ChemicalReactionEngineering

Ph.D.Qualifierexamination

Openbook(ScottFogler)exam

  1. AsecondorderirreversibleliquidphasereactionA+BCtakesplaceinaPlugflowreactor(PFR). Thefeedtothereactoris50kmol/hrofeachreactant. Thetotalconversionis50%. ThereactionkineticsisrA=-kCACBwherekis0.5m3/kmol/hr. ThesamereactionistobeperformedinaCSTRofequalvolume.Calculatetheconversioninthelattercase.TheconcentrationofAinthefeedis5mol/lit.

Ifthereactionwasingasphase,wouldtheanswerbedifferent?Ifyes,writetherelevantequations(donotsolve)torecalculatetheconversion. [20]

  1. a.ForareactionABC(allareirreversibleandelementaryreactions),givetheequationstobesolvedtoobtaintheconcentrationofBinabatchreactorasafunctionoftime.Givequalitativeprofilesofallthespeciesasafunctionoftime.
  2. Foranirreversiblereactionthereactionratedoubleswhentemperatureisincreasedfrom300Kto310K.Calculatetheactivationenergy.
  3. Forthefollowinggraphofasolid-catalyticreaction,ineachcasewhichprocessgovernstheoverallrate?-intrinsickinetics,externalmasstransferorintraparticlediffusion.Justifyyouranswer.

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  1. Afirstorderhomogeneousliquid-phasereactioniscarriedoutinanidealstirredtankreactor. Theconcentrationofthereactantinthefeedis3.0kmol/m3andthevolumetricflowrateis60x10-6m3/sec.Thedensityandspecificheatforthereactionmixtureareconstantat1000kg/m3and4.19kJ/kg.K,respectively.Thereactorvolumeis18lit.Thereisnoproductinthefeedstreamandreactoroperatesadiabatically.Theheatandrateofreactionare-2.09x108J/kmoland

rA=-4.48 x106CAexp(-62,800/RT)kmol/m3/sec

where,activationenergyisinSIunits.CAisthereactantconcentrationinkmol/m3.TisinKandR=8.314J/mol/K.Ifthefeedisat273Kwhatisthesteadystateproducttemperatureandconversion?(Hint:theconversionisbeyond90%). [20]

  1. Therateofisomerizationofn-butaneonasilica-alumnasphericalcatalystmeasuredat5atmand50oC,inalaboratoryreactorwithhighturbulenceinthegasphasesurroundingthecatalystpelletisgivenbelow.Turbulenceensuresthattheexternaldiffusionresistancesarenegligible.Kineticstudiesindicatethattherateisfirstorderandirreversible.Theeffectivediffusivityis0.08cm2/secatthereactionconditions,andthedensityofthecatalystpelletis1g/cm3regardlessofthesize.Themeasuredrateswhenpuren-butanesurroundsthecatalystareasfollows:

Particlediameter(in) / 1/16 / 1/8 / ¼ / 3/8 / 1
Ratemol/sec/gofcatalyst / 4.88x10-4 / 4.85x10-4 / 4.01x10-4 / 3.54x10-4 / 1x10-5

Fromtheabovedata,determinetheintrinsicfirstorderrateconstantintheabsenceofintraparticlediffusion.Alsopredicttherateiftheparticlesizeis1.5inch.Itmaybeassumedthateffectivenessfactor()isinverseofThielemodulus() (i.e.=1/) when0.25. [20]

  1. AreactorofirregulargeometryoffersfollowingEcurve.Calculatetheaverageresidencetime.Alsodeterminetheconversionineachofthefollowingcases(iandii)ifcompletesegregationoffeedstreamsisassumedtotakeplace.

i)ForafirstorderreactionrA=-0.1CA(kmols/hr/m3)

ii)Forasecondorderreactioninproblem1,

Also,whatwillbetheconversionforthefirstorderreactionincase-iforthemaximummixednesscase?

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