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.

Key words: Mixed matrix membrane, Gas separation, Surface modification, Polyimide, ZIF-8