Generation of Active Oxidant Species by Pulsed Dielectric Barrier Discharge in Water-Air Mixtures

Experimental research into the electrical and optical parameters of pulsed dielectric barrier discharge (PDBD) was undertaken. PDBD was applied to humid air containing water droplets as a means of water oxidative treatment with short-living species generated in the discharge zone. In spectral analysis of PDBD, only small concentrations of nitric oxides were detected at the resulting electric field strength and electron mean energy sufficient for generation of OH-radicals. The water droplets served as electric field strength concentrators: PDBD was ignited close to the water droplets' surface.     

Formation of Nitrates in Aqueous Solutions Treated with Pulsed Corona Discharge: The Impact of Organic Pollutants

Pulsed corona discharge (PCD) in oxygen-nitrogen mixtures results in formation of nitrogen oxides, transformed to aqueous nitrates in contact with water. The experimental research into the impact of formate and oxalate to nitrate formation in aqueous solutions treated with PCD was undertaken. The impact of paracetamol, ibuprofen, indomethacin and their oxidation products to nitrate formation was also analyzed. Pharmaceuticals obstructed nitrate formation, while carboxylic anions and pharmaceuticals’ oxidation products noticeably improved nitrate formation in treated solutions as compared to water. The nitrate formation enhancement is explained by the aqueous ozone decomposition and hydroxyl radical formation known to be improved by carboxylic anions.     

On the Performance of Ozone Generators Working with Dielectric Barrier Discharges

The parameters, which determine the performance of ozone generators, are efficiency and maximum ozone concentration. The efficiency from oxygen has been found to be nearly independent on the kind of barrier discharge arrangement (volume, surface, coplanar), while the ozone concentration saturation level depends on the specific design of the generator. These phenomena are explained with features of the discharge process and the properties of chemical reactions, respectively. The importance of a limit in the energy density of the discharge is highlighted.     

Kinetic Modeling of Ozone Generation via Dielectric Barrier Discharges

A mathematical model combining chemical kinetic and reactor geometry is developed for ozone synthesis in dry O₂ streams with a wire-tube dielectric barrier discharge (DBD) reactor. Good agreement is found between the predicted ozone concentrations and experimental data. Sensitivity analysis is conducted to elucidate the relative importance of individual reactions. Results indicate that the ground-state oxygen atom is the most important species for O₃ generation; however, ozone generation will be inhibited if the O atom is overdosed. The excited species, that is, O(¹ D) and O₂(b ¹Σ), can decompose O₃ and suppress ozone synthesis. The model developed is then applied to modify the original DBD reactor design for the enhancement of ozone yield. With a thinner dielectric thickness, more than 10% increase of ozone concentration is achieved.     

The Benefits of Small Quantities of Nitrogen in the Oxygen Feed to Ozone Generators

This paper reports the ozone generation in pulsed multichannel dielectric barrier discharge. The influence of nitrogen addition (0.1%–10%) on ozone concentration and ozone generation efficiency in nitrogen–oxygen gas mixtures is studied. Results show that adding 0.1% N₂ would not seriously increase the ozone production. Meanwhile, 1% N₂ content exhibits the highest ozone production efficiency in low SIE (J/L, defined as the ratio of power to gas flow rate) region (0–200 J/L) while adding 0.3% N₂ would lead to the highest ozone generation efficiency in high SIE region (300–800 J/L). The increase of ozone production induced by N₂ addition is more significant in low SIE region compared with that in high SIE region. At 100 J/L, ozone production efficiency increases 26.9% to 201.6 g/kWh with 1% N₂ addition when compared with that in oxygen. At 18 J/L, the observed maximum ozone generation efficiency reaches 252 g/kWh at 1.3 g/Nm³ with 1% N₂ addition. An increase of ozone production can be obtained with 0.3%–2% N₂ addition in all explored SIE ranges.     

