Pressure Microwave Plasma Research Articles

Reference organism selection for microwave atmospheric pressure plasma jet treatment of young coconut liquid endosperm

This study identified a reference organism for the establishment of microwave atmospheric pressure plasma jet treatment of young coconut liquid endosperm. Three different, predominant spoilage bacteria were isolated from spoiled liquid endosperm and identified through 16S rDNA sequencing, prior to propagation and eventual challenge studies. Basic Local Alignment Search Tool comparisons revealed that the isolated spoilage bacteria were Klebsiella sp., Staphylococcus sp., and Kluyvera sp (%Identity 97.34–97.82%). The isolates were propagated to mid-stationary growth phase (17 h) and thereafter suspended in liquid endosperm. The inactivation rates of the spoilage isolates in liquid endosperm subjected to plasma jet at 450 and 650 W input power settings were determined and compared to those of pathogens Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes. Inactivation rates of all test organisms at 450 W (2.76–5.98 min) were significantly less (p < 0.05) than those at 650 W (1.86–3.11 min). In both power settings, S. enterica exhibited the significantly (p < 0.05) greatest resistance towards plasma treatment, while Staphylococcus sp. exhibited the least. Heat penetration studies in both power settings revealed that the temperature of the liquid endosperm did not significantly increase and did not reach bactericidal ranges (<30 °C) during plasma jet treatment, hence the observed inactivation were attributed to antimicrobial species generated by the plasma. Optical emission spectroscopy revealed that these antimicrobial species included atomic oxygen (777.41 and 844.67 nm) and ultraviolet radiation (200–280 nm). Thus, this study determined S. enterica as an appropriate target organism for the establishment of plasma jet process for coconut liquid endosperm, the inactivation rate of which shall be soon established in higher scale treatment process.

Gas mixing enhanced by power modulations in atmospheric pressure microwave plasma jet

Microwave plasma jet operating in atmospheric pressure argon was power modulated by audio frequency sine envelope in the 102 W power range. Its effluent was imaged using interference filters and ICCD camera for several different phases of the modulating signal. The combination of this fast imaging with spatially resolved optical emission spectroscopy provides useful insights into the plasmachemical processes involved. Phase-resolved schlieren photography was performed to visualize the gas dynamics. The results show that for higher modulation frequencies the plasma chemistry is strongly influenced by formation of transient flow perturbation resembling a vortex during each period. The perturbation formation and speed are strongly influenced by the frequency and power variations while they depend only weakly on the working gas flow rate. From application point of view, the perturbation presence significantly broadened lateral distribution of active species, effectively increasing cross-sectional area suitable for applications.

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters.

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a stable and continuous operation of the plasma is possible and the plasma torch can be used for many different applications. On one hand, the hot (3,600 K gas temperature) plasma can be used for chemical processes and on the other hand the cold afterglow (temperatures down to almost RT) can be applied for surface processes. For example chemical syntheses are interesting volume processes. Here the microwave plasma torch can be used for the decomposition of waste gases which are harmful and contribute to the global warming but are needed as etching gases in growing industry sectors like the semiconductor branch. Another application is the dissociation of CO2. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 to CO and O2. The CO can be further processed to gaseous or liquid higher hydrocarbons thereby providing chemical storage of the energy, synthetic fuels or platform chemicals for the chemical industry. Applications of the afterglow of the plasma torch are the treatment of surfaces to increase the adhesion of lacquer, glue or paint, and the sterilization or decontamination of different kind of surfaces. The movie will explain how to ignite the plasma solely by microwave power without any additional igniters, e.g., electric sparks. The microwave plasma torch is based on a combination of two resonators - a coaxial one which provides the ignition of the plasma and a cylindrical one which guarantees a continuous and stable operation of the plasma after ignition. The plasma can be operated in a long microwave transparent tube for volume processes or shaped by orifices for surface treatment purposes.

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters

Energy Density Dependence of Hydrogen Combustion Efficiency in Atmospheric Pressure Microwave Plasma

Recovery of tritium in nuclear fusion plants is a key issue for safety. So far, the oxidation procedure using atmospheric pressure plasma is expected to the recovery method. In this study, to clarify the mechanism of hydrogen oxidation by plasma chemistry, we investigated the dependence of hydrogen combustion efficiency on gas flow rate and input power in the atmospheric pressure microwave plasma. It is found that the combustion efficiency depended on energy density of absorbed microwave power. Hence, the energy density is considered as a key parameter for combustion processes.Also neutral gas temperatures in and outside of the plasma were measured by an optical emission spectroscopy method and thermocouple. The result shows that the neutral gas temperature in the plasma is much higher than the outside temperature of plasma. The high neutral gas temperature would affect to the combustion reaction.

