Methanol Purification Version – Daily Question 20200719
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Why is passivation required before removing the catalyst? Answer: Before being put into use, the copper-methanol-based catalyst has its copper oxide reduced to metallic copper atoms; before the catalyst is removed, it needs to be passivated, that is, the metallic copper atoms are oxidized back to copper oxide. If the material is discharged without passivation, the oxygen in the air comes into rapid and thorough contact with the catalyst; it can penetrate deep into the inner surface of the catalyst in a short time, generating a large amount of reaction heat. This can lead to locally high temperatures within the catalyst bed, or a sharp increase in temperature differences. During discharge, this may cause burns to people, trigger combustion when in contact with flammable materials, or damage the internal components of the synthesis tower due to expansion stresses. Typically, before the catalyst is removed, nitrogen is used for circulation along with a small amount of oxygen, to carry out a gradual oxidation of the catalyst; this results in the formation of an oxidized coating on its outer surface, which prevents further reaction between oxygen and copper metal.
After the catalyst has been used, crude oil introduces large amounts of sulfur-containing substances, such as ferrous sulfide； It will catch fire spontaneously when exposed to air, so passivation treatment is required before unloading to reduce the risk
The catalyst is in a reduced state inside the reactor; if it is exposed to air directly when removed, it will oxidize and release a large amount of heat, resulting in an excessive local temperature rise or a sharp increase in temperature differences. Due to the expansion pressure, this can cause certain components inside the synthesis tower to deform or get damaged. At the onset of passivation, the oxygen concentration entering the reactor is maintained at 0.4–0.8, while the reaction temperature is kept around 250°C, with a maximum of 300°C. When the oxygen concentration entering the reactor gradually increases to 2%–3% and the catalyst temperature rises no longer significantly, it indicates that passivation is complete. At this point, the temperature can be lowered to remove the catalyst.
The reduced catalyst will oxidize when exposed to air, releasing a large amount of heat and even catching fire on its own. This can cause the coal to burn and clump together inside the tower tubes, making it difficult to remove the material. Therefore, it is necessary to passivate the catalyst, and for this purpose, instrument air is used for passivation. The oxygen content is controlled at several levels: less than 0.5%, 1%, 3%, and 10%.
Passivation before operation: Passivation before starting up is done to prevent the catalyst from having excessive activity, which could lead to loss of control and ensure that the reaction proceeds smoothly. Shutdown passivation is intended to prevent the reaction from continuing after removal; since the reaction proceeds more rapidly in contact with air, it serves to avoid oxidation and spontaneous combustion.
1. Passivation before startup: Passivation before startup is carried out to prevent the catalyst from having excessive activity, which could lead to loss of control and ensure that the reaction proceeds smoothly. 2. Shutdown passivation is intended to prevent the reaction from continuing after removal; exposure to air accelerates this reaction, and it serves to prevent oxidation and spontaneous ignition.
After the catalyst has been used, crude oil introduces large amounts of sulfur-containing substances, such as ferrous sulfide； It will catch fire spontaneously when exposed to air, so passivation treatment is required before unloading to reduce the risk
After the catalyst has been used, crude oil introduces large amounts of sulfur-containing substances, such as ferrous sulfide； It will catch fire spontaneously when exposed to air, so passivation treatment is required before unloading to reduce the risk
The reduced catalyst oxidizes when exposed to air, releasing a large amount of heat and even catching fire on its own; this can cause the coal to burn and clump together inside the tower tubes, making it difficult to remove them. Therefore, it must be passivated.
Before being put into use, the copper-methanol-based catalyst has its copper oxide reduced to metallic copper atoms; before it is removed, it needs to be passivated, that is, the metallic copper atoms are oxidized back to copper oxide. If the material is discharged without passivation, the oxygen in the air comes into rapid and thorough contact with the catalyst; it can penetrate deep into the inner surface of the catalyst in a short time, generating a large amount of reaction heat. This can lead to locally high temperatures within the catalyst bed, or a sharp increase in temperature differences. During discharge, this may cause burns to people, trigger combustion when in contact with flammable materials, or damage the internal components of the synthesis tower due to expansion stresses. Typically, before the catalyst is removed, nitrogen is used for circulation along with a small amount of oxygen, to carry out a gradual oxidation of the catalyst; this results in the formation of an oxidized coating on its outer surface, which prevents further reaction between oxygen and copper metal.