Ozone Production Influenced by Increasing Gas Pressure in Multichannel Dielectric Barrier Discharge for Positive and Negative Pulse Modes

This paper describes the influence of gas pressure on the conversion of O₂ to O₃ and the ozone production efficiency in a multichannel dielectric barrier discharge (DBD) reactor utilizing positive and negative pulses. Results show that conversion of O₂ to O₃ is continuously enhanced by the increase of gas pressure (0.1–0.24 MPa) while the rising speed of oxygen conversion with the increasing gas pressure at fixed specific input energy is reduced above 0.15 MPa. The maximum ozone generation efficiency is increased with increasing gas pressure (0–0.2 MPa) while positive pulse exhibits higher energy efficiency. The maximum ozone generation efficiency is suppressed with further increase of gas pressure (0.2–0.24 MPa) while no significant difference in ozone generation efficiency is observed for two unipolar pulse modes. Results also show that 0.2 MPa is the optimal working gas pressure to obtain the maximum ozone generation efficiency and increasing gas pressure would lead to remarkable increase of ozone generation efficiency for ozone production at high energy densities in multichannel DBD.     

Ozone Production in a High Frequency Dielectric Barrier Discharge Generator

Factors that affect the performance of an expanded-mesh dielectric barrier discharge ozone cell were investigated. A gas feed pf 94% O₂, 4% Ar and 1% N₂ was used. An improvement in the productivity (g ozone/kWh) of about 20 % was achieved by doubling the gas flow rate through the cell. Decreasing the cell operating frequency (in the range 72 kHz to 19 kHz) increased the productivity of the ozone generator at constant power. The ozone production increased approximately in proportion to the input power; however productivity did not vary significantly with power above a minimum level. As the cell voltage was increased the dependence of productivity on power or frequency was reduced. Changing the feed gas temperature between ? 5^°C and + 42^°C had no effect on productivity. Finer meshes drew more power than coarser ones for a given voltage. Using a thinner mesh for the centre electrode increased productivity. The best results were obtained with a 6 × 3 × 1.86 mm titanium mesh giving a productivity of 110 g ozone/kWhr at 30–60 W, 1500–1900V and 23 KHz.     

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.     

Influence of Field Strength and Energy Distribution of Different Barrier Discharge Arrangements on Ozone Generation

Because of different field strength and energy density distributions in volume (VD), surface (SD) and coplanar discharge (CD) arrangements the ozone yield will differ in general. While in VD configurations the initial field strength distribution is rather uniform, the situation is quite different in CD and especially SD devices. The distributions change during discharge development as well as the energy density in the discharge region and by this the ozone yields. The situation in SD arrangements is discussed in detail and is compared with those in VD and CD configurations.     

Experimental Study on Ozone Synthesis via Dielectric Barrier Discharges

The characteristics of ozone generation using a dielectric barrier discharge reactor were investigated experimentally. Results indicate that ozone concentration increases with increasing applied voltage and gas residence time. In addition to applied voltage, ozone generation rate varies with reactor configuration as well. Optimum ozone generation rates can be reached at the specific gas residence time for a given applied voltage and gas composition. At the same applied voltage, the reactor with a single dielectric barrier results in a higher ozone generation rate in comparison with the reactor having double dielectric barriers. Given a constant N₂/O₂ ratio in the feed gas, NO_x concentration increases as applied voltage and gas residence time increase. Results indicate that maximum NO_x concentration is reached when the N₂/O₂ ratio of feed gas is 4.     

Optimizing Factors on High Concentration of Ozone Production with Dielectric Barrier Discharge

The gap distance, electrode material, voltage and gas flow velocity were optimized with gas pressure variation of dielectric barrier discharge (DBD) for producing high concentration of ozone. There exists an optimum gas pressure at which the highest ozone concentration is produced with other parameters being fixed. This optimum gas pressure value changes accordingly as the other parameters changed. As the discharge continues at the optimum pressure, the ozone concentration could increase or decrease slowly. This aging effect has different characteristics with the metal electrode material and the impurity level of the oxygen gas used for ozone generation. The aging effect is supposed to be related with the catalytic effect of metal oxide, which is generated in the discharge zone. The change in the characteristic of optimum pressure by the other parameters, indicate that the ozone concentration is deeply related with the filament self-organization characteristics of DBD. At the final optimized condition, the ozone concentration was higher than 22.5 wt.%.     

