The document discusses different types of biofuels. It defines first, second, third and fourth generation biofuels and provides examples of their feedstocks. It then focuses on biodiesel, describing its production via transesterification of vegetable oils. The processes of acid and base catalyzed transesterification are summarized. Finally, it discusses bioethanol production via fermentation of sugars or starches by yeast and bacteria.

2.  INTRODUCTION
 CLASIIFICATION OF BIOFUELS
 BIODIESEL
 BIODIESEL PRODUCTION BY TRANSESTERIFICATION
 ACID AND BASE CATALYSED REACTIONS
 ENZYMES INVOLVED IN BIOHYDROGEN PRODUCTION
 BIOETHANOL PRODUCTION BY FERMENTATION

3.  The term biofuel is referred to as solid, liquid,
or gaseous fuels that are predominantly
produced from biorenewable or combustible
renewable feedstocks.
 Rudlof Diesel designed the first diesel engine.
 Liquid biofuels are important for the future
because they replace petroleum fuels.
 Biofuels are generally considered as offering
many priorities, including sustainability,
reduction of greenhouse gas emissions,
regional development, social structure and
agriculture, security of supply.

5. FIRST GENERATION BIOFUELS
 Ist Generation biofuels are also called as conventional biofuels .
 First generation biofuels refer to biofuels made from sugar, starch,
vegetable oils, or animal fats using conventional technology.
 The basic feedstocks for the production of first generation biofuels
are often seeds or grains such as wheat, which yields starch that is
fermented into bioethanol, or sunflower seeds, which are pressed to
yield vegetable oil that can be used in biodiesel.

6. SECOND GENERATION BIOFUELS
 Second generation biofuels are also called advanced biofuels.
 Second generation biofuels are made from non-food crops, wheat straw,
corn, wood, energy crop using advanced technology.
THIRD GENERATION BIOFUELS
 Third generation biofuels are also called as advanced biofuels.
 Third generation biofuels use specially engineered crops such as algae
as the energy source .
 These algae are grown and harvested to extract oil within them.
 The oil can then be converted into biodiesel or it can be refined into
other fuels as replacements to petroleum-based fuels.

7. FOURTH GENERATION BIOFUELS
 Fourth generation is based in the conversion of vegoil and biodiesel
into biogasoline using the most advanced technology.
 This class of biofuels includes electrofuels and photobiological solar
fuels.
Third
Generation
Biofuels

8. Generation Feedstock Example
First Generation
Biofuels
Sugar, starch, vegetable
oils, or animal fats
Bioalcohols, vegetable
oils, Biodiesel,
Biosyngas, Biogas
Second Generation
Biofuels
Non-food crops, wheat
straw, corn, wood, solid
waste, energy crops
Bioalcohols, bio-oil, bio-
DMF, biohydrogen, bio-
Fischer-Tropsch diesel,
wood diesel
Third Generation
Biofuels
Algae Vegetable oil, biodiesel
Fourth Generation
Biofuels
Vegetable oil, biodiesel Biogasoline

10.  Biodiesel (Greek, bio, life + diesel from Rudolf
Diesel) refers to a diesel equivalent, processed fuel
derived from biological sources.
 Biodiesel fuels are attracting increasing attention
worldwide as a blending component or a direct
replacement for diesel fuel in vehicle engines.
 Biodiesel is known as monoalkyl, such as methyl
and ethyl, esters of fatty acids (FAME) derived
from a renewable lipid feedstock, such as
vegetable oil or animal fat.
 Biodiesel typically comprises alkyl fatty acid
(chain length C14–C22) esters of short-chain
alcohols, primarily, methanol, or ethanol.
Biodiesel
formatio
n

11.  The possibility of using vegetable oils as fuel has been recognized since
the beginning of diesel engines.
 Vegetable oil has too high a viscosity for use in most existing diesel
engines as a straight replacement fuel oil.
 There are a number of ways to reduce vegetable oil’s viscosity.
 Dilution, microemulsification, pyrolysis, and transesterification are the
four techniques applied to solve the problems encountered with the
high fuel viscosity.

