ultra low sulfur diesel 2010 - grace brochure... ·...

Ultra Low Sulfur Diesel2010

Advanced Refining Technologies (ART), isthe joint venture of Chevron Products Com-pany and W. R. Grace & Co.’s Grace Davi-son catalysts business unit, created todevelop, market and sell a comprehensiveline of state-of-the-art hydroprocessing cat-alysts. Since our formation in March 2001,we have firmly established ourselves as aleading supplier of premium hydroprocess-ing catalysts and technical service to thepetroleum refining industry worldwide.

ART brings new standards of product inno-vation and customer service to the globalrefining industry by harnessing the techni-cal expertise of both Chevron and GraceDavison in catalyst development and theirbroad experience in supporting refiners.With the combination of Grace Davison’smaterial science, manufacturing, marketingand sales strength, and Chevron’s extensiveexperience from operating its own refineriesand leadership in design and process li-censing, ART offers refiners one-stop ac-cess to hydroprocessing knowledge andtechnical service unparalleled in the indus-try.

ART offers refiners the unique synergies de-rived from our parent joint venture partnersbeing leaders in hydroprocessing catalysttechnologies. Chevron, and now ChevronLummus Global (CLG) represent over 35years of experience designing and licens-ing RDS and VRDS units, as well as operating resid hydroprocessing and distillate hydrotreating units at Chevron re-fineries. Grace Davison has over 50 years of experience in extruding hydroprocessing catalysts. Leveraging the refiningand hydroprocessing experience of Chevron with Grace Davison’s expertise in specialty materials and catalyst tech-nologies makes ART uniquely equipped to quickly commercialize and deliver innovative products to the dynamic hy-droprocessing marketplace.

To keep pace with the high demand for ART catalysts driven by heavy resid hydroprocessing applications and morestringent clean fuels standards, ART has expanded manufacturing capacity at its existing North American plants. ARTacquired Orient Catalyst Company’s (OCC) hydroprocessing catalyst technologies, and the HOP® catalyst product linein 2002; and obtained an ownership position in Kuwait Catalyst Company (KCC) which has manufactured HOP residhydroprocessing catalysts under license since 2001.

ART’s comprehensive line of hydroprocessing catalysts deliver maximum sulfur removal and upgrading for a widerange of feedstocks. ART offers hydroprocessing catalysts for the resid segment of the hydroprocessing market, in-cluding the fixed-bed Onstream Catalyst Replacement (OCR) resid process and ebullating bed applications, as wellas a complete product line of premium catalysts for distillate hydrotreating of heavy VGO/DAO, diesel, kerosene andlight naphtha applications.

Advanced Refining Technologies -Hydroprocessing Catalysts fromChevron and Grace Davison

Cru

de

Tow

er

Vacu

um

Tow

er

ATTM Series

ATTM SeriesDXTM Series

ATTM SeriesDXTM SeriesICR Series

GR® SeriesLSTM SeriesHSLSTM Series

ICR Series

HOP® Series

StARTTM

CatalystSystem

SmARTCatalystSystem®

ApARTTM

CatalystSystem

Coker Naphtha

Naphtha

Kerosene

& Jet

Diesel

AT Series

DX Series

AT, DX Series

FCC Pretreat

Fixed Bed Resid

Fixed Bed Resid

Ebullating BedResid for LC-Finingand H-Oil processes

Hydrocracker

Pretreat

Product Overview Chart

1

Understanding Ultra Low Sulfur DieselBy Gerianne D’Angelo and Charles OlsenThis article discusses the importance of feedstock properties and operating conditions to suc-cessfully producing ultra low sulfur diesel.

The SmART Catalyst System™: Meeting the Challenges of Ultra Low Sulfur DieselBy Charles OlsenA disucssion of the various components of the SmART catalyst system and the factors that gointo designing customized systems to meet a variety of ULSD processing needs.

No Need to Trade ULSD Catalyst Performance for Hydrogen Limits: SmART ApproachesBy Charles Olsen and Geri D’AngeloThe SmART Catalyst System provides the optimum balance between activity and hydrogen con-sumption. This article discusses the chemistry and kinetics involved in designing a system, andreviews the commercial performance observed in several ULSD applications.

ART Excels In ULSD Service: Update on Sulfur minimization By ARTBy Greg Rosinski, Dave Krenzke, and Charles OlsenULSD production with the first SmART Catalyst System® Series began early in 2004 at a North Americanrefinery processing a feed containing 40% of a high endpoint LCO. Since that time DX™ Platform Catalystshave been selected for over 70 ULSD applications as either stand-alone catalysts or as components inSmART System. The technology has been a great success since its introduction with millions of poundsinstalled in commercial units around the world.

Distillate Pool Maximization by Exploiting the use of OpportunityFeedstocks Such as LCO and SyncrudeBy Brian Watkins and Charles OlsenThe use of opportunity feeds such as FCC LCGO, diesel streams from other hydroprocessingunits and feeds from synthetic crude sources has helped refiners to maximize their diesel pool.In this article we highlight differences in feed reactivity for various feed components and explorethe impact of various Hydrotreating Catalysts and operating conditions on diesel production.

Cetane Improvement In Diesel Hydrotreatingby Greg Rosinski and Charles OlsenThis article discusses the importance of cetane in ULSD. The SmART Catalyst System, which uti-lizes both the CoMo and NiMo catalyst, results in a cetane uplift which is nearly two numbershigher than an all-CoMo system with only a small increase in hydrogen consumption. For H2 con-strained refiners this is an ideal solution for improving the product cetane.

Factors Influencing ULSD Product ColorBy Greg Rosinski, Charles Olsen and Brian WatkinsProduct Color of petroleum products such as kerosene, jet fuel, diesel fuel and lube oils is a con-cern. Unit cycle length can be shortened due to product color degradation. In this paper we iden-tify components that contribute to color degradation and report on the effects of feedstocks andoperating conditions on ULSD color.

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Very tight specifications on sulfur content in diesel fuelhave recently been announced by the European Union,the U.S. EPA and others. Refiners will be required toproduce transportation diesel fuel with sulfur levelsbelow ten ppm (Ultra Low Sulfur Diesel or ULSD).These new specifications will place a severe burden ondiesel hydrotreaters as refiners struggle to keep upwith diesel fuel demand and quality.

As the diesel sulfur specification drops to the low ppmrange, it is important to look at the types of sulfur com-pounds that need to be removed in order to meet thelower sulfur levels. The sulfur compounds can be clas-sified into different groups commonly termed “easy”and “hard” sulfur, based on the ease of sulfur removal.The easy sulfur compounds are represented by diben-zothiophenes (DBT) and lighter. The hard sulfurspecies include multi-substituted dibenzothiophenescommonly represented by 4,6 dimethyl-dibenzothio-phene (DMDBT), and these compounds are extremelydifficult to desulfurize. The reason for the reactivity dif-ferences can be explained by the different reactionpathways for sulfur removal from DBT’s and substitutedDBT’s.

DBT’s are more effectively desulfurized via a direct sul-fur abstraction route, and it is the generally acceptedreaction pathway for HDS of diesel to 500 ppm sulfur.Substituted DBT’s, on the other hand, are not effective-ly desulfurized via direct abstraction because themethyl group(s) adjacent to the sulfur atom effectivelyshield the sulfur from the catalyst active sites. However,hydrogenation of an aromatic ring allows the moleculeto flex enabling access to the sulfur atom, and C-Sbond scission readily follows. Direct abstraction iscatalyzed more effectively by CoMo catalysts, while thehydrogenation-abstraction route is typically more facileover NiMo catalysts. This forms the basis for ART’s

UnderstandingUltra Low Sulfur Diesel

Charles OlsenNew Product DevelopmentManager

Gerianne D’AngeloSenior Technical Services Engineer

ADVANCED REFININGTECHNOLOGIESChicago, IL USA

www.artcatalysts.com2

SmART Catalyst System® which is tailored to optimizeboth reaction pathways.

The relative amounts of easy and hard sulfur in a feedare critical parameters to consider when choosing acatalyst and operating conditions for production ofULSD. Their concentration can vary significantly fromfeed to feed depending on crude source, the boilingrange, and the treatment the feed has been subjectedto whether it be thermal (coker) or catalytic treating(cycle oil).

Analysis of a wide array of diesel feeds shows that thefraction of hard sulfur correlates quite well with theend point of the feed. Figure 22 shows the fraction ofhard sulfur as a function of D86 90% point for a varietyof feeds. The figure clearly shows a strong correlationwith the 90% point of the feed. The fraction of hardsulfur increases rapidly for feed T90 between about316˚C and 343˚C. Interestingly, the fraction of hardsulfur does not correlate strongly with feed type;whether it is straight run, light cycle oil, or light cokergas oil the fraction of hard sulfur is largely determinedby the feed endpoint.

The amount of nitrogen in the feedstock is another crit-ical parameter that must be considered. Figure 23demonstrates the detrimental effects nitrogen has onthe removal of hard sulfur. The relative rate constant forhard sulfur removal decreases significantly in going

from a feedstock containing 50 ppm nitrogen to a feed-stock containing 150 ppm nitrogen. The relative rateconstant continues to decrease as nitrogen contentincreases beyond 150 ppm, but the decrease is at asomewhat slower rate. This inhibiting effect of nitrogenis a result of poisoning of the acid sites needed for aro-matic ring saturation, and as discussed above, the sat-uration-abstraction route is the preferred reaction path-way for hard sulfur removal.

Thermodynamic equilibrium is another issue related topoly nuclear aromatic (PNA) saturation which must betaken into account. The saturation of PNA’s does reacha thermodynamic constraint on conversion at highenough temperatures. Figure 24 shows the expectedPNA conversion as a function of temperature for a vari-ety of LHSV’s. The equilibrium constraint is readilyapparent for the higher temperatures in the chart.Decreasing the LHSV serves to increase conversion inthe kinetically controlled region (i.e. low temperatures),but has no effect on conversion in the thermodynami-cally controlled regime (i.e. high temperatures). Thissuggests that adding catalyst volume will help in theremoval of hard sulfur, but a point is reached wheredecreases in sulfur do not occur due to unfavorablethermodynamic equilibrium at those conditions. Thisraises the potential for situations where significantincreases in temperature will not result in appreciabledecreases in product sulfur at very low levels.

Figure 22Fraction Hard Sulfur Correlates with Feed End Point

SR LCGO LCOSR LCGO LCO

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

232 260 288 316 343 371 399

Feed D86 90% Point, ˚C

Fra

ctio

nH

ard

Sul

fur

reprinted from Catalagram® 95 2004 3

Figure 23Nitrogen Inhibits Hard Sulfur Removal

Straight Run 20% LCO/Straight Run

Specific Gravity 0.847 0.868Sulfur, wt.% 1.21 1.56Nitrogen, ppm 95 200D86 Dist., ˚C, IP/50/FP 212/288/354 208/286/353

Table XFeed Properties

A number of operating parameters take on greaterimportance in ultra low diesel HDS due to the issuesraised above. ART has conducted extensive pilot plantwork to define appropriate operating conditions forULSD and to define the influence of cracked stocks.One study utilized a straight run feed and a 20% LCOblend with the same straight run component, andselected properties of the two feeds are shown inTable X.

The operating conditions used in the work are repre-sentative of the pressure and H2/oil ranges typicallyfound in diesel hydrotreaters. Figure 25 summarizesthe influence of H2/oil ratio on ULSD production. It isa plot of the relative HDS rate constant as a function ofthe relative excess hydrogen (H2/oil ratio divided by thehydrogen consumption). Data for both high and lowpressure operation are shown for each feed.

For the high pressure operation, it is apparent thatincreasing H2/oil is beneficial for both feeds up to acertain point. The reactivity of the straight run feedincreases from about 60 at low H2/oil (i.e. 60% of thehighest activity achievable for that feed) to nearly 100at a H2/oil ratio / H2 consumption ratio of about five.Further increases in H2 beyond that provide little addi-tional benefit.

Similarly, the 20% LCO feed shows a reactivity of about20 at low hydrogen rate, and steadily increasestowards 100 near a H2/oil ratio / H2 consumption ratioof about six. Further increases in hydrogen rate againdo not add much additional benefit. These data sug-gest that for high pressure more excess hydrogen isrequired for ULSD compared to conventional dieselhydrotreating (i.e. 500 ppm sulfur) where H2/oil ratioconsumption ratios of between three and four are gen-erally recommended.


Figure 24Thermodynamic Equilibrium Can Limit Conversion

Figure 25Excess Hydrogen Improves Reactivity


The effect of H2/oil ratio at lower pressure is quite dif-ferent. In this case, the relative HDS rate constant forboth feeds shows a steady increase with increasinghydrogen rate. Note that the activity is relative to thestraight run feed at high pressure and high H2 rate.

The benefit of increasing H2/oil never reaches aplateau as observed in the high pressure case, sug-gesting that more hydrogen is always better at lowpressure. The effect of hydrogen pressure is alsoreadily apparent in Figure 25. At relative excess hydro-

Figure 26H2S is Detrimental to Hard Sulfur Removal


gen values around three to four, the straight run feed atlow pressure has a relative rate constant of about 20compared to the high pressure case, and the differ-ence for the LCO feed is even greater.

Figure 26 summarizes these data in another way. Thischart shows the relative activity plotted as a function ofH2S partial pressure at reactor outlet conditions.Again, quite different behavior is observed for the lowand high pressure cases. At high pressure, the datasuggest some tolerance for low H2S pressure and asteady decline in activity as H2S pressure increasesbeyond that. The straight run feed also appears moreforgiving, as it has a slower activity decline comparedto the LCO containing feed. Looking at the low pres-sure data, it is apparent that even a small amount ofH2S is detrimental to activity. There is a rapid initialdecrease in activity with the first increments of H2S,and thereafter a slow steady drop-off in activity as H2Slevel increases further. These data are from the pilotplant where there is no H2S in the treat gas to the unit.A hydrogen stream containing H2S will exacerbate theactivity loss due to H2S especially at low pressure.

