Modeling aqueous two-phase systems: III. Polymers and organic salts as ATPS former

In this work the electrolyte perturbed chain statistical associating fluid theory (ePC-SAFT) is applied to model aqueous two-phase systems (ATPS) containing one of 6 different polymers and one of 8 different organic salts at temperatures between 278.15 K and 313.15 K. To accurately model the thermodynamic properties of organic-salt solutions, a novel modeling approach was applied, which accounts for the non-spherical shape of the anions. Applying this approach, 14 organic salt solutions have been modeled with an overall average relative deviation of 0.23% for solution densities and 1.51% for osmotic coefficients. The modeling of the polymers (PEG, PEGDME, PPG, and poly(ethylene glycol-co-propylene glycol)) has been carried out using a copolymer approach accounting for different molecular interactions of the polymer segments. Applying this approach, ATPS containing polymers and organic salts were modeled accurately. The overall absolute average deviation of the modeling with respect to the concentrations of the phase-forming components was 2.10 wt%. The influence of polymer molecular weight, polymer composition, kind of salt, pH, and temperature on the equilibrium composition and densities of the two phases was modeled correctly with ePC-SAFT. Moreover, it is shown that by applying ion-specific model parameters, ePC-SAFT is even capable of predicting ATPS containing salts which were not used for the parameter estimation.