isolation n-butane

REPUPLIC OF IRAQ
MINISTRY OF HIGHER EDUCATION AND SCIENTIFIC RESEARCH
UNIVERSITY OF TECHNOLOGY
BAGHDAD- IRAQ

IMPROVEMENT OF CATALYSTS
FOR HYDROISOMERIZATION
OF IRAQI LIGHT NAPHTHA

A THESIS
SUBMITED TO THE DEPARTMENT OF CHEMICAL
ENGINEERING OF THE UNIVERSITY OF TECHNOLOGY IN
A PARTIAL FULFILMENT OF THE REQUIREMENTS FOR
THE DEGREE OF MASTER OF SCIENCE IN
CHEMICAL ENGINEERING

BY
Muayad Mohammed Hasan
B.Sc. in CHEMICAL ENGINEERING

March, 2010

‫َ‬ ‫ُ ْ َﺎﻧ َ ِﻠﻢ ﻟﻨ إ َ ﻋﻠﻤﺘﻨ إﻧ‬
‫ﻗَﺎُﻟﻮا ﺳﺒﺤ َﻚ ﻻ ﻋ َ ََـﺎ ِﻻﱠ ﻣﺎ ﱠ ََـﺎ ِﱠﻚ‬
‫ـ‬

‫أَﻧﺖ اﻟﻌِﻴﻢ اﻟﺤﻜﻴﻢ‬
‫ِ‬
‫ْ َ َﻠ َ‬

‫ﺻﺪق اﷲ اﻟﻌﻈﻴﻢ‬

‫ﺳﻮﺭﺓ ﺍﻟﺒﻘﺮﺓ ﺍﻻﻳﺔ )23(‬

CERTIFICATE

We certify that we have read this thesis entitled "Improvement of Catalysts for
Hydroisomerization of Iraqi Light Naphtha" by Muayad Mohammed
Hasan and as on Examining Committee examined the student in its contents and
that in our opinion it meets the standard of a thesis for the degree of Master of
Science in Chemical Engineering.

Signature: Signature:

Asst. Prof. Dr. Khalid A. Sukkar Asst. Prof. Dr. Shahrazad R. Raouf

(Supervisor) (Chairman)

Date: / / 2010 Date: / / 2010

Signature: Signature:

Asst. Prof. Dr. Wadood T. Mohammed Asst. Prof. Dr. Saba A. Ghani

(Member) (Member)

Date: / / 2010 Date: / / 2010

Approved for the University of Technology – Baghdad

Signature:

Prof. Dr. Mumtaz A. Zablouk

Head of Chemical Engineering Department

Date: / / 2010

SUPERVISOR CERTIFICATION

I certify that this thesis entitled:- "Improvement of Catalysts for
Hydroisomerization of Iraqi Light Naphtha" Presented by Muayad
Mohammed Hasan, was prepared under my supervision in a partial fulfillment
of the requirements for the degree of Master of Science in Chemical Engineering
at the Chemical Engineering Department, University of Technology.

Signature:

Name: Asst. Prof. Dr. Khalid Ajmi Sukkar

(Supervisor)

Date: / / 2010

In view of the available recommendations I forward this thesis for debate by the
Examination Committee.

Signature:

Name: Asst. Prof. Dr. Khalid Ajmi Sukkar

Deputy Head of Department of Chemical Engineering

Date: / / 2010

CERTIFICATION

This is to certify that I have read the thesis titled "Improvement of
Hydroisomerization Process to Produce High Octane Gasoline using
Modified Catalysts" and corrected any grammatical mistake I found.
The thesis is therefore qualified for debate.

Signature:

Name:

Date: / / 2010

Acknowledgment

Acknowledgment

First of all praise be to god Who give me patience, strength and the most
important thing: faith to continue...

I wish to present my sincere appreciation with deep respect to my
supervisor Dr. Khalid Ajmee Sukkar for his helpful efforts and advice
during my work.

My great gratitude is due to the Head and the staff of Chemical
Engineering Department of the University of Technology for their help
and assistance in providing facilities throughout this work.

My respectful regards to Mr. Bushier Yosuf Sharhan for his kindness and
helpful efforts to making the characterization of my work.
Finally my grateful thanks are due to my wife for her encouragement and
support.

I

Summary

Summary
In the presented work hydroisomerization of Iraqi light naphtha (produced in Al-
Dura Refinery) has been investigated to produce isomers. Three types of catalysts
were prepared Pt/HY, Pt/BaY, and Pt/Al 2 O 3 with 0.5wt% by impregnation with
hexachloroplatinic acid.

The catalytic unit was constructed from stainless steel and designed to carry out
the hydroisomerization process. The fixed bed reactor dimensions were O.D 3cm,
I.D 2cm, and 21cm high. All experiments were made at atmospheric pressure and
reaction temperature of 230, 250, 270, 290, and 310°C, WHSV 1.5, 3, and 4.5h-1,
under constant H 2 /HC mole ratio of 4.

The results show that the conversion of the main light naphtha components (n-
pentane, n-hexane, 2-methylpentane, and 3-methylpentane) increases with increase
in reaction temperature and decreases with increase in weight hour space velocity.
Also, it was noted that the selectivity to isomers increase with Pt/HY, Pt/BaY
catalysts at low temperature and decrease at high temperature, while with Pt/Al 2 O 3 R R R R

catalyst the aromatics products increase with increase in reaction temperature.

Pt/HY catalyst gives higher selective isomerization than Pt/BaY catalyst which is
(95%) and (89%) respectively at 270°C, and (1.5 hr-1). While, Pt/Al 2 O 3 catalyst
P P R R R R

gives 64.7% as total conversion where 18% as aromatic products. The total
conversion for Pt/HY and Pt/BaY were about 50%. The following sequence for
isomerization selectivity was concluded as:

Pt/HY > Pt/BaY > Pt/Al 2 O 3R R R R

II

Summary

A kinetic model was derived based on the present work results. Then, the kinetic
parameters such as K 1 , K 2 , K o , and activation energy (E) are calculated depending
on the present experimental work results.

The results of model show that the values of apparent activation energy
vary within a range of 22 and 23 kJ/mol for n-pentane, 20 to 24 kJ/mol for
n-hexane, and 15 to 17 kJ/mol for 3mp isomerization reactions. On the
other hand, the model pointed the reactivity order behaves as follows.

3-methylpentane > n-hexane > n-pentane

Derive an equations which are calculating the reaction rate constants (k 1 and k 2 )
parameters as follows:

k1= [(1+ Є) Ln – Єx]

C iso = C A° [1- exp (- k 1 t) - [exp(-k 1 t) – exp(-k 2 t)]
R R R R

III

Contents

CONTENTS

Subject Pages

Acknowledgments I

Summary II

Contents IV

Nomenclature VIII

CHAPTER ONE : INTRODUCTION

1. 1 Introduction 1

1. 2 Aims of the Work 3

CHAPTER TWO: LITERATURE SURVEY

2. 1 Scope 4

2. 2 Gasoline Fuel and its Specifications 5

2. 3 Hydroisomerization Process 9

2. 3. 1 Catalysts for Hydroisomerization Process 14
16
2.3.1.1 Alumina
17
2.3.1.2 Zeolite

2.4 Previous Work 20

IV

Contents

2.5 Catalysts Preparation 27

2.5.1 Impregnation 28

2.5.2 Calcination 30

2.5.3 Reduction 30

2.6 Catalysts Characterization 31

2.6.1 X-ray Diffraction (XRD) 32

2.6.2 Surface Area 32

2.6.3 Scanning Electron Microscopy (SEM) 33

CHAPTER THREE: EXPERIMENTAL WORK

3.1 Materials 34

3.2 Preparation of Modified Zeolites by Ion Exchange 37

3.2.1 Preparation of Barium- Zeolite 37

3.2.2 Preparation of HY- Zeolite 37

3.3 Catalysts Preparation 38

3.3.1 Preparation of Pt/ BaY and Pt/HY 38

3.3.2 Preparation of Pt/ AL 2 O 3
R R R 38

3.4 Experimental Unit 39
3.5 Procedure 42
3.6 Catalysts Characterization 45

V

Contents

3.6.1 X-Ray Diffraction Analysis 45


3.6.3 Scanning Electron Microscopy (SEM) 45

3.6.4 Energy Dispersive X-Ray (EDAX) Analysis 45

CHAPTER FOUR: KINETIC ANALYSIS

4.1 Introduction 46

4.2 Model Development 48

4.3 Reactor Model 51

CHAPTER FIVE: RESULTS AND DISCUSSION

5.1 Characterization of Catalysts 56

5.1.1 X-ray Diffraction 56

5.1.2 Scanning Electron Microscopy (SEM) Analysis 57

5.1.3 Energy Dispersive X-ray (EDAX) Analysis 58


5.2 Effect of Operating Conditions 61

5.2.1 Effect of Temperature 61
5.2.1.1 Effect of Temperature on Conversion of 61
light naphtha

5.2.1.2 Effect of Temperature on Total Conversion 66
of light naphtha and Selectivity

VI

Contents

5.2.2 Effects of WHSV 75

5.2.3 Effect of Time 78

5.3 Results of Kinetic Study
82

CHAPTER SIX: CONCLUSIONS AND
RECOMMENDATIONS

6. 1 Conclusions 90

6. 2 Recommendations 91

REFERENCES 92

APPENDIX A (Volume Percent of Components) 106

APPENDIX B (Concentration of Components) 118

APPENDIX C (Conversion of Light Naphtha) 121

APPENDIX D (Reaction Rate Constants) 123

APPENDIX E (Percentage Selectivity and Conversion) 125

APPENDIX F (Sample of Calculation) 126

VII

Nomenclature

Nomenclature
Symbols Definition Units

Concentration of Normal
CA R gm-mol/lit
Paraffins at any Time
Initial Concentration of
CAo R RP gm-mol/lit
Normal Paraffins
C isoR Concentration of iso-Paraffins gm-mol/lit
CN R Concentration of Olefin gm-mol/lit
A integration constant (-)
-r A R rate of reaction mole/gcat. hr
T Time hr
T Temperature K
To P Initial Temperature K
WHSV Weight Hour Space Velocity hr-1
P

