In the present study, heterogeneous acid catalysts for fatty acid esterification reactions were synthesized using agro-industrial waste from murumuru kernel shells. The waste was carbonized and functionalized with concentrated sulfuric acid under different sulfonation conditions, obtaining the sulfonated biochar. The results indicate that the best sulfonation conditions were obtained with a contact time of 4 h, the temperature of 200 °C, and a solid-acid ratio of 1 : 10 (w/v). The best catalyst was characterized by acid-base titration for the determination of total acid density, X-ray diffraction, scanning electron microscopy, X-ray energy dispersion spectroscopy, Fourier transform infrared spectroscopy and thermal analysis. Reaction conditions of oleic acid with methanol and the viability of catalyst reuse were also investigated. A conversion of 97.2% was achieved under optimum esterification reaction conditions, employing 5% catalyst, 10 : 1 molar ratio of methanol to oleic acid, during 1.5 h at a temperature of 90 °C. After 4 reaction cycles, the catalyst preserved its efficiency at 66.3% conversion. The catalyst activity was evaluated in reactions using palmitic acid, soybean fatty acid distillate, palm fatty acid distillate, and coconut fatty acid distillate. The results demonstrate that the catalyst is applicable and efficient in esterification reactions of raw materials, containing different fatty acid compositions since different carbonized materials have varying abilities to combine acid groups. This work reveals the promising feasibility of using biomass generated in large quantities by the agroindustry for the development of a new heterogeneous acid catalyst for biodiesel production.
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