Mixture Of CH4 Research Articles

Experimental assessment on the explosion pressure of CH4-Air mixtures at flammability limits under high pressure and temperature conditions

High-pressure air injection technique has been extensively used for enhanced oil recovery in oilfields. Yet, it is of great concern on the process safety in terms of the explosion of natural gas-air mixtures. To deeply understand the explosion characteristics in the air injection procedure, explosion experiments for methane (a main component of natural gas) and air mixture were conducted using a cylindrical vessel at elevated pressure and temperature situations. The explosion pressure, the pressure rise rate and deflagration index of CH4 and air mixtures in a closed chamber were investigated under pressure up to 15 MPa and temperature up to 100 °C, and the effect of CH4 concentration on explosion pressure was also examined. The results of this research can provide useful data to quantify the dependency of explosion risk parameters on pressure, temperature and gas concentration. The experimental results indicate that the explosion pressure at flammability limits of CH4 gradually increases with initial pressure, while it can be slightly declined at elevated temperatures. The pressure rise rate and deflagration index increase at high pressures, but these values become lower at higher temperatures. At lower flammability limits and upper flammability limits of CH4-air mixtures, the explosion pressure can be greatly reduced due to the presence of insufficient combustible gas or high content of inerting gas (N2). The explosion pressure data reported in this study can provide guidelines for the prevention and mitigation of explosion disasters in high-pressure air injection process.

Molecular simulations of the adsorption and separation of hydrogen sulfide, carbon dioxide, methane, and nitrogen and their binary mixtures (H2S/CH4), (CO2/CH4) on NUM-3a metal-organic frameworks.

In this work, the adsorptions of carbon dioxide, methane, nitrogen, and hydrogen sulfide and the separation of their binary mixtures into NUM-3a Metal-Organic Framework (MOF) were studied through Grand Canonical Monte Carlo (GCMC) simulation method. The simulated pure gas uptakes using three generic force fields (UFF, Dreiding, and OPLS) at 298K were compared with the experimental values. The accuracy of the applied force fields for each gas was compared with the experimental isotherms and discussed. Our results show that OPLS has the best accuracy in the case of methane while Dreiding was the best for CO2 and N2. Simulated gas uptakes indicated that H2S was more adsorbed by NUM-3a than CO2, CH4, and N2. The calculated adsorption selectivity of NUM-3a for the binary mixtures of CH4 with H2S is larger than that of CO2. NUM-3a possess more affinity for H2S and CO2 than for CH4, where it may be a promising adsorbent material for separating carbon dioxide and hydrogen sulfide from methane. Furthermore, the most probable sites for the adsorption of the studied gases on the NUM-3a were investigated. The heats of adsorptions, as well as Henry's law constants, were also calculated, and it was in line with the observed gas adsorptions. The most preferred sites for the adsorption of carbon dioxide and hydrogen sulfide are the carboxyl groups and inside the channels and around the metal centers. However, methane and nitrogen are mainly accumulating in the channels' s apexes of NUM-3a around the metal center.

Catalytic Decomposition of 2% Methanol in Methane over Metallic Catalyst by Fixed-Bed Catalytic Reactor

The structure and performance of promoted Ni/Al2O3 with Cu via thermocatalytic decomposition (TCD) of CH4 mixture (2% CH3OH) were studied. Mesoporous Cat-1 and Cat-2 were synthesized by the impregnation method. The corresponding peaks of nickel oxide and copper oxide in the XRD showed the presence of nickel and copper oxides as a mixed alloy in the calcined catalyst. Temperature program reduction (TPR) showed that Cu enhanced the reducibility of the catalyst as the peak of nickel oxide shifted toward a lower temperature due to the interaction strength of the metal particles and support. The impregnation of 10% Cu on Cat-1 drastically improved the catalytic performance and exhibited 68% CH4 conversion, and endured its activity for 6 h compared with Cat-1, which deactivated after 4 h. The investigation of the spent carbon showed that various forms of carbon were obtained as a by-product of TCD, including graphene fiber (GF), carbon nanofiber (CNF), and multi-wall carbon nanofibers (MWCNFs) on the active sites of Cat-2 and Cat-1, following various kinds of growth mechanisms. The presence of the D and G bands in the Raman spectroscopy confirmed the mixture of amorphous and crystalline morphology of the deposited carbon.

