Selective CO2 separation from CO2-N-2 mixtures by immobilized glycine-Na-glycerol membranes

This paper reports the results of our continuing efforts to develop glycero l-based immobilized liquid membranes (ILMs) for the selective separation of CO2 from a mixed-gas (CO2, N-2) feed having low CO2 concentrations in spac e-walk and space-cabin atmospheres. The items of specific interest are repl acement 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 re duction, performance of environmentally benign carriers, e.g., glycine-Na v is-a-vis toxic and volatile carriers, e.g., ethylenediamine. The effects of glycine-Na, concentration (range 0-5.0 mol/dm(3)), CO2 partial pressure (b etween 0.006 and 0.8 atm), and feed relative humidity (RH; range 40-100%) h ave been investigated. The sweep gas was always dry helium. As the glycine- Na. concentration was increased, N-2 permeability decreased, while the CO2 permeability increased drastically at lower glycinate concentrations, level ing off at higher glycinate concentrations. Lower feed stream RHs yielded l ower species permeances but greater CO2/N-2 selectivities. For a feed RH of 70%, P-CO2,P-f = 0.006 atm, and a glycine-Na concentration of 2.5 mol/dm(3 ), the CO2/N-2 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 C O2 permeances and high CO2/N-2 selectivity. The ILM stability was also test ed by a 25-day-long run. Permeances of N-2 through glycerol-based membranes and of CO2 through pure glycerol membrane have been estimated and compared with experimentally obtained values.