Showing papers on "Wet oxidation published in 2013"

Hydrothermal conversion of lignin: A review

Abstract: Lignin is a carbon-rich renewable source owning aromatic structure units, which is an important constituent in biomass. Hydrothermal conversion of lignin is widely studied as a promising method to produce not only bioenergy but also value-added useful chemicals. Fuel gas, aromatic aldehydes and phenolic products can be obtained from lignin hydrothermal gasification, wet oxidation and hydrothermal liquefaction, respectively. This article discusses and compares the three methods of lignin hydrothermal conversion, including their process parameters, possible conversion routes, catalysts, application of products. Effects of hot-compressed organic solvent–water mixture solution on conversion of lignin and effects of lignin in biomass hydrothermal conversion are commented. Wet oxidation of lignin is an efficient mean of recovering value-added aromatic aldehydes, especially vanillin. Hydrothermal liquefaction of lignin is a promising way of recovering phenolics-rich bio-oils. Both aromatic aldehyde and phenolic compound are important chemical intermediates. There are strict requirements of process conditions and relative high costs to get fuel gas from direct hydrothermal gasification of lignin. However, further studies on improving gasification of lignin seem necessary in order to get fuel gas from hydrothermal gasification of the whole biomass.

The study of leachate treatment by using three advanced oxidation process based wet air oxidation

Abstract: Wet air oxidation is regarded as appropriate options for wastewater treatment with average organic compounds. The general purpose of this research is to determine the efficiency of three wet air oxidation methods, wet oxidation with hydrogen peroxide and absorption with activated carbon in removing organic matter and nitrogenous compounds from Isfahan's urban leachate. A leachate sample with the volume of 1.5 liters entered into a steel reactor with the volume of three liters and was put under a 10-bar pressure, at temperatures of 100, 200, and 300° as well as three retention times of 30, 60, and 90 minutes. The sample was placed at 18 stages of leachate storage ponds in Isfahan Compost Plant with the volume of 20 liters, using three WPO, WAO methods and a combination of WAO/GAC for leachate pre-treatment. Thirty percent of pure oxygen and hydrogen peroxide were applied as oxidation agents. The COD removal efficiency in WAO method is 7.8-33.3%, in BOD is 14.7-50.6%, the maximum removal percentage (efficiency) for NH4-N is 53.3% and for NO3-N is 56.4-73.9%. The removal efficiency of COD and BOD5 is 4.6%-34 and 24%-50 respectively in WPO method. Adding GAC to the reactor, the removal efficiency of all parameters was improved. The maximum removal efficiency was increased 48% for COD, 31%-43.6 for BOD5 by a combinational method, and the ratio of BOD5/COD was also increased to 90%. In this paper, WAO and WPO process was used for Leachate pre-treatment and WAO/GAC combinational process was applied for improving the organic matter removal and leachate treatment; it was also determined that the recent process is much more efficient in removing resistant organic matter.

Preparation of Cu2(OH)3NO3/ZnO, a novel catalyst for methyl orange oxidation under ambient conditions

Abstract: This work reports a novel process to synthesize copper hydroxyl nitrate/zinc oxide composites (Cu2(OH)3NO3/ZnO), and their application as a highly effective and reusable catalyst for wet oxidation of methyl orange (MO) under ambient conditions. No additional air or oxygen flow is required. Using a metal oxide assisted method, the Cu2(OH)3NO3/ZnO composites were hydrothermally obtained by varying the Cu:Zn mole ratio (2:1, 4:1, and 6:1) and the structural, chemical and surface properties of the composites were investigated. Decolorization of 500 ppm MO can be effectively catalyzed by the Cu2(OH)3NO3/ZnO composite (Cu:Zn = 4:1) with the color, chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiencies being greater than 99%, 98% and 94%, respectively, after 20 min treatments using the catalyst loading of 3 g L−1. Results from systematic catalytic activity tests strongly suggested that MO was oxidized by oxygen dissolved in the dye solution, and that the degradation pathway of MO possibly occurred through radical and H2O2 generation. The application of highly efficient Cu2(OH)3NO3/ZnO catalysts in wastewater remediation may be attractive alternative to existing oxidation catalyst systems as they are low-cost, simple to prepare, feasible to operate under ambient conditions.

