Catalytic Wet Oxidation Research Articles

Sacrificial template-directed fabrication of mesoporous manganese oxide based catalysts: Relationship between the ordering degree of pore structure and Fenton-like catalytic activity

In this study, novel mesoporous MnOx-based catalysts were prepared via the hard template method by using the mesoporous silica as a template. The performances of these catalysts were evaluated in catalytic wet H2O2 oxidation for Rhodamine B (RhB) in high-salinity wastewater (10% Na2SO4 solution containing RhB). The microstructure characterization indicated that the order of pore structures and the MnOx crystallinity in mesoporous materials improved as the number of repetitions of the immersion and calcination–molding process increased. Given good selective adsorption performance for RhB and rich Mn3+/Mn4+ couples, MnOx mesoporous materials with ordered regular pores exhibited excellent Fenton-like catalytic performance and the highest removal rate of RhB in high-salinity wastewater reached approximately 90% after 150 min of degradation. Moreover, because of the accelerated generation of the free radicals catalyzed by the Fe3+/Fe2+ couples, the loading of Fe species increased the performance of the MnOx ordered catalysts for RhB degradation. Furthermore, the Fe-loading MnOx catalyst exhibited only slight activity loss within the five cycles of catalytic degradation (the removal rate for RhB within the five cycles all exceeded 95%), due to the morphological stability of the MnOx ordered catalyst and the presence of stable Fe3+/Fe2+ couples during the RhB degradation process.

Performance of Supported Copper Catalysts for Oxidative Degradation of Phenolics in Aqueous Medium: Optimization of Reaction Conditions, Kinetics, Catalyst Stability, Characterization, and Reusability

Catalytic wet oxidation (CWO) of phenolic wastewater containing phenol, o-cresol, and 2,5-dimethylphenol was carried out in a batch reactor (phenolics = 10 g/L, chemical oxygen demand (COD) = 26 000 mg/L, and total organic carbon (TOC) = 7900 mg/L). Using the Box–Behnken experimental design (BBD) approach, the following optimum CWO conditions (catalyst: 5% Cu/AC) for phenolics degradation were found: Ccat = 3.4 g/L, T = 148 °C, PO2 = 0.61 MPa, and pH = 7.4. Under these conditions, TOC and COD removals of 88 and 90%, respectively, were obtained after 4 h of reaction. p-Benzoquinone and hydroquinone were identified as major intermediates, whereas a mixture of carboxylic acids was detected in treated wastewater. At higher oxygen pressures (stoichiometric and above), mineralization of phenolics was improved although the overall degradation was lower probably due to overoxidation. Reaction kinetics, reusability of the catalysts, and detailed characterization of spent catalysts are also discussed in this paper.

Preparation of heterogeneous catalysts based on CWAO technology

Refractory-biodegradable organic wastewater can be effectively treated by catalytic wet oxidation (CWAO). The preparation of non-catalyst is the core of CWAO technology. The preparation methods of heterogeneous catalysts include precipitation method, impregnation method, precipitation impregnation method, sol-gel method and chemical deposition method. According to the different ways of adding metal solution and precipitant, the precipitation method is divided into positive addition method, reverse addition method and combined addition method. According to the impregnation amount, the impregnation method can be divided into equal amount and excessive impregnation method. According to the principle of chemical reaction engineering, heterogeneous CWAO reaction process can be divided into 7 processes, such as internal diffusion and external diffusion. CWAO method is expected to be applied and expanded in pesticide, printing and dyeing, papermaking and other industries.

Study on heterogeneous catalysts for catalytic wet oxidation

Catalytic wet oxidation is a powerful method for the treatment of high concentration refractory organic wastewater. the support and catalyst components constitute heterogeneous catalysts, and the main catalyst, co-catalyst and co-catalyst components. The main catalyst and co-catalyst are the main influencing factors of the catalyst. The preparation methods of catalyst include precipitation method, impregnation method and impregnation precipitation method. The performance evaluation indexes of heterogeneous catalysts include the activity, stability, selectivity and anti-toxic stability, mechanical stability of the catalysts. according to the principle of chemical transfer, the heterogeneous catalytic reaction process consists of seven steps.

Catalytic wet oxidation of glucose as model compound of wastewater over copper/rare earth oxides catalysts

Catalytic wet oxidation (CWO) is a promising technology for the treatment of wastewater and abatement of organic waste, in which the unique characteristics of water at elevated temperatures and pressures are utilised. In this study, the catalytic wet oxidation reaction of glucose (model compound of carbohydrate) was evaluated using three different rare earth oxides; CeO2, Dy2O3, and Tb4O7 as catalyst supports to the active phase, Cu. The heterogeneous catalysts were prepared using the incipient wetness impregnation method. The catalysts performance was evaluated by comparing the results from catalysts characterization and the chemical oxygen demand (COD) removal efficiency of each catalyst. The highest COD conversion (80 %) was achieved with Cu/Tb4O7 catalyst prepared at a dopant solution concentration of 1.0 M. The COD results revealed that the introduction of Cu metal into the catalyst supports greatly enhances the catalyst activity. However, leaching was detected in all catalysts, suggesting that the stability and reusability of the catalysts were low.

