Vinyl chloride is an organochloride with the chemical formula H2CDouble bond. It is also called vinyl chloride monomer ( VCM) or chloroethene. It is an important industrial chemical chiefly used to produce the polymer polyvinyl chloride (PVC). Vinyl chloride is a colourless flammable gas that has a sweet odor and is . Vinyl chloride monomer is among the top twenty largest (petroleum-derived chemicals) in world production.[ The United States remains the largest vinyl chloride manufacturing region because of its low-production-cost position in chlorine and ethylene raw materials. China is also a large manufacturer and one of the largest consumers of vinyl chloride.]
Uses
Vinyl chloride, also called vinyl chloride monomer (VCM), is exclusively used as a precursor to PVC. Due to its toxic nature, vinyl chloride is not found in other products. Poly(vinyl chloride) (PVC) is very stable, storable and not toxic.[
]
Until 1974, vinyl chloride was used in aerosol spray propellant.
Production
Globally, approximately 40 million tonnes of PVC resin are produced per year,
History
Vinyl chloride was first synthesized in 1835 by Justus von Liebig and his student Henri Victor Regnault. They obtained it by treating 1,2-dichloroethane with a solution of potassium hydroxide in ethanol.
Acetylene-based routes
In 1912, Fritz Klatte, a German chemist working for Griesheim-Elektron, patented a means to produce vinyl chloride from acetylene and hydrogen chloride using mercuric chloride as a catalyst. Acetylene reacts with hydrogen chloride over a mercuric chloride catalyst to give vinyl chloride:
- C2H2 + HCl → CH2=CHCl
The reaction is exothermic and highly selective. Product purity and yields are generally very high.[
]
This route to vinyl chloride was common before ethylene became widely distributed. When vinyl chloride producers shifted to using the thermal cracking of EDC described below, some used byproduct HCl in conjunction with a colocated acetylene-based unit. The hazards of storing and shipping acetylene meant that the vinyl chloride facility needed to be located very close to the acetylene generating facility.
In view of mercury's toxicity, gold- and platinum-based catalysts have been proposed.
The mercury-based technology is the main production method in China due to low price on coal from which acetylene is produced,
Ethylene-based routes
In the United States and Europe, mercury-catalyzed routes widely used in the 20th century have been superseded by more economical and green chemistry processes based on ethylene. Ethylene is made by cracking ethane. Two steps are involved, chlorination and dehydrochlorination:
Possible routes from ethane
Numerous attempts have been made to convert ethane directly to vinyl chloride.[
]
High-temperature chlorination:
High-temperature oxychlorination, which uses oxygen and hydrogen chloride in place of chlorine:
High-temperature oxidative chlorination:
Thermal decomposition of dichloroethane
1,2-Dichloroethane, ClCH2CH2Cl (also known as ethylene dichloride, EDC), can be prepared by halogenation of ethane or ethylene, inexpensive starting materials. EDC thermally converts into vinyl chloride and anhydrous HCl. This production method has become the major route to vinyl chloride since the late 1950s.[
]
The thermal cracking reaction is highly endothermic, and is generally carried out in a fired heater. Even though residence time and temperature are carefully controlled, it produces significant quantities of chlorinated hydrocarbon side products. In practice, the yield for EDC conversion is relatively low (50 to 60 percent). The furnace effluent is immediately quenched with cold EDC to minimize undesirable side reactions. The resulting vapor-liquid mixture then goes to a purification system. Some processes use an absorber-stripper system to separate HCl from the chlorinated hydrocarbons, while other processes use a refrigerated continuous distillation system.[
]
Storage and transportation
Vinyl chloride is stored as a liquid. The accepted upper limit of safety as a health hazard is 500 ppm. Often, the storage containers for the product vinyl chloride are high capacity spheres. The spheres have an inside sphere and an outside sphere. Several inches of space separate the inside sphere from the outside sphere. The interstitial space between the spheres is purged with an inert gas such as nitrogen. As the nitrogen purge gas exits the interstitial space it passes through an analyzer that detects whether any vinyl chloride is leaking from the internal sphere. If vinyl chloride starts to leak from the internal sphere or if a fire is detected on the outside of the sphere then the contents of the sphere are automatically dumped into an emergency underground storage container. Containers used for handling vinyl chloride at atmospheric temperature are always under pressure. Inhibited vinyl chloride may be stored at normal atmospheric conditions in suitable pressure vessels. Uninhibited vinyl chloride may be stored either under refrigeration or at normal atmospheric temperature in the absence of air or sunlight but only for a duration of a few days. If stored for longer periods, regular checks must be made to confirm no polymerization has taken place.
