Aug. 30, 2002 MADISON - In the search for a nonpolluting energy source, hydrogen is often cited as a potential source of unlimited clean power. But hydrogen is only as clean as the process used to make it. Currently, most hydrogen is made from fossil fuels like natural gas using multi-step and high-temperature processes. Now, chemical engineers at the University of Wisconsin-Madison have developed a new process that produces hydrogen fuel from plants. This source of hydrogen is non-toxic, non-flammable and can be safely transported in the form of sugars.
Writing this week (Aug. 29) in the journal Nature, research scientist Randy Cortright, graduate student Rupali Davda and professor James Dumesic describe a process by which glucose, the same energy source used by most plants and animals, is converted to hydrogen, carbon dioxide, and gaseous alkanes with hydrogen constituting 50 percent of the products. More refined molecules such as ethylene glycol and methanol are almost completely converted to hydrogen and carbon dioxide.
"The process should be greenhouse-gas neutral," says Cortright. "Carbon dioxide is produced as a byproduct, but the plant biomass grown for hydrogen production will fix and store the carbon dioxide released the previous year."
Glucose is manufactured in vast quantities -- for example, in the form of corn syrup -- from corn starch, but can also be made from sugar beets, or low-cost biomass waste streams like paper mill sludge, cheese whey, corn stover or wood waste.
While hydrogen yields are higher for more refined molecules, Dumesic says glucose derived from waste biomass is likely to be the more practical candidate for cost effectively generating power.
"We believe we can make improvements to the catalyst and reactor design that will increase the amount of hydrogen we get from glucose," says Dumesic. "The alkane byproduct could be used to power an internal combustion engine or a solid-oxide fuel cell. Very little additional energy would be required to drive the process."
Because the Wisconsin process occurs in a liquid phase at low reaction temperatures (227 degrees C., 440 degrees F.) the hydrogen is made without the need to vaporize water. That represents a major energy savings compared to ethanol production or other conventional methods for producing hydrogen from fossil fuels based on vapor-phase, steam-reforming processes.
In addition, the low reaction temperatures result in very low carbon monoxide (CO) concentrations, making it possible to generate fuel-cell-grade hydrogen in a single-step process. The lack of CO in the hydrogen fuel clears a major obstacle to reliable fuel cell operation. CO poisons the electrode surfaces of low-temperature hydrogen fuel cells.
At current hydrogen yields, the team estimates the process could cost effectively generate electrical power. That, according to the Wisconsin researchers, assumes a low-cost biomass waste stream can be efficiently processed and fed into the system.
To be truly useful, the team says several process improvements must first be made. The platinum-based catalyst that drives the reaction is expensive and new combinations of catalysts and reactor configurations are needed to obtain higher hydrogen yields from more concentrated solutions of sugars.
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