Showing papers on "Wet oxidation published in 2016"

A Short Review of Techniques for Phenol Removal from Wastewater

Abstract: Phenolic compounds are priority pollutants with high toxicity even at low concentrations. In this review, the efficiency of both conventional and advanced treatment methods is discussed. The applicability of these treatments with phenol and some common derivatives is compared. Conventional treatments such as distillation, absorption, extraction, chemical oxidation, and electrochemical oxidation show high efficiencies with various phenolic compounds, while advanced treatments such as Fenton processes, ozonation, wet air oxidation, and photochemical treatment use less chemicals compared to the conventional ones but have high energy costs. Compared to physico-chemical treatment, biological treatment is environmentally friendly and energy saving, but it cannot treat high concentration pollutants. Enzymatic treatment has proven to be the best way to treat various phenolic compounds under mild conditions with different enzymes such as peroxidases, laccases, and tyrosinases. This review covers papers from 2013 through January 2016.

Highly active N-doped carbon nanotubes prepared by an easy ball milling method for advanced oxidation processes

Abstract: The performance of novel N-doped carbon materials prepared by an easy ball milling method was evaluated in two distinct advanced oxidation processes (AOPs): catalytic wet air oxidation (CWAO) and catalytic ozonation (COZ), using oxalic acid as model pollutant. The ball milling method allows the incorporation of large amounts of N-groups onto the surface of carbon nanotubes, namely pyridine-like N atoms (N-6), pyrrole-like N atoms (N-5) and quaternary nitrogen (N-Q), resulting in highly active catalysts for the oxidation of oxalic acid by both AOPs. The material prepared by ball milling with melamine without solvent is the most promising sample, combining an easy preparation with high amount of N-functionalities. Under the operation conditions used, oxalic acid was completely mineralized in 5 min by CWAO and in 4 h by COZ. The novel metal-free catalyst developed by this easy ball milling method demonstrated to be effective, confirming that this solvent-free methodology is quite adequate for the preparation of N-doped carbon materials with enhanced properties for the mineralization of organic pollutants by the studied processes.

Bimetallic Ru–Cu as a highly active, selective and stable catalyst for catalytic wet oxidation of aqueous ammonia to nitrogen

Abstract: Ru/C, Cu/C and bimetallic Ru–Cu/C catalysts are prepared via chemical reduction methods and investigated for catalytic wet oxidation of aqueous ammonia to nitrogen. It is found that the as-prepared bimetallic Ru–Cu/C catalyst is very active and selective as well stable as for selective oxidation of aqueous ammonia toward nitrogen at rather mild conditions. The results show that the Ru–Cu/C catalyst is much more efficient especially stable than the corresponding monometallic Ru/C and Cu/C catalysts, indicating the synergistic effect of Cu and Ru. These catalysts are characterized by XRD, XPS, TEM, and H 2 -TPR, and the results are revealed that there is strong interaction between Ru and Cu over Ru–Cu/C catalysts and the co-presence of Ru and Cu can effectively adjust the reactivity and converge of oxygen species as well as protect the Ru and Cu from leaching. The strong interaction, synergistic effect, proper oxygen nature and ability against leaching could be attributed to the excellent catalytic property of Ru–Cu/C catalyst.

Wet Air Oxidation of Hydrothermal Carbonization (HTC) Process Liquid

Abstract: Hydrothermal carbonization (HTC) is a promising thermochemical treatment of wet biomass The byproduct HTC process liquid often contains a very high total organic carbon (TOC) Various toxic organic compounds (eg, phenol, furfural, 5-HMF, etc) can be found in HTC process liquid As a result, the HTC process liquid often requires further treatment prior to discharge into the environment In this study, wet air oxidation (WAO) is applied to process liquid produced from HTC of dairy manure and wastewater biosolids Different oxygen loadings (25 and 50 atm partial pressure) were charged for WAO at 260 °C for 30 min Furthermore, the oxidation capability of copper oxide (CuO) was evaluated at the same temperature and time In all cases, the resulting liquid product was clear and has reduced TOC With an increase in oxygen partial pressure, TOC is reduced up to 60% compared to the control run and 74% compared to the original HTC process liquid The primary products in the WAO liquid product are short chain o

