The Contact process is the industrial process that manufactures sulfuric acid from sulfur, oxygen and water, using vanadium(V) oxide as the catalyst.
The Contact process is the industrial process used to manufacture sulfuric acid, H₂SO₄, from sulfur, oxygen and water, with vanadium(V) oxide, V₂O₅, acting as the catalyst. Malay: proses sentuh · Chinese: 接触法.
The process runs in three linked stages. First, sulfur is burned in dry air to form sulfur dioxide: S + O₂ → SO₂. Second, and most importantly, the sulfur dioxide is combined with more oxygen in a reversible reaction over the heated V₂O₅ catalyst to form sulfur trioxide: 2SO₂ + O₂ ⇌ 2SO₃. Because the forward reaction is exothermic, this step is run at a moderately high temperature and a low, near-atmospheric pressure, the compromise conditions that give an acceptable rate together with a high yield at a reasonable cost. Third, the sulfur trioxide is absorbed into concentrated sulfuric acid to form oleum, H₂S₂O₇, which is then diluted carefully with water to give more concentrated sulfuric acid.
Example. A sulfuric acid plant feeds sulfur dioxide and clean air over trays of V₂O₅ pellets; the sulfur trioxide that forms is led into absorbers of concentrated acid, and water is added at a controlled rate to build up the product. The catalyst is not used up, so the same pellets keep working batch after batch.
Confusion to avoid. Do not confuse the Contact process with the Haber process: the Contact process makes sulfuric acid, while the Haber process makes ammonia. Also, sulfur trioxide is not passed directly into water, because that would form a thick, uncontrollable acid mist; it is absorbed into concentrated acid instead.
The Contact process is the anchor example of applying rate and equilibrium ideas to industry, and it appears often in SPM Chemistry.
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