From Seed to Power Plant

PurdueAgricultures

From seed to power plant

Seeking a green biofuels future

By Douglas M. Main

Made from biomass and plants that thrive in the fertile Midwest, biofuels may seem like a no-brainer.

As economists say, however, there’s no such thing as a free lunch; biofuels do have real potential to become a major source of sustainable energy but nevertheless present many challenges that have yet to be overcome. Purdue University researchers are working on a myriad of projects to address these obstacles, including developing improved fermentation technologies and energy crops, analyzing economic policies, and crafting guidelines for sustainable biomass production.

Where the magic happens

Biofuels derive their energy from the magic of photosynthesis, wherein plants chemically harness the sun’s power by converting carbon dioxide into energy-storing carbohydrates. The primary technical challenge is how to most efficiently convert these carbohydrates and their energetic relatives—like cellulose—into energy.

One option is to burn the material, done with solid biofuels. Agricultural and biological engineering professor Klein Ileleji does just that with switchgrass. His pilot project at Purdue’s Wade Utility Plant, begun two years ago, will assess the viability of various solid biomass fuels.

Another option is to convert the materials into combustible liquid fuels—like ethanol or soy biodiesel—to create a mobile, energy-dense fuel ideal for automobiles, planes and the like. But not all biofuels are created equal. In the United States today, all commercial ethanol comes from starch in corn grain, a relatively inefficient source that provides just 25 percent more energy than production requires.

Cellulose, the complex carbohydrate within plant cell walls, has potential to be a significantly more efficient fuel source. Present in all plant tissues, cellulose is more abundant than starch, but much of it is tightly bound to a rigid, glue-like material called “lignin.” That makes it difficult to extract, says Nathan Mosier, assistant professor of agricultural and biological engineering, who develops pretreatment techniques to liberate more cellulose for fermentation.

After these pretreatment steps, specialized yeasts ferment cellulose into ethanol. Professor Nancy Ho leads a $5 million project to develop new and more efficient varieties of such yeast, partnering with the world’s largest ethanol producer, Archer Daniels Midland Co.

Never been done

Colleague Michael Ladisch, head of Purdue’s Laboratory of Renewable Resources Engineering, is putting his work to the test. In November of last year, he announced a two-year, halftime leave to sign on as chief technology officer with Mascoma Corp., where he helps lead an effort to establish one of the world’s first full-scale cellulosic ethanol plants.

“It’s never been done before,” Ladisch says. “The only way to know if it can be is to get out there and do it.”

Success would mean a sea change for industry. But where to get all the cellulose? Purdue researchers are investigating agricultural residues as a practical source, including corn stover, sawdust and paper pulp. They also work to develop dedicated energy crops that grow quickly and provide maximum amounts of usable cellulose yet require minimal inputs like water, fertilizer and pesticides. Candidate plants include poplar trees and grasses like Miscanthus, switchgrass and prairie grass.

Developing plants that brim with accessible cellulose isn’t easy, however, explains horticulture professor Angus Murphy. Tinkering with complex cellular machinery, especially that of plant cell walls, has consequences. Cellulose provides important structural support, so changes must be carefully made and thoroughly studied to produce a viable crop.

Bridging the gap

Biofuels are only viable if they are economical. When it comes to cellulosic ethanol, the market by itself won’t deliver the goods, says professor of agricultural economics Wally Tyner.

“The market alone cannot reduce our greenhouse gas emissions or increase our energy independence, goals biofuels are meant to help achieve,” he says. “If we’re going to get to the promised land of cellulosic ethanol, we need a ‘bridge policy’ to get beyond corn.”

Late last year, Congress enacted the Renewable Fuel Standard, mandating that energy companies purchase 35 billion gallons of ethanol by 2022, 20 billion gallons of which must come from non-corn, mostly cellulosic sources. This policy promises a rosy future for biofuels, Tyner predicts, but difficult policy decisions remain to be made.

Vive la revolution

The challenge for policymakers stems in part from ethanol’s monumental impact. “We are living through a revolution in American agriculture,” Tyner says.

Historically, he explains, the price of crude oil and corn moved independently from one another. Things began to change in 2004, when surging oil prices and in-demand ethanol—along with the federal $0.51 per gallon subsidy given to ethanol blenders—made for big profits and a boom in production. Producers built more factories and bought an increasing percentage of corn to make into ethanol and be sold in blended gasoline.

The result: corn and crude oil prices are now tightly linked, which has major implications for the future. In 2007, for instance, 22 percent of the country’s corn was turned into ethanol, double the amount for 2004. This year, about 30 percent of America’s corn will go to this end, notes professor of agricultural economics Chris Hurt.

