On the presulfurization of hydrogenation catalysts
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During the pre-sulfiding of the hydrogenation catalyst, why is not the circulating hydrogen desulfurization tower put into use instead of using a bypass route? And why is the feed water pump not started during this process, but only after sulfiding is completed? The H2S concentration in the gas is so high during sulfidation; it should cause significant corrosion to the equipment. Then why aren’t desulfurization towers used and injection water pumps activated in order to keep the H2S concentration under control?
Purpose and basic principle of catalyst sulfidation: Catalyst presulfidization is based on the hydrogenolysis of a sulfiding agent (DMDS) to produce hydrogen sulfide (H2S), which then reacts with the oxidized states of the active metals in the catalyst to convert them into their corresponding metal sulfides. The relevant sulfidation reactions are as follows: (CH3)2S2 + 3H2 → 2H2S + 2CH4; MoO3 + 2H2S + H2 → MoS2 + 3H2O; 3NiO + 2H2S + H2 → Ni3S2 + 3H2O; WO3 + 2H2S + H2 → WS2 + 3H2O. A large amount of H2S is involved in these reactions, so it can no longer cause corrosion to the equipment. Moreover, low-nitrogen oil is used in the sulfidation process, so very little NH3 is generated, and no crystals are formed with H2S; therefore, it is not necessary to fill the drum with water at such an early stage. I think so; those with different opinions, please share your insights
When pre-sulfidization is carried out using circulating hydrogen for desulfurization, doesn’t that absorb the hydrogen sulfide that has already been formed as a result of the reaction? So it isn’t put into use. As for that slight degree of corrosion, it’s still acceptable for the steel. When the sulfur content reaches over 20,000 PPM during the sulfidation process, we activate the hydrogen sulfide removal tower to prevent excessive hydrogen sulfide concentrations. Stop sulfur injection at the same time.
Water injection is not used during vulcanization because a large amount of water is generated during this process as well. As for the reaction formula, the brother on the second floor has explained it very clearly; at the end of the pre-vulcanization stage, it is necessary to record the amount of water used as well as the amount of vulcanizing agent applied. If water injection is used, it becomes difficult to make accurate judgments.
Keep adding vulcanizing agent while vulcanizing – why bother with desulfurization? Are you just wasting money? (Being practical here, haha :victory:) During desulfurization, it’s necessary to measure the water content at high levels in order to check the degree of sulfur loading on the catalyst. One of the indicators that sulfuration is complete is when no water can be removed from the system for two consecutive times at high levels. Additionally, water injection is mainly used to prevent the precipitation of ammonium chloride and ammonium hydrosulfide; however, this isn’t necessary at this stage. Water injection is generally carried out two hours after ammonia injection for passivation purposes
The main function of the catalyst sulfidation process is to convert the metal in the catalyst from an oxidized state to a sulfided state. Hydrogen sulfide concentration is an important parameter to control throughout this process; too low a concentration can affect the sulfidation process and even lead to the reduction of the catalyst’s metal. At this point, feeding hydrogen into the cyclohydrogen desulfurization tower to reduce the hydrogen sulfide concentration in the cyclohydrogen is clearly a way to create problems for oneself. Furthermore, reactive water injection is primarily used to prevent the deposition of ammonium salts; in dry sulfidation, the entire sulfidation process relies on circulating hydrogen as the carrier medium, with no ammonium salts being produced ； For wet sulfurization, in order to protect the catalyst, the sulfurization carrier oil chosen must be a low-nitrogen oil. Moreover, the maximum sulfurization temperature in wet sulfurization is 290 degrees; at this temperature the denitrification reaction has not yet begun, and no ammonium salts are formed. If water is added at this stage, it will not only affect the determination of when sulfurization is complete but also influence the calculation of the final sulfur content. Therefore, there is no need to add water.
The concentration of hydrogen sulfide is limited; pre-sulfidization is carried out to maintain the catalyst’s activity, as it achieves its highest activity at a certain concentration of hydrogen sulfide. This concentration limit is certainly within the capacity limits of the equipment.
If sulfur is injected while water is also injected, the simplest result is the formation of a hydrogen sulfide aqueous solution, and the corrosivity of this solution is much greater than that of dry hydrogen sulfide.
What was said upstairs makes sense; not only should dehydration not occur, but under suitable conditions, the water should be dehydrated to a higher degree in order to prevent the absorption of excessive hydrogen sulfide, which could lead to high concentrations of sulfurous acid that would corrode the equipment