Gas Mixture Of Methane Research Articles

Measurement and analysis of interfacial tension of decane/water system pressurized with methane + ethane + propane gas mixture

Blockages in natural gas and oil pipelines can be caused by the aggregation of clathrate hydrate crystals which form at the oil-water-gas interfaces. Knowledge of interfacial tensions between components are crucial to understanding the interface physical chemistry and numerically simulating pipeline multiphase flow. This study measures the effect of the presence of natural gas components on the oil-water interfacial tension and its potential implications on flow assurance in oil-gas pipelines. Decane is used to mimic oil and is saturated with the gaseous mixture of methane, ethane, and propane as is consistent with simulations of multiphase dynamics. Water droplets were generated in decane and photographed through a window using pendant drop method in order to determine the oil-water interfacial tension. This study examined both mechanical and thermodynamic phenomena by considering interfacial tension under different pressure/temperature conditions covering the natural gas hydrate formation region. The effect of the gas mixture composition and pressure on the interfacial tension was determined at different temperatures in the range of pipeline operating conditions. The behavior was explained from both experimental and theoretical points of view. At lower pressures, the presence of the C2 and C3 natural gas components lowers the decane-water interfacial tension compared to the case of the decane-water-methane system. In particular, the pressure dependence of the interfacial tension was found to be almost five times higher than that in the absence of C2 and C3. By decreasing the interfacial tension, the presence of ethane and propane may facilitate the mixing of the water and oil phases in pipelines, therefore affecting the rate of hydrate formation.

Diamond synthesis on Si by plasma chemical vapor deposition using microwave sheath-voltage combination plasma

Microwave sheath-voltage combination plasma (MVP) represents a new method to generate plasma and coat diamond-like carbon films onto the three-dimensional metal surfaces . The present work investigates the synthesis of diamonds using MVP deposition, focusing in particular on how pressure and bias voltage affect the diamond structure. Using MVP, silicon wafers were coated with diamond in gas mixtures of methane and hydrogen with the substrate bias ranging from 0 to −200 V and pressure ranging from 800 to 1000 Pa. Although diamond particles are created with the substrate biased between 0 and −200 V at 1% methane concentration, at −200 V the particles are affixed atop Si or SiC cones that form on the Si substrate due to plasma etching . X-ray diffraction analysis reveals that the diamond structure is created up to a bias voltage of −100 V at 3% methane concentration. Nanodiamond is produced at methane concentration of 3%. These experiments suggest that MVP, a new diamond coating method, makes depositing the diamond on 3D shape substrates possible. • Diamond coatings are deposited by microwave sheath-voltage combination plasma. • Higher substrate temperature with nonzero bias voltage than with zero bias voltage • Higher negative bias produces cone-like structures on the substrate.

THERMODYNAMIC CALCULATION OF CARBOTHERMIC REDUCTION OF SILICON USING METHANE

Based on the analysis of the equilibrium thermodynamic calculation results, a range of values of the solid silicon dioxide (%m SiO2) mass content is found for obtaining high values of the mass fractions of liquid silicon formed during pyrolysis of a condensed coal and methane gas mixture at atmospheric pressure. The calculated values of this range of the silicon dioxide mass content are consistent with the experimental data obtained.

Highly Conductive Nanocrystalline Diamond Films and Electronic Metallization Scheme.

By using a methane and hydrogen process gas mixture in an appropriate hot-filament CVD process without further dopant, high electrical conductivity of over 100 S/cm has been achieved in nanocrystalline diamond films deposited on silicon single-crystalline substrates. Furthermore, it was found that an oxygen reactive-ion etching process (O-RIE) can improve the diamond film surface’s electron affinity, thus reducing the specific contact resistance. The reduction of the specific contact resistance by a factor of up to 16 was realized by the oxygen ion etching process, down to . We provide a qualitative explanation for the mechanism behind the contact resistance reduction in terms of the electron affinity of the diamond surface. With the aid of XPS, AFM, and surface wetting measurements, we confirmed that a higher surface electron affinity is responsible for the lower specific contact resistance of the oxygen-terminated nanocrystalline diamond films.

