Asymmetric polyimide mixed matrix membranes with porous materials-modified surfaces for CO2/N2 and CO2/CH4 separations

Abstract

Membranes with both good permeation and selectivity are highly desired for gas separations. We synthesized a polyimide (PI) asymmetric membrane using the phase-inversion method, and then modified the surface with a mixture of porous fillers and poly(amic acid) (PAA). The porous fillers included the metal organic framework (MOF) of Cu3(BTC)2 (copper benzene-1,3,5-tricarboxylate), the zeolite imidazole framework (ZIF) of ZIF-8, and the porous hydrotalcite of MgAl-LDH. A series of asymmetric mixed-matrix membranes (MMMs) were obtained after surface coating and thermal amidation. The MMM structure, CO2, CH4, and N2 permeance, and the ideal gas selectivity were investigated. With the surface modification, the morphology of the surface separation layers of the asymmetric PI/ZIF-8, PI/LDH, and PI/Cu3(BTC)2 MMMs significantly changed, and the gas separation performance changed accordingly. The PI/ZIF-8 asymmetric MMM with 5% (w) ZIF-8 doping exhibited both enhanced ideal gas selectivity and permeance; the CO2/N2 and CO2/CH4 selectivity were as high as 24 and 83, respectively. Thus, this surface modification provides improved MMM gas separation performance.