EMCQ 5161 Bioenergy Technologies. Dr. Eng. Jedidah Maiana notes.

1. Chapter 2
BIOFUELS

2. What are Biofuels?
 Biofuels are biomass based fuels produced from variety of biomass feedstock
such as animal fats, oil crops, sugar plants, starchy plants, cellulosic biomass,
algae etc.
• Such feedstock can be transformed into liquid and gaseous fuels such as
biodiesel, pure plant oil or straight vegetable oil, bioethanol (or ethanol), biogas,
syngas, ethyl tertiary butyl ester etc.
• The main liquid biofuels are biodiesel and bioethanol which are alternatives to
diesel and gasoline fuels respectively.

3. Why Biofuels?
• Climate change impact
• Rising demand and cost fossil. Thus biofuels are considered as the
best alternatives to petroleum based fuels.
• Energy security.
• Rural economic development etc.

4. Overview on Climate Change, Global Warming and
Greenhouse Gas Mitigation
1. Climate Change:
Climate change is any long-term significant change in average temperature,
precipitation and wind patterns.
Or Climate change is a large-scale, long-term shift in the planet's weather
patterns and average temperatures.
UNFCCC refers to climate change as a change of climate that is attributed directly or
indirectly to human activities that alter the composition of the global atmosphere
Climate change was apparent from the mid to late 20th century onwards and is
attributed largely to the increased levels of atmospheric CO2 produced mainly by
the use of fossil fuels.

5. 2. Global Warming
Is the phenomenon of increasing average air temperatures near the
surface of Earth over the past one to two centuries.
• In 2013 the IPCC reported that the interval between 1880 and 2012 saw an
increase in global average surface temperature of approximately 0.9 °C (1.5 °F).
• IPCC predicts that the global mean surface temperature would increase between
3 and 4 °C (5.4 and 7.2 °F) by the year 2100.

9. Carbon neutrality of biofuels

10. 1. Biodiesel

11. • Biodiesel is a renewable fuel composed of fatty acid methyl or ethyl
esters.
• Biodiesel is produced from biological sources such as vegetable oils,
animal fats and algae.
• Animal fats are not preferable since they contain higher saturated
fatty acids and normally exist in solid form at room temperatures.
• Vegetable oils both edible and non-edible are the best raw
materials for biodiesel.

12. Status on Production and use of Biodiesel
• Leading countries for biodiesel production are the US, then Brazil, followed by
Germany and the Netherlands.
• Global biodiesel market was estimated to reach 37 billion gallons by the year
2016.
• The United States produces about 148 million gallons of biodiesel per month.
• Countries such as Thailand and India aimed at 10% and 20% renewable mix
respectively 20% by the year 2020.

14. Companies producing Biodiesel in Kenya
ZIJANI-
is a Renewable Energy Brand owned by Biogen Diesel Kenya
Limited, to commercialize Biodiesel production and refining in Kenya.
KITUI INDUSTRIES –
The company’s main products are lint cotton and bio- diesel. It
ventured into biodiesel production in 2013.
TECHNICAL UNIVERSITY OF KENYA-
A 200 liters prototype bioreactor for the production of biodiesel from waste
cooking oil (WCO) was designed and installed at the TUK. Unfortunately the project
stopped.

15. Biodiesel properties in relative to diesel
Density
(kg/l)
Viscosity
(mm2/s)
Flash
Point
(oC)
Calorific
value at
20oC
(MJ/kg)
Cetane
number
Fuel
equivalence
ratio (l)
Diesel 0.84 5 80 42.7 50 1
Biodiesel 0.88 7.5 120 37.1 56 0.91

16. Flash point- A measure of the flammability of the fuel
Calorific value- the energy contained in a fuel or food, determined by
measuring the heat produced by the complete combustion of a specified
quantity of it.
Cetane number- The Cetane Number (abbreviated CN) refers to the
combustion quality of the fuel. It indicates the ignition
characteristics.
Higher CN indicates higher combustion efficiency and smoother
combustion of the fuel.

