Influence of ZIF-95 on structure and gas separation properties of polyimide-based mixed matrix membranes

Polymeric membranes, especially polyimide membranes, are widely preferred in gas separation processes due to their superior properties such as inherently high permeability, selectivity, and easy processing. Zeolitic imidazolate frames (ZIFs) are crystalline porous materials exhibiting some unique properties, such as tunable pore sizes, thermal and chemical stability. In this study, a series of polyimide/ZIF-95 mixed matrix membranes (MMMs) were prepared by solution casting method and their structural, thermal, thermomechanical, and permselectivity properties were characterized in detail, by XRD, FTIR, SEM, DLS, DMA, BET surface area and gas permeability measurements. In the first step, ZIF-95 powder was synthesized and characterized then incorporated into polyimide (Matrimid (R) 5218) matrix as the loading amounts of 10, 20, and 30 wt%. SEM analysis showed that ZIF particles were homogeneously distributed into polyimide matrix and there were no agglomeration and cracking and visible holes at interfaces between polymer and filler. Increase in storage modulus of MMMs also implied such strong interfacial interactions between polyimide and ZIF-95 particles. It was found that both permeability and selectivity of CO2, CH4, and H-2 gases increased with the increasing of ZIF-95 amount in polymer matrix. The maximum ideal separation factors for the CO2/CH4 and H-2/CH4 were found to be 58.0 and 192.0, respectively. These values are significantly higher than the ideal separation factor of Matrimid (R) 5218. It was also found that the Matrimid (R)/ZIF-95 (70/30) membrane showed improvement in gas selectivity by 75% and 48% for the CO2/CH4 and H-2/CH4, respectively. Consequently, this study suggests a manufacturing route for MMMs having superior properties and improved permselectivity performances and reports their structure-property relations for potential gas separation, particularly CO2 and/or natural gas purification, processes.