Immobilized glycerol-based liquid membranes in hollow fibers for selective CO₂ separation from CO₂-N₂ mixtures

Glycerol-based liquid membranes immobilized in the pores of hydrophilic microporous hollow fibers have been studied for selective separation of CO₂ from a mixed gas (CO₂, N₂) feed having low concentrations of CO₂ characteristic of gases encountered in space walk and space cabin atmosphere. The immobilized liquid membranes (ILMs) investigated consist of sodium carbonate-glycerol or glycine-Na-glycerol solution. Based on the performances of such liquid membranes in flat hydrophilic porous substrates [Chen et al., Ind. Eng. Chem. Res. 38 (1999) 3489; Chen et al., Ind. Eng. Chem. Res. 39 (2000) 2447], hollow fiber-based ILMs were studied at selected CO₂ partial pressure differentials (Δp_CO2 range 0.36-0.50cmHg), relative humidities (RH range 45-100%), as well as carrier concentrations. The sodium carbonate concentration was primarily 1.0mol/dm³; the glycine-Na concentration was 3.0mol/dm³. The sweep gas was always dry helium and it flowed on the shell side. Very high CO₂/N₂ selectivities were observed with porous polysulfone microfiltration membranes as substrate. As in the case of flat film-based ILMs (see references above), feed side RH is an important factor determining the ILM performances. Generally, lower permeances and greater CO₂/N₂ selectivity values were observed at lower feed stream RHs. When the feed side average RH=60%, p CO₂=0.005atm and glycine-Na concentration was 3.0M, the CO₂/N₂ separation factor observed was over 5000. Prolonged runs lasting for 300h showed that the hollow fiber-based ILM permeation performances were stable.