Synthesis of magnetically solid base catalyst of NaOH/Chitosan-Fe3O4 for biodiesel production from waste cooking oil: Optimization, kinetics and thermodynamic studies

Abstract

In this research, biodiesel was produced from waste cooking oil (WCO) via a magnetically and biodegradable heterogeneous base catalyst of NaOH/Chitosan-Fe3O4. The catalyst was characterized using X-ray powder diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-Ray (EDX), EDX-mapping, Vibrating-Sample Magnetometer (VSM), Brunauer-Emmett-Teller (BET), Transmission Electron Microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR) analyses. The catalyst performance was also studied in the transesterification reaction of WCO conversion to biodiesel. The process was optimized via the central composite design (CCD) through the response surface methodology (RSM) method. The influences of major factors, including methanol to oil molar ratio (6:1–12:1), catalyst weight (0.25–1 wt%), and time (4–8 h), were examined on the reaction behavior. The maximum FAME yield was 92% under the following optimal conditions: 0.5 wt% NaOH/Chitosan-Fe3O4 catalyst, methanol to oil ratio of 6:1, reaction time of 4.5 h, and temperature of 25 °C. The Gas Chromatography–Mass Spectrometry (GC–MS) and Inductively Coupled Plasma- Optical Emission Spectroscopy (ICP-OES) were used to determine the fatty acid profile and metal contents of samples, respectively. Based on the physicochemical properties, it was concluded that the produced biodiesel had the same properties as conventional petro-diesel. Further, a kinetic study revealed that the electrolysis method was a situ-transesterification reaction with a pseudo-first-order kinetics and activation energy of 21 kJ/mol. From the thermodynamic calculations, the values of ΔS, ΔΗ, and ΔG were found to be −0.23 kJ/mol K, 18.20 kJ/mol, and 95.13 kJ/mol, respectively.