Temperature-dependent separation of naphthalene/ n-decane mixtures using 6FDA–DABA-copolyimide membranes

Abstract

Literature concerning aromatic/aliphatic separations almost exclusively deal with toluene or benzene as aromatic component, but in real applications also bi- and tricyclic aromatics as well as their substituted derivatives occur in addition to benzene, toluene and xylenes (BTX). The aim of this work was to investigate if naphthalene, e.g. can be separated as well in pervaporation experiments at elevated temperatures using naphthalene/ n-decane mixtures. As membrane material fluorinated copolyimides made of 6FDA (4,4′-hexafluoroisopropylidene diphthalic anhydride), DABA (3,5-diamino benzoic acid) and 4MPD (2,3,5,6-tetramethyl-1,4-phenylene diamine) were used. In order to find appropriate conditions for enhanced permeation of naphthalene, the feed temperature was varied between 60 °C and 150 °C and pre-treatment of the membrane was investigated. Furthermore different copolymer compositions and cross-linking agents were studied. For all tested membranes a strong temperature dependency was found. Enrichment of naphthalene in the permeate was found at temperatures above 80 °C. Remarkably with increasing temperature a higher enrichment factor combined with a higher flux was observed. Enrichment factors β between 1.8 and 2.5 with fluxes between J n = 2 kg μm m −2 h −1 and J n = 40 kg μm m −2 h −1 were measured at 120 °C for different membrane structures.