The document discusses fluid catalytic cracking (FCC), which is a process used in oil refineries to convert high-boiling hydrocarbon fractions into more valuable gasoline, diesel, and other products. It involves cracking heavier petroleum fractions with a catalyst at high temperatures in the presence of steam. The heavier fractions are broken up into lighter molecules like liquefied petroleum gas and gasoline. Key aspects covered include the FCC reactor design, catalyst regeneration process, and products produced including gasoline, diesel and light cycle oil.

1. Professional Development
Fluid Catalytic Cracker
(FCC)
cat cracker
By Kerry Pritchard

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A chemical reactor for converting oils with high
boiling points into fuels with lower boiling points in
the presence of a catalyst

3. Fluid Catalytic Cracker

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• In petroleum geology and chemistry , cracking is the process whereby complex organic
molecules (e.g. kerogens or heavy hydrocarbons ) are converted to simpler molecules (e.g.
light hydrocarbons) by the breaking of carbon - carbon bonds in the precursors. The rate of
cracking and the end products are strongly dependent on the temperature and presence of
any catalysts

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Crude oil is separated into fractions by fractional distillation. The heavier fractions
that emerge from the bottom of the fractionating column are often broken up
(cracked) to make more useful products.

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•Applications
•In an oil refinery cracking processes allow the production of "light"
products (such as LPG and gasoline ) from heavier crude oil
distillation fractions (such as gas oils ) and residues. Fluid Catalytic
Cracking (FCC for short) produces a high yield of gasoline and LPG
while hydrocracking is a major source of jet fuel, gasoline components
and LPG. Thermal cracking is currently used to "upgrade" very heavy
fractions ("upgrading", "visbreaking"), 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 (ca. 750
to 900 °C or more) which produces valuable ethylene and other feeds
for the petrochemical industry, and the milder-temperature delayed
coking (ca. 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 aluminum industries.

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The branched molecules help to give petrol with higher octane number, less inclined
to knocking.

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Fluid catalytic cracking is a commonly used process and a modern oil refinery will typically
include a cat cracker, particularly refineries in the USA due to the high demand for
gasoline. The process was first used in around 1942, and employs a powdered catalyst.
Initial process implementations were based on a low activity alumina catalyst and a reactor
where the catalyst particles were suspended in a rising flow of feed hydrocarbons in a
fluidized bed.
In newer designs, cracking takes place using a very active zeolite-based catalyst in a short-
contact time vertical or upward sloped pipe called the "riser". Pre-heated feed is sprayed
into the base of the riser via feed nozzles where it contacts extremely hot fluidized catalyst
at 665 to 760 °C . The hot catalyst vaporizes the feed and catalyzes the cracking reactions
that break down the high molecular weight oil into lighter components including LPG,
gasoline, and diesel. The catalyst-hydrocarbon mixture flows upward through the riser for
just a few seconds and then the mixture is separated via cyclones. The catalyst-free
hydrocarbons are routed to a main fractionator for separation into fuel gas, LPG, gasoline,
light cycle oils used in diesel and jet fuel, and heavy fuel oil.

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During the trip up the riser, the cracking catalyst is "spent" by reactions which deposit coke on
the catalyst and greatly reduce activity and selectivity. The "spent" catalyst is disengaged
from the cracked hydrocarbon vapors and sent to a stripper where it is contacted with
steam to remove hydrocarbons remaining in the catalyst pores. The "spent" catalyst then
flows into a fluidized-bed regenerator where air (or in some cases air plus oxygen) is used
to burn off the coke to restore catalyst activity and also provide the necessary heat for the
next reaction cycle, cracking being an endothermic reaction. The "regenerated" catalyst
then flows to the base of the riser, repeating the cycle.
The gasoline produced in the FCC unit has an elevated octane rating but is less chemically
stable compared to other gasoline components due to its olefinic profile. Olefins in
gasoline are responsible for the formation of polymeric deposits in storage tanks, fuel ducts
and injectors. The FCC LPG is an important source of C3-C4 olefins and isobutane that are
essential feeds for the alkylation process.

