Eutectic solvents with tuneable hydrophobicity: lipid dissolution and recovery

Despite the promising advantages of eutectic solvents, the application of these solvents as an extraction solvent is still limited due to the challenging product recovery. Previously, it was reported that lipids could be recovered from a hydrophobic eutectic solvent with the principle of switchable hydrophobicity. However, this method still involves additional chemicals, such as polymeric amines, water, and CO₂, which need to be removed later. In this study, we proposed a different approach by shifting the hydrophobicity spectrum of a semi-hydrophobic solvent. Made of hydrophilic imidazole and hydrophobic hexanoic acid, this combination showed tuneable hydrophobicity when the composition was changed, shown by the change of dipolarity (π*) scale from solvatochromic analysis. At low imidazole content, the solvent was able to dissolve sunflower oil and algae oil, whereas, at high imidazole content, the solvent showed high affinity towards water. By adding imidazole to the solution of oil and the solvent, a phase split was induced between the oil-rich upper phase and the solvent-rich lower phase. With this approach, ∼75% of recovery efficiency was achieved for the two oils, with the purity of ∼100% for sunflower oil and 86% for algae oil.