Statistical optimization of biodiesel production from waste cooking oil using magnetic acid heterogeneous catalyst MoO3/SrFe2O4

Abstract

In this study, a heterogeneous magnetic acid catalyst MoO3/SrFe2O4, composed of molybdenum oxide (MoO3) supported on strontium ferrite (SrFe2O4), was synthesized and applied in the transesterification of waste cooking oil. The catalyst was characterized by acid-base titration method in order to determine Surface acidity, Thermogravimetric analysis (TGA/DTGA), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Energy dispersion X-ray spectroscopy (EDX) and Vibrating sample magnetometry (VSM) techniques. A central composite design of centered face 24 and a mathematical model were developed in order to describe the behavior of the ester content as a function of the independent variables reaction temperature, alcohol:oil molar ratio, catalyst dosage and reaction time. The mathematical model (R2 = 0.9900) was validated and showed a relative error below 5% between the experimental and predicted values. Using linear regression methods and response surface methodology the conditions of biodiesel synthesis reaction were optimized and 95.4% conversion into esters was obtained from the use of 164 °C reaction temperature, 40:1 alcohol:oil molar ratio, 10% catalyst dosage and 4 h reaction time. The catalyst was recovered by an external conventional magnet and showed high reusability and stability, such the ester content remains above 84% after five runs. The development of MoO3/SrFe2O4 as a novel heterogeneous magnetic acid catalyst would provide an environmentally friendly approach to biodiesel production.