Showing papers on "Wet oxidation published in 2023"
TL;DR: In this paper , a simple recovery of catalysts from waste ACC for reuse in Catalytic Wet Air Oxidation (CWAO) was investigated, and the optimum removal efficiency was 88% when the reaction conditions were set on the 20 bar of pressure at 111.5 °C over 77 min.
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TL;DR: Wang et al. as discussed by the authors synthesized and applied a highly effective wet catalyst (MoO3) for catalytic wet air oxidation (CWAO) treatment of pharmaceutical wastewater, and the degradation mechanism is also illustrated by the density functional theory (DFT) calculation.
Abstract: In this work, a highly effective catalyst (MoO3) is synthesized and applied for catalytic wet air oxidation (CWAO) treatment of pharmaceutical wastewater. The catalyst is systematically characterized to investigate the morphology, crystal structure and chemical composition, and the findings demostrated that MoO3 catalyst is successfully synthesized. The degradation mechanism is also illustrated by the density functional theory (DFT) calculation. The degradation experiments confirm that MoO3 catalyst exhibits excellent catalytic performance in CWAO, and the removal rate of TOC (Total Organic Carbon) and COD (Chemical Oxygen Demand) is achieved to more than 93%. The catalyst doses, reaction temperature and reaction time have a significant impact on the removal of pollutants. The degradation process of pollutants in CWAO could be satisfactorily fitted by the second-order kinetics. Besides, MoO3 displays a favorable stability as CWAO catalyst. DFT calculation illustrates that MoO3 catalyst is a typical indirect band gap semiconductor. Moreover, the high temperature environment provides the thermal excitation energy, which favors to the free electrons nearing Fermi level to escape the material surface, and excites them to the conduction band, then directly reduces the pollutants in CWAO. These findings demonstrate that MoO3 can be used as an efficient and excellent catalyst for CWAO of pharmaceutical wastewater. 48 C. Chen, T. Cheng, L. Wang, Y. Tian, Q. Deng, Y. Shi produces hydroxyl radical (OH) with strong oxidation ability under the reaction conditions of high temperature and high pressure, electricity, sound, light irradiation, and catalyst. By utilizing the advanced oxidation technology, the refractory organic substances of macromolecules could be oxidized into low toxic or non-toxic small molecular substances. Schrank et al. use diverse advanced oxidation techniques of UV (Ultraviolet Light), TiO2/UV, O3 and O3/UV to degrade pollutants in tannery wastewater; it demonstrates that the biodegradation of wastewater is enhanced through oxidation, and the toxicity of pollutants is also decreased (Schrank et al, 2004). Hofman-Caris et al. removed pharmaceuticals from wastewater effluent and dissolved non-biodegradable organic matter by advanced oxidation technique. The results suggest that advanced oxidation techniques could remove multiple different pharmaceuticals and humic acid to a large extent (Hofman-Caris et al., 2017). Wet air oxidation (WAO) technology is a kind of advanced oxidation technology. It can oxidize organic substances in wastewater to small molecules or inorganic matter under the condition of high temperature (120–320°C) and high pressure (0.5 ~20 MPa). Gaseous oxygen is utilized as oxidant in this reaction. Moreover, it can treat wastewater with refractory substances, and be highly evaluated by many researchers due to its simple operation and easy industrialization. However, the WAO technology requires high temperature, and the cost to treat wastewater is very high. To solve this problem, the existing idea is to add suitable catalysts on the basis of WAO, which calls catalytic wet air oxidation (CWAO), so that the reaction could be carried out under mild conditions. In this way, it could reduce the cost of wastewater treatment, and improve the removal efficiency (Kang et al, 2011). The development of catalysts is crucial to the treatment of pollutants in catalytic wet oxidation technology. So far, the research of catalytic wet oxidation has focused mainly on the synthesis of novel catalysts and investigating the effect of materials on wastewater treatment in CWAO. Researchers have developed a series of catalysts in CWAO, such as TiO2 (Lunagomez Rocha et al, 2015), Al2O3 (Sushma et al, 2018), CeO2 (Parvas et al, 2019), MoO3 (Li et al, 2009, Wang et al, 2017, Wang et al, 2020b) and so on. Among them, MoO3 exhibits favorable catalytic performance in the degradation of organic pollutants. Li et al. synthesized one-dimensional Ce-doped MoO3 nanofibers with different doping