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.     

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.     

A Study of Ozone Synthesis in Coaxial Cylinder Pulse Streamer Corona Discharge Reactors

Synthesis of ozone in coaxial cylinder non-thermal plasma reactors with different structures was investigated in this paper. With digital measuring technology, the absorption energy of non-thermal plasma reactors induced by pulse streamer corona was estimated. In the view of energy absorption of non-thermal plasma reactors, pulse input energy depended on reactor structures, as well as pulse parameters, such as pulse amplitude and DC bias. With coaxial cylinder reactors energized by pulse voltage, the influences on ozone generation of pulse voltage polarity, pulse amplitude, and pulse repetition rate were studied. It was found that positive pulse voltage induced higher ozone generation than negative pulse voltage and higher amplitude pulses generated more ozone. Increasing the pulse repetition rate at a low level increased ozone generation to some extent, but then leveled off with further increasing. A critical repetition rate was found at which the ozone synthesis was the most efficient. Lower pulse amplitude was associated with higher critical repetition rate. Superimposing DC bias on pulse voltage was an effective method to enhance ozone generation. Besides, discharge modes and electrode structures of reactors affect ozone generation. A mixed discharge mode of volume and surface discharges was the most effective mode to generate ozone in all of the experimental discharge modes, namely volume, surface, volume and surface mixed discharge modes. Moreover, helix-cylinder reactors were better than wire-to-cylinder reactors in generating ozone.     

Physicochemical Investigation of Homogeneous Pulsed Discharge in N2/O2 for Ozone Production

The purpose of this work is to draw attention to the plasma kinetics in a nitrogen-oxygen mixture. The model includes the plasma chemistry module and the circuit module investigating the electrical and the physical characteristics of high-pressure homogenous pulsed discharge. The fundamental chemistry governing ozone generation developed in this work is based on a full set of processes regrouped in 117 reactions involving 19 charged particles, atomic, and molecular species. The results of simulations show the temporal variation of the discharge electrical parameters and the effect of the voltage applied to ozone production. The role played by different reactions and species is also given by analyzing the time evolution of species concentrations, as well as the ozone production and loss terms.     

Effect of MnOx/TiO2 Oxidation State on Ozone Concentration in a Nonthermal Plasma-Driven Catalysis Reactor

Manganese oxides on titanium dioxide were prepared by impregnation method at various calcination temperatures and by deposition-precipitation method and the catalysts were characterized using TG-DTA, XRD, XPS, and N₂ adsorption. Various oxidation states for manganese were obtained and activity towards ozone decomposition inside a nonthermal plasma catalysis reactor was investigated. Activity tests show that with increasing manganese oxidation state, the greater the degree of ozone decomposition inside the reactor. MnOx/TiO₂ prepared by impregnation method calcined at 350 °C showed the highest decrease in ozone concentration.     

Hydrogen Production by Steam Reforming of Commercially Available LPG in UAE

Steam reforming of commercially available LPG using Ru/Al₂O₃ and Ni/Al₂O₃ catalysts has been studied at temperatures between 573 and 773 K. Ru/Al₂O₃ catalyst showed higher rates of reaction and lower activation energies of the three main components of LPG, compared with Ni/Al₂O₃. However, Ni/Al₂O₃ catalyst showed a better H₂:CH₄ selectivity. The activation energy of n-butane was the lowest over Ru/Al₂O₃, whereas over Ni/Al₂O₃, propane had the lowest activation energy. The activation energy of i-butane was always the highest over both catalysts, which suggests that both catalysts performed better with unbranched molecules. A slight increase in activation energy was observed, when each component of the LPG mixture was studied separately as a pure gas, compared with being mixed in LPG. At a constant temperature of 773 K, hydrogen production yield and H₂:CH₄ selectivity were determined using Ru/Al₂O₃ at different steam:carbon (S:C) ratios and LPG flow rates. It was found that the yield and selectivity increased with the increase in S:C ratio and the decrease in the flow rate. The highest yield of 0.64 was achieved using S:C ratio of 6.5 and a LPG flow rate of 50 mL min^?1. The work provides valuable information on steam reforming of pure components of LPG, compared with when they are in the mixture. The comparison is done using conventional steam reforming catalyst, Ni/Al₂O₃, and compared with Ru/Al₂O₃. The observed trends and variations in reaction rates, in pure and mixed gases, indicated that the mechanism of steam reforming of a hydrocarbon mixture depends on its composition.     

