November 3, 2010 (One Question per Day)
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This post was last edited by zhezi2009.wang on 2010-11-3 19:27. What are the pathways for the formation of sulfates on the surface of catalysts? Everyone is encouraged to participate actively
The catalyst mentioned by the moderator probably refers to the sulfur recovery catalyst. Due to the reaction between SO2, SO3, and O2 in the process gas and the catalyst, alumina and iron oxide in the catalyst are converted into sulfates, which occupy the surface active sites of the catalyst and reduce its activity. Sulfation on the catalyst surface can occur in several ways. During normal operation of the device, SO2 reacts with oxygen or hydroxyl groups chemically adsorbed on the Al2O3 surface to form sulfates, but in small quantities. If SO3 or O2 is present in the process gas, even at just a few mg/L, it will accelerate the sulfation of the catalyst. The amount of sulfate formed on the catalyst surface does not increase indefinitely, as the sulfate produced can react with H2S in the process gas, thereby being reduced back to Al2O3. When the rate of formation equals the rate of reduction, the amount of sulfate stops increasing and an equilibrium state is reached.
The main reason is the presence of oxygen or other oxidants (such as NO2) in the process gas, which oxidize SO2 to SO3, thereby forming sulfates with the Claus alumina-based catalyst. The main reason for oxygen leakage is problems with the structure of the burner used, or the absence of an oxygen-blocking catalyst in the reactor. NO2, on the other hand, is mainly caused by the reactor temperature not reaching the requirements for ammonia combustion, which leads to the oxidation of ammonia in the acidic gases to NO2. Therefore, to fundamentally solve the sulfate problem, it is necessary to choose a good burner, and the furnace temperature must reach a sufficient level for ammonia combustion.
1. Prolonged operation with high air supply (peroxide effect): SO2 is oxidized to SO3, and sulfate is produced in the presence of a catalyst. 2. Incomplete combustion of ammonia produces nitrogen oxides, which facilitate the oxidation of SO2 to SO3, leading to sulfate formation in the presence of a catalyst
Acidic gases contain ammonia; when oxygen supply is insufficient, NO is formed, which promotes the conversion of SO2 into SO3. SO3 reacts with water to form H2SO4. It sulfatizes catalysts and corrodes equipment.