Thermophysical Properties and CO2 Solubility in Binary and Ternary Mixtures of Polyethylene Glycol 400, Ethylene Glycol, and Thymol–Camphor Deep Eutectic Solvent

Abstract

The solubility of carbon dioxide (CO₂) in binary and ternary solvent mixtures composed of polyethylene glycol 400 (PEG 400), ethylene glycol (EG), and a thymol–camphor-based hydrophobic deep eutectic solvent (TC-HDES) was experimentally investigated at temperatures of 298.15 and 308.15 K and pressures up to 0.5 MPa. In addition, selected thermophysical properties, including density, were measured to support the analysis of gas–liquid equilibrium behavior. All solvent compositions studied for CO₂ absorption were confirmed to remain in the homogeneous liquid phase under the investigated conditions. Henry’s law constants indicate that PEG 400 exhibits the highest CO₂ solubility (4.53 MPa), followed by the TC-HDES (10.3 MPa), while EG shows significantly lower solubility (43.8 MPa). To gain insight into solute–solvent interactions at the molecular level, the preferential solvation model was applied to the experimental data. The results suggest that PEG 400 preferentially occupies the solvation shell of CO₂ in both binary and ternary mixtures, dominating over EG and TC-HDES. This behavior is attributed to the multi-oxyethylene structure of PEG 400, which promotes favorable interactions with CO₂. The combined experimental and modeling results provide useful insight into the design of mixed-solvent systems for CO₂ capture, enabling improved performance through appropriate selection of solvent composition, while considering practical constraints such as viscosity and cost.