Redefining_reforming_catalyst_performance.pdf

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Special Report Refining DevelopmentsP.-Y. Le-Goff, Axens, Rueil-Malmaison, France;

J. LoPez, Axens, Salindres, France; and J. Ross,

Axens, Princeton, New Jersey

Redefining reforming catalyst performance:High selectivity and stability

Over the next 10 years, global demand for oil products isforecast to increase at an average rate of 1.2%/yr through 2020.Demand will be just below 100 million barrels per day of oil

equivalent (MMbdoe). However, this growth will not be dis-tributed evenly around the world.

Developed markets. In the Organization for Economic Co-operation and Development (OECD) countries, reductions inautomobile fuel consumption will decrease oil demand at about0.5%/yr, thus creating refining overcapacity. The situation iscompletely different in nations with growing economies wherethe gross domestic product (GDP) is increasing rapidly and thepopulation aspires to greater mobility. In these (non-OECD)countries, demand for oil products will rise at 2%/yr and willcomprise 53% of world demand by 2020.

Developing markets. Concerning gasoline demand over thenext 10 years, strong growth is mainly expected in Asia (+2.1MMbdoe), the Middle East (+0.3 MMbdoe), the Former So-

viet Union States (+0.37 MMbdoe) and Latin America (+0.6MMbdoe), as shown in Fig. 1. In these regions of developingand growing economies, continued strong growth is projectedfor both gasoline and petrochemical polymers.

Petrochemicals. Worldwide demandfor polymers is growing at a significantlyhigher pace than oil and gas production(Fig. 2) and thus initiating large expan-

sions in olefins and aromatics complex-es. Global paraxylene (PX) consump-tion is forecast to exceed 40 milliontons (MMton) by 2015 compared to 32MMton in 2011. The additional capacity

will be located in the Asia-Pacific region,where PX demand is the highest, fol-lowed by the Middle East. New aromaticcomplexes, which include continuouscatalyst regeneration (CCR) reformingunits, will be required to meet the grow-ing demand in polyester used for bottlesand textiles. To meet both aromatics and

gasoline demand, capacity additions forlight-oil processing are expected in these

regions at about 1.5 MMbpd in combined reforming, isomeri-zation and alkylation capacity by 2020.

Catalytic reforming of naphtha is central in the production

of both high-octane fuel and aromatics to support both rap-idly growing markets. Accordingly, there is a continued strongdemand for catalytic reforming units and improved catalystsfor new and existing units with a global installed capacityover 13 MMbpd. The present annual worldwide market forreforming catalyst represents several thousand metric tons forfixed bed, cyclic and CCR markets.

CATALYTIC RefoRMING fUNDAMeNTALsThe role of catalytic reforming is fundamental in transform-

ing low-octane naphtha from crude oil and hydroprocessingunits into high-octane transportation fuels and aromatics. Theprocess involves transforming or reforming the paraffinic andnaphthenic molecules in the feed into high-octane aromaticsand branched components, and coproducing hydrogen need-ed by other refinery units such as hydrotreaters and hydro-crackers. This is accomplished over a heterogeneous catalystat elevated temperature and preferably low pressure accordingto Le Chateliers principle.

North America

Global demand MMbdoe

2010 88.2

2020 99.8

-0.6-0.4-0.20.0

0.20.40.60.8

Other Asia Pacific

0.0

Unit: MMbdoeSource: Axens estimates

Fuel oilDistillate =Diesel +Kerosine/jetGasolineNaphtha

0.4

0.8

Africa-0.60.0

0.4

0.8

Middle East-0.20.2

0.6

India-0.2

0.2

0.6

Japan-0.4

0.0

0.4Europe

-0.6-0.4-0.2

0.00.20.4

China0.00.40.8

1.2

1.6

2.0FSU0.0

0.2

0.4

Latin America0.00.3

-0.6

Fig. 1. Woldwid incnal finy poduc dand, 20102020.

Originally appeared in:September 2012, pgs 47-52.Used with permission.


