Performance characterization of polyamide reverse osmosis membranes upon supercritical CO2 processing

Stability is one of the most important criteria while selecting the proper membrane for a targeted separation. Use of supercritical carbon dioxide (SC-CO2) as a solvent during the separation of solute molecules by polymeric membranes requires knowledge of the stability of membranes, considering the well known polymer-CO2 interactions. In this study, the effects of different temperature (40, 60 and 80 degrees C), transmembrane pressure (10, 20, 30 and 40 bar), depressurization rate (0.1 and 5 bar/s) and processing time (0-24 h) at 120 bar on the performance of two commercial polyamide membranes were investigated. Performance of the membranes was evaluated by measuring CO2 flux and oleic acid retention factors at 120 bar and 40 degrees C following processing with CO2. High transmembrane pressures (30 and 40 bar) did not exhibit a linear increase in CO2 flux and showed higher oleic acid retention factors whereas high temperature processing and depressurization resulted in higher flux and lower retentions. Each of these effects increased with processing time at each processing condition. The findings demonstrated that the covalently cross-linked polyamide membrane was more robust under supercritical conditions compared to the second polyamide membrane with a high level of hydrogen bonding in its structure. (c) 2011 Elsevier B.V. All rights reserved.