1. ● Dissociation of high molecular weight hydrocarbons into smaller fragments
is termed as cracking.
● In petroleum geology and chemistry, ''cracking‘’ is the process where by
complex organic compound / organic molecule such as kerogen or heavy
hydrocarbons are broken down into simpler molecules such as light
hydrocarbons, by the breaking of carbon-carbon chemical bonds in the
precursors.
CRACKING
1
2. ● Cracking is the breakdown of a large alkane into smaller, more useful
alkanes and alkenes.
● Simply put, hydrocarbon cracking is the process of breaking long-chain
hydrocarbons into short ones.
● The reaction rate of cracking and the end products are strongly dependent
on the temperature and presence of catalysts.
CRACKING
2
5. • The petroleum fractions with 1 to 12 C atoms are in
greater demand than other fractions.
• Cracking is the process of breaking down large, less
useful, hydrocarbon fractions into shorter, but more
useful alkanes and alkenes, which are used as fuels
and petrochemical feedstock.
• This can be achieved by using high pressures and
temperatures without a catalyst, or lower temperatures
and pressures in the presence of a catalyst.
Need of Cracking
5
7. ● By cracking process, less valued or unwanted
fractions are converted into commercially more
valued products. Ethylene + Propylene are the most
important chemical feed stocks. But, due to their
relatively high reactivities, only very limited amounts
of olefins exist in natural gas + crude oil. Thus they
must be produced by cracking processes.
WHY CRACKING IS NECESSARY?
7
9. ● Thermal cracking: carried out at high temp. and
press. without catalyst. It proceeds via free radical
mechanism.
● Catalytic cracking: carried out at low temp. and
press. with catalyst. It proceeds via carbonium ion
mechanism.
TYPES OF CRACKING
9
10. TEMP IN °Ϲ NATURE OF
OPERATION
PRODUCTS
425-460 VISBREAKING FUEL OIL
460-520 THERMAL CRACKING GAS,GASOLINE,TAR
OILS,CIRCULATING
OILS
520-600 LOW TEMP. COKING GAS, GASOLINE,
SOFT COKE
600-800 GAS GAS AND
UNSATURATED
PRODUCTS
800-1000 HIGH TEMP. COKING GAS,HEAVY
AROMATICS,PITCH,
COKE
ABOVE 1000 DECOMPOSITION H2,GAS,CARBON
BLACK
Thermal cracking operations
10
11. ● Modern high-pressure thermal cracking operates at absolute pressures of
about 7,000 kPa. and temp. ranges from 400°Ϲ to 900° Ϲ.
● An overall process of disproportionation can be observed, where "light",
hydrogen-rich products are formed at the expense of heavier molecules
which condense and are depleted of hydrogen.
● The actual reaction is known as homolytic fission and produces alkenes,
which are the basis for the economically important production of polymers.
THERMAL CRACKING
11
12. ● Thermal cracking is currently used to "upgrade" very heavy fractions or to
produce light fractions or distillates, burner fuel and/or petroleum coke.
● Two extremes of the thermal cracking in terms of product range are
represented by the high-temperature process called "steam cracking"
or pyrolysis (750 °C to 900 °C or higher) which produces
valuable ethylene and other feedstocks for the petrochemical industry.
● And the milder-temperature delayed coking ( 500 °C) which can produce,
under the right conditions, valuable needle coke, a highly crystalline
petroleum coke used in the production of electrodes for
the steel and aluminium industry.
12
13. ● Steam cracking is a petrochemical process in which
saturated hydrocarbons are broken down into smaller, often unsaturated,
hydrocarbons.
● It is the principal industrial method for producing the lighter alkenes (or
commonly olefins), including ethene (or ethylene) and propene
● (or propylene).
● Steam cracker units are facilities in which a feedstock such as naphtha,
liquefied petroleum gas (LPG), ethane, propane or butane are diluted with
steam and heated in a pyrolysis furnaces in absence of oxygen to produce
lighter hydrocarbons.
