Phase Equilibria Assessment and Modelling for Aqueous\nTwo-Phase Systems Composed of Poly(vinylpyrrolidone) or Poly(ethylene\nglycol)

In\nthis work, the liquid–liquid equilibria (solubility curves\nand tie-line composition) of the aqueous two-phase systems {poly(ethylene\nglycol) (PEG) with 2000 g·mol<sup>–1</sup> or poly(vinylpyrrolidone)\n(PVP) with 10,000 or 29,000 g·mol<sup>–1</sup> (1) + NaKTartrate\n(2) + water (3)} were determined at 298.15 K and 0.1 MPa. The solubility\ncurves, obtained following the “cloud-point” method,\nwere described with low standard deviations in mass fraction basis\n(σ<sub>w</sub>) using the empirical correlations of Merchuk <i>et al.</i> (3.03 < σ<sub>w</sub> · 10<sup>3</sup> < 11.0), Hu <i>et al.</i> (2.68 < σ<sub>w</sub> ·10<sup>3</sup> < 15.0), and Han <i>et al.</i> (3.47 < σ<sub>w</sub> · 10<sup>3</sup> < 5.21).\nNext, the determination of tie-line composition was achieved using\nthird-degree polynomials of liquid density (ρ) and electrical\nconductivity (κ), and the obtained data were correlated using\nthe empirical models of Othmer–Tobias (0.016 < σ<sub>w</sub> < 0.19) and Bancroft–Hubard (0.012 < σ<sub>w</sub> < 0.23). Moreover, it was observed that longer polymer\nchains induced larger immiscible zones for both PEG and PVP and that\nthe latter was more soluble in aqueous solutions of NaKTartrate due\nto the increased polarity of its monomers. Finally, the nonrandom\ntwo-liquid model was successfully used to describe tie-line composition,\nyielding low standard deviations in mole fraction basis (8.36 ·\n10<sup>–4</sup> < σ<sub>x</sub> < 5.02 · 10<sup>–2</sup>) while considering a fixed value of the nonrandomness\nfactor (α = 0.3333).