The purposes of catalyst reduction and passivation

What is the purpose of passivation? The end criteria are specified in the startup plan provided by the process package supplier; for example, reaching a certain temperature and maintaining it for a certain period of time.

The purpose of reduction is to bring the catalyst from its oxidized state to its reduced state, thereby enabling the active components to function; the purpose of passivation is to reduce the initial activity of the catalyst and prevent the reactor from overheating.

The purpose of reduction is to passivate the catalyst and prevent it from catching fire upon contact with air during unloading

I have excerpted a passage from \"Q&A on Hydrocracking Technology\" for your reference: After sulfidation, hydrocracking catalysts exhibit high hydrocracking activity. Therefore, before feeding the feed oil, it is necessary to pass ammonia through the catalyst to deactivate it, thereby suppressing its excessive initial activity and preventing potential temperature spikes during the oil feeding process, thus ensuring the safety of the catalyst, the equipment, and personnel. For hydrocracking catalysts containing molecular sieves (especially those with a high content of molecular sieves), the use of low-nitrogen feed oil and ammonia injection for passivation are common methods. For hydrocracking catalysts using amorphous silica-alumina as a carrier, their hydrocracking activity is relatively low and they are less sensitive to temperature changes; although ammonia injection for passivation is an option, it does take time. In such cases, direct passivation using the feed oil can be considered. The ammonia injection passivation method is commonly used in single-stage hydrocracking processes, and straight-run diesel fractions are usually selected as the passivation oil for starting up. The specific operating procedures are as follows (taking an 800,000 tons/year hydrocracking unit as an example): ① After sulfidation is completed, the temperature is reduced to 150°C. About 20% of the normal feed rate is used to supply low-nitrogen oil; only after the heat wave associated with adsorption passes through the catalyst bed and a liquid level is established in the high-pressure separator can the feed rate be gradually increased to about 60% of the normal level, thereby establishing a large-scale cycle for reaction and distillation. ②Once the temperature of the catalyst bed in the reactor stabilized, the ammonia injection pump was started to feed ammonia into the reaction system at a rate of 220 kg/h, while raising the inlet temperatures of the refining and cracking reactors to 228°C and 203°C respectively. ③Water injection began 2 hours after ammonia injection, and the ammonia content in the high-pressure wash water was analyzed every half hour. Before high-yield ammonia production, maintain the inlet temperatures of the refining and cracking reactors below 230°C and 205°C. ④During ammonia passivation, a sulfiding agent should be injected as needed to maintain the hydrogen sulfide content in the circulating hydrogen at not less than 0.1 v%. ⑤When the ammonia content in the high-pressure water reaches 1.5% (wt), it is considered that ammonia has penetrated extensively; the ammonia injection rate is then reduced to 75 kg/h (one-third of the initial rate), and the ammonia concentration is maintained at 1.5% until the feed rate reaches 60%. ⑥After ammonia penetrated the catalyst, the inlet temperatures of the purification and cracking reactors were increased at a rate of 15°C/h to 325°C and 315°C respectively. Through automatic control, quench hydrogen was used to maintain a temperature gradient of 3°C decrease per bed inlet. If the temperature rise in any bed exceeded 10°C, the inlet temperature remained unchanged until the rise fell below 6°C. ⑦While increasing the inlet temperature of the cracking reactor, the temperature of the circulating oil should also be raised, but it must not exceed the inlet temperature of the cracking reactor. ⑧When the inlet temperature of the refining reactor reaches 320°C and that of the cracking reactor reaches 315°C, with a bed temperature difference of less than 6°C, it indicates that the passivation is complete. However, the ammonia and sulfur injection facilities must remain in operation until the second hour after 75% of the designed feed rate has been reached, at which point the ammonia and sulfur injection can be stopped.