Chlorodifluoromethane or difluoromonochloromethane is a
hydrochlorofluorocarbon
Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced as volatile derivatives of methane, ethane, and propan ...
(HCFC). This colorless gas is better known as HCFC-22, or R-22, or . It was commonly used as a
propellant
A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the e ...
and
refrigerant
A refrigerant is a working fluid used in the heat pump and refrigeration cycle, refrigeration cycle of air conditioning systems and heat pumps where in most cases they undergo a repeated phase transition from a liquid to a gas and back again. Ref ...
. These applications were phased out under the
Montreal Protocol
The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances that are responsible for ozone depletion
Ozone depletion consists of two related events observed sinc ...
in
developed countries
A developed country (or industrialized country, high-income country, more economically developed country (MEDC), advanced country) is a sovereign state that has a high quality of life, developed economy and advanced technological infrastruct ...
in 2020 due to the compound's
ozone depletion potential
The ozone depletion potential (ODP) of a chemical compound is the relative amount of degradation to the ozone layer it can cause, with trichlorofluoromethane (R-11 or CFC-11) being fixed at an ODP of 1.0. Chlorodifluoromethane (R-22), for example ...
(ODP) and high
global warming potential
Global warming potential (GWP) is the heat absorbed by any greenhouse gas in the atmosphere, as a multiple of the heat that would be absorbed by the same mass of carbon dioxide (). GWP is 1 for . For other gases it depends on the gas and the time f ...
(GWP), and in
developing countries
A developing country is a sovereign state with a lesser developed industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreem ...
this process will be completed by 2030. R-22 is a versatile intermediate in industrial
organofluorine chemistry
Organofluorine chemistry describes the chemistry of the organofluorines, organic compounds that contain the carbon–fluorine bond. Organofluorine compounds find diverse applications ranging from Lipophobicity, oil and hydrophobe, water repellents ...
, e.g. as a precursor to
tetrafluoroethylene
Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula C2 F4. It is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of fluoropolymers.
Properties
Tetrafluoroethylene is a ...
.
Production and current applications
Worldwide production of R-22 in 2008 was about 800Gg per year, up from about 450Gg per year in 1998, with most production in developing countries.
R-22 use is being phased out in developing countries, where it is largely used for
air conditioning
Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
applications. Air conditioning sales are growing 20% annually in India and China.
R-22 is prepared from
chloroform
Chloroform, or trichloromethane, is an organic compound with chemical formula, formula Carbon, CHydrogen, HChlorine, Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to ...
:
:HCCl
3 + 2 HF → HCF
2Cl + 2 HCl
An important application of R-22 is as a precursor to
tetrafluoroethylene
Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula C2 F4. It is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of fluoropolymers.
Properties
Tetrafluoroethylene is a ...
. This conversion involves
pyrolysis
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
to give
difluorocarbene
Difluorocarbene is the chemical compound with formula CF2. It has a short half-life, 0.5 and 20 ms, in solution and in the gas phase, respectively.Douglas A Jean Osteraas "Difluorocarbene Modification of Polymer and Fiber Surfaces," ''Journal ...
, which dimerizes:
:2 CHClF
2 → C
2F
4 + 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 R-22 in the presence of
chlorofluoromethane
Chlorofluoromethane or Freon 31 is the hydrochlorofluorocarbon (HCFC) with the formula CH2ClF. It is a colorless, odorless, flammable gas.
Uses
Pyrolysis of a mixture of dichlorofluoromethane and chlorofluoromethane gives hexafluorobenzene:
:3 C ...
gives
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 ...
.
Environmental effects
![HCFC-22_mm](https://upload.wikimedia.org/wikipedia/commons/8/88/HCFC-22_mm.png)
R-22 is often used as an alternative to the highly ozone-depleting
CFC-11
Trichlorofluoromethane, also called freon-11, CFC-11, or R-11, is a chlorofluorocarbon (CFC). It is a colorless, faintly ethereal, and sweetish-smelling liquid that boils around room temperature. CFC-11 is a Class 1 ozone-depleting substance ...
and
CFC-12
Dichlorodifluoromethane (R-12) is a colorless gas usually sold under the brand name Freon-12, and a chlorofluorocarbon halomethane (CFC) used as a refrigerant and aerosol spray propellant. Complying with the Montreal Protocol, its manufacture was ...