17. Fuel equivalence ratio-
The equivalence ratio is defined as the ratio of the actual fuel/air ratio
to the stoichiometric fuel/air ratio.
Stoichiometric combustion occurs when all the oxygen is consumed in
the reaction, and there is no molecular oxygen(O2) in the products.
If the equivalence ratio is equal to 1, the combustion is
stoichiometric. If it is < 1, the combustion is lean with excess air, and
if it is >1, the combustion is rich with incomplete combustion.

18. Advantages of biodiesel
• Renewable and Biodegradable;
• It is plant based thus carbon neutral;
• In the form of methyl esters it contains just about 0.001% sulphur while ethyl esters contain
virtually no sulphur;
• It reduces unburned hydrocarbons (93% less), CO (50% less) and particulate matter (30% less)
in exhaust fumes, as well as cancer causing PAH (80% less) and nitrated PAH compounds (90%
less) compared to diesel;
• It contains higher CN and higher flash point compared to that of fossil diesel. Thus ignites
faster and combustion efficiency is higher than diesel;
• Biodiesel is used as a means of recycling waste cooking oils;
• Biodiesel can also be used directly in most diesel engines without requiring extensive engine
modifications, etc.

19. Disadvantages of biodiesel
• higher viscosity;
• lower energy content;
• higher cloud point and pour point;
• higher nitrogen oxides (NOx) emissions;
• lower engine speed and power;
• engine compatibility;
• high production cost; and
• higher engine wear.

20. Biodiesel production Technology

21. Raw materials for Biodiesel
Type of oil Species
Edible vegetable oils Soybean
Rapeseed
Sunflower
Palm
Peanut
Corn
Camelina
Canola
Non-edible oils Jatropha curcas L.
Pongamia pinnata
madhuca indica oils
Croton megalocarpus
Others Used cooking oils

22. Biodiesel Production process
• To date, transesterification is the common technology used to convert
vegetable oils/animal fats into biodiesel.
• The transesterification can be performed via non-catalytic or catalytic
processes.
• Catalytic processes involve using homogeneous catalysts,
heterogeneous catalysts, or biocatalysts.

23. Non-catalytic Process
• A new technology
• The non-catalytic transesterification of vegetable oils is a thermochemical process
performed in tubular or bubble column reactors at high temperature (250–500
°C)
• Biodiesel production by non-catalytic transesterification can achieve efficiencies
of up to 95– 99%.
• Factors to be considered during this process include Temperature, Pressure, Oil to
Alcohol Molar ratio and FFA and Water content in the feedstock.

25. Catalytic Transesterification
• Three types of catalyst: Alkalis, acids and enzymes (not commercially used) are
commonly used in biodiesel production.
• The alcohol is added in excess to ensure that the reaction proceeds to completion.
• The commonly used alcohols are ethanol (ethanolysis) and methanol (methanolysis).

26. Block diagram for biodiesel production

27. Homogenous catalysis processes
• Common Catalysts in this process include alkaline and acidic catalysts
• Commonly used alkalis are NaOH and KOH. Others include CH3ONa and
K2CO3.
Advantages
• They are economical due to their relatively low costs.
• low reaction time (30-60min)
• Results into high purity of biodiesel and high yield (> 95% for methanolysis
and 90% for ethanolysis)
• Requires low reaction temperature (60 oC) and pressure (20Psi) processing.
• Conversion to methyl ester is direct with no intermediate steps.

