Destruction of 2,4 Dichlorophenol in an Atmospheric Pressure Dielectric Barrier Discharge in Oxygen

The processes of degradation of 2,4-dichlorophenol (2,4-DCP) under the action of atmospheric pressure of dielectric barrier discharge (DBD) in oxygen were studied. It was shown that the degradation of 2,4-DCP proceeds efficiently. Degree of decomposition reaches 90%. The degradation kinetics of 2,4-DCP obeys the formal first-order kinetic law on concentration of 2,4-DCP. The effective rate constants depend weakly on the experimental conditions and are equal to ~0.2 s^?1. Based on experimental data, the energy efficiency of decomposition of 2,4-DCP was determined. Depending on the conditions, the energy efficiency was in the range of (8–90) × 10^?3 molecules per 100 eV. The composition of the products was studied by gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), energy-dispersive X-ray spectroscopy (EDX), attenuated total reflection-fourier transform infrared (ATR-FTIR) spectroscopy, electron spin resonance (ESR) spectroscopy and UV/Visible spectroscopy. It was shown that about ~20% of 2,4-DCP is converted to CO₂, while the other part forms an organic film on the reactor wall. The substance formed is close to the carboxylic acids in chemical composition and exhibits electrical conductivity and paramagnetic properties. Almost all of the chlorine contained in the 2,4-DCP is released into the gas phase. The active species of the afterglow react with liquid hexane, forming the products of its oxidation. Some assumptions regarding the pathway of the process are discussed.     

Plasma-Catalytic Decomposition of Phenols in Atmospheric Pressure Dielectric Barrier Discharge

This study investigated the processes for the destruction of phenol and its derivatives (resorcin and pyrocatechol) in aqueous solutions under the action of an oxygen dielectric barrier discharge (DBD) at atmospheric pressure in the presence or absence of catalysts in the plasma zone. It was shown that the DBD had a high decomposition efficiency for phenol and its derivatives (up to 99%). Phenol was the most stable and pyrocatechol was the least. In a plasma-catalytic hybrid process, the effective rate constants for phenol, resorcin and pyrocatechol decomposition were 11, 4 and 2.5 times higher, respectively, than those for the DBD treatment without catalysts. The process also resulted in a 1.4, 1.6 and 1.2 times higher rate of carboxylic acid formation for phenol, resorcin and pyrocatechol, respectively. The fractional conversion into the respective carboxylic acids reached 56% for phenol and 68% for resorcin and pyrocatechol.     

Deposition of Polyacrylic Acid Films by Means of an Atmospheric Pressure Dielectric Barrier Discharge

The present work describes the plasma polymerisation of acrylic acid at atmospheric pressure. The influence of two operating parameters (monomer concentration and discharge power) on the properties of the deposited films is investigated. Results show that at a monomer concentration of 2.5 ppm and a discharge power of 9.5 W, the monomer is only slightly fragmented leading to a high amount of carboxylic acid groups on the deposited films. In contrast, when monomer concentration is decreased or discharge power increased, the incidence of monomer fragmentation processes is higher, leading to a lower amount of carboxylic acid groups on the films. This behaviour can be explained by a higher energy amount available per monomer molecule at low monomer concentrations and high discharge powers and a higher flux of positive ions attacking the surface at high discharge powers. Taking into account these results, it can be concluded that the deposition parameters should be carefully selected in order to preserve the stability of the monomer and thus obtain coatings with high carboxylic acid densities.     

The Destruction of Carbon Tetrachloride Dissolved in Water in a Dielectric Barrier Discharge in Oxygen

The kinetics of decomposition of tetrachloromethane (TCM) in its aqueous solutions and the kinetics of decomposition products formation was investigated under the action of DBD at atmospheric pressure in oxygen in a falling-flow reactor. The range of initial concentrations of TCM was 25–325 μmol/l, the discharge power—2–11 W and O₂ flow rates—1–3 cm³/s. It is shown that the kinetics of the TCM decomposition can be described by the equation of pseudo-first kinetic order. The rate constant depended weakly on the discharge parameters and was?~?5 s^?1. The energy efficiency of the decomposition, depending on the parameters, was 0.1–1.3 molecules per 100 eV. When the residence time of the solution with the discharge zone is more than 1 s, it is possible to achieve almost 100% degree of TCM decomposition. It is shown that the main products of the TCM decomposition in the liquid phase are aldehydes and Cl^? ions, and in the gas phase—the molecules CO and CO₂. The results for energy efficiency are compared with the results obtained in other AOP’s processes (Fenton process, photocatalytic process, the radiation process by the action of high-energy electron flux). It is shown that the action of the DBD is more effective than the action of the above processes.

