Showing papers on "Wet oxidation published in 1989"

Kinetics and mechanism of oxidation of SiGe: dry versus wet oxidation

Abstract: The rates of oxidation of SiGe and of Si covered with a thin ‘‘marker’’ of Ge have been measured, and compared with rates of oxidation for pure Si, both for wet and dry ambient. It is shown that the presence of Ge at the SiO2/Si interface increases the rate of wet oxidation by a factor of about 2.5, while it does not affect the rate of dry oxidation. By decreasing the partial pressure of H2O sufficiently, the rate of wet oxidation can be decreased to match that of dry oxidation. In this case again, Ge has no effect on the rate. Contrary to what has been proposed before, Ge is being piled up at the interface both for fast and slow oxidation. We demonstrate that the role of Ge is to suppress the formation of Si interstitials and that this is the rate limiting step in cases of rapid oxidation. For slower oxidation, interstitials have considerably more time to diffuse away and thus their formation and/or diffusion is not rate limiting.

Efficient Elimination of Organic Liquid Wastes: Wet Air Oxidation

Abstract: Wet air oxidation is ideally suited to liquid wastes which are too dilute to be incinerated and too refractory to be handled by chemical or biological oxidation. This process relies on high tempera...

Effluent treatment for alcohol distillery: Thermal pretreatment with energy recovery

Abstract: Stillage from cane molasses based alcohol distillery was thermally treated at 160 to 250°C at high pressure and in the absence of air. A solid charred residue was precipitated that was easily separated by gravity filtration from a liquid suitable for anaerobic digestion or wet oxidation. The charred residue was comparable with typical lignite coal in terms of carbon content and calorific value. Effects of temperature and pH on COD reduction, biodegradability, and filterability were studied.

Method for wet oxidation treatment

Abstract: The present invention provides a method and apparatus for collecting and liquefying off-gases, particularly carbon dioxide, generated by a wet oxidation of organic matter and for the on sight gasification of liquid oxygen for use as an oxidant in the wet oxidation reaction. Through a series of separation and pressurization operations, high pressure off-gases are introduced into a heat exchanger at substantially the same time as liquid oxygen. The liquid oxygen and compressed off-gases are in heat exchange relation in the heat exchanger but are isolated from one another. Heat is transferred from the compressed off-gases to the liquid oxygen whereby the off-gases are liquified and the liquid oxygen is gasified. The liquified off-gases may then be stored in appropriate storage units. The gaseous oxygen is used as the oxidant for the wet oxidation reaction. In another aspect, odor-producing compounds are removed from the off-gases by a condensation process wherein the odor-producing compounds are separated from the off-gases by condensation. In still another aspect, these odor-producing compounds are removed from the off-gases after liquifaction by a chemical operation which chemically strips the odor-producing compounds from the liquified off-gases.

Process for treating caustic cyanide metal wastes

Abstract: A method for operating a continuous wet oxidation system for destroying cyanide in caustic cyanide and metal wastes which scale upon heating. Raw waste is introduced into the wet oxidation reactor without heating while a mixture of heated dilution water and oxygen containing gas is introduced into the reactor by a separate inlet. The reactor is fitted with a pair of valved effluent lines and corresponding valved lines for introducing dilute mineral acid into each effluent line at system pressure. Oxidized effluent and offgases exit through a first effluent line while dilute mineral acid flows through a second effluent line into the reactor to prevent scale buildup. Periodically the flows are alternated such that oxidized effluent and offgases exit through the second effluent line and dilute mineral acid flows through the first effluent line into the reactor to remove scale. The oxidized effluent and offgases are then cooled and separated.

