Biochemical conversion process of biomass

1. BIOCHEMICAL CONVERSION
PROCESS OF BIOMASS
S K Singh
Centre for Energy Studies
IIT Delhi

2. INTRODUCTION
 All plant materials produced through photosynthesis via carbon dioxide
fixation is BIOMASS.
 Major source of biomass is agricultural waste, residues, fuel woods and
industrial wastes.
 Biomass is organic matter produced plants including terrestrial plants
(ones which are grown on land) and aquatic plants (ones which are grown
under water).
 Biomass is renewable source of energy because its supplies are unlimited.
We can always grow trees and crops, and waste will always exist.
 Biomass gets its energy from the sun. During a process called
photosynthesis, sunlight gives plants the energy they need to convert
water and carbon dioxide into oxygen and glucose.

3. BIOFUEL
 Biofuels are the fuel which are produced from biomass.
 Biofuels can be solid, liquid or gas fuel derived from recently dead biological
materials.
 Some common types of biofuels are: Bioethanol, Biomethanol, Biodiesel and
Biogas.
 Biofuels are commonly used in transportation, energy generation, cooking
etc.
Source: Royal Society of Chemistry

4. WHY BIOFUEL?
BIOFUEL FOSSIL FUEL
Biofuel is produced from present day
biomass
Fossil fuel is product of biomass present
millions of years ago
Obtained from renewable sources Obtained mainly from non-renewable
sources
Provides a low amount of energy per
unit mass
Provides a high amount of energy per
unit mass
Causes less pollution than fossil fuels Plays a lead role in environment
pollution
Emits a low amount of unfavourable
gases when burnt
Emits a high amount of unfavourable
gases when burnt
Requires more investment for their
production and are costly
Comparatively less investment and less
cost to biofuel

5. Diagrams & Charts:
Source: BioEnergy Consult
Biomass
Feedstock
Biochemical
conversion
Direct combustion Thermochemical
conversion
Biofuels
Chemical
conversion

6. CONVERSION TECHNOLOGIES
 Direct combustion: Direct combustion of biomass in presence of
oxygen/air to produce heat and by products. Some process involving are
cleaning, chopping, etc.
 Thermochemical conversion: Thermochemical reaction can convert
biomass into more valuable and convenient form of products as gaseous
and liquids fuels, residue and by-products etc. Process involving are
combustion, gasification, pyrolysis and liquefaction.
 Biochemical conversion: In biochemical processes, the bacteria and micro-
organisms are used to transform the raw biomass into useful energy like
methane and ethane gas. Treatments involving are pre-treatment,
detoxification, hydrolysis and fermentation.
 Chemical conversion: In chemical processes, the chemicals are used to
transform the raw biomass into useful energy like methane and ethane
gas. Treatments involving are pre-treatment, detoxification,
transesterification etc.

7. BIOCHEMICAL CONVERSION PROCESS
 Biochemical conversion is a major and an efficient pathway which involves
breaking down biomass to make the carbohydrates available for
processing into sugars, which can then be converted into biofuels and
bioproducts through various processes.
 Biochemical conversion uses biocatalysts, such as enzymes, in addition to
heat and other chemicals, to convert the carbohydrate portion of the
biomass (hemicellulose and cellulose) into an intermediate sugar stream.
These sugars are intermediate building blocks that can then be fermented
or chemically catalyzed into a range of advanced biofuels and value-added
chemicals.
 It involves treatment like pre-treatment, detoxification, hydrolysis and
fermentation.
 It mainly involves hydrolysis of lignocellulose polysaccharides (i.e. cellulose
and hemicellulose) into simple sugars and their further conversion into
fuel example ethanol by fermentation organisms

8. Feedstock
Pre-treatment Detoxification Hydrolysis
Fermentation
PROCESS INVOLVED

9. FEEDSTOCK
 First generation feedstock: Biofuels like biodiesel and bioethanol
generated are directly linked to the biomass comprising of edible stuffs
like sugarcane, corn etc. However, they may come with certain restrictions such
as energy consumption and utilization of arable lands, as well as the fuel versus
food debate.
 Second generation feedstock: Biofuels formed are defined as fuels produced from
a wide array of different feedstocks, especially but not limited to non-edible
lignocellulosic biomass. The price for this biomass is significantly less than the price
for vegetable oil, corn, and sugarcane, which is an incentive.
 Third generation feedstock: The most accepted definition for third-generation
biofuels is fuels that would be produced from algal biomass, which has a very
distinctive growth yield as compared with classical lignocellulosic biomass. Algae
are known to produce biomass faster and on reduced land surface as compared
with lignocellulosic biomass.

