Effect of the CO2-philic ionic liquid [BMIM][Tf2N] on the single and mixed gas transport in PolyActive(TM) membranes

This study reports on the gas transport properties of four different grades of PolyActive(TM) polyether-co-polyester multi-block copolymer membranes containing different concentrations (4.8, 9.1, 16.7, 23.1 and 28.6 wt%) of the low-viscous CO-philic ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TfN]). Single gas permeability, solubility and diffusion coefficients of He, H, N, O, CH and CO were determined at 1 bar and 25 °C in a constant-volume time lag setup. Mixed gas permeability measurements of CO/CH and CO/N mixtures containing 35 and 15 vol% CO, respectively, were carried out at 25 °C in the pressure range from 1 to 6 bar(a). The transport properties were correlated with the ionic liquid content of the samples, the specific PolyActive(TM) grade (i.e. chain length, copolymer composition), and previously determined microstructure, crystallinity, thermal and mechanical properties. For all PolyActive(TM) grades, the single gas permeability decreased in the order CO >> H > He > O ? CH > N and it typically increased with increasing IL content, whereas the ideal selectivity decreased with IL content for most gas pairs. None of the membranes revealed significant dependence on the feed pressure in both single and mixed gas permeation tests. Such behavior is typical for predominantly rubber-like materials. Samples based on PolyActive(TM) 4000PEOT77PBT23 had the strongest dependence on the IL concentration due to its higher weight fraction and higher crystallinity of the polyether phase. The specific behavior of the four polymers was illustrated via their different trends with increasing IL concentration in the Robeson diagrams. The study demonstrates how blending with ionic liquid can be used to tailor the permeability and selectivity of the membranes. It provides insight into the influence of ionic liquid and the weight percentages of the PEO blocks and the PBT blocks in the copolymers on the individual contributions of the solubility and diffusion coefficients on the permeability.