Microwave Plasma Torch Research Articles

Production of hydrogen-rich syngas from methane reforming by steam microwave plasma

Steam-methane reforming (SMR) is most commonly carried out in a catalytic reactor at temperatures from 700 to 1000°C. During the reforming reaction, the catalyst agglomerates under the high temperatures, showing degradation of catalytic performance with carbon deposition on the catalyst surface. Here, we report methane reforming in a steam plasma generated by microwaves at atmospheric pressure without the use of catalysts. The plasma reforming system is mainly composed of a 2.45GHz microwave plasma torch and a plasma nozzle. Methane gas is introduced into the steam microwave plasma, which is stabilized by a swirl flow. The steam microwave plasma provides highly active species and a high-temperature plasma flame, enhancing the chemical reaction rate and eliminating the need for catalysts. We investigated the dependence of the hydrogen concentration on the steam to carbon ratio at a given plasma power. Using a specially designed plasma nozzle, we achieved high hydrogen concentrations (>70vol.%) in the effluent streams.

Disintegration of Carbon Dioxide Molecules in a Microwave Plasma Torch.

A pure carbon dioxide torch is generated by making use of 2.45 GHz microwave. Carbon dioxide gas becomes the working gas and produces a stable carbon dioxide torch. The torch volume is almost linearly proportional to the microwave power. Temperature of the torch flame is measured by making use of optical spectroscopy and thermocouple. Two distinctive regions are exhibited, a bright, whitish region of high-temperature zone and a bluish, dimmer region of relatively low-temperature zone. Study of carbon dioxide disintegration and gas temperature effects on the molecular fraction characteristics in the carbon dioxide plasma of a microwave plasma torch under atmospheric pressure is carried out. An analytical investigation of carbon dioxide disintegration indicates that substantial fraction of carbon dioxide molecules disintegrate and form other compounds in the torch. For example, the normalized particle densities at center of plasma are given by nCO2/nN = 6.12 × 10−3, nCO/nN = 0.13, nC/nN = 0.24, nO/nN = 0.61, nC2/nN = 8.32 × 10−7, nO2/nN = 5.39 × 10−5, where nCO2, nCO, nC, nO, nC2, and nO2 are carbon dioxide, carbon monoxide, carbon and oxygen atom, carbon and oxygen molecule densities, respectively. nN is the neutral particle density. Emission profiles of the oxygen and carbon atom radicals and the carbon monoxide molecules confirm the theoretical predictions of carbon dioxide disintegration in the torch.

Characteristics of plasma sterilizer using microwave torch plasma with AC high-voltage discharge plasma

Microwave plasma sterilization has recently been attracting attention for medical applications. However, it is difficult to perform low-temperature sterilization in short time periods. Increasing the output power shortens the time required for sterilization but causes the temperature to increase. To overcome this issue, we have developed a hybrid plasma system that combines a microwave torch plasma and a high-voltage mesh plasma, which allows radicals to be produced at low temperatures. Using this system, successful sterilization was shown to be possible in a period of 45 min at a temperature of 41 °C.

Experimental research on ethanol-chemistry decomposition routes in a microwave plasma torch for hydrogen production

The study of ethanol decomposition process to produce hydrogen using an argon microwave plasma sustained by a Torche à Injection Axiale sur Guide d’Ondes opened to the atmosphere is presented. Different species in the discharge as well as by-products were detected depending on the amounts of both argon and ethanol flows used to sustain the discharge, which were related to the relative influence of air from the atmosphere surrounding the discharge. Furthermore, plasma gas temperature value was found to have a noticeable influence on ethanol decomposition chemistry; giving place to two different ethanol decomposition routes: (i) for higher temperatures (>4500K), ethanol decomposition produced H2, CO and carbon powder, whereas, (ii) at lower gas temperature (<4500K), ethanol was mainly decomposed forming H2, H2O and CO with CO2. These results indicate that the complete ethanol decomposition by means of a microwave plasma sustained with high gas temperatures results in the production of hydrogen through a clean and simple process.

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

Synthesis of Titanium Dioxide by Microwave Plasma Torch.

