Question
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Are catalyst additives available to boost bottoms processing in the FCC?
Nov-2021
Answers
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Tom Ventham, Unicat B. V. / G. W. Aru, LLC, tom.ventham@gwaru.com
Increased bottoms processing often incurs a dramatic increase in the contaminant metals loading to the FCC unit. Ultra CokeBuster is Unicat & G. W. Aru LLC’s offering for minimising metals contamination at elevated metals operations. When increasing bottoms processing, it is important that riser operation be evaluated to understand if all of the incremental bottoms will be fully vaporised. Many units have operated successfully with small amounts of unvaporised feed, but there have been several unit disturbances caused when feed vaporisation has been unexpectedly poor — severe catalyst deactivation and massive conversion loss have been observed in several sites.
As well as control of additional metals and coke, both of which impact regenerator operation, it should be considered how to reoptimise FCC yields for lower conversion that is likely. A large impact is expected to product profitability due to increased production of low-value streams, such as slurry — also known as main fractionator bottoms among other names. Using FCC additives to correct bottoms yield, as well as that of other liquid yields, is a perfect dynamic handle to optimise bottoms or residue processing, without risk of dilution. Our response pays note to the other important considerations already mentioned but focuses on one important area we wish to discuss in further detail: how increases in slurry yield when processing bottoms in the FCC can be corrected.
Bottoms upgrading additives, such as Ultra MCBuster (UMCB) from Unicat & G. W. Aru, LLC, are known as, ‘high-matrix’ materials. This suggests a high proportion of mesoporous alumina providing activity. Matrix is a basic and fundamental type of catalyst material used in FCC since the birth of the process. On that basis the complexity and chemical fragility of matrix materials are low and the material is very simple and robust. Effective bottoms upgrading additives should comprise a high content of alumina. The real differentiation normally observed in the effectiveness of bottoms upgrading is not the selection of the various available additives on the market, but the physical injection management on offer and a good understanding of optimisation using additives provided by the supplier. The additive supplier should be knowledgeable in FCC additive use as a tool to improve performance of the system.
One key is to examine cutpoint corrected slurry density as an identifier of upgrading potential from the bottoms product. Slurry density approaching 1.15 S.G. signifies a highly aromatic product stream with little upgrading potential. Corrected slurry density closer to 1.0 S.G. or below suggests significant upgrading opportunity. Your technical contact can advise on evaluating bottoms upgrading potential based on dynamic changes in recorded slurry density. Increasing the presence of active matrix in the FCC reaction section gives the opportunity for feed molecules/slurry precursors/reaction intermediates to crack into those more useful products, typically LCO or gasoline depending on base catalyst formulation, rather than remain uncracked or going through thermal processes that result in increased slurry yield.
It is also a common misconception that matrix materials produce large amounts of coke. This is a hangover from laboratory testing that involves long catalyst-hydrocarbon contact times of 30 seconds or more. At these high contact times in the laboratory, matrix additives will produce a high yield of coke. However, commercial FCC and RFCC riser residence time is closer to two seconds or less, particularly in short contact time designs. At these contact times coke production can be the same or incrementally less than Y-zeolite.
Other uses for bottoms busting additives to consider include density control of the slurry product if used for downstream needle coke or petroleum coke processes, or even for consistency and achieving full economic potential of coker feed. By removing long-chain paraffins from the bottoms product, such additives can also help alleviate certain coking issues in the bottoms circuit where the issue is build-up of waxy paraffins. A further use that can be considered is in either a diesel mode operation or high propylene or LPG operation where riser temperature is reduced to target LCO yields or make room in the gas con to use ZSM-5 to boost LPG yields, respectively. In these cases conversion drops and slurry product increases as an unintended consequence. Slurry busting additives, such as UMCB, can be used to rebalance slurry yields and increase yields of more profitable products. The base technology of these additives is very simple, but working with an experienced and knowledgeable supplier to guide and advise to achieve the best end result is the most important step to maximise the potential of this activity.
Nov-2021
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