By-Products NOx Control and Performance Improvement of a Packed-Bed Nonthermal Plasma Reactor

NO_x are main toxic by-products in the effluent gas whendecomposing volatile organic compounds in air by a packed-bed plasmareactor. Several types of materials such as 13X zeolite, BaTiO₃and Pd/Pt catalysts have been selected to be packed in the reactor, andmethane decomposition and NOx by-products in discharged gases areinvestigated at different range of reaction temperature and dischargeenergy density at atmospheric pressure. The ratios of methane decompositionpercentage/NO_x concentration are used to assess these packed bedmaterials and reaction conditions. The results show that usingPd/-Al₂O₃ with lower percentage Pd as packedbed, and discharging with lower discharge density at higher reactiontemperature can reduce NO_x output effectively and greatly improveperformance of the reactor.     

Oxidation of Dilute Benzene in an Alumina Hybrid Plasma Reactor at Atmospheric Pressure

The combination of plasma discharge and adsorption was examined for oxidation of dilute benzene in air in a plasma reactor packed with a mixture of BaTiO ₃ pellets and porous Al ₂ O ₃ pellets (i.e., an alumina hybrid reactor). The oxidative decomposition of benzene was enhanced by the benzene concentrating on the Al ₂ O ₃ pellets. Furthermore, there was a higher selectivity to CO ₂ in the products from the hybrid than from a plasma reactor packed with BaTiO ₃ pellets alone. The presence of the Al ₂ O ₃ pellets suppressed the formation of N ₂ O.     

Oxidation and Reduction Processes During NO x Removal with Corona-Induced Nonthermal Plasma

In this paper, the NO-to-NO ₂ conversion in various gaseous mixtures is experimentally investigated. Streamer coronas are produced with a dc-superimposed high-frequency ac power supply (10–60 kHz). According to NO _x removal experiments in N ₂ +NO _x and N ₂ +O ₂ +NO _x gaseous mixtures, it is supposed that the reverse reaction NO ₂ +ONO+O ₂ may not only limit NO ₂ production in N ₂ +NO _x mixtures, but also increase the energy cost for NO removal. Oxygen could significantly suppress reduction reactions and enhance oxidation processes. The reduction reactions, such as N+NON ₂ +O, induce negligible NO removal provided the O ₂ concentration is larger than 3.6%. With adding H ₂ O into the reactor, the produced NO ₂ per unit removed NO can be significantly reduced due to NO ₂ oxidation. NH ₃ injection could also significantly decrease the produced NO ₂ via NH and NH ₂ - related reduction reactions. Almost 100% of NO ₂ can be removed in gaseous mixtures of N ₂ +O ₂ +H ₂ O+NO ₂ with negligible NO production.     

Converting Methane by Using an RF Plasma Reactor

A radio-frequency (RF) plasma system was used to convert methane gas. The reactants and final products were analyzed by using an FTIR (Fourier transform infrared spectrometer). The effects of plasma operational parameters, including feeding concentration (C) of CH ₄ , operational pressure (P) in the RF plasma reactor, total gas flow rate (Q) and input power wattage (W) for CH ₄ decomposition were evaluated. The results showed that the CH ₄ decomposition fraction increases with increasing power input, decreasing operational pressure in the RF plasma reactor, decreasing CH ₄ feeding concentration, and decreasing total gas flow rate. In addition, mathematical models based on the obtained experimental data were developed and tested by means of sensitivity analysis.     

Catalytic Reduction of Dinitrogen Monoxide with Methane Over Metal Zeolite Catalysts

Pronounced activities on the reduction of N₂O with CH₄ were observed over Fe-ZSM-5, Pd-ZSM-5, and Pt-ZSM-5 catalysts, respectively. No significant deactivation has been detected over Fe-ZSM-5 in the presence of oxygen.     

Deposition of Diamondlike Carbon Film and Mass Spectrometry Measurement in CH4/N2 RF Plasma

The deposition of diamondlike carbon (DLC) film and the measurements of ionic species by means of mass spectrometry were carried out in a CH₄/N₂ RF (13.56 MHz) plasma at 0.1 Torr. The film deposition rate greatly depended on both CH₄/N₂ composition ratio and RF power input. It was decreased monotonically as CH₄ content decreased in the plasma and then rapidly diminished to negligible amounts at a critical CH₄ content, which became large for higher RF power. The rate increased with increasing RF power, reaching a maximum value in 40% CH₄ plasma. The predominant ionic products in CH₄/N₂ plasma were NH⁺ ₄ and CH₄N⁺ ions, which were produced by reactions of hydrocarbon ions, such as CH⁺ ₃, CH⁺ ₂, CH⁺ ₅, and C₂H⁺ ₅ with NH₃ molecules in the plasma. It was speculated that the production of NH⁺ ₄ ion induced the decrease of C₂H⁺ ₅ ion density in the plasma, which caused a reduction in higher hydrocarbon ions densities and, accordingly, in film deposition rate. The N⁺ ₂ ion sputtering also plays a major role in a reduction of film deposition rate for relatively large RF powers. The incorporation of nitrogen atoms into the bonding network of the DLC film deposited was greatly suppressed at present gas pressure conditions.     

