Liquid-liquid equilibria of solvent + polymer solutions with a chain-referenced perturbed hard-sphere-chain equation of state

The chain-referenced perturbed hard-sphere-chain (CR-PHSC) equation of state (EOS) proposed by the authors has been applied to correlate liquid-liquid equilibria (LLE) for the binary systems of hexane + polyethylene (PE), pentane + PE, hexane + linear low density polyethylene (LLDPE) and pentane + polypropylene. Three methods were examined to determine PHSC parameters of PE. The PHSC parameters regressed from only pVT data of liquid PE (method-1) gave too high cloud point pressures and could not be used to correlate the LLE at various temperatures. On the other hand, parameters regressed from the pVT data of PE as well as the binary LLE data of hexane + PE (Mw=15,200) mixture (method-3) could be used to correlate LLE of PE solutions with another solvent or PE of other molecular weights. Moreover, parameters of PE obtained by the extrapolation of the parameters for linear alkanes (method-2) were very close to the method-3 parameters and also gave satisfactory correlation results for the LLE of PE solutions. The CR-PHSC EOS with polymer parameters determined by the method-2 or method-3 was much better than the Sanchez-Lacombe EOS and gave almost the same results as those by the perturbed-chain statistical associating fluid theory (PC-SAFT).