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Chemical Reaction kinetics in practice

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Articulo relacionado con la cinética de reacciones.

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  • FEATURE

    6OLUMENO

    #HEMICALREACTIONKINETICSINPRACTICE

    4HECHEMICALREACTIONSTAKINGPLACEINTHECHEMICALREACTORFORMTHEHEARTOFANYCHEMICALPROCESS2EACTIONKINETICSARETHETRANSLATIONOFOURUNDERSTANDINGOFTHECHEMICALPROCESSESINTOAMATHEMATICALRATEEXPRESSIONTHATCANBEUSEDINREACTORDESIGNANDRATING"ECAUSEOFTHEIMPORTANCEOFCORRECTANDSAFEDESIGNOF CHEMICALREACTORS CHEMICALREACTIONKINETICS ISAKEYASPECT OF RESEARCHANDDEVELOPMENTINCHEMICALINDUSTRIESINRESEARCHINSTITUTESANDACADEMICCENTERSASWELLASININDUSTRIALLABORATORIES4HEREISANDTHEREWILLALWAYSBEASTRONGNEED FORKNOWLEDGEANDA SKILL BASE CONCERNING THEDETERMINATIONOF REACTIONKINETICSANDTHEIRAPPLICATIONINTHEFORMOFAKINETICMODEL4HISPAPER ISA RESULT OF COOPERATIONWITHIN%UROKINA CONSORTIUMOF OVER%UROPEANCOMPANIESANDUNIVERSITIES!NINDUSTRIALQUESTIONNAIRE INHIGHLIGHTEDTHATINDUSTRYISNOTONLYALITTLECONSERVATIVEINTHEMETHODSITUSESTODETERMINEKINETICSBUTALSOTHATTHEREWASAWIDEAWARENESSOFTHESCOPEFORIMPROVEMENT%UROKINWAS THUS FOUNDED IN TO TRYAND ESTABLISH THEBESTPRACTICESANDTOFACILITATEDEVELOPMENTWORKINKINETICSANDASSOCIATEDAREAS4HEPAPERBRIEmYEXPLAINS SOMEUNDERLYINGTHEORYOFHETEROGENEOUSLY CATALYZEDCHEMICALREACTIONSANDTHEIRKINETICS)TDEALSSPECIlCALLYWITHTHEACQUISITIONOFKINETICDATAANDGIVES RECOMMENDATIONS FOR THE SELECTION OF THE EXPERIMENTALREACTORANDCONDITIONS!PRIMARYAIMOFTHISPAPERISDISCUSSKINETICEXPERIMENTATIONANDMODELING THROUGHA SERIES OF CASE STUDIES ATTEMPTING TO ILLUSTRATEGOODPRACTICEMETHODSINKINETICMODELINGPITFALLSANDRECOMMENDATIONS4HEPAPERCLOSESWITHSOMERECOMMENDATIONSANDAPERSPECTIVEONTHEFUTURENEEDSOFINDUSTRIALREACTIONKINETICS

    2OB*"ERGER%(UGH3TITT'UY"-ARIN&REEK+APTEIJN*ACOB!-OULIJN

    CORRESPONDINGAUTHOR3YNETIX0/"OX"ILLINGHAM#LEVELAND43,"53!4EL&AXEMAILHUGH?STITT ICICOM

  • %UROKIN

    CHEMICALREACTIO

    NKINETICSINP

    RACTICE

    7HATAREKINETICSh+INETICSv IS SIMPLY A TECHNICAL TERM USED TO DESCRIBETHERATEOFACHEMICALPROCESS SUCHASACATALYTICREACTIONAS A FUNCTION OF THE CONDITIONS 4HE MODELS AND THEIRMATHEMATICALMANIFESTATIONSVARYENORMOUSLYINTHELEVELOFCOMPLEXITYANDTHEDEGREETOWHICHTHEYREmECTTHEACTUALCHEMICALANDPHYSICALPROCESSESOCCURRING!TTHEIRSIMPLESTTHEYCANBEOFTHEFORMRATEtF4CONCENTRATIONN WHERENISTERMEDTHEORDEROFREACTION7ITHHETEROGENEOUSCATALYTICREACTIONSTHERE ISMORETHANONE RATE PROCESS OCCURRING IN SERIES 4HE REACTION PROCESSCANBEBROKENDOWNINTOANUMBEROFIDENTIlABLESTEPSALLWITHTHEIROWNRELEVANTRATEEQUATIONSOMEOFWHICHMAYBECOMBINEDINTOANOVERALLREACTIONRATEEQUATION4HESTEPSTYPICALLYCITEDARE -ASSTRANSFEROFREACTANTSTOTHECATALYSTSURFACE !DSORPTIONOFREACTANTSONTOCATALYSTACTIVESITES #ATALYTICREACTION $ESORPTIONOFREACTIONPRODUCTS -ASSTRANSFEROFPRODUCTSAWAYFROMSURFACE3TEPS AND ARE IDENTIlABLE mUID PHASE PHENOMENAAS DISTINCT FROM THE SURFACE PROCESSES THAT CHARACTERIZEADSORPTIONANDREACTIONANDSPECIlCALLYACATALYTICREACTION4HEYCANANDINDEEDSHOULDHAVETHEIROWNRATEEQUATIONSBUTDONOTALWAYSDOSOINPRACTICE4HE SURFACE PROCESS ITSELF ALSO TYPICALLY COMPRISES A

    NUMBER OF DISCRETE STEPS !T ITS SIMPLEST THIS MAY BEENVISAGED AS THE SORPTIONnREACTIONnDESORPTION SEQUENCECITED ABOVE4HE NEXT LEVEL OFMODEL COMPLEXITY THEREFOREINCLUDESTHESESTEPSEITHERASSIMPLESTEPSORASCOMPETITIVEADSORPTION OF TWO REACTANTS OR A REACTANT AND ANOTHERCOMPONENTSUCHASASOLVENTORDILUENT4HISCANBEDONE

    IMPLICITLYWITHINAMATHEMATICALEXPRESSIONFORTHEREACTIONRATE !T THEIR MOST COMPLEX THE REACTION RATE EXPRESSIONCANBEBASEDONTHEMECHANISTICORELEMENTAL STEPSOF THEREACTION4HISCANHAVEINCREASEDMATHEMATICALCOMPLEXITYBUTISGENERALLYABETTERPHYSICALREPRESENTATIONOFTHEPROCESS'IVENTHEABOVEANUMBEROFQUESTIONSARISE7HYARE