In addition to its toxicity risk, transporting vinyl chloride also presents the same risks as transporting other flammable gases such as propane, butane, or natural gas.
Fire and explosion hazard
In the U.S., OSHA lists vinyl chloride as a Class IA Flammable Liquid, with a National Fire Protection Association Flammability Rating of 4. Because of its low boiling point, liquid vinyl chloride will undergo flash evaporation (i.e., autorefrigerate) upon its release to atmospheric pressure. The portion vaporized will form a dense cloud (more than twice as heavy as the surrounding air). The risk of subsequent explosion or fire is significant. According to OSHA, the flash point of vinyl chloride is −78 °C (−108.4 °F).["Occupational Safety and Health Guideline for Vinyl Chloride"1988."]
Health effects
Since it is a gas under most ambient conditions, primary exposure is via inhalation, as opposed to the consumption of contaminated food or water, with occupational hazards being highest. Prior to 1974, workers were commonly exposed to 1,000 ppm vinyl chloride, causing "vinyl chloride illness" such as acroosteolysis and Raynaud's Phenomenon. The symptoms of vinyl chloride exposure are classified by ppm levels in ambient air with 4,000 ppm having a threshold effect.[Harrison, Henrietta (2008). Vinyl chloride Toxicological overview, Health Protection Agency, UK] The intensity of symptoms varies from acute (1,000–8,000 ppm), including dizziness, nausea, visual disturbances, headache, and ataxia, to chronic (above 12,000 ppm), including narcotic effect, Heart arrhythmia, and fatal respiratory failure.[International Programme on Chemical Safety (IPCS) (1999). Vinyl chloride. Environmental Health Criteria 215. WHO. Geneva.] RADS (Reactive Airway Dysfunction Syndrome) may be caused by acute exposure to vinyl chloride.[UK Department for Environment, Food, and Rural Affairs (DEFRA) and Environment Agency (EA) (2004). "Contaminants in soil: Collation of toxicological data and intake values for humans. Vinyl chloride."]
Vinyl chloride is a mutagen having effects which affect lymphocyte chromosomal structure.[International Agency for Research on Cancer (IARC). "Vinyl chloride, polyvinyl chloride, and vinyl chloride-vinyl acetate copolymers." Vol 19, 1979. IARC. "Vinyl chloride." Supplement 7, 1987. Lyon.] Chronic exposure leads to common forms of respiratory failure (emphysema, pulmonary fibrosis) and focused hepatotoxicity (hepatomegaly, hepatic fibrosis). Continuous exposure can cause CNS depression including euphoria and disorientation. Decreased male libido, miscarriage, and birth defects are known major reproductive defects associated with vinyl chloride.
Vinyl chloride can have acute dermal and ocular effects. Dermal exposure effects are thickening of skin, edema, decreased elasticity, local frostbites, blistering, and irritation.
Liver toxicity
The hepatotoxicity of vinyl chloride has long been established since the 1930s when the PVC industry was just in its early stages. In the very first study about the dangers of vinyl chloride, published by Patty in 1930, it was disclosed that exposure of test animals to just a single short-term high dose of vinyl chloride caused liver damage.[Tribukh, S L et al. "Working Conditions and Measures for Their Improvement in Production and Use of Vinylchloride Plastics" (1949)] In 1954, B.F. Goodrich Chemical stated that vinyl chloride caused liver injury upon short-term exposures. Almost nothing was known about its long-term effects. They also recommended long-term animal toxicology studies. The study noted that if a chemical did justify the cost of testing, and its ill-effects on workers and the public were known, the chemical should not be made.[Wilson, Rex H et al. "Toxicology of Plastics and Rubber – Plastomers and Monomers." Reprinted from Industrial Medicine and Surgery. 23:11, 479–786. November 1954.] In 1963, research paid for in part by Allied Chemical found liver damage in test animals from exposures below 500 parts per million (ppm).[Kramer, G.C., M.D. "The Correlation of Clinical and Environmental Measurements for Workers Exposed to Vinyl Chloride." The Dow Chemical Company. Midland Michigan.] In a 1969 presentation given in Japan, P. L. Viola, a European researcher working for the European vinyl chloride industry, indicated, "every monomer used in V.C. manufacture is hazardous....various changes were found in bone and liver. Particularly, much more attention should be drawn to liver changes. The findings in rats at the concentration of 4 to 10 ppm are shown in pictures." In light of the finding of liver damage in rats from just 4–10 ppm of vinyl chloride exposure, Viola added that he "should like some precautions to be taken in the manufacturing plants polymerizing vinyl chloride, such as a reduction of the threshold limit value of monomer."[Viola, P.L. "Pathology of Vinyl Chloride" International Congress on Occupational Health. Japan. 1969.]
