Wet Oxidation Research Articles

Efficient removal of piperazine by catalytic wet air oxidation using RuNiCe/γ-Al2O3-activated carbon

The RuNiCe/AAC catalyst represents an efficacious solution for the treatment of industrial wastewater, particularly in instances where the concentration of chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) is elevated.

Improved phenol degradation by catalytic wet air oxidation on the Co3O4 spinel catalysts supported on SBA-15 modified with TiO2

The removal of phenol from aqueous industrial effluents by catalytic wet-air oxidation (CWAO) is a challenging process that requires novel catalysts resistant to leaching of the active phases during residence time in a batch reactor. In this sense, this work demonstrated that this can be archived with the catalyst having the spinel phase Co3O4 supported on mesoporous silica SBA-15 doped with an optimized amount of TiO2 (3 wt%). In the phenol CWAO reaction carried out at 160 °C and 10 bar O2, this best Co3O4/TiO2/SBA-15 catalyst showed an increase of phenol conversion from 49.0 % to 68.3 % and of CO2 selectivity from 87 % to 98 %. The extensive catalyst characterization and overall activity results indicated that this was related to the strength and nature of the acid sites and the oxidation states of the cobalt oxide phases. Combined factors influenced the final behaviour of the catalyst, such as its intrinsic activity, dispersion of the active phase, inhibition of CoSiO4 phase formation, high Lewis acidity and the large amount of active Co3O4 spinel phase. The presence of TiO2 nanoparticles (NPs) decorating the support surface improved the stability of the catalyst by inhibiting the leaching of cobalt species during the reaction. After three reaction cycles, the most efficient Co/3Ti/S15 catalyst showed high CO2 selectivity (∼92.7 %) and low selectivity towards carboxylic acid (∼5.3 %) and polyphenolic compounds (∼2%). It is proposed that surface oxidation is the rate-determining step in the CWAO reaction over TiO2/SBA-15-supported Co3O4 spinel catalysts.

Study on the dispose of landfill leachates over tombarthite catalyst by catalytic wet air oxidation

Study on the dispose of landfill leachates over tombarthite catalyst by catalytic wet air oxidation

In situ growth of an ultrathin Cu/g-C3N4 coating over SBA-15 for catalytic wet air oxidation of pollutants under extremely mild conditions

Catalytic wet air oxidation (CWAO) is a very promising technology for the elimination of various refractory pollutants, but to activate dioxygen under mild conditions is a great challenge.

Advanced Oxidation Processes and Their Application in the Treatment of Different Types of Wastewater Samples

Over the years, urbanization has caused the quality of the water to decline gradually. The production of wastewater has been steadily rising alongside the growth of numerous businesses, including medicines, textiles, processed foods, and many more. Organic molecules from a variety of sources make up the majority of contaminants in wastewater. Some of these chemical molecules are not biodegradable, and it is challenging for anaerobic bacteria to break them down entirely. Because of the molecular structure of them, they can be quite persistent. Several advanced oxidation processes (AOPs) have been studied to remediate wastewater that contains trace organic chemicals (TrOCs). These include ozonation, Fenton oxidation, catalytic wet air oxidation, and photocatalytic oxidation. AOPs have excellent efficiencies, quick oxidation rates, and no secondary pollutants. Each AOP adheres to a particular mechanism in specific circumstances. In this article, we have comprehensively reviewed the underlying mechanism, and factors affecting oxidative pollutant degradation efficiency.

Superhydrophobic, mechanically durable, highly transparent surface covered with CuO/PDMS composite nano-tips using one-step wet oxidation process of Cu/PDMS multilayer

In this study, a mechanically durable, transparent, and superhydrophobic CuO/polydimethylsiloxane (PDMS) composite nano-tips surface was fabricated by a wet oxidation process of a Cu/PDMS multilayer structure. A growth mechanism for the CuO/PDMS composite nano-tips was proposed accounting for the superhydrophobic characteristics of the CuO/PDMS nanostructured surface: During wet oxidation, as CuO nanowires form and grow, the PDMS surface in contact with Cu is dragged up along the CuO nano-tips surface, eventually becoming a CuO/PDMS nanocomposite superhydrophobic surface. The fabricated CuO/PDMS nano-tips surface showed superhydrophobicity with a water contact angle of 158°, and optical transmittance of up to 93.8 % in the 400–700 nm wavelength range. Additionally, the mechanical durability of the fabricated surfaces was also investigated. Repeated touching force (∼1.0 kgf), stretching (∼100 %), and bending (∼100°) 1000-cycle test results confirm the mechanical durability of the CuO/PDMS nanostructured surface. As a mechanically durable, transparent, and superhydrophobic film, the CuO/PDMS nanostructured surface was used as protective film for a touch screen. This study offers novel insights into the durability of artificial superhydrophobic surfaces and the synthesis methods of metal oxide-polymer nanocomposites.

