Oxidative purification

Air-Based Direct Oxidation Process. A schematic flow diagram of the air-based ethylene oxide process is shown in Figure 2. Pubhshed information on the detailed evolution of commercial ethylene oxide processes is very scanty, and Figure 2 does not necessarily correspond to the actual equipment or process employed in any modem ethylene oxide plant. Precise information regarding process technology is proprietary. However, Figure 2 does illustrate all the saUent concepts involved in the manufacturing process. The process can be conveniently divided into three primary sections reaction system, oxide recovery, and oxide purification. 

The third key section of the process deals with ethylene oxide purification. In this section of the process, a variety of column sequences have been practiced. The scheme shown in Figure 2 is typical. The ethylene oxide-rich water streams from both the main and purge absorbers are combined, and after heat exchange are fed to the top section of a desorber where the absorbate is steam stripped. The lean water from the lower section of the desorber is virtually free of oxide, and is recirculated to the main and purge absorbers. The concentrated ethylene oxide vapor overhead is fed to the ensuing stripper for further purification. If the desorber is operated under vacuum, a compressor is required. 

Ethylene Oxide Purification. The main impurities ia ethylene oxide are water, carbon dioxide, and both acetaldehyde and formaldehyde. Water and carbon dioxide are removed by distillation ia columns containing only rectifying or stripping sections. Aldehydes are separated from ethylene... 

Attempts to bnild electrochemical systems for oxidative purification of effluents have met a nnmber of problems ... 

This method involves acid hydrolysis of the urine followed by extraction with toluene, oxidative purification with permanganate, adsorption chromatography, acetylation, column chromatography on alumina, and finally quantification by colorimetric determination of the sulfuric acid chromogen. It is now generally accepted that this method is not as sensitive or as specific as the newer methods of GC. 

Oxidation of CNTs - Oxidative Purification 1.3.2.1 Carboxylation of CNTs... 

Figure 18 Schematic of the steps involved in different methods of oxidative purification of SWNTs. Oxidation is done at a particular temperature (Ti) for a certain period of time (q). Both the T and t] are required to be determined for every sample batch with prior knowledge of decomposition rate using TGA...

Figure 19 SEM images of purified SWNTs. (A) Laser-grown SWNTs subjected to two stage air oxidative purification (scale bar 1 im) (a) before purification and (b) after purification. (Reprinted with permission from Ref 100. 2001 American Chemical Society.) (B) Raw HiPco SWNTs subjected to three stage wet-air oxidation (scale bar 500 nm) (a) before purification and (b) after purification. (Reprinted with permission from Ref. 109. 2001 American Chemical Society)...

Oxidative purification of ND powders was conducted under isothermal conditions using the heating stage and a tube furnace. Isothermal experiments included two steps (1) rapid heating at 50°C/min to the selected temperature and (2) isothermal oxidation for 5 h in ambient air at atmospheric pressure. ND powders used for crystal size characterization were oxidized for 2, 6, 17, 26, and 42 h at 430°C, in a closed tube furnace in static air at atmospheric pressure. 

The sulphide ore is oxidised in the presence of silica which enables the iron to be removed as a silicate slag. The nickel oxide left is reduced at 350° by water gas to an impure metal leaving the iron as ferric oxide. Purification is based on the formation and decomposition of gaseous Ni(CO)4. Carbon monoxide is passed over the impure metal at 60° and the gas containing a few per cent of the tetracarbonyl is brought into contact with agitated nickel pellets at 200°. The pellets grow as nickel is deposited on them the CO is recirculated (Fig. 258). 

A less convenient route for the preparation of cyclopentadienylcopper-ligand complexes involves the use of Cu(I) oxide. Purification of the organocopper complexes is difficult because of the decomposition products formed by subsequent hydrolysis by H2O produced in the metallation reaction, e.g. ° ... 

In the production of uranium(lV) oxide in the wet process, the uranium concentrate is first converted into a uranyl nitrate solution with nitric acid. After the purification of the uranyl nitrate by solvent extraction, it can be converted into uranium(IV) oxide by two different routes either by thermal denitration to uranium(VI) oxide which is then reduced to uranium(IV) oxide or by conversion of uranyl nitrate into ammonium diuranate which is reduced to uranium(IV) oxide. Purification proceeds by extraction of the uranyl nitrate hydrate from the acidic solution with tri-n-butylphosphate in kerosene and stripping this organic phase with water, whereupon uranium goes into the aqueous phase. 

