Suppression of plasticization in polysulfone membranes for gas separations by heat-treatment technique

摘要

Pure gas permeation experiments with CO_2 and CH_4 as test gases have been carried out with asymmetric polysulfone (Udel P1700). Two types of membranes with heat treated and unteated were prepared to study the effect of heat-treatment process on its permeation properties. For untreated membrane, CH_4 permeation rate remained almost constant with applied gas pressure. CO_2 permeation rate exhibited an increase with increasing feed pressure, indicating that CO_2 plasticized the membrane material. The asymmetric membranes were given different heating temperature and different treatment durations to investigate the suppression of undesirable CO_2 plasticization. Permeation rates were reduced with the intensity of heat treatment. Experimental results showed that the membranes were stabilized against CO_2 plasticization after heat-treatment process, especially at temperature of 140 deg C. Heating temperature has tremendous effect on the gas transport properties for treated membrane at 180 deg C, giving an unusual behavior of CO_2. Plasticization is a pressure-dependent and time-dependent phenomenon. For the original membrane, the relaxation permeation rate of CO_2 is linearly related to the logarithmic experimentation time. The CO_2 permeation rate for treated membrane maintains at steady state over the applied feed pressures. Thus, the heat-trreatment method to suppress CO_2 plasticization and achieve better asymmetric membrane performance was effective.