Catalytic reforming is a chemical process used to convert
petroleum refinery
An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefie ...
naphtha
Naphtha ( or ) is a flammable liquid hydrocarbon mixture.
Mixtures labelled ''naphtha'' have been produced from natural gas condensates, petroleum distillates, and the distillation of coal tar and peat. In different industries and regions ''n ...
s distilled from
crude oil
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
(typically having low
octane rating
An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without detonating. The higher the octane number, the more compression the fuel can withstand before detonating ...
s) into high-octane liquid products called reformates, which are premium blending stocks for high-octane
gasoline
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic co ...
. The process converts low-octane linear
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
s (paraffins) into
branched alkane
In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in whi ...
s (isoparaffins) and cyclic
naphthene
In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the ring (chemistry), monocyclic Saturated and unsaturated compounds, saturated hydrocarbons. In other words, a cycloalkane consists only of hydroge ...
s, which are then partially
dehydrogenated
In chemistry, dehydrogenation is a chemical reaction that involves the removal of hydrogen, usually from an organic molecule. It is the reverse of hydrogenation. Dehydrogenation is important, both as a useful reaction and a serious problem. At ...
to produce high-octane
aromatic hydrocarbon
Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past grouping ...
s. The dehydrogenation also produces significant amounts of byproduct
hydrogen gas
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, a ...
, which is fed into other refinery processes such as
hydrocracking
In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of ...
. A side reaction is
hydrogenolysis
Hydrogenolysis is a chemical reaction whereby a carbon–carbon or carbon–heteroatom single bond is cleaved or undergoes lysis (breakdown) by hydrogen.Ralph Connor, Homer Adkins. Hydrogenolysis Of Oxygenated Organic Compounds. J. Am. Chem. Soc. ...
, which produces light hydrocarbons of lower value, such as
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
,
ethane
Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petr ...
,
propane
Propane () is a three-carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used a ...
and
butanes
Butane () or ''n''-butane is an alkane with the formula C4H10. Butane is a gas at room temperature and atmospheric pressure. Butane is a highly flammable, colorless, easily liquefied gas that quickly vaporizes at room temperature. The name bu ...
.
In addition to a gasoline blending stock, reformate is the main source of aromatic bulk chemicals such as
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
,
toluene
Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) at ...
,
xylene
In organic chemistry, xylene or xylol (; IUPAC name: dimethylbenzene) are any of three organic compounds with the formula . They are derived from the substitution of two hydrogen atoms with methyl groups in a benzene ring; which hydrogens are sub ...
and
ethylbenzene
Ethylbenzene is an organic compound with the formula . It is a highly flammable, colorless liquid with an odor similar to that of gasoline. This monocyclic aromatic hydrocarbon is important in the petrochemical industry as an reaction intermediat ...
which have diverse uses, most importantly as raw materials for conversion into plastics. However, the benzene content of reformate makes it
carcinogenic
A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substan ...
, which has led to governmental regulations effectively requiring further processing to reduce its benzene content.
This process is quite different from and not to be confused with the catalytic
steam reforming
Steam reforming or steam methane reforming (SMR) is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly natural gas is the feedstock. The main purpose of this technology is hydrogen product ...
process used industrially to produce products such as
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
,
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
, and
methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
from
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
, naphtha or other petroleum-derived feedstocks. Nor is this process to be confused with various other catalytic reforming processes that use methanol or
biomass-derived feedstocks to produce hydrogen for
fuel cells
A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...
or other uses.
These are the two main classes into which the catalysts utilised for the reforming processes fall.
# Supported noble metals
# non-noble transition metals
#
The best
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
for the synthesis of syngas utilising various procedures has been the subject of several research.
Rhodium
Rhodium is a chemical element with the symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring isoto ...
,
ruthenium
Ruthenium is a chemical element with the Symbol (chemistry), symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to ...
, and
platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Platinu ...
, as well as
palladium
Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself na ...
and
iridium
Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of ...
catalysts, have all been the subject of in-depth study on
hydrogen production
Hydrogen production is the family of industrial methods for generating hydrogen gas. As of 2020, the majority of hydrogen (∼95%) is produced from fossil fuels by steam reforming of natural gas and other light hydrocarbons, partial oxidation of h ...
, catalytic
thermal decomposition
Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is req ...
