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  Sulphuric Acid - (H2SO4)

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.
Lead Chamber Process
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; the succession. 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 was 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., super phosphate 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 C 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.
A molecule of Sulphuric Acid, H2SO4, consists of two atoms of hydrogen, one atom of sulphur and four atoms of oxygen
Sulphuric acid is a colorless viscous corrosive oily liquid, which has

  • Melting Point : 10.3 degC
  • Boiling Point : 338 degC
  • Formula weight 98.08
  • Specific gravity or density 1.94
  • Flash point none
  Sulphuric acid is the strong acid produced by dissolving sulphur trioxide in water.
SO3 + H2O ==> H2SO4
The Strength of Acids is determined by the degree to which they are ionized in aqueous solution For example, Sulphuric Acid, H2SO4, which is a strong acid is fully dissociated, and all the displaceable hydrogen in the acid is present in solution as Hydrogen Ion, H (+).
H2SO4 ==> H (+) + SO4
100% as H (+)
In contrast, the weak acids ethanoic acid, CH3COOH, is partially ionized in solution, and only approximately 5% of the displaceable Hydrogen in the acid is present in solution as hydrogen ion, H (+).
CH3COOH ==> H (+) + CH3COO (-)
5% as H (+)
Properties of Sulphuric Acid
  • Sulphuric acid is a powerful protonating agent.
  • It is also a moderately strong oxidizing agent.
  • Sulphuric acid is also a powerful dehydrating agent and is used to remove a molecule of water from many organic compounds.
  • In dilute solution, sulphuric acid is a strong dibasic acid forming two series of salts.
A Dibasic Acid has two acidic hydrogen atoms in its molecules which can be ionized. Sulphuric Acid, H2SO4, is a dibasic acid, because it contains two hydrogen atoms which ionize in aqueous solution to become Hydrogen Ions, H (+).
H2SO4 ==> 2 H (+) + SO4 (2 - )
Sulphuric acid is an important industrial chemical and it has many uses as a strong oxidizing agent and a powerful dehydrating agent. Commercially available sulphuric acid is as a 96-98% solution of the acid in water. It is a powerful protonating agent. It is also a powerful dehydrating agent and is used to remove a molecule of Water, HO2, from many organic compounds. The Dehydration Reactions of Alcohols results in their converted into an alkenes, and involves the elimination of a molecule of water. Dehydration requires the presence of an acid and the application of heat.

Preparation of Sulphuric Acid

Combustion of Sulphur
When a small amount of Sulphur, S, is kindled on a deflagrating spoon, it burns with a bright blue flame when introduced into a gas jar containing Oxygen, O2. A gas, Sulphur Dioxide, SO2, is the main product of the combustion. However, a little Sulphur Trioxide, SO3, is also formed, which makes the gas slightly cloudy.
S + O2 ==> SO2
Sulphur Dioxide
2S + 3O2 ==> 2SO3
Sulphur Trioxide
When shaken with water, the products of combustion dissolve, forming an acidic solution which turns litmus red.
SO2 + H2O ==> H2SO3
Sulphur Sulphurous
Dioxide Acid
SO2 + H2O ==> H2SO4
Sulphur Sulphuric
Trioxide Acid
Manufacture of Sulphuric Acid
Sulphuric acid was manufactured by the lead-chamber process until the mid-1930s, but this process has now been replaced by the contact process, involving the catalytic oxidation of sulphur dioxide.
Properties of Sulphuric Acid
The Contact Process is used for manufacturing sulphuric acid and fuming sulphuric acid from sulphur dioxide, which is made by burning sulphur or by roasting sulphide ores and oxygen (in the form of air) which combine to form sulphur trioxide in the presence of a catalyst. The reaction is exothermic and the conditions are controlled to keep the temperature at 450 degC. The catalyst used is valadium oxide (V2O5). The sulphur trioxide is dissolved in sulphuric acid to form fuming sulphuric acid, this is called oleum.
S(s) + O2 (g) ==> SO2 (g)
Sulphur Dioxide
2SO2(g) + O2(g) ==> 2SO3(g)
Sulphur Trioxide
SO3 (g) + H2SO4 (l) ==> H2S2O7 (l)
This Oleum, H2S2O7, is then diluted with Water, H2O, to produce concentrated Sulphuric Acid, H2SO4.
H2S2O7 (l) + H2O (l) ==> 2 H2SO4 (l)
Oleum Sulphuric Acid
General specifications
Parameters Content
Total Acidity (as H2SO4) 98.00% min
Residue on ignition 0.050% max
Iron Content (as Fe) 0.005% max
Lead Content (as Pb) 0.002% max
Arsenic content (as As) 0.003 % max
Bulk density 1.840
End Uses
Sulphuric Acid is the bulk commodity chemical used by almost all the industries. It is the basic building molecule for chemical industry; used for different applications. The major consuming end use segments are:
  • Fertilizer (Phosphates Fertilizers: DAP & SSP)
  • Detergent
  • Dyes & Dyes Intermediates
  • Organic & Inorganic Chemicals
  • Textiles
  • Petrochemicals
  • Refineries
  • Pharmaceuticals
  • Explosives
  • Pulp & Paper
  • Rayon
  • Alum Manufacturing
  • Sugar Refining
  • Metal Pickling
  • Electrolysis

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