Chlorodifluoromethane
Overview
Chlorodifluoromethane or difluoromonochloromethane is a hydrochlorofluorocarbon (HCFC). It is better known under its code names of HCFC-22, R-22, Genetron 22 or Freon 22, and is commonly used in air conditioning applications, such as residential split systems in the US, rooftop units and window air conditioners.
Chlorodifluoromethane was first used as an alternative to the ozone depleting CFC-11 and CFC-12, but was later decided to be not environmentally friendly enough, although its ozone depletion potential is 0.055,[1] among the lowest for chlorine-containing haloalkanes. It will be phased out soon under the Montreal Protocol, to be replaced by more environmentally friendly refrigerants such as Propane (R-290), and other refrigerants ( even though not having very similar properties ): R-410A (an azeotropic mixture of difluoromethane and pentafluoroethane), R-502, R-134a (1,1,1,2-tetrafluroethane) and R-409A.
It is an intermediate in the synthesis of tetrafluoroethylene, into which it is converted by pyrolysis. Difluorocarbene is an intermediate in this reaction. The compound also yields difluorocarbene upon treatment with strong base and is used in the laboratory as a source of this reactive intermediate.
The US EPA has enacted regulation which will phase out the use of HCFC-22 in the near future. Air conditioning manufacturers will no longer be allowed to sell R22 equipment as of January 1, 2010. In the aftermarket service business, the allocation rights for producers who manufacture R22 will be cut each year making the remaining R22 supply potentially smaller than the service demand for the product. This could make R22 scarce in the future, and drive prices to consumers higher.
Physical Properties
| Property | Value |
|---|---|
| Density (ρ) at -69 °C (liquid) | 1.49 g.cm-3 |
| Density (ρ) at -41 °C (liquid) | 1.413 g.cm-3 |
| Density (ρ) at -41 °C (gas) | 4.706 kg.m-3 |
| Density (ρ) at 15 °C (gas) | 3.66 kg.m-3 |
| Specific gravity at 21 °C (gas) | 3.08 (air = 1) |
| Specific volume (ν) at 21 °C (gas) | 0.275 m³.kg-1 |
| Density (ρ) at 15 °C (gas) | 3.66 kg.m-3 |
| Triple point temperature (Tt) | -157.39 °C (115.76 K) |
| Critical temperature (Tc) | 96.2 °C (369.3 K) |
| Critical pressure (pc) | 4.936 MPa (49.36 bar) |
| Critical density (ρc) | 6.1 mol.l-1 |
| Latent heat of vaporization (lv) at boiling point (-40.7 °C) | 233.95 kJ.kg-1 |
| Heat capacity at constant pressure (Cp) at 30 °C (86 °F) | 0.057 kJ.mol-1.K-1 |
| Heat capacity at constant volume (Cv) at 30 °C (86 °F) | 0.048 kJ.mol-1.K-1 |
| Heat capacity ratio (γ) at 30 °C (86 °F) | 1.178253 |
| Compressibility factor (Z) at 15 °C | 0.9831 |
| Acentric factor (ω) | 0.22082 |
| Dipole moment | 1.458 D |
| Viscosity (η) at 0 °C | 12.56 µPa.s (0.1256 cP) |
| Ozone depletion potential (ODP) | 0.055 (CCl3F = 1) |
| Global warming potential (GWP) | 1900 (CO2 = 1) |
It has two allotropes: crystaline II below 59 K and crystaline I above 59 K to 115.73 K.
See also
- Haloalkane
- Halomethane
- Trihalomethane
- Hydrochlorofluorocarbon
- Chlorofluoromethane
- Difluoromethane
- Dichlorodifluoromethane
- Chlorotrifluoromethane
External links
- MSDS at Oxford University
- Template:ICSC
- Data at Integrated Risk Information System: IRIS 0657
- Phase change data at webbook.nist.gov
- IR absorption spectra
- IARC Summaries & Evaluations: Vol. 41 (1986), Suppl. 7 (1987), Vol. 71 (1999)
References
- ↑ The Montreal Protocol on Substances that Deplete the Ozone Layer. UNEP, 2000. ISBN 92-807-1888-6