(149c) Poly(ionic liquid) Membranes for CO2/N2 Separation: Insight From Atomistic Simulation

Polymeric ionic liquids (poly(IL)s) are a new class of membrane materials for gas separation. In this study, we conduct atomistic simulation to investigate the membrane structures of poly(IL)s and their capability for CO₂/N₂ separation. The poly(IL)s examined are poly[VBIM][TF₂N] and poly[VBIM][SCN]; for comparison, ionic liquids ([BMIM][TF₂N] and [BMIM][SCN]) are also considered. The densities, solubility parameters, ion mobilities and heats of vaporization for the poly(IL)s and ILs are predicted and compared with available experimental data. The fractional free volume increases in the order of poly[VBIM][TF₂N] < poly[VBIM][SCN] < [BMIM][TF₂N] < [BMIM][SCN]. The poly(IL)s and ILs with [TF₂N]^- have a high percentage of large voids ( > 3 Å). The predicted solubility and diffusion coefficients CO₂ and N₂ are consistent with experimental data. The analysis of radial distribution functions reveals that gas molecules in poly(IL)s have strong interactions with the end groups of poly-cation chains, but with both cations and anions in ILs. This study provides an atomistic insight into experimental observation, in which the anions of a poly(IL)s do not play an important role in CO₂ sorption while the anions of ILs do.