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courseof their duties.ArticlePredictive Modeling and Optimization
for anIndustrial Penex Isomerization Unit - A Case StudyMohanad M.
Said, Tamer Samir Ahmed, and Tarek M. MoustafaEnergy Fuels, Just
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1 ` Predictive Modeling and Optimization for an Industrial Penex
Isomerization Unit - A Case Study Mohanad M. Saida, Tamer S.
Ahmeda,*, Tarek M. Moustafaa
a Chemical Engineering Department, Faculty of Engineering, Cairo
University Giza 12613, Egypt * Corresponding author: Tel.: +20 114
292 4407; E-mail address:
Tamer.S.Ahmed@cu.edu.egAbstract.ThisworkpresentsamodelforUOPHydrogenOnceThrough(HOT)Penex
ProcessusingAspenHYSYSPetroleumRefiningmodule.Themodelreliesonroutinely
takenindustrialdataofprocessstreamsduringnormaloperatingconditions.Acquireddata
sets have been tested and screened to ensure data validity for
building the model and avoiding erroneous results. A reaction
network with 20 reactions and 19 components has been used for the
reactors model. The reactors model has been validated using 4
months of industrial plant data.In
addition,rigoroustray-to-traysimulation
ofisomeratestabilizerhasbeenutilizedto match the performance of
plant stabilizer. The model validated has been used for studying
the effects of each process variable on plant performance. In
addition, the model has been used in optimizingtheoperating
conditionsof the process.This optimizationshowedapotential for
notable fuel savings in the process. Page 1 of 56ACS Paragon Plus
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2 ` 1.Introduction
Sincethe70s,eliminationofleadcompoundsfromgasolinepoolhasincreased
interestintotheisomerizationoflightstraightrunnaphthasoastopreservetheoctane
number ofproduced gasoline1. Recent and future regulations put
strict limits on benzene and
aromaticlevelsinmotorgasoline.Forexample,theU.S.EnvironmentalProtectionAgency
MSATII(MobileSourcesAirToxicsPhase2)regulationsrequiresdecreasingtheaverage
benzene content of U.S. gasoline pool to 0.62 vol.%2,3. This urged
refiners to search for other sources of gasoline with a lower
aromatic content than catalytic reforming.Isomerization is
thoughttobeoneoftheeffectivesolutionstoproducemotorgasolinecompatiblewith
environmental regulations. Isomerate (isomerization product) is
highly desirable with respect to environmental regulations due to
its zero benzene content and high octane number.
Isomerizationreactionsareexothermicequilibrium-limitedreactions.Asconversion
isfarfromequilibriumconversion,anincreaseinreactortemperatureleadstoincreasein
reactionvelocityandsubsequentincreaseinconversion.However,onceequilibriumis
approached,increasingtemperaturedecreasesconversionduetothedecreaseofreaction
equilibriumconstant4.Figure1showsthechangeofconversion(iso-paraffinsyield)with
temperature. Asindicatedin Figure1,conversion
increaseswithtemperatureuntilacertain temperature (optimum
temperature) is reached, then iso-paraffins yield decreases. INSERT
FIGURE 1
Currently,threecatalysttypesareusedcommerciallyfornaphthaisomerization
(Figure2).Allofthemareplatinumcontainingcatalysts6:1)Zeolitecatalysts:zeolite
catalystshavethelowestactivityamongisomerizationcatalysts,hencetheyareusedat
highertemperaturesthatareunfavorablewithrespecttoisomersyield.However,these
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3 ` catalysts have high resistance to feed impurities and can be
regenerated. Zeolite catalyst units use firedheaters forfeedand
hydrogenheatingup tothereaction temperature.Theprocess also employs
a high ratio of hydrogen to hydrocarbon for hydrotreating and
dearomatization
offeedstock.Accordingly,arecyclegascompressorandaproductseparatorareused;2)
Chlorinated alumina catalysts: These are the most active
isomerization catalysts providing the highest octane number and
isomerate yield. These catalysts require continuous injection of a
chlorine compound (CCl4) to maintain catalyst activity. In
addition, they are very sensible to
impurities(oxygen,sulfurandnitrogencompounds).Therefore,feedhydrotreatingand
dryingisamandatory.Lowhydrogentohydrocarbonratioisrequired.Hence,neithera
recycle gas compressor nor a recycle gas is needed; 3) Sulfated
zirconia: These catalysts have
theadvantagesofbothprevioustypes.Theyaremoreactivethanzeolitecatalysts,hence
favoringhigherisomersconversions.Inaddition,theyareresistanttoimpuritiesand
regenerable.However,unitsusingsulfatedzirconianeedarecyclegascompressoranda
product separator. INSERT FIGURE 2 As seen in Figure 2, chlorinated
alumina catalysts provide the highest octane number and isomerate
yield. By good operation of upstream hydrotreating unit and feed
dryers, a long
servicelife(morethan10years)couldbeachieved2.UOPandAxensarethelicensorsof
processesusingchlorinatedalumina-basedcatalysts.UOPlicensestheprocessunderthe
nameof"PenexProcess".ThefirstPenexprocesswasbroughtonstreamatBorgerTexas
Refinery using I-3
catalyst7.Mostoftheliteratureconcentratesondevelopingnewtypesofcatalysts8.Afew
research work paid attention to kinetic modeling of isomerization
reactions and a fewer paid Page 3 of 56ACS Paragon Plus
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4 `
attentiontomodelingisomerizationreactionsoverchlorinatedaluminacatalysts.
Consequently,optimizationforindustrialisomerizationunitsisveryscarceintheopen
literaturesincetherigorouskineticmodelingforthereactoristheheartoftheoptimization
process. Besl et al.9 discussed briefly the optimization of Penex
process in a German refinery.
Ontheotherhand,DudleyandMalloy10developedasimplekineticmodelbasedonlyon
isomerizationandcrackingreactionsthatwasusedinoptimizingaprocessthatusesAlCl3
liquidcatalyst.Ahari and coworkers11investigatedtheeffectsof methyl
cyclopentane inthe
feedofisomerizationfeedusingaprocessmodeldevelopedbyHYSYS.Inaddition,they
studiedexperimentallythehydrogenpartialpressureeffectonPtmordenitezeolitecatalyst
activityandconversionofn-paraffinsandproposedkineticequationsforn-C5andn-C6
conversion12. Brito et al.13 studied experimentally the performance
of Pt-Ni/mordenite zeolite
catalystswithdifferentmetalproportionsandkineticmodelforcatalystdeactivationwas
proposed.Koncsagetal.14proposedakineticmodelforC5/C6isomerizationoverPt/H-zeolite
atindustrial conditions. Surlaet al.15used a single
eventmethodologyto establish a
kineticmodelforC5/C6isomerizationoverchlorinatedaluminacatalyst.Finally,adetailed
kinetic model that is suitable for the three major catalyst types
was proposed by Chekantsev
etal.8.Thereactionnetworktheyproposedcontained36reactions.Theauthorsillustrated
thatthedifferencesinreactionratesoverdifferentcatalystsaremodestexceptforfew
isomerizationreactions.Themodeltheyproposedagreedwellwithexperimentalresultsof
the three catalyst types.
