Chapter 12 : Production of Ethanol from Synthesis Gas

Abstract:

After the oil supply shocks in the 1970s, research on development of alternative sources of liquid fuels was intensified. The initial emphasis was on processes that used coal as a feedstock, but later investigations were on the direct fermentation of lignocellulosic biomass where the biomass is first treated to convert it to fermentable sugars, followed by the familiar alcoholic fermentation, generally by yeast. Synthesis gas can be fermented or otherwise converted to a number of desired products, including ethanol. It can be chemically converted to liquid fuels. Clostridium carboxidivorans has been shown to ferment 100 mmol of fructose to 23 mmol of ethanol, 81 mmol of acetate, and 4 mmol of butanol. Upon fermentation of an equivalent amount of carbon monoxide (600 mmol), the end products produced shifted to 96 mmol of ethanol, 12 mmol of acetate, and 24 mmol of butanol. The presence of reducing agents alone can shift products of fermentation from acetate to ethanol. The ability to produce butanol from synthesis gas appears to be the most attractive feature of Butyribacterium methylotrophicum. C. ljungdahlii was isolated from chicken yard waste based on its ability to ferment synthesis gas to ethanol. The first commercial fermentation of synthesis gas to ethanol will probably use C. ljungdahlii as the microbial catalyst. C. carboxidivorans can directly ferment biomass, at least the cellulose fraction.