Showing papers on "Wet oxidation published in 2005"

Carbon materials and catalytic wet air oxidation of organic pollutants in wastewater

Abstract: The use of carbon materials as catalytic support or direct catalyst in catalytic wet air oxidation (WAO) of organic pollutants is reviewed. The discussion covers important engineering aspects including the characterisation, activity and stability of carbon catalysts, process performance, reaction kinetics and reactor modelling. Recommendations for further research in catalytic WAO are outlined.

Wet hydrogen peroxide catalytic oxidation (WHPCO) of organic waste in agro-food and industrial streams

Abstract: This review discusses the use of iron- or copper-based solid catalysts in the wet oxidation using H2O2 as oxidant of organic molecules present in agro-food and industrial waste aqueous streams. After an introduction on the advantages and limits of using wet hydrogen peroxide catalytic oxidation (WHPCO) as opposite to wet air catalytic oxidation (WACO), the contribution shortly analyses recent results in the field in order to evidence new trends and open issues. More specific examples discussed regard the performances of Fe/zeolite and Fe-containing pillared clays in the oxidation of selected molecules (p-coumaric acid, propionic acid) of relevance for the treatment of organic waste from agro-food production (with reference especially to olive oil milling wastewater). The application of WHPCO in the treatment of complex effluents from electronic industry is also shortly discussed.

Study of the copper leaching in the wet oxidation of phenol with CuO-based catalysts: Causes and effects

Abstract: Catalytic wet oxidation of phenol as a model pollutant has been performed in a three phase fixed-bed reactor (FBR) by using a commercial catalyst based on copper oxide in order to analyze the variables affecting significantly the copper leaching. It has been found that temperature has an almost negligible influence in the range studied (70–160 °C). On the contrary, an important effect of the pH value was noticed. The copper leaching reduces when the pH of the solution fed to the reactor increases, being almost negligible at pH ≥ 5. Moreover, the composition of the reaction media also influences the leaching. Higher copper concentrations than those expected by the effect of the acid aqueous media have been measured in the reactor effluent when phenol, catechol, hydroquinone, p -benzoquinone and maleic acid are present in the reaction media. On the contrary, oxalic acid has a negative influence on the leaching, since it captures the copper in solution to form copper oxalate which precipitates on the catalyst surface. For a previously acidified medium, the acetic and formic acids do not have any other effect on the copper leaching. It has been also demonstrated that as copper in solution decreases, so does phenol conversion, because the homogeneous catalysis contributes significantly to the oxidation reactions even in fixed-bed reactors.

Sodium hypochlorite oxidation reduces soil organic matter concentrations without affecting inorganic soil constituents

Abstract: Summary Oxidative treatment can isolate a stable organic matter pool in soils for process studies of organic matter stabilization. Wet oxidation methods using hydrogen peroxide are widely used for that purpose, but are said to modify poorly crystalline soil constituents. We investigated the effect of a modified NaOCl oxidation (pH 8) on the mineral composition of 12 subsoils (4.9–38.2 g organic C kg−1) containing varying amounts of poorly crystalline mineral phases, i.e. 1.1–20.5 g oxalate-extractable Fe kg−1, and of different phyllosilicate mineralogy. Post-oxidative changes in mineral composition were estimated by (i) the determination of elements released into the NaOCl solution, (ii) the difference in dithionite- and oxalate-extractable Si, Al and Fe, and (iii) the specific surface areas (SSAs) of the soils. The NaOCl procedure reduced the organic C concentrations by 12–72%. The amounts of elements released into the NaOCl extracts were small (≤ 0.14 g kg−1 for Si, ≤ 0.13 g kg−1 for Al, and ≤ 0.03 g kg−1 for Fe). The SSA data and the amounts of dithionite- and oxalate-extractable elements suggest that the NaOCl oxidation at pH 8 does not attack pedogenic oxides and hydroxides and only slightly dissolves Al from the poorly crystalline minerals. Therefore, we recommend NaOCl oxidation at pH 8 for the purpose of isolating a stable organic matter pool in soils for process studies of organic matter stabilization.