● The products obtained depend on the composition of the feed, the
hydrocarbon-to-steam ratio, and on the cracking temperature and furnace
residence time
13
Steam Cracking
14. ● In steam cracking, a gaseous or liquid hydrocarbon feed
like naphtha, LPG or ethane is diluted with steam and briefly heated in a
furnace without the presence of oxygen.
● Typically, the reaction temperature is very high, at around 850 °C, but the
reaction is only allowed to take place very briefly.
● In modern cracking furnaces, the residence time is reduced to milliseconds
to improve yield, resulting in gas velocities up to the speed of sound.
● After the cracking temperature has been reached, the gas is quickly
quenched to stop the reaction in a transfer line heat exchanger or inside a
quenching header using quench oil.
14
Steam Cracking
15. ● Light hydrocarbon feeds such as ethane, LPGs or
light naphtha give product streams rich in the lighter
alkenes, including ethylene, propylene,
and butadiene.
● Heavier hydrocarbon (full range and heavy
naphthas as well as other refinery products) feeds
give some of these, but also give products rich
in aromatic hydrocarbons and hydrocarbons
suitable for inclusion in gasoline or fuel oil.
15
Steam Cracking
17. ● A higher cracking temperature (also referred to as severity) favors the
production of ethene and benzene, whereas lower severity produces higher
amounts of propene, C4-hydrocarbons and liquid products.
● The process also results in the slow deposition of coke, a form of carbon,
on the reactor walls. This degrades the efficiency of the reactor, so reaction
conditions are designed to minimize this.
● A steam cracking furnace can usually only run for a few months at a time
between de-cokings.
● Decokes require the furnace to be isolated from the process and then a flow
of steam or a steam/air mixture is passed through the furnace coils. This
converts the hard solid carbon layer to carbon monoxide and carbon
dioxide. Once this reaction is complete, the furnace can be returned to
service
17
Steam Cracking
18. Effect of steam to hydrocarbon ratio. Cracking
of ethane into ethylene and hydrogen is a
reversible reaction. In order to keep the
reaction favourable towards ethylene, partial
pressure of ethane need to be reduced. Thus,
steam is introduced into the feed stream to
reduce the partial pressure of ethane.
18
Function of steam
19. ● Properties of cracked materials depend on
conditions of cracking.
● A cracked product acquires refractory nature and
hence severe conditions are required for such
stocks.
● For smooth operations a fraction of cracked stock is
mixed with the incoming charge and cracked.
● Properties that undergo changes during cracking
are;
PROPERTIES OF CRACKED MATERIALS
19
20. 1) Characterization factor (decreases)
2) Boiling point, viscosity, pour point (decreases)
3) Unsaturation and aromatisation (increases)
4) Octane no. of gasoline (increases)
5) Sulphur in cracked products(increases)
6) Soaking factor
7) Severity of cracking
PROPERTIES OF CRACKED MATERIALS
20
21. ● Cracking is endothermic in nature and heat is required for the process.
● Pressure, temperature and time are the main parameters which govern the
cracking operations.
● At a given pressure and temperature, the yield of light fractions is a function
of time.
● Time of cracking increases with increase in API gravity of feed, at a given
pressure and temperature.
PROPERTIES OF CRACKED MATERIALS
21
22. ● Pressure has no direct effect on velocity of reaction.
● At low pressures,more gases are produced.
● Increase in pressure retards cracking reactions, but positive pressure of 10
to 15
Kg/cm2 minimize coke formation.
● Increase in pressure decreases yield of light fractions but in the earlier
stages it may be quite favorable for production of diesels or circulating oils.
PROPERTIES OF CRACKED MATERIALS
22
23. ● Reaction velocity is proportional to reaction temperature.
● Recycling increases refractory nature of stocks and hence it should not
exceed 2 to 3 times of fresh stock.
PROPERTIES OF CRACKED MATERIALS
23
24. ● The K factor or characterization factor is a
systematic way of classifying a crude oil according
to which oil is paraffinic, naphthenic, intermediate
or aromatic nature.
● 12.5 or higher indicate a crude oil of predominantly
paraffinic constituents, while 10 or lower indicate a
crude of more aromatic nature.An intermediate
values represent mixed base crudes.