    KINETICMODELSREQUIRED7HYISTHERESUCHDIVERSITYINTHEFORM AND EXACTITUDE OF KINETIC AND RATEMODELS(OW ARETHEEXPERIMENTALDATAMEASURED!NDHOWARE THEMODELSDERIVEDANDlTTED4HISPAPERWILLATTEMPTTOANSWERTHESEQUESTIONSINTHECONTEXTOFANINDUSTRIALVIEWPOINT!KEYISSUEISTHATASKINETICMODELSINCREASEINCOMPLEX

    ITYTHEEXPERIMENTALEFFORTTHERANGEANDSCOPEOFEXPERIMENTATION REQUIRED TO BUILD lT AND VALIDATE THE MODELALSOINCREASE4HEPERCEPTIONININDUSTRYAPPEARSTOBETHATTHEEFFORT REQUIRED INCREASESBEYONDTHEPROPORTIONALGAININ BENElT 4HEREFORE FROM THE POINT OF VIEW OF INDUSTRYTHENEEDFORCOMPLEXMODELSBASEDONTHEPHYSICOCHEMICALEVENTS MUST EITHER BE JUSTIlED OR THE EFFORT REQUIRED TODERIVETHEMSIGNIlCANTLYREDUCED4HIS PAPER WILL THEREFORE EXPLAIN AND ILLUSTRATE THE

    NEED FOR AND THE METHODS USED TO OBTAIN RELIABLEKINETIC DATA FOCUSING ON HETEROGENEOUS CATALYSIS )T WILLDEAL WITH THE ACQUISITION OF KINETIC DATA GIVE SOMETHEORETICAL BACKGROUND ON KINETICS AND KINETIC MODELINGAND WILL PROVIDE RECOMMENDATIONS FOR THE SELECTION OFTHE EXPERIMENTAL REACTOR AND CONDITIONS !MAJOR PART OFTHE PAPERWILL CONSIDER KINETICMODELING THROUGH THE USEOF A SERIES OF CASE STUDIES ATTEMPTING TO ILLUSTRATE GOODPRACTICE METHODS IN KINETIC MODELING AND PITFALLS ANDRECOMMENDATIONS)NVIEWOFTHELIMITEDSPACEMASSTRANSFERANDHYDRODYNAMIC ASPECTSWILL NOTBE COVERED IN THE CASE

    %UROKININDUSTRYACADEMIACOLLABORATIONTOWARDSBETTERKINETICSINTERMEZZO

    %UROKIN ISACONSORTIUMOF%UROPEANBASEDCOMPANIES TOGETHERWITHANUMBEROFACADEMICCENTERSFOCUSEDONDEVELOPINGPRACTICEINKINETICMODELING7EBSITEWWWEUROKINORG)TWASESTABLISHEDINAFTERTHENEEDWASREALIZEDVIAAQUESTIONNAIREEXTENSIVELYCITED IN THIS PAPER AND TWO WORKSHOPS IN TO BETTERDElNE NEEDS AND COLLECTIVE DRIVERS )T CURRENTLY CONSISTS OF COMPANIES !KZO .OBEL $OW "ENELUX $3- 2ESEARCH )&04ECHNIP"ENELUX3HELL2ESEARCHAND4ECHNOLOGY#ENTRE3TATOIL,INDE%NI4ECNOLOGIE3YNETIXAND%##HEM4ECHNOLOGIESANDFOUR ACADEMIC CENTERS $ELFT 5NIVERSITY OF 4ECHNOLOGY 'HENT5NIVERSITY .45 4RONDHEIM AND5# ,OUVAIN 4HEMEMBERSHIPBASE IS EVIDENTLY VERY BROAD FROM SEVEN DIFFERENT COUNTRIESAND COMPANY ACTIVITIES IN OIL AND GAS PETROCHEMICALS BULKAND lNE CHEMICALS MANUFACTURE ENGINEERING CONTRACTING TO THEOIL PETROCHEMICALS AND lNE CHEMICALS MARKETS AND A CATALYSTCOMPANY

    %UROKINS STATED AIM IS TO PRODUCE A PRECOMPETITIVE TOOLKIT FORMEASURINGKINETICDATAANDMODELDEVELOPMENTFORHETEROGENEOUSCATALYTICSYSTEMS4HEACTIVITIESARECURRENTLYFOCUSEDONI %XPERIMENTAL METHODS TO DETERMINE REACTION KINETICS EGINVESTIGATIONOFTHECAPABILITIESOFDIFFERENTTYPESOFLABORATORYREACTORSTOMEASURETHEKINETICSOFSPECIlCREACTIONCLASSES

    II $EVELOPMENTOFMODELSFORASETOFSELECTEDLABORATORYREACTORSYSTEMSTOBEUSEDFORPROCESSINGEXPERIMENTALDATAANDORTHE DETERMINATION OF SUITABLE EXPERIMENTAL CONDITIONS EGTOASSESS IF THEPROPOSEDEXPERIMENTALCONDITIONSARE IN THEKINETICALLYORTHEMASSTRANSFERCONTROLLEDREGIME

    III-ETHODS FOR THE DETERMINATION OF KINETIC MODELS FROMEXPERIMENTALDATAINCLUDINGMODELDISCRIMINATIONPARAMETERESTIMATIONANDDESIGNOFEXPERIMENTS

  • %UROKIN

    #HEMICALREACTIO

    NKINETICSINP

    RACTICE

    STUDIES4HEPAPERWILLCLOSEWITHAFORWARDLOOKINGSECTIONCONSIDERINGTHEFUTURENEEDSOFINDUSTRIALREACTIONKINETICS

    7HYDOWENEEDKINETICMODELS4HISPAPERISARESULTOFCOOPERATIONWITHIN%UROKIN)NTERMEZZOACONSORTIUMOFOVER%UROPEANCOMPANIESAND UNIVERSITIES ESTABLISHED IN SPECIlCALLY TO FACILITATEACTIVECOLLABORATIONINTHElELDOFCATALYTICREACTIONKINETICS4HIS INITIATIVE BY SO MANY LEADING COMPANIES GIVES ANINDICATION OF THE IMPORTANCE THAT THE CHEMICAL INDUSTRYATTACHESTOKINETICS"UTWHYAREKINETICSIMPORTANT+NOWLEDGE OF THE RATE OF A CATALYTIC REACTION AND ITS

