CO₂ and H₂ selectivity properties of PDMS/PSf membrane prepared at different conditions

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.

Key words： gas separation; PDMS/PSf membrane; synthesis parameters; CO₂ selectivity

Acknowledgments

The authors are grateful for the support provided by the Ferdowsi University of Mashhad (Grant No. 35462) and we are also indebted to the National Iranian Oil Refining and Distribution Company for its financial support.

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