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How is contamination of FCC catalysts being resolved to increase yields and cycle length?

Mar-2025

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Jarred Drewry, Johnson Matthey, jarred.drewry@matthey.com

When dealing with FCC catalyst contamination, there are several possible approaches. The first, and most obvious, is to increase your fresh catalyst rate, but this can be an expensive task, particularly for persistent contamination issues. An alternative is to work with your fresh catalyst vendor for a catalyst reformulation. Ideally, a catalyst change would result in improved metals tolerance at similar yields.

A more immediate and flexible solution is the use of metals-trapping additives, which help mitigate the negative effects of contamination. A metal trap additive, such as CAT-AIDTM from Johnson Matthey, effectively traps both vanadium and iron from the FCC feed. This allows the base catalyst to continue to perform its desired reactions unencumbered by the poisons. The result is that the FCC unit is able to recapture/increase yields and reduce increased fresh catalyst usage. Because the undesirable coke/dry gas reactions are reduced with the metals-trapping, there will also be an improvement in operations due to the lower delta coke/regenerator temperature enabled by the additive. The additive-based approach is particularly advantageous because it can be implemented quickly, providing refineries with greater flexibility in managing feedstock variability and contamination challenges.

Mar-2025
Berthold Otzisk, Kurita Europe, Berthold.otzisk@kurita-water.com

In recent years, FCC catalysts have been developed that are much more tolerant of catalyst poisons (contaminants). Nevertheless, contamination of the FCC catalyst still leads to reduced product quantities or shorter cycle lengths. Contaminants act as competitive catalysts to dehydrogenate the hydrocarbons, leading to excess hydrogen production and coke. They reach the FCC catalyst with the feed material and irreversibly destroy the zeolite crystallinity and/or the acidity. Classical impurities are metals such as nickel (Ni), vanadium (V), iron (Fe), copper (Cu), sodium (Na), calcium (Ca), or magnesium (Mg). Nickel (also Cu, V, and Fe) enters the system in the form of large porphyrin molecules, which crack onto the FCC catalyst, leaving the nickel behind.

Nitrogen (N) or carbon (C) are catalyst poisons that deactivate or cover cracking sites on FCC catalysts. However, this is only temporary, and the catalyst activity is recovered. Catalyst destruction by metals is more pronounced and permanent, where catalyst bed activity can only be recovered by adding fresh catalyst.

Nickel is the primary competitive catalyst in the FCC, acting as a dehydrogenation catalyst. Dehydrogenation of hydrocarbons leads to loss of gasoline selectivity and a slight reduction in catalyst activity. By plugging catalyst pores, the conversion is reduced with the negative effects of increased delta coke on FCC heat balance. Nickel should always be considered if the process unit is running against a limit. If nickel on Ecat exceeds around 500 ppm, a chemical treatment programme should be started. A nickel passivation programme reduces the negative effect of nickel by 50-70%.

Alongside nickel, vanadium is another metal that causes problems and production losses. Vanadium acts as a competitive catalyst and a true catalyst poison. Besides dehydrogenation reactions, it may oxidise, becoming mobile and migrate to the zeolite catalyst, permanently destroying it.

There are various passivation programmes with which a reduction of nickel or vanadium dehydrogenation can be achieved. The negative influence of these metals is reduced, and the conversion and yield are increased in addition to the improved gasoline and C3/C4 selectivity and longer cycle length.

Best known in the industry is the use of antimony or bismuth (Bi) to mitigate the effects of nickel. Aqueous antimony pentoxide solution (Sb2O5) is preferred as it works much faster compared to bismuth and is easier to control. Care should be taken to ensure that the particle size of Sb2O5 is preferably <5 nm in order to obtain a stable colloidal dispersion. The more stable dispersion avoids settling problems in storage. Sodium is a catalyst poison, and residual sodium or byproducts such as Sb2O3 (suspected to be carcinogenic) should not be present.

When dosing Sb2O5, an average ratio of 0.35 Sb:Ni should be set. The typical base load to saturate active nickel is reached after five to seven days. An overdose of Sb2O5 must be avoided because Sb in LCO can poison downstream Ni-Mo hydrotreater catalysts.

