1.2.2. Hydrogen make-up The hydrogen make-up is supplied from the isomerization unit or from another unit. It
contains about 95% hydrogen, and hydrocarbons from C
1
to C
5
. Impurities that can be found
are sulphur, nitrogen compounds, carbon oxides, carbonyl sulphide, olefins and chlorides, all
these compounds present in trace amount.
1.2.3. Catalyst Hydrotreating catalysts are oxide supported (generally Al
2
O
3
) and the active phase is
molybdenum or tungsten sulfur with cobalt or nickel.
1.3. Products characteristics
There are two products from naphtha hydrotreating unit: heavy naphtha that goes to catalytic
reforming unit, and light naphtha that goes to isomerization unit.
The following table indicates the typical properties of naphtha hydrotreating products:
Compound Isomerization product Reforming product Parrafins
Olefins
Naphtenes
Aromatics
Sulfur
Nitrogen
82.5 % vol.
-
16.5 % vol.
1 % vol.
< 0.5 ppm
< 0.5 ppm
47.8 % vol.
-
48.6 % vol.
8.6 % vol.
< 0.5 ppm
< 0.5 ppm
Table B-1-2: Typical properties of naphtha hydrotreating products 1.4. Normal operations
The figure B-1-1 is an example of a process flow diagram for a naphtha hydrotreating unit in
normal operations. The process flow diagram can be separated into two sections: the reaction
section and the separation section. Before entering the reaction circuit, naphthas from
different sources are mixed together and with hydrogen.