Separation of coal mine methane gas mixture via sII and sH hydrate formation

The release of coal mine methane (CMM) or coal bed methane (CBM) to the atmosphere leads to the wastage of a valuable energy resource and contributes to the greenhouse effect. In the present work, CMM has been considered as a mixture of methane and nitrogen (CH4-N2, 30:70 mol%), and this gas mixture has been separated by the hydrate-based gas separation (HBGS) process. Formation of sI hydrate with 70% N2 in the mixture requires significantly higher pressure and thus not suitable for scale-up. Therefore, in this work with a suitable thermodynamic promoter, sII and sH hydrates were formed to study the methane separation from CMM gas mixture at moderate temperature and pressure conditions. sII hydrate formation was carried out using polar THF (Tetrahydrofuran) and non-polar cyclopentane (CP) at different molar concentrations and at 274.2 K temperature. sH hydrate formation was facilitated using polar tert-butyl-methyl-ether (TBME) and non-polar neo-hexane (NH) at different molar concentrations and at 274.2 K temperature. Further, water-soluble hydrate promoter sodium dodecyl sulfate (SDS) was used at 500 ppm to enhance the rate of hydrate formation and thus to achieve better separation efficiency in a given time. For the CMM gas mixture, sII hydrate formation showed better methane recovery compared to sH hydrate formation, whereas sH hydrate formation showed a better separation factor compared to sII hydrate formation. Hydrate dissociation was also carried out to recover the hydrated gas via depressurization and thermal stimulation to compare the effect of polar and non-polar hydrate formers.

Effects of methane ratio on MPDF (micro-pilot dual-fuel) combustion characteristic in a heavy-duty single cylinder engine

In this study, the characteristics of micro-pilot dual-fuel combustion with respect to the fuel mixture ratio in a single cylinder dual-fuel engine have been investigated. In order to analyze the characteristics of micro-pilot dual-fuel combustion, a metal engine and an optical single cylinder dual-fuel engine were used. The fuel mixture ratio was varied for experimental purposes; the diesel was directly injected into combustion chamber and the methane gas was supplied via intake port. The present study reports that increasing the methane mixture ratio from 0 to 97.67% changes the diesel combustion to pre-mixed combustion. As a result, the peak cylinder pressure was increased from 184 to 198 bar, and the rate of heat release was greatly advanced. In the MPDF condition, the nitrogen oxides emissions were reduced by about 90%p, and the fuel conversion efficiency increased about 5%p because of the low combustion temperature of pre-mixed combustion. However, for the same reason, the hydrocarbon emissions were increased about 95%p. The fastest combustion speed was found form the results of methane mixture ratio between 40 and 80%. In the condition of diesel combustion and micro-pilot dual-fuel combustion, the combustion periods of middle and initial were increased, respectively, resulting in the low combustion speed. The standard deviation of peak cylinder pressure, which represents the combustion variation, was correlated with initial combustion period. While the condition of methane gas mixture ratio between 40 and 80% shows the lowest combustion variation, the highest combustion variation was occurred by MPDF condition. Through the optical engine experiment, it can be found that the cycle to cycle combustion variation is ascribed to the turbulent flow and the variation of ignition position. The combustion images show that the unpredictable characteristics of the ignition position and slow flame propagation speed caused the combustion variation in micro-pilot dual-fuel combustion.

Гибридная углерод-углеводородная структура

A new hybrid carbon-hydrocarbon structure was discovered after pumping a gas mixture of methane and hydrogen through 314 – 400 µm synthetic diamond powder. The experiment was carried out on the microwave plasmachemical installation designed for deposition of polycrystalline diamond films. The main parameters during the experiment were the following: the power of the microwave generator 3,5 kW, the flow rate of hydrogen 400 ml/min, methane 20 ml/min, the pressure in the reactor chamber 63 torr. The gas mixture was pumped at pressure drop of 13 torr. The diamond powders were placed in molybdenum cups inserted into a copper pedestal. In the gaps between the diamond particles of the surface layer unidirectional thread-like structures (length 100 – 500 μm, diameter 2 μm) were found, some of which ended in spherical formations (average diameter 18 μm). Such a composition of thread-like structures and spherical formations was called “dandelion” one. Raman spectroscopy was performed to examine the nature of these formations. The thread-like structure was determined as monocrystalline graphite. The surface of the spherical formation was represented by spindle-shaped structures of nanocrystalline graphite (length 2 μm, thickness 200 nm) and nanodiamond grains with trans-polyacetylene chains [C2H2]n.