Preparation of porous metakaolin-based alkali-activated materials by microwave curing as supports for non-noble metal catalysts

Generally, alkali activated materials (AAMs) are prepared by curing an alkaline paste via conventional methods such as at room temperature for weeks, even months, or in oven for days to achieve the required properties. In this paper, fast electromagnetic radiation (microwaves) was investigated in detail as an alternative to conventional methods to produce environmentally friendly porous metakaolin-based AAMs as supports for catalysts (MK-AAMs). Hydrogen peroxide was used as a foaming agent to achieve porosity of the porous MK-AAMs. The non-porous MK-AAMs without a foaming agent were used as reference for the porous MK-AAMs. Curing of the MK-AAMs were conducted at room temperature (CU1), in an oven (CU2), and by microwaves (CU3). The specific surface area (SSA) of porous and non-porous MK-AAMs cured via CU1–3 was 36, 49, 90 m2/g and 9.0, 23, 24 m2/g, respectively. The average compressive strength (MPa) was 3.8, 2.7, 2.1 and 8.9, 6.4, 5.2, respectively. The catalytical performance of porous and non- porous MK-AAMs with Cu-catalyst (i.e., Cu-composites) were tested with an aqueous solution of bisphenol A (BPA) in catalytic wet air oxidation (CWAO). After 5 h of oxidation, the highest BPA conversion of 97 % was achieved with the porous Cu-composites. A slight mass loss of 1.5 wt % was observed in the Cu composites due to erosion caused by strong fluid flow in the CWAO experiments. Based on the various analyzes performed, no significant structural or chemical changes were observed in porous and non-porous MK-AAMs regardless of the curing method of CU1–3, which also confirmed that MK-AAMs can be produced by microwaves without losing the desired properties of the materials, such as porosity and mechanical durability.

One-pot synthesis and immobilization of urea-derived graphitic carbon nitride onto ceramic foams for visible-light photocatalytic wet peroxide oxidation in water treatment

A straightforward one-pot in-situ method was employed to successfully obtain urea-derived graphitic carbon nitride (CN) deposited onto a macro-reticulated ceramic alumina-based foam (AF). The resulting CN-coated foams (CN-F) were characterized by different techniques (SEM, N2 adsorption, DRUV–vis, fluorescence spectroscopy), revealing that CN-F structures have visible light absorption and distinctive photoluminescence properties. Moreover, these CN-F materials were investigated for the first time in water treatment, specifically for the degradation of the antibiotic sulfamethoxazole (SMX) in aqueous solutions under visible-LED irradiation and continuous flow mode with total recirculation. The photocatalytic activity of different CN-F was investigated using various CN loads, without or with addition of H2O2 (i.e. Photocatalysis – PC or photocatalytic wet peroxide oxidation – PCWPO, respectively), at different pH (5.0 – 8.5) and a tentative reaction mechanism was described. Thus CN-F with 13.5 mgCN·gAF−1 performed better than with other loads in PCWPO, as demonstrated by a higher conversion of H2O2 and SMX into reaction by-products (short-chain acids and inorganic ions belonging to organic N- or S-containing species). This photocatalyst also succeeded when tested in continuous dead-end mode operation with SMX in ultrapure water or a mixture of 6 pharmaceutical substances (500 ppb each) spiked in a natural river water sample, demonstrating an excellent visible-light PCWPO activity preventing fouling over the catalyst, achieving lower phytotoxicity for the treated water and showing a prolonged stability under 72 h, without CN detachment or any loss of material.

