PREDICTION OF VAPOR-LIQUID-EQUILIBRIUM FOR POLYMER-SOLUTIONS BY A GROUP-CONTRIBUTION REDLICH-KWONG-SOAVE EQUATION OF STATE

The aim of this work is to apply a group-contribution cubic equation o f state to vapor-liquid equilibria calculations of polymer-solvent mix tures. The model is based on a Redlich-Kwong-Soave equation of state w ith Huron-Vidal mixing rules where infinite-pressure activity coeffici ents are predicted by a UNIFAC-type model. An original procedure for e stimating the equation-of-state parameters of the polymer is developed : experimental activity data of solvents in binary systems with the sa me polymer are used to fit parameter b (actually, b/MW) of the polymer , so that only one value of polymer density is needed to calculate par ameter a at the temperature of interest. To show the potential of the proposed approach. a table of parameter b values is provided for sis p olymers, and several examples are presented both for nearly athermal a nd for polar polymer solutions. The model is able to correlate equilib rium pressure and solvent activities of the data base with good accura cy. The proposed method is then applied to predict solvent activities of systems not included in the fitting procedure with satisfactory res ults in all cases.