(399c) Hydrophobic Deep Eutectic Solvents: Their Discovery and Design for Separations

In 2003 a new innovative category of solvents was discovered, namely deep eutectic solvents (DESs).^[1] DESs are stated as the next generation of solvents, overcoming most of the disadvantages of ionic liquids (ILs).^[2] These advantages of DESs are a simple preparation of the solvent by mixing the two components of the DES and the ability to produce sustainable solvents by the choice of components.

The first DESs presented in literature were all produced from hydrophilic components. In 2015 a number of us reported, for the first time, the preparation of hydrophobic DESs by combining decanoic acid with quaternary ammonium salts.^[3] Their hydrophobicity was tested via measuring the amount of quaternary ammonium salt that leached to the water phase in combination with the water uptake of the DES.

The application tested upon the discovery of hydrophobic DESs was their use for the removal of volatile fatty acids from water.^[3]All the tested DESs show better extraction efficiency in comparison with the industrial standard trioctylamine.

Next to their use for the extraction of volatile fatty acids from water, hydrophobic DESs were applied for the removal of metal ions from water.^[4] Transition metal ions could be extracted with high distribution coefficients (D), higher than 0.99, while alkali metal ions only show low to moderate D. The extraction of Co²⁺ from water was used as a model system to investigate the variation of metal concentration, the solvent-to-feed ratio and an investigation into the extraction time. The results show that with an increase of the initial concentration of Co²⁺, the D drops to approximately 0.83. A D of 0.80 was measured when the solvent-to-feed ratio was decreased to 1:10. The results into the extraction time showed that within 5 s 99% of the Co²⁺could be removed.

Another application tested with hydrophobic DESs for the first time, is their use for the capture of carbon dioxide (CO₂). To the best of our knowledge, the results that will be shown report the highest solubilities in DESs measured until now. The solubilities are even similar to the best ones measured in ILs.

Finally, the first results on the formation and use of hydrophobic DESs to form DES-H₂O emulsions, including an application, will also be shown.

References

[1] A. P. Abbott, G. Capper, D. L. Davies, R. K. Rasheed, and V. Tambyrajah, Chemical Communications, 2003, 70–71.

[2] M. Francisco, A. van den Bruinhorst, and M. C. Kroon, Angew. Chem. Int. Ed., 2013, 52, 3074–85.

[3] D. J. G. P. van Osch, L. F. Zubeir, A. van den Bruinhorst, M. A. A. Rocha, and M. C. Kroon, Green Chemistry, 2015, 17, 4518–4521.

[4] D. J. G. P. van Osch, D. Parmentier, C. H. J. T. Dietz, A. van den Bruinhorst, R. Tuinier, and M. C. Kroon, Chemical Communications, 2016, 52, 11987–11990.