Showing papers on "Wet oxidation published in 2021"

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

Abstract: 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.

Long-term oxidation behavior of C/SiC-SiBCN composites in wet oxygen environment

Abstract: Polymer derived SiBCN ceramic was introduced into carbon fiber reinforced SiC composites to prepare C/SiC-SiBCN composites. Weight change and flexural strength of the samples after oxidation at different temperatures and in different atmospheres were tested up to 100 h to investigate their wet oxidation behavior. It was found that the stable silicoboron glassy self-healing phase formed from the oxidation of SiBCN had favorable oxidation resistance in wet oxygen atmosphere. And the SiC-SiBCN matrix can provide about 50 h of protection for carbon fiber in wet oxygen. Besides, the influence of temperature on the oxidation behavior of C/SiC-SiBCN composites were much related to the release speed of gas products (B2O3, HBO2 and Si(OH)4). And the oxidation mechanism of SiC/SiC-SiBCN composites were further explained by the comparation with C/SiC-SiBCN composites.

Characterization of value-added chemicals derived from the thermal hydrolysis and wet oxidation of sewage sludge

Abstract: We evaluated the effect of hydrothermal pretreatments, i.e., thermal hydrolysis (TH) and wet oxidation (WO) on sewage sludge to promote resource recovery. The hydrothermal processes were performed under mild temperature conditions (140°C–180°C) in a high pressure reactor. The reaction in acidic environment (pH = 3.3) suppressed the formation of the color imparting undesirable Maillard’s compounds. The oxidative conditions resulted in higher volatile suspended solids (VSS) reduction (∼90%) and chemical oxygen demand (COD) removal (∼55%) whereas TH caused VSS and COD removals of ∼65% and ∼27%, respectively at a temperature of 180°C. During TH, the concentrations of carbohydrates and proteins in treated sludge were 400–1000 mg/L and 1500–2500 mg/L, respectively. Whereas, WO resulted in solids solubilization followed by oxidative degradation of organics into smaller molecular weight carboxylic acids such as acetic acid (∼400–500 mg/L). Based on sludge transformation products generated during the hydrothermal pretreatments, simplified reaction pathways are predicted. Finally, the application of macromolecules (such as proteins), VFAs and nutrients present in the treated sludge are also discussed. The future study should focus on the development of economic recovery methods for various value-added compounds.

Abatement of 1,2,4-trichlorobencene by wet peroxide oxidation catalysed by goethite and enhanced by visible led light at neutral ph

Abstract: There is significant environmental concern about chlorinated organic compounds (COCs) in wastewater, surface water, and groundwater due to their low biodegradability and high persistence. In this work, 1,2,4-trichlorobenzene (124-TCB) was selected as a model compound to study its abatement using wet peroxide oxidation at neutral pH with goethite as a heterogeneous catalyst, which was enhanced with visible monochromatic light-emitting diode (LED) light (470 nm). A systematic study of the main operating variables (oxidant and catalyst concentration and irradiance) was accomplished to investigate their influence in the abatement of 124-TCB in water. The reaction was carried out in a well-mixed reactor of glass irradiated by a visible LED light. The hydrogen peroxide concentration was tested from 0 to 18 mM, the goethite concentration within the range 0.1–1.0 g·L−1 and the irradiance from 0.10 to 0.24 W·cm−2 at neutral pH. It was found that this oxidation method is a very efficient technique to abate 124-TCB, reaching a pollutant conversion of 0.9 when using 0.1 g·L−1 of goethite, 18 mM of H2O2, and 0.24 of W·cm−2. Moreover, the system performance was evaluated using the photonic efficiency (ratio of the moles of 124-TCB abated and the moles of photons arriving at the reactor window). The maximum photonic efficiencies were obtained using the lowest lamp powers and moderate to high catalyst loads.

Catalytic wet air oxidation of phenol: Review of the reaction mechanism, kinetics, and CFD modeling

Abstract: Advanced oxidation processes, specifically catalytic wet air oxidation (CWAO), are considered as useful and robust methods for the treatment of refractory organic compounds such as phenol in wastew...

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

Abstract: 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.

The Wet-Oxidation of a Cu(111) Foil Coated by Single Crystal Graphene.