●
CHARACTERIZATION FACTOR
24
25. ● K = R1/3/0.827ρ = T° 1/3/ ρ
● Where R = avg .boiling point °K or T° : Rankine
● ρ= s.g. at 15.6 /15.6 °C
CHARACTERIZATION FACTOR
25
26. ● The pour point of a liquid is the temperature below which the liquid loses
its flow characteristics. In crude oil a high pour point is generally
associated with a high paraffin content, typically found in crude deriving
from a larger proportion of plant material.
26
Pour Point
27. ● ASTM D97, Standard Test Method for Pour Point of Crude Oils. The
specimen is cooled inside a cooling bath to allow the formation of paraffin
wax crystals. At about 9 °C above the expected pour point, and for every
subsequent 3 °C, the test jar is removed and tilted to check for surface
movement. When the specimen does not flow when tilted, the jar is held
horizontally for 5 sec. If it does not flow, 3 °C is added to the corresponding
temperature and the result is the pour point temperature.
27
Pour Point
28. ● Octane number is defined as % volume of i-Octane in a mixture of i-Octane
and n-heptane that gives the same knocking characteristics as the fuel
under consideration.
● Knocking is due to untimely burning of fuel in a spark ignition engine which
results in loss of power and sometimes it is so powerful that it causes
damage to engine also.
28
Octane Number
29. ● Octane rating or octane number is a standard measure of the
performance of a motor or aviation fuel.
● The higher the octane number, the more compression the fuel can
withstand before detonating.
● In broad terms, fuels with a higher octane rating are used in high-
compression engines that generally have higher performance.
● In contrast, fuels with low octane numbers (but high cetane numbers) are
ideal for diesel engines. Use of gasoline with less octane numbers may lead
to the problem of engine knocking.
OCTANE NUMBER
29
30. ● Octanes (C8H18)are a family of hydrocarbon that are typical components of
gasoline.
● They are colourless liquids that boil around 125 °C (260 °F). One member
of the octane family, isooctane, is used as a reference standard to
benchmark the tendency of gasoline/petrol or LPG fuels to resist self-
igniting.
● Self-ignition leads to inefficiencies (or even engine damage) if it occurs
during compression prior to the desired position of the piston in the cylinder
as appropriate for valve and ignition timing.
OCTANE NUMBER
30
31. ● The problem of premature ignition is referred to as pre-ignition and also as
engine knock, which is a sound that is made when the fuel ignites too early
in the compression stroke.
● Severe knock causes severe engine damage, such as broken connecting
rods, melted pistons, melted or broken valves and other components.
● The octane rating is a measure of how likely a gasoline or liquid petroleum
fuel is to self ignite. The higher the number, the less likely an engine is to
pre-ignite and suffer damage.
OCTANE NUMBER
31
32. ● Soaking factor is related to product yield and degree of conversion.
● Thermal cracking proceeds along a curve of increasing temperature,i.e. the
cracking progression is expressed by soaking factor.
● Soaking factor is related with temperature and volume of feed per unit time.
SOAKING FACTOR
32
33. ● In the initial stages of cracking ,the concentration of feed remains
unchanged, but as cracking progresses ,mixed products results.
● For a given raw material ,the cracking products depends upon many factors
like temperature ,pressure ,time etc. To express the overall influence of
these factors on reaction a representative value is given which is termed as
severity of cracking . It is related with temperature.
SEVERITY OF CRACKING
33
34. ● It is a wide spectrum thermal cracking operation.
● In visbreaking operation large hydrocarbon
molecules in the oil are thermally cracked by
heating in a furnace to reduce its viscosity and to
produce small quantities of light hydrocarbons (LPG
and gasoline). The process name of "visbreaking"
refers to the fact that the process reduces (i.e.,
breaks) the viscosity of the residual oil. The process
is non-catalytic.
VISBREAKING
34
35. ● Reduce the viscosity of the feed stream: Typically
this is the residue from vacuum distillation of crude
oil but can also be the residue which is not of direct
utility, natural bitumen from seeps in the ground or
tar sands, and even certain high viscosity crude oils.
