Chlorodifluoromethane
Encyclopedia
Chlorodifluoromethane or difluoromonochloromethane is a hydrochlorofluorocarbon (HCFC). This colorless gas is better known as HCFC-22, or R-22. It was once commonly used as a propellant and in air conditioning
applications. These applications are being phased out due to ozone depletion potential
and status as a potent greenhouse gas
, with a high global warming potential
. R22 is a versatile intermediate in industrial organofluorine chemistry
, e.g. as a precursor to tetrafluoroethylene
.
:
The main application of R22 is as a precursor to tetrafluoroethylene. This conversion involves pyrolysis
to give difluorocarbene
, which dimerizes:
The compound also yields difluorocarbene upon treatment with strong base and is used in the laboratory as a source of this reactive intermediate.
The pyrolysis of R22 in the presence of chlorofluoromethane
gives hexafluorobenzene
.
of 0.055, among the lowest for chlorine
-containing haloalkane
s. However, even this lower ozone depletion potential is no longer considered acceptable.
As an additional environmental concern, chlorodifluoromethane has a global warming potential
that is 1810 (1810 times that of carbon dioxide). HFCs such as R-410A have high global warming potential, but has an ODP (or ozone depletion potential) of 0. The GWP of propane (R-290), for example, is only 3.
, to be replaced by other refrigerants with lower ozone depletion potential such as propane
(R-290), R-410A
(an azeotropic
mixture of difluoromethane
and pentafluoroethane
), R-507A, R-134a (1,1,1,2-tetrafluoroethane) and R-409A.
Beginning in 2010 in the U.S., the production and importing of HCFC-22 will be limited to 25% of each country's 1989 consumption level. New and imported HCFC-22 will be available only for use in equipment manufactured before 1/1/2010.
On January 1, 2010, it became illegal to import, produce, or sell R-22 for use in new equipment or pre-charged in new equipment. In 2015, the production and importing of HCFC-22 will be limited to 10% of each country's 1989 consumption level and in 2020, production and importing of HCFC-22 will be illegal. Re-use of recovered HCFC-22 to service existing equipment will be allowed indefinitely.
It has two allotropes: crystalline II below 59 K and crystalline I above 59 K to 115.73 K.
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
applications. These applications are being phased out due to ozone depletion potential
Ozone depletion potential
The ozone depletion potential of a chemical compound is the relative amount of degradation to the ozone layer it can cause, with trichlorofluoromethane being fixed at an ODP of 1.0. Chlorodifluoromethane , for example, has an ODP of 0.055...
and status as a potent greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
, with a high global warming potential
Global warming potential
Global-warming potential is a relative measure of how much heat a greenhouse gas traps in the atmosphere. It compares the amount of heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide. A GWP is calculated over a specific time...
. R22 is a versatile intermediate in industrial organofluorine chemistry
Organofluorine chemistry
Organofluorine chemistry describes the chemistry of organofluorine compounds, organic compounds that contain the carbon–fluorine bond. Organofluorine compounds find diverse applications ranging from oil- and water-repellents to pharmaceuticals, refrigerants and reagents in catalysis...
, e.g. as a precursor to tetrafluoroethylene
Tetrafluoroethylene
Tetrafluoroethylene is a chemical compound with the formula C2F4. It is the simplest alkene fluorocarbon. This gaseous species is used primarily in the industrial preparation of polymers.-Properties:...
.
Production and current applications
Chlorodifluoromethane is prepared from chloroformChloroform
Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
:
- HCCl3 + 2 HF → HCF2Cl + 2 HCl
The main application of R22 is as a precursor to tetrafluoroethylene. This conversion involves pyrolysis
Pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...
to give difluorocarbene
Difluorocarbene
Difluorocarbene is the chemical compound with formula CF2. It has a short half-life, 0.5 and 20 msec, in solution and in the gas phase, respectively...
, which dimerizes:
- 2 CHClF2 → C2F4 + 2 HCl
The compound also yields difluorocarbene upon treatment with strong base and is used in the laboratory as a source of this reactive intermediate.
