Packed-bed Dielectric Barrier Discharge Reactor Research Articles

Effects of chemically-reductive trace gas contaminants on non-thermal plasma inactivation of an airborne virus

Transmission of airborne infectious diseases poses great risk for public health and socio-economic stability, thus, there is a need for an effective control method targeting the spread and transmission of pathogenic aerosols. The existence of chemically-reductive trace air contaminants in animal agriculture may affect the oxidation inactivation process of pathogens. In this study, we report how the presence of such gasses impacts the effectiveness of using non-thermal plasma (NTP) within a packed-bed dielectric barrier discharge reactor to inactivate MS2 bacteriophage. Inactivation of the aerosolized bacteriophage is determined by the combination of viability and polymerase chain reaction assays. Using a plasma power source with a voltage of 20 kV and frequency of 350 Hz, after differentiating and excluding the physical removal effects of viral aerosols potentially caused by plasma, the baseline inactivation of MS2 aerosol in air has been determined based on an overall air flow rate of 200 Liters per minute and plasma discharge power of 1.8 W. When either ammonia or hydrogen sulfide gas is introduced into the airstream at a concentration of 1 part per million, the NTP virus inactivation efficiency is reduced to around 0.5-log from the 1-log baseline inactivation in air alone. Higher concentrations of those gasses will not further inhibit the effectiveness of plasma inactivation.

Experimental study on particulate matter removal using packed-bed dielectric barrier discharge plasma reactor

In this study, a packed-bed dielectric barrier discharge (DBD) reactor was developed for particulate matter (PM) removal. The effects of operating conditions such as the packing materials, applied power, and discharging gap were systematically investigated. The results revealed that Zeolite 13X exhibited the highest PM removal efficiency based on its high electrostatic adsorption capacity. A narrow discharge gap (2.4 mm) and increased power density resulted in an enhancement of the PM removal efficiency in the system. Further, these operating conditions increased the electric field strength, which was proportional to the current density in the system. The energy yield decreased with an increase in the specific energy input into the packed-bed DBD reactor. Among the tested operating parameters, maintaining a narrow discharging gap was determined to be the most important for achieving high energy efficiency and PM removal in the system. Moreover, an air cleaning procedure was applied for the regeneration of the packing materials, resulting in a high recovery rate of over 80%.

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.

Effects of removing carbon particles of different size with nonthermal plasma generated by packed-bed dielectric barrier discharge reactor

A self-designed packed-bed dielectric barrier discharge (PB-DBD) reactor was used to explore the effects of carbon particle size distribution, reaction chamber temperature and reactor inlet flow on the removal effect of carbon particles with different particle sizes. The results indicated that in the process of non-thermal plasma (NTP) oxidation of carbon particles, particles with larger particle size are decomposed into new nanoparticles. When the temperature of the reaction chamber increased from 25 to 200 ℃, the number concentration removal efficiency and rate of nanoparticles, ultrafine particles and total particles increased. With the increase of the inlet flow of the reactor, the O3 concentration first increased and then decreased and the number concentration removal rate of nanoparticles, ultrafine particles and total particles showed the same trend as the O3 concentration. At the inlet oxygen flow of 3 L/min, the O3 concentration and carbon particle removal rate were the maximum.

Plasma-assisted ammonia synthesis in a packed-bed dielectric barrier discharge reactor: effect of argon addition

The effect of argon (Ar) addition on plasma-assisted ammonia (NH3) synthesis in a packed-bed dielectric barrier discharge (DBD) reactor is investigated in this work. Both higher normalized NH3 concentration and N2 conversion are achieved by adding Ar to N2–H2 plasma. The 18.6% increment of normalized NH3 concentration and 15% increment of N2 conversion are realized with 30 vol.% Ar addition compared with the case of N2–H2 plasma only, indicating that Ar addition would contribute to NH3 formation. The mechanisms of NH3 synthesis with Ar addition are proposed based on electrical characteristics and electron energy distribution function of the N2–H2–Ar plasma. The intensity of microdischarges, mean electron energy and quantity of energetic electrons increase upon Ar addition. Hence, the electron-impact reactions would be enhanced upon Ar addition. Meanwhile, the effective capacitance of the plasma reactor is improved, which suggests Ar addition contributes to achieve fully-bridged plasma discharge and transfer energy into chemical process in plasma. Moreover, the presence of Ar introduces Penning excitation and ionization reactions in N2-H2 plasma, which would benefit N2 conversion and then accelerate NH3 formation as well.

