2125_02_26 Petroleum Technology, Volume 1-2

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914TOLUENEVol.

2

TOLUENE

1.Introduction

Toluene[108-88-3],C7H8,isacolorless,mobileliquidwithadistinctivearo-maticodorsomewhatmilderthanthatofbenzene.Thenametoluenederivesfromanaturalresin,balsamofTolu,namedforasmalltowninColombia,SouthAmerica.Toluenewasdiscoveredamongthedegradationproductsobtainedbyheatingthisresin.

PriortoWorldWarI,themainsourceoftoluenewascokeovens.Atthattime,trinitrotoluene(TNT)wasthepreferredhighexplosiveandlargequantitiesoftoluenewererequiredforitsmanufacture.Toaugmentthesup-ply,toluenewasobtainedforthe rsttimefrompetroleumsourcesbysubject-ingnarrow-cutnaphthascontainingrelativelysmallamountsoftoluenetothermalcracking.Thetolueneconcentratesoproducedwasthenpuri edandusedforthemanufactureofTNT.Productionfrompetroleumwasdiscon-tinuedshortlyafterWorldWarI.PetroleumagainbecamethesourcefortoluenewiththeadventofcatalyticreformingandtheneedforlargequantitiesoftolueneforuseinaviationfuelduringWorldWarII.Sincethen,manufac-tureoftoluenefrompetroleumsourceshascontinuedtoincrease,andmanu-facturefromcokeovensandcoal-tarproductshascontinuedtodecrease.

Tolueneisgenerallyproducedalongwithbenzene,xylenes,andC9-aromaticsbythecatalyticreformingofC6–C9naphthas.Theresultingcrudereformateisextracted,mostfrequentlywithsulfolaneortetraethyleneglycolandacosolvent,toyieldamixtureofbenzene,toluene,xylenes,andC9-aromatics,whicharethenseparatedbyfractionation.Therehavebeenrecenttechnologicaldevelopmentstoproducebenzene,toluene,andxylenesfrompyrolysisoflighthydrocarbonsC2–C5,LPG,andnaphthas(seeXYLENES).ThemajorityofthetolueneproducedannuallyintheUnitedStatesisnotisolated,butisblendeddirectlyintothegasolinepoolasacomponentofrefor-mateandofpyrolysisgasoline.Capacityexiststoisolateca12.7Â109galperyear,whichisusedforchemicalsandsolvents.Additionalquantitiesareblendedintogasolinetoincreaseoctanenumber.

2.PhysicalProperties

Thephysicalpropertiesoftoluenehavebeenwellstudiedexperimentally.SeveralphysicalpropertiesarepresentedinTable1(1).Thermodynamicandtransportpropertiescanalsobeobtained,fromothersources(2–7).Thevaporpressureoftoluenecanbecalculatedasfollows(8),wherePisinkPaandTisinK.

3103

310K T 385K

lnP¼14:01Àð1Þ

Kirk-OthmerEncyclopediaofChemicalTechnology.CopyrightJohnWiley&Sons,Inc.Allrightsreserved.10.1002/0471238961.2015122115261511.a01.pub2

Petroleum Technology, Volume 1-2

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Table1.PhysicalPropertiesofTolueneProperty

molecularweightmeltingpoint,K

normalboilingpoint,Kcriticaltemperature,Kcriticalpressure,MPaacriticalvolume,L/(gÁmol)criticalcompressibilityfactoracentricfactor ashpoint,K

autoignitiontemperature,K

Gasproperties,298.15K

Hf,kJ/molGf,kJ/molbCp,J/(molÁK)bHvap,kJ/molbHcomb,kJ/molb

viscosity,mPaÁs(¼cP)

ammabilitylimits,inairc,vol%lowerlimitat1atmupperlimitat1atm

Liquidproperties,298.15K

density,L/molCp,J/(molÁK)b

viscosity,mPaÁs(¼cP)

thermalconductivity,W/(mÁK)surfacetension,mNÁm(¼dyn/cm)

Liquidproperties,178.15Kdensity,L/molCp,J/(molÁK)b

viscosity,mPaÁs(¼cP)

thermalconductivity,W/(mÁK)surfacetension,mNÁm(¼dyn/cm)

Solidproperties

densityat93.15K,L/molCpat178.15K,J/(molÁK)b

heatoffusionat178.15K,kJ/molb

ab

TOLUENE915

Value92.14178.15383.75591.804.1080.3160.2640.26227880950.17122.2104.738.26À37340.006981.27.19.38156.50.5480.13327.910.49135.11.470.16242.811.1890.06.62

b

ToconvertMPatopsi,multiplyby145.ToconvertJtocal,divideby4.184.c

At101.3kPa(1atm).

