(253d) Mixed Gas Selectivities and Permeabilities for Carbon Dioxide/Methane Separation Using Facilitated Transport in Room Temperature Ionic Liquid Membranes

Room Temperature Ionic Liquids (RTILs) are salts that are liquids at room temperatures. RTILs possess a number of unique properties that are useful for membrane separations including high thermal stability, negligible vapor pressure, and non-flammability. Previously, we showed that some RTIL-membranes outperformed standard polymers for carbon dioxide/methane separation, under both ideal and mixed gas permeabilities. Furthermore, we have proven the longevity of these liquid membranes with no degradation in performance during long term (>2 months) tests. Unfortunately, the thermodynamics of these membrane materials limit their CO2/CH4 selectivities to <30, without the addition of facilitated transport. This upper limit on selectivities combined with the inherit difficulty of casting a thin liquid active layer in a membrane seriously limits the potential for RTIL-membranes to compete against polymers in a permeance/selectivity pairing, unless the RTIL-selectivity could be increased via facilitated transport. In this paper, we will review the record of past, ?not entirely successful,? attempts to add facilitated transport carriers to the RTIL-membranes. One factor in this review is the low solubility of carriers in the widely used imidazolium-RTILs. We will conclude the paper with a discussion of facilitated transport in RTILs ?designed? to increase the carrier solubility. These utilized RTILs include both modified imidazolium-based RTILs and quad-ammonium-based RTILs, which show promise in solubilizing facilitated transport carriers. We will report on mixed gas permeabilities and selectivities of these facilitated transport-RTIL membranes, using a continuous flow of the mixed gas pairs at CO2 concentrations of various concentrations between 0% and 100%.