Verylittleattentionwaspaidintheliteraturetotheapplicationofkineticmodeling
andoptimizationtoanexistingindustrialunit.Inthiscontext,wepresentherekinetic
modeling for an existing industrial Penex isomerization unit using
Aspen HYSYS Petroleum Refining isomerization reactor model. In
addition, the model has been used for studying the effect of
different process variables on process performance and for process
optimization. Page 4 of 56ACS Paragon Plus EnvironmentEnergy &
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5 ` 2.Process Description Figure 3 shows a process flow diagram for
Penex process. Feed naphtha and make-up
hydrogenfirstpassthroughdrierstoeliminateanytracesofwaterbecausewaterisa
permanent poison of Penex catalyst. Then, naphtha and hydrogen are
mixed priorto heating
themixtureuptoreactiontemperature.Maintainingaproperhydrogenpartialpressureis
required inside the reactor to prevent coke deposition on catalyst.
The reactor charge mixture
isheatedbyexchangingheatwiththesecondandfirstreactoreffluent,respectively.A
chlorinecompound"CCl4"isinjectedintothereactorchargetoprovideacidsiteson
catalyst'ssurfacethatisrequiredforisomerizationreaction.Thefeedisbroughtuptothe
reactiontemperaturethroughafiredheater.Theeffluentofthefirstreactoristhencooled
throughexchangerspriortoenteringthesecondreactortoremoveheatgeneratedby
exothermic reactions in the first reactor bed so that to favor
equilibrium limited isomerization
inthesecondreactorbed.Thereactors'effluentisthenfedtoastabilizertoseparatelight
gases(C4-
andhydrogen)fromtheproductstream.Theoverheadgasesissenttoapacked
bedscrubberthatemploysacausticwashtoneutralizehydrogenchlorideformedfromthe
decompositionofthechlorinecompound.Finally,theproducedgasesaresenttovapor
recovery for LPG production. Thestabilized isomerate may be sent
directly to gasoline pool or may undergo fractionation to maximize
the octane number of the isomerate. INSERT FIGURE 3 3.Process
Chemistry Praffin Isomerization. Paraffinisomerization is the main
reaction in the process. As mentioned before, paraffin
isomerization is an exothermic equilibrium limited reaction so that
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6 ` a higher conversion is favored at low temperatures. Table 1
lists the research octane numbers (RON) of n-C5 , n-C6 and their
isomers. It is clear that multi branched isomerssuch as
2,2--dimethyl butane (2,2 DMB) and 2,3-dimethyl butane (2,3 DMB)
have higher octane numbers than single branched isomers such as
2-Methyl Pentane (2MP) and 3-Methyl Pentane (3MP). Thus, formation
of multi-branched isomers is highly desirable. INSERT TABLE 1
Naphthenes isomerization. Naphthene isomerization reaction is also
an
equilibrium-limitedreaction.Cyclohexane(CH)andmethylcyclopentane(MCP)existinequilibriumat
reaction conditions but formation of MCP increases as temperature
is increased. Benzene Saturation. Benzene saturation to cyclohexane
is a highly exothermic rapid
reaction.Thehighheatofreactionofbenzenesaturationaffectstheconversionofthe
exothermic isomerization reaction that is favored at low
temperature. This puts a limit on the amount of benzene that can be
tolerated in reactor feed. All benzene in the feed is saturated
completelyintheleadreactor.Actually,theleadreactortemperatureisalwaysadjustedto
maximizeisomerratios.Ifthebenzenecontentoffeedincreasesthenalowerreactorinlet
temperature is used to maximize isomers' conversion attained at
lead reactor outlet and vice versa. Page 6 of 56ACS Paragon Plus
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7 ` Naphthene ring opening. Naphthenes may undergo ring opening and
form paraffins at reactor conditions. Ring opening increases with
increasing reactor bed temperature.
Hydrocracking.Asreactortemperatureincreases,hydrocrackingrateincreases.
Largemolecules(C7)areeasiertocrackthansmallermolecules.AsC5/C6isomerization
approachesequilibrium,theextentofhydrocrackingincreasesleadingtolowerliquidyield
and an increase in stabilizer overhead gas (C4-). 4.Reactor Model
AspenHYSYSv.7.3PetroleumRefiningisomerizationreactormodulewasusedin
developing the process model. The module contains a detailed
kinetic model of reactions that occur
inisomerizationprocess.Thereactormodel containsrate
equationsforisomerization,
benzenesaturation,ringopening,hydrocracking,andheavy(C7+)reactions(Figure4).
The
rateexpressionforeachreactionclassiscodedtomatchliteraturedata.Allreactionsare
irreversible except for isomerization and benzene saturation.
Typically, the reaction network
consistsof20reactionsand8ofthemarereversible.Eachreactionclassisfirstorderwith
respecttotheprimaryreactant andreaction-classrate equationhas
adenominator following
Langmiur-Hinshelwood-Hougen-Watsonmechanism.Thereactionschemecontains
hydrocarbons up to C7. Higher carbon components are mapped into six
ring C8 naphthenes. In
reality,isomerizationfeedusuallycontainstraceamountsofC7+
components.Reactionrate equations are expressed in the model as:
Reaction Rate = Global activity Reaction-class Activity
Heterogeneous Reaction Rate (1)
Reactormodelcanbetunedtomatchplantreactorperformanceviatwoschemes:
basictuningandadvancedtuningschemes.Basictuningincludesthetuningoftheactivity
parametersofthereactorsuchasglobalactivity(overallreactoractivity)andspecific
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8 ` reaction-class activity parameters (activity of each type of
reactions, e,g,: hydrocracking class reactions).Global activity
parameter affects the rates of all the reactions. On the other
hand,
theactivityofeachspecificreaction-classcanbeadjustedviathespecificreaction-class
activity parameter (e.g.: hydrocracking activity parameter for
hydrocracking-class reactions). Ifbasic tuning isnot
sufficient,kineticparametersof each individualreactionmaybetuned to
match plant performance using the advanced tuning.
