Catalytic Wet Air Oxidation Process Research Articles

Optimization of catalytic wet air oxidation process in microchannel reactor for TBBS wastewater treatment

ABSTRACT Catalytic wet air oxidation (CWAO) process is employed for the treatment of N-tert-butyl-2-benzothiazolesulfenamide (TBBS) wastewater in a microchannel reactor that enables continuous operation of the reaction and allows for thorough mixing of oxygen and pollutants. To achieve the optimal process performance, four key parameters of pressure, temperature, time, and the mass ratio of input oxygen to wastewater COD are optimized using both response surface methodology (RSM) and backpropagation artificial neural network (BP-ANN). According to the correlation coefficients of model results and experimental data, BP-ANN performs better than RSM in simulation and prediction. The analysis of variance in RSM shows that all parameters are significant for the obtained quadratic model, but their interactions with each other are not significant. Connection weights algorithm is used to determine the relative importance of these parameters for the process efficiency, and it is demonstrated that temperature is the most influential parameter with a relative importance of 35.61%, followed by pressure (29.74%), time (19.53%) and ROC (15.12%).

Developing Pt-M/C catalyst (M=Pb, Cu) for efficient catalytic wet air oxidation of phenol wastewater under mild conditions

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.

Kinetics and mechanism study of dyes degradation in electric field-promoting catalytic wet air oxidation process

Wet air oxidation (WAO) is a clean and eco-friendly technology for dyes removal, but the high operating temperature and pressure limit its practical application. In the present work, an electric field-promoting (EF-promoting) catalytic WAO process is developed to degrade dyes under room condition. The oxidation kinetics of four different types of dyes and their degradation pathways are studied. A kinetic model is constructed by including the exogenous electric field into the Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism framework, and quantitative structure-activity relationship (QSAR) analysis is conducted to correlate the kinetic parameters to the physicochemical properties of the dyes. A negative linear relationship is found between the adsorption equilibrium constants of the dyes and their first ionization energies, and their surface reaction rate constants are positively linearly associated to Esum (ELUMO + EHOMO). The degradation pathways of the different dyes are proposed according to the degradation intermediates and the activities of the atoms within the dye molecules. The heteroatoms N and S, and the atom C connecting the aromatic rings are identified as the susceptible sites upon the electrophilic attack of O2. Bond cleavage at these sites gives rise to aromatic fragments which are eventually mineralized via carboxyl acids. The results of this work is helpful for guiding the design and operation of the EF-promoting catalytic WAO process into the treatment of various dye wastewaters.

Deactivation characteristics of Ce-modified Cu-based carbon materials for catalytic wet air oxidation of phenol wastewater

In this paper, Ce-modified Cu-based carbon materials (Cu-Ce/AC) were prepared by impregnation method using walnut shell as the carbon precursor, Cu-ammonia solution as Cu source and Ce as modifier. The catalytic wet air oxidation (CWAO) degradation of phenol wastewater was carried out in a self-assembled fixed-bed reactor. The stability of Cu-Ce/AC catalyst under different pH conditions was studied. This study combines XRD, BET, FT-IR, ICP-OES and XPS characterization techniques to study the main reasons for the deactivation of Cu-Ce/AC catalysts. The reaction mechanism of Cu-Ce/AC catalytic wet air oxidation degradation of phenol was clarified. The result indicates that although phenol was completely converted in the CWAO process, the acidic intermediate product produced were difficult to completely degraded. Therefore, the pH of the solution gradually decreased. In acidic environment, the interaction between active component Cu and carbon carrier is weak, resulting in a large amount of metal leaching into the solution. As a result, the COD conversion gradually decreases. The alkaline environment can effectively slow down the leaching of catalyst Cu while maintaining its high catalytic activity. In addition, the incompletely degraded intermediate products are easy to accumulate and deposit on the Cu-Ce/AC surface, block the micropores and cover the surface-active sites, which reduces the catalyst activity. The study also found that there is a redox cycle between Cu+, Cu2+ Ce3+ and Ce4+ during phenol degradation, which enables Cu and Ce to form a strong interaction. The redox cycle can also promote the formation of oxygen vacancy (h+), O2−·, and HO·, making the degradation of phenol more thorough. At the same time, the mutual conversion between metal lattice oxygen and surface chemisorbed oxygen can generate high concentration of oxygen defect sites, which can improve the oxygen storage capacity of Cu-Ce/AC. These oxygen vacancies also provide more reactive sites to further promote adsorption and catalytic oxidation degradation of phenol and intermediate products.

