A petrochemical product
Chlorine + ethylene = PVC
‘Petrochemical’ relates to substances obtained by the refining and processing of petroleum or natural gas. Currently, the majority of PVC is manufactured by combining ethylene with chlorine. As ethylene is a product of the oil & gas industry, PVC is therefore considered to be a petrochemical product. PVC can also be produced from a range of hydrocarbons including coal, and derivatives of plants such as sugar cane, but this method is not used in Europe.Most commodity plastics have carbon and hydrogen as their main component elements, but PVC also contains chlorine, which has several advantages. Chlorines allows PVC to be compatible with a wide range of other materials, making PVC a particularly versatile material. The chlorine content also helps to make PVC flame retardant, and can also be used as a 'marker' to distinguish PVC in automatic sorting systems in plastics recycling.
The production process in detail
PVC’s raw materials, ethylene and chlorine, are provided by upstream industries. These industries include the chlor-alkali (caustic soda) industry and the basic petrochemicals producers (sometimes known as feedstocks). The chlor-alkali industry uses industrial grade salt to supply chlorine (and caustic soda and hydrogen) via electrolysis. The basic petrochemicals producers supply ethylene and propylene through the thermal cracking of naphtha, or natural gas. Natural gas is mainly supplied by the petroleum refinery industry, which uses crude oil as raw material.With these raw materials, the PVC production process can commence. Ethylene is combined with chlorine to produce an intermediate chemical known as EDC (ethylene dichloride or 1,2-dichloroethane). EDC is then transformed into vinyl chloride through the process of polymerization, that involves linking together the simplest units of vinyl chloride, called the monomers, to form long molecular chains, called polymers. This produces polyvinyl chloride (PVC) in the form of a white powder. Through a variety of techniques, this powder is then blended with other ingredients to make a wide range of PVC applications. This process uses considerably little energy.
VCM: Strict Quality & Safety Control
The vinyl chloride monomer is known by its initials, VCM. It is the key material from which PVC is made. VCM is a gas with a molecular weight of 62.5 and boiling point of -13.9°C, and hence has a high vapour pressure at ambient temperature. It is therefore manufactured under strict quality and safety control, and is usually stored in liquid form under pressure. Monomers that may cause health hazards when in direct contact to humans do exist. They are reactive gaseous chemical substances, and are manufactured and processed under strict control for health, safety and environmental protection.