Elimination of Organic Pollutants using Supported Catalysts with Hydrogen Peroxide

Abstract: Picric acid (2, 4, 6, tri-nitro-phenol), which is a hardly-oxidized aromatic compound, was studied as a water pollutant. Different supported catalysts were tested in the presence of hydrogen peroxide as a method for elimination of the organic pollutant from waste water. Among some transition metal ions, Cobalt (II) nitrate immobilized in silica gel was selected for detailed study. The effect of pH, initial concentration of hydrogen peroxide, amount of catalyst, and temperature were studied to find the optimum conditions for the wet oxidation of this organic pollutant. Experimental kinetic study was conducted using visible spectrophotometric techniques and chemical oxygen demand (COD). Supported catalysts demonstrated experimentally some reusability. The present data show that the rate of oxidation is a first order with respect to pollutant concentration, hydrogen peroxide concentration and the amount of catalyst used. The dependence of the reaction rate on the nature of the immobilized transition metal, temperature, and pH of reaction media has also been discussed.

Process for treating waste water

Abstract: PURPOSE:To treat waste water efficiently for a long period of time, by oxidizing waste water containing COD components in wet manner under specific conditions, using catalysts containing compound oxides of titanium and zirconium, and oxides of lanthanoids, as catalyst components. CONSTITUTION:Catalysts for wet oxidation, comprising a component composed of compound oxides of titanium and zirconium such as TiO2-ZrO2 etc.; a component composed of oxides of lanthanoids such as, at least, one kind of oxide selected from a group composed of lanthanum, cerium or neodymium; and a component composed of manganese etc., are used. Waste water containing COD component is oxidized in wet manner at a reaction temperature of 370 deg.C or lower, usually 100-370 deg.C, under a pressure high enough for the waste water to keep liquid phase in a reaction column. i.e., 1 about 200kg/cm , with feed gases containing molecular oxygen having a quantity of 1-1.5 times a theoretical oxygen required for oxidizing and decomposing organic and inorganic substances contained in the waste water.

Method for purification of water

Abstract: A method for the purification of waste water by the use of a heat-exchanger type reaction vessel composed of a plurality of inner tubes and a shell defining jointly with the outer peripheries of the inner tubes a passage for the flow of a heat transfer medium, which method comprises passing said waste water through said inner tubes and, at the same time, feeding a molecular oxygen-containing gas to the flow of said waste water thereby establishing contact between said waste water and said feed gas and consequently effecting wet oxidation of the impurities present in said waste water.

Similarities and differences in pretreating woody biomass by steam explosion, wet oxidation, autohydrolysis, and rapid steam hydrolysis/continuous extraction

Abstract: Steam hydrolysis processes are excellent methods for pretreating and fractionating cellulose from the other major wood components. In this study a comparison was made between four pretreatment processes: steam explosion; wet oxidation; autohydrolysis; and a new process based on rapid steam hydrolysis/continuous extraction. The biomass feedstock used was a low-cost woody substrate consisting of mixed southern hardwoods obtained by total tree chipping. The four pretreatments all employ steam or water and heat; however, there are fundamental differences between each process. The initial reaction involves a mild acid-catalyzed hydrolysis reaction of both the glycosidic bonds of the hemicelluloses and the ..cap alpha..-ether linkage in lignin. Even though the initial reactions for the four processes are similar, the final products are quite different due to the variety of secondary reactions which occur. All four pretreatments dramatically increased the enzymatic hydrolysis rates. However, only the wet oxidation pretreatment increased the acid hydrolysis rate. The hemicelluloses were depolymerized by autohydrolysis, wet oxidation, and steam explosion. The Rapid Steam Hydrolysis/Continuous Extraction process also depolymerized the hemicelluloses but minimized further degradation of the polysaccharides. The lignin was depolymerized by all pretreatments but apparently recondensed at the higher autohydrolysis temperatures. The solid residue remaining after a 260/supmore » 0/C Rapid Steam Hydrolysis pretreatment had an enriched cellulose content of about 70%.« less

