Environment Fluorocarbon

Difluoroethane is usually encountered as a liquefied gas and appropriate precautions for handling such materials should be taken. Eye protection, gloves, and protective clothing are recommended. Difluoroethane should be handled in a well-ventilated environment. Fluorocarbon vapors are heavier than air and do not support life therefore, when cleaning large tanks that have contained these propellants, adequate provision for oxygen supply in the tanks must be made in order to protect workers cleaning the tanks. 

Copolymers of propylene and tetrafluoroethylene, which are sold under the Aflas trademark by 3M, have been added to the fluorocarbon elastomer family (21—26). Also 3M has introduced an incorporated cure copolymer of vinyUdene fluoride, tetrafluoroethylene and propylene under the trademark Fluorel 11 (27). These two polymers (Aflas and Fluorel 11) do not contain hexafluoropropylene. The substitution of hexafluoropropylene with propylene is the main reason why these polymers show excellent resistance toward high pH environments (28). Table 1 Hsts the principal commercial fluorocarbon elastomers in 1993. 

They show good to excellent resistance to highly aromatic solvents, polar solvents, water and salt solutions, aqueous acids, dilute alkaline solutions, oxidative environments, amines, and methyl alcohol. Care must be taken in choice of proper gum and compound. Hexafluoropropylene-containing polymers are not recommended for use in contact with ammonia, strong caustic (50% sodium hydroxide above 70°C), and certain polar solvents such as methyl ethyl ketone and low molecular weight esters. However, perfluoroelastomers can withstand these fluids. Propylene-containing fluorocarbon polymers can tolerate strong caustic. 

Martin JW, J Franklin, ML Hanson, KR Solomon, SA Mabnry, DA Ellis, BE Scott, and DCG Mnir (2000) Detection of chlorodifinoroacetic acid in precipitation a possible prodnct of fluorocarbon degradation. Environ Sci Technol 34 274-281. 

Diffusion of cations in a Nation membrane can formally be treated as in other polymers swollen with an electrolyte solution (Eq. (2.6.21). Particularly illustrative here is the percolation theory, since the conductive sites can easily be identified with the electrolyte clusters, dispersed in the non-conductive environment of hydrophobic fluorocarbon chains (cf. Eq. (2.6.20)). The experimental diffusion coefficients of cations in a Nation membrane are typically 2-4 orders of magnitude lower than in aqueous solution. 

Hexachloroethane is a solid crystalline material that has entered the environment as a result of its use in militaiy pyrotechnics and as a component of smoke-producing devices used for screening or signaling purposes. It is an intermediate in the production of fluorocarbons, cleaning agents, and refrigerants and was... 

Federal Task Force on Inadvertent Modification of the Stratosphere, Fluorocarbons and the Environment. Counc. Environ. Qual., Washington, DC, 1975. 

Szentirmay et al. studied the microchemical environments of Nafion 117 in the acid and Na+ forms using Py and Ru(bpy)32+ probes in fully hydrated ( 40%) samples in various cation forms.Ru(bpy)32+ emission spectra cannot be interpreted in terms of environmental polarity in as straightforward a fashion as in the case of Py, but blue shifts can reflect this aspect. One of the results of this study was that the microenvironment polarities were such that Lj//i values for Py are between those for fluorocarbon and aqueous environments, and this conclusion was strengthened by the results of Ru(bpy)3 + probe studies, as well as the similar conclusion of Lee and Meisel. Another conclusion that was reached was that the SOa" clusters are chemically heterogeneous, an idea that was in line with the view of Yeager and Steck, who spoke of mixed interfacial regions. ... 

Interestingly, we have found that microbubble deflation in the ultrasound field is unusually slow for the microbubbles that contain perfluorocarbon gas when the surrounding medium is depleted of air and saturated with the same fluorocarbon gas [57]. So, perhaps in an air-saturated environment the ultra-sound-mediated destruction of microbubbles may depend on the influx of air into the bubbles, not just on the perfluorocarbon loss. 

McCulloch, A., and P. M. Midgley, Estimated Historic Emissions of Fluorocarbons from the European Union, Atmos. Environ., 32, 1571-1580 (1998). 

Kelly, N. A Characterization of Fluorocarbon-Film Bags as Smog Chambers, Environ. Sci. Technol., 16, 763-770 (1982). 

The Montreal Protocol (1987) called for a phase-out of CFCs. It was determined that the new substances break down in the environment to give predominantly carbon dioxide, water, and inorganic salts of chlorine and fluorine. The only exception is that some substances also break down to yield trifluoroacetic acid (HTFA), a substance resistant to further degradation. Based on available data, one can conclude that environmental levels of TFA resulting from the breakdown of alternative fluorocarbons do not pose a threat to the environment (Boutonnet et al., 1999). 

Aromatic molecules with fluorine or fluorine-containing substituents frequently have high bioactivity [39] and are therefore used for medical and agrochemical applications, in which they are deliberately introduced to organisms and/or the environment (Fig. 2). They are typically less bioaccumulative and less environmentally persistent than saturated fluorocarbons, and may be degraded oxidatively under aerobic conditions, where defluorination may or may not occur.5 The world market for fluoroaromatics was estimated at 10,000 tonne per annum in... 

Z. Ainbinder, L.E. Manzer, M.J. Nappa, Catalytic routes to hydro (chloro) fluorocarbons, Environ. Catal. (1999) 197-212. 

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