(507h) Gas Diffusion in Hybrid Membranes Composed of Ionenes and Ionic Liquids By PFG NMR and Permeation Measurements

Hybrid membranes composed of ionenes and ionic liquids (ILs) represent a promising class of materials for gas separation processes, offering enhanced transport and selective gas permeation. This study investigates a novel class of Doubly Segmented (DS) Ionenes, engineered from independently synthesized neutral and ionic oligomers, tethered to form block copolymer-like structures capable of incorporating free ILs. These DS ionenes leverage the enhanced interconnectivity of ionic domains and a tunable free volume architecture, along with enhanced interactions with polarizable gases such as CO₂, resulting in membranes with significantly improved permeability and selectivity. This is particularly relevant for the critical separation of CO₂ from CH₄ in processes like natural gas purification. In this study, we investigated the microscopic self-diffusion of single-component gases (CO₂ and CH₄) and their binary mixtures (CO₂/CH₄) in DS ionenes embedded with ILs at varying IL concentrations up to one equivalent IL per cation in ionene. Using the pulsed field gradient (PFG) NMR technique, self-diffusion coefficients were quantified for both gases for a broad range of diffusion times between 20 to 500 ms, and the corresponding values of root mean square displacements between 0.3 μm to 14 μm. PFG NMR data demonstrates a significant enhancement in CO₂ self-diffusivity and diffusion selectivity (CO₂/CH₄) as IL concentration increases. Notably, DS ionenes with one equivalent IL exhibit high diffusion selectivities > 10 toward CO₂ over CH₄ for both single-component and mixed-gas measurements. For a subset of the membranes with the highest IL loading, gas permeation measurements were also performed under the same or similar conditions as those used in PFG NMR studies. The PFG NMR data will be compared with the corresponding macroscopic gas permeation data and discussed in detail.