Mixed matrix membrane containing metal oxide nanosheets for efficient CO2 separation

The two-dimensional (2D) nanosheet zinc cobaltate (ZnCo2O4) was added into polyether block amide (Pebax) matrix to prepare mixing matrix membrane (MMM) for separating carbon dioxide (CO2)/methane (CH4) gas mixture. The 2D porous ZnCo2O4 nanosheets were composed of chemically interconnected metal oxide nanoparticles. The ZnCo2O4 nanoparticles in the nanosheets constructed large-quantity pores of 11.78 nm and provided abundant transfer channels for gas molecule. Moreover, the synergistic effect of bimetallic Zn2+ and Co2+ would promote the generation of oxygen vacancies (Oδ−), which could provide more CO2 (Cδ+) adsorption sites, thereby increased the selectivity of the membrane. The large aspect ratio of the ultra-thin ZnCo2O4 nanosheets showed better dispersion in the membrane. The pure gas separation performance data showed the CO2 permeability and CO2/CH4 selectivity of Pebax/ZnCo2O4 membrane were 139.10 Barrer and 15.38, respectively, when the filling amount was 0.5 wt%. Compared with pure Pebax membrane, the separation performance (permeability and selectivity) were increased with 165.67% and 75.57%, respectively.

High-Sensitive Gas-Mixture Detection Using Localized Surface Plasmon Resonance Behavior in an Optimized MDM Array

A gas-mixture sensor based on local surface plasmon resonance (LSPR) behavior in metal-dielectric-metal (MDM) periodic array is proposed. The comparisons of gas sensing performance between metal-dielectric (MD) and MDM structure are discussed for single-gas and gas-mixture separately. The influence of MDM structural parameters on the extinction spectrum and gas sensitivity are analyzed to obtain optimal parameters. By replacing the dielectric with suitable gas-sensitive films, the gas mixture of methane and hydrogen can be accurately measured without interfering with each other. The methane and hydrogen sensitivities can reach to −3.435nm /% and −0.72nm /%, respectively. The results also verify the feasibility of multi-channel gas detection and provide an effective method for gas component analysis.

VECSEL-based virtually imaged phased array spectrometer for rapid gas phase detection in the mid-infrared.

We present a novel, to the best of our knowledge, system for high-resolution, time-resolved spectroscopy in the mid-wave infrared based on a modelocked vertical external cavity surface emitting laser (VECSEL) frequency comb coupled to a virtually imaged phased array (VIPA) spectrometer. The GHz level repetition rate of VECSEL-based systems coupled to VIPA spectrometers enables comb tooth resolved spectra without the use of additional filter cavities often required to increase comb tooth spacing. We demonstrate absorption spectroscopy on a methane (CH4) gas mixture at 2900cm-1 (3.4 µm) with over 35cm-1 spectral bandwidth in a single image. Rapid time-resolved measurements were made using a 300 µs exposure time with an acquisition rate limited to 125 Hz by the available camera. High-resolution absolute frequency measurements were performed by scanning the repetition rate of the VECSEL frequency comb.

Shock-induced ignition and pyrolysis of high-pressure methane and natural gas mixtures

A high-pressure shock tube was used to study ignition delay times (IDT) of CH4/O2/Ar and natural gas/O2/Ar mixtures behind reflected shock waves. Reaction progress was monitored using sidewall pressure and direct laser absorption diagnostics of CH4 near 3.175 µm and ethylene near 10.532 µm. Stoichiometric, fuel-rich and fuel-lean mixtures of CH4/O2, highly dilute in argon, were studied over a temperature range from 1450 to 1850 K and pressures between 10 and 55 atm. Of note are the experiments conducted with fuel-rich mixtures, as there is a lack of literature data in this regime. In the current study, the methane absorption diagnostic provided a unique tool enabling both speciation of methane and a clear definition of ignition delay time. In addition to methane oxidation, we have measured ignition delay times of commercial natural gas blends over a temperature range of 1408–1541 K, at pressures near 12 atm, and at an equivalence ratio of 1. To understand the effects of minor constituents (such as ethane and propane) in commercial natural gas blends, ethylene concentration during pyrolysis experiments was monitored using a two-wavelength scheme (10.532 µm and 10.674 µm) using a CO2 gas laser. The deficiency of existing kinetic models towards predicting the high-temperature kinetics of natural gas blends was highlighted through our measurements. Therefore, this study also provides data critical for refining these models. Extensive sensitivity analysis emphasizes the importance of the reaction CH3+C2H6→CH4+C2H5 during natural gas pyrolysis, and the accuracy of the chemical kinetic models is significantly improved by using a revised reaction rate constant (Shao et al. 2019) for this reaction. These measurements extend the test conditions of earlier studies of methane and commercial natural gas.