OBJECTIVES
35
36. ● Reduce the amount of residual fuel oil produced by a refinery:
● Residual fuel oil is generally regarded as a low value product. Demand for
residual fuel continues to decrease as it is replaced in its traditional
markets, such as fuel needed to generate steam in power stations, by
cleaner burning alternative fuels such as natural gas.
OBJECTIVES
36
37. ● Increase the proportion of middle distillates in the refinery output.
● Middle distillate is used as a diluent with residual oils to bring their viscosity
down to a marketable level.
● By reducing the viscosity of the residual stream in a visbreaker, a fuel oil
can be made using less diluent and the middle distillate saved can be
diverted to higher value diesel or heating oil manufacture.
OBJECTIVES
37
38. ● Product of visbreaking will be liquids and gases.
● The liquid products will be used as feed stocks for catalytic cracking
operations.
● The main liquid product is fuel oil ; light fractions like gas and gasoline will
invariably accompany in all cracking operations.
OBJECTIVES
38
39. ● The term coil or furnace visbreaking is applied to
units where the cracking process occurs in the
furnace tubes (or "coils"). Material exiting the
furnace is quenched to halt the cracking reactions:
● frequently visbreaking is achieved by heat
exchange with the fresh material being fed to the
furnace, which in turn is a good energy efficiency
step, but sometimes a stream of cold oil (usually
gas oil) is used to the same effect.
Coil visbreaking
39
40. ● The gas oil is recovered and re-used. The extent of
the cracking reaction is controlled by regulation of
the speed of flow of the oil through the furnace
tubes.
● The quenched oil then passes to a fractionator
where the products of the cracking (gas, LPG,
gasoline, gas oil and tar) are separated and
recovered.
Coil visbreaking
40
41. ● In soaker visbreaking, the bulk of the cracking reaction occurs not in the
furnace but in a drum located after the furnace called the soaker.
● Here the oil is held at an elevated temperature for a pre-determined period
of time to allow cracking to occur before being quenched.
● The oil then passes to a fractionator. In soaker visbreaking, lower
temperatures are used than in coil visbreaking. The comparatively long
duration of the cracking reaction is used instead.
Soaker visbreaking
41
43. ● Feed stock comprising variety of materials ranging from asphalt, short
residums to medium oils is blended separately and passed through heat
exchanging system.
● The temperature is raised to 250 °Ϲ.
● The preheated stock is heated in either furnace or soaker where
temperature is further increased to 470 °Ϲ .Pressure of 10-15 kg/cm2 is
maintained to avoid coke formation.
● The cracked products pass through a pressure releasing valve to be
quenched in quencher.
Visbreaking
43
44. ● The light fractions and bottom fractions from quencher
are send to the fractioning column.
● The lighter fractions like gas,LPG and gasoline are sent
to an extractor to absorb gases.
● Visbreaker tar can be further refined by feeding it to a
vacuum fractionator. Here additional heavy gas oil may
be recovered and routed either to catalytic cracking,
hydrocracking or thermal cracking units on the refinery.
● The vacuum-flashed tar (sometimes referred to as pitch)
is then routed to fuel oil blending. In a few refinery
locations, visbreaker tar is routed to a delayed Coker for
the production of certain specialist cokes such as anode
coke or needle coke.
Visbreaking
44
45. ● Coking is a severe method of thermal cracking
used to upgrade heavy residuals into lighter
products or distillates.
● Coking produces straight-run gasoline (Coker
naphtha) and various middle-distillate fractions
used as catalytic cracking feedstock.
● The process completely reduces hydrogen so
that the residue is a form of carbon called
"coke."
Delayed cocking
45
49. ● Three typical types of coke are obtained
(sponge coke, honeycomb coke, and needle
coke) depending upon the reaction mechanism,
time, temperature, and the crude feedstock.
● In delayed coking the heated charge (typically
residuum from atmospheric distillation towers) is
transferred to large coke drums which provide
the long residence time needed to allow the
cracking reactions to proceed to completion.
Delayed cocking
49
50. ● Heavy feedstock is fed to a fractionator.