Biogas Conversion to Syngas Using Advanced Ni-Promoted Pyrochlore Catalysts: Effect of the CH4/CO2 Ratio.

Biogas is defined as the mixture of CH4 and CO2 produced by the anaerobic digestion of biomass. This particular mixture can be transformed in high valuable intermediates such as syngas through a process known as dry reforming (DRM). The reaction involved is highly endothermic, and catalysts capable to endure carbon deposition and metal particle sintering are required. Ni-pyrochlore catalysts have shown outstanding results in the DRM. However, most reported data deals with CH4/CO2 stoichiometric ratios resulting is a very narrow picture of the overall biogas upgrading via DRM. Therefore, this study explores the performance of an optimized Ni-doped pyrochlore, and Ni-impregnated pyrochlore catalysts in the dry reforming of methane, under different CH4/CO2 ratios, in order to simulate various representatives waste biomass feedstocks. Long-term stability tests showed that the ratio CH4/CO2 in the feed gas stream has an important influence in the catalysts' deactivation. Ni doped pyrochlore catalyst, presents less deactivation than the Ni-impregnated pyrochlore. However, biogas mixtures with a CH4 content higher than 60%, lead to a stronger deactivation in both Ni-catalysts. These results were in agreement with the thermogravimetric analysis (TGA) of the post reacted samples that showed a very limited carbon formation when using biogas mixtures with CH4 content <60%, but CH4/CO2 ratios higher than 1.25 lead to an evident carbon deposition. TGA analysis of the post reacted Ni impregnated pyrochlore, showed the highest amount of carbon deposited, even with lower stoichiometric CH4/CO2 ratios. The later result indicates that stabilization of Ni in the pyrochlore structure is vital, in order to enhance the coke resistance of this type of catalysts.

Experimental and modeling of autoignition of gaseous hydrocarbon fuels in the presence of H2 and C2H4

The focus of the present work is to understand the effect of H2 and C2H4 on the ignition characteristics of other gaseous fuels, namely, CH4, C2H6 and C3H6. Atmospheric-pressure flow reactor experiments were performed to measure the ignition delay times of CH4, C2H6 and C3H6 binary mixtures with H2 or C2H4 between 800 and 950 K. Most of the experiments were conducted at stochiometric conditions with 21% O2. Select tests were performed to examine the effects of equivalence ratios and oxygen concentrations. Ignition delay time were also measured for ternary mixtures of C3H6-C2H4-H2 at select conditions. Based on the experimental data, the overall effectiveness of H2 or C2H4 in reducing the ignition delay time of the binary mixtures can be listed in the following order: CH4 > C3H6 > C2H6. The experimental data were used to refine and validate the chemical kinetic mechanism for allyl-HO2 system relevant to low-temperature ignition chemistry of C3H6. A detailed sensitivity analysis is presented to identify the important reaction pathways, and their implications for the experimental observations are discussed. Monte Carlo simulations were used to quantify the model uncertainty for ignition delay time predictions, and to identify reactions that have significant contribution to the model uncertainty. Among the binary mixtures studied, CH4-H2 mixture produced the largest model uncertainty, primarily due to the sensitive reactions involving HO2 radical.

Experimental and simulation study on high-pressure V-L-S cryogenic hybrid network for CO2 capture from highly sour natural gas