    SELECTIVITYASAFUNCTIONOFTHEPROCESSCONDITIONSANDREACTANTCONCENTRATIONSISESSENTIALFORTHEAPPLICATIONOFTHECATALYSTIN A COMMERCIAL REACTOR-ORE SPECIlCALLY THE KINETICS OFTHEREACTIONAREREQUIREDINTHEFORMOFAMATHEMATICALRATEEXPRESSIONTHATCANBEUSEDTORELIABLY TRANSLATE LABORATORYANDPILOTSCALEDATAINTOTHEDESIGNOFACOMMERCIALSCALEUNIT4HAT RATEORKINETICEXPRESSION TELLSHOWTHE REACTION RATEVARIESWITHPROCESSCONDITIONSSUCHASTEMPERATUREPRESSUREANDCOMPOSITIONANDPREFERABLYALSOWITHAMEASUREOFTHEVOLUMETRICCONCENTRATIONOFCATALYTICSITES4HEIMPORTANCEOF A REACTIONS KINETICS IS THAT THE RATE AND SELECTIVITY OF AREACTION DETERMINE THE SIZE OF THE CATALYTIC REACTOR FOR AGIVENOVERALLPRODUCTION RATE7ITHOUT A RELIABLEMEANS TOPREDICTTHEREACTIONRATETHEREACTORDESIGNCOULDBEHIGHLYSPECULATIVE4HEREARESEVERALEFFECTSTHATCANARISEFROMTHISUNCERTAINTY&IRSTLYWITHOUTRELIABLEESTIMATESOFTHECAPITALCOSTSNEEDEDTOBUILDAPRODUCTIONPLANTANDTHEPROBABLEOPERATINGCOSTSITISNOTPOSSIBLETOCARRYOUTAMEANINGFULEVALUATION OF THE ECONOMIC MERITS OF BUILDING THE PLANTAND WITHOUT A PERSUASIVE ECONOMIC IMPERATIVE THE PLANTIS UNLIKELY TO BE SANCTIONED 3ECONDLY AND PERHAPS MOREIMPORTANTLYWITHOUTRELIABLEKINETICSITISNOTFULLYPOSSIBLETOEVALUATETHESIDEREACTIONSANDTHEDYNAMICEFFECTSTHATMAYOCCURINTHEREACTORWHICHISACRITICALSTEPINASSESSINGTHEOPERATIONALSAFETYANDENVIRONMENTALIMPACTOFACHEMICALSPRODUCTIONUNIT

    7HATDOESINDUSTRYUSEKINETICSFOR4HE IMPORTANCE OF KNOWLEDGE AND OF HAVING A SKILL BASECONCERNINGTHEDETERMINATIONOFREACTIONKINETICSANDTHEIRAPPLICATION IN THE FORM OF A KINETIC MODEL IS CLEAR 4HISBEGS THE QUESTION OF HOW GOOD INDUSTRY IS AT MEASURINGAND APPLYING CHEMICAL RATE MODELS AND WHAT PRECISELY ITDOES WITH THEM 4HIS WAS PUT TO THE TEST IN WHENTHEh#HEMICAL%NGINEERINGINTHE!PPLICATIONSOF#ATALYSISv7ORKING 0ARTY OF THE %UROPEAN &EDERATION OF #HEMICAL%NGINEERINGAPPROVEDASURVEYOFINDUSTRIALPRACTICEINTHEMEASUREMENTANDEVALUATIONOFKINETICS4HERESULTSOFTHISSURVEYWEREPUBLISHEDININSUMMARYFORM;=4WENTYFOUR CHEMICAL ANDOIL COMPANIES ENGINEERING CONTRACTORSANDCATALYSTMANUFACTURERSRESPONDEDTOTHEQUESTIONNAIREANDTHATLEVELOFRETURNINDICATESHOWSERIOUSLYINDUSTRYTAKESTHIS ISSUE 4HE RESULTS MAKE INTERESTING READING NOT ONLYFROM THE VIEWPOINTOFHOW INDUSTRY TREATS ITS KINETICSBUTALSOTHEDIVERSITYACCORDINGTOTHEINDUSTRYSECTOROFHOWTHEY USE THEM !DDITIONALLY A SURVEY OF THE GAPS ANDNEEDS FOR CATALYSIS IN %UROPEAN INDUSTRY;= STRESSED THEIMPORTANCE OF FURTHER DEVELOPMENTS IN KINETICS RESEARCH#ONSIDER lRSTLY HOW COMPANIES USE THEIR KINETICS THE

    PERCEIVED REASON FOR THEDETERMINATIONOF KINETIC AND RATEMODELS 4HE OVERALL RESULTS FROM THE SURVEY ARE SHOWN IN&IGUREANDINDICATEAFAIRLYEVENTHREEWAYSPLITBETWEENCATALYST DEVELOPMENT PROCESS DEVELOPMENT AND PROCESSOPTIMIZATION3IGNIlCANTLYTHEREISONLYSMALLMINORITYUSEOFKINETICDATAFORMECHANISTICRESEARCHBYCONTRASTAMAJORFORCEINACADEMIA7HENTHESAMEDATAAREPRESENTEDBYTHEINDUSTRYSECTOR

    IN &IGURE SOME CLEAR TRENDS EMERGE 4HE CHEMICAL ANDOILCOMPANIESMAINLYUSEKINETICS FORPROCESSDEVELOPMENTANDPROCESSOPTIMIZATIONANDTOASMALLEREXTENTFORCATALYSTDEVELOPMENT !S MIGHT BE EXPECTED CATALYST PRODUCERSFOCUSONCATALYSTDEVELOPMENTWHILEENGINEERINGCOMPANIESCONCENTRATE ON PROCESS DEVELOPMENT 3OME MECHANISTICRESEARCHISDONEBYTHECATALYSTPRODUCERSANDTHECHEMICALCOMPANIESBUTTHISDOESNOTEXCEEDOFTHEUTILIZATIONOFKINETICDATA

