介质阻挡放电引发氮氧化物等离子体化学反应

在523 K介质阻挡放电条件下,研究了不同气体组分体系中NO的转化.实验表明,在无氧体系(NO/N2)中,转化的NO主要分解为N2和O2.在富氧(NO/O2/N2)条件下,由于NO和NO2的生成, NO的转化率最低.体系中加入C2H4(NO/C2H4/N2)时, NO转化率与NO/N2体系几乎一样,与NO相比,生成的O更易与C2H4作用,几乎没有NO2的生成.当C2H4和O2共存时(NO/O2/C2H4/N2),NO主要被氧化为NO2.当能量密度为125 J•L－1时, 与其它体系相比,NO/O2/C2H4/N2体系中NO转化率和NO2生成量最大,转化每个 NO分子能耗最小(61 eV).体系中C2H4主要被氧化为CO.四个体系中N2O的生成量都较少.讨论了介质阻挡放电条件下上述四个体系可能的反应机制.     

单电极介质阻挡放电离子源研究

介质阻挡放电离子源是一种常压敞开式离子源,由于免试剂、适用范围广、易于小型化等特点而备受关注.该类离子源多采用表面双电极或针-环电极设计方式.表面双电极的接地电极会减弱氦气在强电场中电离形成的流注崩头能量,缩短等离子束喷射距离.针-环电极的电场主要集中在针电极尖端,流注崩头能量小,等离子束喷射距离比表面双电极还短.本研究对放电影响因素进行分析,通过改变电极形状和增加绝缘介质部件进行电场调整,使强电场区域集中于电极一侧,解决了单电极回流放电问题,从而获得稳定、高效的等离子束,其最大长度可达8 cm以上.基于电场调整技术,研制出单电极介质阻挡放电离子源,它主要由惰性载气、高压电极、绝缘介质管、气控以及温控部分组成.使用新型离子源对咖啡因液态样品和扑热息痛固体药片进行了质谱分析,前者的定量曲线R2值为99.66％,100 μg/L的信噪比为23;后者的主要成分对乙酰氨基酚可在质谱中快速检出,响应强度为1.26×106.上述结果表明,新型离子源可以实现样品的定量和快速原位分析.     

介质阻挡放电-发射光谱测定偏二甲肼

基于气相色谱分离、低温等离子放电与发射光谱技术建立了偏二甲肼（UDMH）的测定方法。以介质阻挡放电（DBD）低温等离子体作为偏二甲肼的发射光谱（OES）激发源、DBD-OES微型发射光谱系统产生的384.94 nm特征光谱为检测信号,电荷耦合检测器（CCD）采集信号。仪器检出限为0.48μg/L;UDMH质量浓度为5μg/L时,相对标准偏差（RSD）为1.3%;环境水样的加标回收率为84%～90%。方法可应用于痕量偏二甲肼的检测和应急监测。     

介质阻挡放电中OH自由基对甲醛脱除的影响

对管线式介质阻挡放电中的甲醛脱除进行了实验研究, 测量了介质阻挡放电产生的OH (A²Σ→X ²Π, 0-0)自由基发射光谱. 研究了在一个大气压下不同放电峰值电压、放电频率、添加氩气和氧气时甲醛脱除率与OH自由基发射光谱强度的变化关系. 实验结果表明: 在氮气含甲醛体系中, 提高放电峰值电压、放电频率和增大氩气含量时, 甲醛脱除率随OH (A²Σ→X ²Π, 0-0)自由基发射光谱强度的增强而提高; 当在氮气含甲醛体系中增大氧气含量时, 甲醛脱除率随OH (A²Σ→X ²Π, 0-0)自由基发射光谱强度的减弱而降低. 在11.5 kV放电峰值电压和9 kHz放电频率下, 氮气含甲醛体系中甲醛脱除率达93.8%.     

电子能量对沿面介质阻挡放电等离子体化学产物的影响

基于光电倍增管研制了一套无触发信号的双通道光学探测系统, 并组装了测试样机, 实现了对沿面介质阻挡放电(SDBD)等离子体约化电场的测量, 进而通过BOLSIG+软件获得了电子能量. 采用原位紫外吸收光谱和傅里叶变换红外光谱, 研究了SDBD等离子体在不同电压和频率下的化学产物的浓度变化, 并结合空气等离子体化学反应揭示了产物相互作用的微观机理. 结果表明, 电子能量能够改变电子碰撞反应的速率系数, 调控化学反应的源头活性粒子的浓度, 进而影响到化学产物的生成和猝灭.     

高频介质阻挡放电烟气脱硫研究

采用高频介质阻挡放电的方式产生低温等离子体,研究在不加入NH₃的情况下流动态SO₂的去除情况.实验表明,在输入电压为12 kV,SO₂浓度为5400 mg/m³,气体流量为0.36 m³/h,相对湿度为55%时,脱硫率可达到70%以上;水气的存在对SO₂的去除有较大的促进作用,升高电压和增加O₂量对脱硫率的促进作用有限.对实验结果进行了解释,并提出了反应机理.     

介质阻挡放电等离子体中·OH和HO2·自由基的数值模拟计算

在介质阻挡放电等离子体N2/O2/H2O/HCHO体系中通过解Boitzmann方程,得到电子能量分布函数,利用得到的电子能量分布函数计算电子-分子碰撞反应速率常数.然后把有关的反应速率常数带入速率方程,计算得到该体系在介质阻挡放电时,·OH、HO2·和电子的浓度随时间的演变以及·OH、HO2·浓度随H2O、O2摩尔分数的变化,并将模拟结果与实验值进行了对比,两者符合得较好.     

