A new way to make hydrogen directly from biomass, such as soy oil, reported in the current issue of Science, could cut the cost of electricity production using various cheap fuels.
Researchers at the University of Minnesota have developed a catalytic method for producing hydrogen from fuels such soy oil and even a mixture of glucose and water. The hydrogen could be used in solid-oxide fuel cells, which now run on hydrogen obtained from fossil-fuel sources such as natural gas, to generate electricity. Further, by adjusting the amount of oxygen injected along with the soy oil or sugar water, the method can be adapted to make synthesis gas, a combination of carbon monoxide and hydrogen that can be burned as fuel or converted into synthetic gasoline. The method can also produce chemical feedstocks, such as olefins, which can be made into plastics.
Although the results are preliminary, the new catalysis process represents a fundamentally new way to directly use soy oil and other cheap biomass as fuels; such biomass now needs to be converted into biodiesel or ethanol in order to be used as fuels. “Generally, people have steered clear of nonvolatile liquids–materials that you cannot vaporize,” since these typically produce a carbon residue that stops the process of producing hydrogen, says Ted Krause, head of the basic and applied research department at Argonne National Laboratory, in Argonne, IL. By eliminating the need to process soy oil and sugar water to make volatile fuels such as ethanol, the new method “opens up the number of available biomaterial feedstocks,” he says.
The process begins when the researchers spray fine droplets of soy oil or sugar water onto a super-hot catalyst made of small amounts of cerium and rhodium. The rapid heating combined with catalyst-assisted reactions prevents the formation of carbon sludge that would otherwise deactivate the catalyst. And the reactions produce heat, keeping the catalyst hot enough to continue the reaction. As a result, although fossil fuels are used initially to bring the catalysts up to the 800 °C working temperature, no fossil fuels are needed to continue the process. “One of the virtues of our process is it requires no external process heat–it drives itself,” says chemical-engineering and materials-science professor Lanny Schmidt, who led the research.
The key to the speed of the reactions is the small droplets. Existing processes for converting volatile fuels, such as ethanol or biodiesel, into hydrogen are slower because the fuels are inside pipes, and it takes up to a second for heat to transfer to them. In Schmidt’s process, the droplets heat up instantaneously–in just a few milliseconds–and the system can be faster, cheaper, and smaller, he says. The speed makes it possible to produce more fuel from a smaller reactor, reducing capital costs and potentially making it practical for a farmer to use a small system on the farm.
Schmidt says the process could probably be adapted to work with other biomass, such as slurries or powders made from grass or wood, which are now difficult to convert into practical fuels for electricity generation or transportation because of their high cellulose content. The ability to create hydrogen and syngas directly from cellulosic sources would dramatically increase the amount of fuel that could be made from waste biomass because it would be possible, for example, to use the whole cornstalk, rather than just glucose derived from corn kernels, for fuel. Other researchers are attempting to genetically engineer organisms to convert grass and cornstalks into liquid fuels such as ethanol (see “Redesigning Life to Make Ethanol”).
Such fuels could help reduce the United States’ dependence on foreign oil and provide a renewable source of fuel that produces no net increase of carbon dioxide in the atmosphere, since the carbon released when the fuel is burned is recaptured by the biomass as it grows.
Krause says that initial applications of Schmidt’s current process will likely be in producing distributed power in small amounts, since utility-scale production will be a challenge. For example, controlling the size of the droplets and the temperature of the system to keep the reactions uniform and to avoid damaging the catalysts will be harder in large systems.
Schmidt says he’s not focusing on commercializing the current technique. His next goal is to develop the system to work with sources of waste biomass. Someday it could be possible to use such a system to generate electricity from lawn clippings.
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