Cheap Ethanol from Tires and Trash

Yesterday at the North American International Auto Show in Detroit, General Motors announced a partnership with Coskata of Warrenville, IL, a new company that claims it can make ethanol from wood chips, grass, and trash–including old tires–for a dollar a gallon. That’s significantly less than it costs to make the biofuel from corn grain, which is the source of almost all the ethanol made in the United States.

Coskata executives, who until the announcement had kept the company’s existence and technology under wraps, say they have developed a hybrid approach involving both thermochemical and biological processes for making ethanol. Until now, most researchers have focused on developing either thermochemical or biological methods. Coskata says that besides being cheaper than other ethanol production processes under development, its technology uses less energy and water.
The Coskata process begins with gasification, a well-known technology that involves heating up a wide range of organic materials until their components disassociate and form synthesis gas, a mixture of hydrogen, carbon monoxide, and carbon dioxide. Then, instead of using chemical catalysts to convert the syngas into various alcohols as is done in conventional processes, Coskata uses new strains of bacteria to convert it into ethanol. Since ethanol is the only product, the technique produces a better overall yield than catalytic processes. Bacteria are also easier to work with than catalysts in some ways. For example, they’re not as particular about the ratio of gases in the syngas. “It is theoretically possible to feed our organism exclusively carbon monoxide and it will make ethanol from that,” says Richard Tobey, vice president of R&D and engineering at Coskata. “You can’t do that with the catalytic approaches.”

Technology Review