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CT&F Ciencia, Tecnología y Futuro

ISSN: 0122-5383

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ECOPETROL S.A.

Colombia

Gómez, Maria-Elizabeth; Vargas, Clemencia; Lizcano, Javier

Petrochemical promoters in catalytic cracking

CT&F Ciencia, Tecnología y Futuro, vol. 3, núm. 5, diciembre, 2009, pp. 143-158

ECOPETROL S.A.

Bucaramanga, Colombia

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PETROCHEMICAL PROMOTERS IN CATALYTIC CRACKING

CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 5 Dic. 2009 143


Maria-Elizabeth Gómez*1, Clemencia Vargas1 and Javier Lizcano2

1 Ecopetrol S.A - Instituto Colombiano del Petróleo, A.A. 4185 Bucaramanga, Santander, Colombia2 UT TIP - Petrolabin, Piedecuesta, Santander, Colombia

e-mail: [email protected]

(Received May 5, 2009; Accepted October10, 2009)

T his study is based on the current scheme followed by a refinery with available Catalytic Cracking capacity to process new feedstocks such as Straight Run Naphtha and Naphthas from FCC. These feedstocks are of pe-trochemical interest to produce Ethane, Ethylene, Propylene, i-Butane, Toluene and Xylene.

To evaluate the potential of these new streams versus the Cracking-charged Residues, it was performed a detailed chemical analysis on the structural groups in carbons [C1-C12] at the reactor product obtained in pilot plant. A catalyst with and without Propylene - Promoter Additive was used. This study analyzes the differences in the chemical composition of the feedstocks, relating them to the yield of each petrochemical product. Straight Run Naphthas with a high content of Naphthenes, and Paraffines n[C5-C12] and i[C7-C12] are selective to the production of i-Butane and Propane, while Naphthas from FCC with a high content of n[C5-C12]Olefins, i-Olefins, and Aromatics are more selective to Propylene, Toluene, and Xylene.

Concerning Catalytic Cracking of Naphthas, the Additive has similar selectivity for all the petrochemical products, their yields increase by about one point with 4%wt of Additive, while in cracking of Residues, the Additive increases in three points Propylene yield, corresponding to a selectivity of 50% (ΔC3= / ΔLPG).

Keywords: propylene, catalytic cracking, i-butane, ethylene, naphthas, petrochemicals, Residues, ZSM-5.

Ciencia, Tecnología y Futuro

* To whom correspondence may be addressed

CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 5 Dic. 2009

MARIA-ELIZABETH GÓMEZ et al.

144

El presente estudio se basa en el esquema actual de una refinería con capacidad disponible en Cracking Catalítico, para procesar nuevas cargas tales como Naftas Vírgenes y Naftas de URC (Unidad de Ruptura Catalítica), las cuales son de interés Petroquímico en productos tales como Etano, Etileno,

Propileno, i-Butano, Tolueno y Xilenos.

Para evaluar el Potencial Petroquímico de estas corrientes frente al de los Residuos cargados a Cracking, se realizó un análisis químico detallado de los Grupos Estructurales de los Carbonos [C1-C12] en el producto reactor obtenido en planta piloto, utilizando un catalizador con y sin Aditivo promotor de Propileno.

El estudio analiza las marcadas diferencias en la composición química de las cargas, y las relaciona con los rendimientos de cada uno de los productos petroquímicos. Las Naftas Vírgenes con mayor contenido de Naftenos y de Parafinas n[C5-C12] e i[C7-C12] son selectivas hacia la producción de i-Butano y Propano, mientras que las Naftas de URC con altos contenidos de n[C5-C12] Olefinas, i-Olefinas, y Aromáticos son más selectivas hacia Propileno, Tolueno y Xilenos.

En el craqueo de las Naftas, el Aditivo tiene la misma selectividad para todos los productos petroquímicos, sus rendimientos incrementan en valores cercanos a un punto con 4% peso de Aditivo; mientras que en el craqueo de los Residuos el aditivo incrementa en 3 puntos el rendimiento de Propileno, lo que corresponde a una selectividad del 50% (ΔC3= / ΔLPG).

