Oxidation of benzothiazole, 2‐mercaptobenzothiazole and 2‐hydroxybenzothiazole in aqueous solution by means of H2O2/UV or photoassisted Fenton systems

Oxidative treatments of benzothiazole and benzothiazole derivatives (2‐mercaptobenzothiazole, 2‐hydroxybenzothiazole) in aqueous solution have been studied by using H₂O₂/UV and iron(III) photoassisted Fenton techniques. Experimental runs have been carried out in the pH range 3.0 –8.0 by means of annular reactors and proper UV lamps. The effect of pH, the initial concentration of hydrogen peroxide, the substrate, and the iron(III) concentrations have been investigated. A suitable model has been developed and used for the best estimation of kinetic constants for HO radical attack on the target molecules with the H₂O₂/UV system. The values obtained with this model are consistent with those reported in the literature for other heterocyclic compounds. © 2001 Society of Chemical Industry     

不同物相TiO2对H2O2/O3氧化效能的影响

研究了不同物相TiO₂对H₂O₂/O₃氧化效能的影响,目标有机物为羟基自由基探针化合物乙酸。结果表明,在初始pH为7.0和10.0时,加入TiO₂反而降低了H₂O₂/O₃的氧化效率,其中锐钛矿TiO₂比金红石TiO₂的减弱作用更为明显。当初始pH为3.0时,金红石TiO₂能显著提高H₂O₂/O₃的氧化效率,但锐钛矿TiO₂影响不明显。机理分析表明,H₂O₂浓度及其衰减速率与乙酸的去除效率有很大的相关性。在pH为7.0和10.0时,两种物相TiO₂均能加快H₂O₂的分解,其中锐钛矿TiO₂作用更为显著。此条件下HO₂^-能有效引发臭氧分解产生羟基自由基,故H₂O₂过快分解反而降低了乙酸的去除效果。在pH为3.0时,H₂O₂去质子化反应困难,故O₃/H₂O₂氧化效率极低,H₂O₂浓度也几乎不变。加入TiO₂能明显提高H₂O₂的分解速率,相比金红石TiO₂,锐钛矿TiO₂使H₂O₂在5 min内基本分解完毕,但其对H₂O₂/O₃氧化效率几乎没有影响。饱和臭氧水分解速度的批处理实验也有相似的结果。由此可见,合适引发剂浓度可能是保证臭氧类高级氧化技术较高效率的关键,否则只会导致氧化剂的无效过快分解。利用氯化硝基四氮唑蓝法对比分析了酸性条件下H₂O₂/O₃、锐钛矿TiO₂/H₂O₂/O₃和金红石TiO₂/H₂O₂/O₃体系产生超氧自由基(·O₂^-)的量,其大小顺序为:H₂O₂/O₃< 金红石TiO₂/H₂O₂/O₃< 锐钛矿TiO₂/H₂O₂/O₃,这与前面结果吻合很好。     

Photo‐oxidation of cyanide in aqueous solution by the UV/H2O2 process

Photo‐oxidation of cyanide was studied in aqueous solution using a low‐pressure ultra‐violet (UV) lamp along with H₂O₂ as an oxidant. It was observed that by UV alone, cyanide degradation was slow but when H₂O₂ was used with UV, the degradation rate became faster and complete degradation occurred in 40 min. The rate of degradation increased as the lamp wattage was increased. It was also observed that cyanide oxidation is dependent on initial H₂O₂ concentration and the optimum dose of H₂O₂ was found to be 35.3 mmol dm^?3. Photo‐oxidation reactions were carried out at alkaline pH values (10–11) as at acidic pH values, cyanide ions form highly toxic HCN gas which is volatile and difficult to oxidise. By the UV/H₂O₂ process, using a 25 W low‐pressure UV lamp and at alkaline pH of 10.5 with an H₂O₂ dose of 35.3 mmol dm^?3, cyanide (100 mg dm^?3) was completely degraded in 40 min when air was bubbled through the reactor, but when pure oxygen was bubbled the time reduced to 25 min. The cyanide degradation reaction pathway has been established. It was found that cyanide was first oxidised to cyanate and later the cyanate was oxidised to carbon dioxide and nitrogen. The kinetics of cyanide oxidation were found to be pseudo‐first order and the rate constant estimated to be 9.9 × 10^?2min^?1 at 40 °C. The power required for complete degradation of 1 kg of cyanide was found to be 167 kWh (kilowatt hour). Copyright © 2004 Society of Chemical Industry     

