Back

Question

Submit an Answer

What catalyst additive technologies are available to enhance propylene production in our FCC unit?

Jan-2022

Answers

Lucas Revellon, KBR, Lucas.Revellon@kbr.com

The complex interaction of FCC catalyst and process hardware offers many opportunities for optimising propylene yields, product composition, and quality.

Fundamentally, light olefins from an FCC unit are generated by cracking gasoline range molecules over a shape selective zeolite like ZSM-5. Hence, the key to maximising olefins is to maximise gasoline range molecules, which is a function of the FCC hardware installed in the reactor riser and base catalyst.

There are three key hardware technologies that affect catalytic cracking in a riser and impact gasoline yield (precursor for propylene production) and product selectivity:
- Feed injection system
- Quench injection (to control riser temperature profile)
- Riser termination

A well designed feed injection system like KBR Atomax-R technology will provide a fine atomisation of the oil feedstock and close contact between the oil and catalyst. This will promote rapid feed vaporisation and initial product conversion to gasoline. KBR Riser Quench technology increases the catalyst to oil ratio, resulting in higher gasoline yield and gasoline olefinicity without an increase in dry gas. A well design ed riser termination like KBR Closed Cyclone will preserve the valuable molecules generated in the riser from over-cracking into unwanted products. In addition to these three hardware solutions, the FCC unit can be revamped to add a second riser (KBR Maxofin technology) to overcome maximum propylene limitation from a single riser FCC, and subsequently upgrade any low valued stream in the refinery to light olefins.

Some of the key considerations KBR uses for developing the most optimum base catalyst and additive systems for maximum olefins product are:
- Coke selectivity and activity to produce desired conversion within unit constraints
- Controlling catalyst unit cell size and rare earth levels to minimise hydrogen transfer reactions
- Careful evaluation of the desired equilibrium catalyst metals level (resid FCC operation)

Keeping this complex set of requirements in balance has resulted in the development of KBR’s Maxofin additive technology, which enhances the ability to produce the greatest amount of propylene from any FCC operating mode while delivering all the key operating objectives of each FCC. KBR’s operating and design philosophy for maximising light olefins continues to focus on the improvement of hardware components as well as the correct design of the Maxofin additive technology.

Jan-2022
Carl Keeley, Johnson Matthey, carl.keeley@matthey.com

In general, most FCC operators have several options to increase propylene production:
- A non-selective route through increasing riser severity
- A fresh catalyst reformulation to favour propylene production
- Choosing the correct propylene enhancing additive

The non-selective route can be implemented fast, which is desirable, but this route uses thermal cracking that will increase dry gas production which has a low product value. A fresh catalyst reformulation takes time to design, implement, evaluate, and fine-tune and does not allow refiners to respond quickly to changing market conditions, so opportunities are missed. The best solution is separate additive additions, allowing units to quickly maximise FCC margins when facing different operating constraints.

ZSM-5 is a shape selective zeolite that converts gasoline components into propylene, butylene, and isobutane while increasing FCC gasoline octane. ZSM-5 based additives provide the flexibility to optimise catalyst activity, product selectivity, and cost/performance.

From Johnson Matthey, there are several ZSM-5 based additives that can be used to enhance propylene production. For example, Super Z additive is Johnson Matthey’s most popular olefins enhancement additive. Typically, FCC operations use this additive to enhance LPG production and increase FCC gasoline octane. These users are generally trying to optimise transport fuels production.

However, sometimes, a higher activity ZSM-5 is desirable. Super Z Excel additive provides higher activity and is popular with refiners that are integrated with petrochemicals production. The higher activity also reduces the potential concern for dilution effects that may be present using higher rates of a lower activity additive. These refiners require the flexibility to move smoothly between fuels and LPG olefins production, and separate, high activity ZSM-5 additions provides this capability.
In addition, if even more activity is needed, Super Z Exceed additive is available.

All of Johnson Matthey’s additives have an attrition resistance, bulk density, and particle size distribution fully compatible with the circulating catalyst inventory and are available for delivery in a variety of convenient packaging sizes.

In addition, Johnson Matthey offers state-of-the-art catalyst and additive addition systems to accurately add catalyst and additive throughout the day, allowing performance and cost optimisation.

If any clarifications are needed, please do not hesitate to contact Johnson Matthey. We are able to quickly supply additives, field service, technical support, new loaders, and advanced process control providing an industry leading solution for refiners who want to enhance FCC performance.

Jan-2022
Mark Schmalfeld, BASF - Refining Catalysts, mark.schmalfeld@basf.com

Amit Shah, Technical Service Manager, BASF, Amit.shah@basf.com, Lynne Tan, Technology Manager, BASF, Lynne.tan@basf.com, and Mark Schmalfeld, Global Marketing Manager, BASF, mark.schmalfeld@basf.com

There are various routes for maximum propylene production and the best route is what is suitable for respective refineries’ target and scope. Many licensors provide technological solutions to revamp existing FCC units for more propylene production, but a significant investment and long lead time are expected. A suitable catalyst design is a quick and easy alternative for FCC units to maximise propylene under existing hardware configurations.