3D ball-type self-assemble CeO2 nanostructure produced by facile hydrothermal strategy for catalytic wet air oxidation of N,N-dimethylformamide

CeO2 plays an important role in heterogeneous catalysis, and its performance is highly dependent on the oxygen vacancies and surface defects, which can be easily tuned by manipulating the particle dimensions and morphology. In this article, we report a facile strategy to synthesize a new type of CeO2 with modified surface property which can improve its ability to active oxygen. The obtained ball-type 3D self-assemble CeO2 (M-CeO2) is composed of large amounts of small 1D crystals which are strongly connected with each other. Detailed characterizations confirm its morphology, particle size and improved reducibility with abundant fraction of Ce3+ and more surface active oxygen when compared with CeO2-nanorods and CeO2-nanocubes. In the catalytic wet air oxidation (CWAO) of N,N-dimethylformamide, the total organic carbon (TOC) and total nitrogen (TN) conversion of M-CeO2 at 180 °C in 3 h are 68% and 46%, respectively, which are higher than that of CeO2-nanorods and CeO2-nanocubes. Besides, M-CeO2 presents the lowest activation energy, which is related to its modified surface property. The good stability with consecutive four reactions of M-CeO2 in catalytic reactions suggests its potential application in CWAO processes for industrial wastewater treatment.

Catalytic wet air oxidation of azo dye (reactive red 2) over copper oxide loaded activated carbon catalyst

The degradation of reactive red 2 mono azo dye through catalytic wet air oxidation process using copper oxide loaded activated carbon catalyst showed remarkable a result. The AC was prepared from water hyacinth root using the physic-chemical activation method and the copper oxide loaded activated carbon (CuO/AC) catalyst was prepared through the wet impregnation method. It was characterized by: Fourier transform infrared (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermo gravimetric analysis (TGA) instruments. The influence of operating parameters (catalyst dose (2–6 g/L), reaction temperature (70–120 °C), and oxygen partial pressure (1–3 bar)) on reactive red 2 (RR2) dye decolorization and chemical oxygen demand (COD) conversion at a reaction time of (10–120 min) were investigated. Complete dye decolorization (100%) and 88.57% chemical oxygen demand (COD) conversion were achieved at maximum operating conditions, 6 g/L of catalyst dose, 120 °C reaction temperature, and 3 bar of oxygen partial pressure within 120 min of reaction time. The percentage of dye decolorization was 42.91 and 59% in the presence of free radical scavengers sodium bicarbonate (NaHCO3) and methanol (CH3OH) respectively. Also, the performance of the reused catalyst was decreased. Based on the percentage of germination index of lepidium sativium seed, the phytotoxicity of the treated dye solution has low toxicity (62.67%) than the untreated dye solution (34.80%).

Study on heterogeneous catalytic wet air oxidation process of high concentration MDEA-containing wastewater

