Phase equilibria for the mixtures of the deep eutectic solvent L-menthol + thymol plus CO2 at high pressure

[Display omitted] •The menthol + thymol DES can be dissolved in supercritical CO2 up to ca. yDES = 0.05 at 35–60 °C and 200 bar.•CO2 can also be dissolved in this DES in appreciable quantities and the solubility decreases with temperature.•The mutual solubility of DES and CO2 is lower than that of the components separately.•The phase behaviour of the DES + CO2 system is determined by the hydrogen bonds between menthol and thymol.•The Peng-Robinson Equation of State can describe the main features of the binary and ternary systems. The Vapour-Liquid Equilibrium (VLE) of different mixtures of CO2 + L-menthol, CO2 + thymol and CO2 + L-menthol + thymol has been determined at 35, 40, 50 and 60 °C and pressures up to 220 bar using a variable volume view cell. Menthol + Thymol form a deep eutectic solvent (DES) mixture at a 1:1 molar ratio. For selected conditions, the composition of the vapour phase was determined by 1H NMR. By interpolation of the experimental values, ternary diagrams were built. The mutual solubility between CO2 and DES decreased as the proportion menthol:thymol approached the eutectic composition (1:1). Mutual miscibility also decreased with temperature and increased with pressure. The composition of the mixture of menthol + thymol (1:1) does not remain stable at 60 °C but it does at lower temperatures. The intermolecular interactions between menthol and thymol are responsible for this behaviour. The Peng-Robinson equation of state was used to correlate the results with promising results.