Equation of state associated with activity coefficient model based on elements and chemical bonds

Abstract

A new GE-EoS model(SRK-UNICAC) was proposed to improve the accuracy of the equation of state in predicting the vapor-liquid equilibrium of polar systems and expand its application. It combined the excess Gibbs free energy model with the SRK equation. The excess Gibbs free energy(GE) was calculated by the UNICAC model, which is a group contribution activity coefficient model based on elements and chemical bonds. And the original interaction parameters of the UNICAC model were adopted. The vapor-liquid equilibrium of 87 binary systems under low and medium pressure, 12 binary systems under high pressure, and 14 ternary systems are predicted. The prediction results were compared with some other activity coefficient models. The prediction results of the binary system show that the SRK-UNICAC model is superior to UNIFAC (Lyngby), UNIFAC(2003), and ASOG(2011). The average relative errors of vapor mole fraction and bubble point pressure or temperature are 3.75% and 6.58% in binary systems under high pressure. So it is suitable for high-pressure and polar systems. For ternary vapor-liquid equilibrium, the average relative errors of vapor molar fraction and bubble point temperature or bubble point pressure are 6.50%, 4.76%, and 2.25%. It is also superior to other methods. The SRK-UNICAC model improves the prediction accuracy and expands the application range. So it can be applied to the prediction of vapor-liquid equilibrium.