17/07/2013 22:30Hydrodesulfurization - Wikipedia, the free encyclopedia

Page 1 of 7https://en.wikipedia.org/wiki/Hydrodesulfurization

HydrodesulfurizationFrom Wikipedia, the free encyclopedia

Hydrodesulfurization (HDS) is a catalytic chemical process widely used to remove sulfur (S) from naturalgas and from refined petroleum products such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel

oils.[1][2] The purpose of removing the sulfur is to reduce the sulfur dioxide (SO2) emissions that result fromusing those fuels in automotive vehicles, aircraft, railroad locomotives, ships, gas or oil burning powerplants, residential and industrial furnaces, and other forms of fuel combustion.

Another important reason for removing sulfur from the naphtha streams within a petroleum refinery is thatsulfur, even in extremely low concentrations, poisons the noble metal catalysts (platinum and rhenium) inthe catalytic reforming units that are subsequently used to upgrade the octane rating of the naphtha streams.

The industrial hydrodesulfurization processes include facilities for the capture and removal of the resulting

hydrogen sulfide (H2S) gas. In petroleum refineries, the hydrogen sulfide gas is then subsequently converted

into byproduct elemental sulfur or sulfuric acid (H2SO4). In fact, the vast majority of the 64,000,000 metrictons of sulfur produced worldwide in 2005 was byproduct sulfur from refineries and other hydrocarbonprocessing plants.[3][4]

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

Contents1 History2 Process chemistry3 Process description4 Sulfur compounds in refinery HDS feedstocks

4.1 Thiophenes5 Catalysts and mechanisms

5.1 Catalysts5.2 Supports

6 Other uses6.1 Hydrodenitrogenation6.2 Saturation of olefins6.3 Hydrogenation in the food industry

7 See also8 References9 External links

HistoryAlthough some reactions involving catalytic hydrogenation of organic substances were already known, theproperty of finely divided nickel to catalyze the fixation of hydrogen on hydrocarbon (ethylene, benzene)

17/07/2013 22:30Hydrodesulfurization - Wikipedia, the free encyclopedia

Page 2 of 7https://en.wikipedia.org/wiki/Hydrodesulfurization

double bonds was discovered by the French chemist Paul Sabatier in 1897.[5][6] Through this work, he foundthat unsaturated hydrocarbons in the vapor phase could be converted into saturated hydrocarbons by usinghydrogen and a catalytic metal, laying the foundation of the modern catalytic hydrogenation process.

Soon after Sabatier's work, a German chemist, Wilhelm Normann, found that catalytic hydrogenation couldbe used to convert unsaturated fatty acids or glycerides in the liquid phase into saturated ones. He wasawarded a patent in Germany in 1902[7] and in Britain in 1903,[8] which was the beginning of what is now aworldwide industry.

In the mid-1950s, the first noble metal catalytic reforming process (the Platformer process) wascommercialized. At the same time, the catalytic hydrodesulfurization of the naphtha feed to such reformerswas also commercialized. In the decades that followed, various proprietary catalytic hydrodesulfurizationprocesses, such as the one depicted in the flow diagram below, have been commercialized. Currently,virtually all of the petroleum refineries worldwide have one or more HDS units.

By 2006, miniature microfluidic HDS units had been implemented for treating JP-8 jet fuel to produce cleanfeed stock for a fuel cell hydrogen reformer.[9] By 2007, this had been integrated into an operating 5 kWfuel cell generation system.[10]

Process chemistryHydrogenation is a class of chemical reactions in which the net result is the addition of hydrogen (H).Hydrogenolysis is a type of hydrogenation and results in the cleavage of the C-X chemical bond, where C isa carbon atom and X is a sulfur (S), nitrogen (N) or oxygen (O) atom. The net result of a hydrogenolysisreaction 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 anexample, the hydrodesulfurization reaction can be simply expressed as