, and dry reforming catalysts. Noble metals-based catalysts are much more effective and often less susceptible to deactivation by carbon production or oxidation, but because they are more affordable (costing 100–150 times less then the noble metals), they are less frequently used. In
industrial uses, catalysts depending on
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...
are increasingly often utilised. However, due to
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
accumulation, their resilience is low. The most crucial issue for
methane reforming A methane reformer is a device based on steam reforming, autothermal reforming or partial oxidation and is a type of chemical synthesis which can produce pure hydrogen gas from methane using a catalyst. There are multiple types of reformers in devel ...
, particularly in dry reforming, is the suppression of carbon deposition for non-noble
metal catalysts
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
. Increasing the surface basicity of catalysts and regulating the
particle size
Particle size is a notion introduced for comparing dimensions of solid particles ('' flecks''), liquid particles (''droplets''), or gaseous particles ('' bubbles''). The notion of particle size applies to particles in colloids, in ecology, in gr ...
s of active ingredients are two techniques used to prevent carbon from depositing. The improvement of metal-support interaction, the creation of
solid solutions
Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural ri ...
, and plasma processes are only a few of the strategies that have been developed to manage the metal particle sizes. The surface basicity of catalysts was increased by using basic
metal oxides as a support or
promoter. Increased catalysts and processes as a consequence of the work of several authors have improved overall
efficiency
Efficiency is the often measurable ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without ...
and environmental performance.
History
In the 1940s,
Vladimir Haensel
Vladimir Haensel (1 September 1914 – 15 December 2002) was an American chemical engineer who invented the platforming process - a ''plat''inum catalytic process for re''forming'' petroleum hydrocarbons into gasoline. In addition, he was influe ...
, a research chemist working for
Universal Oil Products
Honeywell UOP, formerly known as UOP LLC or Universal Oil Products, is an American multi-national company developing and delivering technology to the petroleum refining, gas processing, petrochemical production, and major manufacturing industries.
...
(UOP), developed a
catalytic reforming process using a
catalyst containing
platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Platinu ...
. Haensel's process was subsequently commercialized by UOP in 1949 for producing a high octane gasoline from low octane naphthas and the UOP process become known as the Platforming process. The first Platforming unit was built in 1949 at the refinery of the Old Dutch Refining Company in
Muskegon,
Michigan.
In the years since then, many other versions of the process have been developed by some of the major oil companies and other organizations. Today, the large majority of gasoline produced worldwide is derived from the catalytic reforming process.
To name a few of the other catalytic reforming versions that were developed, all of which utilized a platinum and/or a
rhenium catalyst:
*Rheniforming: Developed by
Chevron Oil Company
Chevron Corporation is an American multinational energy corporation. The second-largest direct descendant of Standard Oil, and originally known as the Standard Oil Company of California (shortened to Socal or CalSo), it is headquartered in Sa ...
.
*CCR Platforming: A Platforming version, designed for continuous catalyst regeneration, developed by
Universal Oil Products
Honeywell UOP, formerly known as UOP LLC or Universal Oil Products, is an American multi-national company developing and delivering technology to the petroleum refining, gas processing, petrochemical production, and major manufacturing industries.
...
(UOP).
*Powerforming: Developed by
Esso Oil Company, currently known as
ExxonMobil
ExxonMobil Corporation (commonly shortened to Exxon) is an American multinational oil and gas corporation headquartered in Irving, Texas. It is the largest direct descendant of John D. Rockefeller's Standard Oil, and was formed on November 30, ...
.
*Magnaforming: Developed by
Engelhard and
Atlantic Richfield Oil Company.
*Ultraforming: Developed by
Standard Oil of Indiana
Amoco () is a brand of filling station, fuel stations operating in the United States, and owned by BP since 1998. The Amoco Corporation was an American chemical and petroleum, oil company, founded by Standard Oil Company in 1889 around a oil re ...
, now a part of the
British Petroleum Company.
*Houdriforming: Developed by the Houdry Process Corporation.
*Octanizing: A catalytic reforming version developed by Axens, a subsidiary of
Institut francais du petrole
The IFP Energies nouvelles (IFPEN) also known as French Institute of Petroleum (in French: ''Institut Français du Pétrole, IFP'') is a public research organisation in France founded in 1944 as Institute of Oil, Fuels and Lubricants (''Institut du ...
(IFP), designed for continuous catalyst regeneration.
Chemistry
Before describing the reaction chemistry of the catalytic reforming process as used in petroleum refineries, the typical naphthas used as catalytic reforming feedstocks will be discussed.
