Combustion Reactivity of Hydrochars Derived from Sugarcane Green Harvesting Residues via Hydrothermal Carbonization

Abstract A non-isothermal thermogravimetric analysis was performed on hydrochars produced from sugarcane green harvesting residues (GHR) to assess their combustion reactivity. The Coats–Redfern method was employed to simulate conditions, determining kinetic parameters such as activation energy, pre-exponential factor, and reaction order, and assessing the reactivity of the hydrochars. Additionally, characteristic temperatures (ignition, peak, and burning) and combustion indices were identified. The hydrochars were produced at a rate of 12 °C/min with an airflow of 100 mL/min, reaching a maximum temperature of 900 °C. Results indicate that hydrochars produced at 300 °C with H 2 O/GHR ratios of 5:1 and 10:1 exhibit significantly elevated peak decomposition temperatures (447.1 °C and 465.4 °C, respectively) compared to 324.6 °C for the raw GHR, reflecting enhanced thermal stability. These hydrochars also showed a marked reduction in combustion reactivity indices—Di decreased from 12.3 to 3.78, Sn from 49.7 to 7.58, and Cx from 13.7 to 3.64—when compared to those produced at 200 °C. Furthermore, the activation energy increased substantially at 300 °C (40.92 and 38.00 kJ/mol) relative to raw GHR (21.05 kJ/mol) and HTC at 200 °C (≈25 kJ/mol), accompanied by higher pre-exponential factors, particularly for H–300–5 (31.25 min -1 ), indicating a shift in combustion kinetics and the formation of more recalcitrant, carbon-rich structures at higher HTC severity.