Ethylene Epoxidation over Alumina- and Silica-Supported Silver Catalysts in Low-Temperature AC Dielectric Barrier Discharge

In this work, ethylene epoxidation reaction for ethylene oxide production over silver catalysts loaded on two different supports (silica and alumina particles) in a low-temperature AC dielectric barrier discharge (DBD) reactor was investigated. The DBD plasma system was operated under the following base conditions: an O₂/C₂H₄ feed molar ratio of 1/4, a total feed flow rate of 50 cm³/min, an electrode gap distance of 0.7 cm, an input frequency of 500 Hz, and an applied voltage of 19 kV. From the results, the presence of silver catalysts improved the ethylene oxide production performance. The silica support interestingly provided a higher ethylene oxide selectivity than the alumina support. The optimum Ag loading on the silica support was found to be 20 wt%, exhibiting the highest ethylene oxide selectivity of 30.6%.     

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.     

Ethylene Epoxidation in Low-Temperature AC Dielectric Barrier Discharge: Effects of Oxygen-to-Ethylene Feed Molar Ratio and Operating Parameters

Ethylene oxide (EO), a valuable chemical feedstock in producing many industrial chemicals, which is industrially produced by the partial oxidation of ethylene, so-called ethylene epoxidation, has been of great interest in many global research studies. In this work, the epoxidation of ethylene under a low-temperature dielectric barrier discharge (DBD) was feasibly investigated to find the best operating conditions. It was experimentally found that the EO yield decreased with increasing O₂/C₂H₄ feed molar ratio, feed flow rate, input frequency, and electrode gap distance, while it increased with increasing applied voltage up to 19 kV. The highest EO yield of 5.6% was obtained when an input frequency of 500 Hz and an applied voltage of 19 kV were used, with an O₂/C₂H₄ feed molar ratio of 1:1, a feed flow rate of 50 cm³/min, and an electrode gap distance of 10 mm. Under these best conditions, the power consumption was found to be as low as 6.07 × 10⁻¹⁶ Ws/molecule of EO produced.     

Ethylene Epoxidation in AC Dielectric Barrier Discharge Over Silver-Based Catalysts with Different Second Metals

Plasma Chemistry and Plasma Processing - This work was to investigate the effects of Ag-based catalysts and the addition of a second metal (Sn or Cu) loaded on an 0.1% wt% Ag catalyst on the...     

Ethylene Epoxidation over Alumina-Supported Silver Catalysts in Low-Temperature AC Corona Discharge

In this paper, the epoxidation of ethylene over different catalysts—namely Ag/(low-surface-area, LSA)α-Al₂O₃, Ag/(high-surface-area, HSA)γ-Al₂O₃, and Au–Ag/(HSA)γ-Al₂O₃—in a low-temperature corona discharge system was investigated. In a comparison among the studied catalysts, the Ag/(LSA)α-Al₂O₃ catalyst was found to offer the highest selectivity for ethylene oxide, as well as the lowest selectivity for carbon dioxide and carbon monoxide. The selectivity for ethylene oxide increased with increasing applied voltage, while the selectivity for ethylene oxide remained unchanged when the frequency was varied in the range of 300–500 Hz. Nevertheless, the selectivity for ethylene oxide decreased with increasing frequency beyond 500 Hz. The optimum Ag loading on (LSA)α-Al₂O₃ was found to be 12.5 wt.%, at which a maximum ethylene oxide selectivity of 12.9% was obtained at the optimum applied voltage and input frequency of 15 kV and 500 Hz, respectively. Under these optimum conditions, the power consumption was found to be 12.6 × 10^?16 W s/molecule of ethylene oxide produced. In addition, a low oxygen-to-ethylene molar ratio and a low feed flow rate were also experimentally found to be beneficial for the ethylene epoxidation.     

