Pct 7 Petroleum Processing (Book)

7/28/2019 Pct 7 Petroleum Processing (Book)

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petroleumprovidesprecursors or the world's petrochemicalndustries' Atthe end of 2003, he world was consuming78 million barrelsof oil per day.5In August 2005, hat volume of petroleumwas worth $4'6 billion per day'or $1.7 rill ion PerYear.Table1. Histo of PetroleumBefore 1861Date3000BC

1500 C600BC600-500 C

1200-1300D1500-1600D1735 DEarly1800s1847

I 848I 8491854I 857I 858

1 59

I 859I 860-6

Sumerians use asPhalt asMesopotamiansuse bitumen toroads. Egyptians use Pitch to

Descriptionan adhesive for makingline water canals,seal boats,srease chariot wheels, and

mosaics.and buildasphalt toembalmmummies.The chinese usepetroleum or lampsand for heatinghomes.Confucius writes abbut the drilling of 100-foot (30-meter) natural gaswells in china. The chinesebuild pipelines or oil usingbamboopoles.Arab and Persianchemistsmix petroleumwith quicklime to make Greekfire, the napalmof its daY.The Persiansmine seepoil nearBaku (now in Azerbaijan)'Seep oil from the CarpathianMountains is used in Polish street amps'the chinese dig oi l *.llr Ino.. than 2000 feet (600 meters)deep.Oi l is extracted rom oi l sands n Alsace,France'Oi l is produced n United States rom brine wells in Pennsylvania'JamesOakesbuilds a'orockoil" refinery n Jacksdale, ngland.6 he unitprocesses300 gallons per day to make "paraffin oil" for lamps. JamesYoung builds a coal-oil refinery in Whitburn, Scotland''F .N.Semyenovdr i l l s thef i rs t. .modern, 'o ilwe l lnearBaku 'CanadiangeologistAbraham Gesnerdistills kerosene rom crude oil'Ignacy I-u-tasiewiczdrills oi l wells up to 150 feet (50 meters) deep atB6brka, Poland.Michael Dietz inventsa flat-wick kerosene amp (Patent ssued n 1859)' ^Ignacy Lukasiewiczbuilds a crude oi l distil lery in Ulaszowice,Poland'8T;he first oi l well in North America is drilled near Petrolia, Ontario,Canada.colonel Edwin L. Drake triggers the Pennsylvaniaoi l boom by drilling awell near Titusville, Pennsyivania hat was 69-feet deepand produced35barrels-per-day.An oil refinery is built in Baku (now in Azerbaijan)'Oil refineries are built near Oi l Creek, Pennsylvania;Petrolia, Ontario,Canada;ndUnionCountY. rlqryes.

So what happened n 1859?What beganthe transformationof petroleumfrom a conveniencento the world's primary sourceof energy?As often is thecasewith major socioeconomic hifts, he move towardoil was nstigatednotby just a singleevent,but by the uxtapositionof several:. In the 1850s,most home-basedampsburnedwhale oil or other animalfats. Historically, whale-oil priceshad always fluctuatedwildly, but theypeaked n the *ia-r850s due to the over-huntingof whales;by somef stimates,n 1860several pecieswere almostextinct.Whale oi l sold foran averageprice of US$L77 per gallon between 1845 and 1855' Incontrast,ard oil sold for aboutUS$0.90per gallon.e'r0ard oil was moreabundant, ut it burnedwith a smoky,smelly flame'


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"When oil first started lowing out of the wells in westernPennsylvanianthe 1860's,desperate il men ransackedarmhouses,arns,cellars,stores, ndtrashyards for any kind of barrel - molasses, eer,whiskey, cider, turpentine,sale, ish, andwhateverelsewashandy.But as coopers egan o make barrelsespecially or the oil trade,onestandard izeemerged, nd hat sizecontinuesto be thenorm to the present. t ts 42 gallons."The numberwas borrowed from England,where a statute n 1482 underKing Edward IV established 2 gallonsas the standardsizebarrel for herringin order to endskullduggeryand"divers deceits" n the packing of fish. At thetime, herring fishing was the biggestbusiness n the North Sea.By 1866,sevenyears after Colonel Drake drilled his well, Pennsylvaniaproducersconfirmed the 42-gallonbarrel as their standard,as opposed o, say, the 3lt/zgallon wine barrel or the 32 gallon London ale barrel or the 36 gallon Londonbeerbarrel."In sharpcontrast o the situation oday, n 1870America was the world'sleadingoil producer,and oil was America's 2nobiggestexport."Agriculturalproducts were first, accounting for 79% of exports that were worth, onuu.rug.,US$573million peryear rom 1870 o 1879.14espite heravages fthe U.S.Civil War, the main agriculturalexportwasstill "King Cotton."

What Is Petroleum?Before we go on to talk about petroleumprocessing, t is important toknow something about petroleum itself. Petroleum is called a fossil fuelbecauset is formed from the bodiesof ancientorganisms primarily one-celled plants and animals (seeChapter2). Contrary to modern myth, only atiny fraction (if any) of the molecules n crude oil are from dinosaurs.Whenthesecreaturesdied, their remainsaccumulatedat bottomsof ancient akesor

seas,along with sand and other sediments.Over time, a combinationofpressure,heat,and bacterialaction transformed he deposits nto sedimentaryrock. The incorporated organic matter was transformed into simplerchemicals,such as hydrocarbons,water, carbon dioxide, hydrogen sulfide,andothers.The chemicalsdidn't alwaysstayput. If the surrounding ock wasporous,liquids and gasescould migrate, either up to the surfaceor into a reservoir(Figure 2) that was cappedby impermeable ock or a dome of salt. Today,when petroleum geologists look for oil, they actually are looking forstructureshat might be traps or liquid hydrocarbons.

1.2


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that light crudes thosewith high API gravities)often contain esssulfur andnitrogenthanheavycrudes,but not always.Table2. Properties f 21 SelectedCrudeOils

Specific SulfurCrude Oi l API GravityT Gravity (wto/o) Nitrogen(wl%LAlaskaNorth SlopeArabian LightArabian MediumArabian HeavyAthabasca Canada)Beta(California)Brent (North Sea)Bonny Light (Nigeria)Boscan Venezuela)Ekofisk (Norway)Henan(China)HondoBlend (California)Kern (California)Kuwait ExportLiaohi (China)\Maya (Mexico)Shengli China)TapisBlend (Malaysia)West Hackberry Sweet*West TexasIntermediateXiniiang (China)

26.233 . 830.428.08t6.238.335.4t0.231.7t6.420.813 . 631.417.922.213 . 845.9a 1 1J I . J39.620.5

0.89730.85600.87400.88711 . 01430.95800.83330.84780.99860.83630.9s67092910.97520.86860.94710.92060.97380.79760.83830.82700.9309

l . l1 . 82 .62 .84 .83 . 60 .370 . 145.30.250.324.31 . 12 .50.263.40.820.030.320.340 . 1 5

0.20.070.090 . 1 50.40 . 810 . 1 00 . 100.650 . 1 00.140.620.70 . 210.410.320.72nil0 . 1 00.080.35* Produced rom a storagecavern n the U.S. StrategicPetroleumReserveI ,qpt Gravity is related o specificgravity by the formula:oAPI 141 5+ (specif ic ravi ty@ 60'F) - 131 5

