A modified segment-based nonrandom two-liquid model for the calculation of vapor–liquid equilibrium of aqueous polymer–salt solutions

A new model for representation of the excess Gibbs energy of polymer–electrolyte solutions is proposed. The excess Gibbs energy of a polymer–electrolyte solution is expressed as a sum of contributions of a combinatorial, a long-range and a short-range excess Gibbs energy term. The Flory–Huggins expression and the Pitzer's extension of Debye–Hückel function are used, respectively, as a combinatorial and a long-range contribution to the excess Gibbs energy. A new expression based on the local composition concept, which is the modified nonrandom two-liquid (NRTL) model, is developed to account for the short-range contribution to the excess Gibbs energy. The model provides a versatile and flexible thermodynamic framework for both correlating and predicting the phase equilibrium of electrolyte solutions, polymer solutions and complex systems containing both electrolytes and polymers. The utility of the model is demonstrated with successful representation of vapor–liquid equilibrium of several PEG or PPG–salt–H2OH2O systems at different polymer molar masses. Results are compared with those obtained from the NRTL model.