Questions regarding the use of low-nitrogen oil in the hydrocracking unit for the first time
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The hydrogen cracking unit was put into operation for the first time after pre-sulfurization was completed, using low-nitrogen diesel as the starting oil in order to prevent the cracking catalyst from becoming poisoned and deactivated. Since low-nitrogen diesel is being used, why is aniline still injected to deactivate the catalyst? Could high-nitrogen oil be used instead? Is there anyone who can help clarify this? Thank you
Low-nitrogen diesel is used in hydrocracking units during their first startup to prevent nitrogen-containing compounds from poisoning the fresh catalyst, thereby affecting its activity and lifespan. Aniline is injected as a passivator; it can react with the active metal centers on the catalyst to form stable complexes, thereby temporarily reducing the catalyst’s activity and protecting it from being poisoned by impurities such as those containing sulfur or nitrogen. Even when using low-nitrogen oil, further protective measures may still be necessary in some cases due to the catalyst’s extreme sensitivity to impurities. Using high-nitrogen oil directly can not only cause catalyst poisoning but also increase the difficulty and cost of subsequent catalyst regeneration and treatment during plant operation. Therefore, in practical operations, it is highly necessary to adopt a dual protection measure of using low-nitrogen oil and injecting a passivator. .
High-nitrogen diesel is not necessarily completely denitrified during startup; the basic nitrogen present in the fuel accelerates the reduction of the acidity of the catalyst’s molecular sieve, increasing the tendency for coking. Aniline decomposes to form inorganic ammonia, which only adsorbs on the catalyst under high pressures of ammonia; it is later desorbed in an environment of high-purity hydrogen or hydrogen sulfide, thereby restoring the activity of the catalyst.
Oh, I see. Thank you so much to the expert for taking the time out of your busy schedule to answer my questions; I’m extremely grateful{:1_90:}
Thank you to the expert for the answer: handshake