Preparation of a new B-CNTs/PSSF composite catalyst for catalytic wet peroxide oxidation of phenol in structured fixed bed

A new structured catalyst consisting of boron-doped carbon nanotubes growing directly on paper-like stainless steel fibers support (B-CNTs/PSSF) was developed for continuous catalytic wet peroxide oxidation (CWPO) of phenol in a structured fixed bed. Firstly, B-CNTs/PSSF was synthesized by chemical vapor deposition (CVD) with phenyboronic acid as a single precursor and CNTs/PSSF was prepared with camphor for comparison. Secondly, the effects of different deposition temperatures, deposition times, and phenylboronic acid dosages on the morphology and properties of B-CNTs were investigated, respectively. The results verified that under the conditions of deposition temperature of 750 °C, deposition time of 20 min, and phenylboronic acid dosage of 2 g, the B-CNTs/PSSF composite catalyst with uniform growth density, wavy and kinked morphology, abundant oxygen-containing functional groups and defect sites, and boron-doped content of 2.96% was successfully prepared. Then, the performance of B-CNTs/PSSF for continuous CWPO of phenol was evaluated. Catalytic results revealed that the B-CNTs/PSSF showed excellent catalytic activity in phenol degradation within 7 h (phenol conversion reached about 100% and total organic carbon (TOC) conversion was up to 68%). In contrast, the average phenol and TOC conversion of CNTs/PSSF were about 75% and 35%, respectively. It indicated that boron doping endowed CNTs with higher catalytic activity.

Controlled Stepwise Wet Etching of Polycrystalline Mo Nanowires

AbstractWith the persistent downscaling of integrated circuits, molybdenum (Mo) is currently considered a potential replacement for copper (Cu) as a material for metal interconnects. However, fabricating metal nanostructures with critical dimensions of the order of 10 nm and below is challenging. This is because the very high density of grain boundaries (GBs) results in highly non‐uniform surface profiles during direct wet etching. Moreover, wet etching of Mo with conventional aqueous solutions is problematic, as products of Mo oxidation have different solubility in water, which leads to increased surface roughness. Here, a process is shown for achieving a stable and uniform soluble surface layer of Mo oxide by wet oxidation with H2O2 dissolved in IPA at −20 °C. The oxide layer is then selectively dissolved, and by repeating the oxidation and dissolution multiple times, a uniform etch profile is demonstrated with a fine control over the metal recess. Ultimately, this presents a method of precise and uniform wet etching for Mo and other metals needed to fabricate complex nanostructures that are critical in developing next‐generation electronic devices.

Process modelling and techno-economic analysis of anaerobic digestion of sewage sludge integrated with wet oxidation using a gravity pressure vessel and thermal hydrolysis

Anaerobic digestion (AD) of sewage sludge is used to biodegrade sewage sludge into biomethane and digestate. With the addition of thermal processes such as thermal hydrolysis (TH) and wet oxidation (WO), AD biodegradability generally improves. Implementation of additional treatment is challenging due to the limitation in the mass and energy balances. Hence, tools such as process simulation can be utilized to predict the input and output around the process. In addition, an economic analysis needs to be conducted to check the economic feasibility. The techno-economic analysis (TEA), an integrated method to evaluate a process scheme through simulation and subsequent economic analysis, is effective in providing a systematic understanding of economic implications and the feasibility of a process by identifying the bottlenecks and uncertainties that have a significant impact on the technology. TEA of AD, especially incorporating the TH or WO using gravity pressure vessel (GPV) technology, is limited in the literature. A comprehensive TEA of the AD and the pre- and post-treatment schemes can be utilized to determine the most feasible pathway for sludge treatment for implementation in the wastewater industry. In this study, TEA for four different scenarios of AD was conducted using Aspen Plus and economic analysis tools: (1) without any pre- or post-treatment, (2) with TH pre-treatment, (3) with 100 % WO post-treatment, and (4) with 20 % partial wet oxidation (PWO) and acid hydrolysis pre- or post-treatment. A simulation model (GPVM) was developed using Aspen Plus to mimic the GPV reactor. The study outcomes showed that Scenario 3 with 100 % WO post-treatment was the most suitable for processing parameters and sludge treatment cost. The sensitivity analysis concluded that operating cost and plant capacity are the dominant factors that impact the plant feasibility significantly.

Microplastic contamination in commercially packaged edible seaweeds and exposure of the ethnic minority and local population in Mexico