ko R Pre-Exponential Factor (-)
k1 R R Rate Constant for Paraffins hr-1
P

k2 R Rate Constant for Olefins hr-1
P

E Activation Energy kJ/mole
Molar Flow Rate of
FA R mole/hr
Component A
Initial Molar Flow Rate of
FAo
R RP

Component A mole/hr

VIII

Nomenclature

R Gas Constant atm-lit/gm-mol-K
VA R Volume of Reactor cm3
P

X
R Conversion (-)
Zt Length of Reactor cm
Integration Step for the Reactor
∆z
Length (-)

IX

Nomenclature

Abbreviations

RON Research Octane Number
MON Motor Octane Number
RVP Reid Vapor Pressure
ASTM American Society for Testing Materials
MTBE Methyl Tertiary-Butyl Ether
UOP Universal Oil Product Company
BUTAMER Butane Isomerization Unit
MOR Mordenite
i-C 5 R iso-Pentane
C5
R n-Pentane
C6
R n-Hexane
2MP 2-Methylpentane
3MP 3-Methylpentane
2,2DMB 2,2-Dimethylbutane
2,3DMB 2,3-Dimethylbutane
2,2DMP 2,2-Dimethylpentane
2,4DMP 2,4-Dimethylpentane

X

Chapter One Introduction

Chapter One
Introduction

1.1 Introduction

The interest in improving the efficiency of the automotive motors
encourages the formulation of new catalysts and the development of
processes for gasoline.
Due to the environmental restrictions a reduction in allowable of lead
compounds levels and toxic compounds such as aromatics, in particular
benzene, olefin, sulfur-containing components in automobile gasoline
were imposed, as a result it forced refineries to implement new octane
enhancement projects.

Considering that branched-chain alkanes posses the greatest octane
numbers, the normal alkane's hydroisomerization is one of the most
effective project decisions in a direction favoring the least initial
investment approach as opposed to the best overall payout. The use of
gasoline containing higher content of these compounds is one alternative
to obtain clean fuel with high antiknock characteristics.

In order to increase the gasoline octane number, major petroleum
refineries used different units such as catalytic reforming, cracking,
alkylation, oligomerization, polymerization and isomerization
(hydroisomerization) [Benadda et al., 2003, Nattaporn and James, 2007].
It is important to mention here that the petroleum industry is looking for
economical solutions to meet new regulatory specifications for producing
environmentally clean fuels. Most of the implemented legislations require

1


a reduction and a limitation on the concentration of benzene in the
gasoline pool. This has increased the demand for high performance C 5
and C 6 naphtha isomerization technology because of its ability to reduce
the benzene concentration in the gasoline pool while maintaining or
increasing the pool octane.

Light paraffin isomerization has been used historically to offset octane
loss from lead-phase out and to provide a cost-effective solution to
manage benzene in motor fuels. In the current refining environment,
isomerate octane can be used to offset octane loss from MTBE phase-out
[Anderson et al., 2004]. Therefore, the hydroisomerization of light
naphtha (C 5 -C 6 fractions) is an industrially important process and is used
in the production of high octane gasoline blend stocks. The process
involves the transformation (with minimal cracking) of the low octane
normal (and less branched) paraffin components into the high octane
isomers with greater branching of the carbon chain [Ravishankar and
Sivasanker, 1996, Andreas, 2003, Rachid et al., 2006, María et al., 2008].

In Iraq there is no clear strategies to reduce the demand for leaded
gasoline and aromatics (Benzene). Therefore, the hydroisomerization
units are regarded a good solution and a good start point strategy in
direction of clean fuels.
The metal– acid bifunctional catalysts, such as alumina or zeolite
supported Pt catalysts, are used in hydroisomerization of light paraffins
(n-pentane and n-hexane). It shows high efficiency in the isomerization of
alkanes. The isomerization of pentane and hexane is successfully carried
out using noble metals such as Pt- or Pd- supported on Al 2 O 3 , mordenite,
beta zeolite, and silicon catalyst. However, difficulties are encountered
with hydrocarbons larger than heptane because the cracking reaction

2


becomes more significant over these isomerization catalysts as the chain
length increases. So, some modification and pretreatment processes are
required to increase the catalyst activity, selectivity and life time [Takeshi
et al., 2003, Ping et al., 2009].
The literature mentions many studies which were focused to investigate
the hydroisomerization of n-paraffins [Liu et al., 1996, Chica and Corma,
1999, Yunqi et al., 2004, Salwa et al., 2007]. Few investigations have
used light naphtha as a feedstock for the process. On the other hand, many
authors made a kinetic study on the hydroisomerization unit for n-hexane
and n-heptane [Runstraat et al., 1997, Annemieke et al., 1997, Franciscus,
2002, Toshio, 2004, Matthew, 2008]. But only few studies dealling with
the hydroisomerization of light naphtha were published [Holló et al.,
2002, Carsten, 2006].

1.2 Aims of the Work
The main aims of the present work are:
1- Preparation of modified zeolites (BaY and HY) by ion exchange
method.

2- Preparation of Pt/ BaY and Pt/HY by impregnation method.

3- Study the hydroisomerization of Iraqi light naphtha over
bifunctional zeolite catalysts and test of the prepared catalysts
activity and selectivity under different operating conditions of
temperature, and WHSV.

4- To make a mathematical model to describe the reaction kinetics of
the hydroisomerization process.

5- To estimate kinetics parameters under different operating conditions

depending on the results of present experimental work.

3

Chapter Two Literature Survey

Chapter Two
Literature Survey
2.1 Scope
U

The hydroisomerization of light paraffins is an important industrial process to
obtain branched alkanes which are used as octane boosters in gasoline. Thus,
isoparaffins are considered an alternative to the use of oxygenate and aromatic
compounds, whose maximum contents are subjected to strict regulations in
order to protect the environment [Holló et al., 2002, Satoshi, 2003, Rafael et al.,
2005].

Hydroisomerization reactions are generally carried out over bifunctional
catalysts, often containing platinum. The metal component aids in increasing
the rate of isomerization, besides lowering catalyst deactivation.

The interest in the isomerization process is heightened with the phase out of
tetraethyl lead in 1970's, following the phase out of leaded gasoline due to the
introduction of clean air act amendments of 1990 in the USA and similar
legislation in other countries. Aromatics and olefin react with NO X emission to
R R

form ozone, thus contributing to smog formation [Maloncy et al., 2005].
Therefore, in many plants refineries have to minimize benzene yield. In Europe,
the aromatics content is limited since 2005 to content 35 vol% instead of 42
vol% and benzene to approximately zero level [Liu et al., 1996, Goodarz et al.,
2008].

There are various approaches in petroleum refineries to obtain high octane
number components, which include processes of cracking, reforming and

4


isomerization. Catalytic cracking is the process for converting heavy oils into
more valuable gasoline and lighter products. The cracking process produces
carbon (coke) which remains on the catalyst particle and rapidly lowers its
activity. On the other hand, the catalytic naphtha reforming is the chemical
process which converts low octane compound in heavy naphtha to high-octane
gasoline components, without changing carbon numbers in the molecule. This
is achieved mainly by conversion of straight chain naphtha to iso-paraffins and
aromatics over a solid catalyst. The isomerisation (hydroisomerization) is the
chemical process which converts low octane compound in light naphtha to high
octane number components via rearrangement of the molecular structure of a
hydrocarbon without gain or loss of any of its components. [Ulla, 2003,
Northrop et al., 2007 ].

The most widely applied alkane isomerization catalysts are chlorinated alumina
supported platinum and zeolite supported Pt or Pd. Also there are many of
different catalysts in which the selectivity isomerization increases and the
cracking decreases [Rachid et al., 2006].
A comprehensive literature review is shown in this chapter to include: gasoline
specification, hydroisomerization process catalysts and characterization.