This study also investigated the effects of adding cat-alyst volume and the potential tradeoffs between cata-

lyst volume, operating pressure and H2/oil ratio. Figure27 summarizes the relationship between 1/LHSV orresidence time (i.e. catalyst volume), H2/oil ratio andhydrogen pressure at 10 ppm product sulfur for thestraight run feed. Not surprisingly, there is a signifi-cant difference in required catalyst volume betweenhigh and low pressure operation at constant H2/oilratio. The catalyst volume at low pressure is nearlythree times higher than required for the high pressureoperation at typical H2 rates.

Figure 28 is a similar plot, but in this case it is compar-ing the performance of the straight run feed with the20% LCO blend at an intermediate pressure. The inter-mediate pressure is the practical lower limit for ULSDproduction for the 20% LCO feed. Lower pressuresrequired unreasonably high gas rates and or long res-idence times (very large reactors). This chart clearlyshows the difficulty in treating cracked stocks relativeto a straight run feed. At high H2 rates, 1.5 times high-er catalyst volume is required for the LCO, and thisincreases to nearly two times higher at the low H2 rate.Of course, increasing the pressure helps somewhat,but even at high pressure the LCO case requires 1.3-1.7 times higher catalyst volume depending upon theH2 rate.

Figure 28Cracked Stocks Change The Rules

Figure 27Trade-offs Between Pressure, H2/Oil and LHSV


In summary, it is possible in some cases to trade offpressure, H2/oil and catalyst volume, when designingfor ULSD production. However, there is a limit whichdepends strongly upon the feedstock. For example,

cracked stocks require higher pressure and higherH2/oil ratio compared to a straight run feed. To learnmore about producing ULSD at your refinery, contactyour ART technical or sales representative.

The SmART Catalyst SystemTM:Meeting the Challenges ofUltra Low Sulfur Diesel

In 2001, ART introduced the SmART Catalyst SystemTM

to help refiners deal with the severe demands of ultralow sulfur diesel (ULSD). The SmART Catalyst Systemutilizes state-of-the-art catalyst technology which isstaged in the proper proportions to provide the bestperformance while at the same time meeting individualrefiner requirements. The catalyst staging is designedto take advantage of the different reaction mecha-nisms for sulfur removal; ART CDX, a high activityCoMo catalyst, efficiently removes the unhindered,easy sulfur via the direct abstraction route and ARTCDY, a high activity NiMo catalyst, then attacks theremaining sterically hindered, hard sulfur. Pilot plantwork has proven that the properly configured SmARTCatalyst System provides higher activity than either theCoMo or NiMo catalyst alone.

ART CDX and ART CDY, individually or as part of aSmART Catalyst System, were selected for 14 dieselunits in 2004, and most of these applications aim toevaluate ULSD capability and/or produce ultra low sul-fur fuels in advance of the regulations for economicbenefit.

Optimizing the SmART Catalyst System

An important aspect of the SmART Catalyst System isdetermination of the optimum proportions of the CoMoand NiMo catalysts that will deliver the best perform-ance. This is dependent upon a number of factors,including the refiners’ requirements, and selected feed

properties and operating conditions as discussed indetail previously in Catalagram No. 95 (March 2004).

One clearly important parameter which must be con-sidered is the boiling range of the feedstock. Sulfurspeciation on a wide variety of feedstocks has shownthat there is a strong correlation between the fraction ofmulti-substituted dibenzothiophenes (hard sulfur) andthe feed endpoint. Once the D86 endpoint increasesbeyond about 329˚C there is a rapid increase in thefraction of hard sulfur contained in the feed. This hasa large impact on catalyst activity as shown in Figure21. The figure shows pilot plant data comparingresults from treating two feeds with different endpointsover the same catalyst under identical conditions. Atultra low sulfur levels there is about 17˚C difference inreactivity of the two feeds with the lower endpoint feedmore reactive. Clearly, feed endpoint and the amountof hard sulfur are critical parameters that influence theoptimum SmART configuration.

Another critical feed property that must be accountedfor is the nitrogen content. It is generally accepted thatnitrogen inhibits aromatic saturation reactions throughpoisoning of acidic sites on the catalyst. Recall thatthe primary reaction pathway for removal of hard sulfuris via hydrogenation of an aromatic ring, and it is notsurprising that feed nitrogen content has a serious,negative impact on HDS activity. The magnitude of theimpact can be seen in Figure 22 which summarizesdata for NiMo and CoMo catalyst activity on an SR feed

Charles OlsenNew Product DevelopmentManager




before and after selectively removing the nitrogen viaan adsorption process. The difference in activity onthe two feeds is quite large. Increasing the nitrogencontent from 25 to 160 ppm results in a loss in HDSactivity of 22-28˚C for both catalysts. Comparing thecatalysts on the low nitrogen feed shows that the NiMocatalyst has about 8˚C higher activity relative to theCoMo, and that decreases to an advantage of about3˚C or less on the higher nitrogen feed. This suggeststhe impact of nitrogen is different for NiMo and CoMocatalysts with the CoMo catalyst more tolerant of nitro-

gen. This is another important consideration whendesigning the optimum SmART Catalyst System.

Hydrogen availability, in terms of hydrogen pressureand hydrogen circulation, also takes on greater impor-tance in ULSD. Figure 23 is a chart showing how therelative HDS rate constant changes as a function of theexcess hydrogen (H2/Oil ratio divided by the hydrogenconsumption) for both high and low pressure opera-tion. Note the range in operating pressure from low tohigh represents that typically encountered in diesel

Figure 21Feed Endpoint Impacts HDS Activity

Tem

per

atu

re,˚

C

1

Product Sulfur, ppm

10 100 1000

357˚C D86 EP

390˚C D86 EP

10˚C

31˚F17˚C

Figure 22Nitrogen Impacts Catalysts Differently

160 ppm Nitrogen

CoMo

0

6

11

17

22

28

Incr

ease

inre

qu

ired

Tem

per

atu

re,C

Base

25 ppm Nitrogen

NiMo

hydrotreating. At high pressure, increasing the H2/Oilis beneficial for both SR and 20% LCO feeds up to apoint, after which further increases in H2 rate providelittle additional benefit. At low pressure, the effect ofH2/Oil ratio is quite different. In that case, the relativerate constant for both feeds shows a steady increasewith increasing hydrogen rate. The benefit of increas-ing H2/Oil never reaches a plateau as observed in thehigh pressure case indicating that more hydrogen isalways better at low pressure. The effect of pressureis also readily apparent in the figure. Comparing therelative rate constant for high and low pressure at atypical H2/Oil ratio reveals that the activity at low pres-sure is only 10-20% of that at high pressure for 20%LCO and SR feed respectively.

Controlling Hydrogen Consumption

One of the key advantages of the SmART CatalystSystem is the efficient use of Hydrogen. Figure 24illustrates how the system can be tailored to providethe best balance of high HDS activity while minimizingH2 consumption. The figure shows that as NiMo cata-lyst is added to the system there is a large increase inHDS activity relative to the all CoMo reference, andeventually, a minimum in the product sulfur curve isreached (i.e. maximum HDS activity). The position andmagnitude of this minimum varies with feed and oper-ating conditions such as those discussed above. Thefigure also shows the relative H2 consumption, andagain, as the percentage of the NiMo component

increases, the H2 consumption relative to the baseCoMo system increases. In the region where the sys-tem shows the best activity, the hydrogen consumptionis only slightly greater than that for the all CoMo sys-tem, and well below that for the all NiMo catalyst. Thisis a result of the different kinetics for sulfur and aro-matics removal and is a critical consideration whencustomizing a SmART Catalyst System.

To help understand the differences in kinetics it is usefulto compare the performance of CoMo and NiMo cata-lysts alone. Figure 25 shows a comparison of the hydro-gen consumption over a NiMo and CoMo catalyst for astraight run feed at ULSD conditions. The amount ofhydrogen consumed by sulfur, nitrogen and olefinsremoval is essentially the same for each catalyst and isnot shown. What separates the two catalysts is theamount of aromatics saturation which occurs, and inparticular, the amount of mono ringed aromatics whichare hydrogenated. In this case, an additional 12 Nm3/m3

of hydrogen is consumed with the NiMo catalyst due tomono ringed aromatics saturation. This representsexcess hydrogen consumption above that required forthe removal of sulfur.

Figure 26 is a similar chart for LCGO feed. In thisexample, the NiMo catalyst hydrogenates more PNA (2rings and greater) and mono ringed aromatics com-pared to the CoMo catalyst accounting for an addition-al 19 Nm3/m3 of hydrogen consumption above thatrequired for sulfur, nitrogen and olefins removal.Clearly, in cases where hydrogen consumption needs

Figure 23Hydrogen Availability is Critical



to be minimized, a NiMo catalyst for ULSD is the wrongchoice. Unfortunately, in many of these cases a CoMocatalyst does not provide the best activity for ULSD,and it is precisely these units where the SmARTCatalyst System is ideal as it offers the highest activityand is more efficient with hydrogen compared to an allNiMo system.

It perhaps appears contradictory that a NiMo catalystis included in the SmART Catalyst System due to itshigh hydrogenation activity making it preferred for hardsulfur removal, and yet, under some conditions thehydrogenation activity is too high and excess aromat-ics saturation occurs. This highlights one of the keysto designing the proper system. The design involvesincreasing the hydrogenation selectivity of the systemto provide highest HDS activity, while at the same time

minimizing hydrogen consumption (i.e. minimizingexcess aromatics saturation).

Figure 27 shows a schematic of the reaction pathwayfor poly aromatics saturation. Naphthalene, a tworinged aromatic molecule, is featured at the top of thefigure. The reaction begins with the hydrogenation ofone of the aromatic rings to form tetralin, a mono ringaromatic. The next reaction in the sequence is hydro-genation of the remaining aromatic ring to producedecalin, a fully saturated molecule. Each step isreversible and subject to equilibrium constraints. Theslowest reaction in the sequence is the saturation ofthe mono ring aromatic. The reaction sequence for asubstituted biphenyl is also shown at the bottom of thefigure. The sequence is essentially the same. In bothexamples the hydrogenation of the mono aromatic is

Figure 24Optimizing HDS and H2 Consumption

Figure 25Excess H2 Consumption with SR Feed in ULSD

NiMo

HDSHDN

Poly aromatics

CoMo

HDN

HDS

Poly aromaticsMono aromatics

Mono aromatics

OlefinsOlefins

28 Nm3/m3 32 Nm3/m3

28 Nm3/m3

20 Nm3/m3

the slowest step and also consumes more hydrogencompared to the other hydrogenation reactions shown;three moles of hydrogen per mole of aromatic are con-sumed by the saturation of the mono ring aromaticcompared with two moles of hydrogen/mole for themulti ringed aromatics.

The reaction sequences shown in Figure 27 can betreated as a series of first order reversible reactionswhere the intermediate (the mono ring aromatic) is thedesired product. For these sorts of reaction systemsthe intermediate often tends to be favored at shortercontact times (see Chemical Reaction Engineering byOctave Levenspiel [Wiley, 1998], for example), and itthis tendency which is exploited when customizing aSmART Catalyst System. The effective residence timein both the CoMo and NiMo beds of a system is shortcompared to the overall reactor residence time, andthis helps minimize the hydrogenation of the mono ringaromatic (i.e. minimize hydrogen consumption).

Figure 28 shows the effect of residence time, as indi-cated by 1/LHSV, on aromatics saturation. For PNAsaturation, the two ringed aromatic going to the monoring aromatic, there is a fairly steep curve for conver-sion as a function of residence time below about 1 hr.Above that point, which represents space velocities of1 hr-1 or less there is very little change due to equilibri-um constraints. For mono ring aromatic saturationthere is a steady increase in conversion as the resi-dence time is increased indicating more and more sat-uration as the residence time is increased (i.e., LHSV isdecreased). Both sets of curves suggest aromatic sat-uration can be limited by appropriate choice of LHSV,or in the case of a SmART Catalyst System, by adjust-ing the relative quantities of CoMo and NiMo catalyst.

SmART Catalyst System Experience

The SmART Catalyst System is the culmination of anextensive effort put towards understanding the chem-istry and process conditions required for ultra low sul-fur fuels. In addition, properly designed high activity

Figure 26Excess H2 Consumption with LCGO Feed in ULSD

NiMo

HDSHDN

Poly aromatics

46Nm3/m3

CoMo

HDN

HDS

Poly aromaticsMono aromatics Mono aromatics

OlefinsOlefins

22 Nm3/m342 Nm3/m3

8.0 Nm3/m3

Figure 27Reaction Sequence for Poly Aromatics Hydrogenation



Figure 28Limiting Aromatics Saturation

Table VIICommercial Experience with ART CDX, CDY and the SmART Catalyst System

Refiner 1 2 3 4 5 6 7 8

Pilot Testing Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

Startup Date 4Q04 4Q04 4Q04 2Q05 2Q04 3Q04 1Q05 2006 2006 2006 2006 2006 2006

Catalysts CDX CDX CDX CDX CDX CDX CDX CDX CDX CDX CDX CDX CDX

CDY CDY CDY CDY CDY CDY CDY CDY CDY CDY

Feedstock:% cracked stock 40 10-20 0 0 30 0 10 100 0 0 36 60 0

Sp Gravity 0.8628 0.8514 0.8468 0.8665 0.8735 0.8534 0.8448 0.8956 0.8649 0.8198 0.8676 0.8933 0.8328

Sulfur, wt.% 1.66 0.99 0.07 1.26 0.34 1.26 1.00 0.90 0.86 0.82 0.87 0.89 0.83

EP D86 Dist, ˚C 371 377 335 396 354 380 360 360 285 545 346 363 349

Product:

Sulfur, ppm 7 7 8 10 10 35 50 7 7 7 7 7 7

Conditions

LHSV 0.7 1.5 2.8 0.7 1.1 1.6 1.9 1.0 1.1 2.6 1.3 1.0 1.6

Inlet P, BARG 54 64 48 56 56 51 44 88 56 41 73 88 50

catalysts must be used in order to take full advantageof the SmART System concept. ART has devoted sig-nificant resources to designing the best ULSD cata-lysts for use in the SmART Catalyst System, and thiseffort has lead to the commercialization in 2004 of anew CoMo catalyst CDX, and a new NiMo catalyst CDY.These new technologies benefit from the optimizationof the alumina chemistry to give the right surface areaand pore size distribution, as well as providing the rightsurface chemistry (i.e., acidity).

