Lipid Extraction from Various Species of Wet Microalgae Using Liquefied Ammonia

Energy-intensive drying or cell-disruption processes in lipid extraction procedures reduce efficiency and increase the cost involved in producing biofuels from microalgae. Recently, a simple method was proposed for extracting lipids directly from microalgae by utilizing liquefied ammonia (NH₃(l)), which eliminates the energy-intensive processes. In the present study, the versatility of NH₃(l) extraction was assessed by applying it to six microalgal species with different contents of lipids. This method directly separated 25.6–70.6 wt % of the dry weight of the sample as crude extract. The total fatty acid methyl ester yield was 5.5–17.4 wt %, comparable to or exceeding that obtained by traditional approaches. The crude extract was highly enriched with valuable C12–C24 fatty acids. Furthermore, scanning electron microscopy showed that after NH₃(l) extraction, the cellular structure of the residue was preserved. These results suggest that employing the NH₃(l) extraction method enhances applicability and consequently increases the process value by separating components into extract and useful residual solids.