through the fuel
filter without causing plugging problem. And in this sense, the CFPP of all the biodiesel fuels
were correlated with the parameter long chain saturated factor which is known as LCSF, which
was calculated taking into account the composition of the saturated fatty acids and lending more
weight to the composition of fatty acids with a long chain.
819

The correlation between CFPP values of produced biodiesel fuels and LCSF levels of the
vegetable oil feedstocks was depicted in figure 7, in the next figure I will show you. As can be
seen the biodiesel fuels with the lowest CFPP were from algae, corn and canola oil. As I just
mentioned you that biodiesel lipid content or the free fatty acid content is very good.
So, that is why you always get better fuel properties. So, you can see in the figure 7, the change
of the CFPP value of the biodiesel along with the LCSF; you can again see that here the CFPP
value is better for the sunflower oil and also for some other base oils.
So, the next one oxidation stability; oxidation stability is one of the most critical fuel properties
affecting the long term storage and uses of a biodiesel fuel. It indicates the fuel’s resistance to
auto oxidation. The temperature, the amount of oxygen and the material of the container where
the fuel is stored are the decisive parameters on the oxidation reactions.
820

The changes in oxidation stability of the produced biodiesel with the viscosity and acid numbers
are given in the figure, next figure here.
So, you can see from these 2 figures how the oxidative stability is changing with respect to the
acid number the below figure and the viscosity the top figure for the different oils. So, if you go
back we can see that, it is seen that the biodiesel fuels obtain from the safflower, olive and algae
had the highest oxidative stability. Again algae is supposed to be good in terms of oxidative
stability also.
821

In addition, it is seen that the viscosity and the acid number values of these biodiesels are higher
than those of the other fuels. In the figure 9, the change of oxidation stability of the produced
biodiesel with total unsaturation level - TUS of the feedstock can be seen. As illustrated in the
graphic, it is determined that oxidative stability exhibited an increase with the increase in the
TUS level.
So, this is in this figure you can see here, how the change of the oxidation stability is happening
with the TUS number for different types of vegetable oils even the algae. You can see that algae
it is good and followed by the hazelnut oil, the stability is better and even for the olive oil also.
822

So, with this I conclude today’s lecture. In case you have any query please register your query in
the swayam portal or you can drop a mail to me at kmohanty@iitg.ac.in, thank you very much.
823

Module 08
Lecture-22
Biooil and Biochar Production Reactors
Good morning students. This is lecture 1 under module 8. In this lecture, we will be
discussing about biooil and biochar production, then the factors affecting biooil and biochar
production and about the reactors. So, let us begin.
Biochar is mainly produced through thermochemical conversion processes, such as slow
pyrolysis, fast pyrolysis, torrefaction and gasification, under various process parameters.
These processes irreversibly change the physical state and chemical composition of biomass
into biochar in the absence or limitation of oxygen supply under specific temperatures and
pressures.
Biomass decomposition generally occurs during the primary decomposition to form solid
char at 200 to 400 degrees centigrade, which is responsible for the largest degradation of
biomass; the secondary reactions proceed to take place within the solid matrix with further
rising of the temperature. As you know that in our earlier class also we have discussed that
biooil and biochar are the 2 most valuable and important products of the thermochemical
conversion.
824

So, there are various types of processes that can be used or techniques that can be used
starting from gasification, pyrolysis, torrefaction, hydrothermal liquefaction, there are many
thermochemical conversion processes, which we have already discussed. Now, it has always
been seen that whenever you eye apply for a higher biooil production, then the process and
the reactor process parameters will be a little different than when you are eying the biochar as
the main product and that we are going to discuss today also.
If you look at biochar production from biomass using the thermochemical conversion
technologies - so, we can have 4 different classes of processes. The first let us begin with the
fast pyrolysis; so, this particular slide will make you understand that what are the process
conditions that is required to produce biochar and of course, even biooil also. So, in fast
pyrolysis the reaction conditions are little different. So, it is around 350 to 700 degrees
centigrade in the absence of air and target is actually biooil. So, fast pyrolysis is always used
to produce biooil. The biochar that you get, the quality is not so good. So, the byproducts are
biochar and combustibles.
So, then, slow pyrolysis. In slow pyrolysis, the reaction conditions are again 300 to 700
degrees centigrade, the temperature is almost more or less the same in the absence of air, but
the target product here is majorly the biochar. Apart from that, you may get some biooil and
combustible gases.
Now, the next is gasification. Here the reaction conditions are a little different. So, around
700 to 1200 degrees centigrade, partial air is there - we have discussed about gasification in
825

detail earlier. Here the target product is of course, syngas, byproduct is by biochar and tars.
Now, here the biochar whatever we are getting is okay, moderately quality is fine or
moderate we can say.
Then torrefaction, here the reaction conditions and temperatures are very less compared to
other processes around 200 to 300 degrees centigrade in the absence of air, but the major
product is biochar and we get no byproducts from this torrefaction process.
So, let us understand one by one all the processes. So, first is the slow pyrolysis. So, slow
pyrolysis is a process in which biomass undergoes decomposition at a relatively moderate
temperature 350 to 500 degrees centigrade, which provides the sufficient residence time for
biomass pyrolysis vapour and increases its secondary cracking level as much as possible.
“Slow” in the slow pyrolysis process indicates low heating rate and meanwhile, the optimum
char formation temperature region is also a crucial factor influencing the quality and yield of
biochar.
For instance, biochar obtained from the pyrolysis of wood at a higher temperature 750 to 900
degrees centigrade and long residence time greater than 30 minutes is claimed to be much
better char material to substitute for coal and coke in steelmaking. Higher pyrolysis
temperature is essential for improving the quality of biochar in slow pyrolysis processes since
more volatiles are removed from biochar increasing its carbon content.
826

Then gasification: Gasification usually takes place at 700 to 1000 degrees centigrade, in
which biomass undergoes an incomplete combustion with various gasifying agents, such as
air, pure oxygen or steam and oxygen to produce a gaseous product. The quality of biochar
produced from biomass gasification is closely related to its carbon content. It is mainly
affected by the gasified parameters which increase the equivalence ratio – ER, then feedstock
properties, gasifying agent and of course pressure.
Now among these parameters the equivalence ratio is regarded as the most important factor
that affects the gasification process. And the optimum value is usually 0.25 to 0.28 according
to the physicochemical properties of the biomass. Generally, it has been seen that when you
increase the ER, that leads to an increase in the gasification temperature, which affects the
quality of the biochar that is produced.
827

So, in a significant work Yao et al reported that char yield decreased from 0.22 to 0.14
kilogram per kilogram of biomass with increasing ER from 0.1 to 0.6. Meanwhile, carbon
content of the produced biochar slightly decreased from 88.17% to 71.16%. So, it indicates
that higher ER value needs more oxygen that is required to be fed into the gasifier, which
results in both positive and negative impacts for the quality of the biochar.
On one hand, it strengthens the heterogeneous reactions to convert more carbon from the
solid phase into the gaseous species, facilitating the formation of the micropores and further
increasing the specific surface area of the biochar. On the other hand, more oxygen molecules
in the gasification process may cause the strong ablation of biochar reducing its mechanical
strength and yield as well as increasing its ash content.
828

Let us now understand about torrefaction. So, in a typical torrefaction process, biomass
feedstock is heated directly and/or indirectly to temperatures between 200 to 300 degrees
centigrade in an inert atmosphere at a low heating rate - lower than 50 degrees centigrade per
minute - and a relatively long residence time 20 to 120 minute. The production of the dark
brown solid fuel containing 90% of the initial energy content is the target product of this
process, which is known as the torrefied biochar, and an energy densification of about 1.3 can
be achieved. Now, in order to obtain high energy density of the torrefied biochar, high
torrefaction temperature and long residence time are essential in the torrefaction process,
which result in the reduction of the quality and energy yield of the torrefied biochar. If you
understand, then the main product of torrefaction is biochar. So, it does not produce any other
byproducts. Of course, it will result in some gas, which is of no use or no commercial
application.
829