● The bottoms of the fractionator are fed to coker
drums via a furnace where the hot material
(440°-500°C ) is held approximately 24 hours
(delayed) at pressures of 2-5 bar, until it cracks
into lighter products.
● Vapors from the drums are returned to a
fractionator where gas, naphtha, and gas oils
are separated out. The heavier hydrocarbons
produced in the fractionator are recycled
through the furnace.
Delayed cocking
50
51. ● After the coke reaches a predetermined level in
one drum, the flow is diverted to another drum to
maintain continuous operation.
● The full drum is steamed to strip out uncracked
hydrocarbons, cooled by water injection, and de-
coked by mechanical or hydraulic methods.
● The coke is mechanically removed by an auger
rising from the bottom of the drum. Hydraulic
decoking consists of fracturing the coke bed with
high-pressure water ejected from a rotating
cutter.
Delayed cocking
51
53. ● Fluid catalytic cracking (FCC) is the most important conversion
process used to convert the high-boiling, high-molecular weight
hydrocarbon fractions of petroleum crude oils to more valuable
gasoline,olefinic gases and other products.
● Cracking of petroleum hydrocarbons was originally done by
thermal cracking, which has been almost completely replaced by
catalytic cracking because it produces more gasoline with a
higher octane rating.
● It also produces by product gases that are more olefinic, and
hence more valuable, than those produced by thermal cracking.
53
54. ● The FCC complex usually consists of three major
sections:
● 1. Reactor-riser
● 2.Regenerator-flue gas separation
● 3.Distillation and recycling
� Fluid catalytic cracking
54
55. ● The reactor and regenerator is considered to be the heart
of the Fluid Catalytic Cracking Unit.
● The preheated high-boiling petroleum feedstock (at about
315 to 430 °C) consisting of long-chain hydrocarbon
molecules is combined with recycle slurry oil from the
bottom of the distillation column and injected into the
catalyst riser where it is vaporized and cracked into smaller
molecules of vapour by contact and mixing with the very
hot powdered catalyst from the regenerator.
� Fluid catalytic cracking
55
56. ● All of the cracking reactions take place in the
catalyst riser within a period of 2–4 seconds. The
hydrocarbon vapours "fluidize" the powdered
catalyst and the mixture of hydrocarbon vapours
and catalyst flows upward to enter the reactor at a
temperature of about 535 °C and a pressure of
about 1.72 bar.
� Fluid catalytic cracking
56
57. ● In the more modern FCC units, all cracking takes
place in the riser. The "reactor" no longer functions as
a reactor; it merely serves as a holding vessel for the
cyclones.
● The reactor is a vessel in which the cracked product
vapours are:
● (a) separated from the so-called spent catalyst by
flowing through a set of two-stage cyclones within the
reactor and
� Fluid catalytic cracking
57
58. ● (b) the spent catalyst flows downward through a
steam stripping section to remove any
hydrocarbon vapors before the spent catalyst
returns to the catalyst regenerator.
● The flow of spent catalyst to the regenerator is
regulated by a slide valve in the spent catalyst
line.
� Fluid catalytic cracking
58
59. ● Since the cracking reactions produce some
carbonaceous material (referred to as catalyst coke)
that deposits on the catalyst and very quickly reduces
the catalyst reactivity, the catalyst is regenerated by
burning off the deposited coke with air blown into the
regenerator.
● The regenerator operates at a temperature of about
715 °C and a pressure of about 2.41 bar.
� Fluid catalytic cracking
59
60. ● The combustion of the coke is exothermic and it
produces a large amount of heat that is partially
absorbed by the regenerated catalyst and provides the
heat required for the vaporization of the feedstock and
the endothermic cracking reactions that take place in
the catalyst riser.
● For that reason, FCC units are often referred to as
being 'heat balanced'.
� Fluid catalytic cracking
60
61. ● The hot catalyst (at about 715 °C) leaving the regenerator
flows into a catalyst withdrawal well where any entrained
combustion flue gases are allowed to escape and flow
back into the upper part to the regenerator.
● The flow of regenerated catalyst to the feedstock injection
point below the catalyst riser is regulated by a slide valve in
the regenerated catalyst line.
