Argon-methane Mixture Research Articles

Simulation of a Microwave Plasma Torch Used for Hydrogen Production via Methane Pyrolysis

ABSTRACTHydrogen is often envisioned as a green fuel and energy carrier. However, a greenhouse gas‐free production method is still needed for this purpose. A promising method is the pyrolysis of methane. In this study, we present the three‐dimensional simulation of methane pyrolysis in a microwave plasma torch operated in an argon–methane mixture. Due to the high gas temperatures, the chemistry is dominated by reactions between neutral particles. Therefore, the plasma is treated only as a heat source using space‐resolved gas temperature measurements as input. The end‐of‐pipe results of the simulation are compared to measured values, showing good agreement for methane conversion.

A Multiscale Method for Two-Component, Two-Phase Flow with a Neural Network Surrogate

Understanding the dynamics of phase boundaries in fluids requires quantitative knowledge about the microscale processes at the interface. We consider the sharp-interface motion of the compressible two-component flow and propose a heterogeneous multiscale method (HMM) to describe the flow fields accurately. The multiscale approach combines a hyperbolic system of balance laws on the continuum scale with molecular-dynamics (MD) simulations on the microscale level. Notably, the multiscale approach is necessary to compute the interface dynamics because there is—at present—no closed continuum-scale model. The basic HMM relies on a moving-mesh finite-volume method and has been introduced recently for the compressible one-component flow with phase transitions by Magiera and Rohde in (J Comput Phys 469: 111551, 2022). To overcome the numerical complexity of the MD microscale model, a deep neural network is employed as an efficient surrogate model. The entire approach is finally applied to simulate droplet dynamics for argon-methane mixtures in several space dimensions. To our knowledge, such compressible two-phase dynamics accounting for microscale phase-change transfer rates have not yet been computed.

Spectral study of argon-methane mixture plasma jet generated by a DC plasmatron

We present the results of studying optical emission spectra of Ar:CH4 plasma produced on a DC plasmatron for graphene synthesis. We have identified the basic set of spectral lines and bands in the obtained spectra and shown that H lines and C2 bands appear due to direct excitation by an electron strike of corresponding neutral particles. C2 molecular bands were also identified in the spectra with intensity considerably lower compared to previous studies where He: C2H2 mixture was used as plasma-forming gas.

Photoelectron Collection Efficiency Measurement of Vp81 Photocathode

We present experimental measurement of photoelectron collection efficiency of a new organic semiconductor photocathode Vp81in pure methane and argon methane mixtures in different ratios as a function of applied reduced electric field at a gas pressure of 200 torr. It is confirmed that collection efficiency increases in charge collection mode and reaches near the vacuum value at high gas gain. The general universal behavior was also confirmed as predicted by some authors.

Compression–Expansion Processes for Chemical Energy Storage: Thermodynamic Optimization for Methane, Ethane and Hydrogen

Several methods for chemical energy storage have been discussed recently in the context of fluctuating energy sources, such as wind and solar energy conversion. Here a compression–expansion process, as also used in piston engines or compressors, is investigated to evaluate its potential for the conversion of mechanical energy to chemical energy, or more correctly, exergy. A thermodynamically limiting adiabatic compression–chemical equilibration–expansion cycle is modeled and optimized for the amount of stored energy with realistic parameter bounds of initial temperature, pressure, compression ratio and composition. As an example of the method, initial mixture compositions of methane, ethane, hydrogen and argon are optimized and the results discussed. In addition to the stored exergy, the main products (acetylene, benzene, and hydrogen) and exergetic losses of this thermodynamically limiting cycle are also analyzed, and the volumetric and specific work are discussed as objective functions. It was found that the optimal mixtures are binary methane argon mixtures with high argon content. The predicted exergy losses due to chemical equilibration are generally below 10%, and the chemical exergy of the initial mixture can be increased or chemically up-converted due to the work input by approximately 11% in such a thermodynamically limiting process, which appears promising.

Development of a radio frequency atmospheric pressure plasma jet for diamond-like carbon coatings on stainless steel substrates

In this paper, an atmospheric pressure plasma jet with capacitively coupled radio frequency discharge was developed for diamond-like carbon (DLC) coatings on stainless steel substrates. The plasma jet was generated by argon–methane mixture and its physical parameters were investigated. Relation between the plasma jet length and width of the powered electrode was discussed. Optical and electrical characteristics were studied by optical emission spectroscopy, voltage and current probes, respectively. The evolutions of various species like ArI, C2 and CH along the jet axis were investigated. Electron temperature and density were estimated by Boltzmann plot method and Saha–Boltzmann equation, respectively. Finally, a diamond-like carbon coating was deposited on stainless steel-304 substrates by the atmospheric pressure radio frequency plasma jet in ambient air. Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy and Vickers hardness test were used to study the deposited films. The length of the jet was increased by increasing the width of the powered electrode. The estimated electron temperature and density were 1.43 eV and 1.39 × 1015 cm−3, respectively. Averaged Vicker’s hardness of the coated sample was three times greater than that of the substrate. The SEM images of the deposited thin films revealed a 4.5 μm DLC coated for 20 min.