Catalytic wet air oxidation of substituted phenols using activated carbon as catalyst

Abstract: Continuous catalytic wet air oxidation (CWAO) was investigated as a suitable precursor for the biological treatment of industrial wastewater that contained phenols (phenol, o-cresol, 2-chlorophenol and p-nitrophenol), aniline, sulfolane, nitrobenzene or sodium dodecylbenzene sulfonate (DBS). Seventy-two-hour tests were carried out in a fixed bed reactor in trickle flow regime, using a commercial activated carbon (AC) as catalyst. The temperature and total pressure were 140 8C and 13.1 bar, respectively. The influence of hydroxyl-, methyl-, chloride-, nitro-, sulfo- and sulfonic-substituents on the oxidation mechanism of aromatic compounds, the occurrence of oxidative coupling reactions over the AC, and the catalytic activity (in terms of substrate elimination) were established. The results show that the AC without any supported active metal behaves bifunctionally as adsorbent and catalyst, and is active enough to oxidate phenol, o-cresol, 2-chlorophenol and DBS, giving conversions between 30 and 55% at the conditions tested. The selectivity to the production of carbon dioxide was considerable with total organic carbon (TOC) abatement between 15 and 50%. The chemical oxygen demand (COD) reduction was between 12 and 45%. In turn, aniline, sulfolane, p-nitrophenol and nitrobenzene conversions were below 5% and there was almost no TOC abatement or COD reduction, which shows the refractory nature of these compounds. # 2004 Elsevier B.V. All rights reserved.

Cerium incorporated ordered manganese oxide OMS-2 materials: Improved catalysts for wet oxidation of phenol compounds

Abstract: Cryptomelane type manganese oxide OMS-2 material was synthesized by redox reaction between potassium permanganate and manganese sulphate in acidic medium under reflux or hydrothermal crystallization conditions. Ce was added by ion-exchange, impregnation or directly at crystallization stage. The chemical composition, structure, texture, morphology and thermal stability of the materials were measured by EDX spectroscopy, XRD, N 2 -adsorption, SEM and TGA. Results of the catalytic wet oxidation of phenol at 100 °C indicate best performance of the well-crystallized octahedral molecular sieve with cryptomelane structure where all the accessible potassium ions were exchanged for cerium cations. OMS-2 materials containing pure CeO 2 phase and excess of active oxygen species had lower stability, activity and capacity for oxidative reactive adsorption of phenol. Implementation of Ce-exchanged crystalline OMS-2 catalyst improves the wastewater treatment capacity by a factor of 1.5–2 and 3 compared with co-precipitated Mn–Ce-oxide and activated carbon, respectively.

Synthesis, characterization and catalytic application for wet oxidation of phenol of iron-containing clays

Abstract: High-surface-area pillared clays (PILC) were prepared from naturally occurring montmorillonites by exchanging interlayer ions to polyoxocations containing (i) aluminum (Al13-PILC), (ii) iron adsorpted onto Al13-PILC, and (iii) iron and aluminum located within the same complex (Fe0.8Al12.2-PILC). The obtained Fe0.8Al12.2-PILCs were characterized by DR–UV–vis and IR spectroscopy, XRD, ESR, scanning electron microscopy and low temperature N2 adsorption measurements. Important factors affecting catalyst activity and phenol removal efficiencies have been studied, i.e. the effect of pH, temperature, catalyst concentration and stability of the catalyst.

Thermochemical Precipitation as a Pretreatment Step for the Chemical Oxygen Demand and Color Removal from Pulp and Paper Mill Effluent

Abstract: In the present work, the removal of chemical oxygen demand (COD) and color of paper mill wastewater due to the thermochemical precipitation of dissolved solids was studied in the temperature range from 20 to 95 °C using different catalysts/chemicals. The homogeneous CuSO4 catalyst was found to be the most active in comparison to the other heterogeneous catalysts under similar operating conditions. The pH value showed a pronounced effect on the precipitation process. At an optimum initial pH of 5.0, a maximum COD reduction of 63.3% was obtained with a catalyst concentration of 5 kg m-3, although the maximum color removal was 92.5% using a CuSO4 concentration of 2 kg m-3. The residual copper in the supernatant works as a good catalyst for wet air oxidation of the supernatant. Thermogravimetric analysis showed that the thermal oxidation of the solid residue follows an one-way transport diffusion model with first-order irreversible reaction kinetics. The heating value of the precipitate was found to be compar...