Tunable Diode Laser Diagnostic Studies of H2-Ar-O2 Microwave Plasmas Containing Methane or Methanol

Tunable infrared diode laser absorption spectroscopy has been used to detect the methyl radical and ten stable molecules in H₂-Ar-O₂ microwave plasmas containing up to 7.2% of methane or methanol, under both flowing and static conditions. The degree of dissociation of the hydrocarbons varied between 30 and 90% and the methyl radical concentration was found to be in the range 10 ¹⁰ –10 ¹² molecules cm ^–3 . The methyl radical concentration and the concentrations of the stable C-2 hydrocarbons C ₂ H ₂ , C ₂ H ₄ , and C ₂ H ₆ , produced in the plasma decayed exponentially when increasing amounts of O ₂ were added at fixed methane or methanol partial pressures. In addition to detecting the hydrocarbon species, the major products CO, CO ₂ , and H ₂ O were also monitored. For the first time, formaldehyde, formic acid, and methane were detected in methanol microwave plasmas, formaldehyde was detected in methane microwave plasmas. Chemical modeling with 57 reactions was used to successfully predict the concentrations in methane plasmas in the absence of oxygen and the trends for the major chemical product species as oxygen was added.     

Methane and nitrous oxide concentration and emission flux of Yangtze Delta plain river net

Methane (CH4) and nitrous oxide (N2O) saturation concentration and gas-water interface emission flux in surface water of the Yangtze Delta plain river net were investigated in summer at representative sites including the upper reaches of the Huangpu River and the rivers in the Chongming Island. The results show that the CH4 concentration in river water ranged from 0.30±0.03 to 6.66±0.14 μmol.L-1, and N2O concentration ranged from 13.8±2.33 to 435±116 nmol.L-1. River surface water had a very high satura- tio...     

Influence of Ferroelectric Materials and Catalysts on the Performance of Non-Thermal Plasma (NTP) for the Removal of Air Pollutants

The introduction of ferroelectric and catalytically active materials into the discharge zone of NTP reactors is a promising way to improve their performance for the removal of hazardous substances, especially those appearing in low concentrations. In this study, several coaxial barrier-discharge plasma reactors varying in size and barrier material (glass, Al₂ O₃, and TiO₂) were used. The oxidation of methyl tert-butyl ether (MTBE), toluene and acetone was studied in a gas-phase plasma and in various packed-bed reactors (filled with ferroelectric and catalytically active materials). In the ferroelectric packed-bed reactors, better energy efficiency and CO₂ selectivity were found for the oxidation of the model substances. Studies on the oxidation of a toluene/acetone mixture in air showed an enhanced oxidation of the less reactive acetone related to toluene in the ferroelectric packed-bed reactors. It can be concluded that the change of the electrical discharge behaviour was caused by a larger number of non-selective and highly reactive plasma species formed within the ferroelectric bed. When combining ferroelectric (BaTiO₃) and catalytically active materials (LaCoO₃), only a layered implementation led to synergistic effects utilising both highly energetic species formed in the ferroelectric packed-bed and the potential for total oxidation provided by the catalytically active material in the second part of the packed bed.     

Characterization of Polypropylene Surface Treated in a CO2 Plasma

The polypropylene modification in CO₂ plasma mainly contributes to degradation, functionalization, and cross-linking. The degradation, whose rate is depending on CO₂ dissociation and oxygen atom formation, is a quite slow reaction and it is associated with surface topography alteration, especially of the amorphous phase of the polypropylene. The surface roughness increases with the treatment duration and the amorphous phase is more degraded than the crystallized part. The functionalization, corresponding to an increase of the surface energy (57.3 mJ m ^{– 2} in 30 s), and to an oxidation (23 oxygen at.%) with the appearance of alcohol, ketone, and acid functions is a much faster phenomenon. Cross-linking takes also place during this type of treatment and will reinforce the stability of the modified surface.     

