Abstract The effects of different solvent/water coagulation mediums, different coagulation bath temperatures (CBT) and different coagulants on the performance, morphology and thermal stability of polysulfone membranes were investigated. The CO2/CH4, H2/CH4 and H2/ N2 separation performance of the membranes were studied by gas permeation. Changing the N,N-dimethyl acetamide (DMAc)/water coagulation medium ratio from pure water to 90/10 vol%, resulted in a complete disappearance of the macrovoids throughout the polysulfone (PSf) polymeric matrix. The PSf membrane prepared in a CBT of 25°C showed the best gas separation performance with ideal selectivities of 46.29, 39.81 and 51.02 for H2/CH4, CO2/ CH4 and H2/N2 respectively, and permeances of 25 and 21.5 GPU for H2 and CO2 at 25°C and 10 bar respectively. By increasing the amount of solvent in the gelation bath, the selectivities of H2/CH4, CO2 /CH4 and H2/N2 were dramatically reduced from 46.29, 39.81 and 51.02 to 16.08, 20.2 and 18.5 respectively at 25°C and 10 bar. Reducing the CBT from 80°C to 5°C led to a complete elimination of macrovoids. Using methanol as a coagulant resulted in a less selective membrane compared with membranes from ethanol and water coagulants. The H2 and CO2 permeances were respectively about 3 and 9 times more than those for ethanol and water coagulants. Coated membranes were heated at different temperatures to investigate the suppression of undesirable CO2 plasticization. The membranes were stabilized against CO2 plasticization by a heat-treatment process. Keywords gas separation, PDMS/PSf membrane, synthesis

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