Determination of Mixture Miscibility in Binary and Quaternary Systems of Liquid-Liquid Reactions by Thermodynamics

Abstract

An industrial chemical process commonly involves two types of chemical reaction systems: homogeneous and heterogeneous systems.  Identification of mixing state is important in detail modeling of the system.   This work focuses on determination of equilibrium mixing state for 3 liquid-liquid reaction systems: 2 types of amidation and transesterification.  Each experimental system is binary with two components of reactants at the initial reaction time.  As the reactions proceed, each system becomes quaternary with 4 components of 2 reactants and 2 products.  The state of mixing of the systems was examined based on the change in dimensionless Gibbs free energy of mixing which was related to liquid activity coefficients. The coefficients were obtained from the UNIFAC method.  The results show that the binary mixture of amidation is immiscible in almost all composition ranges except at low reactant concentrations while that of transesterification is immiscible for all compositions of mixture.  The mole fraction values used in all systems at the initial reaction time indicate that the binary mixtures are immiscible.  As the reactions proceed, the quaternary mixture of amidation is converted to miscible within a short reaction time period due to existing of surfactant produced from the reaction.  On the other hand, the quaternary mixture of transesterification is still immiscible throughout the reaction time.  At higher reaction temperature, the quaternary mixture of amidation requires a shorter time to convert from immiscible to miscible because of increased rate of surfactant production.  The information of mixing state is important for choosing appropriate models in process analysis and design.