Microwave Assisted Biodiesel Production from Waste Cooking Oil Using Steel Slags as Catalyst

An innovative catalytic system for biodiesel synthesis starting from waste biomass (waste cooking oil, WCO) in the presence of waste material (steel slags) as the catalyst under microwave irradiation is described. The reaction conditions were optimized by using response surface methodology (RSM) based on Box-Behnken Design (BBD) taking time, temperature, and catalyst weight as factors. The optimum conditions, leading to 97 % conversion of WCO into FAMEs (fatty acid methyl esters) were found to be: 18 min reaction time, 134 °C and 380 mg of catalyst for 1.0 mL of WCO. The recyclability of the catalyst was tested at different experimental conditions, and by increasing the reaction times for subsequent cycles, the catalytic efficiency remained steady. The alkalinity of both as-received steel slags and steel slags recovered after three reaction cycles was tested with the Hammett indicator method. The steel slags were also characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Fluorescence (ED-XRF), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA), X-ray Photoelectron Spectroscopy (XPS).