Hydrogen production from ethanol in nitrogen microwave plasma at atmospheric pressure

Abstract Hydrogen seems to be one of the most promising alternative energy sources. It is a renewable fuel as it could be produced from e.g. waste or bio-ethanol. Furthermore hydrogen is compatible with fuel cells and is environmentally clean. In contrast to conventional methods of hydrogen production such as water electrolysis or coal gasification we propose a method based on atmospheric pressure microwave plasma. In this paper we present results of the experimental investigations of hydrogen production from ethanol in the atmospheric pressure plasma generated in waveguide-supplied cylindrical type nozzleless microwave (2.45 GHz) plasma source (MPS). Nitrogen was used as a working gas. All experimental tests were performed with the nitrogen flow rate Q ranged from 1500 to 3900 NL h-1 and absorbed microwave power PA up to 5 kW. Ethanol was introduced into the plasma using the induction heating vaporizer. The process resulted in an ethanol conversion rate greater than 99%. The hydrogen production rate was up to 728 NL[H2] h-1 and the energy efficiency was 178 NL[H2] per kWh of absorbed microwave energy.

A simple process for synthesizing nano Pt- and/or N-doped titanium dioxide powders by microwave plasma torch

Simultaneous N- and Pt-doped TiO2 powders are usually synthesized via multi-stage processes. In this study, Pt/N-doped (sample Pt/N-TiO2), Pt-doped (sample Pt-TiO2), N-doped (sample N-TiO2), and without doping (sample TiO2) TiO2 in the form of spherical nano to micro-particles are rapidly synthesized in a single-step process by spraying clear Ti- and Pt-containing nano aerosols into an atmospheric-pressure microwave plasma torch. The anatase modified Pt/N-TiO2 powders were produced in about 0.12s. After the collection of 14-stage impactors, the size distribution showed that the most of the particles by number were in the <10nm stage impactor, reaching 95.21%, 96.94%, and 97.94% of the total particle numbers for N-TiO2, Pt-TiO2, and Pt/N-TiO2 powders, respectively, although the mass distribution of the powders was mainly in the 1–2.5μm range. Chemical composition analysis showed that the N doped contents were 0.47, 0.21, and 0.41at.% in the N-TiO2, Pt-TiO2, and Pt/N-TiO2 powders, respectively, levels higher than that of the TiO2 sample (0.12at.%). As a result, the photocatalytic activities of N-containing (N-TiO2 and Pt/N-TiO2 samples) powders are significantly higher than those of TiO2 and P25 under visible light degradation. The rapid production of N- and/or Pt-TiO2 powders by using a simple plasma process can thus be achieved successfully for use in photocatalytic applications.

Invited: Scalable Production of Nanowire Arrays and Powders Using Plasmas

This presentation will highlight our group’s efforts with various scalable methods for continuous manufacturing of nanowires powders and arrays with help of plasmas. These scalable methods can be categorized in to the following: (a) scalable production of nanowires of low-melting metal oxide nanowire powders; (b) scalable production of nanowire arrays and powders for titania and related oxides; and (c) low-temperature growth of nanowires of silicon and related materials. Scalable production method for nanowires of low-melting metal oxides: A novel atmospheric microwave plasma reactor is designed to process about a kilogram of nanowires per day and has already been demonstrated for the synthesis of tin oxide, zinc oxide and aluminum oxide nanowires.1 The resulting nanowires are 50-100 nm in diameter and several microns long. Scalable production of titania and related metal oxide nanowires: We report a new ultrafast (reaction time on the scale of a minute) gas-phase method for synthesizing highly crystalline TiO2 nanowires (NWs) using direct oxidation of either Ti metal (foils or powders) or spherical TiO2 powders using an atmospheric pressure microwave plasma reactor.2 The current state of the art methods involve long reaction time scales (~1 day) for synthesis of TiO2 NWs. Low-temperature synthesis of nanowire arrays of silicon and related materials: This presentation will also highlight our recent experiments on the synthesis of silicon nanowire arrays at temperatures lower than 300 C.This presentation will also highlight our efforts in utilizing the nanowire based materials toward various energy conversion and storage applications including dye sensitized solar cells, lithium ion batteries, and photoelectrochemical water splitting.