Palabras Clave: propileno, craqueo, i-butano, etileno, naftas, petroquímicos, residuos, ZSM-5



NOMENCLATURE

LCO Light Cycle OilC/O Catalyst / Oil ratioDCR Davison Circulating RiserFCCU Fluid Catalytic Cracking UnitLPG LiquefiedPetroleumGasH2 HydrogeniC4 i-ButaneiC5 i-Pentanei[C4-C6] i-ParaffinesC4-C6i[C7-C12] i-ParaffinesC7-C12iP i-ParaffinesNaft NaphthenesnC2 EthaneC2= EthylenenC3 PropanenC3= PropylenenC4 Butanen[C1-C4] n-ParaffinesC1-C4n[C2-C4]Olefins n-OlefinsC2-C4n[C5-C12] n-ParaffinesC5-C12n[C5-C12]Olefins n-OlefinsC5-C12nP n-ParaffinesPIANO Paraffines,i-Paraffines,Aromatics,NaphthenesandOlefinsSimDis Simulated distillationUVVIS VisibleultravioletVGO Vacuum Gas OilΔC3=/ΔLPG PropyleneSelectivitywithAdditive: [C3=increase]/[LPGincrease]



146

INTRODUCTION

The operational constraints of a FluidCatalyticCracking Unit (FCCU) to produce certain products not only depend on its technology or operating conditions, but alsoonthecharacteristicsandqualityofthefeedstockthatdetermine its potential to produce the desired product.

Theobjectiveofthisstudyistodetermineandcom-pare thepetrochemicalpotentialofdifferent typesofNaphthasforaRefinerythathasfourunitsofdifferentFCCU technology,processingdifferent typeof feed-stocks,asfollows:oneModelIVprocessingVacuumGasOil(VGO),twoUniversalOilProductUnits(UOP)andoneOrthoflowUnitprocessingamixtureofResi-dueswithVGO,andVacuumBottomswithorwithoutfurtherhydrotreatment.

TheproductsofinterestareEthane,Ethylene,Propy-lene, i-Butane, Toluene and Xylene. Ethane is pyrolized andconvertedinEthylene.ThePropane-Propylenecu-rrentisseparatedinasplitterandthePropyleneissenttoapolymerizationplant,whilei-Butaneisrequiredasafeedstockforalkylation.ThecurrentschemeoftheRefineryincludestheproductionofMotorGasolineandtherefore,therearenofacilitiestoseparatetheAromaticfraction.Thisfractioncanbeseparatedbyapplyingtheprocess patentedbyTimken,H.K.C.,&Angevine,P. J. (1997) consistingofNaphthahydrotreatment toeliminatesulfur,followedbytherecoveryoftheAro-maticfractionbydistillation.Thisprocessco-producesNaphthaswithlow-sulfurandrelativelyhighoctane.

THEORETICAL FRAMEWORK

ThereactionsoccurringinthecrackingofNaphthaare lesscomplex than those involved in thecrackingofheavyoil.Nevertheless, they involvehundredsofcompoundsinteractinginthousandsofreactions(Yang,et al. 2008). Based on their decreasing reactivity, these reactions are usually grouped as follows (Wang,L.,Yang,B.,&Wang,Z.,2005):

Olefins>Aromatic SideChains> i-Paraffines>Naphthenes>n-Paraffines>>AromaticRings.

StudiesconductedoncatalyticcrackingofGasOilwithcatalystsusingPropyleneAdditiveZSM-5(Zhao,X.,&Harding,R.H.1999)demonstratedthattheyieldofOlefins inducedby theAdditivedecreaseswith thecontentofNaphthenesinthefeedstock.ThisbehaviorisattributedtothefactthatNaphthenesparticipateinthehydrogen-transfer reactions that saturateOlefins. It isthereforeconcludedthattheAdditiveeffectismaximizedwhencatalystsoflowactivityinhydrogentransferreac-tions are used. These catalysts are characterized by the lowdensityofacidsitesandlowcontentofrareearthelements.RegardingthecatalyticcrackingofNaphthafromFCC,theworkdonebyHollader,M.A.,et al. (2002) concludesthattheonlysignificantlyreactivecompoundsinNaphthafromFCCaretheolefinswithmorethan6atomsofcarbon.ItisalsodemonstratedthatbimolecularreactionsofhydrogentransferoccuronthecatalystandnotontheAdditive.Bycontrast,theAdditivewithsmallerpore size promotes monomolecular reactions only to producelightolefins.ItisimportanttounderstandhowNaphthacompositioncanaffectproductselectivitydu-ringcatalyticcrackingreactions.Therefore,theapproachinthisstudyistoanalyzethebehaviorofeachtypeofhydrocarbon in detail.

