Modeling aqueous two-phase systems: I. Polyethylene glycol and inorganic salts as ATPS former

In this work the ePC-SAFT equation of state is applied to model aqueous two-phase systems (ATPS) containing polyethylene glycol (PEG) and one of 16 different inorganic salts at temperatures between 277.15 K and 333.15 K. To ensure an accurate modeling of thermodynamic properties in PEG containing solutions, a novel modeling approach for PEG is applied considering different molecular interactions of PEG chain segments and PEG end-group segments. Applying this approach, the influence of PEG molecular weight, kind of salt, pH, as well as of temperature on the phase split as well as on the densities of the two phases can be modeled accurately. The overall absolute average deviation of the concentrations of the phase-forming components obtained by ePC-SAFT is 2.25 wt%. Moreover, it could be shown that by applying ion-specific model parameters, ePC-SAFT is even capable of predicting ATPS which were not used for the parameter estimation.