Synthesis of Ozone at Atmospheric Pressure by a Quenched Induction-Coupled Plasma Torch

The technical feasibility of using an induction-coupled plasma (ICP) torch to synthesize ozone at atmospheric pressure is explored. Ozone concentrations up to ~250 ppm were achieved using a thermal plasma reactor system based on an ICP torch operating at 2.5 MHz and ~11 kVA with an argon/oxygen mixture as the plasma-forming gas. The corresponding production rate and yield were ~20 g ozone/hr and ~2g ozone/kWh, respectively. A gaseous oxygen quench formed ozone by rapid mixing of molecular oxygen with atomic oxygen produced by the torch. The ozone concentration in the reaction chamber was measured by Fourier Transform infrared (FTIR) spectroscopy over a wide range of experimental conditions and configurations. The geometry of the quench gas flow, the quench flow velocity, and the quench flow rate played important roles in determining the ozone concentration. The ozone concentration was sensitive to the torch RF power, but was insensitive to the torch gas flow rates. These observations are interpreted within the framework of a simple model of ozone synthesis.     

An Ozone Generator of Miniaturization and Modularization with the Narrow Discharge Gap

The method of ionization discharge has a key action on the process of the ionization and decomposition of O₂ molecule as well as the re-decomposition of O₃ molecule. In this paper, an ozone generation of miniaturization which was fabricated by stacking discharge modules with rectangle is introduced, only volume of 23.0×53.0×42.0 cm³ for ozone production capacity of 1 kg/hr. In addition, the ozone concentration and its production efficiency are significantly improved in comparison with a conventional ozone generator, which have the highest ozone concentration of 308 g/Nm³ and the production efficiency of 118 g/kWh at ozone concentration of 200 g/Nm³.     

Coupled Sliding Discharges: A Scalable Nonthermal Plasma System Utilizing Positive and Negative Streamers on Opposite Sides of a Dielectric Layer

A nonthermal plasma system based on simultaneously formed positive and negative streamers on either side of a dielectric layer is described. The coupled sliding discharge (CSD) reactor based on this concept was found to be scalable by stacking and operating multiple electrode assemblies in parallel, similarly to the shielded sliding discharge (SSD) reactor reported earlier. A comparison of the two systems showed that although the energy density in the CSD reactor was lower, the efficiency for NO conversion and ozone synthesis from dry air were significantly higher. The energy cost for 50 % NO removal was ~30 eV/molecule compared to ~60 eV/molecule in the case of the SSD under the same conditions of 330 ppm initial NO concentration in air. The energy cost decreased to ~12 eV/molecule in both cases when NO was mixed with plasma-activated air at the outlet of the reactor to utilize ozone for NO conversion i.e., indirect plasma treatment. The energy yield for ozone generation from dry air was at ~70 g/kWh, comparable in both systems. The results show that the concept of a CSD, as that of SSDs, allows the construction of compact, efficient plasma reactors.     

Characteristics of the Discharge and Ozone Generation in Oxygen-Fed Coaxial DBD Using an Amplitude-Modulated AC Power Supply

In this study, a traditional tubular reactor and an amplitude-modulated AC power supply were employed to develop a unique practical ozone generator with a widely adjustable ozone concentration and simultaneously a constant ozone yield. The characteristics regarding discharge and ozone generation in oxygen were experimentally investigated in detail. The amplitude-modulated AC waveform consisted of T_ON (burst of four consecutive AC cycles) and T_OFF with a duty cycle of 0.4. The experimental results show that a unique ozone generator can be developed through changing the applied voltage amplitude when an amplitude-modulated AC power supply producing periodic bursts of several consecutive AC cycles during the T_ON period is used. A quite high and stable ozone yield of 165?±?16 g/kWh was achieved and a wide range of ozone concentrations could be obtained. Moreover, we observed a very interesting phenomenon that the discharge energy and voltage peak for every AC cycle showed some difference, resulting from the accumulation and release of charge on the dielectric. The first AC cycle had the highest discharge energy and positive voltage peak as well as the lowest negative voltage peak, which was particularly obvious at a high energy density. Additionally, water cooling of the grounded electrode seemed to have a small influence on the basic electrical characteristics of the discharge and had a positive effect on the concentration and yield of ozone due to a reduction in gas temperature in the discharge gap.     

A pathway of free radical generation via copper corrosion and its application to oxygen and ozone activation for the oxidative destruction of organic pollutants

This study investigated the commercially available zero-valent copper powder and copper foil to activate molecular oxygen (O₂) and ozone for the degradation of organic pollutants. Under aerobic atmospheric conditions, copper powder effectively removed 50 mg/L of acetaminophen (ACT) within 2 h, though the degradation rate using the foil was less than 20% of the powder. However, copper foil activated ozone to effectively degrade ACT. The total organic carbon (TOC) removal reached a high of 58.3% at a catalyst concentration of 40 g/L, but only 26.8% with ozone alone. The initial solution pH and dosage of copper foil were key operational parameters affecting the ozone activation process. H₂O₂ and Cu(I) were important intermediates in the process as hydroxyl radicals (^·OH) were identified via EPR (electron paramagnetic resonance) experiments and free radical scavengers. The generation of ^·OH was attributed to a Fenton-like reaction between Cu(I) and H₂O₂; this free-radical generation mechanism differs from typical transition metal oxide catalysts. This study outlines a promising approach to significantly increase the generation of ^·OH and effectively remove refractory organic compounds. Furthermore, these copper products are applied in structural components of practical water treatment. Thus, the study of corrosion resistance to oxygen and ozone in aqueous solution have both a practical and theoretical significance. It was determined that copper products were resistant to oxygen corrosion in aqueous solution, but not resistant to ozone corrosion.     

