Car accidents with leaky ammonia fuel tanks would be nasty. Ethanol is a much safer way to store hydrogen. The University of Minnesota is working on it...
Harvesting hydrogen: Lanny Schmidt's groundbreaking reactor—which extracts hydrogen from ethanol—has set the scientific world on fire
it.umn.edu
By Deane Morrison
As a kid, Lanny Schmidt was a bit of a pyromaniac. He loved making colored flames with his chemistry set, especially when the flames got away from him and caused an explosion. But times have changed. Schmidt, now a Regents Professor of Chemical Engineering and Materials Science, has just invented a reactor that extracts hydrogen from ethanol. He did it by taming a chemical reaction that used to explode, and in the process he has set the scientific world on fire.
What got everybody's attention was that the reactor doesn't burn ethanol like ordinary combustion, which produces water and carbon dioxide. Instead of water it makes hydrogen gas, the long-awaited currency of the heralded “hydrogen economy." But hydrogen as a fuel doesn't represent much of an advance unless it comes from renewable sources like ethanol. At the moment, virtually no free hydrogen exists, except what is made from fossil fuels at a high cost. The Schmidt reactor offers the first real hope of making hydrogen cheaply enough to achieve a hydrogen economy, at least for certain energy uses.
"This work has attracted enormous interest in Minnesota because the state is a huge ethanol producer," says Schmidt. "The rural economy depends on it."
Ethanol is fermented from corn, which the Upper Midwest produces in abundance. The carbon dioxide generated by the reaction would not cause a net increase in the atmospheric level of the gas because the next year's crop would reabsorb the gas to make sugar and starch. As envisioned by Schmidt, the reactor would feed hydrogen gas into a fuel cell, where it would be burned to produce enough power to supply an average home. In fact, Schmidt sees homes in rural areas as the first beneficiaries of the new technology. Eventually, homeowners may be able to buy ethanol and use it to power small hydrogen fuel cells in their basements.
Ethanol is easy to transport and, as Schmidt puts it, "relatively nontoxic." It's already burned in car engines, but it would yield nearly three times as much power if its energy were channeled into hydrogen fuel cells instead.
"We can potentially capture 50 percent of the energy stored in sugar by the corn plant, whereas converting the sugar to ethanol and burning the ethanol in a car harvests only 20 percent of the energy in sugar," says Schmidt.
The difference is largely due to the fact that the last thing you would want to do is put water in your gas tank, says Gregg Deluga, a coinventor of the reactor and a scientist who formerly worked in Schmidt's lab. The fermentation reactions that produce ethanol take place in water, and removing every last drop of water from a batch of ethanol takes plenty of energy. But the Schmidt reactor doesn't require that water and ethanol be separated. In fact, the reaction strips hydrogen from molecules of water as well as from ethanol, yielding a hydrogen bonus.
The reactor is deceptively simple in design. At the top is an automotive fuel injector that vaporizes and mixes the ethanol-water fuel. The vaporized fuel is injected into a tube that contains a porous plug coated with the catalyst. As the fuel passes through the plug, the carbon in the ethanol is burned, but the hydrogen is not. What emerges is mostly carbon dioxide, burnt carbon, and hydrogen gas. The reaction takes only 5 to 50 milliseconds and produces none of the flames and soot that usually accompany ethanol combustion. The reactor needs a small amount of heat to get going, but once it does, it sustains the reaction at more than 700 degrees C.
In most ethanol-water fuel mixtures, one could get up to five molecules of hydrogen for each molecule of ethanolÝthree from ethanol, two from water. So far, the Schmidt team has harvested four hydrogen molecules per ethanol molecule.
"We're confident we can improve this technology to increase the yield of hydrogen and use it to power a workable fuel cell," says graduate student James Salge, another coinventor.
When word of the new reactor hit the pages of Science magazine, calls poured in from around the world. The team has been talking to everyone from corn farmers to ethanol producers. In March, Schmidt traveled to Sweden to talk about the reactor; at the same time, Deluga and Salge drove to the University's Southern Research and Outreach Center in Waseca, Minnesota, to meet with farmers. Companies like Honda, BOC, Delphi Automotive, and Caterpillar have expressed interest, but it was the media attention that really surprised the Schmidt team. Deluga ticks off a few places where he never thought he'd see a chemical engineering story:
"We were on the front page of the Cancun edition of The Miami Herald, and we were in the Iran Daily—that's the English-language newspaper of Tehran," he says. "James and I were both in the Mapleton [Minnesota] paper. James is from Mapleton, so now he's a hometown hero there. Also, [radio personality] Paul Harvey did about 30 seconds on the story."
The publicity seems to have solved one problem common to researchers everywhere: "Our parents—James's and my parents, that is—know what it is we do now," says Deluga.
"We have not gotten many negative comments. We've had surprisingly positive comments," says Schmidt.