2/548 SePtember 2012 | HydocaonPocssing.co

Refining Developments

Structure. Reforming catalysts are complex composites of ahighly active precious metal, platinum (Pt), to efficiently per-form dehydrogenation and hydrogenation reactions, and anactive support or carrier to do complementary reactions. Thecarrier is a high-purity alumina, with a specific pore structure,designed to have an acid functionality, which can be moderated

by controlling the amount of chloride added to the supportand/or by the addition of promoters. Together, these metaland acid components, as shown schematically in Fig. 3, forma dual-function catalytic system capable of transforming low-octane paraffins and naphthenes into high-octane gasoline, aro-matics and byproduct hydrogen.

Functions. A simplistic representation of the main reactionsis shown in Fig. 4 and is linked to the metallic and acid func-tions. The important dehydrogenation reaction to convert acyclohexane component into an aromatic is very rapid andeasily accomplished by the metal function of the catalyst.For many feeds, in particular hydrocracker and coker derived

naphthas, a significant portion of the naphthenic compoundscontain cyclopentane elements that require the acid-catalyzedreaction of ring extension or conversion into a cyclohexane-

bearing component for subsequent dehydrogenation on themetallic sites. Ring extension and dehydrocyclization of paraf-fins are all difficult, but they are critical functions that requirehighly selective catalyst. If the acid and metal functions are nottuned or properly balanced, undesirable side reactions do oc-cur, leading mainly to acid cracking and hydrogenolysis, and,to a lesser extent, dealkylation. In the reforming unit, theseside reactions result in the formation of light petroleum gas(LPG), light gas and coke; all contribute to nonselective con-

version, catalyst deactivation by coke deposition, and light-ends handling limitations.

Catalyst performance. The carrier and highly dispersed Ptmetal interact in a complex way to accomplish the desired re-forming reactions. Performance of the catalyst is described interms of activity, selectivity and stability.

Activity is commonly defined in terms of temperature re-quired to achieve a given objective; it is very similar to the def-

inition used to describe hydrotreating catalysts. A more activecatalyst is able to achieve the same product yield or severity(gasoline octane or aromatics yield) at a lower reactor tem-perature. For fixed-bed units, this means longer cycle lengths,and, for CCR units, it means greater operating flexibility with-in unit constraints.

Selectivity. The selectivity of the catalyst refers to the rela-tive yield of desired product, such as C5

+ reformate gasoline oraromatics, compared to another catalyst operating with the sameseverity target (RONc) under similar process parameters (pres-sure, WHSV, H2 /HC). As with most reaction systems, high se-lectivity is desired, as long as the performance can be maintained.

Stabilityis a measure of how long a desired performance can

be maintained, and it usually reflects the coking tendency of thecatalyst as it affects both activity and selectivity. Higher stabilityin a fixed-bed catalyst translates into a longer cycle length whilemeeting process severity targetsi.e., more profitable onstreamtime. For reforming units equipped with CCR, higher stabilitymeans lower coking tendencies and slower regeneration cycles,thereby adding operational flexibility. Such operating flexibilityprovides opportunities to process more demanding feed, suchas higher endpoint feed or increased amounts of coker naphtha,or an increased catalyst life resulting from a reduced regenera-tion frequency. Higher catalyst stability can also allow reducingthe recycle gas requirement, thus lowering operating costs.

Carrier. The carrier formulation and method of metal im-pregnation have a significant impact on the activity, selectivityand stability of reforming catalysts. But this is only the begin-ning of catalyst design and production technique.

PRoMoTeRs AND eNHANCeD PeRfoRMANCeIn addition to the essential alumina carrier and Pt metal,

other elements known as promoters are introduced to influ-ence, moderate or otherwise change the catalyst activity, se-lectivity and stability. When combined effectively, the catalystsystem allows the refinery to optimize gasoline yield and cycle-length or regeneration frequency to improve profitability andoperability within unit constraints.

GrowthIndex

0

1980

Polymer demandAveragegrowth

rate1990-05

Gas production

Oil production

GDP5.6%

3.2%

1.5%

2.1%

1990 2000 2010 2020 2030

200

300

400

500

600

700

800

900

100

Fig. 2. Woldwid gowh indx in oil, gas and poly scos.

ClM

Al

HCAl-Cl Acid site (Cl-Alumina)

M Metal site (ex. Pt)

HC Hydrocarbon interactions

Carrier

Fig. 3. Schaic of acid and al sis on foing caalys.

