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. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, An oil refinery is an industrial Process plant where Crude oil is processed and refined into more useful Petroleum products, such as Gasoline Jet fuel is a type of Aviation fuel designed for use in Aircraft powered by gas-turbine engines. Kerosene, sometimes spelled kerosine in scientific and industrial usage is a Combustible Hydrocarbon liquid Diesel or Diesel fuel (ˈdiːzəl in general is any Fuel used in Diesel engines The most common is a specific fractional distillate of petroleum Fuel oil is a fraction obtained from Petroleum Distillation, either as a distillate or a residue ^[1][2] The purpose of removing the sulfur is to reduce the sulfur dioxide (SO₂) emissions that result from using those fuels in automotive vehicles, aircraft, railroad locomotives, ships, gas or oil burning power plants, residential and industrial furnaces, and other forms of fuel combustion. Vehicles, derived from the Latin word vehiculum, are non-living Means of transport. A locomotive is a railway Vehicle that provides the motive power for a Train. A ship /ʃɪp/ is a large vessel that floats on water Ships are generally distinguished from Boats based on size A power station (also referred to as generating station, power plant or powerhouse) is an industrial facility for the generation of A furnace is a device used for Heating The name derives from Latin fornax, Oven. Combustion or burning is a complex sequence of Exothermic chemical reactions between a Fuel and an Oxidant accompanied by the production of

Another important reason for removing sulfur from the naphtha streams within a petroleum refinery is that sulfur, even in extremely low concentrations, poisons the noble metal catalysts (platinum and rhenium) in the catalytic reforming units that are subsequently used to upgrade the octane rating of the naphtha streams. Naphtha normally refers to a number of different flammable liquid mixtures of hydrocarbons i Catalyst poisoning refers to the effect that a Catalyst can be 'poisoned' if it reacts with another compound that bonds chemically (similar to an inhibitor Noble metals are Metals that are resistant to Corrosion or Oxidation, unlike most Base metals They tend to be Precious metals often Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 Rhenium (ˈriːniəm is a Chemical element with the symbol Re and Atomic number 75 Catalytic reforming is a chemical process used to convert Petroleum refinery Naphthas typically having low octane ratings, into high-octane liquid products The octane rating is a measure of the resistance of Gasoline and other Fuels to Detonation ( Engine knocking) in spark-ignition Naphtha normally refers to a number of different flammable liquid mixtures of hydrocarbons i

The industrial hydrodesulfurization processes include facilities for the capture and removal of the resulting hydrogen sulfide (H₂S) gas. Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. In petroleum refineries, the hydrogen sulfide gas is then subsequently converted into byproduct elemental sulfur. An oil refinery is an industrial Process plant where Crude oil is processed and refined into more useful Petroleum products, such as Gasoline In fact, the vast majority of the 64,000,000 metric tons of sulfur produced worldwide in 2005 was byproduct sulfur from refineries and other hydrocarbon processing plants. ^[3][4]

An HDS unit in the petroleum refining industry is also often also referred to as a Hydrotreater.

Contents 1 History 2 The process chemistry 3 Process description 4 Sulfur compounds in refinery HDS feedstocks 4.1 Thiophenes 5 Catalysts and mechanisms 5.1 Catalysts 5.2 Supports 6 Other uses 6.1 Hydrodenitrogenation 6.2 Saturation of olefins 6.3 Hydrogenation in the food industry 7 References 8 External links

History

Although reactions involving catalytic hydrogenation of organic substances were known prior to 1897, the property of finely divided nickel to catalyze the fixation of hydrogen on hydrocarbon (ethylene, benzene) double bonds was discovered by the French chemist, Paul Sabatier. This article is about the country For a topic outline on this subject see List of basic France topics. A chemist is a Scientist trained in the Science of Chemistry. Paul Sabatier ( November 5, 1854 &ndash August 14, 1941) was a French chemist born at Carcassonne. ^[5][6] Thus, he found that unsaturated hydrocarbons in the vapor phase could be converted into saturated hydrocarbons by using hydrogen and a catalytic metal. His work was the foundation of the modern catalytic hydrogenation process.

