Surface Discharge Reactor Research Articles

Upcycle hazard against other hazard: Toxic fluorides from plasma fluoropolymer etching turn novel microbial disinfectants

The release of toxic fluoride byproducts is a seemingly unavoidable artifact of surface engineering, causing severe environmental and human health problems. Here we propose and implement a new “upcycle hazard against other hazard” concept in the case study of cold atmospheric plasma surface modification of fluoropolymers such as polytetrafluorethylene (PTFE). Capitalizing on the excellent controllability, precision and energy efficiency of the plasma surface processing, complemented with the recently discovered ability of plasmas to activate water to produce a potent electrochemical disinfectant, referred to as the plasma-activated water (PAW), we demonstrate a radically new solution to capture the hazardous gaseous fluorides into the PAW and use the as-fluorinated PAW (F-PAW) as a very effective antimicrobial disinfectant. A customized surface discharge reactor is developed to evaluate the effects of fluorides released from the plasma etching of PTFE on the chemistries in gas-phase plasmas and F-PAW, as well as the antibacterial effect of F-PAW. The results show that gaseous fluorides, including COF2, CF3COF, and SiF4 are produced in gas-phase plasmas, and the dissolution of thus-generated fluorides into PAW has a strong effect on inactivating catalase and destroying the oxidation resistance of bacterial cells. As a result, the antibacterial effect of PAW-fluorides against the methicillin-resistant Staphylococcus aureus (MRSA) is enhanced by > 5 log reductions, suggesting that otherwise hazardous fluorides from the plasma processing of PTFE can be used to enhance the microbial disinfection efficiency of PAW. The demonstrated approach opens new avenues for sustainable hazard valorization exemplified by converting toxic fluoride-etching products into potent antimicrobial and potentially anti-viral disinfectants.

Effect of catalyst composition and reactor configuration on benzene oxidation with a nonthermal plasma-catalyst combined reactor

Plasma-catalysis system comprising surface discharge reactor (SDR) and catalysts were constructed and tested for benzene decomposition. In benzene oxidation with SDR, benzene conversion and the amount of COx formed monotonically increased with input energy, but the benzene decomposition behavior was not related with ozone formation. The loading of metal oxides, Al2O3, TiO2 and CeO2 in SDR greatly promoted benzene oxidation and CO2 formation. The highest activity was obtained with manganese oxides dispersed on ultrastable zeolite Y (Mn/USY). In the range of low input power, the amount of ozone formed increased with the input power, and ozone can be efficiently consumed in benzene oxidation by loading the Mn/USY catalyst in the latter part of SDR. In the higher power range where the amount of ozone decreased with increasing the power, the loading of Mn/USY catalyst inside the reactor was more effective because not only ozone but also short-lived species formed in SDR were utilized for benzene oxidation. The addition of water vapor to reaction gas did not affect benzene conversion and COx formation with SDR-Mn/USY catalyst system. The preadsorbed benzene on the Mn/USY catalyst can be oxidized to CO2 with high selectivity compared with homogeneous oxidation of benzene in SDR.

A High-Efficiency Double Surface Discharge and Its Application to Ozone Synthesis

Surface discharge with the flat plate configuration tends to generate a uniform and high-density plasma during ozone synthesis, but suffers from relatively low energy yield at high ozone concentration. Here we report that a double surface discharge reactor can produce, at the same input power, two uniform plasma zones that locate two sides of the thin dielectric layer simultaneously, which results in a high ozone energy yield at high ozone concentration. Discharge characteristics confirm that reducing dielectric thickness and discharge gap favors the achievement of high plasma-density and energy efficiency. The optical emission spectroscopy diagnosis suggests that the double surface discharge with thinner dielectric thickness and narrower discharge gap possesses much higher electron density, as well as higher excitation temperature and low rotational temperature, which is responsible for the excellent performance in ozone synthesis. The optimal parameters of 0.25 mm dielectric thickness and 2 mm discharge gap enable ozone synthesis to proceed with an energy yield of 295.2–108.7 g/kWh at ozone concentration of 11.1–48.3 g/Nm3 and exhibit a good stability during a 4-h test. This performance surpasses the performance of many other typical discharge processes for ozone synthesis.

High sensitive and high temporal and spatial resolved image of reactive species in atmospheric pressure surface discharge reactor by laser induced fluorescence.

