Showing papers on "Wet oxidation published in 2018"

Synthesis and application of pillared clay heterogeneous catalysts for wastewater treatment: a review

Abstract: The use of pillared interlayered clays (PILCs) as heterogenous catalysts in wastewater treatment technologies, particularly advanced oxidation processes (AOPs), is gaining popularity for the treatment of refractory wastewater effluents The recent literature involving these solid materials is reviewed, with more focus on studies that aim at reducing the synthesis costs and escalating the synthesis process to industrial scale Their role as active solid materials in the AOPs such as photocatalysis, catalytic wet peroxide oxidation (CWPO), the Fenton process and catalytic wet air oxidation (CWAO) of refractory organic compounds in polluted aqueous streams is also reviewed These processes are evaluated to evidence their main direction for future research, particularly with reference to possible industrial use of these technologies to treat refractory organic wastewater using pillared clay-based catalysts The pillared clay catalysts demonstrate good application prospects for the removal of refractory wastewater effluents using AOP technology The reviewed studies suggest that the photocatalytic process is useful in low concentrations of these compounds, while CWPO, the Fenton process and CWAO are recommended for higher concentrations However, catalyst development to reduce the severity of oxidation reaction conditions, with focus on the low cost, catalyst stability, reusability and environmental friendliness are the key aspects to be addressed by future research work

Phenolic compounds removal by wet air oxidation based processes

Abstract: Wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) are efficient processes to degrade organic pollutants in water. In this paper, we especially reviewed the WAO and CWAO processes for phenolic compounds degradation. It provides a comprehensive introduction to the CWAO processes that could be beneficial to the scientists entering this field of research. The influence of different reaction parameters, such as temperature, oxygen pressure, pH, stirring speed are analyzed in detail; Homogenous catalysts and heterogeneous catalysts including carbon materials, transitional metal oxides and noble metals are extensively discussed, among which Cu based catalysts and Ru catalysts were shown to be the most active. Three different kinds of the reactor implemented for the CWAO (autoclave, packed bed and membrane reactors) are illustrated and compared. To enhance the degradation efficiency and reduce the cost of the CWAO process, biological degradation can be combined to develop an integrated technology.

Integrated oxidation process and biological treatment for highly concentrated petrochemical effluents: A review

Abstract: Biological treatments are the most widely used method in petrochemical complexes to treat wastewaters. However, they are not always effective, especially when refractory nature of certain organic contaminants is introduced into the system. A more promising method, therefore, is the one in which the biological treatment is integrated with the chemical methods where the primary contaminants are first converted into biodegradable compounds before being entered in biological treatment. This paper reviews the application of four oxidation processes that treat petrochemical waste, namely: photo-catalytic oxidation (PCO), Fenton/photo-Fenton, wet air oxidation (WAO), and catalytic wet air oxidation (CWAO), and proposes a new configuration for the treatment of petrochemical wastewaters. This configuration is established based on adding one oxidation process at the effluent of each processing unit before all the effluents are mixed into a single wastewater influent stream for the biological treatment. As the reviewed processes have different capabilities in the degradation of organic compounds and operate under diverse conditions, the selection of the oxidation process best matched to each processing unit will depend on the characteristics of the unit effluent such as organic concentration, toxicity of the effluent to biomass, temperature, and pressure, which will be thoroughly discussed in the paper.

Wet oxidation and absorption procedure for NOx removal

Abstract: The removal of NO x with low oxidation degree, low temperature, and high vapor content from small coal-fired boiler emission through selective catalytic reduction is difficult. This study investigated liquid oxidation and absorption to remove NO x systematically. Thermodynamic calculation showed that the equilibrium constants of the NO oxidation and NO x absorption reaction are high; thus, NO x treatment by liquid oxidation and absorption is feasible. Four oxidants (NaClO2, NaClO, H 2 O2, and KMnO4) and four absorbents (Ca(OH)2, CaCO3, NaOH, and Na2CO3) were used to study the reaction mechanism of the oxidation and absorption processes. Results show that NaClO2 solution is the best oxidant, and the optimum pH value of the oxidation reaction is 5–6. The oxidation degree reaches 100% when the concentration of the NaClO2 solution is 1.0%, and the oxidation degree can still reach approximately 50% when the concentration is 0.1%. Ca(OH)2 slurry has the best absorption performance among the four kinds of absorbents. The NO x removal efficiency of Ca(OH)2 slurry can reach approximately 70% when the oxidation degree is 50%. The removal efficiency is up to 80% when the oxidation degree is 100%.

Efficient degradation of organic phosphorus in glyphosate wastewater by catalytic wet oxidation using modified activated carbon as a catalyst.

