Kinetics Of Ozone Decomposition Research Articles

Dissociation Kinetics of Gaseous Ozone in Onion (Allium Cepa L.) Bulbs

ABSTRACT Ozone decomposition kinetics varies significantly in the presence of biological commodity. This variation depends on many factors but primarily on the active sites in agricultural commodities and storage environments. Ozone decomposition kinetics in onion bulbs at temperatures (2, 10, and 18°C) and relative humidity (RH) (35 & 85%) for different ozone concentrations (100, 200, 300 ppm) and number of exposures (1, 2, 3) were investigated. Zero-order, first-order, and second-order kinetic models were fitted to the ozone decomposition data with respect to time. It was found that the decomposition kinetics follows a first-order reaction and the decomposition rate constant ( k d ) varies from 1.712 × 10−3 s−1 − 5.181 × 10−3 s−1 in the presence of onion. The half-life period ( t 1 / 2 ) was found to increase with concentration and number of exposures and decrease with temperature and relative humidity. The activation energy was found to vary between 1.840 and 10.216 kJ mole−1 and 6.271–12.461 kJ mole−1 for the relative humidity of 85% and 35%, respectively.

The Effect of Halide Ions on the Activity of D-metal Complexes Supported on Natural Bentonite in the Reaction of Low Temperature Ozone Decomposition

The effect of halide ions (X= Cl−, Br−, I−) on the kinetics of ozone decomposition by compositions supported on the natural bentonite of the Dashukovske deposit in Ukraine (N-Bent(D)) has been studied. The obtained results have shown that the activity of the KX/N-Bent(D) composition in the ozone decomposition reaction increases in the row KCl << KBr < KI, which correlates with an increase in their reducing properties (the redox potential of the Х2/2Х− pair decreases). Such catalyst compositions can be recommended for applying in personal protective equipment for the respiratory system.

Control of Listeria monocytogenes in Refrigerated Ozonated Water

ABSTRACT The present work aimed at the effectiveness of ozonated water in the control of Listeria monocytogenes, adopting different combinations of pH, contact time, and storage time under refrigeration. To obtain ozonated water, the dose applied was 21 mg L−1 min−1, for 15 min. Samples of 1.0 L of water were ozonated at the inlet ozone concentration of 21 mg L−1 and a flow rate of 1.0 L min−1. The initial concentrations of ozone dissolved in water were equal to 5.81 mg L−1 at pH 4.0, 5.20 mg L−1, at pH 7.0, and 7.20 mg L−1 at pH 8.2. Samples of ozonated water with different initial pHs were used and stored at 7℃ for up to 24 h. The storage times of the ozonated water under refrigeration were 0, 6, 12, 18, and 24 h. The contact times of L. monocytogenes with ozonated water were 3.0 and 6.0 min. Ozone decomposition kinetics was evaluated. Ozonated water stored at 7℃ proved effective in controlling L. monocytogenes, especially in water pH values of 7.0 and 8.2. The initial pH of the water affects the effectiveness of ozonated water regarding the control of L. monocytogenes. The sharp reduction in ozone concentration was observed in water with pH 4.0, with a half-life of 13 min. For pHs of 7.0 and 8.2, the half-lives were 65 and 45 min, respectively. It is viable to use ozonated water stored at 7℃, for up to 24 h, to inactivate L. monocytogenes, when adopting initial pHs of 7.0 and 8.2, adjusted with sodium bicarbonate.

OZONE DECOMPOSITION OVER ACTIVE COAL ANCHORED Cu(II), Co(II), OR Mn(II) CHLORIDES

The known catalyst based on the inorganic support, MnCl2/SiО2, and used in personal respiratory protective devices showed its lack of prospects because of the very heavy load per a protective device and the short time of its protective action. As opposed to it, metal complex compositions based on activated carbons (AC) hold much promise. Since we intended to use activated carbons or compositions based on them in respirators protection against ozone, such an important parameter as the time of protective action was determined for activated carbons of different ranks and for the best one among MCl 2 /AC compositions (M is Cu, Co, or Mn, AC is activated carbon of KAD-iodnii rank) at initial ozone concentrations, СinО 3 , of 1,5 mg/m 3 and 10 mg/m 3 . For selection of the most effective MCl 2 /KAD-iodnii AC composition, the kinetics of ozone decomposition was investigated at СinО 3 = 500 mg/m3. The results of the latter testing showed that activity of the MCl2/KAD-iodnii AC compositions depended not only on the metal and anion nature but also on a degree of the activated carbon surface filling with metal ions. The maximum degree of ozone decomposition in a steady-state mode was demonstrated by MnCl 2 /KAD-iodnii AC. This fact can be explained by MnO 2 formation as a result of MnCl 2 oxidation with ozone. MnO 2 can be a secondary catalyst and stabilize the process of ozone decomposition. The time of protective action for activated carbons significantly depends on their chemical nature and specific micropore and mesopore volumes and increases in the order SKN-K < ART < KAD-iodnii < AG-3 < SKN-2M. MnCl2 anchoring on activated carbon of KAD-iodnii rank resulted in an essential increase in the time of protective action: an ozone outlet concentration was lower than MPCO 3 even in 48 hours. The protective properties of the catalyst for ozone microconcentration decomposition obtained by activated carbon of KADiodnii rank impregnation with MnCl2 are much better than those of the known domestic and foreign analogues and this composition can be used in the devices for protecting environment and human beings against ozone.