So, according to Niu et al the optimum torrefaction condition of biomass may be to maintain
the solid yield in the range of 60 to 80%, in order to obtain relatively high higher heating
value and mass energy density of the biochar and the energy yield. So, another important
thing is that biomass physicochemical properties such as moisture content, higher heating
value, ash content. So, these properties significantly affect the quality of the torrefied biochar.
Among these, moisture content should be the most crucial, because due to that, it actually
determines the energy that is required to carry out or even initiate the torrefaction process.
So, more the moisture content, the more amount of energy will be required to carry out the
torrefaction process. The yield of the biochar from hemicellulose torrefaction is the lowest
among the 3 major components.
The 3 major components mean hemicellulose, lignin and cellulose. So, with the increase in
the torrefaction temperature and residence time, the content of hemicellulose and cellulose
decreased in the torrefied biochar while the content of lignin increased correspondingly.
830

So, you can see these are the biochars from different biomass sources, these are just
representative to make you understand how they look like actually. So, these are 4 different
types of biomasses. Hardwood, rice hulls, switchgrass and bagasse and they are
corresponding biochar. And this is the mechanism of the primary and secondary pyrolysis of
biomass, the pyrolysis reaction.
So, you can see that when there is a dry fuel. So, whatever you actually are taking as the
feedstock, whether it is lignocellulosic biomass or say any such material, so, you need to dry
it to remove its moisture content to certain level otherwise you cannot put it in the pyrolyser
or pyrolysis reactor. Here whatever is happening after the drying basically the primary
pyrolysis here fragmentation and sinkage is happening.
So, you can see that water, tar and permanent gas and char like this are getting generated
during the primary pyrolysis reactions, then when it goes to again further higher temperature
and you move towards secondary pyrolysis reactions. So, you get again water, tar, permanent
gas and char consisting of different molecules and there are different stages.
And again, it is very important to note that pyrolysis is very complex. There are so many
reactions primary and secondary, which are being simultaneously happening and it is very
difficult to predict exact mechanism. But having said that, people have already studied
pyrolysis reaction mechanism in detail and they have also told that there are various reactions
which are simultaneously happening including the reforming, dehydration, cracking,
oxidation, water gas shift, gasification and polymerization.
831

So, now let us understand the factors that affect the biochar chemical properties, we will be
talking about biochar properties, 2 different types of properties, first is the chemical
properties and second is the physical property. So, let us start with the chemical properties.
Atomic ratio: So, the process of carbonization involves changes in the chemical structure of
the fuel mostly by detachment of functional groups. The release of these hydrogen and
oxygen containing groups results in a decrease in the respective ratios with carbon.
There is something called Van-Krevelen diagram. So, you can read more about this - the
references given here below. So, Van-Krevelen diagram presented by Dirk van Krevelen in
1950 can be used to show the evolution of the 3 main fuel components that is carbon, oxygen
and hydrogen during carbonization.
A variation of only about 100 degrees centigrade may decrease the oxygen carbon ratio from
0.7 to 0.3, but it takes another 700 degrees centigrade to achieve a further reduction from 0.3
to almost 0. Now, it should be noted that the temperature range of 250 to 350 degrees
centigrade leads to the highest decrease in atomic ratios. The further release of almost all
hydrogen from the char requires very high treatment temperatures.
832

So, this is a classical Van-Krevelen diagram for the natural carbonization process. You can
see that it is plotted between O by C ratio mol by mol and H by C ratio, again mol by mol.
So, hydrogen to carbon ratio and oxygen to carbon ratio. Now, you can see that it lies from
anthracite coal and then this is another type of coal, then we have lignite here, we have peat
overlapping.
Then you can see that green one is the biomass. And from there the last one is the cellulose;
here the lignin degradation will happen. So, from here we can get an understanding about
what are the different temperatures also that is required and what is the O by C and H by C
ratio that will give us an insight about the various reaction mechanisms also.
833

So, next is elemental composition. So, one main goal of biochar production is the change in
chemical composition compared to that of raw biomass, most of all the increase in the carbon
content. Now, this is due to the detachment of functional groups containing oxygen and
hydrogen. Therefore, an increase in reaction temperature leads to an increase in the carbon
content while resulting in a lower content of hydrogen and oxygen.
The carbon content of untreated woods is typically slightly above 50% and the oxygen
content is just over 40% that is basically by weight, dry ash free basis. The most significant
changes during biochar production occur in the temperature range of 200 to 400 degrees
centigrade. At higher temperatures both approximate asymptomatically the extreme values
that is 100% carbon and 0% of oxygen.
High temperature biochars may each carbon contents of more than 95% and oxygen content
of less than 5%. The hydrogen content of wood varies between 5% to 7% and is decreased
during pyrolysis to less than 2%. So, when you go beyond or almost touching about 700
degrees centigrade or even below 1% for very high treatment temperatures more than 700 to
800 degrees centigrade.
However, the values are much more scattered and large differences can be seen for chars
produced at the same temperature. Again please note that whatever we are talking about,
these are generalized statements and process parameters and result will vary depending upon
what is the feedstock and feedstock composition - it is better to say that feedstock
composition. So, the carbon content of the untreated straw and grass is typically just below
834

50%. The oxygen content is in the range of 40 to 45%, a little more than the woody biomass.
Carbonization can increase the carbon content to around 90% and reduce almost the entire
amount of oxygen and hydrogen.
At short residence times of a few minutes, even relatively high temperatures might be
insufficient to achieve complete conversion. In this time range, the influence of the residence
time is important. However, the typical production conditions of biochar especially in a
commercial scale involves slow heating rates and residence times of many minutes,
sometimes hours and even days also.
Because the main aim is to produce as much as amount of biochar having excellent or let us
say having the highest carbon content. Now, for these conditions, the influence of the
residence time on the elemental composition is small. At moderate temperatures, even a
significant increase in residence time, you can say from 60 to 180 minute results only in a
decrease in carbon content of few percent. So, there is hardly any effect of the residence time.
So, as the biochar will never be utilized in its, ash free from but as an entity with the
inorganics, it seems more reasonable to give the composition based on the total matter instead
of the dry or ash free matter.
835

So, the next is energy content. So, as a result of the higher carbon content in the biochar the
energy content increases with temperature. The most significant increase in energy content
takes place at temperatures between 250 to 350 degrees centigrade, within this range of only
100 degrees centigrade, the heating value is raised from less than 20 mega joules per kg to a
value of 25 to 30 mega joules per kg.
So, beyond 400 degrees centigrade, the change in energy content is not significant.
Prolonging the residence time also has a positive impact on the heating value, leading to a
further increase. However, the effect is rather small compared to that of the temperature. In
the torrefaction range, prolonging the residence time from 1 to 2 or even 3 hours increases the
heating value by only a few mega joules per kg.
836

So, next is fixed carbon and volatile matter. The carbon content that remains in the solid
structure after the volatile components are driven off is referred to as the fixed carbon. Some
biochar applications, especially metallurgical require very high fixed carbon contents of
almost more than 90% or even 95% in order to substitute for the fossil carbon carriers. The
fixed carbon content of raw biomass is in the range of 10 to 30% and undergoes no
significant change before the torrefaction range. So, which is actually 200 to 300 degrees
centigrade in that range. So, between 250 to 350 degrees centigrade, the amount of fixed
carbon is increased to about 50 to 60%. It is again on ash free basis. Now, even though the
small temperature range shows to have the most effect on the fixed carbon content, fixed
carbon content of more than 90% required temperatures of approximately 700 degrees
centigrade.
The increase in the fixed carbon content is a direct result of the devolatilization process and
hence, decrease in the amount of volatile matter. So, when you are heating it with a higher
temperature basically more than 400, 500 close to 700 degrees centigrade, almost all the
volatile matters will escape. That is why the process is called devolatilization, resulting in
higher amount of fixed carbon.
Then we will talk about functionality. So, the main process during carbonization is the
thermal decomposition of the biomass structure, resulting in the detachment of functional
groups and the release of oxygen and hydrogen. As a result, biochars with low hydrogen to
carbon ratios, so that corresponds to a higher degree of carbonation contain less functional
groups and more aromatic structures then low temperature chars.
837

