Simultaneous calculations of VLE and saturated liquid and vapor volumes by means of a 3P1T cubic EOS

The three-parameter cubic equation of state with one parameter temperature-dependent (3P1T), P = RT/(V - b) - a(T)/[V(V + c) + b(3V + c)], recently developed for asymmetric mixture density calculations for nonpolar substances (Yu and Lu, 1987), has been applied to VLE calculations. The binary interaction parameter k₁₂ obtained from the conventional random VDW mixing rule for the mixture parameter a has been used for the prediction of volumes of saturated liquid (V^ℓ) and saturated vapor (V^ν) at the conditions of the VLE data. The 3P1T equation is as capable for VLE calculations as the Soave-Redlich-Kwong, the Peng-Robinson, the Schmidt-Wenzel and the translated Peng-Robinson equations, but it yields lower V^ℓ deviations than these equations. The improvement is more evident for highly asymmetric mixtures. The suitability of the form of the equation for representing V^ℓ of nonpolar compounds over a wide range of molecular weight is further demonstrated.