(732d) Polymer/Imidazolate Framework and Polymer/Silica Sodalite Mixed Matrix Membranes for Gas Separations

Mixed matrix membranes (MMMs) for gas separations are traditionally comprised of zeolites dispersed in a polymer matrix in order to improve desired penetrant permeability and selectivity from polymer membranes. Zeolites have a variety of drawbacks for this application ? chiefly, a limited number of possible zeolite structures and hydrophilic inorganic surface ? these limit their potential for use in MMMs. Zeolitic imidazolate frameworks (ZIFs) are new class of microporous materials. They are an alternative to the use of zeolites in MMMs because the number of possible structures is effectively infinite. This work describes the preparation of polymer-based mixed matrix membranes (MMMs) by casting from polysulfone (PSf) and polyimide (Ultem) chloroform solutions containing dispersed ZIFs or silica sodalite. The membrane microstructure and transport properties were investigated by SEM, X-ray diffraction, gas adsorption and permeation measurements. The gas transport properties of these MMMs with ZIFs and silica sodalite showed improvement over the pure polymer gas transport properties in both selectivity and permeability. For example, when ZIF-8/polyimide (Ultem) mixed-matrix membranes were studied, the He/CO2 selectivity increased from 7 to 12 and the permeability of He increased from 9.4 to 12.6 Barrers. The increased He/CO2 selectivity in ZIF-8/polyimide (Ultem) membranes was explained by the sieving effect introduced by the pure ZIF-8 crystals (pore window 0.34 nm) that restricted the transport of molecules larger than He.