Catalyst deactivation refers to a phenomenon where the catalytic activity and selectivity of catalysts are significantly reduced or completely lost due to impurities in the system and operating conditions. Substances that trigger deactivation are collectively called catalyst poisons, which mainly originate from impurities in raw materials, intrinsic impurities of catalysts, reaction products and by-products.
1.Main Types of Catalyst Deactivation
①Thermal Deactivation
Excessively high reactor temperature leads to irreversible structural failure. High temperature damages the carrier framework of catalysts and leaches active components. It also causes catalyst melting and bed coking, blocking micropores and reducing the effective specific surface area. Short-term local overheating has minor impacts, while long-term high-temperature operation will permanently deactivate catalysts.
②Physical Deactivation (Mechanical Deactivation)
Dust and fumes block the micropores of catalysts. Ordinary dust accumulates at the top of the catalyst bed, while gaseous heavy metal particles deposit in the lower bed, increasing bed pressure drop and damaging active sites. Catalysts with insufficient mechanical strength will break into fragments, reducing the contact area for reactions and resulting in deactivation.
③Chemical Deactivation (Catalyst Poisoning)
Trace impurities in the system chemically react with the active centers and carriers of catalysts to form inert substances with no catalytic performance. This destroys component structures and passivates catalytic capacity, ultimately deactivating catalysts.
2.Common Substances Causing Catalyst Deactivation
Common deactivation-causing substances in industrial processes include water, heavy metals, nitrogen and amines, oxygen, acids and alkalis, fumes, chlorine, sulfides, carbon oxides, hydrocarbons, as well as arsenic, selenium, tellurium and other elements.
3.Causes of Catalyst Deactivation in SRU Units
Catalyst deactivation in Sulfur Recovery Units (SRU) is mostly caused by improper operating conditions: incomplete purging during startup and shutdown leads to pore blockage by impurities; condensed acid forms under low reactor temperature, corroding catalyst frameworks and triggering sulfation; excessive air supply generates acidic by-products that damage active sites; reactor overheating and temperature out of design range during startup and shutdown all accelerate catalyst deactivation.