Investigation of operating parameters on CO2 splitting by dielectric barrier discharge plasma

Experiments of CO2 splitting by dielectric barrier discharge (DBD) plasma were carried out,and the influence of CO2 flow rate,plasma power,discharge voltage,discharge frequency on CO2 conversion and process energy efficiency were investigated.It was shown that the absolute quantity of CO2 decomposed was only proportional to the amount of conductive electrons across the discharge gap,and the electron amount was proportional to the discharge power;the energy efficiency of CO2 conversion was almost a constant at a lower level,which was limited by CO2 inherent discharge character that determined a constant gap electric field strength.This was the main reason why CO2 conversion rate decreased as the CO2 flow rate increase and process energy efficiency was decreased a little as applied frequency increased.Therefore,one can improve the CO2 conversion by less feed flow rate or larger discharge power in DBD plasma,but the energy efficiency is difficult to improve.     

Strengthening decomposition of oxytetracycline in DBD plasma coupling with Fe-Mn oxide-loaded granular activated carbon

A catalytic approach using a synthesized iron and manganese oxide-supported granular activated carbon (Fe-Mn GAC) under a dielectric barrier discharge (DBD) plasma was investigated to enhance the degradation of oxytetracycline (OTC) in water. The prepared Fe-Mn GAC was characterized by x-ray diffraction and scanning electron microscopy, and the results showed that the bimetallic oxides had been successfully spread on the GAC surface. The experimental results showed that the DBD + Fe-Mn GAC exhibited better OTC removal efficiency than the sole DBD and DBD + virgin GAC systems. Increasing the fabricated catalyst and discharge voltage was favorable to the antibiotic elimination and energy yield in the hybrid process. The coupling process could be elucidated by the ozone decomposition after Fe-Mn GAC addition, and highly hydroxyl and superoxide radicals both play significant roles in the decontamination. The main intermediate products were identified by HPLC-MS to study the mechanism in the collaborative system.     

Decomposition of a gas mixture of four n-alkanes using a DBD reactor

This study investigates the decomposition of a gas mixture of four n-alkanes (n-heptane, n-octane, n-nonane, and n-decane) using a dielectric barrier discharge reactor. We show that the conversion of n-alkanes increased from 7.2% (C₇H₁₆), 9.7% (C₈H₁₈), 8.4% (C₉H₂₀), and 10.5% (C₁₀H₂₂) to 23.8% (C₇H₁₆), 25.0% (C₈H₁₈), 27.9% (C₉H₂₀), and 32.1% (C₁₀H₂₂) when the energy density increased from 84 J l⁻¹ to 324 J l⁻¹. The conversion of n-alkanes when using the gas mixture is close to that found when using a single n-alkane. The influences of reaction temperature and O₂ concentration are also investigated, and the activation energies for the decomposition of each alkane are given.     

High concentration xylene decomposition and diagnostic analysis by non-thermal plasma in a DBD reactor

Dielectric barrier discharge (DBD) is utilized to decompose xylene vapor in mobile gas under normal atmospheric pressure.The plasma is generated by an AC power source with a frequency of 6 kHz.In the experiment,the discharge power on the DBD reactor was calculated by a Lissajous figure,and the specific input energy (SIE) of different discharge voltage or residence time was obtained.The concentrations of xylene,carbon monoxide and carbon dioxide in the gas were analyzed by gas chromatography.The spectra of DBD were diagnosed using a spectrometer.We calculated the conversion rate (CR),mineralization rate (MR) and carbon dioxide selectivity.The relationship between these quantities and the SIE was analyzed.The experimental results show that high concentration xylene can be decomposed mostly by DBD plasma.The CR can reach as high as 90％ with the main product of carbon dioxide.     

Application of DBD and DBCD in SO2 Removal

The dielectric barrier corona discharge(DBCD) in a wire-cylinder configuration and the dielectric barrier discharge(DBD) in a coaxial cylinder configuration are studied. The discharge current in DBD has a higher pulse amplitude than in DBCD. The dissipated power and the gas-gap voltage are calculated by analyzing the measured Lissajous figure. With the increasing applied voltage, the energy utilization factor for SO2 removal increases in DBCD but decreases in DBD because of the difference in their electric field distribution. Experiments of SO2 removal show that in the absence of NH3 the energy utilization factor can reach 31 g/kWh in DBCD and 39 g/kWh in DBD.     