45555API Cravity

O SulfurContent NitrogenContentFigure -1.Sulfur andnitrogen versusAPI gravity for selected rude oils


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Tables 3 and 4 show that isomers have different physical properties.rsThey also can have significantly different chemicalproperties.For gasoline,one of the most important chemicalproperties s octanenumber.The researchoctanenumber (RON) for n-octane is -27 compared o a RON of 100 (bydefinition) for isooctane 2,2,3-trrmethylpentane). or heptane somers,RONvaluesrangefrom 45 for 2-methyl-hexane o >100 for 2,2,3-trtmethylbutane,compared o zero by definition) for n-heptane.Octanenumbersare discussedin moredetail n Section8.2.Table-1.Boiling Pointsof SelectedLight ParaffinsFormula Boilins Point Boilinp PointMethaneEthane

CH+CzHo-2s9.9-127.4-43.7

- t62.2-88.6-42.1

n-ButaneIsobutaneCC+Hro -0 .1-tt.23t.7I 1 . 9

n-PentaneIsopentaneH

CsHrzCsHrz96.982.349.0

36 . 128.09.5eopentanen-OctaneIsooctane

Hexadecane5-Methylpentadecane

The melting points of paraffin isomers also can differ significantly. Asshown n Table 5, long-chainn-paraffinsmelt at relatively high temperatures,while their branched-chainsomersmelt at lower temperatures. his explainstheir different behaviours as lubricants. Long-chain norrnal paraffins arewaxy, so as lubricants they are terrible. Conversely, so-paraffins with thesamenumberof carbonsare excellent ube basestocks.Table4. FusionPoints or SelectedC16Paraffins.Name Formula Melting Point ("F) Melting Point (oC)

C.HCsHrsC

CroH:qCroH:+

258.02 t 0 . 7

64.1-29.s- t23 . r

t25.699.3

17.9-34.27.8 D methvltetradecane CroH:q

1.2.1.2 Aromaticsand NaPhthenesAromatics and naphthenes re also found in petroleum.Aromatics containone or more unsaturated5 to 6-carbonrings. In naphthenes, arbonrings are

saturatedwith hydrogen.Figure J showsstructures or a few of the aromaticsand naphtheneshathave been found in crude oils. For aromaticswith one six-carbon ing, thegeneral formula is CnHzn-6,fld for naphtheneswith one ring, the generalformula is CnH2n.


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--S-.- .CH,HrC' -CH, -CH,

methypropylsulfide

H2C-CH2CrHo

ethylene

HrC\ .zCHs\c 'CH.

coHuisobutene

"CHHrcT -cH.

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-CH -Ch^Hrc/ - \crf - . ' 'CoHu

trans-2-butene

H"Cv - v l I/ \H.C CHrCuH',0

isopentene

nlnrV\Nl,qu ino l ine

dibenzothiophene

-7\'v^t l \ t Il \ ) t It\7\*AoH

2(1H)quinol in-one

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M\ | t vt\/\N-^\7H

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Vanadium-containingorphyrinR = -CH ., -CrH' etc.

Figure 6. Hetero-atom compounds found in crude oil

-c{._ .cHzH.C- \CH -CH,crH,o

trans-2-pentene

Figure 7. Selected ight olefins

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t 2Table5. SignificantEvents n PetroleumProcessing,86l - 2000Description1878 ThomasEdison nvents he ight bulb. The useof keroseneampsstarts o decline.1889 GottliebDaimler,Wilhelm Mayback and(separately) arl Benzbuild gasoline-poweredautomobiles.1901 RansomE. Olds beginsassembly-line roductionof the CurvedDashOldsmobile.1908 Ford Motor CompanyoffersModel T's for US$950each.l9l2 William Burton and Rober t Humphreysdevelop hermalcracking.l9l3 Guif Oil builds he world's first drive-in il l ing station n Pittsburgh,Pennsylvania.l9l9 UOP commercializeshe Dubbs hermalcrackingprocess.1929 StandardOil of Indiana(now BP) commercializes he Burton process or delayedcoking at Whiting, Indiana.1933 UOP introduces he catalyticpolymerizationof olefins to form gasoline.1934 EugeneHoudry, working for Sun Oil, patentsHoudry Catalytic Cracking (HCC).1938 A consortium f refinersdevelops ulfuric acid alkylation,which is first

commercializedat the Humble (now ExxonMobil) refinery in Baytown, Texas.1940 Phill ipsdevelopsHF alkylation.1942 StandardOil of New Jersey now ExxonMobil) commercializeshe FCC process tBatonRouge,Louisiana.1949 Old Dutch Refining in Muskegon, Michigan starts he world's first catalytic reformerbasedon the UOP Platformingprocesses.1950 Catalytic hydrotreating s patentedby Raymond Fleck and Paul Nahin of Union Oil.1960s UOP introducesCa and C5lC6somerization rocesses.196l StandardOil of California (now Chevron) ntroducescatalytic hydrocracking.1970 The world celebratesEarth Day. The newly createdU.S. EnvironmentalProtection

Agencypasseshe CleanAir Act, which requiresa 90o/oeduction n autoemissionsby 197 . The EuropeanUnion issuessimilar requirements.1972 Mobil inventsZSM-5. During the next hreedecades,his shape-selectiveatalystfindsuses n numerous rocesses,ncludingFCC, catalyticdewaxing,and he

conversion f methanol o gasoline.1975 The catalyticconvertergoescommercial.The phase-outof tetraethyl eadbegins.1990 The U.S. Congressssueshe CleanAir Act Amendments f 1990,which lay theframework for reformulatedgasolineand ow-sulfur diesel.1990s Severalprocesses re developed o remove sulfur from gasoline.These ncludeSCANfining (Exxon), OCTGAIN (Mobil), Prime G (Axens), and S Zorb (Phillips).1993 Chevron commercializes sodewaxing or converting waxy paraffins nto high-qualitylube basestock.2000 The EuropeanCommission ssues he Auto Oil il report,which includesa timetablefor low-sulfur easolineand ultra-low-sulfur diesel.

In 1914, JesseA. Dubbs and J. Ogden Armour founded the NationalHydrocarbonCompany,which later becameUniversal Oil Products UOP).20UOP grew to become he world's largest icensorof process echnology orthe oil refining industry. n 1919,UOP commercialized he Dubbs process,which solved some of the problems associatedwith the Burton-Humphreysprocess.The Dubbs processproduced ewer coke deposits, t could processheavierpetroleum ractions,and t ran longerbetweenshutdowns.StandardOil of Indiana commercrahzed he delayed coking processatWhiting, Indiana n 1929.In 1933,UOP commercialized he conversionofolefins to gasolinevia catalyticpolymerizatron.Later in the 1930s, efinersbeganusing tetraethyl ead to boost the octaneof gasoline.A consortiumof


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controls (including catalytic converters)on diesel-powered ars and trucks.Refinersarerespondingby installing additionalhydrotreatingcapacity.