Catalytic wet air oxidation of bisphenol A model solution in a trickle-bed reactor over titanate nanotube-based catalysts

Abstract: Titanate nanotube-based catalysts were prepared via alkaline hydrothermal synthesis route followed by heat-treatment at different temperatures, ranging from 300 to 700 °C. The resulting metal-free solids were then applied as a catalyst in a three-phase trickle-bed reactor, where catalytic wet air oxidation (CWAO) reactions of model aqueous bisphenol A (BPA) solution were performed. Mainly, the CWAO experiments were conducted at 200 °C with oxygen partial pressure of 10 bar over 300 mg of a catalyst. It was observed in the given range of operating conditions that BPA undergoes both non-catalytic as well as catalytic oxidation routes, while the latter is far more pronounced. At 210 °C and in the presence of 0.5 g of titanate nanotube-based catalyst, which was annealed at 600 °C, complete BPA removal was obtained. From TOC point of view, approximately 70% conversion was achieved indicating the persistence of refractory intermediates of lower carboxylic acids. The cross-section of results derived from various analytical techniques, which were used to identify surface, textural and morphological properties, revealed that balanced physicochemical properties are required to achieve meaningful extent of BPA removal. During 2–4 day time on stream, no catalyst deactivation occurred that could be attributed to the dissolution of active powders, or to the carbonaceous deposits accumulated on the catalyst surface. Therefore, these nanotubular materials can be regarded as innocuous and efficient long-term catalysts for oxidation of hazardous organic compounds (such as BPA) in the CWAO process.

Preparation method of catalytic wet oxidation catalyst and treatment method of organic wastewater

Abstract: The invention relates to a preparation method of a catalytic wet oxidation catalyst and a treatment method of organic wastewater. The preparation method of the catalytic wet oxidation catalyst comprises the following steps of: (1) taking a porous inert material as a carrier, performing pre-impregnation treatment on the carrier by adopting an acid solution or an alkaline solution, and drying after pre-impregnation treatment, wherein saturated impregnation or over-saturated impregnation is adopted for pre-impregnation treatment; and (2) preparing an impregnating solution with a water-soluble compound containing precious metal active elements and a water-soluble compound containing auxiliary elements, impregnating the carrier after treatment in the step (1) with the impregnating solution, drying in shade for 12-48 hours, drying and roasting to obtain a final catalyst. When the catalyst prepared by the method disclosed by the invention is used for high-concentration organic wastewater, the characteristics of high activity, good stability and the like are realized, and the energy consumption and the investment can be reduced.

Optimization of pretreatment conditions using full factorial design and enzymatic convertibility of shea tree sawdust

Abstract: In this study alkaline wet air oxidation (WAO), alkaline peroxide assisted wet air oxidation (APAWAO), and enzymatic hydrolysis methods were evaluated for conversion of wood residue (sawdust) to reducing sugars. Cellulose content, hemicellulose solubilization, and ligninremovalforWAOpretreatmentconditionswereoptimizedbystatisticalanalysisusing a2 3 -full factorial design with reaction temperature, air pressure, and reaction time as the

Removal of Bisphenol A and its Oxidation Products from Aqueous Solutions by Sequential Catalytic Wet Air Oxidation and Biodegradation

Abstract: Model aqueous solution of bisphenol A (BPA) of 10 mg L–1 was treated in a continuous and sequential catalytic wet air oxidation (CWAO)/aerobic bioreactor (BR) system. Wet oxidation with titanate nanotube-based catalyst resulted in nearly complete removal of BPA (>99%) at a very short space time of 0.3 min·gCAT·g–1. The main identified oxidation products in the CWAO effluent were acetic acid, formic acid and p-hydroxyacetophenone (p-HAP). All of these compounds were consequently and efficiently removed in the BR system at a hydraulic residence time (HRT) of 7.2 h. Although apparent toxicity of the CWAO effluent was found higher than of the initial BPA solution, the former could be successfully detoxified through aerobic biodegradation. The combined system thus presents a potential treatment process for the efficient removal of BPA and its oxidative derivatives from wastewaters.