● The hot flue gas exits the regenerator after passing through
multiple sets of two-stage cyclones that remove entrained
catalyst from the flue gas,
� Fluid catalytic cracking
61
62. ● The reaction product vapors (at 535 °C and a pressure
of 1.72 bar) flow from the top of the reactor to the bottom
section of the distillation column (commonly referred to
as the main fractionator) where they are distilled into the
FCC end products of cracked naphtha, fuel oil and off
gas.
● After further processing for removal of sulphur
compounds, the cracked naphtha becomes a high-
octane component of the refinery's blended gasoline.
� Fluid catalytic cracking
62
63. ● The main fractionator off gas is sent to what is
called a gas recovery unit where it is separated
into butanes and butylenes, propane and
propylene and lower molecular weight gases (
hydrogen, methane, ethylene and ethane).
● Some FCC gas recovery units may also separate
out some of the ethane and ethylene.
� Fluid catalytic cracking
63
64. ● The bottom product oil from the main fractionator contains
residual catalyst particles which were not completely
removed by the cyclones in the top of the reactor.
● For that reason, the bottom product oil is referred to as a
slurry oil.
● Part of that slurry oil is recycled back into the main
fractionator above the entry point of the hot reaction
product vapors so as to cool and partially condense the
reaction product vapors as they enter the main fractionator.
� Fluid catalytic cracking
64
65. ● The remainder of the slurry oil is pumped through a
slurry settler.
● The bottom oil from the slurry settler contains most of
the slurry oil catalyst particles and is recycled back into
the catalyst riser by combining it with the FCC feedstock
oil.
● The so-called clarified slurry oil or decant oil is
withdrawn from the top of slurry settler for use elsewhere
in the refinery, as a heavy fuel oil blending component,
or as carbon black feedstock.
� Fluid catalytic cracking
65
66. ● Fluid bed catalytic processes are the most
widely used and are characterized by the use of
finely powdered catalyst that is moved through
the processing unit
● Catalyst particles are of such a size that when
aerated with air or hydrocarbon vapor, the
catalyst behaves like a liquid and can be moved
through pipes. Vaporized feedstock and
fluidized catalyst flow together into a reaction
chamber where the cracking reactions take
place. (Speight, 1998)
� Fluid catalytic cracking
66
67. ● Zeolite catalysts have been the primary catalyst
type used in refining in the last two decades.
● Zeolite catalysts can operate in the presence of
substantial concentration of ammonia in marked contrast
to other silica-alumina catalysts.
● Catalyst life of up to 7 years has been obtained
commercially in processing heavy gas oils. Zeolites have
up to 10,000 times the activity of so-called conventional
catalysts in specific cracking tests.
Catalyst for FCC
67
68. ● Zeolites are the alumino silicate members of the
family of micro porous solids known as
“molecular sieves” i.e. they have the ability to
selectively sort molecules based primarily on a
size exclusion process due to a very regular
pore structure of molecular dimensions.
● Crystals are highly porous and are veined with
submicroscopic channels.
Catalyst for FCC
68
69. ● Natural zeolites form where volcanic rocks and
ash layers react with alkaline groundwater.
Zeolites also crystallize in post-depositional
environments over periods ranging from
thousands to millions of years in shallow marine
basins.
Catalyst for FCC
69
70. ● Zeolites can be synthesized hydrothermally
starting from slow crystallization of a silica-
alumina gel in alkaline environment using
organic templates.
● Synthesized from solutions of sodium aluminate,
sodium silicate and sodium hydroxide mimicking
conditions found in the earth’s crust where
zeolites are formed naturally.
Catalyst for FCC
70
71. ● Synthesis temperature is 450-100 with open
framework structure occurring at the lower
temperatures.
● Synthetic zeolites hold some key advantages
over their natural analogs, including more
uniform, phase-pure state. In addition synthesis
allows for the ability to manufacture desirable
zeolite structures which do not appear in nature.
