Hydrofluorocarbon applications

As you know, most countries are phasing out certain refrigerants to lessen damage to the ozone layer. The chemicals being phased out are chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Replacements are hydrofluorocarbons (HFCs) and certain blends. The DuPont web site (www.dupont.com) gives the handy Table I of recommended replacement refrigerants for various applications. 

Radicals derived from hydrofluorocarbons (HFCs) as well as hydrofluo-roethers (HFE) are often destabilized with respect to the methyl radical [51, 57,68,70,79-82], The low stability of these radicals implies that the C-H bonds in the corresponding closed shell parent compounds are comparatively strong and thus rather unreactive towards attack of oxidizing reagents. This latter property is of outstanding importance for the use of these compounds in a variety of technical applications, in which thermally stable, non-oxidizable, non-flammable compounds are needed. However, with respect to the environmental fate of these compounds high C-H bond energies... 

The implication of CFCs in the destruction of stratospheric ozone (Section 6.2.6.) has resulted in their virtual elimination as aerosol propellants, except in MDIs, an essential lifepreserving application, where they will continue to be used until hydrofluorocarbon-based formulations are introduced. 

Hydrofluorocarbon 134a (1,1,1,2-tetrafluoroethane) is used as a replacement for Freon 12 (see Problem 4.2) for refrigeration applications. (Why is such a replacement necessary and what is the advantage of HFC-134a from an environmental... 

The CFC replacements need to be nontoxic, nonflammable and have significantly lower, or zero ozone depletion potentials. Many organic- and aqueous-based systems, that do not contain chlorine or fluorine, have been developed for some applications while others use hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). Unlike hydrocarbon catalysis, the presence of hydrogen, chlorine and fluorine in the same molecule creates a very large number of... 

Hydrofluorocarbons ("HFCs") consist of molecules containing only atoms of hydrogen, fluorine and carbon and were known at the time of the Montreal Protocol to have effectively zero ozone depletion potential (ODP). Following the Montreal Protocol, many participants in the refrigerant manufacturing and end-user industries therefore looked towards HFCs as replacements for CFCs across a range of applications. R-134a is one such HFC. 

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