The effect of polyurethane on the structure and performance of PES membrane for separation of carbon dioxide from methane

Abstract

In the present study, asymmetric gas separation membranes of polyethersulfone (PES) and polyethersulfone/polyurethane (PU) were prepared with different blend compositions. The prepared membranes were investigated for the separation of carbon dioxide from methane. The effect of PU on the microstructure and d-spacing of the membranes was studied by X-ray diffraction analysis and the miscibility of PES and PU was investigated using Differential Scanning Calorimetry (DSC). The thermal properties of PES and PES/PU were compared using Thermal Gravimetric Analysis (TGA). The effect of PES/PU blend composition on the morphology and porosity of the membrane was investigated by Scanning Electron Microscopy (SEM) and porosity experiments. Density Functional Theory (DFT) calculations were used to investigate the relative affinity of CO2, CH4 and H2O for PES and PU. Moreover, the effect of PU on the casting solution viscosity, gas sorption and mechanical properties of the PES membrane was investigated. For comparing gas separation performance of PES and PES/PU membranes, pure and mixed gas experiments were carried out. The obtained results indicated that the presence of PU in the casting solution increases the d-spacing and fractional free volume, and decreases the membrane porosity; Tg and thermal resistance, membrane gas sorption as well as CO2 induced plasticization by decreasing Langmuir capacity, and also increases strength at yield and elongation at yield of PES membrane.The presence of PU decreases the CO2 permeance and enhances the CO2/CH4 selectivity and plasticization pressure of the PES membrane. Furthermore, the presence of the PU changes the membrane behavior against the feed pressure, feed temperature and feed composition in the mixed gas experiments.