A molecular-based model for normal fluid mixtures: Perturbed Lennard-Joneschain equation of state

The perturbed Lennard-Jones chain (PLJC) equation of state, previously used for pure fluids, is extended to normal fluid mixtures. The PLJC equation u tilizes the hard-sphere chain mixture as the reference system, while the pe rturbation term is derived based on the first-order variational theory. Bin ary vapor-liquid equilibrium data of a wide range of fluids were well descr ibed by this model through the use of one binary parameter k(ij). We showed that the PLJC equation of state was able to predict vapor-liquid equilibri um fairly accurately using binary data. Also, the PLJC equation is able to model retrograde condensation and, liquid-liquid-vapor three-phase equilibr ium of ternary mixtures without the need to reevaluate binary parameters. T heoretical phase equilibrium compositions were determined through an isothe rmal-isobaric flash calculation based on global minimization of the Gibbs f ree energy using a genetic algorithm.