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Solvent extraction is a fractionation process applied to separate terpenes and oxygenated compounds from citrus essential oils (EOs). Once the knowledge of the physical properties of phases was found to be crucial for equipment design and the scaling of tubes and accessories, this study focused on the evaluation of density, viscosity, and interfacial tension of phases from the liquid−liquid equilibrium of citrus EO systems. Model mixtures of orange and lemon EOs and real systems at 298.2 K were prepared, and the physical properties of their phases were thus evaluated. Increased water content in the solvent led to higher values of density, viscosity, and interfacial tension, whereas an increased amount of oxygenated compounds caused lower interfacial tensions. Densities estimated by the simple mixing rule provided good results. Parameters of the Grunberg−Nissan model adjusted to the model systems data exhibited a good description of the viscosities of real systems. The UNIFAC-VISCO model provided suitable predictions of viscosities of the solvent phases, and satisfactory results for the interfacial tensions were calculated by linear adjustment and the Bahramian−Danesh thermodynamic model, except for the real acid lime system.

The physical properties density and viscosity of 21 binary mixtures composed of 1-hexanol, 1-heptanol, 1octanol, 1-nonanol, 1-decanol, 1-undecanol, and 1-dodecanol were determined at temperatures from 298.15 to 338.15 K, stepped by 10 K. Well-known methods, based on the physical properties of the pure compounds and their compositions in the mixtures, were used to estimate density (simple form of Kay's rule) and viscosity (logarithmic form of Kay's rule). For density values, the absolute average deviations (AADs) were no higher than 0.06%, when mass fraction was used as the unit of concentration. The viscosity calculations resulted in overall AADs from 1.77% (using molar fraction as the unit of concentration) to 1.85% (using mass fraction as the unit of concentration). Additionally, the predictive capability of the UNIFAC-VISCO and GC-UNIMOD models was tested for viscosity. Satisfactory results were found for all the sets of parameters evaluated in the prediction, with AAD values less than 2%, indicating the appropriate application of these models.

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