Numerical modelling of a low power non-transferred arc plasma reactor for methane conversion

Thermal flow characteristics and the methane conversion reaction in a low power arc plasma reactor for efficient storage and transport of methane, which is the main component of shale gas, were simulated. The temperature and velocity distributions were calculated according to the type of discharge gases and arc current level by a self-developed magnetohydrodynamics (MHD) code and a commercial ANSYS-FLUENT code; the transport of chemical species was analyzed as including the chemical reactions of methane conversion. The simulated results were verified by the comparison of calculated and measured arc voltages with permissible low error as under 4%. Three C₂ hydrocarbon gases with ethane (C₂H₆), ethylene (C₂H₄), and acetylene (C₂H₂) were selected as the converted species of methane from experimental data. The mass fraction of C₂ hydrocarbons and hydrogen as the product of the conversion reaction at the reactor was also calculated. Those values show good agreement with the actual experimental results in that the major conversion reaction occurred in C₂H₂ and hydrogen, and the conversions to C₂H₆, C₂H₄, and hydrogen were minor reactions of methane pyrolysis conversion.     

Enhanced removal of benzene in nonthermal plasma with ozonation,flow recycling,and flow recirculation

A double stage AC/DC sequential high voltage reactor has been developed to study the decomposition of benzene in the air stream at atmospheric pressure. The removal efficiency was measured as a function of ozonation, flow recycling, and flow recirculation. Ozonation in the inlet, and recycling of the exhaust stream increased the removal of benzene, also with increasing of specific input energy (J l⁻¹) the effect of inlet flow ozonation on benzene decomposition was enhanced. The highest removal efficiency was obtained up to >99% in recirculation six times, while CO₂ selectivity reached 99.9% and energy efficiency was 0.59 g kWh⁻¹. O₃ production/ decomposition > production of OH radicals > electronic and ionic collisions were indicated as the main mechanisms influencing benzene abatement in this research.     

Synthesis of vertical graphene nanowalls by cracking n-dodecane using RF inductively-coupled plasma-enhanced chemical vapor deposition

A facile and controllable one-step method to treat liquid hydrocarbons and synthesize vertical graphene nanowalls has been developed by using the technique of inductively-coupled plasma-enhanced chemical vapor deposition for plasma cracking of n-dodecane.Herein,the morphology and microstructure of solid carbon material and graphene nanowalls are characterized in terms of different operating conditions,i.e.input power,H2/Ar ratio,injection rate and reaction temperature.The results reveal that the optimal operating conditions were 500 W,5:10,30μl min^-1 and 800℃ for the input power,H2/Ar ratio,injection rate and reaction temperature,respectively.In addition,the degree of graphitization and the gaseous product are analyzed by Raman spectroscopy and gas chromatography detection.It can be calculated from the Raman spectrum that the relative intensity of ID/IG is approximately 1.55,and I2D/IG is approximately 0.48,indicating that the graphene prepared from n-dodecane has a rich defect structure and a high degree of graphitization.By calculating the mass loading and detecting the outlet gas,we find that the cracking rate of n-dodecane is only 6%-7%and that the gaseous products below C2 mainly include CH4,C2H2,C2H4,C2H6 and H2.Among them,the proportion of hydrogen in the outlet gas of n-dodecane cracking ranges from 1.3%-15.1%under different hydrogen flows.Based on our research,we propose a brand new perspective for both liquid hydrocarbon treatment and other value-added product syntheses.     

Plasma-assisted ammonia synthesis in a packed-bed dielectric barrier discharge reactor: roles of dielectric constant and thermal conductivity of packing materials

In this article, plasma-assisted NH₃ synthesis directly from N₂ and H₂ over packing materials with different dielectric constants (BaTiO₃, TiO₂ and SiO₂) and thermal conductivities (BeO, AlN and Al₂O₃) at room temperature and atmospheric pressure is reported. The higher dielectric constant and thermal conductivity of packing material are found to be the key parameters in enhancing the NH₃ synthesis performance. The NH₃ concentration of 1344 ppm is achieved in the presence of BaTiO₃, which is 106% higher than that of SiO₂, at the specific input energy (SIE) of 5.4 kJ·l⁻¹. The presence of materials with higher dielectric constant, i.e. BaTiO3 and TiO₂ in this work, would contribute to the increase of electron energy and energy injected to plasma, which is conductive to the generation of chemically active species by electron-impact reactions. Therefore, the employment of packing materials with higher dielectric constant has proved to be beneficial for NH₃ synthesis. Compared to that of Al₂O₃, the presence of BeO and AlN yields 31.0% and 16.9% improvement in NH₃ concentration, respectively, at the SIE of 5.4 kJ·l⁻¹. The results of IR imaging show that the addition of BeO decreases the surface temperature of the packed region by 20.5% to 70.3°C and results in an extension of entropy increment compared to that of Al₂O₃, at the SIE of 5.4 kJ·l⁻¹. The results indicate that the presence of materials with higher thermal conductivity is beneficial for NH₃ synthesis, which has been confirmed by the lower surface temperature and higher entropy increment of the packed region. In addition, when SIE is higher than the optimal value, further increasing SIE would lead to the decrease of energy efficiency, which would be related to the exacerbation in reverse reaction of NH₃ formation reactions.     

