WPI Research Publication

FALL 2013

WPI Research is the research magazine of Worcester Polytechnic Institute. It contains news and features about graduate research in the arts and sciences, business, and engineering, along with notes about new grants, books, and faculty achievements.

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CO2 H2 syngas Porous Stainless Steel Support Palladium Membrane CO2 + CO H2O ILLUSTRATION BY CURTIS SAYERS H2 ^ The modules that Ma and his team are developing for the U.S. Department of Energy will contain between seven and 37 individual membrane tubes. Syngas, a mixture of hydrogen, carbon monoxide, carbon dioxide, steam, and impurities that is produced by the coal gasifcation process, is delivered to the outside of the membrane tubes. Through what is known as the water-gas shift reaction, the carbon monoxide and steam are converted to hydrogen and carbon dioxide. The palladium layer on the outside of the membrane tube dissociates the molecular hydrogen into atomic hydrogen, which is able to move to the interior of the tube and recombine into molecular hydrogen. The hydrogen, between 20 and 25 pounds per day, is collected for use as a fuel or a chemical feedstock, or, in pure form, for use in fuel cells. The carbon dioxide, unable to permeate through the membrane, exits through a separate port at high pressure and is sequestered. into two hydrogen atoms. Just small enough to pass through the palladium lattice, the atoms are driven through the membrane to the interior of the membrane tube, where the pressure is lower. There they recombine into H2, release from the surface, and are captured. Unable to permeate through the membrane, the CO2 , still at high pressure, continues on to be stored. Palladium is expensive, Ma acknowledges, but his team keeps the cost of the membrane down by depositing a very thin layer (just 5- to 10-microns thick) to the porous stainless steel support using an electroless plating process (which uses autocatalytic reactions rather than electricity). The steel gives the palladium membrane mechanical strength and enables it to be thinner and more easily integrated into other parts of the process than if it were deposited on a ceramic base (which is standard practice with such membranes). To keep the steel from contaminating the palladium at high temperatures, the WPI researchers developed a method for building up a protective oxide layer between the metals. For some membranes, they also apply a thin layer of gold, using electrodeposition, to protect the palladium from trace amounts of hydrogen sulfde (H2S) in the gas mixture. The methods they developed for building the membrane on porous steel, the products of years of meticulous research, are the basis for most of the seven patents the innovation has earned over the years. 21

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