Phase Equilibrium Study of LiBr–PEG4000/6000–H2O in a 298.2 K/308.2 K Ternary System

As an important energy storage raw material, lithium has extensive research and application value. The phase equilibrium systems of LiBr–PEG4000–H₂O and LiBr–PEG6000–H₂O at 298.2 K and LiBr–PEG4000–H₂O at 308.2 K were experimentally studied, and the effects of PEG4000/6000 at 298.2/308.2 K on the phase equilibrium were examined using the isothermal dissolution method, the refractive index standard curve method and the two-liquidus equation method. The results show that the phase diagrams for all three equilibrium systems contain six phase regions: one unsaturated phase region (L); one two-liquid phase region (2L); one two-liquid–one-solid phase region (2L + S); two one-liquid–one-solid phase region (L + S); the solid phase is LiBr; and one-liquid–two-solid region (L + 2S). The salting-out ability of PEG to LiBr decreases as the temperature increases, whereas the solubilities of PEG and LiBr increase. At the same temperature, the salting-out ability of PEG 4000/6000 to LiBr is similar. However, as the molecular weight of PEG increases, the salting-out rate tends to increase, and the solubility of PEG decreases. Additionally, the area of the unsaturated liquid region (L) also decreases.