离心分离大质量数差混合物的实验研究方法

为探究混合物离心分离性能,提出了使用易于分离的气体介质进行实验研究的方法,选取全氟甲基环己烷（C₇F₁₄）/六氟化硫（SF₆）、C₇F₁₄/氙气（Xe）、一氟三氯甲烷（CCl₃F）/乙烯（C₂H₄）气体混合物作为离心分离介质,开展了分离实验。利用分馏装置分别得到了精、贫料中的各组分气体含量,结合质谱分析结果,得到了各组分气体的基本全分离系数与混合物的全净化系数。结果表明：此方法可方便分离轻重气体混合物,针对二元混合物离心分离,能给出全净化系数和各自组分的基本全分离系数,可用于混合物离心分离性能的实验研究。     

DBD coupled with MnOx/γ-Al2O3 catalysts for the degradation of chlorobenzene

This paper investigates the degradation of chlorobenzene by dielectric barrier discharge(DBD)coupled with MnOx/γ-Al2O3 catalysts.MnOx/γ-Al2O3 catalysts were prepared using the impregnation method and were characterized in detail by N2 adsorption/desorption,x-ray diffraction and x-ray photoelectron spectroscopy.Compared with the single DBD reactor,the coupled reactor has a better performance on the removal rate of chlorobenzene,the selectivity of COx,and the inhibition of ozone production,especially at low discharge voltages.The degradation rate of chlorobenzene and selectivity of COx can reach 96.3%and 53.0%,respectively,at the specific energy density of 1350 J l-1.Moreover,the ozone concentration produced by the discharge is significantly reduced because the MnOx/Al2O3 catalysts contribute to the decomposition of ozone to form oxygen atoms for the oxidation of chlorobenzene.In addition,based on analysis of the byproducts,the decomposition mechanism of chlorobenzene in the coupled reactor is also discussed.     

Enhancing toluene removal in a plasma photocatalytic system through a black TiO_2 photocatalyst

An efficient toluene removal in air using a plasma photocatalytic system(PPS) not only needs favorable surface reactions over photocatalysts under the action of plasma,but also requires the photocatalysts to efficiently absorb light emitted from the discharge for driving the photocatalytic reactions. We report here that the PPS constructed by integrating a black titania(B-TiO_2)photocatalyst with a dielectric barrier discharge(DBD) can effectively remove toluene with above 70% CO_2 selectivity and remarkably reduced the concentration of secondary pollutants of ozone and nitrogen oxides at a specific energy input of 1500 J·l~(-1),while exhibiting good stability. Photocatalyst characterizations suggest that the B-TiO_2 provides a high concentration of oxygen vacancies for the surface oxidation of toluene in DBD,and efficiently absorbs ultraviolet–visible light emitted from the discharge to induce plasma photocatalytic oxidation of toluene. The presence of B-TiO_2 in the plasma region also results in a high discharge efficiency,facilitating the generation of large numbers of reactive species and thus the oxidation of toluene towards CO_2. The greatly enhanced performance of the PPS integrated with B-TiO_2 in toluene removal offers a promising approach to efficiently remove refractory volatile organic compounds from air at low temperatures.     

Design of a MT-DBD reactor for H_2S control

This study aimed to discuss the removal of hydrogen sulfide(H_2S)with non-thermal plasma produced by a multilayer tubular dielectric barrier discharge reactor,which is useful in the field of plasma environmental applications.We explored the influence of various factors upon H_2S removal efficiency(η_(H_2S))and energy yield(Ey),such as specific energy density(SED),initial concentration,gas flow velocity and the reactor configuration.The study showed that we can achieveη_(H_2S)of 91%and the best Ey of 3100 mg kWh~(-1)when we set the SED,gas flow velocity,initial H_2S concentration and layers of quartz tubes at 33.2 J 1~(-1),8.0 m s~(-1),30 mg m~(-3)and five layers,correspondingly.The average rate constant for the decomposition of hydrogen sulfide was 0.206 gm~(-3)s~(-1).In addition,we also presented the optimized working conditions,byproduct analysis and decomposition mechanism.     

