Hydrogen, ethanol and even compressed air all have the shrink-wrapped sheen of the bright, green future. But gasoline? At $1 per gallon?
Researchers at UMass Amherst recently published a new method of refining hydrocarbons from cellulose, paving the way to turn wood scraps into gasoline, diesel fuel, Tupperware--anything, essentially, that's normally refined from petroleum. Many scientists have been working on ways to turn everything from corn stalks to tires into ethanol, sidestepping some of the problems inherent to making fuel from corn and other food products. But ethanol has a number of liabilities, regardless of the source. For instance, it requires automotive engines to be modified and contains less energy than gasoline, driving down fuel economy.
Turning cellulose into gasoline is tricky. Unlike raw crude, which is made up mostly of hydrocarbons to begin with, plant material contains a great deal of oxygen woven into its molecular structure. "Crude oil looks more similar to gasoline than biomass does," says George Huber, lead author of the new study. "So the challenge is how do you efficiently remove the oxygen and make these compounds that look like gasoline or diesel fuel? And how do you do it in the fewest number of steps and in the most economical way?"
Using a catalyst commonly employed in the petroleum industry, Huber and his colleagues heated small amounts of cellulose very quickly for a matter of seconds before cooling it, producing a high-octane liquid similar to gasoline. "The temperature window is very critical," Huber says. If you heat too slowly, you produce mainly coke--elemental carbon residue. If you heat too fast, you make mainly vapors. The sweet spot, about 1000 degrees per second, transfers roughly half the cellulose's energy into hydrocarbons. "If we can get 100 percent yield, we estimate the cost to be about a dollar per gallon," Huber says. "Right now we're at 50 percent. Can we get 100 percent? I don't know. Hopefully we'll bump those numbers up."
Huber and his colleagues aren't the first to derive hydrocarbons from renewable sources. Virent Energy Systems, for example, with Shell to produce gasoline from plant sugars and expects to open a pilot facility in the next two years. UOP is working on a project to produce jet fuel for U.S. and NATO fighters from algal and vegetable oils. But Huber's work stands out as likely the first direct conversion from cellulose, opening up as potential fuel sources virtually anything that grows. Commercialization of the technology may take another five to 10 years, the researchers predict.
Developments in so-called "green hydrocarbons" arrive as ethanol continues to come under attack as expensive, inefficient and a contributor to . (More than a billion bushels of corn are diverted to ethanol production each year.) "There's certainly a lot of historical inertia for ethanol. It's gotten us off to a great start, but I can't see the country transitioning to flex-fuel," says John Regalbuto, director of the Catalysis and Biocatalysis Program at the National Science Foundation. "I almost think, long term, that we will go to plug-in hybrids. But we're still going to need diesel and jet fuel--you can't run trains or fly planes with ethanol or hydrogen."
"We already have the infrastructure in place to distribute liquid fuels," Huber says. "We're using them to power transportation vehicles today, and I think that's what we'll be using in 10 years and in 50 years. And if you want a sustainable liquid transportation fuel, biomass is the only way to go."