Impact of Precipitants on the Structure and Properties of Fe-Co-Ce Composite Catalysts

Abstract: Fe-Co-Ce composite catalysts were prepared by coprecipitation method using CONH22, NaOH, NH4HCO3, and NH3·H2O as precipitant agents. The effects of the precipitant agents on the physicochemical properties of the Fe-Co-Ce based catalysts were investigated by SEM, TEM, BET, TG-DTA, and XRD. It was found that the precipitant agents remarkably influenced the morphology and particle size of the catalysts and affected the COD removal efficiency, decolorization rate, and pH of methyl orange for catalytic wet air oxidation CWAO. The specific surface area of the Fe-Co-Ce composite catalysts successively decreased in the order of NH3·H2O, NH4HCO3, NaOH, and CONH22, which correlated to an increasing particle size that increased for each catalyst. For the CWAO of a methyl orange aqueous solutions, the effects of precipitant agents NH3·H2O and NaOH were superior to those of CONH22 and NH4HCO3. The catalyst prepared using NH3·H2O as the precipitant agent was mostly composed of Fe2O3, CoO, and CeO2. The COD removal efficiency of methyl orange aqueous solution for NH3·H2O reached 92.9% in the catalytic wet air oxidation. Such a catalytic property was maintained for six runs.

Catalytic wet peroxide oxidation of a reactive dye by magnetic copper ferrite nanoparticles.

Abstract: The aim of this work was to study copper ferrite nanoparticles (CFNs) as a catalyst in catalytic wet peroxide oxidation of C.I. Reactive Red 120 (RR120) as a model organic pollutant in aqueous solutions. CFNs were synthesized by polymeric precursor method and characterized with various techniques (e.g. XRD, FTIR, SEM, and TEM and VSM). The prepared nanoparticles had the nanocrystalline pure single-phase structure. Values of saturation magnetization, remanent magnetization and coersivity were found to be 6.5 emu/g, 2.1 emu/g and 380 Oe, respectively. The degradation of RR120 was investigated in the presence of hydrogen peroxide and CFNs at various temperatures and pHs. The most effective RR120 degradation was achieved at pH 3 and 75 °C. The catalyst was recovered and reused 6 times without noticeable loss of activity.

Unprecedented Catalytic Wet Oxidation of Glucose to Succinic Acid Induced by the Addition of n‐Butylamine to a RuIII Catalyst

Abstract: A new pathway for the catalytic wet oxidation (CWO) of glucose is described. Employing a cationic Ru@MNP catalyst, succinic acid is obtained in unprecedently high yield (87.5 %) for a >99.9 % conversion of glucose, most probably through a free radical mechanism combined with catalytic didehydroxylation of vicinal diols and hydrogenation of the resulted unsaturated intermediate.

Fermentative Hydrogen Production from Waste Sludge Solubilized by Low-Pressure Wet Oxidation Treatment

Abstract: The low-pressure wet oxidation was used to solubilize the waste-activated sludge for recovering the carbon source, and the treated sludge was applied for the fermentative hydrogen production. The experimental results showed that, after low-pressure oxidation treatment, the concentration of soluble chemical oxygen demand (SCOD), polysaccharides, and protein present in the liquid phase was increased by 2.0, 2.2, and 102.5 times, respectively. Bio-hydrogen production was successfully achieved using solubilized sludge as the substrate. Through comparison of the hydrogen production from glucose, the treated sludge, and the mixture of the sludge and glucose, it was found that the hydrogen yield of tests using different substrates showed a positive relation with the ratio of acetic acid/butyric acid in soluble metabolites and the ratio of polysaccharides/SCOD in substrates. It can be concluded that the waste-activated sludge treated by low-pressure wet oxidation can be used as low-cost substrate for bio-hydrogen...

