In this paper, the thermodynamic properties of terpene mixtures were investigated because they represent a promising group of compounds, usually extracted from biomass, with their most notable application as fuel performance enhancers. The densities, viscosities, refractive indices, and ultrasonic speeds of sound were measured for three binary mixtures, citral + chloroform, limonene + chloroform, and linalool + chloroform, across the full composition range at temperatures between 288.15 K and 323.15 K under atmospheric pressure. Using experimental data, excess molar volumes, viscosity deviations, refractive index deviations, and isentropic compressibility, deviations were calculated. Additionally, properties such as partial molar volumes, excess partial molar volumes, partial molar volumes at infinite dilution, and apparent molar volumes were derived. The excess and deviation properties were analyzed using the Redlich–Kister equation. A single mathematical model, the Heric–Brewer–Jouyban–Acree model, was used to represent densities, viscosities, refractive indices, and ultrasonic speeds of sound. The results obtained in this work suggest that dispersive interactions dominate in the limonene and linalool binary mixtures, while hydrogen bonding plays a significant role in the citral + chloroform system. In summary, dispersive interactions are dominant in nonpolar systems like limonene and linalool, while hydrogen bonding significantly affects the citral-chloroform mixture, where the polar groups in citral interact with chloroform molecules. These differences in intermolecular forces help explain the distinct behavior of each mixture. The modeling outcomes demonstrated that the Heric–Brewer–Jouyban–Acree model accurately correlated the experimental thermodynamic properties, with average percent deviations below 1% for all three systems.

Terpenes are the most abundant class of chemical compounds present in essential oils. They are considered green solvents, and come from natural sources such as plants, citrus fruits, but also from tree leaves or pinecones. They find wide commercial uses in food industry as natural flavors and food additives, as well as in pharmaceutical and cosmetics industries. In order to study thermodynamic properties of binary mixtures of terpenes (?-pinene, p-cymene and linalool) with 1-propanol, density and viscosity of these mixtures were determined experimentally. Experimental measurements were done over the temperature range from 288.15 to 323.15 K at atmospheric pressure, over the entire composition range. Excess molar volumes, viscosity deviations and thermal expansion coefficients were calculated based on the experimental results of densities and viscosities. Experimentally measured properties were correlated using the Heritz-Brewer-Jouyban-Acree model, while the Redlich-Kister polynomial was used to correlate the derrived properties. All the experimentally obtained data and the derived values were used to analyze non-ideal behavior of the selected mixtures. The Heritz-Brewer-Jouyban-Acree model successfully correlated the experimental values for all three binary systems, while the Redlich-Kister successfully correlated the derived quantities.