Decomposition of 2-Chlorophenol in Aqueous Solutions by Ozone and UV/Ozone Processes in the Presence of t-Butanol

The decomposition of 2-chlorophenol in aqueous solutions by ozone and UV/ozone process was studied with the presence of t-butanol. The addition of t-butanol decreased the surface tension of aqueous solutions and subsequently increased the gas-liquid contact area. The presence of t-butanol did not affect the steady-state dissolved ozone concentration in aqueous solution; however, the ozone transfer rate between gas-liquid interface was noticeably enhanced and the time required to reach the steady state was reduced. The presence of t-butanol was found to promote the decomposition of 2-chlorophenol for both ozone and UV/ozone processes. Nonetheless, the presence of excessive dosages of t-butanol might decrease the reaction rates for experiments conducted in alkaline solutions probably because t-butanol also served as the scavenger for hydroxyl free radicals.     

A refined model for ozone mass transfer in a semibatch stirred vessel

The mathematical model proposed by Anselmi et al. (1984) for a semibatch stirred gas‐liquid contactor is refined to describe the mass transfer of ozone absorption and decomposition in aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C_ALb), the hold‐up gas (C_AGi), and the outlet gas in the free volume above the liquid surface (C_AGe), respectively. The effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E_r) defined as the ratio of mass absorbed per unit area in time t with chemical reaction (r) to that without chemical reaction or of the purely physical absorption, is considered in the refined model. Furthermore, the refined model also takes into account the variation of E_r with C_ALb, which changes with time during the course of gas‐liquid contacting. Thus this analysis extends the applicability of the model of Anselmi et al. (1984) and is of special importance for ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant, and in the system with variable liquid phase ozone concentration.     

Maleic Acid Ozonation: Reactor Modeling and Rate Constants Determination

This work is related to ozone treatment of organic wastes, a gas-liquid reaction. A model has been developed that accounts for mass transfer from the gas to the liquid and for the kinetics of chemical reactions. The theoretical approach of the model firstly refers to the film theory enhanced by a new parameter, the depletion factor. This method allows the part of the reaction occurring within the film and that occurring within the bulk to be distinguished. In relation with the first part of the model, the second part allows the overall behavior of a gas-liquid reactor with time to be described. The model is validated by a set of experiments on maleic acid ozonation in a semi-batch reactor.     

THE USE OF OZONATION TO REDUCE THE POTENTIAL FOR FORMING TRIHALOMETHANE COMPOUNDS IN CHLORINATING RESORCINOL, PHLOROGLUCINOL AND 1,3 CYCLOHEXANEDIONE

This study concerns the ozonation of Resorcinol, Phloroglucinol and 1,3 Cyclohexanedione in the presence of bromide ion in a bubble column, prior to chlorination. Preozonation in aqueous solutions reduces the potential for forming chlorinated trihalomethane compounds. At organic concentrations greater than 10^-4 M a short ozonation time increases the potential for forming trihalo compounds. At longer ozonation times the reverse is true. Finally the influence of mass transfer and chemical reaction on the ozone absorption rate have been evaluated following the film theory.     

THE USE OF OZONATION TO REDUCE THE POTENTIAL FOR FORMING TRIHALOMETHANE COMPOUNDS IN CHLORINATING RESORCINOL,PHLOROGLUCINOL AND 1,3 CYCLOHEXANEDIONE

This study concerns the ozonation of Resorcinol, Phloroglucinol and 1,3 Cyclohexanedione in the presence of bromide ion in a bubble column, prior to chlorination. Preozonation in aqueous solutions reduces the potential for forming chlorinated trihalomethane compounds. At organic concentrations greater than 10^?4?M a short ozonation time increases the potential for forming trihalo compounds. At longer ozonation times the reverse is true. Finally the influence of mass transfer and chemical reaction on the ozone absorption rate have been evaluated following the film theory.     

