High-Pressure Densities and Derived Properties of Thymol/Carboxylic Acid Eutectic Mixtures

Liquid densities of five eutectic mixtures including thymol/butanoic acid, thymol/pentanoic acid, thymol/hexanoic acid, thymol/heptanoic acid, and thymol/octanoic acid at molar ratio 1:1 were measured based on the vibrating-tube method at pressures up to 70 MPa. The temperature range studied in this work is from 293.15 to 363.15 K. The estimated combined expanded uncertainty for density is less than 0.9 kg·m–3 (95% confidence level). For comparison purposes, the Tait equation, PC-SAFT equation, and three empirical equations proposed by Murnaghan, Benito, and Romeo were used to regress the experimental density data. Results show that, for the present eutectic mixtures, the performances of the Tait equation and Murnaghan equation are better than others. In addition, the derived thermodynamic properties of the mixtures including isothermal compressibility, isobaric thermal expansibility, internal pressure, and the difference between heat capacity at constant pressure and heat capacity at constant volume were determined based on the Tait equation, and the effects of pressure, temperature, and alkyl chain length in acid on the properties were analyzed.