Catalytic wet oxidation of phenol with Fe–ZSM-5 catalysts

Abstract: Fe–ZSM-5 and Fe2O3/ZSM-5 zeolite catalysts were prepared and tested for catalytic wet oxidation of phenol. First, Fe–ZSM-5 and Fe2O3/ZSM-5 zeolite catalysts were prepared by the hydrothermal synthetic and incipient wetness impregnation method and characterized to determine the framework and extra-framework Fe3+ species. Second, the catalytic properties of Fe–ZSM-5 in the oxidation of phenol were systematically studied to determine the optimum technological parameters by investigating the effects of reaction temperature, pH, catalyst concentration and stirring rate on the conversion of phenol. In addition to the phenol conversion, selectivity to CO2 and concentration of aromatic intermediates in the oxidation of phenol with the two catalysts were analyzed under the same optimum conditions. Leaching of iron from the catalysts, as well as the catalytic stability of Fe–ZSM-5, was also tested. Finally, the kinetics of catalytic wet oxidation of phenol with Fe–ZSM-5 was studied. The experimental results showed that both the framework and extra-framework Fe3+ species were present in Fe–ZSM-5. The oxidation reaction with Fe–ZSM-5 was performed well at a temperature of 70 °C, pH of 4, catalyst concentration of 2.5 g L−1, stirring rate of 400 rpm and reaction time of 180 min. The conversion of phenol reached 94.1%. From the catalytic results of the two catalysts, it can be concluded that the framework Fe3+ species may be more efficient in phenol oxidation than the extra-framework Fe3+ species, the stability of Fe–ZSM-5 was better and a relatively low decrease in activity could be found after three consecutive runs. The activation energy of 27.42 kJ mol−1 was obtained for phenol oxidation with Fe–ZSM-5.

Study on Catalytic Wet Air Oxidation Process for Phenol Degradation in Synthetic Wastewater Using Trickle Bed Reactor

Abstract: The present work aims to study the feasibility of utilizing a trickle bed reactor, packed with activated carbon catalyst, for phenol degradation in synthetic wastewater. Effect of operating variables (e.g., pH, pressure, temperature, gas flow rate, liquid flow rate, and flow mode) on the performance of the trickle bed reactor was investigated and optimized. Results showed that phenol degradation would be enhanced by increasing temperature, pressure, and gas flow rate, while initial concentration of phenol and liquid flow rate give a different trend. It was found that down-flow mode exhibits better performance than up-flow mode. High degradation rate of phenol of about 97 % was obtained at optimum conditions (liquid space time = 0.143 h, temperature = 160 °C, oxygen partial pressure = 0.9 MPa, and phenol concentration = 5 mg/l). Reaction kinetics including effects of catalyst deactivation on the oxidation process was investigated. Results showed that the oxidation process behaves as pseudo-first-order reaction with respect to phenol concentration, and 0.6 with respect to oxygen solubility. Activation energy is 77.7 kJ/mol. and reaction rate constant is equal to $${1.826 \times 10^{9}{l}/{kg}_{\rm cat}}$$ h. However, when catalyst deactivation was taken into account, the reaction rate constant and activation energy were $${2.9 \times 10^{11} {l}/{kg}_{\rm cat}}$$ h and 114.43 kJ/mol, respectively, and the oxygen order was equal to 1.4. The calculated kinetic parameters were compared with the data reported in the literature.

The role of dissolved oxygen in supercritical water in the oxidation of ferritic–martensitic steel

Abstract: To assess the role of dissolved oxygen in supercritical water on the growth processes of oxide scales, a marker experiment of ferritic–martensitic steel was performed by exposing to supercritical water (H 2 16 O) containing marked 18 O 2 at 600 °C under 25 MPa. The oxide scale was analysed by using Secondary Ion Mass Spectrometry (SIMS). The oxygen isotope profile shows that dissolved oxygen and supercritical water react with metals simultaneously. Dissolved oxygen changes the oxidation/reduction potential of supercritical water leading to an increase in the oxidation rate. The oxidation rate increases with increase in dissolved oxygen content in supercritical water. The mechanism of the effect of dissolved oxygen on oxidation is discussed.