Thesaturatedliquiddensitycanbecalculatedasfollows(7),whererising/LandTisinK.

r¼12:415À0:009548TÀ

65:155

179K T 400K

606:9ÀT

ð2Þ

http://pilationsandbibliographies

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916TOLUENEVol.2

existforvapor–liquidequilibriummeasurements(9,10),liquid–liquidequili-briummeasurements(11),andazeotropicdata(12,13).

3.ChemicalProperties

Toluene,analkylbenzene,hasthechemistrytypicalofeachexampleofthistypeofcompound.However,thetypicalaromaticringoralkenereactionsareaffectedbythepresenceoftheothergroupasasubstituent.Exceptforhydrogenationandoxidation,themostimportantreactionsinvolveeitherelectrophilicsubstitu-tioninthearomaticringorfree-radicalsubstitutiononthemethylgroup.Addi-tionreactionstothedoublebondsoftheringanddisproportionationoftwotoluenemoleculestoyieldonemoleculeofbenzeneandonemoleculeofxylenealsooccur.

Thearomaticringhashighelectrondensity.Asaresultofthiselectronden-sity,toluenebehavesasabase,notonlyinaromaticringsubstitutionreactionsbutalsointheformationofcharge-transfer(p)complexesandintheformationofcomplexeswithsuperacids.Inthisregard,tolueneisintermediateinreactivitybetweenbenzeneandthexylenes,asillustratedinTable2.

Intheformationofp-complexeswithelectrophilessuchassilverion,hydro-genchloride,andtetracyanoethylene,toluenediffersfromeitherbenzeneorthexylenesbyafactoroflessthantwoinrelativebasicity.Thisdifferenceissmallbecausethecomplexisformedalmostentirelywiththepelectronsofthearo-maticring;theinductiveeffectofthemethylgroupprovidesonlyminorenhance-ment.Incontrast,withHForBF3whichformasigma-typecomplex,orinthecaseofreactionaswithnitroniumionorchlorinewhereformationofthesigmabondsandcomplexesplaysasigni cantrole,themethylgrouppartici-patesthroughhyperconjugationandtherelativereactivityoftolueneisenhancedbyseveralordersofmagnitudecomparedtothatofbenzene.Reactivityofxylenesisenhancedagainbyseveralordersofmagnitudeoverthatoftoluene.Thus,whenonlythepelectronsareinvolved,toluenebehavesmuchlikebenzeneandthexylenes.

Table2.RelativeBasicityandReactivityRelativetoToluene¼1.00

Xylene

ElectrophileAgþaHClbTCEc

HF-BF3d

e

NOþ2Cl2f

a

Benzene0.90

0.660.540.0450.003

Toluene1.001.001.001.001.001.00

Ortho1.081.231.89200.0013.1

Meta1.131.371.622000.001250.00

Para0.981.092.05100.006.3

SolubilityinaqueousAgþ(14).b

KforArþHCl! ArÁHClinn-heptaneatÀ788C(15).c

Kforassociationwithtetracyanoethylene(TCE)inCH2Cl2(16).d

Basicitybycompetitiveprotonation(17,18).e

CH3COONO2in(CH3C)OOat248C(19).f

Cl2inCH3COOHat248C(20).

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Vol.2TOLUENE917

Whensigmabondsareinvolved,tolueneisamuchstrongerbasethanben-zeneandamuchweakerbasethanthexylenes.Thereasonsforthisdifferencearereadilyshownbycontrastingthecomplexesoftoluenewithhydrogenchlorideintheabsenceandpresenceofaluminumchloride.Intheabsenceofaluminumchloride,hydrogenchlorideislooselyattachedtothep-cloudofelectronsaboveandbelowtheplaneofthering.Withaluminumchloridepresent,theelectrophili-cityisgreatlyenhancedandasigmabondisformedwithaspeci celectronpair;resonancestructuresinvolvingthemethylgroupcontributetothe

stabilization.