ULSD production with the CDX/CDY SmART Systembegan early in 2004, in a North American refinery pro-cessing a feed containing 20-40% of a high endpointLCO. Since that time, ART CDX and ART CDY havebeen selected for 14 different diesel applications eitheras components in SmART Systems or as a completecharge. A list of commercial applications of CDX, CDYand SmART Catalyst Systems is shown in Table VII. Itis apparent from the table that the SmART catalysttechnology has been successfully applied to a widerange of feeds and conditions. In most cases it hasbeen selected based on the high activity demonstrat-ed in pilot plant testing.

As these and other recent successes demonstrate,Advanced Refining Technologies has developed state-of-the-art technologies aimed at helping refiners meetthe challenges of clean fuels. These successes arethe result of harnessing the unique heritage of ARTwhich includes a collective expertise in material sci-

ence, catalyst formulation, and manufacturing know-how. The science of designing specific catalyst com-ponents to operate in an optimum system is a funda-mental part of ART's catalyst technology. With theadvent of clean fuels, ART seized the opportunity toextrapolate their catalyst system expertise from resid tolighter feedstocks. As a result, ART has been able todeliver high performance technologies ranging fromStART Catalyst Systems for Si tolerance in coker naph-tha applications, SmART Catalyst Systems for ULSD,and ApART Catalyst Systems for cat feed hydrotreat-ing.

ART strives to continuously improve the performance ofits catalysts, and the current focus of that effort is onmaximizing the effectiveness of the catalytic metals.As described in Catalagram No. 96 (October 2004),ART's new CoMo catalyst, CDX, benefits fromimproved metals utilization through the application ofnovel metals chemistry and a unique impregnationtechnique. These same techniques have been suc-cessfully applied to a new NiMo catalyst called ARTNDXi. As shown in Figure 26, this catalyst has signifi-cantly higher activity for ULSD than ART CDY and theconventional reference NiMo catalyst.

ART NDXi will be commercialized in early 2005 and isslated to become the latest NiMo catalyst componentof the SmART Catalyst System.

Figure 29ART NDXi has “Step Out” Activity



t has been widely discussed thatdesulfurization of dibenzothio-phene and substituted diben-

zothiophenes occurs through tworeaction pathways, the direct sulfurabstraction route and the hydrogena-tion-abstraction route. The formerinvolves adsorption of the molecule onthe catalyst surface via the sulfur atomfollowed by C-S bond scission. This isthe primary pathway over cobalt-molybdenum (CoMo) basedhydrotreating catalysts. The second

pathway involves saturation of onearomatic ring of the dibenzothio-phene species followed by theextraction of the sulfur atom.Nickel-molybdenum (NiMo) cata-lysts have a higher activity for desul-furization via this route.

It has become a fairly commonpractice to model ULSD applica-tions by lumping the various sulfurspecies into “easy sulfur” and “hardsulfur”. The so-called easy sulfur

No Need to TradeULSD Catalyst Performancefor Hydrogen Limits:SmART Approaches

ICharles OlsenNew Product DevelopmentManager

Gerianne D’AngeloSenior Technical Services Engineer



is made up of compounds whichare readily desulfurized via directabstraction and boil below about363˚CF whereas hard sulfur ismade up of compounds which aremore readily removed via hydro-genation followed by abstraction.These compounds include4,6

dimethyl-dibenzothiophene andother di- and tri-substituted diben-zothiophenes. The relative amountsof easy and hard sulfur in a feed area critical property to consider sincethe concentration of each can varysignificantly from feed to feeddepending on crude source, boilingrange and the prior thermal or cat-alytic treatment of the feedstock.

ART first introduced the SmARTCatalyst System™ in 2001 (1,2) inanticipation of the stringent newdemands required for ULSD. TheSmART system concept is based ona staged catalyst approachdesigned to exploit the fact thatthere are two reaction pathways fordesulfurization. The system utilizesa high activity CoMo catalyst likeART CDXi for efficient removal ofsulfur via the direct abstractionroute and a high activity NiMo cata-lyst like ART NDXi which effectivelyremoves the multisubstituted diben-zothiophenes via the hydrogenationroute.

A number of factors need to be con-sidered when designing the optimumSmART system for a given application.These have been reviewed in detailpreviously (3, 4), and include feed end-point (amount of hard sulfur), feednitrogen and H2 availability.

One of the big advantages of theSmART System is illustrated in Figure9. The figure shows that as NiMo cat-alyst is added to the SmART systemthere is a large increase in HDS activ-ity relative to the all CoMo reference,and eventually, a maximum in HDSactivity is reached. The position andmagnitude of this maximum varieswith feed and operating conditions,especially H2 partial pressure. Thefigure also includes the relative H2consumption, and again, as the per-centage of the NiMo componentincreases, the H2 consumption relativeto the base CoMo system increases.Notice, however, that in this case therelationship between H2 consumptionand the fraction of NiMo catalyst isnonlinear. In the region where the sys-tem shows the highest activity thehydrogen consumption is only slightlygreater than that for the all CoMo sys-tem, and well below that for the allNiMo catalyst. Again, the nature ofthis relationship varies with feed andoperating conditions, with a strongcorrelation to hydrogen availability. It

is this ability to balance HDS activi-ty and H2 consumption to meet indi-vidual refiner requirements that setsSmART apart.

The balancing of hydrogen con-sumption and HDS activity is possi-ble because of the different kineticsand reaction pathways for sulfurremoval and aromatic hydrogena-tion. The reaction pathways for sul-fur removal were discussed abovewith the main point being the hydro-genation pathway is critical forULSD production. The multisubsti-tuted dibenzothiophenes (hard sul-fur) are polynuclear aromaticspecies containing two aromaticrings, one of which must be hydro-genated for efficient removal of thesulfur atom. Thus, the catalyst sys-tem needs good hydrogenationactivity and selectivity in order tominimize the use of hydrogen.

To more fully understand how thisworks, it is useful to review polynu-clear aromatic hydrogenation ingeneral. To begin with, hydrogena-tion of aromatics is reversible, andequilibrium conversion is less than100% under practical hydrotreatingconditions. The equilibrium conver-sion decreases with increasing tem-perature, and therefore, increasingtemperature to get higher hydro-genation rates may ultimately resultin lower conversion. These reac-tions are also exothermic which canhave an impact on conversion inadiabatic systems.

The hydrogenation of a number ofpoly aromatic species such asnaphthalene and biphenyl havebeen studied by a number of inves-tigators (5) and the work has lead tothe reaction networks presented inFigure 10. In the case of naphtha-lene, the reaction begins with thehydrogenation of one of the aromat-ic rings to form tetralin, a mono ringaromatic. The next reaction is hydro-genation of the remaining aromaticring to produce decalin, the fullysaturated species. As indicated inthe figure, the reactions proceedsequentially with the rate of hydro-

Pro

du

ctS

ulf

ur,

pp

m

Relative

H2

Co

nsu

mp

tion

1.00

1.15

SmART SystemsAll CoMoReference

All NiMoReference

Product Sulfur

H2 Consumption

Figure 9Optimizing HDS and Hydrogen Consumption


genation of the final aromatic ring(tetralin) at least an order of magni-tude lower than saturation of thefirst aromatic ring (naphthalene).Interestingly, the rate of tetralinhydrogenation is about the same asthat observed for benzene hydro-genation. A variety of substitutednaphthalene’s have also beenshown to follow a similar reactionnetwork with the rate of hydrogena-tion of the first aromatic ring rough-ly the same as that observed fornaphthalene.

The hydrogenation of biphenyl pro-ceeds similarly. The hydrogenationis a stepwise reaction with the rateof hydrogenation of the first aromat-ic ring about an order of magnitudefaster than that of the mono ringcompound. An important differ-ence is that the rate of the firsthydrogenation reaction in naphtha-lene is about and an order of mag-nitude faster than the rate of hydro-genation of the first ring in biphenyl.Thus, there is a significant differ-ence between the hydrogenation ofan aromatic with two fused ringscompared to a two ring aromaticwhere the rings are not fused. Thisis an important difference whenconsidering hard sulfur removalsince these species do not containtwo fused aromatic rings and assuch, can be expected to behavemore like a biphenyl species.

The challenge when designing aSmART system is to provide enoughhydrogenation activity to efficientlysaturate the first ring on the two ringaromatic (biphenyl type, sulfur con-taining) molecule, but not so much asto catalyze the final hydrogenationstep in the reaction pathway dis-cussed above.

The poly aromatic hydrogenationreaction networks shown in Figure 10can be modeled as first orderreversible reactions in series. Figure11 shows the species concentrationprofiles as a function of residencetime for a hydrogenation reactionsequence such as that for naphtha-lene. In the example shown, the rate

of the first hydrogenation reaction inthe series is an order of magnitudefaster then the rate of the secondhydrogenation reaction. There is arapid decrease in the concentrationof the two ringed aromatic at shorttimes, and a correspondingincrease in the mono ringedspecies. As time increases howev-er, the mono ring aromatic concen-tration begins to decrease and thefully saturated species begin tobuild up. This type of concentrationprofile suggests that there is a win-dow of residence times correspon-ding to a maximum in the monoringed aromatic concentration. Theway to minimize hydrogen con-sumption is by avoiding saturationof the mono ringed compounds.This can be accomplished byadjusting the residence time in theCoMo and NiMo beds of a SmARTsystem through varying theamounts of each catalyst. Thiseffectively ‘tunes’ the hydrogenationactivity of the overall catalyst bed tomaximize hydrogenation of the polyaromatics and minimize hydrogena-tion of the mono ringed species.

This is explored further on a dieselfeed comparing a CoMo and NiMocatalyst in a pilot plant test. Figure12 compares the HDS activity of thetwo catalysts as a function of resi-dence time at constant reactor tem-perature. It is apparent that theNiMo catalyst is more active thanthe CoMo catalyst at the indicated

naphthalene tetralin decalin

biphenyl cyclohexylbenzene bicyclohexyl

k1>k2, k3>k4, and k1>k3

k1 k2

k3 k4

Figure 10Reaction Pathways for Poly Aromatics Hydrogenation

1.0

Contact time

Co

nce

ntr

atio

n

k1=10*k2

0.8

0.6

0.4

0.2

0.0

mono diSat’d

Figure 11First Order Reversible Reactionsin Series: Concentration Profile


0

10

20

30

40

50

0.00

1/LHSV, hrs

Pro

du

ctS

ulf

ur,

pp

m

0.20 0.40 0.60 0.80 1.00 1.20

CoMo

NiMo

0

10

20

30

40

Co

nce

ntr

atio

n,%

0.00

1/LHSV, hrs

0.20 0.40 0.60 0.80 1.00 1.20

Mono's

Poly'sSat'd

0

10

20

30

40

Co

nce

ntr

atio

n,%

0.00

1/LHSV, hrs

0.20 0.40 0.60 0.80 1.00 1.20

Mono's

Poly'sSat'd

Figure 12HDS Activity Comparison at High Pressure

Figure 13Aromatics Concentration Profile

for CoMo Catalyst at High Pressure

Figure 14Aromatics Concentration Profilefor NiMo Catalyst at High Pressure


conditions, although both catalystsare able to achieve <10 ppm prod-uct sulfur if the residence time islong enough. Figures 13 and 14compare the concentration profilesfor poly aromatics, mono ringed aro-matics and the saturates as a func-tion of residence time for the CoMoand NiMo catalyst respectively.Both charts show the same concen-tration trends as shown in Figure 11.There is a rapid decrease in polyaromatics concentration and a cor-responding increase in monoringed aromatics for both catalysts.Clearly, however, the NiMo catalystis much more efficient at hydro-genating the final aromatic ring asevidenced by a lower maximummono ringed aromatic concentra-tion and a faster increase in satu-rates with increasing residence timecompared to the CoMo catalyst.

At the longest residence time (low-est LHSV), the NiMo catalyst hasabout 15 numbers (absolute) highersaturate concentration (and about15 numbers lower mono ringed aro-matic concentration) than the CoMocatalyst. That translates to about 53Nm3/m3 higher hydrogen consump-tion compared to the CoMo catalyst.This difference decreases rapidlyas the residence time decreases.

Of course, if there is sufficient H2available, the incremental increasein aromatics saturation and the cor-respondingly higher hydrogen con-sumption can offer some benefitssuch as cetane improvement.Figure 15 summarizes the cetaneindex increase observed for thisexample. The cetane index increas-es linearly with increasing H2 con-sumption, and ultimately, a cetaneindex improvement of six numberswas achieved by the high activityNiMo catalyst.

Not surprisingly, pressure has a dra-matic effect on the performance ofNiMo and CoMo catalysts in ULSD.Figure 16 compares the HDS activi-ty of the NiMo and CoMo catalystfor the same feed and conditions asabove, but at lower pressure. At

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

Relative H2 Consumption

Cet

ane

Ind

exIn

crea

se

0.5

CoMo

NiMo

1.0 1.5 2.0 2.0 3.0 3.5

0

10

20

30

40

5060

70

80

90

100

0.00

1/LHSV, hrs

Pro

du

ctS

ulf

ur,

pp

m

0.20 0.40 0.60 0.80 1.00 1.20

CoMo

NiMo

0

10

20

30

40

Co

nce

ntr

atio

n,%

0.00

1/LHSV, hrs

0.20 0.40 0.60 0.80 1.00 1.20

Mono'sPoly'sSat'd

Figure 15Cetane Index Increase with H2 Consumption

Figure 16HDS Activity Comparison at Moderate Pressure

Figure 17Aromatics Concentration Profile for CoMo Catalyst

at Moderate Pressure


these conditions the CoMo catalystis more active at the higher LHSV’s(shorter residence times), while atthe lower LHSV’s the catalysts haveessentially the same activity. Acomparison of the aromatic speciesconcentration profiles is shown inFigures 17 and 18. In this case, thedifference between the catalysts ismuch less than observed for thehigher pressure case, and thedegree of saturation achieved byeither catalyst is lower. For theCoMo catalyst in Figure 17, the con-centration of Mono ringed aromat-ics never begins to decrease, andthe concentration of saturatesremains very low. The NiMo catalystdata shown in Figure 18 looks simi-lar, although at long residence timethere is a decrease in mono ringedaromatics, the poly aromatic level islower and the saturates concentra-tion is higher than for the CoMo cat-alyst case.

