Pervaporation properties of ethynyl-containing copolyimide membranes to aromatic/non-aromatic hydrocarbon mixtures

2,2′-diethynylbenzidine and a series of copolyimides containing such a diamine moiety were synthesized. The crosslinking behaviors of these copolyimides were studied by differential scanning calorimetry and infrared measurements. Pervaporation (PV) properties of these copolyimide membranes to aromatic/non-aromatic hydrocarbon mixtures were investigated. The crosslinked membranes exhibited higher separation factors of benzene over cyclohexane than the corresponding uncrosslinked ones. The sorption results revealed that the increase in diffusivity selectivity was mainly responsible for the improvement in separation factor of PV. However, this improvement seemed still limited. In addition, tetracyanoethylene, an electron acceptor having high affinity for ethynyl-containing materials and aromatics, was homogeneously dispersed in one of these copolyimide matrices and such a membrane displayed high PV performance toward benzene/cyclohexane and toluene/i-octane mixtures. For example, it had a specific permeation flux Q 1 of 0.44 kg μm m − 2  h − 1 and a separation factor α of 48 at the feed composition of 50% benzene in cyclohexane, and Q 1=1.1 kg μm m − 2  h − 1 and α =330 at the feed composition of 45% toluene in i-octane at 70°C. Unlike the case of crosslinking, both the increases in solubility selectivity and diffusivity selectivity contributed to the improvement in separation factor of PV.