Methane-hydrogen Gas Mixture Research Articles

Equilibrium distribution and diffusion of mixed hydrogen-methane gas in gravity field

Repurposing existing natural gas pipelines is a promising solution for large-scale transportation of mixed hydrogen-methane gas. However, it remains debatable whether gravitational stratification can notably affect hydrogen partial pressure in the gas mixture. To address this issue, we combined molecular dynamics simulation with thermodynamic and diffusion theories. Our study systematically examined the equilibrium distribution of hydrogen-methane mixtures in gravity fields. We demonstrated that partial pressures of both gases decrease with altitude, with hydrogen showing a slower decrease due to its smaller molar mass. As a result, the volume fraction of hydrogen is maximized at the top end of pipes. The stratification is more favorable at low temperatures and large altitude drops, with notable gas stratification only occurring at extremely large drops in altitude, being generally negligible even at a drop of 1500 m. Furthermore, we showed that the diffusion time required to achieve the equilibrium distribution is proportional to gas pressure and the square of pipeline height. This requires approximately 300 years for a 1500 m pipeline at 1 bar. Therefore, temporary interruptions in pipeline gas transportation will not cause visible stratification. Our work clarifies the effect of gravity on hydrogen-methane gas mixtures and provides quantitative insights into assessing the stratification of gas mixtures in pipelines.

Influence of hydrogen-methane gas mixtures on the physical and chemical structure of polyethylene pipes of the operating gasdistribution networks of Ukraine

Influence of hydrogen-methane gas mixtures on the physical and chemical structure of polyethylene pipes of the operating gasdistribution networks of Ukraine

Nongrowth regime in microwave chemical vapor deposition reactor due to formation of plasma nonhomogeneity

AbstractA new form of microwave discharge with a filament inside plasma volume was investigated in a microwave plasma‐assisted chemical vapor deposition (CVD) reactor. The threshold values of methane content in a hydrogen–methane gas mixture, gas pressure, and microwave power for discharge transition to the new form were found. The parameters' range of existence of the new form of discharge was investigated in three types of CVD reactors. Measurements of the electron density, gas temperature, and spatial distributions of the plasma optical emission lines intensity were carried out for both forms of the discharge. The reasons for the transition of the discharge to a new form and the possibility of using the new discharge form in the microwave plasma‐assisted (MPA) CVD reactor are discussed.

Investigation of phosphorus-doped nanocrystalline diamond films for photocathode application

This work is devoted to an experimental study of electron photoemission from phosphorus-doped nanocrystalline diamond (NCD) films under the effect of laser radiation with a wavelength of 266 nm and a pulse duration of 15 ns. Homogeneous NCD films with a thickness of 50–1200 nm were grown on conductive silicon substrates using the CVD method. The phosphorus content in the films was changed by varying the phosphine content in the hydrogen–methane gas mixture and the substrate temperature. A relation has been established between the growth conditions, the thickness of NCD films, and the measured quantum efficiency of diamond photocathodes. It was shown that 50 nm thick heavily doped NCD films with H-terminated surface demonstrated the maximum quantum efficiency of 3⋅10−5.

Synthesis of Y3Al5O12:Ce Powders for X-ray Luminescent Diamond Composites

A concentration series of Y3Al5O12:Ce solid solutions were prepared, and the composition demonstrating the highest X-ray luminescence intensity of cerium was identified. Based on the best composition, a series of luminescent diamond–Y3Al5O12:Ce composite films were synthesized using microwave plasma-assisted chemical vapor deposition (CVD) in methane–hydrogen gas mixtures. Variations in the amounts of the embedded Y3Al5O12:Ce powders allowed for the fine-tuning of the luminescence intensity of the composite films.

