EQUATIONS OF STATE - HOW TO RECONCILE FLEXIBLE MIXING RULES, THE VIRIAL-COEFFICIENT CONSTRAINT AND THE MICHELSEN-KISTENMACHER SYNDROME FOR MULTICOMPONENT SYSTEMS

Non-quadratic mixing rules in the attractive parameter of a cubic equation of state are very effective for the correlation of phase behaviour of strongly non-ideal systems. However, these mixing rules are not consistent with the second virial coefficient being a quadratic function of mole fractions. Recently, Michelsen and Kistenmacher pointed out other draw-backs of some of these mixing rules. In this paper, we present a new formulation of such mixing rules which avoids these problems, and a simple form of the density-dependency of the mixing rules which keeps the cubic form of the equation of state, while ensuring consistency with the second virial constraint.