The Effects of Water Vapor and Hydrogen on the High-Temperature Oxidation of Alloys

Abstract: Essentially all alloys and coatings that are resistant to corrosion at high temperature require the formation of a protective (slowly-growing and adherent) oxide layer by a process known as selective oxidation. The fundamental understanding of this process has been developed over the years for exposure in pure oxygen or air. However, the atmospheres in most applications contain significant amounts of water vapor which can greatly modify the behavior of protective oxides. The development of oxy-fuel combustion systems in which fossil fuels are burned in a mixture of recirculated flue gas and oxygen, rather than in air, has caused renewed interest in the effects of water vapor and steam on alloy oxidation. The focus of this paper is on the ways the presence of water vapor can directly alter the selective oxidation process. The paper begins with a brief review of the fundamentals of selective oxidation followed by a description of recent experimental results regarding the effect of water vapor on the oxidation of a variety of chromia-forming alloys (Fe- and Ni-base) in the temperature range 600 to 700 °C. The atmospheres include air, air-H2O, Ar-H2O and Ar-H2O-O2. Then the behavior of alumina-forming alloys in H2O-containing atmospheres is briefly described. As hydrogen is produced during oxidation of alloys in H2O, it can be released back into the gas phase or injected into the metal (where it can diffuse through to the other side). Experiments in which hydrogen concentrations have been measured on both sides of thin specimens during oxidation by H2O on only one side are described. Finally, it is attempted to catalogue the various experimental observations under a few general principles.

Sibunit-based catalytic materials for the deep oxidation of organic ecotoxicants in aqueous solutions. III: Wet air oxidation of phenol over oxidized carbon and Rr/C catalysts

Abstract: This article presents the first systematic study concerning the effect of the oxidative treatment conditions on the surface chemical composition and the catalytic properties in the deep wet oxidation of organic ecotoxicants of a Sibunit type carbon material (S4) which was earlier identified as promising for the oxidative treatment of industrial wastewaters. The influence of the surface chemistry of the carbon materials oxidized under different conditions on the catalytic performances in the wet air oxidation of phenol of the bare carbon materials as well as the ruthenium-containing catalysts (3 wt % Ru) supported on the oxidized carbon samples was studied. The catalytic activity of the bare carbon samples appeared to be moderate and either (i) increased with the total number of carbonyl and phenolic surface groups or (ii) decreased with the total concentration of surface carboxylic and lactonic species. However, the catalytic performances of the Ru-containing catalysts were significantly higher. Based on our results, an optimum pretreatment of the carbon support could be identified to obtain the most stable and active Sibunit-supported ruthenium catalysts in the wet air oxidation of phenols.

Preparation and Study of Pd Catalysts Supported on Activated Carbon Cloth (ACC) for Direct Synthesis of H2O2 from H2 and O2

Abstract: Activated carbon cloths (ACCs) were used as supports for Pd catalysts. The catalyst preparation was carried out by the impregnation method using acidic solution of palladium dichloride (PdCl2) as metal precursor. The effects of the oxidation state of the loaded metal, heat treatment of the catalysts in different atmosphere (H2, air) at different temperatures and surface chemistry of the support on the catalyst characterizations and the catalytic activities were investigated. Wet oxidation of ACC was done by nitric acid in order to induce oxygen-containing surface functional groups. Surface chemistry of the support and oxidation state of the metallic phase was investigated by means of XPS, TPD, SEM, DTA and TGA tests. Direct synthesis of hydrogen peroxide from H2 and O2 was performed batch wise in a stainless steel autoclave. The reactions were conducted under high pressure (38 bar) at 0 °C and methanol was used as reaction medium. The direct synthesis results showed that the oxygen-containing surface functional groups increase the selectivity of the catalysts by reducing the rate of water production. Existence of the oxidized state of Pd (PdO) also makes the catalyst more selective than the corresponding zerovalent state (Pd0). PdO affected on selectivity by increasing the rate of H2O2 production and reducing the amount of production of water, simultaneously.