A multiscale transport model for Lennard-Jones binary mixtures based on interfacial friction.

We propose a one-dimensional isothermal hydrodynamic transport model for non-reacting binary mixtures in slit shaped nanochannels. The coupled species momentum equations contain viscous dissipation and interspecies friction term of Maxwell-Stefan form. Species partial viscosity variations in the confinement are modeled using the van der Waals one fluid approximation and the local average density method. Species specific macroscopic friction coefficient based Robin boundary conditions are provided to capture the species wall slip effects. The value of this friction coefficient is computed using a species specific generalized Langevin formulation. Gravity driven flow of methane-hydrogen and methane-argon mixtures confined between graphene slit shaped nanochannels are considered as examples. The proposed model yields good quantitative agreement with the velocity profiles obtained from the non-equilibrium molecular dynamics simulations. The mixtures considered are observed to behave as single species pseudo fluid, with the interfacial friction displaying linear dependence on molar composition of the mixture. The results also indicate that the different species have different slip lengths, which remain unchanged with the channel width.

Role of gas-phase and surface chemistry in methane reforming using a [formula omitted] oxygen transport membrane

This study investigates the performance of a La0.9Ca0.1FeO3−δ (LCF) membrane for applications including oxyfuel combustion, CO2 reuse and syngas production under a reactive environment using methane (CH4)–argon (Ar)–carbon dioxide (CO2) mixtures in the sweep stream. Through experimental measurements, we show that an LCF membrane can act as a catalyst for methane pyrolysis driven by the presence of iron at the B-site of the perovskite structure. Using methane–argon mixtures, the oxygen flux JO2 increases by one order of magnitude compared to the case with no methane. Measurements in the range of 900–950 °C suggest that the aforementioned enhancement is related to surface reactions consuming oxygen ions at the membrane surface. However, JO2 levels off when the inlet CH4 mole fraction reaches approximately 5%. The same applies for methane conversion. Addition of CO2 into the sweep stream has a significant impact on JO2 rise and syngas production. As more CO2 is added, surface carbon monoxide (CO) and hydrogen (H2) mole fractions increase by an order of magnitude. The high yield of syngas at the membrane surface results in a higher JO2 as more reactants participate in heterogeneous reactions with oxygen ions; methane conversion reaches approximately 100% showing that dry reforming (in the gas-phase) plays an important role. This oxygen flux enhancement is accompanied by significant reuse of CO2. The proposed technology can have a major impact on the CO2 recycle and the effort to mitigate its accumulation in the atmosphere.

Influence of the initial composition of a methane-argon mixture on the electricophysical parameters and plasma composition of DC glow discharge

The stationary parameters and composition of DC glow discharge plasma (p = 40–200 Pa, i = 30–70 mA) in CH4-Ar mixtures of different compositions have been studied by probe diagnostics and mathematical simulation. Data on the influence of the initial composition of the plasma-forming mixture on the reduced electric field strength, energy electron distribution, rate constants of processes under electron impact, stationary concentrations, and flux densities of neutral and charged particles have been obtained.

The effects of dissolved methane upon liquid argon scintillation light

In this paper we report on measurements of the effects of dissolved methane upon argon scintillation light. We monitor the light yield from an alpha source held 20 cm from a cryogenic photomultiplier tube (PMT) assembly as methane is injected into a high-purity liquid argon volume. We observe significant suppression of the scintillation light yield by dissolved methane at the 10 part per billion (ppb) level. By examining the late scintillation light time constant, we determine that this loss is caused by an absorption process and also see some evidence of methane-induced scintillation quenching at higher concentrations (50-100 ppb). Using a second PMT assembly we look for visible re-emission features from the dissolved methane which have been reported in gas-phase argon methane mixtures, and we find no evidence of visible re-emission from liquid-phase argon methane mixtures at concentrations between 10 ppb and 0.1%.