12.  Transesterification (also called alcoholysis) is the reaction of a fat or oil
triglyceride with an alcohol to form esters and glycerol.
 A catalyst is usually used to improve the reaction rate and yield.
 Because the reaction is reversible, excess alcohol is used to shift the
equilibrium to the products side.

13. BASE CATALYZED REACTIONS
 The base-catalyzed transesterification of vegetable oils proceeds faster than the
acid-catalyzed reaction.
 It uses low temperature (60°C) and pressure (20Psi).
 Alkaline metal alkoxides (as CH3ONa for the methanolysis) are the most active
catalysts, since they give very high yields (> 98%) in short reaction times (30 min)
even if they are applied at low molar concentrations (0.5 mol%).
 Alkaline metal hydroxides (KOH and NaOH) are cheaper than metal alkoxides, but
less active.
FIRST STEP:
 The first step is the reaction of the base with the alcohol, producing an alkoxide
and the protonated catalyst.
SECOND STEP:
 The nucleophilic attack of the alkoxide at the carbonyl group of the triglyceride
generates a tetrahedral intermediate from which the alkyl ester and the
corresponding anion of the diglyceride are formed.

14. ACID CATALYSED REACTIONS
 The transesterification process is catalyzed by Bronsted acids, preferably
by sulfonic and sulfuric acids.
 These catalysts give very high yields in alkyl esters, but the reactions are
slow, requiring, typically, temperatures above 100 °C and more than 3 h to
reach complete conversion.
STEP FIRST:
 Acids act by adding a proton to the carbonyl group, making it more
reactive.
STEP SECOND:
 The protonation of the carbonyl group of the ester leads to the
carbocation which after a nucleophillic attack of the alcohol produces the
tetrahedral intermediate.
STEP THIRD:
 This intermediate eliminates glycerol to form the new ester and to
regenerate the catalyst H+.

15.  Hydrogen generation via biological processes can be achieved by a series
of biological electrochemical reactions.
 These reactions are facilitated by a series of biocatalyst enzymes that are
found to play critical roles during the BHP.
 There are three main bio-hydrogen production and consumption
enzymes, which are responsible for the net bio-hydrogen evolution.
 These three different enzymes are reversible hydrogenase, membrane-
bounded uptake hydrogenase, and nitrogenase enzymes.
 Among them, nitrogenase and hydrogenase are the two pivotal
biocatalysts.

16. NITROGENASE:
 Hydrogen generation can be catalyzed by nitrogenase under an
anaerobic environment at photofermentation conditions from
photosynthetic bacteria.
 Nitrogenase is well-known for fixing the nitrogen molecule, and is
commonly found in archaea and bacteria.
 The nitrogen molecule is catalyzed into ammonia by the
nitrogenase, hydrogen gas is generated as a by-product, and the
entire chemical redox balance is maintained during this biological
catalytic nitrogen fixation process.
N2 + 8𝐻+ +8𝑒− + 16 ATP⎯⎯⎯⎯⎯⎯⎯⎯2𝑁H3 + 𝐻2↑+16ADP+ 16Pi
Nitrogenas
e

18. HYDROGENASE:
 Green algae uses hydrogenase enzyme to produce hydrogen.
 H2 production is catalyzed by two hydrogenases.
STRUCTURAL CLASSIFICATION
i) [Fe-Fe]- hydrogenase
 The [Fe-Fe] hydrogenase catalyzes the oxidation of H2, as well as the
reduction of H+, but the enzyme is mainly found in the H2 generating
process.
 The [Fe-Fe] hydrogenase, are sensitive to the presence of oxygen
(which is only active under strictly anaerobic conditions).
 Found in_ Clostridium pasteurianum, Megasphaera elsdenii,
Scenedesmus obliquus.
2H+ + 2Fd- ________ H2 + 2Fd

