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1. Catalytic Reforming and
Isomerization
005-krf-012022

2. 1
INDEX
INTRODUCTION................................................................................................................................ 3
CATALYTIC REFORMING.................................................................................................................... 3
REFORMER FEED CHARACTERIZATION............................................................................................... 3
ROLE OF REFORMER IN THE REFINERY AND FEED PREPARATION ........................................................ 3
RESEARCH OCTANE NUMBER............................................................................................................ 4
REFORMING REACTIONS................................................................................................................... 5
NAPHTHENE DEHYDROGENATION OF CYCLOHEXANES....................................................................... 5
PARAFFIN DEHYDROGENATION......................................................................................................... 5
DEHYDROCYCLIZATION ..................................................................................................................... 5
ISOMERIZATION ............................................................................................................................... 6
HYDROCRACKING REACTIONS .......................................................................................................... 6
PARAFFIN HYDROCRACKING:............................................................................................................. 6
COKE DEPOSITION ............................................................................................................................ 6
THERMODYNAMICS OF REFORMING REACTIONS ............................................................................... 6
EXAMPLE E5.1.................................................................................................................................. 7
REACTION KINETICS AND CATALYSTS................................................................................................. 8
PROCESS TECHNOLOGY .................................................................................................................... 9
SEMI-REGENERATIVE FIXED BED PROCESS ......................................................................................... 9
CONTINUOUS REGENERATIVE (MOVING BED) CCR PLATFORMING UOP PROCESS ............................. 11
ISOMERIZATION OF LIGHT NAPHTHA............................................................................................... 12

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THERMODYNAMICS OF ISOMERIZATION.......................................................................................... 12
ISOMERIZATION REACTIONS ........................................................................................................... 12
ISOMERIZATION CATALYSTS............................................................................................................ 13
STANDARD ISOMERIZATION CATALYST ............................................................................................ 13
ZEOLITE CATALYST.......................................................................................................................... 13
EXAMPLE E5.6................................................................................................................................ 14
SOLUTION: ..................................................................................................................................... 14
REFERENCES................................................................................................................................... 14

4. 3
Catalytic Reforming and
Isomerization
Introduction
Catalytic reforming of heavy naphtha and isomerization of light naphtha constitute a very important
source of products having high octane numbers which are key components in the production of gasoline.
Environmental regulations limit on the benzene content in gasoline. If benzene is present in the final
gasoline, it produces carcinogenic material on combustion. Elimination of benzene forming
hydrocarbons, such as, hexane will prevent the formation of benzene, and this can be achieved by
increasing the initial point of heavy naphtha. These light paraffinic hydrocarbons can be used in an
isomerization unit to produce high octane number isomers.
Catalytic Reforming
Catalytic reforming is the process of transforming C7–C10 hydrocarbons with low octane numbers to
aromatics and iso-paraffins which have high octane numbers. It is a highly endothermic process
requiring large amounts of energy. A schematic presentation of the feedstock, products and process
condition is shown in Figure 5.1. The process can be operated in two modes: a high severity mode to
produce mainly aromatics (80–90 vol%) and a middle severity mode to produce high octane gasoline
(70% aromatics content).
Reformer Feed Characterization
Feeds are characterized by the Watson characterization factor (K), naphthenes (N) vol% and aromatics
(A) vol% in which (N + 2A) must be defined. In addition, initial boiling points (IBP) and end points
(EP) for feeds must be characterized. Feeds can be also characterized by the hydrocarbon family and
their number of carbon atoms. Naphthenic feeds give a much higher yield than paraffinic feeds. The
main feed comes from hydrotreated heavy naphtha, and some feed comes from hydrotreated coker
naphtha.
Figure 5.1 Catalytic reforming process
Role of Reformer in the Refinery and Feed Preparation
The catalytic reformer is one of the major units for gasoline production in refineries. It can produce 37
wt% of the total gasoline pool. Other units such as the fluid catalytic cracker (FCC), the methyl ter-butyl
ether (MTBE) production unit, alkylation unit and isomerization unit, also contribute to this pool.
The straight run naphtha from the crude distillation unit is hydrotreated to remove sulphur, nitrogen and
oxygen which can all deactivate the reform- ing catalyst. The hydrotreated naphtha (HTN) is fractionated
RON : 90 – 100
H2 , C1 , C2 ,
C3 , C4
P : 30 – 50 vol%
N : 5 – 10 vol%
Catalytic Reforming
Feedstock Products
Heavy naphtha
C7– C10
RON : 20 – 50
P: 45– 65 vol%
N: 20–40 vol%
A: 15-20 vol%
Reaction Conditions
Temp : 500°C
Pressure : 5 -25 bar
Platinum-based
catalyst
High heat demand
SR: Semi-
Regenerative
CCR: Continuous
Catalyst