臭氧、臭氧/双氧水催化氧化深度处理化工废水

对比了臭氧、臭氧催化氧化、臭氧/双氧水和臭氧/双氧水催化氧化4种工艺深度处理化工废水的效果,结果表明,当进水COD和色度分别为95.7 mg/L和90倍时,4种工艺出水的COD去除率分别为23.66%、26.77%、29.24%、32.97%,色度去除率分别为64.44%、64.44%、82.22%、82.22%,催化剂和双氧水均能小幅强化臭氧氧化效果。连续臭氧氧化可使出水COD降至20 mg/L,同时当臭氧投加量为60 mg/L时,4种工艺出水均具有一定的可生化性,满足后序生化工艺的需求。     

Kinetics,degradation pathway and reaction mechanism of advanced oxidation of 4‐nitrophenol in water by a UV/H2O2 process

Photooxidation of 4‐nitrophenol (4‐NP) in water by the UV/H₂O₂ advanced oxidation process was carried out in order to investigate the kinetics and pathway of 4‐NP degradation. The experimental results showed that the photodegradation of 4‐NP accorded well with pseudo‐first order kinetics. The effects of different parameters, such as H₂O₂ dosage, pH value and various anion scavengers on the degradation of 4‐NP have been investigated in detail. It was found that acidic conditions are more favorable to the degradation of 4‐NP but many anions, such as HCO₃^?, NO₃^? and Cl^?, slow down the photooxidation rate of 4‐NP. Hydroquinone, 1,2,4‐trihdroxybenzene, 4‐nitropyrogallol, and 4‐nitrocatechol were tentatively identified as the intermediates of 4‐NP degradation by GC/MS after samples were derivatized by N,O‐bis(trimethylsilyl)‐trifluoroacetamide (BSTFA). A degradation pathway was proposed to account for the observed intermediates produced during 4‐NP degradation by the UV/H₂O₂ process. Copyright © 2003 Society of Chemical Industry     

超重力强化O3/H2O2氧化甲苯合成苯甲酸的研究

提出一种超重力环境下甲苯合成苯甲酸的新方法,对比不同臭氧化工艺合成苯甲酸的收率,研究了反应溶剂、臭氧气相浓度、过氧化氢与甲苯的摩尔比、超重力因子、液体流量对苯甲酸收率的影响规律。研究结果表明：RPB (rotating packed bed)-O₃/H₂O₂较其他工艺具有更高的反应性能;得到优化的工艺条件是反应溶剂为乙腈、臭氧气相浓度为80 mg·L^-1、过氧化氢与甲苯的摩尔比为0.15、超重力因子为40、液体流量为120 L·h^-1,在优化的工艺条件下得到苯甲酸收率为45%。通过电子顺磁共振仪 (EPR)对反应过程中产生的活性自由基进行表征,结果表明,O₃/H₂O₂体系中存在·OH。另外,用气相色谱-质谱联用仪(GC-MS)分析了中间产物,结果表明反应过程中生成的中间产物包括苯甲醇和苯甲醛。基于ERP实验和GC-MS表征结果,探索臭氧/双氧水氧化甲苯合成苯甲酸可能的反应历程。     

A comparison of ethanol and water as the liquid phase in the direct formation of H2O2 from H2 and O2 over a palladium catalyst

Ethanol and water have been compared as the media in which hydrogen peroxide is produced from the reaction of H₂ and O₂ over a palladium catalyst. There are significant differences between the reaction in the two media with respect to the net rate of H₂O₂ formation, the state of the active Pd and the mechanism of the reaction. The reactions were carried out at atmospheric pressure and at 10 °C, with O₂ and H₂ being introduced in a 4/1 ratio through a glass frit. In ethanol, using 50 mg of 5 wt % Pd/SiO₂, 1.8 wt% H₂O₂ was attained in 7 h; whereas, about half this amount was attained in water. In addition, the net formation rate did not remain constant in water. Both systems were 0.17 N in HCl, which facilitated the formation of colloidal Pd in water but not in ethanol. The loss of activity in water is attributed to the instability of the colloid, which has been shown previously to be the active state of Pd. By contrast, these results show that supported Pd is the active state of the metal in the ethanol system. The mechanism for the formation of the nonselective product, water, also is affected by the media in which the reaction is carried out. In ethanol, water is formed by the direct reaction of H₂ and O₂, while in the aqueous phase, water appears to be formed both by the direct pathway and by the reduction of H₂O₂.     

