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

Abstract

A poly(ethylene oxide)(PEO)/AgBF₄/1-hexyl-3-methylimidazolium tetrafluoroborate (HMIM⁺BF₄ ^-) composite membrane that exhibits long-term stability was prepared for olefin/paraffin separation. The membrane was prepared by simply adding AgBF₄ and HMIM⁺BF₄ ^- 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⁺BF₄ ^-. In terms of separation performance, the PEO/AgBF₄/HMIM⁺BF₄ ^- 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/AgBF₄/1-butyl-3-methylimidazolium tetrafluoroborate (BMIM⁺BF₄ ^-) composite membrane. The PEO/AgBF₄/HMIM⁺BF₄ ^- composite membrane was characterized by scanning electron microscopy, FT-IR spectroscopy, ultraviolet-visible spectroscopy, thermogravimetric analysis, and Raman spectroscopy.

Fig. 1. Cross-sectional SEM image of PEO/AgBF₄/HMIM⁺BF₄⁻ composite membrane.

Fig. 2. UV-Vis absorption spectra of PEO/AgBF₄/HMIM⁺BF₄⁻ solution with heating time.

Fig. 3. FT-IR spectra of PEO/AgBF₄/HMIM⁺BF₄⁻ complex.

Fig. 4. Separation performance of PEO/AgBF₄/HMIM⁺BF₄⁻ composite membrane. (a) Selectivity for propylene/propane mixture, and (b) mixed gas permeance.

Scheme 1. Ag NPs formation in PEO/AgBF₄/HMIM⁺BF₄⁻ composite membrane upon heating.

Fig. 5. TGA curves for neat PEO (red), PEO/AgBF₄ (blue), and PEO/AgBF₄/HMIM⁺BF₄⁻ (green) complex.

Fig. 6. Raman spectrum of neat HMIM⁺BF₄⁻.