Vinyl chloride monomer: properties and applications / Articles

Vinyl chloride monomer (chloroethene, VCM) is a chlorine-containing unsaturated hydrocarbon and one of the most important large-tonnage monomers of the modern petrochemical industry. Under normal conditions, it is a colourless gas with a sweetish, slightly ethereal odour that readily liquefies upon cooling or under pressure. Its molecular formula is C₂H₃Cl, structural formula CH₂=CHCl, and molecular mass 62.50 g/mol. Vinyl chloride is practically insoluble in water but readily soluble in chloroform, dichloroethane, ethanol, ether and acetone. This monomer is the basis for the production of polyvinyl chloride (PVC) — one of the most in-demand plastics in the world — as well as a wide range of copolymers and chlorinated solvents.

Chemical Nature and Physicochemical Properties

The vinyl chloride molecule combines a reactive double bond with a chlorine atom, which imparts unique properties to polymers based on it: flame resistance, chemical resistance, mechanical strength and durability. The chlorine contained in the monomer gives PVC self-extinguishing properties, making it indispensable in construction, electrical engineering and cable production.

The key physical characteristics of vinyl chloride determine its industrial handling:

Physical state: colourless gas under normal conditions, readily liquefied.
Boiling point: minus 13.9 °C.
Melting point: minus 153.8 °C (according to other data, minus 158.4 °C).
Density (liquid): 911 kg/m³ at 20 °C; 983 kg/m³ at minus 20 °C.
Vapour density (air = 1): 2.15 (heavier than air).
Flash point: 43 °C (according to other data, minus 78 °C for gas).
Explosive limits in air: 3.6–31.0% by volume.
Critical temperature: 142–158 °C; critical pressure: 5.22–5.6 MPa.

Vinyl chloride is extremely hazardous: it belongs to hazard class 1 (extremely hazardous substances) and has carcinogenic, mutagenic, teratogenic and narcotic effects. The maximum allowable concentration (MAC) in the working area air is 5 mg/m³ (according to some data, 1–5 mg/m³), and the average daily MAC in the ambient air of populated areas is 0.01 mg/m³. The International Agency for Research on Cancer (IARC) classifies vinyl chloride as a Group 1 carcinogen capable of causing liver angiosarcoma.

Production Technology

Modern industrial production of vinyl chloride is based on two main technological routes: the ethylene route and the acetylene route. The choice of method depends on the availability and cost of feedstock in a particular region.

Ethylene route (direct chlorination and pyrolysis). In the first stage, ethylene reacts with chlorine in the presence of a catalyst (iron or copper chloride) to form 1,2-dichloroethane (EDC). In the second stage, dichloroethane undergoes thermal pyrolysis at a temperature of 480–500 °C, resulting in the formation of vinyl chloride and the release of hydrogen chloride. The resulting HCl is usually returned to the process through the oxychlorination stage: the reaction of ethylene with HCl and oxygen (or air) at 470–500 °C over a catalyst produces additional dichloroethane and closes the chlorine cycle. This method is dominant in North America, Western Europe and the Middle East.

Acetylene route (hydrochlorination). Vinyl chloride is produced by direct addition of hydrogen chloride to acetylene in the gas phase at a temperature of 130–180 °C in the presence of a catalyst based on mercury chloride on activated carbon. This method was historically the first industrial process, but due to the toxicity of mercury catalysts, its use in developed countries has declined. Nevertheless, it retains a dominant position in China, where cheap acetylene obtained from coal via calcium carbide is available.

High-temperature chlorination. There is also a method of direct high-temperature chlorination of ethylene at 400–600 °C, which allows vinyl chloride to be produced in a single stage, but it is less common due to process control difficulties and the formation of by-products.

Vinyl chloride obtained by any method requires thorough purification from acetylene, hydrogen chloride and other impurities. The commercial product typically contains at least 99.9% of the main substance. To prevent spontaneous polymerisation during storage and transportation, inhibitors (e.g., hydroquinone or phenothiazine) are introduced.

