Hydrothermal processing, also known as “Hydrothermal Upgrading (HTU)”,
is a biomass conversion technology introduced by the Shell Oil Company in the 1980s.
In this method, the thermal degradation of biomass takes place in water and affects the physicochemical properties of water.
For example, its dielectric constant is reduced at high temperatures.
Therefore, while organic substances are insoluble in water under normal conditions,
water can become a good solvent for non-polar substances under supercritical conditions.
An increase in the ionic character of water can facilitate acid–base-catalyzed reactions.
Additionally,mostbiomassescontain significant amounts of moisture.
Raw materials must first be dried if the hydrothermal method is not used.
This requires additional costs in industrial applications.
For these reasons, the conversion of biomass into precious products by hydrothermal processing is a major subject of research.