Poly(1,3-dioxolane)-Based Terpolymer Membranes with 1-Hexyl-3-Methylimidazolium Bis(trifluoromethylsulfonyl)Imide for Carbon Capture and Light Paraffin Separation

Rapid increases in anthropogenic carbon dioxide (CO₂) emissions have motivated research on carbon capture and sequestration (CCS), with CCS of post-combustion flue gas from fossil-fuel fired power plants being one of the most practical approaches. Compared to the already industrialized, yet energy-intensive, amine scrubbing technology, CO₂-selective membranes are expected to better reduce the cost of CCS operations in accordance with DOE targets. Here, we initially developed a dioxolane-based random terpolymer (PDXL) membrane that exhibited a CO₂/N₂ selectivity of 52 and a CO₂ permeability of 330 Barrer. However, for membrane-based CCS to be economically viable, the developed membranes must have as high of a CO₂ permeability as possible since membrane cost scales with membrane area. Therefore, an ionic liquid (IL) was also incorporated into the membrane which resulted in permeabilities of 530 Barrer with only slight losses in selectivity. Additionally, light paraffins, which have become more accessible in the U.S. due to an upsurge in fracking, currently require energy-intensive cryogenic distillation for separation and purification and could benefit from energy efficient advancements. The PDXL membranes also exhibited reverse-selectivity for C₃H₈/CH₄ and C₂H₆/CH₄ and were able to withstand industrial operating pressures (i.e., 7–30 bar), presenting a promising addition/alternative for bulk light paraffin separations. Overall, increasing the IL wt% in the membrane blends decreased the glass transition temperature, allowing for higher permeabilities of all gases and improvements in the light paraffin selectivity, but also resulting in depression of CO₂ selectivity and produced weaker and more stretchy membranes.