Elucidating the Fate of Organic Contaminants in Highly Basic Environments for Temperature Swing Solvent Extraction...

Temperature swing solvent extraction (TSSE) has been shown to effectively desalinate hypersaline brines. However, the fate of organic contaminants during TSSE remains poorly understood. This study elucidates the key physicochemical phenomena governing the equilibrium distribution of organic contaminants in biphasic solvent-aqueous systems relevant to TSSE. Distribution coefficients of organic analytes spanning roughly five orders of magnitude of hydrophobicity were systematically evaluated across five thermomorphic hydrophilicity amine solvents, at extraction and disengagement temperatures, and in hypersaline environments. While hydrophobicity has a principal role in governing distribution, acid-base interactions between the solvent and the contaminant were also found to be significant. Temperature typically has a minimal effect on conventional partitioning behavior but exerts a substantial influence in TSSE due to the thermal sensitivity of solvent solubility in water. Brine salinity does not uniformly affect distribution until the aqueous phases approach saturation, at which point the analytes are salted-out of the brine. A multiple linear regression analysis using K_OW, pK_a's, and solvent solubility to model distribution achieved high accuracy (R² = 0.93), offering a practical framework for a priori determination of contaminant fate. These findings provide key mechanistic insights and design tools for TSSE solvent selection and process engineering.