Kinetics ozonation

Keywords Degradation kinetics, ozone, phenol, pollution... 

The value of E° in eq. 16.10 refers to pH = 0 (see Box 8.1), and at higher pH, E becomes less positive +1.65 V at pH = 7, and +1.24 V at pH = 14. The presence of high concentrations of alkali stabilizes O3 both thermodynamically and kinetically. Ozone is much more reactive than O2 (hence the use of O3 in water purification, see Box 14.1). Reactions 16.11-16.13 typify this high reactivity, as does the reaction of ozone with alkenes to give ozonides. 

Above pH 9, decomposition of ozone to the reactive intermediate, HO, determines the kinetics of ammonia oxidation. Catalysts, such as WO, Pt, Pd, Ir, and Rh, promote the oxidation of dilute aqueous solutions of ammonia at 25°C, only two of the three oxygen atoms of ozone can react, whereas at 75°C, all three atoms react (42). The oxidation of ammonia by ozone depends not only on the pH of the system but also on the presence of other oxidizable species (39,43,44). Because the ozonation rate of organic materials in wastewater is much faster than that of ammonia, oxidation of ammonia does not occur in the presence of ozone-reactive organics. 

The rate of aqueous ozonation reactions is affected by various factors such as the pH, temperature, and concentration of ozone, substrate, and radical scavengers. Kinetic measurements have been carried out in dilute aqueous solution on a large number of organic compounds from different classes (56,57). Some of the chemistry discussed in the foUowing sections occurs more readily at high ozone and high substrate concentrations. 

Chemical kinetic analysis of these simplified reactions allows net ozone formation to be directly related to hydrocarbon consumption by HO on a time-independent basis... 

Atkinson R, Carter WPL. 1984. Kinetics and mechanisms of the gas-phase reactions of ozone with organic compounds under atmospheric conditions. Chem Rev 84 437-470. 

There is a continuing interest in the use of phosphite-ozone adducts as sources of singlet oxygen and as reagents for mimicking the reactions of this species. The commercially available phosphite (54) forms an ozone adduct of striking stability. Decomposition of the adduct only becomes appreciable at temperatures > 0 °C the decomposition exhibits first-order kinetics, so that at 10 °C= 9.10 x 10 min and= 76.2 min. These... 

The kinetics of the various reactions have been explored in detail using large-volume chambers that can be used to simulate reactions in the troposphere. They have frequently used hydroxyl radicals formed by photolysis of methyl (or ethyl) nitrite, with the addition of NO to inhibit photolysis of NO2. This would result in the formation of 0( P) atoms, and subsequent reaction with Oj would produce ozone, and hence NO3 radicals from NOj. Nitrate radicals are produced by the thermal decomposition of NjOj, and in experiments with O3, a scavenger for hydroxyl radicals is added. Details of the different experimental procedures for the measurement of absolute and relative rates have been summarized, and attention drawn to the often considerable spread of values for experiments carried out at room temperature (-298 K) (Atkinson 1986). It should be emphasized that in the real troposphere, both the rates—and possibly the products—of transformation will be determined by seasonal differences both in temperature and the intensity of solar radiation. These are determined both by latitude and altitude. 

Acero JL, K Stemmier, U van Gunten (2000) Degradation kinetics of atrazine and its degradation products with ozone and OH radicals a predictive tool for drinking water treatment. Environ Sci Technol 34 591-597. 

Deborde M, S Rabouan, J-P Duguet, B Legube (2005) Kinetics of aqueous ozone induced oxidation of some endocrine disrupters. Environ Sci Technol 39 6086-6092. 

Kamens R, M Jang, K Leach (1999) Aerosol formation from the reaction of a-pinene and ozone using a gas-phase-kinetics-aerosol partitioning model. Environ Sci Technol 33 1430-1438. 

McDowell DC, MM Huber, M Wagner, U von Gunten, TA Ternes (2005) Ozonation of carbamazepine in drinking water identification and kinetic study of major oxidation products. Environ Sci Technol 39 8014-8022. 

Figure 2. Kinetic curve of POOH groups formation in polypropylene film after 10 hours exposure to ozone.

The formation of POOH during simultaneous exposure of PP films to ozone and light (LI or L2) can not be obtained kinetically. The experimental results show for rapid formation of hydroperoxide groups which are partially decomposed under UV-irradiation. There is no linear dependence on the ozone concentration. 

Figure 4. Kinetics of carbonyl group formation at 1714 cm- in polypropylene samples (0) and ( ) ozone and UV light (L2) (4) and (A) ozone only (0) and ( ) ATR spectra (A) and (A) transmission spectra.

Kinetic curves of fluorescence disappearing (Fig. 7) allow for comparison of the oxidation effect, which is the highest in the case of UV-irradiation in ozone. 

Figure 7. Kinetics of fluorescence disappearing at 340 nm of polypropylene films ( O) treated with ozone only (9) ozone and UV light (L2) (A) UV irradiated (L2) in oxygen. Excitation wavelwngth 240 nm.

Fig. 3. Total kinetic energy distribution for O3 — C Ag) + 0(1D2). Also shown at each wavelength is a comb corresponding to each vibrational level with no rotational excitation. The peaks observed in the 305 nm image are due to rotational structure. The small peak at 0.19eV in the 305nm image is due to an ozone hot band .

Kang J-W, Hoffmann MR (1998) Kinetics and mechanism of the sonolytic destruction of methyl tert butyl ether by ultrasonic irradiation in the presence of ozone. Environ Sci Tech 32 3194-3199... 

Weavers LK, Malmstadt N, Hoffmann MR (2000) Kinetics and mechanism of pentachloro-phenol degradation by sonication, ozonation and sonolytic ozonation. Environ Sci Tech 34 1280-1285... 

The gas phase decomposition of ozone is catalyzed by nitrogen pent oxide. Two mechanisms that purport to explain this process are given below. Can relatively simple kinetic measurements be used to eliminate one of the proposed mechanisms from further consideration Explain. 

Adeniji, S.A., Kerr, J.A., Williams, M.R. (1981) Rate constants for ozone-alkene reactions under atmospheric conditions. Int. J. Chem. Kinet. 13, 209-217. 

Atkinson, R., Aschmann, S.M., Carter, W.L., Pitts, Jr., J.N. (1983) Effects of ring strain on gas-phase rate constants. 1. Ozone reactions with cycloalkenes. Int. J. Chem. Kinet. 15, 721-731. 

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