mervin thesis final

Project Report

SYNTHESIS OF Zn IMPREGNATED ZSM-5 CATALYST FOR THE DIRECT CONVERSION OF n-BUTANE TO ISO-OCTANE

Under the Guidance of

Mr. Rajeshwar Mahajan Dept. of Chemical Engineering

Submitted by, MERVIN J

R670211020/500017986 M.Tech - Process Design Engineering

UPES, Dehradun April, 2013

i

SYNTHESIS OF Zn IMPREGNATED ZSM-5 CATALYST FOR THE DIRECT CONVERSION OF n-BUTANE TO ISO-OCTANE

A thesis submitted in partial fulfillment of the requirements for the Degree of

Master of Technology

(Process Design Engineering)

By

(MERVIN J)

Under the guidance of

Mr. Rajeshwar Mahajan

Assistant Professor

Dept. of Chemical Engineering

Approved

Dean

College of Engineering

University of Petroleum & Energy Studies

Dehradun

April, 2013

ii

CERTIFICATE

THE UNIVERSITY OF PETROLEUM AND ENERGY STUDIES FACULTY OF ENGINEERING

The undersigned certify that they have read, and recommend to the Faculty of Engineering for

acceptance, a thesis entitled “ Synthesis of Zn impregnated ZSM-5 catalyst for the direct

conversion of n-Butane to Isooctane” submitted by Mervin J in partial fulfillment of the

requirements for the degree of M. Tech in Process Design Engineering.

________________

Mr. Rajeshwar Mahajan

Assistant professor

Department of Chemical Engineering

________________

Dr. Ashutosh Panday

Head of the Department

Department of Chemical Engineering

Date______

iii

ACKNOWLEDGEMENT

I sincerely thank Dr. Ashutosh Pandey, Head of the Department, for his priceless motivations

which has inspired me to contribute the best of mine towards my project.

I would like to thank my mentor Mr. Rajeshwar Mahajan, assistant professor who has guided me

throughout my project inspite of his busy schedule and made it possible to deliver a quality

work. Without his esteemed guidance it is impossible to think where I stand today. As a learner I

came to know about latest advancements in the field of process engineering from him. Working

with him gave me a world class exposure. And I feel it is a life time opportunity to work with

him. I learned to be a positive person which is an essential aspect for one’s life.

I would also like to thank Dr. R.P. Badoni for giving me an opportunity to perform my

experiments in the catalyst development lab and the catalyst characterization lab. I feel very

proud to mention his name in my acknowledgements. His knowledge in the current field has

helped to drive myself in an efficient path.

I would specially thank Dr. G. Gopala Krishnan for his invaluable guidance and his constant

support throughout. It is my pleasure in having his in motivational support and encouragement.

I would also like to acknowledge with much appreciation the role of all faculties who taught

subjects which were the foundation for these works. I would like to thank with sincere gratitude

to Dr. Surbhi Semwal for her help in completion of my experimental work.

I am very thankful to Ms. Remya for helping me by encouraging and advising for the completion

of project. I also thank Mr. Amit Kumar for helping me in conducting experiment trails.

It is not possible to complete my acknowledgements without thanking Dr. Vishal Misra. He is

the person who made me to stand in front of the competitive world.

I would like to express my thanks to all my friends who gave me the possibility to complete this

report. Even though many senior members supported me through all my tough times my friends

especially my roommates, helped me through out my journey by adding extra sugar to my

dessert.

Mervin J

M.Tech - Process Design Engineering

iv

LIST OF FIGURES

Figure 3.1.1 Effect of reaction temperature on the non-catalytic oxidative dehydrogenation of n-butane.

...................................................................................................................................................................... 9

Figure 3.1.2 Effect of reaction temperature on the oxidative dehydrogenation of n-butane over

Mg3(VO4)2/MgO........................................................................................................................................... 10

Figure 3.1.3 Dehydrogenation activity of Zn(imp)/K-ZSM-5 as a function of TOS. ..................................... 12

Figure 3.1.4 Feed conversion of different catalysts at WHSV = 6h-1. ........................................................ 14

Figure 3.1.1 Propene selectivity of different catalysts at WHSV = 0. 6h-1. ................................................ 15

Figure 3.2.1 Conversion of Isobutene to Isooctene by dimerization. ......................................................... 16

Figure 3.2.2 Commercial dimerization plant............................................................................................... 17

Figure 3.2.3. Developed dimerization process ........................................................................................... 19

Figure 3.2.1. Influence of operating pressure on conversion, .................................................................... 22

Figure 3.2.2 Influence of reaction temperature on isobutene dimers selectivity. ..................................... 23

Figure 3.2.3 Variation of Nickel load over catalysts HY-Zeolite. ................................................................. 24

Figure 3.2.4 Conversion as function of particle size, catalyst HY-Zeolite with 9% of Nickel load catalyst. 25

v

LIST OF TABLES

Table 1.1 Consumption of MTBE .................................................................................................................. 3

Table 3.1 BET surface area of the catalysts used. ....................................................................................... 13

Table 0.1 Si/Al ration and acidity (mmol/g) of the zeolite frameworks. .................................................... 20

Table 0.2 Total pore volume and avg. pore diameter of the impregnated zeolite frameworks with

different Nickel precursor salts. .................................................................................................................. 21

Table 4.1 Proportion of sample .................................................................................................................. 26

Table 4.2 BET surface area (m2/g) and Langmuir surface area (m2/g) of the calcined zeolite frameworks.

.................................................................................................................................................................... 30

Table 4.3 Total pore volume (cm3/g), micro pore volume (cm3/g) and acidity (mmol/g) of the calcined

zeolite frameworks. .................................................................................................................................... 30

Table 4.4 Amount of EDTA consumed for extrudate of sample 2. ............................................................ 33

Table 4.5 Amount of EDTA consumed for extrudate of sample 3. ............................................................. 33

Table 4.6 Ph and Molarity of the respective Ion exchange. ....................................................................... 34

Table 5.1 Comparison of Total acidty before and after Zn impregnation. ................................................. 34

vi

Contents Certificate ...................................................................................................................................................... ii

Acknowledgement ....................................................................................................................................... iii

List of figures ................................................................................................................................................ iv

List of tables .................................................................................................................................................. v

Nomenclature ............................................................................................................................................. vii

Summary .................................................................................................................................................... viii

1. Introduction ...................................................................................................................................... 1

1.1. Reaction paths .......................................................................................................................... 1

1.2. Background of catalysts ............................................................................................................ 2

2. Catalyst development ....................................................................................................................... 4

2.1. Zeolites ...................................................................................................................................... 4

2.2. Zeolite framework ..................................................................................................................... 5

2.3. ZSM-5 ........................................................................................................................................ 5

3. Literature survey ............................................................................................................................... 6

3.1. Dehydrogenation of alkanes ..................................................................................................... 6

3.2. Dimerization of alkenes .......................................................................................................... 16

4. Experimental methods .................................................................................................................... 26

4.1. Objectives ................................................................................................................................ 26

4.2. Methodology ........................................................................................................................... 26