Hydrocarbon Effects on the Promotion of Non-Thermal Plasma NO–NO2 Conversion

Kinetic modeling of non-thermal plasma chemistry is conducted to investigate hydrocarbon (CH₄, C₂H₄, C₃H₆, and C₃H₈) effects on the promotion of NO–NO₂ conversion. A reduced plasma chemistry model, in which radical reactions are selectively involved, is validated with experimental data. The higher reactivity of hydrocarbon additive with O radicals, which produces initial radicals, is requisite to initiate hydrocarbon decomposition, thus providing NO–NO₂ conversion. Initial radicals by plasma discharge induce continual hydrocarbon decomposition and this self-preserved reaction mechanism greatly contributes to the promotion of energy efficient NO–NO₂ conversion. Increase in the conversion extent by ethylene and propylene additives is substantial because of their stronger affinity with O radical. The primary routes of NO–NO₂ conversion process differed by hydrocarbon additives are presented and discussed with the assistance of sensitivity analysis.     

Difference in Conversions Between Dimethyl Sulfide and Methanethiol in a Cold Plasma Environment

This study compared the conversion of two malodorous substances, dimethyl sulfide (CH₃SCH₃, DMS) and methanethiol (CH₃SH) in a cold plasma reactor. The DMS and CH₃SH were successfully destroyed at room temperature. DMS decomposed less than CH₃SH at the same conditions. In oxygen-free condition, CS₂ and hydrocarbons were the major products, while SO₂ and CO_x were main compounds in oxygen-rich environments. The DMS/Ar plasma yielded more hydrocarbons and less CS₂ than that of CH₃SH/Ar plasma. In the CH₃SH/O₂/Ar plasma, rapid formation of SO and CO resulted in the yields much more amounts of SO₂ and CO₂ than those in the DMS/O₂/Ar plasma; and remained only a trace of total hydrocarbons, CH₂O, CH₃OH, CS₂, and OCS. The major differences between the reaction mechanisms of DMS and CH₃SH were also proposed and discussed.     

硝酸镁在γ-Al2O3上的热分解及MgO/γ-Al2O3

研究了不同载量时Mg(NO     

Comparative Study of the Decomposition of CCl4 in Cold and Thermal Plasma

Decomposition of carbon tetrachloride was studied in an inductively coupled thermal plasma reactor and in a low temperature, non-equilibrium plasma reactor, in neutral and oxidative conditions, respectively. In neutral conditions formation of solid soot, aliphatic- and cyclodienes was observed in equilibrium, and products, such as Cl₂ and C₂Cl₆ were detected in non-equilibrium plasma. Feeding of oxygen into the thermal plasma reactor depressed both soot and dienes formation and induced the formation of oxygen containing intermediates and products. GC-MS analyses of the gaseous products and the extract of the soot referred to as complex decomposition and recombination mechanism at given conditions. Presence of oxygen in the low temperature plasma reactor results in the formation of carbonyl compounds as intermediers. CO₂ and Cl₂ revealed as final products of CCl₄ decomposition in cold plasma.     

Decomposition of P2S2N4(Si(CH3)3)4A12C14 as Studied by FT-Raman and Quantum Chemistry Means

The dimeric title compound decomposes upon heating to give the monomer and desulphurized monomer as shown by FT-Raman and quantum chemical means.     

GC-MS Analysis of Contaminants in Breathing Oxygen

Abstract

Oxygen used for flight crews and for extra-hospital therapies is kept in vacuum containers and maintained as liquid phase (LOX) until use; by using this procedure, the weight of the breathing apparatus is reduced, thus extending breathing oxygen availability and improving safety by using atmosphere pressure sampler.

On the other hand, because of its low boiling point (?183°C), during storage and distribution, LOX shows continuous evaporation with a constant increase in pollutant concentration obtained in the LOX production.

Therefore, LOX is subjected to a strict quality control to evaluate the contamination levels from production until its use.

In this study, an analytical procedure has been optimised to measure the main LOX contaminants (freon, chlorinated solvents, light hydrocarbons, CO₂, CO, and N₂O) based on a single technique (GC-MS) and two chromatographic columns (Poraplot Q/HT and HP-Plot molecular sieve 5 A). The proposed method is an improvement in terms of time as well cost of analysis and selectivity with respect to the present methods based on three chromatographic techniques (GC-ECD, GC-FID, GC-HID) and four different columns.     