ThePenexunitunderinvestigationisaHOT(Hydrogen-Once-Throughunit).The
processflowdiagramoftheunitisidenticaltothatshowninFigure3.Thecurrentworkis
only concerned with the isomerization reactors and the downstream
stabilizer. Dryers and gas scrubber modeling are beyond the scope
of this study. No changes or special procedures were
appliedforbuildingthemodelandthemodelwascalibratedaccordingtosamplesthatare
routinely taken during normal operation. INSERT FIGURE 4
IndustrialData.Data from the industrial unit under investigation
were gathered and
wereorganizedintodatasets.Eachdatasetrepresentsanoperatingday.Eachdataset
includesacomponentanalysisofallinputandoutputstreams(make-uphydrogen,feed
naphtha, isomerate and stabilizer off-gas) and component analysis
of the lead reactor product. In addition, each data set includes
the operating conditions of the reactors and the stabilizing
column. C7+ de-lumping. Isomerization feed usually contains a
little amount of C7+ hydrocarbons and this amount could be
controlled via the upstream naphtha splitter. Figure 5 shows the
varaiation of the amount of C7+ in feed during study. The C7+ is
mostly around 1 Page 8 of 56ACS Paragon Plus EnvironmentEnergy
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9 ` wt%. The C7+lump in isomerization feed is expected to be mostly
normal heptane, heptane isomers and C7naphthenes, with almost no
toluene since the boiling point of tolueneis 110C, which is far
from that existing in the isomerization
feed.ForaccuraterepresentationofC7+lump,thede-lumpingproceduredevelopedby
Riazi18wasusedfortheC7+
lumpinthecurrentstudy.Theprocedureusescorrelationsfor estimating
the paraffins, naphthenes and romatics (PNA) composition of
petroleum fractions
usingonlybulkproperitiessuchasspecificgravity(SG)andmolecularweight(MW).The
results of PNA composition calculations for C7+ in feed are
presented in Table 2. The results
reinforcethepostulationthattolueneisnegligableintheisomerizationfeed.Therefore,the
C7+ fraction is de-lumped into C7 paraffins and C7 naphthenes with
known percentage of each hydrocarbon class. INSERT FIGURE 5 INSERT
TABLE 2
Properitiesofapetroleumfractionofknowncompositioncouldbecalculatedfrom
the properities of constituent pure componentsby applying the
proper mixing role: = (2)
Usingthisprinciple,anoptimizationalgorithmcanbeusedtoestimatethe
compositionofapetroleumfractionbyminimizingtheerrorbetweentheknownproperities
ofthatfractionandthecalculatedproperities.Inthiswork,thefollowingobjectivefunction
was minimized: Page 9 of 56ACS Paragon Plus EnvironmentEnergy &
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10 ` = 100(3) This isthe same principle that was usedin the
literature to estimate the composition of catalytic reformer
feed19,20. However, in the current work, a limited number of
properties of C7+ are available (SG, MW, Reid Vapor Pressure (RVP)
and RON). This limits the number of compositions that can be
estimated.
Usingthepreliminaryde-lumpingobtainedthroughPNAcompositioncalculation,
two additional equations were added for compositions estimate. In
this work, the C7+fraction
wasde-lumpedintofivepesudocomponents:multi-branchedheptaneparaffins(MBP7),
singlebranchedheptaneparaffins(SBP7),normalheptane(NP7),fiveringC7
naphthenes
(5N7),andsixringC7naphthenes(6N7).Propertiesofthesepesudocomponentswere
obtained from Aspen properities data bank. Mole fractions of pesudo
components wereused for the calculation of RVP and MWand volume
fractions were used for SG and RON. Table 3 shows a comparison
between available properities and calculated properities for C7+ in
feed and product streams. Estimated compositions of C7+are shown in
Table 4. INSERT TABLE 3 INSERT TABLE 4 Data Screening. Model
quality depends mainly on the data used. As indictaed earlier,
datasetsusedfordevelopingthisprocessmodelwereobtainedduringnormaloperation
.Obtainingconsistentdatafromindustrialunitsmaysometimesbeanextremedifficult
missionduetofrequentchangesinfeedandprocessconditions.Datasetsindaysthat
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11 `
witnessedanyup-normalchangesinprocessoperationwereexcluded.Inaddition,amass
balancetestwas applied to alldatasets andany datasetshavinga mass
balanceerrormore than 2% wereexcluded. In order to ensure data
verification, a hydrogen balance was applied
alsotodatasetsbycalculatingthehydrogenweightineachstreamthroughsummingthe
hydrogencontributionofeachcomponentandanysetshavinganerrormorethan3%were
omitted.TaskarandRiggs20usedthefollowingformulatocalculatetheweightfractionof
hydrogen in component CiHj (H factor): = + (4) The weight of
hydrogen in each stream could be calculated by: = (5)
Apartfromdatasetsindaysthatwitnessedcapacitychanges,mostdatasetswere
quite consistent having an average mass balance and hydrogen
balance error of -0.969% and-1.481%, respectively.
ModelCalibrationandParametersEstimation.Parameterestimationisthemost
criticalstepinmodelbuilding.Awell-calibratedmodelproducessignificantandrepeatable
predictions over a wide range of operating conditions. Improper
calibration of reactor model
mayleadtoanovercalibratedmodelwithapoorpredictivepower.AspenHYSYS
isomerizationreactormodelenablesusertomatchplantperformancethroughbasictuning
andadvancedtuningbyadjustingkineticparametersforeachreaction.Modeldevelopers
claim that basic tuning of reactor model is sufficient to match
plant data. In this work, a basic
tuningschemewasappliedinordertoavoidovercalibrationofreactormodel.Advanced
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12 `
tuningmayrequireextremelyaccurateplantdatathatwerenotfeasibleinourcase.For
accurate representation of plant reactor, the upcoming steps were
followed: A- Generating
streams:Eachdatasetwasusedtogenerateastreamrepresentingtheleadreactorchargeattheday
that each data set represents. B- Running the model:
Thereactormodelrequiressomemechanicaldatatorun.Thesedataincludereactor
dimensions and catalyst properties (catalyst bed porosity and bulk
density).Then the model is allowed to run generating an output
stream. C- Model calibration: Reactor model calibration is mainly
adjusting the activity parametersto match plantdata. In
thiswork,thereactormodelwascalibratedwiththeaidofAspenHYSYSOptimizerby
minimizing the following objective function: f = +
(6)
Table5liststheadjustmentfactorsusedforreactormodelcalibrationandapplied
bondsforeachparameter.Itwasfoundthatacceptablemodelperformanceisreachedwhen
using those bonds during calibration. It is important not to
include yields of all components in
reactorcalibration.PashikantiandLiu21showedthatincludingallmeasurementsinreactor
calibration may result in a poor calibrated model that responds
wildly even to small changes
toinputvariables.Table6showsthereactormeasurementsthatwereincludedin
optimization function and weighting factors used with them. Page 12
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13 ` INSERT TABLE 5 INSERT TABLE 6
Largerweightingfactorswereappliedfortermswhereacloserfitisrequired.For
example,thereactormodelisrequiredtofittheplantisomerratios.Therefore,larger
weightingfactorswereappliedtonormalandiso-paraffins.Onthecontrary,thelowest
weightingfactorwasgiventoreactortemperaturerisesincetheleadreactortemperatureis
frequentlyadjustedtomaximizeisomerratiosinthereactoreffluentandhencethereactor
temperature rise usually fluctuatesduring operation. In the
availabledata sets, an average of reactor inlet and outlet
temperature is only given. Therefore, temperature rise may be the
least reliable data point in each data set and applying a high
weighting factor for temperature rise may result in poor
calibration. The three previous steps were repeated for each data
set and activity parameters were
calculatedforeachdatasetindividually.Almostallactivityparameterswerefoundtovary
withinanarrow range for different data sets. Consequently, the
average values of calculated activity parameters are expected to be
quite satisfactory for model calibration.