Removal of phenol from water by catalytic wet air oxidation using carbon bead – supported iron nanoparticle – containing carbon nanofibers in an especially configured reactor

Abstract: Catalytic wet air oxidation (CWAO) is extensively used for the destruction of organic contaminants in wastewater. The present study describes the removal of phenol from water, used as a model organic contaminant, by CWAO with iron (Fe) metal nanoparticles (NPs)-doped carbon microbeads (∼0.6 mm) as the catalyst. The Fe-carbon composite was prepared by the carbonization and activation of the phenolic precursor-based polymeric beads in which the Fe NPs were in-situ added during the polymerization stage. Carbon nanofibers (CNFs) were grown on the carbon microbead substrate by catalytic chemical vapor deposition with acetylene as the carbon source. Oxidation reactions were carried out under different operating conditions in a high pressure-stirred reactor, viz., temperature, catalyst loading, and speed of the stirrer. The reactor was fitted with an especially configured impeller cum catalyst basket which held the prepared CNF-decorated Fe-doped carbon beads. The data showed an efficient remediation of the phenol-laden water, indicating the potential scale-up of the proposed CWAO catalyst and impellor cum catalyst holder-assembly in this study.

Catalytic wet oxidation of organic compounds over N-doped carbon nanotubes in batch and continuous operation

Abstract: Multi-walled carbon nanotubes (MWCNTs) were treated by ball milling with and without a nitrogen precursor (melamine) to introduce nitrogen functionalities. These materials were tested as catalysts in batch and continuous catalytic wet oxidation (CWO) experiments for the degradation of phenol in aqueous solution. The influence of several reaction parameters (temperature, dissolved oxygen concentration and initial phenol concentration) were studied in both operating modes. Temperature had a more significant effect on the reaction rate than the dissolved oxygen concentration, an optimal temperature of 160 °C being determined. The experiments with different initial phenol concentrations showed that higher amounts of phenol and carbon contents were removed when the initial concentration of phenol was increased. MWCNTs with N-groups showed high catalytic activity for phenol removal in both operation modes, as also observed when performing some experiments with oxalic acid. For instance, complete phenol degradation and 50% of total organic carbon (TOC) removal were achieved after 2 h in batch operation at 160 °C and 6 bar of oxygen partial pressure with the N-doped catalyst (against 68% and 50%, respectively, with the undoped sample). In the continuous mode reactor, 80% and 50% of phenol and TOC removals were observed at the steady state with the N-doped catalyst, in this case at 160 °C and 12 bar of oxygen partial pressure with an initial phenol concentration of 500 mg L−1. A significant regeneration of the N-doped catalyst was achieved by thermal treatment at 600 °C under nitrogen atmosphere.

Phosphorus poisoning during wet oxidation of methane over Pd@CeO2/graphite model catalysts

Abstract: The influence of phosphorus and water on methane catalytic combustion was studied over Pd@CeO 2 model catalysts supported on graphite, designed to be suitable for X-ray Photoelectron Spectroscopy/Synchrotron Radiation Photoelectron Spectroscopy (XPS/SRPES) analysis. In the absence of P, the catalyst was active for the methane oxidation reaction, although introduction of 15% H 2 O to the reaction mixture did cause reversible deactivation. In the presence of P, both thermal and chemical aging treatments resulted in partial loss of activity due to morphological transformation of the catalyst, as revealed by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) analysis. At 600 °C the combined presence of PO 4 3− and water vapor caused a rapid, irreversible deactivation of the catalyst. XPS/SRPES analysis, combined with operando X-ray Absorption Near Edge Structure (XANES) and AFM measurements, indicated that water induces severe aggregation of CeO 2 nanoparticles, exposure of CePO 4 on the outer layer of the aggregates and incorporation of the catalytic-active Pd nanoparticles into the bulk. This demonstrates a temperature-activated process for P-poisoning of oxidation catalysts in which water vapor plays a crucial role.

Selective Production of Formic Acid by Wet Oxidation of Aqueous-Phase Bio-oil

Abstract: Fractionation of bio-oil is an important step in the development of an effective upgrading strategy of bio-oil to transport fuels and chemicals because it reduces bio-oil complexity and side reactions; however, the strategy should preferably make use of all fractions. We therefore fractionated bio-oil from fast pyrolysis of pine wood using water addition and liquid–liquid extraction and studied its aqueous-phase oxidation to formic acid. One potential use of formic acid is as a hydrogen source for upgrading of the organic phase. The effects of the temperature, oxygen pressure, and concentration of substrates and phenolic compounds on the yield and selectivity of formic acid were investigated. Batch experiments revealed a yield of up to 56 wt % (dry basis) and high selectivity, after 30 min at 170 °C and 5.0 MPa. However, the presence of phenolic compounds in the aqueous phase and substrate concentrations greater than 3% were detrimental. Extraction of the aqueous phase with butyl acetate was effective for...