AlCl4

Forattackateitherofthetwoorthopositionsortheparaposition,threesuchstructurescanbewritten.

3.1.HydrogenationReactions.Hydrogenoveranickel,platinum,orpaladiumcatalystcanpartiallyortotallysaturatethearomaticring.Thermalhyrogenolysisoftolueneyieldsbenzene,methane,and

biphenyl.

3

CH3

H CH4

3.2.OxidationReactions.Althoughbenzeneandmethanearequite

unreactivetowardtheusualoxidizingagents,thebenzeneringrendersthemethylgroupsusceptibletooxidation.Withoxygenintheliquidphaseandpar-ticularlyinthepresenceofcatalysts,eg,bromine-promotedcobaltandmanga-nese,verygoodyieldsofbenzoicacidare

obtained.

Partialoxidationoftolueneyields

stilbene:

2

3

2 H2O

Thereactions

thatgivesubstitutiononthemethylgrouparegenerallyhightemperatureand

3.3.SubstitutionReactionsontheMethylGroup.

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918TOLUENEVol.2

free-radicalreactions.Thus,chlorinationatca1008C,orinthepresenceofultra-violetlightandotherfree-radicalinitiators,successivelygivesbenzylchloride,benzalchloride,and

benzotrichloride.

Cl

Thisoxidationreactionwhichyieldsbenzoicacidisanotherexampleofthistypeofreaction.

Inthepresenceofalkalimetalssuchaspotassiumandsodium,tolueneisalkylatedwithethyleneonthemethylgrouptoyield,successively,normalpro-pylbenzene,3-phenylpentane,and3-ethyl-3-phenylpentane

(21).

CH22CH32CH3)3

http://petitionexperimentsshow,forexample,thatat408Cabenzylichydrogenoftolueneis3.3timesasreactivetowardbromineatomsasthetertiaryhydrogenofanalkaneandnearly100milliontimesasreactiveasahydrogenofmethane.

Inthepresenceofapotassiumcatalystdispersedoncalciumoxide,toluenereactswith1,3-butadienetoyield5-phenyl-2-pentane

(22).

CH2CHCHCH3

Whenlithiumisusedasacatalystinconjunctionwithachelatingcom-poundsuchastetramethylethylenediamine(TMEDA),telomersaregenerallyobtainedfromtolueneandethylene(23),wheren¼

010.

C2H4CH2CH3

Theintermediatesinthesebase-catalyzedreactionsarebelievedtobeofthenatureofabenzylcationbecausethereactionproductfromtolueneandpropy-leneisisobutylbenzene,notn-butylbenzene,andthereactionrateisslowerthanwithethylene(24).

3.4.SubstitutionReactionsontheAromaticRing.Topredictthelocationofelectrophilicaromaticringsubstitutions,theelectrophilicreactionscanbemodeledasproceedingthroughanintermediatestepinwhichanegative

Petroleum Technology, Volume 1-2

Vol.2TOLUENE

Table3.IsomerDistributionsintheMonoalkylationsofToluenea,%Enteringgroupmethylethylisopropylt-butyl

a

919

Ortho53.84537.50

Meta17.33029.87

Para28.82532.793

Ref.25.

andpositivechargeareseparatedonthering.Themoststableintermediatesarethoseinwhichthepositivechargeislocalizedonthecarboncontainingthemethylgroup(tertiarycarbon).Theresonancestructuresindicatethatsubstitu-tionwilloccurattheorthoandparapositionsbutnotthemetapositionbecausethispositioncannotberesonance-stabilizedbythecarbonium–methylhypercon-jugatestructures.Thepresenceofthemethylgroupisthereforeortho-andpara-directing.Thereisalsoastericeffectattheorthoposition,asshownbythedatainTable3.Thesedataclearlydemonstratethatbulkygroupscannotentereasilyintothepositionadjacenttothemethylgroupandthereforeattackselectivelyatthepara

position.

