Study on gas separation by facilitated transport liquid membranes

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Liquid membranes through which gases are transported by the facilitated diffusion mechanism have higher selectivity compared with polymer membranes. In the present study, the transport mechanism of ethylene through supported liquid membrane (SLM) containing <AgNO_3> as a carrier was elucidated. Furthermore, a flowing liquid membrane (FLM), which has higher permeability and stability compared with SLM, was proposed, and its performance was evaluated.In the separation of ethylene from ethane by SLM, the separation factor <(C_2H_4/C_2H_6)_3> increased with increasing carrier concentration, reaching about 1000 when [ <AgNO_3> ] was 4 mol/dm. An approximate method for caclulating the rate of facilitated transport accompanied by instantaneous reversible reaction was proposed. This method is applicable even to the case where the diffusivities of the carrier and the complex differ from each other. The experimentally observed flux of ethylene agreed well with the flux calculated by the approximation method.A flowing liquid membrane cell with three channels for feed gas, carrier solution( <AgNO_3> solution) and strip gas was developed. The channels were separated by hydrophobic microporous membrames. The permeability of gas at high flow rate of carrier solution was about 5 times that of SLM. In the separation of ethylene from ethane, membrane fouling due to the evaporation of the solvent was not observed. When polypropylene membrane was used, however, precipitates, presumably <Ag_2O> , covered the membrane, resulting in low permeability. This fouling was avoided by adding nitric acid to the carrier solution. When Teflon membrane was used, FLM was stable for more than 11 days even without nitric acid. By evacuating strip side of SLM, 98% ethylene was produced. The experimental result was satisfactorily simulated by a permeation model and design equations.