RSM-BBD optimization of transesterification reaction using g-C ₃ N ₄ nanocatalyst with waste cooking oil for biodiesel production

In this study, waste cooking oil was subjected to heterogeneous transesterification using a graphitic carbon nitride (g-C₃N₄) nanocatalyst, with the primary aim of developing a sustainable and cost-effective catalytic system for biodiesel production. The catalyst was synthesized by annealing urea at 500°C for 4 h and characterized using X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. For biodiesel synthesis, WCO was initially esterified to reduce free fatty acids, followed by transesterification using the g-C₃N₄ under various reaction conditions. The Box-Behnken Design coupled with Response Surface Methodology was employed to optimize the critical transesterification parameters, including catalyst concentration, reaction temperature, and reaction time. The developed model demonstrated a high <i>R</i>² value (0.9998), indicating excellent precision and minimal prediction error, thereby confirming its robustness. Under optimized conditions (catalyst dosage = 1.75 wt.%, reaction temperature = 60°C, and reaction time 70 min), a maximum fatty acid methyl ester yield of 89.16% was achieved. Gas chromatography-mass spectrometry and FTIR confirmed the successful conversion of triglycerides into FAME. Physicochemical properties of the biodiesel met the American Society for Testing and Materials standards, validating its suitability as a renewable fuel. The key finding of this study is that the g-C₃N₄ exhibits excellent catalytic activity with relatively low catalyst loading, thereby offering a promising alternative to conventional catalysts. Future research is necessary to examine the long-term stability, reusability of the catalyst, assess large-scale viability, and conduct thorough life-cycle and techno-economic evaluations to determine its sustainability in commercial biodiesel production.