Biomass Hydrochar: A Critical Review of Process Chemistry, Synthesis Methodology, and Applications

Joshua O. Ighalo, Florence C. Akaeme, Jordana Georgin (), Jivago Schumacher de Oliveira and Dison S. P. Franco ()
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Joshua O. Ighalo: Department of Chemical Engineering, Nnamdi Azikiwe University, P. M. B. 5025, Awka 420110, Nigeria
Florence C. Akaeme: Department of Chemical Engineering, Nnamdi Azikiwe University, P. M. B. 5025, Awka 420110, Nigeria
Jordana Georgin: Department of Civil and Environmental, Universidad de La Costa, CUC, Calle 58 # 55–66, Barranquilla 50366, Colombia
Jivago Schumacher de Oliveira: Applied Nanomaterials Research Group (GPNAp), Nanoscience Graduate Program, Franciscan University (UFN), Santa Maria 97010-032, RS, Brazil
Dison S. P. Franco: Department of Civil and Environmental, Universidad de La Costa, CUC, Calle 58 # 55–66, Barranquilla 50366, Colombia

Sustainability, 2025, vol. 17, issue 4, 1-44

Abstract: Hydrothermal carbonization (HTC) is a novel thermochemical process that turns biomass into hydrochar, a substance rich in carbon that has potential uses in advanced material synthesis, energy production, and environmental remediation. With an emphasis on important chemical pathways, such as dehydration, decarboxylation, and polymerization, that control the conversion of lignocellulosic biomass into useful hydrochar, this review critically investigates the fundamental chemistry of HTC. A detailed analysis is conducted on the effects of process variables on the physicochemical characteristics of hydrochar, including temperature, pressure, biomass composition, water ratio, and residence time. Particular focus is placed on new developments in HTC technology that improve sustainability and efficiency, like recirculating process water and microwave-assisted co-hydrothermal carbonization. Furthermore, the improvement of adsorption capacity for organic contaminants and heavy metals is explored in relation to the functionalization and chemical activation of hydrochar, namely through surface modification and KOH treatment. The performance of hydrochar and biochar in adsorption, catalysis, and energy storage is compared, emphasizing the unique benefits and difficulties of each substance. Although hydrochar has a comparatively high higher heating value (HHV) and can be a good substitute for coal, issues with reactor design, process scalability, and secondary waste management continue to limit its widespread use. In order to maximize HTC as a sustainable and profitable avenue for biomass valorization, this study addresses critical research gaps and future initiatives.

Keywords: biomaterials; adsorption; hydrochar; hydrothermal carbonization; sensors (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2025
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