Ethanol Research Breakthrough: Wood Feedstock

The process developed at ESF is the work of Dr. Thomas E. Amidon, chair of the college's Faculty of Paper Science and Engineering. It could help the economically significant pulp and paper industry develop more efficient and sustainable biorefineries.

"We know our sources of fossil fuel aren't going to last forever," Amidon said. "This will allow us to substitute a sustainable energy source: wood."

During the last few years, Amidon collaborated with students, ranging from a home-schooled high school student to ESF doctoral candidates, to devise a new and subtler method for separating wood into its basic components.

Chief among those components is cellulose, the polysaccharide (sugar) that is the single strongest, most widely used component of woody plants. In the context of a paper mill, cellulose becomes pulp for use in making paper. The second largest component of hardwood trees is the polysaccharide xylan, which is primarily dissolved in the pulping process.

The real value in that sugar, Amidon said, was never exploited. Once fermented, the sugar xylan can produce ethanol, which can be used in cars instead of, or in combination with, traditional gasoline.

Although the energy factor is the focus of attention now, there is a second benefit to the process as the nation steps up its development of alternative fuel sources. In addition to extracting sugar from the wood, scientists can separate out the wood's acetic acid, which is used primarily in manufacturing. A major use of acetic acid is the manufacturing of polyvinyl acetate, a plastic used in many aspects of home construction and many other consumer products. The commercial value of acetic acid is nearly three times that of ethanol: 45 cents per pound as opposed to 18 cents per pound.

One of the advantages to the process, according to Amidon, is that is does not use any harsh chemicals.

Ordinary wood chips are mixed with water and heated at high temperatures for a specified length of time. That time can be shortened if the chips are first subjected to biopulping, a process that allows natural wood-decaying fungi to munch through the lignin that binds the cellulose in the wood. That process is also the subject of research at ESF.

"Water is the solvent we use," Amidon said. "It's my preferred solvent because if it gets loose in the world it's just water and the world knows how to deal with it."

The watery solution that remains after the chips are removed is then forced through a membrane that separates the sugars from the water. The acetic acid is removed the same way.

"The trees are here and they can provide year-round employment," Amidon said. "You can also extract these components from grasses, but grasses go dormant in the winter and they're difficult and expensive to store for use in a year-round process. And trees are dense. They can be shipped and stored economically, and they are more efficient energy collectors than annual crops. After the desired components are extracted, the residue can be burned or gasified for combined heat and power uses."

The work, while still in the testing phase, has received support from International Paper, the world's largest paper company, and from Lyonsdale Biomass, a wood-fueled energy producer. Representatives of both companies stated in letters of support that they believe the process "has significant promise of increasing the profitability" of their operations. International Paper has indicated it is a willing partner in exploring technology transfer in the biorefinery work.

Lyonsdale has expressed interest in what the company calls "the potential positive impact" of the process on the company's ability to convert woody materials to energy.

In addition, the ESF team has demonstrated the process for scientists from the National Renewable Energy Laboratory in Colorado.

The process is a natural fit for states with northern hardwood forests, Amidon said, because the sugars in hardwood trees are simpler than those found in softwood trees.

And the process is not choosy about which hardwood trees it uses. Maples, common in the state's forests, work just fine, he said. But so do the willow biomass crops that are being developed by ESF researchers and their colleagues as a commercial crop for energy uses, such as at the Lyonsdale facility.

"If you consider the concept of removing sugars and acetic acid from willow biomass and then burning or gasifying what's left over from that process, the economics of growing willow as an energy crop are significantly improved," Amidon said.