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Made from biomass and plants that thrive in the fertile Midwest, biofuels may seem like a no-brainer.
As economists say, however, there’s no such thing as a free lunch; biofuels do have real potential to become a major source of sustainable energy but nevertheless present many challenges that have yet to be overcome. Purdue University researchers are working on a myriad of projects to address these obstacles, including developing improved fermentation technologies and energy crops, analyzing economic policies, and crafting guidelines for sustainable biomass production.
Where the magic happens
Biofuels derive their energy from the magic of photosynthesis, wherein plants chemically harness the sun’s power by converting carbon dioxide into energy-storing carbohydrates. The primary technical challenge is how to most efficiently convert these carbohydrates and their energetic relatives—like cellulose—into energy.
One option is to burn the material, done with solid biofuels. Agricultural and biological engineering professor Klein Ileleji does just that with switchgrass. His pilot project at Purdue’s Wade Utility Plant, begun two years ago, will assess the viability of various solid biomass fuels.
Another option is to convert the materials into combustible liquid fuels—like ethanol or soy biodiesel—to create a mobile, energy-dense fuel ideal for automobiles, planes and the like. But not all biofuels are created equal. In the United States today, all commercial ethanol comes from starch in corn grain, a relatively inefficient source that provides just 25 percent more energy than production requires.
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Nathan Mosier, a researcher in agricultural and biological engineering, has developed a new technology to free up more cellulose from plant tissue, which increases the amount of ethanol that can be produced from the complex carbohydrate. (Photo by Tom Campbell) |
Cellulose, the complex carbohydrate within plant cell walls, has potential to be a significantly more efficient fuel source. Present in all plant tissues, cellulose is more abundant than starch, but much of it is tightly bound to a rigid, glue-like material called “lignin.” That makes it difficult to extract, says Nathan Mosier, assistant professor of agricultural and biological engineering, who develops pretreatment techniques to liberate more cellulose for fermentation.
After these pretreatment steps, specialized yeasts ferment cellulose into ethanol. Professor Nancy Ho leads a $5 million project to develop new and more efficient varieties of such yeast, partnering with the world’s largest ethanol producer, Archer Daniels Midland Co.
Never been done
Colleague Michael Ladisch, head of Purdue’s Laboratory of Renewable Resources Engineering, is putting his work to the test. In November of last year, he announced a two-year, halftime leave to sign on as chief technology officer with Mascoma Corp., where he helps lead an effort to establish one of the world’s first full-scale cellulosic ethanol plants.
“It’s never been done before,” Ladisch says. “The only way to know if it can be is to get out there and do it.”
Success would mean a sea change for industry. But where to get all the cellulose? Purdue researchers are investigating agricultural residues as a practical source, including corn stover, sawdust and paper pulp. They also work to develop dedicated energy crops that grow quickly and provide maximum amounts of usable cellulose yet require minimal inputs like water, fertilizer and pesticides. Candidate plants include poplar trees and grasses like Miscanthus, switchgrass and prairie grass.
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