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New material promises hydrogen fuel and cheaper petrochem processing Chemical engineers at Te University of Texas (UT) at Austin say they've developed a rubbery material that can purify hydrogen efficiently in its most usable form for fuel cells and oil refining. According to Benny Freeman, a professor of chemical engineering at UT, his laboratory designed the membrane material and tested its ability with colleagues at Research Triangle Institute (RTI) (Research Triangle Park, North Carolina) to successfully separate hydrogen from carbon dioxide (CO2) and other contaminant gases. Tis member of a new family of membrane materials with superior gas-separating ability could lower the costs of purifying hydrogen for hydrogen-fueled vehicles, the engineers maintain. Hydrogen fuel 56 MATERIALS PERFORMANCE March 2006 cells are considered a leading alternative energy for running cars and other devices in the future. Te membrane material may also replace an expensive step in petrochemical processing, or reduce the amount of energy the step requires. Te membrane was tested under conditions that mimic those routinely used by the petrochemical industry to refine petroleum components (crude oil and natural gas). "A significant amount of the hydrogen in use today goes into the refining industry to refine crude oil to produce gasoline or other products, so this membrane could lower refining costs," says Freeman. Te membrane differs structurally and functionally from previous options, the engineers maintain, with a key advantage being its ability to permit hydrogen to remain compressed at high pressure. A compressed form of the lightweight gas is needed to process fossil fuels and to serve as a readily replaceable fuel for fuel cells. Freeman and graduate student Haiqing Lin designed the membrane material Benny Freeman shows a sample of the new transparent membrane. Photo by Jennie Trower. in Freeman's laboratory at the university's Center for Energy and Environmental Resources. Te engineers and RTI collaborators Lora Toy and Raghubir Gupta tested flat, disk-shaped samples of the material for its ability to separate different mixtures of hydrogen and CO2 at different temperatures. Te researchers used the three common temperatures for industrial hydrogen purification: 95°F (35°C), 50°F (10°C), and –4°F (-20°C). Te new membrane not only separated these two gases better than previous membranes, researchers say, but did so when hydrogen sulfide (H2S) and water vapor were present, as occurs in industrial settings. Te membrane worked so well that it was 40 times more permeable to CO2 than hydrogen, according to the engineers. In contrast, current commercial membranes favor the transport of hydrogen, a small molecule, over larger CO2 molecules, which results in hydrogen being transferred to a low-pressure environment that requires expensive recompression of the gas before use. Te team claims that the new membrane eliminates this recompression step by favoring the transport of larger, polar gas molecules as a result of the polar nature of the polymer materials making up the membrane. Te polar, reverse-selective materials, based on ethylene oxide [(CH2)2] interact better with polar gases such as CO2 than with smaller, nonpolar hydrogen gas, which is left behind in a high-pressure state. "Te membrane likes carbon dioxide more than hydrogen, and we optimized that affinity," Freeman says. Plasticization,