Formation of oxygen structures by ozonation of carbonaceous materials prepared from cherry stones: II. Kinetic study

In this second part, the kinetics of the ozonation process of a char prepared from cherry stones (CS) is investigated. The char was obtained by heat treatment of CS at 600°C for 2 h in nitrogen. The effects of reaction time, partial pressure of ozone, and mass transport phenomena on the formation of oxygen complexes are studied. The surface chemistry of the samples was examined by FT-IR spectroscopy and the elemental chemical analysis was also determined for some samples. Results showed that the ozonation of the char led to oxygen chemisorption and to carbon gasification. The amount of oxygen complexes formed in the chemisorption stage (i.e., OH groups, CO structures, and ether structures) was found to be very sensitive to the increase in the ozonation time. The type of oxygen complexes was also time dependent. Ozonated products with relatively high concentrations of CO groups and ether structures were prepared by applying high ozone doses, whereas the formation of OH groups was favored at low ozone contents. The particle size did not influence the surface chemistry of the ozonated products. Only when the gas flow rate was lower than 40 l h⁻¹, restrictions to ozone mass transport developed. For kinetics of the char ozonation process, a mechanism based on the Langmuir-Hinselwood adsorption-desorption model was proposed, and the intrinsic reaction rates were calculated as a function of ozonation temperature. The activation energy for the ozonation stage of the char was equal to 41.6 kJ mol⁻¹.     

Ozonation of the reactive dye intermediate 2‐naphthylamine 3,6,8‐trisulphonic acid (K‐Acid): kinetic assessment,ozonation products and ecotoxicity

Ozonation of the commercially important, recalcitrant reactive dye intermediate 2‐naphthylamine 3,6,8‐trisulphonic acid (K‐Acid) was investigated. Ozonation performance was examined by following ozone absorption rates and K‐Acid, chemical oxygen demand and total organic carbon removals. Mean oxidation states and unidentified organic products were also determined. At pH 3, where direct ozone reactions are dominant, the second‐order rate constant between K‐Acid and molecular ozone was determined as 20 m ^?1 s^?1 for steady‐state aqueous ozone concentration. The competition kinetics approach was also adopted where a reference compound, phenol, and K‐Acid were subjected to ozonation. By applying this method, the second‐order reaction rate constant was found to be 76 m ^?1 s^?1. Common oxidation products formed during ozonation at pH 3, pH 7 and pH 7 with 1 mm hydrogen peroxide were identified as methoxy‐phenyl‐oxime, phenol, benzene, benzaldehyde and oxalic acid via high‐performance liquid chromatography and gas chromatography/mass spectrometry analyses. Continuous nitrate and sulphate evolution were observed during K‐Acid ozonation as a consequence of the abrupt release and subsequent oxidation of its amino and sulphonate groups. The number and amount of reaction products were most intensive for K‐Acid ozonation at pH 7 with 1 mm hydrogen peroxide. According to the acute toxicity tests conducted with Vibrio fischeri, ozonation products were not less toxic than the original K‐Acid solution that caused only 15% inhibition.     

2，4-二氯苯氧乙酸臭氧化过程中过氧化氢的生成

引言2,4-二氯苯氧乙酸(2,4-D,又名2,4-滴)是一种广泛使用的除草剂[1],应用历史较长,是我国主要的除草剂品种之一,用量也比较大。2,4-D属于苯氧羧酸类除草剂的一种,可有效去除阔叶杂草,目前仍广泛用于农作物除草和草坪养护[2]。2,4-D的水溶性较高,挥发性较低,在自然界中难以生物     

Formation of oxygen complexes by ozonation of carbonaceous materials prepared from cherry stones: I. Thermal effects

In this study, the feasible use of ozone to form oxygen complexes in chars prepared from cherry stones (CS) is investigated. CS were charred at 450, 600 or 900°C for 2 h in nitrogen. Char samples were ozonated over the 25-250°C temperature range for 1 h. Elemental chemical analysis was effected for a few selected samples. The oxygen complexes were successfully analyzed by Fourier infrared spectroscopy (FT-IR) and by titration methods. Thermal decomposition of ozone in the gas stream was also studied and the mechanism of the ozonation process dealt with. The ozonation treatment of CS chars was found to yield products with a relatively high concentration of a number of oxygen complexes. These include phenolic hydroxyl, quinonic, carboxylic acid, and ether structures. The content of lactonic structures was very low in the ozonated samples. The type and quantity of oxygen complexes depended on the ozonation and charring temperatures. The formation of oxygen complexes was favored when the charring of CS was effected at 450°C and when the ozonation of the char prepared at 600°C was performed at 100°C. The ozone content in the gas stream was very sensitive to the temperature increase in the reactor. Several reaction routes have been proposed for the transformation of ether, aromatic, and olefinic structures present in CS chars into oxygen complexes.     