1.4 Modern PetroleumProcessingAll refineriesare different. They have different histories, ocations,andmarketdrivers.Therefore, o single llustrationcancaptureal l of the possiblecombinationsand permutationsof the processeshat fit together o comprisean oil refinery.But despite heir differences,mostrefineriesperform he sevenbasicoperations amed n Table6.

Zable 6. SevenBasic Operations n PetroleumProcessingSeparationo Distil lation. SolventrefiningConversiono Carbon removalo Hydrogen additionReforming

o Catalytic reformingo Steam/hydrocarboneformingRearrangement

Combinationo Catalytic polymerization. AlkylationTreating, finishing, blendingo Gasoline, erosene nddieselo Lubes andwaxes. AsphaltProtecting the Environmento Waste water treatmento Disposalof solidso Isomerization Sulfur ecoFigure 8 shows a simplified layout for a high-conversion efinery in theUnited States. The diagram doesn't show product blending and sulfurrecoveryunits, but theseare almostalwayspresent.Lube-oil processing ndhydrogenproductionunitsalsomay be present.The depictedplant is configured for maximum fuels production. In atypical European efinery, the coker would be replacedwith a visbreaker. n

many Asian refineries,wheredieseldemand s higher than gasolinedemand,the coker would be replacedby a visbreakerandthe FCC by a hydrocacker.The rest of this chapterprovidesa brief overviewof the processes hownor mentioned above. The chapters that follow p.rovidedetailed processdescriptions,with emphasis n recentdevelopments.General nformationonrefining technologycan be found in the excellentbooks by E.I. Shaheen,22and W.L. Leffler,23and in a manual publishedby the U.S. OccupationalSafety and Health Administration.2aEach year, Hydrocarbon Processingcompilesa widely read refining processhandbook,which gives descriptionsof about 120 licensed processesoffered by engineeringcontractors,oilcompanies, nd of courseprocessicensors.25


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16suspended olids. n chemicaldesalting,water and surfactants re added o thecrude,heated o dissolvesaltsand other impurities, and then sent o a settlingtank wherethe water and oil separate.n electrostaticdesalting,chemicalsarereplacedwith a strong electrostaticcharge,which drives the separationofwater from oil.

LPG, Propane

Light Naphtha

Desalter

HeavyNaphthaLightGasOil

HeavyGasOilVacuumGasOil

AtmosphericDistil lationUnit

VacuumResidueVacuumDistil lationUnit

Figure 9. Crudedistillation

Modern crude distillation towers can process200,000banels of oi l perday. They can be up to 150 feet (50 meters) tall and contatn 20 to 40fractionation rays spacedat regular ntervals. n some owers,the trays in thetop sectionarereplacedwith structuredpacking.Before reaching he tower, desaltedoil goes hrougha network of pre-heatexchangerso a fired heater,which brings the temperatureup to about 650"F(343'C). If the oil gets much hotter that this, it starts o crack and depositcarbon nside the pipes and equipment hroughwhich it flows. The hot crudeenters he distitlation tower just above he bottom. Steam s added o enhanceseparation;t doesso largely by decreasing aporpressuren the column.When hot oil enters he tower, most of it vaporizes.Unvaportzedheavyfuel oil andlorasphaltresiduedrops to the bottom of the tower' where it isdrawn off. The vapors rise through the distillation trays, which containperforationsand bubble caps (Figure 10).Each tray permits vapors frombelow to bubble hrough he cooler,condensediquid on top of the tray.This

Crude Oi l


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Table Z. Destinations for Straisht-Run Distillates

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Approx. Boiling RangeFraction oC oF

NextDestination UltimateProduct(s)LPGLight NaphthaHeavy NaphthaKeroseneGasOi lVacuum Gas Oil

-40 o 0 -40 o 313 9 - 8 5 8 0 - 1 8 s85 200 185 390t70 270 340 515180 340 350 6s0340 566 650 1050

SweetenerHydrotreaterCat. ReformerHydrotreaterHydrotreaterFCCHydrotreaterLube PlantHydrocrackerCokerVisbreakerAsphalt UnitHydrotreater

Propane uelGasolineGasoline,aromaticsJet uel, No. I dieselHeatingOil, No. 2 dieselGasoline, CO, gasesFuel oil, FCC feedLube basestockGasoline,et, diesel,FCCfeed, ube basestockCoke,cokergasoilVisbreakergasoil, residDeasphalted il, asphaltFCC feed

Vacuum Residue >540 >10 0 0

Table 8 shows that straight-runyields from various crude oils can differsubstantially. he naphtha ontentof Brent is twice as high asRatawi,and tsvacuumresiduecontent s 60oh ower. Bonny Light yields the most middledistillateand he eastvacuum esidue.Iable 8. Typical Straight-runYields from Various Crudes26'27Source fieldCountry

Brent Bonny Lt. Green Canyon RatawiNorway Nigeria USA Mid East

API gravitySpecificgravitySulfur, wto%

38.30.83330.37

35.40.84780 . 14

30.0.87522.00

24.60.90653.90

Yields. wtTo feedLight endsLight naphthaMedium naphthaHeavy naphthaKeroseneAtmosphericgasoi lLight vcoHeary VGOVacuum residue

z . )6.3t4.49.49.91 5 .t 7 . 6t2 .7t2.3

1 . 53.914.49.4t2.s2 r . 620.710 . 55 . 5

1 . 52.88.55.68.5t 4 . l18 . 314.626 . 1

l . l2 .88 .05 . 07.410 . 6t7.215 . 032.9

Total naphthaTotal middle distillate

30.25.0

27.734.1

16.922.6

r5 .818 .0

Atmosphericdistillationof the best crudesyields about 60% naphthaplusmiddle distillates kerosene nd gasoil), but the average s closer o 40Yo.Incontrast,Table 9 shows hat during 199l-2003, he United States onsumed,on average,70yo of its petroleum as gasolineand middle distillates.This


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In traditional solventdeasphalting, esidualoil andpropanearepumped oan extractionower at 150 o 250'F (65 to 120'C) and350 to 600psig (2514to 4240 kPa). Separation ccurs n a tower, which may have a rotatingdisccontactor(Figure 11). Liquid productsare evaporatedand steam stripped torecover hepropane olvent,which is recycled.An advanced ersionof solventdeasphaltings "residuumoil supercriticalextraction," or ROSE. The ROSETMProcesswas developedby the Kerr-McGee Corporationand now is offered for licenseby KBR EngineeringandConstruction,, subsidiaryof Halliburton. n this process,he oil and solventare mixed and heated o abovethe critical temperatureof the solvent, wherethe oil is almost totally insoluble.Advantages nclude higher recovery ofdeasphaltediquids, ower operatingcostsdue to improvedsolvent ecovery,and improved energy efficiency. The ROSE process can employ threedifferentsolvents, he choiceof which depends ponprocess bjectives:Propane: Preparation f lubebasestocksButane: AsphaltproductionPentane: Maximum recoveryof liquid2.2.2 SolventExtraction

Solventextraction s used o removearomaticsand other mpurities romlube andgrease tocks.The feedstocks dried, hencontactedwith the solventin a counter-current r rotating disk extractionunit (F;gure I 1). The solvent sseparated rom the product streamby heating, evaporation,, r fractionation.Remaining racesof solvent are removed rom the raffinateby steamstrippingor flashing.Electrostatic recipitatorsmay be used o enhance eparation finorganiccompounds. he solvent s thenregeneratedndrecycled.

