Fuel (Ethanol) From Agricultural Waste

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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

Fuel (Ethanol) From Agricultural Waste

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