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Corn for ethanol: Divide and conquer

PURDUE (US) — Researchers have discovered a more efficient method to process corn stover to make cellulosic ethanol—based on the fact that the residue’s distinct parts—the rind, pith, and leaves—break down in different ways.

Cellulosic ethanol is created by using enzymes to extract sugars from feedstocks such as corn stover, grasses, and woods, and then fermenting and distilling those sugars into fuels.

“Today, researchers grind the parts together and treat it based on what’s needed to get at the hardest part,” says Eduardo Ximenes, a research scientist at Purdue University. “We show that there are major differences in degradability among the tissues.”

Stover’s pith, the soft core that makes up more than half the weight of a corn stalk, is the easiest for enzymes to digest, according to research findings published in the journal Biotechnology and Bioengineering. Rind is the most difficult, while leaves fall in between. Significant amounts of lignin, the rigid compound in plant cell walls, make the cellulose resistant to hydrolosis, a process in which cellulose is broken down into sugars.

Converting the rinds only adds about 20 percent more ethanol but requires 10 times more enzymes, driving up the price of the process.

“Is that extra 20 percent worth the added cost?” asks Nathan Mosier, associate professor of agricultural and biological engineering and co-author of the study. “Because if there is a way to separate out pith, you could burn the leftover rinds to generate steam, creating energy needed to operate the plant.”

Separating pieces of corn stover and treating them differently would be a new way of approaching cellulosic ethanol production, says Michael Ladisch, a distinguished professor of agricultural and biological engineering.

“It uses existing conversion technology, but it enables us to think about a new way of getting the most from that technology,” Ladisch says. “There is absolutely no reason a ligno-cellulosic non-food material such as corn stalk cannot be used to make ethanol if you understand the science.”

The next step, the researchers say, is to explore ways to improve the ability of enzymes to create sugars from cellulose and remove the compounds that inhibit those enzymes, as well as adapting the findings for other feedstocks such as switchgrass and wood.

Researchers from the University of Florida contributed to the study, which was funded by the U.S. Department of Energy, Purdue Agricultural Research Programs, and a David Ross Fellowship.

More news from Purdue University: http://www.purdue.edu/newsroom/

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