Solubility of polycyclic aromatic hydrocarbons in sub-critical water: A predictive approach using EoS/GE models

Abstract

This study compares the capabilities of predictive equation of State/Gibbs free energy (EoS/GE) models to provide an accurate description of the solid–liquid phase equilibrium (SLE) of solid polycyclic aromatic hydrocarbons (PAHs) in sub-critical water (SBCW). The linear combination of Vidal and Michelsen (LCVM) mixing rule and the modified Huron–Vidal second order mixing rule (MHV2), in conjunction with the Peng–Robinson equation of state (PR-EoS), were used to predict the solubility of PAHs in SBCW, as a function of temperature. We compared the solubility predictions obtained from these EoS/GE models and estimated solubility based on UNIFAC activity coefficient models previously reported in the literature. Our results indicate that all the models provide reasonably good prediction of PAH solubilities, with the PR-LCVM model yielding the most accurate predictions. Further, an analysis of the temperature dependence of the solubility of PAHs in SBCW, shows a significant rise in solubility over and above a specific temperature range. We also examined the partial molar excess entropy, enthalpy and Gibbs energy of selected PAHs and discussed the thermodynamic driving forces responsible for the solubility of PAHs in SBCW.