Measurements and Thermodynamic Modeling of Solid-Liquid Equilibria Data for the Ternary (KCl+PEG8000+H2O) System at 288.2, 298.2, and 308.2 K

The solubilities, densities and refractive indices of the ternary KCl + PEG8000 + H2O system were determined at 288.2, 298.2, and 308.2 K. In terms of phase diagrams at 288.2, 298.2, and 308.2 K, they are all made up of three areas, where the homogeneous area (L) contains unsaturated liquid, area (L + S) contains one saturated liquid and one solid (KCl), and area (L + 2S) contains one saturated liquid and two solids (KCl and PEG8000). The results of these experiments showed that with an addition of PEG8000 to the liquid, the solubility of KCl and density of the liquid phase decreased, whereas the refractive index inceased. By comparing the phase diagrams at 288.2, 298.2, and 308.2 K, it is seen that with an increase of temperature, the areas of (L) and (L + S) enlarged, whereas the area of (L + 2S) reduced. The phase diagrams of the ternary systems KCl + PEG1000/4000/6000/8000 + H2O were also compared and showed that with an increase of the molar mass of PEG, the ovedrall phase diagrams did not change although the areas of each part varied in size. Also, a modified Pitzer model was adopted as the equilibrium thermodynamics model to correlate the experimental data.