Effect Of Discharge Power Research Articles

Experimental analysis of gas- and particle-phase organic byproducts formed by plasma-induced toluene destruction processes

• Organic byproducts were evaluated by NTP degradation of toluene at ambient temperature and atmospheric pressure. • PTR-TOFMS measurement showed that toluene degradation resulted in dozens of organic by-products. • Size distribution and number concentration of particles formed during toluene degradation were measured by SMPS. • NTP-induced polymerization and oxidation contribute to particle formation with diameters in the range of 10 and 100 nm. Non-thermal plasma (NTP) technology has great potential to treat volatile organic compounds (VOCs) at low concentrations and large volumes. In this work, toluene, one of the most stable VOCs, was employed as a model pollutant to study its degradation by double dielectric barrier discharge (DDBD) at ambient temperature and atmospheric pressure. The performance of the DDBD reactor was evaluated in terms of discharge power, removal efficiency, CO x selectivity, and byproduct formation. Online and continuous measurements by PTR-TOFMS showed that toluene degradation resulted in the formation of 12 major volatile organic byproducts as well as 7 minor ones with concentrations ranging from ppbv to ppmv. Moreover, the particle size distribution and number concentration of particles formed during toluene degradation were measured using a scanning mobility particle sizer, and the effects of discharge power, initial toluene concentration, gas flow rate and O 2 content on particle formation were systematically investigated. The results show that both NTP-induced polymerization and oxidation contribute to aerosol formation, and the total concentration of organic byproducts in the aerosol phase is about 10 7 cm −3 with diameters in the range of 10 and 100 nm. This pioneered investigation on gas- and particle-phase organic byproducts from toluene degradation by NTP would deepen the understanding of plasma degradation of VOCs and accelerate the practical application of NTP for VOCs treatment.

A novel process of cyclic adsorption and plasma-desorption for ppm-level CO removal from H2-rich stream

A cyclic adsorption and plasma-desorption (CAPD) process is applied to remove ppm-level carbon monoxide (CO) from the H2-rich stream for the first time. In the CAPD process, CO is first selectively adsorbed on CuCl/γ-Al2O3 till adsorption saturation; Then, the adsorbed CO is in-situ desorbed by plasma generated in dielectric barrier discharge (DBD) and the adsorbent is regenerated simultaneously. The effects of discharge power (Pdis) and flow rate of discharge gas (FD) on performances of plasma-desorption are investigated. The time to reach desorption of 50% (t50) and 90% (t90) significantly decreases with Pdis but is weakly correlated to the FD. At the investigated conditions, t50 and t90 are lower than 2.6 min and 4.5 min, respectively, which indicates that plasma-desorption features high desorption rate. In addition, desorption efficiency of plasma-desorption is higher than 98%. Moreover, CAPD process stability is preliminarily confirmed by six consecutive adsorption-desorption cycles.

Development of a microkinetic model for non-oxidative coupling of methane over a Cu catalyst in a non-thermal plasma reactor

A surface microkinetic plasma model for non-oxidative coupling of methane into H2 and higher hydrocarbons was developed over a Cu catalytic film. Twenty key plasma species including electron, ions, radicals, and neutrals were considered in respective chemical reactions leading to the formation of C2 hydrocarbons onto the catalyst surface. The kinetic model was coupled with a global plasma model to describe the performance of a non-thermal plasma reactor. In the reactor model, the reactant gas flows between the two coaxial cylindrical metal electrodes with a length of 50 mm and a diameter of 2 mm (inner) and 6 mm (outer electrode) coated with a Cu film. The effect of discharge power, initial CH4 concentration, and inlet flow rate on methane conversion was investigated. The surface model shows that the CH4 conversion of 47% is obtained at a discharge power of 70 W with a selectivity of C2H2 (49%). Increase in power increased the conversion of methane while increase in pressure and/or inlet gas flow rate decreased it. Also, the results of the plasma-catalyst model were compared with those of plasma alone (without catalyst). It showed that presence of the catalyst inside the plasma increases the selectivity and yield of acetylene, while it deceases the selectivity and yield of hydrogen. Also, the density of radical CH3 in the plasma phase increased in the presence of catalyst, while CH2 and CH densities decreased with that.

