Chlorofluorocarbons ozone depletion potentials

The cap is the percentage of the calculated level of chlorofluorocarbons consumed in the base year plus the calculated level of hydrofluorocarbons consumed the same base year It applies only to HCFCs Calculated in the context means that the amount of each substance is adjusted by its ozone depletion potential (ODP), a measure of its potential to deplete stratosphenc ozone relative to that of CFC 11... 

Hydrochlorofluorocarbon-141b, or 1,1-dichloro-l-fluoroethane (HCFC141b), has been developed as a replacement for fully halogenated chlorofluorocarbons because its residence time in the atmosphere is shorter, and its ozone depleting potential is lower than that of presently used chlorofluoro... 

Chlorofluorocarbons (CFCs) were once commonly used as blowing agents. For years, pentane has become generally accepted as a blowing agent substitute for CFC. Pentane does not cause problems to the environment with pentane an ozone-depletion potential does not exist (Polke, 1996). 

Within the Montreal Protocol treaty, chlorofluorocarbons (CFCs) were broken up into several groups. Of primary importance was group 1 of annex A of the treaty, shown in Table 9.1. These CFCs are deemed to be more detrimental to the ozone layer on the basis of their ODP values. The ozone depletion potential is the relative amount of damage that a particular chemical causes to the ozone layer relative to R-ll (trichlorofluoromethane), which has an ozone depletion potential of 1.0. 

For the last two decades, attention has been focused on redressing the ozone depletion in the earth s protective layer. It is believed that chlorine radicals dissociated from chlorofluorocarbons (CFCs), upon irradiation of sun s UV in the stratosphere, promotes the ozone depletion. Hence, in addition to development of CFC alternatives there is an urgent need for the safe disposal of CFCs. Several processes such as pyrolysis, incineration, photocatalysis, oxidative destruction over metal oxide or zeolite catalysts and destruction at very high temperatures ( by plasma technique ) are reported in the literature for the disposal of CFCs[ 1-5]. But all these processes yield harmful products like CO, HF/F2 etc. Catalytic conversion of chlorinated organics in presence of hydrogen seems to be a better technique as it yields either hydrofluorocarbons(HFCs) or hydrochlorofluorocarbons(HCFCs) whose ozone depletion potential is either zero or very low and yet most of these products act as CFC alternatives. 

Industry is seeking high yield, zero waste processes. Companies are evaluating the replacement of some base metal catalysts by more selective precious metal catalysts to eliminate troublesome by-product formation and/or contaminated waste waters. In the case of Chlorofluorocarbons (CFC s) industry is trying to develop cost effective processes to manufacture non-toxic Hydrofluorocarbons (HFC s) of zero ozone depleting potential to replace existing CFC s. 

In 1987, the Montreal protocol led to the phase down of the chlorofluorocarbons (CFCs) because of their ozone depletion potential. These products have been replaced in a first step by HCFCs (hydrochlorofluorocarbons), which still contain chlorine, and in a further step by HFCs (hydrofluorocarbons), which are completely... 

Solvents, like contaminants, may be polar or nonpolar. As a general rule, polar solvents dissolve polar residues while nonpolar solvents dissolve nonpolar residues. Thus, ionic residues such as chlorides, salts, acids, acid fluxes, and alkalis are best dissolved and removed with polar solvents such as water, isopropyl alcohol, ethanol, or methylethyl ketone. Greases, oils, silicones, rosin flux, and low-molecular-weight monomers are best dissolved and removed with solvents such as hydrocarbons, Freons , hydrochloro-fluorocarbons, xylene, terpenes, and naphtha. To remove both polar and nonpolar residues, a two-step process using both types of solvents may be used or, more conveniently, an azeotrope mixture of the two solvents can be used in a one-step process. Most of the chlorofluorocarbon solvents (Freons ) and their azeotropes with alcohols, methylene chloride, or ketones are being phased out due to their high ozone-depletion potentials. Solvent blends and azeotropes of hydro-fluoroethers and hydrochlorofluorocarbons (HCFC) are now replacing these solvents. 

