Environmentally sustainable production of biodiesel from waste edible oil using Mn–Fe supported magnetic acid heterogeneous catalyst: Optimization via Taguchi L9 technique

The present work reports the synthesis and application of a novel magnetic acid heterogeneous catalyst (MoO₃/MnFe₂O₄) with efficient performance and practical recoverability for biodiesel production from waste cooking oil (WCO). Manganese ferrite (MnFe₂O₄) was successfully prepared via the co-precipitation method to obtain a magnetic support. A molybdenum precursor was added to MnFe₂O₄ by wet impregnation to develop the MoO₃/MnFe₂O₄ catalyst. Surface acidity, XRD, FTIR, SEM, EDS, and VSM were used to characterize the synthesized materials. The MoO₃/MnFe₂O₄ catalyst was evaluated in the transesterification reaction under different operating conditions, including reaction temperature (130.0–170.0 °C), methanol:WCO molar ratio (20:1–40:1), catalyst amount (4.0–8.0 wt%), and reaction time (2.0–4.0 h). An L9 orthogonal array using the Taguchi method was employed to optimize the biodiesel ester content using a minimal number of experimental runs. The mathematical model (R² = 0.932) showed a good correlation between experimental and predicted ester content values. Investigation of the four independent variables revealed temperature as the most significant parameter in biodiesel production using the MoO₃/MnFe₂O₄ catalyst. Under optimal conditions (temperature = 164.5 °C, methanol:WCO molar ratio = 32:1, catalyst amount = 6.5 wt%, and reaction time = 2.5 h), the biodiesel achieved a maximum ester content of 96.7 %, maintaining stable catalytic activity (∼90.0 %) over eight consecutive reaction cycles. This study highlights the importance of fabricating the MoO₃/MnFe₂O₄ catalyst as a new approach to enhancing the biodiesel production process with low energy consumption as well as minimal negative environmental impact.