Temperature and salt addition effects on the solubility behaviour of some phenolic compounds in water

Solubility-temperature dependence data for six phenolic compounds (PhC), contained in olive mill wastewater (OMWW), in water and in some chloride salts (KCl, NaCl, and LiCl) aqueous solutions have been presented and solution standard molar enthalpies (ΔsolH{ring operator}) were determined using Van't Hoff plots. The temperature was varied from 293.15 K to 318.15 K. Solubility data were estimated using a thermostated reactor and HPLC analysis. It has been observed that solubility, in pure water and in aqueous chloride solutions, increases with increasing temperature. The salting-out LiCl > NaCl > KCl order obtained at 298.15 K is confirmed. Results were interpreted in terms of the salt hydration shells and the ability of the solute to form hydrogen-bond with water. The standard molar Gibbs free energies of transfer of PhC (ΔtrG{ring operator}) from pure water to aqueous solutions of the chloride salts have been calculated from the solubility data. In order to estimate the contribution of enthalpic and entropic terms, standard molar enthalpies (ΔtrH{ring operator}) and entropies (ΔtrS{ring operator}) of transfer have also been calculated. The decrease in solubility is correlated to the positive ΔtrG{ring operator} value which is mainly of enthalpic origin. © 2006 Elsevier Ltd. All rights reserved.