Abstract: The wet-oxidation of a single crystal Cu(111) foil is studied by growing single crystal graphene islands on it followed by soaking it in water. 18 O-labeled water is also used; the oxygen atoms in the formed copper oxides in both the bare and graphene-coated Cu regions come from water. The oxidation of the graphene-coated Cu regions is enabled by water diffusing from the edges of graphene along the bunched Cu steps, and along some graphene ripples where such are present. This interfacial diffusion of water can occur because of the separation between the graphene and the "step corner" of bunched Cu steps. Density functional theory simulations suggest that adsorption of water in this gap is thermodynamically stable; the "step-induced-diffusion model" also applies to graphene-coated Cu surfaces of various other crystal orientations. Since bunched Cu steps and graphene ripples are diffusion pathways for water, ripple-free graphene is prepared on ultrasmooth Cu(111) surfaces and it is found that the graphene completely shields the underlying Cu from wet-oxidation. This study greatly deepens the understanding of how a graphene-coated copper surface is oxidized, and shows that graphene completely prevents the oxidation when that surface is ultrasmooth and when the graphene has no ripples or wrinkles.

Behavior of Silicon Carbide Materials under Dry to Hydrothermal Conditions

Abstract: Silicon carbide materials are excellent candidates for high-performance applications due to their outstanding thermomechanical properties and their strong corrosion resistance. SiC materials can be processed in various forms, from nanomaterials to continuous fibers. Common applications of SiC materials include the aerospace and nuclear fields, where the material is used in severely oxidative environments. Therefore, it is important to understand the kinetics of SiC oxidation and the parameters influencing them. The first part of this review focuses on the oxidation of SiC in dry air according to the Deal and Grove model showing that the oxidation behavior of SiC depends on the temperature and the time of oxidation. The oxidation rate can also be accelerated with the presence of H2O in the system due to its diffusion through the oxide scales. Therefore, wet oxidation is studied in the second part. The third part details the effect of hydrothermal media on the SiC materials that has been explained by different models, namely Yoshimura (1986), Hirayama (1989) and Allongue (1992). The last part of this review focuses on the hydrothermal corrosion of SiC materials from an application point of view and determine whether it is beneficial (manufacturing of materials) or detrimental (use of SiC in latest nuclear reactors).

Noble metal free catalyst with High activity and stability for catalytic wet air oxidation of N, N-dimethylformamide

Abstract: In this study, we propose a simple strategy to prepare a noble-metal free catalyst, i.e., CeO2 supported on multi-wall carbon nanotube (CNTs). CNTs are treated by acid before the loading of CeO2, which is vital to the performance of catalysts. CeO2 on treated CNTs (CNTs-M) presents much higher TOC conversion and stability when compared with CeO2 on raw CNTs (CNTs-Raw). Kinetic study indicates that acid treatment greatly decreases the activation of the DMF oxidation. To investigate these phenomena, detailed characterizations are performed. We found that the acid treatment generated surface functional groups on CNTs which leads to the strong interaction between CNTs and CeO2. As a result, CeO2 on CNTs-M obtained better dispersion and higher amount of surface oxygen, which accounts for its superior performance.

Nitrogen-doped char as a catalyst for wet oxidation of phenol-contaminated water

Abstract: Catalytic wet oxidation (CWO) of aqueous effluents rich in organic compounds is a very promising technology for the treatment of liquid wastes from biomass conversion processes. CWO reactions occur through the formation of free radical species, produced in the presence of an oxidant, which act on organic contaminates in the effluent. Although the reaction is well known, there exists a lack of affordable catalysts to conduct this process at the lower temperatures and pressures in novel bioenergy processes. This study assessed the catalytic effect of nitrogen-doped chars as such an option. Phenol in aqueous solution was used as a model waste effluent. Treatment was conducted at moderate temperatures (190 to 260 °C), oxygen partial pressure of 1 MPa, and reaction times of 15, 30, and 45 min in stainless steel and glass-lined tube reactors. High pressure liquid chromatography (HPLC) analyses of the products quantified phenol and by-product concentrations used in the calculation of reaction activation energy. The char catalyst was studied by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) in order to gain insight into its structure and surface composition. The results indicate that nitrogen-doped char catalysts accelerate the oxidation of phenol by decreasing its reaction activation energy from 82.2 kJ/mol (non-catalyzed) to 40.4 kJ/mol (catalyzed). An analysis from first principles using density functional theory (DFT) was conducted to ascertain which N functional group has the most significant impact on free radical formation in the presence of oxygen. Among all the N functional groups studied, the dipyridinic functional groups showed the most promising characteristics to facilitate the formation of hydroxyl free radicals.