The current paucity of spatial and temporal characterization of reactive oxygen and nitrogen species (RONS) concentration has been a major hurdle to the advancement and clinical translation of low temperature atmospheric plasmas. In this study, an advanced laser induced fluorescence (LIF) system has been developed to be an effective antibacterial surface discharge reactor for the diagnosis of RONS, where the highest spatial and temporal resolution of the LIF system has been achieved to ∼100 μm scale and ∼20 ns scale, respectively. Measurements on an oxidative OH radical have been carried out as typical RONS for the benchmark of the whole LIF system, where absolute number density calibration has been performed on the basis of the laser Rayleigh scattering method. Requirements for pixel resolved spatial distribution and outer plasma region detection become challenging tasks due to the low RONS concentration (∼ppb level) and strong interference, especially the discharge induced emission and pulsed laser induced stray light. In order to design the highly sensitive LIF system, a self-developed fluorescence telescope, the optimization of high precision synchronization among a tunable pulsed laser, a surface discharge generator, intensified Charge Coupled Device (iCCD) camera, and an oscilloscope have been performed. Moreover, an image BOXCAR approach has been developed to remarkably improve the sensitivity of the whole LIF system by optimizing spatial and temporal gating functions via both hardware and software, which has been integrated into our automatic control and data acquisition system on the LabVIEW platform. In addition, a reciprocation averaging measurement has been applied to verify the accuracy of the whole LIF detecting system, indicating the relative standard deviation of ∼3%.

Improved performance of parallel surface/packed-bed discharge reactor for indoor VOCs decomposition: optimization of the reactor structure

The purpose of this paper is to develop a high-efficiency air-cleaning system for volatile organic compounds (VOCs) existing in the workshop of a chemical factory. A novel parallel surface/packed-bed discharge (PSPBD) reactor, which utilized a combination of surface discharge (SD) plasma with packed-bed discharge (PBD) plasma, was designed and employed for VOCs removal in a closed vessel. In order to optimize the structure of the PSPBD reactor, the discharge characteristic, benzene removal efficiency, and energy yield were compared for different discharge lengths, quartz tube diameters, shapes of external high-voltage electrode, packed-bed discharge gaps, and packing pellet sizes, respectively. In the circulation test, 52.8% of benzene was removed and the energy yield achieved 0.79 mg kJ−1 after a 210 min discharge treatment in the PSPBD reactor, which was 10.3% and 0.18 mg kJ−1 higher, respectively, than in the SD reactor, 21.8% and 0.34 mg kJ−1 higher, respectively, than in the PBD reactor at 53 J l−1. The improved performance in benzene removal and energy yield can be attributed to the plasma chemistry effect of the sequential processing in the PSPBD reactor. The VOCs mineralization and organic intermediates generated during discharge treatment were followed by COx selectivity and FT-IR analyses. The experimental results indicate that the PSPBD plasma process is an effective and energy-efficient approach for VOCs removal in an indoor environment.

The effect of non-thermal plasma treatment on wheat germination and early growth

Abstract The influence of non-thermal plasma treatment on wheat seeds ( Triticum aestivum ) has been investigated using a surface discharge reactor at atmospheric pressure and room temperature. Growth parameters, like roots and sprouts length and dry weight were measured on the fourth day of germination and a Gaussian distribution was used for curve-fitting of the obtained results. It was found that plasma had little effect on the germination rate, but influenced growth parameters. In the case of plasma treated seeds, the distribution of roots was shifted towards higher lengths as compared with the untreated samples. The distribution of the sprouts length was about two times narrower for the treated samples as compared with the control seeds. The sprouts and roots of the plasma treated seeds were heavier than those of the control samples. The root-to-shoot (R/S) ratio differed substantially, being 0.88 ± 0.016 for the untreated seeds and reaching 1.2 ± 0.005 for the treated samples. Industrial relevance The results obtained in this research demonstrate that non-thermal plasma treatment has a positive effect on wheat early growth. Due to its advantages (uniform treatment, no destruction of seeds, no requirement for chemicals), plasma might become an effective alternative to traditional pre-sowing seed treatment used in agriculture.

Removal of trimethylamine and isovaleric acid from gas streams in a continuous flow surface discharge plasma reactor

The removal of isovaleric acid (IVA) and trimethylamine (TMA) using nonthermal plasma (NTP) in a continuous surface discharge reactor is investigated. The influence of the energy density shows that its increment is accompanied by the increase of the removal rate. At flowrate equal to 2m3h−1, when energy density extends three times, the removal rates of IVA and TMA are increased from 5 to 15mmolm−2h−1 and from 4 to 11mmolm−2h−1, respectively. The impact of relative humidity (RH) is also studied. An increase in % RH (up to 20%) leads to a decrease of the removal rate. Additionally, the formation of by-products in the surface discharge reactor and the plausible reaction mechanism of the two VOC were also detected and discussed. Moreover, a kinetic model taking into account the mass transfer step is developed in order to represent the experimental results. The model shows a good agreement with experimental results.

