The modelling of the time-dependency of interfacial properties due to chemical equilibrium reactions in demixed liquid systems

Abstract

The interfacial properties between demixed liquid phases are of crucial importance in chemical engineering. This holds especially true considering extraction based processes inhabiting a chemical reaction due to the time-dependency of all thermodynamic properties that comes with it. The purpose of this work is to predict the dynamic interfacial properties in the demixed liquid system water + 1-hexanol + hexylacetate + acetic acid, which is overlaid by the auto-catalyzed chemical equilibrium esterification reaction 1-hexanol + acetic acid ↔ hexylacetate + water. In order to predict the interfacial properties for these reactive mixtures as function of time, the incompressible version of the density gradient theory (inc-DGT) was combined to the first time with differential rate equations describing the kinetics of this reaction by activities instead of concentrations. The quaternary phase equilibrium, the reaction kinetics, the reaction equilibrium as well as the inhomogeneous region of the interface were thereby described with an activity coefficient model, namely the NRTL-model. Particular attention is directed to the time-dependency of the interfacial tension while the system strives towards the thermodynamic equilibrium. It could be demonstrated that the prediction of the interfacial tension of the supposed model is very close to experimental data obtained also in this study using spinning-drop tensiometry. Furthermore, the time-dependency of the mole fraction profiles inside the inhomogeneous region of the interface due to a chemical reaction could be made visible for the first time.