    PROCESSDEVELOPMENT

    PROCESSOPTIMIZATION

    OTHER

    CATALYSTDEVELOPMENT

    MECHANISTICRESEARCH

    &IGURE5TILIZATIONOFKINETICDATAININDUSTRY

  • %UROKIN

    #HEMICALREACTIO

    NKINETICSINP

    RACTICE

    4HE LATERPARTSOF THE SURVEY FOCUSEDONHOW INDUSTRYMEASURESITSDATAANDTHETYPESOFMODELSITUSESTOREPRESENTTHEKINETICS"EFORECONSIDERINGTHESEASPECTSITISTIMELYTOCONSIDERTHEBACKGROUNDTOKINETICTHEORYTHEMEASUREMENTOFKINETICDATAANDREACTIONKINETICMODELING

    PROCESSOPTIMIZATION

    PROCESSOPTIMIZATION

    OTHER

    OTHER

    CATALYSTDEVELOPMENT

    CATALYSTDEVELOPMENT

    MECHANISTICRESEARCH

    MECHANISTICRESEARCH

    ACHEMICALCOMPANIES

    BOILCOMPANIES

    CCATALYSTCOMPANIES

    PROCESSDEVELOPMENT

    PROCESSDEVELOPMENT

    PROCESSOPTIMIZATION

    OTHER

    CATALYSTDEVELOPMENT

    MECHANISTICRESEARCH

    PROCESSDEVELOPMENT

    DENGINEERINGCOMPANIES

    PROCESSOPTIMIZATIONOTHER

    CATALYSTDEVELOPMENT

    MECHANISTICRESEARCH

    PROCESSDEVELOPMENT

    &IGURE5TILIZATIONOFKINETICDATAFORDIFFERENTCHEMICALINDUSTRYSECTORS

    4YPESOFKINETICMODELS2ESEARCHERSINCATALYSISKINETICSANDREACTORENGINEERINGAREGENERALLYWELLINFORMEDABOUTTHEGENERALTHEORYCONCERNINGREACTIONKINETICS!TTHESIMPLERLEVELWECANDISTINGUISHTWOCOMMONBASICAPPROACHESTOREACTIONMODELINGSUMMARIZEDIN4ABLE

    0OWERLAWKINETICS&ORTHEIRREVERSIBLEGASPHASEREACTION!"m#THERATEOFREACTIONMAYBEREPRESENTEDBYANEXPRESSIONOFTHEFORMRKP!NP"M

    WHEREP!ANDP"ARETHEPARTIALPRESSURESOFREACTANTS!AND"RESPECTIVELYANDKISTHERATECONSTANT4HEEXPONENTSNANDMARETERMEDTHEhORDERSOFREACTIONv)TMAYSEEMNATURALTOASSUMEARATEEXPRESSIONRK;!=;"=WHERE THE ORDERS OF REACTION MATCH THE STOICHIOMETRICCOEFlCIENTS AND THUS A SECOND ORDER REACTION FOR THISEXAMPLElRSTORDERINEACHREACTANT4HISISNOTNECESSARILYTHECASE!REACTIONMECHANISMCANINCORPORATEANUMBEROFSUBREACTIONSANDTHEPOWERLAWAPPROACHDISGUISESTHIS4HEREALRATEEXPRESSIONWILLREmECTTHEKINETICSOFTHEPOTENTIALLYSLOWESTORRATEDETERMININGSTEP4HEREACTIONORDERSHOULDTHEREFOREALWAYSBEDETERMINEDEXPERIMENTALLY4HEPOWERLAWEXPRESSIONISCOMMONLYUSEDBECAUSEOF

    ITSSIMPLICITYANDITSPROPERTYTHATITFREQUENTLYlTSTHEDATARATHER EASILY 4HE ANCIENT WONDER OF RECONCILING DATA BYPLOTTING THEM ON LOGLOG GRAPH PAPER HAS NOT FADED EVENIN THIS HIGH TECHNOLOGY AGE )N CATALYSIS THIS EXPRESSIONISNOTHOWEVERBASEDONASOUNDPHYSICOCHEMICALTHEORYANDTHEREFORETHERELIABILITYOFTHERESULTSANDPREDICTIONSISLIMITEDTOTHERANGEOFCONDITIONSUNDERWHICHTHEKINETICEXPERIMENTSWEREPERFORMED

    %FFECTOFEQUILIBRIUM! GIVEN REACTION SUCH AS! "m # CAN OFTEN OCCUR INBOTHDIRECTIONSVIZ!"#7HICHDIRECTIONPREVAILSAT A GIVEN CONDITION DEPENDS ON THE THERMODYNAMICS%QUILIBRIUM CORRESPONDS TO THE MINIMIZATION OF 'IBBSFREEENERGY)FNOBARRIEREGACTIVATIONENERGYEXISTSTHENASYSTEMWILLALWAYSMOVETOWARDSEQUILIBRIUM4WO REACTIONS CAN BE DElNED EACH WITH ITS OWN RATE

    EQUATION!SSUMINGFORTHESAKEOFSIMPLICITYAlRSTORDERDEPENDENCYFOREACHCOMPONENT

    0OWERLAWEXPRESSION

    RKEXPP!P" ,ANGMUIR(INSHELWOOD(OUGEN7ATSONTYPEEXPRESSION

    R

    4YPESOFCOMMONLYUSEDRATEEXPRESSIONSFORTHEREACTION!G"Gm#G

    4ABLE

    N M

    %!24

    KR+!ADSP!+"ADSP"+!ADSP!+"ADSP"+#ADSP#

  • %UROKIN

    #HEMICALREACTIO

    NKINETICSINP

    RACTICE

    ! KINETIC MODEL WAS DERIVED FOR AN EFmUENT TREATMENT PROCESSTHE CATALYTIC DECOMPOSITION OF THE POLLUTANT 4HIS WAS BASEDON EXPERIMENTAL DATA WHERE THE REACTION WAS OBSERVED TO BEIRREVERSIBLE AND lRSTORDER IN THE REACTANT 4HE DATA WERE ONLYMEASUREDOVER A NARROW TEMPERATURE RANGE THAT BELIEVED TO BETHEPROBABLEOPERATINGDOMAINFORTHEINDUSTRIALSCALEREACTOR4HEEXPRESSIONFORTHElRSTORDERRATECONSTANTTHATWASUSEDTOlTTHEEXTENSIVEDATASETWAS

    (EREITCANBESEENTHATTHE!RRHENIUSTERM;!%A4=HASBEENSUPPLEMENTEDBYASECONDTEMPERATURETERMINTENDEDTOIMPROVETHESTATISTICALlTFORATOTALOFFOURlTTINGPARAMETERSFORESSENTIALLYONEVARIABLE4HISWORKEDWELLUNTILAPLANTOPERATINGONEOFTHESE

