New processing steps promise more economical ethanol production
Blacksburg, Va., March 30, 2006 -- Why isn't ethanol production growing by leaps and bounds in the face of higher gasoline prices? Ethanol production from cornstarch is a $10 billion dollar business in the United States and 4 billion gallons of ethanol will be produced in 2006. In his 2006 State of the Union address, President Bush called for doubling ethanol production by 2012, and replacing 75 percent of Middle Eastern oil with bioethanol from renewable materials by 2025.
"We have the technical ability, but making ethanol production economical is the problem," said Y.H. Percival Zhang, assistant professor of biological systems engineering in the College of Agriculture and Life Sciences at Virginia Tech.
Zhang has developed a more cost effective pretreatment process that he will report on at the 231st American Chemical Society National Meeting in Atlanta March 26-30.
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Zhang's cost-effective pretreatment process that integrates three technologies – cellulose solvent pretreatment, concentrated acid saccharification, and organosolv, and overcomes the limitations of existing processes. Instead of a high pressure system that operates at between 150 and 250 degrees C, Zhang's "modest reaction" operates at atmospheric pressure and 50 C (120 F) to pretreat corn residue to free the solid polymeric sugars. In a several-step pretreatment system, Zhang uses a strong cellulose solvent instead of highly corrosive chemicals, high pressure, and high temperature to breakup the linkages among lignin, hemicellulose, and cellulose.
During Zhang's gentler process, there is no sugar degradation and inhibitor formation. In the following step, he creatively uses a highly volatile organic solvent to precipitate dissolved cellulose, extract lignin, and enable effective chemical recycling. After pretreatment and reagent recycling, lignocellulose can be fractionated into four products: lignin, hemicelluose sugars, amorphous cellulose, and acetic acid. "Co-products can generate more income, making biorefinery more profitable, and enable satellite biorefineries that fully utilize scattered lignocellulose resources," said Zhang. "For instance, lignin has many industrial uses, from glue to polymer substitutes and carbon fiber; and xylose can be converted to a healthy sweetening additive – xylitol, or to the precursors for nylon 6."
Amorphous cellulose, which is converted from crystalline cellulose, is another advantageous product from Zhang's process because in this form the cellulose material is more accessible for further hydrolysis, resulting in a higher sugar yield, higher hydrolysis rate, and less enzyme use. Zhang tested amorphous cellulose hydrolysis by adding special enzymes (Trichoderma cellulases) from Genencor International. The result is that about 97 percent of the cellulose is digested after 24 hours of the hydrolysis process.