Ozone generation enhanced by silica catalyst in packed-bed DBD reactor

In this paper, three dielectric barrier discharge (DBD) configurations, which were plain DBD with no packing, DBD with packed pure quartz fibers and DBD with packed loaded quartz fibers, were employed to investigate the effect and catalytic mechanism of catalyst materials in a packed-bed ozone generator. From the experimental results, it was clear that the DBD configuration with packed pure fibers and packed loaded fibers promotes ozone generation. For the packed-bed reactor, ozone concentration and ozone yield were enhanced by an increase of electric field in the discharge gap with the packed-bed effect. Meanwhile, the enhancement of ozone concentration and yield for the DBD reactor packed by loaded fibers with silica nanoparticles was due to the catalysis of silica nanoparticles on the fiber surface. The adsorption of silica nanoparticles on the fiber surface can prolong the retention time of active species and enhance surface reactions.

Burst mode in a cooled packed-bed dielectric barrier discharge reactor for CO2 splitting * *(A manuscript offered to ‘ Plasma Research Express ’).

The so called ‘burst mode’, a rapidly pulsed power regime for dielectric barrier discharges (DBDs) has previously been reported to greatly improve the performance of an uncooled and unpacked DBD reactor for CO2 splitting. Here we explore the interaction between a DBD in burst mode and each of active cooling and a dielectric packing material (1.0–1.2 mm glass beads) in a coaxial, metal-dielectric DBD reactor for CO2 splitting. The effect of burst mode on CO2 conversion and energy efficiency under different combinations of cooling and packing were investigated and compared with those under continuous wave mode operation. The burst mode operation showed similar CO2 conversion and energy efficiency to continuous wave mode in the unpacked and uncooled configuration under the conditions investigated in this study. However, burst mode significantly outperformed continuous wave mode in the packed and uncooled configuration. When active cooling was employed, burst mode was found to provide only minor benefit or no benefit, depending on specific energy input (SEI), compared to continuous wave mode for each the packed and unpacked configurations. Maximum conversion and energy efficiency were achieved with both packing and active cooling across all SEI examined, and performance in this configuration was found to be relatively insensitive to the power delivery mode.

CO2 conversion promoted by potassium intercalated g-C3N4 catalyst in DBD plasma system

The direct conversion of CO2 to CO and O2 has attracted extensive attention as CO is a key C1 feedstock for chemical synthesis. The CO2 conversion promoted by γ-Al2O3 supported potassium intercalated g-C3N4 (KuCN/AO) catalyst in a packed-bed dielectric barrier discharge (DBD) plasma system was investigated. A coaxial cylinder DBD plasma reactor was used with Cu powder as the high voltage electrode. Reactor temperature showed converse effect on CO2 conversion. As the reactor temperature decreased from 120 ℃ to 50 ℃, CO2 conversion rate and energy efficiency both increased by ca. 50%. After the catalyst was filled into the discharge area, the discharge mode changed from filamentary discharge to the combination of filamentary-surface discharge. The morphology and structure of KuCN was characterized by SEM, XRD, FTIR and XPS. KuCN kept a porous structure and K element distributed uniformly between CN interlayer spacing. In KuCN/AO assisted DBD plasma system, the highest CO2 conversion rate, CO yield and energy efficiency were increased from 11.1%, 10.0% and 9.41% to 19.3%, 18.1% and 20.6% compared with pure DBD/γ-Al2O3 system, respectively. The main mechanism of KuCN assisted enhancing CO2 conversion in packed-bed DBD reactor was analyzed. The larger specific surface area, layers bridging and charge redistribution enabled KuCN/AO to obtain good plasma-catalytic CO2 conversion performance.

