Showing papers on "Wet oxidation published in 1994"

Oxidation Kinetics of Chemically Vapor‐Deposited Silicon Carbide in Wet Oxygen

Abstract: The oxidation kinetics of chemically vapor-deposited SiC in dry oxygen and wet oxygen (P(sub H2O) = 0.1 atm) at temperatures between 1200 C and 1400 C were monitored using thermogravimetric analysis. It was found that in a clean environment, 10% water vapor enhanced the oxidation kinetics of SiC only very slightly compared to rates found in dry oxygen. Oxidation kinetics were examined in terms of the Deal and Grove model for oxidation of silicon. It was found that in an environment containing even small amounts of impurities, such as high-purity Al2O3 reaction tubes containing 200 ppm Na, water vapor enhanced the transport of these impurities to the oxidation sample. Oxidation rates increased under these conditions presumably because of the formation of less protective sodium alumino-silicate scales.

improvement of the wet-oxidation procedure for simultaneous determination of particulate organic nitrogen and phosphorus collected on filters

Abstract: A new digestion technique is presented for simultaneous analysis of particulate organic nitrogen (PON) and particulate organic phosphorus (POP) collected on filters. This method is based on a standard persulfate digestion procedure at 120°C and adapted from a former method for the simultaneous determinat~on of total nitrogen and total phosphorus in natural waters. Comparisons 1~1th usual methods using separate determinations for PON and POP indicate a high efficiency of the procedure for cell cultures or natural seawater samples. N~t ra t e and phosphate formed by oxidation can be analysed s~multaneously on an automated system. The procedure is highly suitable for routlne analysis and especially appropriate for shipboard use.

Review of Potential Technologies for the Removal of Dissolved Components from Produced Water

Abstract: A wide range of technologies was assessed for both oil (relatively high produced water flowrates) and gas fields (relatively low produced water flowrates). Technologies that were felt to offer the greatest potential (based on current stages of development) were found to be ion exchange for heavy metal removal, and air (or gas/vapour) stripping, activated carbon adsorption (with regeneration of the carbon by wet air oxidation) and biological treatment for dissolved organic removal. In gas fields, wet air oxidation could be used without the activated carbon adsorption step. However, none of the systems evaluated would be capable of removing all of the groups of dissolved components from produced water alone. This implies that, if removal of all dissolved components is required, 2 or more systems would have to be used in series. In practice, technology selection could be based on the toxicity reduction achieved and/or the organic loading reduction achieved (of the technologies assessed, only biological oxidation and wet air oxidation achieved significant organic loading reduction. (author)

Kinetics of Wet Air Oxidation of Glyoxalic Acid and Oxalic Acid

Abstract: Oxidation of lower molecular weight monobasic and dibasic acids such as formic acid, acetic acid, glyoxalic acid, and oxalic acid is often the rate-controlling step during wet air oxidation (WAO) of an aqueous waste stream exhibiting very high chemical oxygen demand (COD). The kinetics of WAO of glyoxalic acid and oxalic acid was studied in absence and presence of a cupric sulfate catalyst in the temperature range of 120--245 C and oxygen partial pressure of 0.345--1.380 MPa. The wet oxidation of oxalic acid was found to require more severe conditions as compared to glyoxalic acid. The reaction mechanism and kinetic model have been discussed.

Complete treatment of Olive Mill Wastewaters by a wet air oxidation process coupled with a biological step

Abstract: The wet air oxidation (WAO) process catalysed by hydrogen peroxide coupled with bioxidation for the treatment of olive mill wastewaters (OMW) was investigated OMW cannot be conveniently treated by biological processes as they contain important amounts of phenol‐like compounds, toxic and recalcitrant to biodegradation Oxidation was conducted according to the “hydrogen peroxide promoted wet air oxidation”; process between 180 and 200 ∘C It consists of injecting continuously hydrogen peroxide at a low dosage (10% on a COD basis) into a WAO reactor in order to promote the radical reactions and then lowering the temperature and pressure constraints WAO treatment allows a complete decolouration of the solution, a 77% chemical oxygen demand (COD) reduction; the remaining COD is mainly low molecular weight carboxylic acids (chiefly acetic) easy for a biological post‐treatment Compared to the various processes reported in the literature, this two step process offers a good opportunity for OMW depollu

