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 ZnSO4. 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.