Paran and naphthene isomerizationDehydrocyclization

Hydrocracking/dealkylation

Metallic Acid (Cl-Al Carrier)

Hydrogenolysis/ring opening

Coke formationcomplex mechanisms

+

Pt

Pt

Pt

Pt

++

+H+

H+

H+

H2

+ +H2 CH4

+ 3H2

H+

+

Fig. 4. bi-funcional foing caalys acions. th dsid acionsa lald in lu, wih undsial sid-acions lald in d.


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In fixed-bed reformers, promoters have been used for along time to increase the stability (onstream time) of the cata-lyst by moderating the coke formation rate. Platinum-Rheni-um (Pt-Re) catalysts allow for longer cycles or more severeoperation at thermodynamically favored lower pressure wherethe coking tendency is greater. Additional promoters are of-

ten added to fine-tune the selectivity and stability of the cata-lyst. There are trade-offs in performance and response to feedcontaminants, such as sulfur, with these promoted catalystsystems. The challenge in catalyst development is to preparethe right catalyst formulation to achieve the best performance

with the least degree of compromise. Traditionally, this resultsin trading selectivity and introduces a selectivity-stability bar-rier, as shown in Fig. 5.

Metallic and acid functions. The interaction between themetallic and acid functions is complex, and optimizing therelative importance of each function is fundamental to obtainthe desired balance of selectivity, activity and stability. With

the addition of other promoters, the permutations of interac-tions increases, and the relative affinity of molecules to eitherthe metal or acid sites can be tuned for the desired effect, as inthe case of Pt-Re. Fig. 6 is a catalyst system with multiple met-als and varying chloride content.

Identification of promising promoter combinations re-quires extensive laboratory work and pilot testing. The ex-act formulation, impregnation method and manufacture arehighly proprietary. Ultimately, the active site density and loca-tion are critical to achieving both the desired metal and acidfunctions. Moderating the acid site strength on the carrier isone important way to limit cracking reactions, but this is onlypossible if uniform deposition of the promoter(s) is achieved.Equally important is the production trials where proprietarytechniques are applied to produce commercial product meet-ing both the target process chemistry and particle mechanicalproperties. Detailed particle analysis is performed to ensurethat the manufacturing method is effective, as shown in Fig. 7.

Uniform distribution of the carrier and metallic componentsis important to ensure accessibility to these precious constitu-ents and proper function. When the promoter is mainly on theshell of the particle, the metal-to-acid function ratio is not con-stant along the diameter. Thus, hydrocarbons diffusing intothe particle encounter a higher acid-to-metal ratio leading to

undesired cracking reactions. This reduces the intrinsic catalystselectivity and increases coke make. Moreover, when the pro-moter is preferentially on the surface, it is more sensitive to con-tamination, and its elution increases over time.

When the promoters are properly introduced, they remaineffective for the serv ice life of the catalyst, even under harsh op-erating conditions found in cyclic and CCR units. Earlier workon promoted systems demonstrates that the promoters are ro-

bust and do not elute from the catalyst over many regenerationcycles. Fig. 8 demonstrates excellent promoter retention, with-in the analytical accuracy of the test, for various CCR catalysts.

BReAKING THe seLeCTIVITY-sTABILITY

BARRIeRWhen targeting specific catalyst performance, there are

many choices of promoters, method of impregnation and de-sign of the carrier. Two fundamentally different catalyst linesusing unique design approaches were recently compared lead-ing to a new family of catalysts that break the selectivity-stabili-ty barrier commonly encountered in catalyst design.

Carrier

ClAl

Pt

ClAl

ZX

Y

AlAlumina carrier

ClChlorine

PtPlatinum metal

X,Y,ZPromoters

Fig. 6. Schaic of coplx uli-pood caalys sys.

Selectivity

Activity; stability

Low High

Low

High

Desired region

Fig. 5. Slciviy sailiy ad-off o ai.

-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5

Position, R/D

Relative

conc.

Cl

Pt

X

Y

Z

DCl

Pt

X

Y

Z

Fig. 7. CCr caalys paicl coposiion pofil.

50

60

70

80

90

100

110

120

Promoterretention,

%

0 100 200 300 400 500 600 700

Days onstream

Fig. 8. Cocial donsaion of poo nion on CCrfo caalyss.


