Current commercial production of fuel ethanol primarily involves fermentation of sugars that are typically derived from corn grain or grain sorghum in the U.S. or sugarcane in tropical regions such as Brazil. Second generation fuel ethanol is expected to use lignocellulose materials (e.g., grasses, crop residues, wood) as the source of sugars that are fermented into ethanol. An alternative approach is to produce ethanol (and other biofuels) from syngas. The process first converts biomass resources to syngas (a mixture of carbon monoxide, carbon dioxide, and hydrogen) via a process called gasification. Gasification is the partial oxidation of biomass at high temperatures. The syngas can then be converted to biofuels such as methanol, ethanol and hydrogen using either a metal catalyst or a microbial catalyst (e.g. bacteria).
The use of metal catalysts is a reliable technology and currently is used in industry to produce a variety of biofuels and chemicals. However, this method is limited by the need for extreme reaction conditions (high pressures and temperatures), low conversion rates, and the sensitivity of some catalysts to contaminants in the syngas. An alternative method is to use microbial catalysts to convert syngas to ethanol. Several genera of microorganisms (e.g., Clostridium ljungdahlii, Clostridium autoethanogenum, and Eubacterium limosum) are capable of consuming syngas as part of their metabolism and producing chemicals such as ethanol and other products (e.g. acetic acid).
The gasification process can potentially utilize the entire biomass feedstock, both the sugar-containing components of cellulose and hemicellulose and the non-sugar containing components of lignin, which provides a greater conversion efficiency of biomass to energy or chemicals.