Simple packed-bed dielectric barrier discharge reactor for NOx treatment by an adsorption-discharge process without the aid of a solution and catalyst

NO2 adsorbed on activated carbon was decomposed efficiently by a simple packed-bed dielectric barrier discharge reactor with a special electrode that could overcome the problems of the regeneration and desorption of NOx and the problems of residues of deeply adsorbed NO2 without a solution and catalyst at atmospheric pressure and relatively low temperatures. In addition, the heat derived from the plasma and plasma-catalytic reaction had a synergetic effect that could influence the decomposition of NOx adsorbed on the carbonaceous adsorbent. Consequently, almost 94% of the adsorbed NOx could be decomposed efficiently by dividing the outer electrode called the segmented threaded-electrode. This is a promising technology for NOx reduction to substitute for a selective catalytic reduction technology because plasma technology without the use of a chemical solution is eco-friendly.

Plasma Catalytic Conversion of CH4 to Alkanes, Olefins and H2 in a Packed Bed DBD Reactor

Methane is activated at ambient conditions in a dielectric barrier discharge (DBD) plasma reactor packed with Pd/γ-alumina catalyst containing different loadings of Pd (0.5, 1, 5 wt%). Results indicate that the presence of Pd on γ-alumina substantially abates the formation of deposits, leads to a notable increase in the production of alkanes and olefins and additionally improves the energy efficiency compared to those obtained for the non-packed reactor and the bare γ-alumina packed reactor. A low amount of Pd (0.5 and 1 wt%) favors achieving a higher production of olefins (mainly C2H4 and C3H6) and a higher yield of H2. Increasing Pd loading to 5 wt% promotes the interaction of H2 and olefins, which consequently intensifies the successive hydrogenation of unsaturated compounds, thus incurring a higher production of alkanes (mainly C2H6 and C3H8). The substantial abatement of the deposits is ascribed to the role of Palladium in moderating the strength of the electric and shifting the reaction pathways, in the way that hydrogenation reactions of deposits’ precursors become faster than their deposition on the catalyst.

Plasma-enhanced hydrolysis of urea and SCR of NOx over V2O5-MoO3/TiO2: Decrease of reaction temperature and increase of NOx conversion

Plasma-enhanced hydrolysis of urea and selective catalytic reduction (SCR) of NOx over V2O5-MoO3/TiO2 were studied by temperature-programmed experiments using a packed-bed dielectric barrier discharge reactor. Urea over TiO2 and V2O5-MoO3/TiO2 could be hydrolyzed at 110–250 °C to NH3 and CO2 with yields of 79.0%–83.6% and 83.8%–88.6%, respectively. The catalyst type and presence of O2 in the carrier gas hardly affected catalytic urea hydrolysis performance. Introducing plasma reduced urea hydrolysis temperature over V2O5-MoO3/TiO2, without changing NH3 yield under O2-free condition while reducing NH3 yield to lower values at higher discharge power under O2-containing condition. Urea hydrolysis and NOx conversion temperatures decreased and NOx conversion increased after introducing plasma into the urea-SCR process. The presence of NO in the feed gas hardly affected and reduced urea hydrolysis temperature in urea-SCR and plasma-enhanced urea-SCR process, respectively. 5% O2 in the reaction gas favored NOx conversion in urea-SCR regardless of the presence of plasma. In the plasma-enhanced O2-containing urea-SCR process, N(-III) species (urea, NH3 and HNCO) were predominantly consumed in the conversion of NOx rather than being oxidized by oxidative plasma species. Minor slip of HNCO was observed at low temperatures during urea hydrolysis and urea-SCR over V2O5-MoO3/TiO2 and low-concentration N2O was detected during plasma-enhanced urea hydrolysis and urea-SCR process. The BET surface area and TiO2 crystal structure of V2O5-MoO3/TiO2 catalyst remained unchanged after urea hydrolysis and NOx conversion reactions no matter plasma was introduced or not. Plasma enhanced the conversion of NOx partially by enriching the catalyst surface with adsorbed oxygen.

