A perturbed hard-sphere-chain equation of state: prediction from critical point constants

A modified perturbed hard-sphere-chain equation of state has been employed to calculate the PVT properties of fluids. Generally, two temperature-dependent parameters; an effective van der Waals covolume and the strength of the attractive forces between two nonbonded segments, and a third parameter representing the number of chains per molecule appear in the existing perturbed hard-sphere-chain equations of state. Knowing two scale parameters; depth of minimum in pair potential and the separation distance between segment centers at this minimum, are sufficient to calculate the temperature-dependent parameters. These scale parameters are obtainable by fitting of experimental data. In this work it is shown that using the critical constants of fluids as scale constants would correlate the temperature-dependent parameters of the equation of state with sufficient accuracy. We have tested the predicted equation of state against the experimental data for a large number of fluids including a number of diatomics, polyatomic inorganic molecules, saturated hydrocarbons up to n-C20H42, and a number of olefins and aromatics. The agreement with experiment is quite good.