EXPERIMENTAL DEVELOPMENT

TheindustrialNaphthasselectedforthisstudywere:ParaffinicandNaphthenicNaphthasfromatmosphericdistillationandNaphthasfromthe4FCCUs(Table1).

AllNaphthas andResidues from eachUnitwereevaluatedinthepilotplantinabroadoperatingwindow,usingdifferentC/Oseverities,withintheoperatingres-trictionsof the industrialplant.Reaction temperaturewas545°C(1000°F)forNaphthasand525°C(977°F)forResidues.An industrial equilibrium catalystwasused in all cases.

Additionally,inthecaseofNaphtha,theeffectofthePropylene-PromoterAdditive,ZSM-5,wasevalua-tedbyusingaconcentrationof4%,andforResidues2,4,and6%.



Table 1. Quality of Residues and Naphthas to Pilot Plant

Experimental EquipmentPilot Plant.All feedstockswere evaluated in a

continuous Davison Circulating Riser (DCR). The unit operateswith3,3kgofcatalystthatcontinuouslyreactsand regenerates itself.Theoperationwas carriedoutmaintaininganisothermalprofilealongtheRiser,withafeedflowof0,8kg/h.

Gas Chromatograph.Gaseswere analyzed in anANGILENT6890model chromatograph, followingthestandardUOP-539,witha repeatability reportedby the laboratory of ± 0,014%vol, on average foreach compound.The liquid productwas characteri-zedusingtwomethods:thefirstmethodconsistedofthesimulateddistillationdescribedinASTMD-7213wheretheproductwasseparatedintothreefractionsasfollows:Naphtha(<430ºF),LCO(430-650ºF)andSlurry (>650ºF); the second is PIANO (Paraffines,i-Paraffines,Aromatics,Naphthenes andOlefins) as

describedbyASTMD-6729,thatseparatesallcom-poundslessthanorequaltoC12,witharepeatabilityof±0,087%wtonaverageforeachcompoundreportedby the laboratory. Coke yieldwas calculated fromthe composition of the flue gas analyzed followingtheASTMD-1945,witha repeatability reportedbythe laboratoryof±0,035%vol.onaverage for eachreported compound.

RESULTS

TheresultsdiscussedinthisstudyarePIANOsofpilotplantfeedstocks(FCCandStraight-runNaph-thas),ChromatographicandPIANOreportsfromthepilot plant effluents.These results are normalizedthrough a mass balance and reported in Table 2 as reactor products.



148

Table 2. Pilot Plant Yields (%wt) from Catalytic Cracking of Naphthas and Residues, with and without ZSM-5 Additive.



Table 2 shows themost representative results ofthisstudy.Thisprovidesamoregeneraloutlookofthechanges in structural composition resulting from thecracking reactions.

LCO, Slurry, and Coke are also produced in the cata-lyticcrackingofNaphthainyieldsbetween4and9%.Thisusuallycomesfromaromaticdehydrogenationandcondensationreactions(Table2).NaphthasfromFCCproduceahigheryieldoftheseproductswhich,inturn,isrelatedtoitsgreaterAromaticcontent.

For the cracking ofResidues, the sum of LCO,Slurry,andCokeyieldsisnearly40%.Thismeansthattheremaining60%correspondstotheC1-C12fractionanalyzedindetailatthetopofTable2.

Since these Naphthas are injected into the Riser bo-ttom in smaller proportions as compared to Residue, Table 2 shows thecomparisonofReactorProductyieldsofNaphthasandResiduesatdifferentC/Oseverities:15forNaphthasand6forResiduesliketheIndustrialPlant.

ANALYSIS OF RESULTS

Since the potential of petrochemical products arewithinNaphtha,LPGanddrygasstreams,theanalysisofresultsfocusesonthedetailedstudyofcompoundsC1-C12,whicharegroupedinthefollowingfamilies:Paraffines,Olefins,AromaticsandNaphthenes.

n-ParaffinesFigure 1a shows the yield profile of n-Paraffines

obtainedbythecatalyticcrackingofParaffinicNaph-tha.SimilarprofileswereobservedwithallthestudiedNaphthas.TheyieldofnC3increasessignificantlyandis sensitive to variations in C/O severity. The same is observedwithalltheotherNaphthas.