In this study, TiO2 nanoparticles were synthesized from titanium tetraisopropanol (TTIP) using a microwave plasma torch (MPT) and characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermogravimetry analysis (TGA). The visible light photocatalysis was studied by the decomposition of methylene blue. MB present in the aqueous solution could be almost completely (> 70%) decomposed within about 720 min of reaction time under visible light irradiation. This is due to the carbon-compounds on the surface of TiO2 (TiOC) corresponding to the results of FTIR. Furthermore, a decrease in recombination between the electron and hole was induced by the existence of TiOC.

Assessment of the Effects of Nitrogen Plasma and Plasma‐Generated Nitric Oxide on Early Development of Coriandum sativum

Potentiality of non‐thermal atmospheric pressure plasma in activating plant development has been evaluated in this study. Seed germination rate of Coriander sativum, a herbaceous plant with slow germination rate, has been significantly increased over time compared to control after micro DBD (dielectric barrier discharge) plasma treatment with N2 feeding gas. No more increase in seed germination has been observed when the transferred energy dose was over 0.65 J per seed during plasma generation, regardless of feeding gases. Germination and seedling growth have been also elevated by plasma‐generated nitric oxide (PGNO) produced from microwave plasma torch in dose dependent manner and a threshold concentration of nitric oxide (NO) activating coriander development has been observed. Our data indicate that plasma energy transferred to seeds or PGNO can activate developmental processes in plant.

Abatement of fluorinated compounds using a 2.45 GHz microwave plasma torch with a reverse vortex plasma reactor

Abatement of fluorinated compounds (FCs) used in semiconductor and display industries has received an attention due to the increasingly stricter regulation on their emission. We have developed a 2.45GHz microwave plasma torch with reverse vortex reactor (RVR). In order to design a reverse vortex plasma reactor, we calculated a volume fraction and temperature distribution of discharge gas and waste gas in RVR by ANSYS CFX of computational fluid dynamics (CFD) simulation code. Abatement experiments have been performed with respect to SF6, NF3 by varying plasma power and N2 flow rates, and FCs concentration. Detailed experiments were conducted on the abatement of NF3 and SF6 in terms of destruction and removal efficiency (DRE) using Fourier transform infrared (FTIR). The DRE of 99.9% for NF3 was achieved without an additive gas at the N2 flow rate of 150 liter per minute (L/min) by applying a microwave power of 6kW with RVR. Also, a DRE of SF6 was 99.99% at the N2 flow rate of 60 L/min using an applied microwave power of 6kW. The performance of reverse vortex reactor increased about 43% of NF3 and 29% of SF6 abatements results definition by decomposition energy per liter more than conventional vortex reactor.

Production of nitric oxide using a microwave plasma torch and its application to fungal cell differentiation

The generation of nitric oxide by a microwave plasma torch is proposed for its application to cell differentiation. A microwave plasma torch was developed based on basic kinetic theory. The analytical theory indicates that nitric oxide density is nearly proportional to oxygen molecular density and that the high-temperature flame is an effective means of generating nitric oxide. Experimental data pertaining to nitric oxide production are presented in terms of the oxygen input in units of cubic centimeters per minute. The apparent length of the torch flame increases as the oxygen input increases. The various levels of nitric oxide are observed depending on the flow rate of nitrogen gas, the mole fraction of oxygen gas, and the microwave power. In order to evaluate the potential of nitric oxide as an activator of cell differentiation, we applied nitric oxide generated from the microwave plasma torch to a model microbial cell (Neurospora crassa: non-pathogenic fungus). Germination and hyphal differentiation of fungal cells were not dramatically changed but there was a significant increase in spore formation after treatment with nitric oxide. In addition, the expression level of a sporulation related gene acon-3 was significantly elevated after 24 h upon nitric oxide treatment. Increase in the level of nitric oxide, nitrite and nitrate in water after nitric oxide treatment seems to be responsible for activation of fungal sporulation. Our results suggest that nitric oxide generated by plasma can be used as a possible activator of cell differentiation and development.