Catalyst for FCC
71
73. ● In the monomolecular mechanism, an alkane
(paraffin) is protonated by a Bronsted acid site
to form a five-coordinated carbon atom. The
carbonium ion may undergo cracking to yield an
alkane and an alkene, regenerating the acid site
or it may dehydrogenate to yield H2 and an
alkoxide species. Desorption of the alkoxide
yeilds an olefin and regenerates the acid site.
Catalyst for FCC
73
75. ● Reactants are physisorbed in the pores of the
zeolites ( dominant interactions are the van der
Waals interaction) and at high temperature are
activated through proton transfer from the
Bronsted acid sites. Because the rate-limiting
step of monomolecular cracking is the
protonation of the alkane, this reaction is an
acid-base reaction between the zeolite and the
alkane. Therefore, its intrinsic rate is a measure
of zeolitic acidity.
Catalyst for FCC
75
76. ● The better the fit between pore and reactant, the
higher the observed rate per Bronsted acid site
of the reaction.
● Crystalline structure of zeolites provide higher
activities and controlled selectivity compared to
amorphous silica-aluminas.
Catalyst for FCC
76
77. Catalysis using zeolites, combines properties of
excellent thermal stability (>800° C), pore size of
molecular dimensions.
● Almost all reactive surface area and attendant
acid sites of zeolite are located within the
internal pore structure (>99%)
● Catalytic chemistries occur within the pores.
Catalyst for FCC
77
78. ● A gram of zeolite has a surface area of 900 m2
.
● High concentration of active acid sites, their high
thermal stability, and high size selectivity make
zeolites the catalyst of choice in refining
operations limits the outcome of the chemistry to
those products that can either fit into available
space or migrate from the site of their formation
to the exterior of the zeolite.
● More than 90% of cat cracking catalysts in the
US are zeolite based .
● Zeolites are environmentally safe.
78
79. ❖ Upgrading low octane gasoline catalytically is
known as catalytic reforming.
❖ The octane no. is improved by reforming low
octane components into high octane components.
❖ Products of reforming depends upon feed stock
and catalyst.
CATALYTIC REFORMING
79
80. Following reactions takes place.
1.Dehydrogenation
cyclohexane to benzene
2. Isomerization
n-hexane to 2-methyl pentane
3. Paraffin cracking
paraffin to smaller paraffin and olefins
4. hydrogenation of unsaturated
olefin to paraffin
5. hydrodesulfurization, denitrogenation and
deoxidation reactions takes place.
80
CATALYTIC REFORMING
81. ● 1. Stocks suitable for gasoline engines.
● 2. Straight run heavy Naphtha of low Octane no.
● 3. Light products obtained in various cracking
operations of gasoline range.
81
FEEDSTOCK SELECTION
82. ● Low pressure encourages dehydrogenation while no
noticeable effect of pressure on isomerization may be
expected.
⮚ coke deposition is more at low pressures.
● Increasing pressure causes dealkylation very much.
EFFECT OF PRESSURE
82
83. ● Except hydrogenation reaction, all other
reactions are favored by increasing temperature.
● With increase of temp. chances of degradation
of products and coke deposition are more.
● Hence for economic operation the process
should be operated at low pressure and high
temp.
83
EFFECT OF TEMPERATURE:
84. ⮚ About 90% reforming operations are conducted
in fixed beds using platinum catalysts. Moving
beds and fluidized beds mainly use cheap
catalysts of molybdenum and chromium
composition.
⮚ 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 chlorinated prior
to use.
CATALYST SELECTION:
84
85. ● 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.
85
CATALYST SELECTION
86. ● The most commonly used type of catalytic
reforming unit has three reactors, each with a
fixed bed of catalyst, and all of the catalyst is
regenerated during routine catalyst regeneration
shutdowns which occur approximately once each
6 to 24 months. Such a unit is referred to as a
semi-regenerative catalytic reformer (SRR).
CATALYTIC REFORMING-PLATFORMING
86
87. ● Some catalytic reforming units have an extra spare or
swing reactor and each reactor can be individually
isolated so that any one reactor can be undergoing
regeneration while the other reactors are in operation.