Oxidation of Elemental Mercury by Active Species Injection from a Surface Discharge Reactor

Active species injection generated by a surface discharge plasma reactor (SDPR) was studied to oxidize elemental mercury (Hg0) in the flue gas. The reactor was inserted in the simulated flue duct. The effects of several operational parameters, such as applied voltage, inlet Hg0 concentration, applied frequency and air injection flow rate, were well investigated. Experimental results showed that Hg0 oxidation efficiency of 83.8% was achieved at specific energy density of 4.0 J L-1 and the flow rate of 1.6 L min-1. Increasing applied voltage and air injection flow rate was beneficial for Hg0 oxidation due to higher production of active species. Lower Hg0 oxidation efficiency was observed with an increase of initial concentration. With an increase of applied frequency, Hg0 oxidation efficiency significantly increased, but the energy yield dropped.

Innovative Approach for Benzene Degradation Using Hybrid Surface/Packed-Bed Discharge Plasmas

An innovative plasma reactor, which generates hybrid surface/packed-bed discharge (HSPBD) plasmas, was employed for the degradation of benzene. The HSPBD reactor was found to display remarkably better benzene degradation, mineralization, and energy performance than surface or packed-bed discharge reactors alone. The degradation efficiency, CO2 selectivity, and energy yield in the HSPBD reactor were 21%, 11%, and 3.9 g kWh-1 higher, respectively, than in a surface discharge reactor and 30%, 21%, and 5.5 g kWh-1 higher, respectively, than in a packed-bed discharge reactor operated at 280 J L-1. Particularly, the benzene degradation in the HSPBD reactor exhibited an unambiguous synergistic enhancement rather than a simple additive effect using the surface discharge and packed-bed discharge reactors. Moreover, in the HSPBD reactor, the formation of byproducts, such as NO2, was suppressed, while O3 was promoted. The use of N2 as the carrier gas was found to be effective for benzene degradation because of the fast reaction rate of N2(A3∑u+) with benzene, and oxygen species derived from the dissociation of O2 were found to be significant in the mineralization process. Thus, the addition of O2 to N2 allows for efficient degradation of benzene, and the optimized amount of O2 was determined to be 3%.

Oxidation efficiency of elemental mercury in two DBD plasma reactors

Configuration of plasma reactors influences the generation of active species including the energized electrons, active radicals and the distribution of active species in reactor, and thus influences the removal efficiency of pollutants. Oxidation efficiency of elemental mercury (Hg0) in two different DBD plasma reactors was studied in this paper. One plasma reactor is a surface discharge reactor (SDR) with a spiral stainless steel thread as the high voltage electrode, and the other plasma reactor is a concentric cylinder type DBD reactor (CCDR) with a copper screw rod as the high voltage electrode. The oxidation efficiencies of Hg0 under different specific energy density (SED), oxygen content, flue gas residence time and the temperature of flue gas indicate that SDR had a better performance than CCDR in oxidation of Hg0, which can be attributed to the higher generation efficiency of ozone in SDR than in CCDR.

Influence of power supply on the generation of ozone and degradation of phenol in a surface discharge reactor

A surface Dielectric Barrier Discharge (DBD) reactor was utilized to degrade phenol in water. Different power supplies applied to the DBD reactor affect the discharge modes, the formation of chemically active species and thus the removal efficiency of pollutants. It is thus important to select an optimized power supply for the DBD reactor. In this paper, the influence of the types of power supplies including alternate current (AC) and bipolar pulsed power supply on the ozone generation in a surface discharge reactor was measured. It was found that compared with bipolar pulsed power supply, higher energy efficiency of O3 generation was obtained when DBD reactor was supplied with 50Hz AC power supply. The highest O3 generation was approximate 4 mg kJ−1; moreover, COD removal efficiency of phenol wastewater reached 52.3% after 3 h treatment under an AC peak voltage of 2.6 kV.