4.3. Temperature programmed desorption ................................................................................... 29

4.4. Impregnation of extrudates with Zn ....................................................................................... 31

5. Result and conclusion ..................................................................................................................... 34

6. Future study .................................................................................................................................... 35

Bibliography ................................................................................................................................................ 36

vii

NOMENCLATURE

Symbol Definition Unit

M1 Molarity of the filtrate No. of moles/ liter of solution

M2 Molarity of the EDTA solution No. of moles/ liter of solution

V1 Volume of the filtrate mL

V2 Volume of EDTA solution mL

Selectivity %

Conversion %

Yield Mass. %

Temperature ◦C

TOS Min, hr

BET surface area m2/g

Langmuir surface area m2/g

Acidity mmol/g

T Temperature °C

WHSV Weight hourly space velocity h-1

Total pore volume cc/g

Micro pore volume cc/g

Avg. Pore diameter Å

Flow rate mL/h

Pressure Psig

Particle size mm

viii

SUMMARY

The main objective is to prepare a catalyst which can efficiently support simultaneous

dehydrogenation of n-butane and dimerization of butenes to give isooctenes and hydrogenation

of octenes to obtain isooctane as product. A catalyst is made using 10 membered ring ZSM-5 and

zinc is impregnated over the catalyst support surface. The impregnation of zinc is done by ion

exchange method, where zinc nitrate hexa hydrate is used as a medium to impregnate. The

sodium ion in the ZSM-5 is replaced by zinc and ammonium ion, from zinc nitrate hexa hydrate

and ammonium chloride respectively. After the ion exchange, the complex is calcined at 500◦C

where ammonium ions are replaced by protons to increase the bronsted acid sites further. The

hydrogen ions thus contribute to the formation of carbonium ions.

1

CHAPTER 1

1. INTRODUCTION

The world today requires fuel with high efficiency, one way to improve the efficiency of the fuel

is to increase its octane number. Higher the octane number more is the knocking resistance of the

fuel. The recent technologies have made it possible to increase the octane number in an

environment friendly manner. The isooctane is used as a major additive to increase the octane

number of gasoline, which can be obtained from its precursor n-butane. The commercial

production of isooctane is done in petroleum distillation process. Isooctane is used as a raw

material to produce alkyl phenol and isononanic acid.

1.1. REACTION PATHS

There are two reaction paths to obtain isooctane using n-butane as the feedstock.

One is the alkylation process, in which the reaction path follows dehydrogenation of n-butanes to

butenes and its subsequent alkylation with remaining butanes to isooctanes.

Second is the dimerization process, in which butanes are dehydrogenated to butenes followed by

dimerization of butenes to isooctenes and the isooctenes are hydrogenated to yield isooctane.

Both the reaction path involves initiation, propagation and termination steps. The initiation step

in both the reaction path involves the formation of tertiary carbonium ion by the protonation of

butene involving bronsted acid sites. The propagation step in the both the reaction paths involves

the addition of butene to the carbonium ion to form dimeric and oligomeric carbocations. The

termination step in the alkylation reaction path, involves a hydride transfer from isobutane to

carbonium ion to form isoalkenes (2, 4, 4 Trimethyl-2-pentene, 2, 4, 4 Trimethyl-1-pentene) and

tertiary carbonium ion which carries the cycle. The termination step in the dimerization reaction

path, due to the absence of isobutene the carbocation undergoes termination by chain transfer,

thereby releasing the proton which carries the cycle by reacting with another butene and gives

isoalkenes as a product. Selectivity of the dimerization reaction and restricting the oligomers

formed within the allowable gasoline range can be done by optimizing the parameters such as,

WHSV, temperature, composition of feed, catalyst configuration.

2

1.2. BACKGROUND OF CATALYSTS

During the start of the age of industrialization a lot of researches have been done in order to

improve the octane number by trying with various additives. Each additive tend to have an effect

over the environment.

At the very beginning in 1923, the most effective anti-knock agents used were tetraethyl lead or

TEL. By the mid of 1970’s due to the lead poisoning, the use of tetraethyl lead is suppresses. By

1995 it is completely banned in continental US and some of the European countries.

In 1959, manganese based anti-knock agent methylcyclopentadienyl manganese tricarbonyl or

MMT was used. During combustion the manganese present in MMT tends to form manganese

compounds, which settles on spark plugs and combustion chamber. The rest of the compounds

are released into the atmosphere causing air pollution.

3

In 1970, methyl tertiary butyl ether or MTBE has been found as an alternative fuel additive,

mainly for the advantage of phasing out lead. Since 1980’s due to the increase in demand for

premium gasoline, MTBE had remained as a dominant gasoline additive to enhance the octane

number.

Table 1.1 Consumption of MTBE

Year Usage of MTBE (Barrels per day)

1990 83,000

1994 161,000

1997 269,000

The main disadvantage of MTBE is that it is water soluble and do retain in water for long time.

In 2003, US had started using ethanol as an alternative to MTBE as the farmers and agricultural

groups found it to be a safe alternative. But ethanol was found to be affecting the air quality by

causing photochemical smog and the water quality in terms of health oriented problems. A much

safer alternative was found to ETBE, due to the fact that it does not cause smog and its inability

to absorb atmosphere’s moisture. Since ETBE is commercially considered to be expensive, it’s

usage as an anti-knocking agent and oxygenate was not an option. In the recent years isooctane is

found out to be a much more efficient and safer substitute as an anti-knocking agent and also a

better oxygenate used so far. Some of the anti-knocking agents which is in use in the present day

are,

Tetraethyl lead (TEL)

Methylcyclopentadienyl manganese tricarbonyl (MMT)

Ferrocene

Toluene

Isooctane

4

CHAPTER 2

2. CATALYST DEVELOPMENT

The catalyst developed must support dehydrogenation and hydrogenation reactions as well as

alkylation and dimerization reactions. Dehydrogenation of alkanes requires relatively a high

temperature range and low pressure for the reaction to take place, whereas dimerization of

alkenes requires a low temperature range for effective dimerization. The catalyst chosen must

remain stable and catalyze the reactions at the specified temperature ranges and also the high

temperature range must not lead to the thermal cracking of coke and other lighter alkanes.

2.1. ZEOLITES

In 1756, Axel Fredrik Cronstedt a Swedish mineralogist, found that the mineral stilbite upon

rapidly heating generated steam in large quantity. The steam was formed due to the water that

had been absorbed by the mineral. He named this mineral as zeolite, from Greek terminology

where zein means - to boil and lithos means - stone.

In the present day the usage of zeolites are in the scale of million tons per annum. A vast portion

of zeolites are used in petrochemical industry mainly as a catalyst for isomerization, dimerization

and cracking of hydrocarbons.

Zeolites are also utilized for domestic purposes such as softening and purification of water by

ion exchange method and in laboratories they are been used to remove gases and solvents. They

are also being used in the field of construction, agriculture and animal husbandry. Each and

every aspect of zeolites applications is concerned about clean and safe environment.