Effect of transition metal impregnation on oxidative regeneration of activated carbon by catalytic wet air oxidation

Abstract: Impregnation of a commercial activated carbon (AC) with transition metals was investigated to extend its reuse as phenol adsorbent after regeneration by catalytic wet air oxidation (CWAO). Iron and copper catalysts were prepared with varied metal dispersions and oxidation states by using different heat treatments. The main feature of the iron catalysts was to reduce the phenol oligomerization due to oxidative coupling, while the copper catalyst was prone to leaching promoting homogeneous reaction. However their regeneration efficiency was not significantly improved with respect to the starting AC due to an increased adverse effect of CWAO itself on their adsorptive properties.

Catalytic wet air oxidation of high-concentration organic pollutants by upflow packed-bed reactor using a Ru–Ce catalyst derived from a Ru3(CO)12 precursor

Abstract: Low loading catalysts Ru/γ-Al2O3 and Ru–Ce/γ-Al2O3 (Ru: 0.3 wt%) were prepared by thermolysis of Ru3(CO)12, which exhibited high activity in Catalytic Wet Air Oxidation (CWAO) of high concentration organic pollutants by upflow packed-bed reactor with initial COD 200 000 mg L−1. XPS results revealed that two new Ru species (RuA and RuB) were detected due to the chemical interaction between Ru3(CO)12 and the active OH groups on the surface of Al2O3 during the process of Ru3(CO)12 incomplete decomposition, and the reduction of them can lead to more dispersed metallic phases. The TPR spectrum reveals that the catalyst with addition of Ce produced a strong interaction between Ru and the CeO2–Al2O3 support, which was helpful for the catalytic wet air oxidation. Low loading catalyst Ru–Ce/γ-Al2O3 reduced in H2 had the highest activity and the COD removal reached 99.5% above 245 °C. The operating parameters investigated included temperature, reactor pressure, gas flow rate and liquid hourly space velocity (LHSV). The results showed that the COD removal is considerably affected by the temperature; when temperature increased around 2–3 °C, COD removal was improved about 40% due to the obvious exothermic reaction. The experimental results indicated that the 0.3 wt% Ru–Ce/γ-Al2O3 catalyst has excellent activity and stability in the CWAO of high concentration organic pollutants in as packed-bed reactor during 100 hours.

Synthesis, characterization, and catalytic activity of alkali metal molybdate/α-MoO3 hybrids as highly efficient catalytic wet air oxidation catalysts

Abstract: To develop new catalysts which can be used in catalytic wet air oxidation (CWAO) with ambient temperature and atmospheric pressure, a series of M 2 Mo 4 O 13 /α-MoO 3 (M = Li, Na or K) hybrid catalysts for cationic red GTL removal were synthesized by a facile hydrothermal method. The growth of crystals under different synthesis pH and the phase evolution during thermal treatment were carefully monitored using various analytical tools. The influence of synthesis pH, calcination temperature, reaction temperature, degradation time, and bubbling with air or N 2 on the decolorization efficiency, and the removal rates of total organic carbon (TOC) and chemical oxygen demand (COD) were systematically investigated. For all three catalysts, approximately 100% of color and over 93% of TOC could be removed within 30 min. Compared to many catalysts reported in literature, these novel catalysts showed higher catalytic activity in dye wastewater degradation. The catalytic activity tests in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy- N -oxyl (TEMPO) and the electron spin resonance (ESR) analysis suggested that the existence of M 2 Mo 4 O 13 (M = Li, Na or K) promotes the formation of OH radicals and is critical for their superior catalytic activity. Considering the ambient operating condition and the excellent catalytic activity, these novel CWAO catalysts are very promising for practical applications.

