A novel robust CaO/ZnFe2O4 hollow magnetic microspheres heterogenous catalyst for synthesis biodiesel from waste frying sunflower oil

In addition to basicity of CaO, which is suitable for transesterification, synergistic between acidity and hollow structure of ZnFe2O4 support exhibited favorable catalytic activities for esterification of free fatty acids (FFAs), which endowed it to be a heterogenous catalyst with acid-base properties for synthesis of biodiesel from waste frying oil. Hence, magnetic CaO/ZnFe2O4 hollow microspheres heterogenous catalyst was prepared using yeast as green-template by co-precipitation method for synthesis biodiesel from waste frying sunflower oil (WSO). Magnetic CaO/ZnFe2O4 hollow microspheres as an efficient heterogeneous catalyst were characterized by TGA, FESEM, EDX, FT-IR, N2 adsorption–desorption isotherms and VSM analysis. The use of yeast as green and bio-template increased the surface area and subsequent catalytic activity of magnetic CaO/ZnFe2O4 hollow microspheres significantly higher than CaO/ZnFe2O4. The experimental research shows that the optimal operating conditions for improved catalyst activity were: 30% wt of CaO to ZnFe2O4 hollow structure, calcination temperature of 800 °C and calcination time of 2.5 h. High catalytic performance with 98% biodiesel yield with optimum reaction conditions of 65 °C, 3 h reaction time, 12:1 methanol to oil molar ratio, and 6% wt of catalyst to oil. The CaO/ZnFe2O4 hollow microspheres catalysts possessed magnetic behavior and robust catalyst activity, allowing them to be facilely isolated from the reaction environment and used for five times without notable loss of activity.