amounts by combining sol-gel method and electrospinning technology. It was found that 11.86wt% CeO2-doped nanofibers exhibited excellent catalytic activity for the fast degradation of organic dye (Li et al., 2009). Wang et al. synthesized MoO3 catalyst by hydrothermal method, and the catalytic material demonstrated good catalytic performance at 400°C for the degradation of dye wastewater (Wang et al., 2017). Wang et al. synthesized highly active and stable nano-hybrid bimetallic catalysts, and applied to the treatment of organic dyes and obtained excellent degradation efficiencies in catalytic wet air oxidation system (Wang et al., 2020b). This demonstrates that MoO3 catalyst is a very effective and potential material in the field of wet air oxidation treatment of industrial wastewater. However, this research is insufficient in the following two aspects. Firstly, most of the wastewater used in studies is simulated wastewater, while the practical wastewater used in research is relatively rare. The catalytic performances of MoO3 synthetic materials in wet air oxidation of pharmaceutical production wastewater are also rarely reported. Secondly, these studies do not thoroughly analyze the degradation mechanism of catalysts for catalytic wet air oxidation of wastewater. This study has made some supplements to these two aspects. We obtained practical wastewater from pharmaceutical companies to analyze the degradation effect of MoO3 catalyst in CWAO. The organic pollutants produced in pharmaceutical wastewater are in large quantities, do great harm, and are difficult to be degraded due to their complex compositions. If MoO3 catalyst could be applied to the wet air oxidation treatment of pharmaceutical wastewater, it would not only promote the application of MoO3 catalytic material, but also provide a new choice of technique for the treatment of pharmaceutical wastewater, thus alleviate the harm of pharmaceutical wastewater to the environment. Also, with the aid of Density Functional Theory (DFT) calculations, we attempt to reveal the microscopic mechanism of MoO3 as a catalyst to degrade pharmaceutical wastewater in CWAO through analyzing the energy band structure of material. Hence, in this paper, MoO3 catalyst is prepared and synthesized by hydrothermal synthesis methods. The synthetic material properties are fully characterized by liquid specific surface area analyzer, X-ray diffractometer (XRD), scanning electron microscope (SEM), thermogravimetric analyzer, and other modern and advanced analytical techniques. The synthetic catalyst is applied to degrade pharmaceutical wastewater by catalytic wet air oxidation. The impact of catalytic dosage, reaction temperature, and reaction time on the degradation of pollutants is investigated. In addition, the reaction process of catalytic wet air oxidation on the pharmaceutical wastewater is modeled by the first-order and second-order kinetic equation. The recycling of catalyst in wet air oxidation system is also discussed. Furthermore, to illustrate the catalytic mechanism of MoO3 on the degradation of pharmaceutical wastewater, the band structure and Density of States (DOS) of catalyst were obtained through DFT calculation. Experimental equipment and methods Preparation of catalyst The hydrothermal synthesis method is performed for the preparation of catalyst. The mixture of 56 g (NH4)6Mo7O24·4H2O and KNO3 was dissolved in distilled water at 70°C and fully mixed. Among the mixed liquor, the amount of KNO3 was 5.1 g. To control the pH of solution, 0.1 mol/L HNO3 and KOH solution was used to adjust the pH (range from 4 to 7). The solution was transferred to the KH-50 type hydrothermal synthesis reactor at 125°C for 24 h. The outer shell of the hydrothermal reactor was made of stainless steel, and the inner lining was made of polytetrafluoroethylene produced by Beijing Getimes Technology Co., Ltd. Then, the resulting precipitate was filtered and washed with deionized water at room temperature until the pH value of the filtrate reached 7. The mixture was then dispersed in the 450 ml acetone and mixed for 2.5 h. After that, the mixture was filtered, and the residue was collected and dried at 85°C for 16 h in the electroApplication of MoO3 as an efficient catalyst for wet air oxidation treatment of pharmaceutical wastewater... 