On the interplay of gas dynamics and the electromagnetic field in an atmospheric Ar/H2 microwave plasma torch

A complementary simulation and experimental study of an atmospheric pressure microwave torch operating in pure argon or argon/hydrogen mixtures is presented. The modelling part describes a numerical model coupling the gas dynamics and mixing to the electromagnetic field simulations. Since the numerical model is not fully self-consistent and requires the electron density as an input, quite extensive spatially resolved Stark broadening measurements were performed for various gas compositions and input powers. In addition, the experimental part includes Rayleigh scattering measurements, which are used for the validation of the model. The paper comments on the changes in the gas temperature and hydrogen dissociation with the gas composition and input power, showing in particular that the dependence on the gas composition is relatively strong and non-monotonic. In addition, the work provides interesting insight into the plasma sustainment mechanism by showing that the power absorption profile in the plasma has two distinct maxima: one at the nozzle tip and one further upstream.

MEMS Carbon Nanotubes Field Emission Pressure Sensor With Simplified Design: Performance and Field Emission Properties Study

The pressure sensor application gained recently substantial interest in many fields of basic and applied research and applications. In this paper, microelectromechanical system (MEMS)-based pressure sensor contains nanostructured electrode consisting of carbon nanotube (CNT) array. CNTs are directly grown on such electrode by plasma-enhanced chemical vapor deposition method using microwave plasma torch at atmospheric pressure. This growth method enables us to use a simple electrode structure without need of buffer layer and time-consuming lithography process. Combination of CNTs field emission and MEMS membrane mechanical properties make possible to enhance sensitivity of the sensor. Field emission properties of CNTs are measured by newly developed system enabling us precise measurement of expecting properties, such as dependence on diaphragm (upper electrode) distance, applied voltage, and stability of the sensor. Measured values are compared with a numerical modeling of the membrane system in Coventor Ware software by finite-element method. We also suggest encapsulating the sensor using glass frit bonding because such method is more suitable for high vacuum requirements of the field emission operation.

Sensing Properties of Multiwalled Carbon Nanotubes Grown in MW Plasma Torch: Electronic and Electrochemical Behavior, Gas Sensing, Field Emission, IR Absorption

Vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) with an average diameter below 80 nm and a thickness of the uniform VA-MWCNT layer of about 16 μm were grown in microwave plasma torch and tested for selected functional properties. IR absorption important for a construction of bolometers was studied by Fourier transform infrared spectroscopy. Basic electrochemical characterization was performed by cyclic voltammetry. Comparing the obtained results with the standard or MWCNT‐modified screen-printed electrodes, the prepared VA-MWCNT electrodes indicated their high potential for the construction of electrochemical sensors. Resistive CNT gas sensor revealed a good sensitivity to ammonia taking into account room temperature operation. Field emission detected from CNTs was suitable for the pressure sensing application based on the measurement of emission current in the diode structure with bending diaphragm. The advantages of microwave plasma torch growth of CNTs, i.e., fast processing and versatility of the process, can be therefore fully exploited for the integration of surface-bound grown CNTs into various sensing structures.

Some Rare Earth Elements Analysis by Microwave Plasma Torch Coupled with the Linear Ion Trap Mass Spectrometry.

A sensitive mass spectrometric analysis method based on the microwave plasma technique is developed for the fast detection of trace rare earth elements (REEs) in aqueous solution. The plasma was produced from a microwave plasma torch (MPT) under atmospheric pressure and was used as ambient ion source of a linear ion trap mass spectrometer (LTQ). Water samples were directly pneumatically nebulized to flow into the plasma through the central tube of MPT. For some REEs, the generated composite ions were detected in both positive and negative ion modes and further characterized in tandem mass spectrometry. Under the optimized conditions, the limit of detection (LOD) was at the level 0.1 ng/mL using MS2 procedure in negative mode. A single REE analysis can be completed within 2~3 minutes with the relative standard deviation ranging between 2.4% and 21.2% (six repeated measurements) for the 5 experimental runs. Moreover, the recovery rates of these REEs are between the range of 97.6%–122.1%. Two real samples have also been analyzed, including well and orange juice. These experimental data demonstrated that this method is a useful tool for the field analysis of REEs in water and can be used as an alternative supplement of ICP-MS.