5. 4
into light naphtha (LN), which is mainly C5–C6, and heavy naphtha (HN) which is mainly C7–C10
hydrocarbons. It is important to remove C6 from the reformer feed because it will form benzene which
is considered carcinogenic upon combustion. Light naphtha (LN) is isomerized in the isomerization unit
(I). Light naphtha can be cracked if introduced to the reformer. The role of the heavy naphtha (HN)
reformer in the refinery is shown in Figure 5.2. Hydrogen, produced in the reformer can be recycled to
the naphtha hydro- treater, and the rest is sent to other units demanding hydrogen.
Research Octane Number
The research octane number (RON) is defined as the percentage by volume of iso-octane in a mixture
of iso-octane and n-heptane that knocks with some intensity as the fuel is being tested. A list of the RON
of pure hydrocarbon is given in Appendix D. It is seen from this appendix that the RON of paraffins,
iso-paraffins and naphthene’s decrease as the carbon number of the molecule increases. Aromatics have
the opposite trend. This is shown in Figure 5.3.
Figure 5.2 Role of reformer in the refinery
LN
Gases
iC5 /iC6
Feed HTN
C4
D
U
HT
C4
HN
R
H2
To other hydrogen consuming
units
CDU Crude distillation unit
D Distillation
F Flash
I Isomerization
HN Heavy Naphtha
HT Hydrotreater
HTN Hydro Treated Naphtha
LN Light Naphtha
N Naphtha
R Reformer

6. 5
Figure 5.3 Variation of research octane number (RON)
Reforming Reactions
Naphthene Dehydrogenation of Cyclohexanes
Paraffin Dehydrogenation
Dehydrocyclization
All the above reactions are highly endothermic.

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Isomerization
Isomerization is a mildly exothermic reaction and leads to the increase of
an octane number.
Hydrocracking Reactions
Hydrocracking reactions are the main sources of C— hydrocarbons (C1, C2, C3 and C4). The reactions
are highly exothermic and consume high amounts of hydrogen. Cracking results in the loss of the
reformate yield.
Paraffin hydrocracking:
Hydrocracking of aromatics
Other paraffins can crack to give C1–C4 products.
Coke Deposition
Coke can also deposit during hydrocracking resulting in the deactivation of the catalyst. The catalyst in
this case has to be re-activated by burning off the deposited coke. The catalyst is selected to produce a
slow hydrocracking reaction. Coke formation is favoured at low partial pressures of hydrogen.
Hydrocracking is controlled by operating the reaction at low pressure between 5–25 atm (74–368 psia),
not too low for coke deposition and not too high in order to avoid cracking and loss of reformate yield.
A summary of reformer reactions and interactions is shown by the reaction network in Figure 5.4.
Thermodynamics of Reforming Reactions
The dehydrogenation reactions are the main source of reformate product and are considered to be the
most important reactions in reforming. These are highly endothermic reactions and require a great
amount of heat to keep the reaction going. For this reason, three reactors are usually used in the reforming
process with heating the product from each reactor before entering the other.

8. 7
Figure 5.4 Networkof reforming reaction
The dehydrogenation reactions are reversible and equilibrium is established based on temperature and
pressure. It is usually important to calculate the equilibrium conversion for each reaction. In reforming,
a high temperature around 500 ◦C (932◦F) and a low hydrogen pressure are required. The minimum
partial pressure of hydrogen is determined by the amount of the desired aromatics conversion.
Example E5.1
The Gibbs free energy of the following reaction at 500 ◦
C and 20 atm is calculated to be —20.570
kcal/mol
+ 3H2
(CH) (B)
Calculate the reaction equilibrium conversion and barrels of benzene formed per one barrel of
cyclohexane.
The hydrogen feed rate to the reactor is 10,000 SCF/bbl of cyclohexane.
Solution:
The Gibbs free energy of a reaction is defined as:
DG = —RT ln(K)
Using this equation, the equilibrium constant can be evaluated as
—20, 570 = —(1.987)(773) ln(K), K = 6.55 × 105
Normal Paraffins
M/A M/A
I
III
Cracked
Product
II A M
Naphthenes Aromatics
IV
M/A M/A
I
Iso Paraffins
III
M - Metal catalyst
I – Hydrocracking
III – Dehydro-Cyclizing
A - Acid catalyst
II - Isomerization
IV – Dehydrogenation

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Reaction Kinetics and Catalysts
The catalyst used for reforming is a bifunctional catalyst composed of platinum metal on chlorinated
alumina. Platinum acts as the centre for the dehydrogena- tion reaction, and chlorinated alumina acts as
an acidic site to promote structure changes, such as cyclization of paraffins and isomerization of the
naphthenes.
Recently additional elements have been added to platinum to promote additional properties for the
catalyst. Iridium (Ir) is added to boost activity, Rhenium (Re) is added to operate at lower pressures and
Tin (Sn) is added to improve yield at low pressures. The use of Pt/Re is now most common in semi-
regenerative (SR) processes with Pt/Sn is used in moving bed reactors. The quantity of chlorine used is
approximately 1 wt% of the catalyst and the quantity of platinum is from 0.2 to 0.6 wt%. Impurities that
might cause deactivation or poisoning of the catalyst include: coke, sulphur, nitrogen, metals and water.

