Liquid-Liquid-Solid Equillibrium of Water + 2-propanol + Kosmotropic Salts: Construction of Phase Diagrams and Understanding of Salting-out Effects Using Volumetric and Compressibility Studies

Abstract

Triangular phase diagrams are important to understand the phase behaviors in ternary systems. The salting out of alcohol from water by kosmotropic salt has long been known, but the molecular interactions and the mechanism of bond breaking and making processes has not yet been fully understood. To understand the salting-out of 2-propanol from water using kosmotropic salts (Na2S2O3, Na2SO4 and Na2SO3). To study the phase equilibria of liquid-liquid, liquid-solid and liquid-liquid-solid system by constructing ternary phase diagrams. To determine the solute-solute, solute-solvent, and solvent-solvent molecular interactions to resolve the salting- out effect. The solubility data of Na2S2O3/Na2SO4/Na2SO3 salts have been reported in pure water, 2-propanol and water + 2-propanol mixtures in different concentrations at 298.15 ± 1 K. The ternary phase diagrams have been constructed from the obtained solubility data. The volumetric and acoustic data of binary and ternary systems of water + 2-propanol, water + salt and water + 2-propanol + salt has been determined using density meter and interferometer. The ternary phase diagrams have been constructed for water+2-propanol+ Na2S2O3/Na2SO4/Na2SO3 system. The rise in sound velocity signifies more structural interactions in binary water-alcohol and water-salt systems, while the relation is rather change with the ternary system, as the water-alcohol sheath will be broken by the kosmotropic salt which results in to salt-water sheath. The density, sound velocity and adiabatic compressibility results suggest that phase separation phenomenon is due to the bond breaking and bond making process along with hydrophobic hydration and hydrophobic interactions. The anion S2O32-, SO42- and SO3 2- promote salting-out effect and the strength of these effects decreases in the order S2O32->SO42->SO32-.