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 (ΔpCO2 range 0.36–0.50 cmHg), relative humidities (RH range 45–100%), as well as carrier concentrations. The sodium carbonate concentration was primarily 1.0 mol/dm3; the glycine-Na concentration was 3.0 mol/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%, pCO2,f=0.005 atm and glycine-Na concentration was 3.0 M, the CO2/N2 separation factor observed was over 5000. Prolonged runs lasting for 300 h showed that the hollow fiber-based ILM permeation performances were stable.