Zeolites are micro porous materials with a well-defined crystalline structure. They exist naturally

as minerals and some of the zeolite framework is synthesized by researchers all over the world

because of the unique properties showcased by the zeolite framework. Their framework

comprises of aluminium, silicon and oxygen. Water is trapped within the pores along with

cations and molecules. In the case of ZSM-5 catalyst sodium molecules are present inside the

pores.

5

2.2. ZEOLITE FRAMEWORK

Zeolite framework structure is formed by a connected group of oxygen atoms with silicon atom

in the middle, to form a tetrahedral frame. The corners of each tetrahedral frame then can be

linked to form the complete framework of the zeolites. A variety of different types of framework

can be synthesized by rearranging the tetrahedral frames. Until now 130 different zeolite

frameworks had been synthesized. Within the framework linked cavities, channels and cages can

be allowed, which determines the pore size of the zeolite. The pore size can be varied in the

range of 3 to 10 A in diameter. One can synthesize a framework of specific pore size and pore

volume according to their need. E.g. Framework of pore size exist such that, ammonia gas is

separated from air.

Even the tetrahedral atom can be replaced so as to obtain a different frame, by replacing the

usual silicon or aluminium atom with the other atoms such as, boron, gallium, germanium,

beryllium, arsenic, aluminophosphates or ALPO’s.

2.3. ZSM-5

ZSM-5 is abbreviated as Zeolite socony mobil. In 1975 it is synthesized and a patent was made

by mobil Oil Company. Its framework is based on alumino silicate. ZSM-5 comprises of sodium,

aluminium, silicon, oxygen and water. The chemical formula is given as NanAlnSi96-

nO192.16H2O. A major usage is found in the petroleum industry as a heterogeneous catalyst to

catalyze dimerization and isomerization reactions.

6

CHAPTER 3

3. LITERATURE SURVEY

3.1. DEHYDROGENATION OF ALKANES

CnH2n+2 → CnH2n+2 + H2 [1]

The dehydrogenation of alkanes requires a higher temperature and relatively low pressure. It is

been done on a large scale simply due the fact that it requires a less capital and also due to its

efficiency in converting the low cost precursors to their corresponding alkenes. Some of the

well-known processes in alkene production include the CATOFIN, the UOP and the

SNAMPROGETTI- YARSINTEZ. [1]

The drawbacks for conversion of alkenes from alkanes as a continuous process in industries

includes,

Supplying enough heat to the reactor.

Maintaining temperature to avoid any degradation products and also the conversion must

be at maximum.

Regenerating catalysts.

This section includes the literature of commercially used catalysts to obtain alkenes from

alkanes by dehydrogenation process.

Dehydrogenation requires a low temperature for alkanes of longer chains whereas lighter

alkanes require relatively higher dehydrogenation temperatures. [6] The lowering of pressure and

addition of diluents can be done to increase the conversion of alkanes. Dehydrogenation

temperatures to obtain equilibrium conversion of 90 % for ethane and hexane to their

corresponding alkenes (ethene and 1-hexene) are 900 ◦C and 730 ◦C respectively. [1]

The reactions are not selective because all C-H bonds possess the same bonding energy and

hence all have an equal chance of reacting, which leads to dehydrocyclisation and aromatization

if non neighboring C-H bond tends to undergo dehydrogenation. [1] Aromatization occurs if the

7

alkanes consist of six carbons in their chains. When C-H bonds reacting are from two alkane

molecules, long chained hydrocarbons are formed. If the reactions are unselective the formation

of hydrogen gas and coke formed will be in large, due to unwanted C-H and C-C bond

formation. The coke deposited over the catalyst tends to produce more hydrogen than alkenes

overall. Hence regeneration of catalyst must be done in order to expose more acid sites, so that

selectivity is improved resulting in the conversion of alkanes to alkenes. [1]

The dehydrogenation of alkanes can be done in two paths, oxidative dehydrogenation and non-

oxidative dehydrogenation. [1] The most seeked path is the oxidative dehydrogenation due to the

fact that it offers less limitation thermodynamically. [5] And also oxidative dehydrogenation is

more selective towards alkanes and does not tend to form combustion products and aldehydes or

acids, when compared to non-oxidative dehydrogenation.

The selectivity depends on streaming time. Initially selectivity towards alkenes are very low

hence CO, CO2 are formed. After the induction time, the selectivity towards alkenes increases

up to 90 %. [1]

3.1.1. CHROMIUM OXIDE CATALYST

Alkane dehydrogenation to obtain propene and isobutene with the help of chromium oxide

catalysts in the absence of oxygen is a process of commercial interest. This paper deals with the

usage Cr/Al2O3 catalyst in the commercial production of isobutene and propene. [1]

3.1.1.1. CATALYST PREPARATION

Wet incipient impregnation method is utilized to prepare chromium oxide catalyst on porous

alumina with high surface area using aqueous solution containing chromium (VI) trioxide or

chromium (III) nitrate. K2CrO4 aqueous solution is used, if dopant is required. [1]

3.1.1.2. CATALYTIC CHARACTERIZATION

The dehydrogenation activity is based on Cr loading (in Wt. %) over catalyst, reaction

temperature and streaming time. Initially the activity increases linearly with the Cr loading, but

when the Cr loading is in the range of 4 - 10 % the level of activity remains constant or even

deteriorates.

8

The longer the time of streaming, lower would be the dehydrogenation activity. This is due to the

formation of coke. Also the activity depends upon the number of regeneration- dehydrogenation

cycles. The lifecycle of the catalyst can be increased by increasing the temperature as the time on

stream is increased. [1]

From this paper we conclude that at initial, the dehydrogenation activity increases linearly and

the level of activity remains constant or even detoriates when the Cr loading is in the range of 4 -

10 %. The lifecycle of the catalyst can be increased by increasing the temperature as the time on

stream is increased.

3.1.2. VANADIUM MAGNESIUM OXIDE CATALYST

In this paper the conversion of butene and butadiene from butane is obtained by oxidative

dehydrogenation with MgO supported magnesium vanadate as catalyst. For a better selectivity

orthovanadate phase is been used. A detailed study had been made on catalytic and non-catalytic

dehydrogenation of alkanes in terms of temperature and selectivity. [3]

Catalyst preparation

The catalytic characterization is studied after the following steps been done,

Impregnation of MgO powder in varying amounts in a solution consisting of 1 Wt. % of

ammonium vanadate and 0.5 Wt. % of ammonium hydroxide is done and evaporated

until a paste is formed. [3]

The paste obtained is dried at 120 ◦C for 18 hrs.

Calcination of the paste is done at 600 ◦C for 4 hrs.

Particles of desired size is obtained after the calcined material is paletized, crushed and

sieved.

Catalytic characterization

The characterization is done with the residence time of 0.6 s.