28. Disadvantages of alkali catalysts
• Soap formation for feedstock with high free fatty acids
• High energy demand;
• Post-reaction treatment to remove the catalyst from the product-
biodiesel;
• Interferences occasioned by the presence of free fatty acid and
water during the reaction;
• Difficulty in the recovery of glycerol after the reaction; and
• Post-reaction treatment of the alkaline waste-water to obviate the
environmental effects of its disposal

29. Acid catalysts
• They include HCl, BF3, H3PO4, H2SO4 and sulphonic acids.
Advantages
• High yield of biodiesel (> 90%)
• No soap formation during reaction
• Can produce biodiesel from feedstock with high free fatty acids
Disadvantages
• Long reaction time (3 to 48 hrs) to reach complete conversion

30. Transesterification using alkali catalyst.
• For crude oils with high free fatty acids (FFA) (>2.5 % (w/w) ) pre-treatment is
required.
• FFA of >2.5% (w/w) will promote more soap formation during
transesterification reaction makes separation of products very difficult.
• In order to determine the % of FFA in oils, titration is performed.
• During titration, 1% KOH (w/w in water) is used.

31. • To neutralize the FFAs, oil pH should be between 8.3-8.5.
• Phenolphthalein indicator is used to check the pH of the mixture. Colour of
the mixture turns to pink.
• If FFA > 1%, pre-treatment must be carried out.
Pre-treatment methods include:
a. Steam distillation- this methods requires high temperature and
its efficiency is very low.
b. Solvent extraction-
• This methods needs large amount of solvent (alcohol) due to low
solubility of FFA. Thus, it is not economical.

32. c. Esterification-
• This is commonly used method to reduce FFA contained in crude oils.
• During pre-treatment (esterification method), the FFA in the oil is
converted to esters by using methanol (CH3OH) (molar ratio of 6:1
methanol:oil) and sulphuric acid (H2SO4) (1.43%w/w) as a catalyst.
• The esterification reaction is carried out at temperature of about 70oC and
400 kPa with 2 hrs reaction time.
After pre-treatment, the recovery of a catalyst used during pre-treatment is
necessary before proceeding to transesterification (why???).

33. Mixing catalyst with alcohol
• Prior to transesterification, catalyst NaOH 1% (w/w) or KOH (0.6% w/w) is mixed
with alcohol (methanol or ethanol) at 50–60 oC under continuous stirring for 15–
30 min.
• The purpose is to produce methoxide or ethoxide which will react with oils during
transesterification.
Source: Caetano et al., 2019

34. Transesterification reaction and separation
• Oil preheated to reaction temperature is then added to the alcohol–catalyst
mixture and the reaction continues at transesterification conditions.
• To convert 1 m3 of raw oil into biodiesel, from 0.120 up to 0.230 m3 of methanol
can be used.
• The maximum biodiesel yield is achieved after 90 min reaction time at a
temperature of 60oC and pressure of 400kPa.
• After transesterification, the recovery of methanol is required prior to
separation of biodiesel and glycerol.

35. • Multi-stage distillation unit is used to separate methanol from the mixture
since the density of methanol is very low compared to that of biodiesel and
glycerol.
Separation
• Prior to separation, the mixture is washed with water.
• Glycerol is denser than biodiesel and settles at the bottom of the reactor
allowing it to separate from biodiesel but complete separation cannot be
achieved.
• The efficient method for separation of biodiesel and glycerol is liquid-liquid
extraction with four theoretical stages using water.
• The glycerol remains at the bottom stream together with water, methanol
and catalyst.

36. PFD for single vessel Biodiesel reactor
Source: Caetano et al., 2019

37. Biodiesel purification
• Biodiesel is then purified in a multi-stage distillation column so as to obtain a
biodiesel with purity of > 99.6% v/v.
• The used catalyst is later removed from glycerol stream in a neutralization
reactor by adding 100% pure phosphoric acid (H3PO4) into the glycerol.
• The result is glycerol and either Na3PO4 or K3PO4 depending on the catalyst
used which are then separated by gravity.
• After catalyst removal glycerol with 85-90% concentration is purified if
necessary in a four stage distillation column.

