College of Agriculture and Life Sciences
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Researcher Develops New Process to Reduce Cost of Ethanol Production
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Researcher Develops New Process to Reduce Cost of Ethanol
Why isn’t ethanol production growing by leaps and bounds in the face of higher gasoline prices? Ethanol production from corn starch is a $10-billion business and four billion gallons of ethanol will be produced in the United States 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 ethanol from renewable materials by 2025. The Department of Energy predicts that the United States will produce 60 billion gallons of ethanol to replace 30 percent of gas consumption by 2030. Approximately three-quarters of that ethanol will be produced from
lignocellulose.
“We have the technical ability, but making ethanol production economical is the problem,” says Y.H. Percival Zhang, assistant professor of biological systems engineering.
Ethanol now comes from corn kernels. “But that is food,” Zhang says. “If we want to produce 30 to 60 billion gallons of ethanol, which is what is needed to meet the president’s goal, we have to use the entire plant, or the stover (leaves, stalks, and cobs), and leave the kernels as food.”
The largest challenges for bioconversion from raw materials to bioethanol are high processing costs and low revenues of sugar yields, resulting in higher prices for bioethanol than for gasoline.
Corn stover is the most abundant agricultural residue in the United States. The challenge is separating the sugars from the lignocellulose – the combination of lignin, hemicellulose, and cellulose that form plant cell walls. Many technologies have been developed to convert lignocellulose to sugars, but the costs are still high and sugar yields are low. “No one wants to take the risk – to invest $500 million in a large-size biorefinery based on lignocellulose,” says Zhang. “Processing costs are also high. It
requires chemicals, utilities, enzymes, and recycling in the pretreatment and the sequential processing stages.”
Zhang’s cost-effective pretreatment process 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 200 degrees C, Zhang’s “modest reaction” operates at atmospheric pressure and 50 degrees C (120 degrees 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, cellulose, and orderly hydrogen bonds in crystalline cellulose.
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| “We hope to soon establish the first pilot plant in Virginia based on this new technology to process local agricultural and forestry residues and switchgrass,” says Zhang. |