Terminology and explanation

Hydrothermal process

The term hydrothermal is purely of geological origin. It was first used by British geologist, Sir Roderick Murchison (1792-1871) to describe the action of water at elevated temperature and pressure, in bringing about changes in earth’s crust leading to the formation of various rocks and minerals. Hydrothermal processing is an important thermochemical conversion process that is used to convert biomass into valuable products or biofuel. The process is usually performed in water at 250–374 °C under pressures of 4–22 MPa. The biomass is degraded into small components in water. Based on the target products, i.e., bio-oil, bio-gas or bio-carbon, the process conditions (temperature, pressure and time) are chosen. There has been significant effort in evaluating various biomass resources for hydrothermal processing because the process is suitable for any type of biomass including the co-utilization of biomass with waste materials. Additionally, because most biomass resources have high moisture contents, the most efficient way to process them is through hydrothermal processing.

Hydrothermal carbonization

Hydrothermal carbonization is a chemical process for the conversion of organic compounds to structured carbons. The process, which technically imitates the brown coal formation ("coalification" (in German)) taking place in nature within 50,000 to 50 million years within a few hours, was investigated by Friedrich Bergius and first described in 1913. For information about the hydrothermal carbonization at HTCycle GmbH please visit our Process page on our website.


Waste* – materials that are not prime products (that is, products produced for the market) for which the generator has no further use in terms of his/her own purposes of production, transformation or consumption, and of which he/she wants to dispose. Wastes may be generated during the extraction of raw materials, the processing of raw materials into intermediate and final products, the consumption of final products, and other human activities. Residuals recycled or reused at the place of generation are excluded.

Example: municipal solid waste (household trash/refuse), hazardous waste, wastewater (such as sewage, which contains bodily wastes (feces and urine) and surface runoff), radioactive waste, and others.

Biochar – Alternatively, biochar can also be generated through the HTC-process. A product similar to humus which can be used for soil enhancement and to capture and store CO2.

Biomass* – total living weight (generally in dry weight) of all living organisms in a particular area or habitat. It is sometimes expressed as weight per unit area of land or per unit volume of water.

Example: agriculture waste and crops, food, wood, animal manure and human sewage

CO2 (Carbon dioxide)* – colorless, odorless and non-poisonous gas that results from fossil fuel combustion and is normally a part of ambient air. It is also produced in the respiration of living organisms (plants and animals), and considered to be the main greenhouse gas, contributing to climate change.

CO (Carbon Monoxide)* - colourless, odourless and poisonous gas produced by incomplete fossil fuel combustion. Carbon monoxide combines with the hemoglobin of human beings, reducing its oxygen carrying capacity, with effects harmful to human beings.

Carbon* – The chemical element of atomic number 6, a non-metal which has two main forms (diamond and graphite) and which also occurs in impure form in charcoal, soot, and coal.

Coal* – A combustible black or dark brown rock consisting chiefly of carbonized plant matter, found mainly in underground seams and used as fuel.

Biocoal – form of charcoal that is produced by pyrolysis at a temperature and is dark brown in appearance.

Charcoal* - solid residue consisting mainly of carbon obtained by the destructive distillation of wood in the absence of air.

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