38. Heterogenous catalysis
• This new process, which functions continuously. Has been operational since
2006.
• The process involves use of solid alkaline such as alkaline metals carbonates
(Na2CO3, K2CO3), alkaline earth metal carbonates (CaCO3), alkaline earth
metal oxides (CaO, MgO, SrO, BaO) and other oxides as ZnO.
• Using such heterogenous catalysts offers the advantage of eliminating
expensive treatments for neutralizing the acid and for purification of
biodiesel

39. • The reaction takes place at higher temperatures (180 to 220 oC) and pressures
between 40 and 60 bars.
• Two transesterification reactors are installed in series.
• The excess methanol is eliminated by partial evaporation between the two
reactors, allowing a change in the chemical balance, and the yield approaches
100%.
• The final excess of methanol is eliminated by distillation before recycling.
• The glycerol obtained is sufficiently pure to be used directly in many applications.
Homework! Find out the disadvantages of using homogeneous catalysts over
heterogeneous catalysts

40. Industrial heterogeneous catalysis process for production of
biodiesel fuel

42. 2. Hydrogenation Derived Renewable
Diesel (HDRD)

43. • HDRD is produced by refining fats or vegetable oils in a hydrotreating process.
• Hydrodeoxygenation eliminates oxygen by reacting triglycerides and FFAs with
hydrogen to form water and n-paraffins,
•
• Decarboxylation or decarbonylation eliminates oxygen to form of carbon
dioxide or carbon monoxide and n-paraffins.
• The volume yield is 99% and the primary co-product is propane.
• By-products are water and carbon oxides

44. A structure of triglyceride
red=oxygen, white=hydrogen, grey= carbon atoms

45. Feedstock
• HDRD can be produced from a wider range of feedstock than biodiesel.
There are two principal reasons for this:
1. Triglycerides can be converted to biodiesel via transesterfication or to HDRD
via hydroprocessing. Biodiesel contains oxygen thus are susceptible to
oxidation. This makes it unstable during periods of storage and
transportation. On the other hand HDRD results in paraffinic hydrocarbons
which are by nature fully saturated and are therefore not susceptible to
oxidative instability.
2. Biofuel feedstock contain high amount of FFA up to 15%. They can be
detrimental to the biodiesel production process because they react with the
alkali catalyst to form soaps. During hydroprocessing, FFA’s are easily
converted to paraffins and therefore FFA content of the feedstock is not a
concern for HDRD production.

46. Biodiesel and Renewable Diesel Feedstock and their Products

47. Production Pathways for HDRD

48. Hydrotreatment to HDRD
Pre-treatment
• Most feedstock require a pre-treatment step to prepare them
for hydro processing.
• Depending on the quality of the feedstock, it may contain
varying levels of alkali metals, phospholipids and metallolipids,
which can hinder the effectiveness of the hydroprocessing
catalysts.

49. Reaction mechanism
• The principal objectives of hydrotreatment of triglycerides are to remove
oxygen and to saturate C=C double bonds to produce paraffinic n-alkanes in
the diesel boiling range.
• Hydrogen is reacted with the triglycerides under high temperature and
pressure in the presence of catalysts.
• Next, the glycerol backbone is broken and the oxygen removed, leaving
paraffinic n-alkanes.
• There are two principal pathways by which oxygen can be removed from
the triglycerides: hydrodeoxygenation (HDO) and decarboxylation (DCO).

50. 1. Hydrodeoxygenation (HDO)
• HDO reactions of bio- oils/fats operate at elevated temperatures, between
(300-600oC) and under high hydrogen pressure (4.8-15.2 MPa) in the
presence of a heterogeneous catalyst.
• Reaction conditions such as temperature and pressure are adjusted
depending on the feedstock.
• The catalysts used for HDO are Cobalt Molybdenum (Co-Mo) or Nickel
Molybdenum (Ni-Mo).
• The main product is hydrocarbons (n-paraffins) while propane and water
are the by-products.