Soon after Sabatier's work, a German chemist, Wilhelm Normann, found that catalytic hydrogenation could be used to convert unsaturated fatty acids or glycerides in the liquid phase into saturated ones. Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. Wilhelm Normann ( January 16, 1870, Petershagen - May 1, 1939, Chemnitz) (sometimes also spelled Norman) was He was awarded a patent in Germany in 1902^[7] and in Britain in 1903,^[8] which was the beginning of what is now a worldwide industry.

In the mid-1950's, the first noble metal catalytic reforming process (the Platformer process) was commercialized. Noble metals are Metals that are resistant to Corrosion or Oxidation, unlike most Base metals They tend to be Precious metals often Catalytic reforming is a chemical process used to convert Petroleum refinery Naphthas typically having low octane ratings, into high-octane liquid products At the same time, the catalytic hydrodesulfurization of the naphtha feed to such reformers was also commercialized. In the decades that followed, various proprietary catalytic hydrodesulfurization processes such as the one depicted in the flow diagram below have been commercialized. 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 Currently, virtually all of the petroleum refineries world-wide have one or more HDS units.

By 2006 miniature microfluidic HDS units had been implemented for treating JP-8 jet fuel to produce clean feed stock for a fuel cell hydrogen reformer. Microfluidics deals with the behavior precise control and manipulation of Fluids that are geometrically constrained to a small typically sub-millimeter scale JP-8, or JP8 (for "Jet Propellant" is a Jet fuel, specified in 1990 by the U A fuel cell is an electrochemical conversion device It produces electricity from Fuel (on the Anode side and an oxidant (on the Steam reforming (SR hydrogen reforming or catalytic oxidation, is a method of producing Hydrogen from Hydrocarbons. ^[9] By 2007 this had been integrated into an operating 5kW fuel cell generation system. ^[10]

The process chemistry

Hydrogenation is a class of chemical reactions in which the net result is the addition of hydrogen (H). Hydrogenation is the Chemical reaction that results in addition of Hydrogen (H2 A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Hydrogenolysis is a type of hydrogenation and results in the cleavage of the C-X chemical bond, where C is a carbon atom and X is a sulfur, nitrogen (N) or oxygen (O) atom. Hydrogenolysis is a Chemical reaction whereby a carbon-carbon or carbon- Heteroatom single bond is cleaved or undergoes "lysis" by hydrogen A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The net result of a hydrogenolysis reaction is the formation of C-H and H-X chemical bonds. Thus, hydrodesulfurization is a hydrogenolysis reaction. Using ethanethiol (C₂H₅SH), a sulfur compound present in some petroleum products, as an example, the hydrodesulfurization reaction can be simply expressed as

Ethanethiol + Hydrogen	→	Ethane + Hydrogen sulfide
C2H5SH + H2	→	C2H6 + H2S

For the mechanistic aspects of, and the catalysts used in this reaction see the section catalysts and mechanisms

Process description

In an industrial hydrodesulfurization unit, such as in a refinery, the hydrodesulfurization reaction takes place in a fixed-bed reactor at elevated temperatures ranging from 300 to 400 °C and elevated pressures ranging from 30 to 130 atmospheres of absolute pressure, typically in the presence of a catalyst consisting of an alumina base impregnated with cobalt and molybdenum. Ethanethiol is the Organic compound with the formula CH3CH2SH ETHANE is a mnemonic indicating a protocol used by Emergency services to report situations which they may be faced with especially as it relates to major incidents where Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. In Chemical engineering, chemical reactors are vessels designed to contain Chemical reactions The design of a chemical reactor deals with multiple aspects of Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst Cobalt (ˈkoʊbɒlt is a hard lustrous silver-grey Metal, a Chemical element with symbol Co. Molybdenum (məˈlɪbdənəm from the Greek word for the metal " Lead " is a Group 6 Chemical element with the symbol Mo

The image below is a schematic depiction of the equipment and the process flow streams in a typical refinery HDS unit.