Regarding Naphtha and Residues (Figure 1), Metha-neandEthaneyieldsarebetween0,5and1,5%andareduetothermalcracking,therefore,theseproductsdonotdependonthetypeofNaphthaandarenotsignificantlyaffectedbytheseverityortheAdditive(Table2).

Even though nC3 is not directly a petrochemical productforthisrefinery,itisimportanttobeconsideredwhentheobjectiveofFCCisnC3=,sincegreaternC3productionresultsinincreasedcongestionofthecom-pression and recovery zone by less-valuable products.

0

1

2

3

4

5

6

7

nC1 nC2 nC3 nC4 nC5 nC6 nC7 nC8 nC9n C10n C11n C12

n-P

ara

ffin

Yie

ld,

%w

t

C/O= 18

C/O= 15

C/O= 11

C/O= 8

C/O= 6

Paraffinic

Figure 1. Distribution profile of n-Paraffin Yields

YieldofnC3ismoreselectivethannC4(Figure1)and Straight Run Naphthas are much more selective to nC3thanNaphthasfromFCC(Figure2a).Thisdiffe-rence isdue to thefact thatParaffinicNaphthahasahighercontentofn[C5-C12]thanNaphthasfromFCC(22%vs.6%)(Figure2b).BasedonthecompositionofNaphthenic Naphthas, the higher nC3 yield is due to the highcontentofi[C7-C12],whichcracktolightercom-pounds and Naphthenes. Furthermore, these Naphthenes cracktoproduceOlefins,andarethensaturatedwithmoreNaphthenesbyhydrogentransferreactions.



150

Craking

3(Olefins) + 3(Parafines) +

Olefin

Then[C5-C12]inNaphthasfromFCCdonotcrack(Figure2b),thennC3mustbeproducedfromotherreac-

tions,whereOlefinssaturationisoneofthemostlikelyto occur, considering that there is a high concentration ofOlefinsintheseNaphthas(±30%)(Table2)(Zhao,&Harding,1999).

ForallNaphthas,theapplicationofAdditiveincreasednC3yieldsby±1(Figure2a)andforResiduesby±0,5(Figure3a).Noeffectof theAdditiveisobservedonn[C5-C12] (Figures 2b and 3b).

Figure 2. n-Paraffin Yields in Catalytic Cracking of Naphthas

0

1

2

3

4

Base 2%

Adit

4%

Adit

6%

Adit

Base 2%

Adit

4%

Adit

6%

Adit

Orthoflow UOPII

nC

3 Y

ield

, %

wt

C/O= 13

C/O= 11

C/O= 10

C/O= 9

C/O= 7

C/O= 6

C/O= 5

0

1

2

3

4

Base 2%

Adit

4%

Adit

6%

Adit

Base 2%

Adit

4%

Adit

6%

Adit

Orthoflow UOPII

n[C

5-C

12

] Y

ield

, %

wt

C/O= 13

C/O= 11

C/O= 10

C/O= 9

C/O= 7

C/O= 6

C/O= 5

Figure 3. n-Paraffin Yields in Catalytic Cracking of Residues



i-ParaffinesSelectivity of i-Paraffines in catalytic crackingof

NaphthasisclearlydirectedtowardiC4andiC5pro-duction (Figure4).Theseyieldspartiallycome fromcrackingof i[C7-C12]which are reducedduring theprocess(Figure5b).NaphthenicandParaffinicStraightRunNaphthashavehighercontentofi[C7-C12](±30%),andhigherselectivitytowardiC4thanNaphthasfromFCC,9vs.5%(Figure4band5).

Themostabundanti-ParaffininthecatalyticcrackingofNaphthasfromFCCisiC5(Figure4a),reachingvaluesupto12%wt(Table2).

NaphthafromModIVisaspecialcasebecause,unlikeothers, this plant does not process Residues but Light Gas Oil.

Therefore,inmostcases,itshowsanintermediatebe-haviorbetweenStraightRunNaphthasandNaphthasfromFCC.

TheAdditiveboostsiC4yieldswithin±1pointforallNaphthas(Figure5a),and±0,5pointsforcrackingofResidue(Figure6a);however, the totalcontentofi-Paraffines,bothinNaphtha(Table2)andResidues,(Figure6b)decreases.