Ozone Generation by Hybrid Discharge Combined with Catalysis

In this paper, combining hybrid discharge with pellet alumina catalyst is used for ozone generation. The hybrid discharge including corona discharge (CD), surface discharge (SD) and dielectric barrier discharge (DBD) may happen in the device. Factors that affect the ozone production efficiency and concentration are studied, such as energy density, power, gas flow rate, frequency, peak voltage and catalysts.     

Gas Phase Reactions in Silent Electric Discharges. Part I: Exact Calculation of the Charge Passed Through the Discharge Chamber and the Electric Field Using the Electrical Parameters of the Circuit

The rate of a chemical reaction occurring in a silent electric discharge is dependent on the electric charge passing through the gas. In the knowledge of the electrical characteristics of the circuit and its elements (i.e., the ohmic resistance and capacitance), the composition and the pressure of the gas, the electric charge involved in the discharge can be calculated. The application of a purely sinusoidal alternating current to the system allows deduction of the time dependence of the voltage drops across various circuit elements and also the time dependence of the current. Experiments were conducted with two reactor types (static and tubular flow) and their electrical characteristics were varied to test the results of the calculations, which were thereby confirmed.     

Application of Electric Discharges at Atmospheric Pressure and Ambient Temperature for Bio-Decontamination

A new method using an electric discharge at atmospheric pressure and quasi ambient temperature of the gliding arc type is tested for bio-decontamination purposes. Preliminary results are reported on model bacteria of limited pathological character. Inactivation of three strains of Erwinia was tested over 8-minute periods. The inactivation plots of Erwinia chrysanthemi (Ech) show that a 6-minute treatment induces a fall by 10 logarithm units in the number of viable bacteria, i.e., an abatement close to sterilization conditions.     

A Study of the Physical and Chemical Processes Active in Corona Discharges Fed by Carbon Dioxide

Ozone generation in both positive and negative corona discharges DC corona, both operated in glow regime, feed by dry CO₂ has been studied. Higher ozone concentrations were observed in negative corona discharges. Ozone formation was found to be strongly dependent upon both the flow rate of the gas and on the radius of the outer electrode. The physical characteristics of the discharge were monitored through measurement of the discharge current. Small increases in the gas flow rate were observed to cause a significant increase in the discharge current of a negative corona discharge but little/no effect was observed in positive corona.     

A Study of the Physical and Chemical Processes Active in Ozone Generation by Carbon Dioxide Fed Corona Discharges

Ozone generation in both positive and negative corona discharges DC corona, both operated in glow regime, feed by dry CO₂ has been studied. Higher ozone concentrations were observed in negative corona discharges. Ozone formation was found to be strongly dependent upon both the flow rate of the gas and on the radius of the outer electrode. The physical characteristics of the discharge were monitored through measurement of the discharge current. Small increases in the gas flow rate were observed to cause a significant increase in the discharge current of a negative corona discharge but little/no effect was observed in positive corona.     

Ozonation of Aqueous Solutions of Nitrogen Heterocyclic Compounds : Benzotriazoles,Atrazine and Amitrole

Study of the ozonation of aqueous solutions of four heterocyclic nitrogen compounds, at slightly acidic pH in a heterogeneous gas-liquid system, showed that the reactivities of these compounds are different. Amitrole, a five-membered ring heterocycle, has been found to be a highly reactive compound, while atrazine, a six-membered ring heterocycle, has been found to be a poorly reactive compound. The benzotriazoles, benz-fused five-membered ring heterocycles, present intermediate reactivities. Moreovoer, the chemical natures of the ozonation by-products have been found to be different between amitrole and atrazine. With atrazine, ozone did not open the heterocyclic ring, and led to the formation of a trioxotriazine. With amitrole, ozone broke the heterocyclic ring and formed mainly formamide.     