2.2 Gasoline Fuel and Its Specefications
U U

Gasoline is one of petroleum fuels that consists of 5 carbons to 11 carbons in
the hydrocarbon compounds. Actually, gasoline contains up to 500
hydrocarbons, either saturated or unsaturated hydrocarbons and other
compounds. Saturated hydrocarbon known as paraffin or alkane forms the
major component of low octane number gasoline. Unsaturated hydrocarbon
includes olefins or alkenes, isoparaffins or alkyl alkane, arenes or aromatics.

5


Other compounds consist of alcohols and ethers [Lovasic et al., 1990, Carey,
1992].
Although there are several important properties of gasoline, the three that have
the greatest effects on engine performance are the Reid vapor pressure, boiling
range, and antiknock characteristics.

The Reid vapor pressure (RVP) and boiling range of gasoline govern ease of
starting, engine warm-up, rate of acceleration, loss by crankcase dilution,
mileage economy, and tendency toward vapor lock. Engine warm-up time is
affected by the percent distilled at 158°F (70°C) and the 90% ASTM distillation
temperature. Warm-up is expressed in terms of the distance covered to develop
full power without excessive use of the choke. Crankcase dilution is controlled
by the 90% ASTM distillation temperature and is also a function of outside
temperature [Takao, 2003].

The octane number of the gasoline depends on the number of branch carbon
atoms and the length of carbon atom chain. Octane number is a ratio of n-
heptane to iso-octane part by volume and commercially is between 60:40 and
40:60. n-heptane has octane number of zero while iso-octane has octane number
of 100. Higher octane rating is obtained by decreasing normal alkanes while
increasing iso-alkanes and cyclic hydrocarbons. Although unsaturated
hydrocarbons have desirable octane rating, for example acetylene, benzene and
toluene, they are toxic and their content in the gasoline should be reduced.
The octane number represents the ability of gasoline to resist knocking during
combustion of the air-gasoline mixture in the engine cylinder. Gasoline must
have a number of the other properties in order to function properly and to avoid
damage to the environment [Antos et al., 1995, Tore et al., 2007].

6


Octane ratings in gasoline are conventionally boosted by addition of aromatic
and oxygenated compounds. However, as a result of increasingly stringent
environmental legislation, the content of these compounds in gasoline is being
restricted and thus industry has been forced to investigate alternative processes
to reach the required octane levels [Rafael et al., 2008].

There are several types of octane numbers for spark ignition engines with the
two determined by laboratory tests considered most common: those determined
by the ‘‘motor method’’ (MON) and those determined by the ‘‘research
method’’ (RON). Both methods use the same basic type of test engine but
operate under different conditions. The RON (ASTM D-908) represents the
performance during city driving when acceleration is relatively frequent, and
the MON (ASTM D-357) is a guide to engine performance on the highway or
under heavy load conditions.

The difference between the research and motor octane is an indicator of the
sensitivity of the performance of the fuel to the two types of driving conditions
and is known as the ‘‘sensitivity’’ of the fuel. On the other hand, the mean
average of RON and MON is named rating. [Chica et al., 2001, Goodarz et al.,
2008]. An overview of octane numbers of different hydrocarbons, given in
Table (2.1).

In the oil industry C 5 and C 6 paraffins are typically used in hydroisomerization
R R R R

units to obtain high octane number components. Paraffins larger thanC 6 , such
R R

as heptane are usually present in catalytic reforming feed streams and converted
into aromatic compounds [Maloncy et al., 2005] .

7


Table (2.1): Octane number for different hydrocarbons [Goodarz et al.,
2008].

Compound MON RON

n-butane 89.6 93.8

Iso-butane 97.5 98.6

n-pentane 62.6 61.7

Iso-pentane 90.3 92.3

n-hexane 26 24.8

2-methyl pentane 73.5 73.4

3-methyl pentane 74.3 74.5

2,3-dimethyl butane 94.3 94.6

n-heptane 0 0

2-methyl hexane 46.4 42.4

3-methyl hexane 55.8 52

3-ethyl pentane 69.3 65

2,2-dimethyl pentane 95.6 92.8



Iso-octane 100 100

8


2.3 Hydroisomerization Process
U U

One of the important targets in the petroleum industry is the production of
branched alkanes by skeletal isomerisation of n-alkanes using solid acid
catalysts. Environmental concerns are now promoting clean gasoline with high
research octane number (RON) and low content of aromatics such as benzene.
Isomerization of light straight run naphtha has the potential to satisfy these
requirements.

The isomerisation process is catalytic reactions that involve rearrangement of
the molecular structure of a hydrocarbon without gain or loss of any of its
components. This process uses light naphtha (C 5 -C 6 fractions) in the production
R R R R

of high octane gasoline blend stocks. The process involves the transformation
(with minimal cracking) of low octane normal (and less branched) paraffin
components into high octane isomers with greater branching of the carbon
chain. These types of processes are usually accomplished by bifunctional
catalysts that have both metallic and acidic function [Ravishankar and
Sivasanker, 1996, Maha, 2007].

The refineries of petroleum in the world include hydroisomerization unit.
Figure (2.1) shows the position of hydroisomerization unit in a petroleum
refinery. It is important to mention here that many petroleum companies
designed hydroisomerization processes to produce high octane gasoline.

9


Fig. (2.1) Location of hydroizomerization process in a modern petroleum
refinery [Ivanov et al.,2002].
10


Figure (2.2) shows a representative flow scheme hydroisomerization unit for the
the Penex™ process which provides highly isomerized light naphtha products.

Figure (2.2) Penex Process Flow Scheme [Gary, 2001].

Figure (2.3) shows the other flow scheme hydroisomerization unit for the the
Penex DIH process. On the other hand, the Butamer™ process that is shown in
Figure (2.4) provides highly isomerized butane products.

11


Figure (2.3) Penex DIH Process [Mikhail et al., 2001].

Figure (2.4) The Butamer™ process [Mikhail et al., 2001].

12


The dual-functional catalysts used in these processes are platinum on chlorided-
alumina support. These types of catalysts offer the highest activity to take
advantage of higher thermodynamic equilibrium iso- to normal ratios
achievable at lower temperatures. In order to improve the performance of these
processes.

If the normal pentane in the reactor product is separated and recycled, the
product RON can be increased by about 3 numbers (83 to 86 RON) . If both
normal pentane and normal hexane are recycled the product clear RON can be
improved to about 87 to 90. Separation of the normals from the isomers can be
accomplished by fractionation or by vapor phase adsorption of the normals on a
molecular sieve bed. The adsorption process is well developed in several large
units.
On the other hand, it is important to mention here that the isomerization process
is called hydroisomerization because its reaction requires H 2 gas to prevent
R R

deactivation of catalysts. In hydroisomerization process, some hydrocracking
occurs during the reactions resulting in a loss of gasoline and the production of
light gas. The amount of gas formed varies with the catalyst type and age and is
sometimes a significant economic factor. The light gas produced is typically in
the range of 1.0 to 4.0 wt% of the hydrocarbon feed to the reactor. The main
composition of these gases is methane, ethane and propane [Gary, 2001, Shi et
al., 2008].

Two types of hydroisomerization processes of alkanes were developed, having
different objectives and technologies [Satoshi, 2003]:

1. The isomerization of lower n-alkanes (C 5 -C 7 ) for the production of high-
R R R R

octane components and of n-C 4 to i-C 4 as feed for the production of
R R R R

alkylate.

13


2. The isomerization of the n-alkanes contained in paraffinic oils in
order to produce a significant decrease in the freezing temperature
and thus eliminate the need for dewaxing.

2.3.1 Catalysts of Hydroisomerization Process

The first hydroisomerization unit was introduced in 1953 by UOP, followed in
1965 by the first BP unit, while in 1970 the first Shell Co. hydro-isomerization
(HYSOMER) unit was started up. All these processes take place in the gas
phase on a fixed bed catalyst containing platinum on a solid carrier. In the late
1950s and early 1960s, chlorinated platinum loaded alumina was used as a
catalyst. The major advantage of this catalyst was its low temperature activity
(T< 200°C) due to its high acidity. However the catalysts were sensitive
towards water and oxygenates and in addition had corrosive properties.
Furthermore, chlorine addition during the reaction is necessary to guarantee
catalyst stability [Gary, 2001, Maciej et al., 2002, Yunqi et al., 2004].

In the Hysomer process zeolite based catalysts were used which had the major
advantage of resistance to feed impurities. Industrially applied zeolites used
today are Pt-containing, modified synthetic (large-port) mordernite e.g. HS10 of
UOP, or HYSOPAR from Süd- Chemie. As higher hydrogen to hydrocarbon
ratios are needed recycle compressors and separators are required for this
technology [Jens, 1982, Corma et al., 1995, Christian, 2005].

