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

► FTIR shows the intermolecular interactions between surfactants and polyethersulfone. ► Surfactants increased the porosity and CO2 permeance of polyethersulfone membranes. ► Triton X-100 increases the CO2/CH4 selectivity of polyethersulfone membrane. ► Triton X-100 reinforced polyethersulfone against the plasticization effect of CO2. ► Mixed gas permeance of polyethersulfone membrane affected by Triton X-100. In the present study, the effects of three types of surfactants including sodium dodecyl sulphate (SDS), cetyle three methyl ammonium bromide (CTAB), and Triton X-100 on structure and performance of polyethersulfone membranes for carbon dioxide separation from methane were investigated. Flat sheet gas separation membranes of polyethersulfone (PES) and its mixture with different concentration of surfactants in casting solution were fabricated through a dry/wet induced phase inversion process. Ternary phase diagrams of polymer–solvent–nonsolvent for pure PES and its mixture with surfactants were drawn using titration method. Investigation of crystal phase compositions of the prepared membranes were carried out by X-ray diffraction analysis and measuring glass transition temperatures. Scanning electron microscopy (SEM) was used to study the effect of surfactant type and surfactant concentration on the morphology of membranes. Also, to understand the intermolecular interactions, the membranes were characterized by Fourier Transform Infrared (FTIR) spectroscopy. Separation performances of the membranes were evaluated using pure CH4, CO2, N2 and binary CO2/CH4 mixed gas permeance measurement. The results indicate that addition of surfactants in the casting solution increases the membrane porosity and membrane gas permeance and decreases CO2/CH4 ideal selectivity, except for Triton X-100 which increases CO2/CH4 selectivity. The effects of feed pressure, feed temperature and feed composition on the membrane performance were investigated through mixed gas experiments.