Microstructure of oxidized layers formed by the low-temperature ultraviolet-assisted dry oxidation of strained si0.8ge0.2 layers on si

Abstract: Ultraviolet‐assisted low‐temperature (550 °C) dry oxidation of Si0.8Ge0.2 strained layers on (100)Si has been studied. The oxidation rate of this material was found to be a factor of 2 greater than that of pure Si oxidation under identical irradiation conditions. Initially, the structure of the oxidized material consists of a SiO2 layer on top of a strained Si1−xGex layer with a Ge concentration significantly higher (x≳0.2) than the initial value. Increasing the oxidation time produces more SiO2 and a Si1−xGex layer further enriched with Ge. However, the oxidation rate is reduced and some of the Ge becomes trapped inside the growing SiO2 layer. For a prolonged irradiation time (≳5 h) SiGe oxidation still continues, unlike the case for pure Si, while the Ge trapped inside the SiO2 forms isolated microcrystalline regions.

Combined treatment of phenolic wastewater by wet air oxidation and activated sludge

Abstract: Wet air oxidation (WAO) is employed in this work for treating high concentration chemical wastewater containing phenol and/or phenolic compounds. Experimental results indicate that over 90% removal of phenol or phenolic compounds can be efficiently achieved in the WAO process. Despite of the high treatment efficiency of the WAO process, the treated wastewater, however, still retains relatively high chemical oxygen demand (COD) concentration and does not meet the safe discharge standard. Hence further treatment of the WAO treated wastewater by an aerobic biological treatment using acclimatized activated sludge is necessary. It is found in the present studies that the combined process, if appropriately operated, is capable of drastically reducing the COD concentration of the high concentration chemical wastewater to meet the safe discharge requirement. The operating conditions of the combined process are investigated to determine their respective effects on the overall treatment efficiency. The experimental...

Wet air oxidation and activated sludge treatment of phenolic wastewater

Abstract: Wet air oxidation (WAO) is employed in this work for treating high concentration chemical wastewater containing phenol and/or phenolic compounds. Experimental results indicate that over 90% removal of phenol or phenolic compounds can be efficiently achieved in the WAO process. Despite of the high treatment efficiency of the WAO process, the treated wastewater, however, still retains relatively high chemical oxygen demand (COD) concentration and does not meet the safe discharge standard. Hence further treatment of the WAO treated wastewater by an aerobic biological treatment using acclimatized activated sludge is necessary. It is found in the present studies that the combined process, if appropriately operated, is capable of drastically reducing the COD concentration of the high concentration chemical wastewater to meet the safe discharge requirement. The operating conditions of the combined process are investigated to determine their respective effects on the overall treatment effciency. The expe...

Purification of salt-charged waste water by wet oxidation under super-critical conditions

Abstract: With the process according to the invention for the purification of salt-charged waste water by wet oxidation of organic constituents under supercritical conditions, the reaction is performed in the form of a flame (5). In this case the supercritical zone is surrounded with a subcritical by-pass flow (4) formed from cooling water. At one end of the reactor (1) constructed as a cylindrical pressure vessel are provided at least one burner nozzle (2) and at least one annular inlet point (48), surrounding the burner nozzle, for the cooling water; at the other end is disposed at least one common outlet point (160) for cooling water, reaction products and in particular precipitated salts. Thanks to the by-pass flow there are no obstructions caused by salts; and corrosion problems are substantially reduced.

Apparatus for reverse-injection wet oxidation

Abstract: A system for effective utilization of reaction heat and in situ separation of solid and gaseous products in wet oxidation of waste and wastewater. This invention does not require special preheaters for preheating feed streams, therefore reducing the possibility of scale and char formation in the heat exchange zone. The cold feed stream is introduced into the reactor with part of the effluent which has been recycled through a high temperature pumping means to form a hot, near critical oxidant-containing mixture. The cold feed is directly heated up by the oxidant-containing mixture. The reaction mixture is separated by in situ crossflow filtration elements, including sintered material. Catalyzed reactions and sintered material gas separation are also described.