These data are a good example ofthe flexibility of the SmART system.In applications where there is suffi-cient H2 partial pressure, a NiMocatalyst is likely the most active sys-tem for HDS. However, it will con-sume significantly more hydrogendue to its efficiency at catalyzinghydrogenation reactions. If theincremental hydrogen consumptioncannot be tolerated, a SmART sys-tem can be designed which willdeliver high HDS activity and mini-mize hydrogen consumption. Incases where the hydrogen pressureis lower, the SmART system is oftenmore active than either componentalone without increasing the H2 con-sumption significantly over the allCoMo system.

SmART Performance

Since introducing the SmART sys-tem for ULSD, ART has conducted asignificant amount pilot work todemonstrate both the activity andstability of these systems. Figure19 summarizes some of that workcomparing ART CDXi and a SmARTsystem consisting of CDXi andNDXi. This particular study

0

10

20

30

40

Co

nce

ntr

atio

n,%

0.00

1/LHSV, hrs

0.20 0.40 0.60 0.80 1.00 1.20

Mono'sPoly'sSat'd

343

349

354

360

366

371

377

382

388

Tem

per

atu

re,

˚C

0 250 500 750 1000 1250 1500 1750 2000

Normalized to 1.25 LHSV and 55 BARG1.26 wt.% feed sulfur and 10 ppm product sulfur

Hours on Stream

CDXi

SmART

10

12

14

16

18

20

22

24

26

28

30

0 250 500 750 1000 1250 1500 1750 2000

1.25 LHSV and 55 BARG

Hours on Stream

Pro

du

ctA

rom

atic

s,vo

l.%

CDXi

SmART

Figure 18Aromatics Concentration Profile forNiMo Catalyst at Moderate Pressure

Figure 19Pilot Plant Aging of a SmART System

Figure 20Pilot Plant Aging of a SmART System

Aromatics Hydrogenation


spanned about 2000 hours at theconditions shown in the chart pro-cessing a straight run feed from theWest Coast. The H2 partial pressureis quite good in this example whichexplains the large activity advan-tage for the SmART system relativeto the all CoMo system. Notice thatthe slopes of the lines through eachdata set are essentially the sameindicating the ART CDXi and aSmART system of CDXi/NDXi havethe same relative stability when pro-ducing ULSD.

Figure 20 shows how the aromaticsaturation activity changed over thecourse of the 2000 hour run. Thetotal aromatics saturation stayedessentially constant for the SmARTsystem throughout the run, while forCDXi there is a suggestion of someslight loss in saturation activity atthe end of the run. Although notshown in the chart, the PNA contentin the product was also analyzed,and the data tell the same story.Another thing to note is the similari-ty in aromatics (and PNA) conver-sion between the SmART systemand CDXi. This is an indication thatthe hydrogen consumption is similarfor both systems, even though theSmART system has a substantialactivity advantage.

The SmART catalyst system or itscomponents have been selected forover 20 applications since beingintroduced to the market. The tech-nology has been successfullyapplied to a wide range of feeds

and conditions, and in most cases hasbeen chosen based on the high activ-ity demonstrated in pilot plant testing,both in ART labs and refiner testingfacilities. A few of these applicationsare discussed in the paragraphs thatfollow.

ULSD production with the SmARTSystem began early in 2004 in a NorthAmerican refinery processing a feedcontaining 30-50% of a refractory,high endpoint LCO. The LCO endpoint can gat as high as 391˚C, andsulfur speciation indicates that theconcentration of ‘hard sulfur’ oftenexceeds 4000 ppm. The performanceof the SmART system is shown inFigure 12. Despite processing a feedwhich was more difficult than antici-pated, the SmART system providedexcellent performance. The typicaldeactivation period following start upwas exacerbated by the fact that the

refiner had to run off a tank of LCOwhich had built up during the unitturnaround. Even when processinga blend of 50-60% LCO at SOR, theSmART system had no problemsmaking the <10 ppm sulfur target.Once the feed and operating condi-tions lined out the operation wasvery stable with essentially no deac-tivation apparent over the last sever-al months.

In another example, Refiner A con-ducted in-house testing for theirULSD catalyst selection. ART pro-posed a SmART catalyst systemwhich ultimately tested substantiallymore active than other catalysts inthe program including one from theperceived ‘market leader’. As aresult, this refiner selected aCDX/CDY SmART system for theirULSD unit. The commercial unitbegan operation in the fourth quar-ter of 2004, and a snapshot of theperformance thus far is shown inTable V. The feed is a blend of up to40% LCO and light coker gas oilwith a sulfur content of about 1.3wt.%. The unit has decent pres-sure, but the H2/Oil ratio is lowerthan optimum especially given thatthe H2 consumption is typicallyaround 98 Nm3/m3. The perform-ance of the SmART system has metthe high expectations set by thepilot plant testing.

316

343

371

399

427

0 20 40 60 80 100 120 140 160

30-50% LCO blend with 360-393˚C end point

Days on StreamT

emp

erat

ure

,˚C

180

Figure 21Commercial SmART System Performance

Months on stream 0 1.5

LHSV 0.75 0.75

H2/Oil, Nm3/m3 166 166

Inlet pressure, BARG 65 65

WABT, ˚C 336

Product sulfur 7

334

7

15

0.75

166

65

346

7

Table VCommercial ULSD Performance for Refiner A


ART and Refiner B worked togetherto generate data for a plannedULSD unit revamp. The feedstockhad a very high endpoint of 396˚Cwhich corresponded to over 6000ppm of hard sulfur. ART proposeda SmART system consisting of itsnew high activity catalysts ART CDXand CDY. This system wasdesigned to provide high HDSactivity and minimize hydrogen con-sumption in order to stay within therefiners hydrogen availability limits.The refiner conducted pilot planttesting on a variety of proposed cat-alysts, and found that the SmARTsystem easily met the targets andoutperformed the other vendors inthe program.

As a result of this work, Refiner Bselected the SmART system for thefirst cycle in the ULSD unit. The unitstarted up in the second quarter of2005, and has been online for aboutnine months. The performance of theSmART system is shown in Figure 22.This refiner conducted a ULSD testrun early in the cycle, and the per-formance met all expectations and infact, closely matched the pilot plantresults. The unit was then operated toproduce 200 ppm sulfur for severalmonths before pushing again to makeULSD. The hydrogen consumptionincreased from about 55 Nm3/m3 to62 Nm3/m3 when they went from 200ppm sulfur to 10 ppm sulfur. As the

Reactor Train 1

Months on stream 1 9

H2/Oil, Nm3/m3

1.7

Inlet pressure, BARG

247

WABT, ˚C

Product sulfur, ppm

43

45

2

1

LHSV

9

1.7 1.7 1.7

247 247 247

43 43 43

346 347 352 345

45 45 45

Table VISmART System Performance for Refiner C

302

316

329

343

357

371

385

10 ppm sulfur

0 25 50 75 100 125 150 175 200

0.72 LHSV and 43 BARG H2 Pressure, 1.24 wt.% feed sulfur

Days on Stream

Tem

per

atu

re,˚

C

200 ppm sulfur

Figure 22SmART System Performance for Refiner B

chart shows, the SmART system hasexperienced essentially no deacti-vation since start up.

In the final example, Refiner C want-ed to produce <50 ppm sulfurdiesel in an existing reactor. ARToptimized a SmART loading basedon the product sulfur requirementwhile at the same time staying with-in the constraints of the refinery’shydrogen system. The unit startedup with the SmART system in thesecond quarter of 2005, and hasbeen producing <50 ppm sulfurdiesel for about 9 months. A sum-mary of the performance is shownin Table VI. The performance of theSmART system has been excellenteven with the high LHSV and lowhydrogen partial pressure. Therequired temperature is within a fewdegrees of the predicted perform-ance, and the catalyst deactivationobserved to date is minimal.Hydrogen consumption has alsobeen within expectations at 45-48Nm3/m3. Refiner C is extremelypleased, and is now working withART on a unit revamp which willallow production of <10 ppm sulfurdiesel.

References

1. Olsen, C., Krenzke, L.D., Watkins, B.,AICHE Spring National Meeting, NewOrleans, March 2002.

2. Krenzke, D., Armstrong, M., 2001 ERTCMeeting, Madrid, Spain.

3. D’Angelo, G., Olsen, C., DavisonCatalagram 95, March, 2004, pp. 38-44

4. Olsen, C., Krenzke, L.D. 2005 NPRAAnnual Meeting, Paper AM-05-17

5. Girgis, M.J., Gates, B.C., Ind. Eng.Chem. Res., 30, 1991, p 2021.

reprinted from Catalagram® 104 SE 2008 23

RT first introduced the SmARTCatalyst System® Series forultra-low sulfur diesel (ULSD)

in 2001. Since that time the technolo-gy has been widely accepted by therefining industry as top tier for ULSD.As detailed previously (Catalagram®

99, 2006), the SmART System is astaged catalyst system customized tomeet individual refiners objectiveswith the performance of the systemdriven by ART’s DXTM CatalystPlatform.

ULSD production with the first SmARTSystem began early in 2004 at a NorthAmerican refinery processing a feedcontaining 40% of a high endpointLight Cycle Oil (LCO). Since that timeDXCatalyst Platform has been select-ed for over 35 ULSD applications aseither stand-alone catalysts or as

components in SmART System. Thetechnology has been a great suc-cess since its introduction with mil-lions of pounds installed in com-mercial units around the world.Several of the first refiners to utilizea SmART System are still enjoyingbenefits today, or have reloadedanother SmART System based onthe exceptional first cycle theyreceived from the technology.

This article contains several casestudies highlighting the perform-ance of ART catalysts in a variety ofULSD units around the world.These are summarized in Table I.

Refiner A is an initial user of aSmART System in Asia Pacific. Thisrefiner conducted in-house testingfor their ULSD catalyst selection.

ART Excels In ULSD Service: Updateon Sulfur minimization by ART

Greg RosinskiTechnical Service Engineer

Dave KrenzkeRegional Technical ServicesManager

Charles OlsenWorldwide Technical ServicesManager


A

They requested catalyst samplesfrom ART and a “market leading”domestic supplier. The DXTM

Catalyst Platform tested as a sub-stantially more active catalyst thanthe others in the program. As aresult, ART was selected as the cat-alyst supplier for their unit, whichstarted up in the last half of 2004.This refiner was completing arevamp, which involved the additionof a new reactor in front of an exist-ing reactor. They decided to usefresh catalyst in the new lead reac-tor while keeping used ART catalystin the lag reactor. The unit condi-tions are characterized by an inletpressure of 64 BARG and a LHSV of0.7 hr-1. The feed contains up to40% cracked stocks, and the prod-uct sulfur has averaged 5 ppm. Theunit ran for three years before therefiner decided to change out the“used” catalyst in the lag reactorwith fresh catalyst from ART. Theperformance of the unit is summa-rized in Figure 1 and, as the figuredepicts, stability has been excep-tional.

Figure 2 shows data for Refiner B.This was another major Asia Pacificrefiner using a SmART System. Thisrefiner needed to produce 10 ppmsulfur diesel for two years in a newlyrevamped unit. The operating con-ditions for this unit are 53 BARG inletpressure with an LHSV around 0.7hr-1. The feed was a high end point,straight run diesel with typical sulfurcontent of 1.25 wt.%. This refinerwas concerned with minimizinghydrogen consumption as hydrogenavailability was limited at the refin-ery. This was a situation well suitedfor the flexibility of the SmARTSystem to tune the hydrogen con-sumption/activity relationship. Theoptimum loading for this unit was90% cobalt-molybdenum (CoMo)and 10% nickel-molybdenum(NiMo) catalyst. This design wasexpected to be significantly moreactive than an all CoMo loading andwould consume the same amount ofhydrogen as an all CoMo loading.The final selection of the SmARTSystem was based on competitivepilot plant testing by the refiner.

Region

AP

AP

AP

AP

NA

NA

NA

NA

Feed

40% cracked stock

Straight Run

Straight Run

Straight Run

40% coker/LCO

50% LCO

70% LCO

45% LCO/LCGO

Inlet Pressure BARG

64

53

59

78

74

N/A

86

90

LHSV

0.7

0.7

1.2

1.1

1.3

1.1

1.0

0.8

% CoMo/ % NiMo

70/30

90/10

55/45

30/70

35/65

70/30 + Dewax

35/65

25/75

A

B

C

D

E

F

G

H

Table ISummary of ULSD Case Studies

382

0 200 400 600 800 1000

5 ppm product sulfur

Days on Stream

Actual

Normalized

WA

BT

,˚C

360

338

316

293

271

Figure 1Asia Pacific Refiner A

427

0 50 100 150 200 250

High severity modeProduct Sulfur: 85% <8ppm

Days on Stream

WA

BT

,˚C

413

399

385

371

357

Low severity modeProduct Sulfur: 15% <8ppm

Return to low severity mode:WABT dropped about 8˚C

343

329

316300 350 400 450 500 550 600

Actual Normalized to 10 ppm

Figure 2Asia Pacific Refiner B



About eight months into the ULSDportion of the cycle, the refiner sig-nificantly increased the operatingseverity and began producing verylow sulfur diesel. Typically, 8 ppm isthe recommended product sulfurtarget when producing <10 ppmULSD. In the higher severity mode,the product sulfur was well below 8ppm 85% of the time, whereas inthe lower severity mode the productsulfur was below 8 ppm only 15% ofthe time. The higher severity led toa much higher deactivation rate andpotentially jeopardized the two yearcycle length. After discussions withthe refiner, the severity was reducedand the two year cycle length wasachieved.

ART was chosen for the secondcycle which again was based oncompetitive testing and the out-standing performance demonstrat-ed in the first cycle. The current sys-tem is performing very well.

Refiner C, another Asia Pacific refin-er, selected ART catalysts for theirULSD unit based on the strong ref-erence from the refiners mentionedabove. This refiner needed to pro-duce 8 ppm sulfur diesel for twoyears and hydrogen availability wasnot a constraint. The operating con-ditions included an inlet pressure of59 BARG and LHSV of 1.2 hr-1. Thefeed was also a high endpoint,straight run diesel with a sulfur con-tent of 1.8 wt.%. This was a more

demanding operation than those dis-cussed previously, and a required sys-tem designed for maximum activity.The catalyst loading in this case was55% CoMo and 45% NiMo. The per-formance is summarized in Figure 3.

