SiO₂ Beads Decorated with SrO Nanoparticles for Biodiesel Production from Waste Cooking Oil Using Microwave Irradiation

Energy sources are necessary for human existence, comfort, and progress. Limited crude petroleum resources and increasing awareness of the environmental impacts of using fossil fuels motivate the search for new energy sources and alternate fuels. Herein, a low cost, fast, and green methodology for the synthesis of a hybrid solid base catalyst, strontium oxide coated millimetric silica beads (SrO@SiO₂), is designed for the transesterification of cooking oil into biodiesel in a domestic microwave oven. The cost reduction is due to the effective utilization of the catalyst by the homogeneous dispersion of the active sites on the silica beads and their reusability. The catalyst synthesis process was optimized with respect to the amount of glass beads, microwave irradiation time, calcination time, and calcination temperature. Several methods for synthesizing SrO by minimizing energy consumption were investigated, and an optimized process for designing SrO@SiO₂ was developed. The SrO@SiO₂ catalyst produced under optimum conditions was characterized by TGA, XRD, FTIR, ICP, SEM, and TEM. XRD analysis indicated peaks typical of SrO alone. ICP analysis indicated 41.3 wt % deposition of SrO on silica beads. The novel solid base catalyst thus generated was used for the transesterification of waste cooking oil. Conversion values as high as 99.4 wt % in 10 s irradiation were observed from ¹H NMR analysis using this composite catalyst, indicating the feasibility of economical biodiesel production from cooking oil waste in a very short time.