Thesameprocedurewasusedforlagreactorcalibration.Thecompositionofthe
effluent of the calibrated lead reactor was used to simulate the
composition of lag reactor feed
atplantconditions.Thelagreactorwascalibratedbyminimizingerrorbetweenmodeland
plant data using the same objective function. Routine sampling in
the industrial unit does not
includeasampleforlagreactoreffluent.Thus,thecompositionoflagreactoreffluentwas
calculated through back-mixing of isomerate and stabilizer off-gas
streams. The same activity
parameterswereusedformodelcalibrationandsamebondswereusedexceptforglobal
activityparameter.Inisomerizationunits,theleadreactorcatalystlosesactivitybeforelag
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14 ` reactor. When lead reactor performance becomes unsatisfactory,
catalyst in the lead reactor is
replacedwithfreshcatalystandtheorderofreactorsisreversedthatthenewloadedlead
reactorlagstheexistinglagreactor(whichisnowtheleadreactor).Therefore,lagreactor
catalyst is always more active than lead reactor catalyst. Due to
this fact, a higher upper bond
wasgiventoglobalactivityparameterduringlagreactorcalibration.Table7showsthe
average activity parameters estimated through calibration process
for both reactors. INSERT TABLE 7
Modelvalidationandtesting.Figures6and7showthemodelperformanceversus
plantyieldsforthe23datasetsusedinreactormodelcalibrationprocessforleadandlag
reactors,respectively.Themodelpredicationsaresatisfactoryforbothreactor.Itshouldbe
noted that a closer fit may be achieved with advanced tuning of
kinetic parameters (especially
therateconstantsofringopeningreactions).However,advancedtuning
requiresstrictplant measurements, which were not available. INSERT
FIGURE 6 INSERT FIGURE 7 In order to ensure model capability of
predicting plant performance, the model yields were compared with
plant yields for the next 4 months after calibration. Chlorinated
alumina catalysts lose activity very slowly during normal operation
(the catalyst used in the industrial
unitunderinvestigationwasloadedfromabout13yearsandisstillbeingusedwithgood
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15 `
activity).Thus,changesincatalystactivityduringthe4monthsarenegligibleandre-calibrationofreactors'modelsisnotrequired.Figures8and9showthatthemodelwas
useful in tracking plant performance for the 4 months after the
calibration. INSERT FIGURE 8 INSERT FIGURE 9
StabilizerModel.Although this study is concerned with the
optimization of process
variablesofreactionsectiononly,aprecisestabilizermodelisalsorequiredforaccurate
prediction of isomerate yield. The standard inside-out method was
used for stabilizer model22.
Theinside-outmethodconvergesquicklywithawidevarietyofspecifications.Sincethe
isomerate stabilizer is used to adjust the RVP of isomerate product
by limiting the amount of
C4-intheisomerateproduct,itfunctionsverysimilartothefunctionofade-butanizer
column.DataprovidedbyKaes23showthattheoverallefficiencyofade-butanizeris85-90%.Since
actualplant stabilizerhas30 trays,the modelstabilizer should
contain about26 theoretical trays.
AccordingtotheguidelinesprovidedbyKaes23,stabilizerspecificationswere
adopted.
Thefunctionofisomeratestabilizeristostabilizeisomerateproductbyseparating
light ends fromit.Therefore, the RVPofisomerate is
anindicationofthe recovery oflight ends and degree of separation
achieved. Since the stabilizer operates with full reflux, another
specificationwasneededforbuildingstabilizermodel.Therefore,theoverheadcondenser
temperature wasspecified asaperformance
specificationsincethecondenseroperateswith
significantvaporproductflows23.Figure10showsacompleteprocessflowdiagramofthe
process model. Page 15 of 56ACS Paragon Plus EnvironmentEnergy
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16 ` INSERT FIGURE 10 5.Process Variables Having established a
process model for Penex unit, the next step is studying the effects
of each process variable to predict the process performance for a
given change in a process variable. Studying the effects of each
process variable is essential for process optimization. The
following
studywasconductedusingtheaveragecompositionofindustrialunitfeedduringthestudy
period (6 months).
LeadReactorInletTemperature.Isomerizationreactionsareequilibriumlimited
reactions; hence there is a maximum conversion (equilibrium
conversion) that could be attained at each temperature (Figure 1).
Because isomerization reactions are exothermic, the equilibrium
conversiondecreasesastemperatureincreases.Wheneverthereactionisfarfromequilibrium
conversion,anincreaseintemperatureleadstoincreaseinreactionvelocityandanincreasein
conversion(isomersyieldandhenceRON).However,onceequilibriumisreached,increasing
temperatureincreasesbackwardreactionvelocityandreducesconversion.Thisisreflectedin
Figure 11A, which shows the effect of lead reactor temperature on
RON. Actually, i-pentane and 2,2-DMB are the components with the
greatest effect on RON of isomerate. Therefore, the effect
oftemperatureon(I-C5/C5)%and(2,2-DMB/C6)areidenticalwiththatofRON(Figure11B
and 11C). Although, the isomerization of 2,3-DMB is still far from
equilibrium (Figure 11D), but
ithaslittleeffectonRON.Inaddition,increasingtemperatureincreasestherateofother
reactions.Increasedhydrocrackingandringopeningreactionsleadstoincreasedhydrogen
consumption(Figure11E).Finally,theincreaseinhydrocrakingleadstothedecreaseofof
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17 ` isomerate yield (Figure 11F). Isomerate wt.% was defined in
this study as the wt% of isomerate to the total reactor effluent.
INSERT FIGURE 11 Lag Reactor Inlet Temperature. For the lag
reactor, the effect of the inlet temperature is similar in trend to
that of the lead reactor (Figures 12 A-F). INSERT FIGURE 12
Hydrogentohydrocarbonmoleratio.Hydrogenisrequiredforcompletingthe
reactionsanddecreasingcokedepositiononcatalystsurface.Generally,increasinginlet
hydrogenleadstohigherhydrogenpartialpressureinsidethereactorwhichincreases
hydrocracking.Consequently,isomerateyield(Figure13A)andtheRONofisomerate(Figure
13B) decrease due to increased hydrocracking of paraffins isomers
(lower paraffin Isomerization
Number(PIN=i-C5/C5+(2,2-DMB+2,3-DMB)/C6))(Figure13C)).Therefore,thereactors
should be operated at the lowest possible hydrogen to Hydrocarbon
(H2:HC) ratio. However, at
anyinstance,theH2:HCratioshouldnotbelowerthan0.05moleH2/moleHydrocarbonas
claimedbyprocesslicensor.TheH2:HCmoleratioisusuallymeasuredatreactoroutletfor
Hydrogen Once Through Penex units. Page 17 of 56ACS Paragon Plus
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18 ` INSERT FIGURE 13
Feedrate(LHSV).Atthesamereactorinlettemperature,thelowertheliquidhourly
space velocity (LHSV), the higher the PIN (Figure 14A). On the
contrary, the higher the LHSV, the higher the yield of isomerate
due to lower hydrocracking (Figure 14B). This is expected since
increasing feed rate decreases contact time with catalyst, which
results in lower reactions rates. INSERT FIGURE 14
Feedcomposition.A)Methylcyclopentaneandcyclohexane:Generally,cyclic
compounds adsorb on catalyst surface reducing active sites
available for other reactants. Hence, an increase in
methylcyclopentane (MCP) and cyclohexane (CH) % causes slightly
lower isomer
ratiosinisomerate(Figures15Aand15B).Ontheotherhand,theRONofisomeratewillbe
higher due to the increase of MCP or CH in isomerate, which has a
relative high RON (Figures 15C and 15D). This contradicts what was
reported by Ahari et al.11. They investigated the effects of MCP in
isomerization feed and claimed that increasing the amount of MCP in
feed results in reduction of isomerateRON. However, theauthors
carried outthat study usinga mixture ofn-hexane and MCP as a feed
on a different catalyst operating at higher temperature. Therefore,
at
theseconditions,thenaphtheneisomerizationreactionisdrivenstronglyinthedirectionof
formingCH,whichhasarelativelylowerRONcomparedtoMCPandmulti-branchedhexane
isomers.Inaddition,thehigheroperatingtemperatureleadstoincreasedringopeningofMCP
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19 `
andCH,whichleadtolowerRON.Accordingly,thedifferencesinfeedcompositionand
operating conditions may be the reason for the contradicting
results.