Soot Oxidation over γ-Al2O3-Supported Manganese-Based Binary Catalyst in a Dielectric Barrier Discharge Reactor

In this work, soot oxidation was conducted over a series of Mn-X/γ-Al2O3 (M = Ce, Co and Cu) binary catalysts in a dielectric barrier discharge reactor. The soot conversion in the plasma–catalytic system was in the order of Mn/γ-Al2O3 (57.7%) > Mn-Co/γ-Al2O3 (53.9%) > Mn-Ce/γ-Al2O3 (51.6%) > Mn-Cu/γ-Al2O3 (47.7%) during the 30 min soot oxidation process at 14 W and 150 °C. Meanwhile, the doping of Ce, Co and Cu slightly improved the CO2 selectivity of the process by 4.7% to 10.3% compared to soot oxidation over Mn/γ-Al2O3.It is worth to note that the order of CO2 selectivity was in the opposite order with soot oxidation rate. The effects of discharge power, oxygen content in the carrier gas and reaction temperature on plasma–catalytic soot oxidation was systematically analyzed. The catalyst characterizations, including N2 adsorption–desorption, X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction by H2 and temperature-programmed desorption of O2, were conducted to illustrate the reaction mechanisms of plasma–catalytic soot oxidation and reaction pathways.

Soot Oxidation in a Plasma-Catalytic Reactor: A Case Study of Zeolite-Supported Vanadium Catalysts

The plasma-catalytic oxidation of soot was studied over zeolite-supported vanadium catalysts, while four types of zeolites (MCM-41, mordenite, USY and 5A) were used as catalyst supports. The soot oxidation rate followed the order of V/MCM-41 > V/mordenite > V/USY > V/5A, while 100% soot oxidation was achieved at 54th min of reaction over V/MCM-41 and V/mordenite. The CO2 selectivity of the process follows the opposite order of oxidation rate over the V/M catalyst. A wide range of catalyst characterizations including N2 adsorption–desorption, XRD, XPS, H2-TPR and O2-TPD were performed to obtain insights regarding the reaction mechanisms of soot oxidation in plasma-catalytic systems. The redox properties were recognized to be crucial for the soot oxidation process. The effects of discharge power, gas flow rate and reaction temperature on soot oxidation were also investigated. The results showed that higher discharge power, higher gas flow rate and lower reaction temperature were beneficial for soot oxidation rate. However, these factors would impose a negative effect on CO2 selectivity. The proposed “plasma-catalysis” method possessed the unique advantages of quick response, mild operation conditions and system compactness. The method could be potentially applied for the regeneration of diesel particulate filters (DPF) at low temperatures and contribute to the the emission control of diesel engines.

Effect of Discharge Power in a Plasma during Reactive-Ion Etching of Massive Substrates on the Matching of the Lower Electrode with a High-Frequency Bias Generator

Effect of Discharge Power in a Plasma during Reactive-Ion Etching of Massive Substrates on the Matching of the Lower Electrode with a High-Frequency Bias Generator

Enhanced hydrogen production using a tandem biomass pyrolysis and plasma reforming process

Converting biomass into energy and fuels is considered a promising strategy for replacing the exhaustible fossil fuels. In this study, we report on a tandem process that combines cellulose pyrolysis and plasma-assisted reforming for H2 production. The hybrid pyrolysis/plasma reforming process was carried out in a two-stage reaction system incorporating a coaxial dielectric barrier discharge (DBD) plasma reactor. The effects of discharge power, steam, reforming temperature, and catalyst on the reaction performance were investigated. The results show that low temperatures are preferred in the non-catalytic plasma reforming process, whereas high temperatures are desired to achieve a high H2 yield and a high H2 selectivity in the plasma-catalytic reforming system. The synergistic effect of plasma catalysis was dominant in the plasma-catalytic reforming process at 250 °C. In contrast, the catalyst, rather than the plasma, played a dominant role in the plasma-catalytic reforming at higher temperatures (550 °C). Using Ni-Co/Al2O3 at a reforming temperature of 550 °C, a high H2 yield of 26.6 mmol/g was attainted, which was more than 8 times and about 100% greater than that obtained using plasma alone and catalyst alone, respectively. This work highlights the potential of non-thermal plasmas in low-temperature biomass conversion.

