Enhanced CO2/CH4 separation performance of BTDA-TDI/MDI (P84) copolyimide mixed-matrix membranes by incorporating submicrometer-sized [Ni3(HCOO)6] framework crystals

The incorporation of metal-organic frameworks (MOFs) into mixed-matrix membranes (MMMs) is gaining widespread attention because of the combined advantages of easy processability and superior separation performance. In this paper, submicmmeter-sized [Ni-3(HCOO)(6)] frameworks were incorporated into BTDA-TDI/MDI (P84) matrix as filler material to separate CO2 from CH4. When the loadings of [Ni-3(HCOO)(6)] frameworks in MMMs were 7 and 15 wt%, obvious enhancements in gas separation properties were obtained. Especially at the loading of 15 wt%, CO2 permeability and the CO2/CH4 selectivity increased 76% (from 0.72 Barrer to 1.26 Barrer) and 52% (from 44 to 67), respectively, compared with the pristine P84 membrane. The partial pore blockage was found by the high-pressure gravimetric adsorption measurements and it was deemed to be profitable to separate CO2/CH4. In order to better understand the gas separation behavior, the characterizations of [Ni-3(HCOO)(6)] frameworks (XRD, SEM, Ar adsorption-desorption, CO2 and CH4 adsorption, ATR-FTIR, TGA) and P84/[Ni-3(HCOO)(6)] MMMs (SEM, ATR-FTIR, XRD, TGA, stress-strain tests) were performed.