Ethylene Epoxidation in Cylindrical Dielectric Barrier Discharge: Effects of Separate Ethylene/Oxygen Feed

The effects of separate C₂H₄/O₂ feed and C₂H₄ feed position on the ethylene epoxidation reaction in an AC cylindrical dielectric barrier discharge reactor were investigated. The highest EO selectivity of 34?% and EO yield of 7.5?%, as well as the lowest power consumption of 1.72?×?10^?16 Ws/molecule of EO produced, were obtained at a C₂H₄ feed position of 0.25, an O₂/C₂H₄ feed molar ratio of 1/4, an applied voltage of 13?kV, an input frequency of 550?Hz, and a total feed flow rate of 75?cm³/min. The results demonstrated, for the first time, that the separate feed of C₂H₄ and O₂ could provide better ethylene epoxidation performance in terms of higher EO selectivity and yield, and lower power consumption, as compared to the mixed feed. All undesired reactions including C₂H₄ cracking, dehydrogenation, oxidation, and coupling reactions are lowered by the ethylene separate feed because of a decrease in opportunity of ethylene molecules to be activated by generated electrons.     

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%.     

Direct Oxidation of Methane to Methanol Over Cu-Based Catalyst in an AC Dielectric Barrier Discharge

In this paper, the conversion of methane to methanol on CuO/Al₂O₃ and Mo–CuO/Al₂O₃ catalysts in a plasma reactor was tested. A comparison between catalytic and plasma-catalytic systems had been made in tested temperature range of 50–300°C. Experimental results showed that plasma-catalytic system demonstrated a much better methane conversion than catalytic system in tested temperature range and Mo–CuO/Al₂O₃ revealed a higher catalytic activity than CuO/Al₂O₃ for methanol synthesis. Furthermore, an Arrhenius plot was made in order to deduce the mechanism of plasma activation, which revealed that the presence of plasma decreased the activation energy for both catalysts. In the case of Mo-CuO/Al₂O₃ catalyst, the enhanced activity for methanol synthesis was assumed due to the oxygen vacancies on Mo–CuO/Al₂O₃ catalyst, which can utilize plasma-induced species to improve the catalytic efficiency.     

Dielectric Barrier Discharge for Ammonia Production

The leading after-treatment technology for NOx removal process in Diesel engines for stationary and mobile applications is the selective catalytic reduction of oxides of nitrogen [NOx] by ammonia [NH₃]. A novel non-thermal plasma electrode with a needle array in a dielectric barrier discharge reactor, powered by a high frequency neon transformer, is used for the thermal decomposition of solid urea [(NH₂)CO(NH₂)] to produce ammonia. The thermolysis of urea produces iso-cyanic acid [HNCO] as a byproduct, besides ammonia, which can react with water in the gas phase, thus giving carbon dioxide and more ammonia. The presence of water fed before and/or after the plasma reactor was studied to assess its effect on the amount of produced ammonia. Results clearly showed that water fed to the entrance of the reactor can efficiently promote the reaction of iso-cyanic acid to produce ammonia and this result can be improved when air is used as carrier gas for 115 V of input voltage to a neon transformer and with a gas flow rate of 4 L/min.     

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.     

Flue Gas Desulfurization by Dielectric Barrier Discharge

There are many problems with flue gas desulfurization by traditional gas ionization discharge, including the large size of the plasma source, high energy consumption, and the need for a traditional desulfurization method. This paper introduces oxidization of SO₂ to sulfuric acid (H₂SO₄) in a duct by reactive oxygen species (O₂ ⁺, O₃) produced by strong ionization dielectric barrier discharge. The entire plasma reaction process is completed within the duct without the use of absorbents, catalysts, or large plasma source. The reactive oxygen species O₂ ⁺ reacts with gaseous H₂O in the flue gas to generate ·OH radicals, which can oxidize trace amounts of SO₂ in large volumes of the flue gas to produce H₂SO₄. Sulfuric acid is also produced by O₃ oxidation of SO₂ to SO₃, and SO₃ reacting with gaseous H₂O in the flue gas. Experimental results showed that with a gas temperature of 22 °C and reactive oxygen species injection rate of 0.84 mg/L, the SO₂ removal rate was 81.4 %, and the SO₄ ^2? concentration in the recovered liquid H₂SO₄ reached 53.8 g/L.     

