Biodegradability of linear alkylbenzene sulfonates subjected to wet air oxidation

Shake flask experiments were conducted to determine the biodegradability of aqueous linear alkylbenzene sulfonate (LAS) and LAS (1600 mg dm^?3) subjected to wet air oxidation (WAO), to assess the suitability of WAO as a pre‐treatment for biological degradation. The effects of WAO temperature (180–240 °C) and the concentration of the orthophosphoric acid catalyst (0–1.0 mol dm^?3) were investigated. Results showed that a higher WAO temperature increased the biodegradability of the WAO effluent. This was due to a greater removal of both recalcitrant sulfonated organics and organic concentration (TOC and COD). Conversely, greater orthophosphoric acid concentrations decreased the biodegradability of the WAO effluents. This was because the higher acid concentration increased the ionic strength and changed the WAO intermediate and product distribution, inhibiting microbial action. Nevertheless, the effluents from both variations of WAO were still more biodegradable than LAS at equivalent concentrations. However, since higher WAO temperatures can substantially increase capital costs, future work should focus on developing a WAO catalyst that both desulfonates and mildly oxidises LAS at moderate temperatures (200 °C). © 2002 Society of Chemical Industry     

Chloride‐promoted leaching of chalcopyrite concentrate by biologically‐produced ferric sulfate

The effects of chloride ions on chalcopyrite leaching by biologically‐produced ferric sulfate solution and on the iron‐oxidizing culture were determined. Chloride ions significantly increased chalcopyrite leaching by ferric sulfate at 67 °C and 87 °C, but slowed down the leaching at 50 °C. At 90 °C, chloride at 5 g dm^?3 (0.25 g Cl^? g^?1 concentrate) increased the copper yield from 60 to 100% in approximately 2 weeks. Further increase in Cl^? concentration did not affect the leaching. Addition of chloride increased both leaching yields and iron precipitation, which shows that the passivation was not due to iron precipitation. A decreased Ag‐potential of 60 mV against an Ag/AgCl reference electrode in the presence of Cl^? indicates the accumulation of partially oxidized forms of dissolved sulfur compounds such as thiosulfate and polythionate instead of elemental sulfur and, thus, a decrease in sulfur passivation. A chloride concentration of 5 g dm^?3 did not affect the iron oxidation rate of the iron‐oxidizing culture dominated by Leptospirillum ferriphilum. Copyright © 2004 Society of Chemical Industry     

Studies on the oxidation of phenols catalyzed by a copper(II)–Schiff base complex in aqueous solution under mild conditions

The catalytic oxidation of phenol with hydrogen peroxide using a synthetic copper(II)–Schiff base complex as catalyst has been investigated in phosphate buffer at pH 7 and 25 °C. In order to further investigate the reaction pathway, the catalytic oxidation of hydroquinone, p‐benzoquinone and catechol were also studied under the same conditions. These reactions were found to be pseudo‐first‐order with respect to the concentration of phenolic substances. The rate constants were also calculated. In the presence of catalyst, the kinetics and the HPLC analysis showed that for the first step phenol was oxidized to hydroquinone and catechol, and the catalyst easily promoted the formation of hydroquinone but not catechol, for the second step the dihydroxybenzenes were further oxidized to benzoquinone, and lastly short‐chain acids, including maleic acid and oxalic acid, were formed. The activity of the catalyst hardly decreased during the whole reaction. Addition of imidazole accelerated the oxidation of phenol. The catalytic decomposition of hydrogen peroxide using this catalyst was also investigated. Copyright © 2005 Society of Chemical Industry     

Conventional and wet proofed CuO/Al2O3 catalysts for phenol oxidation: deactivation studies in a trickle bed reactor