Platinum and ruthenium catalysts on mesoporous titanium and zirconium oxides for the catalytic wet air oxidation of model compounds

Abstract: Pt and Ru catalysts on mesoporous (MSP) TiO2 and ZrO2 were developed using sonochemical irradiation. The catalysts were characterized by XRD, TEM, HR TEM, EDX, and BET methods. The high homogeneity of the active metal phase was confirmed by electron microscopy. The catalysts were examined for the removal of organic pollutants from model wastewaters using the wet air oxidation (WAO) process of acetic, succinic and p-coumaric acids in an autoclave reactor at 140 and 190 °C and 50 bar total air pressure. The high activity and stability of Pt supported on a TiO2 (MSP) catalyst in the removal of succinic and p-coumaric acids, and intermediates of their oxidation was demonstrated. The catalytic performances of Ru/TiO2 (MSP) were similar to those of the catalysts prepared by incipient-wetness impregnation of commercial TiO2 supports.

Oxone-promoted wet air oxidation of landfill leachates

Abstract: Landfill leachates of the city of Badajoz (in the southwest of Spain) have been treated by wet air oxidation at high temperature (180−270 °C) and pressure (40−70 atm). Typical operating variables such as temperature and oxygen partial pressure have been investigated with no effect of any being found and moderate to low chemical oxygen demand conversions (20−30% depending on initial COD concentration). Initial pH shows a positive influence when acidic conditions are used. Addition of hydrogen peroxide (0.01 M) as a hydroxyl radical promoter is able to provide an additional 15% increase in the final COD removal achieved. If a sulfate radical promoter is used (i.e., Oxone) the process is significantly improved, with COD conversions in the range 60−80%, also depending on the initial COD of the leachates. A first attempt to comprehend the chemistry of this oxidizing system suggests an instantaneous decomposition of Oxone that initiates the radical chain also involving hydroxyl and organic radicals.

Method for manufacturing a semiconductor device having an alignment feature formed using an N-type dopant and a wet oxidation process

Abstract: The present invention provides a method for manufacturing a semiconductor device having an alignment feature. The method for manufacturing the semiconductor device, among other steps, may include implanting an n-type dopant into a substrate thereby forming an implanted region and an unimplanted region in the substrate. The method may further include oxidizing the substrate using a wet oxidation process, the wet oxidation process and n-type dopant causing a ratio of oxidation of the implanted region to the unimplanted region to be 2:1 or greater, and then removing the oxidized portions of the substrate thereby leaving an alignment feature proximate the implanted region.

Role of ceria-supported noble metal catalysts (Ru, Pd, Pt) in wet air oxidation of nitrogen and oxygen containing compounds

Abstract: Catalytic wet air oxidation (CWAO) of aniline, phenol, carboxylic acids and ammonia was carried out in a batch reactor over noble metals (Ru, Pd, Pt) supported on ceria. Ruthenium is very active for the conversion of a wide range of organic compounds and selective into carbon dioxide. The ability of ceria to transfer oxygen is essential for good performances in CWAO. However, Ru/CeO2 is not selective for ammonia oxidation into N2. Addition of small amount of Pd enhances both activity and selectivity of Ru in this reaction. Finally, oxidation of nitrogenous organic compounds requires moderate temperature and oxygen pressure and needs to adjust the oxidizing capacity of the catalyst.

