Synthesis of MnFe2O4@graphene oxide catalyst for biodiesel production from waste edible oil

Abstract In this study, biodiesel production from waste edible oil (WEO) using MnFe2O4/graphene oxide catalyst was investigated. For this purpose, the surface characterization of the catalyst was determined using SEM, EDX/Map, XRD, VSM, BET, TGA-DTG, CO2-TPD and FTIR analyses. The catalyst could be easily removed from the reactant due to its paramagnetic property. The BET analysis showed that the MnFe2O4/GO catalyst has a significant specific surface area, which is suitable for the transesterification reaction. Also, the CO2-TPD analysis showed that the MnFe2O4/GO catalyst has two broad and strong peaks at a temperature range of 800–900 °C, which indicates strong interactions between CO2 and active sites on the catalyst surface. Moreover, the total number of basic sites on the catalyst surface was obtained 3978.6 μmol of CO2/g of the catalyst, which is a significant value. Due to the presence of high free fatty acids (2.43 wt%) in the WEO, a hydrochloric acid catalyst was used to reduce free fatty acid content before the transesterification process using the MnFe2O4/GO catalyst. The highest biodiesel yield was obtained 96.47%, which was a remarkable value compared to previous works. According to HNMR analysis, a peak was observed at 3.7 ppm, which was attributed to the methoxy group (O–CH3) on the methyl ester, indicating that biodiesel was properly produced. Then, biodiesel was blended with petro-diesel in various proportions (B25–B100) to improve its physical properties. According to the results, the physical characteristics of the biodiesel like flash point, viscosity, cloud point, density and pour point were obtained 176 °C, 5.4 mm2/s, 5 °C, −1 °C, and 882 kg/m3, respectively. Among these properties, the cloud point is not suitable and demonstrates that pure biodiesel can’t be used in the engine in cold weather and should be used in combination with diesel. However, other properties were within the standard range.