Feedstock

The manufacture of PVC requires a source of chlorine, and a source of hydrocarbon.

diagram: feedstock for PVC

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.

Photo: ECI p46 (chlorine 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.

Recycled Feedstock
PVC is increasingly being recycled by various methods. This means recycled feedstock is available for the manufacture of PVC products, reducing the amount of oil and salt required. Click here for more on PVC recycling.


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