Applying UNIFAC-based models to predict the solubility of solids in subcritical water

This work explores the capabilities of UNIFAC-based models to predict the solubility of different solid solutes in subcritical water as a function of temperature. The original UNIFAC, its modified (Dortmund) version and the A-UNIFAC model, which explicitly includes association effects between groups, are applied to calculate the solubility of solid compounds in subcritical water in the temperature range 298–500 K. The comparison between the three models is carried out using polycyclic aromatic hydrocarbons (PAHs) as test substances and for which reliable physical properties and experimental solubility data are available in the literature. The results obtained indicate that modified UNIFAC (Dortmund) provides the best representation of the aromatic compounds’ solubility as a function of temperature. In addition, the application of the A-UNIFAC model confirms the hypothesis that a decrease in the level of association between the subcritical water molecules (in accordance with the dielectric constant decrease with temperature), greatly improves the solubility of hydrophobic organic compounds.