High concentration N-methyldiethanolamine (MDEA)-containing wastewater with strong alkaline, high chemical oxygen demand (COD), and toxic organics, cannot be directly treated by biochemical process. In this paper, effect of operation parameters (temperature, reaction pressure and residence time) on removal ratio of COD and MDEA was investigated by catalytic wet air oxidation (CWAO) over commercial activated carbon (AC). The degradation pathway of MDEA in the CWAO was proposed. The results showed that the concentration of MDEA, COD, total organic carbon (TOC), and total nitrogen (TN) were 18.92, 61.2, 21.34 and 5.65 g·L−1, respectively. The contribution rate of MDEA concentration to COD in the wastewater reached up to 89.8%. The removal ratio of MDEA and COD exceeded 98% and ∼90% at temperature of 230 °C, reaction pressure of 5.0 MPa and residence time of 90 min for 168 h continuous running, respectively. The surface carboxylic acid groups of AC played a key role in the formation of hydroxyl radicals (·OH), due to the O2 was adsorbed by the carboxyl groups on the surface of AC to form ·OH, and the ·OH then attacked the CN bond of the MDEA to generate other intermediate products, and then these intermediate products was further oxidized to NH4+, CO2 and H2O. This work provides a promising pretreatment technology of high concentration MDEA-containing wastewater.

Photocatalytic oxidation and catalytic wet air oxidation of real pharmaceutical wastewater in the presence of Fe and LaFeO3 doped activated carbon catalysts

Real pharmaceutical wastewater was treated by photocatalytic oxidation and catalytic wet air oxidation (CWAO) processes. The catalytic performance of Fe/AC and LaFeO3/AC (AC: Commercial activated carbon) was compared in the advanced oxidation processes. The influences of the reaction parameters were determined by using Box–Behnken design. Fe/AC catalyst was more effective in both of the photocatalytic oxidation and catalytic wet air oxidation processes. In the photocatalytic oxidation process, 72.7% COD removal was achieved at pH = 4.5, 2.0 g/L, and [H2O2]o = 0.32 mM. Under the optimum conditions of the CWAO, which were determined as 3 g/L of catalyst loading, pH = 3, and 50℃, 83.1% COD removal efficiency was obtained. CWAO method was determined as more suitable since a higher COD removal efficiency was achieved in a shorter reaction time. The toxicity in terms of L. sativum growth inhibition was evaluated as 4.82% after the CWAO treatment. A two-step first-order reaction kinetics provided the best fit of the CWAO experimental data. The activation energies of the fast and the slow steps were 25,661.16 and 28,327.46 J/mole, respectively.

Biotemplated copper oxide catalysts over graphene oxide for acetaminophen removal: Reaction kinetics analysis and cost estimation

TCuOX-GO (TCuO: Tomato skin inspired copper oxide; GO: Graphene oxide; X, weight percentage of copper oxide: 10, 50, and 90) catalysts were prepared and their performances on acetaminophen removal were tested in catalytic wet air oxidation (CWAO) process. Copper oxide particles were synthesized from tomato skin biotemplates to contribute valorization of food wastes and the development of ecofriendly catalysts. The most effective catalyst was determined as TCuO50-GO. Under the optimum conditions 52.1% TOC removal and 96.2% acetaminophen degradation efficiencies were achieved. The acetaminophen degradation kinetics was found to fit Langmuir-Hinshelwood model. The heat of adsorption and adsorption entropy were calculated as −19148.8 J/mol (for oxygen), −10380.9 J/mol (for acetaminophen), −10.17 J/molK (for oxygen), and −14.5 J/molK (for acetaminophen), respectively. The use of biomimetic catalysts in CWAO process and investigation of treatment cost and reaction kinetics in the presence of the biomimetic catalysts are the main original approaches of this study.

Preparation of Granulated Biomass Carbon Catalysts—Structure Tailoring, Characterization, and Use in Catalytic Wet Air Oxidation of Bisphenol A

New carbonized biomass–metakaolin (PSD/MK_Fe) granular composite catalyst materials were manufactured for the catalytic wet air oxidation (CWAO) of bisphenol A (BPA). These catalysts were characterized using different analytical and spectroscopic techniques, and results showed that the catalysts’ final properties were influenced by the addition of metakaolin (MK), polyvinyl alcohol, boric acid, and iron. Under the optimal CWAO experimental conditions (p: 20 bar, T: 160 °C, initial pH: 5–6, c[catalyst]: 1.0 g/L), nearly complete BPA conversion (>98%) and total organic carbon (TOC) conversion of 70% were reached. A key factor behind the enhanced catalytic activity was high specific surface area, although catalytic activity was also affected by surface acidity. These results confirmed the high efficiency of the current BPA conversion process involving the use of the easily separable and reusable PSD/MK_Fe catalyst. Therefore, biomass composite catalysts can be regarded as efficient catalysts for the oxidation of BPA during the CWAO process.

