Solid–Liquid and Liquid–Liquid Equilibria for the System Composed of Cesium Chloride, Polyethylene Glycol (PEG1000/4000/6000) and Water at 288.15 and 308.15 K

The phase equilibria for CsCl in three polyethylene glycols (PEG) with molecular weights of 1000, 4000, 6000 g⋅mol−1 and water (H2O) mixed solvent were investigated at 288.15 and 308.15 K. The isothermal dissolution equilibrium method was applied for the solid–liquid equilibria experiments; the turbidimetric method was used for the liquid–liquid equilibria experiments. Results show that there is only solid–liquid equilibrium for the ternary system CsCl–PEG1000–H2O at 288.15 K, both solid–liquid and liquid–liquid equilibria coexist in ternary systems CsCl–PEG1000–H2O at 308.15 K and CsCl–PEG4000/6000–H2O at 288.15 and 308.15 K. For liquid–liquid equilibrium, the binodal curve and compositions of the tie-lines were obtained experimentally, and the effect of temperature and molecular weight of PEG on liquid–liquid equilibrium was discussed. It shows that the liquid–liquid equilibrium formed easily at higher temperature and larger molecular weight of PEG. Moreover, three nonlinear expressions were applied to correlate the binodal curve, and the experimental values of tie-line were correlated with a good agreement by using Othmer–Tobias, Bancroft and NRTL models.