Hydrothermal liquefaction (HTL) is an emerging technology that
is able to convert wet biomass (especiallywaste materials) to the oil
(referred to as bio-oil or biocrude), aqueous, gaseous and solid
products at high pressures (5e22 MPa) and moderate temperatures
(250e380 C) in sub-/supercritical water medium [21,22]. HTL is
advantageous over other thermochemical conversion technologies
such as fast pyrolysis and gasification. It is carried out at lower
temperatures; more importantly, it accepts wet biomass, and thus
obviates an energy-intensive pre-drying process. Also, the bio-oil
obtained from the liquefaction process is hydrophobic, typically
has a lower oxygen and water content, giving much higher HHV
(25e35 MJ kg1) compared to those of the fast pyrolysis bio-oil
(14e20 MJ kg1). The HTL crude bio-oil can be mixed with other
fuels and used for combustion or be further upgraded to high
quality hydrocarbon liquid fuels such as gasoline and diesel
[22e26].