ESR法研究Pt催化N2H4分解机制

采用电子自旋共振谱（ESR）法,研究了酸性条件下•NH₂的转化,HClO₄体系下反应时间对溶液中自由基产生的影响、pH值对N₂H₄断键的影响以及HNO₃中N是否对溶液中的•NH₂有贡献,确定了Pt催化N₂H₄分解的反应机理。结果表明：在酸性条件下•NH₂被DMPO捕捉时反应式为•NH⁺₃+HO-H+DMPO=NH⁺₄+DMPO(•OH),硝酸在Pt催化N₂H₄体系中不会发生断键产生•NH₂,所产生的•NH₂是由N₂H₄断键形成的;在HClO₄体系中,随着Pt催化N₂H₄反应时间的延长,N₂H₄中N-N断键的趋势逐渐减小,N-H断键的趋势逐渐增大;随pH值的增大,N₂H₄中N-N断键的速率先快速减小,pH>3后缓慢增大;Pt催化N₂H₄分解反应中N-N断键和N-H断键两种方式共存,但N-N断键占优;反应体系中N₂H₄与H^＋浓度之比决定了N-N断键生成•NH₂的速率,而•NH₂与H^＋的浓度又决定了•NH₂转化成产物的速率,这两方面共同决定了N₂H₄分解的速率。     

Hydrochlorination of acetylene over the Ru-based catalysts treated by plasma under different atmospheres

Ru-based catalysts modified in different atmospheres by plasma technology were prepared to catalyze the acetylene hydrochlorination reaction. The (Ru/AC)-N₂ (AC = activated carbon) catalyst yielded by the plasma modification of Ru/AC catalyst in N₂ atmosphere exhibits the best catalytic performance with a stable C₂H₂ conversion of 87.2%; a relative increase of 27.1% in C₂H₂ conversion was achieved compared with that of the untreated Ru/AC catalyst. The results of the analysis revealed that the modification produced a mutual effect between the generated function groups on carrier AC and the active components, which can disperse and yield more active species in the fresh catalysts. These are benefits of enhancing the activity of the catalysts. Moreover, the modification can restrain coke formation and inhibit the loss of active species in the reaction, as well as strengthen the adsorption ability of reactants on the catalysts. These are benefits of improving the catalysts’ performance.     

Ion implantation doping and electrical conductivity enhancement of C60 films

Pristine C₆₀ films sublimed onto sheet mica were implanted with 20 keV K⁺ ions and I⁺ ions at doses of 1.0 × 10¹⁶/cm², 3.0 × 10¹⁶/cm² and 5.0 × 10¹⁶/cm², and with 20 keV Ar⁺ ions at a dose of 5.0 × 10¹⁶/cm². The distributions of dopants were studied using Rutherford backscattering spectrometry (RBS). The temperature dependence of sheet resistivity of the films was investigated applying a four-probe system. It was proposed that the conductivity enhancement of K⁺ implanted C₆₀ films was due to the implanted ions in the films, while for I⁺ implanted C₆₀ films, both implanted I⁺ ions and irradiation effects of the ions contributed to the enhancement of conductivity.     

Activated persulfate by DBD plasma and activated carbon for the degradation of acid orange Ⅱ

In this study, the effect of activated peroxydisulfate(PDS) by dielectric barrier discharge(DBD) plasma and activated carbon(HGAC) on the removal of acid orange Ⅱ(AOⅡ) was investigated. The effects of applied voltage, PDS dosage, HGAC dosage, initial pH value, and inorganic anions on the removal rate of AOⅡ were discussed. The main free radicals degrading azo dyes during the experiment were also studied. Experimental results show that the removal rate of AOⅡ in DBD/HGAC/PDS synergistic system is much higher than that in the single system. With the applied voltage of 16 kV, HGAC dosage of 1 g l-1, PDS and AOⅡ molar ratio of 200:1, initial pH value of 5.4 and concentration of AOⅡ solution of 20 mg l-1, the removal rate of AOⅡ reached 97.6% in DBD/HGAC/PDS process after 28 min of reaction.Acidic and neutral conditions are beneficial for AOⅡ removal. Sulfate and hydroxyl radicals play an important role in the removal of AOⅡ. Inorganic anions are not conducive to the removal of AOⅡ.     