Non-catalytic oxidative dehydrogenation

As the temperature is increased from 410

31 %) decreases drastically. Butadiene was not detected. The selectivity for combustion products

(CO2) increases slightly and for the cracki

Figure 3.1.1 Effect of reaction temperature on the non

n-butane conversion (●) and selectivities

Catalytic oxidative dehydrogenation

As the temperature is increased from 450

31 %) decreases slightly and the selectivity to butadiene increases (f

selectivity for combustion products (CO

9

The characterization is done with the residence time of 0.6 s.

ve dehydrogenation

As the temperature is increased from 410 ◦C to 550 ◦C, the selectivity for butenes (from 89 % to

decreases drastically. Butadiene was not detected. The selectivity for combustion products

(CO2) increases slightly and for the cracking products it increases (9 % to 53 %).

Effect of reaction temperature on the non-catalytic oxidative dehydrogenation of n

butane.

●) and selectivities for butenes (□), CO2 (◊) and cracking products (∆).

Catalytic oxidative dehydrogenation

As the temperature is increased from 450 ◦C to 550 ◦C, the selectivity for butenes (from 39 % to

decreases slightly and the selectivity to butadiene increases (from 17 % to 32 %). The

selectivity for combustion products (CO2) decreases and the cracking products increase

C, the selectivity for butenes (from 89 % to

decreases drastically. Butadiene was not detected. The selectivity for combustion products

ng products it increases (9 % to 53 %). [3]

ive dehydrogenation of n-

◊) and cracking products (∆).

C, the selectivity for butenes (from 39 % to

rom 17 % to 32 %). The

increase. [3]

Figure 3.1.2 Effect of reaction temperature on the oxidative dehydrogenation of n

n-butane conversion (●), total selectivity for dehydrogenation products (TDS) (■) and selectivities

for butenes (□), butadiene (x), CO2 (

From this paper we conclude that, in the non

for butenes (from 89 % to 31 %)

550 ◦C).

In the catalyzed oxidative dehydrogenation, with

selectivity for butenes decreases slightly (from 39 % to 31 % ) as the temperature is increased

(450 ◦C to 550 ◦C). Maximum conversion of butane to butene is obtained at 550

3.1.3. ZINC MODIFIED ZSM

For the dehydrogenation of n-butane to n

exchange of potassium ions before the zinc metal impregnation, since the acid sites are active in

cyclodimerization and dimerization reactions. The zinc metal contributes to the dehydrogenation

activity of n-butane. [4]

The ZSM-5 catalyst is synthesized

10

Effect of reaction temperature on the oxidative dehydrogenation of n

Mg3(VO4)2/MgO.

●), total selectivity for dehydrogenation products (TDS) (■) and selectivities

□), butadiene (x), CO2 (◊) and cracking products (∆).

From this paper we conclude that, in the non-catalyzed oxidative dehydrogenation, the selectivity

%) decreases drastically as the temperature is increased (450

dehydrogenation, with MgO-supported Mg3(VO3)2

decreases slightly (from 39 % to 31 % ) as the temperature is increased

C). Maximum conversion of butane to butene is obtained at 550 ◦

ZINC MODIFIED ZSM-5 CATALYST

butane to n-butene, the bronsted acid sites must be replaced with



synthesized in the Si/Al ratio of 40.

Effect of reaction temperature on the oxidative dehydrogenation of n-butane over

●), total selectivity for dehydrogenation products (TDS) (■) and selectivities

◊) and cracking products (∆).

oxidative dehydrogenation, the selectivity

decreases drastically as the temperature is increased (450 ◦C to

2 as catalyst, the

decreases slightly (from 39 % to 31 % ) as the temperature is increased

◦C. [3]

sted acid sites must be replaced with



11


Impregnation of zinc over ZSM-5 catalyst can be done in two ways.

First way is, initially the calcination is done with nitrogen for 7 hrs and later calcination is done

for 8 hrs with air. The ZSM-5 is ion exchanged in 1M KNO3 solution for a duration of 24 hrs at

room temperature and it is impregnated with Zn(NO3)2.6H2O.

The other way is, ion-exchange is done with 1M Zn(NO3)2.6H2O solution for a duration of 48

hrs. The calcination is done at 500 ◦C for 4 hrs. [4]

Catalyst characterization

The yield of n-butene isomers decreases (from 14 to 5 Mass. %) drastically as the time on stream

is increased (from 10 to 175 min). The yield of isobutane and 1, 3- butadiene almost is the same

with a very slight decrease as the time on stream is decreased. There is no change in the aromatic

products yield. [4]

3.1.4. PT/SN ZSM-5 CATALYST

In this paper, the catalytic dehydrogenation of

studied with the help of Pt impregn

main product to be attained is propene.


The H-ZSM-5 powder is synthesized

Figure 3.1.3 Dehydrogenation activity of Zn(imp)/K

The WHSV of n- butane in the experiment was 2h

12

5 CATALYST

In this paper, the catalytic dehydrogenation of mixed alkanes to their corresponding alkenes is

studied with the help of Pt impregnated and Pt/Sn impregnated over ZSM-5 as the catalyst. The

main product to be attained is propene. [2]

synthesized with the Si/Al ratio of 140.

Dehydrogenation activity of Zn(imp)/K-ZSM-5 as a function of TOS.

butane in the experiment was 2h-1.

mixed alkanes to their corresponding alkenes is

5 as the catalyst. The

13

Monometallic catalyst

The Pt metal of 0.5 wt. % is impregnated over the H-ZSM-5 with the aqueous solution of 0.03 M

H2PtCl6 at 60 ◦C.

After the impregnation, the sample is dried at 100 ◦C for duration of 4 hrs. Followed by drying of

sample, calcination is done at 500 ◦C for 4 hrs in a muffle furnace. [2]

Bimetallic catalyst

For the preparation of bimetallic catalyst impregnation is done twice.

Initially, the Sn metal of 0.1 wt. % is impregnated over the H-ZSM-5 powder with the aqueous

solution of 0.16 M SnCl2.2H2O at 80 ◦C. After the impregnation, the sample is dried at 100 ◦C for

4 hrs. Followed by drying of sample, calcination is done at 500 ◦C for 4 hrs.

Secondly, the Pt metal of 0.5 wt. % is impregnated on the Sn impregnated catalyst with aqueous

solution of 0.03 M H2PtCl6 at 60 ◦C. The second impregnation is ended with drying of sample.

Both the catalysts are crushed and dechorination is done at 480 ◦C for 4 hrs in the presence of

steam. Each and every catalyst sets are reduced in the presence of hydrogen at 510 ◦C before the

reaction tests. [2]


The BET surface area (m2/g) is analyzed and found out that it is increasing in the order as

follows: bimetallic (Pt-Sn/ZSM-5), monometallic (Pt/ZSM-5) and ZSM-5 without impregnation.

[2]

Table 3.1 BET surface area of the catalysts used.