     

氧气常压介质阻挡放电的发射光谱及能量传递机理

为研究氧气常压介质阻挡放电中的物理化学行为, 以纯氧作为放电体系, 用发射光谱(optical emission spectroscopy)诊断技术分析了等离子体中可能存在的化学活性物种. 利用在500-950 nm范围的氧原子发射光谱计算出等离子体中的电子温度为(1.02±0.03) eV; 观测了760 nm处的具有清晰转动结构的氧气A带(atmospheric band)O2(b1∑+g-X3∑-g), 并用其转动结构计算了转动温度(气体温度)为(650±20) K; 在500-700 nm范围观测了氧气的第一负带系(first negative system) O+2(b4∑-g-a4∏u), 在190-240 nm范围观测了微弱但特征清晰的氧气的Hopfield带系O+2(c4∑+u-b4∑-g). 研究发现, 在氧气常压介质阻挡放电等离子体中存在多种激发态氧原子、激发态氧气分子、基态和激发态氧气分子离子等反应活性物种, 这些活性物种的形成涉及氧气分子的激发、解离和电离等多种过程, 每个过程都包含多个能量传递步骤, 氧分子解离产生的氧原子是导致一系列高激发态氧原子生成和氧气电离激发的主要因素.     

Destruction of Styrene in an Air Stream by Packed Dielectric Barrier Discharge Reactors

This study presents the decomposition rates of styrene vapors with non-packed and packed bed dielectric barrier discharge reactors. The concentrations of intermediate byproducts at various plasma operation conditions were evaluated. The results showed that although styrene vapors could be almost completely removed at low styrene inlet concentration of 132 ppm, the selectivity of CO₂ as the major product was rather low in a non-packed bed reactor. It was found that solid carbon containing compound was the major byproduct. An increase in the styrene inlet concentration tended to reduce the styrene removal efficiency, it also led to increase in the solid byproduct. The reactors that packed with glass, Al₂O₃ or Pt–Pd /Al₂O₃ pellets could improve the styrene decomposition efficiency and reduce the formation of intermediate products, of which the best oxidation of styrene to CO₂ could be achieved with a Pt–Pd /Al₂O₃ packed bed reactor. The carbon byproducts could also be reduced if the rector length was increased. The concentrations of ozone formed during the plasma process were also evaluated for the non-packed and packed bed reactors. The plasma reactor that packed with Pt–Pd /Al₂O₃ pellets was proved to have the lowest O₃ concentration.     

Homogeneous Dielectric Barrier Discharge Reactor with Two L-Shaped Electrodes Operating at Atmospheric Pressure

Homogeneous non-thermal plasma at atmospheric pressure is highly effective for surface treatment of various polymeric substrates. We propose a dielectric barrier discharge (DBD) reactor consisting of two back-to-back L-shaped electrodes, driven by bipolar voltage pulses of opposite polarity. This structure and driving scheme allow the discharge to be initiated earlier inside the reactor than outside the reactor. The plasma formed inside the reactor is ejected through a slit and moves toward the substrate. As a result, an abundance of electrons is provided to the outside region of the reactor at its breakdown stage. These electrons play a role in suppressing the filamentary mode, and hence, homogeneous discharge in He and Ar can be achieved under an open air configuration. The discharge characteristics inside and outside the reactor are analyzed by using the discharge current and the temporal evolution of emission intensity, respectively. The importance of seed electrons available at the gas breakdown stage in achieving a homogeneous discharge is discussed together with the differences between the discharge characteristics of helium and argon gases.     

Dilute Methane Treatment by Atmospheric Pressure Dielectric Barrier Discharge: Effects of Water Vapor

Oxidation of dilute methane in oxygen containing mixtures by atmospheric pressure dielectric barrier discharge at moderate temperature (below 150°C) has been studied with regard to the effect of water vapor. First, the impact of water vapor on methane conversion was studied in nitrogen. In dry nitrogen, methane was converted into hydrogen cyanide and hydrogen in the absence of oxidant. When water was added, it both acted as a scavenger in competition with methane for reactive nitrogen species and changed the reaction product speciation from HCN to carbon monoxide and carbon dioxide. The addition of water also led to the formation of hydrogen and nitrogen oxides. In the presence of oxygen, the addition of 1% water vapor enhanced methane conversion. Increasing water vapor content above 1% had a slight positive effect on methane conversion, and was found to enhance selectivity of the reaction products toward carbon dioxide over carbon monoxide.     

A New Approach to Metal Surface Nitriding Using Dielectric Barrier Discharge at Atmospheric Pressure

A new approach to metal surface nitriding using dielectric barrier discharge (DBD) plasma at atmospheric pressure is presented in this paper. Results of the study show that the plasma nitriding at atmospheric pressure using DBDs is realizable. Harder and thicker compound layer and diffusion layer on the treated surface has been formed in shorter treatment time comparing with the conventional vacuum plasma nitriding, Increasing the applied voltage will facilitate the formation of a thicker nitrided layer using the DBD. The nitrided layer acquired by this new approach is mainly composed of ɛ phase and γ′ phase, and the crystal grains of the ɛ phase is fine and has high dislocations density.     

