Dibenzo-21-crown-7-ether contained 6FDA-based polyimide membrane with improved gas selectivity

Abstract

In the present work, a novel crown ether contained polyimide membrane was synthesized by 4, 4′- (hexafluoro - isopropylidene) diphthalic anhydride, 1, 4 - Bis (4 - aminophenoxy) benzene, and di(aminobenze)-21-Crown-7 ether. The physical property and chemical structure were studied by FTIR, 1HNMR, XRD, TGA, GPC, and tensile testing. Molecular dynamic simulations were applied to investigate the effects of crown ether content on free volume property of membranes. The permselectivity was studied employing He, H2, CO2, N2, and CH4 pure gas as feed. The effects of crown ether content, operation temperature, feed gas pressure, and aging effect on membranes were investigated. Results show that introducing crown ether into polymeric backbone can increase the chains packing density, which lead to reduce d-spacing as well as accessible fractional free volume. These permeabilities followed the order of He > H2 > CO2 > N2 > CH4, indicating a typical molecular sieving separation mechanism in membranes. The introduction of DB21C7 can improve the diffusion selectivity and solubility selectivity. For example, CO2/N2 and CO2/CH4 diffusion selectivity display impressing increase of 53% and 84% respectively by incorporation of 30 mol% DB21C7. As a consequence, the membrane with 30 mol% DB21C7 exhibit remarkable selectivity increase of about 173.5% (for He/CH4), 156.9% (for H2/CH4), 109.4% (for CO2/N2), 88.5% (for CO2/CH4) than non-crown ether contained polyimide membrane. Hence, future membrane material design for high purity gas requirement may be considered as a promising alternative membrane by introducing the crown ether moiety into the polymeric backbone.