Valorization of Amazonian murici seed waste into a sulfonated biochar catalyst: Process optimization and kinetic studies for sustainable biodiesel production

In this study, a novel sulfonated solid acid catalyst was developed from biochar derived from residual murici (Byrsonima crassifolia) seed biomass, a lignocellulosic waste native to the Amazon region, for the methylation of palm fatty acid distillate (PFAD). The BCx−y biochar was obtained via optimized carbonization to enhance the catalytic properties of the sulfonated material (BCSx−y), synthesized through sulfuric acid treatment. Among the prepared catalysts, BCS750–1 exhibited the highest activity and was thoroughly characterized using acidity analysis, TGA, XRD, Raman, FT-IR, SEM, and EDS. Process optimization for biodiesel synthesis from PFAD was conducted using a Box–Behnken design and response surface methodology. In the optimized conditions of 120 °C reaction temperature, 1.7 h reaction time, 6 wt% catalyst concentration and a PFAD:methanol molar ratio of 15:1, the BCS750–1 catalyst achieved a free fatty acid conversion of 98.60 % ± 0.63, with the resulting biodiesel meeting the physicochemical properties required by ASTM D6751. The predictive model demonstrated strong agreement with experimental data (adjusted R2 = 0.9758; relative error < 5 %). Kinetic and thermodynamic analyses indicated pseudo-first-order behavior and an endothermic, non-spontaneous nature. Furthermore, BCS750–1 maintained 63.3 % of its initial catalytic activity after five consecutive cycles, with the free fatty acid conversion decreasing from 98.6 % ± 0.63 to 62.4 % ± 0.83 and proved effective for the conversion of other feedstocks. These findings underscore the potential of Amazonian residual biomass as a sustainable and low-cost precursor for producing efficient sulfonated catalysts for biodiesel manufacturing.