0

1

2

3

4

5

6

7

8

9

10

I-C4 I-C5 2

methyl

C5

3

methyl

C5

2

methyl

C6

3

methyl

C6

2

methyl

C7

4

methyl

C7

3

methyl

C7

Mono

methyl

C8+

Mono

Ethyl

C8+

§ Others

i-P

ara

ffin

Yie

ld,

%w

t

C/O= 20

C/O= 15

C/O= 11

C/O= 8

C/O= 6

Ortho Pdt

Figure 4. Distribution profile of i-Paraffin Yield

0

1

2

3

4

5

6

7

8

9

10

11

12

No Yes No Yes No Yes No Yes No Yes No Yes No Yes No Yes

Naphthenic Paraffinic ModIVDBP ModIV Liv UOPII Liv UOPII Pdt Ortho Pdt UOPI Liv

iC4

Yie

ld,

%w

t

ADDITIVE

C/O= 20C/O= 15C/O= 11C/O= 8C/O= 6FEEDS

02468

101214161820222426283032



i[C

7-C

12

] Y

ield

, %

wt

C/O= 20

C/O= 15C/O= 11

C/O= 8C/O= 6

FEEDS

ADDITIVE

Figure 5. i-Paraffin Yields in Catalytic Cracking of Naphthas



152

0

1

2

3

4

Base 2%

Adit

4%

Adit

6%

Adit

Base 2%

Adit

4%

Adit

6%

Adit

Orthoflow UOPII

iC4

Yie

ld,

%w

t

C/O= 13

C/O= 11

C/O= 10

C/O= 9

C/O= 7

C/O= 6

C/O= 5

7

8

9

10

11

12

13

14

Base 2%

Adit

4%

Adit

6%

Adit

Base 2%

Adit

4%

Adit

6%

Adit

Orthoflow UOPII

i-P

ara

ffin

Yie

ld,

%w

t

C/O= 13

C/O= 11

C/O= 10

C/O= 9

C/O= 7

C/O= 6

C/O= 5

Figure 6. i-Paraffin Yields in Catalytic Cracking of Residues

n-OlefinsIngeneral, total n-Olefins increaseduring cra-

cking and due to a higher severity in C/O (Table 2). Inthisgroup,nC3=istheproductofhigherselecti-vity and sensitivity to changes in C/O severity (Figu-re7). IncatalyticcrackingofNaphthafromFCC,nC3= production increases in similar proportion to thedecreaseofn[C5-C12]Olefins,from±11to±1%(Figure8).NoticethedirectcorrespondencebetweennC3=ofhigherseveritypoints(Figure8a)andthestarsofFigure8bfortheseNaphthas.

n-OlefinsarehighlyreactivemoleculesonZSM-5(Hollander et al., 2002,Zhao,X.,&Roberie,T.,G.1999,Buchanan,J.,S.,1998,Wang,G.,et al., 2008).

This isoneof the reasonswhynC3=yield increasesinonepointduringthecatalyticcrackingofNaphthasfromFCC,exceptinModIV,whentheAdditiveisused(Figure 8).

StraightRunNaphthashavealmostnilcontentofn[C5-C12]Olefins.However,withoutAdditive, theirnC3= yields are similar to that produced by Naphthas fromFCC.TheseyieldscomemainlyfromNaphthenescracking,considering thehighcontentof thesecom-pounds(±30%)inthefeedstocks(Table2).

TheAdditivehasnoeffectonStraightRunNaphthas(Figure 8a) sincetheyhavenoOlefinsactingasnC3=promotersontheAdditive.TheOlefinsformedbythecrackingofNaphthenesarenotabsorbedbytheAddi-