ANALYSIS OF FORMATION THE GREENHOUSE EFFLUENTS TO ATMOSPHERE AND NITROGEN OXIDES PRODUCTION BY COMBUSTION THE METHANE-HYDROGEN MIXTURES

Within the framework of decarbonization of environment, the processes of the greenhouse gases formation in atmosphere by combustion the gas fuels (generally) and the natural gas substitution (particularly) the conditions of reducing the CO2 emission by methane-hydrogen mixtures burning are considered. The data on nitrogen oxides’ effluents are generalized in the work as well.
 An important role of non-isothermal state and of radiation selectivity of three-atomic gases CO2 and H2O for the resulting heat exchange and by evaluation the corresponding heat fluxes has been stated. The data are discussed basing upon the calculations’ results of the radiative heat transfer within the layer of combustion products (CP) of natural gas for the case of non-isothermal emitting layer at partial pressures pH2O : pCO2 = 2 : 1.
 The conclusion has been accepted on limitations regarding the opportunities to reduce the CO2 emission for the case of premixed methane-hydrogen mixtures burning while fuel combustion with an air-oxidant is proceeded. The evaluation under consideration has been proven taking into account only the cases of minor shares of [H2] ≤ 20–30 % (vol.) in fuel used by proper conditions for the domestic gas devices. The expected reduction of [CO2] mass emission fraction under combustion is reduced only by 10 % compared with the natural gas (methane) burning.
 It has been found for the first time that in case of the fuels, not containing the nitrogen, the equilibrium concentrations of two main nitrogen oxides NO and NO2 have practically the same (invariable) NOx values (by each of oxides), independently on fuel composition: methane and higher hydrocarbons, methane-hydrogen gas mixtures at any fixed given temperature (T = idem) and definite air-oxidant’s excess factor (λ = idem).
 This supposition has been numerically grounded and analyzed for the conditions of combustion the mentioned gas fuels under both the cases: of dry or wet air-oxidant. Bibl. 26, Fig. 4, Tab. 3.

Orientation Dependence of Cathodoluminescence and Photoluminescence Spectroscopy of Defects in Chemical-Vapor-Deposited Diamond Microcrystal.

Point defects, impurities, and defect–impurity complexes in diamond microcrystals were studied with the cathodoluminescence (CL) spectroscopy in the scanning electron microscope, photoluminescence (PL), and Raman spectroscopy (RS). Such defects can influence the directions that microcrystals are grown. Micro-diamonds were obtained by a hot-filament chemical vapor deposition (HF CVD) technique from the methane–hydrogen gas mixture. The CL spectra of diamond microcrystals taken from (100) and (111) crystallographic planes were compared to the CL spectrum of a (100) oriented Element Six diamond monocrystal. The following color centers were identified: 2.52, 2.156, 2.055 eV attributed to a nitrogen–vacancy complex and a violet-emitting center (A-band) observed at 2.82 eV associated with dislocation line defects, whose atomic structure is still under discussion. The Raman studies showed that the planes (111) are more defective in comparison to (100) planes. What is reflected in the CL spectra as (111) shows a strong band in the UV region (2.815 eV) which is not observed in the case of the (100) plane.

A simulation study of methane-hydrogen gas mixture permeation through nanoporous palladium membrane using molecular dynamics

We conducted molecular dynamic (MD) calculations to explore the efficiency of H2/CH4 separation through nanoporous palladium membrane. A palladium membrane with engineered-porosity of 0.1%–2.2% is used in our model of gas component separation from a mixture. We use computations of molecular dynamics to measure many trajectories of the molecules and thereby collect low statistical uncertainty projections of the gas flow rates. Our simulations demonstrate that high porosity palladium membranes are permeable to both gasses. As the porosity decreases, the permeability of larger molecules greatly reduced, which contributes to an exclusion effect of molecular size for a range of porosity that can permit smaller molecules. This implies that the determined porosity can achieve high selectivity in the separation of gas molecules while the desired gas molecules exhibiting high permeability. We also found that external driving force has a good effect on hydrogen permeation mechanism through a membrane. The gas flux of hydrogen levels increases as the pressure difference increases. The real mechanism of hydrogen permeability can also be visualized through our simulation, showing time dependence of flux, selectivity and pressure dependence. This work is expected to provide the framework for the development of an energy-efficient palladium-based gas separation system.

