Search

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 [ABSTRACT FROM AUTHOR]

Abstract: Different fluorinated copolyimides have been synthesized using 6FDA (4,4′-(hexafluoroisopropylidene)diphthalic anhydride), DABA (3,5-diaminobenzoic acid), 4MPD (2,3,5,6-tetramethyl-1,4-phenylenediamine) and 3MPD (2,4,6-trimethyl-1,3-phenylenediamine). The copolyimides with different compositions of monomers were used as membrane materials in order to remove benzothiophene from benzothiophene/n-dodecane mixtures by pervaporation. This is especially of interest in fuel cell applications where sulphur components are poisoning the catalyst and therefore reducing the life time of the system. In order to figure out which operation parameters, e.g. temperature, pressure and membrane material are necessary for the enrichment of the sulphur-aromatic component and sufficient transmembrane fluxes, different pervaporation experiments have been performed. Feed temperatures have been varied between 353 and 413K and permeate pressures between 19 and 45mbar, average fluxes and enrichment factors β were determined. Activation energies for permeation were calculated for benzothiophene and n-dodecane in order to understand the temperature-dependent separation characteristics. The influence of the different diamine structures on the separation characteristics was investigated. It was found out that slight differences in structure, e.g. an additional methyl group on the polymer backbone does not have a significant effect on the pervaporation properties. Total fluxes for 6FDA–4MPD/DABA 9:1 and 6FDA–3MPD/DABA 9:1 membranes were 15.2 and 10.3kgμm/(m2 h) at 393K, with the corresponding enrichment factor of benzothiophene of 3.6 and 3.3, respectively. With increasing temperature, enhanced fluxes as well as enhanced enrichment factors were observed. Furthermore it was found that higher permeate pressures led to a decrease of the enrichment factor with no significant change in flux. [Copyright &y& Elsevier]

Industrial applications of aromatic/aliphatic separations by pervaporation require the investigation of multi component mixtures. In this work a multi component aromatic/aliphatic mixture was applied as feed. The aromatic feed components were not only mononuclear but also di- and trinuclear. Different membranes based on 6FDA-4MPD/DABA copolyimides were investigated. The copolyimide composition was varied concerning the number of cross-linking sites. For the preparation of cross-linked membranes different cross-linking agents were used. Additionally pre-treatment of the membranes was investigated. The pervaporation conditions were varied concerning the permeate as well as feed pressure, feed temperature, and feed composition. Experiments were carried out at 100°C and 150°C, a permeate pressure of 25 mbar and 250 mbar respectively was applied and the feed pressure was 1 bar or rather 12 bar. In the course of the measurements acceptable fluxes between 1,9 kg · µm · m-2 · h-1 and 23,6 kg · µm · m-2 · h-1 were found. Enrichment factors for all aromatics over aliphatic components in the range of βarom.=1,3 and βarom.=2,3 were reached. That means in some cases a doubling of the aromatics concentration was achieved. [ABSTRACT FROM AUTHOR]