Tenets of catalyst selection
I have had several suggestions to write about catalyst selection. This is a popular topic in many journals and blogs with some authors taking controversial stands on several issues. I thought I would approach the subject by describing the important tenets that should be part of all catalyst selection processes for hydrocrackers and hydrotreaters.
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Just a word about my approach and background. Many authors approach this topic from a sales perspective, but I have no interest in selling you anything. My view comes from 35 years of experience in selecting, buying, and then being held accountable for my recommendations and choices. My career progression, salary, and bonuses depended on consistently making the right choices. To some degree, the profitability of the refineries I supported depended on consistently making the right choices.
I hope that you can help your refinery’s profitability by following these catalyst selection tenets that apply both to hydrocracking as well as hydrotreating. When I refer to catalysts in this blog, I refer to both singular catalysts as well as catalyst systems. Let me know what you might add to this list.
Tenet #1 – ‘In God we trust, all others bring data’ – W. Edwards Demming
I encourage you to read and understand Dr. Demming’s data science work, but the main lesson he gives is that all decisions should be based on good data. Many catalyst vendors will provide estimates and projections, but these ‘paper’ estimates are sometimes not based on good data or can be based on a wild extrapolation of data. Here is the data you should seek in order of benefit:
Commercial data from a service like yours
• Hopefully, a vendor can provide commercial data in a service that has a reasonably similar LHSV, H2 partial pressure, and feed.
• A back-to-back comparison of two catalyst’s commercial operation can be helpful, even if the operating conditions and feed are not exactly like yours.
• Good commercial data should include both initial activity data and fouling data. I have observed that some catalysts may not have good initial activity, but more than make up for the poor activity with superior fouling resistance.
Pilot plant data
• It is difficult to compare pilot plant data to commercial data. The best way to look at pilot plant data is comparing it to other pilot plant data. One set of pilot plant data by itself with no comparison doesn’t have much value.
• For example, if two sets of pilot plant data at similar conditions with the same feed show that the new catalyst has an activity advantage over the old catalyst, then you might reasonably expect a similar ‘delta’ in commercial operation if the operating conditions are like your service.
• Most pilot plant data will only show initial catalyst activity, but I have observed that accelerated fouling data from two pilot plant runs at the same conditions with the same feed can show a good comparison that can roughly be applied to commercial operation. (Note that many vendors will disagree with this statement simply because they don’t want to run accelerated fouling tests.)
Activity and Fouling Data
There are catalysts out there that may not show great initial activity but show far superior fouling resistance as the example shown in the graph below. Catalyst B has a higher start-of-run temperature, but better fouling resistance than Catalyst A. Overall, Catalyst B gives a much better performance over the entire run. Therefore, both activity and fouling data have value.
Tenet #2 – New catalysts should provide a good payout compared to the previous catalyst
New catalysts with higher cost should provide at least a 3:1 payout compared to a previous catalyst. Purchasing a new, more-expensive catalyst comes with risks:
• The catalyst will not perform as advertised.
• A refinery upset will coke up the new catalyst before you can realise the benefits.
• The reactor will develop a high pressure drop and you will need to dump the catalyst prematurely.
This 3:1 rule-of-thumb is especially true for some of the new step-change catalysts that come at very high costs. Refineries don’t build new units unless the payout is at least 3:1 – why would anyone buy a more expensive catalyst without being sure of a good payout?
Of course, some hydroprocessing services are mild and don’t require high activity catalysts. In this case it may be acceptable to simply choose the cheapest catalyst with reasonable performance.
Tenet #3 – Hydrocracking catalyst choice is all about product YIELDS (and maybe cheaper feedstock)
Ninety per cent of the effort in selecting catalyst for a hydrocracker should be focused on product yields:
• Increased liquid yield volume and volume expansion
• Increased yields of the highest value product(s)
• Flexibility to change product slates when economics dictate
• Improved product quality – higher diesel cetane and jet smoke
• See Tenet #2 for payout requirements on yield improvements
Five per cent of the effort in selecting catalyst for a hydrocracker can be focused on increasing the ability of a unit to feed cheaper feedstocks or allowing cheaper crude to the refinery. The remaining 5% of the effort can focus on everything else: catalyst cost, catalyst quality and delivery.
Get the product yield improvements right and you’ll be a superstar. Get it wrong and they will probably downgrade you to working on the FCC unit.
Hydrocracking data is most valuable when it includes data with the pretreat (hydrotreating) catalyst and the hydrocracking catalyst running together. There are many synergies between the pretreat catalyst and the hydrocracking catalyst and they should always be tested and chosen together to get accurate yield data.
Tenet #4 – Choose grading and support catalysts independently from the active catalyst
Most people don’t buy tyres from the same place they buy the car because they want to choose the best from different vendors. Why would you buy grading and support catalysts from the vendor of the active catalysts unless you were convinced, they had the best equipment? In other words, there are good reasons to choose grading and support catalysts independent of the active catalyst, although some active catalyst vendors also have good grading catalyst.
Even if your active catalyst vendor has access to a variety of grading and support catalysts, they may charge a mark-up price for selling it with the active catalysts. Don’t be afraid to shop around but remember Tenet #1 – base decisions on data.
There are novel support catalysts available in the market that help to minimise the number of layers of support required at the bottom of reactor beds. I recommend you seek out these novel support catalysts to minimise the volume and height of support catalyst needed allowing you to maximise the amount of active catalyst loaded.
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