Ethanol yields hydrogen
By
Kimberly Patch,
Technology Research NewsFuel cells that convert the chemical bonds between hydrogen atoms to energy are about three times more efficient than combustion engines that burn hydrocarbons. And fuel cells powered with pure hydrogen carry out the conversion cleanly.
The trick is finding a cost-effective way to produce hydrogen without polluting the environment.
Researchers from the University of Minnesota and the University of Patras in Greece have devised a way to extract hydrogen directly from ethanol, which would make for a renewable energy cycle. Ethanol is produced by converting biomass like cornstarch to sugar, then fermenting it.
The researchers' method is relatively simple, and an ethanol-to-hydrogen converter designed for home use would be not much larger than a coffee mug, according to Lanny Schmidt, a professor of chemical engineering and materials science at the University of Minnesota.
Historically, there have been two major stumbling blocks to using ethanol as a source for hydrogen. Ethanol is fairly flammable, and the process of extracting hydrogen from ethanol destroys the catalyst traditionally used to extract hydrogen from hydrocarbons like oil.
The University of Minnesota researchers were looking to find a good way to convert ethanol because it packs a lot of energy -- 80 percent that of gasoline -- and is a renewable fuel source. "We tried ethanol," said Schmidt. "And it didn't work for two years."
The researchers eventually solved the flammability problem by using an automotive fuel injector, said Schmidt. "It rapidly vaporizes ethanol water and mixes [it] with air and does this so fast that there's no time for flames to start," he said.
They solved the catalyst problem accidentally, said Schmidt. At first the researchers were using the same rhodium catalyst they'd had success with in extracting hydrogen from diesel fuel and natural gas. This, "forms carbon on the surface and otherwise makes a mess out of things," which destroyed the catalyst within a few hours, said Schmidt. "We... discovered serendipitously that rhodium-ceria as the catalyst had a long life," he said. The researchers are still investigating exactly why the new catalyst works so much better.
The gasoline sold by many service stations around the country is really a mix of ethanol and gasoline, but fuel ethanol must be refined so that it contains no water. The researchers' method not only allows for water to be mixed with ethanol, it extracts some of the hydrogen from the water as well, said Schmidt. This makes producing ethanol for hydrogen potentially cheaper. Ethanol is currently more expensive than gasoline, but the two fuels are in the same realm -- wholesale prices are about $1.10 a gallon versus 70 cents for gasoline, he said.
The researchers' method is relatively simple. "You feed ethanol plus water into the top of a reactor," said Schmidt. The fuel injector vaporizes the fuel and sprays the drops onto a hot surface to make a mixture of mostly ethanol with a little air and water, which hits a catalyst that's glowing bright orange from the heat of the chemical reaction. "That makes hydrogen form very quickly... and that feeds into the fuel cell," he said.
The reactor could be any size depending on the application, said Schmidt. A reactor large enough to extract hydrogen for a washing machine-sized fuel cell designed to power a house could be made as small as a coffee mug, said Schmidt.
The method could be used in practical applications now, said Schmidt. "We'll have the technical capability to switch to a significant extent away from fossil fuels toward renewable fuels, but whether we do... is a political question and an economic question," he said. "It's not cheaper than natural gas or coal... but it's cleaner, and renewable."
Although extracting hydrogen from ethanol produces carbon dioxide, the carbon dioxide is reclaimed by the next year's crop, making for a renewable energy cycle. "If you use biomass as your source of energy instead of fossil fuels, carbon dioxide gets sequestered back into next year's crop," said Schmidt.
Eventually waste products like wood chips, grass clippings and crop wastes could be used to make lower-cost ethanol, said Schmidt. How far down the road this is depends on "when we want to switch to renewable fuels," he said. "Technically we could do it in 10 years."
Schmidt's research colleagues were Gregg A. Deluga and James R. Salge at the University of Minnesota, and Xenephon E. Verykios at the University of Patras in Greece. The work appeared in the February 13, 2004 issue of Science. The research was funded by the National Science Foundation (NSF), the Department of Energy (DOE), and the Initiative for Renewable Energy and the Environment at the University of Minnesota.
Timeline: Now, 10 years
Funding: Government, University
TRN Categories: Energy
Story Type: News
Related Elements: Technical paper, "Renewable Hydrogen from Ethanol by Autothermal Reforming," Science, February 13, 2004
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February 25/March 3, 2004
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