Catalysts For Wet Air Oxidation Research Articles

Ruthenium-decorated carbon nanotubes as catalyst for wet air oxidation

Wet air oxidation (WAO) is a suitable method for the effective destruction of refinery spent caustic. This work suggests the use of Ruthenium catalyst supported on multi-walled carbon nanotubes (Ru/CNT) for WAO of cresylic spent caustic waste. Using model compounds representative of such waste, such as o-cresol, m-cresol and p-cresol, the suitability of lab-made Ru/CNT (Ru = 5%) for the WAO process was investigated in a slurry reactor. At T = 448 K and PO2 = 100 psi, around 55, 49 and 61% of initial TOC (here TOC denotes total organic carbon) was destroyed within 2 h of reaction with o-cresol, m-cresol and p-cresol. From the TOC vs. time data, kinetic study of TOC reduction for WAO of m-cresol was represented by a hyperbolic Langmuir-Hinshelwood model. Several useful features of the catalyst were examined using electron microscopy, X-ray diffraction and adsorption-desorption of nitrogen. In this way, this work has drawn attention toward this prospective WAO catalyst.

Making the Most of Precious Metal Nanoparticles in the Purification of Industrial Wastewater by Catalytic Wet Air Oxidation

The aim of catalytic wet air oxidation is to use air to remove organic contaminants from wastewater through their complete oxidation, without having to vaporise the water. To date, the widespread exploitation of this process has been held back by the low activity of available catalysts, which means that it has to be operated at above-atmospheric pressure in order to keep the water in the liquid phase at the elevated temperatures required to achieve complete oxidation. Here we present an overview of an ongoing study examining the key requirements of both the active phase and the support material in precious metal catalysts for wet air oxidation, using phenol as the model contaminant. The major outcome to date is that the results reveal a synergy between platinum and hydrophobic support materials, which is not apparent when the active phase is ruthenium.

Carbon bead-supported copper-dispersed carbon nanofibers: An efficient catalyst for wet air oxidation of industrial wastewater in a recycle flow reactor

Copper nanoparticle-doped and graphitic carbon nanofibers-covered porous carbon beads were used as an efficient catalyst for treating synthetic phenolic water by catalytic wet air oxidation (CWAO) in a packed bed reactor over 10–30bar and 180–230°C, with air and water flowing co-currently. A mathematical model based on reaction kinetics assuming degradation in both heterogeneous and homogeneous phases was developed to predict reduction in chemical oxygen demand (COD) under a continuous operation with recycle. The catalyst and process also showed complete COD reduction (>99%) without leaching of Cu against a high COD (∼120,000mg/L) containing industrial wastewater.

An efficient MoO3 catalyst for in-practical degradation of dye wastewater under room conditions

The MoO3 catalysts as a wet air oxidation catalyst have been synthesized by a simple hydrothermal method. During the synthetic process, a detailed orthogonal design on the preparation conditions was performed, aiming to optimize the parameters to produce MoO3 with the most prominent catalytic performance. The catalytic activities of the synthesized materials were evaluated via the decolorization of dye wastewater at room conditions. The effects of calcination temperature, catalyst dosage, and initial concentration of Rhodamine B (RhB) on the degradation efficiency were investigated, where it was found that the sample calcinated at 400°C exhibited superior catalytic performance.

Structure, characterization, and dynamic performance of a wet air oxidation catalyst Cu–Fe–La/γ-Al2O3

A Cu–Fe–La/γ-Al2O3 (CFLA) catalyst was prepared by the excessive impregnation method and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results indicate that the catalyst contained mostly Cu2+, Fe3+, and La3+ and a small amount of Cu+, Fe2+, and La. The active components were uniformly distributed in the catalyst, and the particle size of the components was approximately 7.5nm. The CFLA catalyst was used for the treatment of methyl orange (MO) solution by catalytic wet air oxidation (CWAO), and it exhibited a high catalytic activity. The catalytic reaction involved variable valence states of metals and free-radical reaction mechanism. The CWAO reaction of MO solution was fitted by a segmented first-order dynamic model, and the rapid reaction apparent activation energy was 13.9kJ·mol−1.

Effect of Composition and Mass Ratio on the Catalytic Wet Air Oxidation Catalyst Cu–Fe–La/FSC

The catalytic wet air oxidation (CWAO) technology is used for the treatment of the simulated printing and dyeing wastewater and also for investigating the catalyst performance indicators such as catalyst activity and stability. The catalyst activity is mainly reflected from the water decolorization and CODCr removal rates, and the stability of the catalyst is mainly reflected by the quantity of metal dissolution. The experimental results showed that the prepared Cu–Fe–La/FSC catalyst with a 1:1:2 ratio of Cu–Fe–La by the impregnation method exhibited good activity for the treatment of the simulated printing and dyeing wastewater by the CWAO method, and the decolorization and COD Cr removal rates using this catalyst were 98.7% and 78.6%, respectively, with a higher catalytic activity, lower concentration of metal dissolution, and good stability.

