Temperature, Polymer Molecular Weight, and Salt Effects on Phase Equilibria of PVP plus Formate Salts plus Water: Experimental Measurements, Correlations, and Thermodynamic Modeling

The phase diagram and liquid-liquid equilibrium data for poly(vinyl pyrrolidone) (PVP) of different molecular weights (10,000, 24,000, or 40,000) + potassium formate (KCHO2) or sodium formate (NaCHO2) aqueous two-phase systems were determined experimentally at different temperatures (298.15, 308.15, and 318.15 K). The phase composition and the tie-line ends were obtained by measuring and correlating the density (rho) and refractive index (n(D)) of binary and ternary mixtures within the range of 0-46.6 wt % of PVP and 0-30 wt % of used salts. Furthermore, the binodal data were fitted to both the Pirdashti and Merchuk equations. The cloud point of PVP solutions was determined in the presence of salt at different concentrations. Additionally, the influence of the polymer's molecular weight and temperature on the binodal curve, tie-line length, and slope of tie-line is discussed and compared with the literature data. Moreover, the impact of the Hofmeister series on the separation factor of formate ion was determined. Finally, the extended NRTL and modified UNIFAC-NRF were used to compute the phase compositions of the studied systems, and the adjusted parameters of the models were reported. Results show that both models provide satisfactory agreement with experimental data.

Automated summary

The study investigated the effect of different polymer molecular weights and temperatures on PVP and potassium formate or sodium formate aqueous two-phase systems, resulting in phase diagrams and liquid-liquid equilibrium data under different conditions. The phase composition and tie-line ends were determined by measuring density and refractive index, and the binodal data were fitted while the models were used to compute phase compositions.