Typical naphtha feedstocks
A petroleum refinery includes many
unit operations and
unit processes A ''unit process'' is one or more grouped operations in a manufacturing system that can be defined and separated from others.
In life-cycle assessment (LCA) and ISO 14040, a unit process is defined as "smallest element considered in the life cycle ...
. The first unit operation in a refinery is the
continuous distillation of the
petroleum crude oil being refined. The overhead liquid distillate is called naphtha and will become a major component of the refinery's gasoline (petrol) product after it is further processed through a
catalytic hydrodesulfurizer to remove
sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
-containing hydrocarbons and a catalytic reformer to reform its hydrocarbon molecules into more complex molecules with a higher octane rating value. The naphtha is a mixture of very many different hydrocarbon compounds. It has an initial
boiling point
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding envir ...
of about 35 °C and a final boiling point of about 200 °C, and it contains
paraffin Paraffin may refer to:
Substances
* Paraffin wax, a white or colorless soft solid that is used as a lubricant and for other applications
* Liquid paraffin (drug), a very highly refined mineral oil used in cosmetics and for medical purposes
* Alkane ...
,
naphthene
In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the ring (chemistry), monocyclic Saturated and unsaturated compounds, saturated hydrocarbons. In other words, a cycloalkane consists only of hydroge ...
(cyclic paraffins) and
aromatic hydrocarbons ranging from those containing 6
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
atoms to those containing about 10 or 11 carbon atoms.
The naphtha from the crude oil distillation is often further distilled to produce a "light" naphtha containing most (but not all) of the hydrocarbons with 6 or fewer carbon atoms and a "heavy" naphtha containing most (but not all) of the hydrocarbons with more than 6 carbon atoms. The heavy naphtha has an initial boiling point of about 140 to 150 °C and a final boiling point of about 190 to 205 °C. The naphthas derived from the distillation of crude oils are referred to as "straight-run" naphthas.
It is the straight-run heavy naphtha that is usually processed in a catalytic reformer because the light naphtha has molecules with 6 or fewer carbon atoms which, when reformed, tend to crack into butane and lower molecular weight hydrocarbons which are not useful as high-octane gasoline blending components. Also, the molecules with 6 carbon atoms tend to form aromatics which is undesirable because governmental environmental regulations in a number of countries limit the amount of aromatics (most particularly
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
) that gasoline may contain.
There are a great many petroleum
crude oil sources worldwide and each crude oil has its own unique composition or
"assay". Also, not all refineries process the same crude oils and each refinery produces its own straight-run naphthas with their own unique initial and final boiling points. In other words, naphtha is a generic term rather than a specific term.
The table just below lists some fairly typical straight-run heavy naphtha feedstocks, available for catalytic reforming, derived from various crude oils. It can be seen that they differ significantly in their content of paraffins, naphthenes and aromatics:
Some refinery naphthas include
olefinic hydrocarbons, such as naphthas derived from the
fluid catalytic cracking
Fluid Catalytic Cracking (FCC) is the conversion process used in petroleum refineries to convert the high-boiling point, high-molecular weight hydrocarbon fractions of petroleum (crude oils) into gasoline, olefinic gases, and other petroleum prod ...
and
coking
Coking is the heating of coal in the absence of oxygen to a temperature above 600 °C to drive off the volatile components of the raw coal, leaving a hard, strong, porous material of high carbon content called coke. Coke consists almost ent ...
processes used in many refineries. Some refineries may also
desulfurize and catalytically reform those naphthas. However, for the most part, catalytic reforming is mainly used on the straight-run heavy naphthas, such as those in the above table, derived from the distillation of crude oils.
The reaction chemistry
There are 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
In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas ...
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 commonly used catalytic reforming catalysts contain
noble metals
A noble metal is ordinarily regarded as a metallic chemical element that is generally resistant to corrosion and is usually found in nature in its raw form. Gold, platinum, and the other platinum group metals (ruthenium, rhodium, palladium, os ...
such as platinum and/or rhenium, which are very susceptible to
poisoning by sulfur and
nitrogen compounds. Therefore, the naphtha feedstock to a catalytic reformer is always pre-processed in a
hydrodesulfurization
Hydrodesulfurization (HDS) is a catalytic chemical process widely used to remove sulfur (S) from natural gas and from refined petroleum products, such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils. The purpose of remov ...
unit which removes both the sulfur and the nitrogen compounds. Most catalysts require both sulphur and nitrogen content to be lower than 1 ppm.
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
Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) at ...
