Effective October 7, 2004, Porocel has expanded into the catalyst services market, representing three facilities previously owned by CRI International (Louisiana-USA, Luxembourg and Singapore). Now, in addition to offering our well established line of activated aluminas and inert bed supports, we add the following services for our refining and petrochemical industry customers: • State-of-the-art catalyst regeneration, featuring our groundbreaking

optiCATsm and revolutionary optiCAT Plussm processes • Unique ex situ catalyst presulfurizing, using our proprietary actiCAT®

process • High quality regenerated catalyst resale • Advanced, patented length and density grading

The attached article (originally created by CRI) provides more detailed information regarding our new products and capabilities. While the name has changed, the commitment to technology, quality and value hasn’t. With three strategically located plants, we’re ideally positioned to service your needs anywhere in the world. Please visit our web site at www.porocel.com to learn more about our Catalyst Services business and the other fine products and services that Porocel offers.

HYDROCARBON ENGINEERING DECEMBER 1999 39

Driven by cost pressures and increasingly stringentenvironmental legislation, refiners’ use of ex-situ cat-alyst regeneration continues to grow. Refiners con-

tinue to add hydroprocessing capacity to meet lower prod-uct sulfur specifications, while stricter regulations on thedisposal of spent catalyst are encouraging refiners to max-imise reuse of catalyst.

With the increased use of regenerated catalyst, it is crit-ical that refiners understand how the material will performrelative to fresh catalyst, because the downside risk of poorperformance in a unit can quickly erase any benefits. CRIdoes extensive testing of regenerated catalyst to ensurethat it will perform to expectations. This testing includesmeasurement of catalyst physical and chemical propertiesas well as directly measuring catalyst activity in a pilotplant. CRI has fully equipped analytical laboratories at eachof its four plants worldwide, as well as automated four reac-tor Xytel pilot plants at research centres in Singapore andThe Woodlands, Texas, for evaluating catalyst perfor-mance.

Through this combination of analytical and performancetesting, CRI has been able to correlate the effect of twocommon catalyst contaminants, arsenic and vanadium,with regenerated catalyst performance.

Catalyst deactivationHydroprocessing catalysts deactivate continuouslythroughout an operating cycle. Reactor temperature is typ-ically increased to compensate for the declining catalystactivity until the end of run temperature is reached. Thepredominant deactivation mechanisms are coking and poi-soning. Other mechanisms can include fouling, pore block-age via coke or metals deposition, lossof surface area, and active metalsagglomeration or collapse of the sup-port via sintering. These mechanismscan be grouped into two categories:reversible and irreversible.

CokingOne of the most common reversibledeactivation mechanisms is coking.Active sites on the catalyst surface arecovered by carbon that is formed as thefeedstock is processed to remove sul-fur, nitrogen and aromatic species.There are many proposed mechanismsfor coke formation. One of the prevail-ing theories suggests that coke isformed from intermediate reactionproducts that condense or polymerise

on the catalyst surface. The rate and magnitude of cokedeposition is mainly affected by operating temperature,hydrogen partial pressure and feed quality. Depending onthe feedstock and operating conditions, spent catalyst car-bon concentrations can vary from <5 wt% to >30 wt%.

REGENERAREGENERATED TED CACATTALALYST PERFORMANCEYST PERFORMANCE

In an industry where cutting costs can make a competitive difference,and environmental regulations are tightening, Patrick Gripka and Sal

Torrisi, CRI International, Inc., USA, consider the practical aspects of reusing catalysts, in particular the effect of arsenic and

vanadium on regenerated catalyst performance.

Figure 1. Effect of arsenic on regenerated catalyst activity(NiMo and CoMo hydrotreating catalysts).

CRI uses 4-reactor Xytel pilot plants at its researchcentres in Singapore and Texas to directly measureregenerated catalyst performance.

PoisoningCatalysts can also be subjected to irreversible deactivationfrom permanent poisons, such as contaminant metals.These poisons degrade performance by occupying activesites and blocking pores. Common contaminant metals andtheir typical source are listed in Table 1.

There has been a general trend toward increased feedmetals contamination as refiners push for longer cyclelengths while processing lower quality crudes. This resultsin higher contaminant metal levels on spent catalyst. Themetals tend to selectively deposit toward the reactor inletand diminish in concentration down the length of the bed.Depending on the severity of service and degree of feedcontamination, the catalyst in the middle and bottom of thecatalyst system can often be regenerated and reused.

Not every metals contaminant deactivates the catalystto the same degree. Some selective poisons like arsenicgreatly affect performance at low concentrations. Thismeans that the contaminant is strongly coupled with theactive sites and not uniformly distributed across the cata-lyst surface. In other cases, contaminants like vanadiumand nickel can concentrate at the entrance to catalystpores. The phenomenon of pore mouth plugging restrictsmolecular access to active sites, reducing the overall per-formance of the catalyst. Since the deactivation mecha-nisms vary for different contaminants, it is extremely diffi-

cult to assess the combined effects ofmultiple poisons. Therefore, this articlewill focus on the effects of single cont-aminants, arsenic and vanadium, oncatalyst performance.