Abatement of Trichloromethane by Using Nonthermal Plasma Reactors

This work investigated the destruction of a halogenated carbon (trichloromethane) using different types of nonthermal plasma reactors. Three reactors, i.e., a surface discharge reactor, a dielectric-packed bed reactor and a barrier discharge reactor with a perforated dielectric tube, were compared with respected to the trichloromethane destruction efficiency. The effect of oxygen content and input power on the trichloromethane destruction was examined, and the byproducts were analyzed to elucidate the destruction pathways. The dielectric-packed bed reactor was found to show better performance in the trichloromethane destruction than the other two reactors. The increase in the oxygen content decreased the destruction efficiency, and the highest destruction efficiency was obtained at oxygen content 0.5%. The calculations for electron-molecule collisions indicated that the most abundant reactive species initiating the destruction of trichloromethane are metastable nitrogen molecules. The major byproducts were CO and Cl2, and the formations of NO2 and N2O were also significant.

$\hbox{NO}_{\rm x}$ Aftertreatment Using Thermal Desorption and Nitrogen Nonthermal Plasma Reduction

In this paper, the results of two experiments are reported. First, the performances of various types of nonthermal plasma reactors for NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> reduction were compared. It was shown that the surface-discharge reactors have as high NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> reduction capabilities as pulse-powered wire-cylinder reactors. Second, NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> treatment using the surface-discharge reactor with a NO-adsorbent zeolite 13X was performed. Thermal desorption was employed for the regeneration of the zeolite. The NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> of 350 ppm was kept lower than 18 ppm for at least 11 h, whereas it degraded to 75 ppm in the absence of the regeneration. The result suggested the possibility of an aftertreatment system that employed thermal desorption by utilizing the waste heat of diesel engine exhaust and NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> reduction by using a surface-discharge reactor.

Non‐Thermal Plasma‐Based Technology for Soil Treatment

AbstractSummary: Dielectric barrier discharge (DBD) plasma reactors of differing configuration, having a high‐voltage electrode in the form of a screw or pyramid, have been investigated as a potential source of soil treatment agents (ozone and nitric oxide). A special geometry of the high‐voltage electrode allows a relatively large ozone concentration to be obtained both from air and oxygen, which can be controlled by the gas flow rate, cooling conditions, and value and frequency of the supply voltage with reasonable generation efficiency. These results are compared with those generated by a commercially available surface discharge reactor. The resultant properties of treated soils are characterized, such as acidity (pH), electrical conductivity (EC), and content of moisture (pF), nitrogen (NH4N, NO3N), minerals (P2O5, K2O, CaO, MgO, Fe, Mn), and total bacteria and fungi.The variation of ozone concentration with supply voltage for each of the electrodes studied here.magnified imageThe variation of ozone concentration with supply voltage for each of the electrodes studied here.

Comparative Assessment of Different Nonthermal Plasma Reactors on Energy Efficiency and Aerosol Formation From the Decomposition of Gas-Phase Benzene

This work presents a comparative assessment of five different types of plasma reactors (pulsed corona, dielectric-barrier discharge (DBD), surface discharge (SD), BaTiO/sub 3/ packed-bed reactor, and plasma-driven catalyst (PDC) reactor) using the decomposition of gas-phase benzene. The parameters used in the assessment include energy constant, carbon balance, product selectivity, and nanometer-sized aerosol formation. The DBD reactor, the pulsed corona reactor, and the SD reactor, where the gas-phase chemical reactions prevail, showed similar performance both in the decomposition efficiency and in the aerosol formation. Size distribution and number concentration of the aerosol formed in the SD and the pulsed corona were 10-80 nm and /spl sim/10/sup 5/ particles/cm/sup 3/, respectively. The PDC reactor showed the highest removal efficiency as well as the highest CO/sub 2/ yield. Carbon balances were strongly related to the nanometer-sized aerosol formation. Negligible amounts of aerosol were formed in the BaTiO/sub 3/ packed-bed reactor and the PDC reactor packed with Ag/TiO/sub 2/ catalyst.

Optical Investigation of Fast Pulsed Discharge on Surface of Ceramics for Environmental Applications

Pulsed surface discharge on the surface of ceramics was investigated experimentally. The photon counting method was applied to clarify the preceding phase of the discharge. The results indicated the effect of charge injection from electrodes. A pulsed surface discharge reactor for decomposition of nitrogen oxides utilizing honeycomb ceramics was proposed. Discharge processes were observed by framing and streak photographs taken by image converter cameras. The emission spectra from the discharge were investigated using a spectrometer. Uniform surface discharges on honeycomb ceramics were successfully obtained utilizing a fast pulsed power generator with a SI-thyristor.