(an aromatic), as shown below:
:2: The
isomerization of normal paraffins to
isoparaffin
In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which ...
s 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
Heptane or ''n''-heptane is the straight-chain alkane with the chemical formula H3C(CH2)5CH3 or C7H16. When used as a test fuel component in anti-knock test engines, a 100% heptane fuel is the zero point of the octane rating scale (the 100 point ...
to toluene, as shown below:
:4: The
hydrocracking
In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of ...
of paraffins into smaller molecules as exemplified by the cracking of normal heptane into
isopentane and ethane, as shown below:
During the reforming reactions, the carbon number of the reactants remains unchanged, except for hydrocracking reactions which break down the hydrocarbon molecule into molecules with fewer carbon atoms.
The hydrocracking of paraffins is the only one of the above four major reforming reactions that consumes hydrogen. The isomerization of normal paraffins does not consume or produce hydrogen. However, both the dehydrogenation of naphthenes and the dehydrocyclization of paraffins produce hydrogen. The overall net production of hydrogen in the catalytic reforming of petroleum naphthas ranges from about 50 to 200 cubic meters of hydrogen gas (at 0 °C and 1 atm) per cubic meter of liquid naphtha feedstock. In the
United States customary units
United States customary units form a system of measurement units commonly used in the United States and U.S. territories since being standardized and adopted in 1832. The United States customary system (USCS or USC) developed from English units ...
, that is equivalent to 300 to 1200 cubic feet of hydrogen gas (at 60 °F and 1 atm) per
barrel
A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wooden or metal hoops. The word vat is often used for large containers for liquids, ...
of liquid naphtha feedstock. In many petroleum refineries, the net hydrogen produced in catalytic reforming supplies a significant part of the hydrogen used elsewhere in the refinery (for example, in hydrodesulfurization processes). The hydrogen is also necessary in order to
hydrogenolyze any polymers that form on the catalyst.
In practice, the higher the content of naphthenes in the naphtha feedstock, the better will be the quality of the reformate and the higher the production of hydrogen. Crude oils containing the best naphtha for reforming are typically from Western Africa or the North Sea, such as
Bonny light oil
Bonny Light oil was found at Oloibiri in the Niger delta region of Nigeria in 1956 for its commercial use.. Due to its features of generating high profit, it is highly demanded by refiners. Bonny Light crude oil, light oil has an API of 32.9, clas ...
or
Norwegian Troll.
Model reactions using lumping technique
Owing to too many components in catalytic reforming process feedstock, untraceable reactions and the high temperature range, the design and simulation of catalytic reformer reactors is accompanied by complexities. The lumping technique is used extensively for reducing complexities so that the lumps and reaction pathways that properly describe the reforming system and kinetic rate parameters do not depend on feedstock composition.
In one of the recent works, naphtha is considered in terms of 17 hydrocarbon fractions with 15 reactions in which C
1 to C
5 hydrocarbons are specified as
light paraffins
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terahe ...
and the C
6 to C
8+ naphtha cuts are characterized as
isoparaffins, normal paraffins, naphthenes and aromatics.
Reactions in catalytic naphtha reforming are elementary and Hougen-Watson Langmuir-Hinshelwood type reaction rate expressions are used to describe the rate of each reaction. Rate equations of this type explicitly account for the interaction of chemical species with catalyst and contain denominators in which terms characteristic of the adsorption of reacting species are presented.
Process description
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
''in situ'' 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).
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 in situ 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.
The latest and most modern type of catalytic reformers are called continuous catalyst regeneration (CCR) reformers. Such units are defined by continuous in-situ 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 Platformer process and Axens' Octanizing process. The installation and use of CCR units is rapidly increasing.
Many of the earliest catalytic reforming units (in the 1950s and 1960s) were non-regenerative in that they did not perform in situ 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.
The
process flow diagram
A process flow diagram (PFD) is a diagram commonly used in chemical and process engineering to indicate the general flow of plant processes and equipment. The PFD displays the relationship between ''major'' equipment of a plant facility and does n ...
below depicts a typical semi-regenerative catalytic reforming unit.
The liquid feed (at the bottom left in the diagram) is pumped up to the reaction pressure (5–45 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
Vaporization (or vaporisation) of an element or compound is a phase transition from the liquid phase to vapor. There are two types of vaporization: evaporation and boiling. Evaporation is a surface phenomenon, whereas boiling is a bulk phenomenon. ...
and heated to the reaction temperature (495–520 °C) before the vaporized reactants enter the first reactor. 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. 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.
