Biodiesel: A New Way of Turning Plants into Fuel

A breakthrough process for converting biomass into biodiesel fuel promises a cheaper way to go green.

Eco-dreamers have long hoped for a way to drive around without contributing to global warming, but the slow pace of progress in alternative fuel technologies has kept that vision from materializing. Now, a promising new process, designed by researchers at the University of Wisconsin and outlined in a paper that appeared in the journal Science on June 2, could be a significant step toward turning that dream into a reality.

The paper details a new way to produce biodiesel fuel, which is made out of plant matter. Traditional biodiesel refining uses only the fatty acids of a plant, which typically make up less than 10 percent of the mass of dried plants. Rather than converting only the fat, this new method promises to turn all of the dried plant material, including roots, stems, leaves, and fruit, into biodiesel or heat energy.

Ethanol, the most popular and commercial biofuel, has long been refined out of plant matter, but it requires the costly, energy-intensive step of distilling every molecule of water out of the solution. In contrast, the new biodiesel process is based on aqueous phase reactions, which don't need to go through the expensive distillation phase.

"The biggest advance we have to offer is the lack of that distillation process," says George Huber, one of the paper's authors and a graduate student at the University of Wisconsin who will soon be teaching at the University of Massachusetts at Amherst. "That means that our process is exothermic." In other words, it doesn't need a lot of extra energy. And that's important, because the largest cost in the current biofuel refining process is energy.

The new method is divided into four parts. First, a stream of processed biomass consisting of water and sugars is fed over a nickel-tin catalyst to strip off some of its hydrogen atoms. Then the stream is treated with acids that take out most of the water. The resulting "goo" is then transported over a solid base catalyst, which forms it into long carbon chains, called alkanes. Finally, those alkanes are run through a platinum-silica-alumina catalyst at high temperatures, while the hydrogen from the first step is fed into the reactor. The resulting liquid has almost the exact same chemical structure as traditionally refined biodiesel and burns the same way in diesel engines. And the only byproducts are water and heat.

If the process can be scaled up to industrial levels, it could be a major step toward the creation of a transportation fuel that is relatively clean burning, doesn't contribute to global warming, and provides U.S. farmers with billions of dollars of new income.

According to Bill Jones, Chairman of the Board of Pacific Ethanol, a leading biofuel company, the oil industry currently views the emerging bio-fuels industry with fear, rather than acceptance.

"But eventually they'll come around," he says. "They'll understand that this isn't just competition, it's a whole new market for them to get into."

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He points out that the Brazilian petroleum industry also resisted government attempts to promote biofuels, but it is now a big supporter -- more than half of Brazil's oil imports have been replaced with biofuels (see the Technology Review April cover story on world-changing ideas).

Others don't need to be convinced, though. Charles Wyman, a distinguished professor at Dartmouth College in Hanover NH, whose specialty is the biological conversion of cellulosic biomass to ethanol and other products, says this new methodology could give biodiesel a fighting chance to succeed in the commercial marketplace by allowing manufacturers to make either ethanol or biodiesel fuel.