The liquid feed (at the bottom left in the diagram) is pumped up to the required elevated pressure and is joined by a stream of hydrogen-rich recycle gas. For information on Wikipedia project-related discussions see WikipediaVillage pump. The resulting liquid-gas mixture is preheated by flowing through a heat exchanger. A heat exchanger is a device built for efficient Heat transfer from one medium to another whether the media are separated by a solid wall so that they never mix or the media The preheated feed then flows through a fired heater where the feed mixture is totally vaporized and heated to the required elevated temperature before entering the reactor and flowing through a fixed-bed of catalyst where the hydrodesulfurization reaction takes place. A furnace is a device used for Heating The name derives from Latin fornax, Oven. Evaporation is the process by which Molecules in a Liquid state (e

The hot reaction products are partially cooled by flowing through the heat exchanger where the reactor feed was preheated and then flows through a water-cooled heat exchanger before it flows through the pressure controller (PC) and undergoes a pressure reduction down to about 3 to 5 atmospheres. The resulting mixture of liquid and gas enters the gas separator vessel at about 35 °C and 3 to 5 atmospheres of absolute pressure. A pressure vessel is a closed container designed to hold gases or liquids at a Pressure different from the ambient Pressure.

Most of the hydrogen-rich gas from the gas separator vessel is recycle gas which is routed through an amine contactor for removal of the reaction product H₂S that it contains. Amine gas treating, also known as gas sweetening and acid gas removal, refers to a group of processes that use aqueous solutions of various Amines to remove The H₂S-free hydrogen-rich gas is then recycled back for reuse in the reactor section. Any excess gas from the gas separator vessel joins the sour gas from the stripping of the reaction product liquid. Sour gas is Natural gas or any other gas containing significant amounts of Hydrogen sulfide (H2S

The liquid from the gas separator vessel is routed through a reboiled stripper distillation tower. Reboilers are Heat exchangers typically used to provide heat to the bottom of industrial distillation columns Continuous distillation, a form of Distillation, is an ongoing separation in which a mixture is continuously (without interruption fed into the process and separated fractions The bottoms product from the stripper is the final desulfurized liquid product from hydrodesulfurization unit.

The overhead sour gas from the stripper contains hydrogen, methane, ethane, hydrogen sulfide, propane and perhaps some butane and heavier components. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. ETHANE is a mnemonic indicating a protocol used by Emergency services to report situations which they may be faced with especially as it relates to major incidents where Propane is a three- Carbon Alkane, normally a gas but compressible to a liquid that is transportable Butane, also called n -butane, is the unbranched Alkane with four Carbon Atoms CH3CH2CH2CH3 That sour gas is sent to the refinery's central gas processing plant for removal of the hydrogen sulfide in the refinery's main amine gas treating unit and through a series of distillation towers for recovery of propane, butane and pentane or heavier components. Amine gas treating, also known as gas sweetening and acid gas removal, refers to a group of processes that use aqueous solutions of various Amines to remove Pentane is any or one of the Organic compounds with the formula C5H12 The residual hydrogen, methane, ethane and some propane is used as refinery fuel gas. The hydrogen sulfide removed and recovered by the amine gas treating unit is subsequently converted to elemental sulfur in a Claus process unit. The Claus process is the most significant gas desulfurizing process recovering elemental Sulfur from gaseous Hydrogen sulfide.

Note that the above description assumes that the HDS unit feed contains no olefins. In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon If the feed does contain olefins (for example, the feed is a naphtha derived from a refinery fluid catalytic cracker (FCC) unit), then the overhead gas from the HDS stripper may also contain some ethene, propene, butenes and pentenes or heavier components. Structure This Hydrocarbon has four Hydrogen Atoms bound to a pair of Carbon atoms that are connected by a Double bond. Propene, also known as propylene, is an unsaturated organic compound having the Chemical formula C 3 H 6 Isomers Among the molecules which have the Chemical formula 48 four Isomers are Alkenes. Cis-2-pentenesvg|thumb|Cis-2-pentene]] Pentene refers to all the Alkenes with Chemical formula 510 containing a single Double bond

It should also be noted that the amine solution to and from the recycle gas contactor comes from and is returned to the refinery's main amine gas treating unit.