Simultaneous Desulfurization and Denitrification of Mud-Phosphorus Emulsion

AbstractIn this study, a new technology was proposed for removing SO2 and NO from industrial flue gas via wet catalytic oxidation technology that uses a mud-phosphorus emulsion as the absorption li...

Application and Improvement of Wet Oxidation Technology

The common treatment methods for industrial biodegradable industrial waste-water are physical, chemical and biological methods, but the conventional methods have complicated and inefficient treatment processes. Wet air Oxidation (WAO) technology can effectively treat industrial biodegradable industrial waste-water. WAO has achieved good results in the treatment of pesticide waste-water, dye waste-water, activated sludge and phenol-containing waste-water. The CODCr removal rate of waste-water reaches 72.3 %∼95.3 %. In order to further improve the application effect of WAO technology, three improvement approaches have been developed: Catalytic Wet Air Oxidation, Catalytic Wet Supercritical Oxidation, and Catalytic Wet Peroxide Oxidation.

Study on the treatment of actual waste-water by CWAO method

The use of catalytic wet air oxidation (CWAO) technology to treat organic waste-water that is difficult to biodegrade had a significant effect. The following 12 types of waste-water have achieved good results with the CWAO method. The 12 types of waste-water include: papermaking waste-water, dye waste-water, pesticide waste-water, perfume waste-water, phenol waste-water, carbon-containing waste-water, ethanol waste-water, petrochemical company alkali residue waste-water, and oil extraction waste-water, ammonia-containing coking waste-water and pesticide waste-water, cleaning workshop emulsified waste-water and desizing waste-water. A typical homogeneous catalytic wet oxidation system includes 5 processes: Ciba Geigy, Bayer Loprox, WPO, Orcan, and IT Enviroscience. Heterogeneous catalysts lose their activity due to the low pH of the reaction system and the accumulation of activated carbon.

Effect of Calcination Temperature on the Performance of Pd-Based Catalysts

It is difficult to biodegrade organic waste-water, which is treated by catalytic wet oxidation method. The catalyst Pd-Fe-Co-Ce/FSC (ratio 1:1:1:3), and the calcination time was 3 h, and the calcination temperatures were set to 400, 550, 700, and 850 °C, respectively. When the calcination temperature was 550 °C, the experimental results show that: when Pd-Fe-Co-Ce/FSC (ratio 1:1:1:3) is added with, the pH of wastewater is reduced, and then the pH will rise again; the Pd-Fe-Co-Ce/FSC (ratio 1:1:1:3) catalyst has good decolorization effect at 4 calcining temperatures, which can reach 92.7% - 97.9%, and 36.6% - 41.8% higher than the blank without catalyst; the best treatment effect is when the calcination time is 3 h and the calcination temperature is 550 °C. The addition of Pd-Fe-Co-Ce/FSC (ratio 1:1:1:3) after treatment of printing waste-water, its COD removal rate increased significantly, and the final effluent percentage reached 71.7% - 88.8%.

Screening of Homogeneous CWAO Catalysts for Treatment of Ceramic Printing Waste-Water

The ceramic printing and dyeing waste-water was treated by catalytic wet oxidation. The catalytic oxidation reaction was carried out under the conditions of 50 mg/L metal ion concentration, 180 °C of reaction temperature, 2.5 MPa of oxygen partial pressure and 500 rpm of stirring speed, and the time of catalytic oxidation was set at 90 min. Comparing the effect of structural auxiliaries and blank group on COD removal rate of effluent, the structural auxiliaries have no effect on effluent, that is, no catalytic effect; Comparing the blank group without adding catalyst, the copper nitrate has the highest cod removal rate of 72.5% for waste-water, so it can be used as the best homogeneous catalyst to treat waste-water. The order of catalytic effect from high to low is: Cu(NO3)2 > CuSO4 > Fe(NO3)3 > Fe2(SO4)3 > Co(NO3)2 > Cr(NO3)3 > Ni(NO3)2 > AgNO3 > Zr(NO3)4. Among the nine types of homogeneous catalysts, the most effective Cu(NO3)2•H2O catalyst treated the ceramic printing and dyeing waste-water, the COD decreased from 3775 mg/L to 1038 mg/L and the COD removal rate reached 72.5%, when the catalyst was not added under the same operating conditions. The COD removal rate of water samples was increased by 32.9%.

