Chlorofluorocarbons CFCs , Hydrochlorofluorocarbons HCFCs

Chlorofluorocarbons CFCs and hydrochlorofluorocarbons HCFCs are all anthropogenic species and are the causative agents of ozone layer destruction as well as greenhouse gasses. CFCs are the molecules in which aU the hydrogen atoms of hydrocarbons are substituted by chlorine and fluorine atoms. They do not have absorption bands in the tropospheric actinic flux region and also do not react with OH radicals. Therefore, they do not have any dissipation process in the troposphere, and can be photolyzed only after they reached to the stratosphere. On the other hand, HCFCs is molecules in which at least one of chlorine or fluorine atom of CFCs is substituted by hydrogen atom. Since HCFCs react with OH radicals, they are removed in the troposphere, but a portion of them reach the stratosphere and photolyzed, similar to CFCs. 

Among organic chlorinated compounds which do not contain H atoms in molecules, five CFCs CFC-11 (CFCI3), CFC-12 (CF2CI2), CFC-113 

T CH3CF2CI CF2CICF2CI CFCI2CF2CI (Adapted from Hubrich and Stuhl 1980) 

NASA/JPL Evaluation No. 17 (Sander et al. 2011) gives recommended absorption cross sections and their temperature dependence for these compoxmds based on 

Wavelength (nm) CCI4 CFCI3 (CFC-11) CF2CI2 (CFC-12) CF2CICFCI2 (CFC-113) CF2CICF2CI (CFC-114) CF3CF2CI (CFC-115) 

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Acronyms for chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (MFCs)... 

The composition of the Earth s atmosphere, given in Table IV, is controlled by biological processes, with additional influences from photochemistry and human activities. The abundances in Table IV are taken from (75), with updated abundances for the chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrochlorocarbons (HCCs), and perfluorocarbons (PFCs) (76). 

The stratospheric region of the atmosphere is located above 15—35 km from the surface of the earth. It contains a deep layer of ozone that acts as a filter of harmful UV radiation of sunlight to reach the earth s surface and thus protects us from hazardous effect of UV radiation. The massive loss of ozone in the stratosphere occurs daily by atmospheric pollutants, UV-induced photolysis of ozone in the presence of man-made chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons (brominated hydrocarbons), CCU, and methylchloroform (CH3CCI3). These halocarbons generate halogen radicals which have active roles for photolysis of ozone. These are also derived from gaseous chlorine and hydrochloric... 

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. 

In the discussion of ecotoxicity the perhalogenated chlorofluorocarbons (CFCs), hydrogen-containing hydrochlorofluorocarbons (HCFCs) and the chlorine-free hydrofluorocarbons (HCFs) have been for several years in the headlines (the depletion of the ozone layer in the stratosphere, the greenhouse or global warming effects in the troposphere).75... 

Hydrochlorofluorocarbons (HCFCs) are now being produced in very large quantities as substitutes for ozone-depleting chlorofluorocarbons (CFCs). The two most common HCFCs are 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 1,1-dichloro-l-fluoroethane (HCFC-141b) ... 

States would spend 160 billion per year on pollution control. In 1996 Ben Lieberman, an environmental research associate with the Competitive Enterprise Institute, estimated that in the United States the cost of the phaseout of chlorofluorocarbons (CFCs) in accordance with the 1987 Montreal Protocol on Substances That Deplete the Ozone Layer could reach 100 billion over the next ten years. Indeed chemical manufacturers had to develop eco-friendly substitutes such as hydrochlorofluorocarbon (HCFC) and hydro-fluorocarbon (HFC), which are more costly to make, and hundreds of millions of pieces of air-conditioning and refrigeration equipment using CFCs had to be discarded. 

In this chapter, recent advances in our understanding of catalytic fluorination under heterogeneous conditions are surveyed from the standpoint of catalyst properties, including developments based on the use of mixed metal fluorides having different structural types, and reaction mechanisms. Much of the newer work has been the result of the need to replace chlorofluorocarbons (CFCs) by alternatives, hydrofluorocarbons (HFCs) or, more controversially, hydrochlorofluorocarbons (HCFCs), following adoption of the Montreal and successor Protocols [2,3]. Where relevant, aspects of catalytic hydrogenolysis, where fluorides have been used as replacement supports in the conventional palladium/carbon catalysts, and isomerization reactions are included. 

Selective dehydrochlorination of chlorofluorocarbons (CFCs) is a very important environmental issue, and the need to replace these detrimental, ozone-depleting compounds by benign hydrochlorofluorocarbons (HCFCs) and/or hydrofluorocarbons (MFCs) has stimulated intensive work on the subject [172-182]. Palladium has been the most extensively investigated catalytic metal in this reaction, but the moderate selectivity for CH2F2 exhibited by Pd/Si02 (40%) can be significantly increased, up to 95%, with a 20-40 at%. Au addition [180], and, in Pd/C, from 70% to 90% with Au addition [181,182]. 

Direct electroreduction methods are typically used for dechlorination of chlorinated pollutants in waters. The easy removal of Cl from chlorinated organics allows conversion of chlorofluorocarbons (CFCs) into hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and even fluorocarbons (FCs). ECFCs are much less destructive to the atmospheric ozone than CFCs, but HFCs and FCs are harmless to atmospheric ozone, although they may contribute to the greenhouse effect. 

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. 

The HaHCs include the chlorofluorocarbons (CFCs) and their replacements — the hydrochlorofluorocarbons (HCFCs) and the hydrofluorocarbons (HFCs). Also included in the HaHC category are bromo- and iodo-substituted organic compounds and various chlorinated hydrocarbons (CHCs) such as chloroform, 1,1,1-trichloroethane, carbon tetrachloride. 

In the early twenty-first century, more than 90 percent of the chloroform produced in the United States is used in the preparation of hydrochlorofluorocarbons (HCFCs). HCFCs are compounds consisting of carbon, hydrogen, chlorine, and fluorine. They were developed in the 1980s to replace the chlorofluorocarbons (CFCs) that, at the time, were widely used for a number of industrial applications. Replacing CFCs had become necessary because they were also destroying the... 

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