Sonohydrothermal Synthesis of Nanostructured (Ce,Zr)O2 Mixed Oxides with Enhanced Catalytic Performance

Abstract: We report for the first time evidence of sonochemical activity under hydrothermal conditions. Sonolysis of H2O and D2O using 20 kHz power ultrasound at 200 °C and 13 bar in the presence of argon yields H2 and D2 respectively. Formation of hydrogen peroxide is not observed because of its thermal instability. The simultaneous sonohydrothermal treatment was used for the preparation of Ce0.5Zr0.5O2 nanocrystalline mixed oxide with external mesoporous surface area higher than that of similar material prepared by ultrasonically assisted coprecipitation followed by hydrothermal treatment. The obtained mixed oxide loaded with 1.5 wt % of platinum exhibits high activity and stability in catalytic wet air oxidation of formic acid at low temperature.

Influence of Water Vapour on the Rate of Oxidation of a Ni-25wt.%Cr Alloy at High Temperature

Abstract: The effect of water vapor on the oxidation behavior of a Ni–25wt.%Cr alloy in air was studied between 1000 and 1300 °C by comparing, after test in dry air and in a humidified air, mass gain results and surface/sub-surface metallographic observations. It was found that, for the conditions studied, the transient oxidation at the beginning of the isothermal stage and the isothermal oxidation are both slightly slower in wet air than in dry air. The oxide formed in wet air over the surface tended to be less coarse and less thick than the one formed in dry air. The chromium depletion depths in the sub-surface were similar between the two atmospheres but the concentration at the oxide/alloy interface was higher for wet air than for dry air oxidation. The oxide scale formed in wet air seemed more resistant against spallation at cooling than the scale formed in dry air.

A Wet Oxidation Method for AMS Radiocarbon Analysis of Dissolved Organic Carbon in Water

Abstract: We present a method for the extraction of dissolved organic carbon (DOC) from water. The method is adapted from Burr et al. (2001) using the basic steps: 1) sample filtration; 2) acidification to liberate and remove dissolved inorganic carbon (DIC); 3) evaporation of the sample to isolate salts that include trace quantities of carbon; 4) combustion of the salts; and 5) purification of the CO2. Two significant improvements have been made to the earlier method. The first is to use wet oxidation with potassium permanganate to oxidize organics in place of the combustion step and the second is the development of a reduction/oxidation purification procedure to remove sulfur and nitrogen oxides that may form during the oxidation step. Wet oxidation has a practical advantage over the previous method because it proceeds at low temperature (70 ° C). The original method required quartz vessels to oxidize the salts at 900 ° C. At this temperature, salts in the samples formed gases that interfered with the isolation of CO2 and the quartz vessels degraded with each combustion, affecting their structural integrity. The expensive quartz vessels could only be used for a limited number of samples, whereas Pyrex vessels used for wet oxidation are inexpensive and can be used indefinitely. The blank fraction modern carbon ( f ) and its mass dependence for the refined technique was determined from repeat analyses of salicylic acid produced from petrochemicals. For samples with a mass m above 0.5 mg, F = 0.0083 ± 0.0011. For samples below 0.5 mg, the blank follows a 1/ m dependence as observed for other accelerator mass spectrometry (AMS) 14C measurements (Donahue et al. 1990). The reproducibility of the method is demonstrated using repeat measurements from a variety of samples, including a sample measured with the former high-temperature 900 °C combustion technique. The virtues of the wet oxidation method are that it is economical, produces a low blank, and provides good reproducibility. DOI: 10.2458/azu_js_rc.55.16277