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A Weed-Powered Passenger Jet

Jet fuel made from an inedible plant will power an aircraft.
November 21, 2008

On December 3, a Boeing 747 belonging to Air New Zealand is scheduled to take off from Auckland, New Zealand, powered in part by a new type of jet fuel made from a weed. A mixture of equal parts biofuel and conventional fuel will run one of the plane’s engines. The biofuel, which could help reduce carbon-dioxide emissions, was developed by UOP, a Honeywell company that is a major supplier of technology for petroleum refining.

Power plants: Technicians at UOP examine equipment used to convert jatropha oil into jet fuel.

It’s not the first time that an airliner has been powered by biofuel. What’s new is the source of the biofuel: jatropha, a plant that, unlike current sources of biofuels, is not a food crop and can be grown in marginal agricultural land. In the past year, biofuels production has come under fire for contributing to a sharp rise in food prices by diverting grain and other foods for use in fuel. Jatropha provides a potential alternative to soybean oil and palm oil, which are now used as sources of biofuels.

UOP’s new process is part of a larger effort by the company to find alternatives to petroleum, in light of increasing efforts by countries to reduce carbon-dioxide emissions. The company plans to license the technology to refiners, who could easily incorporate it into existing plants, since it’s adapted from UOP’s conventional petroleum refining process. The company developed new catalysts and added a couple of extra steps. For example, jatropha oil, unlike petroleum, contains oxygen. To make the oil into a hydrocarbon compatible with existing refining strategies, UOP included a step to add hydrogen gas, which removes the oxygen. (Other biofuels, such as biodiesel, don’t take this step, which affects the performance of the fuel and can require changes to engines.) The resulting hydrocarbon molecules are then broken into shorter molecules through a common refining process called hydrocracking. During this process, the linear molecules are modified so that they have “kinks in the chain,” says Jennifer Holmgren, the general manager of UOP’s renewable-energy unit. That makes the resulting fuel less susceptible to freezing. The process produces a mixture of primarily jet fuel and diesel fuel.

Unlike many other biofuels, UOP’s jatropha jet fuel can replace conventional fuel without requiring changes to existing engines. Indeed, by several measures, the fuel is better than conventional jet fuel. It has a lower freezing point and can be exposed to higher temperatures onboard a plane without degrading. It also contains slightly more energy than conventional jet fuel, so a plane powered by jatropha could travel farther.

After demonstrating the process at a small scale, UOP has now developed a pilot scale plant that produces thousands of gallons of fuel–enough for the commercial airliner demonstration. Holmgren predicts that production by refiners could quickly grow, reaching billions of gallons within five years.

Perhaps the biggest obstacle to reaching such levels will be acquiring enough of the jatropha feedstock. The perennial shrub hasn’t been farmed, says Roy Beckford, a researcher at the Institute of Food and Agricultural Sciences at the University of Florida, although initial efforts in this direction have started. “It’s very much still an undomesticated crop, so yields are going to be variable,” he says. “You cannot predict what is going to happen, as you can with domesticated crops like corn or soy.”

Nevertheless, Beckford says that studies of jatropha shrubs, which can eventually grow to nearly 20 feet tall and can produce fruit for 50 years, suggest that even the worst plants will produce 100 gallons of oil per acre–significantly more than soybeans can. With cultivation and careful breeding, this could easily reach 600 or more gallons per acre–about as much as oil palms produce, he says. Once farmers start planting the shrubs, they will start producing oil in significant amounts in two years and reach maturity in three to four years–much faster than with palm. Harvesting the oil will likely be easy, Beckford says, by adapting machines made for harvesting crops such as olives and coffee.

Beckman says that jatropha can bring significant environmental benefits. It can replace jet fuel and diesel from petroleum without interfering with food crops or leading to the clearing of forests. “The good thing about jatropha is that you’re producing a tree shrub that lives for a long time and does its job, producing oil, while it also sequesters lots of carbon dioxide from the atmosphere,” he says.

Jatropha is not the only option for UOP, which has tested the process with other vegetable oils and says that it could be compatible with oil from algae as well. The company plans to start licensing the technology starting the first quarter of next year.

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