Mar-2025
Darrell Rainer, Ketjen Corporation, darrell.rainer@ketjen.com

The contaminants exerting the most significant impacts on FCC catalyst and unit performance, along with commonly employed mitigation measures, are as follows:
• Nickel is present in all feeds, with higher concentrations in resids and nickel deposits, and remains in the outer shell of the catalyst particle, promoting dehydrogenation reactions that increase delta coke and hydrogen yield. Many catalysts feature components designed to minimise active nickel surface area on the Ecat, as well as influence the chemical state, limiting the overall dehydrogenation increase. Newer nickel has more dehydrogen effects than older nickel on Ecat.
• Antimony (Sb) has nickel (Ni) passivating properties and can be added to the riser as a liquid stream. Typical Sb/Ni ratio targets would be in the 0.25-0.35 range, which might be lowered according to the intrinsic nickel tolerance of the catalyst. For nickel and other contaminants, the use of purchased Ecat is an option to minimise levels in the circulating inventory by increasing the overall catalyst addition rate. Refiners sometimes resort to the systematic addition of purchased Ecat higher CAR (catalyst addition rate) at a lower cost than fresh catalyst alone. This frequently comes with attendant performance deficits that factor in the decision.
• Vanadium in the fully oxidised state (V2O5) is highly mobile and distributes throughout the catalyst particle. Full combustion units with excess O2 will have elevated V2O5 levels. While the dehydrogenation activity is a fraction of that of nickel (~25%), vanadium also interacts destructively with Y-zeolite. This impact can be mitigated with the inclusion of vanadium traps in the circulating inventory and the use of a high matrix activity catalyst, hedging against activity loss through zeolite destruction by providing significant catalyst matrix cracking.

With iron, the spatial deposition profile of iron is similar to that of nickel, but the impact on particle surface morphology/porosity is significantly greater. Iron interacts with silica (originating both in the catalyst and from the feed) in the presence of other fluxing metals (calcium, sodium, and vanadium) to form eutectics under regenerator conditions that result in the formation of a densified shell in the outer layer of the catalyst particle. This results in a loss of porosity in the surface region, imposing a diffusional barrier that can greatly diminish the accessibility of larger molecules to the interior cracking sites, increasing slurry yields.

Catalyst selection is key in managing the impacts of iron contamination. Employing a high-accessibility catalyst expands the operating safety margin (in terms of avoiding ‘the cliff’ at which point the catalyst accessibility drops sufficiently to cause a precipitous drop in bottoms upgrading), allowing a higher add-on iron on Ecat level to be safely tolerated. Catalysts such as Ketjen’s proprietary SaFeGuard, specifically designed in their chemistry to minimise the surface reactions with iron, calcium, and sodium that result in densification and accessibility loss can play an important role in managing iron risk. Fluidisation issues can also develop with iron contamination, originating from ‘nodulation’ and the attendant drop in apparent bulk density (ABD). This varies significantly from unit to unit.

Sodium attacks zeolite and is also a fluxing metal that promotes the formation of the eutectics associated with the harmful morphological changes that occur in iron poisoning. Mitigation strategies in the FCC unit would mostly be limited to increasing catalyst addition rate and upstream remedies, such as improved desalting of crude.
Calcium also attacks zeolite, though not so severely as sodium. However, it plays a much more significant role in exacerbating the damaging impact of iron poisoning and is frequently implicated in the worst cases. Mitigation approaches would be the same as for sodium.

Chlorides originating either in the feed or in the catalyst can introduce various complications, including intensifying corrosion concerns (NH4Cl), forming unwanted deposits in the fractionator and enhancing the dehydrogenation activity of nickel deposited on the catalyst. Mitigation approaches would include sound catalyst selection (avoiding high chloride-containing catalysts if there is an issue) and upstream solutions, such as (again) improving desalter efficiency.

