Dichlorodifluoromethane

Dichlorodifluoromethane

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Dichlorodifluoromethane (R-12), is a colorless gas, and usually sold under the brand name Freon-12, is a chlorofluorocarbon
Chlorofluorocarbon
A chlorofluorocarbon is an organic compound that contains carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. A common subclass are the hydrochlorofluorocarbons , which contain hydrogen, as well. They are also commonly known by the DuPont trade name Freon...

 halomethane
Halomethane
Halomethane compounds are derivatives of methane with one or more of the hydrogen atoms replaced with halogen atoms . Halomethanes are both naturally occurring, especially in marine environments, and man-made, most notably as refrigerants, solvents, propellants, and fumigants...

 (CFC), used as a refrigerant
Refrigerant
A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase change from a liquid to a gas. Traditionally, fluorocarbons, especially chlorofluorocarbons, were used as refrigerants, but they are being phased out because of their ozone depletion...

 and aerosol spray propellant. Complying with the Montreal Protocol
Montreal 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...

, its manufacture was banned in the United States along with many other countries in 1994 due to concerns about damage to the ozone layer
Ozone layer
The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 97–99% of the Sun's high frequency ultraviolet light, which is potentially damaging to the life forms on Earth...

. It is soluble in many organic solvents.

Use as an aerosol


The use of chlorofluorocarbons as an aerosol in medicine, for example: USP
United States Pharmacopeia
The United States Pharmacopeia is the official pharmacopeia of the United States, published dually with the National Formulary as the USP-NF. The United States Pharmacopeial Convention is the nonprofit organization that owns the trademark and copyright to the USP-NF and publishes it every year...

-approved salbutamol
Salbutamol
Salbutamol or albuterol is a short-acting β2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease. It is marketed as Ventolin among other brand names....

, has been phased out by the U.S. Food and Drug Administration. The use of a different propellant known as hydrofluoroalkane, or HFA, which does not harm the environment has been chosen as the replacement.

Retrofitting


R-12 was used in most refrigeration and vehicle air conditioning applications prior to 1994 before being replaced by R-134a, which has a lower 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...

. When older units leak, retrofit
Retrofit
Retrofitting refers to the addition of new technology or features to older systems.* power plant retrofit, improving power plant efficiency / increasing output / reducing emissions...

s to (1,1,1,2-tetrafluoroethane
1,1,1,2-Tetrafluoroethane
1,1,1,2-Tetrafluoroethane, R-134a, Genetron 134a, Suva 134a or HFC-134a, is a haloalkane refrigerant with thermodynamic properties similar to R-12 , but with less ozone depletion potential...

) are recommended. Retrofits to R-134a require complete flushing and filter/dryer replacement to remove the mineral oil. Mineral oil used for R12 is not compatible with R-134a. Some oils designed for conversion to R-134a are advertised as compatible with residual R-12. New rubber hoses which are R-134a compatible may be needed for the same reason.

In systems where R-134a is not practical, a R-409A blend (60% R-22; 25% R-124; 15% R-142b) may be directly added to an R-12 system without oil change although a filter change is always recommended. R-409A usually runs on the low-pressure side of the system at 12 pounds per square inch
Pounds per square inch
The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...

(psi), while R-12 usually runs on the low side at 10 psi. R-409A runs at higher pressures and is less efficient but works quite well. Manufacturer recommends that existing R-12 charge should be recovered. However, as the two refrigerants are soluble in the same mineral oil there are no complications associated with mixing them.

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