Will wood help fill US energy needs?
Forget corn processing. Don't wait for switch grass. The real key to producing enough ethanol for America's cars and trucks this century is wood.
That's the contention of researchers at the State University of New York (SUNY). By revamping the way paper is made, they've found an economical way to extract important energy-rich sugars from the trees and then convert these sugars into ethanol, a gasoline additive, and other useful chemicals.
It's a process the researchers call a biorefinery. Installed at the nation's paper mills, biorefineries could produce 2.4 billion gallons of ethanol a year, they estimate, or 80 percent of the nation's projected need this year.
"We know our sources of fossil fuel aren't going to last forever," says Thomas Amidon, a professor at SUNY's College of Environmental Science and Forestry. "Biorefineries allow us to substitute a sustainable energy source: wood."
While the major component of hardwood trees is cellulose, from which paper is made, the second largest component is the sugar xylan. "Hardwoods contain about 35 percent xylan, while northern softwoods contain 9 to 14 percent," notes Dr. Amidon.
Currently, xylan is dissolved during wood processing in paper mills and not utilized. But when it is captured and fermented, xylan produces ethanol, which can be blended with gasoline. "We also expect to find uses for xylan for controlled release of pesticides and as a thickener," Amidon says.
In his biorefinery, extremely hot, pressurized water flows over a bed of wood chips to separate the cellulose for paper. Then the water is forced through a membrane that removes the sugars and acetic acid. What remains can be burned or gasified for combined heat and power uses.
The fermentation process does not use any harsh chemicals, Amidon notes. "The materials we dissolve in the water are natural to begin with. We know how to clean up water well. When it is clean, its release to the environment has no long-term negative consequences."
The process also produces smaller but valuable amounts of acetic acid. Acetic acid is a key ingredient in making polyvinyl acetate, which is widely used in construction materials. The commercial value of acetic acid is nearly three times that of ethanol: 45 cents per pound compared with 18 cents per pound.