The process for producing sulfuric acid has four stages:
1. Extraction of sulfur or burn the mineral(contains sulfur) or Wet Gas Sulphuric Acid(WSA)
2. Conversion of sulfur to sulfur dioxide
3. Conversion of sulfur dioxide to sulfur trioxide
4. Conversion of sulfur trioxide to sulfuric acid
Extraction of sulfur
The most easy way to get sulfur is the recovery from natural gas and oil by Claus Process, which contain sulfur compounds, both organic and hydrogen sulfide which must be removed before they can be used as fuels or chemical feedstock to protect the downstream catalyst from poisioning. Another important source of sulfur is as sulfur dioxide from metal refining. Many metal ores occur as sulfides and are roasted to form an oxide and sulfur dioxide, such as lead and other sulfide ores include copper, nickel and zinc.
Conversion of sulfur to sulfur dioxide
Sulfur must first be converted to sulfur dioxide, the molten sulfur is sprayed into a furnace and burnt in a blast of dry air at about 1000 deg C.As excess air is used the emerging gas contains about 10-12% sulfur dioxide and 10% oxygen, by volume.
Conversion of sulfur dioxide to sulfur trioxide
The catalyst, normally is vanadium(V) oxide on silica which is generally in the form of small pellets like hollow cylindrical pellet with promoter, is to promote the oxidation and conversion of SO2 to SO3 in a cylindrical vessel which ascts as a fixed bed reactor with for separate beds loaded with the vanadium oxide catalyst, this is called contacting process.
Conversion of sulfur trioxide to sulfuric acid
The sulfur trioxide formed from the third bed (and the small amount from the fourth bed) are now converted to sulfuric acid when sulfur trioxide reacts with water.