CO2 solubility in amine based deep eutectic solvents: Review of literature data, experimental measurements for choline chloride plus 3-amino-1-propanol or 3-(methylamino)propylamine aqueous solutions and modeling with the modified Kent-Eisenberg model

The effect of water and choline chloride on the CO₂ absorption ability of amine based deep eutectic solvents is investigated. New experimental data are presented for four choline chloride – 3-amino-1-propanol (MPA) aqueous systems of various water contents and for an aqueous choline chloride – 3-(methylamino)propylamine (MAPA) system, which were modelled with the modified Kent-Eisenberg model. It was shown that, starting from an aqueous amine solution, the replacement of a small part of the amine by choline chloride does not significantly influence the moles of the absorbed CO₂ per mole of amine, but reduces the CO₂ solubility in the bulk, expressed as moles of CO₂ per kg of solvent. Furthermore, it was shown that if a small part of water is replaced by choline chloride, the CO₂ solubility in the bulk is not significantly altered. Moreover, the addition of water favors the chemical absorption, as the experimental results show increased absorbed moles of CO₂ per mole of amine. However, such phenomenon is not enough to compensate for the rather low CO₂ solubility in water and the overall absorption ability of the aqueous DES solution, expressed in moles of CO₂ per kg of solvent, decreases. The modified Kent-Eisenberg model satisfactorily correlates the experimental data showing deviations that range between 0.4–6.6 % in all cases. The model predictions for the speciation in the loaded solutions reveal that the unreacted amine content is very low at CO₂ partial pressures of the order of 1 kPa and that the increase of CO₂ solubility at higher partial pressures is attributed to the hydrolysis of the carbamate and the molecular CO₂ dissolution.