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

    Mar-2025

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  • 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


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