Fe3O4协同H2O2气相高级氧化单质汞的机理

利用密度泛函理论分别研究了H₂O₂分子在Fe₃O₄（111）、（110）和（001）表面分解特性,并对单质汞在H₂O₂/Fe₃O₄体系的反应特性进行了研究。对比不同构型的结合能、Mulliken电荷转移和分态密度分析,详细讨论了H₂O₂分解产生羟基的规律以及Hg⁰的氧化态中间产物成键特性。结果表明：H₂O₂分子在Fe₃O₄（111）、（001） A和（110） A表面更容易分解产生羟基;不同表面产生的羟基对Hg⁰具有不同的氧化活性;Hg⁰在表面羟基的作用下可有效通过电荷转移实现氧化。对比分析了三种表面汞氧化态中间产物的脱附路径,HO-Hg-OH和Hg-OH的表面脱附是主要的反应路径。     

[{W(O)(O2)2(H2O)}2(μ‐O)]2–‐Catalyzed Epoxidation of Allylic Alcohols in Water with High Selectivity and Utilization of Hydrogen Peroxide

A dinuclear peroxotungstate, K₂[{W(O)(O₂)₂(H₂O)}₂(μ‐O)]⋅2 H₂O, exhibits high catalytic performance for the epoxidation of various allylic alcohols with only one equivalent of hydrogen peroxide at 305 K in water solvent. The effectiveness of this system is evidenced by high chemo‐, regio‐, and diastereoselectivity, and stereospecificity for the epoxidation of allylic alcohols. Furthermore, products/catalyst separation can be easily carried out by simple extraction and the catalyst recovered can be reused with the maintenance of the catalytic performance.     

Mechanism of the ClO2 generation from the H2O2‐HClO3 reaction

The development of chlorine containing species during the hydrogen peroxide‐based chlorine dioxide generation process has been determined. Accordingly, two distinct phases, namely the induction period and the steady‐state phase, were identified. In the induction period, it was observed that chloride and chlorous acid are generated, while chlorine, a byproduct from some methanol‐based processes, is not detectable. The absence of chlorine is explained by the fast reaction kinetics between hydrogen peroxide and chlorine, which results in the formation of chloride. In the steady‐state phase, due to the accumulation of chloride and chlorous acid during the induction period, the reaction between chloric acid and chlorous acid, which is responsible for the generation of chlorine dioxide in the hydrogen peroxide‐based ClO₂ process, becomes possible. Chloride is a catalyst in such a reaction.     

Catalytic partial oxidation of CH4 over bimetallic Ni‐Re/Al2O3: Kinetic determination for application in microreactor

The activity of a novel Ni‐Re/Al₂O₃ catalyst toward partial oxidation of methane was investigated in comparison with that of a precious‐metal Rh/Al₂O₃ catalyst. Reactions involving CH₄/O₂/Ar, CH₄/H₂O/Ar, CH₄/CO₂/Ar, CO/O₂/Ar, and H₂/O₂/Ar were performed to determine the kinetic expressions based on indirect partial oxidation scheme. A mathematical model comprising of Ergun equation as well as mass and energy balances with lumped indirect partial oxidation network was applied to obtain the kinetic parameters and then used to predict the reactant and product concentrations as well as temperature profiles within a fixed‐bed microreactor. H₂ and CO production as well as H₂/CO₂ and CO/CO₂ ratios from the reaction over Ni‐Re/Al₂O₃ catalyst were higher than those over Rh/Al₂O₃ catalyst. Simulation revealed that much smoother temperature profiles along the microreactor length were obtained when using Ni‐Re/Al₂O₃ catalyst. Steep hot‐spot temperature gradients, particularly at the entrance of the reactor, were, conversely, noted when using Rh/Al₂O₃ catalyst. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1691–1701, 2018     

Use of O3 and O3/H2O2 for degradation of organic matter from Bayer liquor towards new resource management: Kinetic and mechanism

Since the quality of bauxite resources has decreased and the organic carbon content has increased, different approaches are explored to remove the organic matter in alumina production. Advanced oxidative processes (AOPs) represent a possibility since they are widely used as an alternative for treating wastewaters to degrade organic pollutant molecules and in hydrometallurgy processes. For this reason, the goal of the project was the ozonation of Bayer liquor for organic matter removal. The ozone concentration was evaluated over time, as well as the H₂O₂ concentration and temperature. Results showed that the total organic carbon (TOC) removal achieved 19% in the most optimized condition with a kinetic rate of 0.0157 h⁻¹ –21.9 mg/L O₃, 0.05 mol/L H₂O₂ at 80°C. The colour of the liquor changed from dark brown to white-yellow, indicating that the size of the organic compounds had decreased. Also, 95.4% of degraded TOC formed CO₂, and almost 50% of the organic matter was oxalate compounds. The energy required for ozone production versus removed organic matter demonstrated that the technique proposed might be technically and economically feasible to be applied in the Bayer process. The study demonstrates the application of AOP in an extremely alkaline condition.     

