Microwave assisted biodiesel production from waste cooking oil using steel slags as catalyst

Nowadays, the circular economy and the reuse of waste materials are crucial points to reach the ecological conversion. It is also vital to find an alternative source of fuel to oil. The present work reports on the development of 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. The importance of this issue is well documented by the presence of many reports on both the use the use of WCO as a feedstock1 and a waste as the catalyst2. Recently, the use of steel slags as active and selective catalyst for the synthesis of fatty acid methyl esters (FAMEs) by transesterification of soybean oil in methanol under conventional heating (120°C) has been reported to taken several hours (12 h) to reach completion3. In this study, microwave (MW) irradiation protocols were developed for fast and low energy consuming biodiesel synthesis from WCO in the presence of steel slags. After some preliminary tests, the reaction conditions were investigated and optimized by setting a design of experiment. Time, temperature and catalyst weight were set as factors. The almost quantitative conversion of WCO could be achieved in only 18 min at 134°C. Recyclability of the catalysts was also explored. Steel slags were characterised by Scanning Electron Microscopy (SEM), Total X-ray Florescence (TXRF), X-Ray Diffraction (XRD) and Thermogravimetric Analysis (TGA).