Sulphuric Acid: Production methods summary

Production methods summary

In the 15th century it was made either by burning sulphur with saltpetre (potassium nitrate) or by distilling the acid from a mixture of silica and Iron III sulphate (ferric sulphate, known as vitriol, hence the old name of sulphuric acid used by alchemists - 'oil of vitriol').

In 1746, John Roebuck established the lead chamber process, in which sulphur was mixed with saltpetre (potassium nitrate) and a catalyst, and then burnt inside a lead chamber. The sulphur dioxide produced was dissolved in water on the floor of the chamber, lead metal being used because it does not react with the resulting sulphuric acid.

The process was improved in the 19th century by blowing air into the chamber and by recycling most of the nitrogen oxides produced.

The Contact Process

In 1831 Peregrine Phillips, a British vinegar merchant, patented the Contact Process for making sulphuric acid. Serious production did not begin, however, until the 1880s onwards. The Contact Process has been the dominant process used to manufacture sulphuric acid for most of the past 100 years.

In this process, sulphur dioxide is oxidised to sulphur trioxide, and the sulphur trioxide is then reacted with water. A platinum catalyst was used originally, but this was later replaced by vanadium (V) oxide, which is cheaper and less easily poisoned.
For more details of the Contact Process, click here.

The conversion of sulphur dioxide to sulphuric acid is a very efficient process, achieving 98.5% efficiency using conventional methods. Even this can be improved, however, by using two stages of sulphur trioxide absorption, resulting in efficiency up to 99.6%. Click here for more details on this.

Other Methods
The need to reduce sulphur dioxide emissions has led to the contact process and several other methods being used where the primary aim is to remove sulphur dioxide. It would not be acceptable to do this in a way that simply generated a lot of other waste, and so these methods generally produce sulphuric acid.

Process	Used
"Wet" Contact Process	Cleaning emissions from molybdenum smelting, flue gas de-sulphurisation, hydrogen sulphide treatment
Modified Lead Chamber Process	Treating effluent gases with low sulphur dioxide content, and with a SO₂/NOx mixture
Hydrogen Peroxide Process	When local conditions require almost zero sulphur dioxide emissions, this will achieve 99% removal of the gas. It is, however, very expensive!