What is catalyst A

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What is catalyst A

April 2008


Chemical Composition of Petroleum

Crude oil is a mixture of hundreds of hydrocarbon compounds ranging in

size from the smallest, methane, with only one carbon atom, to large

compound containing 300 and more carbon atoms. consisting of

paraffin,naphthene (cycloparaffin), and aromatic hydrocarbons as well as

nitrogen, oxygen-, sulfur- containing compounds and traces of a variety of

metal-containing compounds, and inorganic compounds.


Butane&Heavier

Light Naphtha

Naphtha

Kerosene

Light Gasoil

Heavy Gasoil

RCR

0<

27-93

93-177

177

-293

204- 343

315-565

565>


fraction

Gases

Light Naphtha

Heavy Naphtha

Kerosene

Light Gas Oil

Heavy Gas Oil

Residuum

Petroleum fractions

no. carbons

1-4

5-7

6-10

10-15

13-18

16-40

<

40

Boiling point

0<

27-93

93-177

177-293

204-343

315-565

< 565

%

2

34

11

21

31


Reforming unit

Catalytic reforming is a chemical process used to convert petroleum refinery

naphthas, typically having low octane ratings, into high-octane liquid

products called reformates which are components of high-octane gasoline

(also known as petrol). Basically, the process re-arranges or re-structures

the hydrocarbon molecules in the naphtha feedstocks as well as breaking

some of the molecules into smaller molecules. The overall effect is that the

product reformate contains hydrocarbons with more complex molecular

shapes having higher octane values than the hydrocarbons in the naphtha

feedstock. In so doing, the process separates hydrogen atoms from the

hydrocarbon molecules and produces very significant amounts of byproduct

hydrogen gas for use in a number of the other processes involved in a

modern petroleum refinery. Other byproducts are small amounts of

methane, ethane, propane and butanes.


LPG

Stabilizer


Chemistry

The feed of the unit is hydro –treated naphtha having

an initial boiling point of about 35 C and a final boiling point

of about 200 C , and it contains paraffin , naphthene (cyclic

paraffin ) and aromatics hydrocarbons ranging from those

containing 4 carbon to those containing about 10 or 11 carbon

atoms.

Paraffins 45-55 %

Olefins 0-2 %

Naphthenes 30-40 %

Aromatics 5-10 %

The reaction chemistry

There are a good many chemical reactions that occur in the

catalytic reforming process, all of which occur in the

presence of a catalyst and a high partial pressure of

hydrogen. Depending upon the type or version of catalytic

reforming used as well as the desired reaction severity, the

reaction conditions range from temperatures of about 495

to 525 °C and from pressures of about 5 to 45 atm.


The four major catalytic reforming reactions are

1.The dehydrogenation of naphthenes to

convert them into aromatics as exemplified in

the conversion methylcyclohexane (a

naphthene) to toluene (an aromatic), as

shown below :


2.The isomerization of normal paraffins to

isoparaffins as exemplified in the conversion of

normal octane to 2,5-Dimethylhexane (an

isoparaffin), as shown below:


3. The dehydrogenation and aromatization of

paraffins to aromatics (commonly called

dehydrocyclization) as exemplified in the

conversion of normal heptane to toluene, as shown

below :


4. The hydrocracking of paraffins into smaller

molecules as exemplified by the cracking of normal

heptane into isopentane and ethane, as shown below :


Product

The product is reformate with high Octane number and

contains these portions:

Paraffins 30-50 %

Olefins 0 %

Naphthenes 5 –10 %

Aromatics 45-60 %


What is catalyst

A catalyst is a substance which alters the rate of a

chemical reaction but is chemically unchanged at the end

of the reaction . It has different shapes and sizes.


Reformer catalysts and mechanisms

Most catalytic reforming catalysts

contain platinum or rhenium on a silica

or silica-alumina support base, and

some contain both platinum and

rhenium. Fresh catalyst is chlorided

(chlorinated) prior to use.

The noble metals (platinum and

rhenium) are considered to be catalytic

sites for the dehydrogenation reactions

and the chlorinated alumina provides the

acid sites needed for isomerization,

cyclization and hydrocracking reactions.