A review on physiochemical treatment of sulfolane in aqueous media

Abstract: Sulfolane is an organic solvent that is primarily used in petrochemical industries to remove acid compounds from sour natural gas. In recent years, sulfolane has been reported to contaminate ground and surface waters around many gas processing plant sites in North America. It is highly soluble in water and has poor adsorption on soil, which makes it easy for offsite migration in the subsurface. Numerous methods have been developed and applied in treating sulfolane contaminated waters. In early years, the degradation of sulfolane had focused on biological processes, which utilized microbial metabolism under aerobic conditions. However, biological processes require relatively longer treatment times (>10 h) and are highly dependent on environmental factors such as temperature, dissolved oxygen and presence of nutrients. Recently, to overcome these limitations, abiotic technologies including advanced oxidation processes and activated carbon adsorption have been developed to treat sulfolane impacted water. Both abiotic technologies can degrade or remove sulfolane from water much faster than biological processes. In this review paper, the advances on treating sulfolane impacted water using advanced oxidation processes and activated carbon adsorption is presented. The advanced oxidation processes that have been reported in literature and reviewed here for treating sulfolane include ultraviolet-C (UVC)/H2O2, UVC/O3, UVC/persulfate, TiO2 photocatalysis, Fenton reaction, catalytic ozonation, wet oxidation and others.

Low-temperature oxidation behavior and mechanism of semi-dry desulfurization ash from iron ore sintering flue gas

Abstract: The low-temperature wet oxidation behavior of semi-dry desulfurization ash from iron ore sintering flue gas in ammonium citrate solution was investigated for efficiently utilizing the low-quality desulfurization ash. The effects of the ammonium citrate concentration, oxidation temperature, solid/liquid ratio, and oxidation time on the wet oxidation behavior of desulfurization ash were studied. Simultaneously, the oxidation mechanism of desulfurization ash was revealed by means of X-ray diffraction, Zeta electric resistance, and X-ray photoelectron spectroscopy (XPS) analysis. Under the optimal conditions with ammonium citrate, the oxidation ratio of CaSO3 was up to the maximum value (98.49%), while that of CaSO3 was only 8.92% without ammonium citrate. Zeta electric resistance and XPS results indicate that the dissolution process of CaSO3 could be significantly promoted by complexation derived from the ammonium citrate hydrolysis. As a result, the oxidation process of CaSO3 was transformed from particle oxidation to SO 3 2− ion oxidation, realizing the rapid transformation of desulfurization ash from CaSO3 to CaSO4 at low temperature. It provides a reference for the application of semi-dry desulfurization ash and contributes to sustainable management for semi-dry desulfurization ash.

Heteroatom (N, S) Co-Doped CNTs in the Phenol Oxidation by Catalytic Wet Air Oxidation

Abstract: The N, S-co-doping of commercial carbon nanotubes (CNTs) was performed by a solvent-free mechanothermal approach using thiourea. CNTs were mixed with the N, S-dual precursor in a ball-milling apparatus, and further thermally treated under inert atmosphere between 600 and 1000 °C. The influence of the temperature applied during the thermal procedure was investigated. Textural properties of the materials were not significantly affected either by the mechanical step or by the heating phase. Concerning surface chemistry, the developed methodology allowed the incorporation of N (up to 1.43%) and S (up to 1.3%), distributed by pyridinic (N6), pyrrolic (N5), and quaternary N (NQ) groups, and C–S–, C–S–O, and sulphate functionalities. Catalytic activities of the N, S-doped CNTs were evaluated for the catalytic wet air oxidation (CWAO) of phenol in a batch mode. Although the samples revealed a similar catalytic activity for phenol degradation, a higher total organic carbon removal (60%) was observed using the sample thermally treated at 900 °C. The improved catalytic activity of this sample was attributed to the presence of N6, NQ, and thiophenic groups. This sample was further tested in the oxidation of phenol under a continuous mode, at around 30% of conversion being achieved in the steady-state.