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CFC destruction

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). [Pg.207]

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. [Pg.207]

The combustion of CCI2F2 in oxygen at 500 °C was studied in the presence of more than 20 different catalysts. The combustion products are CO, CO2, and F2. Because of fluorine s tremendous reactivity, metallic and silicon-based catalysts degraded rapidly. The most durable catalyst was found to be BPO4 however, it also did not have a satisfactory life because of fluorine reaction with boron [103], [Pg.207]

CFC-12 was reacted with NH3 (eq 34) over metal catalysts on Lap3 and activated carbon to form HCN, HF, HCl, and N2 [104]. [Pg.207]

CFCs were decomposed to HCl, HF, and CO2 at 150 °C to 350 °C by the reaction of H2O over amorphous alloy catalysts consisting of at least one element selected from the group of Ni and Co, at least one element selected from the group Nb, Ta, Ti, and Zr, and at least one element selected from the group Ru, Rh, Pd, Ir, and Pt. The alloys were activated by immersion in HF [105]. CFCs are decomposed by the reaction of water vapor at temperatures above 300 °C in the presence of iron oxide supported on activated carbon [106]. They are also decomposed by steam in [Pg.207]


In the feed pretreatment section oil and water are removed from the recovered or converted CCI2F2. The reactor type will be a multi-tubular fixed bed reactor because of the exothermic reaction (standard heat of reaction -150 kJ/mol). After the reactor the acids are selectively removed and collected as products of the reaction. In the light removal section the CFCs are condensed and the excess hydrogen is separated and recycled. The product CH2F2 is separated from the waste such as other CFCs produced and unconverted CCI2F2. The waste will be catalytically converted or incinerated. A preliminary process design has shown that such a CFC-destruction process would be both technically and economically feasible. [Pg.377]

CFCs. All "nonessential" uses of CFCs in aerosol propellents were banned in 1978—the first and only major control action under TSCA not specifically mandated by the statute. This action may have helped to reduce the future incidence of skin cancer by diminishing CFCs destructive effects on stratospheric ozone. Making appropriate assumptions about rates of ozone depletion and extrapolating from current disease rates, one could estimate a range of cancers avoided because of this prohibition. However, any health benefit due to the ban on aerosol CFC uses may be masked by the continued increase in non-aerosol uses. [Pg.176]

Table 11 Ozone-Depleting Compounds Destroyed by the Na/NH3 CFC Destruction Process3... Table 11 Ozone-Depleting Compounds Destroyed by the Na/NH3 CFC Destruction Process3...
Nagata et al. [24] have studied the decomposition of a range of CFCs including CFC-113 (CF2CICFCI2), CFC-114 (CF2CICF2CI) and CFC-115 (CF3CF2CI) in the presence of hydrocarbons, which were also oxidised, by a series of acidic metal oxides and supported metal oxides. The relative order for CFCs destruction was ... [Pg.133]

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."... [Pg.16]

Susan Solomon and James Anderson showed that CFCs produce chlorine atoms and chlorine oxide under the conditions of the ozone layer and identified the CFCs emanating from everyday objects, such as cans of hair spray, refrigerators, and air conditioners, as the primary culprits in the destruction of stratospheric ozone. The CFC molecules are not very polar, and so they do not dissolve in rain or the oceans. Instead, they rise to the stratosphere, where they are exposed to ultraviolet radiation from the Sun. They readily dissociate in the presence of this radiation and form chlorine atoms, which destroy ozone by various mechanisms, one of which is... [Pg.689]

The study of the rates of chemical reactions is called kinetics. Chemists study reaction rates for many reasons. To give just one example, Rowland and Molina used kinetic studies to show the destructive potential of CFCs. Kinetic studies are essential to the explorations of reaction mechanisms, because a mechanism can never be determined by calculations alone. Kinetic studies are important in many areas of science, including biochemistry, synthetic chemistry, biology, environmental science, engineering, and geology. The usefulness of chemical kinetics in elucidating mechanisms can be understood by examining the differences in rate behavior of unimolecular and bimolecular elementary reactions. [Pg.1054]

