Optimization of in‐situ transesterification of Scenedesmus acuminatus biomass for ethyl ester synthesis: Effects of temperature, solvent, and agitation on biodiesel yield and composition

This work investigates the optimization of in‐situ transesterification of Scenedesmus acuminatus biomass for the synthesis of ethyl esters, emphasizing the effects of temperature, solvent type, reaction time, and agitation on biodiesel yield and composition. The reactions were carried out using ethanol and hydrochloric acid as the catalytic system, with n‐hexane and chloroform as co‐solvents. The influence of each parameter was systematically evaluated to determine optimal conversion conditions. The maximum yield, 78.6 mg ethyl esters g −1 dry biomass, was obtained at 60°C after 90 min using n‐hexane under static conditions. The effect of agitation was solvent‐dependent. While it did not significantly enhance yields in the n‐hexane system, agitation improved both the final yield and reaction kinetics when chloroform was used as the co‐solvent. Chromatographic analysis revealed that the predominant ethyl esters were C16:0, C16:1, C18:2, and C18:3, indicating a predominance of unsaturated fatty acids. This composition is comparable to that of conventional feedstocks such as soybean and corn oils, suggesting favourable cold‐flow properties but lower oxidative stability. The results demonstrate that ethanol‐based in‐situ transesterification of S. acuminatus provides a sustainable, simplified, and high‐yield route for biodiesel production, reducing process steps and solvent demand relative to conventional extraction methods, reducing process steps by eliminating the need for a separate lipid extraction stage and lowering solvent demand through direct conversion within the biomass, as supported by the high yields achieved with a single reaction mixture and consistent with the efficiencies reported for similar in‐situ systems.