Cryogenic carbon dioxide (CO2) capture technologies showed promising results for the purification of highly sour natural gas reserves. However, quantitative experimental data for solid and liquid CO2 formation during cryogenic separation is not adequately examined in the previous studies. Moreover, an economical and efficient cryogenic CO2 capture technology with reduced energy and hydrocarbon losses is necessary to make it attractive for commercial use. A high-pressure cryogenic hybrid network comprised of the packed bed and the cryogenic separator was developed for the cryogenic experimental study on CO2 capture from binary CO2−CH4 mixture to focus these areas. Feed containing 30, 50 and 70 % CO2 content were used and the separation study was conducted in vapor-solid (V-S), vapor-liquid (V-L), and vapor-liquid-solid (V-L–S) regions of phase equilibria. The packed bed was used in the V-S operational domain to quantify CO2 solid up to 20 bar because of the operational limitations. Separation characteristics and V-L isothermal flash measurements at 20, 30, and 40 bar pressure and temperature ranges from -20 to −60 °C were carried out in the cryogenic separator. The operation in the setups was carried out at different compositions of the CH4−CO2 binary mixture to define the boundaries of the hybrid cryogenic network. Liquid formation at 40 bar for 70 % CO2 feed was 0.15 kg at -55 °C as compared to 0.03 kg for 30 % CO2 feed. The simulation study was carried out using Aspen Plus along with the Peng Robinson Equation of State (EoS), and the results were compared with the experimental data, which showed good agreement. The hybrid cryogenic network showed an energy reduction of 37 % compared to the conventional cryogenic distillation network with 90.6–97.3 % CH4 purity and 2.65–12.39 % methane losses with different arrangements of the hybrid cryogenic network.

Fast synthesis of thin SSZ-13 membranes by a hot-dipping method

Among zeolite membranes with CHA structure, SSZ-13 membrane has certain advantages over all-silica CHA and SAPO-34 membranes, like easy synthesis, good stability and insensitivity to moisture, however, its separation performance is not satisfactory. In this study, SSZ-13 membranes were prepared by a hot-dipping method, where the hot contact of seeded support and mother liquor at synthesis temperature resulted into fast crystallization kinetics and thin membranes. The obtained sub-micron SSZ-13 membranes exhibited outstanding CO2–CH4 mixture separation performance, CO2 permeance ~28 × 10−7 mol/(m2 s Pa) and CO2–CH4 selectivity ~180 at 0.14 MPa and room temperature. The hot-dipping method achieved the complete separation of seeding and crystallization (or membrane growth) by preventing the contact of mother liquor and seeded support before reaching synthesis temperature. This treatment avoids any undesirable change of the seed layer before membrane growth, which may help us to correlate the membrane performance with the properties of seed layer, like seed density, thickness and seed size. On the contrary, the CHA seed layer might be dissolved partially by mother liquor during the heating process of conventional membrane synthesis, which led to thick membranes due to unsatisfactory seeding. This method could be used for the synthesis of other zeolite membranes.

Experimental investigation of combustion dynamics and NOx/CO emissions from densely distributed lean-premixed multinozzle CH4/C3H8/H2/air flames

Lean-premixed fuel-flexible combustion technology capable of operating on a wide range of fuels, including high or pure hydrogen, is expected to play a crucial role in reducing nitrogen oxides and carbon dioxide emissions from heavy-duty gas turbine engines, ultimately in achieving energy system decarbonization. However, fuel-flexible operations, particularly with high hydrogen content fuels, require a fundamental, drastic change from conventional nozzle architecture. The use of a number of small-scale multitube injectors – also referred to as micromix nozzles – is indispensable to reduce the likelihood of flashback events in ultra-fast premixed hydrogen flames. At present, the vast majority of what is known about the fundamental mechanisms of combustion dynamics and emissions stem from intensive research in large-scale swirl-stabilized flames. The behavior of small-scale multinozzle flames governed by isolated or collective movements of constituent flames remains, however, largely unexplored. To address these questions, we use densely distributed sixty-injector mesoscale flames as a platform to explore the influence of a full range of CH4/C3H8/H2 fuel blends – including all possible combinations of a blend of two different fuels (CH4 + C3H8, CH4 + H2, C3H8 + H2) and three different fuels (CH4 + C3H8 + H2), as well as single-component fuels (CH4, C3H8, H2) – on combustion dynamics and exhaust emissions under a constant adiabatic flame temperature condition. Here, we show that while the nitrogen oxide emissions are almost unaffected by the fuel compositions considered here, the variation of fuel composition has a significant impact on self-excited instabilities, which tend toward higher frequency oscillations with increasing hydrogen concentration. From phase-resolved OH PLIF measurements for a 50/50 mixture of CH4 and H2, we identify the creation, evolution, and annihilation of an array of coherent vortical structures as the mechanism responsible for sound generation and flame surface modulations without strong interactions between adjacent flames. In contrast, the behavior of the 50% C3H8 + 50% H2 case is dictated primarily by periodic merging and separation of neighboring reactant jets, leading to large-scale asymmetric oscillations in the transverse direction. Given the substantial change in transport properties, effective Lewis number-related interpretation provides a reasonable explanation for the different behaviors of a cluster of small-scale flames.

