Vergleich der Perturbed‐Hard‐Chain‐Theorie mit der Freien‐Volumen‐Theorie und der Flory‐Huggins‐Theorie zur Berechnung von Phasengleichgewichten von Ethylen/Polyethylen‐Mischungen unter Hochdruck

The perturbed‐hard‐chain theory, the free‐volume‐theory and the well known Flory‐Huggins lattice theory of polymer solutions were applied to phase‐equilibrium calculations for mixtures of ethylene and low density polyethylene. The parameters required for the calculations were determined from a large number of experiments under high pressure. By comparison of calculated and measured phase‐equilibrium data it is shown that the perturbed‐hard‐chain‐theory can be applied to predict accurately composition of phases as well as the molar mass of the polymer in the ethylene‐ and in the polyethylene‐rich phases from ambient to high pressure. The free‐volume‐theory failed for pressures near the critical. The solubility of ethylene in the polymer‐rich dense phase could be calculated by means of Flory‐Huggins‐Theory only for low to medium pressures up to 300 bar in good agreement with the experimental data. By means of the perturbed‐hard‐chain‐theory engineers may interpolate and extrapolated limited experimental data with confidence for optimal design of large scale polymerization reactors and separators.