Vapor–liquid equilibrium in polymer–solvent systems with a cubic equation of state

A cubic equation of state (EoS), the Peng–Robinson (PR) one, is extended to polymers by using a single set of energy (a) and co-volume (b) parameters per polymer fitted to experimental volume data. Excellent results for the volumetric behavior of the polymer up to 2000 bar pressure are obtained. The EoS is applied to the correlation of low pressure vapor–liquid equilibrium (VLE) data for a variety of polymer solutions by employing only one interaction parameter in three mixing rules: the van der Waals one fluid (vdW1f) — using the Berthelot combining rule (B) for aij, and the arithmetic mean (AM) and Lorentz (L) ones for bij — the Zhong and Masuoka (ZM); and the modified Huron–Vidal 1st order (MHV1), by coupling the cubic EoS with the Flory–Huggins (FH) model. Best results are obtained with the ZM mixing rule and the same holds for the extrapolation with respect to temperature and polymer molecular weight (MW). Low errors in correlation and extrapolation are also obtained with the other mixing rules, but phase split is observed in certain cases. The performance of other methods for polymer parameters evaluation is also examined.