Selective CO2 Separation from CO2−N2 Mixtures by Immobilized Glycine-Na−Glycerol Membranes

This paper reports the results of our continuing efforts to develop glycerol-based immobilized liquid membranes (ILMs) for the selective separation of CO2 from a mixed-gas (CO2, N2) feed having low CO2 concentrations in space-walk and space-cabin atmospheres. The items of specific interest are replacement of the carrier sodium carbonate (studied by Chen et al. (Ind. Eng. Chem. Res. 1999, 38, 3489−3498) by glycine-Na in glycerol, ILM thickness reduction, performance of environmentally benign carriers, e.g., glycine-Na vis-a-vis toxic and volatile carriers, e.g., ethylenediamine. The effects of glycine-Na concentration (range 0−5.0 mol/dm3), CO2 partial pressure (between 0.006 and 0.8 atm), and feed relative humidity (RH; range 40−100%) have been investigated. The sweep gas was always dry helium. As the glycine-Na concentration was increased, N2 permeability decreased, while the CO2 permeability increased drastically at lower glycinate concentrations, leveling off at higher glycinate concentrations. Lower f...