Deep Eutectic Solvents in Liquid-Liquid Extraction Processes
Summary
Deep eutectic solvents (DESs) represent a class of designer liquids formed by combining two or more components—typically a hydrogen bond donor and a hydrogen bond acceptor—at specific molar ratios to achieve a eutectic mixture with a melting point significantly lower than that of the individual constituents. These solvents have attracted considerable interest in liquid–liquid extraction owing to their low toxicity, negligible vapour pressure, ease of preparation and cost-effectiveness. By tailoring the nature and ratio of their components, DESs can be tuned to exhibit desired polarity, viscosity and hydrogen-bonding capability, enabling selective partitioning of target solutes such as aromatic hydrocarbons, heterocycles, metal ions and bioactive compounds. In practice, DESs have been applied to the separation of close-boiling azeotropes, removal of nitrogen and sulphur contaminants from fuel streams, recovery of valuable phytochemicals and denitrification of hydrocarbon fractions. Thermodynamic modelling and spectroscopic studies reveal that solute–solvent interactions in DESs are governed by hydrogen bonding, π–π stacking and electrostatic forces, which can be optimised to enhance partition coefficients and selectivity. Advances in process simulation, solvent regeneration and scale-up considerations underscore the potential of DESs to replace conventional organic solvents and ionic liquids in industrial extraction operations, offering a more sustainable alternative without compromising performance.
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Building on predictive design, a recent evaluation of the COSMO-RS thermodynamic model has demonstrated its capability to screen DESs for liquid–liquid equilibrium in binary and ternary systems, achieving average deviations below 10 % for salt-free solvents and highlighting areas for refinement in salt-based mixtures. In application-driven work, a systematic study of DESs for toluene/1-hexene separation identified three highly selective formulations, validated by experimental phase-equilibrium data and ^1H NMR elucidation of hydrogen-bond networks. As a comprehensive perspective, a critical review of eutectic solvents, terpenes and terpenoids has surveyed advances in solvent design, extractive performance, solvent recovery and process modelling, emphasising the environmental and economic benefits of DES-based extraction compared with traditional organic and ionic solvents.
Deep Eutectic Solvents in Liquid-Liquid Extraction Processes publication trend
The graph below shows the total number of articles in deep eutectic solvents in liquid-liquid extraction processes across all publications each year (not limited to Nature Index journals).
Technical terms
Deep eutectic solvent (DES): A eutectic mixture of two or more compounds whose combined melting point is lower than that of each individual component, formed via hydrogen bonding.
Liquid–liquid extraction: A separation technique in which a solute is partitioned between two immiscible liquid phases based on differential solubility.
Partition coefficient: The ratio of a solute’s concentration in the extractant phase to its concentration in the raffinate phase at equilibrium.
Selectivity: A measure of a solvent’s preference for extracting one component over another, defined as the ratio of partition coefficients.
COSMO-RS: A predictive thermodynamic model that estimates chemical potentials and phase equilibria based on quantum-chemical surface charge densities.
References
- A Review of the Use of Eutectic Solvents, Terpenes and Terpenoids in Liquid–liquid Extraction Processes. Processes (2020).
- Separation of Benzene-Cyclohexane Azeotropes Via Extractive Distillation Using Deep Eutectic Solvents as Entrainers. Processes (2021).
- DEEP EUTECTIC SOLVENTS BASED ON BETAINE AND PROPYLENE GLYCOL AS POTENTIAL DENITRIFICATION AGENTS: A LIQUID-LIQUID EQUILIBRIUM STUDY. Brazilian Journal of Chemical Engineering (2019).
- Performance of p-Toluenesulfonic Acid–Based Deep Eutectic Solvent in Denitrogenation: Computational Screening and Experimental Validation. Molecules (2020).
- Assessment of COSMO-RS for Predicting Liquid–Liquid Equilibrium in Systems Containing Deep Eutectic Solvents. Industrial & Engineering Chemistry Research (2024).
- Deep Eutectic Solvents for the Separation of Toluene/1-Hexene via Liquid–Liquid Extraction. Separations (2022).
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