Microbiology of synthesis gas fermentation for biofu

el 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

Gasification

coal

chemistry

Fossil fuelsbiomass

Gasification

Syngas

Acetate EthanolButyrate Others production

Source and application of syngas

Syngas (CO,H2O)

WGS:

Syngas fermentation

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

The way of stimulate gas/liquid mass transfer rate

High gas and liquid flow rates

Large specific gas–liquid interfacial areas

Increased gas solubility (increased pressure or solvents)

Question?

Sparingly soluble gases result in low conversion rate……

Continuous stirred tank reactors (CSTR)

Membrane biofilm reactor (MBfR)

Biotrickling filter

Monolith biofilm reactors

Carboxydotrophic thermophiles

Before

Carboxydocella sporoproducens

Desulfotomaculum carboxydivorans

both convert CO to acetate

optimum growth temperatures of 55 ℃ and 80℃

doubling times of 10 h and 7 h

others might also grow organotrophically

Recently

carboxydotrophic hydrogenogens

Chemolithoautotrophically through the conversion of CO and H2O to H2 and CO2.

optimum growth temperatures of 55 ℃ and 80℃

growth rates between 1 and 2 h

encode CO dehydrogenases

Thermoanaerobacter tengcongensis

Archaeoglobus fulgidus

The acetyl-CoA pathway and CO dehydrogenase

Metabolic engineering

Metabolic engineering of these organisms with the aim of producing

of a specific compound can thus be accompanied by the formation o

f undesired byproducts, which are formed to satisfy the redox balanc

e Additional separation techniques are then required to obtain a purif

ied product.

CO2CO oxidation

NADPH NADP+

Dehydrogenation

ATP

ADP

Syngas fermentation is an attractive technology for the production of biofuels and chemical

s.

A process for ethanol production from syngas is already available, and pureH2 production i

s possible as well.

At present, suitable thermophiles for the production of organic compoundsfrom syngas ar

e not available, although their use could offer potential advantages over the use of mesophil

es.

Thermophiles that employ CO as a substrate for theproduction of chemicals could be selec

ted 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 substrat

e at conditionsthat resemble expected bioreactor conditions.

Conclusions