Aromatic structures have a high thermodynamic stability and are therefore important for
some applications such as soil amendment or metallurgical purposes, where long term
stability of the biochar is required. So, the aromaticity of biochar increases rapidly between
200 to 500 degrees centigrade, the most significant changes are observed in the temperature
range of torrefaction. That is again, if you recall 200 to 300 or 350 degrees centigrade
maximum.
The maximum is reached between 500 to 800 degrees centigrade. So, in this temperature
range, the entire carbon of some biochars may be bound in the aromatic structures. The type
and the amount of functional groups influence the biochar’s alkalinity, the ability to
neutralize acids in the soils. The partial detachment of functional groups leads to unpaired
negative charges and hence the ability to accept protons.
These functional groups include for example, carboxyl and hydroxyl groups. Several
categories of alkalinity can be distinguished like surface organic functional groups, soluble
organic compounds, carbonate and other inorganic alkalis. An increase in the treatment
temperature also leads to an increase in the alkalinity.
838

So, next we will talk about ash content and the composition. Many parameters for example,
elemental composition or fixed carbon content are typically given on a dry and ash free basis.
The water is completely driven off during pyrolysis. The ash however, largely remains in the
solid product. It is important to know the ash content of the biochar, because the amount and
type of inorganics can determine possible applications.
A high ash content may also inhibit the use in high grade industrial applications. The increase
in ash content may intensify ash related problems during the thermochemical conversion of
biomass. The ash content of biochar is largely dependent on the ash content in the parent
biomass. This varies greatly depending on the type of biomass and also on the harvesting
techniques also.
839

Biomass contents noteworthy amounts of alkali and alkaline earth metals. It is called AAEM,
significantly more than other fuels. So, these are mostly sodium, potassium, calcium and
magnesium. A comprehensive review of the composition of biomass presented by Vassilev et
al, - the reference is given below - shows that the main components (given as oxides) of
biomass ash are silicon dioxide, calcium oxide and potassium oxide.
And other noteworthy amounts include this one P2O5 - especially in the animal residues it is
present - and then Al2O3 - which is alumina and magnesium oxide. A number of studies have
also shown that AAEM are partly released into the gas phase during the thermochemical
conversion. The release is both as a result of the decomposition of cellulose, hemicellulose
and lignin as well as the interaction between the volatiles and the char and can be observed
over the entire temperature range of pyrolysis.
However, the dominating release occurs during the 2 temperature ranges either below 500
degrees centigrade or at higher temperatures above 800 degrees centigrade. Here I want to
tell something, you can see the interaction between volatiles and the char. Now, when the
process begins initially at lower temperature, so, the dehydration is happening. So, the
moisture whatever is left is getting out then devolatilization started.
Now, at the same time the char formation is happening. Now, when the volatile components
are getting escaped and still inside the reactor and the char which is getting produced, they
are interacting with each other. Now, this leads to some secondary and tertiary types of
different reactions and thereby resulting in different products, it can be tar, it can be smaller
molecular weight compounds and it may also result in fractions of different types of biooil.
Now, this cannot be stopped, because it is inherently happening inside the reactor which you
cannot control. Because you are heating something inside a closed environment in a
controlled atmosphere. And whatever is getting produced that gas is again reacting with the
feed what is getting converted or getting either gasified or getting either torrefied or getting
either pyrolyzed.
840

So, now we will talk about the physical properties, factors affecting the biochar physical
properties. The first and foremost important are density and porosity. So, if you recall, we
have talked about density of biomass, how it is going to happen, how it is going to affect the
transportation, storage and other things. Now we will talk about the biochar properties. So,
the density of any bulk material is an important property for the design and operation of all
handling and processing facilities, the storage, transportation, all these things.
While the weight-based energy density of biochar increases with the treatment temperature,
the bulk density shows the opposite trend. As the gases devolatilize from the solid biomass
structure, during pyrolysis, they leave a porous char behind, the higher the porosity the lighter
the char per unit volume becomes. The density can be distinguished either as bulk density,
envelope density or particle density.
While all densities bear some information about structural changes of the biomass during
carbonization. The bulk density is the most important design parameter for shipping and
handling, where planning might be based on volume rather than on (or in addition to) weight
basically.
841

The most significant reduction in bulk density is achieved by drying, which may be a separate
step or an integral part of pyrolysis, reducing the bulk density of green wood from about 700
kilogram per meter cube to roughly 400 kilogram per meter cube. A subsequent carbonization
process at temperatures above 300 degrees centigrade reduced the bulk density further to 300
to 330 kilograms per meter cube.
However, a strong temperature correlation cannot be seen in this example. Generally, the
higher the bulk density of the parent biomass is, the higher the bulk density of the produced
char. The carbonization process leads to a slight decrease in the particle density with
increasing temperature. The true density which considers the solid structure only,
disregarding of all the pores increases with increasing the degree of carbonation.
842

So, the next one of the most important parameter of the biochar is the surface area. The
porosity changes as a result of the escaping volatile gases during the carbonization process
and so does that total surface area of the biomass. A large surface area is connected to a
number of other biochar properties, as for example, cation exchange capacity or water
holding capacity and therefore prerequisite for a number of biochar applications.
While a large surface area is characteristic of biochars from pyrolysis, the residues of
hydrothermal carbonization have a very low surface area. The surface area is usually
determined by BET analysis. An increase in residence time leads to a further increase in
surface area, but even a very long residence time of many hours is less efficient in raising the
surface area compared to an increase in temperature.
For most biomasses, a surface area of several 100 meters square per gram can be achieved
under suitable carbonization conditions. For sewage sludge however, the surface area
seemingly remains below 100 meters square per gram regardless of the paralysis conditions.
After an initial increase, the surface area of biochars may decrease again at high
temperatures. Whether this trend is solely due to the heating rate, or also due to the residence
time at higher temperatures, which is an inevitable result of the heating rate, actually, it is not
so clear. The decrease in surface area at high temperatures is likely the result of a shrinking
solid matrix.
843

So, now we will discuss about the various reactors that is required for the biochar production.
So, under slow pyrolysis, biochar yield between 25 to 35% can be reproducibly produced.
During slow pyrolysis the residence time of the feedstock is longer and the temperature are
lower than 700 degrees centigrade. This allows all the volatile components to escape leaving
a chary solid behind.
A pyrolytic gasification is an example of indirectly heated process which utilizes an external
vessel to burn portion of the fuel and uses the heat to pyrolyze the biomass producing
medium energy gas with significant fraction of tars. If you recall, we have discussed this
during our gasification discussion. So, such a design has a great prospect for modification to
produce biochar, because the movement of the ignition front leaves the char behind.
Autothermal reactors provide the necessary heat of reaction by means of partial oxidation of
the biomass within the reactor. The heat produced is sufficient to drive the endothermic
reactions within the reactor to produce biochar, biooil and syngas.
844

So, this is a typical schematic representation of the biomass gas stove. So, air is generally
employed as the oxidation agent. The yield largely depends on the reactor design, operating
conditions and physicochemical properties of the biomass. So, such designs include one of
the most significant design which was being used by many - is called top-lit updraft gasifier
(TLUG) and natural draft.
So, TLUG is a “tar burning, char making” gasifier which has the advantage that tar is much
lower due to the flaming pyrolysis of the biomass and the gases then passing through a layer
of the charcoal on the top. So, you can see that you are passing basically the air here, the
forced air, here primary air is getting inside your reactor. So, here the combustion is
happening. So, the bed of charcoal is present here.
And then secondary air is there and it is a very simple design. So, TLUG are easily adaptable
and can be used for small scale char production, because of their ease of operation simple
technology with ease of fabrication, as well as the ability to generate a substantial char yield.
845

So, Auger pyrolysis reactors are getting increased attention from many small and midsize
industries. In an auger reactor, biomass is continuously fed to a single or twin-screw and then
the auger rotation moves the product along the axis until the end of the heating zone.
So I will show you this image, this is the hopper; it is a feed storage we can say. From here,
through a screw conveyor type of belt rotating system which is rotating. So, it is the feeding
system. It is coming to the reactor. So, this is a single auger reactor. Here also you can see
some sort of screw and belt rotation system that is rotating. And the rotation speed also plays
a very vital role in determining - the residence time - how much time the feed is spending
inside the reactor is all determined by this rotation speed.
846

