RFCCU Project - Cracking Catalyst Evaluation and Selection

The catalyst selection for a new RFCCU is more important, in my opinion, than selecting the technology. A misfit catalyst can cause multiple issues in acheiving the unit performance objectives and can dilute the expected returns. The RFCCU catalyst is, generally, a mix of a base catalyst with multiple additives, often in significant quantities, to address various aspects of processing a residue feed such as bottoms cracking, lower coke make, octane preservation, sulfur reduction, olefins maximization, etc.. In comparison, catalyst for a gas oil FCCU is mainly a base equilibruim catalyst with a few additives in minor quantities

This article is only for educational sharing of my opinion and can have inaccuracies and omissions. This is not professional advice for any real situation of any kind. Readers assume all risks for any deduction or extrapolation. The Disclaimer at the end of this Article should be reviewed. It applies to the entire content and any comments or response

So how to ensure that the correct catalyst is selected for the design residue feed so that looking back after the unit startup does not result in regrets? The objective should be to look for lowest operating cost per barrel of feed that can produce maximum products value. The process starts with characterizing the residue feed as accurately as possible, beyond the usual categories of paraffinic, aromatic or naphthenic, to get a feel for what is most likely to end up as coke on the catalyst and what can be thermally cracked in the matrix into smaller molecules if a large pore size and volume additive is used. Though these things are mainly an educated guess, since a molecular breakdown of crude is impractical, nonetheless, gives an idea what to investigate when buying a catalyst.

From what I understand, on new projects there are two approaches for catalyst selection: The technology provider may take the responsibility to provide the initial load and make up catalyst until the performance test run and for a short while later; Or, the technology provider discloses the catalyst and additives used for the yield estimate and provide a specification sheet for purchasing the same or similar catalyst and the additives, and the names of few approved suppliers. In most instances, I think, when the second approach is used, approval by the licensor of selected catalyst is mandatory for guarantees purpose.

For the sake of this article, let us assume the second approach of the owner buying the catalyst. To make an informed decision on the best optimized catalyst, it is important to get some additional date points from the technology providers. Because the feed conditions vary and the RFCCU controls allow varying the riser temperature and catalyst to oil ratio, C/O, among other things, the yield of critical components in the yield estimate need to be predicted in a family of plots with varying riser temperature for several C/O ratio. The critical yield components are usually unique to each refiner and the project, so a determination needs to be made in-house, but should include, in my opinion, coke on the catalyst, delta coke, critical products yield, gas make and slurry oil yield

But one may ask how technology providers can generate this information? I think this is a matter of expertise and support quality of the licensors. Such data, in my opinion, can be generated by kinetic models or pilot plan test runs if a sample of feed is provided, either by the licensor itself or by working with their preferred catalyst supplier. Most catalyst vendors are also catalyst developers and have some kind of testing facility. In my opinin, a circulating type pilot plan generates better applicable data than a MAT, which is basically a rough screening test for various catalyst concoctions.

With all that information available, catalyst vendors can provide proposals with all relevant details such as physical properties, competitive edge, support structure and price. If several major additives are needed such as ZSM, DeSox, Matrix Cracking, best to have each listed separately with physical properties of each and main chemical components, such as rare earth levels, zeolite framework, matrix dealumination, etc.. The physical property information should include total surface area (SA). and if possible, breakdown in matrix and zeolite SA, particle and bulk density, ratio of large versus small and medium pores, cell size and an accurate and proven particle distribution

The above information on the proposed catalysts can provide an insight on key differences between each vendor catalyst. The next step is clarification cycle to discuss the significance of these difference and how they are relevant to the project in question. The clarifications should lead to a short listing of two final catalyst vendors. At this point, I think, it is pertinent to ask for commercial references where similar catalyst mixes are being used and processing a similar kind of feed. Often such a synchronization is difficult to obtain, in which case the catalyst vendor should be asked to correlate the known operating data with the design project residue feed highligting the differences.

The catalyst formulation at this stage may or may not be complete. If metals in residue are high, some form of Nickel passivation and Vanadium mobility control additive may be needed, along with other additives for reducing slurry, maximizing olefins, reducing coke, etc. One of the advantages of checking the commercial operation is the ability to get feedback on the affects of each of these additives, in combination or on a stand-alone basis if the additive is used on an on/off basis.

Another important aspect is the presence of other contaminants in the feed besides V & Ni. If the feed contains high levels of Nitrogen or Sodium or Iron or Chlorides, evaluation of additives with respect to impact from these is critical to a steady operation. If adjustments are needed, better to discuss before start-up rather than after a month-long operation. The catalyst turnover in a FCC, I think, can take from 3-6 months so an initial error can take a while to fix

The fluidization characteristics of the catalyst is also critical. It must flow smoothly in catalyst transfer piping, stripper and spent and regenerated catalyst systems. Sometimes, a fluidization aid is also added. If really needed, fine, but best is that the fines control should be optimum to make catalyst flow smoothly. Too many fines, either generated from the additives or from the main catalyst can be a major problem. These can cause catalyst losses from the reactor overhead into the main fractionator and end up in the slurry and the filtration system, can pollute the environment from stack emissions, can make opacity target difficult to achieve and increase the operating cost for higher addition rate (CAR)

The above are only a few basic pointers. RFCCU catalyst selection requires careful attention to lots of details that are only available during the design and engineering of the project. As an example, the type of feed nozzles and cyclones may also have impact on the choice of the catalyst. It is a triangular working relationship between the owner, technology licensor and the catalyst vendor and the interest of each is served best if all comes out in a win-win situation.             

Disclaimer: This is not professional advice, directly or indirectly, and can be edited or deleted at any time. Anyone accessing this Blog unconditionally agrees that the expressed views are only the personal opinions of the Author for educational sharing only, basis author’s knowledge only, and may contain omissions and inaccuracies. It must not be used for any actual new project or on an existing facility. Readers accept all risks and responsibility for any interpretation or extrapolation and any consequences stemming from such reliance