Effect of microwave plasma torch on the pyrolysis fuel oil in the presence of methane and ethane to increase hydrogen production

Pyrolysis fuel oil (PFO) processing by microwave plasma torch was developed for the production of hydrogen. The PFO cracking process was performed at atmospheric pressure in the absence of catalyst and effect of plasma gas on the production rate of hydrogen and light hydrocarbons (C2–C4) was evaluated. In the first step, effect of the applied power and the working gas flow rate was investigated. In the second step, the applied power and working gas rate were set to 650 W and 4000 sccm, respectively, which were provided by combining methane or ethane as 0%, 2.5%, 7.5%, and 20% with argon. By increasing the percentage of the existing methane in argon, production rate of the sum of the light hydrocarbons was increased and that of hydrogen was reduced, but it was more than the case when argon was applied alone. By increasing ethane percentage, hydrogen production and light hydrocarbon rate were increased. The best conditions of the plasma gas for producing hydrogen at the power of 650 W were obtained as 5CC PFO feed, 2500 sccm (80%) argon, and 500 sccm (20%). The hydrogen production rate in optimized conditions was 2343.16SCCM with selectivity of 84.41%. Sum of the obtained hydrocarbons in this test was 434.25 sccm. Another parameter in the present study was the feed volume processed by plasma. In this case, 5 cc, 3 cc, and 1 cc of the feed were tested when the plasma gas was 3000 sccm argon with the power of 650 W. The results showed that, by increasing the feed, the products were increased. In the processing of 5 cc feed with plasma, 896.41 sccm hydrogen and 61 sccm light hydrocarbon were produced.

Hydrogen and By-Products Formation After the Decomposition of Ethanol by Means of a Microwave Plasma Torch at Atmospheric Pressure

Argon TIAGO torch plasma in air ambience has been studied to produce the decomposition of ethanol obtaining hydrogen at the plasma exit. Dependence of by-products formed on ethanol flows has been studied. Ethanol molecules were completely decomposed, and an important conversion to hydrogen was obtained. Images of plasma generated in these conditions are presented.

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.

Volatile Organic Compound Elimination Improved on Inlet Position of Vortex Gas in Microwave Torch Plasma

A simulated experiment on purification of volatile organic compounds (VOCs) was carried out in two vortex flow reactors, which consisted of a microwave plasma torch and a reaction chamber with a fuel injector. One is the reactor with a conventional vortex flow, and the other is with a reverse vortex flow. Injection of hydrocarbon fuels into a high-temperature microwave torch plasma provides a plasma flame. The plasma flame can eliminate the odorous chemical agent diluted in air or purify the contaminated air of a large volume from continuous emission. The reverse vortex reactor eliminated VOCs diluted in an airflow rate of 10000 lpm, showing β-value of 80.39 J/L, while the conventional vortex reactor eliminated VOCs with β-value of 100.26 J/L.

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.

Optical and Structural Properties of ZnO Nanoparticles Synthesized by CO2 Microwave Plasma at Atmospheric Pressure

The results of carbon-doped zinc oxide nanoparticles synthesized by CO2 microwave plasma at atmospheric pressure are presented. The 2.45-GHz microwave plasma torch and feeder for injecting Zn granules are used in the synthesis of zinc oxide nanoparticles. The Zn granules (13.5 g/min) were introduced into the microwave plasma by CO2 (5 l/min) swirl gas. The microwave power delivered to the CO2 microwave plasma was 1 kW. The synthesis of carbon-doped zinc oxide nanoparticles was carried out in accordance with CO2 + Zn → carbon-doped ZnO + CO. The synthesized carbon-doped zinc oxide nanoparticles have a high purity hexagonal phase. The absorption edge of carbon-doped zinc oxide nanoparticles exhibited a red shift from a high-energy wavelength to lower in the UV-visible spectrum, due to band gap narrowing. A UV-NIR spectrometer, X-ray diffraction, emission scanning electron-microscopy, energy dispersive X-ray microanalysis, Fourier transform infrared spectroscopy, and a UV-Vis-NIR spectrophotometer were used for the characterization of the as-produced products.