低温等离子体合成氨研究进展

氨是人们生产生活最重要的化工原料之一,但传统的合成氨过程需要在高温高压条件下进行,其年均能耗约占到世界能源总消耗的1％～2％.同时,由于其能量来自于化石燃料燃烧,此过程会不可避免地加重温室气体的排放.因此,寻找合适的绿色替代方案,在温和条件下实现高效、低能耗、低排放合成氨,成为该领域的研究热点.低温等离子体合成氨技术可...     

低温等离子体原子荧光光谱法直接测定固体样品中的汞

建立了低温等离子体(LTP)与原子荧光光谱仪(AFS)联用直接检测ABS固体样品中Hg的方法.实验采用介质阻挡放电(DBD)方式产生低温等离子体,剥蚀固体样品后产生的元素蒸气引入到原子荧光光谱仪进行检测.优化的实验条件为:DBD外接电源的放电功率为16～18 W,放电气体流速为400 mL/min;采样距离为1～5 mm;原子荧光光谱仪的原子化器高度为10 mm.本系统测定Hg的检出限为0.91 mg/kg,线性范围为91.5～1096 mg/kg;精密度(RSD,n=7)为1.9％～2.3％,并对标准样品以及实际样品进行测定,测定结果与标准值与ICPMS及CVG-AFS一致,表明本方法可作为直接检测固体样品的新型元素分析技术.     

介质阻挡放电等离子体与吸附在CuZSM-5上的NO或NO/O2的相互作用

采用吸附和程序升温脱附(TPD)技术研究了介质阻挡放电等离子体对CuZSM-5催化剂上吸附的氮氧化物作用.实验表明,介质阻挡放电等离子体使催化剂表面吸附的NO及Cu活性位上吸附的NOx物种脱附,并引发表面化学反应生成新的氮氧化物.对于NO/N2体系,介质阻挡放电等离子体与吸附在CuZSM-5上NO作用,主要生成N2O和O2.在富氧体系NO/O2/N2,则生成较大量的N2O、NO2和NO.等离子体预处理活性下降的CuZSM-5,可明显提高其催化分解NO活性.对比有或无介质阻挡放电等离子体预处理NO或NO/O2饱和吸附的CuZSM-5上的NO-TPD结果表明,等离子体提高催化剂活性的原因与其使催化剂Cu活性位上吸附的NOx物种脱附有关.     

低温等离子体剥蚀-电感耦合等离子体质谱联用对电路板镀层的深度分析

建立了基于低温等离子体(Low temperature plasma)剥蚀系统将固体样品直接引入电感耦合等离子体质谱(ICP-MS)并用于电路板镀层中Au,Ni和Cu的深度分析.此实验中采用介质阻挡放电(DBD)方式产生低温等离子体探针,逐层剥蚀样品表面,由ICPMS检测元素信号.对DBD所用放电气体种类、外加电场功率、放电气体流速和采样深度等实验条件进行优化.在优化条件下,应用LTP-ICPMS在30 s内完成电路板镀层(20 μm Au/10 μm Ni/Cu基底)的逐层剥蚀和深度分析,元素种类和分层顺序与X射线光电子能谱(XpS)相吻合,镀层的分辨率可拓展至微米水平,表明此技术可直接用于固体样品的深度分析.     

介质阻挡放电等离子体与吸附在CuZSM-5上的NO或NO/O2的相互作用

采用吸附和程序升温脱附(TPD)技术研究了介质阻挡放电等离子体对CuZSM-5催化剂上吸附的氮氧化物作用. 实验表明, 介质阻挡放电等离子体使催化剂表面吸附的NO及Cu活性位上吸附的NOx物种脱附, 并引发表面化学反应生成新的氮氧化物. 对于NO/N2体系, 介质阻挡放电等离子体与吸附在CuZSM-5上NO作用, 主要生成N2O和O2. 在富氧体系NO/O2/N2, 则生成较大量的N2O、NO2和NO. 等离子体预处理活性下降的CuZSM-5, 可明显提高其催化分解NO活性. 对比有或无介质阻挡放电等离子体预处理NO或NO/O2饱和吸附的CuZSM-5上的NO-TPD结果表明, 等离子体提高催化剂活性的原因与其使催化剂Cu活性位上吸附的NOx物种脱附有关.     