Glyoxal Ozonation Process in Aqueous Solution

The process of ozonation of glyoxal in aqueous solution has been studied by following its chemical and kinetic evolution. Results show that the oxidative process leads to formation of carboxylic functions and carbon dioxide according to a constant selectivity ratio at varying conversion degree.. Comparison between the oxygen amounts of reaction products and the corresponding ozone consumptions reveals that molecular oxygen takes part in the reaction process. System behavior is explained on the basis of radical reaction mechanism.     

Ozonation of organic compounds in alkaline aqueous media

Effect of pH on the aqueous phase ozonation of various organic compounds was investigated. The reaction was accelerated in alkaline media due to the formation of active hydroxyl radical by an interaction of ozone with hydroxide ion. However, in a strongly alkaline media (pH < 11.9), hydroxyl radical dissociated into less reactive oxygen ion and the efficiency of ozonation decreased. By means of the theory of gas absorption accompanied by chemical reaction, it was found that the rate of the decomposition of ozone in the presence of about 300 ppm of 1-butanol was 5-80 times larger than that catalyzed only by hydroxide ion in the pH range of 11-13. Efficiency of ozonation showed that an optimum range of pH for the removal of total organic carbon was 9-10.     

Experimental and theoretical study on catalytic ozonation of humic acid by ZnO catalyst

Ozonation and catalytic ozonation of humic acid (HA) in the presence of ZnO were examined in a batch scale reactor. The degradation of HA by catalytic ozonation was found to be much more effective than ozonation alone. The quantum chemistry calculations showed that the reaction of the O₃ disproportionation on the surface of ZnO corresponds to the barrierless mechanism. The activation energy of the transition state formation was ?5.25 eV. The active oxygen atom formed on the surface of ZnO was found as interacting with both water molecules and dissolved organic molecules, which might lead to further oxidizing reactions.     

Formaldehyde Formation During Ozonation Of Drinking Water

Partial oxidation of natural organic material during ozonation produces oxygenated by-products of low molecular weight. Formaldehyde, being the most common oxygenated by-product of ozone, is considered to be a problematic compound by the water industry due to its potential adverse health effects. This research attempts to provide specific information on the effects of water quality parameters, specifically, pH and alkalinity, the structure of humic material, and the operational parameters, e.g., ozone dosage and contact time, on generation of formaldehyde. The results showed that ozonation caused almost an immediate formation of formaldehyde, which reached a peak value, and then started to decrease with continued ozonation. Ozonation of aqueous fulvic acid produced higher concentrations of formaldehyde compared to other types of humic material. Formaldehyde formation was suppressed by high bicarbonate levels, and enhanced at higher pH. Formaldehyde accumulation was more dramatic at low ozone dosages.     

Ozonation of Aqueous Solutions of Nitrobenzene

The ozonation of nitrobenzene in aqueous solution is investigated by determining COD removal, ozone consumption and product distribution at different degrees of ozonation.Results reveal that complete nitro benzene elimination is achieved at relatively short ozonation times, with no appreciable accumulation of unsaturated intermediates.Oxida–tive consumption of about 2.5 oxygen atoms per mole of absorbed ozone is observed in this ozonation stage. Much longer ozonation times are required to reach complete oxidation of intermediates to oxalic acid and carbon dioxide, with an oxidative consumption corresponding to 1.8 oxygen atoms per mole of absorbed ozone. A reaction scheme is proposed on the basis of the observed product distribution.     