Substitutionoftheringhydrogenatomsbyelectrophilicattackoccurswithallofthesamereagentsthatreactwithbenzene.Someofthecommongroupswithwhichtoluenecanbesubstituteddirectly

are

TypicalelectrophilicreactionsaresummarizedinTables3and4.ThereactivityratiosinTable4showthatunderthesameconditions,toluenereactsmorerapidlythanbenzeneandthatthosereactionsthatexhibitthehighestselectivitytotheorthoandparapositionsalsoshowthemostgreatlyenhancedreactivityrelativetobenzene.Inadditiontothesereactions,nitrationcanbeperformedwithHNO3inH2SO4,sulfonationcanbeperformedwithH2SO4andSO3,alkylationcanbeperformedwithRX(X¼ClorBr)withAlCl3,andhalogenationcanbeperformedwithX2(X¼ClorBr)withFeX3.

Thehalogenationreactionconditionscanbechosentodirectattacktothemethylgroup(hightemperatureorlighttoformfree-radicals)orthearomaticring(dark,coldconditionswithFeX3presenttoformelectrophilicconditions).

Tolueneitselfdoesnotundergosubstitutionbynucleophilicattackofanionsbutrequiressubstitutionbystronglyelectronegativegroups,suchasnitrogroups,beforetheringbecomessuf cientlyelectrophilictoreactwithanions.

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920TOLUENEVol.2

Table4.IsomerDistributionandReactivityRatioforSelectedReactionsa

Isomerdistribution

Reactionchlorination

Conditions

Cl2 in HO3 at 24 C

Ortho58

Meta<1

Para42

ratio

353

chloromethylation

CH2O in HOCCH3 at 60 Cwith HCl and ZnCl2

34.71.364.0112

nitration

90% HO3 at 45 C

56.53.540.024.5

mercuration21.09.569.57.9

sulfonylationisopropylation

a

CH3SO2ClwithAlCl3at1008C

C3H6at408CwithAlCl3

4937.0

1528.5

3633.9

2.1

Ref.25.

3.5.AdditionReactionstotheAromaticRing.Additionstothe

doublebondsinthearomaticringoftolueneresultfrombothfree-radicalandcatalyticreactions.Chlorinationusingfree-radicalinitiatorsattempe-ratures<08Csaturatesthering.However,thisreactionisnotentirelyselec-tive,forinadditiontosaturatingtheringtoyieldhexachlorohexanederivatives,thereactionalsoeffectssubstitutiononthemethylgroup(26).Hydrogenationwithtypicalhydrogenationcatalystsreadilyyieldsmethylcy-clohexane.However,ratesforhydrogenationoftolueneareonly60–70%ofthatforbenzene(27).Thecommercialtechnologyusedforhydrogenatingbenzenetocyclohexane(28)canbeapplieddirectlytothemanufactureofmethylcyclohexane.Bothofthesering-saturatingreactionsprobablyproceedstepwise,butsincetheinitialreactionmustovercomethehighresonanceenergyofthearomaticring,saturationofthesecondandthethirddoublebondismuchmorerapid,withtheresultthatpartiallysaturatedintermedi-atesarenotnormallydetected(29).

4.ManufactureandProcessing

Theprincipalsourceoftolueneiscatalyticreformingofre nerystreams.Thissourceaccountsforca94%ofthetotaltolueneproduced.Anadditional15%is

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separatedfrompyrolysisgasolineproducedinsteamcrackersduringthemanu-factureofethylene(qv)andpropylene(qv).Othersourcesareanadditional1%recoveredasaby-productofstyrenemanufactureand4%enteringthemarketviaseparationfromcoaltars.Thereactionstakingplaceincatalyticreformingtoyieldaromaticsaredehydrogenationoraromatizationofcyclo-hexanes,dehydroisomerizationofsubstitutedcyclopentanes,andthecyclo-dehydrogenationofparaf ns.Theformationoftoluenebythesereactionsis

shown.

CH3

H2

CH3CH2CH2CH2CH2CH2CH3

3

H2

3

3 H2

Ofthemainreactions,aromatizationtakesplacemostreadilyandproceedsca7timesasfastasthedehydroisomerizationreactionandca20timesasfastasthedehydrocyclization.Hence,feedsrichestincycloparaf nsaremosteasilyreformed.Hydrocrackingtoyieldparaf nshavingalowerboilingpointthanfeedstockproceedsataboutthesamerateasdehydrocyclization.

Inordertoobtainpurearomatics,crudereformateisextractedtoseparatethearomaticsfromunreactedparaf nsandcycloparaf ns.Thearomaticsare,inturn,separatedbysimplefractionaldistillationtoyieldhighpuritybenzene,toluene,xylenes,andC9aromatics.