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• Hydrocracking is a catalytic cracking process assisted by the presence of an elevated partial
pressure of hydrogen. The products resulted are saturated hydrocarbons; depending on the
process severity (temperature, pressure, catalyst activity) these products range from
ethane, LPG to heavier hydrocarbons comprising mostly of isoparaffins. Hydrocracking is
normally facilitated by a bifunctional catalyst that is capable of rearranging and breaking
hydrocarbon chains as well as adding hydrogen to aromatics and olefins to produce
naphthenes and alkanes.
• Major products from hydrocracking are jet fuel, relatively high octane rating gasoline
fractions and LPG. All these products have a very low content of sulfur and contaminants.

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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).
• In steam cracking, a gaseous or liquid hydrocarbon feed is diluted with steam and then briefly
heated in a furnace. Typically, the reaction temperature is very hot—over 900°C—but the
reaction is only allowed to proceed for a few tenths of a second before being quenched by
contact with a colder fluid.
• The products produced in the reaction depend on the composition of the feed, the hydrocarbon
to steam ratio and on the cracking temperature & furnace residence time. Light hydrocarbon
feeds (such as ethane, LPGs or light naphtha's) give product streams rich in the lighter alkenes,
including ethylene, propylene, and butadiene. Heavier hydrocarbon (full range & heavy
naphtha's 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. The
higher cracking temperature (also referred to as severity) favors the production of ethene and
benzene, whereas lower severity produces relatively 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 effectiveness of the reactor, so reaction conditions are designed to minimize
this. Nonetheless, a steam cracking furnace can usually only run for a few months at a time
between de-cokings.

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• Chemistry
• "Cracking" breaks larger molecules into smaller ones. This can be done with a thermic or
catalytic method. The thermal cracking process follows a homolytic mechanism, that is,
bonds break symmetrically and thus pairs of free radicals are formed. The catalytic cracking
process involves the presence of acid catalysts (usually solid acids such as silica-alumina
and zeolites) which promote a heterolytic (asymmetric) breakage of bonds yielding pairs of
ions of opposite charges, usually a carbocation and the very unstable hydride anion.
Carbon-localized free radicals and cations are both highly unstable and undergo processes
of chain rearrangement, C-C scission in position beta (i.e., cracking) and intra- and
intermolecular hydrogen transfer or hydride transfer. In both types of processes, the
corresponding reactive intermediates (radicals, ions) are permanently regenerated, and
thus they proceed by a self-propagating chain mechanism. The chain of reactions is
eventually terminated by radical or ion recombination

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• Catalytic cracking uses a catalyst (often a zeolite catalyst) to aid the process of breaking
down large hydrocarbon molecules into smaller ones, as well as using high temperatures
and slight pressure. During this process, less reactive and therefore more stable and longer
lived intermediate cations accumulate on the catalysts' active sites generating deposits of
carbonaceous products generally (and in many cases inappropriately) known as coke. Such
deposits need to be removed (usually by controlled burning) in order to restore catalyst
activity.

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• Thermal Cracking
• In thermal cracking elevated temperatures and pressures are used. 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.
• A large number of chemical reactions take place during steam cracking, most of them based on
free radicals. Computer simulations aimed at modeling what takes place during steam cracking
have included hundreds or even thousands of reactions in their models. The major sorts of
reactions that take place, with examples, include:
• Initiation reactions, where a single molecule breaks apart into two free radicals. Only a small
fraction of the feed molecules actually undergo initiation, but these reactions are necessary to
produce the free radicals that drive the rest of the reactions. In steam cracking, initiation usually
involves breaking a chemical bond between two carbon atoms, rather than the bond between a
carbon and a hydrogen atom.
• CH3CH3 → 2 CH3•

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• Hydrogen abstraction, where a free radical removes a hydrogen atom from another
molecule, turning the second molecule into a free radical.
• CH3• + CH3CH3 → CH4 + CH3CH2•
• Radical decomposition, where a free radical breaks apart into two molecules, one an
alkene, the other a free radical. This is the process that results in the alkene products of
steam cracking.
• CH3CH2• → CH2=CH2 + H•
• Radical addition, the reverse of radical decomposition, in which a radical reacts with an
alkene to form a single, larger free radical. These processes are involved in forming the
aromatic products that result when heavier feedstocks are used.
• CH3CH2• + CH2=CH2 → CH3CH2CH2CH2•
• Termination reactions, which happen when two free radicals react with each other to
produce products that are not free radicals. Two common forms of termination are
recombination, where the two radicals combine to form one larger molecule, and
disproportionation, where one radical transfers a hydrogen atom to the other, giving an
alkene and an alkane.
• CH3• + CH3CH2• → CH3CH2CH3
• CH3CH2• + CH3CH2• → CH2=CH2 + CH3CH3

