This study was conducted to investigate the use of clay/CaO heterogeneous catalyst for the production of biodiesel from waste cooking oil. The catalyst was synthesized from clay and calcined using calcium oxide under controlled conditions. Clay is a natural soil material containing a large amount of amorphous silica. After processing calcium oxide and heating under controlled conditions at 800 °C, high surface area silica with amorphous structure was produced. The amorphous structure of the synthesized catalyst was confirmed by XRD analysis. The results of SEM analysis indicated that the particles had a spherical structure, distributed evenly and uniformly. The effect of five parameters of reaction temperature, catalyst concentration, oil to methanol volume ratio, toluene concentration, and reaction time on the purity of the biodiesel was evaluated through utilizing the response surface methodology (RSM). Under optimal conditions i.e. temperature of 54.97 °C, catalyst concentration of 9.6 wt%, oil to methanol volume ratio of 1.94 vol:vol, toluene concentration of 16.13 wt%, and reaction time of 74.32 min, the conversion rate was 97.16%. The results of catalyst recovery test showed that the prepared catalyst could be reused up to 5 times; thus, it can be used as a stable and cost-effective catalyst for the production of biodiesel.