Effect of Calcination Time on Catalyst’s Activity and Stability

Based on the catalyst Pd-Fe-Co-Ce/FSC(ratio 1:1:1:3), a catalytic wet oxidation method was used to treat organic waste-water that is difficult to biodegrade. The calcination temperature of the catalyst was set to 550 °C, and the calcination time was set to 1 h, 3 h, 5 h, 7 h in order. From the analysis, it is found that the effluent pH first decreases and then increases. With the extension of the reaction time, the absorbance of the treated waste-water decreases, and the decolorization rate increases. With the extension of the reaction time, the COD of the treated water sample decreased and the COD removal rate increased. For catalysts No.1, No.2, No.3 and No.4, the COD of wastewater was 10851, 768, 1149 and 1238 mg/L at 120 min of catalytic wet oxidation of wastewater, and the corresponding COD removal rates was 84.1%, 88.7%, 83.1% and 81.8%, respectively. The experimental results showed that the catalyst prepared by calcining for 3 h had a COD removal rate and a decolorization rate of 88.7% and 97.9%, respectively, and the metal dissolution solubility of the treated water was relatively low. 3 h is a suitable catalyst’s calcination time.

Effect of Precious Metals on the Activity of Multi-Component Supported Catalysts

Organic waste-water is treated by catalytic wet oxidation method (CWAO). The catalysts are prepared by the same amount of impregnation method. Fe and Co are used as active components of the catalyst, and Ce is used as the catalytic assistant, and the precious metal Pd is added to prepare a multi-component composite catalysts. When the Pd-based catalyst is added to the waste-water, the pH decreases and then increases. The process of organic matter degradation is first converted to small molecule organic acids, the pH is reduced, and then the small molecule organic acids are gradually decomposed. In the proportion of Pd-catalyst, as the Pd content in the catalyst increases, the treatment effect of the waste-water is enhanced; Effect of different ratios on the stability of Pd-Fe-Co-Ce/FSC catalysts showed that, CODCr removal rate increased from 65.7% to 84.7%, and decolorization rate increased from 72.5% to 97.2%. The average concentration of Pd3+, Fe3+, Co2+ and Ce3+ dissolved is 0.0015, 2.2519, 0.2281 and 0.2300, respectively. The Pd-catalyst Pd-Fe-Co-Ce/FSC with metal ion ratio Pd-Fe-Co-Ce=1:1:1:3 has the highest activity in waste-water treatment, and CODCr removal rates and decolorization rates reach 88.7% and 97.9%, respectively.

Catalytic wet oxidation treatment of landfill leachate

The landfill leachate was treated by catalytic wet oxidation. The catalysts was prepared by impregnation method, and FSC was used as catalyst carrier. Fe and Co were used as catalyst active components and Ce was used as catalyst auxiliary, and noble metal ruthenium was added to prepare supported multi-component composite catalyst of Fe-Co-Ru-Ce/γ-Al2O3. The water sample pH, decolorization rate, COD removal rate and turbidity removal rate were used as evaluation indexes of catalyst activity. The catalysts were prepared under the conditions of calcination temperature of 450 °C and calcination time of 3 h. Under the same conditions, for the Landfill Leachate, the COD removal rate, decolorization rate, turbidity removal rate of the water samples reached 78.1%, 60.4% and 92.7%, respectively.

Effect of calcination time on degradation of landfill leachate by Fe-Co-Ru-Ce / γ-Al2O3 catalytic wet oxidation system

The landfill leachate was used as the target pollutant, and the degradation was carried out by catalytic wet oxidation. The heterogeneous catalyst Fe-Co-Ru-Ce/γ-Al2O3 was prepared by impregnation method. The calcination time was set to 1.5, 3, 4.5, 6, 7.5 h respectively, the catalyst was calcined at a constant temperature for a set time to prepare five catalysts, and the influence of the calcination time on the activity of the catalyst was investigated. The results showed that when the calcination time was 3 h, the activity of the catalyst reached the maximum. At this time, the COD removal rate and decolorization rate of the treated water were 78.1% and 60.4%, respectively.

Elaboration of Copper Zinc Ferrite Nanoparticles: Application in Catalytic Wet H2O2 Oxidation of Phenol

Elaboration of Copper Zinc Ferrite Nanoparticles: Application in Catalytic Wet H2O2 Oxidation of Phenol

Catalytic Wet Air Oxidation of Pulp and Paper Industry Wastewater

Paper bleaching effluent was treated by catalytic wet oxidation method and the effect of the type of the catalyst on the efficiency was investigated. Cerium oxide, cobalt oxide and copper oxide based (CuOx-CoOx-CeO2) composite catalysts which were varying with regard to CuOx, CoOx and CeO2 compositions were prepared by co-precipitation method. The efficiency of the process was determined by measuring the chemical oxygen demand (COD), total organic carbon (TOC), adsorbable organic halides (AOX) and Cl− removal yields. When the COD, TOC and AOX removal yields were considered, better results were achieved with copper and ceria based catalysts than the cobalt based catalysts. At the optimum reaction conditions (T—473 K, t—120 min, P—130–250 psig), the maximum removal yields obtained by the 50% CuOx–50% CeO2 catalyst. When the wastewater of the I stage of paper bleaching process was treated, removal yields of TOC, COD and AOX were detected as 89; 94 and 95%, respectively Whereas, removal yields of 53% COD, 84% TOC, 90% AOX and 76% Cl− were achieved for the III stage wastewater. It was shown that removal of the toxicity of wastewater samples that were collected from the paper bleaching process by the proposed treatment methods.