Catalyticreforming,whichwasintroducedprimarilytoincreaseoctanevaluesforbothaviationandautomotivefuels,hassincebecomethemainsourceofbenzeneandxylenesaswellasoftoluene.Before1940,both xed-bedand ui-dized-bedunits,typicallyusinga10–15%Mo–Al2O3catalystorsimilarcatalystspromotedwith0.5–2%cobalt,predominated.Improvedoperationwasobtainedin1940bytheintroductionofa0.3–0.6%Pt–Al2O3catalyst.Sinceca1970,furtherimprovementhasbeenobtainedbypromotingthePt–Al2O3catalystwithupto1%chloride,byusingbimetalliccatalystscontaining0.3–0.6%ofbothplatinumandrheniumtoretarddeactivation,andbyusingmolecularsievesaspartofthecatalystbasetogainactivity.Continuouscatalyticreformingwasintroducedca1971.

Becausecatalyticreformingisanendothermicreaction,mostreformingunitscompriseaboutthreereactorswithreheatfurnacesinbetweentominimizekineticandthermodynamiclimitationscausedbydecreasingtemperature.Therearethreebasictypesofoperations,ie,semiregenerative,cyclic,andcontinuous.Inthesemiregenerativeoperation,feedstocksandoperatingconditionsarecontrolledsothattheunitcanbemaintainedon-streamfrom6mo–2yrbeforeshutdownandcatalystregeneration.Incyclicoperation,aswingreactorisemployedsothatonereactorcanberegeneratedwhiletheotherthreearein

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922TOLUENE

Rheniformer reactors

Vol.2

Fig.1.ChevronResearchCo.Rheniformingprocess(30).(CourtesyofGulfPublishingCo.)

operation.Regeneration,whichmaybeasfrequentasevery24h,permitscontin-uousoperationathighseverity.Sinceca1970,continuousunitshavebeenusedcommercially.Inthistypeofoperation,thecatalystiscontinuouslywithdrawn,regenerated,andfedbacktothesystem.Flowsheetsforrepresentativesofeachofthethreetypesofprocesses,ie,Rheniforming(30),Ultraforming(31),andPlatforming(32),areshowninFigures1,2,and3,respectively.

Thepredominantfeedsforreformingarestraight-runnaphthasfromcrudestills.Naphthasfromcatalystcrackersandnaphthasfromcodestillsarealsoused.TypicalcompositionsaresummarizedinTable5.Typicaloperatingcondi-tionsforcatalyticreformingare1.135–3.548MPa(150–500psi),455–5498C,0.356–1.069m3H2/L(2000–6000ft3/bbl)ofliquidfeed,andaspacevelocity(wtfeedperwtcatalyst)of1–5h.Operationofreformersatlowpressure,high

Fig.2.StandardOil(In)Co.Ultraformingprocess(31).(CourtesyofGulfPublishingCo.)

Petroleum Technology, Volume 1-2

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Reactors

Productseparator

Net gas –liquidTOLUENE

Stabilizer

923

Fig.3.UniversalOilProductsPlatformingprocess(32).(CourtesyofGulfPublishingCo.)

http://positionofTypical93–2048CReformerFeeds,Vol%Source

crudestill

catalyticcrackercokingstill

Paraf ns40–5530–4050–55

Cycloparaf ns

40–3015–2530–35

Aromatics10–2040–5010–15

temperature,andlowhydrogenrecycleratesfavorsthekineticsandthethermo-dynamicsforaromaticsproductionandreducesoperatingcosts.However,allthreeofthesefactors,whichtendtoincreasecoking,increasethedeactivationrateofthecatalyst;therefore,operatingconditionsareacompromise.Moredetailedtreatmentofthecatalysisandchemistryofcatalyticreformingisavail-able(33–35).TypicalreformatecompositionsareshowninTable6.

4.1.Toluene,Benzene,andBTXRecovery.Thecompositionofaro-maticscentersontheC7-andC8-fraction,dependingsomewhatontheboilingrangeofthefeedstockused.Mostcatalyticreformateisuseddirectlyingasoline.

http://positionofTypicalReformate,Vol%Componentparaf ns

cycloparaf nsaromaticsC6C7C8C9C10

Value20–302–367–772–315–2020–2815–251–10

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924TOLUENEVol.2

Thatpartwhichisconvertedtobenzene,toluene,andxylenesforcommercialsaleisseparatedfromtheunreactedparaf nsandcycloparaf nsornaphthenesbyliquid–liquidextractionorbyextractivedistillation.Itisimpossibletoseparatecommercialpurityaromaticproductsfromreformatesbydistillationonlybecauseofthepresenceofazeotropes,althoughcomplicatedfurtherbytheclosenessinboilingpointsofthearomatics,cyclo-paraf n,andunreactedC6-,C7-,andC8-paraf ns.

