Experimental and theoretical investigation of CO2 solubility in amine-based deep eutectic solvents

Deep eutectic solvents (DESs) have appealed increasing research interest across various scientific and industrial applications, notably in relation to efforts in CO₂ capture. This study presents a novel series of DESs were synthesized on the basis of monoethanolamine (MEA) and N-methyldiethanolamine (MDEA) as hydrogen bond donors with tetrabutylammonium bromide (TBAB) and tetrabutylphosphine bromide (TBPB) salt as hydrogen bond acceptors. A gas solubility measurement experimental system based on pressure drop method has been established to evaluate the solubility of CO₂ in amine-based deep eutectic solvents. The evaluation was performed over a temperature range of 303.15 to 323.15 K and a pressure range of 100 to 1000 kPa. The results indicated that as the molar ratio of hydrogen bond donors increases, the solubility of CO₂ in DESs increases, while it was found to be less affected by the hydrogen bond acceptor. Of these, the solubility of CO₂ is strongest at a 1:10 molar ratio of TBAB and MEA. The nuclear magnetic resonance spectroscopy spectra (NMR) and FTIR spectroscopy revealed that the MEA-based DES mixture primarily exhibited chemical absorption of CO₂, while the MDEA-based DES predominantly showed physical dissolution of CO₂. In addition, it was observed that both temperature and pressure significantly influenced the CO₂ solubility, and a successful correlation was developed using different semi-empirical models.