Then, you get the solid fraction here, all the volatiles can be condensed and gaseous fraction
can be collected if it is useful, otherwise other condensable parts can be condensed if
required. So, as the biomass decomposes, gases and organic volatiles leave the reactor and
the biochar is collected at the bottom. Auger pyrolysis reactors are simple to operate, require
little or no carrier gas and consume little energy.
Moreover, one advantage of auger reactor is that, the residence time of biomass in the heated
zone can be controlled easily by varying the rotation speed; this is what I just told you - speed
of the screw or the flight pitch. Vapour residence time is much longer in auger reactors than
in the fluidized bed reactors and hence increases the likelihood of the secondary reactions and
consequently increases the yield of the char to the detriment of the yield of biooil. So, yes,
this we have already discussed.
And now we will discuss about biooil. So, till now we have just discussed about the biochar.
We will now focus our discussion on biooil which is another significant product of interest
especially from the pyrolysis. So, fast pyrolysis is a high temperature process in which
biomass is rapidly heated in absence of oxygen. As a result, it decomposes to generate mostly
vapours and aerosols and some charcoal.
Liquid production requires very low vapour residence time to minimize secondary reactions
of typically one second, although acceptable yields can be obtained at residence times up to 5
second, if the vapour temperature is kept below 400 degrees centigrade. After cooling and
847

condensation, a dark brown mobile liquid is formed which has a heating below about half of
that of the conventional fuel oil.
Both residence time and temperature control is important to freeze the intermediates of most
chemical interest in conjunction with moderate gas/vapour phase temperatures of 400 to 500
degrees centigrade before recovery of the product to maximize organic liquid yields.
So, this is the typical graphical abstract of the pyrolysis of the biomass. So, the biomass. so
you talk about the particular size, moisture, composition, these things we have discussed
already and then it goes to the pyrolysis reactor, you can have different types of pyrolysis
reactors, we have already discussed about that. So, the feed rate, reaction time, gases flow
rate, temperature, heating rate, all this will affect the quality of the biochar or biooil that you
are going to produce.
So, you get a char here. Then all the volatile components go to a condenser, whatever
condensable will be condensed as a liquid phase, which you get as biooil and whatever non-
condensable - It will be left off. Now, it also contains some of the important gaseous
components. If required, it can be also captured and converted to value added fuel.
So, whatever biooil you get here, there are many things that you need to do - we will discuss
about the fuel properties, calorific value, viscosity, water content, all these things are very
important features of the biooil. Now, whatever biooil you get here are usually containing a
848

huge amount of the aqueous phase. So, if you leave it under the density separation, it will be
separated into 2 distinct phases.
One phase is your organic rich phase - the heavier part, which is actually the oil part and the
another part is the more aqueous part the lighter part, but please remember in one class I have
already told you again I am repeating that even that lighter part also contains so many
valuable chemicals. Now, again what type of chemicals that depend upon the what type of
biomass we are using.
And some of the chemicals, some are rare - we have also done some work in this thing. And
there are various interesting works already reported in literature you can see. Depending upon
that biomass we get very different types of platform chemicals and some chemicals are of
very high value like D-glucose and all. So, those can be purified even if it is in small
quantity, you are producing in a large quantity biooil then you can do some downstream
processing, purify it. And it can be used as different value added products.
So, we will talk about the essential features of a fast pyrolysis process, towards biooil
production as you understand that for biooil production, the most important pyrolysis is the
fast pyrolysis process. So, very high heating and heat transfer rates, which usually requires
finely ground biomass feed; carefully control pyrolysis reaction temperature about 500
degrees centigrade in the vapour phase, with short vapour residence times of typically less
than 2 second; rapid cooling of the pyrolysis vapours to give the biooil products.
849

So, all these are very important. The main product biooil is a miscible mixture of polar
organics, this is what exactly I was mentioning just one slide before, it is about 75 to 80% by
weight and rest is water requires about 20 to 25%. So, very short residence times results in
complete depolymerization of the lignin due to random bond cleavage and the interaction of
the lignin macromolecules resulting in a less homogeneous liquid product. While longer
residence times can cause secondary cracking of the primary products, reducing yield and
adversely affecting biooil properties.
As fast pyrolysis for liquids occurs in a few seconds are less, heat and mass transfer processes
and phase transition phenomena as well as chemical reaction kinetics play important roles.
The critical issue is to bring the reacting biomass particles to the optimum process parameter
and minimize their exposure to the lower temperatures that favor formation of charcoal.
Another possibility is to transfer heat very fast only to the particule surface that contacts the
heat source, which is used in ablative processes. Fast pyrolysis process includes drying the
feed to typically less than 10% water in order to minimize the water in the product liquid oil,
grinding the feed to give sufficiently small particles to ensure rapid reaction, then fast
pyrolysis, rapid and efficient separation of solids - that is also very important part (basically
solid means char here) and rapid quenching and collection of the liquid product (often
referred to as the biooil).
850

So, this particular plot or graph will make you understand about the broad spectrum of
different types of pyrolysis products. So, you can see here we have compared this fast,
intermediate, slow carbonization, gasification and slow torrefaction. So, let us see the fast
paralysis here. In the fast pyrolysis the amount of the gas is very low - you can see this is the
black one – gas, followed by the char.
The second portion here is the char, then this is your water and whatever the rest all left out
till the 100% is all your organic compounds. So, you can understand that we are getting more
amount of biooil in the fast pyrolysis - it is quite clear. So, if you compare to intermediate,
slow and all these things, you can see that the gaseous components are increasing in the
gasification of course, the product is syngas. So, that is why the gaseous component is
highest. And in the slow torrefaction, you can see that the char, there is no organics and water
phase, it is either little gas phase here and the rest everything is char. So, in all cases, a
commercial process comprises 3 main stages from the feed reception to the delivery of one or
more of the useful products. So, these are the different steps or we can say stages.
The first one is the feed reception, storage handling, preparation and pre-treatment. The
second is the conversion of solid biomass by fast pyrolysis to a more usable form of energy in
liquid form, which is known as biooil and the third is the conversion of this primary liquid
product by processing, refining or cleanup (or we many times call as upgradation) to a
marketable end product such as electricity, heat, biofuels and/or different platform chemicals.
851

Now, we will talk about the heat transport. So, there are 2 important requirements for heat
transfer in a pyrolysis reactor. The first is that transfer of heat to the reactor heat transfer
medium. So, it is solid reactor wall in ablative reactors, gas and solid in the fluid and
transport bed reactors and gas in the entrained flow reactors. And the second is, from the heat
transfer medium to the pyrolysing biomass.
Now, the important feature of the ablative heat transfer is that, the contact of the biomass and
the hot solid abrades the product char of the particle exposing fresh biomass for reaction.
Now, this is actually not good. So, attrition of the char from the pyrolysing particle can also
occur in both fluid and circulating fluid beds due to the contact of the biomass with in-bed
solids where the solid mixing occurs.
The important feature of the ablative heat transfer is that the contact of the biomass and the
hot solid abrades the product char of the particle exposing fresh biomass for reaction.
852

Char removal is an essential requirement for the larger particles especially if it is greater than
2 mm to avoid the slow pyrolysis reactions. Now, the low thermal conductivity of biomass
gives low heating rates through larger particles which lead to increased char formation and
the hot char is known as the catalytically active char. Since the thermal conductivity of
biomass is very poor, reliance on gas-solid heat transfer means that biomass particles have to
be very small to fuel the requirements of rapid heating to achieve high liquid yields.
It is recommended that the water in the feed should be discounted in the final pyrolysis
products with only the water of pyrolysis being quoted, because that is what is getting
produced during pyrolysis, the biomass is not having that water content. So, that is known as
water of pyrolysis. And the product yields expressed on a dry feed basis. As a rule of thumb,
the water of pyrolysis is typically 12 weight percent of the dry feed.
853

So, the next is heat supply. The high heat transfer rate that is necessary to heat the particles
sufficiently quickly imposes a major design requirement on achieving the high heat fluxes
required to match the high heating rates and endothermic pyrolysis reactions. The 2 dominant
modes of heat transport in the fast pyrolysis technologies are conductive and convective.
Other possibilities to achieve the pyrolysis temperature and heat transfer rates necessary have
included vapour condensation such as sodium, induction heating of the reactor wall and the
use of the contact electrical heaters.
In a circulating fluid bed the majority of the heat transfer will be from the hot circulating
sand, typically at a sand to biomass ratio of 20 which therefore requires an efficient sand
reheating system.
854

