Optimization of biodiesel production from wet microalgal biomass by direct transesterification using the surface response methodology

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 degrees 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. (C) 2018 Elsevier Ltd. All rights reserved.