Modeling and optimization of biodiesel synthesis using TiO2–ZnO nanocatalyst and characteristics of biodiesel made from waste sunflower oil

Biodiesel as a renewable fuel is made from renewable materials such as animal fats, plant oils, and can be used in compression ignition (diesel) engines by mixing with conventional diesel. Recently, nanocatalysts are being used to generate biodiesel, as they are able to make these reactions more sufficient by having a large surface-to-volume ratio. TiO2 and ZnO nanoparticles are categorized as metal oxide nanoparticles. Each of them has its own special characteristics. Besides, they show a level of cooperation which is discussed below. In this paper, in addition to the surface method employed for numerical analysis, the experiments on the biodiesel production from waste sunflower oil are implemented by transesterification method using TiO2ZnO nanocatalyst. Effective process parameters, including the reaction temperature, oil: alcohol molar ratio, catalyst percentage, and optimal conditions are determined and optimized accordingly. The highest product yield was 96.4% in the ratio of 1–6 methanol to oil, 60 ​°C, and 200 ​mg/L TiO2–ZnO nanocatalyst. An optimization study shows that the highest biodiesel production is possible using nanocatalysts of 264 ​mg/L at a temperature of 66 ​°C. •Vegetable oil is used as a promising alternative sustainable fuel for diesel engines, due to its great potential for making biodiesel.•Using ZnO on TiO2 as nanocatalyst leads to an increase in accessibility of methanol and triglycerides in transesterification process.•Synergistic effect between waste oil and nanocatalyst is examined using RSM method.•Outcomes of experiments designed by the RSM method using nanocatalysts through transesterification, are discussed.