Modeling viscosity of methane, nitrogen, and hydrocarbon gas mixtures at ultra-high pressures and temperatures using group method of data handling and gene expression programming techniques

Accurate gas viscosity determination is an important issue in the oil and gas industries. Experimental approaches for gas viscosity measurement are time-consuming, expensive and hardly possible at high pressures and high temperatures (HPHT). In this study, a number of correlations were developed to estimate gas viscosity by the use of group method of data handling (GMDH)-type neural network and gene expression programming (GEP) techniques using a large data set containing more than 3000 experimental data points for methane, nitrogen, and hydrocarbon gas mixtures. It is worth mentioning that unlike many of viscosity correlations, the proposed ones in this study could compute gas viscosity at pressures ranging between 34 and 172 MPa and temperatures between 310 and 1300 K. Also, a comparison was performed between the results of these established models and the results of ten well-known models reported in the literature. Average absolute relative errors of GMDH models were obtained 4.23%, 0.64%, and 0.61% for hydrocarbon gas mixtures, methane, and nitrogen, respectively. In addition, graphical analyses indicate that the GMDH can predict gas viscosity with higher accuracy than GEP at HPHT conditions. Also, using leverage technique, valid, suspected and outlier data points were determined. Finally, trends of gas viscosity models at different conditions were evaluated.

Adsorption kinetics and thermodynamics of CO2 and CH4 on activated carbon modified by acetic acid

AbstractIn order to improve the properties of activated carbons in the separation of carbon dioxide/methane mixture, organic acid, namely acetic acid, is used to modify the commercial coconut shell activated carbons. The modified sample 15H‐AC shows greater adsorption capacity than the raw material. To further explore the adsorption mechanism of carbon dioxide and methane on 15H‐AC, adsorption kinetics and thermodynamics are studied and compared with that on R‐AC. According to the results of adsorption kinetic study, it can be observed that the diffusion of both carbon dioxide and methane on 15H‐AC is faster than that on the raw material. The findings obtained in the adsorption thermodynamics indicate that the interaction of both carbon dioxide and methane with the modified sample is stronger and the spontaneity degree is higher. The physical adsorption of carbon dioxide on 15H‐AC indicates that the regeneration of the adsorbents is easy. The modified activated carbon, which possesses higher adsorption capacity, faster adsorption rate and good reproducing property, is promising in the separation of carbon dioxide / methane gas mixtures industrially.

Carbon-rich amorphous silicon carbide and silicon carbonitride films for silicon-based photoelectric devices and optical elements: Application from UV to mid-IR spectral range

In the work we demonstrated the possibility to apply amorphous non-stoichiometric silicon carbide (a-SixC1-x:H) and silicon carbonitride (a-SixC1-x-yNy:H) films for improvement of exploitation characteristics of silicon-based photoelectric devices and optical elements in very wide spectral range - from UV to mid-IR. The a-SixC1-x:H films possessing optical properties required for effective antireflection (AR) effects for silicon (refractive index (n) at λ = 632 nm from 1.86 to 1.98, optical bandgap (Eopt) from 2.7 to 3.1 eV, and extinction coefficient (k) is close to zero practically in all spectral range) were obtained by PE-CVD from methane, silane, hydrogen, and argon gas mixture. To deposit silicon carbonitride films some amount of nitrogen was added to the gas mixture. For the a-SixC1-x-yNy:H films the following optical parameters were obtained: n = 1.76–1.93, Eopt = 3.1–3.4 eV, k~0. It has been shown that the proposed films possess unique mechanical properties and ratio of the films hardness to their Young modulus is very high (H/E > 0.13). It is evidence of the films high wear resistance that is of great importance when the films are used for protection of silicon optical elements in IR spectral range. It is established that the films of both types are very suitable as excellent AR coatings for silicon in the spectral range of Si-based solar cell photosensitivity, telecommunication windows, and mid-IR. Deposition of even single layer AR film allowed us to reduce reflection losses significantly (reflection coefficient (R) at minimum of reflection becomes close to zero). As a result, efficiency of etched multicrystalline Si-based solar cell (SC) was significantly improved. Transmittance of Si-based optical elements with front and rear AR films reached practically 100% in the telecommunication windows spectral range.

