Study of Mechanism for Hexane Decomposition with Gliding Arc Gas Discharge

The mechanism of hexane decomposition under gliding arc gas discharge conditions is studied from both qualitative and quantitative analyses of its products for various hexane initial concentrations and different background atmospheres : nitrogen, argon, air (O₂ 21% N₂ 79% vol.) and N₂–O₂ mixtures. The decomposition rate, which decreases with increasing hexane initial concentration, can reach 94% when the carrier gas is air. Due to the electron energy consumed by the dissociation of nitrogen, the decomposition rate of hexane in nitrogen is lower than in argon. The radical channel plays a predominant role in the hexane decomposition process. With increasing oxygen concentration in the carrier gas, the hexane decomposition rate increases and promotes the conversion of CO– CO₂, but it also leads to the formation of NO₂.     

The Dependence of Gliding Arc Gas Discharge Characteristics on Reactor Geometrical Configuration

The dependence of gliding arc gas discharge characteristics, including gas flow field, arc column motion and volatile organic compounds (VOCs) decomposition performance, on reactor configuration parameters was investigated based on numerical simulation and laboratory experimental findings. For a given supply voltage (10 kV) and a certain nozzle outlet diameter (1.5 mm), increasing the electrodes gap (1–4 mm) or decreasing vertical distance between electrode throat and nozzle outlet (25–10 mm) will increase the gas flow rate through the electrode throat, the gas velocity in the plasma region, the arc column velocity, the maximum attainable position of the arc column and the electrical power consumption, also, higher VOCs decomposition rate and lower specific energy requirement are observed according to the n-butane and toluene decomposition experiments.     

Reforming of CO<Subscript>2</Subscript>-Containing Natural Gas Using an AC Gliding Arc System: Effect of Gas Components in Natural Gas

The objective of the present work was to study the reforming of simulated natural gas via the nonthermal plasma process with the focus on the production of hydrogen and higher hydrocarbons. The reforming of simulated natural gas was conducted in an alternating current (AC) gliding arc reactor under ambient conditions. The feed composition of the simulated natural gas contained a CH₄:C₂H₆:C₃H₈:CO₂ molar ratio of 70:5:5:20. To investigate the effects of all gaseous hydrocarbons and CO₂ present in the natural gas, the plasma reactor was operated with different feed compositions: pure CH₄, CH₄/He, CH₄/C₂H₆/He, CH₄/C₂H₆/C₃H₈/He and CH₄/C₂H₆/C₃H₈/CO₂. The results showed that the addition of gas components to the feed strongly influenced the reaction performance and the plasma stability. In comparisons among all the studied feed systems, both hydrogen and C₂ hydrocarbon yields were found to depend on the feed gas composition in the following order: CH₄/C₂H₆/C₃H₈/CO₂ > CH₄/C₂H₆/C₃H₈/He > CH₄/C₂H₆/He > CH₄/He > CH₄. The maximum yields of hydrogen and C₂ products of approximately 35% and 42%, respectively, were achieved in the CH₄/C₂H₆/C₃H₈/CO₂ feed system. In terms of energy consumption for producing hydrogen, the feed system of the CH₄/C₂H₆/C₃H₈/CO₂ mixture required the lowest input energy, in the range of 3.58 × 10⁻¹⁸–4.14 × 10⁻¹⁸ W s (22.35–25.82 eV) per molecule of produced hydrogen.     

Degradation of 4-Chlorophenol using a Gas–Liquid Gliding Arc Discharge Plasma Reactor

The gas–liquid gliding arc discharge plasma is used directly to study degradation and dechlorination of 4-Chlorophenol (4-CP) in solution. The typical AC waveforms of discharge voltage and current revealed that the discharge behavior was not definitely periodic. The chemical oxygen demand (COD) abatement of 4-CP solution with stainless steel electrode is higher than that with aluminum or brass electrode; When air was used as carrier gas the COD abated from 1,679.2 to 190 mg/L (i.e., 88.68% abatement) after 76 min plasma treatment; Increasing gas–liquid mixing rate could also increase the degradation of 4-CP; adding appropriate amounts of Fe²⁺ or iron chips to the solution were found to be favorable for 4-CP degradation. The main intermediates of 4-CP degradation are p-benzoquinone, hydroquinone, 4-chlorocatechol, p-chloronitrobenzene, and ring cleavage products (acetic acid, glycol, propanone, and others). Furthermore, possible pathways of 4-CP degradation in solution are proposed.     

