Efficient and Reusable Magnetic Sulfonated Biochar from Amazonian Waste for Sustainable Production of Glycerol Acetals: Statistical Optimization of Catalytic Process

Abstract Glycerol valorization, the main coproduct of biodiesel production, has driven the development of catalytic routes to obtain higher value-added products, such as acetals. This study reports the synthesis of a novel magnetic heterogeneous acid catalyst derived from a sulfonated biochar obtained from an Amazonian agro-industrial waste and impregnated with nickel ferrite (NiFe2O4). Characterization techniques (surface acidity, XRD, FT-IR, SEM/EDS, and VSM) confirmed the effective sulfonation and magnetization of the CM750 biochar. Optimization of glycerol acetylation with acetic acid was performed using Taguchi orthogonal design. Under optimized conditions (120 °C, 2.5 h, 7.5% catalyst, 1:5 glycerol:acetic acid molar ratio), the CMS750-NiFe2O4 catalyst achieved 99.79% glycerol conversion, with high selectivity for DAG (40.16%) and TAG (50.16%) and low selectivity for MAG (9.58%). The predictive models developed for glycerol conversion and MAG, DAG, and TAG selectivities exhibited high goodness of fit (adjusted R2 > 0.95) and relative errors below 5%. The CMS750-NiFe2O4 catalyst maintained catalytic activity after four reuse cycles, with glycerol conversion above 81% and selectivities of 65.44% (MAG), 35.82% (DAG), and 1.75% (TAG). Thus, Amazonian agro-industrial waste proves viable as a renewable source for developing efficient, sustainable, and low-cost catalysts.