Measurement and correlation of phase equilibria of ethylene + n-hexane + metallocene polyethylene at temperatures between 373 and 473 K and at pressures up to 20 MPa

The purpose of this work was to measure phase equilibria of importance for producing industrial linear low-density polyethylene (LLDPE) using metallocene catalysis technology. Phase equilibria for n-hexane + polyethylene (PE) mixtures and for ethylene + n-hexane + PE mixtures were measured at temperatures from 373.2 to 473.2 K and at pressures up to 20 MPa. Nearly monodisperse PE15k, PE108k and their mixtures were used in the investigations to explore the effect of polymer molecular weight on the phase behavior. All the systems exhibited liquid–liquid equilibria with an upper critical solution pressure. The Sanchez–Lacombe equation of state is used to correlate the phase behavior of these systems and the effect of adding supercritical ethylene. The Hosemann–Schramek function was found to provide a suitable description of the molecular weight distribution used in some of the calculations. The cloud point pressure of ethylene + n-hexane + PE was found to increase proportionally with the weight fraction of supercritical ethylene.