The Solubility of Deep Eutectic Solvents Derived from Allytriphenylphosphonium Bromide in Supercritical Carbon Dioxide in the Presence of Ethanol as a Cosolvent

Abstract

Two distinct deep eutectic solvents (DESs) were prepared by combining allyltriphenylphosphonium bromide (ATPPB) as a hydrogen bond acceptor (HBA) and ethylene glycol as a hydrogen bond donor (HBD) at molar ratios of 6:1 and 8:1, respectively. The study investigated the solubility of these DESs in supercritical carbon dioxide, with ethanol serving as a cosolvent, under varying conditions of temperatures 308.2, 313.2, and 318.2 K and pressures up to 18.89 MPa. Solubilities were determined by measuring both bubble point and cloud point pressures in ternary mixtures comprising CO2, ethanol, and DES, utilizing a phase equilibrium apparatus equipped with a high-pressure variable-volume view cell. Higher molar ratios between ethylene glycol and ATPPB resulted in significantly higher pressures required for the solubility of DES. The occurrence of either bubble point or cloud point depended on the molar ratios between the cosolvent (ethanol) and the solvent (scCO2) for both DESs. Increasing system temperature at a constant DES mole fraction led to an elevation in both bubble point and cloud point pressures. Furthermore, an increases in the amount of cosolvent (ethanol) resulted in a substantial decrease in both bubble point and cloud point pressures. The experimental data exhibited robust correlation with three models: the modified Chrastil equation, the Kumar–Johnston equation, and the Adachi–Lu equation. © The Author(s), under exclusive licence to Korean Institute of Chemical Engineers, Seoul, Korea 2024.