Catalytic wet oxidation : Micro-meso-macro methodology from catalyst synthesis to reactor design

Abstract: Compared to alternative mature wet oxidation technologies that have tremendously proliferated in industry, heterogeneously mediated catalytic wet oxidation (CWO) has achieved, thus far, poor commercial penetration. The two factors that are likely responsible for this situation are (i) the lack of efficient and robust catalysts that pass with success the acid-test for commercial exploitation remote from the aseptic academic conditions, (ii) and the lack of a comprehensive reactor design framework and methodology for scale-up, reactor selection and operation inherent to the multiphase nature of the CWO reactors. This synthetic review summarizes the recent research and development work conducted at Laval University on the CWO from both the perspectives of catalyst development and testing, and multiphase reactor simulations and selection. Specific emphasis was put, on the one hand, on the development brought to some manganese oxide–ceria composites against deactivation, and on the other hand, on the formulation of multidimensional unsteady–steady non-isothermal mass-energy transport/reaction models, embedding catalyst deactivation or not, for trickle bed reactors, packed bubble column reactors, three-phase fluidized beds and slurry bubble columns. A micro–Meso–macro scale methodology was adopted from the materials synthesis up to reactor selection in which the catalyst performance (conversion, selectivity, and deactivation), the intrinsic chemical kinetics, the fluid phase thermodynamics, the pellet scale transport, and the reactor scale physical phenomena (heat, mass transport and hydrodynamics) were integrated. As a result, several aspects relevant to reactor behaviour such as solvent evaporation due to CWO reaction exothermic effects, catalyst partial wetting and catalyst deactivation, and back-mixing effects were covered, and recommendations were formulated.

Catalytic wet air oxidation of stearic acid on cerium oxide supported noble metal catalysts

Abstract: Catalytic wet air oxidation (CWAO) of stearic acid was carried out in a batch reactor over noble metals (Ru, Pd, Pt, Ir) catalysts supported on ceria. The influence of reaction conditions such as temperature, oxygen pressure and stearic acid concentration were investigated. The reaction occurs via a complex mechanism. The molecule of stearic acid can be oxidized by successive carboxy–decarboxylation (Rn COOH + O2 → Rn−1 COOH +CO2) yielding essentially CO2 (route A). It may also be oxidized after C C bond rupture within the alkyl chain, which gives rise to significant amounts of acetic acid besides CO2 (route B). Pt/CeO2 is a very active catalyst in the conversion of stearic acid and extremely selective to carbon dioxide (route A), while the mechanism via C C bond splitting is much more marked on Ru/CeO2. The catalyst characterization indicates that both noble metal and CeO2 particles remain stable during the reaction.

Influence of pH on the wet oxidation of phenol with copper catalyst

Abstract: This work reports the influence of pH on the catalytic wet oxidation (CWO) of phenol performed with a commercial copper-based catalyst. The results obtained show that pH is a critical parameter able to modify the chemical stability of the catalyst, the significance of the oxidation reaction in the liquid phase, the reaction mechanism and, consequently, the oxidation route of phenol. Experiments have been carried out to study the mentioned aspects. Stirred basket and fixed bed reactors (FBRs) have been employed, at 140 °C and at 16 bar of oxygen pressure. Three initial pH values have been used: 6 (the pH of the phenol solution), 3.5 (adjusted by H2SO4) and 8 (by addition of Na2CO3). Furthermore, some phenol oxidation runs without solid catalyst but with different concentrations of copper in solution have been accomplish at pHo=3.5. At acid pH, important leaching of copper from the catalyst to the solution was achieved, finding this negligible at pH 8. It was found that the major contribution to the phenol conversion reached at acid pH by using the solid catalyst was due to the catalytic activity of the leached copper. Both oxidation mechanisms at acid and basic conditions have been elucidated to explain the differences in the type and distribution of the intermediates obtained. The catalytic phenol oxidation route found at pH=8 comprises intermediates less toxic than phenol while at acid pH the cyclic intermediates formed as first oxidation intermediates are far more toxic than phenol.

Stability of ruthenium catalysts supported on TiO2 or ZrO2 in catalytic wet air oxidation

Abstract: The stability of ruthenium catalysts supported on TiO2 and ZrO2 were studied in the wet air oxidation of aqueous solution of succinic and p-hydroxybenzoic acids taken as model effluent and on real effluents from the paper-pulp industry. Catalyst recycling experiments were conducted in batch reactor and long-term stability tests were conducted in trickle-bed reactor. In all experiments, ruthenium and support materials were perfectly stable to leaching, sintering and fouling. Ruthenium catalysts experienced a weak deactivation as they were exposed to air, e.g., in recycling experiments however the loss of activity occurred only after the first exposure and was completely reversible upon catalyst reduction. The deactivation was attributed to an over-oxidation of the catalyst surface particularly noticeable in the case of very small Ru-clusters (1 nm).

