Liquid–Liquid Equilibrium and Physical Properties of Aqueous Mixtures of Poly(ethylene glycol) with Zinc Sulfate at Different pH Values: Experiment, Correlation, and Thermodynamic Modeling

The current study measured liquid–liquid equilibrium data for poly(ethylene glycol) (PEG) 1500 + zinc sulfate + water at 298.15 K and in various pH values (2.54, 3.57, and 4.70). Accordingly, the binodal curve was fitted to the Merchuk equation, and the tie-line compositions were fitted to the equations of Othmer–Tobias and Bancroft. Moreover, the study measured the refractive indices and densities of several homogeneous binary and ternary solutions. These solutions are used for calibration within a range of 0–35 mass % of PEG and 0–30 mass % of ZnSO 4 . Then, the viscosities, densities, electrical conductivities, and refractive indices of binary (PEG 1500 + water; zinc sulfate + water) and ternary (PEG 1500 + zinc sulfate + water) systems were measured and correlated. According to the results obtained from the density data, there was a linear variation of the polymer and the salt mass fractions. The viscosity data of PEG 1500 solutions were correlated as a function of the mass fractions by using a nonlinear equation. Also, the effects of the tie line lengths on the densities and viscosities of the aqueous two-phase systems were represented. Finally, the extended UNIQUAC, UNIFAC, and modified UNIQUAC-FV are used to predict the phase equilibria of mention systems. The fitted binary interaction parameters of the model were reported.