Synthesis of MIL-68 (Al) Catalyst and Optimization of Green Biodiesel Production from Waste Cooking Oil

Given the ongoing crisis of depleting fossil fuel reserves and rising demand for biofuels, scientists are increasingly driven to explore more environmentally friendly and sustainable energy options in today’s global landscape. Consequently, the utilization of solid catalysts, specifically Metal–Organic Frameworks (MOFs), in the transesterification process to produce biodiesel emerges as a promising avenue. This marks the innovative adoption of the metal–organic catalyst MIL-68 (Al) in the context of biodiesel production. This study focuses on the generation of green and efficient biodiesel using Waste Cooking Oil (WCO) as the primary raw material which involves a transesterification process utilizing of MIL-68 (Al). Using the Box-Behnken Design (BBD), a well-established method in Response Surface Methodology (RSM), we optimized key variables including catalyst quantity, duration, and temperature in the transesterification process. The optimization study includes parameter ranges: time (3–8 h), temperature (100–150 °C), and catalyst dosage (5–25%).

The catalyst characteristics were investigated through AFM, BET, DLS, SEM, ICP, FTIR, NH3-TPD, TEM, TGA, and XRD analyses. Using a temperature of 145 °C and incorporating a catalyst quantity of 24.18%, a maximum oil conversion efficiency of 98.8% was attained within 7.5 h. Kinetic analysis showed that the experimental behavior followed a pseudo-first-order reaction kinetic model (R² = 0.9991), and the transesterification reaction demanded an activation energy of Ea = 65.47 kJ/mol. The catalyst demonstrates excellent stability, maintaining consistent performance over four cycles without any noticeable decline. The yield after four cycles of reusability remains high at 92.6%.