Ozone Self-decomposition Research Articles

Development and Experimental Validation of the Model of a Continuous-Flow Countercurrent Ozone Contactor

The objective of the research described in this paper was the development of a fully mechanistic model for ozone mass transfer from the gaseous to aqueous phase and aqueous ozone self-decomposition in a continuous-flow countercurrent ozone contactor. The developed model incorporated concepts describing the rate and extent of ozone mass transfer from gaseous phase to aqueous phase and comprehensive consideration of ozone decomposition reactions in the aqueous phase. Simulation of the effects of changes in the influent gaseous ozone concentration, aqueous-phase pH, and scavenger concentration on the ozone mass transfer and decomposition was accompanied by an explanation of the simulation results based on the current understanding of ozone mass transfer and aqueous ozone chemistry. Experimental work included fabrication and operation of a laboratory-scale continuous-flow countercurrent ozone contactor. Experimental data concerning the steady-state aqueous ozone concentration in the reactor and the effluent g...

Taking mass transfer limitation into account during ozonation of pollutants reacting fairly quickly

Various situations observed when oxidizing organic compounds via ozone in a semi-batch reactor are illustrated. The resistance to the transfer of ozone from gas to liquid is accounted for using the film model. The mass balances are numerically solved simultaneously within the reactor and within the film to produce time dependent profiles of concentrations, Hatta, enhancement and depletion factors. Firstly, theoretical profiles are exemplified for various kinetic regimes from slow to fast; reaction occurs either in the bulk, in the film or in both. This shows the drastic importance of the shapes of the gas concentration profiles both at the exit of the reactor and in the liquid phase - in determining the regime. Then, a typical example dealing with fumaric acid ozonation is shown. Firstly, the acid itself oxidizes rapidly producing an intermediate regime: part of the reaction occurs within the film, part within the bulk and the rate constant can be determined. Then, the by-products oxidize more slowly producing a typical regime: reaction occurs within the bulk, the concentration of dissolved ozone is almost 0 and the mass transfer coefficient can be determined. Finally, when all organics have oxidized, the self-decomposition of ozone governs a slow kinetic regime: the concentration of dissolved ozone is close to equilibrium.

Catalytic ozonation of 2-dichlorophenol by metallic ions

This research is mainly to explore functional improvement by adding various kinds of metallic ions in the ozonation of 2-chlorophenol solution. During the experiment, various kinds of metallic ions (Pb+, Cu2+, Zn2+, Fe2+, Ti2+, and Mn2+) were added; it was found that the reaction rate increased in all cases. The best result was obtained by using manganese ions, followed by iron and titanium ions. At pH = 3 and 1 ppm Mn2+ concentration, the reaction rate was increased by three times. TOC removal rate was also increased from 12.6% to 38% at 60 min reaction time. Ozone self-decomposition with various kinds of metallic ions alone was tested. It was found the ozone self-decomposition coefficient is highly dependent on the reaction rate constant for ozonation of 2-chlorophenol. The improvement of reaction was relevant to the mechanism of reaction between ozone and metallic ions. Furthermore, the effect of adding manganese ions was studied. With the initial manganese concentration at 0-2 ppm, after gas exposure for 20 min the removal rate can be increased from 38% to 93%. TOC removal rate was increased from 11% to 38%. The reaction rate was improved more greatly at the initial pH = 3.

Treatment Rate Improvement of the Ozone Oxidation Method for Laundry Waste Water

Radioactive laundry waste water generated in nuclear power plants includes organic compounds to be removed, for which ozone oxidation treatment is a possibility. To verify the applicability, its total organic carbon concentration (TOC) lowering rate improvement was examined in 0.5x10-3 m3 batch and 3x10-2 m3 pilot equipment experiments. In the batch experiments, ozone at a concentration of 200g/Nm3 was dispersed into 0.5x10-3 m3 of Simulated Laundry Waste Water (SLWW) with TOC of 11 mM. Total organic carbon concentration was measured every hour to see the effects of the temperature, and the initial concentrations of both H2O2 and NaOH which were added to urge OH radical generation from ozone. In the pilot equipment experiments, 1x10-2 to 3x10-2 m3 of the SLWW were circulated using an ejector to disperse the ozone. The influences of the flow rate and the SLWW volume on lowering TOC were examined, because they were related to the ejector dispersion performance and the appropriate ozone addition per SLWW volume. Appropriate initial H2O2 and NaOH concentrations in the batch experiments were 14.7mM and ImM, respectively. Lowering of TOC became faster at higher temperatures, because ozone self-decomposition and OH radical diffusion to the organic compound molecules were promoted. Lowering of TOC also became faster at higher flow rates, while the influence of the volume became saturated.

