Biodiesel production from waste cooking oil using an innovative magnetic solid acid catalyst based on Ni−Fe ferrite: RSM-BBD optimization approach

In the present study, a novel solid acid magnetic catalyst composed of nickel ferrite (NiFe2O4) and impregnated with molybdenum oxide (MoO3) was synthesized by wet method and applied in the production of biodiesel from the methyl transesterification reaction of waste cooking oil (WCO). The catalyst was characterized by the following techniques: surface acidity, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and Vibrating Sample Magnetometry (VSM). The optimization of the variables of the methyl transesterification reaction was carried out through the Box-Behnken 24 experimental design (BBD) and the response surface methodology (RSM). The optimized experimental results led to the obtainment of a biodiesel with 95.4% conversion to esters under the following reaction conditions: 168 °C temperature, 30:1 methanol:WCO molar ratio, 10 wt.% catalyst amount, and 1 h reaction time. The mathematical model developed showed an error of less than 5% between the observed and predicted values. In addition, the catalyst showed bifunctional character (catalytic and magnetic) and high stability after seven reaction cycles, with conversion to esters above 90.3%, as well as high versatility in the presence of various raw materials, indicating its high potential for development and application.