lignocellulosic biomass to ethanol-hydrolysis and fermentation
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Lignocellulosic biomass to ethanol-hydrolysis and fermentation. Agenda. Enzymatic hydrolysis Cellulases What is fermentation? Fermentation inhibitors Separate Hydrolysis and Fermentation (SHF) and Simultaneous Saccharification and Fermentation (SSF). - PowerPoint PPT PresentationTRANSCRIPT
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Lignocellulosic biomass to ethanol-hydrolysis and
fermentation
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Agenda
Enzymatic hydrolysis» Cellulases
What is fermentation?» Fermentation inhibitors» Separate Hydrolysis and Fermentation
(SHF) and Simultaneous Saccharification and Fermentation (SSF)
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BiomassPretreatment
Liquid phase
Solid phase
Cellulose
Sugars EthanolFermentation
Ethanol SugarsFermentation
Hydrolysis
LigninRecovery
Bioconversion of biomass to ethanol (hydrolysis)
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Enzyme Function There are a large number of fungal enzymes
responsible for the breakdown of each wood component. Each enzyme plays specific roles:» Endo-beta-1,4-glucanase acts within the chain,
breaking it into smaller units and providing more "ends" for CBH.
» Cellobiohydrolase (CBH), acts on the end of the molecule successively cleaving off the disaccharide cellobiose.
» Beta-glucosidase (or cellobiase) which cleaves cellobiose to two glucose units.
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Trichoderma reesei Trichoderma reesei
is an industrially important cellulolytic filamentous fungus.
T. reesei:» present in nearly all
soils and other diverse habitats
» favored by the presence of high levels of plant roots.
Trichoderma reesei
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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 domain Catalytic domain
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7 Pretreated substrate Handsheet Microplate
“Rapid microassay method (1)”
Pretreated substrate Flasks
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“Rapid microassay method (2)”
Handsheets
Microplate
ShakerMicroplate
Reader
HPLC
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Equipment
1mL 200 mL 4L
40L
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BiomassPretreatment
Liquid phase
Solid phase
Cellulose
Sugars EthanolFermentation
Ethanol SugarsFermentation
Hydrolysis
LigninRecovery
Bioconversion of biomass to ethanol (pretreatment)
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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» Butanol» Acetic acid» Propionic acid» Lactic acid
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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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Why S. cerevisiae? Has been selected over thousands of years High ethanol yield and productivity Relatively simple to culture G.R.A.S organism Robust:
» High ethanol tolerance» Resistant to inhibitors
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Fermentation (1)
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Fermentation (2)
Conversion factor 0.51
1g/L of glucose: 0.51g/L ethanol (maximum)
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Inhibitors 5 groups of inhibitors
» Released during pretreatment and hydrolysis– Acetic acid and extractives
» By-products of pretreatment and hydrolysis– HMFs and furfurals, formic acid
» Lignin degradation products– Aromatic compounds
» Fermentation products– Ethanol, acetic acid, glycerol, lactic acid
» Metals released from equipment
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HMFs and Furfurals
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Experimental
Corn
fibre Hydrolysis Fermentation
SteamExplosion(solid +liquid
fraction)
Corn
fibre SSF
SteamExplosion(solid +liquid
fraction)
SHF50°C, pH 4.848 hours
30°C, pH 612 hours
37°C, pH 524 hours
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Pros and cons of SHF and SSF
Pros Separate temp. for
each step (hydrolysis 50°C, fermentation 30°C)
Possibility of yeast and enzyme recovery
Cons Requires two sets of
fermenters End-product inhibition
Pros Minimized end-product
inhibition Requires only one set of
fermenters Cons
Difficulties in recovery and yeast and enzyme recycling
Temperature/pH compromise (37°C)
SHF SSF