Diet is an important pathway for microplastic exposure. This study examined distinct edible seaweed products sold at ethnic food stores in Mexico for microplastic contamination, as well as the exposure of the Asian ethnic minority and local population to microplastics. Microplastics were extracted from seaweed samples using a wet oxide digestion with hydrogen peroxide followed by zinc chloride density separation. They were subsequently detected, quantified, and the polymer type was determined via microscopic inspection and Fourier transform infrared spectroscopy. Microplastic contamination was detected in all samples, with an average abundance of 24.0 ± 9.4 items g−1. Fibrous-shaped (61 %) and non-colored (57 %) microplastics were prevalent. Microplastics with sizes smaller than 0.2 mm prevailed (60 %), and they have the potential to penetrate gut barriers and endanger human health. Polymers identified consisted of polyethylene-polypropylene, polyamide, cellophane, rayon, and polyethylene terephthalate. According to pollution load index values, seaweed samples were minimally contaminated with microplastics, with values ranging between 3.7 and 6.0. The estimated yearly intake of microplastic from seaweed consumption by the South Korean and Chinese populations in Mexico was 5.8 × 104 ± 2.3 × 104 and 5.7 × 104 ± 4.9 × 104, respectively. This study's findings highlight the importance of improved control measures for minimizing microplastics in foods for export.

Application of MoO3 as an efficient catalyst for wet air oxidation treatment of pharmaceutical wastewater (Experimental and DFT study)

Application of MoO3 as an efficient catalyst for wet air oxidation treatment of pharmaceutical wastewater (Experimental and DFT study)

HF Compatibility Study on KrF and I-Line System Resist

Advance nanoscale patterning technology requires high resolution lithography, from ultraviolet (UV, i-line system) to deep ultraviolet (DUV, KrF system) until extreme ultraviolet (EUV), but the compatibility study of new resist types and wet etchant is lacking. The compatibility is defined as the duration of a photoresist being able to withstand in wet oxide etchant. Poor compatibility has potential resist lifting and/or penetration during wet etch process, which causes electronic device performance drifting. Currently, wet oxide etching is widely used in the gate oxide wet etch using patterned resist, as well as in the backside oxide removal with blanket resist front-side coverage. In this paper, we explore the compatibility and understand the impact factors, based on commonly used resist (i.e., KrF and i-line system resist) and wet etch chemicals (i.e. HF based etchant) in industry. It is important to do a quick and straightforward compatibility check before we implement new resists on actual product wafers, to prevent poor compatibility caused resist lifting and/or penetration during wet etch process. Based on oxide thickness check and resist lifting phenomena, it is found that resist baking condition, resist polymer type, resist composition, and lag time from resist coating to wet oxide etching all will affect the compatibility between HF based etchant and resist.

Enhanced NOx absorption in flue gas by wet oxidation of red mud and phosphorus sludge

The environmental problem caused by industrial emissions of NOx has been studied in the past dacades. In this study, red mud coupling with phosphorus sludge were used to enhance the solution to absorb NOx from the flue gas. Firstly, red mud reacted with the binder silicic acid in the phosphorus sludge, destroying the emulsion structure of the phosphorus sludge. Then, the P4 in the phosphorus sludge is completely released, and the P4 reacted with O2 in the flue gas to produce O3 and O. NO and NO2 contained in the flue gas reacted with the active O and O3 to produce high-valent NOx, such as NO3, N2O5. At last, the mixed slurry of red mud and phosphorus sludge absorbed the high-valent NOx, resulting in the formation of Ca5(PO4)3F along with HNO3. Using phosphorus sludge to produce O3 in the reaction process can reduce the production cost of O3 and achieve waste utilization. Meanwhile, the interaction between red mud and phosphorus sludge can promote phosphorus sludge to produce O3 and remove F- from phosphorus sludge, as well as avoid the problem of secondary pollution. This study should be helpful for red mud and phosphorus sludge utilization and flue gas denitration.

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%).

Sustainability assessment of lignocellulosic biorefineries based on sequential pretreatments

AbstractBACKGROUNDPretreatments are critical in biorefinery analysis, affecting further reactions and downstream processes. However, most pretreatments are studied and optimized as single‐step schemes, focusing on maximizing a side stream. Sequential pretreatments have been shown to improve the selective isolation of platforms for further valorization. However, pretreatment performance can consider not only technical but also economic, environmental, and social concerns. This work assessed the sustainability of sequential pretreatments in rice husk‐based biorefineries.RESULTSFour biorefinery scenarios were designed, simulated, and assessed considering dilute acid and wet air oxidation pretreatment technologies in sequential and single‐step schemes. Economic feasibility was demonstrated for sequential pretreatments when phenolic compounds are contemplated, generating gross incomes of 4.76 M‐USD yr−1. From an environmental perspective, the rice supply chain generated a carbon footprint of 2.17 kg CO2 eq kg−1 of rice husks, where the producer link is the largest contributor due to fertilizer use. Likewise, it was shown that supplying energy demands using black liquor as fuel relieves operating costs and reduces the carbon footprint. The social dimension showed that between 69 and 77 jobs could be generated annually along the value chain and the biorefinery schemes. However, biorefineries have a high risk due to the high volume of cooling water.CONCLUSIONSAll dimensions were weighted to calculate a sustainability index, where it was concluded that sequential pretreatment biorefineries improved sustainability against the single‐step schemes. However, the scenario of valorization of the three fractions (Sc1) is the best scheme to be implemented as it has always demonstrated economic feasibility. © 2023 Society of Chemical Industry (SCI).