, because of its relatively low ozone depletion potential of 0.055, among the lowest for
chlorine
Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...
-containing
haloalkane
The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely us ...
s. However, even this lower ozone depletion potential is no longer considered acceptable.
As an additional environmental concern, R-22 is a powerful
greenhouse gas
A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
with a GWP equal to 1810 (which indicates 1810 times as powerful as
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
).
Hydrofluorocarbons
Hydrofluorocarbons (HFCs) are man-made organic compounds that contain fluorine and hydrogen atoms, and are the most common type of organofluorine compounds. Most are gases at room temperature and pressure. They are frequently used in air conditi ...
(HFCs) are often substituted for R-22 because of their lower ozone depletion potential, but these refrigerants often have a higher GWP.
R-410A
R-410A, sold under the trademarked names AZ-20, EcoFluor R410, Forane 410A, Genetron R410A, Puron, and Suva 410A, is a zeotropic but near-azeotropic mixture of difluoromethane (CH2F2, called R-32) and pentafluoroethane (CHF2CF3, called R-125) that ...
, for example, is often substituted, but has a GWP of 1725. Another substitute is
R-404A
A refrigerant is a working fluid used in the refrigeration cycle of air conditioning systems and heat pumps where in most cases they undergo a repeated phase transition from a liquid to a gas and back again. Refrigerants are heavily regulated du ...
with a GWP of 3900. Other substitute refrigerants are available with low GWP.
Ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
(R-717), popular in the early years of refrigeration, has a GWP of <1 and remains a popular substitute on fishing vessels. Ammonia’s toxicity and flammability limit its safe application.
Propane
Propane () is a three-carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used a ...
(R-290), is another example, and has a GWP of 3. Propane was the de facto refrigerant in systems smaller than industrial scale before the introduction of CFCs. The reputation of propane refrigerators as a fire hazard kept delivered ice and the ice box the overwhelming consumer choice despite its inconvenience and higher cost until safe CFC systems overcame the negative perceptions of refrigerators. Illegal to use as a refrigerant in the USA for decades, propane is now permitted for use in limited mass suitable for small refrigerators. It is not lawful to use in air conditioners, or larger refrigerators because of its flammability and potential for explosion.
Phaseout in the European Union
Since January 1, 2010, it has been illegal to use newly manufactured HCFCs to service refrigeration and air-conditioning equipment - only reclaimed and recycled HCFCs may be used. In practice this means that the gas has to be removed from the equipment before servicing and replaced afterwards, rather than refilling with new gas.
Since January 1, 2015, it has been illegal to use any HCFCs to service refrigeration and air-conditioning equipment; broken equipment that used HCFC refrigerants must be replaced with equipment that does not use them.
Phaseout in the United States
R-22 was mostly phased out in new equipment in the United States by regulatory action by the US EPA under the SNAP, Significant New Alternatives Program by rules 20 and 21 of the program, due to its high global warming potential. The EPA program was consistent with the Montreal Accords, but international agreements must be ratified by the US Senate to have legal effect. A 2017 decision of the US Court of Appeals for the District of Columbia Circuit held that the US EPA lacked authority to regulate the use of R-22 under the SNAP program. In essence the court ruled the EPA’s statutory authority, was for ozone reduction not global warming. The EPA subsequently issued guidance to the effect that the EPA would no longer regulate R-22. A 2018 ruling by same court in held that the EPA failed to conform with required procedure when it issued its guidance pursuant to the 2017 ruling, voiding the guidance, but not the prior ruling that required it. The refrigeration and air conditioning industry had already discontinued production of new R-22 equipment. The practical effect of these rulings is to reduce the cost of imported R-22 to maintain aging equipment extending its service life while keeping the use of R-22 in new equipment too risky to pursue.
R-22, retrofit using substitute refrigerants
The energy efficiency and system capacity of systems designed for R-22 is slightly greater using R-22 than the available substitutes.