Ethanethiol + Hydrogen → Ethane + Hydrogen sulfideC2H5SH + H2 → C2H6 + H2S

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

Process descriptionIn an industrial hydrodesulfurization unit, such as in a refinery, the hydrodesulfurization reaction takes placein a fixed-bed reactor at elevated temperatures ranging from 300 to 400 °C and elevated pressures rangingfrom 30 to 130 atmospheres of absolute pressure, typically in the presence of a catalyst consisting of analumina base impregnated with cobalt and molybdenum (usually called a CoMo catalyst). Occasionally, acombination of nickel and molybdenum (called NiMo) is used, in addition to the CoMo catalyst, for specificdifficult-to-treat feed stocks, such as those containing a high level of chemically bound nitrogen.

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

17/07/2013 22:30Hydrodesulfurization - Wikipedia, the free encyclopedia

Page 3 of 7https://en.wikipedia.org/wiki/Hydrodesulfurization

Schematic diagram of a typical Hydrodesulfurization (HDS) unit in a petroleum refinery

The liquid feed (at the bottom left in the diagram) is pumped up to the required elevated pressure and isjoined by a stream of hydrogen-rich recycle gas. The resulting liquid-gas mixture is preheated by flowingthrough a heat exchanger. The preheated feed then flows through a fired heater where the feed mixture istotally vaporized and heated to the required elevated temperature before entering the reactor and flowingthrough a fixed-bed of catalyst where the hydrodesulfurization reaction takes place.

The hot reaction products are partially cooled by flowing through the heat exchanger where the reactor feedwas preheated and then flows through a water-cooled heat exchanger before it flows through the pressurecontroller (PC) and undergoes a pressure reduction down to about 3 to 5 atmospheres. The resulting mixtureof liquid and gas enters the gas separator vessel at about 35 °C and 3 to 5 atmospheres of absolute 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. The H2S-free hydrogen-rich gas is thenrecycled back for reuse in the reactor section. Any excess gas from the gas separator vessel joins the sourgas from the stripping of the reaction product liquid.

The liquid from the gas separator vessel is routed through a reboiled stripper distillation tower. The bottomsproduct 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. That sour gas is sent to the refinery's central gasprocessing plant for removal of the hydrogen sulfide in the refinery's main amine gas treating unit andthrough a series of distillation towers for recovery of propane, butane and pentane or heavier components.The residual hydrogen, methane, ethane, and some propane is used as refinery fuel gas. The hydrogensulfide removed and recovered by the amine gas treating unit is subsequently converted to elemental sulfurin a Claus process unit or to sulfuric acid in a wet sulfuric acid process or in the conventional ContactProcess.

17/07/2013 22:30Hydrodesulfurization - Wikipedia, the free encyclopedia

Page 4 of 7https://en.wikipedia.org/wiki/Hydrodesulfurization

Note that the above description assumes that the HDS unit feed contains no olefins. If the feed does containolefins (for example, the feed is a naphtha derived from a refinery fluid catalytic cracker (FCC) unit), thenthe overhead gas from the HDS stripper may also contain some ethene, propene, butenes and pentenes, orheavier components.

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

Sulfur compounds in refinery HDS feedstocksThe refinery HDS feedstocks (naphtha, kerosene, diesel oil, and heavier oils) contain a wide range oforganic sulfur compounds, including thiols, thiophenes, organic sulfides and disulfides, and many others.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.

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

When the process is used for desulfurizing diesel oils, the latest environmental regulations in the UnitedStates and Europe, requiring what is referred to as ultra-low sulfur diesel (ULSD), in turn requires that verydeep hydrodesulfurization is needed. In the very early 2000s, the governmental regulatory limits forhighway vehicle diesel was within the range of 300 to 500 ppm by weight of total sulfur. As of 2006, thetotal 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-containingheterocycles called thiophenes. Many kinds of thiophenes occur in petroleum ranging from thiophene itselfto more condensed derivatives called benzothiophenes and dibenzothiophenes. Thiophene itself and its alkylderivatives are easier to hydrogenolyse, whereas dibenzothiophene, especially its 4,6-disubstitutedderivatives, are considered the most challenging substrates. Benzothiophenes are midway between thesimple thiophenes and dibenzothiophenes in their susceptibility to HDS.

