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Bioconversion of biomass to ethanol-an overview Renata Bura November 25 th, 2008
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Overview What is bioconversion? Why bioconversion? Sugar cane to ethanol Corn to ethanol Biomass composition Bioconversion to ethanol process –Pretreatment –Hydrolysis –Fermentation Pros and cons of bioethanol
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What is bioconversion? General: a process which uses biological agents (microorganisms or protein) to transform a feedstock into desirable products. Bioethanol A chemical/biochemical process by which lignocellulosic materials are converted to ethanol and other co- products.
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Bioconversion Biomass Pretreatment Hydrolysis Fermentation Distillation Ethanol
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Why bioethanol?
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Ethanol (CH 3 CH 2 OH) Ethyl alcohol, grain alcohol –Clear, colorless liquid Ethanol made from cellulosic biomass instead of starch crops-bioethanol Advantages of bioethanol –Domestic renewable fuel sources –Reduces reliance on foreign oil –Cleaner fuel sources –Easily produced and stored –Increases fuel octane number for little cost
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Energy content Gasoline Ethanol Biodiesel 100% 67% 86%
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World ethanol production
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Sugar cane, sugar cane bagasse Sugar cane bagasse Processing Ethanol
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Sugar cane bioethanol Brazil produces 3,96 billion gallons of ethanol from sugar cane Production cost $0.87/gallon, the lowest in the world Fossil fuel energy used to make the fuel (input) compared with energy in the fuel (output) 1:8 Green house emission during production and use 56% less compared with gasoline
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Corn plant Corn kernel (without the fibre)-starch alcohol Corn fibre-lignocellulosic alcohol Corn stover-lignocellulosic alcohol
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Corn to ethanol US produces 4,86 billion gallons of ethanol from corn (2006) Production cost ~ $1.09/gallon Fossil fuel energy used to make the fuel (input) compared with energy in the fuel (output) 1:1.3 or negatives values Greenhouse gas emission during production and use 22% less compared with gasoline
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“We can get fuel from apples, weeds, sawdust, almost anything….. And it remains for someone to find how this fuel can be produced commercially- better fuel at a better price than we now know.” Henry Ford Henry Ford
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Why bioconversion? Energy –An alternative source of energy for the transportation sector produced locally Air pollution –Reduction in greenhouse gas emission Waste elimination –Elimination of problems with field burning/incineration, stockpiling, etc. Socio/economical benefits –Creation of new jobs, rural development
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Possible lignocellulosic feedstocks Agricultural residues (corn stover, corn fibre, wheat straw, rice straw) Wood residues Paper waste Municipal solids waste
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Biomass composition
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Cellulose
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Hemicellulose
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Lignin
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Bioconversion of biomass to ethanol (pretreatment) Biomass Pretreatment Liquid phase Solid phase Cellulose Sugars Ethanol Fermentation Ethanol Sugars Fermentation Hydrolysis Lignin Recovery
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Pretreatment-”disruption” Helps in separation of main biomass components (cellulose, hemicellulose and lignin) Increase available surface area Reduce particle size
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Steam explosion Treatment of biomass with high-pressure steam for a short period of time followed by sudden decompression Acid (H 2 SO 4, SO 2 ) impregnation of biomass increases SE efficiency Typical conditions: –Temperature: 170-250 o C, 338-482 F –Time: 10sec-10min
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Steam gun Karin Fill valve Steam valve Blow valve Receiving vessel Receiving vessel Pretreated corn stover
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Bioconversion of biomass to ethanol (hydrolysis) Biomass Pretreatment Liquid phase Solid phase Cellulose Sugars Ethanol Fermentation Ethanol Sugars Fermentation Hydrolysis Lignin Recovery
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What are cellulases? Produced by many strains of bacteria and fungi Catalyzes the depolymerization of cellulose chains –Endoglucanases –Exoglucanases –β-glucosidases
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Cellulases Endoglucanases (EG) cutting the cellulose chains randomly Cellobiohydrolyses (CBH) cutting cellobiose units of the ends of the cellulose chains Binding domainCatalytic domain
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Bioconversion of biomass to ethanol (fermentation) Biomass Pretreatment Liquid phase Solid phase Cellulose Sugars Ethanol Fermentation Ethanol Sugars Fermentation Hydrolysis Lignin Recovery
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Fermentation Defined as: Cellular metabolism under anaerobic conditions (absence of oxygen) for the production of energy and metabolic intermediates Many organisms can “ferment” (i.e., grow anaerobically) Not all produce ethanol as an end-product of fermentation
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Strain selection Choice of microorganism for ethanol production has traditionally been a Yeast Yeast: –Single cell microorganism –Fungi –Facultative anaerobe Most common industrial fermenter is Saccharomyces cerevisiae (baker’s or brewer’s yeast) Why?
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Fermentation Conversion factor 0.51 1g/L of glucose: 0.51g/L ethanol (maximum)
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Biofuels-comparison Production (billion gallons) Production cost ($) Energy balance GHE reduction (%) Corn4.861.091.322 Cane3.960.878.055-90 LignocelluloseNA 2-3691 Biodiesel0.50NA2.568
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Alternative options??…….
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Flexible-Fuel Vehicles (FFV) Use E85 (85% ethanol and 15% gasoline) Cost of FFV is similar to traditional gasoline vehicle 1gallon of E85 provides the same energy as 0.72 gallons of gasoline (lower E content) Special materials required for fuel lines, hoses, valves, gaskets, fuel tank (corrosive ethanol) Washington state more than 35, 000 of FFVs (U.S. over 4 million FFVs) –Ford Focus, Chrysler Sebring, Dodge Stratus, Dodge Caravan, Chevrolet Avalanche
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Summary What is bioconversion? Why bioconversion? Sugar cane to ethanol Corn to ethanol Biomass composition Bioconversion to ethanol process –Pretreatment –Hydrolysis –Fermentation Pros and cons FFV
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References www.ento.vt.edu/~salom/SPBbiology/blustain.html www.pherotech.com/new_products.html www.dnr.wa.gov/../issues/2002issues.html www.laco.ufpe.br/prh28/ www.bio-pro.de/en/region.rhein/magazin/01440 www.maize.agron.iastate.edu/corngrows.html www.nrel.gov www.energy.iastae.edu www.usda.gov/wps/portal/usdahome www.ethanol-gec.org/clean/cf13.htm www.eere.energy.gov/biomass/
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