    4HROUGH OVERPARAMETERIZATION THE ABILITY OF THE MODEL TO EXTRAPOLATE BEYOND THEINTERMEZZO

    REACTORSWANTED TO INCREASE THROUGHPUT AND PROPOSED INCREASINGTHEOPERATINGTEMPERATURETOACHIEVETHIS4HERESULTOBTAINEDWITHTHE ABOVE MODEL IS SHOWN IN &IGURE )T WAS SURPRISING THAT ATHIGHERTEMPERATURESTHECONVERSIONWASESSENTIALLYINDEPENDENTOFTEMPERATUREANDEVENTUALLYEXPERIMENTALDATASHOWEDTHATTHISWASNOTTRUE4HEPROBLEMLAYINTHEADDITIONALTEMPERATURETERMINTHEKINETICEXPRESSION)N THE lRST INSTANCE THIS ADDITIONAL TEMPERATURE TERM WAS SIMPLYREMOVED AND A SIMPLE !RRHENIUSTYPE RELATIONSHIP WAS lTTEDTHROUGH THE DATA 4HISMODIlED EXPRESSION WAS FAR MORE ABLE TOPREDICT PERFORMANCE OUTSIDE THE EXPERIMENTAL TEMPERATURE RANGE!COMPARISONOF THEPREDICTEDDESIGNCATALYSTVOLUMES TOACHIEVEAGIVENCONVERSION ISSHOWN IN&IGURE4HEREVISEDMODELMOREACCURATELY PREDICTS THE EXPECTED TREND WHICHWAS ALSO OBSERVEDEXPERIMENTALLY

    LNK!%A#4

    4#

    #

    FORWARDREACTION !"m# RATE RFKF;!=;"=BACKREACTION #m!" RATE RBKB;#=4HESEARENOTINDEPENDENTEXCEPTAThVERYLOWvCONVERSIONSWHEREEQUILIBRIUMISNOTAPPROACHED!TOTHERCONDITIONSTHENETFORWARDREACTIONRATEFOR!"#ISGIVENBYRRFRBKF;!=;"=KB;#=4HUS EQUILIBRIUM OCCURS WHEN THE FORWARD AND REVERSEREACTION RATESAREEQUAL RF RB ANDHENCENONET REACTIONOCCURS&ORTHEREACTION!"#THEEQUILIBRIUMCONSTANTISGIVENBY+EQ[;#=;!=;"=] EQ)TMAYTHUSBESHOWNTHAT+EQKBKF4HENETFORWARDREACTIONRATEISTHEREFOREGIVENBYRKF[;!=;"=n;#=+EQ]

    %FFECTOFTEMPERATURE4HEVALUEOFTHEEQUILIBRIUMCONSTANTISASTRONGFUNCTIONOFTEMPERATURE&ORENDOTHERMICREACTIONS+EQANDEQUILIBRIUMCONVERSIONINCREASEWITHTEMPERATUREWHILEFOREXOTHERMICREACTIONS THE CONVERSE IS TRUE4HIS STRONGDEPENDENCEONTEMPERATUREISALSOPREVALENTINREACTIONRATECONSTANTSANDSO THE NEXT LEVEL OF DETAIL TO BE INTRODUCED MAY BE THETEMPERATUREDEPENDENCEOFTHERATEOFREACTION4HISISMOSTCOMMONLYDONEUSINGAN!RRHENIUSTYPEEXPRESSIONK!EXP%A24(ERE%AISKNOWNASTHEh!CTIVATION%NERGYv2EACTION

    RATE CONSTANTS AND EQUILIBRIUM CONSTANTS COMMONLY SHOWAGREEMENTWITHTHISRELATIONSHIP4HISRELATIONSHIPISSHOWNIN&IGUREWITHCURVESPLOTTEDFORDIFFERENTACTIVATIONENERGIESALLBASEDAROUNDASIMILARRATECONSTANTAT+)TCANBESEENTHATTHEVALUEOF%AHASAVERYSTRONGINmUENCEONTHERATEDEPENDENCYONTEMPERATURE4HISISIMPORTANTINTHEDESIGNOFCHEMICALREACTORS

    4HE ACTIVATION ENERGY IS A COMMONLY CITED PARAMETERANDITSVALUEOFCOURSETELLSTHEREACTIONENGINEERHOWDEPENDENTTHEREACTIONRATEISONTEMPERATURE6ALUESOFnK*MOL ARE TYPICAL FORMANY CATALYZED REACTIONS#OMBUSTIONANDMANYOTHERNONEQUILIBRIUMLIMITEDREACTIONSMAYHAVEMUCHHIGHERVALUESK*MOLFOREXAMPLE!RULEOFTHUMBOFTENQUOTEDISTHATTHERATEOFAREACTIONWILLDOUBLEFOREVERY+RISEINTHEREACTIONTEMPERATURE4HISCORRESPONDSTOANACTIVATIONENERGYINTHERANGE nK*MOLATTYPICALREACTIONTEMPERATURES4HUSTHEREACTIONENGINEER

    EXPERIMANTALDOMAINISSEVERELYCOMPROMISEDCATALYTICDECOMPOSITIONREACTION

    4EMPERATURE#

    RELATIVEREACTIONRATECONSTANT ACTIVATIONENERGYK*MOL

    INCREASING%!