Cerium Oxide Based Catalysts for Wet Air Oxidation of Bisphenol A

Catalytic wet air oxidation of an aqueous solution, bisphenol A (BPA), was carried out at 160 °C and at 20 bar of air in a batch reactor. Silver catalysts (2.5 wt%) prepared by wet impregnation and complexation on commercial CeO2 in addition to Ce0.85Zr0.15O2 and Ce0.2Zr0.8O2 sol–gel mixed oxides were synthesized and used as catalysts in the reaction. Characterizations of the catalysts were performed by using FESEM, XRD, BET, XPS and ICP–OES techniques. Residual BPA concentration was analyzed by using an UV–Vis technique and organic compound content was measured via the total organic carbon method. Commercial CeO2 showed a smaller specific surface area and a larger crystallite size than laboratory prepared Ce–Zr mixed oxides. The highest BPA removal (76 %) was achieved after 3 h with CeO2, Ce0.85Zr0.15O2 and Ag/Ce0.85Zr0.15O2 catalysts revealing that the addition of silver had no effect on the catalytic activity of the pure supports. However, the loading of active metal to the supports by complexation decreased the adsorption of the BPA during the heating period and hence the Ag/Ce0.85Zr0.15O2 prepared via complexation was the most active catalyst with only 1 % adsorption of BPA. Moreover, the activity of the catalysts was not related to the surface area of the samples. According to the ICP–OES analysis of the terminal water samples, leaching of the silver was occurred during oxidation experiments explaining the behavior of Ag catalysts in the reaction.

Graphene oxide as an effective catalyst for wet air oxidation of phenol

The graphene oxide (GO) and chemically reduced graphene oxides, used as catalysts in absence of any metals, were investigated in the catalytic wet air oxidation (CWAO) of phenol in a batch reactor. The characterization of the materials was measured with scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The carbon materials exhibited good phenol and total organic compounds (TOC) removals in the CWAO of phenol. The GO had the highest catalytic activity, total phenol removal was achieved after 40min, and ca. 84% TOC removal was obtained after 120min at reaction temperature of 155°C, total pressure of 2.5MPa and catalyst loading of 0.2gL−1.

Rectorite as catalyst for wet air oxidation of phenol

Rectorite was characterized by XRF, BET, XRD, FT-IR, SEM and TPR, and investigated as catalyst for wet air oxidation of phenol in a batch reactor at 150 °C. The iron impurity, mainly presented as highly dispersed hematite, acted as active centers and showed good performance without significant iron leaching. The catalyst can be also used as adsorbent to remove leached iron in solution.

Characteristics of titania supported copper oxide catalysts for wet air oxidation of phenol

Various techniques have been used to characterize the CuO x /TiO 2 catalysts with different copper loading. Surface area, pore volume and pore size distribution of the prepared catalysts were estimated from nitrogen adsorption isotherm. Temperature programmed reduction (TPR), X-ray diffraction (XRD), electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) experiments were performed to investigate the chemical state of the copper species. The chemical state of copper in the CuO x /TiO 2 catalysts varied with copper loading (1–25 wt.%): highly dispersed Cu 2+ cluster for 1 and 5 wt.%, and bulk CuO for 7–25 wt.%. The activity and mineralization selectivity of the CuO x /TiO 2 catalysts increased with copper loading up to 20 wt.%, and remained almost constant for higher copper loading. The optimum copper loading was 20 wt.% for the wet air oxidation of phenol over the CuO x /TiO 2 catalysts in this work. The stability of the CuO x /TiO 2 catalysts with different copper loading was also studied with respect to carbonaceous deposits and copper leaching.

Activity and stability of iron-containing pillared clay catalysts for wet air oxidation of phenol

Catalytic wet air oxidation of an aqueous phenol solution over Fe–Al pillared catalyst was conducted in a stirred tank and packed bed reactor. Semi-batch experiments in the stirred tank reactor were designed to investigate the effects of temperature, air pressure, initial phenol concentration, catalyst loading, and catalyst size on the conversion of total organic carbon. The catalyst exhibited an important activity in degrading total organic carbon at mild conditions. Its internal mass transfer resistance was assessed over different catalyst sizes via a chosen criterion. Packed bed runs were conducted under selected temperature and pressure (170 °C, 3.2 MPa) over a long duration (240 h). Various characterization methods were employed for fresh and aged pillared clay catalysts. Occurrence of catalyst deactivation by carbonaceous deposits during the packed bed operation was observed through scanning electron microscopy (SEM) and elemental analysis. Insignificant metal leaching was observed because trace amounts of metal elements were detected in the hot acidic liquid solution.

