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 experimen tal data for liquid-liquid equilibrium in polymer-solvent systems. Bot h equations of state are shown to be capable of predicting upper criti cal solution temperatures, lower critical solution temperatures, simul taneous upper and lower critical temperatures and ''hour glass'' behav ior in which there is no upper or lower critical temperature. The pred ictions 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 inc lude: acetic acid/dodecane, polyisobutylene/n-pentane, polyethylene/n- hexane, polystyrene/n-hexane, polyisobutylene/n-pentane, and polystyre ne/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 pr essure. The enhanced performance of the GCLF model was attributed to u sing saturated vapor and liquid properties simultaneously to regress t he group parameters for the model.