review · Sustainability
Hydrothermal carbonisation converts biomass into carbon-rich hydrochar, an adaptable material with potential applications in energy production, advanced materials, and environmental remediation. The conversion relies on core chemical pathways, including dehydration, decarboxylation, and polymerisation. Operating variables such as temperature, pressure, residence time, water ratio, and biomass feedstock strongly dictate the resulting physicochemical characteristics of the hydrochar. Emerging techniques, including process water recirculation and microwave-assisted co-hydrothermal carbonisation, aim to improve overall efficiency and sustainability. Furthermore, surface modification and chemical activation, notably with potassium hydroxide, enhance hydrochar capacity to adsorb heavy metals and organic contaminants. Although hydrochar has a high higher heating value that makes it an attractive alternative to coal, alongside potential in catalysis and energy storage, broader deployment faces obstacles. Significant challenges remain in reactor design, process scalability, and managing secondary waste.
Converting organic waste into hydrochar offers a sustainable route to replace coal, store energy, and clean contaminated water. Clarifying the reaction chemistry and processing conditions helps optimise production efficiency. Overcoming current barriers in scaling and waste management could turn low-value agricultural and forestry residues into valuable functional materials, reducing dependence on fossil fuels and supporting circular economy initiatives.
Potential commercial applications include solid fuel replacement for coal users, adsorbents for water treatment facilities, and components for energy storage and catalysis. The technology appears to be at an early to intermediate research stage. Reaching commercial viability will require developers and engineering partners to resolve clear bottlenecks in reactor design, large-scale process expansion, and the handling of secondary waste.
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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.
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DOI: 10.3390/su17041660
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