Mo(VI) and W(VI) complexes as heterogeneous catalysts for degradation of azo dyes

Oxomolybdenum(VI) and polyoxotungstate(VI) complexes, [C2H10N2][(MoO2)4O3(Hcit)2].6H2O (1) and Al2W24O85C96H64Cl1.33Cu5 (2) (H4cit = citric acid) were synthesized and structurally characterized by single crystal X-ray diffraction analysis. Compound 1 is a tetranuclear oxomolybdenum complex and 2 is a Keggin-type polyoxotungstate hybrid containing phen ligand (phen = 1,10-phenanthroline). The obtained materials were further characterized by powder X-ray diffraction (PXRD), inductive coupled plasma optical emission spectroscopy (ICP-OES) and Fourier transformation infrared (FT-IR). The prepared complexes exhibit good activity for the catalytic wet air oxidation (CWAO) and catalytic wet oxidation (CWO) of Bismarck Brown (BB) and Direct Blue 71 (DB) as typical examples of di- and three-azo dye pollutants in water. The degradation products were analyzed by ion chromatography (IC) and the catalysts could be reused without observable loss of their activity.

Preliminary investigation of the degradation mechanism of o, m and p-cresol using sludge-derived carbon nanosheets by catalytic oxidation based on quantum chemistry

Advanced oxidation technology is widely used to oxidize organic compounds in the liquid phase by OH conventionally. Here, we prepared a sludge-derived carbon nanosheets, which was applied in the catalytic wet air oxidation (CWAO), catalytic wet peroxide oxidation (CWPO) and catalytic wet ozone oxidation (CWOO) systems. Because of its abundant oxygen-containing functional groups, the catalytic activity of nanosheets was much higher than some conventional catalysts. It was found that the first-order reaction model did not have similar characteristics as expected. Combining with molecular descriptors calculated by the DFT method and PLS analysis, we try to explain this phenomenon for the first time and proposed possible mechanisms for the three advanced oxidation technologies.

Catalytic wet oxidation of N,N-dimethyl formamide over ruthenium supported on CeO2 and Ce0.7Zr0.3O2 catalysts

A series of Ru supported on CeO2 and Ce0.7Zr0.3O2(CeZrO) was prepared by incipient-wet impregnation method and investigated in the catalytic wet oxidation of N,N-dimethyl formamide (DMF) in batch reactor. The physicochemical property of the catalysts was characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and thermogravimetry (TG). Compared with 3%Ru/CeO2, 3%Ru/Ce0.7Zr0.3O2 catalyst exhibits much higher performance for DMF degradation due to the promotion of Ru dispersion and the transfer of active oxygen, and 99% DMF conversion and 97% COD elimination are obtained at 453 K, 2.5 MPa oxygen pressure after 5 h. The reaction mechanism of DMF degradation was suggested. The carbonaceous species deposition and oxidation of Ru can be responsible for catalyst deactivation. And the catalyst activity can be recovered by air calcination and H2 reduction.

Highly efficient degradation of pharmaceutical sludge by catalytic wet oxidation using CuO-CeO2/γ-Al2O3 as a catalyst.

Pharmaceutical sludge is considered as a hazardous material with high treatment and disposal costs. In the present study, the catalytic wet oxidation (CWO) of pharmaceutical sludge by CuO-CeO2/γ-Al2O3 as the catalyst was investigated. The catalyst was prepared by traditional wet impregnation. The catalyst was characterized using X-ray Powder Diffraction (XRD) and Scanning Electron Microscopy (SEM). CWO was performed in an experimental batch reactor. Several parameters that could affect the catalytic degradation efficiency, including catalyst dose, temperature, time, oxygen pressure and pH, were investigated. Under optimum conditions, the highest removal rate of volatile suspended solids (VSS) was 87.3% and was achieved at 260°C for 60 min with an oxygen pressure of 1.0 MPa and 10 g/L of catalyst. At the same time, the chemical oxygen demand (COD) removal rate reached as high as 72.6%. This work implies that catalytic wet oxidation is a promising method for the highly efficient degradation of pharmaceutical sludge.