Development of cost-effective biodiesel from microalgae using protic ionic liquids

Abstract

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.