Deposition of diamond films on Si by microwave plasma CVD in varied CH4-H2 mixtures: Reverse nanocrystalline-to-microcrystalline structure transition at very high methane concentrations

Microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) films were synthesized on Si substrates by a microwave plasma chemical vapor deposition in methane-hydrogen gas mixtures with a wide range of methane concentrations of 0.5–40%. The samples were investigated with scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. We observed an unusual transition of the produced material structure from MCD to NCD and again to MCD with the increase in CH4 content in the gas. The deposition rate, grain size, and the roughness of the films exhibited extrema in the middle of the methane concentration range ([CH4] = 20%). Further increase of CH4 percentage leads to improvement of the diamond film quality, as confirmed by Raman spectra and SEM images while keeping a high deposition rate. These results may be used for the growth of the wide range of PCD films to be used as multipurpose protective layers, hard coatings for the cutting tools, and the diamond base for composite MCD/NCD structures.

Determination of metallization degree of pre-reduced chromite with image and rietveld analysis

Metallization degree of pre-reduced chromite was determined using two methods. The chromite samples were reduced in the solid state by methane-hydrogen gas mixtures. First method was image analysis of micrographs obtained by scanning electron microscope where heavier metallic phases appeared as bright white areas which were relatively easy to segment using a thresholding algorithm. The second technique was Rietveld analysis of X-ray powder diffraction pattern which fitted a calculated profile onto a measured X-ray diffraction pattern to gain information about phase quantities. Rietveld refinement and phase composition analysis was performed with PANalytical?s X?Pert HighScore Plus software from the XRPD (X-ray powder diffraction) data. Both techniques were in good agreement. Metallization degrees for the investigated samples ranged from 15 to 65 % depending on the extent of reduction which was a function of time, reduction temperature, and methane content of the gas mixture. These results were promising and indicate that either image analysis or X-ray Rietveld analysis can be used as a relatively fast method to determine the degree of metallization of pre-reduced samples in comparison to the slow and tedious chemical analysis.

Reduction of perovskite-geikielite by methane–hydrogen gas mixture: Thermodynamic analysis and experimental results

The present study investigated the reduction and carbonization behavior of perovskite-geikielite by using CH4–H2 gas mixture, which aimed to recycle the titanium resource in titanium-bearing blast furnace slag. Thermodynamic phase equilibrium analysis in the CaTiO3–CH4–H2, MgTiO3–CH4–H2 and CaTiO3–MgTiO3–CH4–H2 systems was performed by FactSage. The analysis indicated that CaTiO3 could be ultimately reduced and carbonized to TiCxOy by CH4–H2 gas mixture at temperature above 1300 °C, while the temperature for reduction of MgTiO3 was above 1200 °C. MgTiO3 is found to be reduced prior to CaTiO3 in the CaTiO3–MgTiO3–CH4–H2 systems. The reduction experiments of perovskite-geikielite were carried out in a temperature range of 1300 °C to 1450 °C in a flowing CH4–H2 atmosphere. Experimental results showed that perovskite-geikielite could be reduced completely to TiCxOy at 1400 °C and above after 8 h reduction, while geikielite was reduced prior to perovskite. The reduction and carbonization extent of samples increased with increasing time and temperature when in a low temperature range (below 1400 °C). However, a much higher temperature (above 1400 °C) would hinder further carbonization of TiCxOy for the production of deposited carbon. Addition of iron oxides to sample strongly facilitated the reduction reaction, and even promoted the reduction of titanium to be completed at only 1300 °C after 8 h reduction. The gas-solid reaction provided a low temperature method to reduce and carbonize perovskite and geikielite, and thus it provided a possible way to use titanium-bearing blast furnace slag.

