Phase Equilibria Assessment and Modelling for Aqueous Two-Phase Systems Composed of Poly(vinylpyrrolidone) or Poly(ethylene glycol)

In this work, the liquid–liquid equilibria (solubility curves and tie-line composition) of the aqueous two-phase systems {poly(ethylene glycol) (PEG) with 2000 g·mol^–1 or poly(vinylpyrrolidone) (PVP) with 10,000 or 29,000 g·mol^–1 (1) + NaKTartrate (2) + water (3)} were determined at 298.15 K and 0.1 MPa. The solubility curves, obtained following the “cloud-point” method, were described with low standard deviations in mass fraction basis (σ_w) using the empirical correlations of Merchuk et al. (3.03 < σ_w · 10³ < 11.0), Hu et al. (2.68 < σ_w ·10³ < 15.0), and Han et al. (3.47 < σ_w · 10³ < 5.21). Next, the determination of tie-line composition was achieved using third-degree polynomials of liquid density (ρ) and electrical conductivity (κ), and the obtained data were correlated using the empirical models of Othmer–Tobias (0.016 < σ_w < 0.19) and Bancroft–Hubard (0.012 < σ_w < 0.23). Moreover, it was observed that longer polymer chains induced larger immiscible zones for both PEG and PVP and that the latter was more soluble in aqueous solutions of NaKTartrate due to the increased polarity of its monomers. Finally, the nonrandom two-liquid model was successfully used to describe tie-line composition, yielding low standard deviations in mole fraction basis (8.36 · 10^–4 < σ_x < 5.02 · 10^–2) while considering a fixed value of the nonrandomness factor (α = 0.3333).