10. PRETREATMENT
 Due to structural characteristics of biomass, pretreatment is essential for
enzyme catalyzed cellulose conversion. Without a pretreatment, enzymatic
hydrolysis of cellulose is ineffective as native cellulose is well protected by
hemicellulose and lignin.
 A pretreatment process is used to disrupt the physical and chemical
barriers of lignocellulose and make the cellulose polymers more accessible
for the enzymatic degradation.
 The factors affecting the accessibility of biomass cellulose can be divided into
direct and indirect factors.
 Direct factors: This factor is related to accessibility to surface area.
 Indirect factors: This factor is related to biomass structure-relevant
characteristic (pore size and volume, particle size, and specific surface area),
chemical compositions (lignin, hemicelluloses, and other), and cellulose
structure-relevant factors (cellulose crystallinity and degree of polymerization)

11. PRETREATMENT
 Pretreatment is actually the process, with an objective of removing the unwanted
barriers of biomass by altering its indirect factors and improving direct factors thus
enhancing the cellulose accessibility to enzymes that would degrade carbohydrate
polymers into simple sugars.
 Feedstock pretreatment technologies are majorly classified into 4 categories:
 Physical & Mechanical: Treatments like chipping, milling, grinding, extrusion etc. are
performed. The aim of these treatments include increasing the accessible surface area
and pores size, decreasing cellulose crystallinity and densification of feedstock.
 Chemical and Physico-chemical: A variety of pretreatments are being developed using
chemical reactions to disrupt the crystalline structure of lignocellulose and to partially or
completely hydrolyze lignin and/or (hemi) celluloses. Hemicelluloses can be readily
hydrolyzed e.g. under mild acidic or alkaline conditions, but cellulose is more resistant
and requires a rigorous treatment.
 Biological: Biological pretreatment involves the use of lignocellulose degrading
microorganisms, mainly white, brown and soft rot-fungi, to alter the material. These bio-
catalysts are capable of degrading hemicellulose and lignin.

12. DETOXIFICATION
 Use of pretreatment technique that do not result in formation of by-products or
use of less sever pretreatment to minimize the by-product formation is one way to
avoid the inhibitory problems of lignocellulose compounds. Hence, removal of
inhibitory compounds present in lignocellulose compound is an important area of
research.
 Different techniques categorized mainly as physical, chemical, biological and in
their combination were developed to lighten the toxic effect of lignocellulose
compounds.
 Some of these includes the use of chemical additives, microbial treatments,
enzymatic treatments, heating and vaporization, liquid-solid extraction.
 Physical detoxification: Evaporation, heating and absorptive processes are used to
detoxify the compounds. However, the drawback is that this method is energy
intensive and the non-volatile inhibitory compounds are unaffected – they remain
in the compounds.
 Chemical detoxification: Chemical detoxifications have been the most popular
approaches to either remove or alter the structure of lignocellulose inhibitors.
Some of the popular approaches are listed:

13. DETOXIFICATION
 Treatment with hydrogen peroxide (H2O2) and ferrous sulphate (FeSO4)
 Alkaline treatments with NH4(OH), Ca(OH)2 and NaOH.
 Treatment with reducing agents such as sodium sulphite, sodium dithionite, and sodium
borohydride.
 Liquid-solid extraction using activated charcoal.
 Biological detoxification: Several biological methods including treatment with
enzymes such as laccases or use of the natural or targeted genetic engineered
micro-organism are proposed to overcome the inhibitory effects of pre-treated
lignocellulose materials. Some methods involving biological detoxification are:
 Micro-organisms, such as some species of yeasts, fungi and bacteria can naturally
detoxify inhibitory compounds, specifically furanaldehydes, aliphatic acids, and aromatic
compounds.
 Enzymatic, laccases and peroxidases - particularly produced from white-rot fungi
treatment is another approach to detoxify lignocellulose hydrolysates. Advantages of
using these enzymes is that the detoxification can be achieved faster than what possible
by microbial cultures.

14. HYDROLYSIS
 Hydrolysis is any chemical reaction in which a molecule of water ruptures one or
more chemical bonds. Hydrolysis of lignocellulose compounds can comply with
either a concentrated acid or enzyme catalysts.
 Hydrolysis in biochemical conversion is a process of breaking down of
lignocellulose polysaccharides (i.e. cellulose and hemicellulose) into simple sugars
and their further conversion into e.g. fuel ethanol by fermentation organisms.
 Concentrated acid:
 Biomass is treated with mineral acids (e.g. H2SO4, HCl) at relatively low temperatures
(T<50◦C) and a high acid concentration 30–70 wt.% .
 Hydrolysis of (hemi) cellulose then occur, releasing the sugars into hydrolysate and
leaving mostly lignin in the solid phase.
 Sugar yield from concentrated acid hydrolysis is usually significantly higher compare to
dilute acid hydrolysis.
 In addition, concentrated acid hydrolysis is flexible in terms of feedstock choice which
means that it can be principally applied to any kind of biomass.

