Microbiology of synthesis gas
fermentation for biofuel
production
朱琴娥
2008.05.14
Background
What we shoud do with these problem?
What way we can obtain clean and
sustainable energy supply?
MethodⅠ
Shorting: the conversion rate is very low.
MethodⅡ
biomass
Gasification
coal
Fossil fuels
Gasification
chemistry
Syngas
Acetate Butyrate
Ethanol
Others production
Source and application of syngas
Syngas (CO,H2O)
Syngas fermentation
WGS:
Higher specificity biocatalysting
Lower energy costs
Resistance to catalyst poisoning
Independence of a fixed H2:CO ratio
For example:
Clostridium ljungdahlii
commercial process step:
Biomass gasification
Syngas fermentation
Distillation of ethanol from the reactor effluent
Question?
Sparingly soluble gases result in low conversion rate……
High gas and liquid flow rates
Large specific gas–liquid interfacial areas
Increased gas solubility (increased pressure or solvents)
The way of stimulate gas/liquid mass transfer rate
Continuous stirred tank reactors (CSTR)
Monolith biofilm reactors
Membrane biofilm reactor (MBfR)
Biotrickling filter
Carboxydotrophic thermophiles
Before
Carboxydocella sporoproducens
Desulfotomaculum carboxydivorans
both convert CO to acetate
Recently
Archaeoglobus fulgidus
Thermoanaerobacter tengcongensis
carboxydotrophic hydrogenogens
optimum growth temperatures of 55 ℃ and 80℃
optimum growth temperatures of 55 ℃ and 80℃
doubling times of 10 h and 7 h
Chemolithoautotrophically through the conversion of CO
and H2O to H2 and CO2.
growth rates between 1 and 2 h
others might also grow organotrophically
encode CO dehydrogenases
The acetyl-CoA pathway and CO
dehydrogenase
Metabolic engineering
oxidation
CO
CO2
ADP
Dehydrogenation
NADPH
NADP+
ATP
Metabolic engineering of these organisms with the aim of producing
of a specific compound can thus be accompanied by the formation
of undesired byproducts, which are formed to satisfy the redox
balance Additional separation techniques are then required to obtain
a purified product.
Conclusions
Syngas fermentation is an attractive technology for the production of biofuels and
chemicals.
A process for ethanol production from syngas is already available, and pureH2 production
is possible as well.
 At present, suitable thermophiles for the production of organic compoundsfrom syngas are
not available, although their use could offer potential advantages over the use of mesophiles.
Thermophiles that employ CO as a substrate for theproduction of chemicals could be
selected based on theidentification of CO dehydrogenase genes in their genome.
Better still would be the isolation of new thermophiles that use CO or syngas as a substrate
at conditionsthat resemble expected bioreactor conditions.