Effect of hydrothermal carbonization conditions on the chemical composition and quality of sugarcane bagasse-based hydrochars.

This study evaluates the influence of hydrothermal carbonization (HTC) conditions on the chemical composition and quality of sugarcane bagasse-based hydrochars, with potential relevance for agricultural applications. A limitation in current literature is the lack of detailed assessments of HTC operating conditions when organic matter quality is the primary focus. Sugarcane bagasse was subjected to HTC using a combined 3² × 2¹ experimental design, varying reaction time (10, 12, and 14 h), temperature (180, 190, and 200 °C), and reaction medium (H₂O and HNO₃ 0.1 mol L⁻¹). Hydrochar yield, organic matter (OM), total organic carbon (TOC), and atomic ratios (H/C and O/C) were determined. Structural and chemical features were evaluated by FTIR and SEM, while Py-GC/MS was applied to investigate molecular composition, with emphasis on compounds associated with plant growth. Principal component analysis (PCA) was used to correlate chemical profiles with hydrochar quality. Hydrochars produced in acidic medium exhibited lower yields but higher OM and TOC contents compared to those obtained in water, indicating enhanced carbon concentration. FTIR results suggested progressive biomass carbonisation, whereas SEM revealed marked surface modifications, including fibre grooving, reduced interstitial material, and increased surface area under more severe HTC conditions. Py-GC/MS revealed distinct chemical profiles, with higher concentrations of bioactive compounds in acid-assisted treatments. PCA indicated that reaction medium and temperature were the dominant factors controlling organic matter transformation, followed by residence time. Overall, HTC conditions strongly influenced hydrochar chemical quality, and samples A/200/12 and A/200/14 exhibited the most favourable combination of quality-related chemical indicators.