Efficient extraction of lipids from microalgal biomass for the production of biofuels using low-cost protic ionic solvents

The valorization of lipids available in microalgal biomass supports the indispensable transition from fossil fuels to renewable energy systems such as biofuels. Ionic liquids have been long investigated for the effective extraction of those lipids, however; the complex and expensive synthesis of traditional ionic liquids (i.e., >$50/ kg) hindered their employment in commercial applications. Protic ionic liquids are a class of ionic liquids that possess a simple method of preparation and a low cost of around $1-3/kg, rendering them viable for industrial implementation. This study investigates, for the first time, the deployment of protic ionic liquids with methanol co-solvent for the extraction of lipids from Coelastrella sp. and Haematococcus sp. microalgae. The treatment process focused on the use of N,N,N-dimethyl-butylammonium hydrogen sulfate due to its high lipid extraction performance of 323.3 mg lipids/g biomass from Coelastrella sp. (81% of available lipids) compared to other screened ionic liquids. Process parameters such as temperature, time, and ionic liquid to methanol mass ratio exhibited a key impact on the lipid yield. The fatty acid profile of the extracted lipids from Coelastrella sp. demonstrated suitability to produce biofuels. The treatment has also shown selectivity in extracting lipids while leaving behind a protein/carbohydrate rich solid residue. The results obtained suggest that protic ionic liquids are promising candidates for the cost-effective and eco-friendly treatment of microalgal biomass.