Supercritical CO₂ Treatment of Mixed Matrix Membranes Based on Polyimides for Improvement of Their Gas Transport Properties

Abstract: In this work, mixed matrix membranes (MMMs) were obtained based on polyimides synthesized from a mixture of diethyltoluene diamine (DETDA) isomers and BPDA and 6FDA dianhydrides by introducing metal-organic framework compounds ZIF-8 and ZIF-67 in a concentration of up to 20 wt % in chloroform solution. The starting polyimides were synthesized by one-stage high-temperature catalytic polycondensation in a benzoic acid melt. The studied MMMs were treated with sc-CO₂ followed by decompression. The gas transport and gas selective properties of the original and modified membranes were studied. Experimental values of the effective coefficients of permeability and diffusion of gases for He, H₂, O₂, N₂, CO₂, CH₄ were obtained, and the effective solubility coefficients of these gases were calculated. It was found that treatment of the studied MMMs in sc-CO₂ can significantly increase the level of gas permeability of membranes with gas selectivity at the level of initial values, while the achieved effect of changing the permeability of membranes depends on the gas, the nature of the matrix, and the concentration of the introduced particles. It was found that the treatment effect persists over time with a slight decrease in permeability of gases, which remains at a level significantly higher than the initial values. The demonstrated effect of improving gas transport properties when treating MMMs based on polyimide matrices 6FDA-DETDA and BPDA-DETDA in sc-CO₂ can be used for further application of the proposed modification method in order to increase gas transport through MMMs based on other polymers, including highly permeable ones.