Catalyst type BET surface area (m2/g)

Bimetallic (Pt-Sn/ZSM-5) 354.1

Monometallic (Pt/ZSM-5) 346.9

Simple ZSM-5 341.9

Comparison of catalysts in terms of dehydrogenating capability

The conversion of feed is way better when bimetallic catalyst is compared with monometallic

and simple ZSM-5 catalyst. The dehydrogenating capability of simple ZSM

the monometallic catalyst is higher than simple ZSM

bimetallic catalyst is way better than simple ZSM

Figure 3.1.4 Feed conversion of different catalysts at WHSV = 6h

Comparison of propene selectivity for Pt

and time on stream (TOS):

For bimetallic catalyst, the ideal temperature for maximum selectivity to propene is 550

the start, the selectivity to propene is 25 % and as the time on stream incre

jumps to 55 %. Likewise a comparison is made for propene selectivity at temperatures of 575

600 ◦C and 625 ◦C. [2]

However the time on stream is increased from 1 to 10 hrs, the yield

significantly.

The major product to be obtained is the propene and initially its yield increases drastically (from

3 % to 8 %) for 1 hr time on stream. After one hour however the time on stream is increased,

there is no increase in the yield. [2]

14

Comparison of catalysts in terms of dehydrogenating capability:


5 catalyst. The dehydrogenating capability of simple ZSM-5 is very low and of

lyst is higher than simple ZSM-5. The dehydrogenating capability of

bimetallic catalyst is way better than simple ZSM-5 and monometallic catalysts.

Feed conversion of different catalysts at WHSV = 6h-1.

selectivity for Pt-Sn/ZSM-5 at different temperatures

and time on stream (TOS):

For bimetallic catalyst, the ideal temperature for maximum selectivity to propene is 550

the start, the selectivity to propene is 25 % and as the time on stream increases the selectivity

jumps to 55 %. Likewise a comparison is made for propene selectivity at temperatures of 575

However the time on stream is increased from 1 to 10 hrs, the yield of butene

or product to be obtained is the propene and initially its yield increases drastically (from


[2]


5 is very low and of

nating capability of

[2]

1.

5 at different temperatures

For bimetallic catalyst, the ideal temperature for maximum selectivity to propene is 550 ◦C. At

ases the selectivity

jumps to 55 %. Likewise a comparison is made for propene selectivity at temperatures of 575 ◦C,

of butene does not vary

or product to be obtained is the propene and initially its yield increases drastically (from


Figure 3.1

1.

15

3.1.1 Propene selectivity of different catalysts at WHSV =

Propene selectivity of different catalysts at WHSV = 0. 6h-

3.2. DIMERIZATION OF ALKE

Dimerization is a process of producing

presence of catalyst. It is utilized

precursor in the production of isooctanes. Since 2006 iso

scale of 40,000 tons per year at a plant in Kawasaki, Japan. The octane number (RON) of octene

is 115. [7]

Figure 3.2.1 Conversion of Isobutene to Isooctene by dimerization.

The formation of oligomers from n

is a difficult task. As the conversion of iso

corresponding dimers. [9] The main objective of today’s researchers is to develop a catalyst

which has a high selectivity to dimers. For decades solid acid catalysts have been used as the

catalyst for dimerization, especially catalysts consisting of Ni over zeolite framework, oxides and

organo metallic nickel complexes.

isooctane are isoether process developed by Snamprogetti and CDIsoether technology by

CDTECH. [7, 8] In the latter process, butenes

etherified to obtain iso-octane. [9]

16

DIMERIZATION OF ALKENES

of producing dimer by attaching two similar monomers together in the

ilized in the production of isooctenes. İsooctenes are used as a

cursor in the production of isooctanes. Since 2006 isooctenes are produced commercially on a

40,000 tons per year at a plant in Kawasaki, Japan. The octane number (RON) of octene

Conversion of Isobutene to Isooctene by dimerization.

The formation of oligomers from n-butane is a consecutive process and obtaining only the dimer

task. As the conversion of isobutenes increases less is the chance of obtaining their

The main objective of today’s researchers is to develop a catalyst

as a high selectivity to dimers. For decades solid acid catalysts have been used as the


organo metallic nickel complexes. [10] Some of the commercial available methods to obtain

octane are isoether process developed by Snamprogetti and CDIsoether technology by

In the latter process, butenes are dimerized, partially dimeriz

[9]

dimer by attaching two similar monomers together in the

octenes are used as a

octenes are produced commercially on a

40,000 tons per year at a plant in Kawasaki, Japan. The octane number (RON) of octene

Conversion of Isobutene to Isooctene by dimerization.

is a consecutive process and obtaining only the dimer

butenes increases less is the chance of obtaining their

The main objective of today’s researchers is to develop a catalyst

as a high selectivity to dimers. For decades solid acid catalysts have been used as the


ble methods to obtain

octane are isoether process developed by Snamprogetti and CDIsoether technology by

are dimerized, partially dimerized or partially

Figure

Significance of Lewis and Bronsted acid sites in dimerization

Unsaturated compounds forms if strong lewis acid sites are present, where

to the formation of essential carbenium ions for dimerisation to occur.

İsobutene are adsorbed at lewis acid sites and near the bronsted acid sites alkene formation

increases. The formation of alkenes at the bronsted acid sites increases the chance of

dimerization. In all the catalyst both the bronsted and lewis acid sites must be high.

3.2.1. NOVEL PHOSPHORIC ACI

In this paper the developed catalyst is compared with silica alumina catalyst. In general when the

catalyst used is silica alumina, as the conversion of iso

isooctenes decreases. But when novel phosphoric acid is used

increases even at higher conversion of iso

17

Figure 3.2.2 Commercial dimerization plant

Significance of Lewis and Bronsted acid sites in dimerization

Unsaturated compounds forms if strong lewis acid sites are present, where these compounds lead

to the formation of essential carbenium ions for dimerisation to occur. [8]




NOVEL PHOSPHORIC ACID CATALYST


a, as the conversion of isobutenes increases the chance of obtaining

octenes decreases. But when novel phosphoric acid is used, the selectivity towards iso

ven at higher conversion of isobutenes. [7]

these compounds lead





ses the chance of obtaining

the selectivity towards isooctenes

18

Reaction mechanism

The reaction mechanism followed by both the catalyst explains the reason in the dimer

selectivity. The former catalyst leads to the formation of alkyl cation, the carbonium ion’s

reactivity does not depend upon the number of carbon atoms. Hence the reaction does not limit

to dimers. The dimer formed undergoes polymerization to form polymers. [7]

The latter one leads to the formation of acid ester, formed from the reaction between isobutene

and phosphoric acid. The phosphoric acid ester has a three dimensional structure which restricts

the reaction to yield dimers. There is no room for alkyl groups to form polymers. The ortho

phosphoric acid monomer supported over silica has more acidity and selectivity towards

isooctene than compared to SPA (Solid phosphoric acid) catalyst.

Factors affecting the activity

The developed catalyst life is affected by factors including outflow of phosphoric acid and

change in state due to condensation- dehydration of phosphoric acid. The outflow can only be

controlled by careful optimization of the operation. The reason for the outflow is that, the

phosphoric acid monomer is not chemically bonded to the silica support.

The moisture level in the reactor also affects the acidity and selectivity of the catalyst. At low

moisture level, the phosphoric acid monomer changes to polymer due to dehydration. The

moisture density can be maintained by adding sufficient amount of water to the butene feedstock.