    &IGURE2EACTIONRATESTRONGLYDEPENDSONTEMPERATURE

  • %UROKIN

    #HEMICALREACTIO

    NKINETICSINP

    RACTICE

    ,ANGMUIRn(INSHELWOODn(OUGENn7ATSONKINETICS)NORDERTOOBTAINAMOREMEANINGFULKINETICEXPRESSIONITISNECESSARYTOSTARTINTRODUCINGPHYSICALANDCHEMICALPROCESSESOCCURRING AT THE CATALYST SURFACE INTO THE MATHEMATICALREPRESENTATION/NEOFTHESIMPLESTMETHODSANDMOSTPOPULARAPPROACHESTOTHISISVIATHE,ANGMUIRn(INSHELWOODMODELAND THE ASSOCIATED ,ANGMUIRn(INSHELWOODn(OUGENn7ATSON,((7TYPEKINETICEXPRESSION ! ,ANGMUIRn(INSHELWOODn(OUGENn7ATSON TYPE EXPRESSIONISDERIVEDUSINGTHEASSUMPTIONSTHATTHEADSORPTIONOF ALL COMPONENTS CAN BE DESCRIBED BY THE ,ANGMUIRn(INSHELWOODMODEL AND THAT ONE SURFACE REACTION IS RATEDETERMINING4HE SHAPEOF THE RATEEXPRESSIONDEPENDSONTHE CHOICE OF THE RATEDETERMINING STEP ! STUDY OF THETHEORETICAL BACKGROUND CAN HELP THE RESEARCHER TO lNDTHE MOST PROBABLE RATEDETERMINING STEP AND TO OBTAINPROPER ESTIMATES OF THE KINETIC PARAMETERS WHICH CAN BEUSED AS INITIAL ESTIMATES FOR THE PARAMETER lTTING 4HESEINITIAL ESTIMATES SHOULD ALSO BE USED TO CHECK AFTERWARDSIF THE PARAMETERS FOUND BY THE lTTING ROUTINE ARE INPHYSICOCHEMICALLYACCEPTABLERANGES4HISMODEL THUSMAKES ASSUMPTIONS ABOUT ADSORPTION

    ANDDESORPTIONONTHECATALYST SURFACE!T ITS SIMPLEST THE,ANGMUIRn(INSHELWOOD MODEL ASSUMES THAT ALL REACTANTSADSORBONTOCATALYST SURFACESAND THAT REACTIONOCCURSASASURFACEPROCESS4HISYIELDSAKINETICEXPRESSIONOFTHEFORM

    RATEt

    4HROUGH OVERPARAMETERIZATION THE ABILITY OF THE MODEL TO EXTRAPOLATE BEYOND THE

    CAN IMMEDIATELY START JUDGING THE SUSCEPTIBILITY OF A REACTION TO RUNAWAY SELECTIVITY LOSS OR EFFECTIVE EXTINCTION IFTHETEMPERATUREGOESOUTSIDETHEIDEALOPERATINGWINDOW!SIDEREACTIONWITHFOREXAMPLEANACTIVATIONENERGYOFK*MOLTELLSTHEDESIGNCHEMICALENGINEERTHATIFTHETEMPERATUREISALLOWEDTORISETHESELECTIVITYWILLFALLRAPIDLY&URTHERMOREUNLESSTHATSIDEREACTIONISCONSTRAINEDTHENTHISREPRESENTSARUNAWAYPOTENTIALANDTHATMUSTBECONSIDEREDINTHEREACTORANDCONTROLSYSTEMDESIGN'IVEN THEPHYSICAL INTERPRETATIONS THATCANBEATTACHED

    TO THE ACTIVATION ENERGY IT CAN EASILY BE SEEN WHY THISAPPROACH IS POPULAR )T IS STILL HOWEVER CONSTRAINED BYTHE mAWS OF THE EMPIRICAL POWER LAW APPROACH "ECAUSEOF THE LACK OF PHYSICOCHEMICAL RELEVANCE THE ACCURACY OFTHE KINETIC EXPRESSION AND THE APPLICATIONOF THEMODEL ISRESTRICTEDTOTHEEXPERIMENTALCONDITIONSUNDERWHICHITWASDETERMINED&OREXAMPLEITMAYBETEMPTINGTOIMPROVEATEMPERATURE

    lT BY INCREASING THE NUMBER OF TEMPERATURE TERMS IN THEEXPRESSION 4HIS IS NOT ADVISABLE SEE )NTERMEZZO "YSTATISTICALLYIMPROVINGTHElTWITHATERMTHATHASNOPHYSICALMEANING THEAPPLICATIONOF THEMODEL IS TIGHTLY RESTRICTEDTOTHEEXPERIMENTALRANGEWHICHINTHISCASEPREVENTEDUSEOFTHEORIGINALMODELTOEVALUATEAREACTOROPERATINGATANINCREASED TEMPERATURE4HIS EMPHASIZES THE IMPORTANCEOFNOTINCLUDINGTOOMANYPARAMETERSINAMODELPARTICULARLYWITH THOSE PARAMETERS THAT DO NOT HAVE ANY PHYSICALSIGNIlCANCE )T IS ALWAYS WORTH REMEMBERING THAT WITHENOUGHlTTINGPARAMETERSAMODELCANBEFORCEDTOlTANYDATASETBUTJUSTBECAUSETHEREISAGOODSTATISTICALlTDOESNECESSARILYNOTMEANTHATITISAGOODMODEL

    &IGURE0REDICTEDEXITCONCENTRATIONUSING2ATEEXPRESSION &IGURE0REDICTEDCATALYSTVOLUMETOACHIEVEAGIVENCONVERSION

    TEMPERATURE

    LOGEXITCONCENTRATION

    TEMPERATURE

    DESIGNCATALYSTVOLUME

    NEWMODEL

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    2ATEEXPRESSIONS!CCORDING TO THEDIFFERENTASSUMPTIONSSEVERAL RATEEXPRESSIONSFOR THESURFACE REACTIONHAVEBEENPROPOSED )N&IGURE SOMEREACTIONRATEEXPRESSIONSAREDISPLAYED4HECONSTANTSABCANDDAPPLYTOTHEPOWER LAWMODEL4HERATECONSTANT ISGIVENBYK4HEPARAMETERS+./+.(AND+(/ARETHEADSORPTIONCONSTANTS4HE RATEEXPRESSIONSDEPENDON THE LOCALPARTIALPRESSURES0./0.(0/AND0(/!TGIVENINLETCONCENTRATIONSTHE./AND.(OUTLETVALUESARECOMPUTEDUSINGTHEREACTORCONTINUITYEQUATIONSFOR.(AND./4HEPARAMETERSAREADJUSTEDSUCHTHATTHESUMOF

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    #HEMICALREACTIO

    NKINETICSINP

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    3TATISTICALTECHNIQUESHELPTOPERFORMEXPERIMENTALDESIGNANDTOlNDOPTIMALKINETIC MODELS!CASESTUDYOFTHESELECTIVEREDUCTIONOF./BY.(

