Phase equilibria measurements and correlation of aqueous solvent of PEG4000 with rubidium chloride at (288.15, 298.15, and 308.15) K

Abstract

The phase equilibria of ternary system polyethylene glycol with molar mass of 4000 g∙mol−1(PEG 4000), rubidium chloride (RbCl) and water (H2O) were determined at T=(288.15, 298.15, 308.15) K. Results show that there is only solid-liquid equilibrium (SLE) relationship in the system at 288.15 K, both of solid-liquid equilibrium (SLE) and liquid-liquid equilibrium (LLE) are found in the system at 298.15 K and 308.15 K. The phase diagram at 288.15 K was divided into 3 areas including the region L (unsaturated liquid phase), the region L + S (saturated solutions with a solid phase RbCl) and the region L + 2S (saturated liquid phase with two solid phases of PEG4000 and RbCl) and the solubility of RbCl decreased with PEG4000 increasing. The complete phase diagrams at 298.15 K and 308.15 K including 6 areas (L (unsaturated liquid phase), 2L (aqueous two-phase), L + 2S (saturated liquid phase with two solid phases of PEG4000 and RbCl), 2L + S (two liquids with one solid phase RbCl), and 2 areas of L + S (saturated solutions with one solid phase RbCl) were constructed. Furthermore, the binodal curves, compositions, length of the tie-line (TLL) and slope of tie-line (STL) were obtained for these mixed solvent systems at 298.15 K and 308.15 K. Three nonlinear expressions, proposed by Mistry, Hu, and Jayapal, were used to fit the binodal curves. The data of tie-line were correlated by using Othmer-Tobias equations, Bancroft equations, Hand equation, Bachman equations and the Chen-NRTL model. All the presented results, both the experimental and calculated data, show convincing values.