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][Tf2N]), 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][Tf2N]) 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][Tf2N])–[bmim][Tf2N] composite membranes results in an increase in solubility, diffusivity, and permeability coefficients of CO2 and N2 but does not change the CO2/N2 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][Tf2N] 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 CO2/N2 (50:50) as the feed.