4/550 SePtember 2012 | HydocaonPocssing.co


At the macroscopic level, the two lines of catalyst producedsimilar results, but at the micro level, one exhibited better car-rier production technique and the other better promoter char-acteristics. There were clearly opportunities to optimize thesystems at the micro level to provide better performance. Thefirst products to be explored were the CCR catalysts as used insevere, high-profit-margin aromatics units.

CCR catalyst formulations are built around a platinum-tin(Pt-Sn) base system. This provides significantly greater selec-

tivity over Pt-only catalyst, but requires low pressure for bestresults and continuous regeneration to overcome the greatercoke formation tendency. Additional metals, other than Ptand Sn, can be added as promoters to further optimize thecatalyst systems. The importance of promoter selection can

be demonstrated in Fig. 9.Pilot-plant testing results are shown in Fig. 9A of the C5

+

reformate yield selectivity over time for four catalyst systems:Pt+Sn (bimetallic), tri-metallic 1, tri-metallic 2 and optimizedQuad-metallic. In this batch pilot testing strategy, the unit isoperated at a constant RON target to reflect either a constantconversion toward aromatics for aromatics application or a con-stant octane in the case of gasoline application. As the test pro-gresses, catalyst selectivity is measured by the reformate yieldand stability by the rate of reformate-yield decay over time asthe fixed batch of catalyst age.

During the test, coke is progressively deposited on the cata-lyst and the required temperature to maintain the target RONincreases (Fig. 9B). Low coke formation and catalyst deactiva-tion is indicated by a slow increase in reactor temperature tomaintain the target RON. A small slope of the temperaturecurve indicates high catalyst stability, while the duration ofthe C5

+ plateau and the slow rate of yield decay is the comple-mentary indicator of the C5

+ stability of the catalyst. From acommercial unit perspective, the latter part of the test, wheretemperature increases sharply to maintain severity, defines theultimate catalyst stability (cycle life) within unit constraints.

Looking more closely at Fig. 9, the two tri-metallic systemsshow initial selectivity performance higher than the base Pt-Sn, but the performance falls over time as a result of the lower

stability (higher coke yield), shown in Fig. 9B, for these sys-tems. When a fourth metal is properly introduced, the quadmetallic or simply Quad system, a superior yield selectivityand equal stability is attained relative to the Pt-Sn system. Inthis case, the selectivity-stability barrier is broken, and stabil-ity does not suffer to attain superior selectivity. Significantly,this improvement was obtained while reducing the Pt loadingon the catalyst by 20%, thereby offering a substantial cost re-duction for our customers.

When the optimized carrier and promoter system were ap-plied to the low-density CCR catalyst platform, a new Quadcatalyst was developed. Fig. 10 shows the performance of thisnew system. The reformate yield is increased by 0.8 wt%; hy-

drogen increased by 0.1 wt% (50 scf/bbl), while the activityand stability are slightly improved.

50 75 100 125 150

50 75 100 125 150

Time

Tri-metallic Quad-metallic

480

490

500

510

520

WABT,

C

50 75 100 125 150

2.90

2.95

3.00

3.05

3.10

3.15

3.20

H2

88.0

88.4

88.8

89.2

89.6

C5+

Tri-metallic Quad-metallic

Tri-metallic Quad-metallicA

B

C

Fig. 10. Opiizd quad-allic caalyss copaison: A) foayild, b) hydogn yild, and C) aciviy/sailiy.

87

88

89

90

C5+,

wt%

0 20 40 60 80 100 120 140Time

A

Pt+SnTri-metallic 1

Quad-metallic

Tri-metallic 2

Fig. 9A. rfoa yild vs. poo sys, and 9B. Sailiy and cok yild vs. poo sys.

Coke 7 wt %

Coke 6.5 wt %

Coke 6 wt %

485

490

495

500

505

510

0 20 40 60 80 100 120 140Time

Temperature,

C

Pt+SnB

Tri-metallic 1

Quad-metallic

Tri-metallic 2


5/5


52

eNHANCeD PHYsICAL PRoPeRTIesCCR moving bed catalysts also require careful attention

to the physical properties to ensure mechanical strength andsurface-area stability over many regeneration cycles, which isindicative of catalyst life and chlorine retention.

