Catalytic wet oxidation of phenol in a trickle bed reactor

ChemicalEngineeringJournal103(2004)

51–57

Catalyticwetoxidationofphenolinatricklebedreactor

A.Singh,K.K.Pant ,K.D.P.Nigam

DepartmentofChemicalEngineering,IndianInstituteofTechnology,HauzKhas,NewDelhi-110016,India

Received7January2004;accepted17June2004

Abstract

Catalyticliquidphaseoxidationofaqueousphenolwasstudiedinapilotplanttricklebedreactorusingacopperoxidecatalystsupportedonalumina.CatalystswerepreparedbyimpregnatingCuOonaluminaextrudatesandoncomputerdesignedshape(CDS)aluminapellets.Phenoloxidationwascarriedoutina2.54cmdiameterreactorwithacatalystbedlengthof60cmandinthepressurerangeof1–15atmandtemperaturerangeof373–403KComparedtoaluminaextrudateshigherphenolconversionwasachievedoverCDSpelletsunderidenticalconditions.Phenoloxidationreactionwasstronglyaffectedbythetemperatureandpressure,however,pressurehadlesseffect.Hydrodynamicsofthereactorhadstrongin uenceonphenoloxidationreaction.Aonedimensionalaxialdispersionmodelwasproposedtosimulatetheexperimentalresults.Themodelsatisfactorilyexplainstheexperimentalresultswithadeviationof±15%.©2004ElsevierB.V.Allrightsreserved.

Keywords:Tricklebedreactor;Oxidation;Phenol;Catalyst;Modelling

1.Introduction

Manyindustrieslikepetroleum,petrochemicalandpharmaceuticalgeneratewastewaterthatcontainsorganicproductshazardoustotheenvironmentespeciallytonaturalwaterresources.Phenolistheoneofthemostseriousorganicpollutant.Theimportanceofphenolinwaterpollutionstemsfromtheirextremetoxicitytotheaquaticlifeandresistancetobiodegradation.Phenolimpartsastrongdisagreeableodorandtastetowatereveninverysmallconcentration.Directbiologicaltreatmentisunfeasibleforwastewaterstreamhav-ingphenolconcentrationmorethan200mg/l.Inthesecasesitmaybenecessarytoemploylessconventionaltechniques,suchaschemicaloxidationorwetairoxidationtoachievedestructionoftherecalcitrantorganicspresent.Apartfromthesemethodsothertechniques,suchasphotoassistedhet-erogeneouscatalysis[1]andoxidationatsupercriticalwaterconditionsareusedorbeingusedatvariousstageofdevel-opment,however,thesetechniquesarecostintensive[2].Wetairorthermalliquidphaseoxidationprocessesareknowntohaveagreatpotentialinadvancewastewatertreat-

Correspondingauthor.Tel.:+911126596172;fax:+911126581120.E-mailaddress:kkpant@chemical.iitd.ac.in(K.K.Pant).

mentfacilities[3].However,thereactionconditionsrequiredtoachieveoxidationaresevere,typicallybeingintherangeoftemperature473–573Kandpressure70–130kg/cm2.Undersuchextremeconditions,theselectionofmaterialforconstructionbecomescritical,ascorrosionratesareratherhighduetothepresenceofawiderangeofoxygenatedcompounds;oxidationofdiluteaqueoussolutionsoforganicpollutantsusingoxygenasanoxidizingagentoverasolidcatalystoffersanalternativetowetairoxidationasmeansofpurifyingofwastewater[4–6,8].Inthisprocessorganicsareoxidizedtocarbondioxideandwateratmuchlowertemper-aturesandpressures.Dependingonthetypeandamountoforganiccompounddissolvedinwastewater,theprocesscanbedesignedeithertoreducetheirconcentrationortoulti-matelydestroythem.Moreover,incatalyticwetoxidation,thecatalystcanbeeasilyrecovered,regeneratedandreused.Extensivestudieshavebeencarriedoutforremovalofor-ganiccompoundsfromwastewaterusingsmall-scalereactorsoveraseriesofcatalyst[7,9,10].Relativelyfewstudieshavebeenpublishedconcerningcatalyticliquidphaseoxidationoforganiccompoundsinlarge-scaletricklebedreactorswherehydrodynamicparametersprevail.Thepresentstudyaimsphenoloxidationinatricklebedreactorusingcopperoxideimpregnatedonaluminacatalysts.Effectofcatalyst

