Phase equilibria insights into amine-water-NaCl interactions in liquid-liquid biphasic systems for temperature swing solvent extraction desalination

• Published in: Desalination 2023-02, Vol.548, p.116259, Article 116259
• Main Authors: Shah, Kinnari M., Dach, Elizabeth, Winton, Robert, Fan, Hanqing, Yip, Ngai Yin
• Format: Article
• Language: English
• Subjects: Hypersaline brines; Liquid-liquid biphasic systems; Partitioning behavior; Phase equilibria; Temperature swing solvent extraction
• ISSN: 0011-9164; 1873-4464
• DOI: 10.1016/j.desal.2022.116259

This study sheds light on the fundamental phenomena governing temperature swing solvent extraction (TSSE) desalination by investigating the influence of temperature on the equilibrium partitioning of water, salt, and solvent. The distribution of components across a range of temperatures and feed salinities typical to TSSE hypersaline desalination was examined for two amine solvents. A tradeoff between selectivity and productivity is established, providing a novel framework to assess TSSE performance. Salt was shown to be a key determinant in equilibrium partitioning by diminishing the ability of the solvent to extract water at lowered temperatures and salting-out amines from the aqueous phase. Na+ and Cl− ions consistently partition into the solvent phase in equimolar ratios. Analysis further reveals a linear correlation between the natural logarithms of salt activity coefficients and water contents of the organic phase. The two collaborating results suggest that water-ion interactions are more important than amine-ion interactions in the organic phase, resolving a critical gap in the understanding of salt transport. The findings of this study can provide important insights for the informed development of temperature swing solvent extraction for hypersaline desalination. [Display omitted] •Effect of temperature on equilibrium partitioning in TSSE is studied.•A tradeoff between productivity and selectivity is observed.•Transport of Na+ and Cl− ions into the solvent phase is equimolar.•Salt activity is strongly correlated with water content of organic phase.•Ion interactions with water are more important than with amine in the organic phase.