IsomerateyieldincreaseswiththeincreaseofMCPorCHcontentinfeed.Bothcyclo
componentsdonotundergohydrocrackingasparaffins,howeverringopeningreactionsmay
occur.Generally,ringopeningreactionisfavoredslightlycomparedtohydrocrackingwith
increasingtemperature,becauseofitshigheractivationenergy(e.g.MCPringopeninghasa
higher activation energy compared to C6 paraffins hydrocracking).
Moreover, reduction of active
sitesavailableforparaffinsreducesparaffinshydrocracking,andhenceincreasesliquidyield
(Figures 15E and
15F).Methylcyclopentaneandcyclohexanearealsomajorhydrogenconsumersthroughring
opening.Therefore,hydrogenconsumptionincreasesastheamountofMCPorCHinthefeed
increases. It should be notedthat the overall hydrogen
consumptionmay notincrease(Figures 15G and 15H) due to that the
increase of MCP or CH content in feed is on the account of other
componentsincludingbenzenethatisthemajorhydrogenconsumer.However,thehydrogen
consumptioninthelagreactorshowsanincreasewiththeincreaseinMCPorCHcontent
(Figures 15I and 15J). INSERT FIGURE 15
B)Benzene:Figure16Ashowstheactualvariationofbenzenecontentinthefeed.As
mentionedearlier,benzeneishydrogenatedcompletelytoCHintheleadreactor.Benzene
saturationishighlyexothermicreactionthatisunfavorablebytheequilibriumlimited
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20 `
isomerization.Figure16Bshowstheeffectoffeedbenzenecontentontheleadreactor
temperaturerise.Smallchangesinfeedbenzenecontentgreatlyaffecttheleadreactor
temperature rise. However, this does not affect isomerate RON much
(Figure 16C) since benzene
isconvertedtoCHthathasamoderateRONormayundergoisomerizationtoformMCPthat
has higher
RON.Ontheotherhand,theexothermicheatofbenzenesaturationaffectsPINsignificantly
(Figure 16D). In actual operation, the lead reactor inlet
temperature is always varied in order to
maintainaconstanttemperaturerisethroughthereactorbed.Theallowabletemperatureriseis
increasedwithfeedrateinordertoobtainareasonableconversionofnormalparaffins.This
operating scheme may be effective but it is very tedious,
especially when wide variations in feed benzene content
occur.Moreover,theincreaseinfeedbenzenecontentleadstoanincreaseinisomerateyield
(Figure 16E) since the produced CH or MCP undergo slow ring opening
and adsorb on catalyst surfacereducingactivesitesavailable
forpraffinshydrocracking.Finally,benzenesaturationis
themajorhydrogenconsumingreactioninPenexprocess.Figure16Fshowstheincreasein
hydrogen consumption with increase of benzene in feed. INSERT
FIGURE 16 6.Model application to process optimization From previous
analysis, it can be concludedthat feed composition and feed rate
arethe dominant process variables. Benzene composition may be the
most important variable. As seen Page 20 of 56ACS Paragon Plus
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21 `
inFigure16D,atconstantinlettemperaturetotheleadreactor,thePINisgreatlyaffectedby
variationoffeedbenzenecontent.Thus,continuousmonitoringoffeedbenzenecontentis
alwaysrequired.Although,feedbenzenecontentdoesnotchangewidely(Figure16A),evena
small change in benzene has a great impact on isomerization degree.
Refiners offset this impact by continuous variation of lead reactor
inlet temperature so as to obtain a fixed temperature rise through
lead reactor. The amount of allowable temperature rise is increased
as feed rate increases
toincreasereactionsrates.Thisoperatingtechniquemaybeeffective,howeverifthefeed
witnesses frequent variations in benzene level, this operating
scheme will be nearly impossible. For more effective operation and
more profits, some refiners developed rigorous models for real time
optimization of penex process9. This shows the necessity of
developing rigorous models in modern refineries.
AnotherimportantvariableistheH2:HCmoleratioinsidethereactor.Asindicated
before,hydrogenisrequiredforcompletingisomerizationandreducingcokelay-downon
catalyst.However,anincreaseinhydrogenpartialpressureinsidethereactorsleadstoan
increaseinhydrocrackingandreductionofisomerateyield.Therefore,thereactorsshouldbe
operatedwiththelowestpossiblehydrogenpartialpressure.However,asaruleofthumbto
avoidcokedeposition,thereactorsshouldnotbeoperatedatH2:H.Cratiolessthan0.05
measured at lag reactor outlet at any time.
Refinersfacetwooperationalscenariosinoptimizingrefineryprocesses.Thefirst
scenariois"what-if"scenariowheretherefinerswanttopredicttheprocessperformanceifa
change occurred to one or more of the process variables. This
scenario has been covered in the
previousanalysisofoperatingvariables.Theotherscenarioisthe"how-to"scenario.Refiners
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22 `
usuallyaimatmaximizingprofits.Hence,thefrequentquestioninrefiners'mindsis"Howto
increase profit?"
Inordertooptimizetheprocess,thenotesobtainedfromthefirstscenarioshouldbe
implemented.Table8presentsthebaseoperatingconditionsoftheinvestigatedindustrialunit
andthelimitboundsinducedbyprocesslicensor.Itisclearthatthereactorsareoperatedwith
H2:HCratiomuchhigherthanrequired.Then,thefirststepwasreducinghydrogenpartial
pressuretothelowestpossiblevaluewiththesamereactors'inlettemperature.Actually,the
lowestpossibleH2:HCratioatthereactors'outletwas0.0865whichisstillfarfromthe
allowable minimum. INSERT TABLE 8
LowerH2:HCratioscouldbeobtainedbuteitheratlowerleadreactortemperatureor
higher lag reactor inlet temperature because the amount of make-up
hydrogen used affects heat transfer coefficients in both the hot
and cold combined exchangers and consequently affects the
outlettemperatures.Havingobtainedthelowestpossiblehydrogenpartialpressureinreactors,
thenextstepwasvaryingtheleadandlagreactorinlettemperaturesimultaneouslysoasto
obtain the optimum operating point. Figures 17, 18 and 19 show the
obtained results. From Figure 17, the lower the reactors inlet
temperatures, the higher the isomerate yield.
