Phase diagrams for liquid–liquid equilibrium of ternary poly(ethylene glycol) + di-sodium tartrate aqueous system and vapor–liquid equilibrium of constituting binary aqueous systems at T = (298.15, 308.15, and 318.15) K: Experiment and correlation

Liquid–liquid equilibria (LLE) for the aqueous polyethylene glycol 4000 (PEG4000) + di-sodium tartrate system and the vapor–liquid equilibria (VLE) of the corresponding binary aqueous systems (i.e. PEG4000 + water and di-sodium tartrate + water) have been determined experimentally at T = (298.15, 308.15 and 318.15) K. The effects of temperature on the binodals and tie-lines for the investigated aqueous two-phase system (ATPS), as well as the water activities obtained from the VLE data for the aforementioned binary aqueous systems have been studied. Furthermore, the modified local composition segment-based NRTL and Wilson models, proposed recently by Sadeghi to describe the VLE of several aqueous polymer–salt systems, have been used for the correlation of the phase behavior of the studied systems. Good agreement was obtained with the experimental VLE data with these models. For the studied ATPS, while the successful regeneration of the experimental LLE data were demonstrated with the modified NRTL and Wilson models, especially with the unrestricted parameters, no satisfactory results were obtained for the temperatures 308.15 and 318.15 K, using the modified Wilson model with restricted parameters in which the binary model parameters between water and the segments of polymer or salt obtained from the VLE data. Results are also compared with those obtained from the extended NRTL and the extended Wilson models.