Are catalyst additives available to boost bottoms processing in the FCC?Nov-2021
King Yen Yung, Petrogenium, email@example.com
The FCC process was invented to convert vacuum gas oils into more valuable oil products, primarily motor gasoline. The FCC process has proven to be extremely versatile and thanks to, amongst others, innovations in process design, process operation strategies, and catalyst technologies it has widened its application vastly.
Nowadays fluid catalytic cracking units are applied worldwide to convert not only vacuum gas oils but also heavier residual feedstocks to more valuable products. These valuable products are not only motor gasoline but for example also light cycle oils for the diesel pool and, even more important, propylene, butylenes, and amylenes for the production of premium gasoline components, such as alkylates and/or increasingly important for propylene as feedstock for the production of polypropylene.
A premium FCC catalyst is designed by the catalyst manufacturer to fulfill the objectives of the customer with regards to yield structure, product quality, and bottoms conversion. If needed, special FCC additives (co-catalysts) are applied to enhance the production of, for example, propylene by using a ZSM-5 containing additive. Additives to reduce SOx and NOx emissions from the FCC regenerator are widely used too.
More specifically for maximum bottoms conversion, a special bottoms conversion additive is generally not required as the regular host catalysts should have enough bottoms conversion potential for the envisaged feed diet.
But due to the extreme versatility of the process, more and more refiners route unconventional feedstocks to their FCC units. The unconventional feedstocks include off-spec gasoline, off-spec luboils, tar oils, tight oils, and also extremely heavy feedstocks. These opportunity feedstocks are used on a temporary basis and might jeopardise bottoms conversion as the host FCC catalysts might not have been designed for such a wide variety of feedstocks. All major FCC catalyst suppliers and some dedicated FCC additives suppliers have the capability and are able to provide refiners with a bottoms conversion additive to boost bottoms conversion in case the need for this arises.
Tom Ventham, Unicat B. V. / G. W. Aru, LLC, firstname.lastname@example.org
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.
Jarred Drewry, Johnson Matthey USA, email@example.com
Yes, there are multiple approaches to increase bottoms processing in the FCC with additives. With heavier feed in the unit, the base fresh catalyst may lack sufficient matrix activity to crack the larger feed compounds, resulting in lower conversion and higher slurry yields. In this situation, a high matrix additive, such as Johnson Matthey’s BCA-105, can provide additional matrix activity, allowing for cracking of the heavy components with reduced slurry production. BCA-105 reduces bottoms yield through easing of reaction pathways. It pre-cracks feed into LCO boiling range material, but the final yield structure of converted material is primarily determined by the properties of the catalyst system in terms of MAT activity (F-cat adds), hydrogen-transfer opportunities, and presence of ZSM-5. For instance, if BCA-105 is added on top of the main catalyst, higher MAT activity will lead to higher conversion and higher gasoline selectivity; if BCA-105 is added replacing part of the main catalyst, the selectivity will lead to LCO maximisation (see Figure 1), and finally the conversion to LPG would be influenced by ZSM-5 present in the system.
Additionally, increased bottoms processing will likely introduce higher metals to the unit which poison the base catalyst. These poisons, along with the heavier feed, will result in reduced yields and higher delta coke which can then cause process constraints such as regenerator temperature limits. In this situation, a proven metals-trapping additive, such as Johnson Matthey’s Cat-Aid, can mitigate the impacts of poisons while decreasing delta coke, resulting in lower regenerator temperatures. This additive approach for metals control will also increase conversion while reducing slurry. In any case, the advantage of this approach is that an additive can be started and stopped as needed, depending on the feed. This allows the refiner to maintain its standard fresh catalyst blend while being able to quickly shift to additional bottoms processing.
Melissa Clough Mastry, BASF, firstname.lastname@example.org
In terms of FCC additives, there are two methods available. The first is an additive that can rapidly increase conversion. For this, the Converter additive is an effective way to achieve bottoms upgrading through increased conversion, pushing the bottoms material into more valuable products. The second is an additive that introduces high active matrix content. For this, the HDUltra additive is effective at rapidly changing your Z/M ratio and thus your bottoms cracking potential. For an even more effective and long lasting change in bottoms upgrading, we recommend an overall catalyst change. A catalyst change is a more permanent solution to a bottoms cracking target and allows the refiner to customise the method (activity and/or matrix, and often a mix of both) to employ, since each refinery requires a different solution to their bottoms upgrading objectives. A catalyst change allows the refinery to take into account all input variables, including feedstock characteristics and importantly the FCC unit’s downstream constraints, along with the target of bottoms upgrading.
Lamma Khodeir, W. R. Grace & Co, Lamma.Khodeir@Grace.com
Increasing bottoms processing in the FCC will result in more undesirable slurry which means improved bottoms cracking is needed. Grace does offer additives that provide a boost to bottoms cracking. Such additives are typically applied when the base catalyst is not optimised for bottoms cracking performance and can have a quick impact on bottoms cracking performance. However, the more typical and recommended approach is to integrate the bottoms cracking functionality into the FCC catalyst itself, which avoids some potential negative impacts on yields associated with the additive approach, as subsequently described.
When using the additive approach for bottoms cracking, the large feed molecule diffuses into the separate additive particle and is subsequently cracked into intermediate products. These smaller molecules must then exit the additive before diffusing into the base catalyst particle where they are selectively cracked into more valuable FCC products. However, before the intermediate molecules can exit the additive they can undergo additional and less selective cracking reactions, resulting in higher amounts of coke and gas.
Other advantages of optimising the base catalyst for bottoms cracking vs using an additive approach include:
• Avoids the use of a separate additive injection facility, as well as the associated logistics.
• Bottoms cracking additives can dilute the base catalyst activity, resulting in higher daily catalyst additions and opex.
• Retention and fluidisation characteristics of the additive may differ from base catalyst.
• Slow activity decay rate of additives can result in a prolonged period where undesired selectivity shifts are observed.
• For catalysts incorporating integral metals trapping technology, contaminant feed metals are passivated, resulting in lower coke and gas make, unlike for additives which often contain no metals trapping functionality.
For resid applications, hydrogen and coke selectivities cannot be neglected as these units are typically constrained by air blower rates, wet gas compressor, and/or maximum regenerator temperature. Additives might not be compatible with these constraints, leading to reduced conversion and/or feed rate and an overall loss in unit profitability.
Grace has a diverse and robust resid FCC catalysts portfolio to offer refiners with a highly customised catalyst to combine maximum bottoms conversion with optimum product yields. In addition, these catalysts incorporate state-of-the-art metals tolerance functionality, enabling refiners to process the most challenging feedstocks, unlocking significant operational flexibility and economic value.