Sulfur compounds in refinery HDS feedstocks

The refinery HDS feedstocks (naphtha, kerosene, diesel oil and heavier oils) contain a wide range of organic sulfur compounds, including thiols, thiophenes, organic sulfides and disulfides, and many others. An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. In Organic chemistry, a thiol is a compound that contains the functional group composed of a Sulfur atom and a Hydrogen atom (-SH Thiophene is the Heterocyclic compound with the formula C4H4S The term sulfide ( sulphide in British English) refers to several types of Chemical compounds containing Sulfur in its lowest Oxidation In Chemistry, a disulfide usually refers to the structural unit composed of a linked pair of sulfur atoms These organic sulfur compounds are products of the degradation of sulfur containing biological components, present during the natural formation of the fossil fuel, petroleum crude oil. Fossil fuels or mineral fuels are fossil source Fuels that is Hydrocarbons found within the top layer of the Earth’s crust.

When the HDS process is used to desulfurize a refinery naphtha, it is necessary to remove the total sulfur down to the parts per million range or lower in order to prevent poisoning the noble metal catalysts in the subsequent catalytic reforming of the naphthas.

When the process is used for desulfurizing diesel oils, the latest environmental regulations in the United States and Europe, requiring what is referred to as ultra-low sulfur diesel (ULSD), in turn requires that very deep hydrodesulfurization is needed. In the very early 2000's, the governmental regulatory limits for highway vehicle diesel was within the range of 300 to 500 ppm by weight of total sulfur. As of 2006, the total sulfur limit for highway diesel is in the range of 15 to 30 ppm by weight. ^[11]

Thiophenes

A family of substrates that are particularly common in petroleum are the aromatic sulfur-containing heterocycles called thiophenes. Many kinds of thiophenes occur in petroleum ranging from thiophene itself to more condensed derivatives called benzothiophenes and dibenzothiophenes. Benzothiophene is an Aromatic Organic compound with a molecular formula C8H6S and an odor similar to Naphthalene (mothballs Dibenzothiophene is the Organic compound consisting of two benzene rings fused to a central Thiophene ring Thiophene itself and its alkyl derivatives are easier to hydrogenolyse, whereas dibenzothiophene, especially its 4,6-disubstituted derivatives, are considered the most challenging substrates. Benzothiophenes are midway between the simple thiophenes and dibenzothiophenes in their susceptibility to HDS.

Catalysts and mechanisms

The main HDS catalysts are based on MoS₂ together with smaller amounts of other metals. Molybdenum disulfide is the inorganic compound with the formula MoS2 ^[12] The nature of the sites of catalytic activity remains an active area of investigation, but it is generally assumed basal planes of the MoS₂ structure are not relevant to catalysis, rather the edges or rims of these sheet. ^[13] At the edges of the MoS₂ crystallites, the molybdenum centre can stabilize a coordinatively unsaturated site (CUS), also known as an anion vacancy. Substrates, such as thiophene, bind to this site and undergo a series a reactions that result in both C-S scission and C=C hydrogenation. Thus, the hydrogen serves multiple roles - generation of anion vacancy by removal of sulfide, hydrogenation, and hydrogenolysis. A simplified diagram for the cycle is shown:

Catalysts

Most metals catalyse HDS, but it is those at the middle of the transition metal series that are most active. Ruthenium disulfide appears to be the single most active catalyst, but binary combinations of cobalt and molybdenum are also highly active. Laurite is an opaque black metallic Ruthenium Sulfide mineral with formula RuS2 ^[14] Aside from the basic cobalt-modified MoS₂ catalyst, nickel and tungsten are also used, depending on the nature of the feed. For example, Ni-W catalysts are more effective for hydrodenitrification (HDN).

Supports

Metal sulfides are "supported" on materials with high surface areas. A typical support for HDS catalyst is γ-alumina. The support allows the more expensive catalyst to be more widely distributed, giving rise to a larger fraction of the MoS₂ that is catalytically active. The interaction between the support and the catalyst is an area of intense interest, since the support is often not fully inert but participates in the catalysis.