Enhancement of ozonation efficiency employing dead-end hollow fiber membranes

Dead end membrane operation maximizes O3 dissolution.

Near-ambient temperature ozone decomposition kinetics on manganese oxide-based catalysts

Catalytic ozone decomposition on various manganese oxide-based catalysts was investigated at 40 °C for ozone concentrations in the range 2–20 ppm in dry and humid conditions. Ozone conversion efficiency shows a slight dependence with ozone concentration, slightly decreasing when ozone concentration increases. A strong but reversible inhibiting effect was observed when water is present in the gas phase likely due to the reversible adsorption of water on ozone reaction sites. Whatever the catalyst used, the same behavior was observed which is characterized by a transient decrease in efficiency at the beginning of the reaction until reaching the steady-state. A kinetic model was developed, based on the mechanism of ozone decomposition proposed by Oyama and co-workers, allowing us to properly describe the reaction behavior of ozone on manganese oxide catalysts for variable initial reactant concentrations. Additionally, the transient behavior of the MnO2 catalysts experimentally observed at the beginning of the ozone decomposition reaction was kinetically described for the first time, as well as the steady-state.

Kinetics of ozone decomposition in porous In2O3 monoliths.

The performance of many chemical gas-phase reactions is strongly influenced by the interaction of reactants with interfaces. Nanoporous materials, which exhibit pore diameters up to 100 nm and high specific surface areas, can be utilized to reduce the amount of cost-intensive materials (e.g. noble metals). However, due to limitations in material transport and reaction kinetics detailed knowledge of the diffusion and the kinetics of a chemical reaction is necessary to improve the performance of chemical processes in industry and research. To experimentally study the diffusion and reaction kinetics of gaseous species inside such pores, the chemoresistive behavior of certain metal oxides such as In2O3 can be utilized. In this work, we present a model system based on hierarchically porous monolithic indium oxide (In2O3) which allows the determination of kinetic effects by utilizing its gas transducing properties. The experimental data obtained by electrical measurements are compared to two diffusion and diffusion-reaction models. Using these methods, the rate constant of ozone decomposition in porous In2O3 is estimated. The results are the basis for a suitable material design for semiconducting gas sensors, on the nano-, meso- and macroscale, which helps in understanding the underlying mechanisms of diffusion and reaction.

Surface modification of activated carbon fabric with ozone, part 1: Kinetics and oxidation degree

ABSTRACTTwo samples of activated carbon fabrics (ACF) with very high surface area (>1300 to >1800 m2/g) were reacted with ozone inside a closed flask under static conditions. The kinetics of ozone decomposition and reaction with the ACF surface was measured in the gas phase using Fourier transform infrared analysis (FT-IR) spectroscopy. The ozone consumption under these conditions was following the pseudofirst-order kinetics law and was accompanied by the production of CO2 and CO. The ozone-oxidized ACF were studied by FT-IR spectroscopy following the growth of key oxidized functional groups, i.e. phenolic OH, ketone groups intended as carboxyl, lactone, and anhydride, as well as quinone groups as a function of the amount of ozone reacted. The weight uptake of the ACF reacted with ozone was followed gravimetrically. The ACF having >1800 m2/g was able to reach a weight increase of 25% of its original weight due to the formation of oxygenated surface functional groups. Raman spectroscopy was used for the evaluation of defective structures formed in ACF because of ozonization reaction.