基于电解液微弧放电的碳氮化钛厚膜形成机理分析

采用电解液微弧碳氮化技术(PECN),在钛合金表面沉积出较厚的Ti(CxN1-x)膜层,用红外光谱研究了改性过程中的气封组成,分析了膜层的形成机理。结果表明:PECN处理过程中的气相产物主要是:CH4、NH3、C2H2、CO、CO2和H2O。各气体产物来自于PECN处理过程中有机物的分解,并且气体之间存在相互作用。随放电时间延长,各气体浓度呈现不同的变化趋势,导致气封中碳、氮势随之改变,继而引起Ti(CxN1-x)膜层中C/N原子比亦相应变化。PECN过程大致可分为:阴极电解析氢、有机物的热分解以形成气封,反应气体在等离子体的作用下分解、电离产生含碳、氮活性粒子,活性粒子向试样表面扩散,在试样表面吸附并发生化学反应形成Ti(CxN1-x)膜。     

Adsorption separation of carbon dioxide,methane, and nitrogen on Hβ and Na-exchanged β-zeolite

Adsorption isotherms of carbon dioxide （CO2）, methane （CH4）, and nitrogen （N2） on Hβand sodium exchanged β-zeolite （Naβ） were volumetrically measured at 273 and 303 K. The results show that all isotherms were of Brunauer type I and well correlated with Langmuir-Freundlich model. After sodium ions exchange, the adsorption amounts of three adsorbates increased, while the increase magnitude of CO2 adsorption capacity was much higher than that of CH4 and N2. The selectivities of CO2 over CH4 and CO2 over N2 enhanced after sodium exchange. Also, the initial heat of adsorption data implied a stronger interaction of CO2 molecules with Na＋ ions in Naβ . These results can be attributed to the larger electrostatic interaction of CO2 with extraframework cations in zeolites. However, Naβ showed a decrease in the selectivity of CH4 over N2, which can be ascribed to the moderate affinity of N2 with Naβ. The variation of isosteric heats of adsorption as a function of loading indicates that the adsorption of CO2 in Naβ presents an energetically heterogeneous profile. On the contrary, the adsorption of CH4 was found to be essentially homogeneous, which suggests the dispersion interaction between CH4 and lattice oxygen atoms, and such interaction does not depend on the exchangeable cations of zeolite.     

A comparative study of CH4 and CF4 rf discharges using a consistent plasma physics and chemistry simulator

A self-consistent, one-dimensional simulator for the physics and chemistry of radio frequency (rf) plasmas was developed and applied for CH₄ and CF₄. The simulator consists of a fluid model for the discharge physics, a commercial Boltzmann equation solver for calculations of electron energy distribution fuction (EEDF), a generalized plasma chemistry code, and an interface module among the three models. The CH₄ and CF₄ discharges are compared and contrasted: CH₄ plasmas are electropositive, with negative ion densities one order of magnitude less than those of electrons, whereas CF₄ plasmas are electronegative, with ten times more negative ions than electrons. The high-energy tail of tire EEDF in CH₄, lies below both the Druyvensteyn and Maxwell distributions, whereas tire EEDF high-energy tail in CF₄ lies between the two. For CH₄, the chemistry model was applied for four species, namely, CH₄ CH₃ CH₂, and H, whereas for CF₄, five species were examined namely CF₄, CF₃, CF₂, CF, and F The predicted densities and profiles compare favorably with experimental data. Finally, the chemistry results were fedback into the physics model until convergence was obtained.     

IR-Spectroscopic Study of Complex Formation of Nitrogen Oxides (NO,N2O) with Cationic Forms of Zeolites and the Reactivity of Adsorbed Species in CO and CH4 Oxidation

The formation of complexes and disproportionation of nitrogen oxides (NO, N₂O) on cationic forms of LTA, FAU, and MOR zeolites was investigated by diffuse-reflectance IR spectroscopy. N₂O is adsorbed on the samples under study in the molecular form and the frequencies of the first overtone of the stretching vibrations ν¹_0–2 and the combination bands of the stretching vibrations with other vibrational modes for N₂O complexes with cationic sites in zeolites (ν³_0–1 + ν¹_0–1, ν¹_0–1 + δ_0–2) are more significantly influenced by the nature of the zeolite. The presence of several IR bands in the region of 2400–2600 cm⁻¹ (the ν¹_0–1 + δ_0–2 transitions) for different zeolite types was explained by the availability of different localization sites for cations in these zeolites. The frequencies in this region also depend on the nature of the cation (its charge and radius). The data can be explained by the specific geometry of the N₂O complex formed, presumably two-point adsorption of N₂O on a cation and a neighboring oxygen atom of the framework. Adsorption of CO or CH₄ on the samples with preliminarily adsorbed N₂O at 20–180 °C does not result in any oxidation of these molecules. NO⁺ and N₂O₃ species formed by disproportionation of NO are capable of oxidizing CO and CH₄ molecules to CO₂, whereas NO_x is reduced simultaneously to N₂ or N₂O. The peculiarities in the behavior of cationic forms of different zeolites with respect to adsorbed nitrogen oxides determined by different density and localization of cations have been established.