N-Decane Reforming by Gliding Arc Plasma in Air and Nitrogen

Plasma cracking of n-decane is carried out in a new type of gliding arc flow reactor in the atmosphere of nitrogen and air, at a flow range of 25–45 L/min with an interval of 5 L/min. The relationship between arc evolution and discharge voltage and current signals is established by synchronous recording with high-speed camera and oscilloscope. It is recorded that the rotating frequency of the gliding arc is in the range of 81–176 Hz, which increases with the rise of the flow rate and has no direct relationship with the type of gas. When air is used as the discharge medium, although the luminous intensity of the arc is weak, arc rotation is relatively stable, and the specific input energy is higher, which is 58% higher than that of nitrogen. In addition, the partial oxidation of n-decane provides extra heat for cracking, which is helpful to improve the efficiency of plasma cracking. The cracking products mainly include hydrogen, ethylene, acetylene, methane, propylene and ethane. The concentration of each component is higher, reaching the maximum value at the flow rate of 40 L/min, with the hydrogen selectivity of 23.1%. However, when nitrogen plasma is selected, the kinds of products are reduced, containing only hydrogen, ethylene and acetylene, and the concentrations are lower than 0.5%. Two parameters, energy conversion efficiency and carbon based characterization effective cracking rate, were proposed to evaluate the cracking effect of flow reactor.

     

Influence of Operating Parameters on Plasma-Assisted Dry Reforming of Methane in a Rotating Gliding Arc Reactor

Plasma Chemistry and Plasma Processing - The environmental impact of greenhouse gases such as carbon dioxide and methane can be reduced if they are used as feedstock to synthesize chemical building...     

Surface Modification of Smectite Clay Induced by Non-thermal Gliding Arc Plasma at Atmospheric Pressure

Smectite clay from Sabga (west-Cameroon) was treated in aqueous suspension by gliding arc plasma to modify its surface properties. The evolution of the modifications was followed with the exposure time and post-discharge duration using Fourier transformed infra red spectroscopy and scanning electron microscopy. X-ray diffraction and nitrogen physisorption analyses were also performed to evaluate if both crystalline and textural properties of the material are affected by the treatment. The results obtained show that the plasma treatment causes the breakdown of structural bounds at the clay surface and induces the formation of new hydroxyl groups (Si–OH and Al–OH) on the clay edges. Crystallinity, sheet structure and textural properties are not significantly affected by the plasma treatment. However, it should be noted that an intensive treatment of the clay lowers the pH of the suspension, which subsequently induces an acid attack of the clay. In such case, the specific surface area of the clay increases. This study demonstrates that gliding arc plasma treatments can be used to activate clay minerals for environmental application.     

Plasma Nitrogen Oxides Synthesis in a Milli-Scale Gliding Arc Reactor: Investigating the Electrical and Process Parameters

Nitrogen fixed in the form of nitrogen oxides is essential to produce fertilizers and many other chemical products, which is vital to sustain life. The performance of a milli-scale gliding arc reactor operated under atmospheric pressure has been studied for nitrogen oxides synthesis. In this work, the electrical and process parameters of the gliding arc reactor, such as frequency, pulse width, amplitude and feed ratio were investigated respectively. The experiments were performed at 1 L/min in a gliding arc discharge regime. The highest concentration of NO_x was found to be ~1 % at energy consumption of 10 kWh/kg of NO_x. Increase in frequency, pulse width and amplitude resulted in an increased specific energy input and NO_x concentration. The feed ratio (N₂/O₂) affected the amount of NO and NO₂ produced, which gives possibility to independently obtain the desired ratio of NO/NO₂ by tuning the electrical and process parameters.     

Plasma-Assisted Synthesis of TiO2 Nanorods by Gliding Arc Discharge Processing at Atmospheric Pressure for Photocatalytic Applications

The present study explores a new method of synthesis of TiO₂ nano-particles in an aqueous medium from TiCl₃ precursor by non-thermal plasma in humid air as feeding gas obtained at atmospheric pressure. The precursor solution, TiCl₃ is oxidized by strongly reactive species generated by gliding arc plasma (HO^· = 2.85 V/SHE) to produce titanium oxide powders. The synthesized powder was characterised by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, FTIR spectroscopy, nitrogen physisorption, and UV–Vis spectroscopy. The results obtained showed that the material consists of rod-shaped nanoparticles of rutile and anatase phases. The presence of TiO₂ phases was confirmed by FTIR spectrum and textural analyses showed that the material is mesoporous with specific surface area of 158 m² g^?1. UV–Visible spectrum of the plasma-synthesized TiO₂ sample showed that it absorbs in the UV–A region leading to effective use as a photocatalyst under visible light.     

Experimental Observations of Constricted and Diffuse Anode Attachment in a Magnetically Rotating Arc at Atmospheric Pressure

Plasma Chemistry and Plasma Processing - At atmospheric pressure, the anode attachment can appear in two different modes: constricted and diffuse. In this paper, a magnetically rotating arc plasma...     