Ammonia synthesis over γ-Al2O3 pellets in a packed-bed dielectric barrier discharge reactor

In this work, ammonia (NH3) synthesis from N2 and H2 was carried out in a packed-bed dielectric barrier discharge (DBD) reactor, while three kinds of commercial packing materials including acidic γ-Al2O3, alkaline γ-Al2O3 and neutral alumina pellets were employed. The effect of packing materials on plasma-assisted NH3 synthesis was investigated and compared with an unpacked DBD reactor. The results show that the presence of packing materials enhanced the plasma-assisted NH3 synthesis by 15.6% to 44.4% compared to the plasma reaction without a packing. The highest NH3 concentration of 1565.5 ppm was obtained over the alkaline γ-Al2O3 packed plasma reactor. The improvement of packing materials on plasma-assisted NH3 synthesis followed the order of alkaline γ-Al2O3 > neutral γ-Al2O3 > acidic γ-Al2O3 > blank tube only. A series of characterizations were performed to illustrate the structure-performance relationships between plasma-induced NH3 synthesis process and packing materials. The results showed that the basicity of the packing materials played an important role in the plasma-assisted NH3 synthesis process. The reaction mechanisms of NH3 synthesis in the packed-bed DBD reactor were also discussed.

Inactivation of airborne viruses using a packed bed non-thermal plasma reactor

Outbreaks of airborne infectious diseases such as measles or severe acute respiratory syndrome can cause significant public alarm. Where ventilation systems facilitate disease transmission to humans or animals, there exists a need for control measures that provide effective protection while imposing minimal pressure differential. In the present study, viral aerosols in an airstream were subjected to non-thermal plasma (NTP) exposure within a packed-bed dielectric barrier discharge reactor. Comparisons of plaque assays before and after NTP treatment found exponentially increasing inactivation of aerosolized MS2 phage with increasing applied voltage. At 30 kV and an air flow rate of 170 standard liters per minute, a greater than 2.3 log reduction of infective virus was achieved across the reactor. This reduction represented ~2 log of the MS2 inactivated and ~0.35 log physically removed in the packed bed. Increasing the air flow rate from 170 to 330 liters per minute did not significantly impact virus inactivation effectiveness. Activated carbon-based ozone filters greatly reduced residual ozone, in some cases down to background levels, while adding less than 20 Pa pressure differential to the 45 Pa differential pressure across the packed bed at the flow rate of 170 standard liters per minute.

Mechanisms of Toluene Removal in Relation to the Main Components of Biosyngas in a Catalytic Nonthermal Plasma Process

In this study, a packed-bed dielectric barrier discharge reactor was built for the removal of biomass gasification tar. Two kinds of packing materials, glass pellets and a Ni/γ-Al2O3 catalyst, were employed for the plasma-alone process and the plasma catalytic process, respectively. Toluene was used as the tar surrogate, and five typical gas combinations, N2, N2 + CO2, N2 + CO2 + CO, N2 + CO + H2, and simulated gasification gas (SGG), were selected as carrier gases. The effects of the main components of the gasification gas on toluene removal under plasma and/or catalysis treatment were studied. The results indicated that the highest removal efficiency in the plasma-alone process was achieved in the N2 atmosphere, and the addition of H2, CO, or CO2 to N2 led to a decrease in the removal performance. When Ni/γ-Al2O3 was introduced into the plasma process, the best removal efficiency was obtained in the N2 + CO2 atmosphere. However, the positive effect of CO2 on toluene removal switched to a negative effect...