0

1

2

3

4

5

6

7

C2=C3= 1-

C4=

i-

C4=

t-

C4=

c-

C4=

1-

C5=

t2-

C5=

C2-

C5=

1-

C6=

t3-

C6=

c3-

C6=

t2-

C6=

c2-

C6=

n-O

lefi

n Y

ield

, %

wt C/O= 20

C/O= 15

C/O= 11

C/O= 8

C/O= 6

Ortho Pdt

0

1

2

3

4

5

6

7

C2=C3= 1-

C4=

i-

C4=

t-

C4=

c-

C4=

1-

C5=

t2-

C5=

C2-

C5=

1-

C6=

t3-

C6=

c3-

C6=

t2-

C6=

c2-

C6=

n-O

lefi

n Y

ield

, %

wt

C/O= 12

C/O= 11

C/O= 10

C/O= 8

C/O= 6

C/O= 8

C/O= 5

Figure 7. Distribution profile of n-Olefin Yields



Note: The total content of n-Olefin in Straight Run Naphtha is ZERO

a. nC3=

4

5

6

7

8

9

10



nC

3=

Yie

ld,

%w

t


ADDITIVE

b. n[C5-C12]Olefins

n[C

5-C

12

]Ole

fin

s Y

ield

, %

wt

0

1

2

3

4

5

6

7

8

9

10

11

12



ADDITIVE


Figure 8. n-Olefin Yields in Catalytic Cracking of Naphthas

tive.ThismeansthattheindustrialuseoftheAdditiveisnotjustifiedwiththistypeoffeedstock.RegardingNaphthasfromFCC,AdditiveincreasesnC3=yieldsby more than one point (Figure 8a).

Concerning Cracking of Residue, theAdditiveismuchmore selective toward nC3= as comparedto crackingofNaphthas, increasingyieldbyup to4pointsinUOPIIcase(Figure9a)whenusing6%

ofAdditive in theCatalyst.Thismatcheswith theselectivityspecifications(greaterthan50%)givenbyAdditiveSuppliersinthecrackingofheavyfeedstocks(Table 2).

AsfarasEthylene(C2=),allNaphthasshowedasimilaryieldof±1,8%andResidues±1,0%(Figure10).UnlikecrackingofResidues,crackingofNaphthain-creases yield to Ethylene upon increase in C/O severity.

3

4

5

6

7

8

9

10

11

Base 2%

Adit

4%

Adit

6%

Adit

Base 2%

Adit

4%

Adit

6%

Adit

Orthoflow UOPII

nC

3=

Yie

ld,

%w

t

C/O= 13

C/O= 11

C/O= 10

C/O= 9

C/O= 7

C/O= 6

C/O= 5

b. n[C5-C12]Olefins

0

1

2

3

4

5

Base 2%

Adit

4%

Adit

6%

Adit

Base 2%

Adit

4%

Adit

6%

Adit

Orthoflow UOPII

n[C

5-C

12

]Ole

fin

s Y

ield

, %

wt

C/O= 13

C/O= 11

C/O= 10

C/O= 9

C/O= 7

C/O= 6

C/O= 5

Figure 9. n-Olefin Yields in Catalytic Cracking of Residues



154

0

1

2

3

4



C2

= Y

ield

, %

wt

ADDITIVE


0

1

2

3

4

Base 2%

Adit

4%

Adit

6%

Adit

Base 2%

Adit

4%

Adit

6%

Adit

Orthoflow UOPII

C2

= Y

ield

, %

wt

C/O= 13

C/O= 11

C/O= 10

C/O= 9

C/O= 7

C/O= 6

C/O= 5

Figure 10. C2= Yield in Catalytic Cracking of Naphthas and Residues

TheAdditivepromotestheC2=yieldsforallNaph-thas,particularlyinNaphthasfromFCC(Figure10).ForResidues,theeffectofAdditivesisbetterobservedinUOPII,where an increaseofAdditive results in aslightlinearincreaseofC2=.OtherpapersonGasOilcrackinghavereportedthesametrendforC2=(Zhao&Roberie,1999).

i-Olefinsi-Olefins are very reactive and are almost fully

consumedduring cracking reactions, from±19% to2%(Figure11a). i-Olefins, liken-Olefins,arenC3=

promoters that favor properAdditive performance.(Hollander et al., 2002).

AccordingtoBuchanan,J.,S.(1998),i-OlefinsonAdditivesexhibitthehighestreactionrate.Theycracktoproducen-Olefinsoflowmolecularweight.NaphthasfromFCChavehighi-Olefincontent(±19%)(Figure11a):consequently, theyhavehighnC3=yieldswiththe use of theAdditive (Figure 8a). For cracking ofResidues (Figure 11b), onlyUOPII, that has highernC3=yields,showsaprogressivereductionini-Olefinsyields as the use ofAdditive increases (Figure 9a).

