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The End of Oil? Breakthrough Turns Coal Into Clean Diesel

Sean Markey
for National Geographic News
April 18, 2006
 
With the price of oil topping a wallet-busting U.S. $70 a barrel
yesterday, the search for alternative fuels keeps heating up.

Last week, scientists announced what may be a new end-run around the oil problem: producing diesel fuel from coal, natural gas, and organic material.

Reporting in the current issue of the Journal Science, researchers say they have developed a way to shuffle the carbon atoms derived from cheap fuel sources like coal to form more desirable combinations, such as ethane gas and diesel fuel.

In their study, scientists scrambled the makeup of hydrocarbons—organic compounds found in fossil fuels—using two chemical processes, one of which earned last year's Nobel Prize in chemistry.

The reaction produced ethane gas and diesel fuel.

The synthetic diesel "is much cleaner burning than conventional diesel, even cleaner burning than gasoline," said Rutgers University chemist Alan Goldman.

Goldman co-developed the process with Maurice Brookhart, a chemistry professor at the University of North Carolina at Chapel Hill.

"It's a very clever idea," Robert Bergman, a chemist at the University of California, Berkeley, told Science in an accompanying news report.

"I don't think this will be an industrial process tomorrow. But conceptually, it is important."

Nazi Germany

The technology might one day wring more diesel fuel and ethane gas from hydrocarbon byproducts produced by oil refineries.

But the new chemistry's greatest potential may be as a follow-up to an 80-year-old technology known as Fischer Trospch (FT) synthesis.

Developed by German scientists Franz Fischer and Hans Tropsch in the 1920s, FT synthesis converts carbon from coal, natural gas, or wood into hydrocarbons, including propane-like gas and diesel fuel.

Nazi Germany used the technique during World War II to manufacture synthetic fuel from coal, churning out 124,000 barrels a day by 1944.

Today oil-poor South Africa uses FT synthesis to distill most of the nation's diesel from its extensive coal deposits.

One downside to the process, however, is the output of so-called mid-size hydrocarbons—molecules with 4 to 8 carbon atoms—which can't be used as fuel.

Hydrocarbons consist of hydrogen and carbon atoms. The number of carbon atoms (anywhere from 1 to, say, 99) determines whether a particular hydrocarbon is a gas, liquid, or solid and whether it's the proper weight to burn as fuel.

Goldman says his new method can convert the otherwise low-value byproducts of the FT process into high-value fuels.

He says, for example, that two mid-size hydrocarbons with six carbon atoms each could be broken up and reassembled into a two-carbon molecule (ethane gas) and a ten-carbon molecule (diesel fuel).

The chemist thinks the breakthrough could deliver U.S. energy independence.

"The United States, for example, has 40 times as much energy in coal than we do in oil, and we have even more than that in oil shale," Goldman said.

"So I think Fischer-Tropsch chemistry is really the key to energy independence for the U.S., China, [and] India."

Key to Energy Independence?

In the U.S. the governors of Pennsylvania and Montana, both coal-rich states, have touted FT technology as a future source of homegrown diesel fuel.

Last September, Pennsylvania governor Edward Rendell said his state's government would buy fuel from a planned FT plant in the state designed to convert waste coal from mining operations into low-sulfur diesel.

Montana governor Brian Schweitzer has expressed even more ambitious plans. He believes Montana's 120 billion tons (109 billion metric tons) of coal could supply the nation's gas, diesel, and jet fuel needs for the next 40 years.

Because FT plants are expensive to build and maintain (an entry-level plant falls in the range of 1.5 billion U.S. dollars), the higher cost of FT synthetic fuels have made them too pricey for U.S. markets in the past.

"When oil was $20 a barrel, it really wasn't considered economical," Goldman, the Rutgers University chemist, said.

But today's high oil prices are now tipping the scales in favor of alternative fuels.

(See National Geographic magazine's "The End of Cheap Oil.")

"Our hope is that what we've discovered will lead to something a little bit more economical [and] efficient," Goldman said.

Environmental Impact

One thorny issue is the net environmental impact of coal-based synthetic fuels.

According to the U.S. Environmental Protection Agency, FT fuels are cleaner burning than petroleum-derived products, producing fewer particulates and less dangerous nitrogen oxide.

But as FT fuels burn, they also release carbon dioxide and other greenhouse gases.

According to the U.S. Department of Energy's National Renewable Energy Laboratory, coal-based synthetic fuels may produce twice the greenhouse gas emissions of petroleum-based fuels.

Experts say one alternative may be the use of carbon collectors derived from animal waste, plants, and other organic material, which trap carbon from the atmosphere.

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