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Published January 20, 2021 | Supplemental Material
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Salt-Induced Liquid–Liquid Phase Separation: Combined Experimental and Theoretical Investigation of Water–Acetonitrile–Salt Mixtures


Salt-induced liquid–liquid phase separation in liquid mixtures is a common phenomenon in nature and in various applications, such as in separation and extraction of chemicals. Here, we present results of a systematic investigation of the phase behaviors in water–acetonitrile–salt mixtures using a combination of experiment and theory. We obtain complete ternary phase diagrams for nine representative salts in water–acetonitrile mixtures by cloud point and component analysis. We construct a thermodynamic free energy model by accounting for the nonideal mixing of the liquids, ion hydration, electrostatic interactions, and Born energy. Our theory yields phase diagrams in good agreement with the experimental data. By comparing the contributions due to the electrostatic interaction, Born energy, and hydration, we find that hydration is the main driving force for the liquid–liquid separation and is a major contributor to the specific ion effects. Our theory highlights the important role of entropy in the hydration driving force. We discuss the implications of our findings in the context of salting-out assisted liquid–liquid extraction and make suggestions for selecting salt ions to optimize the separation performance.

Additional Information

© 2021 American Chemical Society. Received 1 September 2020. Published online 8 January 2021. Y.L. and L.A. acknowledge the National Natural Science Foundation of China (Grant Nos. 21790340 and 21674113) and the Programs of Chinese Academy of Sciences (Grant No. QYZDY-SSW-SLH027) for financial support. Y.L. also acknowledges the Key Science and Technology Project of Jilin Province (Grant No. 20200504001YY) for financial support. We thank Dr. Pengfei Zhang (Donghua University) for helpful discussions, and we thank the anonymous reviewers whose comments have helped improve the presentation of our work. Author Contributions. M.L. and B.Z. contributed equally to this work. The authors declare no competing financial interest.

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August 20, 2023
October 23, 2023