Efficient extraction of lipids from magnetically separated microalgae using ionic liquids and their transesterification to biodiesel

In this work, the efficiency of extracting lipids from magnetically separated microalgae using ionic liquids (ILs) with subsequent recycling of ILs and magnetic nanoparticles (MNPs) was fully demonstrated for the first time. MNPs were used to separate microalgae from the aqueous phase at a separation efficiency of 99%. The separated microalgae/MNPs slurry was subjected to IL treatment to lyse the microalgae cell wall thereby exposing lipids for efficient solvent extraction using hexane. The lysed cells were mixed with hexane for 2 h to extract the lipids. The extraction efficiency of 99% was achieved when ILs/hexane was used compared to only 5% with hexane only. The extracted lipids were analyzed using gas chromatography-mass spectrometry (GC–MS), Fourier-transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance (¹H NMR). These then were transesterified to biodiesel. The MNPs were recovered from cell biomass by sonicating in de-ionized (DI) water and recycled via magnetic separation to harvest more microalgae at a separation efficiency of 96%. Thermogravimetric analysis (TGA) of recycled MNPs confirmed the absence of algal biomass attached to the particles. The ILs were also recycled and analyzed using ¹H NMR, mass spectrometry, and FT-IR analysis. All these confirmed the absence of structural alteration in the recycled ILs. Magnetic separation can potentially lower the cost of microalgae harvesting and IL extraction can lower the cost of lipid extraction by 30–50%. A combination of the two processes implies that the extraction of lipids from magnetically separated microalgae could potentially lower the processing cost of biofuels and essential compounds. Recycling MNPs and ILs and extraction of essential compounds alongside microalgae lipids could further lower the processing costs potentially culminating in a lower cost of biofuels compared to petroleum-derived fuels.