The potential for producing butanol as a biofuel has become a bit more promising, thanks to U.S. Department of Agriculture (USDA) scientists and their partners. Work by Agricultural Research Service (ARS) chemical engineer Nasib Qureshi suggests that barley straw and corn stover—both agricultural byproducts—could be cost-effective feedstocks for producing “biobutanol.” ARS is USDA’s chief scientific research agency, and this work supports the USDA priority of developing new sources of bioenergy.
Gallon for gallon, butanol has 30 percent more energy than ethanol and only around 4 percent less energy than a gallon of petroleum-based gasoline. Qureshi has confirmed that both barley straw and corn stover can be converted to butanol via separate hydrolysis, fermentation, and recovery (SHFR) or by simultaneous saccharification, fermentation, and recovery (SSFR). In SSFR, releasing the plant sugars, fermenting them to butanol, and recovering the butanol are combined into a single operation that is performed in a single reactor.
In a recent study, Qureshi’s team used a process called gas stripping to “harvest” butanol fermented during SSFR. They obtained a final butanol yield that was 182 percent of the yield obtained from a control study that used glucose.
Using the same protocols, the scientists were able to ferment over 99 percent of the sugars in pretreated corn stover. This resulted in butanol yields that were 212 percent greater than yields observed from the controls, and 117 percent greater than the butanol yields from the barley straw.
Qureshi, University of Illinois professor Vijay Singh, Ohio State University associate professor Thaddeus Ezeji, and others also evaluated the effectiveness of producing butanol from corn stover in an SSFR process that used vacuum technology—not gas stripping—to simultaneously recover butanol during fermentation. The new process released more than 97 percent of the stover sugars, making them available for fermentation. The total butanol yield was 0.34 grams per liter per hour—higher than the glucose control yield of 0.31 grams per liter per hour.