Modeling of solid–liquid equilibria for systems with solid-complex phase formation

The Perturbed-Chain SAFT (PC-SAFT) equation of state (EOS) is applied to model the solid–liquid equilibria (SLE) of binary and ternary systems showing a solid-complex phase formation. Modeling results for mixtures composed of associating components, e.g. water, alcohols, phenol, bisphenol A (BPA), as well as acetamide are presented. The solid-complex phase formation is modeled as a chemical reaction between species in liquid phase and governed by an equilibrium constant. To calculate the crystallization line of the solid-complex, the stoichiometric composition of the solid-complex and the enthalpy of melting at a reference temperature are required. The phase diagrams for the systems under consideration with various types of SLE are successfully described using only one binary interaction parameter kij for the PC-SAFT EOS. This approach even allows the simultaneous description of vapor–liquid, liquid–liquid as well as solid–liquid equilibria as shown for the phenol–water mixture. Moreover, it was successfully extended to describe the ternary BPA–phenol–water system.