Treatment of high-concentration organic sewage

Abstract: PURPOSE:To prevent the deterioration in catalyst activity and to remove the phosphorus and polluting components in high-concn. org. sewage by adding iron ions to said sewage and subjecting the sewage to a wet oxidation treatment, then removing the SS suspended in the treated water by a solid-liquid sepn. CONSTITUTION:The coarse extraneous materials in night soil are first removed by a screen 2, then the iron ions 3 such as ferrous sulfate and ferric sulfate are added to the night soil in the wet oxidation treatment for the high-concn. org. sewage such as urea sewage by making combination use of catalysts. The night soil is thereafter supplied into a high-pressure vessel 5. The reducing materials such as BOD and COD in the night soil are oxidized when the wet oxidation reaction vessel 5 is kept at 150-370 deg.C. The liquid flowing out of the vessel is highly decomposed in the reducing polluting components. This liquid is suppled through a gas-liquid separator 9 to a solid-liquid separator 10 where the liquid is separated to clean treated water 11 and sludge 12 essen tially consisting of iron oxide and iron phosphate. The night soil is thus perma nently and stably oxidized without deteriorating the catalysts.

The Mechanism of Epitaxial Si-Ge/Si Heterostructure Formation by Wet Oxidation of Amorphous Si-Ge Thin Films

Abstract: Epitaxial SiGe/Si heterostructures have been formed by wet oxidation from amorphous SiGe films deposited on Si(100) Amorphous SixGe1-x films were deposited at a vacuum of 10-7 Torr The presence of an initial native oxide precluded solid phase epitaxy under standard annealing conditions, but epitaxy could be achieved by the use of wet oxidation The samples were oxidized at 900°C for various times and examined in reflection electron diffraction, ellipsometry, cross-sectional and plan-view transmission electron diffraction, and electron spin resonance The formation of the epitaxial layer and oxide has been examined, and an epitaxial growth model is suggested

Transfer of patterns from the backside of a silicon wafer coated with Si3N4 to its front surface during wet oxidation

Abstract: Patterns on the backside of silicon wafers coated with Si3N4 films have been observed on their front surfaces after wet oxidation. This pattern transfer phenomenon is the result of a reduction in the oxidation rate of the front‐surface nitride film over areas where the backside films have been removed. This reduction has been attributed to the influence of the stress in the nitride film on its oxidation rate. In areas where the backside nitride has been removed, localized sample bowing results in stress relief in the front‐surface film and a lower oxidation rate of the nitride film.

Device for treating waste water by wet oxidation

Abstract: PURPOSE:To effectively decompose an org. component and nitrogen component by providing a wet oxidation reaction column and a gas-liquid sepn. column. CONSTITUTION:The waste water boosted by a boosting pump 2 is supplied to a heat exchanger 3 and is heated up by the treated water in a high-temp. state emitted from the gas-liquid sepn. column 11. Further, the waste water is heated up to the temp. adequate for a wet oxidation treatment in the wet oxidation reaction column by a heater 8. The org. component is oxidized and decomposed to carbon dioxide by the oxygen in the air sent together with the waste water in the wet oxidation reaction column 9. The nitrogen component essentially consisting of ammonia is sent to the gas-liquid sepn. column 11 where the component is separated to gas and liquid. The treatment of the waste water to pollution-free water is executed in this way.

Catalyst for treating waste water

Abstract: PURPOSE:To reduce the cost of equipment by specifying the equivalent diameter of the through holes in a catalyst, the thickness of the cells and the rate of opening. CONSTITUTION:The shape of a catalyst used to decompose waste water into nitrogen, CO2 and water by wet oxidation is so regulated that the through holes have 2-20mum equivalent diameter, the cells have 0.5-3mm thickness and the rate of opening is 50-80%. The catalyst is obtd. by kneading powder of titania, zirconia, silica, alumina, etc., with a molding assistant and a proper amt. of slowly added water, molding the kneaded material into a honeycomb shape with a press molding machine, drying and calcining the molded body. The catalyst can maintain high activity over a long period.