SolventEvaporator

Raffinate(lubeoil)Extractand

SolventxtractedaromaticsFigure 11. Rotating-disksolventextraction


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Robinson22carbon is removed from every molecule. Rather, it means that heavymoleculesare split ("cracked") into a smallermoleculewith a higher H/C andanother smaller molecule with a lower HlC. Molecules with low H/C -polyaromatichydrocarbons PAH) - can condense o form coke (Figure l2).^Cond.ntationreactions elease ydrogen,oweringH/C evenmore'3.1 Visbreaking

Visbreaking is a mild form of thermal cracking that achievesabout 15%conversionof atmospheric esidue o gas oils andnaphtha.At the same ime' alow-viscosity esidual uel is produced.Visbreakingcomes n two basic flavors

- "short-contact"and "soaker." Inshort-contact isbreaking, he feed s heated o about900'F (480'C) and sentto a "soaking zone" (reactor)at 140 to 300 psig (1067 to 2110 kPa). Theelevatedpressureallows cracking to occur while restricting coke formation.To avoid over-cracking, he residence ime in the soakingzone is short -severalminutescompared o severalhours n a delayedcoker- andthe hot oilis quenchedwith cold gasoil to inhibit further crackingand sent o a vacuumtower for product separation."Soaker" visbreaking keeps the hot oil atelevated temperature for a longer time to increase the yield of middledistillates.The low-viscosityvisbreakergas oil canbe sent o an FCC unit orhydrocracker or further processing, f usedasheavyfuel oil'3.2 Coking

Coking processes ome in two basic forms - delayedcoking,which is asemi-batch rocess, nd luid-bedcoking,which is continuous'3.2.1 DelaYedCoking

In a delayedcoker,vacuumresidue eed is heated o about900 to 970"F(4gj to 520"C) and sentto a largecoke drum. Cracking begins immediately'generatingcoke and cracked,vap orizedproducts. Coke staysbehind in thed-* while the vapors ise to the top andflow to the product fractionator.Liquid products nclude coker naphtha, ight coker gas oil (LCGO), andheavy-cokergas oil (HCGO). A11of these equire further processingdue totheir high olefins content,which makes hem unstableand poorly suited fordirect blending into finished products. The coker naphtha and LCGO arehydrotreated.The HCGO cango eitherto an FCC unit or a hydrocracker.


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24 Robinson

coke rapidly grow due to the heat produced by asphaltenepolymerization,producingdiscretemini-balls 0.1 to 0.2 inches 2 to 5 mm) in diameter. n thecenterof the drum, the mini-balls can stick together o form clustersas largeas 10 inches(25 cm). On occasion,a clusterbreaks apartwhen the coke drumis opened, spraying a volley of hot mini-balls in every direction. Addingaromatic feeds, such as FCC decantoil, can eliminate shot coke formation.Other methodsof eliminating shot coke - decreasing emperature, ncreasingdrum pressure, ncreasing the amount of product recycle - decrease iquidyields,which is not desired.A quantitativemeasureof the quality of coke is the coefficient of thermalexpansion CTE). A low CTE means hat the product has a low tendency oexpandwhen heated.Rangesof CTE for the three major types of petroleumcokeareshown n Table I I .Table 11. Coefficientsof Thermal Ex nsion for PetroleumCoke Products

CTE (cm/cm/oCx 10-')NeedlecokeSpongecokeShotcoke

0 t o 48 o 18>20Shot coke cannot be used in making anodes for aluminum production,because he outer layer of a shot spherehas a very low CTE while the insidehasa very high CTE. When rapidly heated, he interior expands,crackingtheouter layer like an egg shell. Consequently,n aluminum smelters,shot-cokeanodesquickly turn to dust.Otherspecialtycarbonproductsmade rom petroleum ncluderecarburizercoke,which is used o makespecialtysteel,and itanium dioxide coke,which isusedas a reducingagent n the titanium dioxide pigment industry.2e

3.2.2 Fluid CokingFluid coking, also called continuouscoking, is a moving-bedprocess orwhich the operating temperature s higher than the temperaturesused fordelayed coking. In continuous coking, hot recycled coke particles arecombined with liquid feed in a radtal mixer (reactor) at about 50 psig (446kPa). Vapors are taken from the reactor, quenched to stop any furtherreaction,and fractionated.The coke goes o a surgedrum, then to a classifier,

where the larger particlesare removedas product. The smallercoke particlesare recycled to a preheater,where they mix with fresh feed. Coking occursboth in the reactorand n the surgedrum.Installation costs for fluid coking are somewhathigher than for delayedcoking,but feedscan be heavierand heat ossesare ower.


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specific information on the manufactureand use of catalystsused for FCCandother efiningprocesses.The cracking reaction s very fast. It produces ight gases,high-octanegasoline,and heavierproductscalled light cycle oil (LCO), heavy cycle oi l(HCO), slurry oil, and decantoil. It also eavesa layer of cokeon the catalystparticles,making hem nactive.At the top of the riser, the temperature an reach900 to 1020"F(482 to549'C). The temperatureat the riser outlet is a key factor in determiningconversionand product selectivity, SoFCC operatorscontrol it as tightly aspossible.Higher temperaturesavor productionof olefin-rich ight gasat theexpenseof gasoline,moderate emperaturesavor gasolineproduction, and atlower temperaturesasoline ieldsdecreasen favor of middle distillates.

In the disengagingsection, steam is used to help separate he now-deactivatedcatalyst from the reaction products.The catalyst goes to theregenerator,where the coke is burned away by fluidized combustion in thepresence f air. The hot catalystat temperaturesp to 1350'F (132"C) returnsto theriser/reactor, here hecycle beginsagain.In a 60,000 banels-per-dayunit processinga typical mixture of vacuumgas oils, the total catalyst n the unit (the "inventory") is 400 to 500 tons. Tomaintain activity, about0.5 to I wtoAof the inventory is replacedeachday. Ifthe feed to the unit containssignificant amounts of residue, he replacementrate is higher.The discharged atalyst s cooledand shippedeither o a landfilI for disposal or to another refiner, which may have a particular use for"conditioned"FCC catalvst.3.3.2 Heat Balance

FCC units must be heat-balanced, r they won't run. Understandingheatbalance s the key to understanding ow FCC variables nteract.The burningof coke in the regeneratorprovides all of the heat required by the process.Table 3 givesa representativereakdownof FCC heat equirements.Table 13. Breakdownof FCC Heat ReHeat-ConsumingEvent Percent of TotalHeatup and vaporize resh feedHeat ecycledoi lHeatof reaction(endothermic)Heat steamHeat ossesHeat air to regeneratoremperatureHeat coke from the reactor o regenerator emperature