Combined Absorption and Self-Decomposition of Ozone in Aqueous Solutions with Interfacial Resistance

Abstract A theoretical analysis is performed employing the film model for the isothermal absorption and self-decomposition of ozone in aqueous solutions with interfacial resistance, which is inversely proportional to the interfacial mass transfer coefficient ks. A closed-form solution has been obtained. The effects of system parameters on the ozone mass transfer rate are examined. These parameters include the interfacial resistance (1/ks), the acidic and basic self-decomposition reaction rate parameters (Mm 0.5, Mn 0.5.; Mm = [2DAkmCAi m-1/(m+1)]/(kL 0)2, Mn=(2DAknCAi n-1/(n+1))/(kL 0)2, the reaction orders (m,n), the pH value of solution, and the liquid-phase mass transfer coefficient (kL 0). The results indicate that the reduction effect of the interfacial resistance on the absorption rate is most significant for the situation with the larger values of Mm and Mn as well as with higher pH values. Also, for any particular finite value of kL 0/ks, the reduction effect encountered is greater for a gas liqui...

Ozone Solubility in Phosphate-Buffered Aqueous Solutions: Effect of Temperature, tert-Butyl Alcohol, and pH

Ozone solubilities in aqueous solutions containing phosphate buffers and tert-butyl alcohol have been measured in the ranges 0 < I < 0.48 M, 18 °C < T < 42 °C, and 2 < pH < 6. The experimental method adopted accounts for the reaction of ozone self-decomposition, by evaluating the relevant rate constant for each experiment. The results obtained at constant pH can be coherently explained in terms of a salting-out effect. In contrast, a rather complex behavior has been observed when changing the pH. This effect can be tentatively explained when accounting for the detailed composition of the solutions and for the activity coefficients of the ionic species.

Influence of Lignins on the Degradation of Cellulose During Ozone Treatment

Abstract Three lignin-carbohydrate model systems were studied to determine the mechanism of the effect of lignin on cellulose degradation during ozone bleaching. The three model systems are: methyl β-D-glucopyranoside, dextran and fully-bleached kraft pulps in the presence of various lignin model compounds. It was found that the lignin models can both promote and suppress the degradation of the carbohydrate during ozone treatment. The presence of the lignin models can exhibit a protective effect by competing with the carbohydrates for the ozone available in the system. On the other hand, the ozone-lignin reactions give rise to the formation of hydroxyl radicals which promote the carbohydrate degradation. It is suggested that much more hydroxyl radicals are formed via the ozone-lignin reaction route than via ozone self-decomposition. Among the lignin model compounds studied, the phenolic lignin structures have a more pronounced effect on carbohydrate degradation. This is explained by the easier formation o...

Decomposition rate of volatile organochlorines by ozone and utilization efficiency of ozone with ultraviolet radiation in a bubble-column contactor

Decomposition of volatile chlorohydrocarbons in the gas and aqueous phases is tested in a thin, rectangular-channel reactor. In the absence of u.v. irradiation, destruction of pollutants in the gas phase hardly occurs, while there is a little in the aqueous phase. Ultraviolet irradiation accelerates the destruction of pollutants in both the gas and aqueous phases, and the destruction rate is proportional to the concentration of reactants and the u.v. intensity. To evaluate the effect of reactor configuration and operational conditions on the performance of the actual water treatment process, a bubble column equipped with a diffuse lamp along the central axis is adopted as a model reactor. The conversion of volatile chlorohydrocarbons and the ozone utilization efficiency are calculated by considering the mass transfer of ozone and pollutants between the gas and aqueous phases, and the self-decomposition of ozone and destruction rate of pollutants in each phase under u.v. irradiation. A simulation on the basis of the experimental data obtained predicts that excessive u.v. radiation decomposes ozone in the gas phase before it is transferred into the aqueous phase, causing a decrease in the utilization efficiency of ozone.

Kinetics of ozone decomposition and oxidation of a model organic compound in water

The decomposition of ozone and oxidation of a model, polychlorinated organic compound, 2,3,4,5,6-pentachlorobiphenyl were studied. The parameters included self-decomposition of ozone at various pH values, mass transfer of ozone, and the rate of oxidation of 2,3,4,5,6-pentachlorobiphenyl. The decomposition of ozone follows a second-order reaction kinetics. Below pH 5, the rate of decomposition is not pH dependent and is slow. Above pH 5, the rate is pH sensitive and k o is specific to the ionic strength of the solution. The decomposition of 2,3,4,5,6-pentachlorobiphenyl follows pseudo-first-order reaction kinetics. The decomposition rate varies with temperature, ozone, and substrate concentration in a complex manner even though the dependence of the rate on ozone and substrate concentration is first-order dependent.

Kinetics of the self-decomposition of ozone and the ozonation of cyanide ion and dyes in aqueous solutions.

Kinetic studies on the self-decomposition of ozone in water, the decomposition of CN- and CNO-, and the decolorization of several dyes by ozone were performed over a wide range of pH using a stopped-flow apparatus under homogeneous conditions at 298 K. The rate of selfdecomposition of ozone was measured in the pH range from 1 to 13.5, and it was found that in the pH range above 8 the rate was expressed by -d[03]/dt=314 [03] [OH-]0.88while in the acidic region the concentration dependence of the rate was complicated, and a simple rate expression could not be obtained. The rate of decomposition of CN- by ozone was expressed by -d[CN-]/dt=310 [O3]0.8 [CN-]0.55 (9.4<pH<11.6)and the rate of decomposition of CNO- was found to be much slower than that of CN-. The decolorization rates of naphthol yellow and methylene blue followed second-order kinetics. Rate constants are presented.

