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Length of the Unused Bed (LUB) methods for scaling sorbers have confusing and complicated pedagogically elements. One method limits feeds to C/C[subscript F] < 0.3; a limitation not stated in the established textbooks. Discussed is a new LUB method with no limitation on the feed C/C[subscript F]. It fixes the pedagogically confusing and complicated elements while giving equivalent results. Also discussed: teaching module content, student outcomes, common student misconceptions, reduction-to-practice caveats, examples of class and homework problems.

Abstract: 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 2bars 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 106days, without performance degradation. Furthermore, the RTIL-membranes operated under CO2-partial pressures of at least 207kPa without decrease in separation ability. The RTIL-membranes tested include [emim][BF4], [emim][dca], [emim][CF3SO3], [emim][Tf2N], and [bmim][BETI]. [Copyright &y& Elsevier]

Previously, we reported on using Room temperature ionic liquids (RTILs) in place of traditional solvents for supported liquid membranes to take advantage of their unique properties. This previous work used RTILs with the hexafluorophosphate [PF6]- anion. However, the [PF6]- anion in the presence of water can break down into HF. In the current work, we studied RTIL-membranes made from the following water stable anions: bis(trifluoromethanesulfonyl)amide [Tf2N]-, trifluoromethanesulfone [CF3SO3]-, chloride [Cl]-, and dicyanamide [dca]-. We report CO2 permeabilities of 350 barrers (for [Cl]-) to 1000 barrers (for [Tf2N]-) combined with CO2/N2 ideal selectivities of 15 (for [Cl]-) to 61 (for [dca]-). Note that these permeability/selectivities place RTIL-membranes above the upper-bound in a CO2/N2 Robeson plot of representative polymers. The CO2/CH4 ideal selectivities range from 4 (for [Cl]-) to 20 (for [dca]-), thereby placing the [dca]-membrane above the upper-bound for the CO2/CH4 Robeson plot. [Copyright &y& Elsevier]