Long-term, continuous mixed-gas dry fed CO2/CH4 and CO2/N2 separation performance and selectivities for room temperature ionic liquid membranes

Previously, we reported on using room temperature ionic liquids (RTILs) in place of traditional solvents in liquid membranes and showed that stabilized RTIL-membranes outperformed standard polymers for the separations of CO2/CH4 and CO2/N2 (considering ideal gas permeabilities). Here, we report on mixed-gas permeances and selectivities for the gas pairs CO2/CH4 and CO2/N2 using continuous flows of the mixed gases at various carbon dioxide concentrations (up to 2 bars of CO2 partial pressure). Under mixed-gas test conditions, three of the tested membranes still operated with commercially attractive mixed-gas selectivity combined with CO2-permeability for CO2/CH4 separations. In addition, one of the tested membranes is, potentially, economically viable for CO2 capture from flue gas. We answer three objections to reduction-to-practice of RTIL-membranes for gas separations; namely, mixed-gas operations did not reduced the gas selectivities, membranes give advantageous performance even under dry gas feed conditions, and we achieved long-term stability in continuous operation, up to 106 days, without performance degradation. Furthermore, the RTIL-membranes operated under CO2-partial pressures of at least 207 kPa without decrease in separation ability. The RTIL-membranes tested include [emim][BF4], [emim][dca], [emim][CF3SO3], [emim][Tf2N], and [bmim][BETI].