[7]

Regeneration of catalyst

Since phosphoric acid in SPA catalyst is chemically bonded, the process regenerating is

impossible. On the other hand, the developed catalyst can be regenerated due to fact that

phosphoric acid monomer is not chemically bonded to the silica support. Regeneration can be

done by immersing the support in the solution of phosphoric acid. The usage of developed

catalyst is cost effective, it makes possible to obtain large amount of isooctene in a single step. In

general, at low conversion of butenes the selectivity towards isooctene is high.

Hence in the case of low selective catalyst, the conversion is kept low in the first reactor so as to

obtain maximum dimer. The unreacted butenes are removed by distillation and it is fed into the

second reactor so as the process is

dimer selectivity can be obtained in a single step reaction with the help of single reactor.

Figure

3.2.2. NICKEL MODIFIED ZEOL

In this paper zeolites with three different frameworks HY

taken and nickel is impregnated over the zeolites using three prescursor salts including NiCl

NiSO4 and NiCO3. The acidic properties of nickel modified zeolite

stability, acidity and the selectivity towards iso

NiCO3 is the most effective modified

compared to the other modified catalysts

19

process is repeated. [7] Whereas in the developed catalyst case, high

r selectivity can be obtained in a single step reaction with the help of single reactor.

Figure 3.2.3. Developed dimerization process

NICKEL MODIFIED ZEOLITES

In this paper zeolites with three different frameworks HY-zeolite, Hβ zeolite, H

taken and nickel is impregnated over the zeolites using three prescursor salts including NiCl

. The acidic properties of nickel modified zeolites are responsible for the

and the selectivity towards isooctene. The Ni impregnated HY

is the most effective modified catalyst; the selectivity towards dimerization

compared to the other modified catalysts. The Ni contributes to the acidity of the catalyst by

Whereas in the developed catalyst case, high

r selectivity can be obtained in a single step reaction with the help of single reactor.

zeolite, Hβ zeolite, H-mordenite are

taken and nickel is impregnated over the zeolites using three prescursor salts including NiCl2,

s are responsible for the

octene. The Ni impregnated HY-zeolite with

dimerization is more when

. The Ni contributes to the acidity of the catalyst by

20

replacing the aluminium ion present in the zeolite. The Si/Al ratio of the framework also affects

the acidity.

Table 0.1 Si/Al ration and acidity (mmol/g) of the zeolite frameworks.

Zeolite framework Si/Al ratio Acidity (mmol/g)

HY-zeolite 5.2 0.82

Hβ zeolite 150 0.82

H-mordenite 90 0.37


All the zeolite frameworks are immersed in solutions of NiCl2, NiSO4 and NiCO3. The solutions

are then filtered and the precipitate obtained is for duration of 12 hr at 373 K. Followed by

drying, calcination is done for 5 hr at 773 K. The impregnation of Ni over the framework is done

so that the concentration range is 0 to 16.5. Wt. % [8]


Influence of precursors over total pore volume and average pore diameter.

In the characterization part the properties including BET total area, total acidity, pore size

distribution, pore volume and average pore diameter are determined by TPD analysis.

The avg. pore size diameter of the HβZ catalyst when compared to the other catalyst as HM,

HYZ is almost double the size. [8] Whatever the precursor salt used to impregnate Ni over the

zeolite framework does not vary the pore size diameter at large.

21

Table 0.2 Total pore volume and avg. pore diameter of the impregnated zeolite frameworks with

different Nickel precursor salts.

Precursor salt/support Total pore volume (cc/g) Avg. Pore diameter (Å)

NiSO4.6H2O/HM 0.003 35.6

NiSO4.6H2O/HβZ 0.94 89.7

NiSO4.6H2O/HYZ 0.124 36

NiCl2.6H2O/HM 0.003 35.6

NiCl2.6H2O/HβZ n.m n.m

NiCl2.6H2O/HYZ 0.2097 36.34

NiCO3.2Ni(OH)2.4H2O/HM 0.178 35.9

NiCO3.2Ni(OH)2.4H2O/HβZ 1.005 88.31

NiCO3.2Ni(OH)2.4H2O/HYZ 0.4085 36.12

HM 0.0086 36.2

HβZ 0.886 87.54

HYZ 0.1654 36.08

The total pore volume of the framework happens to be dependent upon the nickel precursors

used. When we compare the HM catalysts which is impregnated with different precursors, the

nickel carbonate salt used as the precursor have high total pore volume.

In case of HβZ catalysts, the nickel carbonate salt used as precursor have high total pore volume

when compared to the other precursors used. [8]

In case of HYZ catalysts, the nickel carbonate salt used as precursor have high total pore volume

when compared to the other precursors used.

We conclude than NiCO3.2Ni(OH)2.4H2O when used as the precursor improves the total pore

volume irrespective of the zeolite framework used.

Influence of operating pressure on conversion

We know that increasing the pressure tend

isobutene there will be an increase in conversion due to the increase in con

and isobutene. But increase in pressure has

octene. The ideal operation pressure is found out to be 90 psig

The B6 zeolite sample is chosen and a graph is plotted for conversion

for the following reaction conditions T = 25

mL/h. [8]

Figure 3.2.1. Influence of operating pressure on conversion,

Operation condition: T = 25

Influence of operation temperature on selectivity

At low temperature range, the selectivity towards dimers ten

carried out room temperature.

For the B6 zeolite sample a graph is plotted for conversion

following reaction conditions P = 15 psig, WHSV = 0.09 h

22

Influence of operating pressure on conversion

We know that increasing the pressure tends to induce condensation of isobutene. By condensing

butene there will be an increase in conversion due to the increase in contact between acid sites

. But increase in pressure has a direct effect in reducing the selectivity towards

octene. The ideal operation pressure is found out to be 90 psig.

The B6 zeolite sample is chosen and a graph is plotted for conversion vs. time on stream (TOS)

for the following reaction conditions T = 25 ◦C, WHSV = 0.09 h-1 and isobutene flow = 9.6

. Influence of operating pressure on conversion,

T = 25 ◦C, WHSV = 9h-1 and isobutene flow = 9.6 mL/h, B6 catalyst.

Influence of operation temperature on selectivity

At low temperature range, the selectivity towards dimers tends to be less. Hence the reaction is

For the B6 zeolite sample a graph is plotted for conversion vs. time on stream (TOS) for the

following reaction conditions P = 15 psig, WHSV = 0.09 h-1 and isobutene flow = 9.6 mL/h.

s to induce condensation of isobutene. By condensing

tact between acid sites

educing the selectivity towards

time on stream (TOS)

and isobutene flow = 9.6

1 and isobutene flow = 9.6 mL/h, B6 catalyst.

ds to be less. Hence the reaction is

time on stream (TOS) for the

and isobutene flow = 9.6 mL/h.

At room temperature, the selectivity is steady and is high and also there is a slight increase when

the time on stream is increased.

for a few hours initially and as the time on stream increases the selectivity falls. At intermediate

temperature like 60 ◦C, the selectivity increases with time on stream.