Spectroscopic characterization of soil dissolved organic matter during dielectric barrier discharge (DBD) plasma treatment: Effects of discharge power, atmosphere and soil moisture content

Non-thermal plasma (NTP) technology is an emerging advanced oxidation process, which has shown excellent performances in soil organic pollution remediation. Dissolved organic matter (DOM) is one of the most important components in soil, however, investigations on the structural and compositional changes of DOM during NTP process are lacking. Therefore, in the present study, we systematically investigated the soil DOM changes under different discharge voltages, atmospheres or soils with different moisture contents. The results indicated that after NTP treatment, substantial soil organic matters were released and dissolved in water. For instance, the DOC value of DOM increased dramatically from 21.1 to 197.3 mg L−1 after being discharged for 120 min under the discharge voltage of 80 V. The UV–Vis characterization results indicated the significant increase of hydrophilicity, and decreases of aromaticity and molecular weight for soil DOM during the initial discharge period. However, long time discharge resulted in slight recovery of aromaticity and hydrophobicity, possibly due to the dehydration and re-condensation of small molecules. EEM-FRI results indicated that the total fluorescence intensity of DOM decreased obviously, indicating the destruction of fluorescent dissolved organic matter (FDOM). While the proportions of humic-like and microbial byproduct-like substances increased, indicating that those substances were more recalcitrant under NTP treatment compared with fulvic acid-like and aromatic protein-like substances. Four fluorescence components were identified by PARAFAC, and microbial and terrestrial humic-like substances were more difficult to degrade compared to other humic-like substances and fulvic acid-like substances. Additionally, discharge voltage and atmosphere had great influences on DOM changes, while the impact of soil moisture content was not significant. Overall, this study provided insights into the DOM changes during NTP process, which is valuable for more comprehensive evaluation of the NTP technique application in practical soil remediation.

Real‐time measurement of axial temperature in a coaxial dielectric barrier discharge reactor and synergistic effect evaluation for in‐plasma catalytic CO2 reduction

AbstractDue to serious difficulty in the measurement of catalyst‐bed temperature (Tb) for in‐plasma catalysis (IPC), the evaluation of the IPC synergistic effect is still disputed. Herein, we reported a real‐time measurement of axial temperature (Tax), which is much closer to Tb than wall temperature (Tw), using a thermocouple in a catalyst‐packed coaxial dielectric barrier discharge reactor for the first time. In plasma catalytic CO2 reduction, the effects of discharge power and flow rate on Tax, Tw, and CO2 conversion were examined. On the basis of Tax, compared with the thermal catalytic case, the plasma catalytic case only shows a weak synergistic effect. It was confirmed that the synergistic effect is overestimated if based on Tw (except for the heat‐insulated or quasi‐adiabatic reactors).

Plasma-Catalytic Hydrolysis of Urea for Ammonia Production: Optimization and Kinetic Study

ZrO2 was combined with dielectric barrier discharge plasma for hydrolysis of urea under ambient conditions. Effects of discharge power, O2 presence in carrier gas, repeated use of ZrO2 on hydrolysi...

Decomposition of Tars on a Nickel Honeycomb Catalyst

Biomass can be considered a renewable energy source. It undergoes a gasification process to obtain gaseous fuel, which converts it into combustible gaseous products such as hydrogen, carbon monoxide, and methane. The process also generates undesirable tars that can condense in gas lines and cause corrosion, and after processing, can be an additional source of combustible gases. This study focused on the processing of tar substances with toluene as a model substance. The effect of discharge power and carrier gas composition on toluene conversion was tested. The process was conducted in a plasma-catalytic system with a new Ni3Al system in the form of a honeycomb. The toluene conversion reached 90%, and small amounts of ethane, ethylene, acetylene, benzene, and C3 and C4 hydrocarbons were detected in the post-reaction mixture. Changes in the surface composition of the Ni3Al catalyst were observed throughout the experiments. These changes did not affect the toluene conversion.