Catalysts and mechanisms

The main HDS catalysts are based on molybdenum disulfide (MoS2) together with smaller amounts of othermetals.[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 acoordinatively unsaturated site (CUS), also known as an anion vacancy. Substrates, such as thiophene, bindto 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, andhydrogenolysis. A simplified diagram for the cycle is shown:

17/07/2013 22:30Hydrodesulfurization - Wikipedia, the free encyclopedia

Page 5 of 7https://en.wikipedia.org/wiki/Hydrodesulfurization

Simplified diagram of a HDS cycle for thiophene

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 andmolybdenum are also highly active.[14] Aside from the basic cobalt-modified MoS2 catalyst, nickel andtungsten are also used, depending on the nature of the feed. For example, Ni-W catalysts are more effectivefor hydrodenitrogenation (HDN).

Supports

Metal sulfides are "supported" on materials with high surface areas. A typical support for HDS catalyst isγ-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 isan area of intense interest, since the support is often not fully inert but participates in the catalysis.

Other usesThe 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 in a processreferred to as hydrodenitrogenation (HDN). The process flow is the same as that for an HDS unit.

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

Pyridine + Hydrogen → Piperdine + Hydrogen → Amylamine + Hydrogen → Pentane + AmmoniaC5H5N + 5H2 → C5H11N + 2H2 → C5H11NH2 + H2 → C5H12 + NH3

and the overall reaction may be simply expressed as:

17/07/2013 22:30Hydrodesulfurization - Wikipedia, the free encyclopedia

Page 6 of 7https://en.wikipedia.org/wiki/Hydrodesulfurization

Pyridine + Hydrogen → Pentane + AmmoniaC5H5N + 5H2 → C5H12 + NH3

Many HDS units for desulfurizing naphthas within petroleum refineries are actually simultaneouslydenitrogenating to some extent as well.

Saturation of olefins

The hydrogenolysis reaction may also be used to saturate or convert olefins (alkenes) into paraffins(alkanes). 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 → PentaneC5H10 + H2 → C5H12

Some hydrogenolysis units within a petroleum refinery or a petrochemical plant may be used solely for thesaturation of olefins or they may be used for simultaneously desulfurizing as well as denitrogenating andsaturating 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 liquidvegetable fats and oils to convert them into solid or semi-solid fats, such as those in margarine andshortening.

See alsoClaus processHydrogen pinchTimeline of hydrogen technologies

References1. ^ Gary, J.H. and Handwerk, G.E. (1984). Petroleum Refining Technology and Economics (2nd Edition ed.). Marcel

Dekker, Inc. ISBN 0-8247-7150-8.2. ^ Hydrodesulfurization Technologies and Costs (http://www.theicct.org/documents/Yamaguchi_Mexico_2003.pdf)

Nancy Yamaguchi, Trans Energy Associates, William and Flora Hewlett Foundation Sulfur Workshop, Mexico City,May 29–30, 2003

3. ^ Sulfur production report (http://minerals.usgs.gov/minerals/pubs/commodity/sulfur/sulfumcs06.pdf) by the UnitedStates Geological Survey

4. ^ Discussion of recovered byproduct sulfur (http://www.agiweb.org/geotimes/july03/resources.html)5. ^ C.R.Acad.Sci. 1897, 132, 2106. ^ C.R.Acad.Sci. 1901, 132, 2107. ^ DE Patent DE141029 (Espacenet, record not available) (http://v3.espacenet.com/textdoc?

