Large Volume Inorganic Chemicals - Ammonia ... - ammk-rks.net

Chapter 44.2.2 CatalystsOnly vanadium compounds, platinum and iron oxide have proven to be technically satisfactorywhen tested for catalytic activity for sulphur dioxide oxidation. At present, vanadium pentoxideis used almost exclusively.Commercial catalysts contain 4 – 9 % w/w vanadium pentoxide (V 2 O 5 ) as the active component,together with alkali metal sulphate promoters. Under operating conditions, these form a liquidmelt in which the reaction is thought to take place. Normally potassium sulphate is used as apromoter but in recent years caesium sulphate has also been used. Caesium sulphate lowers themelting point, which means that the catalyst can be used at lower temperatures. The catalystsupport is different forms of silica.The catalyst support is mixed together to form a paste and then usually extruded into solidcylindrical pellets, rings or star-rings which are then baked at high temperatures. Ring (or starring)shaped catalysts, which are mostly used today, give a lower pressure drop and are lesssensitive to dust build-up.In industrial practice, the lower temperature range is 410 – 440 ºC for conventional catalysts and380 – 410 ºC for caesium treated catalysts. The upper temperature range is 600 – 650 ºC, abovethis, catalytic activity can be permanently lost due to internal surface area reduction. Theaverage operating life for the catalyst is approximately 10 years. Operating life is generallydetermined as a result of catalyst losses during screening of the catalyst, which has to be carriedout periodically to remove dust.See also Sections 4.4.4 “Application of a Cs-promoted catalyst” and 4.4.12 “Prevention ofcatalyst activity loss”.Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers 155