Catalyst sulfidation operation in ammonia synthesis desulfurization
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In the desulfurization of synthetic ammonia, cobalt-molybdenum catalysts need to be sulfided first. Why is liquid hydrocarbon pre-sulfidization carried out using sulfides and hydrogen? In the sulfidation reaction of catalysts, is it necessary to first use hydrogen to reduce the oxides to their elemental form before reacting them with sulfides, or can the cobalt-molybdenum catalysts react directly with sulfides? What is the role of hydrogen? Thank you!
The reaction of cobalt-molybdenum oxides with hydrogen sulfide involves reduction followed by sulfidation; however, since they are attached to alumina, reduction and sulfidation occur almost simultaneously. Throughout the sulfidation process, the presence of cobalt promotes the sulfidation of molybdenum, while the presence of molybdenum promotes the sulfidation of cobalt. At the same time, the presence of potassium also promotes the sulfidation of cobalt and molybdenum. Hydrogen has a reducing effect.
Why can a process using natural gas as a raw material directly sulfuretize the cobalt-molybdenum catalyst by feeding in natural gas?
Because natural gas contains H2S
The correct statement should be: 1. After sulfidation, cobalt-molybdenum catalysts are mainly used for conversion and the transformation of organic sulfur； 2. Cobalt-molybdenum oxides can directly react with hydrogen sulfide to form sulfides ； 3. The reduction reaction in the sulfidation process refers to the reaction of the commonly used sulfiding agent CS2 with hydrogen to produce methane and hydrogen sulfide; this is also known as hydrogenolysis, and it is highly exothermic.
The first floor is for coal-based enterprises; in the natural gas industry, cobalt-molybdenum low-temperature shift catalysts are not used at all, as copper-zinc low-temperature shift catalysts are employed instead.
In methanol or synthetic ammonia plants that use natural gas as a raw material, although no shift reaction takes place, the catalysts used for converting natural gas are highly sensitive to sulfur. In some areas, the organic sulfur components in natural gas are quite complex (the quality of natural gas in Sichuan is inferior to that in northern Shaanxi and Ordos), and it may even contain thiophene. Therefore, after using iron oxide desulfurization agents, cobalt-molybdenum hydrogenation catalysts are generally employed to convert organic sulfur into inorganic sulfur, with zinc oxide desulfurization agents being used subsequently for further purification. At present, not many synthetic ammonia plants in China that use coal as a raw material employ cobalt-molybdenum hydrogenation desulfurization methods, as catalysts based on cobalt and molybdenum can also convert organic sulfur.
What was said on the 5th floor is correct; whether cobalt-molybdenum catalysts are used for hydrodesulfurization or sulfur-resistant shift reactions, sulfidation is required. The sulfidation process is the reaction of cobalt-molybdenum oxides with hydrogen sulfide to produce cobalt-molybdenum sulfides. Since the sulfiding agent hydrogen sulfide is difficult to obtain directly, carbon disulfide, sulfur, or thioethers must be used to undergo a hydrogenolysis reaction with hydrogen in order to produce hydrogen sulfide. Of course, some cobalt-molybdenum catalysts can react with hydrogen sulfide in the feed gas to undergo natural sulfidation; in other words, there are various ways in which cobalt-molybdenum catalysts can be sulfided, but the principle remains the same.
What was said on the 5th and 8th floors is correct; it is recommended that the original poster take a look at \"Ammonia Synthesis Process\" and \"Handbook of Industrial Catalysts\" – then things will become clear: lol
During the production process, what happens if the sulfur content in the natural gas is very low for a certain period of time? ? ? Please give me your advice
No one answered? ? ? Let me talk about what I saw at Lutian Chemical*. During a certain production period, the plant discovered penetration in the natural gas zinc oxide desulfurization tank. According to their technical staff’s analysis, the low sulfur content in the natural gas at the inlet of the cobalt-molybdenum hydrodesulfurization unit located before the zinc oxide tank was to blame, as this caused the cobalt-molybdenum catalyst to lose its activity. Then, it is required that the sulfur content in imported cobalt-molybdenum be no less than 5PPM. I’ve always been puzzled: when natural gas enters the cobalt-molybdenum component while driving, it already sulfides the catalyst. The catalyst becomes active after sulfidation. How did the sulfur content decrease during production, and as a result, this activity was lost? ? ? ? ? I appreciate your advice!