A large variety of catalytic systems have been studied for the catalytic wet air oxidation of phenolic solutions. Most of them show good activity, but serious stability problems. In this contribution, stability studies were performed over CuO/Al₂O₃ conventional (CNT) and polytetrafluorethylene coated (C3T) catalysts used for the oxidation of 5 g L^?1 phenol solutions in a trickle bed reactor (140 °C and 7 atm of oxygen pressure). For the hydrophilic catalyst, phenol conversion decreased with usage due to the formation of Cu₂O and copper oxalate phases. For the wet proofed catalyst, the hydrophobic layer prevented the appearence of those phases, and conversion levels remained practically constant with reaction time. After usage, both catalysts were oxidized at 400 °C and tested for reaction: in the case of the C3T catalyst, the phenol conversion was increased over its initial level; for CNT catalyst, the phenol conversion was also increased, but initial levels were not completely restored. The deactivation mechanism of the CNT catalyst is associated with the formation of the Cu₂O and copper oxalate phases during reaction. For catalyst C3T, practically no deactivation was observed. Copyright © 2007 Society of Chemical Industry     

催化湿式空气氧化处理磷霉素钠、黄连素制药废水试验研究

研究了用催化湿式空气氧化技术处理高含量、难降解的磷霉素钠和黄连素制药混合废水,考察了非贵金属Mn及稀土元素Ce协同Cu催化反应时CWAO处理效率。结果表明,以黄连素废水中的Cu2+作催化剂,反应温度为250℃、初始氧分压为1.3 MPa、反应停留时间0.5 h的条件下,COD平均去除率可达50%,此时废水中有机磷转化为PO43-;Mn、Ce的加入可使COD的去除率提高12%～18%,其中Mn与Cu协同作用效率最高,在初始氧分压为1.3 MPa下,COD去除率可提高至72%,99%以上的有机磷转化为PO43-,出水BOD5/COD提高至0.85,达到了CWAO预处理即提高2种制药废水可生化性的目的。     

Oxygen diffusion mechanisms during high‐temperature oxidation of ZrB2‐SiC

Oxygen diffusion mechanisms during oxidation of ZrB₂‐30 vol% SiC were explored at temperatures of 1500°C and 1650°C using an ¹⁸O tracer technique. Double oxidation experiments in ¹⁶O₂ and ¹⁸O₂ were performed using a modified resistive heating system. A combination of scanning electron microscopy, energy‐dispersive spectroscopy, and time‐of‐flight secondary ion mass spectrometry was used to characterize the borosilicate and ZrO₂ oxidation products. Oxygen exchange with the borosilicate network was observed to occur quickly at the oxygen‐borosilicate surface at both 1500°C and 1650°C, while evidence of oxygen permeation was only observed at 1650°C for short time (<1 min) exposures. At longer times, >5‐9 min, complete oxygen exchange throughout both the borosilicate glass and ZrO₂ was observed at both temperatures preventing identification of the oxygen transport mechanisms, but demonstrating that oxygen transport is rapid in both oxide phases.     

Preparation and characterization of wet-proofed CuO/Al2O3 catalysts for the oxidation of phenol solutions

Two wet-proofed catalysts were prepared by subsequent coating steps with polytetrafluoroethylene fibers over a CuO/Al₂O₃ catalyst. They were tested for the oxidation of phenol solutions in a semi-batch reactor. Phenol conversion as well as Chemical Oxygen Demand (COD) was recorded. The hydrophobic coverage reduces the loss of active phase by leaching. Therefore, deactivation was attributed to the deposition of carbonaceous residues on the catalytic surface.     

Catalytic removal of phenol from aqueous solutions in a trickle‐bed reactor

The degradation of high concentrations of phenol (1g/dm^?3) in aqueous media at high temperatures (100–190 °C) and pressures (2.0 MPa) has been studied by catalytic wet air oxidation in a trickle‐bed reactor. The effect of reaction temperature, weight hourly space velocity (WHSV) and hydrogen peroxide concentration on phenol concentration, total organic carbon (TOC) and chemical oxygen demand (COD) conversion by using a commercial copper catalyst has been investigated. At 150 °C, TOC removal increased by 28% with the WHSV of 62.5 h^?1. The addition of hydrogen peroxide as a free radical promoter significantly enhanced the depletion rate of phenol. A kinetic study has been carried out leading to the determination of the kinetic constants for the removal of TOC. Copyright © 2005 Society of Chemical Industry     

