Ozone decomposition rate constants

Species formed during the ozonization behave like classical initiators. It was, thus, interesting to evaluate their decomposition rate constant Kj. For this purpose, several methods were used by various authors working on this subject. 

Reaction 1 is the rate-controlling step. The decomposition rate of pure ozone decreases markedly as oxygen builds up due to the effect of reaction 2, which reforms ozone from oxygen atoms. Temperature-dependent equations for the three rate constants obtained by measuriag the decomposition of concentrated and dilute ozone have been given (17—19). 

Ozone can be destroyed thermally, by electron impact, by reaction with oxygen atoms, and by reaction with electronically and vibrationaHy excited oxygen molecules (90). Rate constants for these reactions are given ia References 11 and 93. Processes involving ions such as 0/, 0/, 0 , 0 , and 0/ are of minor importance. The reaction O3 + 0( P) — 2 O2, is exothermic and can contribute significantly to heat evolution. Efftcientiy cooled ozone generators with typical short residence times (seconds) can operate near ambient temperature where thermal decomposition is small. 

A single chlorine atom can bring about the decomposition of tens of thousands of ozone molecules. Bromine atoms can substitute for chlorine indeed the rate constant for the Br-catalyzed reaction is larger than that tor the reaction just cited. 

As a final example of numerical simulations, consider the base-catalyzed decomposition of ozone in aqueous solution. This multistep reaction is controversial in that contradictory mechanisms have been suggested.33 34 The set of reactions that appears to be the most consistent with the experimental data is shown in Table 5-1, with a set of rate constants. Most of these values were reported in the literature, but several were refined to give agreement with experiments that measured the decline in concentration O3. 

Reactions" and rate constants"6 for the decomposition of ozone in alkaline solutions... 

In this study, the degradability of phenol in aqueous solutions was investigated with using ozone. Additionally, decomposition kinetic of phenol in the presence of ozone was calculated using maximum rate constants, from graphics of concentration versus time. 

Benson, S.W., and A.E. Axworthy (1965) Reconsiderations of the rate constants from the thermal decomposition of ozone, J. Chem. Phys., 42,2614. 

Ozone decomposition is usually a first-order process, where the apparent pseudo first-order rate constant depends on the concentration of... 

Gehringer irradiated TCE contaminated waters in the presence and absence of ozone [52]. The use of ozone dramatically increased the rate of 100 ppb TCE decomposition, as shown in Fig. 6 and in Table 7. It was also found that the Z)10 (and thus dose constant) values were independent of initial TCE concentration over a wide range, indicating that the mechanism of decomposition was constant. Thus, the factors for reduction in Dw shown in Table 7 are useful predictive process parameters. 

Results are compared in Figure 5 for the ozonation of cyanide at 13 , 20°, 25°, and 30° C. Although the value of K increases slightly with increase in temperature, it can only be concluded that the temperature coefficient of the reaction rate constant is small. Thus, the rate of ozonation of cyanide does not depend, for practical purposes, on the temperature in the range of 13° to 30° C. It would be highly interesting to study the temperature effect of this reaction in the light of the rate of ozone decomposition and ozone solubility in solution. 

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