49 -thermostatic blast oven. The sample was ground and roasted in a muffle furnace at 430°C for 4 h. Finally, the catalytic material was obtained by naturally cooling at room temperature in the Carbolite muffle furnace. Characterization of catalyst The synthetic catalyst is characterized by liquid specific surface area analyzer, X-ray diffractometer, scanning electron microscope, Fourier transform infrared spectroscopy, thermogravimetric analyzer, X-ray photoelectron spectroscopy spectra (XPS), and so on. In this experiment, we used Xigo liquid specific surface area analyzer (XiGo Nanotools, USA) to measure the specific surface area of the catalyst, and evaluate the properties of synthetic material. The morphology and composition of the catalyst was determined by S-3400N II scanning electron microscope (Hitachi Company, Japan). The characteristic functional group structure, molecular structure and chemical composition of the catalyst are analyzed by Thermo Scientific Nicolet is 5 Fourier transform infrared spectroscopy (FTIR) using pressed KBr discs. Moreover, the image of the catalyst was analyzed by X’tra X-ray diffractometer (ARL Company of Switzerland). The thermoweight of the catalyst was measured by Pyris 1 DSC thermal analyzer (PerKinElmer Company, the United States). The X-ray photoelectron spectroscopy spectra were recorded on PHI 5000 VersaProbe XPS equipment. The UV-vis spectrum research was carried out by PerkinElmer Ultraviolet spectrophotometer. Catalytic wet air oxidation The experiment of catalytic wet air oxidation to treat the wastewater was carried out in G
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TL;DR: In this article , the results indicate that wet oxidation is a promising method for the highly efficient degradation of pharmaceutical sludge using homogeneous and heterogeneous catalysts and that the inorganic residues can be utilized for the building materials production.
Abstract: Abstract In this work, wet oxidation and catalytic wet oxidation of pharmaceutical sludge using homogeneous and heterogeneous catalysts were investigated. The results indicate that wet oxidation is a promising method for the highly efficient degradation of pharmaceutical sludge. Under optimal conditions, the highest removal efficiencies of volatile suspended solids (VSS) 86.8% and chemical oxygen demand (COD) 62.5% were achieved at 260 °C for 60 min with an initial oxygen pressure of 1.0 MPa. NaOH exhibited excellent acceleration performance on the VSS removal. The highest VSS removal efficiency of 95.2% was obtained at 260 °C for 60 min with an initial oxygen pressure of 1.0 MPa and 10 g·L −1 of NaOH. By using a Cu–Ce/γ-Al 2 O 3 catalyst, the highest removal rates of VSS 87.3% and COD 72.6% were achieved at 260 °C for 60 min with an initial oxygen pressure of 1.0 MPa and 10 g·L −1 of catalyst. The wet oxidation reaction can be maintained itself owing to the exothermic heat. The produced low-molecular-weight carboxylic acids have potential commercial utilization as organic carbon sources in the biological wastewater treatment processes. The inorganic residues can be utilized for the building materials production. These results implied that the catalytic wet oxidation is a promising method for the volume reduction and resource utilization of pharmaceutical sludge.
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TL;DR: In this article , the effects of reaction parameters, including the moisture content, the additional dose of sludge, reaction temperature and the additional amount of oxygen, were discussed, and it was suggested that wet oxidation technology provides a suitable alternative method for the treatment of excess sludge from coal chemical industries.
Abstract: Excess activated sludge produced from coal chemical industries has gained much attention, because of the huge volume and high hazardous risk of the sludge. The wet oxidation of coal chemical sludge was studied in this study by using a stainless steel batch reactor. The effects of reaction parameters, including the moisture content, the additional dose of sludge, reaction temperature and the additional amount of oxygen, were discussed. The results showed that the highest removal ratios of COD and TS could reach up to 72.3% and 56.4% respectively with moisture content of sludge 93%, initial oxygen pressure 1.7 MPa under 240°C for 60 min. The mass transfer processes of sludge and oxygen, and the reaction temperature, are very important parameters for the treatment. It was suggested that wet oxidation technology provides a suitable alternative method for the treatment of excess sludge from coal chemical industries.
TL;DR: Different operating conditions of wet air oxidation and catalytic wet air oxidization have been studied for the treatment of highly concentrated methyldiethanolamine wastewater streams from amine units of acid gas recovery in petrol refineries as discussed by the authors .
TL;DR: In this paper , the catalytic wet air oxidation (CWAO) of phenol has been studied in a trickle bed reactor using active carbon (FAC) and zinc chloride activation (ZAC).
