title: Crosslinked copolyimide membranes for phenol recovery from process water by pervaporation.
abstract: The effectiveness of different copolyimide membranes in the process of recovering phenol from water by pervaporation has been investigated. The polyimides were obtained by the polycondensation of 6FDA (4,4'-hexafluoro-isopropylidene diphthalic anhydride) with different diamines. The diamines 4 MPD (2,3,5,6-tetramethyl-1,4-phenylene diamine), 6FpDA (4,4'-hexafluoro-isopropylidene dianiline), 6FpODA (4,4'-bis-(4'-aminophenoxyphenyl)-hexafluoropropane), and DABA (3,5-diaminobenzoic acid) as a monomer providing a crosslinkable group, were used. In order to reach chemical stability at high phenol concentrations, the polymer structures were crosslinked with 1,10-decanediol and OFHD (2,2,3,3,4,4,5,5-octafluorohexanediol). Pervaporation experiments were performed at 60 degrees C, covering a concentration range of phenol between 2 and 11 wt.%. The best separation characteristics were obtained with a 6FDA-6FpDA/DABA 2:1 membrane crosslinked with 1,10-decanediol. Using a 7.8 wt.% phenol feed mixture, a total flux of 14 kg microns m-2 h-1 was reached with an enrichment of 40 wt.% phenol in the permeate. It was found that conditioning the membrane using high phenol concentrations (between 8 and 11 wt.%) is a necessary pretreatment in order to enhance the flux and improve enrichment, especially if process water with low phenol concentrations is to be treated. In addition to the experimental results, a comparison with rubbery membrane materials is presented in the discussion.
authors.affiliation: Institute of Physical Chemistry, University of Heidelberg, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany.
authors.forename: Frankie
authors.initials: F
authors.lastname: Pithan
authors.forename: Claudia
authors.initials: C
authors.lastname: Staudt-Bickel