The isomerization of hydrocarbons < C 6 is currently carried out very
R R

successfully using bifunctional supported platinum catalysts. However,
difficulties are encountered with hydrocarbons larger than hexane since the
cracking reactions become more significant over platinum catalysts as the chain
length increases [Cuong et al., 1995]. Catalysts used in state of the art

14


isomerization-cracking reactors are bifunctional. They have a metal function
providing de-hydrogenation and hydrogen activation properties that are usually
supplied by group VIII noble metals like Pt, Pd, Ni or Co. The acid function is
the support itself and some examples include acid zeolites, chlorided alumina
and amorphous silica alumina. Noble metals have a positive effect on the
activity and stability of the catalyst. However they have a low resistance to
poisoning by sulfur and nitrogen compounds present in the processed cuts
[Busto et al., 2008].
In order to prepare a suitable catalyst for hydroconversion of alkanes, good
balance between the metal and acid functions must be obtained. Rapid
molecular transfer between the metal and acid sites is necessary for selective
conversion of alkanes into desirable products [Vagif et al., 2003].

Two of the attractive features of zeolite are that the catalysts are tolerant of
contaminants and that they are regenerable. The chlorinated alumina catalysts
are very sensitive to contaminants such as water, carbon oxides, oxygenates,
and sulfur. Thus, feeds and hydrogen must be hydrotreated and dried to remove
water and sulfur. Furthermore, the chlorinated alumina catalysts require the
addition of organic chloride to the feed in order to maintain their activities. This
causes contamination in the waste gas of hydrogen chloride, a scrubber is
needed to remove such contamination [Satoshi, 2003].

The UOP BenSat process uses a commercially proven noble metal catalyst,
which has been used for many years for the production of petrochemical-grade
cyclohexane. The catalyst is selective and has no measurable side reactions.
Because no cracking occurs, no appreciable coke forms on the catalyst to
reduce activity. Sulfur contamination in the feed reduces catalyst activity, but
the effect is not permanent. Catalyst activity recovers when the sulfur is
removed from the system [Meyers, 2004].
15


2.3.1.1 Alumina
Alumina or aluminum oxide (Al 2 O 3 ) is a chemical compound with melting
R R R R

point of about 2000°C and sp. gr. of about 4.0. It is insoluble in water and
organic liquids and very slightly soluble in strong acids and alkalies. Alumina
occurs in two crystalline forms. Alpha alumina is composed of colorless
hexagonal crystals with the properties given above; gamma alumina is
composed of minute colorless cubic crystals with sp. gr. of about 3.6 that are
transformed to the alpha form at high temperatures. Figure (2.5) shows the
shape of Al 2 O 3 [Ulla, 2003].
R R R R

The most common form of crystalline alumina, α-aluminium oxide, is known as
corundum. If a trace of the element is present it appears red, it is known as
ruby, but all other colorations fall under the designation sapphire. The primitive
cell contains two formula units of aluminium oxide. The oxygen ions nearly
form a hexagonal close-packed structure with aluminium ions filling two-thirds
of the octahedral interstices.

Identifiers Aluminium oxide

Figure (2.5) The shape of aluminium oxide

16


Typical alumina characteristics include:

 Good strength and stiffness
 Good hardness and wear resistance
 Good corrosion resistance
 Good thermal stability
 Excellent dielectric properties (from DC to GHz frequencies)
 Low dielectric constant
 Low loss tangent

2.3.1.2 Zeolite

Zeolites are microporous crystalline solids with well-defined structures.
Generally they contain silicon, aluminium and oxygen in their framework and
cations, water and/or other molecules wthin their pores. Zeolites occur naturally
as minerals or synthetic, Figure (2.6) shows the shape of different types of
zeolites [Matthew, 2008].
Because of their unique porous properties, zeolites are used in a variety of
applications with a global market of several milliion tonnes per annum. In the
western world, major uses are in petrochemical cracking, ion-exchange (water
softening and purification), and in the separation and removal of gases and
solvents. Other applications are in agriculture, animal husbandry and
construction. They are often also referred to as molecular sieves [Danny, 2002].

Zeolites have the ability to act as catalysts for chemical reactions which take
place within the internal cavities. An important class of reactions is that
catalysed by hydrogen-exchanged zeolites, whose framework-bound protons
give rise to very high acidity. This is exploited in many organic reactions,
including crude oil cracking, isomerisation and fuel synthesis [Jirong, 1990].

17


Figure (2.6) Structures and dimensions of different types
of zeolite [Tirena, 2005].

Underpinning all these types of reaction is the unique microporous nature of
zeolites, where the shape and size of a particular pore system exert a steric
influence on the reaction, controlling the access of reactants and products. Thus
zeolites are often said to act as shape-selective catalysts. Increasingly, attention
has focused on fine-tuning the properties of zeolite catalysts in order to carry
out very specific syntheses of high-value chemicals e.g. pharmaceuticals and
cosmetics [Eisuke et al., 2005].

The following properties make zeolites attractive as catalysts, sorbents,
and ion-exchangers [Jirong, 1990, Liu et al., 1996, Danny, 2002].

18


(1) well-defined crystalline structure.
(2) high internal surface areas (>600 m2/g). P P

(3) uniform pores with one or more discrete sizes.
(4) good thermal stability.
(5) highly acidic sites when ion is exchanged with protons.
(6) ability to sorb and concentrate hydrocarbons.

The tetrahedral arrangements of [SiO 4 ] -4 and [AlO 4 ] -5 coordination polyhedra
R R P P R R P P

create numerous lattices where the oxygen atoms are shared with another unit
cell. The net negative charge is then balanced by cations (e.g. K+ or P P

NH 4 +). Small recurring units can be defined for zeolites named, ‘secondary
R RP P

building units [Tirena, 2005].

The primary building blocks of all zeolites are silicon Si+4 and P P

aluminum Al+3 cations that are surrounded by four oxygen anions O-2.
P P P P

This occurs in a way that periodic three dimensional framework
structures are formed, with net neutral SiO 2 and negatively charged R R

AlO 2 . R R

The negative framework charge is compensated by cation (often Na + ) R
R

or by proton (H+) that forms bond with negatively charged oxygen
P P

anion of zeolite.

The secondary building blocks differ between different types of
zeolites. In the top line of Figure (2.6) the structure of a faujasite type
zeolite is shown. The secondary building block of this zeolite is a
sodalite cage, which consists of 24 tetrahedra in the geometrical form of
a cubo-octahedron. The sodalite cages are linked to each other via a
hexagonal prism.

19


2.4 Previous Work
U

Numerous researchers which have dealt with hydroisomerization using
different types of catalysts as follows:
Diaz et al., [1983] studied the isomerization and hydrogenolysis of hexanes on
an alumina-supported Pt-Ru catalyst. On ruthenium/ alumina catalysts, no
isomer products were detected in C6
R R hydrocarbon reactions.
Methylcyclopentane hydrogenolysis was selective as confirmed by the high 3-
methylpentane/n-hexane ratios. Isomerization reactions on Pt(9.6 at.%)-Ru (0.4
at.%)/Al 2 O 3 were studied between 220 and 300°C. Skeletal rearrangements
R R R R

proceeded from 220°C where Pt is inactive for this type of reactions, Very low
apparent activation energies in isomerization reactions of Cs-labeled
hydrocarbons were found for selective and nonselective cyclic mechanisms: 2-
methylpentane 3- methylpentane and 2-methylpentane n-
hexane, respectively. The results were explained using a bimolecular kinetic
model which can take into account the phenomenon as an increase either in
hydrocarbon coverage or in hydrocarbon adsorption strength on the catalyst
surface.

Raouf, [1994] investigated hydroconversion (isomerization, cracking and
cyclization of n-heptane) using three types of a crystalline zeolites as supports.
It was noted platinum supported zeolite catalyst vary in their activity and
selectivity towards n-heptane hydroconversion. Support types were found to
behave differently when impregnated with hexachloroplatinic acid. Applying
H 2 PtCl 6 on acidic decationized and cationic zeolite type Y produce most active
R R R R

catalyst toward isomerization at lower temperature and for hydrocrackingat
higher temperature. On the other hand, applying H 2 PtCl 6 on zeolite type X
R R R R

produce an active catalyst. The isomerizing activity is, however, lower than Y
type with moderate hydroisomerization and hydrocracking selectivity. While

20


for A type produces an active catalyst with low isomerizayion activity and a
higher cracking ability. catalytic activity of all types of Pt-zeolite catalysts
strongly depends on the Si/Al ratio. The order of the catalytic activity for the
catalysts is type Y > type X > Y type A.

Ravishankar and Sivasanker [1996] studied the hydroisomerization of n-hexane
was carried out at atmospheric pressure in the temperature range 473-573 K
over Pt-MCM-22. The influence of Pt content, the SiO 2 /A1 2 O 3 ratio of
R R R R R R

thezeolite and the reaction parameters on the isomerization efficiency of the
catalyst was investigated. The optimum Pt content for the reaction was found to
be around 0.5 wt.%. At a constant Pt content of 0.5 wt.%, increasing the A1
content of the zeolite increased the catalytic activities and
isomerization/cracking ratios. The studies suggest that the reaction proceeds by
a bifunctional mechanism. Preliminary activity comparisons between Pt-H-
MCM-22, Pt-H-β and Pt-Hmordenite are reported.

