Sustainable biodiesel synthesis: Valorization of waste materials as heterogeneous catalysts

Recently, research efforts have intensified to develop biodiesel production techniques that are both cost‐effective and environmentally responsible, driven by the growing demand for sustainable alternatives to fossil fuels. This study investigates the potential of waste‐derived heterogeneous catalysts supported on Iranian clinoptilolite for biodiesel synthesis from waste cooking oil. The novelty of this work lies in the fabrication of CaO‐rich catalysts from locally available waste materials (construction lime, mussel shell, and kettle limescale) supported on natural clinoptilolite and the systematic optimization of acetone‐assisted transesterification using Box–Behnken design. The transesterification process was optimized by varying catalyst concentration, methanol‐to‐oil ratio, and solvent‐to‐oil ratio at a constant temperature of 60°C and a reaction time of 120 min. The synthesized catalysts were characterized using XRD, FT‐IR, and SEM techniques. The results revealed that identical optimum conditions (8 wt% catalyst, methanol‐to‐oil ratio of 0.7 v / v , and solvent‐to‐oil ratio of 0.4 v / v ) were obtained for all three catalysts. Among them, the kettle limescale/clinoptilolite catalyst achieved the highest biodiesel conversion of 98.75%. These findings demonstrate that waste‐derived clinoptilolite‐supported catalysts provide a sustainable, low‐cost, and efficient alternative for biodiesel production while promoting waste valorization and circular economy principles.