Microsoft Word master thesis report fina doc

Destination 
Disposal in landfill, recycling / reuse, or regeneration 
Quantity 
Depends on dryers / column size
Composition 
Contaminated molecular sieves 
Solid adsorbents are used in three locations in the isomerization process: naphtha feed 
purification, hydrogen feed purification and separation of the product. These adsorbents are 
regularly regenerated but when they are no longer efficient, they are replaced by fresh 
adsorbents. Used adsorbents are either disposed of in landfill or reused in cement plant and 
road materials or stored in pile.
2.7. Emissions reduction proposals 
2.7.1. Air emissions 
Air emissions from isomerization unit in normal operations arise from process heaters, vents 
and fugitive emissions.
In order to reduce fugitive emissions, a leak detection and repair program can be established 
(see part A of this report). 
Concerning process heaters, old furnaces that produce NOx, SOx and particulate matters 
should be replaced with emission controls furnaces. 
2.7.2. Water emissions 
Two types of water emissions occur in this process: spent caustics and oily water. 
Spent caustics do not contain sulfur and phenols but about 10 % of NaCl salt and dissolved 
hydrocarbons. These hydrocarbons can be removed and recycled. These spent caustics are 
free of phenols and sulfur compounds so it should not be mixed with other spent caustics 
(which can be sent to phenol recovery units for example). 
Oily water removed from the regeneration degasser is also expected to be free from impurities 
such as sulfur or nitrogen compounds. It represents a very small amount. 
2.7.3. Solid wastes 
Concerning the catalyst, source reduction methods are those that extend its life. Its time life is 
comprised between three and five years but it can sometimes be replaced after more years. 
Currently, recycling of the spent catalyst by sending to metals reclamation is a common 
practice since the catalyst is platinum. 
Adsorbents are used to extend catalyst life; they are consequently a source reduction 
technique for other residuals. They do not have themselves source reduction methods. Their 
time life is about three years. 

---

33
2.8. Dioxins emissions 
Dioxin compounds are in fact polychlorodibenzo-p-dioxins (PCDD), which include also 
furans and pyralens. PCDD are aromatic tricyclic chrorinated molecules. Below is an example 
of a compound from this family: 
Figure B-2-6: 2,3,7,8-Tetrachlordibenzodioxin 
Dioxins and furans are formed only in two refining processes: naphtha catalytic reforming 
and isomerization units. 
Three major mechanisms are nowadays identified for the formation of dioxins. The first 
mechanism involves PCDDs/PCDFs (polychlorinated dibenzo-p-dioxin/polychlorinated 
dibenzofuran) contained in the feed and released intact to the environment after combustion, 
the second mechanism (precursor mechanism) involves the formation of PCDDs/PCDFs from 
the thermal breakdown and molecular rearrangement of aromatic precursors either originating 
in the feed or forming as a product of incomplete combustion and the third mechanism 
involves the heterogeneous solid-phase formation of PCDDs/PCDFs in the post-combustion 
environment on the surface of fly ash.
The formation of dioxins occurs then in case of combustion. It can be supposed nevertheless 
that the second mechanism could occur in an isomerization process in the petroleum industry.
An aromatic compound like benzene reacts with chlorine, causing hydrogen abstraction and 
the formation of chlorobenzenes and chlorophenols. Homogeneous gas-phase formation of 
PCDDs/PCDFs occurs from these precursor compounds at temperatures higher than 500°C, 
catalyzed by the presence of copper compounds or other heavy metals. Heterogeneous 
formation of PCDDs/PCDFs from gas-phase precursors has been observed at temperature 
comprised between 200 and 450°C and by the presence of a transition metal. 
Dioxin formation mechanisms are not well-known so we can suppose that the heating of 
organic molecules in presence of a chlorine source in industrial processes can produce dioxins 
that are released to the atmosphere in case of gas relieves or depressurization. 
However, in the literature, source of dioxins concerning petroleum industry is the reforming 
and isomerization catalyst regeneration (isomerization catalyst regeneration is very rare). 
 
Nothing either is specified in the European Legislation concerning dioxins emissions in the 
petroleum industry. 
Conclusion 
The isomerization process is different from the others because of the presence of chlorine. 
This chlorine is scrubbed in normal operation but can be released in case of gas relieves and 
depressurization.

---

34
3. Catalytic reforming
9,14,15,16,17,18,19 
 
Catalytic reforming is a key process in gasoline production. It allows upgrading naphtha cut 
to high-octane products by the obtaining of aromatic products. These compounds are formed 
through complex series of reactions such as cyclohexanes dehydrogenation, cyclopentanes 
isomerization and dehydrogenation, paraffins isomerization and dehydrocyclization.
Moreover, catalytic reforming is great source of hydrogen. Axens offers several types of 
catalytic reforming: semi-regenerative process, cyclic process (Dualforming
®
) and continuous 
process (Octanizing). 
3.1. Purpose of the unit 
The purpose of the unit is to produce high-octane products thanks to different type of reaction 
explained later in this chapter. Catalytic reforming unit is located after the hydrotreating unit 
because the catalyst is very sensitive to impurities. The product obtained (reformate) enters in 
gasoline composition. It can also be sent to the isomerization unit. 
3.2. Raw materials and resources input characteristics