(sodium chloride) obtained from dried-up prehistoric seas is dissolved
in water to form a solution called brine. This solution is placed
in a cell and a current of electricity is passed through it. Chlorine
gas bubbles off in one part of the cell and sodium metal is produced
in the other. The sodium reacts with water to form caustic soda
(sodium hydroxide) and hydrogen gas. Both of which have important
of chlorine gas involves the liquid metal mercury (compounds of
which are toxic) and can cause disastrous effects on the environment.
One such example was in 1950s in Japan at Minamata Bay where mercury
escaped and contaminated fish and entered the food chain which led
to the death of many local people. Industrial plants therefore take
the utmost care in preventing mercury from escaping however there
is always some mercury lost which is why a new method for making
chlorine is now used. This new method involves an asbestos diaphragm
in a cell which is porous and allows an electric current to flow
as well as resisting corrosion from chlorine and caustic soda. This
method is safer as no asbestos is lost and when the diaphragm is
replaced it can be disposed of safely and easily. However, one downfall
of this method is that it forms a more dilute solution of caustic
soda so requires steam heating to remove excess water and make it
more concentrated before it can be sold on for commercial use.
manufacture of PVC accounts for 30% of the chlorine produced industrially.
The presence of chlorine makes PVC compatible with a wide range
of other materials making PVC very versatile. Also, chlorine makes
PVC flame retardant and allows PVC to be distinguished when sorting
plastics for recycling. However chlorine itself is highly corrosive
and is a lethal gas. It is dangerous to handle and people have died
in industrial incidents involving chlorine. Rigorous safety measures
are therefore taken where chlorine is concerned including in the
transportation of this chemical.