51. Figure. The oxygen removal from the triglycerides (HDO
reaction)

52. Optimum hydro processing temperatures and pressures

53. 2. Decarboxylation
• Decarboxylation is the chemical reaction where a carboxyl group (-
COOH) is removed from a molecule as carbon dioxide (CO2).
• Because fatty acids are carboxylic acids, they can be processed in the
same way to form straight chain hydrocarbons (n-hydrocarbons).
• During DCO, the CO2 group is separated completely from the propyl
group of the glycerol and the aliphatic chains of the fatty acids,
which are then hydrogenated.
• DCO produces the propane as the byproduct, but it also produces
CO2, CO and water

55. 3. Bioethanol

56. • Bioethanol also known as ethyl alcohol is a biomass based ethanol which
is an alternative to conventional gasoline.
• It is produced from materials containing appreciable amounts of sugar or
materials that can be converted into sugar such as starch or cellulose and
hemicelluloses.
• Bioethanol has a molecular formula of C2H5OH.
• It has similar properties with gasoline.

57. Density
(kg/L)
Viscosity
(mm2/s)
Flash
point (oC)
Calorific
value at
20oC
(MJ/kg)
Calorific
value
(MJ/L)
Octane
number
(RON)
Fuel
equivalen
ce (L)
Petrol 0.76 0.6 <21 42.7 32.45 92 1
Bioethanol 0.79 1.5 <2 26.8 21.17 >100 0.65

58. Advantages of bioethanol
• It is biodegradable;
• less explosive;
• low toxicity to humans;
• low volatility;
• low evaporation and photochemical activities;
• high heat of vaporization and
• easier to extinguish if burning than petrol and diesel

59. Disadvantages of bioethanol
• Due to its lower energy output (26.8 MJ/kg) its fuel efficiency is lower than that of
gasoline. In order to meet the same energy output as that of 1 kg of gasoline has
to be compensated with 1.6 kg of bioethanol.
• When bioethanol is blended with gasoline, corrosion of inners parts of fuel tank
and engine increases, which means more corrosion resistant materials are
needed (why???)
• Large area is required to produce raw materials.
• Pure ethanol is also difficult to vaporise which can make starting a car in cold
weather difficult

60. Bioethanol feedstock

61. Bioethanol production Technologies

62. Depending on type of feedstock the process for production of fuel bioethanol from
biomass can be broken down as follows:
• Feedstock production: harvesting , reception, storage
• Physical pretreatment: milling
• Saccharification (hydrolysis): conversion of starch and cellulose into sugar
(glucose).
• Chemical treatment: dilution of the sugars with water and addition of yeast or
other organisms
• Fermentation: production of ethanol in solution with water along with waste
and by-products
• Distillation: separation of ethanol
• Dehydration: Removal of the remaining water by molecular sieves (anhydrous
ethanol)
• Co-product treatment:

63. Sugar to bioethanol (ethanol) Process
• This is the simplest way to produce bioethanol.
• Biomass that contains six-carbon sugars can be fermented
directly to ethanol.
• Typical sugary feedstock are sugarcane and sugar beets.
C6H12O6 + Yeast → 2CO2 + 2C2 H5OH
Glucose Carbon dioxide Ethanol
(100 g) (48.8 g) (51.4 g)

64. • The optimum temperature for fermentation ranges between 90-95oF (32-
35oC),
• Beer produced from fermentation is in the concentration of about 7-15 wt
% in water.
• Distillation is used to separate ethanol from water. A 96% (v/v) of
bioethanol is obtained after distillation.
• Fuel bioethanol is obtained by dehydration of ethanol after distillation.
• Two technologies the Azeotropic Distillation and Molecular Sieve
Technology are commonly used for dehydration of ethanol to >99.5%

65. Starch to bioethanol process
• Starch molecules are made up of long chains of glucose
molecules which have to be broken into simple glucose
molecules (fermentable sugars). A processes known as
saccharification or hydrolysis.
• Hydrolysis is a chemical process in which a molecule of
water is added to a starchy material.
• Hydrolysis is performed in the presence of a catalyst (dilute
acids, concentrated acids or enzymes) which breaks the
chemical bonds at 105 oC.

66. Acid hydrolysis advantages:
• Faster acting reaction
• Less residence time in reactor
Enzymatic hydrolysis advantages:
• Run at lower temperature
• Higher yields
• Environmentally friendly
• Low maintenance cost
Find out their disadvantages!!!