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Because of these problems, the reformer feed has to be severely hydrotreated to remove most of these
impurities, and the reformer should be operated at high temperature and low pressure to minimize coke
deposition.
Paraffin and naphthene dehydrogenation reactions are very rapid and usually occur in the first reactor.
The isomerization of paraffin and naphthenes is fast, whereas hydrocracking is slow and takes place in
the last reactor. The effect of operating conditions on reaction rate and other properties is shown in Table
5.1.
Process Technology
There are several commercial processes available for reforming. These include Platforming (UOP),
Powerforming (Exxon), Magna forming (Engelhard), Catalytic reforming (IFP), Rheniforming
(Chevron) and Ultra forming (Amoco). The old technologies are fixed bed configuration. Moving bed
technology has also recently been introduced.
Semi-regenerative Fixed Bed Process
The schematic flow diagram of this process is shown in Figure 5.5. The name semi-regenerative comes
from regeneration of the catalyst in the fixed bed reactors after shut down by burning off the carbon
formed on the catalyst surface.
Reactions such as dehydrogenation of paraffins and naphthenes which are very rapid and highly
endothermic (Table 5.1) occur in the first reactor, with high temperature drop. Reactions that are
considered rapid, such as paraffin isomerization and naphthens dehydroisomerization, give moderate
temperature decline in the second reactor. Furthermore, slow reactions such as dehydrocyclization and
hydrocracking (Table 5.1) give low temperature decline in the third reactor.
Figure 5.5 Semi-regenerative (SR) fixed bed reforming process
Compressor
Net H2
Recycle H2
1st
Reactor
2nd
Reactor
3rd
Reactor
Off gases
Heater Heater Heater
C3’s and C4’s
Heavy
Naphtha
Stabilizer
Separator
Reformate

11. 10
Table 5.1 Thermodynamic and kinetic comparison and effect of operating condition on main
reactions and products
The temperature and concentration profile in each reactor is shown in Figure 5.6. To prevent catalyst
coking, the hydrogen partial pressure is maintained at a level such that the hydrogen-to-hydrocarbon
ratio by weight (H2/HC) is greater than 25 for monometallic catalyst. This is done by recycling some of
the hydrogen produced (Figure 5.5). Some light hydrocarbons (C1–C4) are separated from the reformate
in the stabilizer. At the top of the stabilizer residual hydrogen and C1 to C4 are withdrawn as condenser
products, which are then sent to gas processing, and part of the liquid product (C3 and C4) is returned
from the reflux drum back to the stabilizer (Figure 5.6). The main product of the column is stabilized
reformate, which is sent to the gasoline blending plant.
A slight modification to the semi-regenerative process is to add an extra- reactor to avoid shutting down
the whole unit during regeneration. Three reactors can be running while the forth is being regenerated.
This modified process is called the ‘‘cyclic fixed bed’’ process.

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Figure 5.6 (A) Furnace and reactor layout for fixed bed reformer (B) Variation of tem- perature in the
reactors. (C) Variation in effluent compositions; P0, initial Paraffins; N0, initial Napthenes and A0, intial
Aromatics
Continuous Regenerative (moving bed) CCR Platforming UOP Process
In this process, three or four reactors are installed one on the top of the other. The schematic flow diagram
of the continuous regenerative process (CCR) is shown in Figure 5.7 UOP has licensed this process
under the CCR Platforming process The effluent from each reactor is sent to a common furnace for
heating. The catalyst moves downwards by gravity from the first reactor (R1) to the forth reactor (R4).
The catalyst is sent to the regenerator to burn off the coke and then sent back to the first reactor R1. The
final product from R4 is sent to the stabilizer and gas recovery section.
The process can be operated at lower hydrogen partial pressure (PH2 = 3 bar) compared to the semi-
generative process (PH2 = 35 bar), with a reformate yield gain of nearly 10 vol%.