This unit met all performance targetsduring the two year cycle and has justbeen reloaded with a new SmARTSystem.

Operating data for Refiner D is shownin Figure 4. This is a grass roots ULSDunit in Asia Pacific. ART was chosento participate in this project becauseof the excellent performance of theSmART System from previous refer-ences in the region. ART workedclosely with the refiner and engineer-

ing construction firm on the designbasis for this project. A 30% CoMoand 70% NiMo SmART Systemwasdesigned for this unit in order todeliver maximum activity. The oper-ating conditions for this unit includ-ed an inlet pressure of 78 BARGand LHSV of 1.1 hr-1. This unit alsoprocesses a straight run feed whichhas a relatively high level of nitrogenand an endpoint of 388˚C (by D86).

The unit is running well and meetingall performance expectations with asomewhat lower than estimateddeactivation rate, and is well ontrack to meet the targeted three-year cycle length.

Refiner E is another grassrootsULSD unit, which started up in thesecond quarter of 2006 in NorthAmerica. ART worked with thelicensor on the unit design and pro-posed a SmART System loadingconsisting of about 65% NiMo. Thisloading was designed for maximumactivity as the design feed con-tained a high percentage ofcracked stocks. The conditions ofthe unit included an inlet pressure of74 BARG with an LHSV of 1.25 hr-1.This refinery processes mostlysweet crudes, and the feed to theunit typically contains about 40%FCC LCO and coker LGO. Theactivity of the system has beenextremely high, allowing this refinerto operate at 20% over designcharge rate. Figure 5 shows the

382

WA

BT

,˚C 360

338

316

327

349

371

0 50 100 150 200 250Days on Stream

300


Figure 3Asia Pacific Refiner C

382

0 50 100 150 200 250

Days on Stream

WA

BT

,˚C

371

360

349

338

327

316300 350 375325275225175


25 75 125

Figure 4Asia Pacific Refiner D

performance for the cycle thus far,and it is evident from the figure thatthe catalyst stability has been excel-lent. In fact, the unit was designedfor a 24-month cycle, but 48 monthsappears possible even at higherthan design feed rates.

This unit also typically processes10% kerosene with occasionalincreases to as much as 30%. Ascan be seen in Figure 5, the addi-tion of kerosene to the feed has nonegative impact on the activity ofthe system, and may even improvethe performance. Notice how theWABT decreases when processinghigher amounts of kerosene. Thissuggests that the increase in feedvaporization (decrease in H2 pres-sure) is offset by the decrease inhard to treat, substituted dibenzoth-iophene sulfur species.

Figure 6 summarizes data fromRefiner F in North America. Thisrefiner had completed a project torevamp an existing hydrocracker toULSD service. The objectives wereto increase feed capacity from 4770to 7155 MTD, while ensuring thecapability to process 50% or moreLCO, as well as provide for cold flowimprovement during the wintermonths. This refiner also wanted tominimize the hydrogen consumptionso that feed rate could be maxi-mized within make-up hydrogenconstraints. Along with SüdChemie, ART designed a dewax-ing/ULSD catalyst system meetingthe unit objectives. The unit startedup successfully in the 2nd quarterof 2006 and processes both sweetand sour crude derived feeds inblock operation. The feed is alsocomprised of 40-50 vol.% of a highendpoint LCO. The performance ofthe unit is summarized in Figure 6.The unit came on stream with high-er than expected activity, and is wellon its way to exceeding the targetthree year cycle length. Additionaldetails on this unit can be found inCatalagram® 103, Spring 2008.

Refiner G is another grassroots unitwhich started up in the fourth quar-

382

0 100 200 800

Days on StreamW

AB

T,˚

C

371

360

349

338

327

316

300 500 600400 700

WABT Kerosene

304

5045

4035

30

25

15

10

0

20

Ker

ose

ne,

vol.%

5

Figure 5North American Refiner E

382

0 500100 200Days on Stream

No

rmal

ized

WA

BT

,˚C

327

316

300 400 600

371

360

349

338

304

Figure 6North American Refiner F

382

0 500100 200

Days on Stream

No

rmal

ized

WA

BT

,˚C

327

316

300 400 600

393

371

360

349

338

304

5 ppm average product sulfur

Figure 7North American Refiner G



97

0 100 200

Days on Stream

Inle

tP

ress

ure

,BA

RG 90

83

76

69

62300 500 600400

Pressure Recycle H2

100

95

90

85

80

75

65

60

70

Rec

ycle

H2

Pu

rity

,vo

l.%

Figure 8North American Refiner G Hydrogen Availability

2930 100 200 350

Days on Stream

WA

BT

,˚C

371

360

349

338

327

316

30050 150 400250

WABT API Uplift

304

20

1816141210

64

0

8

AP

IGra

vity

Incr

ease

2

450 500 550

Figure 9North American Refiner H

ter of 2006. The performance ofthis unit is summarized in Figure 7.ART again worked closely with thelicensor on the new unit design andproposed a SmART System loadingusing 65% NiMo catalyst for maxi-mum activity. The unit typicallyprocesses >70% LCO, includingboth LCO produced within the refin-ery and purchased externally. Theinitial deactivation rate of the unitwas significantly higher thanexpected, and it was determinedthat this was due to lower H2 partialpressure than design combinedwith lower H2/Oil ratio. This can beseen in Figure 8 which shows thetrend of reactor inlet pressure andthe recycle hydrogen purity. Early inthe cycle there were control issuesand the inlet pressure showed asteady decline. The recycle hydro-gen purity also decreased steadilyand had periods where it fell dra-matically. Once the H2 partial pres-sure concerns were addressed,combined with better bed tempera-ture management, the deactivationrate decreased significantly. Theoperation became much more con-sistent, and since that time thedeactivation rate indicates that theunit will easily meet the expected24-month cycle length.

Finally for Refiner H, Figure 9 sum-marizes the performance of a

SmART System at a U.S. Gulf Coastrefinery. This was another grassrootsunit that started up in the Fall of 2006.SOR activity met expectations, andsince that time the unit operatingseverity has steadily increased. Thecurrent feedrate is 22% over designand the feedstock endpoint hasincreased by 17-22˚C. Typical unitconditions include 0.8 hr-1 LHSV and90 BARG inlet pressure, and, on aver-age, the unit processes a feed con-taining 15% FCC LCO, 30% LCGOand 5% coker naphtha. At times theunit has processed as much as 80%cracked stocks in the feed, and stillthe product sulfur has averaged lessthan 6 ppm for the cycle. The targetcycle length was 24 months, and theunit is currently on track for a 36-

month cycle. Also shown in Figure9 is the API uplift from the unit. Fromthe chart, the API typically increas-es 6-10 numbers depending on thefeedstock.

As this sampling of case studiesdemonstrates, the SmART Systemhas been employed in a wide vari-ety of ULSD applications aroundthe world. The technology has beensuccessfully operating over a broadrange of operating conditions fromlow to high pressure with feedsranging from straight run to 80%cracked stocks. In each applica-tion, all expectations have beenmet or exceeded, and in a numberof cases ART catalyst has beenselected for the second cyclebased on the excellent perform-ance. ADVANCED REFININGTECHNOLOGIES continues todevelop higher performance prod-ucts for ULSD as evidenced by therecent introduction of the newestDXTMCatalyst Platform, 420DX. Theaddition of this catalyst to theULSD portfolio is an example ofthe commitment that ART will con-tinue to deliver state-of-the-arttechnology for ULSD.

Editor’s Note:

A lot has changed since ART first introduced the SmART Catalyst System® series for ULSD in 2001. Many ULSD unitshave been built or retrofitted and are now into their second or third cycles. Most countries in the world are either man-dating ULSD from their refineries, or in the process of doing so.

ART has made many improvements in its offerings for making ULSD as a result of extensive investment in theresearch and development of new and improved catalysts for expanding performance and flexibility. Since the intro-duction of CDY and CDX, ART is already on its third generation of catalysts. The premier catalysts used in today’sSmART system are 420DX and NDXi.

The table below shows the commercial experience of the SmART System. There are many repeat users among themore than 70 unit start-ups that have occurred using the SmART catalyst system. A wide variety of feedstocks andoperating conditions are represented from units all over the world.

Country/RegionStart-up

Date% Cracked

StockProduct Sulfur

(ppm)Pressure

BARG% NiMoCatalyst

Mid Continent, USA

Japan

Japan

Japan

Mid Continent, USA

Mid Continent, USA

Japan

Japan

Korea

Russia

South Africa

West Coast

Mid Continent, USA

Eastern Canada

South America

Korea

Russia

Mid Continent, USA

Mid Continent, USA

Gulf Coast, USA

Gulf Coast, USA

Gulf Coast, USA

Western Canada

2004

2004

2004

2004

2004

2005

2005

2005

2005

2005

2006

2006

2006

2006

2006

2006

2006

2006

2006

2006

2006

2006

2007

0

10-20

40

0

20

15

35

0

10

15

0

35-50

36

60

100

0

0

15

8

7

7

35

10

7

7

10

50

400

7

7

25

8

50

7

7

7

7

7

9

48

65

55

52

57

52

88

57

45

53

51

145

87

59

48

74

89

89

57

41

61

35%

55%

25%

0%

25%

25%

100%

100%

10%

30%

15%

100%

0%

30%

100%

50%

25%

0%

67%

67%

67%

0%

30%

SmART Catalyst System Users List


Country/RegionStart-up

Date% Cracked

StockProduct Sulfur

(ppm)Pressure

BARG% NiMoCatalyst

Gulf Coast

United Kingdom

Mid Continent, USA

Taiwan

Korea

Japan

South America

South America

Korea

Korea

Korea

Singapore

Russia

Russia

Russia

Thailand

Thailand

Russia

South Africa

Gulf Coast, USA

India

India

Thailand

Korea

Korea

Gulf Coast, USA

Russia

Australia

United Kingdom

Gulf Coast, USA

Chile

Gulf Coast, USA

Japan

Poland

Singapore

Singapore

East Coast, USA

Russia

Taiwan

Taiwan

Mid Continent, USA

2007

2007

2007

2007

2007

2007

2007

2007

2007

2007

2007

2007

2007

2007

2007

2008

2008

2008

2008

2008

2008

2008

2008

2008

2008

2008

2009

2009

2009

2009

2009

2009

2009

2009

2009

2009

2009

2009

2009

2009

2010

50

32

60-100

0

0

35

0

0

0

15

10

10

15

60

10

0

0

0

0

0

40

30-40

40

60

10

30

0

10

40

35

350

5

8

450

10

7

25

25

8

8

8

7

8

50

50

45

45

50

400

15

50

50

50

8

8

7

50

8

8

4

10

4

10

3000

7

20

50

450

5

7

69

54

110

42

79

88

54

54

57

53

65

66

50

32

45

60

60

45

53

69

51

51

42

59

52

57

39

50

40

74

97

66

23

66

27

45

41

52

52

50%

50v

70%

0%

70%

100%

100%

100%

70%

10%

10%

0%

25%

0%

45%

70%

70%

45%

15%

50%

65%

0%

0%

10%

50%

0%

0%

33%

0%

100%

100%

20%

0%

60%

0%

70%

0%

30%

0%

100%

50%


s the distillate market demandhas increased over the last fewyears, the production of ultra

low sulfur diesel (ULSD) has prompt-ed refiners to look for ways to maxi-mize their diesel pool. One way toaccomplish this has been to increasethe use of opportunity feedstockssuch as additional LCO, dieselstreams from other hydroprocessingunits, and feeds from various synthet-ic crudes. Some of these opportunityfeedstocks, having already beenprocessed through conventional refin-ery processes, may pose unexpectedchallenges to refiners wishing to incor-porate them into the distillate pool.Some of these streams have proven tobe significantly more difficult toprocess, underscoring the fact that itis important to understand the poten-

Brian WatkinsHydrotreating Technical ServicesEngineer



A tial impact of processing new feedstreams in order to avoid unpleas-ant surprises. This paper highlightsa few examples demonstrating sig-nificant differences in feed reactivityfor a variety of different feed com-ponents which are not necessarilyanticipated from the usual bulk feedanalyses.

FCC LCO and coker diesels havelong been used as feed compo-nents combined with a straight run(SR) feed source to produce ULSDproducts. The quality of the LCOvaries with distillation range, anddepends on the severity of the pre-treatment of the FCC feed as well ason the conditions in the FCC andthe FCC catalyst employed. A com-mon element in LCO is a very high

Distillate Pool Maximization byExploiting the Use of OpportunityFeedstocks Such as LCO and Syncrude



concentration of polynuclear aro-matic compounds relative to otherfeeds.

Synthetic diesel material is often ini-tially processed by either a coker orebullating bed residue hydrocrack-ing unit, and then processedthrough a hydrotreater orhydrotreater/hydrocracker combina-tion. These hydrocracking unitstend to operate at severe conditionsin conjunction with high hydrogenpartial pressures. At these condi-tions, the removal of all the easy,less refractory sulfur is readilyachieved, and the majority of themulti-ring aromatics are saturated.This leaves a product which is rela-tively low in sulfur and PNA’s and,when added to the feed to a ULSDunit, gives rise to a surprisingly diffi-cult feedstock to process.

Likewise, the use of diesel rangeproducts from an H-Oil®, LC-FIN-INGTM unit or fixed bed resid desul-furizer can also have a significant

impact on downstream diesel catalystactivity for similar reasons. The gener-al properties of these types of dieselfeeds often indicate that they may berelatively easy to hydrotreat due totheir low sulfur content and API gravi-ty which is often similar to SR materi-als. Table I lists the properties for sev-eral diesel feeds including the dieselproduct fractions from an ebullatingbed resid (EB) unit, a fixed bed resid(FB) unit, and a diesel fraction from aCanadian synthetic crude.

ART conducted pilot plant testing toinvestigate the impact of variousdiesel feed components on catalystactivity. The pilot work utilized the SRdiesel shown in Table I as the basecase feed. The other componentsshown in Table I were blended into thebase feed at 20% by volume to showthe effects on catalyst performance.The pilot plant work involved severaltailored catalyst systems as well aschanges to operating pressure andhydrogen rate in order to cover abroad range of operation.