As the saying goes, Schmidt has worked long and hard to become an overnight sensation. He began as a chemistry student at Wheaton College in Illinois and earned a Ph.D. in physical chemistry from the University of Chicago. When he came to the University of Minnesota in 1965, he studied the behavior of molecules on surfaces. He was a fundamental chemist then, but somewhere along the way he transformed himself into one of the "most applied" chemical engineers in his department.
"Right now Lanny is doing the best research of his career, and that's very unusual for somebody who's been doing so well for 35 years," says Distinguished McKnight University Professor Frank Bates, head of the chemical engineering and materials science department. "We're absolutely thrilled, and we're all jealous."
The engineering world has been taking note of him for a long time. In 1994, for example, Schmidt was elected to the National Academy of Engineering and received the Alexander von Humboldt Prize, Germany's highest research award for senior U.S. scientists and scholars.
For the last 20 years Schmidt has had about 10 students working with him at any given time. The work is tough and not for the easily discouraged. Deluga recounts how prototypes of the reactor used to blow up inside a hood on a weekly basis, but Schmidt kept pressing him to keep working on the design. Despite such rigors, Schmidt's students call him "Lanny" and have great fun with each other. The lab's signature success is probably its work with novel catalysts that transform organic molecules into useful products. The hydrogen reactor is only the latest project in that vein.
"We started 15 years ago, trying to turn natural gas into synthetic diesel fuel," says Deluga. "That process will go commercial someday."
Making diesel fuel involves, essentially, stringing molecules of methane (natural gas) together. Marilyn Huff, a former graduate student of Schmidt's, tried the process on ethane—a two-methane string—and found she could make olefins, the building blocks of economically important polymers like polyethylene and polypropylene. Schmidt and his team have also succeeded in converting methane to "syngas," a mixture of hydrogen gas and carbon monoxide that can be used to make synthetic diesel fuel and a variety of industrial chemicals.
"We'd been working with fossil fuels until this molecule, ethanol, came along," says Schmidt. "The hydrogen economy became important during the last five years, and all these processes we've been talking about make hydrogen. Now we're trying to tune the process to maximize hydrogen output instead of olefins. This is fundamental research, and a lot of steps are still required to turn it into a viable technology."
Confident it can perfect the reactor, the team is studying the rhodium-ceria catalyst to find out exactly why it works so well and how it could be improved. But several speed bumps still lie on the reactor's road to becoming the linchpin of the hydrogen economy.
For one thing, it matters where the hydrogen comes from. If its source is a plant like corn or soybeans, then the real powerhouse is the sun. But if the U.S., let alone the world, were to switch to ethanol and biodiesel, farmers would have to supply much more corn or soybeans, and the effort of growing these crops would consume extra energy and may devour more pristine land. Also, corn requires high inputs of nitrogen fertilizer. Crops like switchgrass or hybrid poplar have been suggested as possible hydrogen sources that would exact a lesser environmental cost. Nevertheless, the question of how to supply hydrogen without despoiling the environment will probably not be answered soon. Wind power, although sporadic, can generate electricity to extract hydrogen from water and may ease the situation somewhat.
However hydrogen is generated, it's of little use without fuel cells to extract its energy. That technology is just now moving from infancy to the demonstration stage.
"Once fuel cells become popular, the hydrogen reactor technology will be a very competitive option," says Schmidt. But the combination of his reactor and fuel cells won't replace current technologies until a new infrastructure is ready.
"The hydrogen economy means cars and electricity powered by hydrogen," he says. "But hydrogen is hard to come by. You can't pipe it long distances. There are a few hydrogen fueling stations, but they strip hydrogen from methane on site. It's expensive, and because it uses fossil fuels it increases carbon dioxide emissions, so it's only a short-term solution until renewable hydrogen is available."
As engineers create a system of fuel cells and fueling stations for hydrogen-powered vehicles, they will need a steady supply of hydrogen. Currently, however, only fossil fuels can deliver it. Schmidt estimates it will take at least a decade for the system to develop enough to convert to renewable hydrogen fuels.
Schmidt is not waiting for the hydrogen economy to come to him. He is a coprincipal investigator in a national project to build hydrogen fueling stations. Also, California's Electric Power Research Institute has submitted a proposal to Xcel Energy for a hydrogen fueling station on the University's Minneapolis campus. If it should come to fruition, Schmidt would certainly be a major player. Minneapolis may soon get in the game, too.
"The Minneapolis City Council is interested in hydrogen buses," says Schmidt. "We may get a demonstration model."
A fleet of 30 buses running on hydrogen fuel cells is being introduced this year in 10 European cities, according to Rolf Nordstrom, director of the Upper Midwest Hydrogen Initiative (UMHI), a public-private entity working to make the region a leader in the conversion to hydrogen-based energy. In addition to his work with UMHI, Schmidt is a key member of the University's Initiative for Renewable Energy and the Environment [see related article].
At home, Schmidt loves to grow plants, especially orange and lemon trees, which he tends in a two-story glass enclosure. Besides producing delicious fruits, the trees symbolize the increasingly important role of plants in giving us tomorrow's energy and materials.
FOR MORE INFORMATION see www.cems.umn.edu/research/schmidt. |
