Tetrafluoroethylene

Tetrafluoroethylene
Names
IUPAC name
tetrafluoroethene
Other names
perfluoroethylene
TFE
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.003.752
KEGG
UNII
Properties
C2F4
Molar mass 100.02 g/mol
Appearance Colorless gas
Odor Odorless
Density 1.519 g/cm3 at -76 °C
Melting point −142.5 °C (−224.5 °F; 130.7 K)
Boiling point −76.3 °C (−105.3 °F; 196.8 K)
Hazards
NFPA 704
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g., propane Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g., fluorine Special hazards (white): no codeNFPA 704 four-colored diamond
4
3
3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Tetrafluoroethylene (TFE) is a chemical compound with the formula C2F4. It belongs to the family of fluorocarbons and is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of polymers.

Properties

Tetrafluoroethylene is a colorless, odorless gas. Like all unsaturated fluorocarbons it is susceptible to nucleophilic attack. It is unstable towards decomposition to C and CF
4 and prone to form explosive peroxides in contact with air.[1]

Industrial use

Polymerization of tetrafluoroethylene produces polytetrafluoroethylene (PTFE) polymers such as Teflon and Fluon. PTFE is one of the two fluorocarbon resins composed wholly of fluorine and carbon. The other resin composed purely of carbon and fluorine is the copolymer of TFE with typically 6–9% hexafluoropropene (HFP), which is known as FEP (fluorinated ethylene propylene copolymer). TFE is also used in the preparation of numerous copolymers that also include hydrogen and/or oxygen, including both fluoroplastics and fluoroelastomers. Typical TFE-based fluoroplastics include ETFE, the alternating 1:1 copolymer with ethylene, and PFA, which is a random copolymer similar to FEP but with a minor amount of a perfluoroalkyl vinyl ether (PAVE) rather than HFP. DuPont uses primarily perfluoro(methylvinylether), whereas Daikin uses primarily perfluoro(propylvinylether) in manufacturing PFA. There are numerous other fluoropolymers that contain tetrafluoroethylene, but usually not at greater than 50% by weight.

Manufacture

TFE is manufactured from chloroform.[2] Chloroform is fluorinated by reaction with hydrogen fluoride to produce chlorodifluoromethane (R-22). Pyrolysis of chlorodifluoromethane (at 550-750 °C) yields TFE, with difluorocarbene as an intermediate.

CHCl3 + 2 HF → CHClF2 + 2 HCl
2 CHClF2 → C2F4 + 2 HCl

The reverse polymerization reaction – vacuum pyrolysis of PTFE at 650–700 °C (1,200–1,290 °F) in a quartz vessel – is a convenient laboratory synthesis of TFE. The PTFE polymer cracks, and at a pressure below 5 Torr (670 Pa) exclusively C2F4 is obtained. At higher pressures the product mixture contains hexafluoropropylene and octafluorocyclobutane.[3]

Safety

TFE is an alkylating agent, albeit a weak one, and as such is expected to be carcinogenic. LD50(rat, inhalation) = 40000 ppm.[4] The compound is best handled diluted with an inert gas, as localized heating can provoke explosive decomposition to C and CF4. When working with TFE, oxygen must be carefully excluded, as it catalyzes autopolymerization, which can take place with great force.

There is also a danger of explosion when working with TFE, from adiabatic compression. If pressurized TFE is allowed into a vessel/pipework at a lower pressure the heat generated from compression may be sufficient to trigger the TFE explosive decomposition.

In industry, pipework is flushed with pressurized nitrogen, before the introduction of TFE, both to exclude oxygen and to avoid adiabatic compression .

See also

References

  1. ↑ U.S. Patent 5,345,013 issued to du Pont de Nemours
  2. ↑ Dae Jin Sung; Dong Ju Moon; Yong Jun Lee; Suk-In Hong (2004). "Catalytic Pyrolysis of Difluorochloromethane to Produce Tetrafluoroethylene". International Journal of Chemical Reactor Engineering. 2: A6. doi:10.2202/1542-6580.1065.
  3. ↑ R. J. Hunadi & K. Baum (1982). "Tetrafluoroethylene: A Convenient Laboratory Preparation". Synthesis. 39: 454. doi:10.1055/s-1982-29830.
  4. ↑ NIH Substance Profile for TFE
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