Atmospheric-Pressure DBD Cold Plasma for Preparation of High Active Au/P25 Catalysts for Low-Temperature CO Oxidation

Cold plasma generated by dielectric barrier discharge (DBD) at atmospheric pressure was adopted for preparation of commercial TiO2 Degussa P25 supported Au catalysts (Au/P25-P) with the assistance of the deposition-precipitation procedure.The influences of the plasma reduction time and calcination on the performance of the Au/P25-P catalysts were investigated.CO oxidation was performed to investigate the catalytic activity of thc Au/P25 catalysts.The results show that DBD cold plasma for the fabrication of Au/P25-P catalysts is a fast process,and Au/P25-P (4 min) exhibited the highest CO oxidation activity due to the complete reduction of Au compounds and less consumption of oxygen vacancies.In order to form more oxygen vacancies active species,Au/P25-P was calcined to obtain Au/P25-PC catalysts.Interestingly,Au/P25-PC exhibited the highest activity for CO oxidation among the Au/P25 samples.The results of transmission electron microscopy (TEM) indicated that the smaller size and high distribution of Au nanoparticles are the mean reasons for a high performance of Au/P25-PC.Atmospheric-pressure DBD cold plasma was proved to be of great efficiency in preparing high performance supported Au catalysts.     

Effects of O2 addition on the plasma uniformity and reactivity of Ar DBD excited by ns pulsed and AC power supplies

Dielectric barrier discharges (DBDs) have been widely used in ozone synthesis, materials surface treatment, and plasma medicine for their advantages of uniform discharge and high plasma-chemical reactivity. To improve the reactivity of DBDs, in this work, the O₂ is added into Ar nanosecond (ns) pulsed and AC DBDs. The uniformity and discharge characteristics of Ar ns pulsed and AC DBDs with different O₂ contents are investigated with optical and electrical diagnosis methods. The DBD uniformity is quantitatively analyzed by gray value standard deviation method. The electrical parameters are extracted from voltage and current waveforms separation to characterize the discharge processes and calculate electron density n_e. The optical emission spectroscopy is measured to show the plasma reactivity and calculate the trend of electron temperature T_e with the ratio of two emission lines. It is found that the ns pulsed DBD has a much better uniformity than AC DBD for the fast rising and falling time. With the addition of O₂, the uniformity of ns pulsed DBD gets worse for the space electric field distortion by O₂⁻, which promotes the filamentary formation. While, in AC DBD, the added O₂ can reduce the intensity of filaments, which enhances the discharge uniformity. The ns pulsed DBD has a much higher instantaneous power and energy efficiency than AC DBD. The ratio of Ar emission intensities indicates that the T_e drops quickly with the addition of O₂ both ns pulsed and AC DBDs and the ns pulsed DBD has an obvious higher T_e and n_e than AC DBD. The results are helpful for the realization of the reactive and uniform low temperature plasma sources.     

Enhanced removal of ultrafine particles from kerosene combustion using a dielectric barrier discharge reactor packed with porous alumina balls

Ultrafine particles(UFPs) are harmful to human beings, and their effective removal from the environment is an urgent necessity. In this study, a dielectric barrier discharge(DBD) reactor packed with porous alumina(PA) balls driven by a pulse power supply was developed to remove the UFPs(ranging from 20 to 100 nm) from the exhaust gases of kerosene combustion. Five types of DBD reactors were established to evaluate the effect of plasma catalysis on the removal efficiency of UFPs. The influences of gas flow rate, peak voltage and pulse frequency of different reactors on UFPs removal were investigated. It was found that a high total UFP removal of91.4% can be achieved in the DBD reactor entirely packed with PA balls. The results can be attributed to the enhanced charge effect of the UFPs with PA balls in the discharge space. The UFP removals by diffusion deposition and electrostatic attraction were further calculated,indicating that particle charging is vital to achieve high removal efficiency for UFPs.     

