Extracting Bromine from sea water

• Bromine is used in a variety of ways:
  • In flame retardants
  • In bromomethane, a chemical used as a fumigant against pests.
  • It used to be used as an anti-knock substance with lead, but this has been phased out as lead compounds damage the environment, and catalytic converters.

Manufacturing Bromine

• The manufacturing process of bromine involves four main stages:

1. Oxidation of bromide ions into bromine.
2. Bromine vapour removal.
3. Hydrogen bromide production.
4. Oxidation of hydrogen bromide to bromine.

Oxidation of bromide ions to form bromine

• Sea water contains approximately 65,000 tonnes of bromine. This bromine is removed from the sea water by displacement of the bromide ions using chlorine: Cl_2(g) + 2Br^-2Cl^-_(aq) + Br_2(g)
• The acidity is adjusted to pH 3.5 to prevent hydrolysis of the liberated bromine and chlorine:

Bromine vapour removal

• Bromine mixture is air blown, by large fans, through the reaction mixture.

Production of hydrogen bromide

• A fine mist of sulphur dioxide and water are mixed with the bromine vapour.
• The hydrogen bromide and sulphuric acid mist formed are removed from the air by passing the mist through a layer of glass fibre, causing the acids to condense.

• The bromine at this stage is 2200 times more concentrated than it is in sea water.

Oxidation of hydrogen bromide to bromine

• The acid is oxidised with chlorine to liberate bromine: 2HBr_(g) + Cl_2(g) Br_2(aq) + 2HCl_(aq)
• This is achieved by feeding the hydrogen bromide into the top of a tower to meet a counter-current stream of steam and chlorine.
• The bromine vapour is removed from the mixture by steam distillation.
• The hot vapour mixture is condensed to form an aqueous layer of bromine, which is then dried using concentrated sulphuric acid.

How a Hazardous chemical like Bromine is handled

• Bromine is an extremely nasty substance. Bromine has a dark and dense choking vapour (its name comes from the Greek Bromos which translates to “Stench”).
• Due to its unsavoury properties, bromine has to be handled very carefully.
• When working with bromine protective suits must be warn, with special breathing apparatus (right).
• Bromine storage tanks are lined with glass, which is hard to corrode and allows the bromine to be visible.
• The tanks have bromine detectors that can sense when concentrations rise above the permitted 0.1 ppm.

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