Some installations use three separate fired heaters as shown in the schematic diagram and some installations use a single fired heater with three separate heating coils.
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.
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).
The liquid from the gas separator vessel is routed into a
fractionating column commonly called a ''stabilizer''. The overhead offgas product from the stabilizer contains the byproduct methane, ethane, propane and butane gases produced by the hydrocracking reactions as explained in the above discussion of the reaction chemistry of a catalytic reformer, and it may also contain some small amount of hydrogen. That offgas 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.
Reformate can be blended directly in the gasoline pool but often it is separated in two or more streams. A common refining scheme consists in fractionating the reformate in two streams, light and heavy reformate. The light reformate has lower octane and can be used as
isomerization feedstock if this unit is available. The heavy reformate is high in octane and low in benzene, hence it is an excellent blending component for the gasoline pool.
Benzene is often removed with a specific operation to reduce the content of benzene in the reformate as the finished gasoline has often an upper limit of benzene content (in the UE this is 1% volume). The benzene extracted can be marketed as feedstock for the chemical industry.
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
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
sites needed for isomerization, cyclization and hydrocracking reactions.
[ The biggest care has to be exercised during the chlorination. Indeed, if not chlorinated (or insufficiently chlorinated) the platinum and rhenium in the catalyst would be reduced almost immediately to metallic state by the hydrogen in the vapour phase. On the other hand, an excessive chlorination could depress excessively the activity of the catalyst.
The activity (i.e., effectiveness) of the catalyst in a semi-regenerative catalytic reformer is reduced over time during operation by carbonaceous coke deposition and chloride loss. The activity of the catalyst can be periodically regenerated or restored by in situ high temperature oxidation of the coke followed by chlorination. As stated earlier herein, semi-regenerative catalytic reformers are regenerated about once per 6 to 24 months. The higher the severity of the reacting conditions (temperature), the higher the octane of the produced reformate but also the shorter the duration of the cycle between two regenerations. Catalyst's cycle duration is also very dependent on the quality of the feedstock. However, independently of the crude oil used in the refinery, all catalysts require a maximum final boiling point of the naphtha feedstock of 180 °C.
Normally, the catalyst can be regenerated perhaps 3 or 4 times before it must be returned to the manufacturer for reclamation of the valuable platinum and/or rhenium content.][
]
Weaknesses and Competition
The sensitivity of catalytic reforming to contamination by sulfur and nitrogen requires hydrotreating the naphtha before it enters the reformer, adding to the cost and complexity of the process.
Dehydrogenation, an important component of reforming, is a strongly endothermic reaction, and as such, requires the reactor vessel to be externally heated. This contributes both to costs and the emissions of the process.
Catalytic reforming has a limited ability to process naphthas with a high content of normal paraffins, e.g. naphthas from the gas-to-liquids (GTL) units.
The reformate has a much higher content of benzene than is permissible by the current regulations in many countries. This means that the reformate should either be further processed in an aromatics extraction unit, or blended with appropriate hydrocarbon streams with low content of aromatics.
Catalytic reforming requires a whole range of other processing units at the refinery (apart from the distillation tower, a naphtha hydrotreater, usually an isomerization unit to process light naphtha, an aromatics extraction unit, etc.) which puts it out of reach for smaller (micro-)refineries.
Main licensors of catalytic reforming processes, UOP and Axens, constantly work on improving the catalysts, but the rate of improvement seems to be reaching its physical limits. This is driving the emergence of new technologies to process naphtha into gasoline by companies like Chevron Phillips Chemical
Aromax
) and NGT Synthesis
Methaforming
).
Economics
Catalytic reformation is profitable in that it converts long-chain hydrocarbons, for which there is limited demand despite high supply, into short-chained hydrocarbons, which, due to their uses in petrol fuel, are in much greater demand. It can also be used to improve the octane rating of short-chained hydrocarbons by aromatizing them.
References
External links
Oil Refinery Processes, A Brief Overview
Colorado School of Mines, Lecture Notes
(''Chapter 10, Refining Processes, Catalytic Refinery'' by John Jechura, Adjunct Professor)
Students' Guide to Refining
(scroll down to ''Platforming'')
Modern Refinery
Website of Delft University of Technology, Netherlands (use search function for ''Reforming'')
Major scientific and technical challenges about development of new refining processes
(IFP website)
{{Organic reactions
Chemical processes
Fuel technology
Oil refining