Abstract: The catalytic wet air oxidation (CWAO) of phenol has been studied in a trickle bed reactor
using active carbon prepared from date stones as catalyst by ferric and zinc chloride activation (FAC and ZAC). The activated carbons were characterized by measuring their surface area and adsorption capacity besides conventional properties, and then checked for CWAO using a trickle bed reactor operating at different conditions (i.e. pH, gas flow rate, LHSV, temperature and oxygen partial pressure). The results showed that the active carbon (FAC and ZAC), without any active metal supported, gives the highest phenol conversion. The reaction network proposed accounts for all detected intermediate products of phenol oxidation that composed by several consecutive and parallel reactions. The parameters of the model estimated using experimental data obtained from a continuous trickle bed reactor at different temperatures (120-160 C) and oxygen partial pressures (8-12 bar). Simple power law as well as Langmuir-Hinshelwood (L-H) expressions accounting for the adsorption effects were checked in the modeling of the reaction network. A non-linear multi-parameter estimation approach was used to simultaneously evaluate the high number of model parameters. Approach by simple power law only succeeds in fitting phenol disappearance. Instead, when L-H expressions are incorporated for the intermediate reaction steps, the model accurately describes all the experimental concentration profiles, giving mean deviations below 10%.
TL;DR: In this article , a novel nano-catalyst based on iron oxide (MnO2/Fe2O3) was developed to promote wet oxidation of phenol, and the optimal operating conditions were 294 min residence time and 70oC reaction temperature.
Abstract: A novel nano-catalyst based on iron oxide (MnO2/Fe2O3) was developed to promote wet oxidation of phenol. MnO2 was doped in Fe2O3 matrix to prepare composite nano-catalyst with different doping percentage (0, 2 and 5%). The catalytic phenol oxidation was conducted under different reaction temperatures and residence times. To evaluate the optimal kinetic parameters aiming to maximize phenol removal under the optimal conditions for the catalytic wet phenol oxidation process, modeling was applied on the batch reactor using the novel synthesis nano-catalyst (MnO2/Fe2O3) and the model developed was fed with the experimental data. gPROMS package was used to model the process of phenol oxidation and to optimize the experimental data. The error predicted between the simulated and experimental data was less than 5%. The optimal operating conditions were 294 min residence time, 70oC reaction temperature, and 764 ppm initial concentration of phenol over the prepared 5% MnO2/Fe2O3. Running of wet oxidation of phenol under the optimal operating conditions resulted in 98% removal of phenol from refinery wastewater.
TL;DR: In this paper , the authors performed wet air oxidation of the PPE mixture at temperatures ranging from 300 °C to 350 °C, with initial air pressures of 30 bar and 60 bar, respectively.
Abstract: Wet air oxidation (WAO) of the PPE mixture was performed at temperatures ranging from 300 °C to 350 °C, with initial air pressures of 30 bar and 60 bar, respectively. Total suspended solids (TSS) were reduced by up to 99%, while total chemical oxygen demand (tCOD) and soluble chemical oxygen demand (sCOD) were significantly reduced to 360 mg/L and 110 mg/L, respectively. The main products were volatile fatty acids such as acetic and propionic acids and ammonia nitrogen (NH3-N) with concentrations of up to 1117 mg/L, 975 mg/L, and 18 mg/L, respectively. Nitrogen and oxygen were the most abundant gaseous products, reaching 72% (w/w) and 14% (w/w), respectively. Semi-batch WAO treatments were carried out at 300 °C and 350 °C to achieve comparable waste reduction. The results suggest that non-catalytic WAO is a viable PPE waste management solution.
TL;DR: In this article , enhanced wet oxidation of excess sludge from pharmaceutical wastewater by NaOH as an alkaline homogeneous catalyst was investigated, and the experiments were carried out in a stainless-steel batch autoclave reactor.
Abstract: In the present study, enhanced wet oxidation of excess sludge from pharmaceutical wastewater by NaOH as an alkaline homogeneous catalyst was investigated. The experiments were carried out in a stainless-steel batch autoclave reactor. The highest volatile suspended solids (VSS) removal rate, 95.2%, was achieved at 260 °C within 60 min with an initial oxygen pressure of 1.0 MPa and NaOH 0.5 g·L−1. Simultaneously, the chemical oxygen demand (COD) removal rate of 57.3% was reached. The increase in volatile fatty acids (VFAs) demonstrated that the degradation of sludge was greatly accelerated by NaOH. Interestingly, the production of acetic acid, an intermediate by-product generated from the oxidation of organic compounds, increased significantly. These results illustrated that NaOH is a promising catalyst for the utilization of wet oxidation liquid of excess sludge as a carbon source for the treatment of wastewater.
