Catalytic Reforming, Isomerization

Petrochemical & Petroleum
Refining Technology

Conversion Process

(Catalytic Reforming & Isomerization)

Refining Concept

1. Pre-treatment
2. Separation
3. Conversion

 Decomposition (cracking)
[thermal & catalytic cracking, coking and visbreaking]

 Unification (combining)
[alkylation & polymerization]

 Alteration (rearranging)
[catalytic reforming & isomerization]

4. Treatment
5. Blending

Conversion

Introduction

1. 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.

2. Environmental regulations limit on the benzene content in gasoline. If
benzene is present in the final gasoline it produces carcinogenic
material on combustion.

3. 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.

4. These light paraffinic hydrocarbons can be used in an isomerization
unit to produce high octane number isomers.

Catalytic Reforming

1. Catalytic reforming is the process of transforming C7–C10
hydrocarbons with low octane numbers to aromatics and iso-paraffins
which have high octane numbers.

2. A schematic presentation of the feedstock, products and process.

3. 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).

Role of Reformer in the Refinery and Feed
Preparation

1. The catalytic reformer is one of the major units for gasoline
production in refineries. It can produce 37 wt % of the total gasoline
pool.

2. The straight run naphtha from the crude distillation unit is
hydrotreated to remove sulphur, nitrogen and oxygen which can all
deactivate the reforming catalyst.

3. The hydrotreated naphtha (HTN) is fractionated into light naphtha
(LN), which is mainly C5–C6, and heavy naphtha (HN) which is mainly
C7–C10 hydrocarbons.

4. It is important to remove C6 from the reformer feed because it will
form benzene which is considered carcinogenic upon combustion.

5. Light naphtha (LN) is isomerized in the isomerization unit. Light
naphtha can be cracked if introduced to the reformer.

6. Hydrogen, produced in the reformer can be recycled to the naphtha
hydrotreater, and the rest is sent to other units demanding hydrogen.

Role of reformer in the refinery

Research Octane Number

1. 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.

2. RON of paraffins, iso-paraffins and naphthenes decrease as the
carbon number of the molecule increases. Aromatics have the
opposite trend.

RON for pure hydrocarbon

Process Technology

1. 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).

2. The old technologies are fixed bed configuration.
3. Moving bed technology has also recently been introduced.

Semi-regenerative Fixed Bed Process

1. The 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.

2. Reactions such as dehydrogenation of paraffins and naphthenes
which are very rapid and highly endothermic occur in the first reactor,
with high temperature drop.

3. Reactions that are considered rapid, such as paraffin isomerization
and naphthens dehydroisomerization, give moderate temperature
decline in the second reactor.

4. Slow reactions such as dehydrocyclization and hydrocracking give low
temperature decline in the third reactor.

5. 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.

Semi-regenerative Fixed Bed Process

6. Some light hydrocarbons (C1–C4) are separated from the reformate in
the stabilizer.

7. 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.

8. The main product of the column is stabilized reformate, which is sent
to the gasoline blending plant.

Semi-regenerative (SR) fixed bed reforming process

Continuous Regenerative CCR Platforming
UOP Process

1. In this process, three or four reactors are installed one on the top of
the other.

2. UOP has licensed this process under the CCR Platforming process.

3. The effluent from each reactor is sent to a common furnace for
heating.

4. 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.

5. The final product from R4 is sent to the stabilizer and gas recovery
section.

Continuous regenerative reformer (CCR), UOP Platforming process



Isomerization of Light Naphta

1. 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.

2. 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.

3. Light naphtha C5-80C (180F) is used as a feed to the isomerization
unit.

4. 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.

5. Gasoline specifications require a very low value of benzene due to its
carcinogenic effect.

Isomerization Reaction

1. Isomerization is a reversible and slightly exothermic reaction:

n-paraffin  i-paraffin

2. 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.

3. Operation at low temperatures will decrease the reaction rate. For
this reason a very active catalyst must be used.

Isomerization Catalysts

1. 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

1. This bi-functional nature catalyst consists of highly chlorinated
alumina (8–15 w% Cl2) responsible for the acidic function of the
catalyst.

2. Platinumis 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.

3. The reaction is performed at low temperature at about 130C (266F)
to improve the equilibrium yield and to lower chlorine elution.

4. The standard isomerization catalyst is sensitive to impurities such as
water and sulphur traces which will poison the catalyst and lower its
activity.

5. For this reason, the feed must be hydrotreated before isomerization.

6. Furthermore, carbon tetrachloride must be injected into the feed to
activate the catalyst.

Zeolite Catalyst

1. Zeolites are crystallized silico-aluminates that are used to give an
acidic function to the catalyst.

2. Metallic particles of platinum are impregnated on the surface of
zeolites and act as hydrogen transfer centres.

3. 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).

Isomerization Yields

1. The reformate yield from light naphtha isomerization is usually
very high (>97 wt%).