Novel SiC Nanoporous Materials for Separation Applications

摘要：纳米多孔碳分子筛膜(CMSM)在混合物分离方面一直是研究的热点。尽管CMSM表现出比聚合物膜更好的性能，但它们本身在高于300摄氏度的氧气和水蒸气存在下不稳定；这些条件通常是在反应分离制氢和燃料电池应用中遇到的。到目前为止，其他无机膜，如陶瓷(如氧化铝、二氧化硅和沸石)和金属(钯、银及其合金)在这些高温应用中也被证明是不稳定的，特别是在蒸汽和CO存在的情况下。在这个项目中，我们建议对碳化硅薄膜进行研究，以显示出克服其中一些困难的潜力。碳化硅材料具有断裂韧性高、抗热震性能好、耐高温和耐腐蚀等特点，是一种很有前途的材料。碳化硅纳米孔膜的制备包括两个关键步骤。首先，制备合适的碳化硅载体，然后在这些载体上沉积无裂纹和无针孔的薄纳米多孔碳化硅薄膜。以往的研究主要集中在制备合适的大孔和中孔碳化硅薄膜载体。在这个项目中，南加州大学将通过热解陶瓷前驱体在这些衬底上沉积薄的纳米多孔膜。与CMSM一样，研究人员将根据分子迁移率和分子-孔表面相互作用的差异，重点了解决定这些碳化硅材料分离气体混合物能力的因素。研究将沿着两条途径进行：(1)碳化硅薄膜的制备和表征，以及其分子结构的计算模拟；(2)混合物在这些薄膜中的吸附和传输的测量和同时的计算机模拟。耦合实验和模拟将有助于努力将膜的分子结构与其传输特性和分离效率联系起来。这反过来又将使第一原理分子工程和设计用于吸附和分离的改进材料的长期目标取得进展。这项研究项目将为相关的研究生和本科生提供宝贵的教育经验和培训，培训他们准备和表征一门新材料的新课程，并学习许多最先进的计算和实验技术。南加州大学的城市环境提供了与该地区各种2-4年制大学合作的机会。研究人员将招募合格的本科生作为暑期实习生，并可能作为即将到来的研究生。实验结果将通过同行评议的出版物、在技术会议上的陈述以及在网上提供的所有报告来传播。PIs设想将研究成果和他们工作的各个方面整合为反应堆分析、运输现象和分离课程的学位项目。所提出的新型碳化硅薄膜在反应制氢和燃料电池应用方面显示出良好的潜力。除了将注意力集中在一类重要的材料上外，该项目还将产生基本的见解，这将影响纳米多孔介质中更广泛的传输和反应领域的知识库，并可能催化该领域的新思维和快速新进展。

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.