0

2

4

6

8

10

12

14

16

18

20

22



i-O

lefi

n Y

ield

, %

wt

ADDITIVE

C/O= 20

C/O= 15

C/O= 11

C/O= 8

C/O= 6

FEEDS

0

1

2

3

4

5

6

7

8

Base 2%

Adit

4%

Adit

6%

Adit

Base 2%

Adit

4%

Adit

6%

Adit

Orthoflow UOPII

i-O

lefi

n Y

ield

, %

wt

C/O= 13

C/O= 11

C/O= 10

C/O= 9

C/O= 7

C/O= 6

C/O= 5

Figure 11. i-Olefin Yields in Catalytic Cracking of Naphthas and Residues



Naphthene OlefinsNaphtheneOlefins content is higher inNaphthas

fromFCC(exceptModIV)thaninStraightRunNaph-thas.Likei-Olefins,theyarereducedtoalmostnothingas C/O severity increases (Figure 12a).

Naphthenic compounds do not interact over the Additive since thesemolecules are bigger than theaccessibilitydiameterofZSM-5(5,4Å),(Hollander et al., 2002) (Figure 12b).

Aromatics During cracking reactions, totalAromatic com-

poundsinproductsincrease(Table2).MonoAromatic

compounds inNaphthas are generally the result ofhydrogentransferreactionsbetweenOlefinsandNaph-thenes(Wanget al.,2008,Wang,L.,Yang,B.,&Wang,Z.2005).Therefore,StraightRunNaphthaswithhigherNaphthenes content cause a larger increase in yield toward total aromatic compounds, from 15 to 24%(Table2).However,totalAromaticcontentishigherinNaphthasfromFCC.

TheAromaticdistributionprofile (Figure13aand13b)showsthatthemainAromaticcompoundresultingfromcatalyticcrackingofNaphthaisToluene,followedby m-Xylenes. For Residues, Toluene and m-Xylene yields are produced in equal proportion (Figure 13b).

a. Naphtha feedstock

0

1

2

3

4

5

6



Na

ph

the

n-O

lefi

n Y

ield

, %

wt


ADDITIVE

b. Residue feedstock

0

1

2

3

4

Base 2%

Adit

4%

Adit

6%

Adit

Base 2%

Adit

4%

Adit

6%

Adit

Orthoflow UOPII

Nap

hth

en

-Ole

fin

Yie

ld, %

wt

C/O= 13

C/O= 11

C/O= 10

C/O= 9

C/O= 7

C/O= 6

C/O= 5

Figure 12. Naphthen-Olefin Yields in Catalytic Cracking of Naphthas and Residues

a. Cracking of UOPII Naphtha

0

1

2

3

4

5

6

7

8

9

BenceneToluene ethylBencene

mXylene

pXylene

oXylene

1methyl3ethylBenc

1methyl4ethylBenc

1,3,5Trimethyl

Benc

1methyl2ethylBenc

1,2,4Trimethyl

Benc

1,2,3Trimethyl

Benc

C/O= 19

C/O= 16

C/O= 11

C/O= 9

C/O= 6

UOPII Pdt

Aro

ma

tic Y

ield

, %

wt

b. Cracking of UOPII Residue

0,0

0,5

1,0

1,5

2,0

2,5

3,0

BenceneToluene ethyl

Bencene

m

Xylene

p

Xylene

o

Xylene

1methyl

3ethyl

Benc

1methyl

4ethyl

Benc

1,3,5

Trimethyl

Benc

1methyl

2ethyl

Benc

1,2,4

Trimethyl

Benc

1,2,3

Trimethyl

Benc

Aro

ma

tic Y

ield

, %

wt C/O= 12

C/O= 11C/O= 10C/O= 8

C/O= 8C/O= 6C/O= 5

Figure 13. Distribution profile of Aromatic Yields



156

InNaphthasfromFCC,totalTolueneandXylenesyieldsare greater than in Straight Run Naphthas (Figure 14a and 14b). This is not due to higher selectivity but to the fact thatNaphthas fromFCCfeedstockshavehigherinitialcontentof thesecompounds thanStraightRunNaphthas.Tolueneandm-XyleneyieldsaresignificantlyaffectedbyC/Oseverity.

Figure 14. Aromatic Yields in Catalytic Cracking of Naphthas and Residues

TheyieldsofTolueneandXyleneinthecrackingofResiduesaretoomuchlowerthanthosefromcrackingofNaphthas(Figure14).

Naphthenes According to Figure 15,Naphthenes are always

reduced during cracking reactions (Table 2). Since Naphthenes are the main components in Straight Run Naphthas(±34%),theirreactivityishigherbecausethereisnocompetitionwithOlefinsforactivesites(StraightRunNaphthasdonothaveOlefins).Theirreactivityisevident in their sensitivity to C/O severity.