Chica and Corma, [1999] tested The hydroisomerization of n-heptane to
dibranched and tribranched products for producing high octane gasoline has
been studied using unidirectional 12 Membered Ring (MR) zeolites with
different pore diameters, and zeolites with other pore topologies including one
with connected 12×10MRpores and two tridirectional 12 MR zeolites. Besides
the pore topology, the crystallite size of the zeolite was seen to be of paramount
importance for improving activity and selectivity. In a second part of the work,
a Light Straight Run naphtha including n-pentane and n-hexane and another
feed containing n-pentane, n-hexane, and n-heptane have been successfully
isomerized using a nanocrystalline Beta (BEA) zeolite. This can be a favorable
alternative to the commercial zeolite catalyst based on mordenite (MOR),
especially when n-heptane is present in the feed. They found, that with

21


increasing of reaction temperature within the range 240-380ºC, the conversion
P P

of n-parafins increased. Also, the results clearly show that regardless of the
zeolite used the reactivity follows the order n-heptane> n-hexane> n-pentane.
Mordenite cracks n-heptane products very quickly, giving low selectivities to
branched products. While a larger unidirectional pore zeolite (SSZ-24) gives
better results than H-mordenite, the 12 MR tridirectional zeolites are the best
catalysts for the branching isomerization of n-heptane, owing to the faster
diffusion rates of reactants and products through the micropores. The zeolite
crystal size has been found to be of paramount importance, because the catalytic
activity and selectivity of a nanocrystalline Beta zeolite was better than that of
Beta zeolites with larger crystallites.

Shuguang et al., [2000] investigated the hydroisomerization of normal
hexadecane using three Pt/WO 3 /ZrO 2 catalysts prepared by different methods.
R R R R

They found that preparation of the catalyst by impregnation with H 2 PtCl 6 .6H 2 O
R R R R R R

solution and another calcinations at 500°C results in a highly active and
selective platinum-promoted tungstate-modified zirconia catalyst
(Pt/WO 3 /ZrO 2 ) for the hydroisomerization of n-hexadecane. The optimum
R R R R

range of tungsten loading to achieve high isomerization selectivity at high n-
hexadecane conversion is between 6.5 and 8 wt%.

Falco et al. [2000] studied the effect of platinum concentration on tungsten
oxide-promoted zirconia over the catalytic activity for n-hexane isomerization
was studied. Catalysts were prepared by impregnation of tungsten oxide
promoted zirconia reaching up to 1.50% platinum, followed by calcination at
500℃. The n-hexane reaction was studied at 200℃, 5.9 bar, WHSV 4 and H 2 : R R

n-hexane (molar) ratio 7. It was found that catalytic activity and stability
increase for platinum concentrations above 0.05% because of higher hydrogen

22


availability at the surface, measured as a function of the methylcyclopentane/C 6 R R

isomers ratio. Further increments in platinum concentration do not produce
important modifications in catalytic activity or hydrogen availability.

Srikant and Panagiotis, [2003] used Pt/H-ZSM-12 as a catalyst for the
hydroisomerization of C 5 –C 7 n-alkanes and simultaneous saturation of benzene.
R R R R

The performance of a Pt/H-ZSM-12 catalyst was compared with a Pt/H-beta
and a Pt/H-mordenite catalysts having a similar Si/Al ratio. It was concluded
that both the paraffin conversion and benzene conversion activity of all the
three catalysts remain stable even in the presence of sulfur. However, the results
showed that the conversion levels over the Pt/H-ZSM-12 and Pt/H-Mor catalyst
are lower compared to the levels obtained in the absence of sulfur at the same
temperature.

Abbass [2004], studied the transformation of n-hexane over
0.5wt%Pt/HY-Zeolite at 250-325˚C and WHSV=1.6hr-1. The pressure P P

and hydrogen to feed mole ratio were kept constant at 1 bar and 2,
respectively. He use three type of promoter to study the activity of
isomerization catalyst Sn, Ni and Ti .The comparison between prepared
catalysts shows that the total isomer yield during the process with Sn-
Pt/HY-Zeolite catalyst was higher than the others and the total isomer
yield reach 63.95% vol. He found that adding a 0.5 wt% of W and Zr to
Sn-Pt/HY-zeolite catalyst obtains co-metal promoters catalysts, and the
total isomer yield reached to 81.14% vol. and 79.07% vol. respectively.
The results show that the co-metal promoters enhanced the yield of the
product more than that obtained by other types of promoters

Wong et al., [2005] Skeletal isomerization of npentane over Pt/HZSM5 and
Pt/WP/HZSM5 has been studied. Platinum (Pt) and Tungstophosphoric acid

23


(WP) have been immobilized on protonated ZSM5 by impregnation method
followed by calcinations at 823K. The state of WP on the zeolite surface was
characterized by XRD, FTIR, pyridine adsorption FTIR, TG/DTA and BET
surface area techniques. Catalytic testing in npentane isomerization was
performed in a continuous flow microreactor at 523K under hydrogen flow.
Prior to the reaction, catalyst was treated by heating at 573K under oxygen (30
min), nitrogen (10 min) and hydrogen (180 min) flow. Both of Pt/HZSM5 and
Pt/WP/HZSM5 shows high conversion of npentane and stable catalysts towards
the deactivation compare to those of HZSM5. Although, Pt/HZSM5 and
Pt/WP/HZSM5 exhibit high catalytic activity, Pt/WP/HZSM5 catalyzed the
isomerization of npentane more selectively compare to those of Pt/HZSM5due
to the presence of a strong acid.

Jafar et al., [2006] investigated C 5 -C 6 isomerization in light straight run
R R R R

gasoline over platinum/mordenite zeolite. They studied effects of hydrogen
partial pressure on catalyst activity and n-paraffins conversions at T=260°C and
P=7-7.3 bar. They concluded that the activity increases with relatively sharp
slope for n-pentane, n-hexane and n-heptane which show the positive effect of
hydrogen on decreasing deactivation. The behavior of the curves in the
mentioned pressure range shows that the activity is constant while increasing
PH 2 . At T=270°C it seems as if the deactivation phenomenon takes place in
R R

the pressure less than PH 2 . Also, at this temperature and while PH 2 >8.5, the
R R R R

activity decreases evidently. By increasing the temperature, the slop of the
initial activity curve decreases but activity reduction is more evident in higher
pressures.

Rachid et al. [2006] investigated the present work is an evaluation of 1 wt.%
Pd/sulfated zirconium pillared montmorillonite catalyst in the
hydroisomerization reaction of two mfractions of light naphtha composed
24


mainly of C 5 and C 6 paraffins (feeds 1 and 2). Catalyst activity test was carried
R R R R

out in a fixed-bed flow reactor at reaction temperature of 300 8C, under
atmospheric hydrogen pressure and weight hourly space velocity of 0.825 h-1. P P

The reaction products showed high isomer and cyclane selectivity.
Monobranched and multibranched isomers were formed as well as C5 and C6
cyclane products. After the catalytic reaction, the total amount of benzene and
cyclohexane decreased by 30% for the ‘‘feed 1’’ and by 40% for the ‘‘feed 2’’
leading to methylcyclopentane formation in the products. A long-term
performance test catalyst for the two light naphtha fractions was also performed
and we observed an improving of the research octane number (RON) by 15–17
for, respectively, feeds 1 and 2.

Rachid et al., [2006] the present work is an evaluation of 1 wt.% Pd/sulfated
zirconium pillared montmorillonite catalyst in the hydroisomerization reaction
of two fractions of light naphtha composed mainly of C 5 and C 6 paraffins R R R R

(feeds 1 and 2). Catalyst activity test was carried out in a fixed-bed flow reactor
at reaction temperature of 300 8C, under atmospheric hydrogen pressure and
weight hourly space velocity of 0.825 h-1. The reaction products showed high
P P

isomer and cyclane selectivity. Monobranched and multibranched isomers were
formed as well as C 5 and C 6 cyclane products. After the catalytic reaction, the
R R R R

total amount of benzene and cyclohexane decreased by 30% for the ‘‘feed 1’’
and by 40% for the ‘‘feed 2’’ leading to methylcyclopentane formation in the
products. A long-term performance test catalyst for the two light naphtha
fractions was also performed and we observed an improving of the research
octane number (RON) by 15–17 for, respectively, feeds 1 and 2.

