Bromine (freezing point: –7.3oC, boiling point: 58.8oC, density: 3.1226) is a member of the halogen family and is a heavy, dark-red liquid.
Bromine is produced from seawater, in which bromine occurs in concentrations of 60 to 70 ppm, and from natural brine, where the concentration of bromine may be as high as 1300 ppm. It can also be produced from waste liquors resulting from the extraction of potash salts from carnallite deposits.
Bromine is isolated from sea water by air-blowing it out of chlorinated seawater.
2NaBr + Cl2 → 2NaCl + Br2
In ocean water, where the concentration of bromine is relatively dilute, air has proved to be the most economical blowing-out agent. However, in the treatment of relatively rich bromine sources such as brines, steaming out the bromine vapor is more satisfactory.
The steaming-out process (Fig. 1) process involves preheating the brine to 90oC in a heat exchanger and passing it down a chlorinator tower. After partial chlorination, the brine flows into a steaming-out tower, where steam is injected at the bottom and the remaining chlorine is introduced.
The halogen-containing vapor is condensed and gravity separated. The top water-halogen layer is returned to the steaming-out tower, and the crude halogen (predominantly bromine) bottom layer is separated and purified.
Crude bromine is purified by redistillation or by passing the vapors over iron filings that remove any chlorine impurity.
Bromine is used for the production of alkali bromides that cannot be manufactured by the action of caustic soda on bromine because hypobromites and bromates are also produced. Thus, the van der Meulen process from the production of potassium bromide involves treating bromine with potassium carbonate in the presence of ammonia.
K2CO3 + 3Br2 + 2NH3 → 6KBr + N2 + 3CO2 + 3H2O
Manufacture of bromine from brine.
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