基于大气压下介质阻挡放电抑制LA-ICP-MS分析中元素分馏效应研究

采用自制的大气压下介质阻挡放电装置串联在激光剥蚀池与ICP炬管之间, 对激光剥蚀产生的气溶胶进行预电离. 结果表明, 元素瞬时信号轮廓的平滑度得以改善, 元素分析信号精密度(RSD, n=3)可提高2.55％. 在ArF准分子激光(193 nm)和Nd∶YAG 固体激光(213 nm)两种不同波长的激光剥蚀系统中, 元素分馏因子均比常规模式下更接近于1, 表明采用介质阻挡放电对气溶胶预电离后元素分馏效应得以有效抑制. 相比两种不同波长的激光剥蚀系统, 介质阻挡放电对213 nm固体激光的元素分馏效应改善作用明显.     

The Effect of pH on OH Radical Generation in Aqueous Solutions by Atmospheric Pressure Glow Discharge

Formation of hydroxyl radicals in aqueous solutions by atmospheric pressure DC glow discharge was investigated. The ferrocyanide was used as an OH scavenger at different pH. Experimental results indicated that pH effect on hydroxyl radical formation rate could be explained by particularities of [Fe(CN)₆]^4? and reactive species interaction in different media.     

高气压氮气介质阻挡放电激发态氮的实验研究

本文通过等离子体发射光谱研究了高气压介质阻挡放电中压力对于激发态氮的影响。其中压力变化范围是0.1MPa到0.5MPa,不同能级的N_2(C~3Π_u)是典型的活性物质。实验结果显示,随着实验气压增加,等离子体主体活性物质数密度从7×10~(15)cm~(-3)降至1×10~(15)cm~(-3)。电子温度随着气压的增加从5eV降至3eV。电子数密度和气压的关系较为复杂,会受到中性分子和电子温度的影响。氮分子激发过程速率常数则随着压力增加近似线性减少,从6×10~(-16)m~3/s降至3×10~(-16)m~3/s。实验结果显示,介质阻挡放电气压增加会显著减少活性物质数量、电子温度,同时近似线性减少氮分子激发过程速率常数。     

Catalytic Effects of Metal-loaded Membrane-like Alumina Tubes on Ammonia Synthesis in Atmospheric Pressure Plasma by Dielectric Barrier Discharge

Plasma synthesis of ammonia was studied at atmospheric pressure using a dielectric-barrier-discharge-plasma reactor equipped with a metal-loaded membrane-like alumina tube as a catalyst between the electrodes. Introducing the pure alumina into N₂–H₂ plasma resulted in an increase in the ammonia yield and the further improvement was achieved by loading the alumina with Ru, Pt, Ni, and Fe. These results clearly demonstrate the catalytic effects of the alumina and the metals in the plasma reaction. Temperature-programmed desorption and isotope exchange reaction of nitrogen revealed that plasma-excited N₂ molecules were subjected to dissociative adsorptions mainly on the alumina to form atomic N(a) (The suffix “(a)” denotes adsorbed species) species, which were converted into ammonia by H₂ plasma. A role of the metals is considered to be acceleration of ammonia formation by the reaction of the alumina-adsorbed N(a) atoms with plasma-activated hydrogen species.     

Theoretical Kinetics Investigation of Krypton Dielectric Barrier Discharge for UV Lamp

Plasma Chemistry and Plasma Processing - This work presents an electric and kinetic study of homogeneous dielectric barrier discharge (DBD) in pure krypton (Kr). The electrical characterization and...     

Plasma-Aided Cotton Bioscouring: Dielectric Barrier Discharge Versus Low-Pressure Oxygen Plasma

The hydrophobic cuticle of the cotton fiber has formed a natural barrier for pectinase to catalyze its substrates (pectins beneath the cuticle), thus resulting in an insufficient scouring for cotton. Two plasma-based treatments, dielectric barrier discharge (DBD) at atmospheric pressure and cold oxygen plasma at low pressure in a vacuum system, were used as the pretreatments prior to cotton bioscouring, aiming at increasing the accessibility of pectinases to the pectic substances on the cotton fiber. The effects of different processing parameters of DBD and oxygen plasmas on the wettability, whiteness and burst strength of pectinase-scoured cotton were determined and compared. Although both of the pretreatments could enhance cotton bioscouring, DBD might be more suitable for current bioscouring due to its continuous processing mode and lower requirements to the equipment.     

