New ATPSs Containing Choline Salts and Propan-1-ol: Phase Equilibria, eNRTL Modeling, and Partitioning Studies

In this work, the liquid–liquid equilibria (LLE) of the Aqueous Two-Phase Systems (ATPSs) {propan-1-ol (1) + choline bicarbonate ([Ch][Bic]) or choline dihydrogen citrate ([Ch][H2Cit]) (2) + water (3)} were assessed at 298.15 K and 0.1 MPa. Solubility curves were estimated by the “cloud-point” method, while tie-line composition data were determined using third-degree polynomials of liquid density (ρ) and electrical conductivity (κ). The obtained LLE data were correlated with low standard deviations (σSD) using various empirical models, such as the ones of Han et al. for solubility data (3.8 < σSD × 103 < 11) and Bancroft-Hubard for tie-line composition data (3.4 < σSD × 102 < 4.6). Tie-line composition data were also described with the electrolyte-Non-Random Two-Liquid (eNRTL) model, considering the ATPSs as mixed solvent media with strong salts and obtaining low standard deviations (7.3 < σSD × 107 < 7.7). Although very successful, this modeling approach required a significant number of adjustable parameters to describe all the interacting species, which may be intensive from a computational point of view. Moreover, during thermodynamic modeling, nonrandomness factors based on calculations at the Density Functional Theory (DFT) level were applied for propan-1-ol (α = 0.1970) and water (α = 0.3333), while a fixed value was used for the choline salts (α = 0.2). Finally, to demonstrate the practical potential of these ATPSs for removing pharmaceutical pollutants from water, partition studies of salicylic acid (Sa) were conducted in these systems, attaining promising partition coefficients (2.1 ± 0.3 < K < 5.6 ± 0.9) and extraction efficiencies (53 ± 2 < E/% < 87 ± 3), specially for the system containing [Ch][H2Cit] (4.4 ± 0.5 < K < 5.6 ± 0.9) and (77 ± 2 < E/% < 87 ± 3). Moreover, a positive effect on these performance indicators was observed with growing lengths of tie-line (TLLs), for which a significant affinity exists between the target solute and propan-1-ol.