Phase Oxidation Techniques

Gray, L.W., Adamson, M.G.A., Hickman, R.G., Farmer, J.C., Chiba, Z., Gregg, D.W., and Wang, F.T., Aqueous phase oxidation techniques as an alternative to incineration, Lawrence Livermore National Laboratory, UCRL-JC-108867, Albuquerque, NM, 1992. 

Itatani, K., Sakai, H., Scott Howell, F., Kishioka, A. and Kinoshita, M., Sinterability of spinel (MgAl204) powder prepared by vapour-phase oxidation technique , Brit. Ceram. Trans., 1989 88 13-16. 

Other large-volume esters are vinyl acetate [108-05-4] (VAM, 1.15 x 10 t/yr), methyl methacrylate [80-62-6] (MMA, 0.54 x 10 t/yr), and dioctyl phthalate [117-81-7] (DOP, 0.14 x 10 t/yr). VAM (see Vinyl polymers) is produced for the most part by the vapor-phase oxidative acetoxylation of ethylene. MMA (see Methacrylic polymers) and DOP (see Phthalic acids) are produced by direct esterification techniques involving methacryHc acid and phthaHc anhydride, respectively. 

Synthesis depends on gas-phase pyrolysis techniques , and interconversion is by electrochemical oxidation . Understanding of the mechanisms by which the boranes interconvert and build up into larger clusters is growing . 

Thermal treatments can be applied to modify the properties of a material, for example, dealumination and optimization of crystalHne phases. These techniques do not require oxidants. Oxidative thermal treatments are generally employed to activate molecular sieves, by removing the organic templates employed during synthesis. This is one of the key steps when preparing porous catalysts or adsorbents. In air-atmosphere calcination, the templates are typically combusted between 400... 

These instruments employ a continuous flow of persulfate solution to promote oxidation prior to ultraviolet irradiation, and have a low system blank and low detection limit. Since all reactions take place in the liquid phase, problems suffered by combustion techniques, such as catalyst poisoning, reactor corrosion, and high-temperature element burnouts, are obviated. However, the ultraviolet-promoted chemical oxidation technique is not designed to handle particulate-containing samples, and tends to give incomplete oxidation for certain types of compounds such as cyanuric acid. 

CL accompanies many reactions of the liquid-phase oxidation of hydrocarbons, ketones, and other compounds. It was discovered in 1959 for liquid-phase ethylbenzene oxidation [219,220]. This phenomenon was intensively studied in the 1960s and 1970s, providing foundation for several methods of study of oxidation, decay of initiators, and kinetics of antioxidant action [12,17,221], Later this technique was effectively used to study the mechanism of solid polymer oxidation (see Chapter 13). 

At the present time, gas-phase oxidation is the favored technique. 

Oxidation of dihydroquinacridone to quinacridone may be achieved, for instance, with the sodium salt of m-nitrobenzene sulfonic acid in aqueous ethanol in the presence of sodium hydroxide solution [7]. A distinction is made between heterogeneous and homogeneous oxidation. The reaction is referred to as a solid state oxidation if the solvent contains approximately 2% sodium hydroxide solution. A content of approximately 30% sodium hydroxide solution relative to the solvent mixture, on the other hand, converts the reaction into a so-called solution oxidation . The type of ring closure defines the crystal modification of the resulting dihydroquinacridone, while the oxidation technique defines the crystal phase of the quinacridone pigment. 

Research on liquid-phase oxidation processes has opened up a tremendous area for research on free radical mechanisms. Such research will be concerned, not with hypothetical particles like those studied a few years ago, but with thoroughly material active centers, amenable to investigation by experimental techniques currently in use. Problems of foremost importance are involved in correlating data on unit processes... 

Husain and co-workers, for example (Husain, 1989 Husain et al., 1991 Husain and Dutkiewicz, 1992 Burkhard et al., 1995 Dutkiewicz et al., 1995), have developed techniques using Se, As, and Sb as tracers to follow the oxidation of S02 with time in clouds at Whiteface Mountain in New York State. The principle is based on the fact that the major sources of these metals are high-temperature combustion, e.g., of coal and oil. Thus these metals are found in particles (see Chapter 9) that act as condensation nuclei for cloud formation. These particles also contain sulfate formed from the gas-phase oxidation of S02. Because of the low vapor pressure of H2S04, it becomes associated with particles, either by homogeneous condensation or by condensing out on preexisting particles (see Chapter 9.C). As a result, the metals can be used as tracers for sulfate formed in the gas phase, as opposed to sulfate formed by the uptake of S02 into cloudwater followed by oxidation. 

These factors have led researchers to examine novel methods for tire degradation of these contaminants, including liquid-phase photocatalytic oxidation. The treatment of wastewaters contaminated with agents like chlorinated aromatics has also prompted research into the optimum methods of integrating chemical oxidation techniques with existing water treatment methods, particularly biological treatment and ozonation techniques [37],... 

Up to now three chemical vapor deposition (CVD) techniques have proved suitable for the preparation of high quality optical fibers the outside vapour phase oxidation (OVPO) process8, the modified CVD (MCVD) process9 and the plasma-activated CVD (PCVD) process10. The last mentioned process will be the main subject of this article. To give a better appreciation of the principles the alternative processes will be described briefly. 

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