蒜头果油中长链脂肪酸选择性合成大环内酯

研究了蒜头果油脂中长链不饱和脂肪酸的臭氧氧化以及ω-羟基脂肪酸的催化关环合成大环内酯,考察了臭氧氧化切断双键选择性和大环内酯化选择性。结果表明,不饱和脂肪酸的碳链越长,越有利于臭氧氧化反应和生成大环内酯。蒜头果油脂合成大环内酯的产率为:环十五内酯36.9%,环十三内酯为22.4%,环十一内酯1.0%,并探讨了蒜头果油脂中油酸的反应特性。     

Ozonated Multiwalled Carbon Nanotubes as Highly Active and Selective Catalyst in the Oxidative Dehydrogenation of Ethyl Benzene to Styrene

Purification and ozonation protocols for the functionalization of multiwalled carbon nanotubes (MWCNT) were developed to modify the surface with respect to increasing the catalytic activity of the samples in the oxidative dehydrogenation of ethyl benzene (ODEB) to styrene. The modification processes drastically enhance the Brunauer‐Emmett‐Teller surface area and the number of oxygen‐containing groups on the surface of the nanotubes. The modified MWCNT exhibit significantly improved conversion and styrene selectivity in the ODEB reaction. For instance, ozonation led to MWCNT‐based catalysts revealing conversion and selectivity values of 80 % and 92 %, respectively. An increase in surface oxygen accompanied by high catalytic activity observed on the catalysts suggests that oxygen‐containing groups are the dominant active sites for the reaction.     

Adsorption selectivity of phenylalanine imprinted polymer prepared by the Wet Phase Inversion Method

A phenylalanine (Phe) imprinted polymer was prepared by the wet phase inversion method to investigate the optimum preparation condition which endows the polymer matrix with prominent adsorption selectivity. The addition of a large amount of porogen (dimethyl sulfoxide: DMSO) was needed to form macrovoids in the polymer matrix. For the high adsorption selectivity of the polymer matrix, a complex between functional monomers and a template molecule must be formed before the copolymerization of acrylomtnle (AN: crosslinker) and acrylic acid (AA: functional monomer). The formation of a phenyl group in the polymer matrix by the coupling reaction between D-Phe and AA seemed to cause the reverse adsorption selectivity of the polymer matrix. The adsorption selectivity of the Phe imprinted polymer was dependent on the pH of the racemate solution. The adsorption selectivity of the D-Phe imprinted polymer prepared by the post implanting method reached 11 at pH 2 and showed a reverse adsorption selectivity at pH 4 and 6.     

An Investigation in the Use of Ozone Gas in the Bleaching of Cotton Fabrics

Ozone, composed of three atoms of oxygen, can be used to oxidize many inorganic and organic impurities. Because of its high oxidizing capacity, the opportunities and parameters of ozone gas use in bleaching of cotton fabrics were researched in this study. It was found that in a very short time cotton fabrics can be bleached if the water content of cotton-woven fabric was 60% and the pH of the water impregnated was 7. Moreover, ozonation at room temperature was shown to be more efficient than ozonation at high to medium temperatures.     

Ozone treatment of textile effluents and dyes: effect of applied ozone dose,pH and dye concentration

The ozonation of wastewater supplied from a treatment plant (Samples A and B) and dye‐bath effluent (Sample C) from a dyeing and finishing mill and acid dye solutions in a semi‐batch reactor has been examined to explore the impact of ozone dose, pH, and initial dye concentration. Results revealed that the apparent rate constants were raised with increases in applied ozone dose and pH, and decreases in initial dye concentration. While the color removal efficiencies of both wastewater Samples A and C for 15 min ozonation at high ozone dosage were 95 and 97%, respectively, these were 81 and 87%, respectively at low ozone dosage. The chemical oxygen demand (COD) and dissolved organic carbon (DOC) removal efficiencies at several ozone dose applications for a 15 min ozonation time were in the ranges of 15–46% and 10–20%, respectively for Sample A and 15–33% and 9–19% respectively for Sample C. Ozone consumption per unit color, COD and DOC removal at any time was found to be almost the same while the applied ozone dose was different. Ozonation could improve the BOD₅ (biological oxygen demand) COD ratio of Sample A by 1.6 times with 300 mg dm^?3 ozone consumption. Ozonation of acid dyes was a pseudo‐first order reaction with respect to dye. Increases in dye concentration increased specific ozone consumption. Specific ozone consumption for Acid Red 183 (AR‐183) dye solution with a concentration of 50 mg dm^?3 rose from 0.32 to 0.72 mg‐O₃ per mg dye decomposed as the dye concentration was increased to 500 mg dm^?3. © 2002 Society of Chemical Industry     

Enhancing Biodegradability of Textile Wastewater by Ozonation Processes: Optimization with Response Surface Methodology