Complex Phase Behaviors and Structural Coexistence of Natural Gas Hydrates Containing Large-Molecule Guest Substances

The complex phase behaviors and structural coexistence of natural gas hydrates (NGHs) that contain large-molecule guest substances (LMGSs) were examined for their significance in the exploration and exploitation of NGHs as well as natural gas storage and transportation. Methylcyclopentane (MCP) and 2,2-dimethylbutane [neohexane (NH)] were chosen as LMGSs, and the simplest composition of NGHs and natural gas was simulated by a gas mixture of CH4 (90%) + C2H6 (10%). The coexistence of structure II (sII) and structure H (sH) hydrates in the CH4 + C2H6 + LMGS + water mixtures was revealed by 13C nuclear magnetic resonance (NMR) and powder X-ray diffraction (PXRD). CH4 and LMGSs were captured in sH, whereas CH4 and C2H6 were enclathrated in sII. Endothermic heat flow curves, which were obtained by a differential scanning calorimeter (DSC), and pressure (P)–temperature (T) traces exhibited two-step dissociation of formed gas hydrates (sH dissociation followed by sII dissociation). The experimental results for the PXRD patterns, 13C NMR spectra, phase equilibria, DSC heating curves, and P–T traces clearly demonstrated that the CH4 (90%) + C2H6 (10%) + LMGS + water mixtures formed both sII hydrates and sH hydrates and that the final hydrate structure at equilibrium dissociation points was sII.

Epitaxial growth of 3C-SiC film by microwave plasma chemical vapor deposition in H2-CH4-SiH4 mixtures: Optical emission spectroscopy study

Microwave (MW) plasma in silane-hydrogen and silane-hydrogen-methane mixtures is used effectively for chemical vapor deposition of Si, SiC, diamond, and SiC-diamond composite films; however, the properties of such plasma at pressures of the order of 100 Torr remain largely unexplored. Here we characterize the MW plasma (2.45 GHz) in SiH4 + H2 and SiH4 + СH4 + H2 mixtures (72 Torr) with silane content ranging from 0% to 5% in the process gas using high-resolution optical emission (OE) spectroscopy. Besides the OE lines of C2 dimer, Balmer series of excited atomic hydrogen (Hα, Hβ, Hγ, Hδ, and Hε), and CH radical, we observed atomic Si lines at 263, 288, and 391 nm and a relatively weak SiH emission. Gas temperature Tg of ≈3160 K is assessed from the rotational structure of the C2 dimer (Δν = 0, λ = 516.5 nm) emission band, and the absorbed microwave power density (MWPD) in the plasma fluctuates in the narrow range between 36 and 43 W/cm3 with a slight tendency to decrease with silane addition. The MWPD, intensity ratio Hα/Hβ of hydrogen Balmer series lines (related to excitation temperature Texc), and Si lines’ intensities in OE spectra as functions of SiH4 concentration in H2 and H2 + CH4 mixtures all show an extremum or a kink in slope near a special point at ≈0.5% SiH4. Finally, we produced a silicon carbide film of cubic polytype 3C-SiC on a (111) oriented Si substrate, which was characterized with Raman spectroscopy and x-ray diffraction, and its monocrystalline structure was confirmed.

Utilization of zeolite as a potential multi-functional proppant for CO2 enhanced shale gas recovery and CO2 sequestration: A molecular simulation study of the impact of water on adsorption in zeolite and organic matter

We proposed to use zeolites as multi-functional proppants for enhanced shale gas recovery and CO2 sequestration in our previous paper and studied the competitive adsorption of CO2 and CH4 in silicalite-1 and kerogen organic matter. It is proved that CO2 released from proppants can be preferentially adsorbed by kerogen and replace the adsorbed CH4. In the present paper, we aim at studying the impact of water on the gas adsorption capacity and selectivity of CO2 over CH4 since water can significantly alter gas adsorption behaviors in zeolites and organic matter. We carry out grand canonical Monte Carlo simulations of water adsorption and the competitive adsorption of a CO2, CH4, and water mixture in silicalite-1 and in kerogen. It is found that water is less favored in both adsorbents but could suppress the adsorption of CO2 and CH4 when the water content is high, it can also enhance CO2/CH4 selectivity under some circumstances. Kerogen shows a stronger preference for adsorbing CO2 over CH4 under most conditions; thus, the replacement process of CO2 and CH4 with water present can still happen in the positive direction.