40-50%0- r0%t5-30%2-8%2-5%15-25%r-2%Total Heat Duty 500-1000 tr/lbl160-2325 J/ke


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28 Robinson

3.3.4 ResidueFCCMany modernFCC units are designed o processsignificantamountsof

vacuum residue.Theseunits use catalystcoolers(e.g., steamcoils) in theregenerator r a second egeneration one to remove excessheat from theunit. This is because acuumresiduegenerates ubstantiallymore coke thanconventionalFCC feeds,and excess eat s generatedwhen the extracoke sburnedaway from catalYst.In vacuum esidue, he metalscontentcanbe very high - sometimesmorethan 200 wppm nickel-plus-vanadium.n an FCC unit, thesemetalsare badnews.Nickel increases okeformationanddecreasesiquid yields. Vanadiumreducesconversion,decreasesiquid yields, and destroys he catalyst.Forthesereasons, efinerspretreat he residue n a hydrotreaterbefore sending ton to the FCC.In addition o removingmost of the Ni and V, the pretreater ecreasesheconcentrationof sulfur, nitrogen,and aromatics. n the FCC, part of the feedsulfur endsup in liquid productsand part endsup as sulfur oxides(SOx) inthe flue g&S,so removing sulfur from the feed is beneficial. Removingnitrogen s beneficialbecauseeed nitrogensuppressesCC catalystactivity.Saturatingeed aromaticsncreases CC conversion y asmuch as l0 volo/o.This alonecan ustify the costof building the pretreater.3.4 Hydrotreating and Hydrocracking

A modern petroleumrefinery may have four or more hydrotreatingunits.Strictly speaking,hydrotreatersare not conversionunits becausehe breakingof carbon-to-carbononds s minimal. However, t is convenient o discusshydrotreating together with hydrocracking and mild hydrocracking becausethey employsimilarcatalysts ndprocess low schemes.The key differencesare presented n Table 14. Hydrocrackers end tooperateat higher pressure,using different catalysts,and with lower linearhourly space elocity (LHSV). LHSV is equal o the volumeof feedper hourdivided by the catalystvolume.A lower requiredLHSV means hat a givenvolume of feed requiresmore catalyst. n terms of processconditionsandconversion,mild hydrocracking ies somewherebetweenhydrotreatingandfull-conversion ydrocracking.


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Hydrotreating is exothermic (heat-releasing),,o many commercial unitscompriseseveralcatalystbedsseparated y quenchzones. n a quenchzone,hot process luids from the precedingbed are mixed with relatively cold,hydrogen-rich uenchgasbeforepassing o the nextbed.RecycleGasCompressor

Make-upCompressor

High-PressureAmine Absorber

To GasPlant

Low-PressureSeparatorAir Cooler

WashWater NH*SH(aq)To Stripper,Fractionator

Figure 14. Gas-oil hydrotreatingand once-throughhydrocracking

HDS andHDN reactions roduceHzS andNH:, respectively.Washwateris injected into the effluent from the last reactor to remove ammonia,whichgoes into the aqueousphase as ammonium bisulfide, NH+HS(aq).TheNH+HS(aq) s rejected rom the unit as sourwater in downstream lash drums.In the high-pressure lash drum, liquid products are separated rom thehydrogen-richgas,which is recycled to the reactors. n most hydrotreatersdesigned or deepdesulfurization,H2S s removed rom the recyclegaswith ahigh-pressureamine absorber.The liquids go to a stripping column, whichremovesentrainedHzS and other light gases.These go to a low-pressureamineabsorberandthen to eithera gasplant or the refinery fuel-gassystem.

High-PressureSeparator


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34 Robinson

3.4.8 Hydrocracker ProductsMiddle distillates fiet and diesel) from high-conversion hydrocrackersmeetor exceed inishedproductspecifications. he heavynaphtha,however,usually goes o a catalytic reformer for octane mprovement.The fractionatorbottoms from partial conversionunits can be sentto an FCC unit, an olefinsplant, or a lubePlant.Due to the fact that productsfrom a hydrocrackerare lessdense han thefeeds, he total volume of liquid products s greater han the feed volume by10 o 30 vol%. This phenomenons calledvolumeswell.

Table 17. Hydrocracking n a Nutshel!Pu Convert heaw hydrocarbons into lighter hydtqgqllgrtg

FCC feed Lube basestockUses or UnconvertedOi l

Other ReactionsOlefin plant feed Recvcle o extinction

Nitrogenremoval (HDN)Aromatic saturationSulfur removal (HDS)Olefin saturationLicensors Axens (IFP) (IFP)ExxonMobilShellGlobalSolutions

Chevron ummusKBRUOPCatalysts NiMo on y-alumina(HDS, HDN, aromaticsaturation)NiMo or NiW on zeolite (hydrocracking)NiMo or NiW on amorphoussilica-alumina hydrocracking)Feeds

Pd on zeolite (hvdrocrackiHeavy gasoil Vacuum gasoi lResidualoilsoker easoil

Typical ProcessConditionsReactor emperature 600 800'F 315 425"C)ReactororessureRangeof Product Yields

Conversion once-through)Conversion with recYcle)Ca-Plus aPhthaMiddle distil latesHydrogen consumPtion

1200 2500 sig 8375 17,338Pa

20 - 90 volo/o90 -99 vol% fresh eedUp to 120 volo/o resh feedUp to 90 volo/oresh feed1000 o 3000scf/bbl175 o 525 Nm3/m3

3.5 EbullatedBed UnitsIn fixed-bedhydrocrackers esignedo processVGO, residualoils in thefeed can reducecatalystcycle life if they contain even raceamountsof salts,asphaltenes,efractory carbon, racemetals (Fe, Ni, V), or particulatematter.Ai mentioned n Section3.4.2, fixed-bedunits designed o process esidueremovemetalsand other contaminantswith upstreamguard bedsor onstreamcatalyst eplacementechnology. n contrast, bullatedbed hydrocrackers anand do processsignificant amountsof residual oils. This is because resh


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36 Robinson

3 H z

T"nr6lc\ "6"

'-"6""-". -

Figure 16. Hydrocracking n catalytic reformers.

cHs

1,2-dimethylcyclohexane

cHe

2 CaHspropane

CHet"-cn -cHzHrct -c4 --cH,2-methylpentane

tl\-/cyclohexane

&CHqt"6avo-xyleneH2

cHs

2-methylheptane

&1,2-dimethylcyclohexaneFigure 15. Dehydrocyclizationand dehydrogenationHydrocracking and isomervation reactionsare shown in Figure 16 andFigure 17, respectively. ydrocracking,which is undesirablen this process,occurs o a greaterextentat high temperatures.

CH.l " H 2I..CH -CHz ----+Hrc/ -c4 --cH,2-methylpentane

Hrg/cH'-"6""'"6"*'

1,2-dimethylcyclopentaneFigure 12. Isomerizationof paraffins and naphthenesn catalyticreformers.