An Interfacial Solar Heating Assisted Liquid Sorbent Atmospheric Water Generator

Harvesting water from air is a promising strategy for fresh‐water production, and it is particularly desirable for areas that lack direct access to clean water. While high‐concentration liquid sorbent is well‐known for high sorption, it has not been widely used for atmospheric water collection, being primarily limited by the difficulty in desorption. Interfacial solar heating based on a salt‐resistant GO‐based aerogel is now shown to enable a high‐concentration liquid sorbent (CaCl₂ 50 wt % solution) based atmospheric water generator. Fresh water (2.89 kg m^?2 day^?1) can be produced at about 70 % relative humidity, with only solar energy input and energy efficiency of desorption as high as 66.9 %. This low‐cost and effective approach provides an attractive pathway to extract water from air, to relieve the thirst of arid, land‐locked, and other areas where fresh water is scarce.     

An Experimental Investigation of Cathode Spot Motion in a Magnetically Rotating Arc Plasma Generator at Atmospheric Pressure

Plasma Chemistry and Plasma Processing - Cathode spots present complex forms in magnetically rotating arc plasma generators due to the coupling effect of the plasma flow and electromagnetic fields....     

Kinetic Modeling of Plasma Methane Conversion Using Gliding Arc

Plasma methane (CH4) conversion in gliding arc discharge was examined. The result data of experiments regarding the performance of gliding arc discharge were presented in this paper. A simulation which is consisted some chemical kinetic mechanisms has been provided to analyze and describe the plasma process. The effect of total gas flow rate and input frequency refers to power consumption have been studied to evaluate the performance of gliding arc plasma system and the reaction mechanism of decomposition.Experiment results indicated that the maximum conversion of CH4 reached 50% at the total gas flow rate of 1 L/min. The plasma reaction was occurred at the atmospheric pressure and the main products were C (solid), hydrogen, and acetylene (C2H2). The plasma reaction of methane conversion was exothermic reaction which increased the product stream temperature around 30～50℃.     

Effects of Oxygen and Water Vapor on Volatile Organic Compounds Decomposition Using Gliding Arc Gas Discharge

The combined effects of oxygen and water vapor on three typical volatile organic compounds, i.e. tetrachloromethane, n-butane and toluene, decomposition efficiency under gliding arc gas discharge conditions are studied. The electron density and the density of the reactive radicals such as O and OH are modified by addition of oxygen and water vapor. Consequently, the decomposition process can be enhanced or suppressed, depending on the involved chemical structures and reaction channels. The addition of oxygen and water vapor suppresses the tetrachloromethane decomposition which indicates that this process is mainly controlled by the electron dissociation reactions. By contrast, the n-butane and toluene decompositions are enhanced, which shows that they can be mainly ascribed to the radical induced reactions. Especially, in a moist atmosphere the OH radicals are supposed to play the most important role in the n-butane decomposition process.     

The Effects of Gas Composition on Active Species and Byproducts Formation in Gas–Water Gliding Arc Discharge

The effects of gas composition on hybrid gas–water gliding arc discharge plasma reactor have been studied. The voltage cycles are characterized by a moderate increase in the tension which is represented by a peak followed by an abrupt decrease and a current peak in the half period (10 ms). Emission spectrum measurements revealed that ^•OH hydroxyl radicals are present in the discharge with feeding any gas. The H₂O₂ concentrations reach 38.0, 15.0, 10.0, and 8.0 mg/l after 25 min plasma treatment with oxygen, argon, air, and nitrogen, respectively. O₃ was produced when oxygen and air are used, but not when nitrogen and argon. The O₃ concentration reached the highest value 1.0 mg/l after 25 min plasma treatment with oxygen feeding gas, but gradually decreased to 0.2 mg/l after that. With feeding nitrogenous gas, NO₂ ⁻ and NO₃ ⁻ byproducts were formed by the plasma chemical process.     

Electric Field‐Assisted Photochemical Water Splitting Should Operate with 287 nm Light

The major photoreaction of water is the homolytic splitting of one O–H bond starting from the 1¹B₁ excited state (λ_max = 167 nm). This reaction produces H? and ?OH radicals. The combination of two H? atoms leads to the potential energy carrier dihydrogen. However, the energy required to obtain the photoreactive 1¹B₁ electronic state is about 7.4 eV, which cannot be effectively provided by solar radiation. The sun light spectrum on earth comprises the visible and ultraviolet region, but shows vanishing intensity near 7 eV (177.1 nm). This work provides theoretical evidence that the photoreactive 1¹B₁ state of water can be shifted into the ultraviolet (UV‐B) light region (≈287 nm) by including explicitly an electric field in the calculations of the water absorption spectrum. To accomplish such bathochromic shift, a large field strength of 3.08 VÅ^?1 is required. The field‐dependent excitation energies were calculated by applying the symmetry‐adapted cluster configuration interaction (SAC‐CI) procedure. Based on this theoretical analysis, we propose that photochemical water splitting can be accomplished by means of 287 nm light provided the water molecule is favorably oriented by an external electric field and is subsequently activated by a reversal of the field orientation.     