Influence of electrical parameters on H2O2 generation in DBD non-thermal reactor with water mist

A dielectric barrier discharge (DBD) reactor is introduced to generate H2O2 by non-thermal plasma with a mixture of oxygen and water mist produced by an ultrasonic atomizer.The results of our experiment show that the energy yield and concentration of the generated H2O2 in the pulsed discharge are much higher than that in AC discharge,due to its high energy efficiency and low heating effect.Micron-sized liquid droplets produced by an ultrasonic atomizer in water mist have large specific surface area,which greatly reduces mass transfer resistance between hydroxyl radicals and water liquids,leading to higher energy yield and H2O2 concentration than in our previous research.The influence of applied voltage,discharge frequency,and environmental temperature on the generated H2O2 is discussed in detail from the viewpoint of the DBD mechanism.The H2O2 concentration of 30 mg 1-1,with the energy yield of 2 g kW-1h 1 is obtained by pulsed discharge in our research.     

Measurement ofHe2* density with an auxiliary measuring electrode in atmospheric pressure plasma jet

In this study, the density of metastable He₂* in an atmospheric-pressure plasma jet operating in helium with 0.001% nitrogen has been measured using an auxiliary measuring electrode technique. In the glow discharge mode, waveforms from two grounding electrodes, including one main discharge electrode and one auxiliary electrode, are captured. The isolated current peak formed by Penning ionization in waveforms from the auxiliary measuring electrode is identified to calculate the density of metastable He₂*. In our discharge environment, the helium metastable densities along the jet axis direction are between 2.26× 10¹³ and 1.74× 10¹³ cm^-3, which is in good agreement with the results measured by other techniques. This measurement technique can be conveniently applied to the diagnosis of metastableHe₂* in an atmospheric-pressure plasma jet array.     

Comparison of Yeast Inactivation Treated in He, Air and N2 DBD Plasma

In this paper, the mechanism of yeast inactivation in low temperature atmospheric pressure helium, nitrogen and air plasmas generated by dielectric barrier discharge is analysed and compared. The results show that all the three gas plasmas have a high germicidal efficiency. The morphology of the yeast is observed by scanning electron microscopy, which reveals that the yeast treated in helium plasma is ruptured completely but there are only some flaws on the cell walls in the nitrogen and air plasma treated samples. Also, the flaws on the cell walls treated by air plasma are more significant than that by nitrogen treatment. Simultaneously, the pH values of the samples after 5 rain nitrogen and air plasma treatment have no remarkable change either, while the sample treated with helium plasma descends below 4.0, which is beyond the optimum one for the yeast＇s living environment. The difference in pH values may be caused by the treatment effect and the degree of the cell＇s rupture when the gas discharge plasma treatment is applied.     

Degradation of tiamulin by a packed bed dielectric barrier plasma combined with TiO2 catalyst

Recently, a plasma catalyst was employed to efficiently degrade antibiotic residues in the environment. In this study, the plasma generated in a packed bed dielectric barrier reactor combined with TiO2 catalyst is used to degrade the antibiotic tiamulin (TIA) loaded on the surface of simulated soil particles. The effects of applied voltage, composition of the working gas, gas flow rate and presence or absence of catalyst on the degradation effect were studied. It was found that plasma and catalyst can produce a synergistic effect under optimal conditions (applied voltage 25 kV, oxygen ratio 1%, gas flow rate 0.6 l min−1, treatment time 5 min). The degradation efficiency of the plasma combined with catalyst can reach 78.6%, which is 18.4% higher than that of plasma without catalyst. When the applied voltage is 30 kV, the gas flow rate is 1 l min−1, the oxygen ratio is 1% and the plasma combined with TiO2 catalyst treats the sample for 5 min the degradation efficiency of TIA reached 97%. It can be concluded that a higher applied voltage and longer processing times not only lead to more degradation but also result in a lower energy efficiency. Decreasing the oxygen ratio and gas flow rate could improve the degradation efficiency. The relative distribution and identity of the major TIA degradation product generated was determined by high-performance liquid chromatography–mass spectrometry analysis. The mechanism of TIA removal by plasma and TiO2 catalyst was analyzed, and the possible degradation path is discussed.     

