Biodiesel production from wet microalgal biomass by direct transesterification

•A simple procedure for obtaining biodiesel from wet microalgal biomass was developed.•Biodiesel was formed by direct acid catalyzed transesterification of SLs in the biomass.•100% of microalgal saponifiable lipids (SLs) were transformed and extracted as FAMEs.•FAME purity was increased from 75 to 83 wt% by adsorption with bentonite.•Influence of methanol/SL ratio, catalyst concentration, temperature and reaction time was studied.

The aim of this work was to optimize the production of fatty acid methyl esters (FAMEs, biodiesel) from marine Nannochloropsis gaditana wet microalgal biomass (25 wt% dry biomass and 11.1 wt% saponifiable lipids, SLs, of dry biomass) by direct acid catalyzed methylation of SLs in the microagal biomass and extraction of FAMEs with hexane. The best FAME yield was attainted with a methanol/SL ratio of 171.1 mL/g, an acetyl chloride (catalyst) concentration of 5% (v/v), 100 °C and a reaction time of 105 min. In these conditions 100% of SLs were transformed to FAMEs. Similar yields were obtained at lower temperatures and higher reaction times. The pretreatment of wet biomass by homogenization did not improve the above results. Finally, the FAME purity was increased from 74.5 to 82.7 wt% by a treatment of adsorption with bentonite.