Ozone depletion potential represents the potential of depletion of the ozone layer due to the emissions of chlorofluorocarbon compounds and other halogenated hydrocarbons. 

FIGURE 54.8 Ozone-depleting potential and global warming potential of chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFC) relative to Rll = 1. 

During the 1980s, it was recognized that chlorofluorocarbons (CFCs) and chlo-rofluorohydrocarbons have a significant ozone depleting potential with the Montreal Protocol (1987) [8] all critical CFC s were banned for dispersive applications and... 

The principal application of chloroform is the the production of the refrigerant monochlordifluormethane, HCFC 22, CHCIF2, and other chlorofluoroalkanes. Because of the ozone depletion potential of chlorofluorocarbons (CFC), their open use had been restricted for some years and afterwards prohibited by the Montreal Protocol in 1987 and subsequent international meetings. The role of CFC in stratospheric chemistry is discussed in detail in [357]. HCFCs are less active, they will be phased out about 2005. 

In order to enable the fast discontinuation of the production and use of fully halogenated CFCs, hydro-chlorofluorocarbons were introduced in industry as a transition stage. The atmospheric fate and impact of these hydrochlorofluorocarbons and chlorinated solvents are described in [387]. The authors come to the conclusion, that these compounds, with the exception of 1,1,1-trichIoroethane, make a small or insignificant contribution to the stratospheric ozone depletion, global warming, photochemical smog , acid rain or chloride and fluoride levels in precipitations. The ozone depletion potentials are 10 to 50 times lower than that of CFCll or CFC12, mainly as a consequence of their shorter atmospheric lifetime—some months to 10 years—due to destruction in the atmosphere. 

The other global environmental problem, stratospheric ozone depletion, was less controversial and more imminent. The U.S. Senate Committee Report supporting the Clean Air Act Amendments of 1990 states, Destruction of the ozone layer is caused primarily by the release into the atmosphere of chlorofluorocarbons (CFCs) and similar manufactured substances—persistent chemicals that rise into the stratosphere where they catalyze the destruction of stratospheric ozone. A decrease in stratospheric ozone will allow more ultraviolet (UV) radiation to reach Earth, resulting in increased rates of disease in humans, including increased incidence of skin cancer, cataracts, and, potentially, suppression of the immune system. Increased UV radiation has also been shown to damage crops and marine resources."... 

Thus, the mean temperature of the atmosphere, which is about 20°C at sea level, falls steadily to about —55° at an altitude of 10 km and then rises to almost 0°C at 50 km before dropping steadily again to about —90° at 90 km. Concern was expressed in 1974 that interaction of ozone with man-made chlorofluorocarbons would deplete the equilibrium concentration of ozone with potentially disastrous consequences, and this was dramatically confirmed by the discovery of a seasonally recurring ozone hole above Antarctica in 1985. A less prominent ozone hole was subsequently detected above the Arctic Ocean. The detailed physical and chemical conditions required to generate these large seasonal depletions of ozone are extremely complex but the main features have now been elucidated (see p. 848). Several accounts of various aspects of the emerging story, and of the consequent international governmental actions to... 

Recognition of the threat of stratospheric ozone depletion posed by chlorofluorocarbons and chloro-fltiorohydrocarbons led 131 countries to sign the Montreal Protocol in 1987. Production of chlorofluorocarbons was banned as of January 1, 1996, because of their potential to further deplete stratospheric ozone. Chlorofluorohydrocarboiis will be... 

Over the past several decades, there has been increasing recognition in a number of areas of the environmental impacts, both realized and potential, of human activities not only on local and regional scales but also globally. This is particularly true of changes to the composition and chemistry of the atmosphere caused by such anthropogenic activities. One example, for which there is irrefutable evidence, is stratospheric ozone depletion by chlorofluorocarbons, discussed in detail in Chapters 12 and 13. 

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