What is the aging, poisoning, and temporary deactivation of catalysts?

1. Catalyst poisoning: Highly active catalysts lose their catalytic capacity after operating for a short period of time. This phenomenon is often caused by the presence of trace amounts of substances in the reaction materials that can deactivate the catalyst; such substances are known as catalytic poisons, and this phenomenon is referred to as catalyst poisoning. 2. Catalyst poisoning: It is divided into reversible poisoning, irreversible poisoning, and selective poisoning. --1– Reversible poisoning occurs when a toxin adsorbs onto or reacts with the active site; the bonds formed in this process are relatively weak, and appropriate methods can be used to remove the toxin, thereby restoring the catalyst’s activity without affecting its properties. As in ammonia passivation, ammonia temporarily poisons the cracking catalyst, suppressing its activity; as the ammonia desorbs, the catalyst’s activity is restored. --2-- Irreversible poisoning occurs when a strong chemical bond is formed between the poison and the active components of the catalyst, making it difficult to remove the poison using conventional methods and resulting in a decrease in the catalyst’s activity. When basic nitrogen poisons the cracking catalyst, it falls into this category. --3-- Selective poisoning occurs when a catalyst loses its catalytic ability for a certain reaction after being poisoned, but remains catalytically active for other reactions. There are advantages to choosing poisoning; for example, in a cascade reaction, if the toxin only poisons the active centers that catalyze subsequent reactions, it is possible to halt the reaction at the intermediate products, thereby obtaining the desired intermediate products with high yields. 3. Catalyst aging: The process by which a catalyst gradually loses its activity under normal operating conditions. This deactivation is caused by factors such as the loss of low-melting-point active components, surface sintering at low temperatures, migration of internal impurities to the surface, and mechanical crushing resulting from the alternating action of cold and heat stresses. The higher the operating temperature, the faster the aging rate. The service life of a catalyst in industrial installations is referred to as its catalyst life; it depends on the type of chemical reaction and the operating conditions, ranging from just a few hours to several years. 4. Catalyst deactivation: This is primarily observed by checking the reactor operation parameters such as outlet temperature and bed pressure drop, to determine whether there is a problem with the catalyst!

Deactivation can be determined from the reaction temperature in the reactor, the properties of the product, and the bed pressure drop. By the end of operation, the catalyst is subject to high reaction temperatures, the properties of the product deteriorate sharply, and the pressure drop across the bed increases.

The aging of a catalyst, simply put, refers to the loss of its catalytic properties due to sintering, melting, crystal damage, or loss of activity of the catalyst’s matrix or active components under the influence of high temperatures, water vapor, and other factors. Catalyst poisoning occurs when heavy metals present in the feedstock, such as nickel, vanadium, iron, and copper, adhere to the catalyst. This reduces the catalyst’s selectivity, increases the yields of coke and gases, decreases the yield of the desired product, and raises the degree of unsaturation. Also known as heavy metal pollution. It is irreversible. The temporary deactivation of catalysts mainly refers to coking-induced deactivation, and it can be reversed by regeneration, allowing the catalyst to regain its activity.