Abstract: Glyphosate (PMG) wastewater, which is an organic phosphorus (OP) wastewater containing 200–3000 mg/L PMG, was treated via catalytic wet oxidation (CWO) to degrade PMG to orthophosphate (). The catalysts were activated carbons (ACs) modified by H2O2 oxidation and thermal treatment with ammonia or melamine. The catalysts were characterized using N2 adsorption/desorption, Boehm titration, and X-ray photoelectron spectroscopy. The CWO experiments were performed in a co-current upflow fixed-bed reactor at 110–130°C and under 1.0 MPa. The AC modified by H2O2 and melamine had the highest catalytic activity and had excellent stability in the continuous 55-day test: 100% PMG removal and over 93% OP removal for different samples of real PMG wastewater. More pyrrolic nitrogen, pyridinic nitrogen, and graphitic nitrogen along with quinone oxygen functional groups on the surface of the AC showed higher catalytic activity according to linear fitting results. The identification and quantification of critical react...

Constructing Pd/CeO2/C To Achieve High Leaching Resistance and Activity for Catalytic Wet Air Oxidation of Aqueous Amide

Abstract: Strong metal–support interactions involving electron and oxygen transfer in Pd/C (no leaching but less active) and Pd/CeO2 (active but leaching) catalysts determine their catalytic performance in the catalytic wet air oxidation of amide. To control these two types of interactions, the triple-layer structure Pd/CeO2/C, where Pd is predominantly located on CeO2 and CeO2 on a C support, was designed and prepared. As a result, the electrons could be transferred from carbon to Pd via CeO2 for excellent leaching resistance, while oxygen was transferred from CeO2 to Pd for high oxidation activity. In addition, both of these interactions could be easily adjusted by changing the amount of CeO2.

Synthesis and characterization of an efficient and stable Al/Fe pillared clay catalyst for the catalytic wet air oxidation of phenol

Abstract: A facile method for synthesizing Al/Fe pillared clays (PILCs) from natural bentonite clay, by using ultrasonic treatment during the aging and intercalation steps, has been established. Single metal (Fe-PILCs and Al-PILCs) and mixed metal (Al/Fe-PILCs, with varying compositions of the pillaring precursors) pillared clays were prepared and characterized with a combination of chemical and instrumental methods. The pillared clays were evaluated as catalysts in the catalytic wet air oxidation (CWAO) of phenol and the mixed metal pillared clay catalysts, especially with an Al/Fe ratio of 3 : 1, were found to be highly active and stable, with superior properties such as surface areas, basal spacing, high porosity and thermal stability. The catalysts could also be reused several times without significant loss of activity. The results of the study show that Al/Fe-pillared clay catalysts are effective catalysts for the oxidation of phenol and removal of TOC in aqueous solutions. The main intermediate products in the CWAO of phenol were hydroquinone, pyrocatechol, and benzoquinone and oxalic, formic, malonic, oxalic, malonic and maleic acids.

Wastewater treatment by catalytic wet air oxidation process over Al-Fe pillared clays synthesized using microwave irradiation

Abstract: Microwave irradiation has been used to prepare Al, Fe-pillared clays from a natural Tunisian smectite from the El Hicha deposit (province of Gabes). Chemical analysis, XRD spectra and surface properties evidenced the success of pillaring process. The obtained solids present higher surface area and pore volume than conventionally prepared Al-Fe pillared clays. The main advantages of the microwave methodology are the considerable reduction of the synthesis time and the consumption of water. The microwave-derived Al-Fe pillared clays have been tested for catalytic wet air oxidation (CWAO) of phenol in a stirred tank at 160°C and 20 bar of pure oxygen pressure. These materials are efficient for CWAO of phenol and are highly stable despite the severe operating conditions (acidic media, high pressure, high temperature). The catalyst deactivation was also significantly hindered when compared to conventionally prepared clays. Al-Fe pillared clays prepared by microwave methodology are promising as catalysts for CWAO industrial water treatment.

Catalytic wet oxidation of quinoline over Ru/C catalyst

Abstract: In the present work, catalytic wet air oxidation of the model nitrogenous organic compound quinoline was studied in a slurry reactor over 5% Ru/C catalyst between 423 and 598 K temperature, 0.34 and 2.07 MPa oxygen (O2) partial pressure, and 0.025 and 0.1 kg m−3 catalyst loading. This catalyst was very effective, thereby suggesting its utility for the oxidative destruction of wastewaters polluted by nitrogenous organic compounds. From analysis of the mass transfer effects, it was found that the investigated reaction belonged to the kinetics-controlled reaction regime. Kinetic data on TOC destruction were fitted to a two-step first-order power law model: the first step was fast, whereas the second step was slow. The values of activation energy for the two steps were 29 and 93 kJ mol−1. Among the hyperbolic models tested, the model with a slow surface reaction between chemisorbed TOC and dissociatively adsorbed O2 was most appropriate. The fate of the nitrogen atom in the feed solution and its conversion to nitrite and nitrate ions, ammonia and nicotinic acid was established. Finally, it was corroborated that the reaction was fast when pyrex liner was used inside the reactor because free radicals were not destroyed by the reactor wall.

Flue Gas Denitration by Wet Oxidation Absorption Methods: Current Status and Development

Abstract: Controlling NOx is not only the key to improving air quality but it is also an important issue for air pollution control. In view of the performance of the wet oxidation absorption method ...

