Enhanced CO2 separation in ZIF-8+TpPa-1/PEBAX®2533 mixed-matrix membranes: insights into diffusion and sorption contributions

This study investigates how a previously developed ZIF-8+TpPa-1 MOF–COF composite filler modifies gas transport in dense PEBAX®2533 mixed-matrix membranes. The composite, prepared by the authors using a combined solvothermal–mechanochemical approach, was evaluated here as a filler for CO 2 separation membranes. This composite was characterized by SEM, TEM, FTIR, XRD, N 2 adsorption, and thermal analysis. TEM observations revealed TpPa-1 particles decorated with ZIF-8 crystallites, with close interfacial contact between the two phases. Mixed-matrix membranes containing 2 or 5 wt% ZIF-8, TpPa-1, or ZIF-8+TpPa-1 were evaluated using the time-lag method. Among the investigated materials, the membrane containing 5 wt% ZIF-8+TpPa-1 showed the best overall performance. At 25°C and 4 bar, the composite filler increased CO 2 permeability by 60.4% relative to pristine PEBAX®2533, while simultaneously improving the ideal CO 2 /CH 4 , CO 2 /N 2 , and CO 2 /H 2 selectivities by 35.6%, 30.2%, and 22.9%, respectively. At 8 bar, the CO 2 /H 2 ideal selectivity increased from 5.2 for the pristine membrane to 8.4 for the composite-filled membrane. Mixed-gas sorption measurements further showed increases in the CO 2 sorption coefficient of approximately 41% for the CO 2 /N 2 mixture and 84% for the CO 2 /CH 4 mixture. Arrhenius analysis demonstrated that the apparent diffusion activation energy of CO 2 decreased from 33.5 to 22.1 kJ/mol after filler incorporation. Overall, the enhanced separation performance results from the combined modification of diffusion and sorption, with preferential CO 2 sorption becoming increasingly important at elevated feed pressure.