Next is feed preparation. The cost of size reduction in financial and energy terms is clear
qualitatively but data is not available to define such a penalty associated with the small
particle sizes demanded of fluid bed and circulating fluid bed system. Drying is usually
required to less than 10 weight percent water unless a naturally dry material such as straw is
available.
As moisture is generated in fast pyrolysis, biooil always contains at least about 15% water at
an assumed product yield of around 60 weight % organics and 11 weight % reaction water.
This water cannot be removed by conventional methods such as distillation. Now, selective
condensation may reduce the water content of one or more fractions, but at the expense of
operating problems and a possible loss of low molecular weight volatile components.
855

Then temperature of reaction. Now it is necessary to understand that there is a distinction
between the temperature of reaction and the reactor temperature. The latter that is the reactor
temperature is much, much higher due to the need for the temperature gradient to do the heat
transfer. For fast paralysis the lower limit on wood decomposition is approximately 435
degree centigrade for obtaining acceptable liquid yields of at least 50% with low reaction
time.
Again that particular temperature which is mentioned here may vary slightly this side or that
side depending upon the type of biomass. The effect of temperature is well understood in
terms of total product yield with the maximum typically about 500 to 520 degree centigrade
for most forms of woody biomass. The other crops may have a maximum at different
temperatures.
But as I have mentioned you again I am telling you that it is not so significant difference
maybe 25, 30 degrees or something like that sometimes may be 50 not more than that. At
prolonged residence times (>1 second) the lignin derived fraction may be further
depolymerised to produce more homogenous liquid. This is also influenced by the reactor
configuration.
856

The next is vapour residence time, one of the most important parameter. The effect of vapour
residence time on organic liquid yield is relatively well understood, although the interaction
of temperature and residence time is less understood. It is believed that at temperatures below
400 degree centigrade secondary condensation reactions occur and the average molecular
weight of the liquid product decreases.
Boroson et al have demonstrated that average molecular weight decreases with degree of
secondary reaction that is basically increasing the residence time and temperature. The
reference is given below. There is no definition of product quality in terms of physical or
chemical properties or composition and this area needs further or need to be addressed as
more applications are tested and alternative supplies of bio fuel oil become available.
857

Then the next one is how do you collect the liquid basically? The pyrolysis vapours have
similar properties to cigarette smoke and capture by almost all collection devices is very
inefficient. The product vapours are not true vapours but rather the mist or fume and typically
present in an inert gas at relatively low concentrations which increases the cooling and
condensation problem. They can be characterized as a combination of true vapours, micron
size droplets and polar molecules bonded with water vapour molecules.
It is a complex mixture basically. Now this contributes to the collection problem as the
aerosols need to be impinged onto a surface to permit collection, even after cooling to below
the dew point temperature.
858

Electrostatic precipitators are effective and are now used by many researchers, but can create
problems from the polar nature of the product and arcing of the liquid as they flow, causing
the electrostatic precipitator to short out. Larger scale processing usually employs some type
of quenching or contact with cooled liquid product which is effective. The rate of cooling
appears to be very important.
Now slow cooling leads to preferential collection of the lignin derived components which
results in a viscous liquid and it can also lead to the blockage of the heat exchange equipment
and liquid fractionation. Very rapid cooling of the product has been suggested to be effective
as occurs typically in a direct contact quench. Transfer lines from the reactor to the cyclones
to the liquid collection system should be maintained at more than or greater than 400 degree
centigrade to minimise the liquid deposition and collection.
Then the next one is the char separation. Now some char is inevitably carried over from the
cyclones and collects in the liquid. Subsequent separation has proved difficult, because they
are very fine and it is very difficult to separate them from a very high viscous liquid. So,
liquid filtration has also proved difficult as the liquid can have a gel like consistency
apparently due to some interaction of lignin derived fraction with the char.
Now this aspect of char reduction and/or removal will be increasingly important as more
demanding applications are introduced which require lowered char tolerances in terms of
particle size and total quantity. Possible solutions include changing process conditions to
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reduce the nature of the pyrolytic lignin, increasing the degree of the depolymerization of the
lignin derived fraction of the liquid or adding chemicals to the liquid.
For example, to improve the handling properties or reduce the char lignin interaction, some
sort of additives - chemical additives.
So, now we will talk about the reactors for biooil production. So, this is one classical
circulating fluidized bed. You can see that it is a simplified schematic representation. So,
circulating fluid bed and transport bed reactor systems have many of the features of bubbling
bed except that the residence time of the char is almost the same as for vapours and gas.
And the char is more attrited due to the higher gas velocities. So, you can see that biomass
that is dried and made into the desired particle size is being fed through some Hopper
mechanism to the pyrolyser. So, this is the pyrolyzer. Then whatever the gas that is coming -
the volatiles, the vapours, that is passing through the cyclones either 1 cyclone, 2 cyclone, or
multiple cyclones and it will remove the sand and char.
Then this sand, then it goes to another system or it is another cyclone where the hot sand will
be recycled back to the pyrolyzer and the ash will be collected here. And the vapours that is
coming will go to a quenching facility or we can say that a condensing facility where the oil
will be basically separated and some of the gas whatever is left out it can be taken out or can
be recycled back to the system depending upon what it contains basically.
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So, heat supply is usually from recirculation of the heated sand from a secondary char
combustor which can be either a bubbling a circulating fluid bed. Now in this respect, the
process is similar to a twin fluid bed gasifier except that the reactor temperature is much
lower and the closely integrated char combustion in a secondary reactor requires careful
control to ensure that the temperature, heat flux and solid flow match the process and feed
requirements.
Heat transfer is a mixture of conduction and convection in the riser. All the char is burned in
the secondary reactor to reheat the circulating sand. This is you can say that the secondary
reactor - the combustor - to reheat the char and all the char is burned in the secondary reactor
to reheat the circulating sand, so there is no char available for export unless an alternative
heating source is used. If separated, the char would be a fine powder, but this fine powder
biochar is of no much commercial value. However, it can be used for some processes like soil
amendments and all.
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So, this is another reactor which is also been widely adapted. It is called a rotating cone
reactor. So, the rotating cone reactor - it was invented by the University of Twente and
developed by the BTG group, is a relatively recent development and effectively operates as a
transported bed reactor but with transport effected by the centrifugal forces in a rotating cone
rather than gas. So, this is the cone - will explain.
So, how it happens? So, some of the key features. So, the centrifugation drives hot sand and
biomass up a rotating heated cone; vapours are collected and processed conveniently. So, this
is a cone you can see that this is a cone is rotating basically. So, here saw dust (this is written
sawdust, but it can be any biomass) and sand is being fed to the cone, now it is rotating and
here the temperature is maintained.
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So, the pyrolysis gases and vapours are escaping from here. This is the large view. This is the
reactor. Then the sand and char can be collected and recycled back. The vapours goes to a
condenser where the uncondensable gas will be left out and whatever you get is the biooil
storage. Anyway you get aqueous fraction mixed with that and you need to do further
processing of that.
The char and sand drop into the fluid bed surrounding the cone, whence they are lifted to a
separate fluid bed combustor where char is burned to heat the sand which is then dropped
back into the rotating cone. So, basically we are talking about this one. So, where the char
and sand are getting separated and the sand is again re-circulated back. Char is burned in a
secondary bubbling fluid bed combustor. The hot sand is re-circulated to the pyrolyzer;
carrier gas requirements in the pyrolysis reactor are much less than for the fluid bed and
transported bed systems.
However, gas is needed for the char to burn off and the sand transport. Liquid yields of about
60 to 70% on dry feed are typically obtained in this type of a rotating corn bed pyrolysis.
So, then we will talk about ablative reactor. Ablative pyrolysis is substantially different in
concept compared to other methods of fast pyrolysis. In all the other methods the rate of
reaction is limited by the rate of heat transfer through the biomass particles which is why
small particles are required. In fast pyrolysis, slow pyrolysis whatever you talk about. So, the
mode of reaction ablative pyrolysis is like melting butter in the frying pan.
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So, the rate of melting can be significantly enhanced by pressing the butter down and moving
it over or spreading it over the heated pan surface. So, similar things happen actually. So, in
ablative pyrolysis heat is transferred from the hot reactor wall to melt wood that is in contact
with it under pressure. As the wood is moved away the molten layer then vaporizers to a
product very similar to that derived from the fluid bed system. The pyrolysis front thus moves
uni-directionally through the biomass particle.
As the wood is mechanically moved away the residual oil film both provides lubrication for
successive biomass particles and also rapidly evaporates to give pyrolysis vapour for
collection in the same way as other processes.
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So, you can have a look here, this is how the ablative reactor looks like. So, you can see this
is the reactor heating zone, this actually moves like this. So, from here starting to the end. So
the entire reaction or the heat transfer zone is moving along with the wood particles. So, the
vapors will be collected here and it will be further condensed to get the biooil and the char
will be taken out from that side.
There is an element of cracking on the hot surface from the char that is also deposited. The
rate of reaction is strongly influenced by the pressure of the wood onto the heated surface; the
relative velocity of the wood and the heat exchange surface; and the reactor surface
temperature. As reaction rates are not limited by heat transfer through the biomass particles,
larger particles can be used and in principle there is no upper limit to the size that can be
processed. The process, in fact, is limited by the rate of heat supplied to the reactor rather
than the rate of heat absorption by the pyrolysing biomass as in other reactors.
There is no requirement for inert gas so the processing equipment is smaller and the reaction
system is thus more intensive. In addition, the absence of fluidising gas substantially
increases the partial pressure of the condensable vapour leading to more efficient collection
and smaller equipment. However, the process is surface area controlled so scaling is less
effective and the reactor is mechanically driven and is thus more complex.
The char is a fine powder which can be separated by cyclones and hot vapour filters as for the
fluid bed reaction system. Aston University has developed an ablative plate reactor - which I
just showed you - in which pressure and motion is derived mechanically obviating the need
865

