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

Abstract

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 (σ_SD) using various empirical models, such as the ones of Han et al. for solubility data (3.8 < σ_SD × 10³ < 11) and Bancroft-Hubard for tie-line composition data (3.4 < σ_SD × 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 < σ_SD × 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.