Effect of Solvent on CO2 Sorption Capacity in Supported Ionic Liquid Membranes

Anthropogenic emissions have turned into one of the greatest issues of our time, warming up our planet. With rapidly increasing demand for energy, the dependence on fossil fuels has exacerbated greenhouse gas emission levels and contributed to global warming. To that end, carbon capture and storage technologies are currently utilized to reduce carbon emissions. The monoethanolamine (MEA) system, for example, works to absorb CO₂ from flue gases; however, this system has a high operational cost and energy demand. Consequently, membrane technologies have gained significant attention as a potential solution for CO₂ separation. Polymeric membranes containing ionic liquids (ILs) have emerged as promising candidates for efficient gas separation. This is primarily attributed to the unique properties of ILs, including their favorable CO₂ absorption characteristics and tunable chemistries. However, the high viscosity of ILs due to CO₂ absorption presents challenges in their practical use, especially in absorption columns. To overcome this limitation, the concept of supported ionic liquid membranes (SILMs) has gained attention.

In this study, we employed 1-ethyl-3-methylimidazolium bis (trifluoromethyl sulfonyl) imide ([Emim][TF2N]) as the ionic liquid and poly (vinylidene fluoride) (PVDF) as the host polymer to fabricate the SILMs. We conducted CO₂ sorption measurements using a quartz crystal microbalance (QCM) gas sorption system. To cast and fabricate SILMs, different solvents were investigated. Dimethylacetamide (DMAc) was shown to be the best solvent choice over dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or triethyl phosphate (TEP). This was attributed to the variation in PVDF crystallinity and the formation of distinct phases when cast from different solvents. Our polarized microcopy data revealed a direct correlation between macroscale structural variations and gas sorption capacities in SILMs.