Energy pooling mechanism for catalyst-free methane activation in nanosecond pulsed non-thermal plasmas

Methane activation at low temperature remains a major challenge for its utilization in the field of reduction of greenhouse gases and generation of value-add products, while non-thermal plasmas provide a promising catalyst-free methane activation approach. In this work, an innovative energy pooling mechanism for catalyst-free methane activation at low temperature enabled by the nanosecond pulsed non-thermal plasma in argon and methane gas mixture is investigated by both optical diagnostic and kinetics modelling. Importantly, the evolution of the absolute density of the hydrogen atom at the ground state, as a real-time and in-situ indicator of the methane dissociation degree, is measured using the two-photon absorption laser induced fluorescence (TALIF) method. A simple zero-dimensional reaction kinetics model is built-up to perform a quantitative interpretation on the density evolution of active species. Especially, a good agreement is achieved between the measured hydrogen atom density and that from the kinetics model, validating the reaction pathways of active species. It is demonstrated that, except for the direct electron impact dissociation during the pulse-on period, both the charge transfer between argon ion and methane and the quenching of argon metastable species by methane contribute to a further increase of the hydrogen atom density during the pulse-off period, i.e. the argon ions and metastable species can function as an energy pooling for the formation of hydrogen atom and hydrocarbon radicals. The innovative mechanism proposed in this work may contribute to the catalyst-free and cost-effective strategies for methane utilization at low temperature.

Dithiazine vapour saturation in natural gas mixtures

Dithiazine is a reaction product resulting from the use of triazine as a scavenging agent to remove H2S from oil and gas streams at well-head or at gas treating facilities using contactors. In some cases, MEA-dithiazine product has been found in the sales gas in downstream transmission and distribution pipeline systems. MEA-dithiazine can subsequently precipitate when the solubility conditions become unfavourable, e.g. within regulating valves on a fuel gas skid at a gas turbine driven compressor station or at distribution regulating stations. The present work utilizes experimentally-obtained solubility data in methane and lean natural gas mixtures, along with fundamentals of chemical equilibrium based on equality of fugacity, and a closed-form analytical expression of Peng-Robinson EOS. The data shows that natural gas composition does not appear to have a significant effect on the solubility of dithiazine up to ~4 MPa; however, as pressure increases above this range, dithiazine tends to be more soluble in richer than in leaner gas mixtures. More importantly, the solubility isotherms of dithiazine in natural gas mixtures exhibit minima at 2–3 MPa. The implication of this is significant in terms of the amount of dithiazine that could potentially precipitate out of the gas stream if the gas undergoes throttling at pressure regulating valves. As an example, at a gas flow rate of 20 × 106 m3/day, the rate of dithiazine precipitation may be as high as 3.3 kg/day.

Adsorption of Natural Gas Mixtures of Methane, Ethane, and Propane in Nanoporous Carbon: Fully Atomistic Numerical Studies.

Natural gas (NG) is an interesting primary fuel; its larger-scale use is hindered by the difficulties of storing it under high pressures or low temperatures; a viable alternative is its storage via physisorption in porous materials. Most NG adsorption studies have focused on adsorption of pure methane, its primary component. Here we investigate the influence of heavier alkanes commonly found in NG (propane, ethane) on the adsorption process. We present the results of extensive molecular dynamics simulations of mixtures of methane-propane and methane-ethane at T = 300 and 400 K and P = 0-1500 bar in slit-shaped pores with interlayer spacings H = 8-20 Å. We observed that heavier hydrocarbons adsorb preferentially but remain mobile, which is promising for the intended application. We also solved a common problem with simulations of molecules with high adsorption affinity: the difficulty to determine their partial pressure. We developed an Arrhenius-type relationship allowing the calculation of these partial pressures from relationships between energy distributions of the different molecules in the simulations in conditions where a direct determination of these is impractical or impossible.

