Semi-hydrophobic eutectic solvents: Sequential extraction of lipids, proteins & carbohydrates, recycling, scalability of microalga Nannochloropsis oceanica

Semi-hydrophobic eutectic solvents (ES) possess a great potential as lipid extraction solvent from untreated microalgae. However, the low vapor pressure of these solvents and the unknown effects on other biomolecules (e.g., proteins, carbohydrates) limit their application in microalgae biorefinery. In this work, recovery of the extracted lipids was performed by addition of antisolvents and the affecting parameters (i.e., antisolvent type, amount, temperature, ES imidazole content) were studied. The highest recovery was obtained with methanol addition to ES with 15 mol% imidazole at -20 °C, where lipid crystals were formed consisting mainly of saturated fatty acids. The remaining soluble lipids under the same condition were found to be fractions with mono- and poly-unsaturated fatty acids. Furthermore, based on the iterative extractions, the regenerated solvents could create sufficient driving force for lipid extraction despite the lipid accumulation. In addition, a scale-up study of lipid extraction and solvent recycling was performed (2 mL vs 500 mL), whereby the larger scale also showed a good performance. Finally, protein and carbohydrate isolation from the defatted biomass was feasible, but the proposed ES process was not sufficiently mild to maintain native proteins. On the other hand, opportunities are discussed to create new functionalities for proteins and carbohydrates so that a multiproduct biorefinery is feasible for this ES.