(211e) Long Term Stability of Thin Film Cross-Linked Ionic Liquid Membranes for CO2 Separation

CO₂/light gas (CH₄ and N₂) separation performance, physical aging and plasticization of thick film (> 100 microns) cross-linked poly(ionic liquid)-ionic liquid (PIL-IL) composite membranes were previously evaluated at elevated temperatures (up to 50 C) and feed pressures (up to 40 atm). PIL-IL composite membranes made with IL-based multifunctional cross-linkers exhibited higher CO₂ permeability and CO₂/light gas selectivity compared to the membranes made with a conventional, nonionic cross-linker, divinylbenzene (DVB). For example, a crosslinked PIL-IL composite membrane prepared using 70 wt % 1-vinyl-3-methylimidazolium bistriflimide as the IL monomer, 30 wt % 1-ethyl-3-methylimidazolium bistriflimide as the free IL, and 8 wt % 1,3,5-tris(1’-methylene-3’- vinylimidazolium bistriflimide)benzene as the IL cross-linker exhibited 90% retention of its initial CO₂ permeability after testing at 50 °C and 40 atm pressure for 42 weeks (7100 h). In comparison, an analogous PIL-IL composite membrane cross-linked with DVB shattered after testing for 5 h at the same testing conditions. These cross-linked PIL-IL composite membranes can also be formed into thin film composite (TFC) membranes.
A thin film (~5 micron) composite membrane was prepared to make a direct comparison of aging effects with conventional polymer membranes. The membrane was tested periodically for CO₂ permeation and CO₂/N₂ selectivity at 5 bar feed pressure and 20 C. The membrane retained it’s initial permeance over 6 months demonstrating that ionic liquid membranes can greatly reduce or eliminate aging effects in polymer membranes used for gas separations.