Reforming of CO<Subscript>2</Subscript>-Containing Natural Gas Using an AC Gliding Arc System: Effects of Operational Parameters and Oxygen Addition in Feed

In this research, the reforming of simulated natural gas containing a high CO₂ content under AC non-thermal gliding arc discharge with partial oxidation was conducted at ambient temperature and atmospheric pressure, with specific regards to the concept of the direct utilization of natural gas. This work aimed at investigating the effects of applied voltage and input frequency, as well as the effect of adding oxygen on the reaction performance and discharge stability in the reforming of the simulated natural gas having a CH₄:C₂H₆:C₃H₈:CO₂ molar ratio of 70:5:5:20. The results showed marked increases in both CH₄ conversion and product yield with increasing applied voltage and decreasing input frequency. The selectivities for H₂, C₂H₆, C₂H₄, C₄H₁₀, and CO were observed to be enhanced at a higher applied voltage and at a lower frequency, whereas the selectivity for C₂H₂ showed an opposite trend. The use of oxygen was found to provide a great enhancement of the plasma reforming of the simulated natural gas. For the combined plasma and partial oxidation in the reforming of CO₂-containing natural gas, air was found to be superior to pure oxygen in terms of reactant conversions, product selectivities, and specific energy consumption. The optimum conditions were found to be a hydrocarbons-to-oxygen feed molar ratio of 2/1 using air as an oxygen source, an applied voltage of 17.5 kV, and a frequency of 300 Hz, in providing the highest CH₄ conversion and synthesis gas selectivity, as well as extremely low specific energy consumption. The energy consumption was as low as 2.73 × 10⁻¹⁸ W s (17.02 eV) per molecule of converted reactant and 2.49 × 10⁻¹⁸ W s (16.60 eV) per molecule of produced hydrogen.     

Chlorinated Organic Compounds Decomposition in a Dielectric Barrier Discharge

The decomposition of chlorinated volatile organic compounds by non-thermal plasma generated in a dielectric barrier discharge was investigated. As model compounds trichloroethylene (TCE) and 1,2-dichloroethane (DCE) were chosen. It was found that TCE removal exceeds 95% for input energy densities above 0.2 eV/molecule, regardless of the initial concentration of TCE, in the range 100–750 ppm. On the other hand, DCE was more difficult to decompose, the removal rate reached a maximum of 60% at the highest input energy used. For both investigated compounds the selectivity towards carbon dioxide was significantly influenced by their initial concentration, increasing when low concentrations were used. The gas flow rate had also an effect on CO₂ selectivity, which is higher at low flow rate, due to the higher residence time of the gas in the plasma. The best values obtained in these experiments were around 80%.     

多孔膜萃取/微捕集方法及在线测定水中挥发性有机物

基于多孔膜萃取水中挥发性有机物和微捕集技术,构建了一套水中挥发性有机物(Volatile OrganicCompounds,VOCs)样品前处理装置,可自动、在线、连续完成水中挥发性有机物萃取、富集、热解析,传输给气相色谱分离检测。实验分别对膜萃取材料、萃取温度、萃取时间、吹扫气流速等进行了系统优化,并用于氯仿、1,2-二氯甲烷、四氯化碳、三氯乙烯、甲苯、四氯乙烯、乙苯、氯苯、苯乙烯9种挥发性有机物的检测。研究结果表明,采用膜萃取/微捕集装置,与气相色谱联用,在萃取温度60℃,萃取时间30 min,吹扫气流速8 mL/min条件下,采用氢焰离子化检测器(Flame ionization detector,FID),对氯代烃的检出限达到0.003～0.041μg/L,精确度为2.7%～13.0%,线性相关系数均大于0.9936,适用于在线检测水中挥发性有机物。     

Evaluation of a Continuous Composite Sampler for Volatile Organic Compounds in Water

Abstract

The high volatility and low water solubility of volatile organic compounds (VOCs), make the collection of representative samples difficult. The standard grab sampling method only gives information of that moment in time when the sample is taken. When the composition of VOCs is varying, continuous composite sampling will give a more representative sample. However, no thorough evaluation of its use for VOCs has been reported.