Silicon (silica) contamination does not get much discussion or attention as it is essentially undetectable against the background of silica in the catalyst itself, and the impacts have not been thoroughly documented and quantified. It is reasonable to assume that silicon introduced in the feed (for example, from such sources as defoaming agents employed in the delayed coker) might interact with iron in a similar way as silica originating with the catalyst. While the total amount of silica contaminant is going to be very low relative to the catalyst baseline, mobile silica is the real issue. That ratio is going to be significantly higher. So, while it is tempting to draw the conclusion that silica in the feed is simply not present in large enough quantities to have an impact, this has not rigorously been shown to be true. In fact, Ketjen has lab data indicating the opposite. A catalyst specifically designed to minimise iron and silica interactions (SaFeGuard) can alleviate this impact.

Mar-2025
Scott Sayles, Becht, ssayles@becht.com

Contamination in FCC feeds is minimised by endpoint control and hydrotreating to remove catalyst fouling. The newer catalysts can tolerate higher levels of metal contamination, allowing the ability to either process higher endpoint feeds or lower hydrotreating severity. The balance between hydrotreating, yields, naphtha/light cycle oil (LCO) sulphur, and catalyst replacement requires consideration of the interactions between the variables.

In general, an economic balance is reached between these variables at the highest C4+ liquid yields. An economic optimum is reached for two separate conditions:
• Maximum gasoline or the naphtha peak point conversion.
• Maximum distillate occurs at a lower conversion, further augmented by fractionator cut points.

The two optimums require separate operating conditions, feedstock quality, and catalyst replacement strategies. These conditions are best controlled via an online advanced control system. Catalyst selection will also improve selectivity to naphtha or distillate but is a longer-term change and does not capture seasonal effects. Recent strategies are to optimise distillate production using a distillate selective catalyst.

Mar-2025
Mark Schmalfeld, BASF Refinery Catalysts, mark.schmalfeld@basf.com

FCC catalysts, specifically BASF FCC catalysts, are specifically designed to enhance the operation of fluid catalytic cracking (FCC) units. Catalyst design considers the context of contamination management expected for the feed types used by the FCC unit. Here are several ways in which FCC catalysts contribute to improved FCC performance, even in the presence of catalyst feed contamination.

FCC catalysts have been developed with enhanced metal tolerance, allowing them to maintain activity and selectivity even when exposed to feedstocks containing metals such as nickel and vanadium. This capability helps mitigate the negative effects of these contaminants, leading to more stable operation and improved yields, in addition to catalysts with near-zero levels of chlorides. Low sodium levels in FCC catalyst improve the zeolite stability. Use of an in situ manufacturing process designs the pore volume distribution to ensure a high level of iron tolerance.

FCC catalysts often incorporate advanced zeolite structures engineered to resist the deposition of contaminants. These optimised structures provide greater surface area and improved diffusion pathways, allowing for better hydrocarbon access and reduced accumulation of coke and other contaminants.

FCC catalysts are designed to facilitate effective regeneration as coke and hydrocarbon deposits are combusted in the FCC regenerator. Their design allows for the efficient removal of carbon deposits and some contaminants during the regeneration process, helping to restore and maintain the catalyst activity. This means that even in the presence of contamination, the catalysts can be regenerated more effectively when tailored to the specific unit constraints and targeted operating conditions.

FCC catalysts may include proprietary additives and design elements that specifically target and mitigate the effects of contaminants. For example, these additives can help neutralise harmful compounds or enhance the catalyst’s ability to cope with specific impurities, thus maintaining performance levels. Enhanced catalysts and activity can help offset the impact of contamination by ensuring that the FCC unit operates efficiently, even when feed quality fluctuates. An optimised activity level is required based on unit constraints and economics.

BASF’s FCC technical team can adjust catalyst design to provide refiners with operational flexibility to manage unexpected changes in feed quality. Additionally, catalyst design can be utilised to adjust how contaminated metals are removed from the FCC unit over time. This adaptability is crucial in maintaining stable performance and ensuring that the FCC unit can respond effectively to variations in contamination levels.

Equilibrium catalyst (Ecat) analysis is conducted and combined with operating data for refiners to enable continuous improvements in operational adjustments, troubleshooting, and opportunity development. This collaboration and partnership approach allows for ongoing optimisation of catalyst usage and operational practices, further enhancing overall performance.

Mar-2025