Simultaneous removal of COD and NH3‐N in secondary effluent of high‐salinity industrial waste‐water by electrochemical oxidation

BACKGROUND: Electrochemical oxidation has been applied successfully in industrial waste‐water treatment. The simultaneous removal of COD_Cr and NH₃‐N, as well as the corresponding mechanisms and reaction zone, were examined in this study. The reaction kinetics and the significant factors that affect removal performance were also studied. RESULTS: The COD_Cr removal efficiency without chlorides in waste‐water was only 11.8% after 120 min of treatment, which was much lower than the efficiency with chlorides, and agitation did not improve the performance. When the current density was increased from 2.5 to 10 mA cm^?2, the removal efficiency was improved. The removal efficiencies of COD_Cr and NH₃‐N were less at initial pH = 11 than at pH = 3 and 8.7 (without adjustment). The COD_Cr and NH₃‐N removal efficiencies were decreased by about 30% and 50%, respectively, when the electrode distance was increased from 4 to 12 cm. Instantaneous current efficiency decreased with increase in current density. CONCLUSIONS: The degradation of pollutants occurred mainly at the boundary layer between the electrode and the bulk solution. The indirect oxidation by active chlorine generated from the chlorides was proven to be the primary mechanism of electrochemical oxidation treatment. The removal of COD_Cr in this study followed a pseudo‐first‐order kinetic model. Copyright © 2011 Society of Chemical Industry     

Photodegradation of tetracyclines in aqueous solution by using UV and UV/H2O2 oxidation processes

BACKGROUND: The objective of the present study was to analyse the kinetics of photodegradation of three antibiotics from the tetracycline group (tetracycline (TC), chlortetracycline (CTC) and oxytetracycline (OTC)), and the influence of the operational variables: (1) initial concentration; (2) initial solution pH; (3) addition of hydrogen peroxide; (4) effect of the aqueous matrix (ultrapure water (UW), surface water (SW), groundwater (GW) and waste‐water (WW) on these processes. RESULTS: The results obtained show that the photodegradation of the three tetracyclines fits first‐order kinetics. The degradation rate depends on initial concentration and pH. Low concentrations of H₂O₂ markedly increased the efficacy of TC photolysis, with a linear relationship between degradation rate and H₂O₂ concentration for concentrations of 2 × 10^?2 to 2 × 10^?1 mmol L^?1. The photodegradation rate is higher in real waters than in ultrapure water. The toxicity of oxidation by‐products formed during tetracyclines photooxidation process was determined by a bioluminescent test, showing that toxicity increases during the process. CONCLUSIONS: Oxidation of tetracyclines by UV radiation alone is slow due to the low quantum yield determined. The UV/H₂O₂ process is an interesting alternative to oxidise tetracyclines in aqueous solution, because this process decreases total organic carbon concentration and tetracyclines oxidation by‐products toxicity. Copyright © 2010 Society of Chemical Industry     

Advanced oxidation of raw and biotreated textile industry wastewater with O3, H2O2 /UV‐C and their sequential application

The advanced chemical oxidation of raw and biologically pretreated textile wastewater by (1) ozonation, (2) H₂O₂ /UV − C oxidation and (3) sequential application of ozonation followed by H₂O₂ /UV − C oxidation was investigated at the natural pH values (8 and 11) of the textile effluents for 1 h. Analysis of the reduction in the pollution load was followed by total environmental parameters such as TOC, COD, UV–VIS absorption kinetics and the biodegradability factor, f_B. The successive treatment combination, where a preliminary ozonation step was carried out prior to H₂O₂ /UV − C oxidation without changing the total treatment time, enhanced the COD and TOC removal efficiency of the H₂O₂ /UV − C oxidation by a factor of 13 and 4, respectively, for the raw wastewater. In the case of biotreated textile effluent, a preliminary ozonation step increased COD removal of the H₂O₂ /UV − C treatment system from 15% to 62%, and TOC removal from 0% to 34%. However, the sequential process did not appear to be more effective than applying a single ozonation step in terms of TOC abatement rates. Enhancement of the biodegradability factor (f_B) was more pronounced for the biologically pretreated wastewater with an almost two‐fold increase for the optimized Advanced Oxidation Technologies (AOTs). For H₂O₂ /UV − C oxidation of raw textile wastewater, apparent zero order COD removal rate constants (k_app), and the second order OH· formation rates (r_i) have been calculated. © 2001 Society of Chemical Industry     

Chemical vapor deposition of gold on Al2O3, SiO2, and TiO2 for the oxidation of CO and of H2

In order to clarify the effect of metal oxide support on the catalytic activity of gold for CO oxidation, gold has been deposited on SiO₂ with high dispersion by chemical vapor deposition (CVD) of an organo-gold complex. Comparison of Au/SiO₂ with Au/Al₂O₃ and Au/TiO₂, which were prepared by both CVD and liquid phase methods, showed that there were no appreciable differences in their catalytic activities as far as gold is deposited as nanoparticles with strong interaction. The perimeter interface around gold particles in contact with the metal oxide supports appears to be essential for the genesis of high catalytic activities at low temperatures. This revised version was published online in July 2006 with corrections to the Cover Date.