Shape………………………………………. Cylinder

Nominal size , mm(in)…………………… 1.6(0.064)

Chemical composition , % wt.dry basis

Platinum…………………………………… 0.25

Rhenium…………………………………… 0.25

Chloride……………………………………. 1.00

Physical properties

Compact bulk density g/cc……………. 0.74

Surface area , m2/g…………………….. 200

Pore vol. cc/g(H2O)…………………….. 0.55

Anvil crush strength N/CM2………… 200


Catalyst deactivation

catalyst deactivation is defined as a phenomenon in which the

structure and state of the catalyst change, leading to the loss of

active sites on the catalyst’s surface and thus causing a

decrease in the catalyst’s performance.

Catalyst deactivation is a result of a number of unwanted

chemical and physical changes. The causes of deactivation are

classically divided to three categories: chemical, thermal and

mechanical

Mechanical deactivation as a result of physical breakage,

attrition or crushing is also an important deactivation

phenomenon.

The three major categories of deactivation mechanisms are

sintering, poisoning, and coke formation or fouling. They may

occur separately or in combination, but the net effect is always

the removal of active sites from the catalytic surface.


Sintering, as illustrated in Figures below, is the loss of catalyst’s

active surface due to crystal growth of either the bulk material or

the active phase. In the case of supported metal catalysts, reduction

of the active surface area is provoked via agglomeration and

coalescence of small metal crystallites into larger ones

Two different models have been proposed for sintering i.e., the

atomic migration and the crystallite migration models. As such,

sintering occurs either due to metal atoms migrating from one

crystallite to another via the surface or gas phase by diminishing

small crystallites in size and increasing the larger ones (atomic

migration model). Or sintering can occur via migration of the

crystallites along the surface, followed by collision and

) coalescence of two crystallites (crystallite migration model)


sintering is strongly temperature-dependent

The rate of sintering increases

exponentially with temperature and,

for example, the sintering of precious

metals becomes significant above

600°C. The underlying mechanism of

sintering of small metal particles is the

surface diffusion, or at higher

temperatures, the mobility of larger

agglomerates.


Coke formation

Coke formation is the most widely known form of fouling (it is .

even used as a synonym for fouling). Coke formation is not very

clearly defined. There are probably as many mechanisms of coke

formation as there are reactions and catalysts where this

phenomenon is encountered. During the coke formation,

carbonaceous residues cover the active surface sites, and decrease

the active surface area. First, this blocks out the active compounds

to reach the surface sites, and second, the amount of coke might be

so large that carbon deposits block the internal pores in the

catalyst. In many cases, hydrocarbons and aromatic materials are

primarily responsible for coke formation


Poisoning

Catalysts may also be poisoned in the presence of some pollutants, such

as sulfur or Lead (Pb) , Phosphorus (P) , Zinc (Zn) , Calcium (Ca) and

Magnesium (Mg). These components contaminate the precious metals and

reduce the active catalytic area by blocking the active sites.


Catalyst regeneration

Catalyst regeneration is an operation achieved to

get back the activity of the de-activated catalyst

by getting rid of contaminants ,sintering and

rearranging the active centers.

The operation is carried out through these steps:

Burning ,sulfate removal ,oxy-chlorination

,reduction and sulfiding.

Burning: which means the burning of carbon

deposited on the catalyst surface in the existance

of O2 at high temperature .This step consists of 2

stages of burning.

Here below is a sketch showing how the burning

is progressing:


catalyst

Contaminated

with carbon


Burning front


Clean catalyst


Oxy-chlorination

In this step we can re- disperse the metal (Pt) and increase

the distance between the crystals from 0.1-10 A using high

temperature (510 C) in the existence of chlore and air as

shown in the figure below:

Platinum crystal

AlCl3

O

O

O2

o

o

o

O O O

o

O

O

o

o

o

o

o

O

O

Cl2

O

O O O

Cl O O O

Cl

O

Cl

O

O

Cl

Cl

O

O

O

O

Cl

Re-dispersed platinum


Reduction

Reduction is the elimination of Oxygene by means of

electrolytic (pure) H2 at high temperature (510 C ),i.e. to

change the Platinum from oxide to free pattern.

Presulfiding

When the catalyst has been regenerated it becomes very

active to any reaction andwill lose its operating age rapidly,

so we have to add any type of sulfur compound with

calculated amount to limit its high activity.

Unit operation

After the sulfiding step we increase the temperature

according to a program and then the unit is ready to operate

and we can make a feed injection.


Now, we will see Catalyst

regeneration schedule Which I had

prepared in 1998 in SALLAHUDIN

/II refinery as per constructions of

catalyst supplier company

CRITEREON as an example to this

lecture.

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