介质阻挡放电等离子体中·OH和HO2·自由基的数值模拟计算

在介质阻挡放电等离子体N2/O2/H2O/HCHO体系中通过解Boltzmann方程, 得到电子能量分布函数, 利用得到的电子能量分布函数计算电子-分子碰撞反应速率常数. 然后把有关的反应速率常数带入速率方程, 计算得到该体系在介质阻挡放电时,·OH、HO2·和电子的浓度随时间的演变以及·OH、HO2·浓度随H2O、O2摩尔分数的变化, 并将模拟结果与实验值进行了对比, 两者符合得较好.     

介质阻挡放电离子源质谱分析

敞开式离子化质谱可对表面样品进行直接快速分析而受到关注,成为质谱分析的热点研究方向.介质阻挡放电离子源是一种基于等离子体放电机理的敞开式离子源,近年来得到了较快的发展.本文着重介绍该离子源的基本原理、性能特征以及应用进展,并对其发展趋势进行了展望.     

介质阻挡放电净化恶臭气体的实验研究

低温等离子体技术是一种新型的污染治理技术,国内外都对其进行了广泛而深入的研究。等离子体是电子,正、负离子,激发态原子、分子,以及自由基混杂的状态,是一种高反应活性的气体,理论上可以引发许多用常规方法难以发生的化学反应,已在废气、废水、固体废物以及放射性废物等方面     

A Study of Two-Dimensional Microdischarge Pattern Formation in Dielectric Barrier Discharges

Although microdischarges in dielectric-barrier discharges (DBDs) have been studied for the past century, their mutual interaction was explained only recently. This interaction is responsible for the formation of microdischarge patterns reminiscent of two-dimensional crystals. Depending on the application, microdischarge patterns may have a significant influence on DBD performance, particularly when spatial uniformity is desired. This paper presents the results of study of regular microdischarge pattern formation in DBD in air at atmospheric pressure. Experimental images of DBD (Lichtenberg figures) were obtained using photostimulable phosphors. A new method for analysis of microdischarge patterns that allow measuring the degree of pattern regularity was developed. Simulated and experimental patterns were compared using the newly developed method and comparison indicates the presence of interaction between microdischarges. Analysis of microdischarge patterns shows that regularity of the patterns increases with the number of excitation cycles used to produce the pattern.     

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.     

Abatement of Gas-phase p-Xylene via Dielectric Barrier Discharges

The effectiveness of applying dielectric barrier discharges (DBDs) to remove p-xylene from gas streams was experimentally investigated in this study. Parameters investigated include applied voltage, gas flow rate, gas temperature and gas composition. Experimental results indicate that as high as 100% p-xylene removal efficiency is achieved for the gas stream containing low p-xylene concentration of 26 ppmv. Removal efficiency of p-xylene achieved with DBDs increases with increasing applied voltage. However, energy consumption is also increased with increasing applied voltage. The best energy efficiency of 7.1 g/kWh is achieved for the gas streams containing 500 ppmv p-xylene, 5% O₂, 1.6% H₂O_(g), and balanced N₂ at the applied voltage of 18 kV. Product analysis indicates that around 70 or 95% of the carbons in p-xylene molecules are transformed into carbon dioxide for the gas streams without or with water vapor, respectively.     

Concentration Dependence of VOC Decomposition by Dielectric Barrier Discharges

A comparative study of the decomposition of Volatile Organic Compounds (VOCs: Vinyl Chloride (VC), Ethyl Acetate (EA), Toluene (T), Acetone (A)) in dielectric barrier discharges (DBD) in zero and humidified air at atmospheric pressure was performed. Small scale tubular-flow with pulse excitation and large scale planar-flow with sinusoidal excitation were used to determine the removal efficiency in dependence on inlet concentration S₀ and air humidity. According to the destruction law S=S₀ exp(–E/), where E is the plasma energy density, linear functions were found for the -parameters with respect to S₀ containing an absolute term ₀. By modeling the reaction kinetics it was possible to discriminate active species responsible for the decomposition. Ozone was confirmed to be involved in VC decomposition in zero air whereas OH radicals were best suited to explain the absolute efficiency of EA and toluene destruction in humid air. Their decomposition in zero air however, as well as the degradation of acetone cannot be explained in a similar way.     

Treatment of Soot by Dielectric Barrier Discharges and Ozone

The results of the presented special treatment method indicate a soot decomposition mechanism due to long-living species like ozone and a multistage process between diesel soot and ozone. Measurements inside a dielectric barrier discharge (DBD) and measurements with ozone externally generated show a strong dependence of the decomposition rate on the temperature. In addition the temperature dependence of the lifetime of ozone up to 180°C and the oxidation of carbonmonoxide to carbondioxide were investigated.     

Simultaneous Removal of Nitrogen Oxides and Particulate Matters from Diesel Engine Exhaust using Dielectric Barrier Discharge and Catalysis Hybrid System

Dielectric barrier discharge (DBD) and catalysis hybrid process was used to remove nitrogen oxides and particulate matters from diesel engine exhaust. The DBD reactor converts a part of NO into NO₂, and then the exhaust gas containing the mixture of NO and NO₂ enters the catalytic reactor where both NO and NO₂ are reduced to N₂. The effect of energy density (power input divided by gas flow rate) and reaction temperature on the removal of nitrogen oxides was investigated with a stationary diesel engine. The hybrid process was able to remove about 80% of the initial nitrogen oxides at an energy density of 25 J/L and 150°C. The removal of particulate matters did not largely depend on the electrode structure, but it was a strong function of the energy density. On the basis of 80% removal efficiency, the energy yield for nitrogen oxides was 40 eV/molecule while that for particulate matters was 83 kJ/mg. The present study suggests that this kind of hybrid process can be applied to simultaneous removal of nitrogen oxides and particulate matters from diesel engine exhausts.     

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.