Novel SiC Nanoporous Materials for Separation Applications

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Abstract: Nanoporous carbon molecular sieve membranes (CMSM) have been the focus of much previous research for separation of mixtures. Though CMSM exhibit improved properties over polymeric membranes, they are themselves unstable in the presence of O2 and steam at temperatures higher than 300 oC; these are the conditions typically encountered in reactive separations for H2 production, and in fuel-cell applications. Other inorganic membranes, like ceramic (e.g., alumina, silica, and zeolite) and metal (Pd, Ag, and their alloys) have, so far, also proven unstable, in these high-temperature applications, particularly in the presence of steam and CO. In this project we propose the study of SiC membranes that show the potential to overcome some of these difficulties. SiC is a promising material that has high fracture toughness, good thermal shock resistance, and is capable of withstanding high temperatures and corrosive environments. The preparation of SiC nanoporous membranes involves two key steps. First, the preparation of appropriate SiC supports, and second the deposition on these supports of crack- and pinhole-free, thin nanoporous SiC films. Previous research focused on the preparation of appropriate macro and mesoporous SiC membrane supports. In this project, the University of Southern California will deposit thin nanoporous films on these substrates by the pyrolysis of pre-ceramic polymeric precursors. As with the CMSM, the researchers emphasis will be on understanding the factors determining the ability of these SiC materials to separate gas mixtures, based on differences in molecular mobility and molecule-pore surface interactions. Research will proceed along two paths: (1) the preparation and characterization of SiC membranes, and the computational modeling of their molecular structure; and (2) the measurement and simultaneous computer simulation of sorption and transport of mixtures through these membranes. Coupling experiments and simulations will facilitate efforts to relate the membrane's molecular structure with its transport properties, and separation efficacy. This, in turn, will enable progress toward the long-term goal of first-principle molecular engineering and design of improved materials for adsorption and separation. This research project will provide a valuable educational experience and training for the graduate and undergraduate students involved, by training them to prepare and characterize a novel class of new materials, and to learn a host of state-of-the-art computational and experimental techniques. The urban setting of USC affords the opportunity to work with a variety of 2-4 year colleges in the area. The researchers will recruit qualified undergraduates as summer interns, and potentially as incoming graduate students. The experimental results will be disseminated through peer-reviewed publications, presentations at technical meetings, and by makings all reports available on the Web. The PIs envision integrating research findings and aspects of their work as the degree projects in the Reactor Analysis, Transport Phenomena, and Separation courses. The proposed novel SiC membranes show good potential for reactive applications for the production of hydrogen and for fuel-cell applications. In addition to focusing attention on an important class of materials, this project will also generate fundamental insight, which will impact the knowledge-base of the broader field of transport and reaction in nanoporous media, and is likely to catalyze new thinking and rapid new advances in the area.