Catalysts are immensely beneficial in industry, but accidental catalysis in the atmosphere can be disastrous. Recall from Box that the chemishy of ozone in the stratosphere involves a delicate balance of reactions that maintain a stable concentration of ozone. Chlorofiuorocarbons (CFCs) shift that balance by acting as catalysts for the destruction of O3 molecules. [Pg.1104]

The net reaction for this two-step mechanism is the conversion of an O3 molecule and an oxygen atom into two O2 molecules. In this mechanism, chlorine atoms catalyze ozone decomposition. They participate in the mechanism, but they do not appear in the overall stoichiometry. Although chlorine atoms are consumed in the first step, they are regenerated in the second. The cyclical nature of this process means that each chlorine atom can catalyze the destruction of many O3 molecules. It has been estimated that each chlorine atom produced by a CFC molecule in the upper stratosphere destroys about 100,000 molecules of ozone before it is removed by other reactions such as recombination CF2 Cl -b Cl CF2 CI2... [Pg.1105]

The term CFCs is a general abbreviation for ChloroFluoroCarbons. They have been extensively used since their discovery in the thirties, mainly as refrigerant, foam blowing agent, or solvent because of their unique properties (non toxic, non flammable, cheap). However, after the first warning of Rowland and Molina [1] in 1974 that CFCs could destroy the protective ozone layer, the world has moved rapidly towards a phase-out of CFCs. Because the destruction of stratospheric ozone would lead to an increase of harmful UV-B radiation reaching the earth s surface, the production and use of CFCs is prohibited (since January 1, 1995 in the European Union and since January 1, 1996 worldwide). [Pg.369]

For the next thirty years, Thomas Midgley was revered as a scientist who had made our lives healthier and happier. Only in the closing decades of the twentieth century could other scientists detect the far-reaching damage caused by our reliance on his leaded gasoline and chlorofluorocarbon refrigerants. Yet such was his creativity that many years ago he and his associates also invented some of today s substitutes for their destructive CFCs. [Pg.79]

Wallis, A.E., Whitehead, J. C. and Zhang, K. (2007) Plasma-assisted catalysis for the destruction of CFC-12 in atmospheric pressure gas streams using Ti02, Catal. Lett. 113, 29-33. [Pg.395]

You probably know that compounds called chlorofluorocarbons (CFCs) are responsible for depleting the ozone layer in Earth s stratosphere. Did you know, however, that CFCs do their destructive work by acting as homogeneous catalysts Use the Internet to find out how CFCs catalyze the decomposition of ozone in the stratosphere. To start your research, go to the web site above and click on Web Links. Communicate your findings as a two-page press release. [Pg.304]

When CFCs slowly rise in the atmosphere and reach the ozone layer, they are broken down into component molecular compounds and atoms by the UV rays of the sun. Some of these chemicals then react with ozone to break it down, thus reducing the amount of O3. Further, some chlorine (also from the oceans) and some other elements combine with the O and to form other chemicals. This also contributes to the reduction of ozone faster than natural processes can reform it. Ozone is a renewable resource. The issue is this can a balance be obtained between the destruction of ozone in the atmosphere, by both natural and man-made causes, and its natural regeneration ... [Pg.232]


See other pages where CFC destruction is mentioned: [Pg.369]    [Pg.370]    [Pg.207]    [Pg.207]    [Pg.11]    [Pg.845]    [Pg.845]    [Pg.233]    [Pg.369]    [Pg.370]    [Pg.207]    [Pg.207]    [Pg.11]    [Pg.845]    [Pg.845]    [Pg.233]    [Pg.2339]    [Pg.40]    [Pg.28]    [Pg.242]    [Pg.689]    [Pg.24]    [Pg.463]    [Pg.54]    [Pg.370]    [Pg.35]    [Pg.49]    [Pg.105]    [Pg.152]    [Pg.306]    [Pg.84]    [Pg.458]    [Pg.1643]    [Pg.44]    [Pg.11]    [Pg.305]   
See also in sourсe #XX -- [ Pg.207 ]




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