for a carrier gas. Liquid yields of 70 to 75 weight percent on dry-feed basis are typically
obtained. So, this we have already discussed.
So, with this I conclude today's lecture and in our next class we will discuss about the fuel
property characterization. And the most important aspect of the biooil production is a biooil
upgradation technology. How do you upgrade the biooil so that you can use the major
transportation fuel or at least as a blending agent. Thank you very much. If you have any
query please register your queries in the swayam portal or drop a mail to me at
kmohanty@iitg.ac.in.
866

Module 08
Lecture-23
Factors Affecting Biooil, Biochar production, Fuel Properties Characterization
Good morning students. This is lecture 2 under module 8. As you know, we have been
discussing biooil and biochar. Under this lecture we will be discussing about the various fuel
characterization techniques. I will tell you the details about the procedures which will help
you immensely later when you try to carry out such analysis for the biofuel that you are going
to produce - especially the liquid biofuels. And then today we will also talk about the biooil
upgradation technologies. So, let us begin.
Biodiesels from different sources like vegetable oil and animal have become popular over the
last few years. Although the main constraints of applications of biodiesel are their high
market price and need for many of their feedstock as food sources, the other important factor
to restrict them from being used more is that they can damage the engine parts due to some of
their properties and thereby reduce the engine life.
The threats of pollution due to the use of conventional and non conventional fuels are
becoming evident. It is found that biofuels including biodiesels are more eco-friendly than
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petro-diesel. Only the NOX emissions from the combustion of biodiesels have been reported
to be little more than that of the petro-diesel.
So, this table will tell you the different types of fuel properties, the testing apparatus and the
respective standard. Now there are 8 here we have listed which are the standard
characterization parameters that needs to be carried out for any biodiesel or biooil that you
actually produce. So, the first is acid number, the testing apparatus require is a burette and
pipette, it is very simple.
Then next is calorific value, you need a digital bomb calorimeter for that and the plain bomb
calorimeter digital or not digital is not an issue actually. So, then kinematic viscosity you
need a viscometer. Relative density you can calculate it using pycnometer. Flash and fire
point using the respective apparatus. Cloud and pour point using the respective apparatus.
Ash content you need a muffle furnace it is a simple thing. Carbon residue, also you can carry
out using a carbon residue content apparatus.
You can see the standards are given the international standards ASTMs and all these things.
So, the properties of the biodiesel give an indication of whether it would be suitable or not for
the performance, life and emission of the engine. Some of the properties we have already
discussed under this table.
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So, we will see one by one. The first is acid number. Titration method is used to estimate the
acid number of the biodiesel. Usually 0.1 to 0.5 ml of biodiesel is taken in a conical flask. A
50 ml of the solvent mixture which is usually 95% ethanol and diethyl ether in 1 : 1 ratio is
added to it and mixed thoroughly. Now this solvent oil mixture is titrated against 0.1 molar
KOH using a 1% phenolphthalein indicator.
So, you can find out the acid number from this formula. So, 56.1 into normality of the KOH
solution into volume of KOH used divided by weight of the sample taken.
Now besides the quality control of biodiesel the acid number plays a significant role in the
quality control of the feedstock also. Additionally, increasing acid numbers when compared
to the initial acid number of the biodiesel can point to ongoing fuel degradation or the
intrusion of the water. So, which actually happens by the hydrolysis of the free fatty acids.
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Then the next is calorific value. Biodiesel about 0.5 gram in a container is placed in the bomb
and the 8 centimeter cotton thread hanging from an 8 centimeter nichrome wire is dipped into
the biodiesel. The bomb is then filled with oxygen at 400 psi. Then it is placed inside the
insulated container containing distilled water and the fuse wires are placed in their position
on the bomb. The nichrome wire is stuck to 2 sticks attached to the fuse wires.
The initial temperature is noted and then it is reduced to 0 degree centigrade. The fire button
is pressed to make a short circuit on the nichrome wire and ignite the biodiesel. The
temperature kept on increasing for a certain time. The temperature is noted when it was
stable. So, the calorific value in kilo joules per kilogram can be calculated by this equation.
So, weight of the water plus water equivalent into temperature rise into specific heat of water
divided by weight of the sample.
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Then kinematic viscosity: The biodiesel is poured into the heat chamber of a Redwood
viscometer and heated up to 40 degree centigrade. The stopper of the viscometer is displaced
to let the heater biodiesel drain out of it and be collected in a measuring cylinder placed
underneath. As 50 ml of the biodiesel is collected in the measuring cylinder the stopper is
placed again to stop the flow of the biodiesel.
The time taken for the collection of 50 ml biodiesel is noted. So, you can calculate the
viscosity using this equation A into time - B by time. So, here A and B are 2 constants for the
specific redwood viscometer A = 0.26 and B = 179, when the time taken is less than 100
second and A becomes 0.24 and B becomes 50 when the time taken is more than 100 second.
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So, the next is relative density. The pycnometer is kept inside a refrigerator after filling them
up with biodiesel. They are taken out of the refrigerator when the temperature of the biodiesel
reached 15 degrees centigrade. The mass and volume of the biodiesel are measured and the
density of the biodiesel is calculated. The formula for measuring the density is as follows. So,
the relative density in kilograms per meter cube equals to mass of the pycnometer containing
the biodiesel minus mass of the empty pycnometer divided by the volume of the biodiesel.
So, then we will talk about the flash point, fire point, cloud and pour point. These are very
important properties for any liquid fuels. So, flash and fire point: the biodiesel is kept inside
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the flash and fire point apparatus and a cotton thread is placed in it. The biodiesel is heated
with a gas stove; another ignited cotton thread is dragged on the surface of the former thread.
The temperature at which the spark came out of the first thread is noted as the flash point of
the biodiesel. And the temperature at which the thread started burning is noted as the fire
point of the biodiesel. These are very simple experiments.
Then similarly cloud and pour point: the cloud and pour point apparatus is filled up with ice,
the glass vessels of these apparatus filled up with biodiesel are placed in their slots of the
apparatus. The temperature at which the paraffin in the biodiesel started solidifying and
cloudiness appeared in the biodiesel was noted as the cloud point. The temperature at which
the biodiesel becomes semi-solid is noted as the pour point of the biodiesel.
Then ash content: The sample (5 gram) is taken in a pre-weight quartz crucible and placed
inside a muffle furnace usually at 450 degrees centigrade preheated. After half an hour when
the biodiesel burnt completely to ash the crucible is taken out. The crucible is weighed again
when its temperature drops to room temperature. So, you basically keep it in a desiccator.
The formula for calculating the ash content is given below. Ash content of biodiesel in
percentage equals to initial weight of the crucible minus final weight of the crucible divided
by weight of the biodiesel into 100.
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Then the another one is the carbon residue content. So, what you do is that you take 5 gram
of biodiesel and put it inside a pre-weighed heat proof glass bulb and place inside the carbon
residue apparatus, preheated at 450 degree centigrade and kept there for half an hour. The
weight of the bulb is measured after its temperature drop to room temperature. So, the carbon
residue content of the biodiesel in percentage can be calculated by this equation: Initial
weight of the bulb minus final weight of the bulb divided by weight of the biodiesel taken
into 100.
So, another very important parameter for any liquid fuel is the water content determination.
Water contamination of biodiesel plays a significant role in the quality control of the
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feedstock and the end product. Biodiesel although considered hydrophobic, can contain as
much as 1500 parts per million (ppm) of dissolved water excluding that of the suspended
water droplets.
Now the presence of water in biofuels reduces the calorific value, enhances corrosion,
promotes the growth of microorganisms and also increases the probability of oxidation
products that are formed during long term storage. Additionally, water cleaves the ester bond
of the FAMEs via hydrolytic degradation. The same applies for the glycerides in the
feedstock also.
The liberated free fatty acids consume the added sodium hydroxide thereby forming soaps
and emulsions that increase viscosity and seriously hinder the phase separation of the
glycerine. But due to these all materials used in the biodiesel production process should be
essentially anhydrous.
Several methods exist for the determination of water, so like loss on drying, reaction with
calcium hydride, Karl Fischer titration which is the most adapted one, then Fourier transform
infrared or Raman spectroscopy and dielectric measurements. Now among these the KFT or
the Karl Fischer titration is certainly the method of choice when trace amounts of free
emulsified or dissolved water have to be accurately determined in a reasonable time.
The principle of KF titration is based on the Bunsen reaction between the iodine and sulfur
dioxide in an aqueous medium. A primary alcohol can be used as the solvent and a base as
875

