A New Magnetically Separable BaFe 2 O 4 Acid Catalyst for Sustainable Biodiesel Production: L 9 Taguchi Optimization and Robust Recyclability

The MoO3/BaFe2O4 catalyst was synthesized via a combined coprecipitation and wet impregnation approach and subsequently applied in the methyl biodiesel production from waste cooking oil (WCO). The material was characterized using surface acidity measurements, XRD, FTIR, SEM, EDS, and VSM techniques. The results confirmed: (i) the successful synthesis of barium ferrite (BaFe2O4), and (ii) the effective impregnation of MoO3 onto the ferrite matrix. Process optimization was conducted using the Taguchi L9 methodology, evaluating four operational parameters: temperature (120-180 °C), methanol:WCO molar ratio (20:1-40:1), catalyst concentration (2-10 wt %), and reaction time (1-5 h). The high coefficient of determination (R 2 = 0.9410) confirmed the model's robustness and predictive capability for ester content. The optimal conditions (temperature = 172 °C, methanol:WCO molar ratio = 28:1, catalyst concentration = 7.5 wt %, time = 4 h) yielded a maximum conversion of 96.4% into methyl esters. Notably, the catalyst exhibited: (i) exceptional recyclability, maintaining efficiency above 90% after seven consecutive cycles, and (ii) facile magnetic separation under an external magnetic field. Furthermore, the physicochemical properties of the produced biodiesel fully complied with ASTM D6751 and EN 14214 standards, underscoring the catalyst's potential for industrial-scale transesterification processes.