Kinetics and mechanism of wet oxidation of GexSi1−x alloys

Abstract: The thermal oxidation of polycrystalline GexSi1−x (0.10≤x≤0.47) and pseudomorphic Ge0.2Si0.8 has been studied in wet ambient at 550 to 900 °C. A uniform GexSi1−xO2 oxide is observed by backscattering spectrometry for a high Ge content at low oxidation temperatures; a SiO2 oxide is obtained for a low Ge content at high temperatures; a GeySi1−yO2 oxide with reduced Ge content (y

Method and apparatus for reverse-injection wet oxidation, sintered material catalytic reaction, sintered material filtration at supercritical conditions, sintered material gas separation, and high temperature pressurization

Abstract: A system for effective utilization of reaction heat and in situ separation of solid and gaseous products in wet oxidation of waste and wastewater. This invention does not require special preheaters for preheating feed streams, therefore reducing the possibility of scale and char formation in the heat exchange zone. The cold feed stream is introduced into the reactor with part of the effluent which has been recycled through a high temperature pumping means to form a hot, near critical oxidant-containing mixture. The cold feed is directly heated up by the oxidant-containing mixture. The reaction mixture is separated by in situ crossflow filtration elements, including sintered material. Catalyzed reactions and sintered material gas separation are also described.

Wet oxidation of AlAs grown by molecular beam epitaxy

Abstract: A 1 μm thick n‐type GaAs layer with Si doping density of 1×1017/cm3 and a 1000 A thick undoped AlAs layer was subsequently grown by molecular beam epitaxy on the n+ GaAs substrate. To perform selective oxidation of the AlAs layer, the wafer was oxidized in N2 bubbled H2O vapor ambient at 370 °C, 400 °C, and 430 °C, each for 3 hours. It is found that the defect‐free selective oxidation of AlAs is very critically dependent on oxidation temperature. Both GaAs and AlAs layers were oxidized at the oxidation temperature of 430 °C, and some defects were found by scanning electron microscopy (SEM) on the surface oxidized at 370 °C. Oxidation was, however, stopped at the AlAs/GaAs interface at the oxidation temperature of 400 °C, and no defects were found on the surface. By the slow ramp rate (5 mV/sec) high frequency (100 kHz) C‐V measurement, the fixed charge density was estimated to be about 1×1011/cm2 for the metal‐oxide‐semiconductor (MOS) capacitor fabricated from the oxidized sample at 400 °C.

A comparative study of wastewater treatment by chemical wet oxidation

Abstract: A leachate from a municipal landfill and an industrial wastewater from an emulsion-breaking unit have been treated by chemical wet oxidation using ozone and hydrogen peroxide as oxidants. The best results were obtained with UV radiation resulting in the formation of OH· radicals. If ozone is used, mass transfer will be the limiting step in the degradation reactions. The specific consumption of hydrogen peroxide is drastically reduced if pure oxygen or air is dispersed into the wastewater. Under optimum conditions, the COD of the leachate and of the industrial wastewater could be reduced by 90% in c. 3 and 5 h, respectively.

Autothermal oxidation of dilute aqueous wastes under supercritical conditions

Abstract: Analysis of the autothermal wet oxidation of dilute aqueous wastes reveals some important differences between the subcritical and supercritical operation of this process. The energy requirements are considerably higher for supercritical operation and are comparable to those for incineration. The calculations show that the efficiency of the heat exchanger in the near-critical region decreases significantly and using a regenerative heat exchanger for supercritical operation requires excessive heat-transfer area even for wastewaters with heating values around 1,000 kJ/kg. Better results are obtained at higher pressures. This study demonstrates that autothermal operation of the supercritical wet oxidation process for dilute wastewaters is feasible only with the addition of auxiliary fuel.

Process for the treatment of organic pollutants in wastewaters by wet oxidation

Abstract: Organic pollutants in wastewaters are wet-oxidized by addition of pure oxygen or an oxygen-containing gas at temperatures of 80° to 330° C., under pressures of 1 bar to 200 bar and at a pH value below 7. For the wet oxidation process, iron ions and digested sludge or surplus sludge from a biological sewage treatment plant are added to the wastewater.

