Development of cost-effective biodiesel from microalgae using protic ionic liquids
There are still constraints to algae-sourced biodiesel commercialization owing to the high cost and energy consumption of biomass cultivation and lipid extraction. The use of “low-cost” protic ILs based on tetramethylguanidinium and 1,8-diazabicyclo[5.4.0]undec-7-ene cations (some of them generated in situ by reaction of the corresponding bases with CO2 in the presence of methanol) for lipid extraction was assessed using Scenedesmus obliquus and compared to conventional methods. High extraction yields (up to 88% compared to conventional solvents, hexane–methanol) were obtained in most of the investigated ILs using wet microalgae (85% water). Furthermore, [HDBU][MeOCO2/HCO3] and [HTMG][MeOCO2/HCO3] resulted in the direct isolation of fatty acid methyl esters ((FAMEs)-biodiesel), formed in situ through transesterification/esterification reactions.