Efficient catalytic ozonation by ruthenium nanoparticles supported on SiO2 or TiO2: Towards the use of a non-woven fiber paper as original support

This work focuses on the use of Ru(0) nanoparticles as heterogeneous catalyst for ozone decomposition and radical production. In a first set of experiments, the nanoparticles have been deposited on two inorganic supports (TiO2 or SiO2) by a wet impregnation approach. This study confirmed the high potential of Ru nanoparticles as active species for ozone decomposition at pH 3, since the ozone half-life time decreases by a factor 20–25, compared to the reference experiment carried out without any catalyst. The enhancement of the ozone decomposition kinetics provided an improved radical production and a higher transient radical concentration in a shorten ozone exposure. Consequently, lower oxidant dosage and contact time would be necessary. Thus, very significant atrazine consumption kinetics enhancements were measured. In a second set of experiments, a non-woven fiber paper composed of a TiO2/SiO2/zeolite mixture has been evaluated as an original support for ruthenium nanoparticles. Even if lower ozone decomposition kinetics was observed compared to TiO2 or SiO2, this support would be a promising alternative to inorganic powders to avoid the catalyst recovery step and to design reactors such as tubular reactors. A new numerical procedure is presented for the evaluation of the transient HO concentration and of the Rct.

Ozone decomposition.

Catalytic ozone decomposition is of great significance because ozone is a toxic substance commonly found or generated in human environments (aircraft cabins, offices with photocopiers, laser printers, sterilizers). Considerable work has been done on ozone decomposition reported in the literature. This review provides a comprehensive summary of the literature, concentrating on analysis of the physico-chemical properties, synthesis and catalytic decomposition of ozone. This is supplemented by a review on kinetics and catalyst characterization which ties together the previously reported results. Noble metals and oxides of transition metals have been found to be the most active substances for ozone decomposition. The high price of precious metals stimulated the use of metal oxide catalysts and particularly the catalysts based on manganese oxide. It has been determined that the kinetics of ozone decomposition is of first order importance. A mechanism of the reaction of catalytic ozone decomposition is discussed, based on detailed spectroscopic investigations of the catalytic surface, showing the existence of peroxide and superoxide surface intermediates.

Atmospheric Pressure Atomic Layer Deposition of Al2O3 Using Trimethyl Aluminum and Ozone

High throughput spatial atomic layer deposition (ALD) often uses higher reactor pressure than typical batch processes, but the specific effects of pressure on species transport and reaction rates are not fully understood. For aluminum oxide (Al2O3) ALD, water or ozone can be used as oxygen sources, but how reaction pressure influences deposition using ozone has not previously been reported. This work describes the effect of deposition pressure, between ∼2 and 760 Torr, on ALD Al2O3 using TMA and ozone. Similar to reports for pressure dependence during TMA/water ALD, surface reaction saturation studies show self-limiting growth at low and high pressure across a reasonable temperature range. Higher pressure tends to increase the growth per cycle, especially at lower gas velocities and temperatures. However, growth saturation at high pressure requires longer O3 dose times per cycle. Results are consistent with a model of ozone decomposition kinetics versus pressure and temperature. Quartz crystal microbalance (QCM) results confirm the trends in growth rate and indicate that the surface reaction mechanisms for Al2O3 growth using ozone are similar under low and high total pressure, including expected trends in the reaction mechanism at different temperatures.

Effect of silver and copper ions on the decomposition of ozone in water

Features of the kinetics of ozone decomposition in water at pH 2 are studied depending on the concentration of silver and copper ions that are present. The existence of a critical concentration of metal ions (∼3−6 × 10−6 M) is established, below which ions slow the rate of ozone decomposition and above which the accelerate the process. It is concluded that the first region is due to the capture of hydroxyl and other radicals by metal ions, inhibiting the chain of ozone decomposition in water. A further increase in the concentration of ions leads to dominance of their direct interaction with molecules of ozone. A mechanism for the process is proposed and the rate constants of reaction of ozone with silver ions and copper are calculated (0.033 and 0.06 M−1 s−1, respectively).

Kinetic regularities of ozone decomposition in water

The paper studied the impact of the pH and temperature on kinetics of ozone decomposition in water. It has been shown that in the pH range 4 to 8 it is well described by the equation of the second order reaction. At an increase of the pH and temperature the rate of ozone decomposition increases. The relationship between the logarithm of the constant and the pH at 19°C corresponds to the equation log k(pH) = −0.7 + (0.49 ± 0.03)(pH 4). The energy of ozone decomposition activation constitutes 76.0 ± 8.3 kJ/mol. The presence in the solution of phosphate ions and tert-butyl alcohol substantially increases the rate of the decomposition chain process.

Mathematical simulation as a method to study the influence of oxygen, hydrogen peroxide, and phosphate and carbonate ions on the kinetics of ozone decomposition in aqueous solution

The influence of oxygen, hydrogen peroxide, and phosphate and carbonate ions on the kinetics of ozone decomposition in an aqueous solutions was studied by using mathematical simulation. The apparent rate constants of ozone decomposition and the hydroxyl radical concentration in the presence of compounds accelerating and inhibiting the ozone decomposition process were calculated. The calculated data were compared with the experimental results taken from literature sources.

