Poly(ethylene oxide)/Ag ions and nanoparticles/1-hexyl-3-methylimidazolium tetrafluoroborate composite membranes with long-term stability for olefin/paraffin separation

A poly(ethylene oxide)(PEO)/AgBF(4)/1-hexyl-3-methylimidazolium tetrafluoroborate (HMIM(+)BF(4)(−)) composite membrane that exhibits long-term stability was prepared for olefin/paraffin separation. The membrane was prepared by simply adding AgBF(4) and HMIM(+)BF(4)(−) to a solution of PEO. Long-term stability testing showed that the separation performance of the membrane is maintained for ≈100 h owing to the Ag NPs formed in the membrane, which are olefin carriers, being stabilized by HMIM(+)BF(4)(−). In terms of separation performance, the PEO/AgBF(4)/HMIM(+)BF(4)(−) composite membrane exhibited a propylene/propane selectivity of 11.8 and a mixed-gas permeance of 11.3 GPU. We also investigated the factors that determine separation performance by comparison with a PEO/AgBF(4)/1-butyl-3-methylimidazolium tetrafluoroborate (BMIM(+)BF(4)(−)) composite membrane. The PEO/AgBF(4)/HMIM(+)BF(4)(−) composite membrane was characterized by scanning electron microscopy, FT-IR spectroscopy, ultraviolet-visible spectroscopy, thermogravimetric analysis, and Raman spectroscopy.