The pyrolysis of R22 in the presence of chlorofluoromethane
Chlorofluoromethane
Chlorofluoromethane or Freon 31 is a gaseous mixed halomethane .Its crystal structure is monoclinic with space group P21 and lattice constants a = 6.7676, b = 4.1477, c = 5.0206 , β = 108.205°....
gives hexafluorobenzene
Hexafluorobenzene
Hexafluorobenzene, HFB, , or perfluorobenzene is an organic, aromatic compound. In this derivative of benzene all hydrogen atoms have been replaced by fluorine atoms. The technical uses of the compound are limited, although it is recommended as a solvent in a number of Photochemical reactions...
.
Environmental effects
Chlorodifluoromethane was used as an alternative to the highly ozone-depleting CFC-11 and CFC-12, because of its relatively low ozone depletion potentialOzone depletion potential
The ozone depletion potential of a chemical compound is the relative amount of degradation to the ozone layer it can cause, with trichlorofluoromethane being fixed at an ODP of 1.0. Chlorodifluoromethane , for example, has an ODP of 0.055...
of 0.055, among the lowest for chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
-containing haloalkane
Haloalkane
The haloalkanes are a group of chemical compounds derived from alkanes containing one or more halogens. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely used commercially and, consequently, are known under many chemical and...
s. However, even this lower ozone depletion potential is no longer considered acceptable.
As an additional environmental concern, chlorodifluoromethane has a global warming potential
Global warming potential
Global-warming potential is a relative measure of how much heat a greenhouse gas traps in the atmosphere. It compares the amount of heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide. A GWP is calculated over a specific time...
that is 1810 (1810 times that of carbon dioxide). HFCs such as R-410A have high global warming potential, but has an ODP (or ozone depletion potential) of 0. The GWP of propane (R-290), for example, is only 3.
EPA Phaseout
It will be phased out soon under the Montreal ProtocolMontreal Protocol
The Montreal Protocol on Substances That Deplete the Ozone Layer is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances believed to be responsible for ozone depletion...
, to be replaced by other refrigerants with lower ozone depletion potential such as propane
Propane
Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...
(R-290), R-410A
R-410A
R-410A, sold under the trademarked names Puron, EcoFluor R410, Genetron R410A, and AZ-20, is a zeotropic, but near-azeotropic mixture of difluoromethane and pentafluoroethane , which is used as a refrigerant in air conditioning applications.-Environmental effects:Unlike many alkyl halide...
(an azeotropic
Azeotrope
An azeotrope is a mixture of two or more liquids in such a ratio that its composition cannot be changed by simple distillation. This occurs because, when an azeotrope is boiled, the resulting vapor has the same ratio of constituents as the original mixture....
mixture of difluoromethane
Difluoromethane
Difluoromethane, also called HFC-32 or R-32, is an organic compound of the dihalogenoalkane variety. It is based on methane, except that two of the four hydrogen atoms have been replaced by fluorine atoms...
and pentafluoroethane
Pentafluoroethane
Pentafluoroethane is a refrigerant that has zero ozone depletion potential.It has the formula CF3CHF2. Although it has zero ozone depletion potential, it has high global warming potential, reported by the United States Environmental Protection Agency as 3450 times that of carbon...
), R-507A, R-134a (1,1,1,2-tetrafluoroethane) and R-409A.
- Beginning January 1, 2004: The Montreal Protocol required the U.S. to reduce its consumption of HCFCs by 35% below the U.S. baseline cap. As of January 1, 2003, EPA banned production and import of HCFC-141b, the most ozone-destructive HCFC. This action allowed the United States to meet its obligations under the Montreal Protocol. EPA was able to issue 100% of company baseline allowances for production and import of HCFC-22 and HCFC-142b.
- Beginning January 1, 2010: The Montreal Protocol requires the U.S. to reduce its consumption of HCFCs by 75% below the U.S. baseline. Allowance holders may only produce or import HCFC-22 to service existing equipment. Virgin R-22 may not be used in new equipment. As a result, heating, ventilation and air-conditioning (HVAC) system manufacturers may not produce new air conditioners and heat pumps containing R-22.
