New Variant of the Universal Constants in the Perturbed Chain-Statistical Associating Fluid Theory Equation of State

The Perturbed Chain-Statistical Associating Fluid Theory Equation of State (PC-SAFT EOS) has been successfully applied to model phase behavior of various types of systems, while it is also well-known that the PC-SAFT EOS has difficulties in describing some second-order derivative properties. In this work, the temperature and volume dependencies of the PC-SAFT EOS have been analyzed based on the total reduced residual Helmholtz free energy from the well-established reference equations. The ranges of parameters and temperature, in which the original PC-SAFT EOS give zero or more than three volume roots, have been analyzed. Then, a practical procedure has been proposed to refit the universal constants of the PC-SAFT EOS with the purpose of fixing the numerical pitfalls in the real application ranges and reusing the original parameters. It is shown that the new universal constants have practically resolved the mostly criticized numerical pitfall, that is, the presence of more than three volume roots at real application conditions. Finally, the possibility of using the original PC-SAFT EOS parameters with the new universal constants has been investigated for the phase equilibria of the systems containing hydrocarbons, chemicals, water, or polymers.