Cheap Ethanol from Tires and Trash

GM teams with a startup aiming to produce low-cost biofuels.

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.

Fuel fibers: A bundle of hollow fibers is the heart of a new process for making ethanol from sources other than corn. Organic materials are heated up to form a mixture of hydrogen, carbon dioxide, and carbon monoxide. When the pictured bioreactor is in operation, the gases flow through the center of the fibers and feed bacteria growing on the outside. The bacteria convert the gases into ethanol. Credit: Kevin Bullis

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.

GM will give financial, technical, and marketing support to Coskata to help it scale up its process, which so far has been demonstrated only at the lab scale. Coskata is completing a pilot-scale ethanol production facility and will announce locations for a 40,000-gallon-per-year facility and a 100-million-gallon-per-year commercial-scale plant later this year.

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Coskata joins a number of other companies looking for ways to make biofuels from alternative sources. A new federal mandate, signed into law late last month, calls for 36 billion gallons of biofuels to be produced by 2022; of that, 21 billion gallons is to come from sources other than corn grain. But so far technology for making ethanol from such feedstocks has not been proved commercially.

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 (see "Breaking Ground on Cellulosic Ethanol"), 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."