Comparative analysis of different catalysts in conventional and In-Situ transesterification for enhanced biodiesel yield and quality from Scenedesmus obliquus

Abstract This study compares a less toxic hexane-based extraction with the modified Bligh-Dyer method for lipid extraction from dried Scenedesmus obliquus biomass, focusing on FAME yield and biodiesel quality. Additionally, various catalyst combinations were tested under consistent reaction conditions across both conventional methods and one- and two-step in-situ processes. The findings indicate that hexane-based extraction achieved a 17.7% lipid recovery, marking an 18% decrease compared to the Bligh-Dyer method. This reduction was reflected in the final FAME yield, with hexane extraction producing 23% less FAME than the chloroform-based method. However, hexane extraction contributed to a higher cetane number (CN:69.2) with increased saturated fatty acid ratios, improving the ignition and combustion properties of the resulting biodiesel. Across transesterification methods, FAME yields ranged from 14.0% to 30.6%. While NaOH as a single catalyst resulted in the lowest FAME content (C1: 12.4%; IS1: 14.1%) in both conventional and in-situ transesterifications, single-step acid-catalyzed reactions using HCl (IS2: 30.3 wt%) and H₂SO₄ (IS3: 30.1 wt%), along with two-step reactions involving an acid catalyst followed by NaOH (IS6: 28 wt%), demonstrated significant potential for enhancing efficiency in in-situ transesterifications. These findings highlight in-situ transesterification as a viable alternative to conventional methods, with the choice of catalyst and reaction sequence playing a key role in maximizing yield and fuel quality. By potentially minimizing solvent and chemical use, in in-situ methods offer a more sustainable and cost-effective pathway for biodiesel production.