The base case testing was done ata hydrogen pressure of about 48BAR, a LHSV of 0.7 and 232Nm3/m3 hydrogen/oil ratio. The cat-alyst system was a stacked systemof high activity CoMo and NiMo cat-alysts containing >80% CoMo cata-lyst. This system was chosen dueto limited hydrogen availability anda desire to minimize hydrogen con-sumption Additional information onthe theory, design and use of thistype of staged catalyst loading canbe found in references 1-5.

Table II shows the analysis of thedifferent feed blends. The 20% LCOhas 1600 ppm lower sulfur, a onenumber lower API, and 20 ppmhigher nitrogen content comparedto the SR feed. The total aromaticcontent in the blend is also higherby 10 volume percent absolute.

Compare this to the feed blendscontaining the EB diesel, FB diesel,or the synthetic diesel where allthree have even lower sulfur com-

Table IDiesel Feedstock Analysis

Light SRGas Oil LCO EB Diesel

SyntheticDiesel FB Diesel

Sulfur, wt.% 1.11 0.17 0.017 0.07 0.006

Nitrogen, wppm 138 203 135 261 71

Specific Gravity 0.8635 0.9094 0.8695 0.8657 0.8685

Aromatics, vol.%

Total 24.18 64.61 41.26 36.58 44.83

Mono 14.47 31.97 36.55 32.52 41.95

Poly 9.71 32.64 4.71 4.06 2.88

Distillation, D2887, ˚C

0.5 141 104 151 97 141

10 256 186 208 176 193

50 316 243 309 269 268

90 388 303 375 350 344

99.5 426 340 404 392 413

Thiophenes 8 0 0 0 0

Benzothiophenes (BT) 2 69 0 0 0

Substituted BT’s 2793 1083 0 26 0

Di Benzothiophene (DBT) 222 110 0 7 0

C2-DBT’s 3453 436 72 266 154,6 DiMethyl DBT 199 0 78 29 43C3-DBT’s 4410 0 17 370 24


pared to the SR, and slightly higherAPI gravities, despite having a high-er total aromatic content. Otherchanges to note are the fact thefeed nitrogen content stays fairlyconstant, and the mono aromaticcontent is higher and PNA contentlower for these blends compared tothe SR feed.

Figure 1 summarizes some of thepilot plant data comparing the SRand LCO feed blends. It shows thatthe SR diesel requires a 23˚Cincrease in temperature to go fromabout 100 ppm sulfur down to 10ppm sulfur at base LHSV and pres-sure. The LCO blend requiresalmost 11˚C higher temperature toachieve the same product sulfur rel-ative to the SR feed. The productfrom the LCO blend has a two tothree number lower API comparedto the SR product, and hydrogenconsumption increases significantlyfor the LCO blend due to saturationof additional polyaromatic com-pounds found in the LCO. These lat-

Table IIBlended Diesel Feedstock Analysis

Light SRGas Oil 20% LCO

20%20% Syncrude

20%EB Diesel FB Diesel

Sulfur, wt.% 1.11 0.95 0.88 0.92 0.92

Nitrogen, wppm 138 158 144 179 131

Specific Gravity 0.8635 0.8668 0.8593 0.8589 0.8592

Aromatics, vol.%

Total 24.18 34.58 30.1 29.09 30.12

Mono 14.47 19.7 21.2 20.33 21.94

Poly 9.71 14.9 8.8 8.76 8.18

Distillation, D2887, ˚C

0.5 141 125 142 129 150

10 256 220 243 228 238

50 316 301 314 308 311

90 388 379 383 381 384

99.5 426 424 423 424 427

Thiophenes 8 12 8 10 8

Benzothiophenes (BT) 2 13 1 1 0

Substituted BT’s 2793 2279 2161 2105 1861

Di Benzothiophene (DBT) 222 206 35 148 133

C2-DBT’s 3453 2497 2324 2809 2464

4,6 DM-DBT 199 119 116 148 130

C3-DBT’s 4410 3598 3508 4061 3583

Figure 1Activity Comparison on SR and Blended SR/LCO

0

6

11

17

22

28

33

39

0 20 40 60 80 100 120

LCO

SR

Req

uir

edTe

mp

erat

ure

Incr

ease

,C

Product Sulfur, ppm


ter consequences set limits on theamount of LCO which can beprocessed and still meet productcetane specifications and hydrogenavailability constraints.

Results indicate that both feedshave similar API number upgrades(i.e. product – feed) as the reactorincreases in temperature; however,the actual product API is different atequal product sulfur. Even thoughthe LCO blended feedstock requiresa higher temperature to achieve thesame product sulfur, the productAPI is still about a full number loweras shown in Figure 2.

The LCO also has the additionalissue of increasing hydrogen con-sumption when added to the ULSDoperation. Figure 3 compares thearomatic saturation achieved on theblended LCO feedstock as com-pared to the SR. The majority of thearomatic saturation occurs with thepoly aromatic compounds and, asshown in Table II, the LCO blendcontains significantly more PNA’scompared to the SR feed. Thehydrogen consumption is estimatedto be 22-27 Nm3/m3 higher for theLCO blend at 10 ppm product sulfur.The figure above shows that pro-cessing LCO is significantly moredifficult than processing the SRfeed. One option to gain back someof the lost activity is to change the

end point of the LCO in the feed. ARTcompleted pilot plant testing on anLCO stock as received and the sameLCO with a 22˚C end point reductionto simulate how this can affect catalystperformance. Table III lists the majorcomponent analysis of the two LCOfeeds. The decrease in endpoint low-ers the total sulfur by almost 1000ppm and total nitrogen decreases by129 ppm.

The impact this degree of LCO end-point reduction has on ULSD perform-ance is over 17˚C difference in activitywhich corresponds to additional life in

the hydrotreater. A comparison ofthe two LCO feeds blended at 30%into SR feed is shown in Figure 4.

The addition of LCO has a majorimpact on activity for both the lowand high endpoint LCO materials.The required temperature increasefor ULSD in going from 0 to 30%LCO for the lower endpoint materialis about 0.7˚C per percent LCO.Processing the higher endpointLCO increases the required temper-ature to about 0.8˚C per percentLCO. Figure 5 demonstrates thismore clearly in the form of a plot ofthe required temperature increaseas a function of LCO content.Notice from the chart that the activ-ity effects are not exactly linear withincreasing LCO content. The first15% LCO has a larger impact onactivity than the next 15%.

The diesel products from an EB unit,a FB unit and the synthetic crudediesel provide very different sulfurdistribution patterns compared tothe SR feed and LCO shown inTable I. Almost all of the sulfurspecies in those feeds are multi-substituted dibenzothiophenes, theso-called hard sulfur species. Thespecies groupings from sulfur spe-ciation using a GC-AED technique,however, indicate little about whatthe actual molecular structure is

Figure 2Comparison of Product Gravity for the SR and LCO Blend

0.855

0.852

0.850

0.847

0.845

0.842

0.840

0.837

0.835

0.832

0 11 22 33 44 55 66

Increasing WABT, ˚C

Sp

ecif

icG

ravi

ty

LCO

SR

Figure 3Comparison of Aromatic Saturation


Ch

ang

ein

Tota

lAro

mat

ics,

vol.%

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

10 11 22 33 44 55 66

LCO

SR


since the basic technique sepa-rates out the sulfur based on boilingpoint distribution. The sulfur mole-cules left in these previously treatedfeeds have already been processedonce in a high temperature, highpressure hydrotreating application.Those conditions easily remove themajority of sulfur molecules andleave only those sulfur species thatare multi-ring, sterically hinderedmolecules and other aromatic nitro-gen compounds. It is these speciesthat require a greater level of satu-ration or ring opening before thenitrogen or sulfur can be removed.It is likely for there to be very lowconcentrations of multiple-ring, par-tially saturated compounds thatneed to be more fully saturated inorder to remove the sulfur. This isenough to make it more difficult toproduce 10 ppm sulfur productfrom such feeds.

An understanding of the upstreamprocessing is important when con-sidering the use of syntheticcrudes. Production of syntheticfuels involves a combination of sev-eral processes in order to accom-modate downstream processing.These upstream processes includecoking or an ebullating bed residoperation, followed by a hydrotreat-ing or hydrocracking operation inorder to produce a lighter gradematerial. These products are thenblended in with other heavier mate-rials as a diluting or cutting stockand sent downstream as syntheticcrude. The synthetic diesel used inthis work is taken from a productdiesel cut from a synthetic VGOhydrocracker. Figure 6 shows theactivity difference between the SRand the blended SR/syntheticdiesel. Note that at higher productsulfur, the two feedstocks respondfairly similarly to each other. As theapplication becomes more de-manding, the required reactor tem-perature increases dramatically forthe synthetic diesel feed as com-pared to the SR feed. The blendedfeed requires more than 14˚C high-er temperature relative to the SR toachieve ULSD sulfur levels.

Table IIIImpact of End Point Reduction on FCC LCO

Type

Specific GravitySulfur, wt.%Nitrogen, ppmAromatics, lv.%

Mono-, lv.%Poly-, lv.%

Dist., D2887, ˚CIBP10%50%70%90%FBP

LCO(Low FBP)

0.9450.948708

66.8622.6544.21

121218277316358411

LCO(High FBP)

0.9641.041837

68.8118.4450.37

124222288327371433

Figure 4Impact of LCO Endpoint Reductionon Hydrotreating Performance

Product Sulfur, ppm

Req

uir

edTe

mp

erat

ure

Incr

ease

,˚C

0

11

22

33

44

55

66

78

89

0 100 200 300 400 500 600

30% Hi FBP LCO

SR

30% Lo FBP LCO

Figure 5Activity Comparisons at Different LCO

FBP and Concentration

% LCO

Req

uir

edTe

mp

erat

ure

Incr

ease

,C

0

3

6

8

11

14

17

19

22

25

28

0 5 10 15 20 25 30 35

Hi EP LCO

Lo EP LCO


It is reasonable to expect that theupstream hydroprocessing of thesynthetic diesel material results in afeed which behaves similarly toother previously hydrotreated feed-stocks like those from the EB andFB resid applications. Two feed-stocks from these sources areshown in Figure 7. These two feed-stocks have a remarkably similarresponse as that observed for thesynthetic diesel feedstock. Thefixed bed diesel fraction, which hassignificantly lower sulfur and nitro-gen than the other two feedstocks,shows over 22˚C higher SOR thaneither the EB or synthetic diesels at10 ppm sulfur. These data showthat upstream processing prior totreating in a ULSD unit can have adramatic effect on the activity of theunit and consequently decreasecycle length.

Figure 8 examines how the productAPI is changed during processingfor the synthetic diesel blend. Ascan be seen, there is only a onenumber increase in product APIover an almost 56˚C WABT changecompared to greater than two num-ber increase for the SR feed over asimilar temperature span.

Aromatic saturation in the ULSD unitis also a concern in order to meetrequired cetane and aromatic tar-gets. The higher temperaturerequired to process these previous-ly processed streams may make itdifficult to achieve much aromaticssaturation because of the approachto the thermodynamic equilibriumlimit for aromatic saturation. Figure9 compares the aromatic saturationachieved for the SR diesel and thesynthetic diesel blend. The synthet-ic diesel has a low level of poly aro-matic compounds, and the blendactually has a slightly lower concen-tration of PNA’s compared to the SRfeed. Less saturation is achievedon the synthetic blend, probably areflection of the fact that mono aro-matic molecules are the predomi-nant species, and these are quitedifficult to saturate. The equilibriumlimit on conversion is readily appar-ent in the figure. The synthetic

Figure 6Activity Comparison of the SR and Synthetic Diesel Blend

Product Sulfur, ppm

Req

uir

edTe

mp

erat

ure

Incr

ease

,C

0

6

11

17

22

28

33

39

44

50

0 20 40 60 80 100 120

SR

Synthetic

Figure 7Activity Comparison of Previously Hydrotreated Streams

Product Sulfur, ppm

Req

uir

edTe

mp

erat

ure

Incr

ease

,˚C

0

11

22

33

44

55

66

0 20 40 60 80 100 120

FB

Synthetic

EB

Figure 8Comparison in Specific Gravity


Sp

ecif

icG

ravi

ty

0.847

0.845

0.842

0.840

0.837

0.835

0.832

0 11 22 33 44 56 67 78 89

Syn Diesel

SR


diesel provides a two numberdecrease in total aromatics whilethe SR diesel has an almost 10 num-ber decrease. This can be prob-lematic if trying to meet an aromatictarget in the diesel pool.

When evaluating opportunities tohydrotreat previously treatedstreams for ULSD, the need toexamine the catalytic effects ofthese feeds is important. ART com-pleted a series of pilot tests usingthe synthetic diesel feed blend cov-ering a wide range in operating con-ditions. Figure 10 summarizessome of the results for one of ART’shigh activity CoMo catalysts. Thebase case condition was again 48BAR, 232 Nm3/m3 hydrogen/oil ratioand 0.7 LHSV. As you can see fromthe figure, the base case conditionsresult in the highest start of run tem-perature for ULSD. Increasing theH2/Oil ratio to 463 Nm3/m3 results ina decrease in the SOR WABT ofover 8˚C. The third data set showsresults for higher hydrogen partialpressure, 90 BAR, and 463Nm3/m3hydrogen to oil ratio. Thisresults in a gain of 14˚C lower SORcompared to the base case condi-tions or an incremental 6˚C lowertemperature due to the increase inhydrogen pressure. Finally, increas-ing the hydrogen rate to 712Nm3/m3 at high pressure providesover 17˚C lower SOR as comparedto the base case system, but onlyan additional 3˚C relative to the highpressure lower gas rate case.These data clearly demonstrate thesignificant benefits of increasinghydrogen partial pressure whentreating these types of difficultfeeds.

