Halogens and Halogen Compounds

From the whole range of substances of this group, chlorine, hydrochloric acid, hydrofluoric acid and silicon tetrafluoride are the most important with respect to the amounts released into the atmosphere and to their toxicity. These harmful substances can enter into the atmosphere from natural sources as well as from industrial sources. 

The fluorine concentrations in a clean atmosphere are low in polluted regions, in the vicinity of emissions, for example close to aluminium works, the values are as high as 0.02-0.22 mg m [53], and in city areas the values range between 0.2 and 1.9 /xg m [54]. 

In the course of reactions with hydroxides or carbonates, fluorosilicates are formed, which are mostly readily soluble in water. 

Some fluorine compounds enter into the atmosphere in the form of solid particles, such as cryolite, fluoroapatite, aluminium fluoride and sodium fluoride. 

In the case of bromine compounds, ethylene dibromide is a component of the pollutants in a city atmosphere. It is added to petrol containing 

The Changing Sulfuric Acid Industry Chem. Week. 2/1982,40-42. 

Stanford Research Institute, Publ. 1995. Sulfuric Acid-, in Chemical Economics Handbook, Menlo Park, California, USA. 

Statistisches Bundesamt, Hrsg. 1994. Produktion im produzierenden Gewerbe nach Waren und Warengruppen. Reihe. 7.1, Wiesbaden. 

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Plants producing and handling halogens and halogen compounds Tantalum finds extensive use in the production and handling of hydrochloric and hydrobromic acid, chlorine and bromine and many of their derivatives. Absorbers, coolers and heaters which show considerable advantages in terms of heat-flux capabilities and corrosion resistance have been used on hydrochloric acid duties for over 40 years and condensers have been used in bromine plants for at least the same period. Typical applications of tantalum in the bromine and chlorine industries are listed in Table 5.27 . 

The Interaction of Alkali Metal Vapours with Halogens and Halogen Compounds. 

The halogens and halogenic compounds are used in a multitude of different ways (Figure 9.15). 

Iodine accelerates the decomposition of acetaldehyde In the steady-state range, the order is approximately 1.0 and 0.5 in aldehyde and iodine, respectively. The experimental results of Rollefson and Faull have been reinterpreted and added to by O Neal and Benson . The iodine-catalysed reaction is a free radical chain process initiated by the attack of an iodine atom on the acetaldehyde molecule. The proposed mechanism fits the experimental data very well. The thermal decomposition of acetaldehyde is catalysed also by other halogens and halogen compounds . 

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