Recovery of free volume in PIM-1 membranes through alcohol vapor treatment

Physical aging is currently a major obstacle for the commercialization of PIM-1 membranes for gas separation applications. A well-known approach to reversing physical aging effects of PIM-1 membranes at laboratory scale is soaking them in lower alcohols, such as methanol and ethanol. However, this procedure does not seem applicable at industrial level, and other strategies must be investigated. In this work, a regeneration method with alcohol vapors (ethanol or methanol) was developed to recover permeability of aged PIM-1 membranes, in comparison with the conventional soaking-in-liquid approach. The gas permeability and separation performance, before and post the regeneration methods, were assessed using a binary mixture of CO2 and CH4 (1:1, v:v). Our results show that an 8-hour methanol vapor treatment was sufficient to recover the original gas permeability, reaching a CO2 permeability > 7000 barrer.

Structure and emission properties of structures based on carbon walls and aluminum nitride

To create field emission cathodes (autocathodes) used in the manufacture of displays and other devices, carbon nanowalls (CNW) are promising. The CNW layers are a porous material consisting of curved plates formed by graphene layers. The industrial use of CNW autocathodes is impeded by the heterogeneity and instability of the magnitude and density of the cathode current. To improve the characteristics of autocathodes, an AlN film is formed on the surface of the emitting substance, which also has the property of field emission. CNW was obtained from a gas mixture of H2 and CH4 activated by a dc glow discharge. The CNW layers were deposited on silicon substrates and substrates representing a layered structure made by forming an opal matrix (OM) layer on a Si substrate. AlN films with controlled composition and structure were prepared by RF magnetron reactive sputtering. CNW layers with a thickness of &gt; 4 μm were obtained by successive growth of two CNW layers (Si/CNW/CNW structure). An additional CNW layer was also grown on the surface of the first layer coated with Ni (Si/CNW/Ni/CNW structure). AlN films were grown on a CNW layer (Si/CNW/AlN and Si/OM/Ni/CNW/AlN structures). It is shown that CNW plates are formed from graphene layers partially connected by atomic bonds (up to 30 layers) packed in a hexagonal lattice, and AlN films consisted of amorphous and axially textured crystalline phases. The current-voltage characteristics of the autocathodes were measured in a pulsed mode at a pressure of ~10−3 Pa. The Si/CNW/CNW structures are characterized by a threshold of autoemission of ≤ 3.6 V/μm and a high density of centers of emission. The current-voltage characteristics of the layered structures Si/CNW/AlN, Si/OM/Ni/CNW and Si/OM/Ni/CNW /AlN showed better emission properties compared to the Si/CNW structure. The current-voltage characteristics considered make it possible to predict the structure and composition of the emitting layer to improve the operational characteristics of multilayer autocathodes.

Propagation mechanism of gaseous detonations in annular channels with spiral for acetylene-oxygen mixtures

The propagation mechanism of detonations in the annular channel with a spiral is experimentally studied for an acetylene and oxygen mixture with different levels of argon dilution. Detonation velocity is measured through the placement of regularly spaced photodiodes along the test tube. A high-speed camera is also used to supplement the photodiodes when the luminosity decreases. Smoked foils of long length are inserted into the annular channel to register the cellular structures. The results indicate that the effect of the spiral on detonation propagation highly depends on the intrinsic instability of the detonation. With a decrease in the initial pressure, the propagation changes from spiral-induced multi-head mode to spiral-induced single-head mode and then spiral-induced shock-flame complex mode; then, the propagation fails as the limit is approached. Discontinuities in normalized velocity are found for mixtures with high argon dilution, which indicates the transition from single-head spin to shock-flame complex, as observed from the smoked foils. Such a phenomenon is not observed in cases with an unstable mixture of C2H2 + 2.5O2 or in cases with large roughness. This is because of the different mechanisms stable and unstable detonations and the corresponding response to the boundary change. The critical width of the annular channel normalized by cell size for the discontinuity is found to slightly larger than 1/π, which corresponds to the lowest quenching limit in smooth tubes, particularly for stable detonations. The critical diameter normalized by cell size for the discontinuity in the circular tube is almost twice the critical width in the annular channel, equal to the geometrical scaling based on front curvature theory.

