The Contact Process typically involves three main stages:
Combustion: Sulfur or pyrite is burnt in air to produce sulfur dioxide (SO2). Oxidation: The SO2 is passed over a V2O5 catalyst at high temperatures, converting it to SO3. This step is exothermic and crucial for high conversion rates. Absorption: The produced SO3 is absorbed in concentrated sulfuric acid to give oleum, which is then diluted with water to produce sulfuric acid of the desired concentration.
