From Biomass to Efficient Lipid Recovery: Choline-Based Ionic Liquids and Microwave Extraction of Chlorella vulgaris

The sustainable extraction of microalgal lipids represents a critical step toward the valorization of biomass for nutraceutical, pharmaceutical, and biofuel applications. In this study, a microwave-assisted extraction approach using a biocompatible ionic liquid (IL), [N_{1 1 2OH 2OH}][C₆H₁₁O₂], was investigated for lipid recovery from Chlorella vulgaris. Conventional methods (Soxhlet, Folch, and Bligh & Dyer) were first evaluated for benchmarking. Optimization of microwave power, extraction time, and algae-to-IL mass ratio demonstrated that a 1:8 (m/m) ratio under 5 min and 750 W microwave pretreatment achieved the highest lipid yield, with 10.61 ± 0.39% lipids recovered from the supernatant alone. Subsequent extraction of the pretreated biomass using an environmentally benign solvent mixture (ethyl acetate/ethanol, 1:1 v/v) raised the total lipid recovery to 14.29 ± 0.75%, surpassing Soxhlet extraction with chloroform/methanol (13.04 ± 0.16%). Importantly, the IL was efficiently recovered (≈85%) and reused without significant loss of performance or structural integrity, as confirmed by NMR, DSC, and FTIR analyses. The combined process yielded up to 42.56 ± 0.64 mg FAMEs/g algae, comparable to conventional Soxhlet extraction but with superior environmental compatibility. The relative distribution of FAMEs (in weight percent, wt%) was as follows: C16:2 trans 6.05%, C16:3 trans 13.99%, C16:1 cis 1.85%, C16:1 trans 0.82%, C16:0 16.72%, C18:2 cis 13.74%, C18:3 trans + C18:1 cis + C18:2 trans 26.91%, C18:1 trans 1.67% and C18:0 3.61%. These findings demonstrate that microwave-assisted extraction with choline-based ILs offers an efficient, recyclable, and greener alternative for lipid and fatty acid recovery from microalgae.