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

Michael McShea and Paul Scovazzo. Chemical Engineering, The University of Mississippi, 134 Anderson Hall, University, MS 38677

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%.