The use of an automatic continuous composite sampler for the analysis of VOCs in water was studied. The causes and magnitude of the VOCs losses during the sampling process were determined.

Adsorbent cartridges were used to trap the VOCs escaping from solution during the sampling process. Sorption phenomena occurring on the containers and/or tubings were also evaluated. Sorption losses were much more significant than volatilization losses.

The results indicate that a modified version of this sampler can be an alternative for the long term sampling of water for VOC analysis.     

脉冲放电氦光离子化检测器分析有机化合物的性能研究

研究本实验室组装的脉冲放电氦光离子化检测系统上PDPID的性能、各种操作参数对信号的影响、操作最佳化及信号线性。用该系统分析了汽油、酮醇混合物和痕量挥发性有机化合物等样品,它们的色谱图可以同FID相比。     

气相色谱-质谱法测定水中25种挥发性有机物及其在污水厂应急溯源中的应用

采用吹扫捕集-气相色谱-质谱法测定水中25种挥发性有机物的含量,并研究了其在污水厂应急溯源中的应用。25种挥发性有机物在一定的质量浓度范围内与其峰面积呈线性关系,方法的检出限(3.143s)在0.6~5.0μg·L-1之间。以空白样品为基体进行加标回收试验,所得回收率在91.6%~102%之间,测定值的相对标准偏差(n=6)在2.7%~4.6%之间。在一起污水厂冲击案例中,通过污水管网采样及污水样品分析,确定污染因子二氯甲烷,并根据二氯甲烷浓度变化快速锁定污染源头,确保污水厂出口水质达标。     

气相色谱-质谱法测定地板材料中8种挥发性有机物质

应用气相色谱-质谱法测定了地板中甲苯、乙苯、邻二甲苯、间二甲苯、对二甲苯、苯乙烯、乙酸丁酯、正十一烷等8种挥发性有机物质的含量。地板样品(5g)用甲醇(15mL)超声提取20min,所得提取液用Rxi-5ms毛细管色谱柱分离,在选择离子监测模式下测定。8种挥发性有机物质的质量浓度(间二甲苯与对二甲苯合并计算)均在0.5~10.0mg·L-1范围内与其峰面积呈线性关系,方法的检出限(3S/N)在0.05~1.0mg·L-1之间。加标回收率在98.0%~105%之间,测定值的相对标准偏差(n=5)在2.3%~6.6%之间。     

热解吸-气相色谱法测定植物源挥发性有机物

以Tenax-TA、Carboxen 1000和Carbosieve SⅢ为采样管填充料,将植物源挥发性有机物吸附于采样管内,样品通过二次热解吸仪解吸后,随载气进入气相色谱仪,采用氢火焰离子化检测器(FID)测定,建立了利用二次热解吸仪与气相色谱联用技术测定植物挥发性有机物的分析方法。载气N2流速为30 mL/min,60℃下吹扫吸附管2 min,然后在250℃下解吸吸附管5 min,冷却1 min后,在275℃下解吸聚焦管3 min,样品经传输线进入气相色谱。气相色谱载气N2压力为190 kPa,FID检测器温度280℃;进样口温度225℃;初始柱温40℃,停留5 min,以2℃/min升温至120℃,保留1 min,然后以20℃/min升温至200℃,保留10 min。方法重现性好,精密度高,线性相关系数大于0.99;检出限均低于9×10-9g/L;解吸效率大于96%,适用于植物源挥发性有机物的测定。     

热脱附-气相色谱-质谱法测定空气中挥发性有机物

提出了热脱附-气相色谱-质谱法测定空气中54种挥发性有机物含量的方法。用HP-INNOWAX毛细管色谱柱分离,电子轰击离子源全扫描和选择离子检测模式检测。54种挥发性有机物的方法检出限在0.11～0.28μg.m-3之间。回收率在85%～107%之间,相对标准偏差(n=7)小于15%。     

