AN IMPROVED METHOD FOR PREDICTING THE VAPOR-LIQUID-EQUILIBRIA OF SUBCRITICAL MIXTURES

A simple modification of a previous method for calculating the vapor-l iquid equilibria of mixtures of subcritical compounds is proposed. The improvement mainly consists of the use of an ad hoc value of the cons tant m in the Vetere equation of state (EOS) for each family of mixtur es considered instead of a fixed value equal to 2.4. Better results wi th respect to the previous work are obtained for the following classes of mixtures: aqueous soluble mixtures, aqueous mixtures with a miscib ility gap, polar-polar mixtures, polar-non-polar mixtures, mixtures wh ich exhibit a negative deviation from Raoult's law, and nearly ideal m ixtures. For the remaining case, i.e. non-aqueous mixtures with a misc ibility gap, the improvement is negligible. The possibility of introdu cing a binary interaction value for the entropy part of the Vetere EOS , instead of assuming a nil value for this quantity, is also considere d.