Accelerated aging tests have been performed on the new

Quad-metallic catalyst to compare surface area retention to con-ventional Pt-Sn bimetallic catalyst. Fig. 11 shows the surface areadecline over time following such test protocols. A conventionalPt/Sn catalyst reaches its end-of-life surface area (approximate-ly 140 m2/g) relatively quickly, whereas the new Quad catalyst

retains a higher surface area in the range of 160 m 2/g. Highersurface area is associated with improved regeneration (Pt redis-persion) and better chloride (C1) retention. As a consequence,the new Quad catalysts will exhibit longer life, reduced salt de-posit in downstream units, and lower chloride content in thehydrogen-rich gas, resulting in longer chloride trap life.

Put in quantitative terms, the better surface area retention andintrinsically higher chloride retention resulting from a new quadcatalyst with a proprietary promoter system results in 30% lowerchloride injection over the life of the catalyst vs. standard Pt/Sn.

The mechanical properties of the catalyst are also impor-tant in CCR applications. Unlike fixed-bed catalysts, which aremainly concerned about crush strength to endure the staticload forces within a fixed bed, CCR catalysts are spherical anddesigned to resist the dynamic forces from slow movement in

the catalyst beds to pneumatic lifting between reactor and re-generator. These forces lead to particle attrition and fines pro-duction. Although the fines or broken pieces of the catalyst arecaptured within the system, they can lead to fouling of screensand increase pressure drop.

Highly developed CCR catalysts are more robust to ensure

extended service over 79 years. New formulations are subject-ed to large-scale circulating test units to accurately representcommercial conditions and the forces leading to attrition. Thenew carrier and multi-promoted catalyst systems have provento be as robust as previous-generation catalysts with an excel-lent track record of low particle attrition.

NOTES

As a licensor of catalytic reforming and aromatics chain technologies, andsupplier of catalysts for these units, Axens is focused on continuous improvementin both process technology and catalyst development. The recent acquisition ofthe Criterion catalytic reforming catalyst business in 2011, including productionfacilities and know-how, provided a unique opportunity to compare, contrast and

build upon two different approaches to reforming catalyst development and pro-duction. New proprietary formulations and production techniques have emergedfrom this union resulting in breakthrough catalysts for both fixed-bed and moving-

bed CCR units that provide superior selectivity without compromising activ-ity and stability. Re-engineered fixed-bed catalysts are under development andon-track for release in 2013. These new products promise the benefits of higherselectivity and reduced cost through promoter selection and loading optimization.

Pierre-Yves Le Goff is Axns snio chnical anag fofoing caalyss and pojc lad fo caalys dvlopn.

D. L Goff sad his ca as a sach ngin a rhodia,wh h spcializd in caalys suppo dsign and pocss

dvlopn. D. L Goff holds an ngining dg fo hcol d Chii d mulhous, an mbA fo Univsi d laSoonn in Pais, and a PhD fo Univsi d Hau-Alsac.

JaY ross is a snio chnology and aking anag foAxns coving h fild of anspoaion fuls including FCC,

caalyic foing, isoizaion and iodisl poducion. Hhas ov 30 yas of xpinc in h fining and pochical

indusy including pocss ngining dsign, r&D, licnsingand chnical assisanc. m. ross is a gadua fo PinconUnivsiy wih a dg in chical ngining.

JosePh LoPez is a dvlopn and indusializaion

ngin in Axns poducion plan of adsons andcaalyss in Salinds, Fanc. H is sponsil fo hdvlopn and scal-up of foing suppos and

caalyss. H sad his pofssional ca as a sachngin a rhodia woking ainly in h fild of

hognous and hoognous caalysis. D. Lopz holds anngining dg fo h ecol Naional Supiu d Chii dmonplli and a PhD in caalysis fo h Univsi Claud bnad of Lyon.

Quad

20 m2/gBi-metallic

120

140

160

180

200

220

0 100 200 300 400

Time

Specificsurfacearea,

m2/g

Bi-metallicQuad-metallic

Fig. 11. Caalys sufac aa aging s, quad allic vs. iallic P-Sn.

Article copyright 2012 by Gulf Publishing Company. All rights reserved. Printed in U.S.A.Not to be distributed in electronic or printed form, or posted on a Website, without express written permission of copyright holder.

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Redefining_reforming_catalyst_performance.pdf