Boozy reactor hikes hydrogen hopes Getting hydrogen from alcohol could make for greener energy. 13 February 2004 MARK PEPLOW A reactor has been made that turns alcohol into hydrogen more cheaply than previous attempts at hydrogen production. Its inventors say the device could one day be linked up to fuel cells, which can turn hydrogen into environmentally friendly electricity. Fuel cells have long been lauded as the 'green dream' of energy. The cells combine oxygen and hydrogen in a kind of battery, producing electricity. The only waste product is water. But there is a snag. Although oxygen can be extracted free from the air, hydrogen is harder to come by. The main method of large-scale production involves reacting hydrocarbons with steam at high temperatures and pressures. This requires huge amounts of electricity, which is largely generated by burning fossil fuels. And that does little to reduce the production of greenhouse gases, or to free countries from relying on oil and coal for their energy needs.

Ethanol from corn could be a cheap source of hydrogen - an environmentally friendly fuel. © LD Schmidt

Another potential source of hydrogen is alcohols such as ethanol. The United States produces about 2.8 billion gallons of industrial alcohol a year by fermenting plant matter such as corn. This ethanol is added to petrol to make it burn more cleanly.

Researchers have found several ways to pull hydrogen from ethanol, but this has generally proven difficult and costly. Now Lanny Schmidt and colleagues at the University of Minnesota have made the process cheaper and easier - perhaps enough so to make it an economically viable source of hydrogen1.

The team says that when their process is optimized it should be able to produce electricity at around four cents per kilowatt-hour, rivalling the costs of conventional electricity.

Watery fuel

The reactor pushes a mixture of watery ethanol and air over a rhodium-based catalyst heated to about 700 ?C. It takes only five seconds to start up, and produces a steady stream of hydrogen and carbon dioxide with very few other waste products.

The process therefore still produces greenhouse gas, but because it is more efficient than burning fuel it should belch out less pollution for the energy it produces, say the researchers.

"Ethanol in car engines is burned with 20% efficiency, but if you used ethanol to make hydrogen for a fuel cell, you would get 60% efficiency," says Schmidt. Ethanol can usually only be burnt if it is completely free of water - and getting the water out is an energy-intensive process. Schmidt's reactor works with wet ethanol.

The hydrogen that comes from the reactor is only about 50% pure, which makes it unsuitable for some fuel cells that easily become clogged by impurities. But the mix can be tolerated by one type of cell called a solid oxide fuel cell. Such cells are typically better for stationary applications, such as powering a house that's far from power lines, as they tend to run best at very high temperatures.

For cars, most research has focused on another type of fuel cell - a proton exchange membrane (PEM) - which generally requires a cleaner source of hydrogen.

For portable devices there may be even better options, says Anthony Kucernak, who works on fuel cells at Imperial College London. He thinks that the best solution for 'green' transportation is fuel cells that burn methanol, rather than hydrogen. Methanol, or wood alcohol, can be produced from plant cellulose on a much larger scale than ethanol, and the process makes more efficient use of the whole plant, he says.


References
Schmidt, L. D. et al. Renewable Hydrogen from Ethanol by Autothermal Reforming. Science, 303, 993 - 997, (2004).