Catalyst regenerationThe catalyst regeneration processeliminates the reversible deactivationexperienced during an operating cycle.Coke contaminants can be effectivelyremoved from the catalyst by ex-situregeneration. This provides a con-trolled oxidation that removes the car-bon and regulates catalyst particletemperature. Effective temperaturecontrol during regeneration is critical toavoid irreversible damage like sinteringof catalytic metals, collapsing pores,and reducing surface area. A regener-ated catalyst that is relatively free ofmetals poisons can usually be restoredto >90% of fresh catalyst activity.

Estimating regenerated catalyst performanceAfter shutdown, it is critical to quicklyassess the regeneration potential of arepresentative cross section of spentcatalyst dumped from the unit. CRI typ-ically performs laboratory scale regen-eration on samples of the spent mater-ial and evaluates resultant physicaland chemical properties.

As ex-situ regeneration becamecommon in the late 1970s and 1980s,a regenerated catalyst’s surface arearecovery was used as the primary indi-cator of performance. However, boththe increase in complexity of catalysts

and the increased severity of the applications in whichthese catalysts are used have made the regenerated cata-lyst evaluation process more difficult. Other physical prop-erties like pore volume, pore size distribution, bulk density,particle length distribution and crush strength are requiredto assist in the catalyst reuse evaluation process. The infor-mation in Table 2 describes the importance of these criticalcatalyst properties.

In many cases, physical and chemical properties aloneare not enough to predict catalyst performance with a highenough degree of confidence. This frequently occurs whensome physical and chemical property measurements nar-rowly violate reuse criteria. In these situations, an activitytest using a hydrotreating pilot plant is required to moreaccurately gauge catalyst performance.

Arsenic contaminationHistorically, very little data have been collected on theeffect of arsenic contamination on catalyst performance.Most prior data were developed from studies involvingshale oil processing.

More recently, CRI has observed an increase in arseniccontaminated catalysts being evaluated for regeneration orresale potential. This phenomenon is likely to be the resultof increased processing of both As containing crude oilsand synthetic crudes generated from the processing of tar

40 HYDROCARBON ENGINEERING DECEMBER 1999

Figure 2. Arsenic distribution on individual regeneratedNiMo catalyst pellets.

CRI analyses metals contaminants on spent catalyst usinginductively coupled plasma spectroscopy (ICP).

sands. In any event, the number of regenerated samplesevaluated by CRI was sufficient to develop a correlation forboth NiMo and CoMo catalysts. It is important to distinguishthe effects of both types of catalysts because catalyst func-tionality and processing objectives vary greatly for NiMoand CoMo catalysts.

To quantify the effect of arsenic contamination on rela-tive activity, only regenerated catalysts with good physicalproperties and low levels of other contaminant metals wereexamined. All performance data represents activity relativeto the fresh parent of the regenerated catalyst.

Arsenic deactivation on NiMo catalystThe pilot plant activity data used to generate the NiMocurves shown in Figure 1 are based on a single commer-cial hydrotreating catalyst. The data indicate that arsenic isa fairly selective poison for NiMo catalysts; that is, it doesnot take very high contamination levels to quickly reducecatalyst performance. This is particularly true for the HDNor saturation function of NiMo catalysts, which appear to bevery sensitive to arsenic poisoning. Regenerated NiMo cat-alysts with good physical and chemical properties and <0.2wt% arsenic contamination may still provide acceptablecatalyst activity depending on the service requirements. Ingeneral, any NiMo catalyst having contamination exceed-ing that level should not be reused.

Arsenic deactivation on CoMo catalystThe CoMo activity data were generated using two differentcommercial hydrotreating catalysts. The data show that theeffect of arsenic deactivation appears to be less selective(but still significant) with CoMo catalysts, probably becausearsenic has a less inhibiting effect on desulfurisation reac-tions. Regenerated CoMo catalysts with good physicalproperties but with higher levels (<0.4 wt%) of arsenic con-tamination can still provide acceptable catalyst activity.

In both the NiMo and CoMo evaluations, the questionarose regarding the homogeneity of and possible variationof arsenic levels within a given sample. Was it possible thata few highly contaminated pellets could skew the arseniclevels, but have minimal impact on activity? To determinethe range of arsenic contamination within a sample, ninecatalyst pellets were randomly chosen from one of thearsenic contaminated NiMo catalysts. As shown in Figure 2,the range of arsenic contamination varied from 0.13 to0.47 wt%. The average arsenic contamination of these pel-lets (0.28 wt%) agreed favourably with the arsenic contami-nation measured on the bulk composite sample (0.27 wt%).The pellet analysis indicates that a range of arsenic conta-mination exists, but all particles appear to have measurablelevels of arsenic contamination. Thus, it does not appearthat a few highly contaminated pellets control the arseniclevel of the bulk catalyst system.

Vanadium contaminationVanadium and nickel are much more common catalyst poi-sons than arsenic and affect catalyst performance in verydifferent ways. Vanadium and nickel appear together natu-rally, but since vanadium is typically higher in concentrationand is not a catalyst constituent like nickel, the author haschosen to track vanadium for the purposes of this study.