A new metal-organic framework based on rare [Zn4F4] cores for efficient separation of C2H2.

Assembly via 1,4-benzenedicarboxylate linkers and Zn2+ ions afforded an MOF containing rare [Zn4F4] cubane core, showing excellent separation for C2H2-CO2 and C2H2-CH4 mixtures. Dynamic breakthrough experiments and grand canonical Monte Carlo calculations were carried out to confirm the feasibility of the MOF for the separation application of C2H2.

The experimental study of flame height and lift-off height of propane diffusion flames diluted by carbon dioxide

The flame height and lift-off height of the turbulent jet diffusion flame of gas mixture at ambient temperature and pressure were studied. Different diameter nozzles (2, 3 and 4 mm), heat release rates, and concentrations of carbon dioxide (CO2) were considered. The flow rates of propane (C3H8) and CO2 were controlled by two rotameters. The experimental results showed that the flame height firstly increased with an increase in the concentration of CO2 in the gas mixture under the same heat release rate, and then decreased with a further increase in the concentration of CO2. The flame height decreased with an increase in the concentration of CO2 when the heat release rate was sufficiently large. The lift-off height of the gas mixture increased with an increase in the concentration of CO2 under the same heat release rate and nozzle diameter. Considering the stoichiometric air fuel ratio and laminar flame speed, two correlations of flame height and lift-off height for a mixture of C3H8 and CO2 have been proposed, respectively.

The influence of CO2 and CH4 mixture on water wettability in organic rich shale nanopore

CO2 has been considered as an effective fluid to replace CH4 in shale rock. Wetting behavior of water in CO2/CH4 mixtures in organic nanopores is a key parameter influencing CO2 based enhanced gas recovery processes in shale. However, there is lack of fundamental understanding of water wetting in such systems. We perform Molecular Dynamics (MD) simulations of nanoscopic liquid water drops on a graphite substrate mimicking an organic-rich shale pore in the presence of CH4/CO2 mixtures at temperatures in the range 300 K–400 K. The equilibrium contact angle of the water droplets on graphite is a pronounced function of CH4 as well as CO2 pressure with the water droplet lifting-off, that is reaching a 180° contact angle, at a threshold pressure of 12 MPa for CO2 and 78 MPa for CH4. The contact angles recovered from simulations match well with experimental literature via the modified Young's equation. The line tension in our studied systems does not show a specific dependence on temperature. As compared to methane, CO2 exhibits a stronger interaction with organic-rich surfaces, which has strong impact on wettability. For CH4/CO2 mixtures, this translates in an approximately linear increase of the contact angle with the CO2 mole fraction.

Advanced pore characterization and adsorption of light gases over aerogel-derived activated carbon

Abstract Activated carbon produced by etching with CO2 is an attractive adsorbent material because of its ultrahigh surface area above 1000 m2/g and substantial pore volume. This being stated, because etched carbon was only reported recently, many of its properties, such as its textural properties, high-pressure adsorption capacities towards CO2, N2, H2, CO, and CH4, and dynamic performance, have never been thoroughly investigated. Accordingly, this study explored these characteristics for the first time. The textural and adsorptive properties were also assessed for zeolite 5A, a metal-organic framework (Ni MOF-74), and activated carbon provided by Ingevity corporation to allow for comparison to established benchmarks. The textural properties were assessed by a combination of N2 physisorption at 77 K and CO2 adsorption at 273 K using a combination of t-plot, Dubinin–Radushkevich, 2D-NLDFT, and Horvath–Kawazoe models. Therein, it was determined that the etched carbon had a hierarchical porosity, with pores appearing in both the ultramicro- and meso-porous ranges. From the adsorption isotherms at 298 K and 0–20 bar, the etched carbon exhibited adsorption capacities of 20, 9, 5, 4.5, and 1 mmol g−1 for CO2, CH4, CO, N2, and H2 respectively, indicating that the samples high (i.e., 95%) pore volume made it selective towards multiple species at high pressure. Having said this, when the material was examined for dynamic CO2 adsorption from N2, H2, and CH4 mixtures at 25 °C and 1 bar, it achieved CO2/CH4, CO2/H2, and CO2/N2 selectivities of 2.4, 15.4, and 6.6 mol/mol, respectively, meaning that it can be used for kinetic separations. The high dynamic selectivity was retained for CO2/H2 at 20 bar, however, the CO2/CH4 breakthrough fronts were much broader compared to the low-pressure experiments, meaning that the two species' diffusivities were competitive. As such, EC-RF was concluded to be effective for low-pressure CO2 separations as well as for high pressure CO2/H2 separations. More importantly, this study provides an in-depth characterization and better understanding of EC-RF's properties, which is imperative to its use as an adsorbent material.