Biogas Reforming Conversion Character on Microwave-heating Carbon Receptor

Objectives:Methane (CH<sub>4</sub>) and carbon dioxide (CO<sub>2</sub>) are the main components of biogas and are produced from biomass gasification. These two gases are a by-product gases that can be used as an energy source and is known as a greenhouse gas that affects global warming. In order to convert the gas which is the main cause of global warming into high-quality fuel energy, the microwave reforming characteristic research was conducted. In this study, the reforming characteristics of microwave carbon receptor pyrolysis-gasification gas were investigated. In addition, reforming gas conversion characteristics according to the reforming temperature, flow rate, and CH<sub>4</sub> / CO<sub>2</sub> ratio, which are the main influence variables, were studied.Methods:Experiment was achieved in a microwave convertor which was installed a quartz tube reactor. The reactor was irritated by a microwave energy to heat carbon receptor in a sample basket which was placed at the center of the quartz tube. A simulated gas mixture of methane and carbon dioxide was fed into the carbon receptor in the reactor, and a reformed product gas was collected and analyzed using a GC-TCD.Results and Discussion:In the case of microwave reforming of a mixture gas of carbon dioxide and methane, hydrogen and carbon was produced by thermal decomposition of methane. The produced carbon was adsorbed to the receptor and interfered with the catalytic activity. The attached carbon was reacted with the carbon dioxide by gasification reaction to produce carbon monoxide, and was cleaned to maintain a constant reforming conversion.Conclusions:As a result, the conversion rate and the product gas yield were high when the receptor bad reforming temperature was high and the space velocity in the convertor was low. The increase in methane in the simulated gas resulted in low conversion due to carbon adsorption.

Direct reforming of Methane–Ammonia mixed fuel on Ni–YSZ anode of solid oxide fuel cells

To control the temperature distribution in the Ni–YSZ (yttria-stabilized zirconia) anode of solid oxide fuel cells (SOFCs) by efficiently utilizing the heat generated by electrochemical reactions, the supply of methane–ammonia mixed fuel is proposed. The reaction characteristics of reforming/decomposition of the mixed fuel on a Ni–YSZ catalyst are experimentally investigated. A mixture gas of methane, steam, ammonia, and balance argon is supplied to a packed bed catalyst placed in a quartz tube in an electric furnace. The crushed Ni–YSZ anode of SOFCs is used as the catalyst. The exhaust gas composition is analyzed by gas chromatography and the streamwise temperature distribution of the catalyst bed is measured by an infrared camera. It is found that ammonia decomposition preferentially proceeds and steam methane reforming becomes active after sufficient ammonia has been consumed. A low-temperature region is formed by steam methane reforming owing to its strongly endothermic nature. Its position moves downstream while its magnitude decreases as the ammonia concentration in the fuel increases. This shows that the local temperature distribution can be controlled by tuning the ratio of methane to ammonia in the mixed fuel. It is also found that, at a certain mixture ratio, the mixed fuel realizes a hydrogen production rate higher than that for only methane or ammonia.

Lidar Probing of a Mixture of Hydrogen Sulfide and Methane Molecules in the Atmosphere from a Flying Platform

The results of numerical solution of the lidar equation for the Raman scattering on the molecules of a gas mixture of hydrogen sulfide and methane in the 180° direction when probing the molecules of hydrogen sulfide and methane in the atmospheric boundary layer with concentrations in the range of 1010–1016 cm–3 from a flying platform at altitudes of up to 500 m in the synchronous photon counting mode are presented. It is shown that concentrations of the studied hydrogen sulfide and methane molecules below the level of the maximum permissible concentration (MPC) for such a version of the Raman scattering lidar can be recorded within a measurement time of 10 s when probing at a laser radiation wavelength of 405 nm and a platform flight height in the range of up to 500 m.