Challenging ethanol’s dirty reputation

Wood chips could yield a clean, inexpensive biofuel

CHICAGO — A propriety process for making ethanol from leftover sawmill woodchips significantly reduces the fuel’s lifetime greenhouse gas emissions relative to gasoline, a new analysis concludes.

The 60 to 80 percent relative reduction in emissions “is comparable with other wood-based bioethanol processes,” says May Wu of Argonne National Laboratory in Argonne, Ill., who led the independent analysis. If the wood chips contained little moisture, the reduction could be as much as 96 percent.

While emissions for the process are similar to other wood-based processes, costs are considerably lower, according to Coskata Inc., the Warrenville, Ill.–based company that developed it. Typical costs for making second generation biofuels — which are produced from stalks, leaves or wood instead of corn — range from $2 to $5 per gallon of ethanol. Coskata’s method costs less than $1 per gallon, company representatives claim.

In January the company announced a partnership with General Motors to develop the technology, and last week the two companies announced that they will build a $25 million demonstration plant in Madison, Pa., by 2009.

The Argonne study results, announced April 30 in Chicago at the World Congress on Industrial Biotechnology and Bioprocessing, include emissions from the energy needed to haul the wood chips, make and refine the ethanol, transport the fuel to the pump and burn the fuel. The researchers previously estimated that the reduction for corn-based ethanol is almost 20 percent, and that ethanol made from switchgrass reduced emissions by 85 percent, but using switchgrass is currently more expensive.

Though the study focused only on wood chips, Coskata’s method can also make ethanol from other plant matter, old tires or even trash. Whatever the feedstock, the process first applies heat and pressure to convert the feedstock into a mixture of gases including carbon monoxide and hydrogen. These gases then pass through a bioreactor containing bacteria that convert the gases into ethanol. Other methods typically use expensive enzymes instead of gasification to break down the tough cellulose molecules in the plant cell walls.

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