Phase equilibria of ternary system RbCl - polyethylene glycol (PEG6000) - H2O at T = (288.2, 298.2, and 308.2) K: Measurement, correlation, and thermodynamic modeling

The phase equilibria relationship of the system RbCl-PEG6000-H₂O were investigated at temperatures of 288.2, 298.2, and 308.2 K, the compositions of solid-liquid equilibria(SLE) and liquid-liquid equilibria(LLE) were determined. The complete phase diagrams, binodal curve diagrams, and tie-line diagrams were all plotted. Results show that both solid-liquid equilibria and liquid-liquid equilibria relationships at each studied temperature. The complete phase diagrams at 288.2 K, 298.2 K and 308.2 K consist of six phase regions: unsaturated liquid region (L), two saturated solutions with one solid phase of RbCl (L + S), one saturated liquid phase with two solid phases of PEG6000 and RbCl (2S + L), an aqueous two-phase region (2L), and a region with two liquids and one solid phase of RbCl (2L + S). With the increase in temperature, the layering ability of the aqueous two-phase system increases, and both regions (2L) and (2L + S) increase. The binodal curves were fitted using the nonlinear equations proposed by Mistry, Hu, and Jayapal. Additionally, the tie-line data were correlated with the Othmer-Tobias, Bancroft, Hand, and Bachman equations. The liquid-liquid equilibria at 288.2 K, 298.2 K and 308.2 K were calculated using the NRTL model. The findings confirm that the experimental and calculated values are in close agreement, demonstrating the model’s effectiveness in representing the system’s behavior.