Catalyst in catalytic cracking units
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From what aspects can we ensure that the activity of the catalyst does not lead to its deactivation?
Generally speaking, it is manifested in two main aspects: the properties of the raw materials (fraction composition, content of alkaline nitrogen, sulfur, and heavy metals, etc.)； Process conditions (regeneration temperature, coking capacity, steam consumption, etc.).
The raw materials must be purified thoroughly. The reduction and heating processes should proceed slowly; the entire operation needs to be carried out at a gradual pace. The temperature should also be increased slowly, and the load must be raised gradually as well. During operation, care must be taken to prevent sudden increases in temperature, pressure, or space velocity
The desalting of crude oil generally involves removing elements such as sodium, iron, and calcium, but vanadium and nickel cannot be removed; these elements pose the greatest threat to catalysts. If the amount of passivator is not controlled properly, it can also cause catalyst poisoning. Antimony poisoning occurs as well. The degree of coking does not alter the inherent activity of the catalyst, but poor coking results can affect the reaction between the oil and gas and the catalyst.
The main goals are to prevent catalyst poisoning and hydrothermal deactivation. To avoid catalyst poisoning, it is necessary to ensure effective electrodialysis and an appropriate amount of metal passivators to be used. To prevent hydrothermal deactivation of the catalyst, it is essential to use an appropriate amount of water vapor
The last edit to this post was made by linweihua6 on 2011-10-15 07:13: 1. Catalyst selection (wear resistance), 2. Heavy metal content in the raw materials, 3. Operating conditions (temperature, water vapor partial pressure, residence time, use of combustion oil). The most important thing is to properly control the operation of the regenerator as well as the effectiveness of electrodialysis in the raw materials
Catalyst deactivation can be divided into two types. One is reversible or treatable deactivation; for example, carbon deposition on the catalyst can be removed by calcination to restore its activity, and heavy metal contamination can be addressed using metal passivators. The other type is permanent deactivation, which occurs due to the destruction of the catalyst’s crystal structure, such as hydrothermal deactivation (thermal decomposition), resulting in the formation of eutectics with sodium ions.