Figure 3.2.2 Influence of react

Operation condition: P = 15 psig, WHSV = 0.9 h

Influence of Ni loading on co

A set of HY-Zeolites are taken and their Ni loading is varied. All the sets are compared by

plotting a graph between conversion and time on stream for operation

= 25 ◦C and WHSV = 0.09 h-1. [8]

The catalyst set with Ni loading of 3.2 % shows higher conversion and it remains almost the

same whatever the time on stream is. Even when the

increases, the selectivity towards the desired products

23

m temperature, the selectivity is steady and is high and also there is a slight increase when

[8] For temperatures as high as 184 ◦C the selectivity increases

and as the time on stream increases the selectivity falls. At intermediate

C, the selectivity increases with time on stream.

Influence of reaction temperature on isobutene dimers selectivity

P = 15 psig, WHSV = 0.9 h-1, isobutene flow = 9.6 mL/h, B6

Influence of Ni loading on conversion

Zeolites are taken and their Ni loading is varied. All the sets are compared by

raph between conversion and time on stream for operation conditions

[8]


same whatever the time on stream is. Even when the conversion reduces as the time on stream

increases, the selectivity towards the desired products is high.

m temperature, the selectivity is steady and is high and also there is a slight increase when

C the selectivity increases

and as the time on stream increases the selectivity falls. At intermediate

mers selectivity.

, isobutene flow = 9.6 mL/h, B6 catalyst.

Zeolites are taken and their Ni loading is varied. All the sets are compared by

s of P = 5 psig, T


as the time on stream

Figure 3.2.3 Variation of Nickel

Operational condition:

Influence of particle size on conversion

The mass transfer resistances can be avoided by choosing very small particle size (0.7 mm as

maximum). For HY-zeolite consisting of 9 % Ni loading and at operation conditions of T = 25

◦C, P = 4 psig and WHSV = 0.09 h

particle size. [8]

The conversion is high when the catalyst particle is very less. As the size of the particle increases

the conversion decreases along with it. From 0.7 mm onwards as the particle size increases the

conversion remains constant.

24

Variation of Nickel load over catalysts HY-Zeolite.

Operational condition: WHSV = 0.09 h-1, T = 25 ◦C, P = 5 psig.

ence of particle size on conversion


zeolite consisting of 9 % Ni loading and at operation conditions of T = 25

C, P = 4 psig and WHSV = 0.09 h-1, a graph has been plotted between conversion and catalyst




zeolite consisting of 9 % Ni loading and at operation conditions of T = 25

nversion and catalyst



Figure 3.2.4 Conversion as function of particle size, catalyst HY

Operational condition:

25

Conversion as function of particle size, catalyst HY-Zeolite with 9% of Nickel load

catalyst.

Operational condition: P = 4 psig, T = 25 ◦C, WHSV = 0.09 h-1.

with 9% of Nickel load

26

4. EXPERIMENTAL METHODS

4.1. OBJECTIVES

The main focus is to develop a 10 membered ring ZSM-5 catalyst support and impregnate it with

Zn metal to increase the total acidity. Higher the acidity of the catalyst higher the conversion will

be. A set of three catalyst supports are prepared with different proportions of binding agent.

4.2. METHODOLOGY

4.2.1. PREPARATION OF CATALYST SUPPORT

Extrudation

A set of three samples are extruded with the following proportions of Pural SB and Al(OH)3 as

the alumina class binders. In all the samples to provide a better integrity and strength kaolin

another binder is used.

Table 4.1 Proportion of sample

Sample number Proportion

1 ZSM-5 extruded with

5 % Al(OH)3 + 5 % Pural SB + 5 % Kaolin





Peptization is done using 1.5 % acetic acid solution. For each sample 10 mL of 1.5 % acetic acid

solution is made by adding 0.15 mL of acetic acid to 10 mL of distilled water.

27

The extrudates are made in the mortar. In the mortar, the alumina binding agents are made a

paste by adding the prepared acetic acid solution. To the paste made ZSM-5 is added and well

grinded to obtain a homogenous paste. The paste been made is extruded with the help of the

extruder.

Material balance of extrudate preparation:

1st sample:

Weight of ZSM-5 = 20 g

Weight of hydrated alumina = 1 g

Weight of Pural SB = 1 g

Weight of kaolin = 1 g

1st sample weight in mortar = 20 + 1 + 1 + 1 = 23 g

Weight of 1st extrudate = 1.632 g

2nd sample:

2nd sample weight in mortar (initial) = 21.368 g

To the paste in the mortar, 1 g of Pural SB is added and 10 mL of 1.5% of acetic acid solution

made is also added so as to obtain a homogenous mixture.

2nd sample weight in mortar = 21.368 + 1 = 22.368 g

2nd sample extrudate weight = 4.585 g

3rd sample:

3rd sample weight in mortar (initial) = 17.783 g

28

To the remaining paste in the mortar, 1 g of kaolin is added and 10 mL of 1.5% of acetic acid

solution made is also added to obtain a homogenous mixture.

3rd sample weight in mortar = 17.783 + 1 = 18.783 g

3rd sample extrudate weight = 5.612 g

4.2.2. DRYING OF THE EXTRUDED SAMPLE

The extruded sample is dried at room temperature until it becomes free from moisture. After a

significant amount of moisture is removed, drying of extrudates is done using a vacuum oven. In

the oven extrudates are placed for a duration of 8 hrs at 110 ◦C. Due to the extrudates are exposed

to high temperature, most of the water content are removed. The weight of the sample before and

after drying indicates the amount of water content removed.

Sample 1:

Weight before drying = 1.582 g

Weight after drying at 110◦ C = 1.509 g

Sample 2:



Sample 3:



29

4.2.3. CALCINATION OF DRIED EXTRUDATES

Calcination is done in the muffle furnace for an intermediate stay of every half an hour 100◦ C is

increased and when 500 ◦C is reached the extrudate sample is maintained at for duration of 5 hrs.

After calcination, the oxides and the other impurities present are burnt off.

Weight of the sample after calcination:

Weight of sample 1 = 1.487 g



4.3. TEMPERATURE PROGRAMMED DESORPTION

TPD analysis helps us to determine the number, type and strength of acid sites on the catalyst

surface by keeping track of the amount of gas desorbed at various temperatures.

TPD procedure is as follows,

Degassing of the sample is done to remove the moisture content by introducing Ar/He

gas mixture at 120 ◦C for duration of 30 minutes.

The degassed sample is exposed to a gas mixture of NH3 and He at room temperature for

30 minutes. At this point, the NH3 occupies the acid sites present on the surface.

The NH3 gas which is not adsorbed is flushed by passing He gas for 1 hr.

The temperature of the sample is raised linearly from 120 ◦C to 800 ◦C. When the

activation energy is reached the bond between the adsorbate and the adsorbent are broke

and the ammonia gas is desorbed from the surface.

The desorbed gas is sensed through the TCD. The volume of gas desorbed is directly

proportional to the acid sites.

30

Table 4.2 BET surface area (m2/g) and Langmuir surface area (m2/g) of the calcined zeolite

frameworks.