Ozone Decomposition on α-Fe2O3 Catalyst

The catalytic decomposition of ozone on an α-Fe₂O₃ catalyst has been investigated within the temperature range 23-65°C. A high initial decomposition degree followed by a decrease is observed. It is found that the water vapor in the air-ozone mixture exercises almost no effect on the process. IR-spectroscopy has shown that the nitrogen oxides formed in the ozone generator are the main reason for the deactivation of the catalyst. A scheme of the deactivation process is proposed.     

Optimization of binder removal for ceramic microfabrication via polymer co-extrusion

The objective of this study is to assess the feasibility of solvent extraction (SE) for partial binder removal in the context of polymer co-extrusion with a thermoplastic binder component. Polymer co-extrusion is able to produce multilayered, functionally graded and/or textured structures in an efficient manufacturing process, but requires a polymer binder system with suitable flow characteristics. Traditionally, the binder is removed by thermal debinding (TD), which, however, is prone to form cracks or blisters, both of which are attributed to a lack of initial pore space that allows pyrolysis products to escape. The primary focus of this work is to demonstrate that a binder system with a high soluble binder content is suitable for conventional polymer co-extrusion and to document that a two-step binder removal process involving both SE and TD eliminates debinding defects. The overall fabrication process is documented for the extrusion of solid ceramic rods and co-extrusion of tubes, where alumina powder was batched with polyethylene butyl acrylate (PEBA) as backbone polymer and polyethylene glycol (PEG) as water soluble binder. SE for specimen with varying PEBA:PEG ratios was tested in water at three different temperatures for various times. The 1:1 mixture showed a PEG removal up to 80 wt.% of the original PEG content after 6 h extraction; after subsequent thermal debinding, rods and tubes sintered successfully without defects, demonstrating the viability of the process.     

Performance of a slurry bubble column reactor for Fischer-Tropsch synthesis: Determination of optimum condition

The CO conversion and selectivity to C₁+ and C₁₁+ wax products over Co/Al₂O₃ as well as Ru/Co/Al₂O₃ Fischer-Tropsch (F-T)catalysts were investigated by varying reaction temperature (210-250 °C), system pressure (1.0-3.0 MPa), GHSV (1000-6000 L/kg/h), superficial gas velocity (1.7-13.6 cm/s) and slurry concentration (9.09-26.67 wt.%) in a slurry bubble column reactor (0.05 m diameter × 1.5 m height) to determine the optimum operating conditions. Squalane or paraffin wax was used as initial liquid media. The overall CO conversion increased with increasing reaction temperature, system pressure and catalyst concentration. However, the local maximum CO conversion was exhibited at GHSV of 1500-2000 L/kg/h and superficial gas velocity of 3.4-5.0 cm/s. The CO conversion in the case of Ru/Co/Al₂O₃ was much higher and stable than that in the case of Co/Al₂O₃. The selectivity to C₁₁+ wax products increased slightly with increasing GHSV; on the other hand, it decreased with increasing reaction temperature, system pressure, and solid concentration in a slurry bubble column reactor. It could be concluded that the optimum operating conditions based on the yield of hydrocarbons and wax products were; U_G = 6.8-10 cm/s, Cs = 15 wt.%, T = 220-230 °C, P = 2.0 MPa in a slurry bubble column reactor for F-T synthesis.     

