Feedstock

The main feedstock for sulphuric acid production is sulphur dioxide, from several different sources:

  • Sulphur mining (now the least significant source)
  • Recovery of sulphur from oil and gas
  • Recovery of sulphur dioxide from metal smelting and ore roasting, or flue gas emissions in power stations
  • Recycling spent (used) sulphuric acid

Sulphur is mined as the element in volcanic areas or above salt domes in buried sedimentary strata associated with natural gas and crude oil deposits. The sulphur can be mined directly or extracted using the Frasch Process, and used to produce sulphur dioxide. (for more details of this see the section on sulphur mining)

Photo: Sulphur deposits Hawaii

 

 

 

 

 

 

 

 

 

Metal Ores

The metal ores Galena (lead) and Sphalerite (zinc) are both sulphides and are usually found together. They are mined in several countries including China, Australia, and parts of North and South America. A considerable amount of sulphur dioxide is produced when they are roasted to convert them into the oxide.

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In the past, the sulphur dioxide was vented to the atmosphere, contributing to air pollution, but today the sulphur dioxide is recovered from the emission gases. See the section on sulphur recovery from oil for more detail.

 

Acid Recycling

Acid recycling takes place in two ways. A significant volume of sulphuric acid is now recovered, cleaned and re-used on site using plant designed by a specialist company. If it is too contaminated for this, it may be processed to produce sulphur dioxide.

Acid recovery and concentration systems, remove impurities (often volatile organic compounds) and concentrate the purified acid. For more information on this, click here.

The SATCO process generates sulphur dioxide from spent acid, and this can then be used directly in the manufacture of more sulphuric acid. Click here for more information.

 

Sulphur is recovered from oil and natural gas and now accounts for about 70% of all sulphur used. It is present in both crude oil and natural gas as hydrogen sulphide, H2S, or as alkyl sulphides. These have to be removed before further use to meet increasingly strict sulphur emission targets. Hydrogen sulphide is also highly toxic and strongly corrosive to equipment used, and will poison catalysts used, for example, in ammonia production.For more details of this see the section on sulphur recovery from oil.

diagram: an alkyl sulphide

 

 

 

 

 

 

 

 

Feedstock Shift

The proportions of sulphur dioxide from metal smelting, flue gas recovery, recovery from oil/gas and acid recycling are growing in response to increasingly strict controls on permitted sulphur dioxide emission levels to protect air quality. This is at the expense of direct mining and pyrites roasting.

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