Basedontheabove,NaphthenesbecomeindirectPro-pylenepromotersinthecrackingofStraightRunNaphthasduetothefactthattheyhavenoOlefinsand,therefore,theyareproducedbycrackingofNaphthenes.

Figure 15. Naphthene Yields in Catalytic Cracking of Naphthas and Residues

c. Toluene and Xylenes in Residues

0

1

2

3

4

5

Toluene Xylenes Toluene Xylenes

Orthoflow Base UOPII Base

To

lue

ne

an

d X

yle

ne

s Y

ield

, %

wt

C/O= 13

C/O= 11

C/O= 10

C/O= 9

C/O= 7

C/O= 6

C/O= 5



Due to their molecular size, Naphthenes cannot access theZSM-5Zeolite.Therefore,thereductionobservedin Figure 15a can be attributed to additional reactions ofNaphtheneswithOlefins,beingthelatterpromotedbyZSM-5.

CONCLUSIONS

The differences between the composition ofStraight Run Naphthas and Naphthas from FCCare significant.StraightRunNaphthashavehighercontent of n[C5-C12] i[C7-C12], andNaphthenesthanNaphthasfromFCC.ComparedtoStraightRunNaphthas,NaphthasfromFCCarerichinAromatics,n[C5-C12],Olefins,andi-Olefins(Table2).

Thesemarkeddifferencesinfeedstockcompositionresult in the orientation of yields toward a specificpetrochemical compound after catalytic cracking ofNaphthas,asfollows:

● StraightRunNaphthasareselectivetowardi-Bu-tane, and their yields are almost double the amount producedbyNaphthasfromFCC(9%vs.5%).AnincrementofonepointiniC4yieldisobtainedforallNaphthaswiththeuseoftheAdditive.i-Butaneyieldsaredirectlyrelatedtocompoundsofthesamefamily,i.e.,withthehighi[C7-C12]contentinthefeedstock(30%inthecasesstudied).

● StraightRunNaphthas produce the samePropy-leneyieldsasNaphthasfromFCC(between6and8%). Propylene yields are directly related to thecontent of both n[C5-C12]Olefins and i-Olefins.IntheStraightRunNaphthawithverylowcontentofolefins,thehighcontentofNaphthenes(34%)actaspromoterswhicharecrackedintoolefinsandproducethesameyieldofPropyleneasNaphthasfromFCC.However,StraightRunNaphthasdonothaveenoughOlefinstoproduceadditionalyieldswith the use of theAdditive.Therefore, the useoftheAdditiveZSM-5isnotadvisablewhenthefeedstockiscomposedofStraightRunNaphthas.

● Straight Run Naphthas are highly selective to-wardPropane.TheyieldsarealmostdoublewhencomparedtoNaphthafromFCC(6%vs.3%).TheAdditiveincreasesbyapproximatelyonepointforallNaphthas.Propaneyieldsaredirectlycorrelatedwithhighn[C5-C12]contentsinthesefeedstocks(10-22%)orwithNaphthenesandi-Paraffinesalsoinhighconcentration(30and34%respectivelyinthe cases studied).

● YieldstowardEthaneandEthyleneforallNaphthasarebetween0,5%and1,0%forEthaneand±1,8%forEthylene.TheAdditivepromotes±1pointin-crease in Ethylene yields in Naphthas.

● Naphthas fromFCC can produce up to 10%ofTolueneand10%Xylenes.

Ingeneralterms,theyieldsofpetrochemicalpro-ductsfromcatalyticcrackingofNaphthasfromFCC,exceptPropylene,areabouttwicethoseobtainedbycrackingofResidue.

InNaphthas,theAdditivehasthesameselectivityforallpetrochemicalproducts.ItsapplicationincreasesEthylene,Propane,Propyleneandi-Butaneyieldsinabout one point each.

Ontheotherhand,for thesameconcentrationof

AdditiveusedinNaphthas,i.e.,4%,theAdditiveonResiduesincreasesPropyleneyieldsby3points,thatmeansaPropyleneselectivityof50%.

ACKNOWLEDGEMENTS

TheauthorsexpresstheirgratitudetothepersonnelattheCatalyticCrackingPilotPlantandLaboratoriesofRefiningandTransportlocatedattheICPfortheircooperation in trial development. The authors also thankCT&F editors and evaluatorswhomade thepublicationofthisarticlepossiblewiththeircarefulobservations.



158

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