67. Enzymes used in starch hydrolysis
Enzyme Commission (EC)
number is a numerical
classification scheme for
enzymes, based on the
chemical reactions they
catalyze.

68. Block diagram for starch to bioethanol production

69. Lignocellulose-to-Ethanol Process
• Lignocellulosic materials are comprised of lignin, hemicellulose.
• Main function of lignin is to provide structural support for the plant.
• Unfortunately, lignin which contains no sugars encloses the cellulose and
hemicellulose molecules, making them difficult to reach.
• Lignocellulosic materials have to be converted to five- and six- carbon
sugars, before they can be converted into ethanol.
• Therefore, lignocellulosic materials require pre-treatment prior to
hydrolysis.

71. Production pathways

72. Why pre-treatment?
• Destroy lignin shell protecting cellulose and hemicellulose
for enzyme to access substrate (sugar)
• Decrease crystallinity of cellulose.
• Increase porosity.
Figure. Schematic diagram of the role of pretreatment in the conversion
of biomass to fuel.

73. Pretreatment must meet the following requirements:
i. improve the formation of sugars or the ability to subsequently form
sugars by hydrolysis;
ii. avoid the degradation or loss of carbohydrate;
iii. avoid the formation of byproducts that are inhibitory to the
subsequent hydrolysis and fermentation processes; and
iv. be cost-effective.
Pre-Treatment methods
• Physical
• Chemical
• Biological

74. A. Physical Pre-treatment
1. Mechanical Comminution
• Comminution is the reduction of solid materials from one average particle size
to a smaller average particle size, by crushing, grinding, etc.
• Comminution of lignocellulosic materials reduce celluloses crystallinity.
• The size of the materials is usually 10-30 mm after chipping and 0.2-2 mm after
milling or grinding.

75. 2. Pyrolysis
• Pyrolysis is a thermochemical decomposition of organic material at elevated
temperatures in the absence of oxygen.
• Cellulose rapidly decomposes to gaseous products and residual char when biomass is
treated at temperatures greater than 300 °C.
B. Physico-Chemical Pre-treatment
Steam Explosion
• Steam explosion is the most commonly used method for the pretreatment
of lignocellulosic materials.
• In this method, biomass is treated with high-pressure saturated steam,
and then the pressure is suddenly reduced, which makes the materials
undergo an explosive decompression

76. • Steam explosion is typically initiated at a temperature of 160-
260 °C (corresponding pressure, 0.69-4.83 MPa) for several
seconds to a few minutes before the material is exposed to
atmospheric pressure.
• The biomass/steam mixture is held for a period of time to
promote hemicellulose hydrolysis, and the process is
terminated by an explosive decompression.
• The process causes hemicellulose degradation and lignin
transformation due to high temperature, thus increasing the
potential of cellulose hydrolysis.

78. Ammonia Fiber Explosion (AFEX)
• Ammonia fiber explosion is a physicochemical pretreatment process in which
lignocellulosic biomass is exposed to liquid ammonia at high temperature
and pressure for a period of time, and then the pressure is suddenly reduced.
• The AFEX process is very similar to steam explosion
• In a typical AFEX process, the dosage of liquid ammonia is 1-2 kg of
ammonia/kg of dry biomass, the temperature is 90 °C, and the residence time
is 30 min.

79. C. Chemical Pre-treatment
Ozonolysis
• Ozone treatment is one way of reducing the lignin content of lignocellulosic
wastes.
• Ozone attacks lignin and hemicellulose in preference to cellulose giving water
soluble products.
Acid Hydrolysis
• Concentrated acids such as H2SO4 and HCl are also used to treat
lignocellulosic materials.

80. Alkaline Hydrolysis
• Some bases can be used for the pretreatment of lignocellulosic materials,
and the effect of alkaline pretreatment depends on the lignin content of the
materials
• Alkali pretreatment processes are carried out at lower temperatures and
pressures than other pretreatment technologies.

81. End of chapter