土壤中挥发性有机化合物的GC-MS测定

利用气相色谱－质谱联用技术，对某废弃化工厂原厂区及附近农田的土壤中可能存在的60种挥发性有机化合物进行了定性和定量分析；采用质量保证和质量控制步骤对分析结果进行监测，结果令人满意。     

吹扫捕集和GC-MS测定水中26种挥发性有机物

用吹扫捕集和气相色谱―质谱联用技术对地表水中的26种挥发性有机污染物进行同时测定。实验结果在2.0～50.0μg/L范围内线性良好,相关系数均大于0.99,检出限在0.08～0.91μg/L范围内。方法的平均回收率为87.33%～116.68%,相对标准偏差(RSD)均小于5%。该方法前处理简单快速,采用内标法定量准确度高,重复性好,适用于清洁水中挥发性有机物的测定。     

顶空/气相色谱-质谱法分析方便面印刷包装材料中挥发性有机物

利用顶空/气相色谱-质谱(HS/GC-MS)联用法对袋装方便面印刷包装材料中7种挥发性有机物(异丙醇、乙酸乙酯、苯、乙酸丁酯、乙苯、间/对二甲苯、邻二甲苯)进行了检测分析.优化的实验参数为:平衡温度80℃,平衡时间40 min.本方法线性关系良好,7种挥发性有机物的相关系数均大于0.9991,检出限为0.004～0.0...     

热脱附-单体稳定同位素技术测定挥发性有机物

采用热脱附与稳定同位素质谱联用技术分析了城市不同源及大气环境中挥发性有机物排放的单体同位素特征。系统考察了样品进样量、进样方式和样品分离度对同位素分馏影响情况。使用填有Tenax TA的吸附管采集汽油车尾气、汽油挥发、柴油车尾气、柴油挥发、溶剂挥发和餐饮油烟等污染源,以及城市不同功能区的挥发性有机物(VOCs)样品,不同污染源中挥发性有机物的稳定碳同位素δ13C值不同,97#汽油车尾气的δ13 C值偏重,平均值为-25.84‰,富集13 C;餐饮油烟的δ13 C值偏轻,平均值为-30.26‰。油品挥发比燃烧后以尾气的形式排放的苯系物δ13 C值重。厦门市各功能区挥发性有机物的δ13 C平均范围在-27.03‰~-25.40‰,接近于汽油和柴油挥发及尾气中的δ13 C值,表明厦门市空气中挥发性有机物以机动车排放源为主。     

静态顶空-气相色谱/质谱法同时检测环境水体中59种挥发性有机物

静态顶空法是一种简单、环保的样品前处理方法.通过对比试验,优化了影响静态顶空进样方法灵敏度的主要因素,确定了较佳的样品盐度(40%)、平衡温度(80℃)、平衡时间(10 min)、平衡压力(0.103 4 MPa)、定量环平衡时间(20 s)、进样时间(3 min)等前处理方法参数.采用优化后水样前处理条件及1.00 k V的检测器电压,59种挥发性有机物在特定的线性范围内,标准曲线线性相关系数均大于0.998,方法检出限为丙烯腈4.4μg/L、硝基苯7.6μg/L,其余挥发性有机物(VOCs)介于0.06~1.4μg/L,饮用水源水及污水处理厂进水实际样品加标回收率为60%~110%,精密度(RSD)为0.33%~22%(n=6).建立的静态顶空-气相色谱/质谱法(HS-GC/MS)水样前处理过程自动化,可同时对水中59种挥发性有机物进行检测.     

Effects of Water Vapor and Ammonia on SO2 Removal from Flue Gases Using Pulsed Corona Discharge

Plasma Chemistry and Plasma Processing - In the study of SO2 removal using pulsed corona discharge, there exists a serious confusion, that is, which kind of reactions, the thermal chemical...     

挥发性有机物的气相光解及光催化降解研究

研究了三氯乙烯、丙酮、苯、甲苯、二氯甲烷、三氯甲烷、四氯化碳的气相光解及光催化反应,对反应过程中反应物及CO2的浓度进行了定量监测。结果表明,在253.7nm的紫外灯光照射下,三氯乙烯可迅速被光解,反应产生CO2;甲苯和丙酮蒸气也可以被光解,但不产生CO2;在空气介质中,除CCl4外,其它几种有机物均可被光催化降解。