Measurement and thermodynamic correlation of liquid–liquid equilibria of water + n-propanol + toluene at 20°C and atmospheric pressure

Abstract

Although the system water + n-propanol + toluene is important for research and industry, its liquid–liquid equilibria LLE are scarcely covered in literature, with no thermodynamic modeling reported using typical equations of state or activity coefficient models. The current work addresses this gap by presenting the equilibria of the system at 20°C and atmospheric pressure. That includes the binodal curve and twelve tie lines covering the entire miscibility gap, whereby the compositions of the conjugate phases are determined using high-precision refractive index measurements. The quality of the data is verified by applying the techniques of conjugate lines and mass balances, whereas it is shown that empirical correlations cannot be used for that purpose. Three different methods to extrapolate the critical point are then employed and, using the more reliable one, that point is located and added to the dataset. Further thermodynamic correlation of the data is conducted using the activity coefficient models, UNIQUAC and NRTL. While the former did not perform well, the latter was able to model the LLE and adapt to temperature changes.