13. 12
Figure 5.7 Continuous regenerative reformer (CCR), UOP Platforming process
Isomerization of Light Naphtha
Isomerization is the process in which light straight chain paraffins of low RON (C6, C5 and C4) are
transformed with proper catalyst into branched chains with the same carbon number and high octane
numbers. The hydrotreated naphtha (HTN) is fractionated into heavy naphtha between 90–190 ◦C (190–
380 ◦F) which is used as a feed to the reforming unit. Light naphtha C5 — 80 ◦C (C5 — 180 ◦F) is used
as a feed to the isomerization unit. There are two reasons for this fractionation: the first is that light
hydrocarbons tend to hydrocrack in the reformer. The second is that C6 hydrocarbons tend to form
benzene in the reformer. Gasoline specifications require a very low value of benzene due to its
carcinogenic effect.
Thermodynamics of Isomerization
The isomerization reactions are slightly exothermic, and the reactor works in the equilibrium mode.
There is no change in the number of moles and thus the reaction is not affected by pressure change.
Better conversions are achieved at lower temperature as shown in Figure 5.8. Operating the reactor at
130 ◦C (260 ◦F) will give good results. In this figure, the degree of conversion to iso-paraffins is
measured by the increase of the RON. Paraffin recycle substantially increases the conversion.
Isomerization Reactions
Isomerization is a reversible and slightly exothermic reaction:
n-paraffin E —▶ i-paraffin

14. 13
The conversion to iso-paraffin is not complete since the reaction is equilibrium conversion limited. It
does not depend on pressure, but it can be increased by lowering the temperature. However operating at
low temperatures will decrease the reaction rate. For this reason a very active catalyst must be used.
Isomerization Catalysts
There are two types of isomerization catalysts: the standard Pt/chlorinated alumina with high chlorine
content, which is considered quite active, and the Pt/zeolite catalyst.
Standard Isomerization Catalyst
This bi-functional nature catalyst consists of highly chlorinated alumina (8–15 w% Cl2) responsible for
the acidic function of the catalyst. Platinum is deposited (0.3–0.5 wt%) on the alumina matrix. Platinum
in the presence of hydrogen will prevent coke deposition, thus ensuring high catalyst activity. The
reaction is performed at low temperature at about 130 ◦C (266 ◦F) to improve the equilibrium yield and
to lower chlorine elution.
The standard isomerization catalyst is sensitive to impurities such as water and sulphur traces which will
poison the catalyst and lower its activity. For this reason, the feed must be hydrotreated before isomeriza-
tion. Furthermore, carbon tetrachloride must be injected into the feed to activate the catalyst. The
pressure of the hydrogen in the reactor will result in the elution of chlorine from the catalyst as hydrogen
chloride. For all these reasons, the zeolite catalyst, which is resistant to impurities, was developed.
Zeolite Catalyst
Zeolites are crystallized silico-aluminates that are used to give an acidic function to the catalyst. Metallic
particles of platinum are impregnated on the surface of zeolites and act as hydrogen transfer centres. The
zeolite catalyst can resist impurities and does not require feed pretreatment, but it does have lower
activity and thus the reaction must be performed at a higher temperature of 250 ◦C (482 ◦F). A
comparison of the operating conditions for the alumina and zeolite processes is shown in Table 5.6.
Table 5.6 Comparison of operating conditions of isomerization
Table 5.7 Isomerization yield
Operating condition
Pt/Chlorine
Alumina catalyst Pt/Zeolite catalyst
Temperature (◦
C) 120–180 250–270
Pressure (bar) 20–30 15–30
Space velocity (h—1) 1–2 1–2
H2/HC (mol/mol) 0.1–2 2–4
Product RON 83–84 78–80
Component Yield (wt%)
C3 0.348
iC4 0.619
nC4 1.770
C+ 97.261
5

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Example E5.6
Light naphtha with a specific gravity of 0.724 is used as a feed to the isomerization unit at a rate of 100
m3/h. Find the product composition.
Solution:
Appling the yield guidelines of Table 5.7, the product composition is presented in Table E5.6.1.
Table E5.6.1 Isomerization yields
REFERENCES
Antos, G. J. et al. (1995). ‘‘Catalytic Naphtha Reforming.’’ Marcel Dekker, New York.
Gary, J. H., and Handwerk, G. E. (2001). ‘‘Petroleum Refining.’’ Marcel Dekker, New
York.
Kaes, G. L. (2000). ‘‘Refinery Process Modeling.’’ Kaes Enterprises Inc., Colbert (Georgia).
Maples, R. E. (1993). ‘‘Petroleum Refining Process Economics.’’ PennWell Book, Tulsa.
Martino, G. (2001). ‘‘Catalytic Reforming’’ Chapter 4 in ‘‘Conversion Processes’’ Petro-
leum Refining, Vol. 3, Leprince, P., ed., TECHNIP, France.
Travers, C. (2001). ‘‘Isomerization of light paraffins’’ Chapter 6 in ‘‘Conversion Processes’’
Petroleum Refining, Vol. 3, Leprince, P., ed., TECHNIP, France.
UNISIM Design Suite R370, Honeywell Process Solutions, Calgary, Alberta, Canada.
wt% kg/h
Feed 100 72,400
Product
C3 0.348 251.9
iC4 0.619 448.2
nC4 1.770 1281.5
C+ 97.261 70,417
Total 72,399