● When that reactor is regenerated, it replaces another
reactor which, in turn, is isolated so that it can then be
regenerated. Such units, referred to as cyclic catalytic
reformers, are not very common.
● Cyclic catalytic reformers serve to extend the period
between required shutdowns.
PLATFORMING
87
88. ● Many of the earliest catalytic reforming units (in the
1950s and 1960s) were non-regenerative in that they
did not perform catalyst regeneration.
● Instead, when needed, the aged catalyst was replaced
by fresh catalyst and the aged catalyst was shipped to
catalyst manufacturers to be either regenerated or to
recover the platinum content of the aged catalyst.
● Very few, if any, catalytic reformers currently in
operation are non-regenerative.
PLATFORMING
88
90. ● The liquid feed(naptha) (at the bottom left in the
diagram)(68-180°Ϲ) is pumped up to the reaction pressure
(5 to 45 atm) and is joined by a stream of hydrogen-rich
recycle gas.
● The resulting liquid-gas mixture is preheated by flowing
through a heat exchanger. The preheated feed mixture is
then totally vaporized and heated to the reaction
temperature (495 to 520 °C) in the furnace before the
vaporized reactants enter the first reactor.
CATALYTIC REFORMING
90
91. ● As the vaporized reactants flow through the fixed bed of
catalyst in the reactor, the major reaction is the
dehydrogenation of naphthenes to aromatics (as
described earlier herein) which is highly endothermic
and results in a large temperature decrease between the
inlet and outlet of the reactor.
● To maintain the required reaction temperature and the
rate of reaction, the vaporized stream is reheated in the
second fired heater before it flows through the second
reactor.
CATALYTIC REFORMING
91
92. ● The temperature again decreases across the second
reactor and the vaporized stream must again be reheated
in the third fired heater before it flows through the third
reactor.
● As the vaporized stream proceeds through the three
reactors, the reaction rates decrease and the reactors
therefore become larger. At the same time, the amount of
reheat required between the reactors becomes smaller.
● Usually, three reactors are all that is required to provide the
desired performance of the catalytic reforming unit.
CATALYTIC REFORMING
92
93. ● The hot reaction products from the third reactor are
partially cooled by flowing through the heat
exchanger where the feed to the first reactor is
preheated and then flow through a water-cooled
heat exchanger before flowing through the pressure
controller (PC) into the gas separator.
CATALYTIC REFORMING
93
94. ● Most of the hydrogen-rich gas from the gas separator
vessel returns to the suction of the recycle hydrogen
gas compressor and the net production of hydrogen-
rich gas from the reforming reactions is exported for
use in the other refinery processes that consume
hydrogen (such as hydrodesulfurization units and/or a
hydrocracker unit).
CATALYTIC REFORMING
94
95. ● The liquid from the gas separator vessel is routed
into a fractionating column commonly called a
stabilizer. The overhead off gas product from the
stabilizer contains the by product methane, ethane,
propane and butane gases produced by the hydro
cracking reactions and it may also contain some
small amount of hydrogen.
CATALYTIC REFORMING
95
96. ● That off gas is routed to the refinery's central gas
processing plant for removal and recovery of propane
and butane. The residual gas after such processing
becomes part of the refinery's fuel gas system.
● The bottoms product from the stabilizer is the high-
octane liquid reformate that will become a component
of the refinery's product gasoline.
CATALYTIC REFORMING
96
97. ● The latest and most modern type of catalytic reformers are
called continuous catalyst regeneration reformers (CCR).
● Such units are characterized by continuous regeneration
of part of the catalyst in a special regenerator, and by
continuous addition of the regenerated catalyst to the
operating reactors.
● As of 2006, two CCR versions available: UOP's CCR Plat
former process and Axen's Octanizing process. The
installation and use of CCR units is rapidly increasing.
CATALYTIC REFORMING
97
98. Feed and Catalyst travel co currently in all these reactors from
top to bottom. Heating the reactants in between is same as in
semi regenerative process.
The catalyst from the bottom of the third reactor is transferred
to a separate regenerator.
After regeneration the catalyst is transferred to the first reactor
continuously.
98
CATALYTIC REFORMING