- Beginning January 1, 2015: The Montreal Protocol requires the U.S. to reduce its consumption of HCFCs by 90% below the U.S. baseline.
- Beginning January 1, 2020: The Montreal Protocol requires the U.S. to reduce its consumption of HCFCs by 99.5% below the U.S. baseline. Refrigerant that has been recovered and recycled/reclaimed will be allowed beyond 2020 to service existing systems, but chemical manufacturers will no longer be able to produce R-22 to service existing air conditioners and heat pumps.
Beginning in 2010 in the U.S., the production and importing of HCFC-22 will be limited to 25% of each country's 1989 consumption level. New and imported HCFC-22 will be available only for use in equipment manufactured before 1/1/2010.
On January 1, 2010, it became illegal to import, produce, or sell R-22 for use in new equipment or pre-charged in new equipment. In 2015, the production and importing of HCFC-22 will be limited to 10% of each country's 1989 consumption level and in 2020, production and importing of HCFC-22 will be illegal. Re-use of recovered HCFC-22 to service existing equipment will be allowed indefinitely.
Physical Properties
| Property | Value |
|---|---|
| Density Density The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight... (ρ) at -69 °C (liquid) |
1.49 g.cm−3 |
| Density Density The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight... (ρ) at -41 °C (liquid) |
1.413 g.cm−3 |
| Density Density The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight... (ρ) at -41 °C (gas) |
4.706 kg.m−3 |
| Density Density The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight... (ρ) at 15 °C (gas) |
3.66 kg.m−3 |
| Specific gravity at 21 °C (gas) | 3.08 (air = 1) |
| Specific volume Specific volume In thermodynamics, the specific volume of a substance is the ratio of the substance's volume to its mass. It is the reciprocal of density:In thermodynamics, the specific volume of a substance is the ratio of the substance's volume to its mass... (ν) at 21 °C (gas) |
0.275 m³.kg−1 |
| Density Density The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight... (ρ) at 15 °C (gas) |
3.66 kg.m−3 |
| Triple point Triple point In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases of that substance coexist in thermodynamic equilibrium... 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 Heat capacity ratio The heat capacity ratio or adiabatic index or ratio of specific heats, is the ratio of the heat capacity at constant pressure to heat capacity at constant volume . It is sometimes also known as the isentropic expansion factor and is denoted by \gamma or \kappa . The latter symbol kappa is... (γ) at 30 °C (86 °F) |
1.178253 |
| Compressibility factor Compressibility factor The compressibility factor , also known as the compression factor, is a useful thermodynamic property for modifying the ideal gas law to account for the real gas behavior. In general, deviation from ideal behavior becomes more significant the closer a gas is to a phase change, the lower the... (Z) at 15 °C |
0.9831 |
| Acentric factor Acentric factor The acentric factor \omega is a conceptual number introduced by Pitzer in 1955, proven to be very useful in the description of matter. It has become a standard for the phase characterization of single & pure components... (ω) |
0.22082 |
| Molecular dipole moment | 1.458 D |
| Viscosity Viscosity Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity... (η) at 0 °C |
12.56 µPa.s (0.1256 cP) |
| Ozone depletion potential Ozone depletion potential The ozone depletion potential of a chemical compound is the relative amount of degradation to the ozone layer it can cause, with trichlorofluoromethane being fixed at an ODP of 1.0. Chlorodifluoromethane , for example, has an ODP of 0.055... (ODP) |
0.055 (CCl3F Trichlorofluoromethane Trichlorofluoromethane, also called freon-11, CFC-11, or R-11, is a chlorofluorocarbon. It is a colorless, nearly odorless liquid that boils at about room temperature.- Uses :It was the first widely used refrigerant... = 1) |
| Global warming potential Global warming potential Global-warming potential is a relative measure of how much heat a greenhouse gas traps in the atmosphere. It compares the amount of heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide. A GWP is calculated over a specific time... (GWP) |
1810 (CO2 Carbon dioxide Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom... = 1) |
It has two allotropes: crystalline II below 59 K and crystalline I above 59 K to 115.73 K.