1385-8947/$–seefrontmatter©2004ElsevierB.V.Allrightsreserved.doi:10.1016/j.cej.2004.06.006

52A.Singhetal./ChemicalEngineeringJournal103(2004)51–57

Nomenclatureaeffectiveexternalsurfaceareaformasstransfer(cm2/(cm3ofemptytube))cconcentration(mol/cm3)dpcatalystpelletdiameter(cm)

Dmoleculardiffusivityinliquid(cm2/s)DLaxialdispersioncoef cient(cm2/s)Ggasmass ux(kg/m2s)GalGalaleonumber

GLliquidmassvelocity(g/(cm2/s))

HHenry’sLawconstant,(cm3ofliquid/cm3ofgas)

kLmasstransfercoef cientfromgastoliquid(cm/s)

ksmasstransfercoef cientfromliquidtoparticle(cm/s)

ksr,appapparentsurfacereactionconstant(mol/(gcats))

Kadsorptionconstant(cm3/mol)Lliquidmass ux(kg/m2s)PPecletnumber

PeOoxygenpartialpressure(kg/cm2)

P2totaloperatingpressure(kg/cm2absolute) totalrPhOHphenoldisappearancerate(mol/(gcats))RELReynoldsnumber

Treactiontemperature(K)usuper cialvelocity(cm/s)

z

axialcoordinateintricklebedreactors(cm)

Greeklettersηµeffectivenessρ uidviscosityfactor,(gm/cmdimensionlesss)Bbulkdensityofparticlesinbed(gm/cm3)SubscriptseqequilibriumffeedggasphaseLliquidphaseO2oxygenPhOHphenolsexternalsurfaceofcatalyst

shape,temperature,pressureandeffectofhydrodynamicsoftricklebedhasbeeninvestigatedonphenoloxidation.2.Experimentaldetails2.1.Catalystpreparation

Catalysts(10%CuO/Al2O3)werepreparedbyim-pregnationtechnique.Inthistechniquealuminaextru-

dates(0.159cm)orcomputerdesignedshape(CDS)trilobe(0.127cm)(Sud–ChemieIndiaPvt.Ltd.)weredippedinthecoppernitratesolutionfor6hinordertocompletesoakingoftheliquid.TheCDSpelletsaretrilobeinshapehavinghighersurfaceareawithminimalpressuredropcomparedtoextrudates.ThephysicalpropertiesofthepelletsaregiveninTable1.Thesepelletsweredriedovernightat383Ktore-movetheexcesswaterandthencalcinedfor5hat823Kforcalcinations.Thepelletswerecrushedanddippedinconc.HNO3solutionfor1hunderstirringtodissolvethecopperintoacid.ThesolutionwasdilutedwithdistilledwaterandCuconcentrationwasmeasuredbyatomicabsorptionspec-troscopy.TherewassomeweightlossofCuOduringprepa-rationandheattreatmentandthe nalwt.%ofCuOonthecatalystwas8.5±0.5%.Thetotalsurfaceareasofthecat-alystpelletsweredeterminedbyBETsurfaceareaanalyzer(MicromeriticsUSA)usingN2asadsorbent.Thesurfacear-easofaluminaextrudatesandCDSshapedpelletswere210and235m2/grespectively.AfterimpregnatingwithCuOthesurfaceareaissigni cantlyreducedto190and210 …… 此处隐藏：17288字，全部文档内容请下载后查看。喜欢就下载吧 ……