This new demand for corn helps raise food prices, reduce corn exports and strain infrastructure. The U.S. gasoline blending industry has limited capability to receive rail shipments, which are ideal for ethanol, explains Frank Dooley, professor of agricultural economics. In 2002, for example, only 11 percent of fuel blenders could receive rail shipments. Petroleum typically arrives via pipelines that cannot currently accommodate ethanol, due to its water-absorbing and corrosive nature.

Blending capacity also lags behind at urban terminals, where demand is high but space is limited for railways and excess fuel storage. With the Midwest producing 90 percent of the country’s ethanol, trains and an ever-growing number of trucks must carry it long distances, stressing rural roads and releasing additional emissions.

“These infrastructure concerns will cause some real problems in the near-term and help create pressure for lower ethanol prices. However, we should be able to resolve them within a few years,” Dooley says.

Too much ethanol?

One of the biggest challenges, short- and long-term, will be to find a market for all the ethanol produced. Like other Midwestern states, Indiana will see increased production, with six operating ethanol plants, six under construction and some 25 more under consideration, Hurt says. The national production capacity, which surpassed 7 billion gallons last year, is expected to reach 11 billion gallons by July and approach 13 billion by year’s end.

But 12 billion gallons is the maximum that can be sold domestically in 2008, Tyner predicts. That’s because ethanol may only be blended into regular gasoline at 10 percent, known as “E10 fuel,” and gasoline blenders are nowhere near being able to blend the 140 billion gallons of gasoline consumed annually. Selling more E85, an 85-percent ethanol fuel used by flex-fuel vehicles, is an obvious choice—except it is sold at only 1,530 stations nationwide, less than 1 percent of the nation’s total stations, Dooley explains.

“It’s a chicken-and-egg situation,” Tyner says. “People are unwilling to get flex-fuel vehicles because there are so few stations; companies are unwilling to build more stations because there are few vehicles.”

Moreover, E85 pumps are expensive to install; gas stations need to charge an extra 5 to 7 cents per gallon to recover costs, according to a U.S. Department of Energy report.

“It might not seem like much, but consumers are fickle—everything equal, we’d choose the cheaper gas, even if it’s only a few cents less per gallon,” Dooley says.

Toward sustainability

Besides being affordable, biofuels also must contribute to America’s energy independence, reduce greenhouse gases and be maximally sustainable—a tall order, to say the least.

Ideally, biofuels trump fossil fuels because they can be grown locally and, upon combustion, release only carbon captured during their brief lifetime. Conversely, fossil fuels—contained in some politically volatile regions—release carbon sequestered for eons, increasing net levels of atmospheric carbon dioxide, the heat-trapping gas behind climate change.

Past a certain point, however, sustainability becomes subjective and difficult to define. For example, is it more important to reduce runoff or carbon emissions? The short answer: It depends. Purdue researchers, including Tyner, agricultural and biological engineering professor Bernie Engel, and agronomy professors Sylvie Brouder, Ron Turco, and Jeff Volenec, are among the first to tackle such difficult questions. They seek, among other things, to establish guidelines for quantifying biofuels’ environmental impacts and to bridge the gap between scientists, policymakers and farmers.

When compared with grassland, for example, corn acreage requires relatively high levels of nutrients and pesticides. “Corn is leaky,” as agronomy professor Eileen Kladivko puts it. Kladivko and other Purdue researchers develop practices to mitigate such runoff and drainage. Her work has shown that planting winter cover crops like wheat or rye after fall harvest can reduce nutrient escape. Agronomy professor Tony Vyn has shown that no-till practices limit soil erosion and greenhouse gas emissions; unfortunately, the continuous corn cultivation encouraged by growing ethanol production usually coincides with intensified tillage.

Another biofuel, soy biodiesel, requires fewer agricultural inputs than corn and is more efficient but less economical due to high non-energy demands. “People can’t afford to convert $4.50 soybean oil to $3.50 diesel,” Tyner says, referring to the commodity’s prices as of early 2008.

Candidate crops like grasses and trees are likely to have environmental advantages over traditional row crops, although even these will likely require fertilizer and other inputs to be economically viable. Purdue researchers work to quantify inputs necessary for optimizing yields of such crops, so as to reduce unintended consequences of the shift toward biofuels.

The road ahead

Active research on solid biofuels and cellulosic ethanol offers clues to biofuel’s future. Environmental engineer Larry Nies points to a quote by pioneering physicist Niels Bohr, “‘Prediction is very difficult, especially if it’s about the future.’ It’s quite possible that in 25 years, our cars will run on something we haven’t yet considered,” Nies says.

Other potential biofuels include synthetic gas, or syngas, green diesel from grass or vegetable oils, and even algae-derived fuels. New pyrolitic processes may also be able to create gasoline-like fuels from biomass.

Though the future is uncertain, biofuels do have potential to become a major part of an overall energy solution, and Purdue researchers are among the leaders in biofuel science and industry who guide the path toward a more sustainable future.

“It’s just a matter of finding the right bridge,” Tyner says.

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