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4.4.3. Gasoline hydrogenation 
Figure B-4-3: Flow sheet of the gasoline hydrogenation process 
First stage reaction section 
The raw pyrolysis gasoline coming from the debutanizer bottom is routed to the feed drum 
where a boot allows trapping and draining water if any. It is then mixed with hydrogen make-
feed
H
2
make-up
feed
drum
pump
pump
pump
pump
H
2
O
H
2
O
reactor 1
separator
hot
separator
cold
air cooler
reactor 2
separator
compressors
compressor
column
product
air cooler
vent to 
sour gas

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up and recycle diluent from separators, enters the reactor top and flows downwards through 
two beds of the same catalyst. Reactions occur in mixed phase (mainly liquid).
Main reactions happening are:
- Hydrogenation of diolefins. 
- Hydrogenation of alkenyl aromatics (hydrogenation of the linear side chain). 
- Isomerization of olefins. 
- Hydrogenation of olefins 
- Thermal and catalytic polymerization of unstable compounds. 
The two last reactions must be avoided. 
After being cooled, reactor effluent is sent to hot separator. Vapor from the separator, which 
contains light hydrocarbons, is partially condensed and sent to cold separator. Vapor from the 
cold separator is sent to second stage reaction section as hydrogen make-up. Liquid effluents 
from hot and cold separators are mixed together. Part of this liquid is recycled, the remaining 
is sent to the second stage reaction section. 
Second stage reaction section 
The feed coming from the first stage reaction section is mixed with the recycle gas. The 
mixture is heated before entering the second reactor top and flows downward through two 
types of catalysts: the first one to finish hydrogenation, the second one for desulphurization.
Main desirable reactions occurring are: 
- Hydrogenation of olefins. 
- Hydrogenation of sulphur compounds. 
After consecutive cooling, reactor effluent enters a separator in which the vapour phase is 
partly purged, partly recycled, and the liquid phase is partly recycled, partly fed to stabilizer 
column. 
Stabilization section 
The purpose of this column is to eliminate light components such as hydrogen and hydrogen 
sulphide dissolved in the gasoline. 
The stabilizer overhead is condensed and sent in a reflux drum where vapour and liquids 
phases are separated. Vapour phase is routed to sour gas and decanted water is sent to battery 
limit. 
The column bottom stream constitutes the final product. This desulphurized product is cooled 
down and routed to battery limit.