HFC and HCFC

Hjdrofluorocarbons andHjdrochloroJluorocarhons. The properties of HFC and HCFC propellants are given in Table 3. Propellant 22 is nonflammable and can be mixed to form nonflammable blends. Some of these propellants are scheduled for phase-out by 2015—2030. 

Refrigeration, Air Conditioning, and Heat Pumps - Immediate replacements for many applications include hydrocarbons, HFCs, and HCFCs. Some of these will also be candidates for long-term replacement of the currently used CFCs. This following briefly describes the alternatives that are available for specific refrigeration, air conditioning, and heat pump applications. 

Reductive cleavages of carbon-chlorine bonds by active metals and with photochemical activation figure in recent studies aimed at HFCs and HCFCs Sodium amalgam [3J] (equation 25), zinc powder [34] (equation 26), and alumi-mun/tin chloride [35] (equation 26) are all used in conjunction with protic solvents in reactions giving high yields and conversions... 

Wallington, T. J., D. R. Worsnop, O. J. Nielsen, J. Sehested, W. J. Debruyn, and J. A. Shorter, The Environmental Impact of CFC Replacements—HFCs and HCFCs, Enriron. Sci. Technol., 28, 320A-326A (1994a). 

In this chapter we will examine the atmospheric degradation mechanisms of the following important classes of anthropogenic molecules alkanes, alkenes, aromatics, nitrogen oxides, S()2, CFCs and Halons, and finally HFCs and HCFCs. Our intent is not to give an exhaustive account of the photochemical oxidation of every man-made chemical species but rather to present examples of the degradation mechanisms of a few representative members of each class of pollutant. First, we need to consider the general features of atmospheric chemistry. 

Table 7 Gas-phase atmospheric degradation products of HFCs and HCFCs [84] ...

This review has described the synthetic routes available to several of the HFC and HCFC alternatives to CFCs under consideration for commercial development, as well as some that have already been commercialized. Much of the information has been gleaned from the patent literature. As can be seen, several options to each product are available. Choice of a commercial process is dependent on several factors, including countries in which they are manufactured and raw material availability. There are still many opportunities for innovation, improved catalysts, and above all a fundamental understanding of catalytic mechanisms associated with these interesting new processes. 

The chlorofluorination reaction typically gives perhalogenated products although it is now possible through new catalysts to prepare HFCs and HCFCs such as the HCFC-225S [101], and HFC-125 [102] (eqs 32 and 33). 

A variety of methods have been proposed for removing CFCs from the environment. These include combustion in air, oxygen, ammonia, or water atmospheres. CFCs can also be reacted with HCl to afford starting materials for the preparation of some of the HFCs and HCFCs discussed in this review. 

HFCs and HCFCs both act as greenhouse gases, so environmental concerns about those effects have not yet been resolved by using them as replacements for CFCs. However, their atmospheric lifetimes are only a few years, in contrast to those of the CFC, which may be many decades. 

The dominant loss process for HFCs and HCFCs in the atmosphere is reaction with the OH radical. Rate constants for the OH reaction with a wide variety of HFCs and HCFCs are available (Table B.l). A mechanism for the OH reaction of the generalized HFC or HCFC species... 

Sidebottom, H. (1995) Degradation of HFCs and HCFCs in the atmosphere, in Tropospheric Oxidation Mechanisms, K. H. Becker, ed., European Commission, Report EUR 16171 EN, Luxembourg, pp. 153-162. 

Can the tropospheric degradation of HFCs and HCFCs lead to toxic products ... 

III. Experimental investigation of the atmospheric degradation of HFCs and HCFCs... 

Summary of the primary steps in HFC and HCFC atmospheric degradation... 

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