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Dec-2021

Controlling hyper-active catalysts with injection (ERTC)

Starting up a hydrocracker after a catalyst change-out can be complex and operationally challenging, especially when high-activity cracking catalysts have been loaded in the unit.

Randy Alexander
Reactor Resources LLC

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Article Summary

Following the sulphiding step, most catalysts are very active and may even become “hyper-active”, preventing the introduction of reactive feed without serious temperature control issues or excursions. To moderate the activity of the cracking bed catalyst, a nitrogen compound is often injected into the reactor in the form of aqueous or anhydrous ammonia. This step, called nitrogen passivation, effectively tempers catalytic activity when nitrogen atoms from the ammonia absorb to the acidic sites on the zeolitic cracking catalyst. Detection of nitrogen breakthrough or “N slip” at the reactor outlet indicates that the cracking catalyst bed has absorbed a sufficient amount of nitrogen to temper the catalytic activity. Straight-run feed can then be introduced to the unit without the risk of excessive exotherms.

Handling ammonia is hazardous, however, and leaks or spills can lead to serious health and safety issues. This is particularly true with anhydrous ammonia, which forms a toxic vapour cloud if allowed to escape from a tank or piping. To exacerbate the problem, ammonia is typically injected at pressures of 70-140 bar (1000-2000 psi). The pumps used to inject ammonia are notoriously difficult to prime and start up at these conditions.

To minimise the hazards of passivating hydrocracking catalysts with high-pressure ammonia injection, Reactor Resources has replaced NH3 with methyl diethanolamine (MDEA) injection. When injected into a reactor pressurised with hydrogen at temperatures above 185°C, MDEA readily decomposes to form the ammonia needed to passivate the cracking catalyst. The other decomposition by-products of MDEA are methane, ethane, and water. Note that the amount of water created is negligible compared to the quantity of water produced from the sulphiding reaction when metal oxides are converted to active metal sulphides.
MDEA has many advantages over ammonia and other amine compounds:

• With a health hazard rating (HHR) of “1”, MDEA is much safer to handle than ammonia, which has an HHR of “3” (severe health hazard / poison)
• MDEA is less odorous and is easier to pump at high pressure than ammonia
• The cost of MDEA is quite low compared to other amine compounds, and many refiners already use MDEA in their sulphur plant as a hydrogen sulphide absorbent
• Any excess MDEA remaining after the passivation step can be off-loaded into the refiner’s on-site amine tank, eliminating restocking fees
• MDEA will not cavitate the charge pump like ammonia can

MDEA has now been successfully used to control catalytic hyper-activity on 20 hydrocracker start-ups without any catalyst performance or safety issues. Our reference list includes several repeat customers. In addition, two catalyst manufacturers have evaluated MDEA in pilot studies and found that there is no difference in performance when compared to ammonia passivation. MDEA eliminates the handling of toxic ammonia and allows for a quick and safe start-up of your hydrocracker after a catalyst change.

Reactor Resources can also provide an Online pH Analyser system to measure the pH change of water coming from the separator boot. As with our other analyser systems, accurate and timely measurement of pH is an invaluable tool for optimising the amine injection and determining exactly when pH shift/nitrogen slip (N-slip) has occurred.

Over-injection of amine causes several issues:

• Oversaturated cracking catalyst can cause yield degradation
• MDEA is wasted
• Excess ammonia will react with H2S in the system, forming ammonium sulphide
• Additional DMDS will need to be injected to make up for the H2S that was consumed by the ammonia
• Ammonium sulphide will dissolve in the liquid effluent and then evolve when the reactor product is heated up in another unit downstream, evolving sulphur in undesirable places

Real-time data from the Online pH Analyser is viewable on our cloud-connected pump telemetry, allowing engineers and operators to make informed decisions on the quantity of amine required to adequately passivate the catalyst bed without over-injection.

MDEA injection is the latest innovation from Reactor Resources and complements our other sulphiding technologies and analyser systems, which includes the SmartSkidTM Injection System, Online H2S Analyser, Hydrogen Purity Analyser, and Total Sulfur Analyser.

For more information contact: randy.alexander@reactor-resources.com

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This short article originally appeared in the 2021 ERTC Newspapers, produced by PTQ / DigitalRefining.

You can view the Day 1 Newspaper HERE
You can view the Day 2 Newspaper HERE


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