The quenching effect of hydrogen on the nitrogen in metastable state in atmospheric-pressure N2-H2 microwave plasma torch

The atmospheric-pressure microwave N2-H2 plasma torch is generated and diagnosed by optical emission spectroscopy. It is found that a large amount of N atoms and NH radicals are generated in the plasma torch and the emission intensity of N2+ first negative band is the strongest over the spectra. The mixture of hydrogen in nitrogen plasma torch causes the morphology of the plasma discharge to change with appearance that the afterglow shrinks greatly and the emission intensity of N2+ first negative band decreases with more hydrogen mixed into nitrogen plasma. In atmospheric-pressure microwave-induced plasma torch, the hydrogen imposes a great influence on the characteristics of nitrogen plasma through the quenching effect of the hydrogen on the metastable state of N2.

Application of atmospheric pressure microwave plasma source for hydrogen production from ethanol

In contrast to conventional technologies of hydrogen production like water electrolysis or coal gasification we propose a method based on the atmospheric pressure microwave plasma. In this paper we present results of the experimental investigations of the hydrogen production from ethanol in the atmospheric pressure plasma generated in waveguide-supplied cylindrical type nozzleless microwave (915 MHz and 2.45 GHz) plasma source (MPS). Argon, nitrogen and carbon dioxide were used as a working gas. All experimental tests were performed with the working gas flow rate Q ranged from 1500 to 3900 NL/h and absorbed microwave power PA up to 6 kW. Ethanol was introduced into the plasma as vapours carried with the working gas. The process resulted in the ethanol conversion rate greater than 99%. The hydrogen production rate was up to 210 NL[H2]/h and the energy efficiency was 77 NL[H2] per kWh of absorbed microwave energy.

Hydrogen production from banyan leaves using an atmospheric-pressure microwave plasma reactor

Growth of the hydrogen market has motivated increased study of hydrogen production. Understanding how biomass is converted to hydrogen gas can help in evaluating opportunities for reducing the environmental impact of petroleum-based fuels. The microwave power used in the reaction is found to be proportional to the rate of production of hydrogen gas, mass of hydrogen gas produced per gram of banyan leaves consumed, and amount of hydrogen gas formed with respect to the H-atom content of banyan leaves decomposed. Increase the microwave power levels results in an increase of H2 and decrease of CO2 concentrations in the gaseous products. This finding may possibly be ascribed to the water-gas shift reaction. These results will help to expand our knowledge concerning banyan leaves and hydrogen yield on the basis of microwave-assisted pyrolysis, which will improve the design of hydrogen production technologies.

Roles of the state-resolved OH(A) and OH(X) radicals in microwave plasma assisted combustion of premixed methane/air: An exploratory study

We report a novel microwave plasma-assisted combustion (PAC) system that is developed as a new test platform to study roles of plasma in PAC. The system included two major components, an atmospheric pressure microwave plasma cavity and a cross-shape quartz combustor. This new PAC system allows one to study PAC using complicated yet well-controlled combinations of operating parameters, such as fuel equivalence ratio (ϕ), fuel mixture flow rate, plasma gas flow rate, plasma gases, symmetric or asymmetric fuel-oxidant injection patterns, with and without plasma. In this work, ignitions at the fuel (lean and rich) flammability limits at different plasma powers and fuel flow rates were investigated. The ignition curves of plasma power versus ϕFL at the different flow rates revealed a stretched U-shape, showing clear evidences of the plasma enhancement effects on ignition and flame stabilization, i.e. the fuel lean flammability limit (ϕLFL) was extended to ϕ=0.2, as compared to ϕ=0.6 at the same combustion parameters except with no plasma. Optical emission spectroscopy (OES) showed that the combustor had three distinct reaction zones: plasma zone, hybrid plasma-flame zone, and flame zone; and each of the reaction zones was well defined by its OES features. Furthermore, a detailed survey of OES of OH (A–X) conducted along the plasma jet axis (x direction) with a spatial resolution of 0.5mm revealed that OH(A) had a double-peak feature in its relative emission intensity curve (I∼x) in the hybrid zone where plasma-assisted ignition (PAI) started, as evidenced by a significant surge of OH(A) and by a large increase in OH rotational temperature, i.e. from 1450K to 2400K. Moving from the hybrid zone to the flame zone, OH(A) decreased by more than four orders of magnitude. However, the electronic ground state OH(X) measured simultaneously using pulsed cavity ringdown spectroscopy around 308nm showed that absolute number density of the OH(X) decreased by smaller than a factor of ten from the downstream of the hybrid zone to the flame zone. The different changing rates of the OH(A) and OH(X) radicals from the hybrid zone to the flame zone allow us to propose a hypothesis that if both the electronically excited state OH(A) and the electronic ground state OH(X) assisted the ignition and flame stabilization processes, the role of OH(X) radicals was more dominant in the flame stabilization but the role of OH(A) radicals was more dominant in the ignition enhancement.