Gut J, Meier UT, Catin T, et al. Mephenytoin-type polymorphism of drug oxidation purification and characterization of a human liver cytochrome P-450 isozyme catalyzing microsomal mephenytoin hydroxylation. Biochim Biophys Acta I986 884(3) 435—47. 

T. T. Shih, Lower alkylene oxide purification, US Patent 5,133,839, July 28, 1992, To ARCO Chemical Technology, L.P. 

Gut, J., Gasser, R., Dayer, P., Kronbach, T., Catin, T., and Meyer, U. A. (1984) Dehrisoquine-type polymorphism of drug oxidation purification from human liver of a cytochrome P450 isozyme with high activity for bufuralol hydroxylation. FEES Lett. 173 (2), 287-290. 

Other methods of oxidative purification include the treatment with super-critical water (hydrothermal procedure), thermal oxidation in air and plasma oxidation in the presence of water. All of them make use of the different reactivity of amorphous carbon and nanotubes, with the latter being more stable than the unordered material. The difference, however, is not very big, and so an extensive removal of amorphous carbon inevitably causes massive losses of nanotubes as well. Consequently the application of oxidizing methods always represents a compromise between complete elimination of impurities and retaining the largest possible amount of product. 

In some cases, the oxidative purification is followed by a thermal treatment that is, heating the sample to ca. 700 C in an atmosphere of argon. It helps annealing surface defects and, partially, causes a thermal removal of functional groups from the surface, too. However, it also leads to a further graphitization of the surface. Hence careful consideration is required whether graphitized or functionalized nanodiamond is more advantageous for a certain experiment or application. 

Gut, X, T. Catin, P. Dayer, T. Kronbach, U. Zanger, and U.A. Meyer (1986). Debrisoquine/sparteine-type polymorphism of drug oxidation Purification and characterization of two functionally different human liver cytochrome P-450 isozymes involved in impaired hydroxylation of the prototype substrate bufuralol. J. Biol. Chem. 261, 11734-11743. 

Novikov, O.K., Vanhove, G., Carchon, H., Asselberghs, S, Eyssen, H.J., Van Veldhoven, RR Mannaerts, G.P. (1994)7. Biol Chem. 269, 27125-27135. Peroxisomal oxidation Purification offournovel 3-hydroxyacyl-CoA dehydrogenases from rat liver peroxisomes. 

The Giammarco Vetrocoke Process uses arsenate as an additive to the potash solution. A modified version of this process has become state of the art as an oxidative purification unit for selective removal of H2S. 

The zinc dust piuification circuit in the oxide leaching plant was originally conunissioned as a purification system for an old oxide cellhouse, decommissioned about 20 years ago when the oxide and calcine leaching plant electrolytes were combined. However, the oxide purification circuit continued to operate with about one gram per liter addition of dry zinc dust, principally to cement cadmium in the oxide electrolyte prior to entering the calcine leaching plant. A portion of the purification residue was then forwarded directly to the cadmium plant. Some arsenic was also removed fix>m solution. 

There were several problems with the oxide electrolyte purification circuit. The arsenic concentration in the zinc fiime fi-om the smelter had increased since the start-up of KIVCET, resulting in an increased tendency for arsenic breakthrough to the oxide electrolyte. This, in turn, had led to an increased potential for arsine generation during zinc dust purification as well as in the storage tank for purification residues in the cadmium plant. In addition, the oxide purification equipment was in very poor working condition. 

In mid-1999, the oxide electrolyte purification circuit shown in Figure 3 was shut down on an interim basis. The arsine outbreaks were essentially eliminated and the calcine leaching plant performance was not detrimentally affected. Therefore, the oxide purification process has been permanently decommissioned. 

Figure 17-2 Oxidative purification of wastewater with electrochemicaiiy generated Fe(yi). [From S. LIcht and X. Yu. Envimn. Sd. Technot. 2005,39,8071.]...

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