Catalytic wet air oxidation of aqueous solution of phenol in a fixed bed reactor over Ru catalysts supported on ceria promoted MCM-41

Abstract: Catalytic wet air oxidation (CWAO) of phenol was carried out in a fixed bed reactor over a noble metal (Ru) supported on silica MCM-41 material. The addition of small amounts of ceria as a promoter to the MCM-41 material enhanced both the activity and selectivity of Ru in this reaction, with significant conversions of about 99% obtained at 413 K and 18 bar oxygen pressure. The oxidation of phenol required moderate temperature and oxygen pressure, and the oxidizing capacity of the catalyst required adjustment. The activation energy of the oxidation reaction was found to be 33 kJ mol−1 at 413 K using the ceria promoted Ru/MCM-41 catalyst. The supports and catalysts were characterized using the Brunauer–Emmett–Teller (BET) surface area, temperature programmed reduction (TPR), CO chemisorption, temperature programmed desorption (TPD), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), and inductively coupled plasma atomic emission spectroscopy (ICP-AES).

Comparison of the quantitative determination of soil organic carbon in coastal wetlands containing reduced forms of Fe and S

Abstract: The performance of the Walkley–Black wet oxidation chemical method for soil organic carbon (SOC) determination in coastal wetland soils (mangroves, coastal lagoons, and hypersaline tidal flats) was evaluated in the state of Ceara along the semiarid coast of Brazil, assessing pyrite oxidation and its effects on soil C stock (SCS) quantification. SOC determined by the chemical oxidation method (CWB) was compared to that assessed by means of a standard elemental analyzer (CEA) for surficial samples (<30 cm depth) from the three wetland settings. The pyrite fraction was quantified in various steps of the chemical oxidation method, evaluating the effects of pyrite oxidation. Regardless of the method used, and consistent with site-specific physicochemical conditions, higher pyrite and SOC contents were recorded in the mangroves, whereas lower values were found in the other settings. CWB values were higher than CEA values. Significant differences in SCS calculations based on CWB and CEA were recorded for the coastal lagoons and hypersaline tidal flats. Nevertheless, the CWB and CEA values were strongly correlated, indicating that the wet oxidation chemical method can be used in such settings. In contrast, the absence of correlation for the mangroves provides evidence of the inadequacy of this method for these soils. Air drying and oxidation decrease the pyrite content, with larger effects rooted in oxidation. Thus, the wet oxidation chemical method is not recommended for mangrove soils, but seems appropriate for SOC/SCS quantification in hypersaline tidal flat and coastal lagoon soils characterized by lower pyrite contents.

Wet oxidation of sewage sludge from municipal and industrial WWTPs

Abstract: In the last years, sewage sludge management turned out to be a topic of great interest due to the increasing sludge production and the high cost of sludge treatment and disposal. In this context, several methods are being studied for sewage sludge minimization: among them, wet oxidation (WO) was proposed as an effective hydrothermal oxidation based technology. The aim of this work, carried out within the European project “ROUTES,” was the assessment of the influence of sludge composition on process performance: for this purpose, seven different types of sewage sludge were submitted to WO tests at lab scale. Moreover, each operating condition (temperature, reaction time, and initial oxygen pressure) was varied so as to highlight the effect of process parameters on oxidation efficiency; this was essentially evaluated in terms of chemical oxygen demand (COD), volatile suspended solid (VSS) and total suspended solid (TSS) reduction. COD and VSS abatement varied in the ranges 44–85%, 71–99% depending o...

Experimental Study on Catalytic Hydroprocessing of Solubilized Asphaltene in Water: A Proof of Concept To Upgrade Asphaltene in the Aqueous Phase

Abstract: To prepare the solubilized asphaltene in water (SAW), the feedstock of hydroprocessing experiments, oxidation reactions were conducted in a 550 mL batch reactor in the presence of NaOH in aqueous phase. At 240 °C and 2 h residence time the asphaltenes conversion reached 80% with 50% yield to SAW. The characterization of solubilized asphaltene in water (SAW) revealed that it contains a wide range of carboxylic acids with various alkyl tails. The presence of carboxylate and carboxylic functional groups in the SAW structure was also confirmed with FTIR analyses. The catalytic hydroprocessing of SAW was studied in a 100 mL batch reactor with presulfided NiMo/γ-Al2O3 catalyst. The hydroprocessing results at 320 °C and 3 h residence time for SAW prepared at different severities shows that higher oxidation temperature produces the lighter liquid hydrocarbons, which suggests the oxy-cracking of asphaltene through wet oxidation. Increasing the concentration of solubilized asphaltene in water increased solids forma...