19. ii) [Ni-Fe]-hydrogenase:
 The [Ni-Fe] hydrogenases are found to catalyse both H2 evolution and
uptake.
 The [Ni-Fe] hydrogenases present better O2 tolerance than the
hydrogenase with [FeFe] metal centers.
 [Ni-Fe] widely exists in bacteria during hydrogen fermentation.
Cyanobacterial catalysis:
 They posses up to three enzymes that are directly involved in H2
metabolism:
i) An uptake hydrogenase( Hup)
ii) A bidirectional hydrogenase ( Hox)
iii) Nitrogenase

20.  Hup hydrogenase comprises of 2 subunits_ HupL and HupS, which
regenerate electrons from H2.
 A bidirectional Hox hydrogenase either consumes or produces H2.

21.  Bioethanol also called as pure alcohol or ethyl alcohol or grain alcohol
or drinking alcohol.
 Bioethanol is an alcohol made by fermentation, mostly from
carbohydrates produced in sugar or starch crops such as corn or
sugarcane.
 Cellulosic biomass, derived from non-food sources such as trees and
grasses, is also being developed as a feedstock for ethanol production.

22. PROPERTIES OF BIOETHANOL:
 Colorless and clear liquid.
 One of the widely used alternative
automotive fuel in the world( Brazil &
U.S.A are the largest ethanol producers).
 Much more environmental friendly.
 Lower toxicity level.
 Principle fuel used as a petrol substitute

23.  Many countries have started production of ethanol by fermentation
process.
 Certain yeasts and bacteria are employed for alcohol fermentation.
 The type of organism chosen mostly depends on the nature of the
substrate used.
 Among the yeast saccharomyces cerevisiae is the most commonly used,
while among the bacteria zymomonas mobilis is the most frequently
employed for the alcohol production.
RAW MATERIALS:
 Sugary materials_ molasses, glucose, sucrose and whey.
 Starchy materials: wheat, rice, maize and potato.
 Cellulosic material: wood and agricultural wastes

25. The fermentation method generally uses three steps:
(a) The formation of a solution of fermentable sugars,
(b) The fermentation of these sugars to ethanol, and
(c) The separation and purification of the ethanol, usually by
distillation.
PREPRATION OF NUTRIENT SOLUTION( MEDIA):
• The most commonly used raw materials are molasses, grains, whey,
potatoes and wood wastes.
• When molasses are used for fermentation, it is diluted with water so
that the sugar concentration is in the range of 10-18%.
• When starchy materials are used, they have to be first hydrolyzed by
pretreatment for use as nutrients.
• This may be done by barley malt, dilute acids or fungal amylases( e.g.,

26. FERMENTATION OF SUGARS TO ETHANOL:
 Fermentation involves microorganisms that use the fermentable sugars
for food and in the process produces ethyl alcohol and other byproducts.
 These microorganisms can typically use the 6-carbon sugars, one of the
most common being glucose.
 Therefore, cellulosic biomass materials containing high levels of glucose
or precursors to glucose are the easiest to convert to ethanol.
 Microorganisms, termed ethanologens, presently convert an inadequate
portion of the sugars from biomass to ethanol.
 Although fungi, bacteria, and yeast microorganisms can be used for
fermentation, specific yeast (Saccharomyces cerevisiae also known as
Bakers’ yeast) is frequently used to ferment glucose to ethanol.

27. Separation and purification of the ethanol by distillation:
 Ethanol from fermentation broth can be recovered by successive
distillations for a conc. above 95%, special techniques of distillation
have to be adopted.
 For a preparation of absolute (100 % )alcohol, an azetropic mixture of
benzene, water and alcohol is first prepared. This mixture is then
distilled by gradually increasing the temperature.
 By this technique, it is possible to first remove benzene-ethanol-water
mixture, and then ethanol-benzene mixture. Thus, absolute alcohol is
left out.