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38 Robinson

In a semi-regenerative nit, desulfurizednaphtha s mixed with hydrogen,heated o >900oF >480"C)andpassedhrough a seriesof fixed-bed eactors.The major chemicalreactions dehydrogenation nd dehydrocyclization areendothermic (heat absorbing), and the reactors themselves are essentiallyadiabatic.This means hat heat can't enter or leave exceptby the cooling orheating of reaction fluids Consequently, he temperaturedrops as reactantsflow througha reactor.Between eactors, ired heatersbring the process luidsback to desired eactor nlet temperatures.Heaters, Reactors

RecycleGas

NaphthaFeed

H2 RichMakeGas

Recycle GasCompressor

High-PressureSeparator

ReformateProduct

F igure / 8. Semi-regenerativecatalytic reformingSome catalytic reformersoperateat low pressure 100 psig, 791 kPa),while others operate at >500 psig (3549 kPa). Low operating pressureimproves yields of aromatics and hydrogen, but it acceleratescatalystdeactivationby increasing he rate at which coke forms on the catalyst. n aCCR reformer, he catalystalways s being regenerated, o increased oking islessproblematic.Therefore, CCR units can operateat very low pressures.n

most reformers, he feed is spikedwith an organic chloride,which converts ohydrogen chloride (HCl) in the reactors.The HCI increasescatalyst acidifyandhelps o minimrze catalystcoking.The effluent from the last reactor is cooled and sent to a separator, romwhich hydrogen-richgas is removed and recycled to the reactors.The liquidproduct flows to a stabtlizer column, where entrained gasesare removed,beforegoing to the gasolineblenderor aromaticsplant.


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40

4.2 Isomerization4.2.1 Isomerization Objectives

As we have seen, somerizationoccursaSa side-reactionn all conversionprocesses.But in refining, when we say "isomerizationprocess,"we areiefening specifically to the on-purpose somerizationof n-butane,n-pentane,andn_hexane. he main purposeof n-pu.uffin isomerizatton s to produce so-faraffins with substantiuity tigtter octanenumbers.An isomerization eactionio. no*al hexanewas shown n Figure 17 r in Tabte 20.Somedetailsaboutparaffin isomerizationprocesses re glverTable20. Isomerization n a NutshellConvert n-butaneto isobutane

Convertn-pentaneandn-hexane o branched somersLicensor (Ca)

Licensors(CsCo)

ABB Lummus GlobalUOPAxens (IFP)UOP

BPBP

Catalysts(Ca)Catalysts(CsCo)

Pt on y-alumina,HCI PromoterPt on y-alumina,HCI Promoter

Pt on zeolitePt on zeolite

Feeds(Ca)Feeds(C5)

dry n-butaneLightstraight-run,ndpoint


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42 Robinson

Processobjectivesdeterminewhetheroneor two reactorsareused'In two-reactor units (Figure 20), the feed flows first to a saturationreactor' whichremoves olefins *a (to a large extent) benzene'After saturation' the feedgo.r to an isomerization reactor, where normal paraffins are converted toisoparaffins.

HydrogenationResctor

Gas toScrubber

i'r""ff:?"Figure 20.csc6isomerization: wo reactors,once-throughhydrogen

The reactor effluent flows to a product separator,where hydrogen isseparatedrom the other reactionproducts.Recoveredhydrogen can go to arecycle compressor,which returns t to the reactors,or it can be treatedandsent o the fuel gassystem.Separatoriquids go to a stabilizer

column, whichremoves ight gur., and remaining dissolvedhydrogen.The stabilized iquidgoes o storageor gasolineblending. f sent o a fractionator,n-pentaneandn-hexanecanbe ,..ytl.d to the isomerizationunit for increased onversion'

Desulfurized


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Recycle

QuenchStabilizer

Propylene,ButyleneFeed

Figure 22. Catalytic oligomerization of olefins

4.4 Atkylation4.4.1 Alkylation Objectives

Alkylation processescombine light olefins (primarily propylene andbutylene) with isobutane n the presenceof a highly acidic catalyst, eithersulfuric acid or hydrofluoric acid. The product (alkylate)containsa mixture ofhigh-octane,branched-chain araffinic hydrocarbons.Figure 23 illustrates hereactionbetween sobutaneand trans-2-butene.Alkylate is a highly desirablegasolineblend stock because,n addition to its high octane, t has a low vaporpressure.The octane of the product dependson the operatingcondition andthekindsof olefinsused.

-cH -cH.Hrc/ \cricoHu

trans-2-butene

HsC..- ..CHscHIcHacoH',0

isobutane

cHe 9HaHscr / |lc-.- ,.c\/ -ct-i, -cH,HsCcrH,,

isooctane

Figure 23. Alkylation of trans-2-butene

4.4.2 ProcessFlow: Sulfuric Acid AlkylationIn sulfuric acid (H2SO4)alkylation units, the feeds- propylene,butylene,amvlene"and fresh isobutane- enter the reactor and contact sulfuric acid

Recycle

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40

5. LUBES,WAXESAND GREASES"Bottom of the barrel" fractions- atmosphericandvacuum

be convertedby the processes escribedn Sections2 and 3,used o make ubes,waxesandgreases.

Robinson

residues canor they can be

5.1 Lube BaseStocksRefiners prepare lube base stocks from residual oils by removingasphaltenes, romatics,and waxes. Lube base stocks are hydrofinished,btended with other distillate streams for viscosity adjustment, andcompounded ith additives o produce inished ubricants.Solvent-based rocessesor removing asphaltenes, romaticsand waxeswerediscussedn Section2.2.The next few paragraphs ive a quick overviewof catalyticdewaxing.

5.1.1 CatalYticdewaxingCatalyticdewaxing CDW) wasdeveloped y ExxonMobil in the 1980s.TheprocessLmploys a shape-selectiveeolite called ZSM-5, which selectively

convertswaxy n-paraffins nto lighter hydrocarbons.The IsodewaxingProcess,,ommercialized n 1993 by ChevronTexaco,catalytically somerizesn-paraffins nto iso-paraffins.This decreaseshe waxcontentand increaseshe concentrationow-viscosityhydrocarbons, oth ofwhich are desirable. sodewaxingalso removessulfur and nitrogen,, nd itsaturates romatics.Products avea high viscosity ndex(VI), low pourpoint,andexcellent esponseo additives.Catalyticdewaxingand Isodewaxingare discussedn more detail in thesecond olumeof this book.5.2 Waxes

The raffinate from the solvent extraction unit in a traditional lube plantcontainsa considerableamount of wax. To recover the wax, the raffinate ismixed with a solvent, usually propane,and cooled in a series of heatexchangers.Further cooling is provided by the evaporationof propane n thechiller and filter feed tanks.The wax forms crystals,which are continuouslyremoved, iltered,andwashedwith cold solvent.The solvent s recovered yflashing and steamstripping.The wax is purified by heatingwith hot solvent,afterwhich it is re-chilled, e-filteredandgivena final wash.paraffin waxes are used to make candlesand coated papers for use asbreadwrappers,cold-drink cups,andbeverugecartons.They are also used n


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48 Robinson. Saturating he paper elt with asphalt. Coating he saturatedelt with filled asphalt. Pressing ranules f sand, alc or mica nto the coating. Cooling with water, drying, cutting and trimming, andpackagingIf fiberglass s used as the base nsteadof paper elt, the saturation tep seliminated.7. DRYING,SWEETENING,AND TREATING

Drying, sweeteningand treating are not as glamorousas extraction andconversion, r evendistillation,but they are essentialo the performance ndsafety of finished products. In lubricating oils, tracesof olefins and sulfurcompounds can form gums and acceleratedegradation.At high altitude,excesswater in jet fuel can freezeand plug fuel lines. Tracesof mercaptansand disulfides in "sour" gasoline can react with water in storage tanks toproduce oxic levelsof hydrogensulfide.