the buffering agent. The alcohol reacts with sulfur dioxide and base to form an intermediate
alkyl sulphide salt which is then oxidized by iodine to an alkyl sulfate salt. So, this is the
reaction.
The reactive alcohol is typically methanol or 2-2 ethoxyethoxyethanol or another suitable
alcohol. Water and iodine are consumed in a 1 : 1 ratio in the above reaction. Once all of the
water present in consumed the presence of excess iodine is detected by the titrators indicator
electrode that signals the end point of the titration. The amount of water present in the sample
is calculated based on the concentration of iodine in the KF titrating reagent that is titre and
the amount of KF reagent consumed in the titration.
In most cases of the KF titration the sample can be directly injected into the KF solution and
xylene can also be injected in order to improve biodiesel solubility. However, as many
biodiesel fuels contain additives or impurities that can undergo side reactions during titration
they should not be injected directly.
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So, now we understand the different types of the fuel properties that needs to be actually
characterized for a biodiesel or biooil. Now we will talk about the biooil which is the major
product from the pyrolysis of biomass and as we have discussed many times that biooil
suffers so many different types of drawbacks like high water content, high oxygen content,
higher viscosity, there are many other things also we will discuss now.
So, there is a need to upgrade the biooil. So, now we will discuss the different biooil
upgradation techniques and how they can be performed. So, why there is a need to upgrade
the biooil? Now biooil can be upgraded in a number of ways, so we can do it either
physically or chemically or catalytically. So, there are number of objectives for upgrading of
which the main ones are: first one is the most important of course the improvement of the
biooil quality to overcome or reduce one or more of the fuel quality deficiencies.
And the second is, towards the production of chemicals and if you remove oxygen then you
can produce hydrocarbon biofuels. So, the most important properties that inhibit the
widespread use of biooil are - first is the phase separation. So, phase separation from use of
wet feedstock and or secondary cracking of vapours leading to high water content in the
liquid product. Phase separation cannot be reversed except though relatively high additions of
co-solvents such as ethanol.
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Then incompatibility and immiscibility with conventional fuels from the high oxygen content
of the bio-oil. So, if you cannot do that then the problem is that you cannot blend it with the
petrol fuels. And then high solids content that affect the catalyst and utilization in engines and
burners. High viscosity that hinders pumping and combustion and which cannot readily be
controlled by raising temperature as for heavy fossil fuels due to the temperature sensitivity.
Now high water content that lowers heating value but also lowers viscosity. Chemical or
thermal instability which limits the use of the higher temperatures for controlling properties.
And again another one is the high acidity which actually leads to corrosion in storage and
utilization. So, as you understand from these so many drawbacks you have to understand
what is the intention?
So, the intention of producing biodiesel and upgrade it to a certain quality so that its fuel
properties matches to that of the petrol-diesel, if it matches then only you can blend it or you
can directly use it in the engines which were used to burn actually the petro-diesel. So, to
achieve that there are various upgradation technologies available, so we will discuss one by
one.
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So, the first one physical upgradation of the biooil using the simple filtration mechanism.
Now the most important properties that may adversely affect biooil fuel quality are
incompatibility with the conventional fuels, from the high oxygen content of the biooil, high
solids content, high viscosity and chemical instability. Now hot vapour filtration can reduce
the ash content of the oil to less than 0.01% and the alkali content to less than 10 ppm much
lower than reported for biomass oils produced in systems using only cyclones.
Now this gives a higher quality product with lower char however accumulated char on the
filter medium is catalytically active and potentially cracks the vapours, reduces yield by up to
20%, reduces viscosity and lowers the average molecular weight of the liquid product. Now
there is limited information available on the performance or operation of hot vapour filters
but they can be specified and perform similarly to hot gas filters in gasification processes.
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So, this is a classical study. In the below you can see that the reference is given. So, it is ACS
sustainable chemistry and engineering and it is a nice work, what they have done here? They
have performed the catalytic hot gas filtration with a supported heteropolyacid acid catalyst.
So, the diesel engine test performed on crude and hot filtered oil showed a substantial
increase in burning rate and a lower ignition delay for the latter due to the lower average
molecular weight of the filter oil.
Liquid filtration to very low particle sizes of below around let us say 5 microns is very
difficult due to the physicochemical nature of the liquid and usually requires very high
pressure drops and self cleaning filters. Although improvement is claimed with filter pores of
around 10 micron.
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So, the next physical upgradation is solvent addition and emulsions. Polar solvents have been
used for many years to homogenize and reduce the viscosity of biomass oils. The addition of
solvent especially methanol showed a significant effect on the oil stability. Diebold and
Czernik found that the rate of viscosity increase or we can say that due to the ageing actually
for the oil with 10 weight percent of methanol was almost 20 times less than that of the oil
without additive.
Now use of co-solvents to compatibilize biooil with other sustainable liquid fuels as blends is
tested. Pyrolysis oils or biooils are not miscible with hydrocarbon fuels but they can be
emulsified with diesel oil with the aid of surfactants. A process for producing stable micro
emulsion with 5 to 30% of the biooil in diesel has been developed at CANMET. So, the
reference is given below.
So, this is what they have done actually. This was done at the University of Florence, Italy.
So, they have been working on emulsions of 5 to 95% biooil in diesel to make either a
transport fuel or a fuel for power generation in engines that does not require engine
modification to dual fuel operation. Now there is limited experience of using such fuels in
engines or burners but significantly higher levels of corrosion erosion were observed in
engine applications compared to biooil or diesel alone.
A further drawback of this approach is the cost of surfactants and the high energy required for
the emulsification. So, what they have done? It is a simple experiment. So, the biooil if it is
not suitable for emulsification basically the heavier fraction whatever the lighter fractions are,
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can be emulsified, will be mixed with different emulsifying agents like these surfactants -
tween 60, span 80 and all these things and diesel in different proportions.
So, once that is done so you can get something like this is the mixture, this is the stratified
one, this is the stable one. So at different proportions or you can say the different blends
using different surfactants so different mixtures were prepared, their stability is tested and
their engine performance is also carried out. So, a further drawback of this approach is the
cost of the surfactants and the high energy required for the emulsification.
So, the next one is physical upgradation using the blends. So, more recently some success has
been achieved through production of blends of biooil with a variety of co-solvents and other
sustainable or green fuels as well as conventional transport fuels. Therefore some exploratory
work was initiated in 2012 to produce homogeneous blends of biooil with biodiesel and an
alcohol co-solvent.
So, both ethanol and butanol were tried. A key result was that single phase and stable blends
of biooil, biodiesel and either ethanol or butanol could be prepared which utilize the whole
biooil including the water content. So, this is one of the best things regarding this blending
actually. So, use the entire biooil that is coming out of the pyrolysis reactor including that of
the water part or aqueous part.
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So, a key requirement is to maximize the use of biooil, maximize the sustainability of the
resultant blend by use of renewable solvents and satisfy marine oil specifications of which
flash point above 60 degree centigrade is the key.
So, this is the overview of the fast pyrolysis upgrading technologies. So, another important
upgradation method. So, this is the direct route of the fast pyrolysis and this is indirect route.
