CO2/H2 separation through poly(ionic liquid)-ionic liquid membranes: the effect of multicomponent gas mixtures, temperature and gas feed pressure

Abstract

This work presents mixed gas separation performance through PIL–IL membranes bearing pyrrolidinium-based PILs with [NTf2]– and [C(CN)3]– anions and different weight percentages of the corresponding ILs using a ternary mixture of H2, CO2 and N2 and different feed pressures ranging from 1 to 4 bar and temperatures from 20 to 80 °C. COSMO-RS was successfully used to understand the separation behavior of the PIL–IL composites for the H2 + CO2 + N2 mixture. The effect of temperature between 20 °C and 80 °C and feed pressure between 1 bar and 4 bar was also studied and is here discussed. The increased of the mixed H2, CO2 and N2 permeabilities with increasing temperature was shown to be due to dominant role of gas solubility at low temperature, and diffusivity at high temperature. The small pronounced differences between mixed and ideal CO2/H2 permselectivities through the prepared PIL–IL composites indicated that membrane separation efficiency can be maintained, despite the competition effect between gases in mixed gas experiments. Depending on the operating conditions, the best mixed separation performance was obtained for PIL C(CN)3–60 [C2mim][C(CN)3], with a CO2 permeability of 324.7 Barrer and a CO2/H2 permselectivity of 11.4. The great potential of the studied PIL–IL membranes for biohydrogen separation is here clearly evidenced, since they revealed mixed CO2/H2 separation performances above the Robeson upper bound even at the highest temperature and feed pressure tested.