Atmospheric-pressure plasma treatment of ultrahigh molecular weight polyethylene fibers

The performance properties of composite materials reinforced by ultrahigh molecular weight polyethylene (UHMW-PE) fibres depend critically on the fiber/matrix interfacial characteristics. The chemical inertness and very low surface energy of UHMWPE fibers, however, results in a fiber/matrix interfacial strength much less than ideal for such applications [1]. Several teams made remarkable achievements in the surface modification of UHMW-PE by low-pressure plasma treatment at pressures below one Torr (130 Pa) [2–6]. However, these low-pressure plasma treatments require vacuum systems and do not lend themselves easily to an industrial implementation. In this study UHMW-PE fibers were treated by a nitrogen plasma at atmospheric pressure, where the plasma treatment can potentially be realised with less technical effort. A nitrogen plasma was chosen because of its low degrading effect and high radical density creation [6, 7]. A commercially available UHMW-PE filament bundle of 150 filaments (Dyneema SKX 65, dtex 165) was cleaned with acetone before the treatment. The plasma treatment was performed using a pulsed surface discharge reactor that consisted of two on-axis-arranged electrodes housed in a glass chamber [8]. Nitrogen of a technical purity was introduced into the chamber with a flow rate of 1 cm3 s−1. The ground stainless-steel tubular anode was 1 mm in inner diameter. The cathode was a 15 mm-diam. hemispherically capped brass rod with a 2 mm-diam. hole in its axis. The distance between electrodes was adjusted to 15 mm. The treated filament bundle moved on the axis of the electrode system with a speed of 100 mm s−1. The cathode was connected with a tyratron source of pulsed high voltage with a pulse frequency of 100 Hz, a peak voltage of 25 kV, pulse rise time of 75 ns, and pulse half-width of 400 ns. The discharge power was approximately 10 W. To illustrate the effect of the plasma treatment on fiber surface properties, the fiber/rubber matrix adhesion values measured using the untreated and treated fibers were compared. The samples were prepared by pressing the filament bundle between two slides from a conventional polybutadiene rubber blend. Subsequently, the samples were vulcanised at a temperature of 145 ◦C. Adhesion of the fibers to rubber was characterised in a standard H-peel test by the force required to draw out the filament bundle of a rubber block. The adhesion values (the averages of twenty measurements) for the reference and plasma-treated fibers were 1.7 and 2.5 kN m−1, respectively, i.e. an increase of 44% was obtained by the plasma treatment. As stated by Jacobasch et al. [9], some insight into the adhesion behavior of polymer surfaces can be obtained also by zeta potential measurements with varied electrolyte concentration. Preliminary results of our ζ -potential measurements are shown in Fig. 1. From the results it is evident that anions (Cl− and OH−) present in KCl electrolyte are preferably adsorbed by the treated fiber surface. The observed decrease in negative ζ -potential values due to the plasma treatment (corresponding to a decrease of the electrical double layer thickness [9]) indicates a higher hydrophilicity of the plasma-treated fibers. An increase in the pH corresponding to the zero ζ -potential (isoelectric point) indicates a creation of basic surface groups by the plasma-treatment. This is consistent with the basicity of polyethylene tapes treated by atmospheric pressure nitrogen plasma [10] found on the base of contact angle measurements. Our ζ -potential measurements, in an agreement with the results of Gresseer et al. [11] and Wakida et al. [12], affirm that ζ -potential measurements can be a useful technique in determining of technologically

Superposed effect of UV rays on ozone generation by electrical discharge

Generally, ozone is generated by using silent discharge or surface discharge; however, the energy efficiency of ozone generation by using only one kind of discharge is about 200 g/kWh. The energy efficiency of ozone generation is about one-fifth of the theoretical energy efficiency. Ozone decomposition occurs at high concentrations, high temperatures, and so on. In order to increase ozone generation efficiency, many studies of ozone generation methods have been carried out to date. Experiments on ozone generation by using surface discharge and UV rays were carried out. In an experiment on superposing surface discharge and UV rays in the same space, the ozone yield by the superposing mode is lower than either the ozone yield by surface discharge or by UV rays at the same power. It appears that noticeable ozone dissociation by UV rays occurs because a high ozone concentration is achieved by the superposing mode. In cascade connection of a surface discharge reactor and UV lamp reactor, the ozone yield of the cascade mode (from the UV lamp reactor to the surface discharge reactor) is higher than that of the superposing mode at the same power. It is confirmed that cumulative disassociation is an effective reaction of ozone generation. © 1998 Scripta Technica, Electr Eng Jpn, 123(4): 8–14, 1998