Ozone Production in a Dielectric Barrier Discharge with Ultrasonic Irradiation

Ozone production has been investigated using an atmospheric pressure dielectric barrier discharge in pure O₂ at room temperature with and without ultrasonic irradiation. It was driven at a frequency of either 15 kHz or ～40 kHz. The ozone production was highly dependent on the O₂ flow rate and the discharge power. Furthermore, powerful ultrasonic irradiation at a fundamental frequency of ～30 kHz with the sound pressure level of ～150 dB into the discharge can improve the ozone production efficiency, particularly when operated at the frequency of 15 kHz at the flow rate of 15 L/min.     

Obtaining Tungsten,Titanium, and Molybdenum Powders during their Dispersion in Pulsed Discharges in Aqueous Solutions

Theoretical Foundations of Chemical Engineering - The study continues research into the dispersion of metals in pulsed discharges in nitric and sulfuric acid solutions. It was revealed that metal...     

Rates of Ozonation of Cresol Isomers in Aqueous Solutions

This research used a stopped–flow spectrophotometer system to study the kinetics of the fast oxidation of cresols by ozone in aqueous solutions. The overall reaction between ozone and a cresol isotner is second order, with first order in each reactant. At the same operating condition, the ozonation rate of m–cresol is the fastest and that of o–cresol the slowest. For the oxidation of o–cresol in neutral solutions, the overall rate constant increases from 422,000 to 1,550,000 1/M–s as the temperature changes from 10 to 40°C. In aqueous solutions with the pH range of 2.4 to 9.0 at temperatures varying from 5 to 40°C, the ozonation rate of the cresols increases with temperature and pH.     

Effective Ozone Generation in Oxygen Using a Mesh Electrode in an Ozonizer with Variable Linear Velocity

Results of studies on ozone synthesis under discharges proceeding in a metal mesh-ceramic dielectric system have been presented. The experiments were carried out in the reactor with unique reaction space geometry, in which the reacting gas flew with consequently increasing linear velocity. The high voltage electrode was made of a metal mesh, which caused intensification of the gas mixing in the reaction space. Using a simple reactor with one-side cooling of the reaction space, high ozone maximum concentrations (100 g/Nm³) and energy efficiencies (180–200 g/kWh) were obtained at 25 °C.     

Experimental Study of Ozone Generation by Negative Corona Discharge in Mixtures of N2 and O2

Ozone generation by negative DC corona discharge in N₂-O₂ mixtures has been experimentally investigated using a coaxial wire-cylinder corona reactor operating at room temperature and atmospheric pressure. The experiments have been carried out under different gas flows (15 cm³ min^?1 to 200 cm³ min^?1) and gas compositions (5% to 90% of O₂), and the effect of these parameters on the corona current, the ozone density and the efficiency of the ozone generator have been analyzed. The global rate coefficients for ozone formation and destruction have also been evaluated, and their values compared with those reported by other authors. The maximum efficiency for ozone production was found in gas mixtures with oxygen content about 70–80%.     

Ozone Synthesis and Decomposition in Oxygen-Fed Pulsed DBD System: Effect of Ozone Concentration,Power Density,and Residence Time

The process of ozone production in pure oxygen was studied. It was shown how the ozone concentration changes along the discharge gap, both during its generation and decomposition processes. The effect of ozone inlet concentration, power, and gas residence time on ozone concentration was analyzed. It has been shown that concentrated ozone is easily decomposed at very low discharge powers, i.e., when the increase of the average gas temperature in the gap is negligibly small. It was hypothesized that the most intense decomposition takes place in the microdischarge channels, because the process of gas heating in the gap begins inside them.     

Decomposition of Ozone in Highly Concentrated Aqueous Solutions Under semi-Commercial Conditions

The use of ozone in the treatment of drinking water in the form of a highly concentrated aqueous solution yields technological advantages compared with the traditional use of ozone in its gaseous state. However, for a comparative calculation of profitability, it is essential to know the ozone decomposition rate in the water solution in question. The present paper reports for the first time investigations with respect to this question under semi-commercial conditions and compares the results with laboratory tests made at another place.