Conversion of CO2 in a packed-bed dielectric barrier discharge reactor

The conversion of CO2 into CO and O2 in a quartz cylindrical packed-bed dielectric reactor has been studied using CO2 and Ar gas mixtures at atmospheric pressure and near ambient temperature with quartz wool, γ-Al2O3, and TiO2 packing. The highest energy efficiencies and conversion rates were observed with TiO2 packing in 20% CO2 in Ar: 30% conversion with 2.9% energy efficiency, and 17.5% conversion with 5.0% energy efficiency. Both γ-Al2O3 and quartz wool also showed an enhancement in conversion over an unpacked reactor. The percentage of CO2 to Ar in the range of 20%–60% is shown to have only a minor effect on reactor performance. Conversion as a function of power input and flow rate is studied in detail for γ-Al2O3 and TiO2 packing with similar particle sizes. In both cases, simple chemical kinetic models show that the CO production rate is nearly equal for both materials, while reverse reaction rates to CO2 are doubled for γ-Al2O3 compared to TiO2. From detailed charge–voltage (Q-V) analysis of all four reactor configurations, it is revealed that the electric field at which discharging occurs is higher for both γ-Al2O3 and TiO2 as compared to the empty or quartz wool filled reactors. Comparing kinetic model results with the electrical Q-V analysis, it appears likely that the higher and similar magnitude electric fields occurring with γ-Al2O3 and TiO2 are directly responsible for the increased CO production rates via increased electron energies in the discharge. The higher reverse reaction rates for γ-Al2O3, and its subsequent poorer performance compared to TiO2, can be attributed to a significantly higher effective surface area, which increases undesirable surface reactions between CO and oxygen species.

Streamer propagation in a packed bed plasma reactor for plasma catalysis applications

A packed bed dielectric barrier discharge (DBD) is widely used for plasma catalysis applications, but the exact plasma characteristics in between the packing beads are far from understood. Therefore, we study here these plasma characteristics by means of fluid modelling and experimental observations using ICCD imaging, for packing materials with different dielectric constants. Our study reveals that a packed bed DBD reactor in dry air at atmospheric pressure may show three types of discharges, i.e. positive restrikes, filamentary microdischarges, which can also be localized between two packing beads, and surface discharges (so-called surface ionization waves). Restrikes between the dielectric surfaces result in the formation of filamentary microdischarges, while surface charging creates electric field components parallel to the dielectric surfaces, leading to the formation of surface discharges. A transition in discharge mode occurs from surface discharges to local filamentary discharges between the packing beads when the dielectric constant of the packing rises from 5 to 1000. This may have implications for the efficiency of plasma catalytic gas treatment, because the catalyst activation may be limited by constraining the discharge to the contact points of the beads. The production of reactive species occurs most in the positive restrikes, the surface discharges and the local microdischarges in between the beads, and is less significant in the longer filamentary microdischarges. The faster streamer propagation and discharge development with higher dielectric constant of the packing beads leads to a faster production of reactive species. This study is of great interest for plasma catalysis, where packing beads with different dielectric constants are often used as supports for the catalytic materials. It allows us to better understand how different packing materials can influence the performance of packed bed plasma reactors for environmental applications.

Conversion of NO with a catalytic packed-bed dielectric barrier discharge reactor

This paper discusses the conversion of nitric oxide (NO) with a low-temperature plasma induced by a catalytic packed-bed dielectric barrier discharge (DBD) reactor. Alumina oxide (Al2O3), glass (SiO2) and zirconium oxide (ZrO2), three different spherical packed materials of the same size, were each present in the DBD reactor. The NO conversion under varying input voltage and specific energy density, and the effects of catalysts (titanium dioxide (TiO2) and manganese oxide (MnOx) coated on Al2O3) on NO conversion were investigated. The experimental results showed that NO conversion was greatly enhanced in the presence of packed materials in the reactor, and the catalytic packed bed of MnOx/Al2O3 showed better performance than that of TiO2/Al2O3. The surface and crystal structures of the materials and catalysts were characterized through scanning electron microscopy analysis. The final products were clearly observed by a Fourier transform infrared spectrometer and provided a better understanding of NO conversion.

