Polymeric ionic liquid-based membranes: Influence of polycation variation on gas transport and CO2 selectivity properties

This work evaluates the CO2, CH4 and N-2 permeation properties of five novel composite membranes based on polymeric ionic liquids (Pits) having different cation pendant units, namely imidazolium, pyridinium, pyrrolidinium, ammonium and cholinium, combined with the same counter anion ([NTf2](-)). The results show that the CO2 permeability in the composite membranes is related to their respective CO2 diffusivities, which are dependent on the PIL polycaLion nature. The composite membranes of the PILs containing different polycations and 10 wL% of free ionic liquid (IL) with similar structures to each PIL monomeric unit have CO2 permeabililies between 3.66 and 20.4 Barrer, while they exhibit permselectivities ranging from 28.3 to 43.0 for CO2/CH4 and from 25.8 to 34.7 for CO2/N-2. The best CO2 permselectivities were obtained when tetra alkyl ammonium based [Us (pyrrolidinium, ammonium and cholinium) are used rather than imidazolium or pyridinium. Also, the results of this work indicate that the polycation backbones of PILs can also play a significant role in the design of PIL-IL membranes with the finest gas permeation properties and improved CO2 separation performances. (C) 2015 Elsevier B.V. All rights reserved.