Degradation of aqueous methylparaben by non-thermal plasma combined with ZnFe2O4-rGO nanocomposites: Performance, multi-catalytic mechanism, influencing factors and degradation pathways

Non-thermal plasma (NTP) combined with zinc ferrite-reduced graphene oxide (ZnFe2O4-rGO) nanocomposites were used for the degradation of aqueous methylparaben (MeP). ZnFe2O4-rGO nanocomposites were prepared using the hydrothermal method, with the structure and photoelectric properties of nanocomposites then characterized. The effects of discharge power, initial MeP concentration, initial pH, and air flow rate on MeP degradation efficiency were investigated, and the multi-catalytic mechanism and MeP degradation pathways were established. Results showed that ZnFe2O4-rGO nanocomposites with a 10%:90% mass ratio of GO:ZnFe2O4 had an optimal catalytic effect. The MeP degradation efficiency of NTP combined with ZnFe2O4-rGO (10 wt%), was approximately 25% higher than that of NTP alone. Conditions favorable for MeP degradation included higher discharge power, lower MeP concentration, neutral pH value, and higher air flow rate. The degradation of MeP by NTP combined with ZnFe2O4-rGO nanocomposites followed pseudo-first-order kinetics. O2•-, •OH, H2O2, and O3 were found to play important roles in the MeP degradation, as part of the multi-catalytic mechanism of NTP combined with ZnFe2O4-rGO nanocomposites. MeP degradation pathways were proposed based on the degradation intermediates detected by gas chromatography mass spectrometry, including demethylation, hydroxylation, carboxylation, ring-opening, and mineralization reactions. The prepared ZnFe2O4-rGO nanocomposites provide an approach for improved contaminant degradation efficiency, with reduced energy consumption in the NTP process.

Spectroscopic Characterization of Soil Dissolved Organic Matter During Dielectric Barrier Discharge (Dbd) Plasma Treatment: Effects of Discharge Power, Atmosphere and Soil Moisture Content

Spectroscopic Characterization of Soil Dissolved Organic Matter During Dielectric Barrier Discharge (Dbd) Plasma Treatment: Effects of Discharge Power, Atmosphere and Soil Moisture Content

Anchoring of premixed jet flames in vitiated crossflow with pulsed nanosecond spark discharge

This paper deals with the effect of non-equilibrium plasma on the anchoring of a premixed jet flame in hot vitiated crossflow at atmospheric pressure. The turbulent vitiated crossflow was generated by an array of 4×4 premixed turbulent jet flames burning a lean mixture of air and natural gas at an equivalence ratio of 0.7 and a thermal power of 50 kW. The rich jet, with equivalence ratio ϕjet varied between 1 and 3, was injected perpendicularly to the vitiated crossflow in a rectangular duct, with jet-to-crossflow momentum flux ratios J ranging from 1 to 26. A nanosecond repetitively pulsed discharge was initiated in the vicinity of the windward side of the jet root. The effect of discharge power and repetition rate on the lift-off height of the flame is systematically analyzed for different combinations of ϕjet and J. High speed chemiluminescence imaging of the flame and of the discharge shows that the initiation of the discharge on the windward side of the jet enhances the combustion chemistry, reducing the ignition time and the lift-off height of the flame. It is shown that the nanosecond repetitively pulsed discharges are able to maintain a robust anchoring of the flame for a wide range of operating conditions at relatively low electric power cost. Emission spectroscopy and OH-PLIF measurements were carried out to show that the plasma has both thermal and kinetic effects on flame anchoring respectively via intense localized heating of the mixture at temperatures exceeding 3000 K and via an intense production of OH radicals.