CO2 dissociation in a packed bed DBD reactor: First steps towards a better understanding of plasma catalysis

Plasma catalysis is gaining increasing interest for CO2 conversion, but the interaction between the plasma and catalyst is still poorly understood. This is caused by limited systematic materials research, since most works combine a plasma with commercial supported catalysts and packings. In the present paper, we study the influence of specific material and reactor properties, as well as reactor/bead configuration, on the conversion and energy efficiency of CO2 dissociation in a packed bed dielectric barrier discharge (DBD) reactor. Of the various packing materials investigated, BaTiO3 yields the highest conversion and energy efficiency, i.e., 25% and 4.5%.Our results show that, when evaluating the influence of catalysts, the impact of the packing (support) material itself cannot be neglected, since it can largely affect the conversion and energy efficiency. This shows the large potential for further improvement of packed bed plasma reactors for CO2 conversion and other chemical conversion reactions by adjusting both packing (support) properties and catalytically active sites. Moreover, we clearly prove that comparison of results obtained in different reactor setups should be done with care, since there is a large effect of the reactor setup and reactor/bead configuration.

Kinetic modelling of NH3 production in N2–H2 non-equilibrium atmospheric-pressure plasma catalysis

Detailed plasma kinetics modelling is presented of a low electron energy N2–H2 atmospheric-pressure discharge for ammonia synthesis. The model considers both electron and vibrational kinetics, including excited N2(X, ν) and H2(X, ν) species, and surface reactions such as those occurring by the Eley–Rideal and Langmuir–Hinshelwood mechanisms and dissociative adsorption of molecules. The predictions of the model are compared to the measured NH3 concentration produced in a packed-bed dielectric barrier discharge reactor as a function of process parameters such as input gas composition and applied voltage. Unlike typical low-pressure plasma processes, under the plasma conditions considered here (reduced electric field E/N in the range 30–50 Td, electron density of the order 108 cm−3), the influence of ions is not significant. Instead, the reactions between radicals and vibrationally-excited molecules are more important. The active species in surface reactions, such as surface-adsorbed atomic nitrogen N(s) or hydrogen H(s), are found to be predominantly generated through the dissociative adsorption of molecules, in contrast to previously proposed mechanisms for plasma catalysis under low-pressure, high-E/N conditions. It is found that NH radicals play an important role at the early stages of the NH3-generation process, NH in turn is produced from N and H2(ν). Electron kinetics is shown to play a critical role in the molecular dissociation and vibrational excitation reactions that produce these precursors. It is further found that surface-adsorbed atomic hydrogen H(s) takes a leading role in the formation of NH3, which is another significant difference from the mechanisms in conventional thermo-chemical processes and low-pressure plasmas. The applied voltage, the gas temperature, the N2:H2 ratio in the input gas mixture and the reactivity of the surface material are all found to influence the ammonia production. The calculated results reproduce the observed trends in the dependence of NH3 production on the N2/H2 ratio in the input gas mixture and the applied voltage.

Influence of Gap Size and Dielectric Constant of the Packing Material on the Plasma Behaviour in a Packed Bed DBD Reactor: A Fluid Modelling Study

A packed bed dielectric barrier discharge (DBD) was studied by means of fluid modelling, to investigate the influence of the dielectric constant of the packing on the plasma characteristics, for two different gap sizes. The electric field strength and electron temperature are much more enhanced in a microgap reactor than in a mm‐gap reactor, leading to more current peaks per half‐cycle, but also to non‐quasineutral plasma. Increasing the dielectric constant enhances the electric field further, but only up to a certain value of dielectric constant, being 9 for a microgap and 100 for a mm‐gap reactor. The enhanced electric field results in a higher electron temperature, but also lower electron density. This last one strongly affects the reaction rate.