DB=EPODOC&IDX=DE141029&F=0)8. ^ UK Patent GB190301515 GB190301515 (Espacenet) (http://v3.espacenet.com/textdoc?

17/07/2013 22:30Hydrodesulfurization - Wikipedia, the free encyclopedia

Page 7 of 7https://en.wikipedia.org/wiki/Hydrodesulfurization

DB=EPODOC&IDX=GB190301515&F=0)9. ^ Microchannel HDS (March 2006) (http://www.greencarcongress.com/2006/03/microchannel_de.html)

10. ^ Fuel cells help make noisy, hot generators a thing of the past (December 2007) Pacific Northwest NationalLaboratory (http://www.pnl.gov/topstory.asp?id=282)

11. ^ Diesel Sulfur (http://www.npradc.org/issues/fuels/diesel_sulfur.cfm) published online by the NationalPetrochemical & Refiners Association (NPRA)

12. ^ Topsøe, H.; Clausen, B. S.; Massoth, F. E., Hydrotreating Catalysis, Science and Technology, Springer-Verlag:Berlin, 1996.

13. ^ Daage, M.; Chianelli, R. R., "Structure-Function Relations in Molybdenum Sulfide Catalysts - the Rim-EdgeModel", J. of Catalysis, 1994, 149, 414-427.

14. ^ Chianelli, R. R.; Berhault, G.; Raybaud, P.; Kasztelan, S.; Hafner, J. and Toulhoat, H., "Periodic trends inhydrodesulfurization: in support of the Sabatier principle", Applied Catalysis, A, 2002, volume 227, pages 83-96.

15. ^ Kinetics and Interactions of the Simultaneous Catalytic Hydrodenitrogenation of Pyridine andHydrodesulfurization of Thiophene (https://dspace.mit.edu/bitstream/1721.1/27892/1/03740017.pdf) (John Wilkins,PhD Thesis, MIT, 1977)

16. ^ Simultaneous Catalytic Hydrodenitrogenation of Pyridine and Hydrodesulfurization of Thiophene(http://pubs.acs.org/cgi-bin/abstract.cgi/iepdaw/1980/19/i01/f-pdf/f_i260073a027.pdf?sessid=6006l3)(Satterfield,C.N., Modell, M. and Wilkens, J.A., Ind. Eng. Chem. Process Des. Dev., 1980 Vol. 19, pages 154-160)

External linksCriterion Catalysts (http://www.criterioncatalysts.com) (Hydroprocessing Catalyst Supplier)Haldor Topsoe (http://www.topsoe.com) (Catalyzing Your Business)Albemarle Catalyst Company (http://www.albemarle.com/Products_and_services/Catalysts/)(Petrochemical catalysts supplier)UOP-Honeywell (http://www.uop.com/refining/1060.html) (Engineering design and construction oflarge-scale, industrial HDS plants)Hydrogenation for Low Trans and High Conjugated Fatty Acids(http://members.ift.org/NR/rdonlyres/27B49B9B-EA63-4D73-BAB4-42FEFCD72C68/0/crfsfsv4n1p00220030ms20040577.pdf) by E.S. Jang, M.Y. Jung, D.B. Min,Comprehensive Reviews in Food Science and Food Safety, Vol.1, 2005Oxo Alcohols(http://www.akerkvaerner.com/Internet/IndustriesAndServices/Process/Petrochemicals/ChemicalImtermediates/OxoAlcohols.htm) (Engineered and constructed by Aker Kvaerner)Catalysts and technology for Oxo-Alcohols (http://www.jmcatalysts.com/pct/marketshome.asp?marketid=10&id=373)

Retrieved from "http://en.wikipedia.org/w/index.php?title=Hydrodesulfurization&oldid=544244164"Categories: Chemical engineering Oil refining Chemical processes Unit processes

This page was last modified on 15 March 2013 at 01:23.Text is available under the Creative Commons Attribution-ShareAlike License; additional terms mayapply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.