Overall rate of ozone oxidation of cyanide in bubble column.

Oxidation of cyanide with ozone was carried out using a semi-continuous bubble column and a continuous bubble column. It was found that the overall reaction rate was strongly controlled by liquid-film mass transfer resistance. The observed rate was satisfactorily explained by the theory of gas absorption with chemical reactions if the intrinsic rate expressions of self-decomposition of ozone and the ozone oxidation of cyanide which had been obtained by the present authors were applied to the theoretical equations. A method for evaluating capacity coefficient of liquid-phase mass transfer from the absorption rate of ozone into water of high pH is also presented.

Ozone treatment of water-soluble polymers. IV. Ozone degradability of water-soluble polymers

The ozone degradability of water-soluble polymers, i.e., polyethylene glycol, poly(vinyl alcohol), poly(vinyl pyrrolidone), polyacrylamide, and sodium polyacrylate, was studied in the aspects of ozonization rate and degradation efficiency. The reactions of ozone with polymers were first order, respectively, with respect to ozone and polymer, except poly(vinyl alcohol) under basic condition (1/2 order with respect to ozone). The reaction rate of poly(vinyl pyrrolidone) was the largest, while those of polyacrylamide and sodium polyacrylate were almost zero. The absorption rate of ozone into the polymer solution was affected by the reaction rate, the foaming property of solution, and the self-decomposition of ozone. In terms of chain breakage and complete oxidation to CO2, the degradation efficiency of polyethylene glycol was the best, and that of poly(vinyl pyrrolidone) was poor in spite of the high reaction rate. A little degradation was observed also in the case of polyacrylamide and sodium polyacrylate.

DECOLORING OF WATER-SOLUBLE AZO DYES BY OZONE

In recent years, the ozone treatments of waste water has attracted attention because of its extensive uses. In this report, the conditions of decoloring reaction by ozone, mainly for a watersoluble azo dye, C. I. Acid Orange 12 (A. O. 12), have been reported. The results obtained are as follows:1) In the decoloring of A. O. 12 by ozonea) The reaction is of pseudo first order.b) The dissociation of OH group of the dye and the self-decomposition of ozone appear to accelerate the reaction.c) The aromatic rings are cloven to form carboxylic acids.2) Ozone mainly attacks N=N bond in mono azo dyes.3) A. O. 12 is considered to decompose to the final products via intermediates containing active oxygen.

パルプのオゾン漂白に及ぼすオゾン濃度ならびに漂白温度の影響

The effects of ozone concentration, bleaching temperature and kinds of such carrier gases as oxygen and air on the properties of pulp bleached with ozone were studied to obtain the fundamental informations on the bleaching of kraft pulp with ozone gas. The results obtained are as follows : (1) The properties of bleached pulp were independent of ozone gas-concentrations (1 and 3 vol. % in oxygen gas), and kinds of carrier gases (oxygen and air), although they were affected by amounts of consumed ozone. (2) In the comparison of bleaching effects at 2 (±2) °C and 30 (±2) °C, the efficiency of ozone utilization, the ratio of increased brightness to consumed ozone by pulp, was improved by lowering temperature and the decrease in viscosity of bleached pulp was also somewhat prevented. (3) The effects described in (2) were presumably attributed to the prevention of self-decomposition of ozone, the retardation of the reaction of carbohydrates, e. g. cellulose, with ozone and the promotion of interaction between lignin and ozone.

パルプのオゾン漂白に及ぼすパルプシートの厚さならびにｐＨの影響

The effects of thickness and pH of pulp sheets on the properties of pulp bleached with ozone were studied to obtain the fundamental informations on the ozone bleached kraft pulp.The results obtained are as follows : (1) In ozone bleaching, the increasing degree of brightness of pulp in thinner sheets, basis weight of which was beyond approximately 95cm2/g, was greater than that of thicker sheets below that value. The brightness of the latter sheets decreased with thickness of sheets.This is presumably explained by the fact that bleach of sheets proceeded only in the surfaces because of poor air-permeability of pulp and high reactivity of ozone.(2) The efficiency of ozone consumption was independent of thickness of pulp sheets.(3) The brightness of bleached pulp decreased with increasing pH of pulp in ozone bleaching.The efficiency of ozone consumption increased with increasing pH of pulp. On the other hand, both yield and viscosity of bleached pulp decreased with increasing pH of pulp.(4) The effect of pH of pulp on ozone bleaching is probably attributed to the variation of oxidation potentials, rate of self-decomposition of ozone, and difference of reactivity of carbohydrates (such as cellulose and hemicellulose) with ozone.