Water/polyethylene glycol/sodium citrate: from the aqueous two-phase system to the complete phase diagram

Abstract

Polyethylene glycol (PEG) 6000, 10,000, or 20,000/sodium citrate Aqueous Two-Phase Systems (ATPS) were characterized at 283.2, 298.2, and 313.2 K. The compositions of the equilibrium phases were determined using an analysis procedure based on density and refractive index measurements. The complete liquid-liquid equilibrium region was obtained up to the point of solid phase precipitation, and the binodal curve was constructed from the endpoints of the experimental tie-lines. The effects of both temperature and polymer molecular weight were analyzed. Furthermore, the entire phase diagram was established using the analysis procedure based on physical property measurements, enabling experimental determination of all singular points that define the solid-liquid, solid-liquid-liquid, and solid-solid-liquid regions. Data correlation for all equilibrium compositions was carried out individually at 283.2 K, where the solid salt was present as a pentahydrate, and simultaneously at 298.2 and 313.2 K, where the salt was dihydrated, using the classical NRTL equation. The model successfully correlated all phase diagrams with standard deviations between experimental and correlated data below 1.6 wt% in all cases