Temperature swing solvent extraction (TSSE) is a novel desalination method for hypersaline water. In TSSE, a solvent that has temperature-switchable miscibility with water is used to absorb water, but not salt, from brine. The water-laden solvent is separated and heated, causing it to split into a water-rich and solvent-rich phase. TSSE shows great promise for desalination: since it is membrane-less and non-evaporative, it avoids many downsides of traditional desalination techniques. To date, the leading TSSE solvents have been aliphatic amines. However, the fundamental mechanisms behind TSSE are poorly understood. For example, some amines are more water-miscible than others, and some reject salt more completely than others. Understanding the interplay between these two factors and other attributes is vitally important to selecting solvents, finding proper operating conditions, and creating second-generation desalination solvents. To date, knowledge of these and other attributes is mainly phenomenological, with little insight into the molecular-level chemical interactions that drive TSSE. In this work, we present a combined x-ray scattering and molecular dynamics approach to study TSSE solvents at the molecular scale. Using this approach, we investigate diisopropylamine, the leading TSSE solvent, in mixtures with water at different temperatures and concentrations. The approach presents qualitative and quantitative insights about the mixture as it nears the de-mixing temperature, with broad implications for TSSE and other solvent-based water treatment solutions.

Molecular-level insights into temperature-swing solvent extraction desalination: a combined x-ray scattering and molecular dynamics approach

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ACS Fall 2022

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