Applications

Production of polyvinyl chloride (PVC). This is the absolutely dominant consumption area for vinyl chloride — it accounts for more than 99% of global demand. PVC is produced by radical polymerisation of vinyl chloride in bulk, suspension or emulsion. The suspension method is the most common. PVC is widely used for the production of pipes, window and door profiles, siding, cable insulation, floor coverings, artificial leather, films, packaging and medical products. Due to its high chlorine content (about 56%), PVC has low flammability and does not support combustion.

Production of copolymers. Vinyl chloride is copolymerised with vinyl acetate, vinylidene chloride, acrylonitrile, butadiene, acrylic esters and other monomers. Copolymers with vinyl acetate are used for the production of varnishes, adhesives, films and coatings. Copolymers with vinylidene chloride (Saran) are used for food packaging due to their high barrier properties. Copolymers with acrylonitrile are used for the production of fibres and packaging materials.

Production of chlorinated solvents. Vinyl chloride is an intermediate for the production of 1,1,1-trichloroethane (methyl chloroform) and perchloroethylene (tetrachloroethylene), which are widely used as solvents in metalworking, dry cleaning and the electronics industry.

Other applications. In small volumes, vinyl chloride is used as a refrigerant, an extractant for oils and fats, and as a fumigant. In the past, it was used in the production of aerosols and as an anaesthetic, but due to high toxicity and carcinogenicity, these applications have been completely discontinued.

Safety and Storage

Vinyl chloride belongs to extremely hazardous substances (hazard class 1). It is toxic by inhalation and has general toxic, narcotic, carcinogenic, mutagenic and teratogenic effects. Acute poisoning may be accompanied by headache, dizziness, nausea, impaired coordination, and in severe cases — loss of consciousness and liver damage. Long-term exposure to even low concentrations is associated with the risk of developing liver angiosarcoma and other cancers.

When working with vinyl chloride, personal protective equipment must be used: filtering gas masks, rubber gloves, safety goggles and protective clothing. All technological operations must be carried out in sealed equipment with effective ventilation and continuous air monitoring.

Vinyl chloride is highly flammable, and its vapours form explosive mixtures with air over a wide concentration range. Combustion releases toxic substances, including hydrogen chloride and phosgene. Storage and transportation are carried out in liquefied form under pressure in steel tank cars and cylinders, with the addition of a polymerisation inhibitor. Containers must be protected from direct sunlight and heating. In emergency situations, immediate evacuation of personnel and the use of isolating respiratory protection equipment are required.

Market and Trends

The global vinyl chloride market is inextricably linked to the PVC market: more than 99% of all monomer produced is consumed for the production of polyvinyl chloride resins. The largest consuming region is Northeast Asia, dominated by China, which accounts for a significant share of global demand. North America and Western Europe occupy second and third places, respectively. The main demand driver is the construction industry, as PVC is widely used for pipes, profiles, cables and finishing materials.

Key industry trends include the modernisation of production facilities to improve energy efficiency and reduce emissions, the gradual phasing out of mercury catalysts in the acetylene process, and the development of technologies for capturing and utilising hydrogen chloride. Requirements for residual vinyl chloride content in finished polymers (particularly PVC for food and medical applications) are tightening. Organising supplies of vinyl chloride, including the selection of logistics solutions taking into account dangerous goods requirements, requires an individual approach and a reliable partner.

Conclusion

Vinyl chloride remains one of the key monomers of the global petrochemical industry, providing for the production of PVC, copolymers and chlorinated solvents. Its unique properties — the ability to polymerise, the flame resistance of polymers and the availability of feedstock — make it indispensable in modern industry. At the same time, its high toxicity and carcinogenicity require strict adherence to safety measures at all stages of handling this substance. Organising supplies of vinyl chloride, including grade selection, quality confirmation and logistics, requires an individual approach that takes into account specific technological requirements and operating conditions.