Vinyl chloride was first reported to induce Angiosarcoma in 1974
Vinyl chloride is now an IARC group 1 carcinogen known to cause hepatic angiosarcoma (HAS) in highly exposed industrial workers.
Cancerous tumors
Animals exposed to 30,000 ppm of vinyl chloride developed cancerous tumors. Studies on vinyl chloride workers were a "red flag" to B.F. Goodrich and the industry.[Viola, P L. "Carcinogenic Effect of Vinyl Chloride" Presented at the Tenth International Cancer Congress. Houston, Texas. May 22–29, 1970.] In 1972, Maltoni, another Italian researcher for the European vinyl chloride industry, found liver tumors (including angiosarcoma) from vinyl chloride exposures as low as 250 ppm for four hours a day.[Maltoni, C. "Cancer Detection and Prevention" (1972) Presented at the Second International Symposium on Cancer Detection and Prevention. Bologna, April 9–12, 1973.]
In 1997 the U.S. Centers for Disease Control and Prevention (CDC) concluded that the development and acceptance by the PVC industry of a closed loop polymerization process in the late 1970s "almost completely eliminated worker exposures" and that "new cases of hepatic angiosarcoma in vinyl chloride polymerization workers have been virtually eliminated."[ Epidemiologic Notes and Reports Angiosarcoma of the Liver Among Polyvinyl Chloride Workers – Kentucky . Centers for Disease Control and Prevention. 1997.]
The Houston Chronicle claimed in 1998 that the vinyl industry manipulated vinyl chloride studies to avoid liability for worker exposure and hid extensive and severe chemical spills in local communities.[Jim Morris, "In Strictest Confidence. The chemical industry's secrets," Houston Chronicle. Part One: "Toxic Secrecy," June 28, 1998, pp. 1A, 24A–27A; Part Two: "High-Level Crime," June 29, 1998, pp. 1A, 8A, 9A; and Part Three: "Bane on the Bayou," July 26, 1998, pgs. 1A, 16A.]
Environment pollution
According to the U.S. EPA, "vinyl chloride emissions from poly(vinyl chloride) (PVC), ethylene dichloride (EDC), and vinyl chloride monomer (VCM) plants cause or contribute to air pollution that may reasonably be anticipated to result in an increase in mortality or an increase in serious irreversible, or incapacitating reversible illness. Vinyl chloride is a known human carcinogen that causes a rare cancer of the liver."[National Emission Standards for Hazardous Air Pollutants (NESHAP) for Vinyl Chloride Subpart F, OMB Control Number 2060-0071, EPA ICR Number 0186.09 ( Federal Register: September 25, 2001 (Volume 66, Number 186) )] EPA's 2001 updated Toxicological Profile and Summary Health Assessment for vinyl chloride in its Integrated Risk Information System (IRIS) database lowers EPA's previous risk factor estimate by a factor of 20 and concludes that "because of the consistent evidence for liver cancer in all the studies ... and the weaker association for other sites, it is concluded that the liver is the most sensitive site, and protection against liver cancer will protect against possible cancer induction in other tissues."[EPA Toxicological Review of Vinyl Chloride in Support of Information on the IRIS. May 2000]
Mechanism
The carcinogenicity of VC is attributed to the action of two metabolites, chloroethylene oxide and chloroacetaldehyde. The former is produced by the action of cytochrome P-450 on VC. Both chloroethylene oxide and chloroacetaldehyde are .
Microbial remediation
The bacteria species Nitrosomonas europaea can degrade a variety of halogenated compounds including trichloroethylene, and vinyl chloride.
See also
-
Vinyl group
-
List of refrigerants, for R-1140
-
2023 Ohio train derailment, in which a large amount of vinyl chloride was spilled
Additional references for environmental pollution
-
International Programme on Chemical Safety (IPCS) (1999). Vinyl chloride. Environmental Health Criteria 215. WHO, Geneva.
-
National Poisons Information Service (NPIS) (2004). "Vinyl chloride." TOXBASE®.
-
World Health Organisation (WHO) (2000). "Air quality guidelines for Europe." WHO Regional Publications, European Series, No. 91. 2nd edition. WHO Regional Office for Europe. Copenhagen.
-
Hathaway G.J. and Proctor N.H. (2004). Chemical Hazards of the Workplace. 5th edition. John Wiley & Sons, New Jersey.
-
Risk Assessment Information System (RAIS) (1993). "Toxicity summary for vinyl chloride. "Chemical Hazard Evaluation and Communication Group, Biomedical and Environmental Information Analysis Section, Health and Safety Research Division.
Inline citations
Further reading
External links
(
Chloroalkenes
)