Proportion BET surface

area (m2/g)

Langmuir

surface area

(m2/g)

ZSM-5 extruded with

5 % Al(OH)3 + 5 % Pural SB + 5 % Kaolin 346.0706 504.4675

ZSM-5 extruded with

5 % Al(OH)3 + 10 % Pural SB + 5 % Kaolin 349.9457 518.6510

ZSM-5 extruded with

5 % Al(OH)3 + 10 % Pural SB + 10 %

Kaolin

319.3378 467.7131

Table 4.3 Total pore volume (cm3/g), micro pore volume (cm3/g) and acidity (mmol/g) of the

calcined zeolite frameworks.

Proportion

Total pore

volume

(cm3/g)

Micro pore

volume

(cm3/g)

Acidity

(mmol/g)

ZSM-5 extruded with

5 % Al(OH)3 + 5 % Pural SB + 5 % Kaolin 0.20505 0.10262 0.2363

ZSM-5 extruded with


ZSM-5 extruded with


31

4.4. IMPREGNATION OF EXTRUDATES WITH ZN

The calcined sample is impregnated with Zn by ion exchange method. The Zn ion contributes to

the dehydrogenation of the alkanes to alkenes. The Zinc nitrate hexa hydrate [Zn(NO3)2.6H2O] is

utilized for impregnating Zn over the catalyst and the ammonium chloride [NH4Cl] is used to

increase the acid sites.

4.4.1. ION EXCHANGE SOLUTION PREPARATION

0.5 M solutions of Zinc nitrate hexa hydrate and ammonium chloride are made by dissolving

74.372 g of Zinc nitrate hexa hydrate and 13.372 g of ammonium chloride in 500 mL of distilled

water respectively.

4.4.2. APPARATUS SETUP

Two necked round bottom flask is placed in an oil bath. A thermometer is fixed to one of the

neck with an aid of cork. It is fitted such that the bulb is just immersed in the solution to measure

the solution’s temperature. To the other neck water Liebieg condenser is fitted. The experimental

setup is placed over a magnetic stirrer with hot plate.

4.4.3. ION EXCHANGE METHOD

4 g of the extrudates sample and 100 mL solutions of zinc nitrate hexa hydrate and ammonium

chloride solutions made are taken in the round bottom flask. A magnetic bead is used to stir the

solution to achieve efficient impregnation. The solutions are maintained at 75 ◦C for 3 hrs, while

the magnetic stirrer stirs the bead inside the solution. The Liebieg condenser circulates water

with the help of immersed pump to reduce the vapor losses After 3 hrs the filtrate is withdrawn

from the flask and stored in a conical flask for further titration.

The experiment is repeated in the same manner for 2 more times continuously and their

corresponding filtrates are withdrawn and stored in separate conical flasks.

In the process of ion exchange a significant amount of sample are dissolved in the filtrate due to

the attrition experienced by the sample.

32

4.4.4. DRYING OF IMPREGNATED SAMPLE

The extrudate sample in the two necked round bottom flask after impregnation is withdrawn and

dried at room temperature in order to remove the moisture content from the extrudates. After

drying at room temperature, the extrudates are dried in the vacuum oven at 110 ◦C for 3 hrs.

Weight of sample 2 after drying = 1.815 g

Weight of sample 3 after drying = 2.610 g

4.4.5. CALCINATION OF IMPREGNATED SAMPLE

The impregnated sample are calcined in a muffle furnace, for an intermediate stay of every half

an hour 100 ◦C is increased and when 500 ◦C is reached the extrudate sample are maintained at

for a duration of 5 hrs. After calcination, the oxides and the other impurities present are burnt off.

The Na+ ion in ZSM-5 which is replaced by NH4+ ion are replaced by H+ ion. Thus the calcined

extrudate sample’s acidity increases.

Weight of sample 2 after calcination = 1.701 g

Weight of sample 3 after calcination = 2.468 g

4.4.6. TITRATION

The amount of Zn which is impregnated in the catalyst by replacing sodium ions of the zeolite

framework is found out by titrating the collected filtrate against the EDTA solution.

Solution preparation

0.01 M EDTA solution is prepared by dissolving 1.865 g in 500 mL of distilled water. The EBT

is used as an indicator; it is prepared by dissolving 0.5 g of EBT in 50 mL of methanol. The

buffer solution of 10 Ph is prepared by dissolving 17.5 g of NH4Cl in 117 mL of NH4OH and

133 mL distilled water.

Titration procedure

In the conical flask 1 mL of the filtrate, 1 mL of buffer solution and 2 drops of indicator are

added. The solution initially is blood red in colour and it is titrated against EDTA solution till the

33

solution changes colour from blood red to iodine blue in colour. The titration procedure is done

to all the filtrate set obtained.

Calculation of the molarity of the filtrate

The volume of EDTA consumed while titrating against the filtrate which is obtained after the

impregnation process is noted down.

Table 4.4 Amount of EDTA consumed for extrudate of sample 2.

Filtrate number Volume of EDTA used (mL)

1 12

2 13.3

3 13.1

Table 4.5 Amount of EDTA consumed for extrudate of sample 3.

Filtrate number Volume of EDTA used (mL)

1 12

2 12.9

3 14

34

Table 4.6 Ph and Molarity of the respective Ion exchange.

SAMPLE ION EXCHANGE 1 ION EXCHANGE 2 ION EXCHANGE 3

Ph Molarity (M) Ph Molarity (M) Ph Molarity (M)

2 3.5 0.24 3.5 0.266 3.5 0.262

3 4 0.24 4 0.258 4 0.28

5. RESULT AND CONCLUSION

For the Ist phase of ion exchange concentration of Zn present in filtrate is less than the

concentration of Zn in the starting of ion exchange solution. This indicates Zn is transferred from

ion exchange solution to the zeolite.

In the consequent ion exchange phase II & III the concentration od Zn in the filtrate after ion

exchange is more than the concentration of Zn in the starting ion exchange solution. This

indicates the Zn ion is coming back from zeolite into the aqueous phase.

Table 5.1 Comparison of Total acidty before and after Zn impregnation.

Sample Number Proportion

Total acidity

before

impregnation

(mmol/g)

Total acidity

after

impregnation

(mmol/g)

1

ZSM-5 extruded with

5 % Al(OH)3 + 5 % Pural SB

+ 5 % Kaolin

0.2363 N/A

2

ZSM-5 extruded with

5 % Al(OH)3 + 10 % Pural

SB + 5 % Kaolin

0.2436 N/A

3

ZSM-5 extruded with

5 % Al(OH)3 + 10 % Pural

SB + 10 % Kaolin

0.3361 0.363

35

From the data obtained from TPD analysis for the sample 3, the total acidity of the sample after

impregnation has become high when compared to the total acidity of the sample after

impregnation. This indicates that the availability of H+ ions for the formation of carbenium ions

has increased which in turn contributes to the conversion of n-butane to isooctane. And the

maximum NH3 desorption is found at 223.9 ◦C.

6. FUTURE STUDY

The ion exchanged zeolites have to be analysed for its Zn content so as to verify the material

balance of Zn ions.

36

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