Toward Sustainable Solid Biofuels: Impact of Extraction and Carbonization Pathways on Combustion of Hydrochars

This study investigates the use of combined solvent extraction and hydrothermal carbonization (HTC) to enhance the fuel properties of lignocellulosic biomass.. Focusing on Johnsongrass biomass, we investigate the influence of solvent pretreatment and HTC temperature on the physicochemical characteristics and combustion behavior of the resulting hydrochars. Elemental and proximate analyses indicate that solvent extraction enhances carbon contentwhile reducing heteroatoms (e.g., nitrogen), contributing to improved fuel quality and cleaner combustion. Increasing HTC temperature further promotes carbon densification and aromaticity, as evidenced by elevated ignition and burnout temperatures and higher activation energies, implying enhanced thermal stability. Advanced characterization techniques (FTIR and thermal analysis) reveal that structural transformations leading to oxygen depletion and formation of condensed carbon domains-features favorable for energy harvesting and conversion applications. These nanoscale modifications impart improved combustion performance and reduced emission potential, underscoring the value of extraction-HTC integration as a green and scalable route for producing nanostructured bio-carbon materials. The results offer significant implications for the development of environmentally friendly, high-efficiency solid fuels within the framework of sustainable energy harvesting technologies.