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• History
• In 1855, petroleum cracking methods were pioneered by Chemistry Professor Benjamin Silliman, Jr., of Yale
University (then Sheffield Scientific School at Yale University). Silliman, like his father, were Skull and Bones
members and both Chemistry Professors at SSS.
• The first thermal cracking method, the Burton process, was invented by William M. Burton; the oil industry
first using it to produce gasoline in 1913.
• Catalytic cracking, based upon a process developed by Dr. Alex Golden Oblad at Standard Oil of Indiana has
been used from around 1936. Typical catalysts include alumina, silica, zeolites, and various types of clay
• The world's first oil refinery opened at Ploieşti, Romania in 1856 [1]. Several other refineries were built at that
location with investment from United States companies before being taken over by Nazi Germany during
World War II. Most of these refineries were bombarded by the US Air Force in Operation Tidal Wave, August 1,
1943.
• Another early example is Oljeön preserved as a museum at the UNESCO world heritage site Engelsberg. It
started operation in 1875 and is part of the Ecomuseum Bergslagen.
• The largest oil refinery in the world is in Ras Tanura, Saudi Arabia, owned by Saudi Aramco. The city was
originally built as a sea port, but actually developed because of the huge refinery area. For most of the 20th
century the largest refinery of the world was that of Abadan in Iran.

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An oil refinery. The tapering vertical elements are smokestacks to create draft for heating units. Most of the complex
vertical units are fractionating towers. Others are flares, at this refinery (Shell at Martinez, California) designed and
permitted for emergency use only in case of process upset. (Flares are alleged by some to be used to dispose of unwanted
waste materials by incomplete burning with the actual pollution figures grossly underreported.)

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• http://www.uop.com/refining/1080.html
• http://catcracking.com/
• http://www.tceq.state.tx.us/assets/public/permitting/air/Guidance/NewSource
Review/fccu.pdf
• http://catalysis.che.wsu.edu/~aplaton/interests/1_intro_to_oil_refining/
• http://www.schoolscience.co.uk/content/index.asp
• http://www.ekomuseum.se/english/besoksmal/oljeon.html

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• Item Definition
Activation energy The amount by which the energy of reactants must be raised for reaction to take place
Analgesic A substance with pain-relieving properties
Aromatic Compounds based on the “benzene ring”
Atom economy The proportion of reactant atoms that appear in the desired product
Autoclave Apparatus used for small-scale reactions in a contained environment, usually at high pressure
Biocatalysis Catalysed reactions where the catalyst is an enzyme
Biotransformation Chemical reaction carried out using biological catalysts
Candida rugosa A fungus used in biocatalysis
Carbocation (“Carbo – cation”, not “carbocashun”!) A positive ion formed from an organic molecule
Cat cracker “Catalytic cracker” – industrial scale equipment used to break large alkane molecules from fractional
distillation of oil into smaller molecules
Chemical promoter A substance which, though not itself a catalyst, improves the effectiveness of the catalyst by
chemical means
Chiral Term used to describe molecules that contain a carbon atom that is surrounded by four different
groups, allowing for isomers that are mirror-images (leading to optical isomerism)
Co-catalyst A second catalyst used in conjunction with another
Co-monomer Monomer molecules used in addition to main monomer when making a polymer (introduces
controlled branching)
Cracking Breaking large alkane molecules from heavier oil fractions into smaller ones
Creep Polymer chains sliding over one another in a plastic, leading to a change in dimensions
Diffraction An interference effect that leads to the scattering of beams of electromagnetic radiation and small
particles (like electrons) in specific directions - used to help determine structure
Enantiomers Two mirror-image molecules
Envirocats A group of catalysts using clay supports
Enzyme A catalyst of biological origin
Ferrocene The first of the metallocenes, transition metal complexes consisting of a metal atom “sandwiched”
between two 5-membered rings

