A Purdue University researcher has found a way to get more bang for fewer bucks when it comes to processing cellulosic material to make ethanol.
By shredding corn stover instead of chopping it, as is commonly done, about 40% less energy is needed to gain access to more of the material stored in the plant. Dennis Buckmaster, ag engineer, says that shredding corn stover provides better access to cellulose, which is the main part of plant cell walls necessary to make ethanol.
"You can't just use a big chunk of cellulosic material. You need small particles," Buckmaster says. "What we want is access to what's in there."
The next step in Buckmaster’s research will be to compare shredded and chopped cellulosic material to see which produces more ethanol. He will also work to design machinery for farmers to shred plant materials during harvest.
Buckmaster made his current discovery using a technique employed in food processing and other industries to measure cell damage. He put chopped and shredded cornstalks in water and compared the amount of leachates in each solution. A leachate is any plant substance that is dissolved out of a plant or soil when placed in water.
According to his results, shredded cornstalks produced about 11% more leachates than chopped and 5% more than stalks that had been chopped and put through a roller. Buckmaster says those differences are all the more impressive when considering the energy savings tied to shredding, giving ethanol makers potentially more cellulose for less cost.
Shredding cornstalks increases the surface area of the plant material. And because stalks can be shredded along the grain of the plants, like splitting a log with an ax, it takes less energy. The current chopping method, he says, is like putting the log on its side and trying to chop it with the same axe.
"It takes much less force to shear the plant material in the direction of the fibers," Buckmaster says.
Plants can be chopped again after storage to increase surface area, but that would raise energy costs. Shredding produces different-size pieces, but even the largest pieces produced about as many leachates as the smallest shredded pieces. When comparing the chopped materials, the largest pieces produced fewer leachates than the smallest pieces.
"The shredded material, even with the long particles, gives you more access to plant nutrients," Buckmaster says. "You can use chopping to reduce the size of particles, but that takes more energy and is not as efficient as shredding at harvest."
Buckmaster's study was published in the last 2008 edition of Transactions of the American Society of Agricultural and Biological Engineers. His research was funded through the USDA’s Cooperative State Research, Education and Extension Service.