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2.4.1. Reactions 
With platinum on chlorinated alumina based catalyst, the process must include feed and 
hydrogen dryers and continuous chlorine injection.
Figure B-2-1 is an example of simplified process flow diagrams for a naphtha isomerization 
unit in normal operations.

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27
Naphtha
H
2
dryers
Chlorine
Reactor
Stabilization
column
Isomerate
Gas
Scrubber
Figure B-2-1: Simplified process flow diagram for isomerization with chlorinated Pt/Al
2
O
3
 
catalyst 
Chlorine injection is necessary to maintain the chlorine amount on the catalyst. Carbon 
tetrachloride (CCl
4
) and tetrachloroethylene (C
2
Cl
4
) are usually utilized. A scrubber with 
caustic soda and feed water is necessary to eliminate chlorhydric acid present in gases. 
Axens offers several types of isomerization processes: one through or recycle. In order to 
recycle n-paraffins which have not been transformed, it is necessary to separate it from 
isoparaffins. This separation can be achieved either by distillation (diisopentanizer or 
deisohexaniser) which is big energy consumer or by adsorption on molecular sieve. A 
combination of both can also be designed (IPSORB
®
and HEXORB
®
). (See figures B-2-2 and 
B-2-3). 
Light naphtha
(C
5
/C
6
)
H
2
Diisopentanizer
Reactor
Stabilization
column
Molecular
sieve
Isomerate
Gas
Figure B-2-2: IPSORB
®
 isomerization process 

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28
Light naphtha
(C
5
/C
6
)
H
2
Reactor
Stabilization
column
Isomerate
Gas
Separation on 
molecular sieve
Deisohexanizer
Figure B-2-3: HEXORB
®
 isomerization process 
Examples of reactions occurring are given below: 
CH ─ CH
2 
─ CH
3
CH
3
CH
3
CH
3
─ (CH
2
)
3
─ CH
3
CH
3
─ (CH
2
)
4
─ CH
3
CH ─ (CH
2
)
2 
─ CH
3
CH
3
CH
3
+
CH
3 
─ CH
2
─ CH ─ CH
2 
─ CH
3
CH
3
CH
3
─ C ─ CH
2 
─ CH
3
CH
3
CH
3
CH
3
─ CH ─ CH
2 
─ CH
3
CH
3