ABSTRACT

In this study, an ozonation process was used to increase biodegradability of textile wastewater by considering chemical oxygen demand (COD) and color removal. Response surface methodology was applied in order to determine the significance of independent variables which are initial pH, reaction time and ozone dose. While a biological oxygen demand (BOD)/COD rate of 0.315 was obtained at optimum conditions, which are pH 9, 75 min of reaction time and 26 mg/L ozone dose, color and COD removal was obtained at 74% and 39%, respectively. BOD/COD ratio value increased from 0.18 to 0.32 by ozonation process. In addition, k coefficient for BOD also increased from 0.21 to 0.30 d^?1.     

Catalytic oxidation of isobutane to methacrylic acid with molecular oxygen over activated pyridinium 12-molybdophosphate

Isobutane was catalytically oxidized to methacrylic acid with molecular oxygen above 300°C over 0 crystalline particles of pyridinium 12-molybdophosphates which were activated by heat-treatment under a nitrogen stream up to 420°C. During the treatment two third of pyridine were released from the sample and one third remained accompanied by the formation of orthorhombic structure. It was proved by IR studies that the catalyst became a reduced state by this treatment. The reduced state was highly stable even under catalytic oxidation conditions with molecular oxygen. 50% selectivity to methacrylic acid and 22% to acetic acid were achieved at 22% conversion of isobutane. The highly stable reduced state and structure of the activated heteropolymolybdophosphate catalyst seem to be responsible for the high activity for isobutane oxidation and high selectivity to methacrylic acid formation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparative study of catalytic ozonation and Fenton-like processes using iron-loaded rice husk ash as catalyst for the removal of methylene blue in wastewater

This study intends to compare the effectiveness of catalytic ozonation and Fenton-like processes for the decolorization of methylene blue using iron-loaded rice husk ash as catalyst. In both processes, effect of initial pH, adsorption, hydroxyl radical scavenger, and chemical oxygen demand removal was studied. The results revealed that catalytic processes were found to be pH dependent with the highest activity at pH 3.0. Unlike Fenton-like process, catalytic ozonation also found to be effective at pH 7.0. It is therefore, concluded that catalytic ozonation process is more effective than Fenton-like process near wastewater pH values.     

Ozonation Of Sulfur-Containing Aliphatic Compounds In Aqueous Solutions. II. Cysteine,Cystine and Thioglycolic Acid

In view of the possible reaction of ozone with sulfur-containing natural and anthropogenic compounds, the ozonation of cysteine, cystine, thioglycolic acid and their oxidation products at pH 3 and 7 (initial concentration 1 mmol/L) was investigated. The oxidation of cysteine at pH 3 leads to cysteic acid; at pH 7 sulfoacetic acid, sulfate, ammonia and nitrate are formed besides cysteic acid. Cysteinesulfinic acid as intermediate oxidation product was not identified because of the very fast reaction with ozone forming cysteic acid.     

Delignification of Bagasse with Acetic Acid and Ozone. II. Ozone Stage

Ozone gas was applied as second stage in delignification of bagasse pulp obtained with acetic acid. The kappa number was reduced from 44 to 10 with 3% ozone (based on dry pulp). Because bagasse was pulped with an aqueous solution of acetic acid (80% volume), selectivity of the ozone stage was favored and does not necessary acidulate pulp, which had pH = 1.7. Consistency of pulp for ozonation was 40% and this stage was carried out at room temperature. Physical properties of pulp were improved with ozone treatment.     

Degradation of cationic dye methylene blue by ozonation assisted with kaolin

An enhanced ozonation process, methylene blue (MB) wastewater treated by MnO₂/O₃ assisted with kaolin in a slurry reactor, at room temperature and atmospheric pressure, MB wastewater can be effectively purified, a chemical oxygen demand (COD) of 88.3% and a decoloration rate of 98.9% were obtained in 10 min at pH 11. Compared with MnO₂/O₃ catalytic ozonation (16.0% of decoloration and 33.3% of COD reduction), decoloration and COD reduction were markedly increased, indicating that kaolin can significantly improve the catalytic ozonation process. According to the experimental results, the hypothetical mechanism of degradation and the reaction kinetics were also proposed. COD reduction can be described by a second-order model and the reaction rate constant in the presence of kaolin was higher than that of absence of kaolin.