Towards High Selectivity MFI Molecular Sieve Membranes through Microstructural Optimization

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Proposal No.: CTS-0091406Proposal Type: Investigator InitiatedPrincipal Investigators: Michael Tsapatsis Institution: University of Massachusetts Amherst Towards High Selectivity Molecular Sieve Membranes through MicrostructuralOptimizationThe objective of this project is to relate the microstructure of polycrystalline zeolite films to membrane separation performance. The project involves the study of two classes of films of the same zeolite (high-silica MFI) with distinctly different microstructure, stability and separation performance. These films are prepared by the secondary growth technique. Optical and electron microscopy are combined with X-ray diffraction to unravel the microstructural differences of these films at the nanometer level. The structural information is used to relate these differences to membrane properties likeselectivity and susceptibility to membrane cracking. Approaches for avoiding crackformation and methods for selective crack sealing are being investigated.Zeolites and related molecular sieves are crystalline materials with microporous frameworks capable of filtering molecules at the subnanometer level. The formation of crystalline molecular sieve membranes enables separations of molecules with similar physicochemical properties that are difficult to separate by other methods. As a result,efforts towards zeolite membrane preparation are receiving increasing attention worldwide. Recent advances have resulted in commercialization efforts and suggest new opportunities for applications in gas, liquid and vapor separations. Potential applications include separations of specialty chemicals, hydrocarbon isomers, and permanent gases as well as water/alcohol solutions by pervaporation. In order to sustain the initial success of first-generation zeolite membranes, and to find uses in new processing strategies unattainable with the current membrane technology (e.g., isomerization membrane reactors, chiral separations, etc.), research efforts are required that will combine synthetic innovation with fundamental understanding of the synthesis-microstructure-performanceinterrelationships. This work emphasizes the microstructure-performance issues. Its outcome will contribute to the development of rational rather than trial-and-error strategies for the formation of high performance molecular-sieve membranes tailored to specific separation applications.