甲烷二氧化碳介质阻挡放电转化产物分布研究

针对介质阻挡放电甲烷二氧化碳转化实验,分析了反应的产物分布,探讨了进料组成和反应器结构对反应的影响.反应产物包括:高H2/CO摩尔比的合成气、气态烃、高辛烷值的汽油组分、醇和酸等含氧有机物.对所述电极结构,产物的选择性随碳数增加而降低;高的甲烷进料浓度有利于烃的生成,对醇和酸的最佳甲烷进料体积分数范围在67.4％～75.1％;放电间隙越小,原料转化率和烃、酸的选择性越大,大的放电间隙对醇的生成有利.     

介质阻挡放电等离子体脱除氮氧化物的发射光谱研究

在大气压下, NO/N2体系中, 利用发射光谱技术对50 Hz和5 kHz交流介质阻挡放电等离子体在200～900 nm范围内进行了诊断. 在632、674.5、715.5和742 nm等处测得了N原子的谱线. 利用化学发光法NOx分析仪, 模块式红外吸收气体分析检测仪, 大气压下直连质谱多种检测手段对放电前后的稳定物种进行了分析, 观察到O2的生成. 初步讨论了无氧条件下介质阻挡放电等离子体中NO脱除的反应机制.     

低温等离子体原子化器-原子荧光光谱法测定碲

基于介质阻挡放电(DBD)原理和结构,建立了适用于原子荧光光谱仪(AFS)的低温等离子体小型原子化器(Atomizer),并研究了氢化物发生-低温等离子体原子化器-原子荧光光谱(HG-DBDAtomizer-AFS)测定环境样品中痕量碲(Te)的分析方法。DBD等离子体原子化器具有小型、低温等优点。对DBD放电结构和放电功率、载气气体流速,氢化物发生过程中的酸度、KBH4浓度,以及观测高度等实验条件进行了详细的考察并优化。本系统测定Te的检出限(3σ)为0.08μg/L;线性范围为0.5～80μg/L;测定精密度为2.1%(n=7);加标回收率为90%～103%。对国家级标准样品(GBW07404,GBW07405,GBW07406)进行测定,测定结果与标准值一致,证明本方法准确可行。     

大尺寸大气压空气等离子体射流设备研究

本文提出了一种特殊的大尺寸大气压空气等离子体射流设备。该设备采用一种高分子耐高温涂料作为介质进行放电,通过气体渐扩通道,产生大尺寸空气等离子体射流,射流直径最宽处可以达到28mm,长度可以达到数十mm。本文对射流中的活性物质进行光谱测量,同时对射流宏观温度进行测量,指出该射流温度非常接近室温,可以用于温度敏感材料的表面处理等方面。     

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.     

Study of SO2 Removal Using Non-thermal Plasma Induced by Dielectric Barrier Discharge (DBD)

Dielectric Barrier Discharge (DBD) non-thermal plasma reactors built with three different dielectric materials for SO₂ removal were studied. The discharge characteristics of the three dielectrics, namely glass, Teflon, and glass fiber-based epoxy resin, were analyzed using Lissajous figures. From the Lissajous figures, the transition charge and energy deposition for each dielectric material were determined. When both the discharge characteristics and mechanical processability were considered, glass fiber-based epoxy resin was regarded as the best dielectric barrier among the three for DBD plasma reactors. A multi-cell DBD reactor built with glass fiber-based epoxy resin was used for treating air stream containing SO₂. SO₂ % removal decreased with increasing initial SO₂ concentration in a biphasic fashion. SO₂ removal was greatly improved by adding NH₃ into the air stream. Raising the relative humidity of the air stream also helped SO₂ removal. A SEM (scanning electron microscope) test illustrated some changes in surface morphology of Teflon and glass fiber-based epoxy resin.     

Methane Conversion Using Dielectric Barrier Discharge：Comparison with Thermal Process and Catalyst Effects

The direct conversion of methane using a dielectric barrier discharge has been experimentally studied. Experiments with different values of flow rates and discharge voltages have been performed to investigate the effects on the conversion and reaction products both qualitatively and quantitatively. Experimental results indicate that the maximum conversion of methane has been 80% at an input flow rate of 5 ml/min and a discharge voltage of 4 kV. Experimental results also show that the optimum condition has occurred at a high discharge voltage and higher input flow rate. In terms of product distribution, a higher flow rate or shorter residence time can increase the selectivity for higher hydrocarbons. No hydrocarbon product was detected using the thermal method, except hydrogen and carbon. Increasing selectivity for ethane was found when Pt and Ru catalysts presented in the plasma reaction. Hydrogenation of acetylene in the catalyst surface could have been the reason for this phenomenon as the selectivity for acetylene in the products was decreasing.     