So, under the direct route biomass undergoes the fast pyrolysis so the cracking is happening,
so part of that directly goes to refining and part of that again further processed using the
hydro processing. And you then refined and you get these hydrocarbons, SNG, diesel,
gasoline etcetera or various different fractions.
The liquid biooil part can be modified as for example to esters and can be used as chemicals
and also part of that can be refined to get the biofuels. And you can prepare directly the
blends and use as fuels. Under the indirect routes you can use the gasification that means the
syngas and then convert it using the Fischer Tropsch synthesis to different types of alcohols
and then you can get another fuel platform here or from here the FT synthesis directly goes to
the refining platform and you get the different types of biofuels.
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Then catalytic upgradation of the biooil so natural ash in biomass. Before considering
catalytic upgradation of biooil it is important to appreciate firstly that biomass contains very
active catalyst within its structures. So, these are called the alkali metals that form ash and
which are essential for nutrient transfer and growth of the biomass. The most active is of
course potassium followed by sodium.
Now these act by causing secondary cracking of vapours and reducing liquid yield and liquid
quality and depending on the concentration the effect can be more severe than even the char
cracking. Ash can be managed to some extent by selection of the crops and harvesting time
but it cannot be eliminated from growing biomass. Ash can be reduced by washing in water
or dilute acid and the more extreme the conditions in temperature or concentration
respectively the more complete removal of the ash will happen.
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However as washing conditions becomes more extreme, firstly hemicellulose and then
cellulose is lost through hydrolysis. Now this reduces the liquid yield as well as the quality.
In addition, washed biomass needs to have an acid removed as completely as possible and
recovered or disposed of and the wet biomass has to be dried again. So washing is therefore
not considered as a viable possibility, unless there are some unusual circumstances such as
removal of the contaminants.
Another consequence of high ash removal is the increased production of levoglucosan which
can reach levels in biooil where recovery becomes an interesting proposition. Although
commercially market needs to be identified and/or developed. You know levoglucosan is one
of the most important chemical that forms during pyrolysis directly as a decomposition
product from the carbohydrates starch and other things cellulose and hemicellulose whatever
it is.
Now levoglucosan is also an important chemical it has various widespread application - one
of the most important application is its use as a tracer. So, there are many other applications
also.
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The next is hydrocarbon biofuels. Now direct production of high yields of liquids by fast
pyrolysis inevitably caused attention to focus on their use as biofuels (basically looking
towards the sustainable transport fuels) to supplement and replace fossil fuel derived
transport fuels. However, the high oxygen content of biooil and the non miscibility or
incompatibility with hydrocarbon fuels have prevented simple adoption of biooil as a
transport fuel at least as a blend.
Now the main methods for upgrading biooil to transport fuels are the first one is
hydrodeoxygenation. So, hydrodeoxygenation of biooil to a substantially deoxygenated
product, then catalytic vapour cracking of fast pyrolysis vapours in a closed coupled
atmosphere to aromatics that can be followed by hydrodeoxygenation and/or introduction
into a refinery for further processing basically. So, partial upgrading by hydrodeoxygenation
followed by introduction into a refinery direct introduction of crude biooil into a refinery.
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So, hydrotreating is another option actually for upgradation. So, hydro-processing rejects
oxygen as water by catalytic reaction with hydrogen. This is usually considered as a separate
and distinct process to fast pyrolysis that can therefore be carried out remotely. The process is
typically high pressure up to 20 mega pascal and moderate temperature up to 400 degree
centigrade and requires a hydrogen supply or source.
Full hydrotreating gives a naphtha-like product that requires orthodox refining to derive
conventional transport fuels. So, you basically distilled it to different cuts. So, a projected
typical yield of naphtha equivalent from biomass is about 25% weight or 55% in energy
terms excluding the provision of the hydrogen. Inclusion of hydrogen production by
gasification of biomass reduces the yields to around 15 weight percent or 33% in terms of
energy.
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The process can be depicted by the following conceptual reaction. So, CHO + 0.77 hydrogen
gives CH 2 + 0.43 water.
The catalyst originally tested in 1980s and 1990s were based on sulfided CoMo or NiMo. So,
cobalt molybdenum or nickel molybdenum supported on alumina and aluminosilicate and the
process conditions are much similar to those used in the desulphurization process.
Now you know this CoMo, NiMo catalysts are the desulphurization catalyst which are used
in the petroleum industries. However, a number of fundamental problems arose including that
the catalyst supports of typically alumina or aluminosilicates were found to be unstable in the
high water content environment of biooil and the sulfur was stripped up from the catalyst
requiring constant re-sulfurization.
So, this is a big problem. More recently attention turned to precious metal catalyst on less
susceptible supports and considerable academic and industrial research has been carried out.
One of the most important aspect of this type of catalyst is that how the catalyst is supported
on the base material? In this case alumina aluminosilicates, they should not come out when
the processing is happening.
When the water content is higher so there is a huge chance that though the catalyst will be
dug up. So, that is why there is a need to look out for the proper doping methods as well as
there should be a proper susceptible supports which will take care of this problem.
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Tests have been carried out on both batch and continuous flow processes focusing on an
initial low temperature stabilization step followed by more extensive catalytic deoxygenation
using different metal catalyst and processing conditions to give a range of products including
that of the petroleum refinery feedstock. Now remaining challenges include complete
deoxygenation especially of phenols without saturation with the hydrogen.
A key aspect is of course the production of hydrogen very important. Since the hydrogen
requirement is significant it should be renewable and sustainable. Having said that the
meaning of renewable and sustainable it is a complex you can say some sort of biorefinery
concept, where the requirement of hydrogen whatever it is should be made from in-house
hydrogen production, you cannot buy hydrogen from outside its very costly and
transportation also makes it not feasible.
So, few refineries have a hydrogen surplus, so this has to be provided. There are many ways
of providing hydrogen such as gasification of biomass followed by shifting to hydrogen, then
scrubbing the carbon dioxide.
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Product biooil or the aqueous phase from the phase separated product can be steam reformed
to hydrogen or hydrogen can also be generated locally by the electrolysis of water preferably
using the renewably produced electricity. Again we are talking about the renewable
electricity because the electricity has to be generated in house so as to meet the energy
requirement as well as the make the entire process sustainable.
Supply of the hydrogen from external sources is unlikely to be feasible due to the very high
cost of storage and transport. The necessary purity of hydrogen is unknown but some carbon
monoxide shifting may take place in the hydroprocessing reactor removing the need for
dedicated shift reactors. The high cost of hydrogen means that unused hydrogen would have
to be recovered and recycled as only a fraction of the hydrogen would be utilized due to the
need for high hydrogen partial pressures.
Recovery and recycling of unused hydrogen is both technically and economically very, very
challenging and lot of work has been going on this particular aspect.
890

There is increasing interest in supercritical processing of biooil, another important study has
been done, to either improve the properties of the biooil or to deoxygenate into a hydrocarbon
fuel. The supercritical fluid studied included water, carbon dioxide, methanol, ethanol,
butanol and cyclohexane using traditional CoMo type catalyst, precious met

NPTEL - Biomass refinery book.pdf

NPTEL - Biomass refinery book.pdf

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NPTEL - Biomass refinery book.pdf