Hadi [2007], studied the transformation of n-hexane over 0.3wt%
Pt/HY-zeolite, 0.5wt% Pt/HY-zeolite, 1wt% Pt/HY-zeolite and

25


0.3wt%Pt/Zr/W/HY-zeolite catalysts at 240-270˚C and LHSV=1-3hr-1. P P

The pressure and hydrogen to feed mole ratio were kept atmospheric
and 1-4, respectively. She concluded that the n-hexane conversion
increases with increasing temperature, decreasing LHSV and increasing
Pt content. Also isomerization rate is independent of the Pt loading this
lead to the conclusion that dehydrogenation step is not rate limiting.
The effect of the P H2 and P nC6 orders on the overall reaction rate was
R R R R

also studied by the author. She conclude that the value of hydrogen
order varies between -0.388 to -0.342, while the values of n-hexane
order were 0.262 to 0.219. The values of E act, R
isom
R were also obtained
and found to be equal to 119.7 kJ/mole.
Hadi also study the n-Hexane conversion enhancement by adding TCE
and by co-impregnation with Zr and W using 0.3wt%Pt/HY-zeolite
catalyst, and found that by adding 435ppm of TCE a 49.5mol.%
conversion was achieved at LHSV 1 h-1, temperature 270°C and H 2 /nC 6
P P R R R R

mole ratio= 4, while the conversion was 32.4mol.% on
0.3wt%Pt/Zr/W/HY-zeolite at the same condition.

María et al. [2008] studied Three different distillatednaphthas streamsprovided
by REPSOLYPF, being formed by n-paraffins, iso-paraffins, aromatics and
naphthenes, were isomerized using an agglomerated catalyst based on beta
zeolite.Methane and ethane were not observed as final products revealing that
hydrogenolysis did not contribute to the cracking reaction. The highest overall
paraffin conversion value was obtained when feed A was introduced to the
process, due to its high molar composition of linear paraffins. It was observed
the presence of aromatic compounds (benzene and toluene) in the three feeds. A
total hydrogenation of benzene was achieved, keeping the rest of the aromatic

26


compounds under the limit imposed by legislation. Different naphthenic
compounds were obtained as a result of the hydrogenation of aromatic ones.

Goodarz et al. [2008] investigated two types of beta zeolites, different amounts
of platinum (0.2%, 0.5% and 1.2%) were loaded on the protonated form of
zeolite by incipient wet impregnation method applying hexachloroplatinic acid
in 0.2N Cl- progressive ion solutions. Catalytic hydroisomerization reactions
P P

were carried out at atmospheric pressure in a fixed bed reactor with vertical
placing and downward flow at three different temperatures, various WHSV
(weight hourly space velocity) and n-H 2 /n-HC (molar hydrogen/hydrocarbon)
R R

ratio. Increase in Si/Al ratio in zeolites structures from 11.7 to 24.5 promoted
selectivity and yield. It was found that optimum platinum content depends on
the Si/Al ratio (zeolite acidity) in catalysts. Monobranched to dibranched
isomers ratio were correlated with a linear function of n-heptane conversion.
Such a correlation was found to be valid for various Si/Al ratios, metal content,
processing temperature and pressure, WHSV and hydrogen to hydrocarbon
ratio. Increase in WHSV, decreased n-heptane conversion, but enhanced
isomers selectivity. On the other hand, increasing the ratio of hydrogen to
hydrocarbon in the feed decreased conversion, while promoted isomers
selectivity.

2.5 Catalysts Preperation
U

A typical catalyst comprises one or more catalytically active components
supported on a catalyst support. Typically, the catalytically active components
are metals and/or metal-containing compounds. The support materials are
generally high surface area materials with specific pore volumes and

27


distribution [Lovasic et al., 1990, Raouf 1994, Novaro et al., 2000, Ramze,
2008].

Various methods for depositing catalytically active components on catalyst
supports are known, the catalyst support may be impregnated with an aqueous
solution of the catalytically active components. The impregnated support may
then be dried and calcined. The catalytically active component may also be
deposited onto the catalyst support by precipitation, a catalyst support is first
impregnated in an aqueous solution of a noble metal. The metal is then
precipitated on to the support by contacting the impregnated support with an
aqueous solution of an alkali metal salt [Iker, 2004].

Many factors influence catalysts preparation, such as solution concentration,
contact time, washing, temperature and method of reduction. Figure (2.7)
illustrates the general procedure for catalysts preparation [Shuguang et al.,
2000, Sergio et al., 2005].

2.5.1 Impregnation
The manner in which a metal is introduced to a support will influence its
dispersion as well as the nature of the metal-support interaction. Supported
catalysts with low concentration of metal are generally prepared by
impregnation (or in some cases by ion exchanging). The choice of precursor salt
is made both for its solubility in water, and preferred solvent, and for its ability
to disperse throughout the support. Impregnation of pore supported catalyst is
achieved by filling the pores of support with solution of active species of metal
salt from which solvent is evaporated. The concentration of the metal content
can be increased by successive impregnation with intermediate precipitation
and thermal activation to isolubilize the supported species [Jensen et al., 1997,
Shuguang et al., 2000].

28


Figure (2.7): Typical arrangement of the catalysts
preparation [Anderson, 1975]

Impregnation with interaction occurs when the solute to be deposited
establishes a bond with the surface of the support at the time of wetting. Such
interaction results in a near-atomic dispersion of the active species precursor.
The interaction can be an ion exchange, an adsorption, or a chemical reaction
since ion exchanges occur much more frequently than the others [Lepage,
1987].

29


2.5.2 Calcination
Calcination means any thermal treatment carried out with the purpose of
decomposing precursor compounds (usually with the evolution of gaseous
product) and / or allowing solid-state reactions to occur among different catalyst
components and / or making the catalyst sinter. The calcination temperature is
usually not lower than that of operation at the industrial plant [Thomas, 2004].

The type of calcination is assumed to be calcination in air, typically at a
temperature higher than the anticipated temperatures of the catalytic reaction
and catalyst regeneration.
The objectives of calcination are to obtain:
1- A well determined structure for the active agents or supports.
2- The parallel adjustment of the texture with respect to the surface and pore
volume.
3- A good mechanical resistance if it does not already exist
Among the various types of chemical or physico-chemical transformations that
occur during calcination, the following are the most important:
A- The creation of a generally macroporous texture through decomposition
and volatilization of substances previously added to the solid at the
moment of its shaping.
B- Modifications of texture through sintering: small crystals or particles will
turn into bigger ones.
C- Modifications of structure through sintering.

2.5.3 Reduction
Reduction process is the final step in activation of supported metal catalyst,
which consists of the transformation of the metal precursor compound or its
oxide into the metallic state (metal atoms, small metal clusters).

30


Reduction involves reaction where the initiation process proceeds at distinct
sites (potential centers) on the surface of solid, followed by propagation of the
reaction zone from such a center through the solid, until complete conversion is
achieved upon contact of a metal oxide with hydrogen, oxygen ions are created.
The reaction process of oxides and halides can be represented by the following
equations [Vanden and Rijnten, 1979, Anderson et al., 1984]

MO (s) + H 2
R R R M (s) + H 2 O (g)
R R R R R R

2MX (s) +H 2(g)
R R R 2M (s) +2HX (g)
R R R R

There are many factors affecting the reduction step, calcination of the deposited
precursor might cause several transformation and solid state reaction. Water
vapor inhibits reduction by blocking nucleus forming sites.

2.6 Catalysts Characterization
U U

Characterization of the catalyst is a predominate step in every catalyst study and
at every stage of the catalyst development. Critical parameters are measured not
only to check the effectiveness of each operation but also to provide
specification for future products. Characterization might be studied or
controlled in terms of support properties, metal dispersion and location and
surface morphology [Tirena, 2005].

In general, the quality of any catalyst is determined by a number of factors,
such as activity, selectivity for certain product, and stability. These parameters
are themselves functions of pretreatment conditions of the catalyst preparation
and reaction conditions. The interpretation of catalytic performance through the
mechanism of catalytic action depends on the study of the intrinsic chemical
and physical characteristics of the solid and a recognition of correlations

31


between some of these characteristics and catalytic performance [Sergio et
al., 2005]. Table (2.4) offer presents the general physcochemical properties of
catalysts and methods of measuring them.

2.6.1 X-ray Diffraction (XRD)
X-ray diffraction is a technique to identify the crystallinity of catalysts. This
technique is based on the knowledge that each compound in catalyst has a
different diffraction pattern. The crystallinity can be determined by comparing
the intensity of a number of particular peaks to the intensity of the same peaks
obtained by standard samples [Marı´a et al., 1997, Benitez et al., 2006].
The diffraction pattern is plotted based on the intensity of the diffracted beams.
These beams represent a map of reciprocal lattice parameter, known as Miller
index (hkl) as a function of 2θ, which satisfies Bragg equation:

nλ = 2d sin θ -------------------------(2.1)
where n is an integer number, λ is the wavelength of the beam d is interplanar
spacing and θ is a diffraction angle. Equation (2.1) is obtained from Bragg
diffraction as shown in Figure (2.8).