Therefore,itisalwaystherefiner'sdecisiontoraisethereactorstemperaturetoincreasethe
isomerizationdegree(Figure18)toobtainahigherRON(Figure19)withthesacrificeof
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23 `
isomerateyield.Table9showsacomparisonbetweenplantyieldsatbasepointandoptimum
operating point. INSERT FIGURE 17 INSERT FIGURE 18 INSERT FIGURE 19
INSERT TABLE 9 Results shown in Table 9 indicate that about 210
kg/hr can be added to the total regular
isomerateyieldbyfollowingtheoptimizationscheme.Savingsinisomerateyieldaremainly
attributedtodecreasedhydrocrackingbyreducinghydrogenpartialpressureinsidereactors.In
addition,itisshownthatthereactorchargeheaterdutyhasdeclinedduetoreducedinlet
temperatureofleadreactorandreducedloadonheaterbyeliminatingapartofmake-up
hydrogenthatwasusedoriginally.However,thedecreaseinreactorcharge-heaterdutyis
overcome by the increase in stabilizer bottom reboiler, resulting
in apparent energy deficiency of
about96,635kJ/hr.However,followingtheoptimizedoperatingschemewillnotonlyimprove
isomerate yield and RON, but it will also reduce the consumption of
make-up gas. Make-up gas
fromnaphthareformermaybedirectedtofuelgassystemintherefinery.Thenewoperating
schemewilladdabout161kg/hrofmake-upgastothefuelgassystem.Thiswillprovide
approximately 11.3 x 106 kJ/hr. This may not only cover the
increase in stabilizer bottom reboiler duty, but also it may cover
the total energy consumption of the fired heaters in the Penex
unit. It should be noted here that savings in energy and product
yield are proportional to plant capacity. Page 23 of 56ACS Paragon
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24 `
Finally,themodelmaybeusedtopredicttheplantperformanceatvariousoperating
points.Themodelisextremelyusefulforpredictingsuitableoperatingconditions,especially
whenplantexperiencesvariationsinfeedbenzenecontent.Thiscanbeachievedby
incorporatingthemodelintoarealtimeoptimization(RTO)scheme.Inthiscase,itis
recommended that the model be finely tuned to match plant
performance closely. 7.Conclusions
AprocessmodelforanindustrialPenexprocesswasdevelopedusingAspenHYSYS
Petroleum Refining isomerization reactor module. The model could
track the plant performance satisfactorily. In addition, the model
was used for studying the effect of each process variable on
process performance. Among all process variables, benzene feed
content and H2:HC ratio were
themostprominentfactorstoaffecttheprocessperformance.Finally,themodelwasusedforoptimizingprocessatsteadystateconditions.Resultsobtainedfromthemodelshowedthat
considerablesavingsinproductyieldcanbeachievedbyloweringhydrogenpartialpressure
inside reactors to the lowest possible practical value. The surplus
in make-up gas may be directed
tofuelgasresultinginsignificantfuelsavings.Themodelmayalsobeincorporatedinareal
time optimization (RTO) scheme. In this case, the model should be
finely tuned to match plant performance closely. NomenclatureA6
Benzene C1 Methane Page 24 of 56ACS Paragon Plus EnvironmentEnergy
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25 ` C2 Ethane C3 Propane i-C4Iso butane n-C4 Normal butane i-C5Iso
pentane n-C5Normal pentane n-C6Normal hexane n-C7 Normal heptane
CHCyclo hexane 2,2-DMB 2,2 Dimethyl butane 2,3-DMB 2,3 Dimethyl
butane H factorifactor of component i MCH Methyl cyclo hexane MCP
Methyl cyclopentaneMBP7 Multi branched heptanes 2MP2-Methyl pentane
3MP3-Methyl pentane 5N5Cyclo pentane 5N7Five ring, seven carbon
naphthene Page 25 of 56ACS Paragon Plus EnvironmentEnergy &
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26 ` 6N7Six ring, seven carbon naphthene NP7Normal heptane
SBP7Single branched heptanes Temperature rise in reactor model
Temperature rise in plant reactor Property of a petroleum fraction
Property of a pure component i Mole , volume or mass fraction of
component i Known property of C7+ fraction Weighting factor for
component i Mass fraction of component i in model outlet stream
Mass fraction of component i in plant reactor outlet stream
PINParaffin Isomerization Number = i-C5/C5 + (2,2-DMB+2,3-DMB)/C6
References (1) Moulijn, J. A.; Makkee, M.; van Diepen, A. E.
Chemical Process Technology; 2nd ed.; Wiley, 2013. (2) Deak, V. G.;
Rosin, R. R.; Sullivan, D. K. In AICHE 2008 Spring National
Meeting; New Orleans, LA, USA, 2008. (3) Laredo, G. C.; Castillo,
J.; Cano, J. L. Fuel 2014, 135, 459467. Page 26 of 56ACS Paragon
Plus EnvironmentEnergy &
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27 ` (4) Smith, J. M.; van Ness, H. C.; Abbott, M. M. Introduction
to Chemical Engineering Thermodynamics; 6th ed.; McGraw-Hill, 2001.
(5) Yasakova, E. A.; Sitdikova, A. V; Achmetov, A. F. Oil Gas Bus.
2010. (6) Meyers, R. A. Handbook of Petroleum Refining Processes;
3rd ed.; McGraw-Hill, 2004. (7) Dean, L. E.; Harris, H. R.; Belden,
D. H.; Haensel, V. Platin. Met. Rev. 1959, 3, 911. (8) Chekantsev,
N. V.; Gyngazova, M. S.; Ivanchina, E. D. Chem. Eng. J. 2014, 238,
120128. (9) Besl, H.; Kossman, W.; Crowe, T. J.; Caracotsios, M.
Oil Gas J. 1998, 96, 6164. (10) Dudley, R. E.; Malloy, J. B. Ind.
Eng. Chem. Process Des. Dev. 1963, 2, 239244. (11) Ahari, J. S.;
Ahmadpanah, S. J.; Khaleghinasab, A.; Kakavand, M. Pet. Coal 2005,
47, 2631. (12) Ahari, J. S.; Khorsand, K.; Hosseini, A. A.; Farshi,
A. Pet. Coal 2006, 48, 4250. (13) Brito, K. D.; Sousa, B. V.;
Rodrigues, M. G. F.; Alves, J. J. N. Brazilian J. Pet. Gas 2008, 2,
18. (14) Koncsag, C. I.; Tutun, I. A.; SAFTA, C. Ovidius Univ. Ann.
Chem. 2011, 22, 102106. (15) Surla, K.; Guillaume, D.; Verstraete,
J. J.; Galtier, P. Oil Gas Sci. Technol. 2011, 66, 343365. (16)
Ghosh, P.; Hickey, K. J.; Jaffe, S. B. Ind. Eng. Chem. Res. 2006,
45, 337345. (17) Perdih, A.; Perdih, F. Acta Chim. Slov. 2006, 53,
306315. (18) Riazi, M. R. Characterization and Properties of
Petroleum Fractions; 1st ed.; ASTM International, 2005. (19)
Mahdavian, M.; Fatemi, S.; Fazeli, A. Int. J. Chem. React. Eng.
