General Motors, eager to ensure fuel for the big fleet of flex-fuel vehicles it is building, has joined the rush into alternative energy...

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General Motors, eager to ensure fuel for the big fleet of flex-fuel vehicles it is building, has joined the rush into alternative energy and invested in a company that intends to produce ethanol from crop wastes, wood chips, scrap plastic, rubber and even garbage.

GM bought an equity stake in Coskata, a startup in Warrenville, Ill., that plans to make ethanol without using corn.

Rick Wagoner, GM’s chairman and chief executive, announced the investment Sunday at the opening of the North American International Auto Show in Detroit. GM would not say how much it paid or how big a stake it took.

Coskata, financed in part by Sun Microsystems co-founder Vinod Khosla, plans to build a pilot-scale plant this year at GM’s test track in Warrenville.

Putting money into the fuel business is new for automakers, said Jeffrey Leetsma, of the Automotive Hall of Fame, in Dearborn, Mich.

“I don’t really see the logic of it,” said Christopher Flavin, president of the Worldwatch Institute, an environmental group. “It’s not particularly an industry they know well, or have expertise in.”

Coskata is one of many companies, and far from the leader, in an emerging world of startup firms to make alternative fuels with a mix-and-match approach to existing technologies. In Coskata’s case it is a combination of gasification and bacterial action.

The first step is cooking the raw feedstock into synthesis gas, a mixture of hydrogen and carbon monoxide. That gas is cooled and consumed by bacteria that then excrete ethanol.

Coskata is not the only one pursuing the gas-to-bacteria-to-fuel route, but claims its process gives more ethanol per ton of raw material — 100 gallons — and uses less than 1 gallon for each gallon of ethanol.

If it can be done economically, the Coskata process has three large advantages over corn-based ethanol, GM says. First, it uses a cheaper feedstock that wouldn’t compete with food production. Second, the feedstock is found all over, a key point since ethanol cannot be shipped from the Corn Belt to areas of high gasoline demand in existing pipelines.

In addition, the process appears to require less electricity and natural gas, meaning that making it would not release as much carbon. The product would qualify for a federal tax exemption for ethanol.

Coskata CEO William Roe said that “at full production, Coskata ethanol should be 50 cents to $1 cheaper than gasoline at the pump.”