Competitive sorption and diffusion of methane and carbon dioxide mixture in Carboniferous-Permian anthracite of south Qinshui Basin, China

A comprehensive understanding of the migration and competitive adsorption of methane and carbon dioxide in coal is crucial for the injection optimization design and injection displacement evaluation of the CO2 enhanced coalbed methane recovery (ECBM) project. In this paper, adsorption-desorption tests of three gaseous mixtures (75% CH4 + 25% CO2, 50% CH4 + 50% CO2, and 25% CH4 + 75% CO2) and pure CH4 and CO2 were performed on the anthracite from the southern Qinshui Basin. The results show that (1) there was an apparent hysteresis in sorption isotherms, and the size of hysteresis loops was related to the proportion of CO2 in the mixture. There was also a non-negligible error in using the extended Langmuir model to predict mixture sorption. (2) Separation factor (SCO2-CH4) for the sorption of CH4 and CO2 mixture varied with the equilibrium pressure and the equilibrium concentration of gas components. Its value was usually between 4 and 20. During the adsorption process, the SCO2-CH4 at low pressure was generally greater than that at high pressure. Moreover, SCO2-CH4 in the desorption process was generally higher than the adsorption process. (3) Bidisperse diffusion model could better describe the diffusion process of the mixture. In general, the macropore effective diffusivity varied as a power function with pressure. Under the same pressure, the macropore effective diffusivity increased with the increasing CO2 content. Further, the macropore effective diffusivity in the desorption process was larger than that in the adsorption process. The micropore effective diffusivity and the ratio of macropore uptake to micropore uptake had no apparent relationship with the gas component concentration and pressure. The results will help to comprehensively understand the sorption processes of the CH4 and CO2 mixture and provide basic numerical simulation data for the CO2-ECBM project in the southern Qinshui Basin.

A comparative investigation of premixed flame propagating of combustible gases-methane mixtures across an obstructed closed tube

In this study, the premixed flame behaviour of CH4/air mixtures (7 vol%, 9.5 vol% and 11 vol%) is investigated upon the addition of four emblematic combustible gases (0–2 vol%)—CO, H2, C2H4, and C2H6. The investigation is carried out in a closed tube (L/D = 9) containing an obstacle (BR = 18%) acting as a radiator at 0.1 MPa and 25 °C. The flame structure, flame-tip speed, and flame-tip position were obtained by analysing the images captured by a high-speed camera. The explosion pressure history was recorded and analysed to study the effects of these parameters on the flame propagation process. Meanwhile, the flame brightness and flow field near the obstacle were discussed. The results indicate that the existence of obstacles deformed the generated tulip flame, resulting in a special triple flame, and the pressure history appeared stepped. The order of impact on the explosion reaction of rich conditions of the CH4 mixtures was C2H4, C2H6, H2, and CO; however, the order of impact on that of the stoichiometric and lean conditions of the CH4 mixtures was C2H6, C2H4, CO, and H2. After the flame crossed the obstacle, a crescent-shaped backward flow field in the burned area. The brightness curve was also stepped like the pressure history when the flame crossed the obstacle, and the flame brightness started to rise rapidly at the maximum flame tip speed. This is evidence that the flame brightness was closely related to the flame-tip speed and explosion pressure.