15. HYDROLYSIS
 Some setbacks of using concentrated acid are:
• The released sugars would further degrade into by-products (furanaldehydes, organic
acids) and lignin degradation products would also form.
• Concentrated acids are highly corrosive, toxic and hazardous, and require corrosion
resistant equipment.
• Also the spent acid must be recovered in order to make the process economically viable
and the hydrolysate pH neutralization requires a high amount of alkali which would results
in formation of solid waste.
• Hence, considering environmental impacts, high investment and maintenance costs have
greatly limited the commercial interests of concentrated acid hydrolysis process.
 Enzymatic process:
 Enzymatic hydrolysis is regarded as the most attractive way over concentrated acid hydrolysis.
 Due to the complex chemical structure of lignocellulose, multiple enzymes are often needed for
the degradation of its carbohydrate polymers. For example, cellulose is hydrolyzed by a mixture
of cellulase enzymes and hemicellulose is hydrolyzed by the action of different hemicellulases
e.g. xylanases, mannanases, etc.

16. HYDROLYSIS
 Some advantages of enzymatic hydrolysis are:
• High sugar yield.
• Moderate temperatures are required for the reactions.
• Does not create problems related to the equipment corrosion.
• The formation of by-products is very low.
Source: PNAS

17. FERMENTATION
 Fermentation is a metabolic process in which an organism converts a carbohydrate,
such as starch or a sugar, into an alcohol or an acid.
 The sugar rich lignocellulose hydrolysates, obtained from pretreatment and
enzymatic hydrolysis can be fermented to ethanol using different types of
microorganisms.
 The yeast (Saccharomyces cerevisiae) is the most frequently used and commercially
dominant organism employed for this purpose.
 The advantages of S. cerevisiae are that give high ethanol yields, exhibit relatively
high ethanol and general inhibitors tolerance.
Source: Bioenergy research group

18. FERMENTATION
 Modes of fermentation: Fermentation can be performed in three different
modes namely, Batch, Fed-batch and Continuous.
 Batch Mode:
 A microorganism is inoculated to a specific volume and the fermentation is performed
until the sugars are depleted.
 Advantages: This mode is simple, inexpensive, contain low risk of contamination and
possibility to utilize the sugars efficiently.
 Disadvantages: However, this process is labor intensive, time consuming (cleaning,
sterilization, cell lag phase, cell growth and harvesting for each batch), and the overall
productivity is low.
 Fed-batch mode:
 Microorganism is continuously added to the fermentation, and substrate concentration
can be kept low.
 Advantage: It allows to overall achieve higher product quantities overall.
 Disadvantages: It allows build up of inhibitory agents and toxins. Also, maximum working
volume of the fermentation vessel is not utilized all the time.

19. FERMENTATION
 Continuous Mode:
 Reactant is constantly added to the fermentation vessel and at the same rate the product
(fermentation broth) is removed. Hence, fermentation volume is kept constant.
 Advantages: This mode allows the maximum productivity and less time for cleaning,
sterilization and handling of the vessel.
 Disadvantages: It is difficult to keep a constant population density over prolonged
periods as cells are constantly drained out from the reactor.
Source: Research gate

20. CONCLUSION AND FUTURE PERSPECTIVE
 We have seen that biofuels are made from biomass which directly comes from
plant materials making it completely renewable.
 They are biodegradable and produce less pollution when compared to fossil fuels.
 However, on the other hand large areas of land are eradicated (deforestation), high
level of investment is needed, high amount of water is needed.
 We have also seen various methods are involved in the conversion of biomass to
biofuels especially biochemical conversion methods.
 With the passage of time bio-based fuels are taking over the market because of
their environment friendly nature and inexpensive production. Since biofuels are
produced from the plant-derived polysaccharides, CO2 does not increase when
biofuels are used (combusted), which refers to the concept of carbon neutrality.
 Biofuels can be boon for us if proper research is conducted to analyze and identify
the issues and concerns related to them; and then decimate those issues. We can’t
rely on the fossil fuels as they are going to be depleted eventually, and they pose a
serious concern to our environment as well. Eventually we would need renewable
energy sources like biofuels.


21. REFRENCES
 Biochemical conversion of biomass to biofuels (VENKATA PRABHAKAR SOUDHAM)
 https://www.slideshare.net/GurpreetSingh1377/conversion-of-biomass
 Characteristics of biomass (AK Jain)
 Non-conventional renewable resources (GD Rai)
 Production of Bioethanol from Agro-industrial Residues as Feedstocks(Julián
A.Quintero, Luis E.Rincón, Carlos A.Cardona)
 https://www.infors-ht.com/en/blog/the-difference-between-batch-fed-batch-and-
continuous-processes/