2125_02_26 Petroleum Technology, Volume 1-2

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914TOLUENEVol.

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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

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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