Phase equilibrium calculation with a local composition model based on Lennard-Jones potential

A new density-dependent local composition model was derived for calculating phase equilibria of supercritical fluid mixtures. In the model, the probability of finding j-molecules about an i-molecule is given by a Wilson type equation in which the j-i interaction is represented by a Lennard-Jones (LJ) potential. The local composition in both nearest and second-nearest neighbors was considered for developing an equation of state for mixtures from two-fluid theory. Phase equilibrium calculations with the new model were performed for representative argon-hydrocarbon, hydrocarbon-hydrocarbon and CO₂-alcohol binary mixtures. Accurate prediction could be obtained for the systems whose components are well known to be LJ fluids.