Removal of volatile organic compounds from air streams by making use of a microwave plasma burner with reverse vortex flows

We developed an atmospheric-pressure microwave plasma burner for removing volatile organic compounds (VOCs) from polluted air streams. This study focused on the destruction of the VOCs in the high flow rate polluted streams required for industrial use. Plasma flames were sustained by injecting liquefied natural gas (LNG), which is composed of CH4, into the microwave plasma torch. With its high temperature and high density of atomic oxygen, the microwave torch attained nearly complete combustion of LNG, thereby providing a large-volume, high-temperature plasma flame. The plasma flame was applied to reactors in which the polluted streams were in one of two vortex flows: a conventional vortex reactor (CVR) or a reverse vortex reactor (RVR). The RVR, using a plasma power of 2 kW and an LNG flow of 20 liters per minute achieved a destruction removal efficiency (DRE) of 98% for an air flow rate of 5 Nm3/min polluted with 550 pm of VOCs.. For the same experimental parameters, the CVR provided a DRE of 90.2%. We expect that this decontamination system will prove effective in purifying contaminated air at high flow rates.

Microwave Plasmas at Atmospheric Pressure

AbstractMicrowave plasmas at atmospheric pressure are used for surface treatments like for example cleaning, sterilization or decontamination purposes, for a pre‐treatment to increase the adhesion of lacquer, paint, or glue, and for the deposition of different kind of layers and coatings. Micro plasma jets can also be applied for biomedical applications and for treatment of small and complex geometries like for example the inside of capillaries. Larger plasma torches which exhibit higher gas temperatures can also be used for chemical syntheses like waste gas decomposition, methane pyrolysis, or carbon dioxide dissociation and for plasma spraying purposes.In the present publication an overview on the development and the investigation of the operating principle of two atmospheric pressure microwave plasma torches at frequencies of 2.45 GHz and 915 MHz will be presented. The plasma sources are based on a cylindrical resonator combined with coaxial structures. To explain how these plasma sources work, simulations of the electric field distribution will be discussed. Furthermore, some physical characteristics of an air and an Ar/H2 atmospheric plasma like gas temperatures, excitation temperatures and densities as well as the heating of the plasma by the microwave will be investigated. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

High H Radical Density Produced by 1-m-Long Atmospheric Pressure Microwave Plasma System

We have developed an atmospheric pressure microwave plasma system with a microwave antenna consisting of two microwave guides, which have a discharge line with 41 slots. The antenna is set against a movable stage with a heater in a process chamber. The process gas used is a 1% H2 gas diluted by Ar gas. We clarified various characteristics, such as gas temperature, electron density, and hydrogen radical density, using this system, and found that the gas temperature is about 1000 K, the electron density is 1×1015 cm-3, and the H radical density is 1×1016 cm-3 at the slot under the condition of a 10 GHz, 1.5 kW, pulsed microwave with a pulsed voltage of 2.5, a pulsed frequency of 4 kHz, and a duty ratio of 0.16.

