Molten salts give biofuels a boost

Liquids break down cellulose without producing toxic chemicals

CHICAGO — A new approach for breaking down cellulose could improve prospects for energy-efficient biofuels, researchers report.

Although making biofuels from the cellulose in cell walls of switchgrass or wood chips should require less energy than making corn-based ethanol, finding efficient ways to degrade cellulose has been difficult.

But molten salts can help break down the tough, energy-containing cellulose molecules without creating unwanted by-products, researchers said Monday at the World Congress on Industrial Biotechnology and Bioprocessing in Chicago.

The process “gives a much cleaner biomass than we’ve seen with these other processes,” said Jay Keasling of the Lawrence Berkeley National Laboratory in California. “It looks really promising.”

Keasling heads the Joint BioEnergy Institute, one of three biofuel research centers funded by the U.S. Department of Energy.

Existing techniques use strong acids or high temperatures to start degrading cellulose into simple sugars, but these methods also produce toxic chemical by-products. For reasons that aren’t well understood, those unwanted chemicals inhibit the microbes that ferment the sugars into fuels, thus reducing yields.

“It’s a good potential use because molten salts are such strong and unique solvents,” comments Bruce Hammock, an agricultural biotechnology researcher who has worked with molten salts at the University of California, Davis.

Also called ionic liquids, molten salts consist almost entirely of electrically charged atoms or molecules called ions. The electrostatic forces exerted by these charged particles make the liquids exceptionally good for dissolving a wide range of substances.

The liquid “completely disrupts the crystalline structure of the cellulose,” says Blake Simmons, a biochemical engineer at JBEI and leader of the group performing the research. The resulting amorphous structure “is much easier to break down into glucose,” a simple sugar.

Chemists have studied ionic liquids as a “green” alternative to other industrial solvents for years, but Simmons says research on using ionic liquids to help break down plant matter for making fuels began only a few months ago.

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