Making the switch to using a NiMocatalyst in this application has muchmore significant effect on unit per-formance. In Figure 11 the basecase conditions of low pressureand low hydrogen/oil ratio actuallyresult in activity which is similar towhat was observed at these condi-tions for the CoMo catalyst. Afterincreasing the hydrogen rate at lowpressure, the all NiMo system gainsover 14˚C relative to the base condi-

Figure 9Change in Total Aromatics on SR and Synthetic Diesel

Tota

lAro

mat

ics,

vol.%

15.0

17.0

19.0

21.0

23.0

25.0

27.0

29.0

31.0

33.0

0 11 22 33 44 56 67 78 89

Increasing WABT, °C

Syn Diesel

SR

Figure 10CoMo Catalyst Activity on Synthetic Diesel

Req

uir

edTe

mp

erat

ure

Incr

ease

,˚C

Product Sulfur, ppm

0

11

22

33

44

55

66

0 20 40 60 80 100 120

48 BAR & 232 H2/Oil

48 BAR & 463 H2/Oil

90 BAR & 463 H2/Oil

90 BAR & 712 H2/Oil

Figure 11NiMo Catalyst Activity on Synthetic Diesel

Req

uir

edTe

mp

erat

ure

Incr

ease

,˚C

Product Sulfur, ppm

0

11

22

33

44

55

66

0 20 40 60 80 100 120

49 BAR & 232 H2/Oil

48 BAR & 463 H2/Oil

90 BAR & 463 H2/Oil

90 BAR & 712 H2/Oil


tions, a larger activity gain thanobserved for the CoMo catalyst.The activity benefit increases toover 22˚C lower required tempera-ture at 1300 psia, and increasingthe hydrogen rate to 712 Nm3/m3

results in over 28˚C lower tempera-ture compared to the base condi-tions. The NiMo catalyst is at least11˚C more active than the CoMocatalyst at this last set of conditions.

Clearly there is a need to maximizesaturation when treating these pre-processed types of feeds. Anyincrease in hydrogen partial pres-sure helps this and, as the data justdiscussed indicates, the catalystselection has a significant impact.High activity NiMo catalysts are bet-ter saturation catalysts compared to

high activity CoMo catalysts, and thisappears critical to removing the hard-er sulfur species present in these pre-processed feeds. In units that areconstrained by limited hydrogen orlower hydrogen pressures, the use ofeven a small amount of NiMo catalystwill prove to be beneficial in order toremove the remaining difficult sulfurs.

Advanced Refining Technologies canwork closely with refining technicalstaff to help plan for processingopportunity feeds such as those dis-cussed above. One of the keys isbeing aware of the potential impactprocessing certain feeds will have onunit performance. Feeds which havebeen previously processed presentunique challenges and ART is wellpositioned with its experience at pro-

viding customized catalyst systemsfor ULSD applications. Opportunityfeeds provide yet another objectiveto consider when designing theappropriate catalyst system to max-imize unit performance.

References

1. Olsen, C., Krenzke, L.D., Watkins, B.,AICHE Spring National Meeting, NewOrleans, March 2002.

2. Krenzke, D., Armstrong, M., 2001 ERTCMeeting, Madrid, Spain.

3. Olsen, C., Krenzke, L.D., 2005 NPRAAnnual Meeting, Paper AM-05-17.

4. Olsen, C., D’Angelo, G., 2006 NPRAAnnual Meeting, Paper AM-06-06.

5. Olsen, C., Watkins, B., Shiflett, W., ERTCMeeting, Barcelona, Spain, November 2007


emand for higher performancein diesel engines has resultedin an increase in minimum

cetane numbers for diesel fuel. It isexpected that the desire for highercetane will continue as indicated bythe recommendations of the WorldWide Fuels Charter. Thus, it is impor-tant for refiners to understand theeffects of both feedstock and pro-cessing parameters on the cetane ofdiesel fuel to enable them to moreeffectively manage their distillatehydrotreating units to meet ever morestringent fuels specifications.

While some diesel is produced inhydrocrackers, the vast majority ofdiesel is processed in dieselhydrotreaters (DHT’s) which usuallyco-process streams such as FCC

Cetane Improvement In DieselHydrotreating

Greg RosinskiTechnical Services Engineer



DLCO, LCGO, SR diesel, andKerosene. The units processingsignificant amounts of crackedstocks need special attention inorder to meet product cetanerequirements. To understand whythis is so it is necessary to knowwhat cetane is, and how the differ-ent molecular species influence it.

The cetane number is a measure ofthe ignition quality of diesel fuel andis based upon the compoundcetane or hexadecane which isassigned a cetane number of 100.It is analogous to the octane num-ber in gasoline. Gasoline octaneincreases with olefin, aromatic, andiso-paraffin contents, whereascetane number increases withparaffin and naphthene contents.

reprinted fromCatalagram® 106 SE 2009 39

Table ICetane Number of Pure Compunds

Compound Formula CetaneNumber

n-Decane C10H22 76n-Pentadecane C15H32 95

Paraffins

n-Eicosane C20H42 1103-Ethyldecane C12H26 484,5-Diethyloctane C12H26 20Heptamethylnonane C16H34 158-Propylpentadecane C18H38 487,8-Diethyltetradecane C18H38 67

Isoparaffins

9,10-Dimethyloctadecane C20H42 59Decalin C10H18 483-Cyclohexylhexane C12H24 362-Methyl-3-cyclohexylnonane C16H32 70

Naphthenes

2-Cyclohexyltetradecane C20H40 571-Methylnaphthalene C11H10 0n-Pentylbenzene C11H16 8Biphenyl C12H10 211-Butylnaphthalene C14H16 6n-Nonylbenzene C15H24 502-Octylnaphthalene C18H24 18

Aromatics

n-Tetradecylbenzene C20H34 72

Thus, a fuel with a high cetane valuehas low octane and visa versa.

Table 1 lists some pure compoundsand their corresponding cetanenumber. As can be seen, paraffins,particularly normal paraffins, havevery high cetane numbers whilearomatics, especially naphthalenetype aromatics, have very lowcetane numbers. Certain distillaterange materials like FCC LCO arehigh in naphthalenes whichexplains the low cetane number ofLCO feedstocks.

The actual cetane number is rarelyanalyzed in refineries since itrequires a specialized motor for itsdetermination. Most refiners’ usecetane index, typically, ASTM D-976and ASTM D-4737. D976 uses theAPI gravity and the 50% distillationpoint, whereas D4737 uses thegravity with the 10%, 50% and 90%distillation points. The two equa-tions are shown below.

ASTM D-976cetane index = -420.34+0.016*API2

+0.192*API*(log(T50))2+65.01*log(T50)–0.0001809 *T502

Where T50 is the D86 50% point indegrees °F

ASTM D-4737Cetane index= 45.2+0.0892*(T10-215)+[0.131+0.901* B]*[T50-260]+ [ 0 . 0 5 2 3 – ( 0 . 4 2 0 ) * ( B ) ] [ T 9 0 -310]+[0.00049]*[(T10-215)2

–(T90-310)2] + (107)*(B) + (60)*B2

Where: B = Exp[-3.5*(sp. gr. – 0.85)] –1 and the D86 temperatures are in °C

Figure 1 compares the cetane index(D976) for a number of different distil-late feed sources. It is readily appar-ent that FCC LCO’s have the lowestcetane while straight run (SR) materi-als have the highest cetane. Distillatefeeds derived from coking operationstend to have a cetane similar to SRmaterial, while kerosene tends to havesomewhat lower cetane owing to thelower boiling point. For the diesel

range materials, the feeds withlower API gravity (LCO) have lowercetane index demonstrating thatwithin a given boiling range the APIis a reasonable tool for estimatingthe cetane index.

Figure 2 shows the cetane index asa function of poly aromatics contentfor a variety of distillate feeds. TheLCO’s clearly have the highest con-centration of poly aromatics andcorrespondingly lower cetaneindex. The SR, LCGO and vacuumbottom gas oil (VBGO) all have con-siderably lower PNA content withhigher cetane index values com-pared to the LCO’s. Keroseneshave very low polynuclear aromatics(PNA) content, but because of thelower molecular weight (kerosenegenerally has compounds contain-ing less than 16 carbon atoms) thecetane index is slightly lower thanfor SR diesel material. The figuresmake it clear that when it comes tocetane, LCO is a problem due to thehigh PNA content.

Figure 1Cetane Index of Various Distillate Feeds

1.037 1.000 0.966 0.934 0.904 0.876

Feed Specific Gravity

Cet

ane

Ind

ex(D

976)

0.850 0.825 0.802 0.780

LCO

10

15

20

25

30

35

40

45

50

55

60

LCGO/VBGO Straight Run Kerosene

Figure 2Cetane Index and Polynuclear Aromatics (PNA’s)

Feed PNA’s, vol.%

Fee

dC

etan

eIn

dex

(D97

6)

LCO LCGO/VBGO Straight Run Kerosene

10

15

20

25

30

35

40

45

50

55

60

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Figure 3Effect of LHSV on Cetane in a Variety of Commercial Units

LHSV

Del

taC

etan

eIn

dex

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

14.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Refiner A Refiner B Refiner C Refiner D Refiner E Refiner F

Treating feedstocks that containLCO will become more challengingas LCO yields increase and cetanerequirements become more strin-gent. With this in mind, it is useful tosurvey the level of performance cur-rently being achieved in commercialdiesel hydrotreating units today.This will help to define what the rea-sonable level of cetane uplift thatcan be expected is, and if there is apractical maximum uplift that canbe achieved via hydrotreating. It isalso useful to ascertain whethercurrent operations indicate ifcetane changes (decreases) duringthe cycle. All of these are importantquestions for refiners interested inincreasing diesel yields from lowerquality feedstocks.

There are a number of parameterswhich influence cetane improve-ment in the diesel hydrotreater.Hydrogen partial pressure andLHSV are key operating conditionswhich effect the product cetane.Catalyst selection also plays animportant role since at higher pres-sures NiMo catalysts have a higherPNA saturation activity compared toCoMo catalysts.

Figures 3 shows the level of cetaneincrease (measured by delta cetaneindex) that has been achieved com-mercially as a function of unit LHSV.Generally speaking, as LHSVdecreases the potential cetaneimprovement increases. At a LHSVaround 1 hr-1 or less, cetane indexincreases of 10 or more numbersare achievable (provided the H2pressure is high enough), while at aLHSV greater than about 1.7 hr-1the cetane improvement is about 4numbers or less.

Figure 4 summarizes the cetaneincrease as a function of unit pres-sure. Not surprisingly, higher pres-sure units tend to achieve muchlarger cetane increases. In theseexamples, the cetane uplift is typi-cally less than 6 numbers when theunit pressure is less than 69 BARG.Cetane uplift increases to 8-10 num-bers as pressure increases beyond69 BARG. The data in Figures 3 and4 also suggest there might be a


reprinted fromCatalagram® 106 SE 2009 41

Figure 4Effect of Unit Pressure on Product Cetane

Reactor Inlet Pressure, BARG

Del

taC

etan

eIn

dex

Refiner A Refiner B Refiner C Refiner D Refiner E Refiner F

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

14.0

28 41 55 69 83 97 110 124 138 152

Figure 5Feed Gravity Has a Significant Impact on Cetane Uplift

Feed Specific Gravity

Del

taC

etan

eIn

dex

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

0.959 0.934 0.910 0.887 0.865 0.845 0.825 0.806

Refiner A Refiner B Refiner D Refiner E Refiner F

Figure 6API Uplift and Cetane Increasefor Several Commercial Units

Delta, API

Del

taC

etan

eIn

dex

Refiner A Refiner B Refiner D Refiner E Refiner F

0

1

2

3

4

5

6

7

8

9

10

11

0 1 2 3 4 5 6 7 8 9 10

practical limit to cetane improve-ment achieved from typicalhydrotreating. Comparing thecetane uplift achieve by Refiners Aand C shows about 8-10 numberimprovement for both units despitethe difference in operating pressureat similar LHSV.

Figure 5 summarizes the commer-cial data in another way. It showshow the cetane increase correlateswith the API gravity of the feed. Ingeneral, the cetane uplift increasesas the feed API decreases. Figure 6shows how the observed APIincrease correlates with the cetaneindex increase. This data showsthat the API uplift is a reasonablepredictor for the cetane increase.

The hydrogen consumption isanother important considerationwhen discussing cetane improve-ment. There is a general rule ofthumb that says the hydrogen con-sumption is roughly equal to (100*API Uplift) or (100* Cetane uplift).Averaging the H2 consumptionrequired for the observed cetaneincrease with the units discussedhere indicates that the H2 consump-tion varies from about (80*Cetaneuplift) at low pressure (Refiner D) to(150-175* Cetane uplift) for the highpressure units (Refiners A & C). Thedata suggests the rule of thumb is areasonable estimate for H2 con-sumption for units operating belowabout 69 BARG.

These data demonstrate that as theunit conditions (LHSV and pressure)get more favorable for PNA satura-tion, the cetane uplift increases.However, is cetane uplift constantduring an entire cycle?

Figure 7 summarizes the observedcetane from three ULSD units cur-rently using SmART systems.Refiner A is a high pressure unit witha LHSV around 1. The feed to thisunit contains 40-50 vol.% LCO. Thisunit has not experienced a signifi-cant decline in cetane uplift duringthe cycle. Refiner B is a higherLHSV unit, with a lower pressurethan Refiner A, but the feed is rela-

Figure 7Variation in Cetane Uplift During a Cycle

Days on StreamD

elta

Cet

ane

Ind

exRefiner A Refiner B Refiner C

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

0 100 200 300 400 500 600 700 800 900 1000 1100

Figure 8The Catalyst System Has a Large Impact on Cetane Uplift

Temperature, ˚C

Cet

ane

Ind

exIn

crea

se

NiMo CoMo SmART

4

5

6

7

8

9

10

11

12

13

14

15

327 329 332 335 338 341 343 346 349 352 354

tively light with about 35-40 vol.%LCO and LCGO. Despite the lowerpressure and higher LHSV, thisrefiner also did not see an appre-ciable decline in cetane uplift dur-ing the cycle. Refiner C is a higherpressure unit with a lower LHSVcompared to Refiner B. The feed ishigh in sulfur with large (>80 vol.%)amounts of cracked stock, espe-cially LCO. This unit does show aslow, steady decline in cetane uplift;the cetane uplift is 2-3 numberslower after more than two years onstream. This suggests that unitswith difficult feeds containing highfractions of LCO and other crackedstocks, or units without sufficienthydrogen, will experience decreas-ing cetane uplift during the cycle.