Performance investigation of the hybrid methods of adsorption or catalytic wet air oxidation subsequent to electrocoagulation in treatment of real textile wastewater and kinetic modelling

The performances of two hybrid wastewater treatment methods were compared to determine which method is more effective for improving the reusability of textile industry wastewater as irrigation water. In the hybrid treatment processes, either adsorption or catalytic wet air oxidation (CWAO) was performed subsequent to the electrocoagulation. The performances of the adsorption and catalytic wet air oxidation methods were evaluated according to the irrigation water criteria. Rice husk based activated carbon (RHAC) was used as adsorbent and catalyst support material in the adsorption and CWAO, respectively. BiNiO3-RHAC catalyst was prepared and used in CWAO process. The irrigation water criteria for total organic carbon (TOC), turbidity, and color were met and 91 % TOC reduction was achieved after the sequential application of electrocoagulation and adsorption. Freundlich isotherm and second order adsorption kinetics were regarded as the most suitable models to fit the adsorption data. The application of electrocoagulation and catalytic wet air oxidation yielded 62 % TOC removal whereas the oxidation reaction followed a two-step second order reaction kinetics.

Highly Efficient Ru Supported on Carbon Nanosphere Nanoparticles for Ciprofloxacin Removal: Effects of Operating Parameters, Degradation Pathways, and Kinetic Study

In this work, the capability of the catalytic wet air oxidation process (CWAO) using a ruthenium-carbon nanosphere catalyst (CNS-Ru) for the degradation of the widely spread antibiotic ciprofloxaci...

Study on Heterogeneous Catalyst Classification Based on CWAO Process of Organic Waste-Water

Catalytic wet air oxidation (CWAO) technology has the characteristics of wide application range, high organic matter removal rate, low secondary pollution and high efficiency, etc., and it has significant effects on the treatment of difficult biodegradable organic waste-water. According to the homogeneity of the phases of the catalytic reaction system, the catalytic reactions can be divided into two categories: homogeneous catalysis and heterogeneous catalysis. The reported catalysts or their active components mainly include four categories: metal salts, metals/supports, oxides/supports, and composite oxides/supports.

Influence of operational parameters and kinetic modelling of catalytic wet air oxidation of phenol by Al/Zr pillared clay catalyst.

Single and mixed oxide Al/Zr-pillared clay (Al/Zr-PILC) catalysts were synthesized and tested for catalytic wet air oxidation (CWAO) of aqueous phenol solution under milder conditions, in a semi-batch reactor. The catalysts were synthesized from natural bentonite clay using ultrasonic treatment during the aging and intercalation steps and were characterized using High Resolution Scanning Electron Microscopy-Energy Dispersive angle X-ray spectrometry (HRSEM-EDX), powder X-ray diffraction (p-XRD), nitrogen adsorption/desorption, Fourier Transforms InfraRed Spectroscopy (FTIR) and zeta potential. Successful pillaring of aluminum and zirconium oxides into the clay was confirmed by p-XRD with increased basal spacing (1.92 nm) and higher specific surface area (230 m2/g). The influence of stirrer speed (200-1000 rpm), catalyst dosage (1-3 g/L), initial pH (1-3), initial phenol concentration (500-1500 mg/L), the effect of temperature (80-150 °C) and oxygen pressure (5-15 bar) was evaluated on phenol conversion and their reaction kinetics. At the optimum conditions of initial pH of 3, catalyst dosage of 2 g/L, initial phenol concentration of 1000 mg/L, reaction temperature of 100 °C, and oxygen pressure of 10 bar, the complete removal of phenol was achieved by Al/Zr-PILC within 120 min. The CWAO process was well-described by the first-order power rate law kinetics model. The apparent activation energy of the reaction calculated by Arrhenius equation was 21.306 kJ/mol.

