CO₂ separation from flue gas using polyvinyl-(room temperature ionic liquid)-room temperature ionic liquid composite membranes

In this work, a vinyl-functionalized room temperature ionic liquid (RTIL), 1-vinyl-3-butylimidazolium bis(trifluoromethylsulfonyl)imide ([vbim][Tf ₂N]), has been successfully synthesized. The RTIL was further polymerized and mixed with 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf₂N]) to form the free-standing poly([vbim][Tf₂N])-[bmim][Tf₂N] composite films. The compositions of [bmim][Tf₂N] in the composite membranes were designed at 15, 30, 45, and 60 wt %. The pristine poly([vbim][Tf ₂N]) and poly([vbim][Tf₂N])-[bmim][Tf₂N] composite membranes exhibit similar permeability selectivities as the standard [bmim][Tf₂N] but permeabilities are enhanced up to 5 times higher than the equivalent polystyrene-RTIL and polyacrylate-RTIL membranes. An increase in [bmim][Tf₂N] concentration of poly([vbim][Tf ₂N])-[bmim][Tf₂N] composite membranes results in an increase in solubility, diffusivity, and permeability coefficients of CO ₂ and N₂ but does not change the CO₂/N ₂ selectivities of the solubility, diffusivity, and permeability. The CO₂ permeability of the 60 wt % composite at 35 °C, 10 atm is 559 barrers in pure gas tests which is closer to 60% of the [bmim][Tf ₂N] permeability (i.e., 1344 barrers). In addition, the 60 wt % composite membrane exhibits a CO₂ permeability of 491.2 barrers and a CO₂/N₂ selectivity of 20 in mixed gas tests using CO ₂/N₂ (50:50) as the feed.