|Schematic of reactor. Click to enlarge.|
University of Minnesota researchers have developed a process that flash evaporates nonvolatile liquid bio-feedstocks such as soy oil or glucose-water solutions by catalytic partial oxidation to produce hydrogen in high yields with a total reactor time of less than 50 milliseconds.
The new process works 10 to 100 times faster than current technology, with no input of fossil fuels (except for the use of methane at reactor startup and shutdown) and in reactors at least 10 times smaller than current models. The work, which will be published in the 3 Nov 2006 issue of Science, could significantly improve the efficiency of fuel production from renewable energy sources.
It’s a way to take cheap, worthless biomass and turn it into useful fuels and chemicals. Potentially, the biomass could be used cooking oil or even products from cow manure, yard clippings, cornstalks or trees.—Prof. Lanny Schmidt, U of M
The liquid feedstocks are sprayed as fine droplets from an automotive fuel injector through a tube onto a ceramic disk made of a rhodium and cerium catalyst material. At reactor startup, CH4 (methane) and air are passed over the catalyst at 350° C and reacted to form synthesis gas (H2 and CO), releasing high levels of heat.
Once the catalyst surface reaches temperatures of 1,000° C or higher, the injectors spray a liquid fuel-air mix directly onto the hot surface. With the appropriate mix, the bio-feedstocks reform autothermally in air without the addition of more methane.
The catalytic reactions of these products generate approximately 1 megawatt of heat per square meter, which maintains the catalyst surface above 800°C at high drop impact rates. At these temperatures, heavy fuels can be catalytically transformed directly into hydrogen, carbon monoxide, and other small molecules in very short contact times without the formation of carbon.
Pyrolysis, coupled with the catalytic oxidation of the liquids upon impact with the hot rhodium-cerium catalyst surface, avoids the formation of deactivating carbon layers on the catalyst.
Because the catalytic disk is porous, the syngas passes through it and is collected downstream in the tube.
In trials using soy oil as a feedstock, the process converted about 70% of the hydrogen in the oil to hydrogen gas. Schmidt and his university colleagues—graduate students James Salge, Brady Dreyer and Paul Dauenhauer—have produced a pound of synthesis gas in a day using their small-scale reactor.
The research work was supported by the Department of Energy and the University of Minnesota Initiative for Renewable Energy and the Environment.
“Renewable Hydrogen from Nonvolatile Fuels by Reactive Flash Volatilization”; J. R. Salge, B. J. Dreyer, P. J. Dauenhauer, L. D. Schmidt; Science 3 November 2006: Vol. 314. no. 5800, pp. 801 - 804 DOI: 10.1126/science.1131244