Thermodynamic and experimental study on the reduction and carbonization of TiO 2 through gas‐solid reaction

Titanium oxycarbide (TiCxOy) has attracted much attention recently as a soluble anode used in the USTB (University of Science and Technology Beijing) or MER (Materials and Electrochemical Research) molten-salt electrolysis process to produce sponge titanium. The present study aimed to investigate the production of titanium oxycarbide from TiO2 by using CH4–H2 gas mixture, and both thermodynamic and experimental studies were carried out. First, thermodynamic analysis in the TiO2–CH4–H2 system was performed by the method of equilibrium calculation. The analysis indicated that TiO2 could be ultimately reduced and carbonized to TiCxOy by CH4 and H2 gas at temperature above 1200°C, and the increase of temperature was theoretically favorable to the final carbonization extent of TiCxOy. The experimental process involved the reduction of both pure TiO2 powder and TiO2 with additives using methane–hydrogen gas mixture in the temperature range from 1200°C to 1450°C. Experimental results showed that pure TiO2 could be reduced completely to TiCxOy at 1350°C and above after 8-hour reduction. It was also found that the reduction extent of TiO2 increased with increasing time and temperature when at a low temperature range; however, a much higher temperature (above 1350°C) would hinder further carbonization for the production of deposited carbon. Addition of iron oxides to TiO2 powders strongly facilitated the reduction reaction, even prompting the reaction of TiO2 to TiCxOy completely at only 1200°C after 8-hour reduction. The gas-solid reaction provided a simple and quick way to produce titanium oxycarbide.

Hydrogen Recovery from Hydrogen-Methane Gas Mixture Utilized by Palm Shell Based Bioadsorbent Activated Carbon

The objective of the study is to obtain suitable adsorbent to be applied for the purification of hydrogen from hydrogen-methane gas mixture. The application will be used to increase the efficiency of process in refinery unit focusing on hydrogen supply as the feed of hydrocracking unit. One of the promising technology is adsorption. In this study, adsorbent used is utilized by palm shell based bioadsorbent activated carbon which is a potential raw material among others due to its carbon and lignin content also its abundant supply. The activated carbon is going through chemical activation using H3PO4 to increase its surface area. Characteristic test of produced activated carbon is measured to obtain surface area which resulted in BET surface area of 414.91 m2/g and iodine number of 716 mg/g. In this case, a detailed experimental study has been made for the adsorption of pure methane, and pure hydrogen at 20°C and CH4/H2 gas mixture at 10, 20, and 30°C isothermal condition with pressure variation for each isothermal condition 1 – 6 bar. Measurement were made using volumetric technique coupled with gas chromatographic analysis. The result of adsorption test shows at 20°C adsorption of pure CH4 was highest followed by mixture gas of CH4/H2 with 1.5% methane then pure H2. The adsorption of gas mixture for any composition of gas were increased with increasing pressure at all temperatures. At the same pressure, adsorption of gas mixture that composed of 8.5% methane at 10 and 30°C increased in lower isothermal condition. Based on gas chromatograph analysis, in all conditions methane in gas mixture is all adsorbed to activated carbon. The trend of isothermal adsorption also fits the Langmuir model of isothermal adsorption.

Hydrogen Recovery from Hydrogen-Methane Gas Mixture Using Coffee Grounds Based Activated Carbon Bioadsorbent

Hydrogen recovery from off-gas of hydrocracking unit by adsorption is one of the process that could increase the efficiency processes of refinery unit. The purpose of this research is to make coffee grounds based activated carbon bioadsorbent that will be used in hydrogen recovery proses. The carbon was prepared by chemical activation using ZnCl2 at temperature 600°C. The surface area of produced activated carbon was measured using BET and Iodine number, while its surface morphology and composition were characterized using SEM-EDX. The adsorption capacity of activated carbon and its selectivity will be tested using hydrogen-methane gas mixture. The test was carried out on pure methane and hydrogen gas at 20°C and a mixture of CH4/H2 (mole ratio: 4:1) at 10°C, 20°C and 30°C and pressures from 1 to 6 bars. The results of this study show that the activated carbon can be successfully produced having the specific surface area of 728.07 m2/g and the iodine number of 2160 mg/g. The result shows that the adsorption of pure CH4 gas at the same pressure was 2.4 times greater than pure H2. The adsorption test indicates that the produced activated carbon might be used for hydrogen/methane separation.