Influence of CHx thickness layer on the sensing properties of CHx/PS/Si structure against CO2 gas

In this work, we report a study on the influence of hydrocarbon groups (CHx) thickness layer on sensing properties of CHx/Porous Silicon (PS)/Si structures against CO2 gas. The hydrocarbon groups were deposited by plasma of methane–argon mixture. The properties of these structures are investigated by current–voltage, current–time and capacitance–voltage measurements from where a different behaviour depending on CHx layer thickness has been observed. The results show that current–voltage and impedance–voltage characteristics are modified by the gas reactivity on the CHx/PS surface. As the CHx layer thickness increases, the series resistance and the ideality factor of the structure increase. In addition, the response and recovery times of the sensor decrease with increasing the CHx thickness. Finally, the results point out the effect of CHx coating on the sensitivity of the CHx/PS/Si sensor.

Hydrogen production through plasma cracking of hydrocarbons: Effect of carrier gas and hydrocarbon type

In this study, characteristics of the nano-second pulsed dielectric barrier discharge (DBD) are experimentally investigated to clarify the effect of hydrocarbon feed chain length and carrier gas type (Ar–CH4 mixtures) on hydrogen production through plasma cracking. C1–C16 straight-chain alkanes are employed to survey the effect of hydrocarbon feed chain length. It is concluded that nonthermal plasma (NTP) is effective in cracking of wide range of fuels from light gaseous to heavy hydrocarbons into hydrogen. The reactor performance increases significantly due to increase of carbon number of hydrocarbon feed. Energy efficiency and hydrogen production rate vary between 23.8 and 121.1l/kWh and 17.04 and 34.05ml/min in the produced gas respectively. The highest energy efficiency is achieved when n-hexadecane is used as a feed with 55.5W discharge power. Due to electron energy consumed in dissociation of methane, hydrocarbon cracking is more efficient in argon than in argon–methane mixtures. The absence of carbon monoxide and carbon dioxide as by-products in the product gas is also highly desirable for proton-exchange membrane (PEM) fuel cells.

Mass-Spectrometry of Supersonic Cluster Jets of Methane and Argon-Methane Mixtures

We describe a new experimental facility LEMPUS-2, which provides experimental research in supersonic flows of gases and gas mixtures in the oil-free vacuum. Model experiments in a flow of pure argon in order to verify and test the diagnostic equipment of set-up were performed. Experimental studies of the formation of cluster beams of methane and argon-methane mixtures have been performed to determine the optimal conditions for the formation of intense molecular beams of methane clusters. We obtain an intense molecular beam of methane clusters. It was found that in a supersonic jet of large size pure methane clusters are not diagnosed by the mass spectrum of oligomeric fragments, whereas in mixtures of argon with small admixtures of methane is recorded in the mass spectrum, apparently as oligomers of methane and mixed clusters of argon-methane . It was confirmed that the clustering of methane starts at lower pressures of inhibition than argon and lead to further delay of cluster formation in argon. It is shown that for high intensity methane clusters fluxes should be used specially selected gas mixtures

Optical and mechanical properties of hydrogenated amorphous carbon

We have measured the refractive index and microhardness of hydrogenated amorphous carbon films grown on quartz and silicon substrates from a methane-argon mixture under various conditions: E/p = 40–180 V/mPa (E is the electric field between electrodes and p is the gas pressure in the deposition chamber) and substrate temperatures from 50 to 300°C. Such conditions enable the growth of diamond-, polymer-, and graphite-like a-C:H films with wide ranges of microhardness values and refractive indices.

Numerical simulation of a tubular solar reactor for methane cracking

This study addresses the solar thermal cracking of methane for the co-production of hydrogen and carbon black as a medium to avoid CO 2 emissions from natural gas combustion processes. The objective of this work is to numerically simulate the transport processes of momentum heat and mass in an indirect heating solar reactor, which is fed with an argon-methane mixture. The reactor is composed of a cubic cavity receiver, which absorbs concentrated solar irradiation through a quartz window and a graphite reaction tube is settled vertically inside this cavity. A series of numerical experiments were carried out in order to gain a better understanding of the interaction between the several transport phenomena taking place. The simulations showed that, in general, when the temperature of the reaction chamber is higher than 2000 K, the methane conversion is practically 100%. To validate our simulation results we compared them with available experimental data obtaining good agreement. Moreover, our results clearly evidence that most of the reaction takes place at the bottom of the reactor, which is the zone with the highest temperature profiles. Therefore, we propose modifications in the reactor design to increase conversion. The results of this work can thus serve to improve design and control of solar reactors for light hydrocarbons.

