Prediction of phase equilibrium and interfacial properties in the quaternary system water + 1-hexanol + hexylacetate + acetic acid

Abstract The knowledge of the liquid-liquid phase equilibrium and the corresponding interfacial properties of quaternary liquid mixtures can be used for the optimization of extraction processes relevant for industrial application. The purpose of this work is the theoretical prediction of the above mentioned interfacial properties for the quaternary mixtures water + 1-hexanol + hexylacetate + acetic acid using the incompressible version of the density gradient theory in combination with the NRTL activity coefficient model. The prediction is based on phase equilibria data including vapor-liquid and liquid-liquid equilibria of the corresponding binary and ternary subsystems and binary experimental interfacial tension data of the two binary subsystems water + 1-hexanol and water + hexylacetate forming a miscibility gap. The predicted interfacial tensions of the quaternary were verified by new measurements utilizing the spinning drop method and an excellent agreement was achieved. Additionally, for the first time, the simultaneous enrichment of two different components inside the liquid-liquid interfacial layer could be observed.