Influence parameters in the ozonation of phenol wastewater treatment using bubble column reactor under continuous circulation

The ozonation of phenol wastewater treatment system has been investigated with effective mass transfer between gas and liquid phase in a bubble column reactor. The designed bubble column reactor was investigated for increasing the rate of mass transfer of ozone, the rate of oxidation of phenol in the solution, the solubility and decomposition rate of ozone in the distilled water were also studied at different flow rates. The decomposition rate constants were calculated based on pseudo first order kinetics. The oxidation of phenol was investigated in order to provide the overall reaction rate constant for the reaction between ozone and phenol at 25 °C. The influence of the operating parameters like initial phenol concentration, ozone flow rate and pH for the destruction of phenol by ozonation were studied. The pseudo first order rate constant was depending on the initial concentration of phenol solution. A comparison of TOC removal percentage between bubble column reactor and bubble diffuser using ozonation were reported.     

Intensification of nitrous acid oxidation

An alternative solution to the reduction of a discharge of residual nitric oxide and nitrogen dioxide into atmosphere has been proposed. Instead of using methane or ammonia for SCR or gas absorption into alkali solutions, which are the most popular treatment methods of tail gases, now the use of powerful oxidant—ozone capable of transforming nitrous acid and nitric oxides into nitrogen of the highest oxidation level—could be employed for this purpose. As the intensive oxidation and ozonation of nitrous acid is the heterogeneous gas-liquid process, the solubility of oxygen and ozone in HNO₂/HNO₃ aqueous solution was necessary to be determined. Variations of reaction rates depending on temperature, ozone dose and nitrous and nitric acid concentrations were studied experimentally. The kinetic model of the reactions, 2HNO₂+O₂→2HNO₃ and HNO₂+O₃→O₂+HNO₃, were proposed and the kinetic parameters (rate constants and activation energies) were estimated on the basis of experimental data in semi-batch laboratory gas-liquid contactor with the liquid phase drawn from an absorption column in the nitric acid plant. The determined kinetic parameters were then used in designing and modeling of the oxidation of nitrous acid using ozone-oxygen mixture in a continuous bubble column. The model consists of mass transfer kinetic equations and material balance equations for the gas and liquid phases. The co-current flow of gas and liquid phases and the complex kinetics of chemical reaction in the liquid phase were taken into account. The variation of the following process conditions, flow rate, compositions of the gas and liquid phases, temperature, and pressure in the bubble column of different diameters and heights, were studied in numerical solutions of the proposed model.     

2,4-Xylidine Degradation with Ozonation: Mass Transfer and Reaction Kinetics

The kinetics of the degradation of 2,4-xylidine by ozonation as well as the ozone mass transfer in a wetted-wall column were investigated. A laboratory-scale ozone contactor was designed, and a steady-state wetted wall reactor model was developed. The model was based on countercurrent-connected and perfectly mixed mass transfer stages. It was possible to describe the evolution of the pollutant and ozone concentrations along the reactor length coordinate in various conditions. The model was used for the evaluation of the ozone mass transfer coefficient, reaction rate kinetics, and stoichiometric coefficient from experimental data. The ozone mass transfer coefficient for the wetted-wall column was estimated from the experiments in the absence of chemical reactions. When the estimated parameters were applied, the ozonation model of the wetted-wall column showed good agreement between the fitted and experimental data.     

Ozonation of Cycloalkenes Dissolved in Ethanol

The ozonation of cyclooctene and cyclododecene in ethanol was studied at 278 K in a stirred reactor with a flat gas/liquid interface. The parallel reactions with ethanol in the gas and the liquid phase had to be accounted for. At high cyclooctene concentrations, ozone transfer into the liquid phase was enhanced by up to a factor of E = 325. Due to the high ozone solubility and the high enhancement factors, up to half of the mass transfer resistance was on the gas-side. The reaction rate constant k₂ is more than threefold higher for cyclooctene as compared to cyclododecene.     

Vapor and Liquid Phase Ozonation of Benzene

A comparative study is made of the benzene-ozone reaction in the gaseous and aqueous phase reactors at atmospheric pressure and 25°C. The vapor phase ozonation of benzene is first order in ozone and independent of benzene concentration. In distilled water (pH ranging from 5.2 to 5.4), the reaction is one-half order with respect to both concentrations of dissolved benzene and ozone. The overall rate constants are 0.0011 and 2.67 s^?1, respectively, in the vapor and liquid phase reactions. Results of this study suggest that it is technically feasible to remove benzene from a gas stream by the ozonation process, although the reaction rate is slow.     