Catalytic Wet Air Oxidation of Sodium Sulfide Solutions. Effect of the Metal-Support and Acidity of the Catalysts

This work evaluates the catalytic wet air oxidation of sulfide present in spent caustic wastes generated during petroleum refining. Operating conditions were 70 °C and atmospheric pressure, with and without catalyst. Two supports (silica and clinoptilolite) and two metal oxides (vanadium and copper) were employed to produce different catalysts. The sulfide oxidation without catalyst displays a short induction period and complete oxidation of sulfide at 210 min. The most active catalysts were Cu/silica (CS) and V/clinoptilolite (VC), which improved the sulfide oxidation, achieving complete oxidation in 20 and 26 min, respectively.     

ACCELERATION OF THE WET OXIDATION REACTION OF PIPERAZINE BY HETEROGENEOUS Ru/TiO2 CATALYST

Wet air oxidation is a candidate technique for the effective treatment of wastewater contaminated by nitrogenous organic pollutants. Piperazine (PZ) is a cyclic diamine representing this class of compounds. In the present work, the wet oxidation reaction of PZ was studied for the first time. It was found that, in the studied range of temperatures of 180°–230°C and O₂ partial pressures of 0.69–2.07 MPa, the oxidation process was slow. Total organic carbon (TOC) conversion at 230°C and 0.69 MPa O₂ partial pressure was just 52% after 2 h. The investigated reaction was accelerated by a heterogeneous Ru/TiO₂ catalyst. Maximum TOC conversion (91%) was achieved during catalytic wet oxidation at 210°C and 1.38 MPa O₂ pressure. Kinetic data were collected over the range of temperatures 180°–210°C, O₂ partial pressures 0.34–1.38 MPa, and catalyst loading 0.11–0.66 kg/m³. The lumped TOC concentration decay was a two-step first-order process.     

Dynamic and isothermal thermogravimetric analysis of a polycyanurate thermosetting system

Isothermal and dynamic thermogravimetric analysis (TGA) were performed on a polycyanurate thermosetting material. The effects on thermal stability of the copper naphthenate catalyst were studied by comparing two systems with different amounts of catalyst. Tests were performed isothermally at temperatures ranging from 200°C to 240°C for times up to one week. Dynamic tests were also performed at rates from 0.1°C/min to 40°C/min at temperatures ranging from 180°C to 600°C. It is found that increasing the concentration of copper increased the weight loss in isothermal tests, but did not affect the overall activation energy. Conversely, in dynamic tests, copper concentration had no effect on weight loss. The results demonstrate the difficulties of extrapolating dynamic TGA data to use conditions in order to predict long-term thermal stability.     

Base‐free catalytic aerobic oxidation of mercaptans for gasoline sweetening over HTLcs‐derived CuZnAl catalyst

An aerobic oxidative removal of mercaptans from gasoline in the absence of liquid base has been demonstrated for gasoline sweetening over CuZnAl catalyst. This process could proceed at large WHSV of gasoline (50–70 h^?1) with >95% mercaptan conversion at 150°C (or 300°C) using an O₂/S molar ratio of 20–40. At 150°C, dimerization of mercaptans occurred dominantly to form their disulfides. At 300°C, deep oxidation of the mercaptans to SO₂ was the dominant process in the first tens of hours, but it decreased then with prolonged time on stream and meanwhile the dimerization increased. The spent catalyst could be restored to its fresh activity level only through a calcination treatment in air. This process was also demonstrated to be effective and efficient for sweetening of a real cracking gasoline. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Influence of Experimental Parameters in the Treatment of Distillery Effluent by Electrochemical Oxidation

