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Part B: Analysis of processes 
1. Naphtha hydrotreating unit
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In gasoline production, naphtha hydrotreating is an essential step. Its purpose is to reduce 
sulfur, nitrogen and olefins contents in naphtha before it is fed in paraffin isomerization and 
catalytic reforming as catalysts used in these processes are very sensitive to impurities. 
Approximately 200 processes have been commercialized by Axens. 
1.1. Purpose of the unit 
The purpose of the unit is to produce clean desulfurized naphtha cut able to be processed in 
isomerization and reforming units. Indeed these processes involve catalysts that are very 
sensitive to impurities such as sulfur, nitrogen, water, halogen, diolefins, olefins, arsenic, 
mercury and other metals. The high performances of isomerization and reforming units are 
very much dependent upon the efficiency of the naphtha pretreater. Naphtha hydrotreating 
unit is located after the crude oil distillation and before isomerization and catalytic reforming 
units. It pretreats different types of naphtha such as straight run naphthas (paraffinic naphthas 
from crude oil distillation), coker naphtha (from coking unit), wild naphtha and naphtha from 
hydrocraking unit.
1.2. Raw materials and resources input characteristics 
1.2.1. Naphtha feeds 
The feed of the naphtha hydrotreating unit is a blend of different raw naphtha feeds. It 
contains many different compounds such as paraffins, isoparaffins, olefins, naphtenes and 
aromatics, from C
1
to C
11
. Raw naphtha feeds impurities are principally sulphur, nitrogen and 
diolefins. Finally, silicon, mercury, lead, arsenic, chlorine, fluorine, oxygenates and oxygen, 
and mercapts can be present in trace amounts.
The following table indicates the typical properties of a crude oil distillation naphtha: 
Compound Quantity 
Parrafins 
Olefins 
Naphtenes 
Aromatics 
Sulfur 
Nitrogen 
55.6 % vol. 
0.2 % vol. 
37.5 % vol. 
6.7 % vol. 
500 ppm 
1 ppm 
Table B-1-1: Typical properties of crude oil distillation naphtha 
Naphtha molecular weight is generally between 100 and 215 g/mol. Its boiling point is 
comprised between 80 °C and 180 °C. 

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