Nitrogen Fixation as NOx Enabled by a Three-Level Coupled Rotating Electrodes Air Plasma at Atmospheric Pressure

In this paper, a three-level coupled rotating electrodes air plasma at atmospheric pressure is developed for evaluation of nitrogen fixation. Factors influencing the NO_x production rate and energy cost, including airflow rate, the input H₂O concentration, blade numbers at each rotating electrode and rotating speed, are examined. Air flow rates prove to have no effect on the rotational temperature of N₂ 337.1 nm and the emission intensities of N₂⁺ and N₂, but specific energy input (SEI) and species’ residence time can be shorter with higher air flow rates, resulting in lower NO_x concentration and energy cost. The addition of H₂O also has a positive effect on both NO_x concentration and energy cost. Optical emission spectrum (OES) shows that air?+?H₂O plasma has stronger 336 nm (NH) and 309 nm (OH) emission lines than air plasma, suggests NH and OH are the key species in NO_x enhancement. The most energy efficient conditions are found at airflow rate of 15 l min^?1, 12% H₂O concentration, with 4 blades on each rotating speed. Under these conditions, the lowest energy cost is observed to be 165 GJ/tN.

     

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.     

Fixation of Atmospheric Nitrogen: Synthesis of Heterocycles with Atmospheric Nitrogen as the Nitrogen Source

Dry air is the source of molecular nitrogen for reactions with TiL₄, Li, and TMSCl (L = Cl, OiPr; TMS = trimethylsilyl). The nitrogen–titanium complexes thus prepared can be used to synthesize indoles, pyrroles, and lactams from carbonyl compounds. Applying this method to 1 provides access to 2 , the key compound in the synthesis of (±)-lycopodine.     

Degradation of PCDD/Fs in Fly Ash by Vortex-shaped Gliding Arc Plasma

PCDD/Fs in fly ash from municipal solid waste incinerators (MSWIs) can be decomposed in non-thermal plasma, more in particular in a vortex-shaped gliding arc. Typical operating conditions are 10 kV voltage, 40 kΩB external current-limited resistor, 11 L/min tangential gas and 2 L/min axial carrier gas flow rates. Degradation efficiencies of PCDD/Fs are respectively 54.9, 61.7 and 66.8 % on mass basis and 60.7, 73.3 and 70.1 % on toxicity basis under N₂, air and O₂ condition. After treatment the morphology of fly ash has changed: needle-shaped crystals increasing, pores and fragments appearing and high-temperature melting showing which is leaded by direct contact with high-temperature core of arc. The results are explained tentatively by the creation of reactive intermediates leading to dechlorination and oxidation of PCDD/Fs and finally producing end-products such as CO₂, CO, HCl and CH₄.     

Scaling Up of Non-Thermal Gliding Arc Plasma Systems for Industrial Applications

Plasma Chemistry and Plasma Processing - Scaling up of transitional “warm” plasmas to industrial level gives possibility to develop plasma systems that combine advantages of thermal and...     

Degradation of Phenol in Aqueous Solutions by Gas–Liquid Gliding Arc Discharges

The efficiency of a gliding arc reactor designed with the aim to degrade aqueous phenol solutions is studied as a function of supply voltage, electrode gap distance, and gas–liquid flow properties. This efficiency, which steeply increases when increasing the supply voltage, can reach 96% when the minimum electrode distance is fixed at 3 mm. Experiments show that phenol degradation efficiency also depends on solution pH, Fe²⁺ addition, gas nature and gas flow rate. Furthermore, degradation pathways of phenol in aqueous solutions are proposed.     

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.     

Gliding Arc Plasma Synthesis of Crystalline TiO2 Nanopowders with High Photocatalytic Activity

A warm plasma generated by gliding arc discharge, combining the advantages of both thermal and cold plasmas, is explored to synthesize TiO₂ nanopowders for the first time. Air is used as the discharge gas and titanium tetraisopropoxide aerosol is carried by N₂ into the plasma. X-ray diffraction and X-ray photoelectron spectroscopy characterizations confirm that the as-synthesized nanopowders are fully crystalline TiO₂. The weight fraction of anatase (f _A) is higher than that of rutile and increases from 68.8 to 96.8 % by increasing specific energy input (SEI) from 46 to 76 kJ/mol. The effect of SEI on specific surface area (S _BET) and BET-equivalent diameter (d _BET) of the nanopowders is investigated. The typically spheric morphology of the particles is observed by transmission electron microscopy (TEM) and the most probable d _TEM approaches the d _BET. All the as-synthesized nanopowders show a high photocatalytic activity comparable to that of Degussa P25.