7.1 Drying and SweeteningLight gas streamsproduced by various refinery units are collected andpiped o treatingplants,where:o Propanes recovered or LPGo Propylenes removed or use n petrochemical lantso Butanesand butenesareremoved or use asalkylation feeds. Heaviercomponents re ecovered nd sent o gasoline lendingKnock-outdrumscollect easy-to-condenseiquids,but if necessary rying

agents alumina, silica, or molecularsieves are used to remove the finaltraces of water. Some processes se beds of molecular sieves o dry andsweeten t the same ime.Gasescontaining hydrogensulfide are scrubbed n trayed contactorswithaqueousamines such as diethanolamine DEA). Hydrogen sulfide is strippedfrom the "rich" amine with steamand recycled o the contactor. n a properlyoperating nit, the sweetened ascontains


49/78

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8.2 GasolineBlendingForty yearsago,makinggasolinewasa relativelysimple ask. f a mixture

of componentsmet specificationsor volatility and octane, t couldbe shippedto retail outletsand sold as-was. f the octanewas low,, he problem could befixed by addinga little tetraethyl ead.Butanescould be addedas needed oadjustvolatility.In fact, volatility and octaneare still the two most importantpropertiesofgasoline.The volatility must be high enough o vaporizeduringcold weather;otherwise, ngineswon't start.And octane s still oneof the bestpredictorsofperformancen a spark-ignition asoline ngine.8.2.1 OctaneNumbers for Hydrocarbons

In a spark-ignition ngine,somecompounds tart o burn before hey reachthe sparkplug. This premature gnition causes nocking,which reduces hepower of the engine, ncreases nginewear,and'in somecases auses eriousdamage.Octanenumber s a measure f the propensityof fuels o knock in gasolineengines. t is basedon an arbitraryscale n which the octanenumber of n-heptanes zeroand he octanenumberof isooctane2,2,4-trimethylpentane)s100.When a fuel is tested n a standard ingle-cylinderengine,mixturesofisooctaneand n-heptaneare used as standards.ASTM D2699 and ASTMD2100 describemethods or measuring esearchoctanenumber (RON) andmotor octanenumber (MON), respectively.The enginespeed or the RONtest s 600 rpm, while 900 rpm is used or the MON test.RONC and MONCare sometimesused instead o RON and MON. The "C" stands or clear,which means hat he fuel doesnot contain eador manganesedditives.

Table 22 presentsRON and MON values for severalpure compounds.Aromatics,olefins, and branched somershave higher octanenumbers hanstraight-chain somers with similar carbon numbers. Octane numbers fornaphthenesresubstantiallyower than hose or aromatics.Octanenumbersdo not blend linearly. For example,while the RON forpure4-methyl-2-pentenes 99, its blendedRON is 130.In North America, he pump octaneof gasoline s the average f RON and

MON: (R+M)/2. This is thenumberdisplayedon pumpsat filling stations.Typicalgrades re"regular"with a pump octaneof 87, "mid-grade"with apump octaneof 89, and "premium" with a pump octaneof 91 to 93. In some

locales, ustomers andial in any octane heywant between87 and 93.


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52 Robinsonto impose emissions imits on automobilesand to require reformulatedgasoline RFG).

Phase I RFG regulations (Table 24) required a minimum amount ofchemicallybound oxygen, mposedupper imits on benzeneand Reid VaporPressure RVP), and ordereda l5o/o eduction n volatile organic compounds(VOC) and air toxics.VOC reactwith atmosphericNOx to produceground-level ozone. Air toxics include 1,3-butadiene, cetaldehyde, enzene,andformaldehyde.Oxygen can be suppliedas ethanolor C5 to C7 ethers.The ethers Table25) have excellentblending octanesand low vapor pressures. his makesthemhighly desirable asoline lendstocks.Due to the Cetection f MTBE ingroundwater, he future for MTBE is questionable, speciallysince 1999,whenthe Governorof California ssuedan executiveorder requiringthe phase-outof MTBE as a componentof gasoline. But in Finland and many otherEuropean countries,MTBE is still considereda premium, relatively safeblendstock."Table24. SimpleModel RFG SpecificationsProperty SpecificationOxygen,wto%Benzene, volo/oRVP, SummerClassB (psi)ClassB (kPa)ClassC (psi)ClassC (kPa)VOC (summer)Air toxicsSulfurT90*, olefins,aromatics

2.0 max1.0max7.2 max50 max8.1max56 max15%reductionl5o% eductionSame s 1990Sameas 1990*T90 is the temperature t which 90o/o f a gasolineblend evaporates.

RFG was mplementedn two phases. he Phase programstarted n 1995and mandatedRFG for 10 large metropolttan areas.Several other cities andfour entire statesoined the programvoluntarily. In the year2000,about 35%of the gasolinen theUnited Stateswas refonnulated.The regulations or Phase I, which took force n January2000,are basedon the EPA Complex Model, which estimates xhaustemissions or a regionTqble 25. Blending octaneand RVP of ethersandalcohols

Blending Octane Blending RVP Blending RVP(RON) (nsi) (kPa)ther or AlcoholMethanolEthanolMethyl-t-butyl ether(MTBE)Ethyl-t-butyl ether(ETBE)t-Amyl methyl ether(TAME)

13 31 3 01 1 81 1 8l l l

58-62t8-228 - 0J - )t -2

400-427124-15255-692r -347 14


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548.2.4 Low-Sulfur Gasolineand Ultra-Low-Sulfur Diesel

Robinson

In recentyears, he U.S. EnvironmentalProtectionAgency (EPA) and theEuropeanParliament romulgated lean-fuel egulations hat are owering thesulfur contentof gasolineand diesel fuel. New sulfur-content tandardsorseveraldevelopedcountriesare shown in Table 28, which also shows thetargetdates or implementation.Table 28.CleanFuels:Limits on Sulfur Fuel Sulfur Content,wppm

GasolineDiesel,on-roadDiesel,off-road

>300500

2000 3500

301 5

5001 5

2004 2008July1,2006July1 2010200720r0

CanadaGasolineDiesel1 5 0500 301 5 20052006

Germany 20032003l 01 0t 0l 0GasolineDieselSwedenDiesel l 00 r995Other EUGasoline

Diesel1 5 0350

501 050l 0

2005200820052008AustraliaGasolineDiesel

500500 1 5 030 20052008Korea(South)GasolineDiesel

3050100300 20062006JapanGasolineDiesel

l 0501 0100500 200820042008

Table 29 shows hat, prior to 2004, FCC gasolinewas by far the majorsourceof sulfur in gasoline,a3ypically accounting or 85 - 95% of the totalsulfur in the blending pool.aaObviously, to reduce the sulfur content ofgasoline,sulfur either must be kept out of FCC feed or removed rom FCCproduct(s).Both approaches re being used. FCC feed desulfurization sdiscussedn Section .4.2.FCC gasoline ost-treatings discussedelow.


