Amino-functionalized ZIF-7 embedded polymers of intrinsic microporosity membrane with enhanced selectivity for biogas upgrading

Membrane separation is an energy-efficient technology to achieve biogas upgrading. However, their broad application is limited by the relatively low gas permeability and thus the large membrane area. Polymers of intrinsic microporosity (PIMs), as a kind of highly permeable polymers, hold great promise to solve this problem but are restricted by their relatively low selectivity. In this study, significant enhancement in the selectivity of highly permeable PIM-1 membranes was achieved through incorporating amino-functionalized zeolitic imidazolate framework ZIF-7 to prepare mixed matrix membranes (MMMs). NH2-ZIF-7 exhibits not only excellent intrinsic CO2/CH4 separation ability but also favorable interaction with the PIM-1 polymer. The fortified interfacial interaction generates the rigidification of polymer chains at the interface and partial blockage of NH2-ZIF-7 particles, which both contributes to the enhancement of CO2/CH4 diffusion selectivity. Notably, the CO2/CH4 selectivity of the mixed matrix membrane containing 20 wt% NH2-ZIF-7 increased to 20.6 with CO2 permeability of 2953 Barrer, which transcended the reported 2008 upper bound of polymer membranes. To analyze the gas transport behavior within MMMs and explain the enhanced selectivity, a modified Maxwell model considering rigidified polymer region and partially blocked particle skin was proposed and validated by the good consistency between the experimental and predicted data.