Conventional thermal swing processes that use zeolites are energy intensive. On the other hand, liquid sorbents based on aqueous amines are also energy intensive to regenerate and non-ideal for space application as they are volatile and hard to handle. In this study, we demonstrate the design of functionalized ILs and deep eutectic solvents (DESs), composed of imidazolium cation, pyrrolide anion, and ethylene glycol, for energy-efficient and benign CO2 separations. Compacting of the liquid sorbent was observed upon mixing the ILs with hydrogen bond donors (HBDs) into DES. CO2 capacity of DES was measured to exceed that of the IL and the viscosity was lower. A detailed mechanistic study was performed by FTIR, quantitative 13C-NMR, and ab initio calculations that show significant CO2 absorption capacity below 5000 ppm of CO2 in N2. Three reversible complexing routes (carbonate, carbamate, and carboxylate) were confirmed to take place via HBD, anion, and cation components through extended hydrogen bonds and coulombic interaction among all species. This study provides a potential green solvent for selective CO2 separation in low concentration environments.

Functionalized deep eutectic solvents for CO2 separations

ACS Fall 2021

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