Magnetic acid catalyst produced from acai seeds and red mud for biofuel production

Highlights: • Magnetic catalyst was prepared from two residues namely red mud and acai seeds. • Acid catalyst showed yielding 88% conversion to methyl oleate. • Catalyst was easily separated by an external magnet with good reuse capacity. • Red mud was used as a magnetic source for sulfonated catalysts for the first time. In this study, a highly efficient, heterogeneous magnetic acid catalyst was developed for biofuel production. Two abundant residues found in the eastern Amazon region were used as precursors, namely, red mud and acai seeds. The catalyst was prepared for the impregnation method followed by carbonization and sulfonation. The materials were characterized using X-ray diffraction, scanning electron microscopy coupled with an energy dispersive X-ray spectroscopy system for elemental mapping, thermogravimetry, Fourier transform infrared spectroscopy, low temperature N₂ adsorption, vibratory sample magnetometry and acid-base titration. The best yield obtained in the esterification reaction was for the acai seed sample and red mud in a 1:1 ratio, carbonized at 400 °C for 3 h and sulfonated at 80 °C for 3 h. This sample presented 88% conversion to methyl oleate under reaction conditions of 5% catalyst loading and a 1:12 oleic acid to methanol molar ratio at 100 °C for 1 h. At the end of the reaction, the catalyst was easily separated from the reaction by a magnet and exhibited good capacity for reuse for at least three reaction cycles. The experiments yielded promising results for obtaining magnetic carbon materials from waste generated in the Amazon region. In addition, to the best of our knowledge, the use of red mud as a magnetic source in the synthesis of sulfonated carbon-based catalysts has not been reported to date.