Aqueous Two-Phase Systems: A Correlation Analysis

Aqueous two-phase systems involve a limited region of a complicated phase diagram usually containing solid phases. Studies regarding these systems generally focus on the liquid–liquid region because it provides a suitable medium for liquid extraction of biomolecules and metal ions. In this work, the whole phase diagram was determined for ternary mixtures of water, dipotassium tartrate, and ethanol or 1-propanol at several temperatures and atmospheric pressure. In addition, density and refractive index of a diluted region of the mixtures were measured for compositional analysis of samples. Different regions were found involving solid and liquid phases, or the anhydrous and hemihydrated salt. The correlation of equilibrium data within the different regions was carried out with the nonrandom two-liquid model. To that aim, some restrictions were required to ensure the miscibility of the binary subsystem with water and alcohol. Individual correlation at each temperature and simultaneous correlation of data at all temperatures led to adequate phase diagram representation and low deviations. Despite the use of temperature-dependent parameters, results were slightly worse in the latter case (around or below 1%). The liquid–liquid equilibrium (LLE) data alone were also correlated, obtaining similar deviations to those obtained considering all equilibrium data. In all cases deviations found with 1-propanol are higher (in the range of 3–4%) due to the proximity of the LLE region to the miscible water + 1-propanol binary subsystem. The correlation of exclusive LLE data is easier from the point of view of computation but leads to model parameters with limited utility.The authors are grateful to Xunta de Galicia for support through Project ED431B 2017/023 and the Galician Network of Ionic Liquids (ED431D 2017/06) and the CRETUS Strategic Partnership (ED431E 2018/01), cofunded by the European Regional Development Fund