    SQUAREDRESIDUALS332THEDIFFERENCESBETWEENTHEMEASUREDANDTHECOMPUTED./AND.(OUTLETVALUESISMINIMIZED

    %XPERIMENTALDATA&IGUREDISPLAYSTHELEVELSOFTHEINLETCONCENTRATIONS4HEVALUESHAVEBEENARRANGEDUSINGA CENTRAL COMPOSITE DESIGN CONSISTINGOF CORNERS OF THE CUBE LOWHIGH VALUES STAR POINTS ORANGEOUTSIDE THE CUBE AND ONE OR MORE REPLICATES IN THE CENTER !COMPOSITEDESIGNHASBEENCHOSENASITISSUITABLEFORDETERMINATIONOF THE NONLINEAR EFFECTS ARISING FROM THE RATE EXPRESSIONS AND THESOLUTIONOFTHEDIFFERENTIALMASSBALANCES

    &IGURE#ENTRALCOMPOSTEDESIGN

    0ARAMETERESTIMATION&OR ALL SELECTEDMODELS THE LEASTSQUARES ESTIMATES OF THE RATECONSTANTANDTHEADSORPTIONCOEFlCIENTSHAVEBEENlTTED(OWEVERIN MANY CASES EXTREMELY LARGE STANDARD ERRORS AND MUTUALCORRELATIONS OF THE ESTIMATED PARAMETERS WERE EXPERIENCED )NTHE,ANGMUIRn(INSHELWOODMODELTHECORRELATIONSBETWEENKAND+./ANDBETWEEN+.(AND+(/WEREANDRESPECTIVELY4HIS INDICATES ILLCONDITIONEDBEHAVIOROF THEESTIMATIONPROBLEMINCLUDING VERY SENSITIVE AND LESS RELIABLE PARAMETER RESULTS5SINGTHEhPARAMETERINDENOMINATORvPRINCIPLESTHESEINACCURATERESULTS HAVE BEEN CONSIDERABLY IMPROVED !FTER DIVISION OF THENUMERATOR AND THE DENOMINATOR OF THE ,ANGMUIRn(INSHELWOODRATEBYTHECOMMONPARAMETERPRODUCTK+.(+./ANDREARRANGINGTHE PARAMETERS IN THE DENOMINATOR NEARLY ALL HIGH CORRELATIONSAND HIGH STANDARD ERRORS DISAPPEARED 4HIS REPARAMETERIZATIONPRODUCESA@CLOSETOLINEARMODELBYCLEARINGOFFCONSTANTSINTHENUMERATOROFTHERATEEXPRESSION

    -ODELSELECTION)NORDERTOSELECTTHEBESTMODELAFURTHERMODELDISCRIMINATIONWASCARRIEDOUT&IGUREDISPLAYSTHEREACTIONRATESOFFOURRIVALMODELSSEVERAL FORMS OF ,ANGMUIRn(INSHELWOOD INCLUDING AMODEL WITHSURFACEDISSOCIATION CALCULATEDWITHAHIGH(/ FRACTIONOFAT THE REACTOR INLET (ARDLY ANY STATISTICALLY SIGNIlCANT DIFFERENCEIS EXPERIENCED &IGURE DISPLAYS THE RATES COMPUTED WITH THESAME PARAMETERS AT A MUCH LOWER (/ CONTENT OF 4HEDIFFERENCES BETWEEN THE RATE VALUES ARE EVIDENT PARTICULARLY ATHIGH ./ CONCENTRATIONS !DDING EXPERIMENTS CARRIED OUT AT LOW(/CONCENTRATIONINCREASEDTHEDISCRIMINATIVEPOWERBETWEENTHERELEVANTMODELS IN THESAMEWAYOTHEREXPERIMENTALCONDITIONS

    III 4HERE IS CONSIDERABLE OPPORTUNITY TO IMPROVE THE USERFRIENDLINESSOFSOFTWAREFORMODELINGOFREACTORSFORTHEREGRESSIONOFKINETICDATATORATEEXPRESSIONSANDFORITSAPPLICATIONTOEXPERIMENTALDESIGN

    4HEMAJORITY OF THE RESPONDENTS STATED THAT THE PROBLEMSINDICATED SHOULD BE SOLVED BY COOPERATION AND THIS OFCOURSEWASTHEIMPETUSTHATLEDTOTHEFORMATIONOF%UROKIN)NTERMEZZO4HEABOVE LISTESSENTIALLY RELATES TOSIMPLYIMPROVING THE WAY WE USE THE CURRENT TOOLS AND THEIRINCREMENTALDEVELOPMENT4HEALTERNATEQUESTIONISWHATARETHEPOTENTIALMAJORSTEPCHANGESTHATAREGOINGTOIMPINGEONKINETICSRESEARCHINTHEFUTURE4AKINGTHEMEDIUMANDLONGTERM PERSPECTIVES AS ONE HERE ARE SOME THOUGHTS ASTOWHAT THE FUTUREMIGHTBRINGORWHATWE INVOLVED INKINETICSRESEARCHOUGHTTOBECONSIDERINGv 3OFTWARE TOOLS SIMULATION REGRESSION EXPERIMENTALDESIGN WILL BE IMPROVED 4HIS WILL RELATE NOT ONLYTO IMPROVED USERFRIENDLINESS AND CALCULATION ROUTINESLEADING TO REDUCED COMPUTATIONAL TIMES BUT ALSO TO

    DEVELOPMENTS IN STATISTICAL SEARCH AND OPTIMIZATIONTECHNIQUESv -OLECULARMODELINGCANBEEXPECTEDTOCONTRIBUTEMORETO USEFUL MECHANISTIC INFORMATION AND TO ESTIMATIONOF INITIAL PARAMETER VALUES 4HIS RELATES TO THE RAPIDDEVELOPMENTS IN THE THEORETICAL CHEMISTRY AND COMPUTATIONALTOOLSASWELLASTOTHEDEVELOPMENTINASSOCIATEDCOMPUTER HARDWARE 4HE LEADING COMPANIES ARE NOWTARGETINGINCREASEDCOMPUTATIONALPOWERONTHEDESKTOPTOFACILITATETHISv (IGH THROUGHPUT EXPERIMENTATION HAS LARGELY BEENASSOCIATED WITH COMBINATORIAL CHEMISTRY DISCOVERYAND SCREENING 4HE POTENTIAL IMPACT OF THE GROSSPARALLELIZATION OF EXPERIMENTAL EQUIPMENT ON KINETICMEASUREMENTSSHOULDNOTHOWEVERBEUNDERESTIMATED;=0ARALLELMICROREACTORUNITSAREINUSEININDUSTRYANDARENOWBECOMINGCOMMERCIALLYAVAILABLE&IGURESHOWSTWOEXAMPLESOFhOFFTHESHELFvPARALLELSCREENINGUNITS+INETIC DATAMAY BEMORE RAPIDLYMEASURED BUT THIS