Betung bamboo-based activated carbon bioadsorbent for the separation of hydrogen-methane gas mixture

Hydrogen recovery from off gas of hydrocracking and hydrotreating unit is one of the crucial processes in an oil and gas refinery unit as this process helps in lowering the expenses for operations. This study aims to obtain activated carbon that is made from Betung bamboo which can be used as the adsorbent in this process. The activated agents used are H3PO4 and K2CO3, respectively. Each activation lasts for 30 minutes. The results of the characterization test shows that the Iodine number of the activated carbon produced reaches 916.4 mg/g with BET surface area of 465.2 m2/g. SEM-EDX analysis shows that the carbon content is 74.83%. The activated carbon obtained is used to separate Hydrogen and Methane from its mixture at 10, 20 and 30oC with pressure variations of 1 - 6 bar. The results indicate that the maximum number of moles adsorbed from CH4(21.5%)/H2 gas mixture is 0.247 mmol/g, that has been carried out at 6 bar with temperature of 10oC. Methane has 2.2 times higher adsorption capacity than hydrogen, therefore, the Betung bamboo based activated carbon produced from this research can be applied as the adsorbent in the separation process of CH4/H2 mixture and it fits the Langmuir model.

A study on the carbonization and alloying process of MnO2 by methane-hydrogen gas mixture in the presence of Fe2O3

Carbonization of pure MnO2 by CH4-H2 gas mixture with various CH4/(CH4+H2) molar ratios in the temperature range of 900–1250°C had been performed in our previous work. This study further investigated the carbonization and alloying process of MnO2 by CH4-H2 gas mixture in the presence of Fe2O3 at 900–1300°C using XRD, optical microstructure, SEM-EDS and phase diagram analyses. Carbonization test of pure Fe2O3 was also conducted to understand the effect of Fe2O3 on the carbonization of MnO2 more explicitly. It was found that Fe2O3 could be carbonized to Fe3C at 900–1150°C. The Fe2O3 briquettes began to melt at 1100°C and a large amount of Fe-C melts appeared as the temperature went up to 1150°C. When the MnO2+25 wt%Fe2O3 briquettes were reduced at 900–1000°C in CH4-H2 gas mixture, the Fe2O3 was preferentially carbonized to Fe-C phase while the MnO2 was only reduced to MnO. The formation of Fe-C phase was beneficial to the carbonization of MnO since the carbonization temperature of MnO can decrease from 1100°C to 1000°C. The carbonization degree of MnO was dramatically accelerated over 1100°C due to the transformation of Fe-C phase from solid state to melts. Morphology analysis indicated that the MnO core was wrapped by the shell of Fe-C melts. The alloying process of Mn-Fe-C was conducted through the elements migration of Fe and Mn between the core and shell. At 1300°C, the Mn-Fe-C alloy turned to melt and aggregated since the highest melting temperature of the Mn-C-25 wt% Fe system was only 1274°C. Finally, a ferromanganese crude alloy with 68–72wt% Mn, 20–25wt% Fe and 6.0–8.0wt% C was obtained when the MnO2+25wt% Fe2O3 briquettes were carbonized by CH4-H2 gas mixture at 1300°C for 60min.

Heteroepitaxial diamond growth on 4H-SiC using microwave plasma chemical vapor deposition.

