High-Pressure Phase Behavior and Thermodynamic Modeling of the CO₂ + L-Menthol:Eucalyptol Deep Eutectic Solvent System

The deep eutectic solvent (DES) based on L-menthol and eucalyptol (1,8-cineol) combined with supercritical carbon dioxide is still an underexplored system for extractive processes, and the investigation of its phase behavior of this system is essential to understanding its thermodynamic properties. In this study, phase behavior data for the binary system CO₂ (1) + DES Men:Eu (2) are reported. The synthetic visual method was used with CO₂ molar fractions ranging from 0.60 to 0.99 at temperatures of 313.15, 323.15 and 333.15 K. Vapor-liquid equilibrium (VLE) with bubble point (BP) and dew point (DP), liquid-liquid equilibrium (LLE), and vapor-liquid-liquid equilibrium (VLLE) were visually identified within the pressure range of 6.39 and 14.08 MPa. VLE-BP and VLE-DP was observed at 323.15-333.15 K, with only the VLE-BP being observed at 313.15 K. LLE and VLLE at CO₂ ratios above 0.90 was observed at 323.15 and 333.15 K. The Peng-Robinson equation of state with the Wong-Sandler (PR_WS) mixing rules was applied to correlate experimental results, providing a satisfactory representation of the equilibrium data for this system, making it possible to understand the thermophysical properties of this green solvent under the pressure, composition, and temperature conditions required for its use in supercritical technology.