Study on the Phase Equilibrium of the PEG4000/8000 + LiBr + H2O Ternary System at 318.15 K

In this article, the phase equilibrium of a ternary PEG4000/8000 (polyethylene glycol) + LiBr + H2O system was explored at a temperature of 318.15 K. The compositions of the solid‒liquid phase and the two-liquid phase of this ternary system were determined via the isothermal dissolution equilibrium method, refractive index standard curve method, cloud point method, and empirical equation method. On the basis of the experimental data, phase diagrams were generated. The results indicated that both phase diagrams can be divided into solid‒liquid phase regions and liquid phase regions. The solid‒liquid phase regions include a region with one liquid phase and one solid phase (L + S), a region with one liquid phase and two solid phases (L + 2S), and a region with two liquid phases and one solid phase (2L + S). The liquid phase regions include an unsaturated liquid phase region (L) and a two-liquid phase region (2L). In the liquid phase region of the phase diagram, the unsaturated liquid phase region is the largest. In the solid‒liquid phase region of the phase diagram, the region with one liquid phase and one solid phase is the largest. With increasing relative molecular weight of polyethylene glycol, the solubility of the lithium bromide salt solution decreases.