Solid-Liquid Equilibria of KCl in Polyethylene Glycol 6000-H2O Mixed Solvent at 288.2, 298.2, and 308.2 K: Experiment and Correlation

The present study investigates the measurement of the phase equilibria of ternary systems KCl-PEG6000(PEG with molecular weight 6000)-H2O at 288.2, 298.2 and 308.2 K. All the experimental data concluding the solubility of KCl in PEG6000-H2O mixed solvents, corresponding density, and refractive index were determined. According to the results, the phase diagrams at 288.2, 298.2, and 308.2 K are divided into the three parts of regions: unsaturated homogeneous liquid (L), one liquid and one solid KCl (L+S), one liquid and two solids KCl and PEG6000 (L+25); the area of (L+ 2S) decreases with an increase of temperature, while the areas of (L) and (L+S) increase with an increase of temperature. With an increment of PEG6000 in mixed solvents, the solubilities of KCl and the density decreased; inversely, the refractive index increased at three temperatures. Comparing the diagrams of KCI-PEG1000/4000/6000-H2O at 288.2, 298.2, and 308.2 K, the sizes of regions of (L) and (L+S) decreased and that of (L+25) increased with the increase of the molecular weight of PEG. A modified Pitzer model and Pitzer activity coefficient model were applied to simulate the equilibrium thermodynamics of the KCl-PEG6000-H2O system at 288.2, 298.2, and 308.2 K. Comparing the experimental data and calculated dada, the thermodynamic models can give precise results with little error.