CO2 conversion in a coaxial dielectric barrier discharge plasma reactor in the presence of mixed ZrO2-CeO2

Dielectric barrier discharge (DBD) plasma in packed bed reactors are widely used in the environment and energy (such as CO2 conversion). Packing material is a key factor in the reaction of splitting CO2 into CO and O2 by dielectric barrier discharge plasma. To get higher CO2 conversion, grinding balls made of a mixture of ZrO2 and CeO2 in a certain proportion was employed as packing material in this work. The effects of discharge power, feed flow rate, packing length, circulating water temperature and particle size on discharge characteristics and CO2 conversion were investigated to have a better understanding of the performance of the packing material. The reactor discharge behavior was observed by determining the product gas composition and plasma power consumption to determine CO2 conversion and energy efficiency. The packing of the catalyst in the reactor makes the discharge mode from the initial filament discharge to the combination of filament discharge and surface discharge. Compared with oxides composed of a single substance, the two oxides of the composite catalyst can interact, possibly achieving a synergistic effect. Typical results showed that this mixed material had a better property than the reported materials like BaTiO3, Al2O3, ZrO2 and so on which consist of a single substance. The maximum CO2 conversion reached 64.38 % and the maximum energy efficiency reached 8.76 %, which is currently the highest in the known literature. The higher circulating water temperature and larger particle size lead to the decrease of CO2 conversion and energy efficiency. The best performance of the mixture catalyst may be attributed to the oxygen vacancies, which stabilizes the atomic oxygen produced in the reaction and thus facilitates the conversion of CO2.

Decomposition of Toluene in Coupled Plasma-Catalytic System

The study of toluene conversion, in a gas such as the one obtained during the pyrolysis of biomass, was conducted at atmospheric pressure in homogeneous and in coupled plasma-catalytic systems. The effects of discharge power, initial concentration of toluene, and the presence of the bed of NiO/Al2O3 - G-0117 (industrial catalyst for methane water shift) on the conversion of C7H8, the composition of the outlet gas, and its calorific value have been investigated. The gas flow rate was 1000 Nl/h and the initial gas composition was CO (0.13), CO2 (0.12), H2 (0.25), and N2 (0.5). The initial toluene concentration was in the range of 2000–4000 ppm. The obtained results show that the conversion of toluene increases with discharge power and the highest one was obtained in the coupled plasma-catalytic system. It was higher than that in the homogeneous system of gliding discharge plasma. The composition of gas changed within the range of a few percent. In the outlet gas acetylene, ethylene and ethane were observed. Trace amounts of toluene were reduced to benzene and formed C3 and C4 hydrocarbons. In an extended process, the reduction of NiO to metallic nickel, methanation reaction of carbon oxides, and an increase of the conversion of toluene were observed. The conversion of toluene in the extended process was 92%. The catalytic activity of G-0117 in a coupled system increased during the study conducted for about 40 min. The use of G-0117 catalyst led to an increase in the calorific value of the outlet gas. In every examined system, it was above the minimal level demanded by engines and turbines. After the process, carbon deposits were present.

Investigation of toluene removal by DC discharge with MgO/NiO/Ni cathode under different operating parameters

The degradation of toluene by DC discharge has been evaluated in a multi-wire-plate reactor with MgO/NiO/Ni (MNN) cathode and compared with a normal discharge with Ni cathode. The effects of various operating parameters, including the position distribution of wire electrodes, discharge gap, gas flow rate and toluene initial concentration have been systematically investigated. Morphological characterizations demonstrate that in addition to the normal discharge around the wire electrodes, extra discharge also occurs on the MNN cathode surface which is mainly concentrated in the vertical corresponding region of the wire electrodes and diffuses to both sides. The position distribution of two wires influences the total discharge current. It is because that it affects not only the discharge around the wire electrode, but also the discharge on MNN cathode surface. Beside, a wire–wire spacing of 25 mm in discharge reactor with MNN cathode is optimized due to a relative large discharge current. A small discharge gap between wire electrode and cathode contributes to the improvement of toluene degradation and mineralization and it is optimized of 15.3 mm. The effects of discharge power, gas flow rate and toluene initial concentration and the interactions between these parameters on toluene removal performance by discharge with MNN cathode are investigated using Box–Behnken design (BBD). The analysis of variance (ANOVA) is employed to evaluate the significance of the independent variables and their interactions. The results show that the initial concentration plays the most important role in determining the toluene removal efficiency, while discharge power is the most significant factor affecting the energy efficiency in this discharge process.

