CO2/CH4 Separation Using Synthesized Co-polyimide/ZIF-8 Mixed Matrix Membranes

Using three 6FDA-based polyimides and nano-size zeolitic imidazolate framework-8, we have fabricated mixed matrix membranes(MMMs). Permeability of CO2 and CH4 increases rapidly with an increase in ZIF-8 loading. The addition of ZIF-8 nano-particles into the polymer matrix increases the ideal CO2/CH4 selectivity of only 6.87%. Experimental data show that the plasticization resistance and gas pair selectivity of MMMs are strongly dependent on the amount of cross-linkable moiety and annealing temperature. MMMs made of 6FDA-Durene do not show considerable improvements on resistance against CO2-induced plasticization after annealing at 200 – 400 C, while MMMs synthesized from cross-linkable co-polyimides (6FDA-Durene/DABA (9/1) and 6FDA-Durene/DABA (7/3)) show significant enhancements in CO2/CH4 selectivity as well as plasticization suppression characteristics up to a CO2 pressure of 30 atm after annealing at 400 °C due to the cross-linking reaction of the carboxyl acid (COOH) in the DABA moiety. After thermally annealed at 400 °C, the MMM made of 6FDA-Durene/DABA (9/1) and 20 wt% ZIF-8 shows a CO2/CH4 selectivity of 19.61 and an impressive CO2 permeability 728 Barrer in mixed gas tests.