Optimizing catalytic hydrothermal carbonization of Eucalyptus grandis sawdust for enhanced biomass energy production: Statistical analysis and insights of sustainable carbon-neutral pathways

This study advances carbon neutrality potential by examining the Hydrothermal Carbonization (HTC) of Eucalyptus grandis sawdust in Brazil. This research fills a critical gap in the literature by employing Response Surface Methodology (RSM) with a Central Composite Design (CCD) to evaluate and optimize the catalytic HTC of biomass residues. The optimization focuses on acid concentration (0–0.2 mol/L H₂SO₄), temperature (180–220 °C), and reaction time (30–90 min), aiming to reduce processes cost and produce higher-quality hydrochar. H2SO4 significantly catalyzes degradation and alters hydrochar composition, while higher process temperatures enhance coalification, yielding hydrochars with lower H/C (0.77) and O/C (0.21) ratios and up to 25.6 MJ/kg higher heating values. Acid concentration was the most critical parameter, followed by temperature and time. Optimal HTC conditions (185 °C, 30 min, and 0.038 mol/L H2SO4) maximized hydrochar quality and minimized costs. This configuration resulted in a hydrochar with 67.62 % solid yield, 72.27 % energetic yield, and a fuel ratio of 0.25. Experimental validation confirmed the process's effectiveness, with errors under ±10 %. The results led to a novel stoichiometry diagram comparing different valuation routes for Eucalyptus, highlighting HTC as a viable option for its residue valorization in sustainable biomass utilization towards carbon neutrality. To comprehensively assess the process's efficiency, energy consumption, and overall sustainability, further research is required to evaluate its technical aspects (including reactor pressure parameters and advanced chemical characterization), as well as its economic viability and life cycle impacts.