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INTRODUCTION
Biofuels are fuels made from organic
matter , which can be divided into threecategories:
First-generation biofuels are madelargely from edible sugars and
starches. Second-generation biofuels are made
from nonedible plant materials(cellulosic material).
Third-generation biofuels are madefrom algae and other microbes.
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INTRODUCTION CONTD
Biofuels are
Renewable
Advanced biofuels can offer
environmental benefits such as lower
carbon emissions and lower sulfur.
Advanced biofuels could help meet the
world's future energy needs.
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FUEL FROM AGRICULTURAL WASTE
Ethanol is a renewable energy sourcebecause plants use sunlight which cannot
be depleted; and ethanol are produced by
agricultural waste.
Creation of ethanol starts with the use of
starchy feedstock e.g sugar cane or maize
(corn), as well as advances using
cellulosic feedstock which can be usedindustrially to produce ethanol e.g
switchgrass (a non food plant) and scrap
wood.
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PRODUCTION PROCESS
The basic steps for large scaleproduction of ethanol are:
Microbial (yeast) fermentation of
sugars,
Distillation and
Dehydration
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PRODUCTION PROCESS CONTD
Prior to fermentation
Some crops require saccharification orhydrolysis of carbohydrates such ascellulose and starch into sugars.
Saccharification of cellulose is calledcellulolysis
Enzymes are used to convert starch intosugar.
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STEP 1: FERMENTATION
1. Ethanol is produced by microbial fermentation of
the sugar. By fermentation, the yeast speciesSaccharomyces cerevis iaeconverts
carbohydrates to carbon dioxide and alcohols, or
Zymomonas mobi l isis a bacterium belonging to
the genus Zymomonas can also be used for
bioethanol-production, which surpass yeast in
some aspects.
2. Z. m ob il is degrades sugars to pyruvate using the
Entner-Doudoroff pathway. The pyruvate is then
fermented to produce ethanol and carbon dioxideas the only products (analogous to yeast).
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STEP 2: DISTILLATION For the ethanol to be usable as a fuel,
most of the water is removed bydistillation, but the purity is limited to
9596% due to the formation of a low-
boiling water-ethanol azeotrope with
maximum (95.6% m/m (96.5% v/v)
ethanol and 4.4% m/m (3.5% v/v) water).
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STEP 3: DEHYDRATION
There are basically three dehydration processes
from an azeotropic ethanol/water mixture.
The first process, used in many early fuel
ethanol plants, is called azeotropic distillation.
When these components are added to the
mixture, it forms a heterogeneous azeotropic
mixture in vapor-liquid-liquid equilibrium, which
when distilled produces anhydrous ethanol in
the column bottom, and a vapor mixture of
water, ethanol, and cyclohexane/benzene.
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STEP 3: DEHYDRATION CONTD
When condensed, this becomes a two-
phase liquid mixture. The heavier phase,
poor in the entrainer (benzene or
cyclohexane), is stripped of the
entrainer and recycled to the feed, whilethe lighter phase together with
condensate from the stripping is
recycled to the second column.
The last process uses molecular sievesto remove water from fuel ethanol.
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PROCESS OF CELLULOSIC ETHANOL
Cellulosic resources are widespread and
abundant; being abundant and outside thehuman food chain makes cellulosic materials
relatively inexpensive feedstock for ethanol
production.
Cellulosic materials are composed of lignin,hemicellulose and cellulose which are
sometimes called lignocellulosic materials.
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CELLULOSIC ETHANOL PRODUCTION
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ETHANOL- FROM CELLULOSE (EFC)
There are three types of EFC processes
Acid Hydrolysis: this is where dilute acid e.g sulphuricacid, is used to convert cellulosic materials to sugar,
OR
Enzymatic Hydrolysis: enzymes naturally occuring in plant
protein cause chemical reaction to occur which breakdown
the crystalline structure of the linocellulose and remove
lignin to expose hemicellulose and cellulose molecules
Thermochemical: A microorganism that is capable of
converting the synthesis gas( a mixture of hydrogen and
carbon oxides) is introduced to bring about fermentation
under specific process to yield ethanol.
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FUEL FROM ACETIC ACID
Methane, the chief of component natural gas,
is produced in nature by the microbial
decay of vegetation and animal waste in
the absence of atmospheric oxygen. This
process is termed anaerobic digestion.The production of methane from biomass has
been suggested as a means of lessening
our demand for natural gas and utilizing
reservoirs of methane in the naturalenvironment.
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FUEL FROM ACETIC ACID CONTD
Methane fermentation is a versatile biotechnology
capable of converting almost all types ofpolymeric materials to methane and carbon
dioxide under anaerobic conditions
It is achieved as a result of the consecutive
biochemical breakdown of polymers in anenvironment in which a variety of
microorganisms harmoniously grow and
produce reduced end-products which include
fermentative microbes (acidogens); hydrogen-producing, acetate-forming microbes
(acetogens); and methane-producing microbes
(methanogens).
