Amino-functionalized ionic liquids as carbon dioxide scavengers. Ab initio thermodynamics for chemisorption

Abstract

Carbon dioxide (CO2) capture by aqueous amine solutions is an industry grade technology nowadays. Some drawbacks of this technology motivate development of new CO2 scavengers. Due to low volatility, thermal stability, non-flammability, and tunability, room-temperature ionic liquids (RTILs) are viewed as prospective universal solvents. The amino groups can be grafted to the organic cations yielding species with the increased CO2 capture performance. Many favorable physical properties of the original RTILs can be retained in this way. We report systematic computational analysis (enthalpy, entropy, Gibbs free energy, geometric parameters, partial charges, vibrational frequencies) of six organic cations, each representing a different family of RTILs. We found that the longer side hydrocarbon chain of the cations offer the most prospective sites in view of the CO2 capture. In turn, chemisorption in the rings is less thermodynamically favorable. It was possible to corroborate the thermodynamic regularities in terms of electrophile+nucleophile organic reactions involving partial charges and structure perturbations due to carbamate formation. The reported results foster development of alternative CO2 scavengers by eliminating their volatility and increasing reaction yields.