R-407A R-407A is a mixture of gasses used as a refrigerant. It is a zeotropic blend of difluoromethane (HFC-32), pentafluoroethane (HFC-125) and 1,1,1,2-tetrafluoroethane (HFC-134a). R-407A was developed as a close match to R-22's capacities and flow ra ...
is for use in low- and medium-temp refrigeration. Uses a
polyolester
Polyolester oil (POE oil) is a type of synthetic oil used in refrigeration compressors that is compatible with the refrigerants R-134a, R-410A and R-12. (POE) oil.
R-407C is for use in air conditioning. Uses a minimum of 20 percent POE oil.
R-407F is for use in medium- and low-temperature refrigeration applications (supermarkets, cold storage, and process refrigeration); direct expansion system design only. Uses a POE oil.
R-407H is for use in medium- and low-temperature refrigeration applications (supermarkets, cold storage, and process refrigeration); direct expansion system design only. Uses a POE oil.
R-421A is for use in “air conditioning split systems, heat pumps, supermarket pak systems, dairy chillers, reach-in storage, bakery applications, refrigerated transport, self-contained display cabinets, and walk-in coolers.” Uses
mineral oil
Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils.
The name 'mineral oil' by itself is imprecise, ...
(MO), Alkylbenzene (AB), and POE.
R-422B is for use in low-, medium-, and high-temperature applications. It is not recommended for use in flooded applications.
R-422C is for use in medium- and low-temperature applications. The TXV power element will need to be changed to a 404A/507A element and critical seals (elastomers) may need to be replaced.
R-422D is for use in low-temp applications, and is mineral oil compatible.
R-424A is for use in air conditioning as well as medium-temp refrigeration temperature ranges of 20 to 50˚F. It works with MO,
alkylbenzene
The alkylbenzenes are derivatives of benzene, in which one or more hydrogen atoms are replaced by alkyl groups of different sizes. They are a subset of the aromatic hydrocarbons. The simplest member is toluene, in which a hydrogen atom of the benze ...
s (AB), and POE oils.
R-427A is for use in air conditioning and refrigeration applications. It does not require all the mineral oil to be removed. It works with MO, AB, and POE oils.
R-434A is for use in water cooled and process chillers for air conditioning and medium- and low-temperature applications. It works with MO, AB, and POE oils.
R-438A (MO-99) is for use in low-, medium-, and high-temperature applications. It is compatible with all lubricants.
R-458A is for use in air conditioning and refrigeration applications, without capacity or efficiency loss. Works with MO, AB, and POE oils.
R-32 or HFC-32 (
difluoromethane
Difluoromethane, also called difluoromethylene, HFC-32 Methylene Fluoride or R-32, is an organic compound of the dihalogenoalkane variety. It has the formula of CH2F2. It is a colorless gas in the ambient atmosphere and is slightly soluble in th ...
) is for use in air conditioning and refrigeration applications. it has zero ozone depletion potential (ODP)
and a global warming potential (GWP) index 675 times that of carbon dioxide.
Physical properties
It has two
allotrope
Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Allotropes are different structural modifications of an element: the ...
s: crystalline II below 59K and crystalline I above 59K and below 115.73K.
Next diagram represents the pressure-enthalpy R22 properties, using Refprop 9.0 database, using the International Institute of Refrigeration reference.
![R22 ph](https://upload.wikimedia.org/wikipedia/commons/2/24/R22_ph.gif)
Table of thermal and physical properties of saturated liquid refrigerant 22:
Price history and availability
EPA's analysis indicated the amount of existing inventory was between 22,700t and 45,400t.
TBD: To be determined
In 2012 the EPA reduced the amount of R-22 by 45%, causing the price to rise by more than 300%. For 2013, the EPA has reduced the amount of R-22 by 29%.
Specialty Cooling and Heating (Blog) January 22, 2013
References
External links
MSDS from DuPont
*
* ttp://webbook.nist.gov/cgi/cbook.cgi?ID=C75456&Units=SI&Mask=4#Thermo-Phase Phase change data at webbook.nist.gov
IR absorption spectra
* IARC summaries and evaluations
{{Authority control
Halomethanes
Hydrochlorofluorocarbons
Ozone depletion
Greenhouse gases
Refrigerants
Propellants
Airsoft
IARC Group 3 carcinogens