Interfacial properties of fast chemical reactions occurring in demixed ternary mixtures

Abstract

A new theoretical framework regarding the interfacial properties of reactive liquid mixtures forming a liquid-liquid phase split has been introduced. Based on the kinetic rate equations, which rely on activities rather than concentrations, and the incompressible density gradient theory, which provides an expression for the Gibbs energy of a nonuniform system, a method is developed to study the dynamics of chemical reactions taking place in the coexisting liquid bulk phases as well as in the interface between them. The assumption that the chemical reaction is much faster than the diffusion leads to a set of partial differential equations describing the spatial and temporal evolution of the mole fractions of all the involved components in the interface and the temporal evolution of the mole fractions in the bulk phases. The obtained equations were used to investigate the dynamics of the interfacial concentration profiles of a ternary mixture with a large miscibility gap, applied to a simple example. Due to the fast chemical reaction and the slow diffusion, the mixture will not remain in phase equilibrium anymore. It was found that the chemical reaction reaches chemical equilibrium first in both bulk phases and afterward in the interface existing between them, which is in contrast to the classical two-film theory often used for mass transport calculations in chemical engineering.