Reversed CO2/C2H2 separation via combined adsorption kinetics and diffusion differences in MOF-polymer mixed matrix membrane

Abstract

The reverse separation of CO₂/C₂H₂ offers energy benefits while presents strategical challenges due to the similar molecular sizes of CO₂/C₂H₂ and the preferential adsorption/solution of C₂H₂ by most adsorbents and membranes. However, except for thermodynamic factors, kinetic diffusion can also play a pivotal role, particularly embodied in the membrane-based separation process where permeation is governed by the combined effects of solubility and diffusion. Here, we report a mixed matrix membrane (MMM) incorporating a metal-organic framework (MOF), KAUST-7, that selectively blocks C₂H₂ while allowing rapid CO₂ diffusion to implement a diffusion dominated, CO₂-selective reverse separation process. Tetrafluoroborate ions (BF₄⁻) is introduced in situ as a structure-directing agent (SDA) during the synthesis of KAUST-7(BF₄⁻), which offers a regular and nanoscale morphology, and more uniform dispersion and enhanced interfacial compatibility within the polymer matrix. The resulting MMM, incorporating 10 wt% of KAUST-7(BF₄⁻), exhibits a CO₂/C₂H₂ selectivity of 11.36 and a CO₂ permeability of 571.74 Barrer, demonstrating for the first time the potential of membrane-based CO₂/C₂H₂ separation and probably stimulating intense exploration of CO₂/C₂H₂ separation membranes.