A cubic equation of state with a new alpha function and a new mixing rule

Abstract

Abstract Twu C.H., Bluck D., Cunningham J.R. and Coon J.E., 1991. A cubic equation of state with a new alpha function and a new mixing rule. Fluid Phase Equilibria, 69: 33-50. A new temperature-dependent function (α) for a cubic equation of state is proposed. The new α function used in the cubic equation of state not only correlates the vapor pressures of pure components, but extrapolates correctly to the supercritical region. The new cubic equation of state has been used to accurately describe the vapor pressure and liquid heat capacity for over 1000 chemical components. The accuracy of reproducing the vapor pressure from the triple point to the critical point is generally within the experimental error. A new mixing rule has also been developed for correlating phase equilibrium data. The mixing rule can reproduce the activity coefficients in the infinite dilution region as well as model phase behavior throughout the finite range of concentration. This mixing rule allows the accurate representation of polar/non-polar systems and can be extended to multicomponent systems. The cubic equation of state with the proposed new α function and the new mixing rule is applicable to important systems encountered in industrial practice.