Microwave plasma studies of Spirulina algae pyrolysis with relevance to hydrogen production

Growth of the hydrogen market has motivated increased study of hydrogen production. Understanding how biomass is converted to hydrogen gas can help in evaluating opportunities for reducing the environmental impact of petroleum-based fuels. Using an atmospheric-pressure microwave plasma reactor coupled with species-selective analysis, experiments are conducted at microwave power levels of 800, 900 and 1000 W, a reactant flow rate of 12 slm, and 1 g of dry Spirulina algae in nitrogen. At the absorbed microwave power levels used in this experiment, hydrogen gas produced is in the range of 36.75–45.13% volume fraction, 13.42–15.48 mg per minute, and 12.37–31.46 mg per gram of Spirulina algae consumed. Moreover, the selection of power levels demonstrates that 20.62–52.43% hydrogen atom mass content in dry algae is converted to hydrogen gas. In general, the effect of reaction temperatures on the gas product formation is qualitatively consistent with those produced from other biomass materials reported in literature. Overall, these results will help to expand our knowledge concerning Spirulina algae and hydrogen yield on the basis of microwave-assisted pyrolysis and reaction temperatures, which will inform the study and design of hydrogen production technologies.

Hydrogen Production from Ethanol Decomposition by Two Microwave Atmospheric Pressure Plasma Sources: Surfatron and TIAGO Torch

Molecular hydrogen production from ethanol decomposition by two microwave atmospheric pressure plasma sources (surfatron and Torche a Injection Axiale sur Guide d’Onde (TIAGO) torch) was studied by optical emission spectroscopy and mass spectrometry. In both cases ethanol was almost completely decomposed, thus giving place to molecular hydrogen. However, the atmosphere surrounding the discharge significantly influences the overall decomposition process. When the surfatron is used, C2H2 and CO are obtained as exhaust gases. Likewise, H2O and HCN are also detected at plasma exit when sustained with the TIAGO torch.

Atomic oxygen TALIF measurements in an atmospheric-pressure microwave plasma jet with in situ xenon calibration

Two-photon absorption laser-induced fluorescence (TALIF) is used to measure the absolute density of atomic oxygen (O) in a coaxial microwave jet in ambient air at atmospheric pressure, operated with a mixture of He and a few per cent of air. The TALIF signal is calibrated using a gas mixture containing Xe. A novel method to perform calibration in situ, at atmospheric pressure, is introduced. The branching ratios of several Xe mixtures are reported, to enable us to perform the Xe calibration without the need for a vacuum vessel. The O densities are measured spatially resolved, and as a function of admixed air to the He, and microwave power. The electron density and temperatures are measured using Thomson scattering, and the N2 and O2 densities are measured using Raman scattering. O densities are found to have a maximum of (4–6) × 1022 m−3, which indicate that O2 is close to fully dissociated in the plasma. This is confirmed by the Raman scattering measurements. O is found to recombine mainly into species other than O2 in the afterglow, which is suggested to consist of O3 and oxidized components of NO.

Atmospheric pressure microwave plasma source for hydrogen production

Nowadays hydrogen is considered as a clean energy carrier and fuel of the future. That is why the interest in production and storage of hydrogen is still increasing. One of the promising technology is using microwave plasma for hydrogen production. In this study we propose two types of an atmospheric pressure microwave plasma source (MPS) for hydrogen production via methane conversion. The first one was a nozzleless waveguide-supplied coaxial-line-based. The second one was a nozzleless waveguide-supplied metal-cylinder-based. They can be operated with microwave frequency of 2.45 GHz and power up to a few kW with a high gas flow rates (up to several thousands l/h). We present experimental results concerning electrical properties of the MPS, plasma visualization, spectroscopic diagnostics and hydrogen production. The experiment was carried out with methane flow rate up to 12,000 l/h. An additional nitrogen or carbon dioxide swirl flow was used. The absorbed microwave power was up to 5000 W. Our experiments show that MPSs presented in this paper have a high potential for hydrogen production via hydrocarbon conversion.

Disinfection of Bacillus globigii Spores Using an Atmospheric Pressure Microwave Plasma System

AbstractThis paper examines the application of atmospheric pressure microwave plasma (APMP) for disinfection of water contaminated by Bacillus globigii spores. The results were most promising when He−H2 or O2 were used as plasma gases. The most probable cause for disinfection due to He−H2 plasma can be attributed to the presence of germicidal ultraviolet radiation. On the other hand, the presence of metastable oxygen species (which are very reactive) in the oxygen plasma effluents was attributed as the most likely cause of sterilization of Bacillus globigii spores. By choosing the correct combination of gas mixtures and microwave power level, the authors were able to achieve greater than log5 inactivation. AMPM may be a suitable alternative to traditional disinfection techniques (e.g. chlorination) when they are difficult or impracticable.