Immobilized glycerol-based liquid membranes in hollow fibers for selectiveCO2 separation from CO2-N-2 mixtures

Glycerol-based liquid membranes immobilized in the pores of hydrophilic mic roporous hollow fibers have been studied for selective separation of CO2 fr om a mixed gas (CO2, N-2) feed having low concentrations of CO2 characteris tic of gases encountered in space walk and space cabin atmosphere. The immo bilized liquid membranes (ILMs) investigated consist of sodium carbonate-gl ycerol or glycine-Na-glycerol solution. Based on the performances of such l iquid membranes in flat hydrophilic porous substrates [Chen et al., Ind. En g. Chem. Res. 38 (1999) 3489; Chen et al., Ind. Eng. Chem. Res. 39 (2000) 2 447], hollow fiber-based ILMs were studied at selected CO2 partial pressure differentials (Deltap(CO2), range 0.36-0.50 cmHg), relative humidities (RH range 45-100%), as well as carrier concentrations. The sodium carbonate co ncentration was primarily 1.0 mol/dm(3): the glycine-Na concentration was 3 .0 mol/dm(3). The sweep gas was always dry helium and it flowed on the shel l side. Very high CO2/N-2 selectivities were observed with porous polysulfo ne microfiltration membranes as substrate. As in the case of flat film-base d ILMs (see references above), feed side RH is an important factor determin ing the ILM performances. Generally, lower permeances and greater CO2/N-2 s electivity values were observed at lower feed stream RHs. When the feed sid e average RH = 60%, p(CO2.f) = 0.005 arm and glycine-Na concentration was 3 .0 M, the CO2/N-2 Separation factor observed was over 5000. Prolonged runs lasting for 300 h showed that the hollow fiber-based ILM permeation perform ances were stable. (C) 2001 Elsevier Science B.V. All rights reserved.