Other uses

The basic hydrogenolysis reaction has a number of uses other than hydrodesulfurization.

Hydrodenitrogenation

The hydrogenolysis reaction is also used to reduce the nitrogen content of a petroleum stream and, in that case, is referred to Hydrodenitrogenation (HDN). The process flow scheme is the same as for an HDS unit.

Using pyridine (C₅H₅N), a nitrogen compound present in some petroleum fractionation products, as an example, the hydrodenitrogenation reaction has been postulated as occurring in three steps:^[15][16]

Pyridine + Hydrogen	→	Piperdine + Hydrogen	→	Amylamine + Hydrogen	→	Pentane + Ammonia
C5H5N + 5H2	→	C5H11N + 2H2	→	C5H11NH2 + H2	→	C5H12 + NH3

and the overall reaction may be simply expressed as:

Pyridine + Hydrogen	→	Pentane + Ammonia
C5H5N + 5H2	→	C5H12 + NH3

Many HDS units for desulfurizing naphthas within petroleum refineries are actually simultaneously denitrogenating to some extent as well. Pyridine is a Chemical compound with the formula C5[[Hydrogen H5]] N. Piperidine is an Organic compound with the molecular formula (CH25NH Amines are Organic compounds and Functional groups that contain a basic Nitrogen Atom with a Lone pair. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor

Saturation of olefins

The hydrogenolysis reaction may also be used to saturate or convert olefins (alkenes) into paraffins (alkanes). In Chemistry, saturation has five different meanings In Physical chemistry, saturation is the point at which a Solution of a substance In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon In chemistry paraffin is the common name for the Alkane Hydrocarbons with the general formula C n H2 n +2 Alkanes, also known as Paraffins are Chemical compounds that consist only of the elements Carbon (C and Hydrogen (H (i The process used is the same as for an HDS unit.

As an example, the saturation of the olefin, pentene, can be simply expressed as:

Pentene + Hydrogen	→	Pentane
C5H10 + H2	→	C5H12

Some hydrogenolysis units within a petroleum refinery or a petrochemical plant may be used solely for the saturation of olefins or they may be used for simultaneously desulfurizing as well as denitrogenating and saturating olefins to some extent.

Hydrogenation in the food industry

Further information: Hydrogenation, Wilhelm Normann, and Trans fat

The food industry uses hydrogenation to completely or partially saturate the unsaturated fatty acids in liquid vegetable fats and oils to convert them into solid or semi-solid fats, such as those in margarine and shortening. Hydrogenation is the Chemical reaction that results in addition of Hydrogen (H2 Wilhelm Normann ( January 16, 1870, Petershagen - May 1, 1939, Chemnitz) (sometimes also spelled Norman) was Trans fat is the common name for a type of Unsaturated fat with trans - isomer Fatty acid (s Saturated fat is Fat that consists of Triglycerides containing only saturated Fatty acids Explanation Fat that occurs An unsaturated fat is a Fat or Fatty acid in which there are one or more Double bonds in the fatty acid chain In Chemistry, especially Biochemistry, a fatty acid is a Carboxylic acid often with a long unbranched Aliphatic tail ( chain) which Margarine (ˈmɑrdʒərɨn /ˈmɑrdʒəriːn/ or /ˈmɑrgəriːn/ as a generic term can indicate any of a wide range of Butter substitutes Shortening is a semisolid Fat used in food preparation especially baked goods and is so called because it promotes a "short" or crumbly texture (as in Shortbread

References

External links

• Albemarle Catalyst Company (Petrochemical catalysts supplier)
• UOP Company (Engineering design and construction of large-scale, industrial HDS plants)
• Mustang Engineering Company (Description and flow diagram of an HDS unit, from an article published in the Oil & Gas Journal)
• Hydrogenation for Low Trans and High Conjugated Fatty Acids by E. S. Jang, M. Y. Jung, D. B. Min, Comprehensive Reviews in Food Science and Food Safety, Vol. 1, 2005
• Oxo Alcohols (Engineered and constructed by Aker Kvaerner)
• Catalysts and technology for Oxo-Alcohols

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