Hydrophobic deep eutectic solvents consisting of decanoic acid and various quaternary ammonium salts are presented and evaluated as extractants.

The solubility of CO₂ in hydrophobic deep eutectic solvents (DESs) has been measured for the first time. Six different hydrophobic DESs are studied in the temperature range from 298 to 323 K and at CO₂ pressures up to 2 MPa. The results are evaluated by comparing the solubility data with existing hydrophilic DESs and currently applied physical solvents and fluorinated ionic liquids. The DESs are prepared by mixing decanoic acid with a quaternary ammonium salt with different halide anions and alkyl chain lengths. The measured CO₂ solubilities are similar to those found in renowned fluorinated ILs, while the heats of CO₂ absorption are in the range of nonpolar solvents. The presented DESs show good potential to be used as CO₂ capture agents.