Photooxidation kinetics

Bhowmick and Semmens (1994) studied the photooxidation kinetics of five halogenated VOCs, including chloroform (CHL), carbon tetrachloride (CTC), trichloroethylene (TCE), tetrachloroethylene (PCE), and 1,1,2-trichloroethane (TCA) by UV/ozone. In the low to intermediate concentration range of 0.07 to 1.11 mg/L, the reactivities of the organics rank in the following order TCE > PCE > CTC > CHL > TCA. This order indicates that the reaction between ozone and saturated hydrocarbons is much slower than that of ozone with unsaturated compounds such as alkenes. For CHL, TCA, and CTC, an increase in ozone concentration had little effect on the rate constant. By comparison, the rates of oxidation for TCE and PCE increased with added... 

A pseudo first-order reaction with a half-life of 2 h was deduced for the photooxidation kinetics of anthracene in aqueous media under simulated solar radiation conditions [11]. Bertilsson and Anneli report that photochemical degradation of anthracene and phenanthrene in water proceeds rapidly (half-lives 1 and 20.4 h, respectively) while that of naphthalene (half-life > 100 h) does not [12], In the presence of humic substances, the anthracene degradation rate was unaffected while that of phenanthrene was slowed down considerably. Differences in the spectral absorbance of anthracene and... 

Photooxidation kinetic studies carried out using dGuo instead of CT-DNA resulted in a similar rate constant (0.018 min ), confirming that deoxyguanosine is the preferential target for 02( A ). 

The photooxidation kinetics of branched polyethylenes has been found to be strongly influenced by processing history and the incorporation of poly(2,6-dimethyl-l,4-phenylene... 

As it is seen from Figure 2.6 (curve 2) at the moment of light source switching off the rate of O2 absorption decreases up to stationary rate in dark process and oxidation reaction proceeds for some time. This effect is the effect of photochemical aftereffect or post-effect. It is explained [173] by lasting radical-chain process of oxidation, consisting of two stages reactions of continuation and breaks of chain of photooxidation. Kinetic curve of oxygen... 

At the present time, a discussion of the results of our model investigations in terms of possible consequences for polypropylene must be completely speculative. Apart from the differences expected between liquid phase and solid polymer photooxidation kinetics, differences in the chemical structure between our model substance, isooctane, and the structural unit of polypropylene have to be also considered. With respect to the number of CH,-groups per structural unit, isooctane and polypropylene differ by a ratio of 5 1. 

Photooxidation kinetics are generally interpreted in terms of free radical reactions. A typical scheme is given below ... 

Sample Preparation The PnBA used was provided by the Jet Propulsion Laboratory. The material was prepared by thermal polymerization of nBA by refluxing the monomer in cyclohexane under high purity nitrogen for periods up to 48 hours (5). This method was chosen to avoid contamination of the polymer by trace amounts of Initiator which might affect the photooxidation kinetics. Molecular weight, as measure by HPLC, was about ... 

D.R. Bauer, D.P. Mielewski, J.L. Gerlock, Photooxidation kinetics in crosslinked polymer coatings, Polym. Deg. Stab. 38 (1992) 57-67. 

The basic free-radical oxidation process that is used to interpret polymer coating photooxidation kinetics has been described in detail and is presented briefly below ... 

Surface vs Solution Reactions, Anotliei issue of debate in pliotocatalyzed mineialization of oiganic substrates is whether the initial oxidation occurs on the photocatalyst s surface or in solution. Kinetic data of photooxidations and photoreductions have often been fitted to the simple... 

First the interaction of selected tetramethylpiperidine (TMP) derivatives with radicals arising from Norrish-type I cleavage of diisopropyl ketone under oxygen was studied. These species are most probably the isopropyl peroxy and isobutyryl peroxy radicals immediately formed after a-splitting of diisopropyl ketone and subsequent addition of O2 to the initially generated radicals. Product analysis and kinetic studies showed that the investigated TMP derivatives exercise a marked controlling influence over the nature of the products formed in the photooxidative process. The results obtained point to an interaction between TMP derivatives and especially the isobutyryl peroxy radical. 

Kinetics of the photooxidation of organic water impurities on illuminated titania surfaces has been generally regarded to be based on the Langmuir-Hinshelwood equation with first-order reaction kinetics vs. initial substrate concentration was established univocally by many authors... 

Glasson, W. A., and C. S. Tuesday. Hydrocarbon reactivity and the kinetics of the atmospheric photooxidation of nitric oxide. J. Air Pollut. Control Assoc. 20 239-243, 1970. 

Grimsrud, E. P., H. H. Westberg, and R. A. Rasmussen. Atmospheric reactivity of monoterpene hydrocarbons, NOs photooxidation and ozonolysis. Int. J. Chem. Kinet. Symp. 1 (Chemical Kinetics Data for the Lower and Upper Atmosphere) 183-195, 1975. 

The observed ambient organic aerosol formation rates are also consistent with those estimated by extrapolation of smog-chamber kinetic data. Other heavy unsaturates, such as styrene and indene, are present in the atmosphere and may contribute, in part, to the formation of benzoic acid and homophthalic acid, respectively. Diesel exhaust and industrial emission are possible sources of such heavy unsaturates. Diolefins of C6+ are not present in gasolines and exhaust gases and have not been found in the atmosphere, and their possible role as precursors of the Cs-7 difiinctional acidic compounds is seriously challenged. Lower diolefins are emitted in automobile exhaust. Examination of vapor-pressure data indicates that the bulk of their expected photooxidation products remains in the gas phase, including most of the less volatile C3-4 dicarboxylic acids. 

Leone JA, Flagan RC, Grosjean D, et al. 1985. An outdoor smog chamber and modeling study of toluene-NO photooxidation. Int J Chem Kinet 17(2) 177-216. 

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