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STEP 1: HYDROLYSIS
Polymeric materials such as lipids,
carbohydrates etc. are hydrolyzed by
extracellular hydrolases into primary
monomeric units .
Hydrolysis is carried out by bacteriafrom the group of relative anaerobes of
genera: Streptococcus, Enterobacter ium .
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STEP 2: ACIDOGENESIS
Here acidifying bacteria convert water soluble
chemical substances (usually the products from step1) into short chain organic acids, alcohol, aldehydes,carbon dioxide and hydrogen. This process isbidirectional. It is divided into hydrogenation anddehydrogenation.
The acid phase bacteria belonging to facultativeanaerobes use oxygen accidentally introduced intothe process, creating two favourable conditions forthe development of obligatory anaerobes of thefollowing genera: Pseudomonas, Baci l lus,Clostr id ium , Micrococcu sorFlavobacter ium.
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STEP 3: ACETOGENESIS
Conversion of the products of the acid phase (step 2)into acetate (acetic acid) and hydrogen by acetatebacteria.
The genera of Syntrophomonas and Syntrophobacterare responsible for this phase.
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STEP 4: METHANOGENESIS
Here there is production of methane by
methanogens. Methane is produced from acetic
acid, hydrogen, carbon dioxide, formate and
methanol, methylamine or dimethyl sulphide
produced in the previous phases.
Microorganisms which facilitate the breakdown
od acetic acid to methane are referred to as
Methanogenic archeons: Methanothermobacter,
Methanococcus, Methanobacter ium
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Summary ofMicroorganisms
cooperation in organicmatter degradation.
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Microorganism
FermentativeBacteria
Acid phasebacteria
AcetogenicBacteria
MethanogenicBacteria
ElectronDonor
Organic Carbon
Organic Carbon
OrganicCarbon/H
2
OrganicCarbon/H2
Electronacceptor
Organic Carbon
Organic Carbon
CO2
CO2
Product
CO2
H2
CH3COOH
CH4
Reaction type
Fermentation
Acidogenesis
Acetogenesis
Methanogenesis
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REFERENCES
Chisti, Y. 2007. Biodiesel from microalgae. Biotechnol. Adv.25:294-306.
Food and Agriculture Organization of the United Nations.2008. The state of food and agriculture. Biofuels:prospects, risks and opportunities.
National Science Foundation. 2008. Breaking the chemicaland engineering barrier to lignocellulosic biofuels: nextgeneration hydrocarbon biorefineries. National ScienceFoundation. Chemical, Bioengineering Environmental andTransport systems division, Washington, D.C.
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CONTD
Rogers P; Lee K, Skotnicki M, Tribe D (1982). Microbia l react ions:
Ethanol Product ion by Zymomon as mobi l is. New York: Spinger-Verlag.
pp. 3784. ISBN978-3-540-11698-1.
^ Swings, J; De Ley, J (1977 Mar). "The biology of
Zymomonas". Bacter io logical reviews41 (1): 146. PMID16585
Ziemiski, K. & Frc, M. 2012 Methane fermentat ion p rocess as
anaerobic d igest ion of biom ass: Transform at ions, stages and
microorgan isms. Academic Journals Vol. 11(18), pp. 4127-4139
http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Special:BookSources/978-3-540-11698-1http://en.wikipedia.org/wiki/Zymomonas_mobilishttp://en.wikipedia.org/wiki/PubMed_Identifierhttp://www.ncbi.nlm.nih.gov/pubmed/16585http://www.ncbi.nlm.nih.gov/pubmed/16585http://en.wikipedia.org/wiki/PubMed_Identifierhttp://en.wikipedia.org/wiki/Zymomonas_mobilishttp://en.wikipedia.org/wiki/Special:BookSources/978-3-540-11698-1http://en.wikipedia.org/wiki/Special:BookSources/978-3-540-11698-1http://en.wikipedia.org/wiki/Special:BookSources/978-3-540-11698-1http://en.wikipedia.org/wiki/Special:BookSources/978-3-540-11698-1http://en.wikipedia.org/wiki/Special:BookSources/978-3-540-11698-1http://en.wikipedia.org/wiki/Special:BookSources/978-3-540-11698-1http://en.wikipedia.org/wiki/Special:BookSources/978-3-540-11698-1http://en.wikipedia.org/wiki/Special:BookSources/978-3-540-11698-1http://en.wikipedia.org/wiki/Special:BookSources/978-3-540-11698-1http://en.wikipedia.org/wiki/International_Standard_Book_Number