超重力强化臭氧高级氧化技术的研究进展

臭氧高级氧化技术因其绿色高效、适用性广、操作简便等优势,成为当前水处理领域前沿技术之一,但臭氧在传统反应器内普遍存在吸收效果差,臭氧利用率低等缺陷。旋转填料床（RPB）利用高速旋转的填料产生超重力场,将液体剪切破碎为细小的液膜、液丝或液滴,其较高的相界面积、不断更新的界面以及内部流体的强制湍动,加快了臭氧的传质与分解,该技术对于传质受限的臭氧高级氧化过程的强化有着突出的优势。本文简述了超重力强化臭氧氧化过程的原理,介绍了RPB与O₃、O₃/H₂O₂、O₃/Fenton、O₃/PS（过硫酸盐）、催化臭氧氧化等高级氧化法耦合应用处理有机废水的研究现状,并对超重力技术的优势及技术突破进行了述评,总结了超重力应用臭氧高级氧化技术的潜在经济效益和环境效益,提出功能化填料及大型RPB的开发需求,以期为超重力技术在废水处理领域的拓展应用提供理论基础和技术参考。     

Catalysts to improve the abatement of sulfamethoxazole and the resulting organic carbon in water during ozonation

Sulfamethoxazole (SMX), one pharmaceutical compound, has been treated in aqueous solutions with catalysts (copper and cobalt type perovskites and cobalt–alumina) and promoters (activated carbons). Hydrogen peroxide and saturated carboxylic acids were identified as intermediates. The effects of adsorption and pH have been investigated. Removal of the starting SMX accomplished with ozone alone is a fast process but catalytic or promoted ozonation is needed to significantly reduce the resulting organic carbon. SMX is, thus, mainly removed through direct ozone reaction while hydroxyl radical oxidation is the mechanism of removal the remaining TOC. The kinetics of the process has also been investigated. Perovskite catalytic ozonation resulted to be a chemical control process and apparent rate constants for homogeneous and heterogeneous ozonation were determined. For activated carbon ozonation, external diffusion of ozone to solid particles controlled the process rate.     

臭氧吸收中的增强因子

臭氧吸收中的增强因子程江，杨卓如，陈焕钦（华南理工大学化工研究所，广州５１０６４１）关键词臭氧，吸收，增强因子１前言臭氧化法在饮水消毒和废水处理中的应用日趋普及，但有关臭氧吸收理论的研究报导还不多。在臭氧吸收过程中，由于臭氧很不稳定，在臭氧与水中污染...     

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.     

Kinetic Study of the Ozonation of Some Industrial Wastewaters

Kinetic studies of the ozonation of two wastewaters released by distillery and tomato processing plants have been carried out. Once it has been assumed that an irreversible gas-liquid reaction is developed between ozone and the matter present in the water, the film theory concept was applied to this system for kinetic determinations. The evolution of the organic and inorganic matter with ozonation time has been followed by the chemical oxygen demand. The procedure allows the determination of the rate coefficients of ozone with the wastewaters treated. According to the results obtained, ozone is consumed through fast reactions which take place near the water-gas interface during an initial period. This period is used to determine the rate coefficients. Then, at more advanced ozonation times, the reactions become slower and hence they take place in the bulk of the water, articularly for the case of tomato wastewaters. Values of the rate coefficient allow us to establish both the kinetic regime of absorption and to compare the reactivity of ozone with the wastewaters and single compounds.     