The electrochemical oxidation of distillery effluent was studied in a batch reactor in the presence of supporting electrolyte NaCl using Mixed Metal Oxide (MMO) electrode. The effect of operating parameters such as current density, initial pH, and initial electrolyte concentration on the percentage of Chemical Oxygen Demand (COD) removal, power consumption, and current efficiency were studied. The maximum percentage removal of COD was observed to be 84% at a current density of 3 A/dm²at an electrolyte concentration of 10 g/l with an effluent COD concentration of 1000 ppm and at an initial pH of 6. The operating parameters for the treatment of distillery effluent by electrochemical process were optimized using response surface methodology by CCD. The quadratic regression models with estimated coefficients were developed for the percentage removal of COD and power consumption. It was observed that the model predictions matched with experimental values with an R² value of 0.9504 and 0.9083 for COD removal and power consumption respectively. The extent of color removal and oxidation of organic compounds were analyzed using UV spectrophotometer and HPLC.     

Formation and decomposition of stigmasterol hydroperoxides and secondary oxidation products during thermo‐oxidation

The oxidation mechanisms of stigmasterol at 100 and 180 °C were investigated by using the HPLC‐UV‐FL method. An overall picture of the oxidation status was achieved with a single HPLC analysis, enabling us to monitor the formation and decomposition of both primary and secondary oxidation products. The oxidation behavior of stigmasterol was different at the two temperatures. At 180 °C, the amounts of hydroperoxides increased sharply during the first 10 min and then began to decrease. At 100 °C, the amounts of hydroperoxides increased over the entire experimental period. At 180 °C, all major secondary oxidation products, except 7‐ketostigmasterol, reached a plateau after 40 min of oxidation, while at 100 °C their amounts increased constantly. The same oxidation products were formed at both temperatures, but their distribution differed. At 180 °C, the formation of free radicals at position 7 was more favorable than formation of radicals at position 25. The situation was the opposite at 100 °C; radicals formed more easily at the tertiary position 25. At 180 °C, 7‐ketostigmasterol was dominant after 40 min of oxidation, whereas at 100 °C it was the main oxidation product over the entire experiment.     

Sodium diclofenac removal from a pharmaceutical wastewater by electro-Fenton process

ABSTRACT

In this study, the experiments were carried out to evaluate the effect of five independent variables on the Chemical Oxygen Demand (COD) removal in a pharmaceutical wastewater contaminated with sodium diclofenac. The parameters were statistically optimized under response surface mythology. The optimum conditions for 97.21% of COD removal experimentally were at reaction time of 59.68 min, current density of 58.47 mA/cm², pH of 2.89, volume ratio of 0.32 ml/l and H₂O₂/Fe²⁺ molar ratio of 3.60.     

Anchoring of Copper(II) Schiff Base Complex into Aminopropyl-Functionalised MCM-41: A Novel,Efficient and Reusable Catalyst for Selective Oxidation of Alcohols

A copper(II) complex containing tetradentate N₂O₂ Schiff base ligand immobilized into aminopropyl-functionalised MCM-41 (mobile crystalline material number 41), was prepared and characterized by Fourier-transform infrared, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, N₂ adsorption–desorption and inductively coupled plasma analysis techniques. The novel heterogeneous catalyst, MCM-41-pr-NH₂-CuL, can be successfully applied for efficient and selective oxidation of different primary and secondary alcohols to the corresponding carbonyl compounds using hydrogen peroxide as an oxidant in acetonitrile at 60 °C. The effect of reaction parameters such as solvent, amount of catalyst, temperature and kind of oxidant on the oxidation of benzyl alcohol was also studied. The prepared catalyst could be recovered and reused four times without important loss of its catalytic performance. The heterogeneous MCM-41-pr-NH₂-CuL catalyst was found to be catalytically more active in the oxidation of alcohols compared to the similar type of copper(II) Schiff base complex in homogeneous media under the same reaction conditions.     

Combined CO2 reforming and partial oxidation of fuel compounds

CO₂ reforming and the combined CO₂ reforming and partial oxidation reaction of selected fuel compounds were studied on a commercial 15 wt% NiO/Al₂O₃ catalyst and a 0.25 wt% Rh/ZrO₂ catalyst at 600–900 °C. Oxygen reduced the energy requirement and catalyst coking. Ethanol was a more suitable starting material than the hydrocarbons.     

