Ozone decomposition rate

Grasso D, Weber W J (1989) Mathematical Interpretation of Aqueous-Phase Ozone Decomposition Rates, Journal of Environmental Engineering 115 541-559. 

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). 

Mechanism II begins with fast reversible ozone decomposition followed by a rate-determining bimolecular collision of an oxygen atom with a molecule of NO. The rate of the slow step is as follows Rate = 2[N0][0 This rate expression contains the concentration of an intermediate, atomic oxygen. To convert the rate expression into a form that can be compared with the experimental rate law, assume that the rate of the first step is equal to the rate of its reverse process. Then solve the equality for the concentration of the intermediate ... 

C15-0051. Do the following for the ozone decomposition mechanism (a) Express the rate in terms of O2 formation, (b) Relate the rate of O3 consumption to the rate of O2 production, (c) If O2 forms at a rate of 2.7 X 10" M, state how fast ozone disappears. 

The Effect of Mineral Matters on the Decomposition Ethers. Recently, the effect of mineral matters of coal on the coal liquefaction has received much attention. It was shown that small amounts of FeS or pyrite are responsible for the hydro-genative liquefaction of coal. Therefore, it is interesting to elucidate the effect of mineral matters of coal on the decomposition rate and products of aromatic ethers, and so three diaryl ethers were thermally treated in the presence of coal ash obtained by low temperature combustion of Illinois No.6 coal at about 200°C with ozone containing oxygen. 

Due to high activity in reactions with free radicals, ozone undergoes the chain decomposition in solutions also. The chain reaction of ozone decomposition was evidenced in 1973 in the kinetic study of cyclohexane and butanone-2 oxidation by a mixture of 02 and 03 [146-151], It was observed that the rate of ozone consumption obeys the equation [112] ... 

Comparison of the initial reaction with H02 (k9 = 2.2 106M s 1) and with OH (k[ = 70 M 1 s 1) shows that in the 0,/H202 -system the initiation step by OH is negligible. Whenever the concentration of hydrogen peroxide is above 10 7 M and the pH-value less than 12, H02 has a greater effect than OH has on the decomposition rate of ozone in water. 

Photon Chain. In the ultraviolet region quantum yields of over two (14) and as high as six (44) have been reported. Although the evidence seems to be sufficient to this author, Benson (11,13) does not believe that quantum yields of greater than two in dry ozone have been unequivocally demonstrated. He has pointed out that traces of water could greatly accelerate the rate of ozone decomposition. Nevertheless, Benson has postulated that a photon chain could yield a chain decomposition and account for quantum yields of over two, a proposal which was first made by Noyes and Leighton (64). 

Flash photolysis studies of mixtures of ozone and hydrogen (6,56) have shown that the reaction of 0(1D) atoms with hydrogen yields vibra-tionally excited OH radicals. Studies of ozone and hydrogen mixtures in the visible (35) and in the ultraviolet (94) have shown that water is formed and that the rate of ozone decomposition is increased in the presence of hydrogen. 

Kusakabe et al. (1990) reported that total organic carbon (TOC) concentrations decrease rapidly during the first 100 min of treatment with ozone, leveling off somewhat after 100 min. Furthermore, the decomposition rate of TOC was accentuated by UV irradiation however, no direct correlation between UV intensity and TOC concentration was found. Low concentrations of TOC were still detected even after a 5-hour sampling period, indicating that the destruction of humic substances produces refractory compounds that are oxidized quite slowly (Kusakabe et al., 1990). 

Kusakabe et al. (1990) reported that the destruction rate coefficients increase as temperature increases. UV light intensity of 8.7 W/m2 yielded a slightly more than tenfold increase in the decomposition rate. The decomposition rate of ozone increases with UV intensity. These results imply that, under UV irradiation, radical chain reactions are predominant over molecular ozone reactions. When light intensity is greater than 3 W/m2, the degradation rate of TOC by UV/03 can be expressed as follows ... 

Volatile organic compounds (VOCs), especially trihalomethanes, are frequently found in drinking water due to the chlorination of humic acids. When UV irradiation is applied to the pre-ozonation of humic acids, the decomposition of VOC precursors increases (Hayashi et al., 1993). The ozonation rates of compounds such as trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane, 1,2-dichloroethane, and 1,2-dichloropropane were found to be dependent on UV intensity and ozone concentration in the aqueous phase by Kusakabe et al. (1991), who reported a linear relationship between the logarithmic value of [C]/[C0] and [03]f for 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene. The other two organochlorines followed the same first-order kinetics with and without UV irradiation (Kusakabe et al., 1991). Thus, the decomposition rate can be expressed as ... 

The general equation for the decomposition rate of ozone under UV light, in the gas phase, is given as follows ... 

Hayashi, J.-I., Ikeda, J., Kusakabe, K., and Shigeharu, M., Decomposition rate of volatile organochlorines by ozone and utilization efficiency of ozone with ultraviolet radiation in a bubble-column contactor, Water Res., 27, 1091-1097, 1993. 

Figure 14.21 illustrates the effect of humic acid or carbonate on the efficiency of the oxidation of TCB. The rate of TCB degradation decreased at both 1.6 and 10 mg/L humic acid. It appears that humic acid scavenges OH and other radicals responsible for the degradation of TCB. Furthermore, the presence of humic acid is likely to reduce the transmission of UV light, thereby decreasing the rate of ozone decomposition through OH radicals (Masten et al., 1996). 

The effectiveness of the gas-solid mass transfer in a circulating fluidized bed (see Chapter 10) can be reflected by the contact efficiency, which is a measure of the extent to which the particles are exposed to the gas stream. As noted in Chapter 10, fine particles tend to form clusters, which yield contact resistance of the main gas stream with inner particles in the cluster. The contact efficiency was evaluated by using hot gas as a tracer [Dry et al., 1987] and using the ozone decomposition reaction with iron oxide catalyst as particles [Jiang etal., 1991], It was found that the contact efficiency decreases as the particle concentration in the bed increases. At lower gas velocities, the contact efficiency is lower as a result of lower turbulence levels, allowing a greater extent of aggregate formation. The contact efficiency increases with the gas velocity, but the rate of increase falls with the gas velocity. 

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