2.6.2 Surface Area
In practice, the surface area is calculated from the Brunauer-Emmett-Teller
(BET) equation based on the physical adsorption of an inert gas at constant
temperature, usually nitrogen at the temperature of liquid nitrogen. The
principle of measurement consists in determining the point when a mono-
molecular layer of gas covers the surface of the catalyst [Antonio et al., 2006].

32


Figure (2.8) Bragg diffraction [Tirena, 2005].

2.6.3 Scanning Electron Microscopy (SEM)
Scanning electron microscopy is an extremely powerful technique for obtaining
information on the morphology and structural characteristics of catalysts. There
are some advantages in this technique, which are great depth of focus, the
possibility of direct observation of external form of real objects, and the ability
to switch over a wide range of magnification, so as to zoom down to fine detail
on some part identified in position on the whole object [Shuguang et al., 2000].

33

Chapter Three Experimental Work

Chapter Three
Experimental Work
3.1 Materials
U

In the present work, different materials and compounds are used as
follows:
• Iraqi-Light-Naphtha
Iraqi light-naphtha is used as a feedstock in the present investigation. It was
supplied by Al-Dura Refinery (Baghdad). Table (3.1) shows the specifications
of Iraqi-light naphtha.
• Hydrogen
Hydrogen gas was obtained from Al-Mansour Factory/Baghdad with
a high purity of (99.9%).
• Zeolite
NaY-zeolite was supplied from Zeolyst International UWE Ohlrogge (VF)
as an extrudate (2mm×4mm). The chemical analysis of this zeolite was done
by the General Establishment of Geological Survey and Mining, and the
results are shown in Table (3.2).

• Alumina
Alumina support (γ-Al 2 O 3 ) with spherical shape and average size of 3mm
R R R R

was supplied by FLUKA AG company.

• Hexachloroplatinic Acid
Hexachloroplatinic acid (H 2 PtCl 6 .6H 2 O) was supplied by REIDEL- DE
R R R R R R

HAEN AG SEELZE -HANNOVER chemicals Ltd.This hexachloroplatinic
acid contains 40 wt% of Pt and has a molecular weight of 517.92 g/mol. On
34


the other hand, other chemicals used such as Barium Chloride (BaCl 2 ), R R

Ammonium Chloride (NH 4 Cl) and Hydrochloric acid (HCl) were supplied
R R

from FLUKA AG Company.
In the present work the Iraqi light naphtha are used as a feedstock in
hydroisomerization process to produce high octane gasoline. Table (3.3)
shows the chemical composition of light naphtha. It is important to mention
here that the main products of hydroisomerization process are i-pentane, 2,2-
DMB, and 2,3-DMB.
Table (3. 1) The propetries of Iraqi light naphtha.
Property Data
Sp.gr. at 15.6℃ 0.702
API 80.5
Distillation
I.B.P. 37℃
5 Vol.% distillated 42℃
E.B.P. 124℃
Total distillate 96 Vol.%
Total recovery residue 0.7 Vol.%
Loss 3.3 Vol.%

Octane Number 68.2
Sulfur Content < 3ppm (Desulfurized)

Kinematic Viscosity at 25℃ 5.4 10-7 m2/s
P P P P

35


Table (3.2): Chemical composition of zeolite

Compound SiO 2 R AL 2 O 3
R R R Na 2 O
R R CaO Fe 2 O 3
R R R MgO TiO 2
R L.O.I

Percentage 45.85 20.50 12.00 0.140 0.060 0.120 0.010 19.14

Table (3.3) The composition of Iraqi light naphtha.

Composition Vol.%
n-Butane 0.20
iso-Pentane 3.80
n-Pentane 15.27
2,2DMB 7.20
2,3DMB 7.98
2MP 12.47
3MP 10.50
n-Hexane 12.74
2,2DMP 3.37
Cyclohexane 2.87
2,4DMP 5.65
Methylcyclopentane 3.34
Benzene 3.88
n-Heptane 1.85
Toluene 2.47
C7+
R RP 3.14

36


3.2 Preparation of Modified Zeolites by Ion Exchange:
U

3.2.1 Preparation of Barium- Zeolite:
BaY form was prepared by ion exchanging of the parent zeolite NaY with
(3N) barium chloride solution. Thus, 36.642 gm of barium chloride in 100
ml distilled water was contacted with 20 gm of zeolite with stirring for 1 hr
at 50℃. The batch of zeolite was left in the solution for 72 hr at 25 . The
exchanged barium zeolite was then filtered off, washed with deionized water
to be free of chloride ions and dried at 110℃ over night. The dried samples

temperature was increased to 550 ℃ at a rate of 10°C/min. The chemical
were then calcined at 550℃ for 5 hr in the presence of O 2 . Then the
R R

analysis showed that a 82% of Na was exchanged by Ba in zeolite Y. It was
done by the General Establishment of Geological Survey and Mining.

3.2.2 Preparation of HY- Zeolite:
HY form was prepared by ion exchanging of the parent NaY zeolite with
(3N) ammonium chloride solution. Thus, 16.047 gm of ammonium chloride
in 100 ml distilled water was contacted with 20 gm of zeolite with stirring
for 1 hr at 50℃. The batch of zeolite was left in the solution for 72 hr at
25℃. The exchanged ammonium zeolite were then filtered off, washed with
deionized water to be free of chloride ions and dried at 110℃ over night.

Then the temperature was increased to 500 ℃ at a rate of 10°C/min. The
The dried samples was then calcined at 500℃ for 7 hr in presence of O 2 . R R

chemical analysis showed that a 87% of Na was exchanged by ammonium
chloride to form HY. It was done by the General Establishment of
Geological Survey and Mining

37


3.3 Catalysts Preparation
U

3.3.1 Preparation of Pt/ BaY and Pt/HY
The barium and hydrogen exchanged zeolites were loaded with 0.5 wt % Pt
by impregnation with aqueous solution of hexachloroplatinc acid
(H 2 PtCl 6 .6H 2 O). The platinum content of the catalyst was calculated from
R R R R R R

the weight of the support and the amount of the metal in impregnation
solution.
Thus, 0.25 gm of hexachloroplatinc acid (40 wt % Pt) was dissolved in 25 ml
of distilled water. Then the solution was added for 20 gm of the zeolite
sample as drop wise with mixing for 2 hr at 25℃. The mixture was left at
room temperature for 24 hr, it was stirred intermediately during this time.
The mixture was then slowly evaporated to dryness over a period of 8 hr by

additional 24 hr. Then the dried catalyst was calcined at 400 ℃ for 3 hr and
heating on a heat mantle. The resulting catalyst was dried in air at 110℃ for

reduced with hydrogen at 350℃ for 2 hr [Satoshi, 2003, Goodarz, 2008,
Dhanapalan et al., 2008].
The prepared catalysts at this time is called Pt/BaY and Pt/HY.

3.3.2 Preparation of Pt/ AL 2 O 3 R R R

The γ-Al 2 O 3 (spherical shape with an average size of 3mm) was loaded with
R R R R

0.5 wt % Pt by impregnation with aqueous solution of hexachloroplatinc acid
(40% Pt). Thus, 0.25 gm of hexachloroplatinc acid (40 wt % Pt) was
dissolved in 25 ml of distilled water. Then, the solution was added 20 gm of
γ-Al 2 O 3 sample as drop wise with mixing for 4 hr at 25℃. The mixture was
R R R R

left at room temperature for 24 hr, The mixture was stirred intermediately
during this time. The resulting catalyst was dried in air at 110℃ for
additional 24 hr. Then, the dried catalyst was calcined at 400℃ for 3 hr and
reduced with hydrogen at 350℃ for 3 hr.

38


3.4 Experimental Unit
U U

The experiments were carried out in a continuous catalytic unit. Figure (3.1)
shows the general view of pilot plant for light naphtha hydroisomerization
process, and Figure (3.2) shows a schematic diagram of the apparatus. The
reaction was carried out in catalytic fixed bed tubular reactor, which is made
of stainless steel. The reactor dimensions were 2cm internal diameter, 3cm
external diameter and 21cm height (reactor volume 66 cm3). The reactor was
P P

charged for each experiment with 20g of catalyst located in the middle zone,
while, the upper and lower zones were filled with glass beads.

The reactor was heated and controlled automatically using an electrical
furnace type Heraeushan (Germany) with maximum temperature of 1000 °C, P P

it was possible to measure the temperature of the catalyst bed using
calibrated thermocouple sensor type K (iron-constantan) inserted into the
middle of the catalyst bed in order to measure and the control reaction
temperature.

The reactor was fitted with accurate means for control of pressure, gas and
liquid flow rate. The liquid (light naphtha) was pumped with a dosing pump
type Prominent (Beta/4- Germany). The liquid hydrocarbons were stored in a
QVF storage tank with capacity of 2000cm3. The liquid flow was passed
P P

through calibrated burette of 52cm3.
P P

39

Chapter Three

40
Experimental Work

Figure (3.1): General view of pilot plant for light naphtha hydroisomerization process.

Chapter Three

41
Experimental Work

Figure (3.2): Schematic diagram of the experimental apparatus.


