Concentration dependent surface area parameter model for calculation of activity coefficients

A new model is proposed for the calculation of activity coefficients. The proposed model is based on the quasi-chemical theory. The surface area parameters in the model depend on partner molecules and concentrations. The surface area parameters for pure components are cited from the surface area parameters of UNIQUAC model. The number of fitting parameters are three for each binary system in the model. These are q21∞ (surface area parameter of component 1 in component 2 at infinite dilution), q12∞ (surface area parameter of component 2 in component 1 at infinite dilution), and τ12 (interaction parameter) for component (1) + component (2) binary system. The activity coefficients of multi-component systems can be calculated with the binary parameters of constituting binary systems. The calculated results by the model are in good agreement with the experimental data of vapor–liquid and liquid–liquid equilibria for binary systems. The ternary liquid–liquid equilibria are calculated by using the binary parameters of constituting binary systems. The calculated results by the model are much better than those by NRTL and UNIQUAC models.

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► A new model is proposed for the calculation of activity coefficients.
► The surface area parameters depend on partner molecules and concentrations.
► The number of fitting parameters are three for each binary system.
► Multi-component systems can be calculated with binary parameters.
► Ternary LLE and binary VLE can be correlated well with the same parameter set.