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

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...

The effect of micro-morphology of Bi2O3on catalytic properties of Co/Bi catalyst for wet air oxidation of acetic acid

Two catalysts that consist of cobalt-bismuth complex oxides were prepared by different methods. These two catalysts, which exhibited different catalytic properties for wet oxidation of acetic acid, were investigated by XRD, TEM, ESR and XPS, and the interaction between Co and Bi was studied. It has been found that this kind of interaction was reinforced due to a close contact of the nanometer-sized Bi2O3 with Co3O4 and the catalytic activity of Co-Bi catalyst was greatly improved by this kind of interaction. The mechanism of the wet oxidation of acetic acid over Co-Bi catalyst is also discussed in this paper.

Copper Oxide Mounted on Activated Carbon as Catalyst for Wet Air Oxidation of Aqueous Phenol. 1. Kinetic and Mechanistic Approaches

This paper describes the kinetics and an approach to the mechanism of the catalytic wet air oxidation of aqueous phenol. Copper oxide supported over activated carbon was used as catalyst. Experimen...

Copper Oxide Mounted on Activated Carbon as Catalyst for Wet Air Oxidation of Aqueous Phenol. 2. Catalyst Stability

Stability aspects of the Sofnocarb A21 catalyst (5% CuO on activated carbon) have been studied for catalytic wet air oxidation of phenol. The study focused on copper leaching, the main factor affecting the catalyst stability. It was found that no copper leaching took place in the experiments using fresh catalyst, when the initial phenol concentration was lower than 1.5 kg/m3. Nevertheless, copper leaching and fouling were observed through consecutive experiments reusing the catalyst, leading to deactivation of catalyst and therefore a lower phenol oxidation rate. The main reaction intermediates, namely acetic acid and p-benzoquinone, together with polymeric products are highlighted to be responsible for copper leaching and fouling. Nonetheless, the leaching of active substance measured for Sofnocarb A21 was much lower than those found for other catalysts (G-66 A, Süd Chemie, Germany) also used for catalytic decomposition of phenol. Basic conditions were demonstrated to be useful to prevent both copper leaching and fouling, thereby enhancing the catalyst lifetime.

ChemInform Abstract: Hydrogen‐Treated Active Carbon Supported Palladium Catalysts for Wet Air Oxidation of Ammonia.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Hydrogen-Treated Active Carbon Supported Palladium Catalysts for Wet Air Oxidation of Ammonia

Abstract Almost complete conversion of dilute aqueous ammonia (1.5 g-NH3 dm−3) to dinitrogen has been attained over a hydrogen-treated active carbon supported (3 wt%) Pd catalyst under a rather mild condition (2.0 MPa of air, 453 K). The hydrophobicity of the support surface is considered to be important to provide high activity and selectivity in Pd catalysis.

Degradation of Pulp-Mill Effluent by Oxygen and Na5[PV2Mo10O40], a Multipurpose Delignification and Wet Air Oxidation Catalyst

Water-soluble salts of polyoxometalate (POM) anions can be used as (net) catalysts for selective, effluent-free oxygen delignification (bleaching) of unbleached kraft wood-pulps. Essential to this process is the use of the POM anions as catalysts for the wet oxidation of the lignin removed from the pulp fibers. In anaerobic bleaching, a 0.5 M solution of {alpha}-Na{sub 5}[PV{sub 2}Mo{sub 10}O{sub 40}] (POM{sub ox}) is combined with wood pulp and the mixture heated to 125 C. This treatment dissolves certain organic compounds (some lignin and polysaccharide fragments) with a combined chemical oxygen demand (COD) of 1,500--2,000 mg of O{sub 2}L. Before the solution can be used again for bleaching, the POM anions (POM{sub red}) must be reoxidized and the dissolved organic compounds removed. Here, a second function of the POM anions is realized. They are used under mild conditions (150 C, 0.7 MPa of O{sub 2}) to catalyze the wet air oxidation of the dissolved organic compounds. After several cycles of anaerobic bleaching and wet oxidation, a steady-state condition in COD (at ca. 550 mg of O{sub 2}/L) is achieved.