Optimizing Biodiesel Production from WCO Using ZnO-CaO Nano Catalysts, Application of Experimental Design

Biodiesel is a renewable fuel made from animal fats and vegetable oils. Heterogeneous nanocatalysts are increasingly used in production due to their efficiency and ability to reduce processing costs. This study aims to maximize biodiesel production from waste cooking oil by developing a stable mixture of oxide catalysts (ZnO-CaO). The ZnO-CaO nanocatalyst was produced by applying a mixture design. The morphology and vibrational energies of the nanocatalysts were analyzed using SEM-EDS and FT-IR, respectively. To identify optimal transesterification conditions, the Box–Behnken design was employed as a statistical tool for process optimization. It was found that a maximum yield of 97.1% was achieved under the following optimal conditions: an ethanol/oil ratio of 10.83:1, a catalyst concentration of 3%, and a reaction time of 3 hours. It was also found that the biodiesel produced from WCO met ASTM D6571 standards, indicating a highly efficient catalytic process using mixed oxide catalysts with moderate basicity. It was additionally determined that the process was environmentally friendly with low E-factors (0.57 with useful glycerol, 0.31 as waste). High RME (80%) and close-to-unity MPI indicated efficient and green production. Ethanol and glycerol were the main waste contributors, but glycerol can be repurposed for valuable products, enhancing waste management.