Influence of Power Modulation on Ozone Production Using an AC Surface Dielectric Barrier Discharge in Oxygen

The measurements of electro-optical discharge characteristics and concentration of produced ozone were performed to evaluate the efficiency of ozone production in an AC surface dielectric barrier discharge (SDBD) in pure oxygen at atmospheric pressure. The discharge was driven in an amplitude-modulated regime with a driving AC frequency of 1 kHz, variable discharge duty cycle of 0.01–0.8 and oxygen flow rate of 2.5–10 slm. We observed asymmetric SDBD behaviour as evidenced by the variation in the ratio of the O^I/O₂ ⁺ emission intensities registered during the positive/negative half-periods and complemented by the transferred charge measurements through the Lissajous figures. We also found a strong dependence of O₃ concentration on the discharge duty cycle. The highest calculated ozone production yield reached 170 g/kWh with a corresponding energy cost of about 10 eV/molecule when combining the lowest inspected duty cycle with the lowest AC high voltage amplitude.     

Spectroscopic Characterization of CH4 + CO2 Plasmas Excited by a Dielectric Barrier Discharge at Atmospheric Pressure

Plasma processing of a (CH ₄ +CO ₂ ) mixture can lead to the formation of synthesis gas (CO+H ₂ ). The use of a nonthermal plasma for this type of process seems very promising. We report here an electric and spectroscopic characteristic of plasma created in a (CH ₄ +CO ₂ ) mixture by a high-voltage, steep front-voltage (>10 ¹² V/s), very-short-pulse triggered dielectric barrier discharge in a tubular cell. Particular attention was payed to the determination of the rotational temperature for C ₂ . Time resolved investigation of the Swan band leads to an estimated value around 3000 K.     

Sterilization of Polymer Foils with Dielectric Barrier Discharges at Atmospheric Pressure

The emission of UV light as well as chemical reaction in plasmas allow them to be used for decontamination of food packaging. Sterilization efficiency of different dielectric barrier discharge (DBD) setups at atmospheric pressure was investigated for spores of B. subtilis and A. niger sprayed onto PET foils. In normal DBDs the efficiency of spore reduction in different gases (nitrogen, argon, synthetic air) can be related to the UV spectra of these gases in the discharge. With special so-called cascaded dielectric barrier discharges (CDBDs) a fast reduction of viable cells by more than four orders of magnitude is possible within few seconds, even for UV resistant cells. The sealing properties of commonly used PE-PET-laminate can be maintained in CDBD which is not observed for single-gap DBD.     

Ethylene Epoxidation in an AC Dielectric Barrier Discharge Jet System

In this work, ethylene epoxidation was investigated in a dielectric barrier discharge jet (DBDJ) with a separate ethylene/oxygen feed under oxygen lean conditions. The ethylene (C₂H₄) stream was directly injected behind the plasma zone in order to reduce all undesired reactions, including C₂H₄ cracking and further reactions, while the oxygen (O₂) balanced with argon was fed through the plasma zone totally to maximize the formation of active oxygen species. The effects of various operating parameters, such as total feed flow rate, O₂/C₂H₄ feed molar ratio, applied voltage, input frequency, and C₂H₄ feed position on the ethylene epoxidation activity, were investigated to determine the optimum operating conditions for this new DBDJ system. The highest ethylene oxide (EO) selectivity (55.2 %) and yield (27.6 %), as well as the lowest power consumption (3.3 × 10^?21 and 6.0 × 10^?21 Ws/molecule C₂H₄ converted and EO produced, respectively) were obtained at a total feed flow rate of 1,625 cm³/min (corresponding to a residence time of 0.022 s), an O₂/C₂H₄ feed molar ratio of 0.25:1, an applied voltage of 9 kV, an input frequency of 300 Hz, and a C₂H₄ feed position of 3 mm behind the plasma zone. The superior activity of the ethylene epoxidation in the DBDJ system resulted from a small reaction volume as well as a separate ethylene/oxygen feed.     

Characteristics of Atmospheric Pressure Air Glow Discharge with Aqueous Electrolyte Cathode

We investigated the characteristics of atmospheric pressure (AP) air glow discharge with aqueous electrolyte cathode. Distilled water or aqueous solutions of HNO₃, KCl, KBr and KI were utilized as a cathode. The cathode voltage drop, electric field strength, gas temperature as well as emission intensity of some lines of OI, H, K, Na and bands of N₂, OH, NO were measured at discharge current from 10 to 50 mA. The procedure of gas temperature measurement on the base of non-resolved structure of N₂(C³Π_u → B³Π_g) bands was described. The reduced electric field strength (E/N) was obtained, which showed that the discharge existed in the normal mode. On the base of these data, the regularities of optical emission were discussed.