Mostofthetechnologiespracticedfortherecoveryoftoluene,benzene,andBTXarebasedonchoiceofsolventtodissolvethearomaticsornonaromaticsinthecaseofliquid–liquidextraction,ortoenhancetherelativevolatilityofthenonaromaticsinthecaseofextractivedistillation.UOPandDowChemicalinthe1950sdevelopedtheUdexprocess,whichusedglycol-basedsolvents,ie,ethy-leneglycol(EG),diethyleneglycol(DEG),triethyleneglycol(TEG),tetraethyleneglycol(TTEG),dipropyleneglycol,anddiglycoamine,inacombinedliquid–liquidextractionandextractivedistillationtoextractaromaticsfromwideboilingrangereformates.Next,theShell-developedsulfolaneprocessalsomarketedbyUOP(Fig.4)increasedthearomaticseparationef ciencybyusingthesolventtetrahydrothiophenedioxide(sulfolane)inacombinedliquid–liquidextractionandextractivedistillationtodissolvethesmallerfractionofnonaromaticsinthefeedmixture.

Inthe1960s,theGermanengineeringcompanyKruppKoppersusedN-formylmorpholine(NFM)todeveloptwoprocesses.Inthe rst,morphylexisusedtorecoverallBTXaromaticsfromafeedstocklowinaromaticscontent.Morphylane,ontheotherhand,isanextractivedistillationpro-cessusedfortherecoveryofsinglearomatics,eg,toluene,benzene,fromappropriatefeedstocks.Octenarisamodi edmorphylaneextractivedistilla-tionprocessusedforrecoveringaromaticsfromcatalyticreformates.Alsoin

Fig.4.Shell-UOP’sSulfolaneextractionprocess(35).(CourtesyofGulfPublishingCo.)

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Vol.2

Extractor

StripperTOLUENE925

regenerator

Fig.5.UnionCarbideCorp.Tetraextractionprocess(36).(CourtesyofGulfPublishingCo.)

the1960s,UnionCarbidedevelopedtheTetraprocess,usingTTEGsolvent(Fig.5).In1986,UnionCarbideintroducedtheCaromprocess.CaromprocessinheriteddesignimprovementsoverUdexandTetraprocessesandusesTTEGcombinedwithaproprietarycosolventthatenhancesthecapacityofthesolventsystem.

SulfolanehasaslightadvantageoverCarominenergyconsumption,whileCaromhas6–8%lesscapitalforthesamecapacitySulfolaneunit.In1995,Exxon(37)commercializedthemostrecenttechnologyforaromaticsrecoverywhenitusedcopolymerhollow- bermembraneinconcentration-drivenpro-cesses,pervaporationandperstraction,foraromatic–paraf nseparation.Oncethenonaromaticparaf nsandcycloparaf nsareremoved,fractionationtosepa-ratetheC6toC9aromaticsisrelativelysimple.

Properchoiceoffeedstocksanduseofrelativelysevereoperatingconditionsinthereformersproducestreamshighenoughintoluenetobedirectlyusableforhydrodemethylationtobenzenewithouttheneedforextraction.

Tolueneisrecoveredfrompyrolysisgasoline,usuallybymixingthepyroly-sisgasolinewithreformateandprocessingthemixtureinatypicalaromaticsextractionunit.Yieldsofpyrolysisgasolineandthetoluenecontentdependonthefeedstocktothesteam-crackingunit,asshowninTable7.Pyrolysisgasolineishydrotreatedtoeliminatedienesandstyrenebeforeprocessingtorecoveraromatics.