The kinetics of ozone decomposition in water, the influence of pH and temperature

The influence of pH on the kinetics of ozone decomposition in water was studied. Over the pH range 1–8, the kinetics was well described by a second-order reaction equation. Starting with approximately pH 3, the pH dependence of the logarithm of the constant at 19°C corresponded to the equation logk= −2.66 + (0.49 ± 0.03)pH. The activation energy of ozone decomposition was found to be 76.0 ± 8.3 kJ/mol.

Numerical simulation of the kinetics of ozone decomposition in an aqueous solution

The kinetic scheme for ozone decomposition in an aqueous solution in a wide pH interval was proposed on the basis of the known literature data. The apparent first-order rate constant for ozone decomposition at pH 1–14 was calculated.

Kinetics of Ozone Decomposition by Granular Activated Carbon

The kinetics of the removal of ozone from air by granular activated carbon (GAC) has been investigated. Twenty GACs with different textural and chemical surface properties were used in this study. The kinetic experiments were carried out in an expanded bed reactor (EBR) and in a packed bed reactor (PBR). A rate equation that takes into account thermal ozone decomposition and removal of ozone by GAC due to chemisorption and catalytic decomposition has been proposed. Deactivation kinetics has also been considered in the reaction model. Intrinsic rate constants for thermal ozone removal (kT), chemisorption of ozone (k1), and GAC-catalyzed decomposition of ozone (k2), as well as deactivation rate constants (kd1 and kd2) have been evaluated from dynamic modeling. At the conditions used in this work, ozone was thermally stable only below 323 K. Above this temperature, ozone partially decomposed even in the absence of GAC. Temperature favored the rate of ozone removal by GAC following Arrhenius behavior while ai...

Kinetic study of ozonation of molasses fermentation wastewater

A kinetic study of molasses wastewater ozonation was carried out in a stirred tank reactor to obtain the rate constants for the decolorization reaction and the regime through which ozone is absorbed. First, fundamental mass transfer parameters such as ozone solubility, volumetric mass transfer coefficients and ozone decomposition kinetics were determined from semi-batch experiments in organic-free solutions with an ionic composition similar that of industrial wastewater. The influence of operating variables such as the stirring rate and gas flow rate on the kinetic and mass transfer parameters was also studied. The application of film theory allows to establish that the reactions between ozone and colored compounds in wastewater take place in the fast and pseudo-first-order regime, within the liquid film. The decolorization rate constants were evaluated at pH 8.7 and 25 °C, varying from 0.6 × 10 7 to 3.8 × 10 7 L mol −1 s −1, depending on the stirring rate and the inlet gas flow.

Ozone decomposition kinetics on alumina: effects of ozone partial pressure, relative humidity and repeated oxidation cycles

Abstract. The room temperature kinetics of gas-phase ozone loss via heterogeneous interactions with thin alumina films has been studied in real-time using 254nm absorption spectroscopy to monitor ozone concentrations. The films were prepared from dispersions of fine alumina powder in methanol and their surface areas were determined by an in situ procedure using adsorption of krypton at 77K. The alumina was found to lose reactivity with increasing ozone exposure. However, some of the lost reactivity could be recovered over timescales of days in an environment free of water, ozone and carbon dioxide. From multiple exposures of ozone to the same film, it was found that the number of active sites is large, greater than 1.4x1014 active sites per cm2 of surface area or comparable to the total number of surface sites. The films maintain some reactivity at this point, which is consistent with there being some degree of active site regeneration during the experiment and with ozone loss being catalytic to some degree. The initial uptake coefficients on fresh films were found to be inversely dependent on the ozone concentration, varying from roughly 10-6 for ozone concentrations of 1014 molecules/cm3 to 10-5 at 1013 molecules/cm3. The initial uptake coefficients were not dependent on the relative humidity, up to 75%, within the precision of the experiment. The reaction mechanism is discussed, as well as the implications these results have for assessing the effect of mineral dust on atmospheric oxidant levels.

A study on the kinetics of ozone decomposition in waters of different quality

The kinetics of ozone decomposition in waters of different quality, namely distilled water, tap water previously treated with ozone, tap water not treated with ozone and raw water from an accumulation lake, were studied in a batch stirred reactor at different temperatures (18-28?C). The dissolved ozone concentration was measured by the iodometric titration method. It was determined that an empirical kinetic equation of the form: dc(O3)/dt= k0 + k1c(O3) fitted the experimental data better than a first-order reaction rate equation. The apparent reaction rate constants in the case of ozone decomposition in distilled water were shown to be a function of temperature in accordance with the Arrhenius equation.