Production of biodiesel from waste cooking oil using simultaneous esterification and transesterification process: an optimization study based on response surface methodology

Waste cooking oil (WCO) is an abundant, low-cost feedstock for biodiesel, but its high free fatty acid (FFA) content challenges conventional base-catalyzed transesterification, often causing soap formation and low yield. This study investigates simultaneous esterification–transesterification of WCO to simplify the process and reduce cost. Response Surface Methodology (RSM) was applied to assess key variables - methanol-to-oil molar ratio, catalyst concentration, temperature, and reaction time - on biodiesel ester content. Optimal conditions were identified at a 4:1 methanol-to-oil ratio, 0.75 wt.% KOH, 65°C, and 60 minutes, yielding biodiesel with >96.5% ester content, meeting EN 14214 standards. These results confirm the feasibility of the integrated process and provide insights for efficient biodiesel production from high-FFA feedstocks.