OCR Text |
Show For example, the instability of CF2=CF2 towards breaking the double bond to form 2 CF2 radicals is manifest. Table 3 contains a summary of pertinent rate constants for bimolecular attack on fluorinated compounds. Here again the earlier deductions based on bond strength values are .bome out Thus the weakness of the O-F bonds coupled with the strength of the C-F bonds means that OH or O-atom attack on fluorine bond to carbon is a very unlikely pathway for radical induced decomposition. This is in contrast to the situation with respect to hydrocarbons where OH attack is in fact one of the most important decomposition channels. This leaves only hydrogen atom as a source of radical attack on the fluorine that is bonded to a carbon. As noted earlier, although the reaction is exothermic, rate constants are very small in comparison to analogous reactions for the abstraction of a hydrogen. Overall, radical attack on hydrofluorocarbon compounds will concentrate on the hydrogen portion of the molecule. RESULTS AND DISCUSSION a:Qualitative Considerations The data summarized above leads inevitably to the conclusion that fluorinated compounds are more difficult to destroy than the comparable chlorinated compounds This may also be the case for a number of hydrocarbon fuels. Perfluorinated compounds represent a special category in the sense that under incineration probably the most likely channel available for destruction is through unimolecular decomposition. With increasing degrees of hydrogenation, 1,1 and 1,2 unimolecular decomposition together with the availability of abstractable hydrogens provide alternative and more facile channels for destruction. For hydrocarbons in a homologous series, the larger molecules are likely to be more labile. Thus the capability of destroying the smallest member of a homologous series provides good evidence for the ability to destroy higher members. This is probably also true for fluorinated organics. It should however be verified. The main confusing factor in setting up a scale of incinerability is the possibility of the waste product being reformed during the course of incineration. These effects are probably most serious for the smaller species or in general the first member of a homologous, since the initial precursors may well 12 |