Optimization of sugarcane bagasse biochar based Sulphonated solid acid catalyst synthesis using response surface methodology

• Sugarcane bagasse converted into sulfonated solid acid catalyst • RSM optimized sulfonation to maximize –SO₃H density • Optimum gave 0.596 mmol/g, matching model prediction • FTIR, SEM, and TGA confirmed successful functionalization • Sustainable catalyst for biomass valorization and catalysis The valorization of sugarcane bagasse into functional carbon-based catalysts provides a sustainable approach to waste utilization and heterogeneous catalysis. In this study, sugarcane bagasse-derived biochar was synthesized and subsequently functionalized with sulfonic acid groups to produce a solid acid catalyst. Unlike previous studies, this work systematically investigates the effects of sulfonation parameters on –SO₃H group formation and applies Response Surface Methodology (RSM) to model and optimize the process , providing predictive insight into the relationships between temperature, reaction time, and acid-to-biochar ratio. RSM using a Box-Behnken design was applied to optimize three key sulfonation parameters: temperature (100, 140 and 180 °C), reaction time (5, 14 and 23 h), and sulfuric acid-to-biochar ratio (5, 15 and 25 mL/g), aiming to maximize sulfonic acid group density. Proximate and thermogravimetric analyses confirmed the suitability of sugarcane bagasse as a precursor. The optimized sulfonation conditions of 134.97 °C, 13.3 h, and 23.9 mL/g acid-to-biochar ratio yielded a sulfonic acid density of 0.596 mmol/g, closely matching the model prediction of 0.602 mmol/g. ANOVA indicated that the acid-to-biochar ratio and temperature were the most significant factors, with notable interactions and quadratic effects, while reaction time had minimal direct effect. Characterization of the optimized catalyst confirmed successful functionalization, with FTIR revealing –SO₃H, –COOH, and –OH groups, SEM showing increased surface roughness, and TGA confirming additional mass loss due to decomposition of oxygen- and sulfur-containing functional groups. These findings demonstrate a predictive and systematically optimized sulfonation process for sugarcane bagasse biochar, providing guidance for tailoring catalyst properties and improving biomass-based solid acid catalysts for heterogeneous reactions.