Pure - and sour mixed-gas transport properties of 4,4′-methylenebis(2,6-diethylaniline)-based copolyimide membranes

Abstract

Three aromatic 6FDA-Durene/MDEA random copolyimides with different Durene:MDEA molar ratios (3:1; 1:1 and 1:3) were synthesized, and pure gas permeation properties through their dense films were investigated. Compared to their corresponding homopolymers (6FDA-MDEA and 6FDA-Durene), the copolymers exhibit significant improvement in gas separation performance, as the membranes display improved gas transport properties. For example, for pure gas, the CO2 permeability for 6FDA-Durene/MDEA (3:1) is around 234 Barrer and CO2/CH4 selectivity equal to 17.8 obtained at 22 °C and feed pressure of 100 psi. In addition, for sweet gas mixture consisting of 10, 59, 30 and 1 vol% CO2, CH4, N2 and C2H6, respectively, the 6FDA-Durene/MDEA (1:3) copolyimide membrane shows CO2 permeability of 73 Barrer and CO2/CH4 selectivity of about 24 at an elevated pressure of 800 psi. For a sour gas mixture with high H2S content (20 vol % H2S in the feed gas), the membrane exhibits H2S/CH4 selectivity of 21; and H2S permeability of 112 Barrer. The transport properties of the herein reported membrane are similar to or even better than the performance exhibited by some polymeric membranes reported in the literature.