硝酸体系中Pt催化肼的分解

研究了肼的初始浓度、硝酸浓度、催化剂的量(S/V)、温度、β放射性对Pt催化肼分解反应速率的影响,获得了其动力学方程。结果表明:增大肼的初始浓度、温度、催化剂的量和降低硝酸浓度,肼的分解速率加快;β放射性对Pt催化体系中肼的分解速率有显著的提高作用,其分解表观速率常数比单独Pt催化提高了19.3倍,比单独β辐解提高了1.35倍,β放射性辐照位置不同肼的分解速率也不同。Pt催化硝酸体系中肼分解的动力学速率方程为:-dc(N₂H⁺₅)/dt=kc(N₂H⁺₅)c^-0.39(HNO₃),296 K时,速率常数k=(5.90±0.35)×10^-3 mol/(L·min),活化能E_a=(333.3±2.9) J/mol。     

工作压强对SiC空心微球结构及性能的影响

采用化学气相沉积（CVD）-高温热解法,在不同工作压强条件下,制备了惯性约束聚变靶用SiC空心微球。利用X射线光电子能谱仪、扫描电子显微镜、白光干涉仪、X射线照相机对SiC空心微球的成分、表面形貌、表面粗糙度、球形度以及壁厚均匀性进行了测试与分析。研究结果表明：随工作压强的增加,SiC空心微球的表面均方根粗糙度先减小后增加,当工作压强为15 Pa时,表面均方根粗糙度达到最小值98 nm;随工作压强的增加,SiC空心微球的球形度未发生明显变化,且均优于97%;而壁厚均匀性则随工作压强的增加先增加后减小,当压强为15 Pa时,壁厚均匀性可达95%。     

Pt催化N2H4还原U(Ⅵ)制备U(Ⅳ)过程中N2H4断键机制研究

为优化硝酸介质下Pt催化N₂H₄还原U(Ⅵ)制备U(Ⅳ)的工艺条件,确定此反应过程的控制步骤,有针对性地提高控制步骤的反应速率,以确定N₂H₄还原U(Ⅵ)制备U(Ⅳ)过程中的反应历程以及反应机理,通过实验研究确定了N₂H₄在Pt催化剂上的断键方式和分解机理。采用气相色谱法、分光光度法、滴定法及排水法对硝酸介质下Pt催化N₂H₄还原U(Ⅵ)制备U(Ⅳ)过程中的产物进行分析,确定反应过程中N₂H₄的断键机制。结果表明,硝酸介质下Pt催化N₂H₄还原U(Ⅵ)制备U(Ⅳ)反应过程中没有叠氮酸、氮氧化物及氢气生成,产物主要是N₂,生成的N₂的量与消耗的N₂H₄的量接近1∶1;当存在U(Ⅵ)时,生成的NH⁺₄产量较低,当U(Ⅵ)反应完全后,NH⁺₄的产生速率急剧增大;N₂H₄以N-N断键和N-H断键两种方式共存;反应温度升高有利于加快由U(Ⅵ)制备U(Ⅳ)还原反应的进行。     

含氚废气中杂质气体去除材料研制

为去除含氚惰性废气中的CH₄、水气、O₂等杂质气体,采用溶胶凝胶法制备了65%Ni-10%Cu-25%SiO₂材料作为杂质气体消除材料,对材料进行XRD、SEM及程序升温还原表征,结果显示,少量Cu的加入增加了Ni的分散度,有助于稳定Ni的形态,避免Ni过早发生氧化。材料可以使Ar中的少量CH₄、O₂和水气得到有效的去除,在空速1000 h^-1时Ar中φ=1%CH₄和φ=1%CO₂重整时CH₄去除率达到81.5%以上,对于Ar中φ=1%O₂的去除率达到91.8%以上,对于Ar中φ=1%水气的去除率达到91.7%以上。实验还发现低浓度的CH₄可以与水气及O₂发生反应而去除,空速10000 h^-1催化φ=1%水气和φ=1%CH₄反应,CH₄的去除率均高于80.7%;空速10000 h^-1催化φ=0.67%CH₄和φ=0.33%O₂的反应,CH₄的去除率均高于84.2%。     

Co-synthesis of vertical graphene nanosheets and high-value gases using inductively coupled plasma enhanced chemical vapor deposition