Wet Oxidation of Process Waters from the Hydrothermal Carbonization of Sewage Sludge

Abstract: Combing hydrothermal carbonization (HTC) of sewage sludge with wet oxidation of the resulting process waters (PWs) is a favorable economic process leading to a wastewater that is better amenable to biological treatments. Five PWs from HTC of sewage sludge and straw were oxidized with molecular oxygen. A good removal of chemical oxygen demand and dissolved organic carbon was shown. The oxidized waters proved good substrates for a subsequent anaerobic digestion. However, the oxidized PWs were identified as more toxic in germination tests with cress (Lepidium sativum L.) compared to the untreated PWs.

Effects of Wet Oxidation Process on Biochar Surface in Acid and Alkaline Soil Environments

Abstract: Biochar has been studied for remediation of heavy metal-contaminated soils by many researchers. When in external conditions, biochar in soils ages, which can transform its structural properties and adsorption capacity. This study was conducted with two oxidation processes, HNO3/H2SO4 and NaOH/H2O2, to simulate the effects of biochar in acid and alkaline soil conditions. The results show that the oxygen-containing functional groups increased in aged biochar, which led to improve the ratio of oxygen and carbon (O/C). Nitro functional groups were found in the acid-oxidation treated biochar. Destroyed ditches and scars were observed on the surface of aged biochar and resulted in growth in their specific surface area and porosity. Specific surface area increased by 21.1%, 164.9%, and 63.0% for reed-derived biochar treated with water washing, acid oxidation, and basic oxidation, respectively. Greater peaks in the Fourier Transform Infrared Spectroscopy (FTIR) results were found in C–O and O–H on the surface of field-aged biochar. Meanwhile, mappings of energy-dispersive spectroscopy showed that biochar aged in soil was abundant in minerals such as silicon, iron, aluminum, and magnesium. In summary, biochar subjected to wet oxidation aging had an increased capacity to immobilize Cd compared to unaged biochar, and the adsorption capacity of oxidized biochar increased by 28.4% and 13.15% compared to unaged biochar due to improvements in porosity and an increase in functional groups.

Dominant Effect of Support Wettability on the Reaction Pathway for Catalytic Wet Air Oxidation over Pt and Ru Nanoparticle Catalysts

Abstract: Support wettability can play a key role in directing the activation of oxygen during catalytic wet air oxidation over nanoparticle catalysts. When the nanoparticles are composed of metallic Pt, the optimum support is hydrophobic, but when they are ionic Ru, a hydrophilic support is more effective. This reversal in support effect is consistent with two distinct surface pathways: one in which gas-phase O2 is directly adsorbed on the Pt0 surface and the other in which dissolved O2 is activated on RuO2 immersed in the contaminated aqueous phase. The known effects of ceria on these precious metal catalysts are of secondary importance to support wettability.

Wet Air Oxidation of Industrial Lignin Case Study: Influence of the Dissolution Pretreatment and Perovskite-type Oxides

Abstract: Wet air oxidation (WAO) of lignocellulosic biomasses is a promising route for the production of renewable and valuable compounds, involving air as primary oxidant and mild reaction temperatures. In this work, an industrial residue of bioethanol production, steam exploded lignin derived from wheat straw, undergoes a WAO process with the aim to achieve more insights on the process performances in terms of potential yields of aromatic compounds and carboxylic acids (CAs). The experiments were carried out in a pressurized 50 ml batch reactor loaded with water or other aqueous solutions as solvent, the standard conditions were 150 °C of temperature, 20 bar of initial air pressure and 2 h. Afterwards, several solvothermal pretreatments were applied in order to depolymerize and solubilize lignin under inert atmosphere; the residues-free solutions obtained in this way were used as substrate for the WAO reaction. The choice of the pretreatment temperature, solvent alkalinity and presence of perovskite catalysts were evaluated with regard to the mass yields of resulting aromatic compounds and CAs, their carbon content, and the products distribution. Best performance exhibits a lignin dissolution ratio of 53% with 1.3% of yield towards aromatic compounds, where vanillin is the principal product (59.1%), but also the 32% of yield in CAs with glycolic acid as major product (40.9%).

Improved biogas generation from biomethanated distillery wastewater by pre-treatment with catalytic wet air oxidation

Abstract: Catalytic wet air oxidation (CWAO) is a prospective method for the treatment of distillery effluents. In this work, the biodegradability of biomethanated distillery spent wash (BOD5=8100 and COD=40000 mg/L) was improved by oxidation over ferrous sulfate catalyst. The homogeneous CWAO process was optimized by investigating the effects of reaction variables such as temperature (150-225 0C), oxygen partial pressure (0.69-2.07 MPa) and catalyst loading (16-48 mg/L). After oxidation at T=175 0C for 1 h, adsorption over activated carbon (loading 5%) was performed at ambient temperature. As a result, 73% reduction in COD and substantial rise (from 0.2 to 0.45) in the BOD5/COD ratio was observed. This ratio further rose to 0.52, when anaerobic digestion was performed using 1% acclimatized biomass. For every m3 of wastewater, 1.1 Nm3 of biogas was formed (methane 69%). After a final polishing step by aerobic treatment, BOD5/COD was 0.58 and 91% COD was destroyed. Clearly, this work has provided a useful solution t...