Propylene maximisation approaches are similar across a wide range of feed types, however it can be more difficult in resid applications. To accomplish maximum propylene from a resid feed, a catalyst needs to have high metals tolerance to prevent activity and conversion loss due to contaminant metals, and good coke selectivity to better manage heat balance, which is often a key challenge. An ideal maximum propylene catalyst will leverage on these unique characteristics to deliver optimal bottoms conversion to produce light naphtha, the precursor for propylene, and accentuates the effects of an olefin additive (using a ZSM-5 type zeolite) to produce high propylene yield and selectivity.

Conventional and easier to implement approaches are changes in operating conditions, feed quality, naphtha recycle, and use of ZSM-5 additives.

Recent developments in olefin additive technology (using ZSM-5 zeolites) may be used for boosting propylene yield from current levels. Typical olefin additives contain significant percentages of ZSM-5 zeolite. Leading catalyst suppliers have now launched latest generation ZSM-5 additives that contains >50% crystals. Using such a high crystal ZSM-5 additive while maintaining the dosing rate the same as the incumbent additive can significantly boost propylene yield, provided sufficient olefin precursors are available in the light gasoline stream. The quantum of incremental propylene that can be achieved depends on specific application.

Additionally, the base FCC catalyst design can have a significant influence on propylene yields. Tuning and optimisation of the rare earth on zeolite, catalyst surface areas, and zeolite to matrix surface areas can play a key role in producing propylene.

Net propylene produced from the FCC unit can also be increased by reducing/minimising the losses in the dry gas/fuel gas. In one patented application, a refinery added a chiller to cool the naphtha used in the primary absorber to minimise the loss of propylene in the fuel gas. The value of propylene in a petro-refinery is high enough to payback additional investment in a short time.

Other developments for boosting propylene yield would involve FCC technology licensors offering latest technologies that can be implemented in an existing FCC unit with hardware additions/modifications.

Jan-2022
Bani Cipriano, W. R. Grace & Co, Bani.Cipriano@Grace.com

Increasing the yield of propylene from the FCC unit can create significant value for refiners. To raise the propylene yield from the FCC unit, refiners can inject additives containing ZSM-5 zeolite. These additives have physical properties (particle size distribution, ABD, attrition resistance) that match those of the base catalyst, yet, on account of their molecular structure, catalyse different reactions in the FCC unit vs Y-zeolite catalyst. ZSM-5 additives are available with varying levels of ZSM-5 zeolite content and therefore cracking activity. While it is common practice to compare additives from different suppliers based on ZSM-5 zeolite content, this does not always reflect true performance in the FCC unit, as the activity of ZSM-5 additive is highly dependent on the chemistry used to stabilise the zeolite.

Aside from zeolite Y, ZSM-5 is the only zeolite that has had commercial significance in FCC. In contrast to zeolite Y, which has 12-membered ring openings, ZSM-5 is a medium-pore zeolite consisting of 10-membered ring openings. The pore dimension of ZSM-5 is 5.4-5.6 Ã…, which is considerably smaller than the 7.4 Ã… openings of zeolite Y. Due to its smaller pore size, ZSM-5 exhibits size-exclusion shape selectivity, which allows it to crack only gasoline range molecules into valuable LPG olefins, namely propylene and butylene. Moreover, unlike zeolite Y, which has a large cavity (supercage) at the intersection of its pore openings, the intersections of the ZSM-5 pore channels do not form a large cavity. Thus, ZSM-5 exhibits transition-state shape selectivity due to its inability to accommodate the large transition state complexes associated with bimolecular reactions. Due to these restrictions, ZSM-5 has very low hydrogen transfer activity.

Using a ZSM-5 zeolite additive in the FCC unit therefore increases the yield of propylene at the expense of gasoline (butylene also increases, and a minor amount of ethylene is produced, although propylene is the predominant specie). Fundamental studies on cracking of model compounds1 reveal that as the gasoline olefin species become smaller (lower carbon number 6 and 5), these are more difficult to crack vs larger gasoline olefins (7 to 9 carbon), yet these smaller olefins when cracked yield higher selectivity towards propylene. Therefore, the key to reaching increasingly higher yields of propylene is to increase ZSM-5 cracking activity, either by increasing the additive level in the FCC unit inventory or increasing the cracking activity of the ZSM-5 additive. It is worth mentioning that use of ZSM-5 additives results in an increase in the octane of the FCC gasoline as well, delivering additional value to octane short refineries.

The traditional route to increasing the cracking activity of ZSM-5 zeolite additive is focused on increasing the content of ZSM-5 zeolite in the additive. However, as mentioned above, the chemistry and methods employed in the manufacturing of the ZSM-5 additive play a critical role in the stabilisation of the zeolite. As a result, two additives may have similar crystal content, yet their performance and effective zeolite activity is very different in the FCC unit. Next generation ZSM-5 additives exploit this concept and through novel chemistry seek to boost the activity of the zeolite itself, delivering step out cracking activity. This is the concept behind Zavanti technology, the newest generation of ZSM-5 additive available from W. R. Grace & Co. and intended for maximum propylene applications.

References
1 For more information about fundamental studies of ZSM-5 cracking of model compounds, the reader is referred to Buchanan, et. al. Journal of Catalysis. Vol 158, 279, 1996.
2 For more information about ZAVANTI™ technology, the newest generation of ZSM-5 additives, the reader is referred to Serban, et. al. PTQ Q3 2021, 43.

Jan-2022