Measurement and correlation of the solubility of juglone in supercritical carbon dioxide

Juglone (5-hydroxy-1,4-naphthoquinone) is an allelopathic compound predominantly abundant in the roots, leaves, bark and wood of Juglans sp. (walnut). Juglone presents cytotoxic properties as well as antibacterial, antiviral and antifungal activities. The selective extraction of this compound using supercritical fluids (SCF) may present clear advantages over conventional extraction methods, particularly if cosmetic, pharmaceutical or food applications are envisaged. However, the optimization of any high pressure extraction process requires the knowledge of the solubility of the target compounds to be extracted. In this work we report the experimental measurement and correlation of the equilibrium solubility of juglone in scCO2. Results were obtained using a static analytical method at 308.2 K, 318.2 K and 328.2 K, and in a pressure range from 9.2 up to 24.4 MPa. Experimental equilibrium solubility was found to be between 2.0 × 10−5 and 1.6 × 10−3 (in terms of juglone mole fraction). Experimental data were correlated with three density-based models (Chrastil, Bartle and Méndez-Santiago–Teja models) and with the Peng-Robinson cubic equation of state (PR-EOS), using the conventional van der Waals mixing and combining rules. Juglone critical and thermophysical properties were estimated by different methods available in the literature and the influence of these estimation methods on its properties (namely on sublimation pressure) was discussed in terms of the final PR-EOS correlation results accuracy. The best obtained average absolute relative deviations (AARD) were 5.5% and 4.1%, for semi-empirical models and for the PR-EOS, respectively.

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► Design of scCO2-based processes which require the dissolution of juglone in scCO2.
► Experimental juglone-scCO2 phase equilibria measurements.
► Density-based and Peng-Robinson cubic equation-of-state correlation of juglone-scCO2 equilibria data.
► Estimation of critical and of thermophysical properties and their effects on Peng-Robinson cubic equation-of-state correlation.