2010, 8, A8. (20) Taskar, U.; Riggs, J. B. AIChE J. 1997, 43,
740753. (21) Pashikanti, K.; Liu, Y. A. Energy & Fuels 2011,
25, 53205344. (22) Russell, R. A. Chem. Eng. - New York 1983, 90,
5359. (23) Kaes, G. L. Refinery Process Modeling: A Practical Guide
to Steady State Modeling of Petroleum Processes; 1st ed.; Athens
Printing Company: Athens, GA, USA, 2000.Page 27 of 56ACS Paragon
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28 ` Tables Table 1: RON of normal and iso paraffins16,17 Component
RON n-pentane 62 i-pentane 92 2-Methyl Pentane(2MP) 73.4 3-Methyl
Pentane (3MP) 74.5 2,2 dimethyl butane (2,2-DMB) 91.8 2,3 dimethyl
butane (2,3-DMB) 105.8 n-hexane 24.8 Page 28 of 56ACS Paragon Plus
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29 ` Table 2: PNA composition of C7+ fraction Hydrocarbon
classVol.% Paraffins 74.24 Naphthenes 23.53 Aromatics 2.22 Page 29
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30 ` Table 3: Available and calculated Properties of C7+ fraction
in feed and product streams PropertyC7+ (Feed)C7+ (Product)
GivenCalc.GivenCalc. SG0.69150.70420.6830.709
MW100.19899.666100.19899.70 RVP (psi)1.971.972.12.187 RON55558282
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31 ` Table 4: Estimated composition of C7+ fraction in feed and
product streams CompnentFeed (wt.%)Product (wt.%) MBP7048.2
SBP752.727.3 N-C721.2 0 5N710.112.2 6N71612.3 Page 31 of 56ACS
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32 ` Table 5: Adjustment factors used for reactor model
calibrationParameter Range of deviation from the base Global
activity0.1-1 Isomerization activity0.1-1.1 Hydrocracking
activity0.1-1.1 Hydrogenation activity0.1-1.1 Ring opening
activity0.1-1.1 Heavy activity0.1-1.1 Page 32 of 56ACS Paragon Plus
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33 ` Table 6: Terms included in objective function for reactor
model calibration and applied weighing factors TermApplied weighing
factor Temperature Rise (C)1 I-Pentane (wt%)5 N-Pentane (wt%)5
Cyclo Pentane (wt%)2 2 Methyl Pentane (wt%)5 3 Methyl Pentane
(wt%)5 2,2 Di-Methyl Butane (wt%)5 2,2 Di-Methyl Butane (wt%)5
N-Hexane (wt%)5 Methyl Cyclo Pentane (wt%)2 Benzene (wt%)2 Cyclo
Hexane (wt%)2 C7+ (wt%)2 Page 33 of 56ACS Paragon Plus
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34 ` Table 7: Estimated average activity parameters for lead and
lag reactors ParameterLead ReactorLag reactor Global
activity0.9122.402 Isomerization activity0.8271.092 Hydrocracking
activity1.0230.968 Hydrogenation activity0.9390.995 Ring opening
activity1.0541.042 Heavy activity1.071.059 Page 34 of 56ACS Paragon
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35 ` Table 8: Operating conditions of the unit at the base
operating point and limit bounds induced by process licensor
Process VariableBase Operating PointBounds H2:HC ratio0.1565min.
0.05 Lead Reactor Inlet T124 C105 - 204C Lag Reactor Inlet T120C105
- 204C Page 35 of 56ACS Paragon Plus EnvironmentEnergy &
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36 ` Table 9: Process performance at base and optimum operating
point Lead Reactor Inlet T (C) Lag Reactor Inlet T (C) Make-up
Hydrogen Flow (kg/hr) Reactor Charge Heater Duty (kJ/hr) Stabilizer
Reboiler Duty (kJ/hr) Isomerate Yield (kg/hr) PIN Base Operating
Point 124120614.21,018,2759,452,82931,6931.18 Optimum Operating
Point 116117453721,6459,846,09431,9031.184 Page 36 of 56ACS Paragon
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37 ` Figures Figure 1: Effect of temperature on isomers yield5 Page
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38 ` Figure 2: Comparison of the activity of different
isomerization catalysts5 Page 38 of 56ACS Paragon Plus
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39 ` Figure 3: UOP Penex process6 Page 39 of 56ACS Paragon Plus
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40 ` Figure 4: Isomerization model reaction network Page 40 of
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41 ` Figure 5: Variation of C7+ wt% in the feed 012345625-Feb
16-Apr 5-Jun 25-Jul 13-SepC7+ wt.%Page 41 of 56ACS Paragon Plus
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42 ` Figure 6: Plant versus model yields with model calibration
data sets forlead reactor 05101520253035400 5 10 15 20 25 30 35
40Model (wt%)Plant (wt.%)i-C-5%n-C55N52,2DMB2,3DMB2MP3MPN-C65N6Page
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43 ` Figure 7: Plant versus model yields with model calibration
data sets for lag reactor 0510152025303540450 5 10 15 20 25 30 35
40 45Model (wt%)Plant
(wt.%)i-C-5%n-C55N52,2DMB2,3DMB2MP3MPN-C65N6Page 43 of 56ACS
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44 ` Figure 8: Plant versus model yields for the 4 months after
calibration for lead reactor 05101520253035400 5 10 15 20 25 30 35
40Model (wt%)Plant (wt%)i-C-5%n-C55N52,2DMB2,3DMB2MP3MPN-C65N6Page
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45 ` Figure 9: Plant versus model yields for the 4 months after
calibration for lag reactor 05101520253035400 5 10 15 20 25 30 35
40Model (wt%)Plant (wt%)i-C-5%n-C55N52,2DMB2,3DMB2MP3MPN-C65N6Page
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46 ` Figure 10: Penex isomerization unit model Page 46 of 56ACS
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47 `
Figure 11: A- Effect of Lead reactor inlet temperature on RON;
B- Variation of (I-C5/C5)%
withleadreactorinlettemperature;C-Variationof(2,2DMB/C6)%withleadreactorinlet
temperature; D- Variation of (2,3DMB/C6)% with lead reactor inlet
temperature; E- Effect of
leadinletreactortemperatureonhydrogenconsumptioninleadreactor;F-Effectoflead
reactor inlet temperature on isomerate yield. Lag reactor inlet
temperature = 120 C, H2:HC = 0.1565, A6 = 2.99 wt.%, LHSV = 1.15
hr-1 84.0684.0784.0884.0984.184.1184.1284.1384.1484.15105 110 115
120 125RONLead Reactor Inlet Temp.
C(A)72.672.87373.273.473.673.874105 110 115 120 125(I-C5/C5)%Lead
Reactor Inlet Temp. C(B)25.82626.226.426.626.82727.227.427.627.8105
110 115 120 125(2,2DMB/C6)%Lead Reactor Inlet Temp.
C(C)8.38.358.48.458.58.55105 110 115 120 125(2,3DMB/C6)%Lead
Reactor Inlet Temp. C(D)892894896898900902904906908105 110 115 120
125Hydrogen consumption (STD_m3/hr)Lead Reactor Inlet Temp.
C(E)95.1895.1995.295.2195.2295.2395.2495.2595.2695.2795.28105 110
115 120 125Isomerate wt.%Lead Reactor Inlet Temp. C(F)Page 47 of
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48 ` Figure12:A-Effect of Lag reactor inlet temperature onRON;
B-Variation of (I-C5/C5)%
withlagreactorinlettemperature;C-Variationof(2,2DMB/C6)%withlagreactorinlet
temperature; D-Variation of (2,3DMB/C6)% with lag reactor inlet
temperature; E-Effect of
leadinletreactortemperatureonhydrogenconsumptioninlagreactor;F-Effectoflag
reactor inlet temperature on isomerate yield. Lead reactor inlet
temperature = 124 C, H2:HC = 0.1565, A6= 2.99 wt%, LHSV = 1.15 hr-1
84.0284.0484.0684.0884.184.1284.14106 111 116 121 126RONLag Reactor
Inlet Temp. (C)(A)76.2576.376.3576.476.4576.576.55106 111 116 121
126(I-C5/C5)%Lag Reactor Inlet Temp.
