Ozone-depleting properties

The possible implication of CFCs in the depletion of stratospheric ozone, postulated in 1974 and reinforced in the late 1980s by the discovery of a possible link to the thinning of the ozone layer over Antarctica during springtime, had profound effects on the fluorocarbon industry. The discovery of the ozone-depleting properties of CFCs led to the Montreal Protocol and the London and Copenhagen amendments (1990, 1992), which scheduled the end of production of CFCs by the end of 1995. 

Many of the most efficient solvents are being disallowed by federal and local regulations because of their high VOC and ozone-depleting properties. Even some of the new replacement solvents may be phased out in the future. 

It is desired to find a replacement for Freon-12 as an alternative refrigerant [Duvedi Achenie (1996)]. The objective is to find replacements that have the same refrigerant related properties as Freon-12 but without the harmfull environmental properties (such as the Ozone depletion potential) - The new refrigerant must absorb heat at temperatures as low as -1.1°C and reject heat at temperatures as high as 313 K. It must also respect the following characteristics ... 

Amorphous fluoropolymers have many applications in the areas of advanced materials where they are used in applications requiring thermal and chemical resistance. Their manufacture is hindered by their low solubility in many solvents. Many fluoropolymerizations cannot be carried out in hydrocarbon solvents because the radical abstraction of hydrogen atoms leads to detrimental side reactions. Chlorofluorocarbons (CFCs) were thus commonly used, but their use is now strictly controlled due to their ozone depleting and greenhouse gas properties. Supercritical carbon dioxide is a very attractive alternative to CFCs and it has been shown that amorphous fluoropolymers can be synthesized by... 

Kayukawa et al. [17] studied the PVT properties of triiluoromethyl methyl ether, because it is a possible refrigerant with zero ozone depletion potential and low global-warming potential. One series of their data is shown in Table 5.6. Calculate Z, the compressibihty factor, and the molar volume in mol m from the given data, and fit the data for Z as a function of 1 /Pm to both a linear and a quadratic equation to see whether a third virial coefficient is warranted by the data. 

Because of the gaseous nature of many of the important primary and secondary pollutants, the emphasis in kinetic studies of atmospheric reactions historically has been on gas-phase systems. However, it is now clear that reactions that occur in the liquid phase and on the surfaces of solids and liquids play important roles in such problems as stratospheric ozone depletion (Chapters 12 and 13), acid rain, and fogs (Chapters 7 and 8) and in the growth and properties of aerosol particles (Chapter 9). We therefore briefly discuss reaction kinetics in solution in this section and heterogeneous kinetics in Section E. 

To start, one must decide whether the substance itself is benign or whether it poses a hazard in the form of toxicity, accident potential, ecosystem destruction, or other form. Hazard can be evaluated in terms for which there is extensive data on properties ranging from dose response to flammability to ozone-depleting potential. In the absence of empirical data, there is a wide range of structure-activity relationship models which can give reasonable approximations for the properties in question. 

Perfluorocarbons are a class of organic compounds in which all of the hydrogen atoms are replaced with fluorine atoms. They possess unique properties that make them very useful as dispersants, carrier solvents, and processing solvent additives. Their lack of chlorine or bromine atoms results in zero-ozone-depletion potential. 

Stratospheric Ozone depletion is largely due to chlorine and bromine radicals released from halogenated hydrocarbons. This paper describes properties, emission histories and budgets of relevant substances and outlines the pertinent photochemical processes, along with a comprehensive presentation of halocarbon measurements and global distributions. 

The substitution of hazardous solvents by those with better EHS properties, such as enhanced biodegradability or low ozone depletion potential23-25... 

---