Gas-Phase Removal of Acetaldehyde via Packed-Bed Dielectric Barrier Discharge Reactor

The effectiveness of applying packed-bed dielectric barrier discharge(PBDBD) technology for removing acetaldehyde from gas streams wasinvestigated. Operating parameters examined in this study include appliedvoltage, oxygen content, and gas-flow rate. Experimental results indicatethat the destruction efficiency of acetaldehyde predominantly depends onthe applied voltage. Removal of 99% of acetaldehyde has been achieved forgas streams containing 1000 ppmv acetaldehyde, 5% oxygen, with nitrogen asthe carrier gas. The oxygen content in the gas stream plays an importantrole in removing acetaldehyde within PBDBD. A higher CH3CHO removalefficiency is achieved for the gas stream containing less oxygen, since itwill dissipate energy due to its electronegative property. Carbon dioxideis the major end product, which is less hazardous to the environment and tohuman health. However, undesirable products, e.g., NO₂ and N₂O,CH₃OC₂H₅, CH₃COOH, CH₃NO₂,HCN, CH₃NO₃, and CH₃OH, are detected as well.     

Conversion of NO in NO/N2, NO/O2/N2, NO/C2H4/N2 and NO/C2H4/O2/N2 Systems by Dielectric Barrier Discharge Plasmas

An experimental study on the conversion of NO in the NO/N₂, NO/O₂/N₂, NO/C₂H₄/N₂ and NO/C₂H₄/O₂/N₂ systems has been carried out using dielectric barrier discharge (DBD) plasmas at atmospheric pressure. In the NO/N₂ system, NO decomposition to N₂ and O₂ is the dominating reaction; NO conversion to NO₂ is less significant. O₂ produced from NO decomposition was detected by an on-line mass spectrometer. With the increase of NO initial concentration, the concentration of O₂ produced decreases at 298 K, but slightly increases at 523 K. In the NO/O₂/N₂ system, NO is mainly oxidized to NO₂, but NO conversion becomes very low at 523 K and over 1.6% of O₂. In the NO/C₂H₄/N₂ system, NO is reduced to N₂ with about the same NO conversion as that in the NO/N₂ system but without NO₂ formation. In the NO/C₂H₄/O₂/N₂ system, the oxidation of NO to NO₂ is dramatically promoted. At 523 K, with the increase of the energy density, NO conversion increases rapidly first, and then almost stabilizes at 93–91% of NO conversion with 61–55% of NO₂ selectivity in the energy density range of 317–550 J L⁻¹. It finally decreases gradually at high energy density. A negligible amount of N₂O is formed in the above four systems. Of the four systems studied, NO conversion and NO₂ selectivity of the NO/C₂H₄/O₂/N₂ system are the highest, and NO/O₂/C₂H₄/N₂ system has the lowest electrical energy consumption per NO molecule converted.     

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.     

甲烷参与下催化剂填充型介质阻挡放电等离子体脱除NOx

 将In/HZSM-5催化剂填充于介质阻挡放电反应器中,考察了甲烷参与下NOx的脱除及其脱除产物. 结果表明,在200～350 ℃间,等离子体与催化剂共同作用时NOx的转化率明显高于等离子体或催化剂单独作用时NOx的转化率. 在0.03%NO-0.05%CH4-2%O2-97.92%N2,空速7200 h-1和300 ℃的条件下,单纯等离子体、单纯催化剂和二者共同作用下NOx的转化率分别为24%,25%和65%. 甲烷参与下等离子体和催化剂共同作用时,在催化剂表面没有硝酸盐或亚硝酸盐生成,仅有少量副产物N2O生成. 由此可以推断,NOx脱除的主要产物为N2. 低于300 ℃时,NOx的脱除以分解途径为主,甲烷的作用主要是抑制放电条件下NOx生成的副反应; 在300～350 ℃间,甲烷作为还原剂被等离子体和催化剂协同活化,NOx的脱除以还原途径为主. 采用催化剂填充型介质阻挡放电反应器,可在非常宽的温度区间实现NOx的脱除.