Solid-liquid phase equilibrium of phenylphosphonic acid in three binary solvents: Determination, correlation and molecular simulation

Abstract

Abstract In this research work, solubility of pyrethroid insecticide phenylphosphonic acid (PPOA) in three binary solvents including methanol (MtOH) + ethyl acetate (EtAC), ethanol (EtOH) + EtAC at (278.15 to 323.15) K and 1,4-dioxane + EtAC at (288.15 to 323.15) K was investigated by laser monitoring method at 0.1 MPa. Solubility of PPOA increased with the increasing temperature while decreased with the increasing mass-fraction of EtAC. The solubility behavior was studied by molecular simulation. The solute-solvent interaction (Einter) suggested that solubility of PPOA increased with values of Einter increasing and there existed the strong interactions between PPOA and most selected binary solvents except 1,4-dioxane + EtAC. The radial distribution function (RDF) between two components of mixed solvent indicated that the tendency to aggregation of two components molecules increased with the increment of corresponding mole fraction of binary solvents. It also confirmed to some extent that the solute – solvent interaction energy would be weaken and the PPOA solubility in binary selected decreased. At the same time, it was found that the hydrogen bond existed in binary solvents namely “MtOH + EtAC and EtOH + EtAC”. So solubility of PPOA resulted from the integrated effect of solute – solvent and solvent – solvent interactions. Moreover, experimental solubility values were correlated by four multi-component activity coefficient models including Wilson, NRTL, Margules and UNIQUAC model. Four thermodynamic functions provided good correlations with solubility values. Furthermore, thermodynamic properties of mixing process were calculated by Wilson equation and corresponding solubility data. Mixing process was entropy-driven in selected solvents and exothermic in most binary solvents except EtAC and 1,4-dioxane (w1 = 0.2016) + EtAC.