Freelance Writer & Editor
By Susan Ladika | The Race To Commercialize Cellulosic Ethanol | May 30, 2009 | Think + Up
As the race for sustainable fuel technology revs up, everything from corn husks and sugar cane to poplar trees and municipal waste—along with a multitude of other materials—are all in the running to help power the nation’s automobiles in the coming years.
While ethanol derived from corn is already found in gas pumps across the country, cellulosic ethanol is often seen as a more promising alternative because it can be produced from a wider variety of materials, with a greater net energy content, while avoiding the whole food vs. fuel debate.
Already, major oil companies such as BP, Royal Dutch Shell and Valero Energy have thrown their muscle behind the process, providing financing for various cellulosic ethanol projects.
As the United States increases its focus on alternative energy sources, ethanol “is important because it’s the only renewable technology that can easily provide liquid fuel,” says Steve Kelley, head of the Wood and Paper Science Department of North Carolina State University in Raleigh.
Kelley, who came to the university from the Department of Energy’s National Renewable Energy Laboratory, where he focused on biomass conversion technologies, says the DOE has given grants to nearly 20 companies to build demonstration cellulosic ethanol plants scattered around the country, though Kelley suspects about half will never come out of the ground.
Part of the impetus comes from the U.S. Energy Independence and Security Act of 2007, which requires that fuels contain 2 billion gallons of advanced biofuels by 2012 and 21 billion gallons by 2022.
To produce cellulosic ethanol, the biomass is typically pretreated, ground, and then an enzyme is added to break it down, and the sugars are fermented and distilled.
But ethanol plants usually need to stick with the same type of biomass, because “enzymes don’t like it when you change their dinner menu,” Kelley says.
The proposed plants use a wide variety of inputs, or feedstock, such as corn stover (leaves and stalks remaining after harvest), switchgrass, and wood, depending on the area of the country where they’re located.
Already, Mascoma Corp., of Boston, is producing cellulosic ethanol at its 200,000 gallon per year demonstration plant in Rome, N.Y., and Verenium Corp., based in Cambridge, Mass., has a 1.4 million gallon per year demonstration plant in the startup and commissioning phase in Jennings, La.
Yet each input “has a series of technical challenges,” Kelley says. It could be an issue of growing season limitations, transportation and storage of the biomass, or the biomass is used for other purposes. Corn stover, for example, helps maintain the productivity of the soil and is also needed for greenhouse gas sequestration.
Sugar cane is limited because of the short growing season in Louisiana, and it can only be harvested four times before it must be replanted, says Sarah Lingle, a research plant physiologist with the U.S. Department of Agriculture in New Orleans. In addition, sugar mills often use bagasse—the fiber left over when juice is pressed out of sugar cane—in their boilers to produce sugar, so not much material remains.
Also under consideration is energy cane, a sugar cane variety that is too fibrous to be used for sugar production, as well as other weedy sugar cane relatives that produce a lot of biomass, but not much sugar, Lingle says.
Part of the challenge with canes is that they contain a large amount of lignin, which serves as a sort of glue, making it difficult for the enzymes to get to the cellulose to break it down. Lingle’s work includes analyzing the bagasse of different species, looking for mutants with less lignin, but so far she hasn’t found much variation.
Producers also need to ensure that plants used for cellulosic ethanol don’t supplant food crops, she says. In Louisiana, land once used to grow rice could be used for sugar cane or energy cane.
Meanwhile in the Upper Peninsula of Michigan, Mascoma is building a cellulosic ethanol facility that will use wood products. The company is working with Michigan Technological and Michigan State universities to ensure the project has a sufficient, reliable, environmentally sustainable wood supply, says Robert Froese, assistant professor in the School of Forest Resources and Environmental Sciences at Michigan Tech in Houghton, Mich.
The schools are working on projects to survey the wood available, and landowners’ attitudes toward being involved in such a project. Because of the state’s extensive woodlands, “by no means would we liquidate our forests,” Froese says.
While many companies and organizations are focusing on the feedstock, others are directing their attention to the enzymes that can be used to break down the cellulose.
To get corn husks broken down to a usable sugar “it’s a pretty tough fight,” says Pete Heinzelman, a post-doctoral scholar at the California Institute of Technology in Pasadena.
Heinzelman was involved in a project using gene recombination to create 15 new enzymes to break down cellulose into sugar at high temperatures. Because enzymes aren’t cheap to produce, developing enzymes that live longer—and hence are capable of doing more work—helps hold down the costs.
The university wants to create a variety of enzymes because one might work best with corn husks, and another with sugar cane. The goal is to “create a buffet where you can mix and match the things,” Heinzelman says.
A second route for producing cellulosic ethanol involves gasification, using biomass to create synthetic gas (or syngas), Kelley says. The Germans used the technology during WWII to turn coal into munitions, rubber, and other products. While wood can be converted into syngas, “it’s not economically attractive unless oil is $70 or $80 a barrel,” Kelley says.
ZeaChem Inc., based in Lakewood, Colo., is planning to take things a bit further by creating a hybrid of the two technologies, designed to break down cellulose. “We’re the Prius of cellulosic ethanol technology,” says Carrie Atiyeh, director of public affairs.
She says ethanol producers typically get 90 to 100 gallons of fuel from each bone dry ton of feedstock, but with its approach, ZeaChem gets 135 gallons per ton.
“Efficiency is absolutely key to economic performance and environmental impact.”
The company uses a bacterium found in termite guts to break down the cellulose and hemicellulose found in the plants, and then uses a thermochemical process to break down the lignin.
ZeaChem now is in the process of designing a demonstration plant in Boardman, Ore., using fast-growing poplar trees as the feedstock. Among its investors is oil refiner Valero. The demonstration plant is expected to be up and running by mid-2010, producing 1.5 million gallons per year, Atiyeh says.
One issue for cellulosic ethanol, Kelley says, is that it has about 75 percent of the energy value of gasoline, so it has to be mixed with gasoline so mileage doesn’t suffer when used in current automobile engines.
Kelley expects that once the demonstration plants are up and running, the best advances from each will then be pieced together to create new plants. He predicts the new plants are still about five years away. “Second-generation plants will be very cost competitive.”
He believes that will occur in the $60 to $80 a barrel price range, and much depends on the price of the feedstock. Currently, wood chips sell for about $40 a ton, for example. If a feedstock sells for $20 to $30 a ton, a private company should be commercially viable if oil sold for $60 a ton. If the feedstock cost more, the threshold to turn a profit becomes higher.
Corn ethanol currently has an advantage in the sense that it receives a government subsidy of about 50 cents a gallon, Kelley says. But cellulosic ethanol will be eligible for a subsidy of about $1 a gallon once a company is producing it on a commercial scale.
While Heinzelman agrees that commercial production of cellulosic ethanol is still several years down the road, he notes that “the sooner this planet becomes less addicted to petroleum, the better off we’re going to be.”