1,2,4-trichlorobenzene decomposition using non-thermal plasma technology

Non-thermal plasma(NTP)is regarded as a potential application for environmental pollution control due to its ability to remove pollutants.As a major precursor of dioxins,the influence of the parameters of 1,2,4-trichlorobenzene(TCB)decomposition using NTP technology was investigated through a series of experiments,including voltage,frequency,water content,initial concentration,flow rate,and oxygen content.The experimental results show that the energy injected into the NTP system has a positive correlation to voltage and frequency.Oxygen has the greatest influence on TCB decomposition.The optimal reaction condition was at 15 kV,1000 Hz,an initial concentration of 20 mg m^?3,a flow rate of 2 l min^?1,H2O at 4%,and O2 at 0%.Under this condition,the TCB removal efficiency could reach 92%.According to the generated product backstepping,the hydroxyl radical(·OH)plays an important role in TCB decomposition due to its strong oxidation,which participates in the dechlorination and oxidation reactions as free radicals,and the possible decomposition pathway of TCB by NTP is inferred from the identified byproducts.It is of great significance to investigate the influence of the parameters of TCB decomposition using NTP technology in order to provide references for industrial application.     

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.     

Advanced oxidation technology for H2S odor gas using non-thermal plasma

Non-thermal plasma technology is a new type of odor treatment processing. We deal with H2S from waste gas emission using non-thermal plasma generated by dielectric barrier discharge. On the basis of two criteria, removal efficiency and absolute removal amount, we deeply investigate the changes in electrical parameters and process parameters, and the reaction process of the influence of ozone on H2S gas removal. The experimental results show that H2S removal efficiency is proportional to the voltage, frequency, power, residence time and energy efficiency,while it is inversely proportional to the initial concentration of H2S gas, and ozone concentration. This study lays the foundations of non-thermal plasma technology for further commercial application.     

Recent Development of CO_2 Reforming of CH_4 by “Arc” Plasma

This paper presents a brief overview of CO_2 reforming of CH_4(CRM) by various forms of "arc" plasma, which is more suitable to CRM, and the energy efficiency is used to evaluate different plasma processes specifically. According to the reported results, the arc thermal plasma with binode exhibited better performance. Moreover, the plasma CRM process was compared with the reported plasma steam reforming of CH_4(SRM) process, and the results showed that the former process has advantages on energy efficiency and CH_4 consumption. Additionally,it is believed that the plasma CRM process would be competitive with the conventional SRM process in both energy efficiency and CO_2 emission once the heat management is emphasized and the renewable power is used. Finally, a concept of plasma reactor for industrial application is proposed.     

Investigation on the Dielectric Properties of CO2 and CO2-Based Gases Based on the Boltzmann Equation Analysis

In this paper,the dielectric properties of CO_2,CO_2/air,CO_2/O2,CO_2/N_2,CO_2/CF_4,CO_2/CH_4,CO_2/He,CO_2/H_2,CO_2/NH_3 and CO_2/CO were investigated based on the Boltzmann equation analysis,in which the reduced critical electric field strength(E/N)crof the gases was derived from the calculated electron energy distribution function(EEDF) by solving the Boltzmann transport equation.In this work,it should be noted that the fundamental data were carefully selected by the published experimental results and calculations to ensure the validity of the calculation.The results indicate that if He,H_2,N_2 and CH_4,in which there are high ionization coefficients or a lack of attachment reactions,are added into CO_2,the dielectric properties will decrease.On the other hand,air,O2,NH_3 and CF_4(ranked in terms of(E/N)_(cr) value in increasing order) have the potential to improve the dielectric property of CO_2 at room temperature.     

Plasma-catalytic degradation of tetracycline hydrochloride over Mn/γ-Al2O3 catalysts in a dielectric barrier discharge reactor

A coaxial dielectric barrier discharge (DBD) reactor was used for plasma-catalytic degradation of tetracycline hydrochloride over a series ofMn/γ-Al₂O₃ catalysts prepared by the incipient wetness impregnation method. The combination of plasma and theMn/γ-Al₂O₃ catalysts significantly enhanced the degradation efficiency of tetracycline hydrochloride compared to the plasma process alone, with the 10%Mn/γ-Al₂O₃ catalyst exhibiting the best tetracycline hydrochloride degradation efficiency. A maximum degradation efficiency of 99.3% can be achieved after 5 min oxidation and a discharge power of 1.3 W, with only 69.7% by a single plasma process. The highest energy yield of the plasma-catalytic process is 91.7 gkWh⁻¹. Probable reaction mechanisms of the plasma-catalytic removal of tetracycline hydrochloride were also proposed.