Bioinspired metal oxide particles as efficient wet air oxidation and photocatalytic oxidation catalysts for the degradation of acetaminophen in aqueous phase

The catalytic performances of the biomimetic metal oxides were tested in photo Fenton-like oxidation and catalytic wet air oxidation processes. Biomimetic copper oxide, iron oxide, and cobalt oxide catalysts were prepared by using pollen grains as biotemplate. The surface characteristics of the biomimetic metal oxides were characterized. SEM micrographs of the biomimetic catalysts demonstrated that pollen grains were successfully mimicked by metal oxide structures. The influences of UV light intensity, catalyst loading, and the initial hydrogen peroxide concentration on acetaminophen degradation were investigated in the photo Fenton-like oxidation process whereas the effects of reaction temperature and catalyst loading were investigated in catalytic wet air oxidation process. The biomimetic copper oxide was the most effective catalyst for the removal of acetaminophen in both of the advanced oxidation processes. The highest acetaminophen degradation efficiency was 86.9% in photo Fenton-like oxidation process when the initial acetaminophen concentration, catalyst loading, and the initial H2O2 concentrations were 10 mg/L, 0.1 g/L and 1 mM, respectively, at room temperature. In the catalytic wet air oxidation process, 98.3% degradation was achieved for the treatment of 100 mg/L acetaminophen solutions at 180 °C and 10 bar by using 1 g/L of catalyst loading at the same reaction time as photo Fenton-like oxidation. Mineralization analysis and the toxicity tests indicated that the biomimetic copper oxide catalysts were promising for the acetaminophen removal in catalytic wet air oxidation processes.

Excellent performance of electro-assisted catalytic wet air oxidation of refractory organic pollutants

Catalytic wet air oxidation (CWAO) is a clean process for the treatment of toxic and/or biorefractory contaminants while it is a challenge to perform the CWAO at room temperature. Herein, we report an electro-assisted CWAO (ECWAO) process using partially oxidized nickel (Ni@NiO) immobilized on a porous graphite felt (GF) as a catalytic anode. Such a process demonstrates extensive effectiveness and good stability in the deep oxidation of various organic pollutants including triclosan (TCS), bisphenol A, ciprofloxacin, sulfamethoxazole, congo red, crystal violent and rodamine B at room temperature. The typical pollutant TCS is rapidly degraded within 105 min with a mineralization efficiency of 86.0 ± 1.4%, at specific energy consumption of 5.3 ± 0.3 kW h kg-TOC−1. NiO is identified as the catalytically active site at which O2 is dissociated and electro-activated to oxidize the TCS at room temperature. The ECWAO process on the anodic Ni@NiO/GF presents a great potential as an environmental-friendly and energy-saving process for treating high concentrations of refractory organic pollutants under ambient condition.

Use of Cu(II)-incorporated zeolite Y for decolourization of dyes in water: a case study with aqueous methylene blue and Congo red

Removal of colour from wastewater discharged by textile and dying industries is a major environmental issue. Catalytic wet air oxidation (CWAO) has emerged as one of the most acceptable, easy and environmental friendly techniques for the treatment of organic pollutants present in wastewater. The present work explores the decolourization of methylene blue and Congo red from aqueous solution by CWAO process using Cu(II)-incorporated zeolite Y as catalyst. The catalyst was prepared by refluxing zeolite Y with aqueous 1 M Cu(NO3)2·3H2O for 6 h. The prepared catalyst was characterized by XRD, FTIR, atomic absorption spectroscopy, SEM, EDAX, BET surface area and pore volume measurement. The oxidation was carried out in a stirred reactor with pH, temperature, amount of catalyst, dye concentration and interaction time as the process variables. Both the oxidation processes follow second-order kinetics. Almost 70% conversion of methylene blue and 90% conversion of Congo red could be achieved under optimum conditions. The results indicate that Cu(II)-incorporated zeolite Y is a promising catalyst for the removal of both cationic and anionic dyes.

