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

Abstract

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+2S); 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 KCl–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+2S) 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.