SCIENCE
Edward Willett
Hydrogen from ethanol
Ethanol has been in the news in Saskatchewan recently with the announcement of federal subsidies for ethanol plants in Llodyminster and Weyburn.
For now, most of the ethanol produced will be blended with gasoline to produce a cleaner-burning fuel for automobiles. But soon ethanol may be even more important as a source of the cleanest-burning fuel of all: hydrogen.
All of the ethanol produced as alcoholic beverages, and most of the ethanol produced for industrial purposes, is created by the fermentation of sugars. Theoretically, pretty much any biomass can be used to produce industrial ethanol; in the States, they use corn, in Western Canada, wheat, and in Brazil, sugar cane.
Hydrogen can’t be made that easily, nor does it exist in large underground reservoirs. Commercially, it’s produced exclusively by steam reforming, in which a fossil fuel such as natural gas is mixed with high-temperature steam. This takes a lot of energy, consumes fossil fuels and releases carbon dioxide.
A report released earlier this month by the National Academies of Science in the U.S. states that the only way hydrogen can achieve widespread use as a fuel, especially in automobiles, is if a means can be found to produce it cost-effectively, either in large plants or in smaller facilities at or near vehicle fueling stations.
Lanny Schmidt, Gregg Deluga and graduate student James Salge of the University of Minnesota’s department of chemical engineering and materials science have created just such a small device to produce hydrogen from ethanol. In their reactor, an automotive fuel injector vaporizes the ethanol and injects it into a tube that contains a porous metal plug, heated to 700 C, made from rhodium and ceria. What comes out the other side of the plug is a steady stream of hydrogen and carbon dioxide, with few other waste products.
The process uses far less energy than current methods of producing hydrogen. And while it still produces carbon dioxide, that’s somewhat offset by the fact that the plants used to make the ethanol used carbon dioxide as they grew.
In addition, the reactor can work with “wet” ethanol–ethanol which still contains some water–something other methods of extracting hydrogen from ethanol can’t do. In fact, it uses the water to produce additional hydrogen.
That’s important because you can never remove all of the water from ethanol by distillation alone. Commercial ethanol usually contains five percent water; producing “absolute” ethanol requires the addition of dehydrating agents. The reactor’s ability to use wet ethanol obviates that additional level of processing.
The best way to turn the resulting hydrogen into electricity is with a fuel cell. There’s more than one kind of fuel cell, and unfortunately, the hydrogen so far produced by the Minnesota reactor contains too many impurities (primarily in the form of carbon monoxide) to work in the proton exchange membrane fuel cells that are the leading contenders for powering automobiles. However, it will work in solid oxide fuel cells. These are best suited for stationary applications, so the first likely use of ethanol reactors will be to provide the hydrogen for fuel cells that could in turn power buildings far from power lines–in, for example, Canada’s Far North.
Once the reactor has been improved to produce cleaner hydrogen, it could take its place at filling stations creating hydrogen for the fuel-cell-powered cars of the not-too-distant future.
Although ethanol in gasoline makes car engines run cleaner, using ethanol to produce hydrogen would be even more environmentally friendly. The ethanol in car engines burns with only 20 percent efficiency, but if ethanol is used to make hydrogen for a fuel cell, you get 60 percent efficiency–or, to put it another way, you get three times as much energy out of each bushel of whatever plant matter is used to make the ethanol if you turn the ethanol into hydrogen than you do by simply burning it.
A full-fledged hydrogen-based energy system is still years, or even decades away–the National Academies of Science report suggest that over the next 25 years any reductions in oil imports and carbon dioxide emissions due to the use of hydrogen are likely to be minor–but the only way we’re going to get there is with incremental steps like the development of this new ethanol reactor.
And with luck, it might even be good news for Saskatchewan farmers, who could surely use some.
