Sulfur‐containing copolyimides for the membrane‐based separation of aromatic/aliphatic mixtures

Recently, sulfur‐containing copolyimides have attracted increasing attention as membrane materials for the separation of gaseous, vaporous, or liquid mixtures because of their superior separation properties. Therefore, a novel sulfur‐containing copolyimide based on 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, 4,4′‐diaminodiphenylsulfide, and 3,5‐diaminobenzoic acid was synthesized, characterized, and extensively investigated in toluene/ n ‐decane pervaporation experiments. To characterize the separation properties of the copolyimide, the flux and selectivity were determined with separation mixtures between 60 and 80 wt % toluene. The separation temperature was varied between 70 and 110°C. Thereby, we observed that when the temperature was increased from 70 to 90°C, the flux and selectivity did not change significantly. In contrast, a temperature change from 90 to 110°C caused an extensive increase in the flux. The most significant change was found for an 80 wt % toluene mixture, where an increase from 1.9 to 7 kg·μm·m −2 ·h −1 was observed. Simultaneously, the selectivity which is a measure of the quality of the separation (α) decreased from α = 11.8 to α = 9.3. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013