Selective separation of H2S and CO2 from CH4 by supported ionic liquid membranes

Supported ionic liquid membranes (SILMs) are considered as promising media for the upgrading of natural gas. However, most research has focused on the selective separation of CO2 and CH4, paying little attention to the selective separation of H2S and CH4 or H2S and CO2 in SILMs. In this work, the permeability of CH4, CO2, and H2S in two different categories of ionic liquids (neutral and basic ionic liquids) were systemically investigated under dry conditions. The ideal selectivity of CO2/CH4, H2S/CH4, and H2S/CO2 were calculated. The effect of anion species, transmembrane pressure difference, and temperature on the permeability of single gas and ideal selectivity of gas pairs were studied. It is found that neutral ionic liquids (1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium trifluoromethanesulfonate) show high permeability of CO2 and H2S, and competitive permselectivity of CO2/CH4 and H2S/CH4, and thus can be used for the simultaneous removal of H2S and CO2 from natural gas. Basic ionic liquids (1-butyl-3-methylimidazolium acetate) show not only high permeability of CO2 and H2S, but also superior permselectivity of CO2/CH4, H2S/CH4 and H2S/CO2, and thus can be potentially used for selective removal of H2S from natural gas. Moreover, facilitated transport of H2S and CO2 were observed in 1-butyl-3-methylimidazolium acetate. To the best of our knowledge, this is the first time that the facilitated transport of H2S in SILMs is reported.