Sulfuric acid industry. Practical work 2

Raw materials for sulfuric acid: sulfur S, pyrite FeS₂, non-ferrous metal sulfides and H₂S. Production has three stages. 1) Making SO₂: roasting pyrite 4FeS₂ + 11O₂ → 2Fe₂O₃ + 8SO₂; pyrite powder falls from the top of a “fluidized-bed” furnace while air is blown from below, so it burns quickly and fully. 2) Cleaning the SO₂: dust is removed in a cyclone and electrostatic filter, moisture is removed in a drying tower with concentrated H₂SO₄ — dust and water vapour poison the catalyst. 3) In the contact converter SO₂ is oxidized over a V₂O₅ catalyst: 2SO₂ + O₂ ⇌ 2SO₃ + Q. The reaction is reversible and exothermic, so the temperature is held at 400–450 °C: a lower temperature gives a higher yield, but if it is too low the rate drops. The heat released warms the incoming gas. Finally SO₃ is absorbed not in water but in 98 % H₂SO₄ (water would make a mist): H₂SO₄ + nSO₃ → oleum, which is then diluted. The process is continuous; SO₂ emissions must be captured so that they do not poison the surroundings.