Bioconversion of biomass to
ethanol-an overview
Renata Bura
November 25th, 2008
Overview
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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 coproducts.
Bioconversion
Pretreatment
Hydrolysis
Biomass
Ethanol
Fermentation
Distillation
Why bioethanol?
Ethanol (CH3CH2OH)
• Ethyl alcohol, grain alcohol
– Clear, colorless liquid
• Ethanol made from cellulosic biomass instead
of starch crops-bioethanol
• Advantages of bioethanol
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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 plant
Corn kernel (without the fibre)-starch alcohol
Corn fibre-lignocellulosic alcohol
Corn 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
Henry Ford
“We can get fuel from apples, weeds, sawdust,
almost anything…..
And it remains for someone to find how this fuel
can be produced commerciallybetter fuel at a better price than we now know.”
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)
Liquid
Pretreatment phase
Sugars
Ethanol
Fermentation
Biomass
Lignin
Recovery
Solid phase
Cellulose
Hydrolysis
Fermentation
Sugars
Ethanol
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
Fill valve
Receiving
Karin
vessel
Receiving
vessel
Steam valve
Blow valve
Pretreated corn stover
Bioconversion of biomass to
ethanol (hydrolysis)
Liquid
Pretreatment phase
Sugars
Ethanol
Fermentation
Biomass
Lignin
Recovery
Solid phase
Cellulose
Hydrolysis
Fermentation
Sugars
Ethanol
What are cellulases?
• Produced by many strains of bacteria and
fungi
• Catalyzes the depolymerization of cellulose
chains
– Endoglucanases
– Exoglucanases
– β-glucosidases
Cellulases
Binding domain
Endoglucanases (EG)
cutting the cellulose chains randomly
Catalytic domain
Cellobiohydrolyses (CBH)
cutting cellobiose units of the ends of the cellulose chains
Bioconversion of biomass to
ethanol (fermentation)
Liquid
Pretreatment phase
Sugars
Ethanol
Fermentation
Biomass
Lignin
Recovery
Solid phase
Cellulose
Hydrolysis
Fermentation
Sugars
Ethanol
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
GHE
reduction
(%)
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
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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
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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/