4.2.OtherTechnologiesfortheProductionofBTXfromLightHydrocarbons.Recenttechnologicaldevelopmentshavecenteredonhigh

temperaturepyrolysisoflighthydrocarbonsC2toC5,LPG,andnaphthatoformaromaticsinhigheryields.Conversionsweretraditionallylowbecause

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926TOLUENE

Table7.TolueneContentofPyrolysisGasoline,C5to2008CFeedstockC2–C4paraf nnaphthasgasoils

Wt%topyrolysisgasoline

5–1015–2117–20

Wt%tolueneinpyrolysisgasoline

7–1511–2213–19

Vol.2

theywereaccompaniedbyahighdegreeofdegradationtocarbonandhydro-gen.Recentimprovementsincludemodi cationofthethermalcrackingpro-cesstoproducehigheryieldsofliquidproductsrichinaromaticsandtheextensionofthecatalytichydroformingprocesstopromoteoligomerizationanddehydrocyclizationofthelowerole ns.Thecommoncoreofthesedevelopmentsistheuseofshape-selectivezeolitecatalyststopromotethevariousreactions.OneexampleisthecommercializationoftheAlphaprocessbyAsahiChemicalIndustryCompanyinTokyo,anaf liateofSanyoPetrochemicalCompany.TheAlphaprocessusesmodi edZSM-5typezeolitecatalysttoconvertC3–C8ole nsat4908Ctoaromaticsat5108Cand5kg/cm2pressure(seeMOLECULARSIEVES).Selectivityfortolueneandxylenespeaksat5508Cbutcontinueswithincreasingtemperatureforbenzene.TheCyclarprocess(Fig.6)developedjointlybyBPandUOPusesaspherical,proprietaryzeolitecatalystwithanon-noblemetallicpromotertoconvertC3orC4paraf nstoaromatics.Thedrawbacktotheprocesseconomicsistheproductionoffuelgas,alowvalueby-product.

Fig.6.UOP-BPCyclarprocessforLPGaromatization(38).(CourtesyofChemSys-temsInc.)

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TOLUENE927

Fig.7.Z-Formingprocess owdiagram(38).(CourtesyofChemSystemsInc.)

BPoperateda1000-bpddemonstrationunitin1989–1991initsre neryatGrangemouth,Scotland.UOPhasagreementwithSaudiBasicIndustriesCorporation(SABIC)touseCyclarprocessinanaromaticsplantatYanbu,SaudiArabia.MitsubishiOilandChiyoda’sZ-formingprocess(Fig.7),whichhasbeenproveninademonstrationunit,shutdowninDecember1991atMitsubishiOil’sKawasakire nery,usesametallosilicatezeolitecatalysttopro-motedehydrogenationofparaf ns,followedbyoligomerizationanddehydrocycli-zationreactions.FeedstockconsistsoflightnaphthaorLPG.TheBTXcomponentoftheproductismostlytoluene.

ExxonMobilhasaprocess(Fig.8)thatusesZSM-5zeolitecatalystwithpalladiumandzincpromoterstooligomerizeC2orC3tocyclohexane,whichinturnisdehydrogenatedtotoluene,benzene,andxylenes.Similarlytothisprocess,theKTI’sPyroformprocess(Fig.9)usesashape-selectivezeolitecatalysttoconvertC2andC3paraf nstoaromatics.Theuniquefeatureofthisprocessisthedesignofproprietaryreactorfurnaceandtheoperatingtemperatureandpressurepro les.IFandSalutearedevelopingtheAroformerprocess(Fig.10)touseC3–C5,LPG,andlightnaphthafeedstocks.Chevron’sAromaxprocess(Fig.11)issimilartoconventionalcatalyticreformingprocess,exceptthatitsfeedstockhashighparaf nicityandithasextrasulfur-removalfacilitiestoavoiddeactivatingitsL-typezeolitecatalyst,whichisverysensi-tivetosulfur.

Table8summarizestheChemSystems’analysisofthecostofproductionofBTXfromthesefeeds,resultinginarecommendationofthebest-suitedtechnol-ogyforeachfeedstock.

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¼steam.(CourtesyofChem928

)

.cnIsmetsySFig.8.ExxonMobil’sprocessforaromaticsfromethane(38).Ref.¼refrigeration;CW¼coolingwater;Stm.

Petroleum Technology, Volume 1-2

Quench1st Stage2nd Stage3rd Stage929

Fig.9.Inc.)

Pyroformprocess owdiagram(38).Ref.¼refrigeration,CW¼coolingwater,andBFW¼boilingfeedwater.(CourtesyofChemSystems