Encapsulated Protic Ionic Liquids as Sustainable Materials for CO₂Separation

Protic ionic liquids (PILs) have been suggested as promising solvents for CO₂capture; however, their high viscosity and consequent poor mass transfer coefficients hinder their large-scale industrial application. To overcome this limitation, PILs (neat or encapsulated) can be incorporated into polymers coated on hollow fiber membranes, to be implemented in gas-liquid contactor units. However, before the immobilization of PIL-based solvents on membranes, fundamental studies on the CO₂sorption process in PILs are still mandatory. Here, the carboxylate-based PILs' ability for CO₂absorption was evaluated using an isochoric solubility cell in a wide range of temperatures (303-343 K) and CO₂partial pressures (0-0.8 MPa). The experimental data revealed the existence of a distinct sorption mechanism than that typically observed in other low-volatile physical solvents, where the solubility was mainly affected by entropic effects. The soft-SAFT equation of state was further applied for modeling of the solubility data, which allowed us to infer the influence of the anion's structure on the system's interactions. Aiming to improve the process kinetics, the PILs were encapsulated in carbonaceous submicrocapsules, herein proposed as an efficient material for CO₂separation. To characterize the composition, morphology, porous structure, and thermal stability of the solvents used, SEM, TEM, TGA, BET, and elemental analyses were performed. The adsorption of CO₂on these materials showed that these materials retained the same sorption capacity as their neat counterparts and with considerably increased sorption rates. These materials also retained their performance after various sorption-desorption cycles and showed fast and complete regeneration and high sorption capacity, thus indicating their potential for CO₂capture.