A High-Efficiency Double Surface Discharge and Its Application to Ozone Synthesis

Surface discharge with the flat plate configuration tends to generate a uniform and high-density plasma during ozone synthesis, but suffers from relatively low energy yield at high ozone concentration. Here we report that a double surface discharge reactor can produce, at the same input power, two uniform plasma zones that locate two sides of the thin dielectric layer simultaneously, which results in a high ozone energy yield at high ozone concentration. Discharge characteristics confirm that reducing dielectric thickness and discharge gap favors the achievement of high plasma-density and energy efficiency. The optical emission spectroscopy diagnosis suggests that the double surface discharge with thinner dielectric thickness and narrower discharge gap possesses much higher electron density, as well as higher excitation temperature and low rotational temperature, which is responsible for the excellent performance in ozone synthesis. The optimal parameters of 0.25 mm dielectric thickness and 2 mm discharge gap enable ozone synthesis to proceed with an energy yield of 295.2–108.7 g/kWh at ozone concentration of 11.1–48.3 g/Nm³ and exhibit a good stability during a 4-h test. This performance surpasses the performance of many other typical discharge processes for ozone synthesis.     

Ozone Production Using a Power Modulated Surface Dielectric Barrier Discharge in Dry Synthetic Air

The measurements of electrical and optical characteristics of the discharge and concentrations of produced ozone and nitrogen oxides were performed to evaluate the efficiency of ozone production in an AC surface dielectric barrier discharge in dry synthetic air at atmospheric pressure. The discharge was driven in an amplitude-modulated regime with driving AC frequencies of 1, 5 and 10?kHz, variable discharge duty cycle of 0.02?C0.8 and synthetic air flow rate of 2?C10?slm. The experimental results show that ozone and nitrogen oxides concentrations increased with increasing AC high-voltage amplitude, increasing discharge duty cycle and with increasing residence time. The highest calculated ozone production yield reached ~90?g/kWh with a corresponding energy cost of about 20?eV/molecule. The production yield was found to be independent of the driving AC frequency and specific energy density in the 10^?4?C10^?2?Wh/l range.     

Characteristics of Dielectric Barrier Discharge Ozone Synthesis for Different Pulse Modes

This paper features the pulse polarity effect on ozone generation efficiency by adjusting the applied voltage and the flow rate in a coaxial dielectric barrier discharge reactor. Results show that utilization of unipolar pulse has better performance when compared with the bipolar mode, but on the other hand, utilization of the positive pulse has slightly higher efficiency than that of negative mode. Meanwhile, changing the gas flow rate shows a minor effect on ozone generation. Utilization of bipolar pulse would decrease the breakdown voltage and ozone generation efficiency when compared with unipolar pulse while it would lead to higher ozone concentrations at fixed applied voltage. The maximum ozone yield reaches 186.9 g/kWh at 6 kV positive pulse with ozone concentration of 11.9 g/Nm³.     

Study of the Process and Mechanism of the Remediation of Phenol Contaminated Soil by Plasma Vibrated Bed

Soil pollution is an important problem. The organic components of soil pollution are complex, and pose a significant threat to human health. In this work, a low-temperature plasma vibrated bed is applied to remediation of soil polluted by organics, with attention focused on phenol as a model pollutant. In the experiment, many factors of phenol degradation are studied and determined, such as discharge voltage, carrier gas, and soil moisture content. Increasing vibration frequency, decreasing electrode spacing, increasing voltage and a weakly alkaline soil are conducive to the degradation of pollutants. Air and oxygen give better degradation than nitrogen. The active particles generated in the discharge, such as ·OH, H₂O₂ and O₃, are shown to play an important role in degradation of phenol. In addition, maleic acid and oxalic acid are found as intermediate product during the process of phenol degradation. Furthermore, according to the qualitative and quantitative analysis of phenol degradation products, the degradation mechanism diagram of phenol in soil is drawn up, which is instructive to improve the performance of the plasma vibrated bed in the future research.     

Degradation of paracetamol in a bubble column reactor with ozone generated in electrolyte-free water using a solid polymer electrolyte filter-press electrochemical reactor

A porous anode composed of β-PbO₂ was electrochemically deposited onto a carbon cloth substrate (e.g., CC/β-PbO₂) aiming for the electrochemical ozone production (EOP) in electrolyte-free water using a solid polymer electrolyte (SPE) filter-press reactor. Scanning electron microscopy (SEM) images revealed the presence of a three-dimensional oxide structure necessary to obtain a fluid-permeable anode. X-ray analysis showed the predominance of the β-PbO₂ phase. The maximum current efficiency for the EOP was 9.5% with an ozone production rate of 1.40 g h^?1. Using a constant ozone production rate of 0.5 g h^?1, the oxidative degradation of paracetamol (PCT) dissolved in water was accomplished as a function of the PCT concentration (20, 30, and 50 mg L^?1) and the pH (acid, natural (without adjustment), and alkaline). The UV-Vis spectrophotometric analysis showed that the degradation process is more pronounced in alkaline media with a strong reduction in the electrical energy per order (E _EO). A reduction of the chemical oxygen demand (COD) of up to 80% was observed. A linear correlation between data referring to COD and HPLC measurements with the UV absorbance measured at 243 nm (UV₂₄₃) was verified indicating that these different techniques can be complementary to each other. The nuclear magnetic resonance (NMR) study of the ozonation by-products revealed that the oxidation of PCT occurred through the rupture of the aromatic ring. The major part of phenol’s ring was oxidized to CO₃ ^2? while no reaction occurs in the acetamide group of paracetamol during the ozonation reaction.