Researchers: Sorghum holds promise as next-gen ethanol crop

By Kris Bevill | July 09, 2012

First-generation ethanol producers who are looking for ways to provide advanced biofuels for the U.S. renewable fuel standard (RFS) may find an easy “in” with sweet or biomass sorghum, according to a group of scientists from Purdue University, the University of Nebraska-Lincoln, the University of Illinois and Cornell University. In a paper published in the scientific journal Biofuels, Bioproducts & Biorefining, titled “Envisioning the Transition to a Next-Generation Biofuels Industry in the U.S. Midwest,” the researchers examine how the existing biofuels infrastructure could be used for second- and third-generation biofuels production and highlight sorghum as a bioenergy crop that is particularly well suited for use in existing facilities.

“In the near future, we need a feedstock that is not corn,” Purdue agronomy professor Cliff Weil said. “Sweet and biomass sorghum meet all the criteria. They use less nitrogen, grow well and grow where other things don’t grow.”

Logistical considerations for biomass-to-fuel processes require further refinement, but Maureen McCann, a Purdue professor of biology and director of the Energy Center and the Center for Direct Catalytic Conversion of Biomass to Biofuels, suggests that sorghum could be transported from harvest locations to collection points such as grain elevators using existing rail lines. From there, sorghum could be densified before being transported to the biorefinery for further processing. “Biomass has roughly half of the energy content of gasoline – even if it’s very compressed and tightly packed,” she said. “The issue is really how to increase the intrinsic energy density by preprocessing conversion steps that could be done on farm or at the silo so that you’re transporting higher-energy products to the refineries.”

The researchers also predict that farmers may be more willing to grow an annual energy crop such as sorghum rather than a perennial crop. “If we’re talking about planting switchgrass, that’s a 15-year commitment,” said Nathan Mosier, a Purdue associate professor of agricultural and biological engineering. “You can’t switch annually based on the economy or other factors. You are committed to that crop.”

According to the National Sorghum Producers, a group representing 1,100 sorghum growers, between 5 million and 7 million acres of sorghum are grown annually in the U.S. About 35 percent of the grain sorghum crop is currently being used for ethanol production, however the majority of the crop is used for animal feed. In 2010, the Top 5 sorghum-producing states were Kansas, Texas, Oklahoma, Colorado and South Dakota, according to the NSP. The group expects biomass and sweet sorghum acreage to expand most noticeably in the Southeast region of the U.S. and in South Texas as demand for biofuels grows. Growers’ main concerns related to sorghum are weed control and lack of a market, and the United Sorghum Checkoff Program is working to address both issues through research and market development.