Abstract
The OH-initiated photo-oxidation of perfluoro ethyl vinyl ether (C2F5OCF[double bond, length as m-dash]CF2, PEVE) in air (298 K, 50 and 750 Torr total pressure) was studied in a photochemical reactor using in situ detection of PEVE and its products by Fourier transform IR absorption spectroscopy. The relative rate technique was used to derive the rate coefficient, k1, for the reaction of PEVE with OH as k1 = (2.8 ± 0.3) × 10-12 cm3 molecule-1 s-1. The photo-oxidation of PEVE in the presence of NOx at 1 bar results in formation of C2F5OCFO, FC(O)C(O)F and CF2O in molar yields of 0.50 ± 0.07, 0.46 ± 0.07 and 1.50 ± 0.22, respectively. FC(O)C(O)F and CF2O are formed partially in secondary, most likely heterogeneous processes. At a reduced pressure of 50 Torr, the product distribution is shifted towards formation of FC(O)C(O)F, indicating the important role of collisional quenching of initially formed association complexes, and enabling details of the reaction mechanism to be elucidated. An atmospheric photo-oxidation mechanism for PEVE is presented and the environmental implications of PEVE release and degradation are discussed.
Highlights
The thermal and chemical resistance of fluoropolymers has led to their use in many industrial processes and to their production in large quantities[1,2] and to their release to the environment
The IR spectrum of PEVE is characterized by a progression of strong absorption bands in the range 1050–1400 cmÀ1, a weak CQC stretching mode at 1842 cmÀ1 and weaker absorption features at 749 to 840 cmÀ1
This OH radical generation scheme generates both OH and HO2 radicals, and under these conditions, the organic peroxy radicals formed in the PEVE photo-oxidation will either react with HO2 radicals or undergo self-reaction
Summary
The thermal and chemical resistance of fluoropolymers has led to their use in many industrial processes and to their production in large quantities[1,2] and to their release to the environment. K1 was found to be independent of pressure but it has a significant negative temperature dependence, indicating that the first step is addition of OH to the CQC double bond. A room temperature value of k1 close to 3 Â 10À12 cm[3] moleculeÀ1 sÀ1 implies an atmospheric lifetime of a few days, indicating that PEVE is not an important greenhouse gas. The main environmental concern about fluorinated vinyl ethers is whether their photo-oxidation leads to formation of persistent, fluorinated pollutants in the environment. The products formed in the atmospheric photo-oxidation of organic trace gases depends on the fate of peroxy-radicals formed in the reaction between the initially generated organic radical fragments and O2. Most short lived anthropogenic pollutants are oxidized under high NOx conditions, but as the two limiting cases have different mechanisms, differences in their product distribution provide valuable information about key reaction steps
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