(C)(B)32.332.432.532.632.732.832.9106 111 116 121
126(2,2DMB/C6)%Lag Reactor Inlet Temp.
(C)(C)8.488.58.528.548.568.588.68.628.64106 111 116 121
126(2,3DMB/C6)%Lag Reactor Inlet Temp. (C)(D)00.511.522.533.54106
111 116 121 126Hydrogen consumption (STD_m3/hr)Lag Reactor Inlet
Temp.
(C)(E)95.17595.1895.18595.1995.19595.295.20595.2195.21595.22110 115
120 125Isomerate wt.%Lag Reactor Inlet Temp. (C)(F)Page 48 of 56ACS
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49 `
Figure 13: A- Effect of H2:HC ratio on isomerate yield; B-
Effect of H2:HC ratio on RON of
isomerate;C-EffectofH2:HCratioonPIN.Leadreactorinlettemperature=124C,lag
reactor inlet temperature = 120 C, A6 = 2.99 wt%, LHSV = 1.15 hr-1
9595.295.495.695.89696.296.40.07 0.09 0.11 0.13 0.15 0.17Isomerate
wt.%H2:HC
(A)84.1284.1384.1484.1584.1684.1784.1884.1984.284.2184.220.07 0.09
0.11 0.13 0.15
0.17RONH2:HC(B)1.17951.181.18051.1811.18151.1821.18251.1830.08 0.1
0.12 0.14 0.16PINH2:HC (C)Page 49 of 56ACS Paragon Plus
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50 `
Figure14:A-Effectoffeedrate(LHSV)onPIN;B-Effectoffeedrate(LHSV)on
isomerate yield. Lag reactor inlet temperature = 120 C, H2:HC =
0.1565, A6 = 2.99 wt% 1.051.061.071.081.091.11.11105 110 115 120
125PINLead Reactor inlet T1.03 hr-1 1.15 hr-1 1.3
hr-1(A)95.1495.1695.1895.295.2295.2495.2695.2895.3105 110 115 120
125Isomerate wt.%Lead Reactor T1.03hr-1 1.15hr-1 1.3 hr-1(B)Page 50
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51 ` 1.1791.17951.181.18051.1810 2 4 6 8PINFeed MCP content, wt%
(base
4.08%)(A)1.179751.17981.179851.17991.179951.181.180051.18011.180150
0.5 1 1.5 2PINFeed CH content, wt% (base
1.18%)(B)83.958484.0584.184.1584.284.2584.30 2 4 6 8RONFeed MCP
content, wt% (base
4.08%)(C)84.0984.184.1184.1284.1384.1484.1584.1684.1784.180 0.5 1
1.5 2RONFeed CH content, wt% (base
1.18%)(D)94.99595.195.295.395.495.50 2 4 6 8Isomerate wt.%Feed MCP
content, wt% (base
4.08%)(E)95.195.1295.1495.1695.1895.295.2295.2495.260 0.5 1 1.5
2Isomerate wt.%Feed CH content, wt% (base 1.18%)(F)Page 51 of 56ACS
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52 `
Figure 15: A- Effect of feed MCP content on PIN; B- Effect of
feed CH content on PIN; C-
EffectoffeedMCPcontentonRON;D-EffectoffeedCHcontentonRON;E-Effectof
feedMCPcontentonisomerateyield;F-EffectoffeedCHcontentonisomerateyield;G-
Effect of feed MCP content on total hydrogen consumption; H- Effect
of feed CH content on total hydrogen consumption; I:- Effect of
feed MCP content on hydrogen consumption in the
lagreactor;J-EffectoffeedCHcontentonhydrogenconsumptioninthelagreactor.Lead
reactor inlet temperature = 124 C, lag reactor Inlet temperature =
120C, LHSV = 1.15hr-1 8908959009059109159209259300 2 4 6 8 Total
Hydrogen Consumption(STD_m3/hr)Feed MCP content, wt% (base 4.08%)
(G)9029049069089109129140 0.5 1 1.5 2Total Hydrogen Consumption
(STD_m3/hr)Feed CH content, wt% (base 1.18%)(H)22.22.42.62.833.20 2
4 6 8Hydrogen Consumption in lag reactor (STD_m3/hr)Feed MCP
content, wt%(base 4.08%)(I)2.62.652.72.752.82.850 0.5 1 1.5
2Hydrogen Consumption in lag reactor (STD_m3/hr)Feed CH content,
wt% (base 1.18%)(J)Page 52 of 56ACS Paragon Plus EnvironmentEnergy
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53 `
Figure16:A-Variation of feed benzene content; B-Effect of feed
benzene content on lead reactortemperature rise; C-Effect of
feedbenzene contenton isomerate RON;D-Effect of
FeedbenzenecontentonPINintheleadreactor;E-Effectoffeedbenzenecontenton
isomerate yield; F- Effect of feed benzene content on hydrogen
consumption in lead reactor. Lead reactor inlet temperature = 124
C, lag reactor inlet temperature = 120C, LHSV = 1.15 hr-1
1.01.52.02.53.03.54.04.55.026-Jan 17-Mar 6-May 25-Jun 14-Aug
3-OctA6 wt%(A)0510152025303540450 2 4 6Temperature Rise in lead
reactorFeed benzene content, wt% (base
2.99%)(B)83.8583.983.958484.0584.184.1584.284.250 2 4
6RONFeedbenzene, wt% (base
2,99%)(C)1.061.0651.071.0751.081.0851.091.0951.10 2 4 6PINFeed
benzene content, wt% (base
2.99%)(D)94.494.694.89595.295.495.695.8960 2 4 6Isomerate wt%Feed
benzene content, wt% (base 2.99%)(E)020040060080010001200140016000
2 4 6Hydrogen Consumption in lead reactor (STD_m3/hr)Feed benzene
content, wt% (base 2.99%)(F)Page 53 of 56ACS Paragon Plus
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54 ` Figure 17: Variation of isomerate yield with reactors inlet
temperatures
11211411611812012212496.3796.3996.4196.4396.4596.4796.49117115113111109107Lag
reactor T, oCIsomerate wt %Lead Reactor T,
oC96.49-96.596.47-96.4996.45-96.4796.43-96.4596.41-96.4396.39-96.4196.37-96.39Page
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55 ` Figure 18: Variation of Paraffin Isomerization Number with
reactors inlet temperatures
1121151181211241.171.1721.1741.1761.1781.181.1821.1841.186117115113111109107Lag
Reactor Inlet T, oCPINLead Reactor Inlet T,
oC1.184-1.1861.182-1.1841.18-1.1821.178-1.181.176-1.1781.174-1.1761.172-1.1741.17-1.172Page
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56 ` Figure 19: Variation of isomerate RON with reactors inlet
temperatures
11211411611812012212484.0884.184.1284.1484.1684.1884.284.2284.24117114111108Lag
reactor inlet T, oCRONLead reactor inlet T,
oC84.24-84.2584.22-84.2484.2-84.2284.18-84.284.16-84.1884.14-84.1684.12-84.1484.1-84.1284.08-84.1Page
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