A comparison of lattice fluid models for the calculation of the liquid-liquid equilibria of polymer solutions

The group contribution lattice-fluid equation of state (GCLF) has been compared to the Sanchez-Lacombe (S-L) equation of state and experimental data for liquid-liquid equilibrium in polymer-solvent systems. Both equations of state are shown to be capable of predicting upper critical solution temperatures, lower critical solution temperatures, simultaneous upper and lower critical temperatures and ''hour glass'' behavior in which there is no upper or lower critical temperature. The predictions of the GCLF model and S-L model are compared to systems which show a LCST and both a LCST and UCST. The specific systems studied include: acetic acid/dodecane, polyisobutylene/n-pentane, polyethylene/n-hexane, polystyrene/n-hexane, polyisobutylene/n-pentane, and polystyrene/acetone. The GCLF showed good agreement with the experimental data for systems with a LCST. In all cases the GCLF model performed better than the S-L model. The GCLF showed good sensitivity to the molecular weight of the polymer, but failed to show the needed sensitivity to pressure. The enhanced performance of the GCLF model was attributed to using saturated vapor and liquid properties simultaneously to regress the group parameters for the model.