{"id":118,"date":"2024-07-05T10:15:58","date_gmt":"2024-07-05T08:15:58","guid":{"rendered":"https:\/\/sites.unica.it\/hydrochar\/?page_id=118"},"modified":"2026-03-27T12:27:12","modified_gmt":"2026-03-27T11:27:12","slug":"hydrothermal-carbonization-htc","status":"publish","type":"page","link":"https:\/\/sites.unica.it\/hydrochar\/wikichar\/hydrothermal-processes-htp\/hydrothermal-carbonization-htc\/","title":{"rendered":"Hydrothermal Carbonization (HTC)"},"content":{"rendered":"\n

A thermochemical process for converting wet biomass into hydrochar under subcritical water conditions<\/em><\/p>\n\n\n\n

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History & Development<\/strong><\/h2>\n\n\n\n

The conceptual origins of hydrothermal carbonization (HTC) trace back to early 20th-century work by Friedrich Bergius, who investigated coal formation under hydrothermal conditions. Modern HTC research re-emerged in the early 2000s with renewed interest in biomass valorization and wet waste treatment (Libra et al., 2011<\/a>; Funke & Ziegler, 2010<\/a>). Hydrothermal carbonization is a thermochemical conversion process that transforms wet organic feedstocks into a carbon-rich solid product known as hydrochar<\/em>, along with a liquid phase containing dissolved organic compounds and a gaseous phase dominated by carbon dioxide (Libra et al., 2011<\/a>; Funke & Ziegler, 2010<\/a>). The process is conducted in liquid water at elevated temperatures, typically between 180 and 250 \u00b0C, in a closed reactor under autogenous pressure generated by heating water above its boiling point. Unlike dry thermochemical processes such as pyrolysis, HTC operates in an aqueous environment and enables direct processing of high-moisture materials such as sewage sludge, digestate, and food waste without prior drying. Water functions simultaneously as solvent, reactant, and heat-transfer medium, promoting chemical pathways that are suppressed under dry conditions (Berge et al., 2011<\/a>; Funke & Ziegler, 2010<\/a>).<\/p>\n<\/div>\n\n\n\n

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Theory & Mechanisms<\/strong><\/h2>\n\n\n\n

HTC converts biomass through a combination of hydrolytic and carbonization reactions occurring in subcritical water. Early stages are dominated by solubilization and depolymerization of biopolymers, followed by secondary reactions that concentrate carbon in the solid phase (Libra et al., 2011<\/a>). Water facilitates bond cleavage, stabilizes reactive intermediates, and enables homogeneous heat transfer. As reaction severity increases, the solid product progressively evolves toward lower hydrogen-to-carbon (H\/C) and oxygen-to-carbon (O\/C) atomic ratios, indicating increasing carbonization (Funke & Ziegler, 2010<\/a>).<\/p>\n\n\n\n

Process Chemistry & Mechanisms<\/strong><\/h2>\n\n\n\n

HTC proceeds through a network of overlapping and parallel reactions rather than a single dominant pathway:<\/p>\n\n\n\n