Study of Different Integrated Physical−Chemical + Adsorption Processes for Landfill Leachate Remediation

Abstract: Some integrated processes to deal with landfill leachates have been investigated and their efficiencies expressed in terms of chemical oxygen demand (COD) removal. The systems tested were the result of different combinations of the following single stages: acidic pH shift (elimination of humic substances), ozonation (O3), coagulation−flocculation with Fe(III) salts, Fenton's oxidation (Fe(III) + H2O2), wet air oxidation (with or without radical promoters), and adsorption onto activated carbon (commercial Norit 0.8 powdered activated carbon). COD removals obtained ranged in the interval of 80−96% for initial COD values close to 11000 mg L-1. None of the processes tested reduced the COD levels sufficiently to allow direct discharge; however, the ratio biochemical oxygen demand (BOD)/COD was significantly increased (up to 1000% in some cases, i.e., from 0.1 to values above 1.0). Total carbon reduction achieved ranged from 60 to 94%, while complete decolorization (measured as the absorbance at 410 nm) was ob...

Nonselective Wet Oxidation of AlGaAs Heterostructure Waveguides Through Controlled Addition of Oxygen

Abstract: We present data showing that the addition of trace amounts of O $_2$ ( $≪1hbox%$ relative to N $_2$ ) to N $_2+$ H $_2$ O process gas during the wet thermal oxidation of Al $_ x$ Ga $_1 -x$ As enhances the oxidation rates of lower Al content $( xle 0.8)$ alloys (a tenfold increase for $ x=0.3$ ), while decreasing the oxidation rate selectivity $ R( x=0.8)/ R( x=0.3)$ by a factor of seven. An increase in the refractive index from 1.49 to 1.68, and a fourfold decrease in surface roughness, indicates the formation of a denser, higher quality oxide for $ x=0.3$ AlGaAs. Oxides are characterized by prism coupling, atomic force microscopy, and scanning electron microscopy. Thermochemical calculations show a probable mechanism in the enhancement of the dry oxidation reactions of AlGaAs for low levels of O $_2$ , while there is still an adequate quantity of H $_2$ produced to reduce As oxides in the wet oxidation process. An AlGaAs quantum well heterostructure p-n laser diode crystal is nonselectively oxidized to create a deep oxide, high-index contrast waveguide with potential applications in semiconductor photonic integrated circuits that require small bend radius, high isolation, low crosstalk optical waveguides.

Nature of carbonaceous deposits on the alumina supported transition metal oxide catalysts in the wet air oxidation of phenol

Abstract: Al2O3 supported transition metal (Mn, Fe, Co, Ni, and Cu) oxide catalysts were prepared and tested for the wet oxidation of phenol. The supported copper oxide catalysts showed the highest catalytic activity due to their highest surface reducibility. There was carbonaceous deposits on the used catalysts for the wet oxidation of phenol and the supported manganese oxide catalysts showed the highest amount of carbonaceous deposits. These carbonaceous deposits must have their own micropores which resulted in the decrease of the pore volume and the increase of the surface area. The NMR and FTIR spectroscopy showed that the carbonaceous deposits were mostly of aromatic nature and contained some oxygen-bearing groups such as carboxylic acids and alcohols.

Method for ground water and wastewater treatment

Abstract: Described is a method of water treatment including the steps of: a) Stripping water or dissolved gas by an inert gas b) Subjecting water to oxidation treatment to precipitate metals; and c) Removing precipitates from water. Oxidation treatment is a multi-stage oxidation treatment including the stages of: (1) contacting water with oxidant under pressure to precipitate metals from water; and (2) catalytic oxidation of water with oxidant, oxidation being catalysed by a catalyst, such as a zeolite catalyst, in a bed reactor or filter. Inert gas stripping is aimed at preventing growth of iron bacteria in the treatment system. Pressurised oxidation reduces the amount of oxidant injection required for catalytic oxidation. The method is particularly suited to removal of contaminants such as iron, manganese and arsenic from ground water.