The catalytic hydrotreatment of liquid biomass converts the contained triglycerides/lipids into hydrocarbons at high temperatures and pressures over catalytic material under excess hydrogen atmosphere. The catalytic hydrotreatment of liquid biomass process is quite similar to the typical process applied to petroleum streams, as shown in Figure 3. A typical cata­lytic hydrotreatment unit consists of four basic sections: a) feed prepara­tion, b) reaction, c) product separation and d) fractionation.

In the feed preparation section the liquid biomass feedstock is mixed with the high pressure hydrogen (mainly from gas recycle with some additional fresh make-up hydrogen) and is preheated before it enters the reactor section. The reactor section consists normally of two hydrotreat­ing reactors, a first guard mild hydrotreating reactor and a second one where the main hydrotreating reactions take place. Each reactor contains two or more catalytic beds in order to maintain constant temperature profile throughout the reactor length. Within the reactor section all as­sociated reactions take place, which will be presented in more detail at a later paragraph.

Light hydrocarbons C1-C4
Isomerization product	Fuel gas
Isomerization
Rotor mate
Naphtha
Hydrotreating
Liquid gas
wyM
Alkylation
Alkylation gasodine
Av at on
I ucls
Straight-run kerozene
Hydrotreating
Straight run diesel
■ ■
Hydrotreatin
Jn ended
Gasoline
Hydrocracking gasoline	Heating
Light Vacuum Gasoil
Hydrocracking
Hydrocracking mid-distillate
Heavy Vacuum Gasoil
	Lubricants
МВМЙ
FIGURE 1: Catalytic hydroprocessing units within a refinery, including distillate hydrotreating and hydrocracking

The reactor product then enters the separator section where, after it is cooled down, it enters the high pressure separator (HPS) flash drum in which the largest portion of the gas and liquid product molecules are separated. The gas product of the HPS includes the excess hydrogen that has not reacted within the reactor section as well as the side products of the reactions including CO, CO2, H2S, NH3 and H2O. The liquid product of the HPS is lead to a second flash drum, the low pressure separator (LPS), for removing any residual gas contained in the liquid product, and subse­quently is fed to a fractionator section. The fractionator section provides the final product separation into the different boiling point fractions that yield the desired products including off-gas, naphtha, kerosene and diesel. The heaviest molecules return from the bottom of the fractionator into the reactor section as a liquid recycle stream.

In order to improve the overall efficiency, a liquid recycle stream is also incorporated, which in essence consists of the heavy molecules that were not converted. The gas product from the HPS and LPS, after being treated to remove the excess NH3, H2S, CO and CO2, is compressed and fed back to the reactor section as a gas recycle stream in order to maintain a high pressure hydrogen atmosphere within the reactor section.