臭氧吸收中液相臭氧浓度和增强因子理论预测

研究了臭氧在鼓泡塔中吸收时,水中溶解臭氧浓度随时间的变化规律以及pH值对它的影响。建立了臭氧吸收数学模型,可较准确地预测水中溶解臭氧浓度;同时基于稳态膜理论,提出了带有一个一级臭氧自分解反应和多个一级或二级臭氧氧化反应臭氧吸收过程的增强因子理论预测模型,与文献值比较,结果合理。     

Development of a tool, using CFD, for the assessment of the disinfection process by ozonation in industrial scale drinking water treatment plants

Foreseen standards regarding microorganism content for drinking water require assessment of the capability of existing plants to reach the upcoming requirements. This paper presents the development of a tool to assess this capability in a commonly encountered key step of water disinfection: ozonation. In this paper, this tool is applied to the test case of an ozonation channel of the Belgian drinking water producer Vivaqua. This tool is based on a mathematical model of the momentum and mass transport phenomena in an ozonation channel. The gas–liquid flow is coupled to ozone mass transfer and kinetics describing the ozone and microorganisms concentrations decay. The degradation of Bacillus subtilis spores, as a representative of resistant microorganisms, is implemented in the model. The model takes explicitly into account the bubble size variation and its impact on mass transfer. Bubbles sizes and kinetics parameters are estimated based on dedicated experiments. The model is partially validated by comparing simulations results, obtained using computational fluid dynamics, to experimental residence time distributions, residual ozone concentration and Bacillus subtilis spores degradation efficiency measurements obtained on the studied ozonation channel. It is shown that, at the industrial scale, bubble diameter variation has a significant impact on ozone concentration in the liquid at the reactor exit. Using the tool, it is also shown that, the ozonation channel of Vivaqua can be used to achieve degradation of resistant microorganisms but only with its maximal flow rate and concentration of ozone injection. Moreover, at low operating temperature, some microorganisms that present latency towards reaction with dissolved ozone might hardly be destroyed.     

Reaction Kinetics of Ozonation of Trichloroethylene and Benzene in Gas and Liquid Phase

The kinetics of ozonation reactions oftrichloroethylene (TCE) and benzene in gas and liquid phases at101.3 kPa and 298 K was investigated in this paper. The ozonation ofTCE is first order with respect to the ozone concentration and one andhalf order to TCE in the gas phase with the average rate constant 57.30(mol*L-1)-1.5 *s-1, and the TCE ozonation inaqueous medium is first order with respect to both ozone andtrichloroethylene with the average rate constant 6.30(mol*L-1)-1 *s-1. The ozonation of benzene inthe gas phase is first order in ozone but independent of the benzeneconcentration with the average reaction rate constant 0.0011 s-1.The overall kinetics of reaction between ozone and benzene in aqueoussolution is found to be first order with one-half order in both ozoneand bezene, with the average reaction rate constant 2.67 s-1. Itis found that the ozonation rate of pallutants is much quicker than that ofself-decomposition of ozone in both gas and aqueous phase.     

Theoretical estimation of the apparent rate constants for ozone decomposition in gas and aqueous phases using ab initio calculations

An ab initio study, using the coupled cluster calculations (CCSD) method was conducted to investigate the kinetics of the ozone degradation in gas and aqueous phases considering the reaction of ozone with the hydroperoxyl radical. Two potential transition state paths, oxygen and hydrogen transfer, are studied and compared. It was revealed by the ab initio quantum chemical calculations that the calculated overall rate constant in the gas phase differs by approximately an order of magnitude from measured values. However, the calculated selectivity (branching fraction), which was measured directly with isotope studies of hydrogen atom transfer, is almost exactly equal to the experimental value at 298.15 K. The sensitivity analysis showed that adding the reaction between ozone and hydroperoxyl radical to the kinetic model accelerates the decomposition process by more than four times in the aqueous phase (pH = 7–8.5), and for an order of magnitude change in the rate constant of this reaction, the decomposition half-life changes by 20–45 %. This result might affect our understanding of atmospheric ozone chemistry.     

Preliminary Investigations On The Reactivity Of Ozone Considering Energy Supplied To Ozone Generators

A simplified engineering analysis developed by investigations of the energy levels and the data of ozone decomposition is presented. Experiments have been conducted by generating ozone from the same ozone generator by two ways and keeping the hydrodynamic conditions identical during ozonation. Ozonation conducted in various media such as gas, gas-liquid and gas-solid supports the assumptions of the presence of excited ozone species and variation in reactivity. The variation in reactivity linked with ozone generation shows an increase in the case of sawdust bleaching. The reactivity is the same for the removal of total organic carbon from water, and a higher ozone decomposition without significant reaction with methyl red solutions and coliform inactivation is observed.