One-step controllable synthesis of vertical graphene nanosheets (VGs) and high-value gases was achieved using inductively coupled plasma enhanced chemical vapor deposition (ICPECVD). The basic physical properties of the ICPECVD process were revealed via electrical diagnosis and optical emission spectroscopy. The coil current and voltage increased linearly with the augmenting of injected power, and CH, C₂, H₂ and H were detected at a wavelength from 300 to 700 nm, implying the generation of abundant graphene-building species. The morphology and structure of solid carbon products, graphene nanosheets, were systemically characterized in terms of the variations of operating conditions, such as pressure, temperature, gas proportion, etc. The results indicated that an appropriate operating condition was indispensable for the growth process of graphene nanosheets. In the present work, the optimized result was achieved at the pressure, heating temperature, applied power and gas proportion of 600mTorr, 800 °C, 500 W and 20:20:15, respectively, and the augmenting of both CH₄ and H₂ concentrations had a positive effect on the etching of amorphous carbon. Additionally, H₂ and C₂ hydrocarbons were detected as the main exhaust gases. The selectivity of H₂ and C₂H₂ , measured in exhaust gases, reached up to 52% and 8%, respectively, which implied a process of free radical reactions and electron collision dissociation. Based on a comprehensive investigation of spectral and electrical parameters and synthesized products, the reaction mechanism of collision, dissociation, diffusion, etc, in ICPECVD could be speculated, providing a probable guide for experimental and industrial applications.     

Analysis of the critical active species for methylene blue decoloration in a dielectric barrier discharge plasma system

In the paper, a hybrid gas–liquid dielectric barrier discharge (DBD) plasma system was set up to treat a methylene blue (MB) solution. The effects of the change of the carrier gas, the gas bubbling rate and different kinds of scavenger addition, including sodium carbonate (Na₂CO₃), para benzoquinone (p-BQ), triethylenediamine and sodium dihydrogen phosphate (NaH₂PO₄), on the MB decoloration were reviewed to clarify the critical active species for the dye decoloration in the DBD plasma system. The obtained results show that higher decoloration of the MB solution could be achieved when O₂ was used as the carrier gas, which could be 100% after 20 min discharge treatment, and the result confirmed the crucial effect of O₃ in the MB decoloration. Based on the experiments of the scavenger addition, it could be concluded that O₂⁻ and ¹O₂ were two other important reactive oxygen species (ROS) for the MB decoloration. The results of the higher chemical oxygen demand removal and faster disappearance of the characteristic peak of the MB from the UV–vis analysis under O₂ bubbling conditions also proved the critical effect of the ROS formed by O₂ on the MB decoloration.     

Study of partial discharge characteristics in HFO-1234ze(E)/N2 mixtures

HFO-1234ze(E)(trans-1,3,3,3-tetrafluoropropene, chemical formula: C₃H₂F₄) is an extremely environmentally friendly SF₆ alternative gas with high electrical strength. In this paper, the partial discharge (PD) characteristics of HFO-1234ze(E)/N₂ mixtures were studied using the gas insulation test platform. The PD inception voltage of insulating gas under positive and negative half cycles of power frequency was tested. Using SF₆/N₂ mixtures as a control group, the effects of electrode spacing, mixing ratio and pressure on the insulation performance of HFO-1234ze(E)/N₂ mixtures were explored. The test results show that the PD inception voltage of the negative half-cycle of pure HFO-1234ze(E) under short electrode spacing can reach 0.96–1.04 times of pure SF₆ under different pressures; the PD inception voltage of 40%HFO-1234ze(E)/60%N₂ mixtures at 0.3 MPa is 0.67–0.89 times that of SF₆/N₂ mixtures under the same conditions, which has great application prospect.     

Improved sensitivity on detection of Cu and Cr in liquids using glow discharge technology assisted with LIBS

Laser-induced breakdown spectroscopy-assisted glow discharge (LIBS-GD) for analysis of elements in liquid was proposed, and it was applied to detect heavy metals in highly sensitive mixed solutions of Cu and Cr. During the experiments of GD and LIBS-GD, the experimental parameters have been optimized and the optimal voltage is 450 V, laser energy is 60 mJ, and the delay time is 4000 ns. Furthermore, the calibration curves of Cu and Cr under GD and LIBS-GD experiments have been established, and the limits of detection (LODs) of Cu and Cr were obtained with the method of GD and LIBS-GD, respectively. The LOD of Cu decreased from 3.37 (GD) to 0.16 mg l⁻¹ (LIBS-GD), and Cr decreased from 3.15 to 0.34 mg l⁻¹. The results prove that the capability of elemental detection under LIBS-GD has improved compared with the GD method. Therefore, LIBS-GD is expected to be developed into a highly sensitive method for sewage detection.