TL;DR: In this paper , the authors developed a Pt-M (M=Pb, Cu) alloy structure where Pt is mainly in the form of Pt0 while M is mainly contained in M2+ for CWAO of phenol wastewater.
Abstract: Catalytic wet air oxidation (CWAO) is a promising process for degrading phenol in wastewater to CO2 and H2O. To achieve an active and stable Pt catalyst working at lower temperature, efficient catalysts are here developed by building a Pt-M (M=Pb, Cu) alloy structure where Pt is mainly in the form of Pt0 while M is mainly in the form of M2+. Firstly, carbon supported Pt-Pb/XC-72R and Pt-Pb/EC-300 catalysts are prepared for CWAO of phenol wastewater. It is found that Pt-Pb/XC-72R is highly active and stable for CWAO of phenol even at 100 °C. The initial TOC conversion is 91.1% and can be maintained higher than 75% in five consecutive cycles. Contrarily, Pt-Pb/EC-300 rapidly deactivates and TOC conversion decreased from 91.2% to 47.1% after five cycles. The characterization results indicate that two Pt-Pb alloy catalysts contained comparably high Pt0 concentration, which is responsible for the high activity. However, the Pb2+ concentration of Pt-Pb/XC-72R is much higher than that of Pt-Pb/EC-300, and higher Pb2+ concentration favors surface oxidation and keeps Pt0 from being oxidized during CWAO process, thus enhancing stability. For Pt-Pb/EC-300, both Pt0 and Pb0 are oxidized during the reaction, resulting in deactivation. To avoid using Pb in environmental considerations, the Pt-Pb is then replaced by Pt-Cu nanoparticles, where high catalytic activity and stability are maintained. More importantly, increasing Cu2+ can further enhance the catalytic performance. Tuning the second metal chemical state of Pt-based bimetallic alloy can be an effective approach to develop new catalysts for CWAO technology.
TL;DR: In this article , the authors used regression techniques to determine the oxide thickness for silicon carbide-based broad materials in nitrided and non-nitrided thermal oxidation process conditions for high-voltage applications.
Abstract: This research has shown that the oxide thickness for silicon carbide (SiC) based wide materials can be predicted using regression techniques in wet/dry nitrided or wet/dry non-nitrided thermal oxidation process conditions for high voltage applications by employing 2 different regression techniques: Polynomial and linear regression. The R-squared (R2) and Mean Absolute Percentage Error (MAPE) techniques are used to evaluate the regression models. Furthermore, this work investigates and presents a calculation of gate oxide thickness that is correlated to gate voltage ranges for high voltage applications. In this work, the thermal oxidation process environment is classified into 3 different processing conditions: conventional (dry and wet), dry nitrided (NO,N2O), and wet nitrided (HNO3 vapour). The findings from this study showed that wet oxidation combined with nitrided elements can produce thicker and better-quality gate oxide as compared to conventional dry and wet oxidation techniques. The outcome of this work clearly shows that gate oxide thickness may be derived from silicon carbide-based wide-bandgap materials utilizing linear and polynomial approaches using thermal oxidation durations at different temperatures for high-power applications. The regression models and formulations produced in this work are expected to aid the researchers in determining appropriate oxide thickness under practicable process conditions, with the exception of real thermal oxidation process conditions. Hence, the outcome of this work is expected to save the processing time, material, and cost of the power semiconductor device fabrication technology, mainly for high voltage applications.
HIGHLIGHTS
Regression approaches are being used to determine the oxide thickness (Tox) for SiC-based broad materials in nitrided and non-nitrided thermal oxidation process conditions for high-voltage applications
The regression models are assessed using the R-squared (R2) and Mean Absolute Percentage Error (MAPE) approaches
The results of this work are anticipated to reduce processing time, material requirements, and manufacturing costs for power semiconductor devices used in high-voltage applications
GRAPHICAL ABSTRACT