Effect of oxidation ambient on the dielectric breakdown characteristics of thermal oxide films of silicon

Abstract: This study investigated the dielectric breakdown characteristics of thermal oxide films grown by dry and wet oxidation. Oxide films grown by wet oxidation have lower B‐mode failure rates and higher B‐mode breakdown fields. On the other hand, the reliability of C mode of oxide films does not differ consistently between films grown by dry and wet oxidation. These results indicate that as‐grown defect causing B‐mode failure may shrink or be reduced during wet oxidation.

Effects of deposition temperature on the oxidation resistance and electrical characteristics of silicon nitride

Abstract: A study was made of the effects of deposition temperature on the oxidation resistance and electrical characteristics of silicon nitride. It was found that silicon nitride below a certain limit thickness has no oxidation resistance. This threshold falls as the deposition temperature is lowered. 3-nm-thick silicon nitride deposited at 600/spl deg/C has sufficient oxidation resistance For wet oxidation at 850/spl deg/C, while 5 nm film deposited at 750/spl deg/C has no oxidation resistance. The electrical characteristics also improve as the deposition temperature is lowered. 6-nm-thick silicon nitride deposited at 600/spl deg/C shows a TDDB lifetime that is about two orders longer than that of 6-nm-thick silicon nitride deposited at 700/spl deg/C. It was also found that the silicon nitride transition layer which is deposited at the initial stage of deposition influences the oxidation resistance and electrical characteristics of thin silicon nitride. It was concluded that lowering the deposition temperature reduces the influence of the transition layer and improves the oxidation resistance and electrical characteristics of thin silicon nitride. >

Investigation of the products of oxidation of methylpyridines under aqueous conditions by gas chromatography–mass spectrometry

Abstract: Wet air oxidation is a waste treatment process known to break down organic compounds at elevated temperatures and pressures under aqueous conditions. We have investigated, by gas chromatography–mass spectrometry, the products arising from the wet air oxidation of 2-, 3- and 4- methylpyridines carried out in a laboratory autoclave. The results indicate that radical chemistry is responsible for the products. The oxidation of each of the methylpyridines by use of Fenton's reagent was also studied, because this is known to generate hydroxyl radicals. Similarities were observed between products generated by Fenton-catalysed oxidations carried out in the laboratory and the uncatalysed autoclave reactions. Further experiments, where Fenton's reagent was incorporated in the laboratory autoclave reactions, were carried out. An improved level of decomposition of the methylpyridines was achieved by the incorporation of a hydroxyl radical-producing catalyst.

Decomposition of polyolefins and higher paraffins by wet oxidation

Abstract: A selection of polyolefins and other paraffins has been studied with respect to the mechanism of their decomposition by wet oxidation in a batch autoclave reactor. The general conditions were 2.0 MPa of O 2 at 260 o C. Virtually all hydrocarbons were decomposed into water-soluble compounds and CO 2 . An analysis of the products indicates that the decomposition proceeds mainly by fragmentation of one or two C-atoms at a time. The yield of the different products was dependent, to some extent, on the type of starting material. A reaction mechanism has been proposed to explain the intriguing occurrence of significant amount of hydrogen in the gas phase

Wet air oxidation of ethylene plant spent caustic

Abstract: The purpose of this paper is to provide insight into the design of a wet air oxidation system as it is applied on a full scale basis for spent caustic treatment. There are numerous design parameters, including temperature and pressure. The variations in spent caustic characteristics and treatment objectives must be carefully considered prior to choosing the optimal design. These issues can have a significant impact on the critical design parameters including the materials of construction.The information included herein is based on the experience of Zimpro Environment, Inc. in designing 12 full scale wet air oxidation systems for treating spent caustic from the production of ethylene.