Humidity Effect on Toluene Decomposition in a Wire-plate Dielectric Barrier Discharge Reactor

Laboratory-scale experiments were performed to evaluate the humidity effect on toluene decomposition by using a wire-plate dielectric barrier discharge (DBD) reactor at room temperature and atmospheric pressure. The toluene decomposition efficiency as well as the carbon dioxide selectivity with/without water in a gas stream of N₂ with 5% O₂ was investigated. Under the optimal humidity of 0.2% the characteristics of toluene decomposition in various background gas, including air, N₂ with 500 ppm O₂, and N₂ with 5% O₂ were observed. In addition, the influence of a catalyst on the decomposition was studied at selected humidities. It was found that the optimum toluene removal efficiency was achieved by the gas stream containing 0.2% H₂O, since the presence of water enhanced the CO₂ selectivity. In addition, the toluene removal efficiency increased significantly in a dry gas stream but decreased with an increase in the humidity when the Co₃O₄/Al₂O₃/nickel foam catalyst was introduced into the discharge area.     

Floating Electrode Dielectric Barrier Discharge Plasma in Air Promoting Apoptotic Behavior in Melanoma Skin Cancer Cell Lines

Initiation of apoptosis, or programmed cell death, is an important issue in cancer treatment as cancer cells frequently have acquired the ability to block apoptosis and thus are more resistant to chemotherapeutic drugs. Targeted and perhaps selective destruction of cancerous tissue is desirable for many reasons, ranging from the enhancement of or aid to current medical methods to problems currently lacking a solution, i.e., lung cancer. Demonstrated in this publication is the inactivation (killing) of human Melanoma skin cancer cell lines, in vitro, by Floating Electrode Dielectric Barrier Discharge (FE-DBD) plasma. Not only are these cells shown to be killed immediately by high doses of plasma treatment, but low doses are shown to promote apoptotic behavior as detected by TUNEL staining and subsequent flow cytometry. It is shown that plasma acts on the cells directly and not by “poisoning” the solution surrounding the cells, even through a layer of such solution. Potential mechanisms of interaction of plasma with cells are discussed and further steps are proposed to develop an understanding of such systems.     

NO Conversion by Dielectric Barrier Discharge and TiO2 Catalyst: Effect of Oxygen

Present study was carried out to investigate the conversion of NO by simultaneous action of the dielectric barrier discharge (DBD) and TiO₂ catalyst. NO conversion was recorded as a function of the input energy density by varying the percentage of NO and O₂. NO conversion efficiency increased at higher content of O₂. The presence of a TiO₂ coating inside the reactor resulted in initially enhanced NO conversion but in few minutes the positive effect of TiO₂ diminished. The increased conversion of NO in initial stage of the process was more pronounced at higher densities of input energy (higher than 100 J/l) and at lower O₂ concentrations, but without O₂ the TiO₂ coating had no effect on the conversion of NO. The results indicate that the conversion of NO during first few minutes is related to the surface reactions with adsorbed atomic oxygen.     

Efficiency of Ozone Production in Coplanar Dielectric Barrier Discharge

Plasma Chemistry and Plasma Processing - Efficient generation of ozone by cold atmospheric plasmas is interesting for sterilisation and decontamination of thermally-sensitive surfaces. This paper...     

添加气对非平衡等离子体转化低碳烷烃的影响

在常压下, 研究了添加气的种类(N₂, He, Ar, H₂, NH₃, CO和CO₂)对介质阻挡放电低碳烷烃(甲烷、 乙烷和丙烷)转化制低碳烯烃的影响. 结果表明, 以甲烷或乙烷为原料时, N₂, He, Ar和CO的引入有利于提高原料的转化率和总烯烃的选择性; 而CO₂, H₂和NH₃的引入对甲烷、 乙烷的转化率无明显影响, 但H₂和NH₃的引入会使总烯烃的选择性显著降低. 以丙烷为原料时, 所研究的添加气均可提高丙烷的转化率, 而只有CO的引入可提高总烯烃选择性. 综上所述, 80%(摩尔分数) CO添加量最有利于低碳烷烃转化成低碳烯烃, 对应的甲烷、 乙烷和丙烷的转化率分别提高了14.4%, 17.6%和42.8%, 总烯烃的选择性分别提高了19.9%, 25.0%和11.9%. 以CH₄为例, 通过对放电电流波形和等离子体区物种的发射光谱(OES)研究发现, 引入CO能显著增加等离子体的电子密度, 并且体系中出现激发态O^*物种(777.5和844.7 nm), 这种O^*物种能够促进C-H键的断裂, 有利于烯烃的生成. 因此, 等离子体区电子密度的增加和激发态O^*物种的出现可能是CH₄-CO体系中CH₄有效转化的主要原因.     

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%.     

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.