High pressure phase behavior for the supercritical ethylene plus cyclohexane plus hexane plus polyethylene systems

Phase behavior of binary, ternary and quaternary systems of ethylene, cyclohexane, hexane and polyethylene (PE, (M) over barw = 15.4 x 10(3)) was investigated. Measurements were carried out at temperatures from 373 to 488K, PE weight fractions from 0.017 to 0.152, and ethylene weight fractions from 0 to 0.100 with a synthetic-type apparatus. The ratios of the weight fractions of cyclohexane to hexane in the mixtures were kept constant at about 1/9 or 2/8 for the cyclohexane + hexane + PE and the ethylene + cyclohexane + hexane + PE systems. Liquid-liquid phase separation for the cyclohexane + PE binary system did not appear in the range from 373 to 473 K and up to 30 MPa. All other systems exhibited LCST (lower critical solution temperature)-type phase behavior. For the cyclohexane + hexane + PE and the ethylene + cyclohexane + hexane + PE systems, liquid-liquid phase separation temperature increased with increasing concentration of cyclohexane. On the other hand, the liquid-liquid phase separation temperature decreased with increasing concentration of ethylene for the ethylene + cyclohexane + PE and the ethylene + cyclohexane + hexane + PE systems. The liquid-liquid phase boundaries of the cyclohexane + hexane + PE and the ethylene + cyclohexane + PE systems were satisfactorily correlated with the Sanchez-Lacombe equation of state and temperature-dependent binary parameters. Moreover, the predicted results reproduced well the phase boundaries of the ethylene + cyclohexane + hexane + PE system. (C) 2009 Elsevier B.V. All rights reserved.