Equilibrium catalyst (Ecat) analysis is conducted and com- bined with operating data for refiners to enable continuous improvements in operational adjustments, troubleshoot- ing, and opportunity development. This collaboration and partnership approach allows for ongoing optimisation of catalyst usage and operational practices, further enhancing overall performance. A Scott Sayles, Manager, Renewable Fuels and Alternate Feeds, Becht, ssayles@becht.com Contamination in FCC feeds is minimised by endpoint con- trol and hydrotreating to remove catalyst fouling. The newer catalysts can tolerate higher levels of metal contamina- tion, 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 C 4 + liquid yields. An economic opti- mum 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 selectiv- ity 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. A Darrell Rainer, Global FCC VGO Specialist, 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 circu- lating inventory by increasing the overall catalyst addition rate. Refiners sometimes resort to the systematic addi - tion 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 (V 2 O 5 ) is highly mobile and distributes throughout the catalyst particle. Full combustion units with excess O 2 will have elevated V 2 O 5 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 inclu- sion of vanadium traps in the circulating inventory and the use of a high matrix activity catalyst, hedging against activ- ity 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 mor- phology/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 poros- ity 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 cata- lyst 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 Catalyst selection is key in managing the impacts of iron contamination. Employing a high- accessibility catalyst expands the operating safety margin, allowing a higher add-on iron on Ecat level to be safely tolerated SaFeGuard, specifically designed in their chemistry to mini - mise 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 den- sity (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 poi- soning. 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.
7
Catalysis 2025
www.digitalrefining.com
Powered by FlippingBook