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Fuel Cell Electrochemical cell used to generate electricity from fuels
Hdpe High Density Poly(ethene)
Heterogeneous catalysis Catalysed reactions in which the catalyst and reactants are in different phases (solid, liquid or gas)
Homogeneous catalysis Catalysed reactions in which the catalyst and reactants are in the same phase (solid, liquid or gas)
IR Spectrum Infra-red radiation can cause a molecule to vibrate, absorbing energy, and the frequencies at which
this happens is different for each substance. A spectrum can be produced showing the frequencies
at which absorption occurs, effectively a fingerprint for the material.
Isomerism The characteristic of substances that have the same formula, but different structures
Kaminsky Walter Kaminsky developed catalysts based on metallocenes
Kevlar A nylon-based fibre with exceptional strength – used to make bullet-proof vests, tyres, heat resistant fabrics
Ldpe Low density poly(ethene)
Lewis acid A substance that is an electron-pair acceptor
Lldpe Linear low density poly(ethene)
MAO Methylalumoxane – formed during activation of a metallocene catalyst for the production of poly(ethene)
Metallocene Transition metal complexes consisting of metal atoms “sandwiched” between 5-membered rings
Montmorillonite A type of clay used as catalyst support in Friedel-Crafts alkylation
Nanotechnology Technology that is on a molecular (or strictly nanometre) scale
Natta Developer of organo-metallic catalysts for production of plastics – shared Nobel Prize with Ziegler
Optical isomerism Isomerism as a result of a molecule existing in two mirror-image forms (which affect polarised light
differently). The two isomers are referred to as the L- and D- isomers, or alternatively as the (R) and
(S) forms
Organometallic Organic compounds that also include one or more metal atoms
PET “Polyethylene terephthalate” (polyethene benzene – 1,4- dicarboxylate) – used to make lightweight
plastic bottles
Polyethylene Poly(ethene) Note that Polythene is an ICI trade name
Item Definition

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Promoter A substance which, though not itself a catalyst, improves the effectiveness of the
catalyst – promoters may act chemically or physically
Protecting groups Groups of atoms that are placed temporarily on parts of a molecule which need to be
protected from a reagent to be used in one of the synthetic steps needed to make the
final product . These protecting groups are removed afterwards.
Racemic mixture An equal mixture of the two optical isomers of a compound, being therefore optically
inactive
Racemisation The process of producing an equal mixture of the two optical isomers of a compound
Recombinant DNA techniques These are a variety of techniques used to analyse and manipulate DNA. They include
methods to modify genes and construct new genes. The techniques also include ways
to express new and modified genes to yield protein products.
Reforming The process of synthesising a suitable material from another less suitable one
Rhodococcus rhodochrous A bacterium used to provide the enzymes used in the biocatalytic manufacture of
Propeneamide. This bacterium is able to use organic substances as its sole source of
carbon for growth
Sintering The fusing of individual solid particles caused by heating.
Spectroscopy Methods for analysing materials based on how the reflection or transmission of
radiation (eg light, IR etc) is affected by the material
Stereo selective Reacting mainly with only one optical isomer
Stoichiometric In the proportions indicated by the chemical equation
Structural promoter A substance which, though not itself a catalyst, improves the effectiveness of the
catalyst by providing a suitable structure
Item Definition

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Supercritical CO2 Carbon dioxide at a temperature and pressure such that distinct liquid and gas phases
do not occur
TAED Tetraacetyl ethylenediamine is used in some washing powder detergents to enable
peroxide-based bleaches to work at lower temperatures
Titanocene A metallocene compound containing the metal titanium
Uhmwpe Ultra High Molecular Weight Poly(ethene)
Zeolite A group of aluminosilicate materials, some of which occur in nature. They are widely
used as catalysts and as catalyst supports.
Ziegler Developer of organo-metallic catalysts (known as Ziegler Catalysts) for production of
plastics –shared Nobel Prize with Natta
Zirconocene A metallocene compound containing the metal zirconium
Item Definition