As mentioned previously, the cata-lyst system will also have an impacton the degree of cetane upliftachieved in a hydrotreater. It iscommon knowledge that NiMo cata-lysts have a higher saturation activi-ty than CoMo catalysts, and there-fore a NiMo catalyst is expected todeliver greater cetane uplift. Figure8 summarizes pilot plant data whichdemonstrates this. These data weregenerated using a 50% LCO con-taining feed, and shows that theNiMo catalyst results in almost twicethe cetane uplift compared to theCoMo catalyst. The SmART CatalystSystem, which utilizes both theCoMo and NiMo catalyst, results ina cetane uplift which is nearly 2numbers higher than the all CoMosystem with only a small increase inhydrogen consumption. For H2 con-strained refiners this is an idealsolution for improving the productcetane.


reprinted from Catalagram 105 2009 43

roduct color is a common con-cern for refiners with a numberof petroleum products includ-

ing kerosene, jet fuel, diesel fuel andlube base oils. With the introduction ofultra low sulfur diesel (ULSD) the issueof diesel product color has becomemore of an issue as the typical ULSDunit cycle length may now be limitedby color degradation of the product.Refiners have been uncertain aboutend of run (EOR) reactor outlet tem-peratures with expectations in therange of 377-404˚C. The typicalULSD unit has a deactivation rate inthe range of 1.1-1.7˚C/month so anincrease in EOR temperature of 6-11°C has a significant impact on arefiner’s planning and economics.

Figure 1 summarizes data from a com-mercial ULSD unit using ART cata-lysts. The data shows that in this case

the product color exceeded 2.5ASTM, the pipeline color specifica-tion for diesel, at a reactor outlettemperature above 388°C. The feedto this unit contained 30% LCO andit was operated at 1.0 LHSV and 59BARG inlet pressure.

It is well known that the color of distil-late products is affected by the reac-tion conditions in the hydrotreater,especially temperature and hydrogenpartial pressure. As (outlet) tempera-ture increases and/or hydrogen par-tial pressure decreases, the productcolor degrades. It is also generallyaccepted that the species responsi-ble for color formation in distillates arepolynuclear aromatic (PNA) mole-cules. Some of these PNA’s aregreen/blue and fluorescent in colorwhich is apparent even at very lowconcentrations of these species.Certain nitrogen (and other polar)

Greg RosinskiTechnical Services Engineer

Brian WatkinsTechnical Services Engineer



P

Factors Influencing ULSD Product Color

compounds have also been impli-cated as problems for distillateproduct color and product instabili-ty. These species can polymerize toform condensed aromatic struc-tures which tend to be green to yel-low/brown in color and can alsoform sediment via oxidation andfree radical reactions.(1) Work con-ducted by Ma et.al.(2) concluded thatthe specific species responsible forcolor degradation are anthracene,fluoranthene and their alkylatedderivatives. These are both threeringed aromatic structures and areshown in Figure 2.

PNA’s such as these are readily sat-urated to one and two ringed aro-matics under typical dieselhydrotreating conditions at start ofrun (SOR), but as the temperatureof the reactor increases towardsEOR, an equilibrium constraint maybe reached whereby the reversedehydrogenation reaction becomesmore favorable. At some combina-tion of low hydrogen partial pres-sure and high temperature thedehydrogenation reaction predomi-nates and PNA’s begin to formresulting in a degradation of thecolor of the diesel product. Otherwork completed by Takatsukaet.al.(3,4) showed that the color bod-

ies responsible for diesel productcolor degradation were concentratedin the higher boiling points in thediesel (>250°C). This suggests thatcolor can be improved by adjustingthe diesel endpoint. They also sug-gest that the color bodies responsiblefor color formation in desulfurizeddiesel are newly formed PNA struc-tures from desulfurized aromatic com-pounds.

To learn more about color degradationin ULSD, ART completed a pilot plantstudy which investigated diesel prod-

uct color over a wide range of oper-ating conditions. The study utilizedspent ART CDXi, a premium highactivity CoMo catalyst for ULSD.The sample of spent catalyst hadbeen in commercial diesel servicefor well over a year and had a car-bon content of 10.9 wt.%. The test-ing program included straight run(SR) diesels, a 30 vol.% LCO blendand a 30 vol.% light coker gas oil(LCGO) blend. The properties ofall the feeds are listed in Table I.The test was designed to examinethe effects of H2 partial pressure,H2/Oil ratio and temperature onULSD product color. H2 partialpressure varied from 20-80 BARand the H2/Oil ratio covered therange of 125-375 Nm3/m3.

Figure 3 shows how the diesel prod-uct color changes with temperatureand pressure for the straight runfeed (SR #1). Not surprisingly, pres-sure clearly has a significantimpact. At the lowest operatingpressure, which corresponds to 21-24 BAR H2 pressure, the productcolor exceeds 2.5 ASTM at a tem-perature greater than 393-399°C.Doubling the unit pressure to 55BARG allows the temperature toincrease to 416°C before the prod-uct color reaches 2.5 ASTM, and ateven higher pressures the productcolor is well below 2.5 ASTM for allpractical temperatures encounteredin ULSD processing. At these con-

Pro

du

ctC

olo

r(A

ST

M)

Reactor Outlet Temperature ˚C

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

304 316 327 338 349 360 371 382 393 404 416

Figure 1ULSD Product Color Using a SmART Catalyst SystemTM

anthracene fluoranthene

Figure 2Primary Fluorescence Species in

Hydrotreated Diesel (Ref 2)



ditions the H2 partial pressureincreases by a factor of about 3.4going from 28 BARG up to 83 BARGtotal pressure for temperaturesaround 400°C.

The data in Figure 3 were generatedat the low end of H2/Oil ratios inves-tigated. Figure 4 shows the effect ofincreasing the H2/Oil ratio at 28BARG on the SR #1 feed. At this lowpressure, the H2/Oil ratio has a sig-nificant impact on product color.The data show that the temperaturecan be increased from 396°C towell above 404°C before productcolor exceeds 2.5 ASTM. AT 28BARG total pressure and 404°C,changing the H2/Oil ratio from 125-375 Nm3/m3 results in a 10%increase in H2 partial pressurewhich appears to be enough tokeep the reaction environment onthe favorable side of the hydro-genation-dehydrogenation equilibri-um curve. At higher operating pres-sures the impact of increasing theH2/Oil ratio is reduced when pro-cessing the SR feed, but still has apositive effect on suppressing prod-uct color.

As might be expected, adding LCOto the ULSD unit feed makes theproduct color situation worse.Figure 5 compares the productcolor for the SR feed and the 30%LCO feed at 375 Nm3/m3 H2/Oilratio and two pressures. The SRfeed results in acceptable color

Specific GravitySulfur, wt.%Nitrogen, wppmTotal Aromatics, vol.%PNA’s (2-ring+), vol.%ASTM ColorDistillation (D2887), ˚C

IBP10%50%90%FBP

SR #10.8588

0.6812031.510.7L3.5

135234304316447

SR #1/LCO0.8887

0.9329340.021.9L6.5

129226296373449

SR #20.85271.1212727.39.5

L2.0

106247323361393

SR #2/LCGO0.8569

1.3424930.110.8L5.5

114225304353401

Table IFeedstock Properties

AS

TM

Co

lor

Temperature, ˚C

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

360 371 382 393 404 416 427

Straight Run

55 BARG

28 BARG

83 BARG

Figure 3Product Color Improves with Pressure

AS

TM

Co

lor

Temperature, ˚C

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

360 366 371 377 382 388 393 399 404 410

Straight Run

125 Nm3/m3 H2

375 Nm3/m3 H2

Figure 4Product Color Improvement with Increased H2/Oil Ratio

over the wide range of tempera-tures for both pressures shown.This compares with the 30% LCOfeed which goes off color at about388-393°C at 55 BARG; and at 83BARG the temperature can exceed404°C before reaching 2.5 ASTMcolor. This data demonstrates thesignificant impact that pressure hason diesel product color when pro-cessing feeds that contain LCO.

Figure 6 demonstrates the effects ofthe H2/Oil ratio on product colorwhen processing the 30% LCOfeed. It shows the temperature atwhich the color reaches 2.5 ASTMas a function of H2/Oil ratio for both55 and 83 BARG total pressure.The temperature increases by about14°C when the H2/Oil ratio isincreased from 125 to 375 Nm3/m3.That range of H2 rates correspondsto an increase in hydrogen partialpressure of 5-10%

The pilot plant program also investi-gated the effects of a coker derivedmaterial on ULSD product color.Figure 7 compares the productcolor for the second SR feed and a30% LCGO/70% SR #2 blend at 55BARG. The data indicates that thefeed containing LCGO behaves sim-ilarly to the SR feed. In both casesthe outlet temperature can exceed416°C before product colorapproaches the ASTM 2.5 level.This is not surprising when compar-ing the properties of the two feeds.The aromatics level, and in particu-lar the PNA concentrations, areessentially the same for the SR andthe coker blend. Compare this withthe LCO blend shown in Table Iwhere the PNA’s are twice that ofthe SR or LCGO feeds.

As mentioned previously, it is gen-erally accepted that product coloris related to PNA’s, and earlier workhas concluded that specific three-ringed aromatics are responsiblefor color degradation in diesel.Figure 8 shows a comparison ofthe product PNA’s (three-ring aro-matics) and diesel product color

AS

TM

Co

lor

Temperature, ˚C

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

338 349 360 371 382 393 404 416 427

LCO

SR

55 BARG

83 BARG55 BARG

83 BARG

Figure 5Comparison of Product Color for SR and 30% LCO

Tem

per

atu

refo

r2.

5A

ST

MC

olo

r,˚C

H2/Oil Ratio, Nm3/m3

371

377

382

388

393

399

404

410

416

89 178 267 356 445

55 BARG

83 BARG

Figure 6Effects of H2/Oil Ratio on Product Color for 30% LCO

Temperature, ˚C

AS

TM

Co

lor

0.0

0.5

1.0

1.5

2.0

338 349 360 371 382 393 404 416 427

SR #2

LCGO

Figure 7Product Color Comparison for LCGO and SR



for all the feeds and conditions ofthe study. It is readily apparent thatthe PNA’s correlate reasonably wellwith product color..

From these data it is clear thathydrogenation of PNA’s is key tomaintaining acceptable productcolor in ULSD. This suggests a cou-ple of approaches that allow anincrease in EOR outlet temperaturesand thereby increase the ULSD unitcycle length.

One approach which has been putto commercial practice is toincrease quench to the bottom bedof the hydrotreater. This accom-plishes two things which are impor-tant to maintaining a good environ-ment for hydrogenation of PNA’s. Itreduces the outlet temperature andhelps to increase the outlet hydro-gen partial pressure relative to no orlower amounts of quench.

This, of course, requires that theupper beds of the hydrotreater berun at higher WABT’s in order tomaintain the required HDS conver-sion. This means that the furnacemust have sufficient capacity toachieve the higher inlet tempera-tures. Operating in this manneroffers the potential to add an addi-tional 6-11°C on to the cycle lengthdepending on the unit capabilities(furnace, quench capacity).

Another approach, which may beimplemented with the one just dis-cussed, involves adjusting the feed tothe unit. The data from this workshows the significant impact LCO hason diesel product color. Reducing (oreliminating) the amount of LCO in thefeed will help to suppress productcolor degradation as the unitapproaches EOR. There is also datashowing that the color bodies thatcause problems for ULSD tend to beconcentrated at the higher boilingpoints of the distillation on thefeed/product. Reducing the endpointof the LCO reduces the concentration

of these species which will helpmaintain acceptable product coloras the unit moves towards EOR.

References

1. J. Pedley et.al, ACS Division of FuelChemistry, 35 (4), 1100-1107 (1990).

2. X. Ma et. al., Energy and Fuels, 10, pp91-96 (1996).

3. T. Takatsuka et.al., 1991 NPRA AnnualMeeting, Paper AM-91-39.

4. T. Takatsuka et.al., Journal of the JapanPetroleum Institute, Vol. 23, No. 2, pp 179-184, 1992.

Product PNAs (3 rings+), vol.%

AS

TM

Co

lor

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.0 1.0 2.0 3.0 4.0 5.0

SR

LCO

LCGO

Figure 83+ Ring Aromatics Correlate with Diesel Product Color

ART delivers innovative and economic hydroprocessing catalyst solutions worldwide, helpingrefiners on their never-ending quest to upgrade difficult petroleum feedstocks into clean fuelsand other valuable products.

Supported by cutting edge research and development and world class technical service, thejoint venture between Chevron and Grace combines over 60 years of material science expertiseand catalyst formulation experience with over 3,300 unit-years operating experience. In addition,our partner affiliate licenses exceed 260 units across the globe.

Let ART be part of your solution. For more information on our products, contact us.

Advanced Refining Technologies ● 7500 Grace Drive ● Columbia, MD 21044 USAV +1.410.531.4000 ● F +1.410.531.8246 ● E artcatalysts.com

Hydroprocessing Catalysts from Chevron and Grace

Advanced Refining Technologies

Columbia, Maryland USA 1.410.531.8282 Fax 1.410.531.4540

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www.e-catalysts.comAdvanced Refining Technologies ® 2010

The information presented herein is derived from our testing and experience. It is offered, free of charge, for your consideration, investigation and verifi-cation. Since operating conditions vary significantly, and since they are not under our control, we disclaim any and all warranties on the results which mightbe obtained from the use of our products. You should make no assumption that all safety or environmental protection measures are indicated or that othermeasures may not be required.

GRACE®, GRACE DAVISON®, GR®, and SmART Catalyst System® are trademarks, registered in the United States and/or other countries, of W. R. Grace& Co.-Conn.

H-OIL® is a registered trademark of Axens North America, Inc. CHEVRON®, ICR®, LC-FINING™ is a trademark of Chevron Lummus Global. OCR® is aregistered trademark of Chevron Intellectual Property LLC. HOP® is a registered trademark of Japan Energy Corporation licensed to Advanced RefiningTechnologies LLC.

This presentation is an independent publication and is not affiliated with, nor has it been authorized, sponsored, or otherwise approved by any of the afore-said companies.

ART® and Advanced Refining Technologies® are trademarks, registered in the United States and/or other countries, of Advanced Refining TechnologiesLLC. ApART™ , AT™, DX™, LS™, HSLS™ and StART™ are trademarks of Advanced Refining Technologies LLC.

This trademark list has been compiled using available published information as of the publication date of this brochure and may not accurately reflect cur-rent trademark ownership.

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