Method of monitoring pH in caustic liquor wet oxidation

Abstract: A process is described for monitoring pH in caustic liquor wet oxidation systems. An offgas carbon dioxide baseline value is established for the operating system where oxidized liquid effluent is at pH 7 or above. Offgas carbon dioxide content deviating by a selected proportion above the baseline vale indicates a drop in liquid effluent pH to 7 or less. Sufficient alkalinity is added to the raw wastewater to bring the effluent pH to 7 or above and prevent excessive corrosion to the materials of construction of the nickel-based or ferrous-based alloy wet oxidation system.

Treatment of photographic processing waste

Abstract: PURPOSE:To remove nitrogen, phosphorus, heavy metals, etc., from the processing waste so as to reduce their contents in the waste to low levels by subjecting the waste to noncatalytic wet oxidation treatment under specific conditions and to solid-liquid separation, then, subjecting the separated waste to catalytic wet oxidation treatment and thereafter, further subjecting the resulting treated waste to biological treatment consisting of a combination of aerobic and anaerobic treatments. CONSTITUTION:In this treatment, a dilute solution of this processing waste, a sodium hydroxide aq. solution and a gas contg. oxygen (air) are pressurized and introduced into a supply line 10 with a pump 3, pump 15 and compressor 5 respectively and then, heated by a heat exchanger 2 and thereafter, introduced into a noncatalytic wet oxidation tower 1 to subject the waste to oxidation treatment there. The resulting treated liquid is cooled and thereafter, fed into a gas-liquid separater 4 and the separated liquid is once stored in a tank 14 and then transferred to a solid-liquid separator 18 to subject it to solid-liquid separation there. The treated liquid thus separated is further subjected to catalytic wet oxidation treatment under conditions of a 140 to 370 deg.C temp. and a sufficient pressure to retain the waste to be treated in a liquid phase while supplying a gas contg. oxygen and subsequently, to biological treatment consisting of a combination of aerobic and anaerobinc treatments.

Homogeneity of Wet Oxidation by RTP

Abstract: The implementation of a wet oxidation process in an RTP system using a bubbler with deionized water is described. A special process related calibration in a wet atmosphere, by means of pyrometer and thermocouple readings, allows one to improve the temperature accuracy during the oxidation to an offset of only + 1 to 2°C. High oxide growth rates, up to a factor of 1.8 above literature data have been achieved. Wet and dry RTO oxides are compared and related to the expectations from growth models. Effects of growth time (10 s to 4 min), growth temperature (675°C-950°C), substrate orientation (100,111), preparation (e.g. HF) and bubbler temperature (20°C-90°C) are presented. The uniformity of oxides on 4 and 6 inch diameter wafers are discussed. Preferentially by the use of a silicon guard ring and by adjusting lamp power and gas flow rates excellent results concerning uniformity (standard deviations 2σ: 1-2 %) and reproducibility (variation of 0.5 to 0.75 % at least over 12 wafers) are obtained.

Defects in SiO2/Si Structures Probed by Using a Monoenergetic Positron Beam

Abstract: Defects in SiO2/Si specimens were probed by using a monoenergetic positron beam. Doppler broadening profiles of the annihilation radiation were measured as a function of incident positron energy for SiO2(100 nm)/Si specimens fabricated by wet, dry and ultradry oxidation. The diffusion of positrons in the Si substrate was found to be enhanced by an electric field caused by positive charges near the SiO2/Si interface. The Doppler broadening profile corresponding to the annihilation of positrons in the Si substrate with the SiO2 film grown by wet oxidation was found to be broader than those in the specimens fabricated by dry or ultradry oxidation. This was attributed to the fact that the concentration of oxygen clusters in the Si substrate for the specimen fabricated by wet oxidation was higher than those for the specimens fabricated by dry or ultradry oxidation.

Formation of electrode protective film

Abstract: PURPOSE:To form an SiO2 film on an electrode layer as a P type polysilicon layer containing boron without lowering the contained concentration of the boron. CONSTITUTION:A gate electrode 14 or an electrode interconnection is formed of a P type polysilicon layer containing boron. An oxidation treatment is executed to the electrode layer 14 by setting an oxidation temperature within a range of 850 to 750 deg.C and by a wet oxidation operation, and a protective film 16 as an SiO2 film is formed on the surface region of the electrode layer.