(5a) Metal Organic Framework Based Mixed Matrix Membranes for Gas Separations

Traditional mixed matrix membranes (MMMs) are comprised of zeolite particles dispersed in a polymer matrix. Zeolites exhibit high penetrant sorption capacities and improved penetrant size-based selectivities compared to polymers due to large micropore volumes and molecular sieving pore windows. However, zeolite-based MMMs have a number of drawbacks. These include 1) the difficulty of preparing defect-free crystals, 2) the limited number of zeolite structures and compositions, 3) the unfavorable aspect ratios of the crystallites, and 4) costly surface chemistries are often used to improve adhesion to polymer matrices, and such modifications can be detrimental to zeolite transport properties.

Metal organic frameworks (MOFs) are a relatively new class of microporous materials that are an attractive alternative to zeolites as a MMM dispersed phase. Many MOFs can be synthesized easily and quickly at low cost, potential MOF compositions and structures?including high aspect ratio MOFs?are effectively infinite, and the organic linkages provide a useful platform to improve adhesion to polymer matrices and to tune the pore window sizes.

In the present work, a MOF of copper terephthalate (CuTPA) was dispersed in poly(vinyl acetate) to create MMMs. Pure He, H2, CO2, O2, Ar, N2, and CH4 permeation experiments were performed. The permeabilities of all penetrants were enhanced due to the large, 1-dimensional pore window of CuTPA (~ 1 nm). Some selectivity enhancements were observed despite the pore window of CuTPA being much larger than the largest penetrant tested. The permeation results and potential for future advances with MOF based MMMs are discussed.