Chemically activated hydrochars as catalysts for the treatment of HTC liquor by catalytic wet air oxidation

Hydrothermal carbonization (HTC) is a highly efficient and valuable technology for treating wet solid wastes and producing solid carbon-based materials named hydrochar. In this work, a hydrochar coming from the HTC of an anaerobic digestion sludge of wastewater treatment plant was used to assess the influence of several activation agents, a base (KOH) and different chloride salts (FeCl3, ZnCl2, and CuCl2) with the exact molar quantities, to develop materials with enhanced surface area and potential inclusion of metal active species for application in wet air oxidation processes. The KOH as an activating agent increased the surface area of hydrochar up to ca. 1000 m2/g of BET surface area. The employment of CuCl2 and FeCl3 as activating agents allows Cu- and Fe-rich doped materials of remarkable surface areas with 49.1 and 42.5 wt% of each metal, respectively. Likewise, the catalytic behavior of the different synthesized carbon-based materials as metal-free and metal-doped catalysts was evaluated for the Catalytic Wet Air Oxidation (CWAO) of a HTC aqueous liquor from a HTC process of animal manure to produce a valuable stream of higher biochemical methane potential in anaerobic digestion. CWAO effluents increased the proportion of carboxylic acids as final by-products due to the oxidation of more complex organic compounds of the initial effluent (ketones, phenols, aromatics and olefins). The CWAO treatments improve the anaerobic digestion rate in biochemical methane potential tests, although the methane production was limited by the lower TOC concentration of the treated streams after CWAO. This research contributes to developing sustainable and efficient strategies for the HTC-liquor treatment, using its solid hydrochar as catalysts, closing the loop of a Circular Economy.

Improvement of the activity of a new nano magnetic titanium catalyst by using alkaline for refinery wastewater oxidation treatment in a batch baffled reactor

In order to reach pure water, it is essential to develop new technology for eliminating phenol from the wastewater. In this work, a nano-composite catalyst (5 % Fe2O3 + 10 % alkaline/TiO2) has been prepared and its performance to enhance the activity of catalytic wet peroxide oxidation (CWPO) process for removal of phenol has been examined. The new nano-composite catalyst is tested by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Energy dispersive X-ray (EDX) and scanning-electron-microscopy (SEM). A baffled batch reactor is used to evaluate the activity of new nano-composite catalyst at various temperatures (30–80 °C) and reaction times (30–90 min), utilizing hydrogen peroxide (H2O2) as oxidizing agent. The new design of digital baffled batch reactor prevents the fuel swirling, thus improving agitation. The experimental data of the CWPO technology prove that the best phenol removal (95.931 %) was carried out at 80 °C, the reaction time of 90 min, and in the presence of nano-composite catalyst ((5 % Fe2O3 + 10 % alkaline)/TiO2). Modeling investigation for the CWPO is examined in order to estimate the better process kinetic. The simulation technique explains dramatic agreement in comparing with the experimental data (error < 5 %). The optimal CWPO conditions in order to achieve pure water (phenol removal >99 %) are at reaction time of 198 min, process temperature of 85 °C, and initial phenol concentration of 1000 ppm.

Effects of reaction conditions on the wet oxidation of excess sludge from the caprolactam wastewater treatment process.

In this study, wet oxidation of excess sludge from the caprolactam wastewater treatment process was investigated. The effects of reaction conditions, including sludge concentration, the amount of sludge, reaction temperature and time and the oxygen supply amount, were discussed. The highest removal rates of chemical oxygen demand (COD) and volatile suspended solid (VSS) that can be attained at 78.6 and 89.3% were acquired separately under 260 °C for 60 min with an initial oxygen gas pressure of 1.3 MPa. The sludge was hydrolyzed and oxidized under hydrothermal conditions, producing small molecule organic acids, such as acetic, formic and oxalic acids, as the main products, which could be used as carbon sources for wastewater treatment. These results indicated that wet oxidation provides a favourable and feasible alternative method for the treatment of excess sludge from the coal chemical industry.