Sulphuric acid

There are two major processes (lead chamber and contact) for production of sulphuric acid, and it is available commercially in a number of grades and concentrations. The lead chamber process, the older of the two processes, is used to produce much of the acid used to make fertilizers; it produces a relatively dilute acid (62%–78% H2SO4). The contact process produces a purer, more concentrated acid but requires purer raw materials and the use of expensive catalysts. In both processes sulphur dioxide is oxidized and dissolved in water. The sulphur dioxide is obtained by burning sulphur, by burning pyrites (iron sulphides), by roasting nonferrous sulphide ores preparatory to smelting, or by burning hydrogen sulphide gas. Some sulphuric acid is also made from ferrous sulphate waste solutions from pickling iron and steel and from waste acid sludge from oil refineries.

In the lead chamber process hot sulphur dioxide gas enters the bottom of a reactor called a Glover tower where it is washed with nitrous vitriol (sulphuric acid with nitric oxide, NO, and nitrogen dioxide, NO2, dissolved in it) and mixed with nitric oxide and nitrogen dioxide gases; some of the sulphur dioxide is oxidized to sulphur trioxide and dissolved in the acid wash to form tower acid or Glover acid (about 78% H2SO4). From the Glover tower a mixture of gases (including sulphur dioxide and trioxide, nitrogen oxides, nitrogen, oxygen, and steam) is transferred to a lead-lined chamber where it is reacted with more water. The chamber may be a large, boxlike room or an enclosure in the form of a truncated cone. sulphuric acid is formed by a complex series of reactions; it condenses on the walls and collects on the floor of the chamber. There may be from three to twelve chambers in a series; theuccession. The acid produced in the chambers, often called chamber acid or fertilizer acid, contains 62% to 68% H2SO4. After the gases have passed through the chambers they are passed into a reactor called the Gay-Lussac tower where they are washed with cooled concentrated acid (from the Glover tower); the nitrogen oxides and unreacted sulphur dioxide dissolve in the acid to form the nitrous vitriol used in the Glover tower. Remaining waste gases are usually discharged into the atmosphere.

sulphuric acid is one of the most important industrial chemicals. More of it is made each year than is made of any other manufactured chemical; more than 40 million tons of it were produced in the United States in 1990. It has widely varied uses and plays some part in the production of nearly all manufactured goods. The major use of sulphuric acid is in the production of fertilizers, e.g., superphosphate of lime and ammonium sulphate. It is widely used in the manufacture of chemicals, e.g., in making hydrochloric acid, nitric acid, sulphate salts, synthetic detergents, dyes and pigments, explosives, and drugs. It is used in petroleum refining to wash impurities out of gasoline and other refinery products. sulphuric acid is used in processing metals, e.g., in pickling (cleaning) iron and steel before plating them with tin or zinc. Rayon is made with sulphuric acid. It serves as the electrolyte in the lead-acid storage battery commonly used in motor vehicles (acid for this use, containing about 33% H2SO4 and with specific gravity about 1.25, is often called battery acid).

Although sulphuric acid is now one of the most widely used chemicals, it was probably little known before the 16th cent. It was prepared by Johann Van Helmont (c.1600) by destructive distillation of green vitriol (ferrous sulphate) and by burning sulphur. The first major industrial demand for sulphuric acid was the Leblanc process for making sodium carbonate (developed c.1790). sulphuric acid was produced at Nordhausen from green vitriol but was expensive. A process for its synthesis by burning sulphur with saltpeter (potassium nitrate) was first used by Johann Glauber in the 17th cent. and developed commercially by Joshua Ward in England c.1740. It was soon superseded by the lead chamber process, invented by John Roebuck in 1746 and since improved by many others. The contact process was originally developed c.1830 by Peregrine Phillips in England; it was little used until a need for concentrated acid arose, particularly for the manufacture of synthetic organic dyes.