A novel technology for microwave-assisted synthesis of new Ca/Si/Al composite oxide-based catalyst for boosting the ultrasound-assisted biodiesel production

This research focuses on the microwave synthesis of the composite based on Ca/Si/Al oxides as a catalyst for effective and sustainable biodiesel production from waste frying oil (WFO) using an ultrasonic transesterification reaction. The novel catalyst Ca(OH)₂-CaCO₃/kaolin (CSAO), was synthesized by impregnation of kaolin with Ca(OH)₂-CaCO₃ to avoid the drawbacks of the sole Ca-based oxides usage and benefiting from the basic and acidic sites of Ca(OH)₂-CaCO₃ and kaolin, respectively. The catalysts have been characterized using XRD, FT-IR, Raman spectroscopy, SEM, TEM, and XPS. Then they utilized in the transesterification of WFO to evaluate and compare their performance in biodiesel production. A multi-variable catalytic transesterification process was performed using the response surface methodology (RSM). The experimental data were analyzed using analysis of variance (ANOVA). The highest biodiesel yield (98.7 %) was achieved using 1.5 % wt. CSAO catalyst/ wt. WFO, 6:1 methanol to oil (M/O) molar ratio, and 4 min reaction time using ultrasonic irradiation with an amplitude of 15 %. This outstanding performance is attributed to the acidic and basic sites of the CSAO. The CSAO catalyst demonstrated great stability against four successive cycles with high biodiesel production efficiency. The petrodiesel physicochemical properties have been significantly improved after blending with the produced biodiesel such as; density, viscosity, calorific value, cetane index, cloud point, pour point, and flash point. Moreover, exhaust gas emissions have been strongly reduced like hydrocarbon (HC), carbon monoxide (CO), and sulfur oxides (SO_x). This work is based on “wastes treat wastes” and provides a promising catalyst from Ca-based wastes without the Ca^2 + leaching and saponification process.