Partial thiosulfate oxidation by steady‐state continuous culture in a bioreactor‐settler system

The design, characterization, and performance of a bioreactor‐settler system that allows the partial biological oxidation of reduced sulfur compounds is described. The design incorporates the physical separation of the aeration from the bioreactor. The reactor has a dynamic flow zone and a static zone. Steady state thiosulfate‐oxidizing cultures were established at different O₂/S₂O₃^2? molar ratios. At O₂/S₂O₃^2? molar ratios > 1.0, sulfate was the main product of the biological oxidation of thiosulfate, while below O₂/S₂O₃^2? molar ratios of about 1.0, formation of elemental sulfur was observed. The maximum sulfur formation (60%) was obtained at a molar ratio of 0.98. The elemental sulfur settled in the bottom of the bioreactor and was removed daily from the system. A recovery efficiency of 70% was obtained. The settled sulfur–biomass particles consisted of 90% sulfur and 6% biomass and had an average size of 150 µ m and a sedimentation rate of 7.50 m h^?1. The hydraulic retention time (HRT of 2 min) of the medium in the aerator vessel showed an influence over the system performance due to the oxidation of thiosulfate and intermediates under the high oxygen concentration found in this vessel. Copyright © 2003 Society of Chemical Industry     

Electrochemical mineralization of sodium dodecylbenzenesulfonate at boron doped diamond anodes

Results are reported of the electrochemical oxidation of sodium dodecylbenzenesulfonate (SDBS), a common surfactant, at boron-doped diamond anodes. The measured critical micelle concentration (CMC) for SDBS in water at 24 °C was almost 150 mg dm⁻³, but this decreased to almost 30 mg dm⁻³ in 0.1 M sodium sulfate. Cyclic voltammetry of a boron doped diamond (BDD) electrode in aqueous SDBS solutions exhibited oxidation current densities at very positive potentials; however, solutions of monomers at concentrations <CMC gave rise to higher current densities than in higher concentration solutions that formed micelles. Galvanostatic electrolyses, with samples analyzed for Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD), were performed in an electrolytic flow cell without separator, operating in batch recycle mode, using solutions containing SDBS at initial concentrations of 25 and 250 ppm. SDBS in basic media (pH = 12) exhibited lower TOC removal rates than in acidic or neutral solutions, due to concurrent oxidation of dissolved carbonates at potentials less positive than required for water oxidation, as evident in cyclic voltammograms. Decreasing the [electrolyte]/[surfactant] ratio from 200 to 10 increased TOC removal rates. For solutions containing monomers, TOC removal rates also increased with flow rate in the second part of the electrolysis, corresponding to reaction of smaller, fragmented organic compounds. When COD removal from a solution containing SDBS micelles was mass transport controlled, current efficiencies were constant at ca. 50%, due to dimerisation of hydroxyl radical to H₂O₂ and its oxidation to dioxygen.     

Antioxidant activity of green teas in different lipid systems

Different commercial green teas from Japan, China, and India, were compared in different lipid systems. Green teas were active antioxidants in bulk corn oil oxidized at 50°C but were prooxidant in the corresponding oil-in-water emulsions. Green teas also were active antioxidants in soybean lecithin liposomes oxidized at 37°C in the presence of cupric acetate as catalyst. At 50°C, however, three of the samples of green tea were active antioxidants in the absence of copper catalyst, and two samples showed prooxidant activity in the presence of copper catalyst. The marked variation in activity among green tea samples may be due partly to differences in their relative partition between phases in different lipid systems. The improved antioxidant activity observed for green teas in lecithin liposomes compared to corn oil emulsions can be explained by the greater affinity of the polar tea catechin gallates for the polar surface of the lecithin bilayers, thus affording better protection against oxidation. Liposomes may thus be appropriate lipid models to evaluate antioxidants for foods containing phospholipids.