Deposition of heteroepitaxial diamond via microwave chemical vapor deposition has been performed on a 4H-SiC substrate using bias enhanced nucleation followed by a growth step. In future work, the diamond film will serve as a protective layer for an alpha particle sensor designed to function in an electrorefiner during pyroprocessing of spent fuel. The diamond deposition on the 4H-SiC substrate was carried out using a methane-hydrogen gas mixture with varying gas flow rates. The nucleation step was conducted for 30 minutes and provided sufficient nucleation sites to grow a diamond film on various locations on the substrate. The resulting diamond film was characterized using Raman spectroscopy exhibiting the strong Raman peak at 1332 cm−1. Scanning electron microscopy was used to observe the surface morphology and the average grain size of the diamond film was observed to be on the order of ∼2–3 μm.

Synthesis of Titanium Oxycarbide from Concentrates of Natural Ilmenite (Weathered and Unweathered) and Natural Rutile, Using a Methane-Hydrogen Gas Mixture

Unweathered ilmenite, weathered ilmenite, and a rutile-rich (zircon-containing) concentrate were reduced with 39 pct H2-6 pct CH4 (balance Ar) reduction gas at 1473 K (1200 °C). Despite differences in initial iron content, phase composition, and thermal stability of the phases, the main steps of the reaction sequence for the three materials were the same. The metallic iron product could be removed by leaching. In all cases, the product after leaching was a carbon-rich titanium oxycarbide.

Thermodynamic Analysis and Reduction of MnO2 by Methane–Hydrogen Gas Mixture

Methane and hydrogen reduction has emerged as promising technology for clean and efficient metallurgy. To understand the reduction process of MnO2 by CH4-H2 gas mixture, the effects of various CH4/(CH4 + H2) molar ratios (0–1) and temperatures (1100°C–1250°C) on the reduction of pure MnO2 were researched. Characterization of the solid carbon derived from the decomposition of CH4 gas was also determined. Thermodynamic analysis indicated that the MnO2 was first reduced to MnO by CH4-H2 gas mixture, and then MnO was reduced to Mn7C3 according to this reaction, 7MnO(s) + 10CH4(g) = Mn7C3(s) + 7CO(g) + 20H2(g). Experimental results showed that under the CH4/(CH4 + H2) molar ratio of 0.2, the reduction extent of MnO2 increased with the rising of temperatures. Nevertheless, the deep reduction of MnO to Mn7C3 was retarded even by increasing the temperature and prolonging the time, which was a result of the formation of deposited solid carbon. The free carbon contents in the reduced samples increased with the increasing of the CH4/(CH4 + H2) molar ratio and reduction time. The reduction of MnO2 and formation of carbon can be regulated by adjusting the CH4/(CH4 + H2) molar ratio in a gas mixture. For example, when MnO2 was reduced by 50 vol.%CH4-50%N2, large amounts of MnO and Mn7C3 particles were wrapped by the platelike and rodlike carbon with nanoscale. Yet, the wrapping phenomenon cannot be observed under 10 vol.%CH4-40 vol.%H2-50 vol.%N2.

Membrane separation study for methane-hydrogen gas mixtures by molecular simulations

Direct simulation results for stationary gas transport through pure silica zeolite membranes (MFI, LTA and DDR types) are presented using a hybrid, non-equilibrium molecular dynamics simulation methodology introduced recently. The intermolecular potential models for the investigated CH$_{4}$ and H$_{2}$ gases were taken from literature. For different zeolites, the same atomic (Si and O) interaction parameters were used, and the membranes were constructed according to their real (MFI, LTA, or DDR) crystal structures. A realistic nature of the applied potential parameters was tested by performing equilibrium adsorption simulations and by comparing the calculated results with the data of experimental adsorption isotherms. The results of transport simulations carried out at 25$^0$C and 125$^0$C, and at 2.5, 5 or 10 bar clearly show that the permeation selectivities of CH$_{4}$ are higher than the corresponding permeability ratios of pure components, and significantly differ from the equilibrium selectivities in mixture adsorptions. We experienced a transport selectivity in favor of CH$_{4}$ in only one case. A large discrepancy between different types of selectivity data can be attributed to dissimilar mobilities of the components in a membrane, their dependence on the loading of a membrane, and the unlike adsorption preferences of the gas molecules.