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

Abstract

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-à-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 feed stream RHs yielded lower species permeances but greater CO2/N2 selectivities. For a feed RH of 70%, pCO2,f = 0.006 atm, and a glycine-Na concentration of 2.5 mol/dm3, the CO2/N2 separation factor was found to be a very high 5000 in an ILM spanning the whole thickness of a hydrophilized poly(vinylidene fluoride) flat film. ILMs containing both carbonate and glycinate demonstrated high CO2 permeances and high CO2/N2 selectivity. The ILM stability was also tested by a 25-day-long run. Permeances of N2 through glycerol-based membranes and of CO2 through pure glycerol membrane have been estimated and compared with experimentally obtained values.