Phase inversion method for the preparation of Pebax® 3533 thin film membranes for CO2/N2 separation

Abstract

Thin film composite membranes of poly(ether-block-amide) copolymer Pebax® 3533 were prepared for the first time on asymmetric polysulfone supports by a phase inversion method. The casting solution concentration and the number of layers were varied to study their influence on the selective layer thickness and the gas separation performance. The casting solution concentrations of polymer dissolved in the 1-propanol/1-butanol mixture were 0.25, 0.5, 1.0 and 1.5 wt%. These conditions produced membranes with selective skin layers with thicknesses from 0.2 to 1.8 µm. All the membranes were characterized by scanning electron microscopy, thermogravimetric analysis and infrared spectroscopy. Furthermore, the intrinsic viscosity of all the casting solutions was studied to understand the effect of the polymer concentration on the homogeneity and the gas separation properties of the obtained membranes. In general, lower viscosity of casting solutions rendered to more defective skin layers, resulting in a higher number of layers required to obtain selective membranes. The gas separation performance was tested for the post-combustion 15/85 CO2/N2 mixture at 25–50 °C and under a feed pressure of 3 bar. The best separation performance was achieved with the 0.5 wt% casting solution membranes after the deposition of four polymer layers, obtaining a CO2 permeance of 127 GPU and a CO2/N2 selectivity of 21.4 at 35 °C, the same selectivity of the corresponding dense membrane but with much higher permeance.