Electrical, optical, and mechanical properties of amorphous hydrogenated carbon obtained under various deposition conditions

Activation energy of dc conductivity, refractive index, and microhardness of amorphous hydrogenated carbon films a-C:H have been studied. The films are produced from a methane-argon mixture under various deposition conditions on quartz and silicon substrates: E/p = 40–180 V/mPa (E is the electric-field strength in the space between the electrodes, and p is the gas mixture pressure in the chamber) and substrate temperature Ts = 50–300°C. In these deposition conditions, diamond-like, polymer-like, and graphite-like a-C:H films can be obtained with widely varying activation energy of conductivity, microhardness, and refractive index.

Experimental Evaluation of Indirect Heating Tubular Reactors for Solar Methane Pyrolysis

Solar thermal pyrolysis of natural gas is studied for the co-production of hydrogen, a promising energy carrier, and Carbon Black, a high-value nano-material, with the bonus of zero CO2 emissions. A 10 kW multi-tubular solar reactor (SR10) based on the indirect heating concept was designed, constructed and tested. It is composed of an insulated cubic cavity receiver (20 cm side) that absorbs concentrated solar irradiation through a quartz window by a 9 cm-diameter aperture. The solar concentrating system is the 1 MW solar furnace of CNRS-PROMES laboratory. An argon-methane mixture flows inside four graphite tubular reaction zones each composed of two concentric tubes that are settled vertically inside the cavity. Experimental runs mainly showed the key influence of the residence time and temperature on the reaction extent. Since SR10 design presented a weak recovery of carbon black in the filter, a single tube configuration was tested with an external plasma heating source. Complete methane conversion and hydrogen yield beyond 80% were achieved at 2073K. Hydrogen and carbon mass balances showed that C2H2 intermediates affect drastically the carbon black production yield: about half of the initial carbon content in the CH4 was found as C2H2 in the outlet gas. Nevertheless, the carbon black recovery in the filtering device was improved with this new configuration. Data are extrapolated to predict the possible hydrogen and carbon production for a future 50 kW solar reactor. The expected production was estimated to be about 2.47 Nm3/h H2 and 386 g/h carbon black for 1.47 Nm3/h of CH4 injected.

Low-Power Microwave-Discharge Forms in Hydrocarbon Atmosphere

Different forms of the steady-state microwave discharges in argon-methane mixture at atmospheric pressure find great interest in exploring both nature phenomena and finding wide-technology applications, like coating, welding, plasma-induced chemical catalysis, or as a plasmatron for the ignitions of flames in different applications. Atmospheric microwave discharges are attractive in that they demand no pumping systems and are easy to access, explore, and manipulate. A 7-GHz generator (15-150 W) coupled with microwave coaxial plasma burner was used for plasma production in argon/methane flow (1-10 L/min). The possibility of synthesizing carbon materials by carbon vapor deposition in conditions of such discharge was demonstrated. Growing of the 5-cm-long carbon filament was observed with the speed of up to 1 cm/min. Pictures of plasma forms and synthesized samples are presented.

The influence of CH x coating on the optical properties of porous silicon

In this work, we report a study on the influence of CH x thickness layer on optical properties of CH x /PS/Si structures. The hydrocarbon groups were deposited by plasma of methane–argon mixture. The properties of these structures are investigated by photoluminescence (PL), reflection and spectral response measurements from where a different behavior depending on CH x layer thickness has been observed. The entire total reflection spectrum is modulated by Fabry–Pérot fringes that are a result of thin film interference. As the CH x layer thickness increases, the amplitude of the interferences decreases and a positive shift of the maximum peak is observed. The PL spectra from CH x /PS samples with two CH x layer thicknesses show more intense luminescence than that observed from PS sample and the existence of an optimum thickness CH x that gives the maximum PL intensity. The spectral response spectra show the presence of an intense peak at 450 nm. Finally, the results point out the importance of CH x coating in optoelectronic applications.

Synthesis of Si nanocones using rf microplasma at atmospheric pressure

We report the synthesis of silicon nanocones using the rf microplasma discharge at atmospheric pressure. The products formed underneath the tube electrode on Fe-coated crystalline silicon were constituted mainly of silicon and silicon oxide despite the use of a methane–argon mixture. Carbon nanotubes and silicon nanowires were also formed around the silicon nanocones. The number density and average size of silicon nanocones increased with the plasma exposure time accompanied by the enlargement of their surface distribution. The growth mechanism of silicon nanocones is discussed in terms of the catalytic growth via diffusion of silicon through FeSi x nanoclusters with nanocrystalline Si particle, and Si oxidation due to the plasma heating.