Specific catalysts, called demet (demetallisation) cata-lysts, have been designed to capture vanadium and nickelwhile also providing some catalytic performance for HDSand HDN. These demet catalysts are commonly used inguard and lead reactor beds, providing protection for down-stream catalysts performing important HDS, HDN, HDCCRand aromatic saturation functions. Demet catalysts areusually disposed of following an operating cycle due toheavy contamination, however the downstream catalystcontaminated with much lower levels of vanadium are oftenconsidered for reuse.

NiMo catalysts are predominant in units processingvanadium contaminated feedstocks. CRI generated data inFigure 3 represent performance of several different widelyused NiMo catalysts. In most cases, there were very lowlevels of other metal contaminants so that the effect ofvanadium (and nickel) could be directly measured. All per-formance data represent activity relative to the fresh parent

HYDROCARBON ENGINEERING DECEMBER 1999 41

Table 2. Significance of catalyst physical propertiesCatalyst property ImportanceSurface area Regenerated catalyst surface area recovery is a

rough indicator of performance recovery. Absolute

surface area should not be used to compare

different catalysts.

Pore volume Indicates available space within catalyst pores that

can be filled with coke and metals contaminants.

Pore size distribution Affects surface area, performance, stability and

ability to withstand contamination.

Bulk density Increases with higher metals contamination

(higher particle density) and decreasing length

distribution (higher particle packing density).

Particle length Assists in determination of catalyst losses and

distribution expected unit pressure drop changes.

Crush strength Indicates structural strength of catalyst particles

and tendency for breakage, which can result in

unacceptably high reactor pressure drop.

Table 3. Pilot plant test summaryCoMo evaluations NiMo evaluations

Feedstock propertiesStraight run heavy gas 100

oil % by vol

Vacuum gas oil, % by vol 34

Light Cycle oil, % by vol 67

Gravity, ˚API 32.0 21.5

Density @ 15 ˚C, g/cc 0.8654 0.9248

Sulfur, wt% 1.83 2.11

Nitrogen, wppm 386 1145

GC distillation, ˚C

IBP 172 138

10% 252

50% 315 327

90% 383

FBP 424 509

Operating conditionsReactor inlet hydrogen 48 69

partial pressure, bar

Temperature, ˚C 330 330

LHSV, hr-1 1.5 1.5

Treat gas rate, Nm3/m3 169 337

Table 1. Contaminant metals on hydroprocessing catalystsContaminant Typical sourceSilicon (Si) Lighter boiling fractions from a coker

fractionator. Source of silicon is from

anti-foaming chemical addition.

Vanadium (V) and Nickel (Ni) Naturally occurring in most crudes.

Typically concentrated in heavy VGO and

residuum boiling fractions or in heavy

products from a coker.

Arsenic (As) Naturally present in many crude and

shale oils. Concentrated in lighter boiling

components.

Sodium (Na) Found in many crudes. Poor crude

desalting can cause Na carryover to

hydroprocessing reactors.

Iron (Fe) Often associated with the byproducts of

corrosion, but can also be naturally

occurring.

42 HYDROCARBON ENGINEERING DECEMBER 1999

of the regenerated catalyst. Depending on the servicerequirements, regenerated NiMo catalysts having <1 wt%vanadium contamination with good physical and chemicalproperties can still provide acceptable catalyst activity.Placement of such catalysts in ‘clean’ service having fewmetals contaminants should be acceptable. Careful consid-eration should be given to placement of such catalyst in ametals contaminated service. Catalysts having low levels ofexisting contamination are frequently subject to pore mouthplugging as they usually have a narrower pore structurethan demet catalysts. Initial catalyst performance is notalways the only criterion for placement of regenerated cat-

alyst and activity maintenance shouldalways be considered when pre-existingvanadium contamination is an issue.

ConclusionTo make good business decisions regardingthis disposition of spent catalyst, it is impor-tant to understand the quality of catalyst so(1) reuse via regeneration can be deter-mined and (2) placement in subsequent ser-vice can be made with confidence.

Using pilot plant activity data to assistwith evaluation of regenerated catalyst per-formance, a refiner can better determinespecifications for maximum acceptablearsenic and vanadium contamination.Generally speaking, specifications are:

Arsenic < 0.4 wt% on CoMo catalystArsenic < 0.2 wt% on NiMo catalystVanadium < 1.0 wt% on NiMo catalyst

Refiners will need to assess their ownsituation to set individual specifications using the data pre-sented. CRI can provide assistance based on years ofexperience in placing regenerated/resale catalysts withmany customers.

References1. NOWACKI P ed., 'Oil Shale Technical Data Handbook', Noyes Data

Company, 1981.2. SPEIGHT J.G., 'The Chemistry and Technology of Petroleum', 2nd

edition, Marcel Dekker, Inc, 1991.3. BUTT J.B and PETERSEN E.E., 'Activation, Deactivation, and

Poisoning of Catalysts', Academic Press, 1988.

Enquiry no: 18

Figure 3. Effect of vanadium on regenerated catalystactivity (NiMo hydrotreating catalyst).