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    #HEMICALREACTIO

    NKINETICSINP

    RACTICE

    THEN PUTS THE EMPHASIS ON THE STATISTICAL TOOLS TO SETTHEEXPERIMENTALDESIGNANDPROCESSTHEACQUIREDDATA4HE THEORY IS THAT COMBINATORIAL OR SIMILARDISCOVERYWILL INCREASE THENUMBEROFNEWPRODUCTS AND SO THISINCREASE IN THE EFlCIENCY OF KINETICS RESEARCH WILL BEREQUIREDSIMPLYTOKEEPPACEv .ONSTATIONARYMETHODSSUCHASTEMPERATUREPROGRAMMEDREACTIONANDTEMPORALANALYSISOFPRODUCTSARECURRENTLYQUITE WIDELY USED TO OBTAIN MECHANISTIC INFORMATIONBUT AS YET THEOUTPUT ISUSED IN APRIMARILYQUALITATIVEFASHION AND RELATIVELY LITTLE QUANTITATIVE INFORMATION ISOBTAINED5NSTEADYSTATETECHNIQUESHAVETHEBENElTTHATDATAISACQUIREDMUCHMORERAPIDLY4HECHALLENGEISTO

    UNDERSTANDHOWDATAMEASUREDINATRANSIENTCONDITIONCANBEAPPLIEDQUANTITATIVELY

    4HOSE IN THE %UROKIN CONSORTIUM AND THEIR ACADEMICPARTNERSWILLBEACTIVELYADDRESSINGTHESEISSUESOVERTHENEXTFEWYEARS4HECHALLENGESSHOULDNOTBEUNDERESTIMATED)TWILL REQUIRE MAJOR EFFORT AND INNOVATION TO ACHIEVE THESEGOALS

    &URTHERREADING4HERE EXIST MANY TEXTBOOKS CONCERNING THE THEORETICALBACKGROUNDOFREACTIONKINETICS4HE FOLLOWING BOOKS ARE SUITABLE FOR A GENERAL AND

    BASIC INTRODUCTIONOF CHEMICAL KINETICSHOMOGENEOUS ANDHETEROGENEOUS CATALYSIS AND THE THERMODYNAMICS RELATEDWITHTHESE"OUDART;="OUDARTAND$JEGA-ARIADASSOU;=

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    #ONCLUSION5SINGSTATISTICALTECHNIQUESOPTIMALMODELANALYSISANDDESIGNFORTHESELECTIVECATALYTICREDUCTIONOF./BY.(HASBEENPERFORMED3PECIAL ATTENTION HAS BEEN PAID TO THE STATISTICAL DESIGN OF THEEXPERIMENTS EFlCIENT REPARAMETERIZATION OF THE MODELS AND THEDESIGNFOROPTIMALMODELDISCRIMINATION

  • %UROKIN

    #HEMICALREACTIO

    NKINETICSINP

    RACTICE

    7HEREK REACTIONRATECOEFFICIENTKO PREEXPONENTIALFACTOR

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    !CKNOWLEDGEMENT4HEAUTHORSAREGRATEFULTO3JOERDVANDER7ALFORMERLY3HELL2ESEARCHAND4ECHNOLOGY#ENTRE!MSTERDAM4HE.ETHERLANDSFORSUPPLYINGTHISCASESTUDY

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    &ROMENTAND"ISCHOFF;=AND+APTEIJNAND-OULIJN;=4HESEBOOKS COVER THE RANGE FROM THE FUNDAMENTALSOF CHEMICALKINETICSUPTOMODELINGOFREACTORS!NEXTENSIVEANDUSEFULPAPERCONCERNINGTHEMODELINGOFCATALYTICKINETICSISGIVENBY&ROMENTAND(OSTEN;=3OURCESOFMORE THOROUGH FUNDAMENTALBACKGROUNDOF

    KINETICSOFHETEROGENEOUSLYCATALYZEDREACTIONSALSODElNEDAS MICROKINETICS ARE $UMESIC ET AL ;= :HDANOV;= 6AN3ANTEN;= AND 'OLDEN AND-ANION;= ! FREQUENTLY USEDMETHOD FORMICROKINETICMODELING IS THE"ONDORDER CONSERVATIONn-ORSEPOTENTIAL APPROACH "/#n-0 APPROACHSEE 3HUSTOROVICH; = AND "ELL;= "ENZIGER;= DESCRIBESSEVERALMETHODSFORESTIMATINGREACTIONENERGETICSONMETALSURFACES+ANGAND7EINBERG;=GIVEANOVERVIEWOFMETHODSFORMODELINGOFSURFACERATEPROCESSES%STIMATIONSOFHEATSOF CHEMISORPTION OF GASES ON METAL SURFACES CAN BE DONEUSINGTHEGENERALRULESDElNEDBY4ANAKAAND4AMARU;=

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    )NSTEAD OF K +A AND +" THE COMBINATIONS K+!+" K+"AND K+! ARE ESTIMATED WHICH ALSO ENHANCES THE lTTINGPROCEDURE

  • %UROKIN

    #HEMICALREACTIO

    NKINETICSINP

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    0ROFDR IR'UY"-ARINIS FULL PROFESSOR OF #HEMICAL%NGINEERING AT THE 5NIVERSITY OF'ENT "ELGIUM (E RECEIVED HISDEGREEFROMTHE5NIVERSITYOF'ENTIN WHERE HE ALSO OBTAINEDHIS 0H$ IN !FTER A POSTDOCTORALSTAYINAT#ATALYTICA!SSOCIATESAND3TANFORD5NIVERSITYHEOBTAINEDTENUREATTHE5NIVERSITY

    OF'ENTIN(ETOOKAPOSITIONOFFULLPROFESSORINATTHE%INDHOVEN5NIVERSITYOF4ECHNOLOGY4HE.ETHERLANDSWHERE HE TAUGHT ABOUT CHEMICAL REACTORS )N HERETURNED TO 'ENT AS DIRECTOR OF THE ,ABORATORIUM VOOR0ETRO