sulfuric acid

sulfuric acid manufacture

Figure 1. To make sulfuric acid, liquid sulfur is blown (1) into a burner (3), also fed with air (2), forming sulfur dioxide. This passes through the filter (4) to the cooling tower (5). In the washing (6) it is washed with water then dried in a packed tower (7) of Raschig rings by means of 98% sulfuric acid entering at 8 and leaving at 9. In the converter (10) the dry sulfur dioxide reacts with oxygen (11), is cooled (12) and the resultant sulfur dioxide is absorbed in 98% sulfuric acid (13) to yield oleum (14). This is diluted (15) with sulfuric acid (16) to produce 98% sulfuric acid (17).

Sulfuric acid (H2SO4), formerly known as oil of vitriol, is a highly corrosive, dense, oily liquid, colorless to dark brown depending on its purity. Sulfuric acid (H2SO4) is an oxidizing agent, reacting with metals, sulfur, and carbon on heating, and is a powerful dehydrating agent. In aqueous solution it is a strong acid, and reacts with bases and most metals to give sulfates. Fuming sulfuring acid, or oleum, is 100% sulfuric acid containing dissolved sulfur trioxide; it is used to manufacture sulfonic acid.


Sulfuric acid is used to manufacture a variety of chemicals including fertilizers, dyestuffs, paints, detergents, and explosives. It is itself manufactured industrially by the oxidation of sulfur dioxide in the contact process (see below).


relative density 1.84
melting point 10.3°C (50.5°F)
boiling point 330°C (626°F)


Manufacture of sulfuric acid


Lead-chamber process

The lead-chamber process was an early process for manufacturing sulfuric acid, which has now been superceded by the contact process. Sulfur dioxide, produced by burning sulfur, is mixed with air and nitric oxide (see nitrogen) and passed in turn through the Glover tower, several lead chambers (where steam is sprayed in), and the Gay-Lussac tower, where concentrated sulfuric acid is sprayed in. The mixture of sulfuric acid and nitrosylsulfuric acid from the Gay-Lussac tower is sprayed back into the Glover tower. The net product is impure 70% sulfuric acid, tapped off from the lead chambers. The nitric oxide is catalytic.


Contact process

The contact process is a major industrial process for manufacturing sulfuric acid. Sulfur is burned in air to give sulfur dioxide, which is then oxidized to sulfur trioxide with a vanadium pentoxide or platinum catalyst. Arsenic, which poisons the catalyst, must first be removed. The sulfur trioxide is absorbed in concentrated sulfuric acid to yield oleum, which is diluted with water to the concentration required. Direct reduction of sulfur trioxide with water is too violent.