SDSU studies corn stover pretreatment

By | March 16, 2010
News release posted April 7, 2010

Using a high shear bioreactor (extrusion) pretreatment process can help prepare corn stover as a feedstock for making cellulosic ethanol, a South Dakota State University study finds.

The SDSU study explored different temperatures, screw speeds, and enzymes to learn what treatments recovered the most sugar from corn stover. Professor Kasiviswanathan Muthukumarappan of SDSU's Department of Agricultural and Biosystems Engineering and graduate research assistant Chinnadurai Karunanithy published the results of their study in September 2009 in the Journal of Applied Biochemistry and Biotechnology.

Extrusion is a widely used process in the snack food, feed and plastic industries, Karunanithy explained. The process subjects materials to heating, mixing and shearing processes, resulting in physical and chemical changes as the material passes through what is called the barrel of the extruder.

Unlike corn grain where the major carbohydrate is starch, biomass is made up of 30 percent to 40 percent cellulose, 25 percent to 35 percent hemicellulose, and 20 percent to 25 percent lignin. Pretreatment is the first and one of the most expensive steps in converting biomass to biofuels, Muthukumarappan said.

"We conducted this experiment to understand the influence of screw speed and barrel temperature on sugar recovery from corn stover. When we used different enzymes and ratios during hydrolysis, we confirmed that screw speed, temperature, and their combinations significantly influenced sugar recovery."

The SDSU study evaluated five screw speeds and five barrel temperatures and also tested different combinations of enzymes during the process of saccharification, or breaking down into simple sugars, of pretreated corn stover.

SDSU researchers got the best results using an extrusion pretreatment process with a screw speed of 75 rpm and a barrel temperature of 125 degrees Celsius (257 degrees Fahrenheit). Pretreatment with those parameters recovered the highest percentage of glucose (75 percent), xylose (49 percent) and combined sugar (61 percent) when researchers added a 1:4 combination of the enzymes cellulase and beta-glucosidase during hydrolysis.

The South Dakota Agricultural Experiment Station and the North Central Sun Grant Center at SDSU through a federal Department of Transportation grant supported the research. Novozymes Inc. supplied the enzymes for the study.