Gas permeability and selectivity properties of ZIF-8/Matrimid mixed-matrix membranes

Zeolitic imidazolate frameworks (ZIFs), that have the potential for gas separation, were used as additives in mixed-matrix membranes (MMMs). ZIF-8, which exhibits the sodalite topology, is composed of zinc (II) ion clusters linked by imidazolate ligands. The ZIF-8 pore size is 3.4 A allowing it to readily absorb small molecules such as H2 and CO 2. ZIF-8 is thermally stable up to 500°C, and has a surface area of 1300 m2/g. The fabrication and characterization of ZIF-8 and MatrimidRTM polymer MMMs are described. The permeability properties were tested for H2, CO2, O2, N 2, CH4, C3H8, and gas mixtures of H 2/CO2 and CO2/CH4. The permeabilities increased as the loading of ZIF-8 increased up to 40% (w/w), where the polymer dominates the separation properties. At higher loadings of 50% (w/w) the permeability decreased and selectivity increased consistent with the influence of the ZIF-8 additive. The ideal selectivities of small gases, such as H2/O 2 and H2/CO2, showed improvement with increased ZIF-8 loading, showing a change from polymer to ZIF-8 driven permselectivity.