Degradation of glucocorticoids in water by dielectric barrier discharge and dielectric barrier discharge combined with calcium peroxide: performance comparison and synergistic effects

AbstractBACKGROUNDDegradation of glucocorticoids (GCs), including fluocinolone acetonide (FA), triamcinolone acetonide (TA) and clobetasol propionate (CP), in water by dielectric barrier discharge (DBD) and DBD combined with calcium peroxide treatment (DBD/CaO2) were investigated. Effects of discharge power, pH, plasma‐working gas and CaO2 dosage were examined during DBD and DBD/CaO2 treatments. The synergistic output from the combination of CaO2 with DBD on •OH concentration, pH, conductivity, CaO2 adsorption and the overall influence on GC removal were assessed. Toxicity variations and feasibility to various water matrices by DBD and DBD/CaO2 treatments also were analyzed and compared.RESULTSThe removal efficiencies of FA, TA and CP achieved were 74%, 70% and 75%, respectively, at 36.68 W over 120 min in air with unadjusted pH (energy yield of 7.47 mg kW−1 h−1). Significant synergistic effects were observed in combining CaO2 with DBD with a CaO2‐concentration‐dependent mechanism. The removal efficiency of FA, TA and CP increased by 7%, 32% and 31%, respectively, by DBD/CaO2 in comparison with DBD alone after 60 min treatments at CaO2 dosage of 0.4 g L−1. In addition, DBD/CaO2 treatment was more effective in controlling toxicity and had better efficacy in various water matrices than DBD alone.CONCLUSIONThis study provides a reference point for the application of DBD and DBD/CaO2 treatments to effectively remove GCs from water. © 2019 Society of Chemical Industry

Effect of discharge power and silicon content on optical and mechanical properties of carbon-rich amorphous silicon carbide films obtained by PECVD

We studied optical and mechanical properties of a-SixC1-x:H films prepared by the PECVD technique from the mixture of CH4, SiH4, H2 and Ar. RF discharge power and silane flow rate were chosen as parameters of the film deposition process that allowed to vary film properties. It was shown that variations of silane flow rate (10, 20 sccm) and discharge power in the 100–300 W range allow to obtain films with the following characteristics: optical bandgap 2.5–4.1 eV; refractive index of 1.8–2.1; hardness (H) 8.6–14.8 GPa; Young modulus (E) 64–143 GPa. The film deposition rate varied from 10 to 35 nm/min. By selecting deposition regimes, we deposited films with high ratio between film hardness and Young modulus (H/E = 0.13). The variations of optical and mechanical properties of the films by changing discharge power and silane flow are interpreted within a model accounting film composition and phase-structural transformations. Good combination of optical and mechanical properties of the developed films makes them promising for application as protective, passivation and anti-reflection coatings.

Degradation of glucocorticoids in aqueous solution by dielectric barrier discharge: Kinetics, mechanisms, and degradation pathways

Performance and mechanism of non-thermal plasma (NTP) technology in removing glucocorticoids (GCs) was investigated using a dielectric barrier discharge (DBD) reactor with fluocinolone acetonide (FA), triamcinolone acetonide (TA) and clobetasol propionate (CP) as representative compounds. Effects of discharge power, plasma-working gases, initial pH, coexistence of ions, and various water matrices (ultrapure water, lake water, drinking water, wastewater effluent) on GC removal and energy yield were evaluated. The results confirm that DBD treatment could efficiently remove FA, TA, and CP, achieving efficiency of 72% (k = 0.0126 min−1), 71% (k = 0.0096 min−1), and 74% (k = 0.0116 min−1), respectively in air-DBD system at 45.2 W, with the process following the first order kinetics and energy yield of 6 mg kW−1h−1. The removal efficiency decreased when adding radical scavengers, indicating that hydroxyl radicals played an important role in GC degradation, while other active species (such as solvated electrons (eaq−), ozone (O3), hydrogen peroxide (H2O2) and ultraviolet photolysis (UV)) also contribute to GC degradation. The intermediates generated during the process were analyzed using quadrupole time-of-flight mass spectrometry (QTOF-MS). A total of 23 transformation products of FA, TA and CP were identified, and it was noted that substitution of halogen atoms with OH, oxidation of hydroxyl group to keto acid, decarboxylation of the keto acid, addition of OH, intramolecular cyclization, and hydrolysis of esters occurred during GC degradation by DBD treatment.