Size Dependent Study of MeOH Decomposition Over Size-selected Pt Nanoparticles Synthesized via Micelle Encapsulation

We communicate experimental results for the oxidation of methane by oxygen over alumina supported Pd and Pt monolith catalysts under transient conditions. Temperature programmed reaction (TPReaction) and reactant pulse-response (PR) experiments have been performed, using a continuous gas-flow reactor equipped with a downstream mass spectrometer for gas phase analysis. Special attention was paid to the influence of gas composition changes, i.e., O₂ and H₂ pulsing, respectively, on the methane conversion. For Pt/Al₂O₃ oxygen pulsing can significantly increase the methane conversion which can be even further improved by pulsing hydrogen instead. Such transient effects are not observed for the Pd/Al₂O₃ catalyst for which instead constantly lean conditions is beneficial. Our results suggest that under lean conditions Pd and Pt crystallites may undergo bulk- and partial (surface oxide formation) oxidation, respectively, which for Pd results in more active surfaces, while for Pt the activity is reduced. The latter seems to connect to a lowering of the ability to dissociate methane.     

High strength alumina joints via transient liquid phase bonding

Low melting boron oxide, instead of metallic materials in other methods of transient liquid phase bonding, was taken as braze in joining alumina in this paper. Pure boron oxide melts at low temperature and reacts with alumina matrix to form a stable high melting compound. This transient liquid phase bonding has the advantage of producing a ceramic joint for high temperature applications at low processing temperature. In this study, alumina pieces coated with boron oxide layers in various thicknesses were bonded at 800 °C for various times in air under minor loading. The average flexural strength of joints were measured by means of four point bending, while the microstructure of the cross-section and fractured surface was observed by means of scanning electron microscopy. Phases at joints were identified by low angle X-ray diffraction. The maximum flexural strength reaches a value of 155 MPa after joining at 800 °C for 15 h with a 21 μm interlayer. Three compounds, 3Al₂O₃–B₃O₃, 2Al₂O₃–B₃O₃ and 9Al₂O₃–2B₃O₃ have been found at the joint. It is also found that 2Al₂O₃–B₃O₃ whiskers dominate at the joint with the maximum strength.     

Influence of preparation method on performance of Cu(Zn)(Zr)-alumina catalysts for the hydrogen production via steam reforming of methanol

The selective production of hydrogen via steam reforming of methanol (SRM) was performed using prepared catalysts at atmospheric pressure over a temperature range 200–260^∘C. Reverse water gas shift reaction and methanol decomposition reactions also take place simultaneously with the steam reforming reaction producing carbon monoxide which is highly poisonous to the platinum anode of PEM fuel cell, therefore the detailed study of effect of catalyst preparation method and of different promoters on SRM has been carried out for the minimization of carbon monoxide formation and maximization of hydrogen production. Wet impregnation and co-precipitation methods have been comparatively examined for the preparation of precursors to Cu(Zn)(Al₂O₃) and Cu(Zn)(Zr)(Al₂O₃). The catalyst preparation method affected the methanol conversion, hydrogen yield and carbon monoxide formation significantly. Incorporation of zirconia in Cu(Zn)(Al₂O₃) catalyst enhanced the catalytic activity, hydrogen selectivity and also lower the CO formation. Catalyst Cu(Zn)(Zr)(Al₂O₃) with composition Cu/Zn/Zr/Al:12/4/4/80 prepared by co-precipitation method was the most active catalyst giving methanol conversion up to 97% and CO concentration up to 400 ppm. Catalysts were characterized by atomic absorption spectroscopy (AAS), Brunauer-Emett-Teller (BET) surface area, pore volume, pore size and X-ray powder diffraction (XRPD). The XRPD patterns revealed that the addition of zirconia improves the dispersion of copper which resulted in the better catalytic performance of Cu(Zn)(Zr)(Al₂O₃). The time-on-stream (TOS) catalysts stability test was also conducted for which the Cu(Zn)(Zr)(Al₂O₃) catalyst gave the consistent performance for a long time compared to other catalysts.