As syngas fermentation leads to lower ethanol concentrations than corn fermentations, the energy and cost to separate the ethanol from water is proportionally higher. To reduce this differential, Coskata has exclusively licensed membrane separation technology to reduce the energy requirements by over 50%.
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Coskata uses existing gasification technology to convert almost any organic material into synthesis gas, which is a mix of carbon monoxide and hydrogen. Rather than fermenting that gas or using thermo-chemical catalysts to produce ethanol, Coskata pumps it into a reactor containing bacteria that consume the gas and excrete ethanol.
http://oblate-spheroid.blogspot.com/2008/01/bacteria-delivers-buck-gallon-biofuel.html
Linked from instapundit