Modified graphene-based materials as effective catalysts for transesterification of rapeseed oil to biodiesel fuel

Abstract

Production of biodiesel by the transesterification process using different modified graphene-based materials as catalysts was studied. Solid acid graphene-based samples were prepared by grafting sulfonic or phosphate groups on the surface of thermally reduced graphene oxide. The obtained materials were thoroughly characterized using scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, N2 adsorption-desorption measurements, potentiometric titration, elemental analysis, and Fourier transform infrared spectroscopy. The prepared catalysts were tested in the transesterification of rapeseed oil with methanol at 130 °C under pressure, and their activities were compared to the performance of a commercially available heterogeneous acidic catalyst, Amberlyst-15. All modified samples were active in the transesterification process; however, significant differences were observed in the yield of biodiesel, depending on the method of catalyst preparation and strength of the acidic sites. The highest yield of fatty acid methyl esters of 70% was obtained for thermally reduced graphene oxide functionalized with 4-benzenediazonium sulfonate after 6 h of processing, and this result was much higher than that obtained for the commercial catalyst Amberlyst-15. The results of the reusability test were also promising.