Cellulosic pilot plant starts operation in Montana

By Ron Kotrba | September 08, 2008
AE Biofuels Inc. brought its pilot-scale ethanol plant in Butte, Mont., on line in August and since then has begun work to prove out its two individual cold-cook enzyme platforms. "We're trying to differentiate ourselves from our competitors, so by having two enzymesone for starch and one for cellulosewe can run an integrated facility where you use both feedstocks," said Todd Casper, vice president of the company's project development division.

Clifford Bradley, coinventor of the AE Biofuels pilot process, said the company's first task is to perfect the simultaneous integration of starch and cellulose hydrolysis. "We're talking corn and corn stover," he told EPM. "We designed the cellulose pretreatment system to use a conventional jet cooker to keep capital costs down. We can do an alkaline pretreatment or an acid, but we like alkaline. It's milder and less messy." He said the company's technology can obtain cellulases capable of hydrolyzing both cellulose and hemicellulose from a single culture.

For corn stover, the gallons-per-ton conversion ratio is still unknown, but it will be the subject of ongoing work in the Butte plant. Bradley said the company achieved 84 gallons of ethanol per ton of wheat straw, which included 62 gallons from the cellulose fraction and up to 22 gallons from the pentose sugars. The plant is scaled to produce up to 150,000 gallons of ethanol per year. Later this year, the company will test sugarcane bagasse. "Our idea is that by using both enzyme systems and converting a plant to no-cook, we can integrate corn- and cellulose-derived ethanol and actually put them in the same fermentor," Bradley said. Work to optimize pentose fermentation is also moving forward.

Still, AE Biofuels isn't excluding conventional ethanol plants. Andy Foster, president of AE Biofuels subsidiary American Ethanol, said the company's technology can most immediately be optimized in existing facilities. "Ethanol producers are a captive audience, and they're constantly looking for ways to reduce operating expenses," he said.