Experimental measurement and thermodynamic modelling of the solubility of carbon dioxide in deep eutectic solvent

In the present work, an amine-based deep eutectic solvent (DES) was prepared using ethanolamine hydrochloride (EAHC) as a hydrogen bond acceptor (HBA) and diethylenetriamine (DETA) as a hydrogen bond donor (HBD) with the molar ratio of 1:9. The synthesized DES was further diluted by adding 30 v% water in the prepared DES. The solubility of carbon dioxide was measured in the aqueous DES at various pressures and temperature ranging from 0.4 to 1.6 MPa and 303.15 to 333.15 K, respectively. The solubility tends to increase at higher pressures and showed a decreasing trend at the higher temperatures i.e. 333.15 K. The highest solubility of 3.770 mol/mol was recorded at 303.15 K and pressure of 1.6 MPa. In modelling the measured CO₂ solubility data in aqueous deep eutectic solvent, the system was deemed as a quasi-binary of CO₂ and a mixed solvent. It was further assumed that the gas phase is solely consisted of CO₂. Then, the gas phase was described by the Peng-Robinson equation of state while the unsymmetrical NRTL, 2-suffix Margules, and a modified Margules equation were utilized for the modelling of the liquid phase. Henry’s law constants for the solubility of CO₂ in the aqueous deep eutectic solvent were estimated and reported. It was found that the NRTL equation described the aqueous solvent phase better than the 2-suffix Margules equation; however, inferior with respect to the modified Margules equation. The coupling of the Peng-Robinson equation of state with the modified Margules equation led to an average absolute relative deviation of 3.36%.