Why is it necessary to increase the temperature of the cracking bed to activate a hydrocracking catalyst after nitrogen poisoning?
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Regarding hydrocracking units, some articles state that if the catalyst in the cracking bed is nitrogen-poisoned, its activity can be restored by increasing the cracking temperature I don’t quite understand the theoretical principles or mechanisms behind it, so I’m here to seek advice from fellow netizens!
Personally, it doesn’t involve increasing the catalyst’s activity; rather, it’s a way of using temperature as a compensation to maintain the conversion rate. However, this isn’t a sustainable solution, as it causes significant damage to the catalyst.
The deactivation of the cracking agent by inorganic nitrogen (NH3) is reversible; therefore, ammonia must be injected during the first start-up to deactivate the cracking agent. Organic nitrogen can permanently deactivate the cracking agent; if the organic nitrogen content in the cracking feed is too high, the pre-treatment units are unable to remove this organic nitrogen, which directly affects the activity of the cracking agent. Therefore, temperature elevation is required as a compensation to maintain the conversion rate.
On page P651 of Han Chongren’s book \"Hydrocracking Processes and Engineering\", there is a passage stating that the nitrogen content in the feedstock is controlled during the refining stage. As can be seen from the graph, when the nitrogen content in the feedstock is 20 μg/g, the cracking conversion rate at 372 °C is around 42%； After increasing the nitrogen content in the feedstock to 100 μg/g, the pyrolysis conversion rate gradually decreased under the same conditions ； When the nitrogen content in the raw material is further reduced to 20 μg/g, the pyrolysis activity cannot be restored ； Raising the reaction temperature to 376 °C and 380 °C did not result in a significant improvement in the cracking reaction activity. When the reaction temperature was raised to 386 °C, the pyrolysis conversion rate increased rapidly and reached 69% ； When the reaction temperature was further reduced to 372 °C, the pyrolysis activity was essentially restored, with a pyrolysis conversion rate of 40%. But it doesn’t explain why either, right?
In the case of pseudo-poisoning, increase the injection volume of cracked sulfurized gas; the hydrogen sulfide content in the recycled hydrogen should be 5000