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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. [ABSTRACT FROM AUTHOR]

The production of fatty acid methyl esters (FAMEs, biodiesel) was optimized from wet Nannochloropsis gaditana microalgal biomass (81.8 wt% water and 28.1 wt% saponifiable lipids, SLs, from the dry biomass). FAME production was carried out by direct acid-catalyzed methylation of the SLs from the microalgal biomass and FAME extraction with hexane. A three-variable, three-level Box-Behnken design (BBD) was applied to optimize the sulphuric acid (catalyst) concentration, the methanol/SL ratio and the hexane/SL ratio. The best FAME yield was obtained with a methanol/SL ratio of 254 mL/g, a sulphuric acid concentration of 3.7% (v/v) and a hexane/SL ratio of 107.7 mL/g at 100 °C and for 105 min. Under these conditions, 100% of the SLs were transformed into FAMEs. Finally, the FAME purity was increased from 78.7 to 86.8 wt% using an adsorption treatment with bentonite. [ABSTRACT FROM AUTHOR]