Porous Matrimid Support Membranes for Organic Solvent Separations

Abstract

Porous Matrimid® polymeric membranes were developed as supports for thin film composites (TFCs) of dense, selective polymers to target organic solvent separations. Selective polymers form dense membranes and must be thinly coated on porous supports to obtain high permeances (pressure-normalized fluxes) of target solvents. The goal of this work was to develop support membranes that demonstrated excellent stability in organic solvents and sufficient porosity to allow toluene permeances of 60-200 Lm-2h-1bar-1 such that a composite has permeance of 0.1-1Lm-2h-1bar-1. A final objective was to quantify the effects of production conditions on membrane morphology and performance. Polymer ‘dopes’ (homogeneous polymer solutions) of Matrimid® containing varying compositions of solvent and non solvent were cast using the phase inversion technique. The resulting flat membranes were then crosslinked to prevent dissolution in harsh solvents. The desired permeance was achieved with a precise control over the dope compositions and production conditions. The impact of several casting parameters such as co-solvent evaporation time, ambient humidity, and post-processing procedures were studied. Generally, a decrease in permeance was observed as the drying time prior to phase inversion was increased. Average permeance at the optimized dope composition was 76.4 Lm-2h-1bar-1, with a standard deviation of 62.5 Lm-2h-1bar-1. The effect of different crosslinkers on membrane swelling and permeability was quantified, with 1,6-hexanediamine emerging as the most suitable crosslinker. Gas porosimetry was used to determine surface pore size, which was found to generally increase with permeance.