Sulphuric acid

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Infobox on Sulphuric acid
Example of Sulphuric acid
Sulphuric acid-1.jpg
Origin -
Stowage factor (in m3/t) 1,67 m3/t (in jars)
Humidity / moisture -
Ventilation -
Risk factors See text

Sulphuric acid

Description / Application

Sulfuric acid is a highly corrosive strong mineral acid with the molecular formula H2SO4. It is a pungent, colourless to slightly yellow viscous liquid which is soluble in water at all concentrations. Sometimes, it is dyed dark brown during production to alert people to its hazards. The historical name of this acid is oil of vitriol.

Sulfuric acid is a diprotic acid and shows different properties depending upon its concentration. Its corrosiveness on other materials, like metals, living tissues (e.g. skin and flesh) or even stones, can be mainly ascribed to its strong acidic nature and, if concentrated, strong dehydrating and oxidizing property. Sulfuric acid at a high concentration can cause very serious damage upon contact, as it not only causes chemical burns via hydrolysis, but also secondary thermal burns via dehydration. It burns cornea and can lead to permanent blindness if splashed onto eyes. Accordingly, safety precautions should be strictly observed when handling it. Moreover, it is hygroscopic, readily absorbing water vapour from the air.

Sulphuric acid can be made in various grades. High purity grades are utilized in the rayon and pharmaceutical industries and low grades are used in the manufacture of superphosphate and ammonium sulphate for the fertilizer industry. The same batch of acid can, in fact, be used for several purposes in succession. The principal uses of sulphuric acid are outlined below:

1) Manufacture of phosphate fertilizer from rock phosphate by converting insoluble rock phosphate into soluble phosphate using 70% concentration (low-grade superphosphate).
2) Manufacture of explosives such as nitrocellulose and trinitrotoluene (TNT) where it is used as a dehydrating agent.
3) Manufacture of plastics such as nitrocellulose and various synthetic fibres such as rayon.
4) Manufacture of other acids. Concentrated sulphuric acid may be used in producing hydrochloric, nitric and other acids. In each case a salt of the acid to be prepared is heated with sulphuric acid.
5) ‘Pickling’ metals. In this process the sulphuric acid is used to remove the coating of oxide from the surface of iron or steel before the metal is plated, coated or galvanized.
6) Purification of petroleum. In this process the sulphuric acid is used to char and remove many organic impurities.
7) In storage batteries. A solution of sulphuric acid is used an electrolyte in the storage battery.

Sulphuric acid is carried in varying concentrations, the most common being 93,2%. In this concentration it is a syrupy oily liquid sometimes called ‘oil of vitriol’. Another popular concentration for shipping is 78% sulphuric acid. Acids of 77% concentration and above do not react with dry mild steel or stainless steel at normal temperature but dilute acids of less than 77% concentration react with and corrode most of the common metals. Concentrations of less than 50% must be carried in rubber-coated tanks. Fuming sulphuric acid contains a concentration of between 20% and 65% of sulphur trioxide in sulphuric acid and is very corrosive to most metals when water is present. Mild steel and stainless steel are suitable containment materials if the tanks are kept free from moisture. Spent sulphuric acid or sulphuric acid which has been used for a chemical process is also carried by sea. The impurities which it contains will vary depending on the process so that shippers must consult various authorities to make sure of all the hazards involved with that particular grade of sulphuric acid.

About 90% of all sulphur goes into the production of sulphuric acid and most of this is subsequently consumed by the phosphoric fertilizer industry. As the two markets are interrelated it is essential to examine the production and movement of the raw material in order to see the resulting pattern, for sulphuric acid.

There are three main sources of sulphur:
1) Brimstone – any type of sulphur produced in its elemental form
2) Pyrite – from the mining of pyrite ores to give sulphides
3) Sulphur-in-other-forms- this type may come from a number of sources, among them:
a) Waste gases from zinc, copper, lead or nickel smelters
b) Gypsum or anhydrite
c) Hydrogen sulphide content of oil refinery or coke oven gases
d) Oil refinery acid sludge

Shipment / Storage

Sulphuric acid should be packed in UN approved packages – certified steel drums lined with HDPE – and carried on deck only. An increase in temperature during transit will cause an expansion of volume of the acid and leakage is likely to occur if the containers have been filled to more than 90% capacity, i.e. filled to a minimum of 10% ullage. Sulphuric acid is very hygroscopic and will absorb moisture from the atmosphere should stoppers become loose. Although the strong acid, more than 70% acid, has no effect on most metals, the diluted product is very corrosive and a container filled with acid which has absorbed moisture from the air may commence to corrode. When shipped is difficult and dangerous cargo to handle after a long voyage because of the possibility of corrosion, expansion and a tendency to blow drum heads and explode. This commodity evolves heat when in contact with water.

Strong irritant to tissue. TLV: 1 mg/m3 of air.

See also Acids

Risk factors

Refer to the applicable IMDG Code and Material Safety Data Sheets.