Bioconversion of biomass to ethanol-an overview

Renata Bura

November 25th, 2008

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

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.

Bioconversion

Biomass

Pretreatment

Hydrolysis

Fermentation Distillation

Ethanol

Why bioethanol?

Ethanol (CH3CH2OH)

• 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

Energy content

Gasoline Ethanol Biodiesel

100% 67% 86%

World ethanol production

Sugar cane, sugar cane bagasse

Sugar cane

bagasse

Processing

Ethanol

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

Corn plantCorn kernel (without the fibre)-starch alcoholCorn fibre-lignocellulosic alcoholCorn stover-lignocellulosic alcohol

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

“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

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

Possible lignocellulosic feedstocks

• Agricultural residues (corn stover, corn fibre, wheat straw, rice straw)

• Wood residues• Paper waste• Municipal solids waste

Biomass composition

Cellulose

Hemicellulose

Lignin

Bioconversion of biomass to ethanol (pretreatment)

Biomass

Pretreatment

Liquid phase

Solid phase

Cellulose

Sugars EthanolFermentation

Ethanol SugarsFermentation

Hydrolysis

LigninRecovery

Pretreatment-”disruption”

• Helps in separation of main biomass components (cellulose, hemicellulose and lignin)

• Increase available surface area• Reduce particle size

Steam explosion

• Treatment of biomass with high-pressure steam for a short period of time followed by sudden decompression

• Acid (H2SO4, SO2) impregnation of biomass increases SE efficiency

• Typical conditions:– Temperature: 170-250oC, 338-482 F– Time: 10sec-10min

Steam gun

KarinFill valve

Steam valve

Blow valve

Receiving vessel

Receiving vessel

Pretreated corn stover

Bioconversion of biomass to ethanol (hydrolysis)

Biomass

Pretreatment

Liquid phase

Solid phase

Cellulose

Sugars EthanolFermentation

Ethanol SugarsFermentation

Hydrolysis

LigninRecovery

What are cellulases?

• Produced by many strains of bacteria and fungi

• Catalyzes the depolymerization of cellulose chains– Endoglucanases– Exoglucanases– β-glucosidases

Cellulases

Endoglucanases  (EG) cutting the cellulose chains randomly

Cellobiohydrolyses (CBH) cutting cellobiose units of the ends of the cellulose chains

Binding domain Catalytic domain

Bioconversion of biomass to ethanol (fermentation)

Biomass

Pretreatment

Liquid phase

Solid phase

Cellulose

Sugars EthanolFermentation

Ethanol SugarsFermentation

Hydrolysis

Lignin Recovery

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

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?

Fermentation

Conversion factor 0.51

1g/L of glucose: 0.51g/L ethanol (maximum)

Biofuels-comparison

Production (billion gallons)

Production cost ($)

Energy balance

GHEreductio

n (%)

Corn 4.86 1.09 1.3 22

Cane 3.96 0.87 8.0 55-90

Lignocellulose

NA NA 2-36 91

Biodiesel 0.50 NA 2.5 68

Alternative options??…….

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

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

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/