Chlorine
Chlorine, a key component of PVC, comes from the electrolysis of sodium
chloride. More information about this can be found in the chlorine
section. 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, Staffordshire and Cleveland,
though they extend under the North Sea and the continent as far as Poland.
Sodium chloride can be mined as rock salt (for example at Winsford,
UK), but most is extracted by dissolving in water under pressure and
pumping to the surface. Sodium carbonate is used to precipitate calcium
and other metal ions, and other reagents are used to remove suspended
particles. High-purity salt solution is required for most electrolytic
cells.
Electrolysis requires electrical energy, and so part of the environmental
impact of chlorine production is related to the use of fossil fuels
for the generation of electricity.
Ethane and Ethene
Most chloroethene is made from ethene, which is a product from petrochemical
cracking. Ethane (used in the EVC process)
is often present with natural gas, and is one of the products from distillation
of oil. PVC is therefore based on non-renewable hydrocarbon feedstock,
as is the case with many common plastics.
