Chlorine is made primarily by the electrolysis of sodium chloride.
Underground deposits of fairly pure sodium chloride are found in several
areas, and these are the result of the evaporation of trapped seas from
some 200 million years ago. In the UK the most accessible deposits are
in Cheshire, Lancashire, Cleveland and Northern Ireland, though they
extend under the North Sea as far as Poland.
Electrolysis requires electrical energy. A mercury cell typically operates
at only 4.5v, but draws a current of 300kA. A single facility may consist
of 100 such cells, drawing a total current of 300MA (million amps).
Part of the environmental impact of chlorine production is related to
the method used for electricity generation.
About half the chlorine used in manufacturing ends up being reduced to hydrogen chloride or a chloride salt. In many cases the chlorine is not present in the final product, but is used as an oxidising agent. This includes the manufacture of:
· Fluorocarbons and hydro-fluorocarbons
· White pigments (titanium dioxide)
If no commercial use can be found for the acid or chloride salt it may have to be disposed of as waste. A better option now being chosen is to use electrolysis or some form of chemical oxidation to convert the hydrogen chloride into chlorine. This is now a significant source of chlorine. Find out more by clicking here