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The flash point is the lowest temperaturc at which a liquid gives offenoughvaporto ignite when an ignition source s present.The freezingpointis esfecialiy important for jet aircraft, which fly at high altitudeswhere theoutside emperatures very low. Sulfur content s a measureof corrosiveness.The measurement f smokepoint goesback to the dayswhen the primaryuse for kerosenewas to fuel lamps.To get more light from a kerosene amp,you could turn a little knob to adjust he wick. But if the flame got too high, it'gaveoff smoke.Even today,per ASTM D1322,smokepoint is the maximumteight of flame that can be achievedwith calibratedwick-fed lamp, using awick "of woven solidcircularcottonof ordinaryquality."The smokepoint of a test fuel is compared o referenceblends.A standard40%160% volume/volume) mixture of toluene with 2,2,4-trimethylpentanehas a smokepoint of 14.J,while pure 2,2,4-trimethylpentaneas a smokepoint of 42.8.Clearly, isoparaffinshavebettersmokepoints thanaromatics.Toble 0 showsspecifications or five gradesof jet fuel' otherwiseknownasaviationturbine fuel. The JP fuels arefor military aircraft'Table30. Specifications ot euiution f"tUln

Robinson

JP.8P-4ecification Jet A38-40 (JetA)-47 (JetA-l)3 1 5 r

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8.4 DieselBlendingDieselblending s simpler han gasolineblendingbecausehe limitationsare fewer. Only sulfur, cetanenumber,and (in somecountries)aromaticsanddensityare regulated or environmental easons.Sulfur contributesheavily toparticulateemissions rom dieselengines,and cetanenumber is a measureof

trrrning quality in a diesel engine. As with octanenumber, cetanenumbermeasures he tendencyof fuels to auto-ignite n a standard est engine. It iseasier o starta dieselenginewhen the cetanenumberof the fuel is high.The referenceuels for ASTM D613, which describeshe testmethod orcetanenumber, are n-cetane,0,-methylnaphthalene,nd heptamethylnonane'for which cetanenumbersare defined o be 100,0, and 15, respectively.Table-31 howscetane umbers or selected urecompounds'4s


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RobinsonTableJJ. EU S ifications or AutomotiveDieselecificationCetanenumberCetane ndexDensityC@ 5"CDist i l lat ion90% boi l ingpoint95% boi l ingpointFinalboi l ingpoint90%boi l ingpoint95% boi l ingpointFinalboilingpoint oC no spec

I I (max)no spec

Units Year 2000Limits PossibleFuture Limits

glcm3

O FO FOFO C"C

5 l (min)No spec

0.845 max)no spec

680 (max)no specno spec

360 (max)

55 (min)52 (min)

0.84608 (max)644 (max)662 (max)320 (max)340 (max)350(max)2 (max)l5 (max)l0 (max)

Polyaromatichydrocarbons PAH) wto/oTotal aromaticsSulfur

wto/owppm 350 (max)*

o As discussed lsewhere, ieselsulfurwill be limited to 50 wppm in 2005.Catalyticconvertersed to the eliminationof lead from gasoline,becauselead poisons he convertercatalyst.Similarly, sulfur poisonscatalysts hatmay be usedon futurevehicles.Hence, he reductionof sulfur n gasolineanddiesel uel to ultra-low evels s a key requirement f Auto oil II.Around the world, the transportation nd fungibility of ultra-clean uels s

a major concern. For common-carrierpipelines, which transport variousproductsmadeby differentrefiners,cross-contaminations a major concern.The interface ayerbetweenshipmentss called "transmix." If a shipmentofgasolinecontaining30 wppm of sulfur follows a batch of dieselcontaining500 wppm of sulfur, the sulfur-contaminatedransmix could comprisemorethan 20o/oof the gasoline.Consequently, everalpipeline companieshaveannouncedhat n the future heywill not transportanyhigh-sulfurmaterial.Other important diesel-fuelproperties nclude flash point, cloud point,pour point, kinematic viscosity, and lubricity. Cloud point and pour pointindicate he temperature t which the fuel tends o thickenand hen gel in coldweather. n addition o providingenergy,diesel uel alsoservesasa lubricantfor fuel pumpsand njectors,which prolongs he life of the engine.Viscositymeasures he tendency of a fluid to flow. In a diesel engine, viscosityindicateshow well a fuel atomizes n spray injectors. t also measurestsqualityas a lubricant or the fuel system.Lubricity measureshe fuel's abilityto reduce riction betweensolid surfacesn relativemotion. It indicateshowthe enginewill performwhen oaded.8.4.1 DieselAdditives

Chemical additives mprove the performanceand extend he tank-life ofdiesel uels.Typical typesof additivesareshown n Table34.


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Robinson

themostexpensive ue o the relativelyhigh costof buying ow-sulfur uel oi lor hydrotreatinghigh-sulfur fuel oil.A largefraction of the sulfur in the feed to an FCC unit endsup in coke onthe catalyst.SOx is formed in the regeneratorwhen the coke is burned away.Therefore, emovingsulfur from the feed decreases Ox emissions.As stated n Section3.4.2,using a hydrotreater r hydrocracker or feedHDS eliminates r minimizes he costof post-FCCdesulfurization quipment.Removing basic nitrogen decreases eactivationof acid sites on the FCCcatalyst, which allows the FCC to reach a given conversion at lowertemperatures.The saturationof aromatics n the feed pretreaterprovides thebiggest benefit, because t convertshard-to-crackaromatics nto easier-to-crack naphthenes. his alone can justify the installation of an FCC feedpretreater.Therefore, n addition to abating SOx, hydrotreating he feed to anFCC cangeneratea substantial eturn.a3

FCGRegeneratorOxidizing nvironment)Coke n catalystsolid) Oz+H2O CO,+ SO2, O3, rSO"gas)SO2, O3, ySO,gas) M (solid) Oz - M'SOasolid)

FCCRiser/ReactorReducing nvironment)M.SO4 sol id)+ 5 Hz --+M (sol id)+ H2S(gas) + 4 HzO

Figure 2-J.Mechanism of SOx transfer n FCC units.SOx Transfer Additives. Arguably, SOx transfer additives are the mostcost-effectiveway to lower SOx emissions n an FCC unit. Thesematerials,first developed y DavisonChemical, eactwith SOx in the FCC regeneratorto form sulfates (Figure 25). When the sulfated additive circulates to theriser/reactor ection, he sulfate is reduced o HzS, which is recoveredbyamine absorptionand sent to the sulfur plant. In some units, these additivesreduceFCC SOx emissions y more than 0o/o.Consequently,f a pre-treateror post-treater till mustbe installed, ts sizecan be reduced.Flue-Gss (Stack-Gul Scrubbing. Flue-gasscrubbing is a refiner's lastchance o keep NOx and SOx out of the air. In wet flue-gas desulfurization,gas streamscontaining SOx react with an aqueousslurry containingcalciumhydroxideCa(OH)2and calciumcarbonateCaCO3.Reactionproducts nclude

calciumsulfite (CaSO:)and calcium sulfate CaSOa),which precipitate romthe solution.NOx removal is more difficult. Wet flue-gas scrubbing removes about20% of the NOx from a typical FCC flue gas.To remove the rest, chemicalreducingagentsareused. n the SelectiveCatalyticReduction SCR) process,anhydrousammonia s injected nto the flue gasas it passeshrough a bed of


61/78

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Pct 7 Petroleum Processing (Book)

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