Studying the Phenol Degradation in Synthetic Wastewater by Catalytic Wet Air Oxidation Process in Batch Reactor

The current paper studies the viability of using a Batch reactor, by five types of Al-Fe pillared clay that prepared from five regions in Iraq for phenol degradation in synthetic wastewater. The operation condition study through variables in (pH, pressure, temperature, pillared load, phenol load). The findings have illustrated that phenol degradation could be increase via incrementing temperature, pressure, pillared load and degrease in phenol load. Phenol good degradation proportion which was 97 %, has been achieved at optimum proportion (pH= 3.9, temperature = 150 °C, pressure = 3.5 MPa, in addition to phenol concentration = 500 mg/l). The two models power-law and Langmuir−Hinshelwood have been used to study the catalytic kinetics of the phenol degradation. From results shown the activation energy for every response equivalent to (37114.014 j/mol) for Anbar (37795, 48783.9, 36628, 40785 j/mol) for Erbil, Mosul, Baghdad and Basra respectively. It was proved that the reaction in this study is under kinetics control.

Studying the Phenol Degradation in Synthetic Wastewater by Catalytic Wet Air Oxidation Process in Batch Reactor

The current paper studies the viability of using a Batch reactor, by five types of Al-Fe pillared clay that prepared from five regions in Iraq for phenol degradation in synthetic wastewater. The operation condition study through variables in (pH, pressure, temperature, pillared load, phenol load). The findings have illustrated that phenol degradation could be increase via incrementing temperature, pressure, pillared load and degrease in phenol load. Phenol good degradation proportion which was 97 %, has been achieved at optimum proportion (pH= 3.9, temperature = 150 °C, pressure = 3.5 MPa, in addition to phenol concentration = 500 mg/l). The two models power-law and Langmuir−Hinshelwood have been used to study the catalytic kinetics of the phenol degradation. From results shown the activation energy for every response equivalent to (37114.014 j/mol) for Anbar (37795, 48783.9, 36628, 40785 j/mol) for Erbil, Mosul, Baghdad and Basra respectively. It was proved that the reaction in this study is under kinetics control.

Catalytic wet air oxidation of bisphenol A aqueous solution in trickle-bed reactor over single TiO2 polymorphs and their mixtures

In this study, two series of TiO2 polymorphs (anatase (A and A1), rutile (R and R1), brookite (B and B1)) and nanocomposite mixtures of TiO2 polymorphs (anatase A/rutile R (AR), anatase A/TiO2-B polymorph (ATB), anatase A1/rutile R1/brookite B1 (ARB)) were synthesized and tested in the process of catalytic wet air oxidation (CWAO). The goal was total removal of the endocrine-disrupting chemical bisphenol A and its intermediates from a model aqueous solution. TiO2 polymorphs A1, B1 and R1 were prepared with a similar synthesis procedure and from the same TiO2 precursor to investigate the influence of catalyst preparation on their performance. To discover which is the main driving property of the catalyst that enables enhanced BPA degradation and mineralization in the CWAO process, different surface, textural and morphological characterization techniques (XRD, SEM, UV–vis-DRS, FT-IR, TG and N2 sorption) were used. CHNS elemental analysis was applied to reveal which of catalysts is suitable for use in a long-term CWAO process.Characterization and catalytic tests of solids examined show that the key factor enabling enhanced activity in the CWAO process is high BET specific surface area of the catalysts. It was found that low specific surface area of a solid can be compensated either by the presence of an appropriate crystallinity, or improved charge separation. Catalysts A, A1 and ATB showed encouraging results of BPA degradation and mineralization in the CWAO process and would also be appropriate for long-term use, since negligibly small amounts of carbonaceous deposits were accumulated on the surface of these solids during tests performed in the period of 40 h.