3.5 Procedure
U

Twenty grams of fresh catalyst was charged into the middle zone of the
reactor. Iraqi light naphtha was fed to the dosing pump from a glass burette
supplied from a feed tank. Feed was pumped at atmospheric pressure. The
hydrogen gas flow to the unit was controlled by a calibrated gas hydrogen
flowmeter. Downstream pressure was controlled with a back pressure valve.
The hydrogen gas before it passed to the reactor passed through molecular
sieve (5A) type to remove any impurities or moisture. The hydrogen gas was
mixed with hydrocarbon before the reactor inlet. The mixture was preheated
before entering the reactor to 150°C, and then passed through the catalyst
P P

bed.

The performance of catalysts was tested under different operating
temperatures of (230, 250, 270, 290, and 310°C). The hydrogen to
P P P P

hydrocarbon molar ratio was kept constant at 4. The weight hourly space
velocities (WHSV) was (1.5, 3, and 4.5hr-1). All types of catalysts were
P P

activated in the catalytic reactor before each run for 2 hr in a flow of
hydrogen. A pre-test period of one hour was used before each run to adjust
the feed rates and temperature to the desired values.

The reaction products was cooled by cooling system and collected in the
separator in order to separate the non-condensed gases from the top of the
separator and the condensed liquid hydrocarbons from bottom of the
separator. Then, the products samples were analyzed using Gas
Chromatograph type Shumids 2014 GC using flame ionization detector
(FID). The column dimensions are 0.22mm internal diameter and length 25m
and film thickness 0.2μm. The analyses were carried out under the
conditions shown in Table (3.3), and the retentions time for the

42


hydrocarbons are shown in Table (3.4). It is important to mention here that,
the calibration of gas chromatography was carried by injection the same
amount of a standard into the Gas Chromatography.

Table (3.3): Gas chromatograph analysis conditions

Temperature program for the column

Initial temperature 50 °C
Final temperature 120 °C
Hold time 5 min
Rate of temperature 5 °C/min
Total time 20 min
Other variables
Pressure at the inlet column 1atm

Pressure of hydrogen 55 KPa

Injection temperature 180 °C
Pressure of carrier gas N 2
R 5 atm
Linear velocity 31.3 cm/min

Split ratio 100

43


Table (3.4): Retention times of hydrocarbons in the catalytic
isomerization of light naphtha reaction.

Components Retention times (Sec)

iso-pentane 1.676

n-pentane 1.724

2,2- dimethyl butane 1.924

2,3- dimethyl butane 1.927

2-methylpentane 1.954

3-methelpentane 1.994

n-hexane 2.037

2,2-dimethelpentane 2.580

Cyclohexane 2.699

2,4-dimethelpentane 2.815

Methylcyclpentane 2.983

Benzene 3.096

n-heptane 3.212

Toluene 4.884

44


3.6 Catalysts Characterization
U

3.6.1 X-Ray Diffraction Analysis.
X-Ray diffraction analysis was done in the Lab of University of Manchester
in United Kendom. Analysis was carried out using Phillips X" Pert Pro PW
3719 X-ray diffractometer with Cu Kα 1 and Cu Kα 2 radiation source
R R R R

(λ=1.54056 Å and 1.54439 Å) respectively. Slits width 1/8 and 1/4 have
been applied. Tension=40 kV, Current=30 mA. The range of angles scanned
was (0 to 80) on 2θ.

3.6.2 Surface Area and Pore Volume
The catalysts surface areas and pore volume were determined using (BET)
method, the apparatus used was Micromeritics ASAP 2400 located in
Petroleum Research Center / Ministry of Oil (Baghdad).
The surface area and pore volume of the catalysts was determined by
measuring the volume of nitrogen gas adsorbed at the liquid nitrogen
temperature (- 196 °C). The volume of gas adsorbed was measured from the
pressure decrease that results from the adsorption of a dose of known volume
of gas.

3.6.3 Scanning Electron Microscopy (SEM)
Scanning electron microscopy (SEM) measurements were carried out using a
Phillips SEM equipped with a XL30 Field Emission Gun, available at the
Lab of University of Manchester in UK.

3.6.4 Energy Dispersive X-Ray (EDAX) Analysis
The modified zeolite catalyst was subjected to the EDAX analyzer that was
done in the Lab of University of Manchester in United Kendom and
connected with the SEM to measure the composition of the zeolite.

45

Chapter Four Kinetic Analysis

Chapter Four
Kinetic Analysis

4.1 Introduction

The main aim of the present study is to analyze the kinetics of hydroisomerization
process by assessing the effect of reaction time and reaction temperature on the
performance of the catalysts. The process feed involves light naphtha which
contains many reactions. Therefore, the hydroisomerization reaction has three
stages as follows: [Sergio et al., 2003, Antonio et al., 2006, Pitz et al., 2007,
Marios et al., 2009]:
1- Adsorption of n- paraffin molecule on dehydrogenation- hydrogenation site
followed by dehydrogenation to n- olefins.
2- Desorption of n- olefin from the dehydrogenation sites and diffusion to a
skeletal rearranged site, which converts n- olefin into iso- olefin.
3- Hydrogenation of iso- olefin into iso- paraffin molecule.

In general, the hydroisomerization of n- paraffin can occur through the bifunctional
scheme shown below:

n-Paraffin n-Olefin i- Olefin i- Parffin

46


The hydroisomerization process of light naphtha is regarded as one of the
complex chemical reactions network, where such types of reactions take on a
metal and acid sites of catalysts [Antonio et al., 2006, Eric et al., 2007 ].
Therefore, the mathematical modeling of the hydroisomerization process is a
very important tool in petroleum refining industries. It translates experimental
data into parameters used as the basis of commercial reactor process optimaization.

In the hydroisomerization of alkanes it is supposed that the alkane is
dehydrogenated to an alkene on the metal site. The alkene is then protonated on the
acid site to a carbenium ion, which is subsequently isomerized to a branched
carbenium ion. The branched carbenium ion gives the proton back to the acid site,
the resulting branched alkene is hydrogenated on the metallic site. The branched
alkane is formed, and can be desorbed from the catalyst surface. The reaction
mechanism scheme is shown in Figure (4.1) [Franciscus, 2002, Maha, 2007,
Matthew, 2008].

Figure (4.1) The general reactions mechanism for isomerization of n-alkane
[Franciscus, 2002].

47


4.2 Model Development
In developing the model of the catalytic hydroisomerization kinetic the following
assumptions are taken into account:
1. The system is isothermal and in steady state operation with first order
reactions.
2. The reaction is carried out in the gas phase with constant physical properties
and without pressure drop.
3. The temperature and concentration gradients in the radial direction can be
neglected.

The objective of kinetic study is to construct from the experimental results of the
process, a mathematical formulation that can be used to predict the kinetic
parameters of the hydroisomerization process. Therefore, the main aim of the
present work is to estimate the reaction parameters (reaction rate constant,
activation energy and pre-exponential factor) depending on the experimental work
results under real isomerization conditions.
In present work, it is suggested kinetic model for the reactions of
hydroisomerizayion for light naphtha (n-paraffin) can be considered by the
following scheme depending on the present model assumptions which can be
formulated to the following equations:

Figure (4.1) The suggested reactions of light naphtha
isomerization of the present work.

48


Let C A denotes the mole fraction of n-paraffin present at any time t,
R R

C N the mole fraction of n-olefin, C iso the mole fraction of i-paraffin.
R R R R

Then, the mole balance can be formulated mathematically as follows:

--------------------------------(4.2) R

= k1CA R R R

-------------------------------(4.3)
= k 1 C A -k 2 C N
R R R R R R R

By integration of equation (4.2) CA = CA°
R R R RP P at t= 0 we get

C A = C A ° exp (- k 1 t)
R R R RP P R R -------------------------------------
(4.4)

Substituting the equation (4.4) in equation (4.3) yield:

= k 1 C A ° exp (- k 1 t) - k 2 C N
R R R RP P R R R R R --------------------------------------
R

(4.5) R

Rearrangement of equation (4.5) gives:

49


R + k 2 C N = k 1 C A ° exp (- k 1 t)
R R R R R R R R R R RP P R R

This is a linear first order differential equation as follows:

°
+ Py =Q where P = k 2 , Q = k 1 C A exp (- k 1 t)
R R R R R RP P R R

Then, can be solving this differential equation as follows:

yρ = Q dx + c where ρ integration factor which can be calculated from:

ρ=

where integration factor is exp (k 2 t). R R

Then by integrate of differential equation will give:

C N exp (k 2 t) = exp (k 2 -k 1 ) t + A
R R R R R R R R ----------------------------------(4.6)

where A is the integration constant, and it can be determined using the following
conditions:
t=0 , CN = 0
R R Thus :

A=- --------------------------------- (4.7)

Then:

C N exp (k 2 t) =
R R R R [exp (k 2 -k 1 )t – 1]. Then
R R R R

50

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