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The fractal theory has been widely applied to the analysis of gas adsorption isotherms, which are used for the pore structure characterization in unconventional reservoirs. Fractal dimension is a key parameter that can indicate the complexity of the pore structures. So far, most fractal models for gas adsorption are for N2 adsorption, while fractal models for CO2 adsorption are rarely reported. In this paper, we built a fractal model for CO2 adsorption by combining a thermodynamic model and the Dubinin–Astakhov model. We then applied the new model to three CO2 adsorption isotherms measured on shale samples. The results show that the fractal dimension from the new model lies between 2 and 3, which agrees with the fractal geometry. The new model presented in this paper can be used for the CO2 adsorption analysis, which allows characterizing micropore structures in shales. [ABSTRACT FROM AUTHOR]

Summary: The term "future material" is referred for activated carbons (AC) due to their easy/scalable preparation, compatible property, and numerous applications. The applications of such materials for gas adsorption and storage play a vital role in the large‐scale feasibility of adsorbed gas storage. This could provide a better alternative to compression‐based storage for vehicular applications due to lower energy and materials input. Currently, compression‐based storage has been thoroughly studied and widely used; however, there are limited reports on LCA. In this paper, a lifecycle‐based approach has been deployed for chemically activated carbon (CAC) production using KOH and compared with inventory‐based physically activated carbon (PAC). The PACs have a far lesser impact than the CACs mainly owing to the chemicals used. Potassium hydroxide and electricity account for nearly 70 to 90% of different ecotoxicity indicators. It has also been estimated that if by‐products generated using chemicals are recovered, the midpoint and endpoint impacts can be brought down substantially up to 60%. In particular, Terrestrial ecotoxicity is reduced by 80%, Human toxicity up to 60%, and Water toxicity up to 60%. However, the CACs/CACRs still have higher impact than the PACs, mainly on four indicators. Their application for methane‐rich gas storage derived from a life cycle study encourages adsorption‐based storage adoption. The metal requirement for cylinder manufacturing is the highest which can be reduced if adsorption‐based storage is adopted. Therefore, the sustainability of the proposed novel process is increased with incorporation of biomass‐based activated carbons, reduction in thickness of cylinders, and lower pressure requirement for storage. It has been observed that Global warming potential due to the cylinder for gas storage is drastically reduced from 73% to 15.6%. The process of activation and application of ACs for gas storage has been investigated using life cycle as an assessment tool. [ABSTRACT FROM AUTHOR]

Many tons of porous carbon materials (including BC and IG-110) are contained in HTGR, which are serving as structural material and fuel matrix material. These materials would absorb moisture and other impurities when exposed to the environment, and these impurities (especially moisture) absorbed in the carbon material must be removed before the reactor operation to prevent corrosion reaction at high temperature (more than 500°C). As the pore microscopic structure characteristic is the significant factor affecting the gas adsorption and flow in the porous materials, the detailed 3D pore structures of the carbon materials (BC and IG-110) in HTGR were studied by Micro-XCT and HPMI methods in this paper. These pore structure characteristics include pore geometry, pore size distribution, and pore throat connectivity. The test results show that the pore size distribution of BC material is wide, and the pore diameter is obviously larger than that of IG-110. Pore connections in BC show radial shape connections at some special points, and the pore connectivity in IG-110 is very complex and presents a huge complex 3D pore network. [ABSTRACT FROM AUTHOR]

In this paper, scanning electron microscopy, low-temperature N2 adsorption and CH4 isothermal adsorption experiments were performed on 11 coal samples with Ro,max between 0.98 and 3.07%. The pore structure characteristics of coals (specific surface area, total volume distribution) were studied to assess the gas adsorption capacity. The results indicate that there is significant heterogeneity on coal surface, containing numerous channel-like pores, bottle-shaped pores and wedge-shaped pores. Both Langmuir volume (VL) and Langmuir pressure (PL ) show a stage change trend with the increase of coalification degree. For different coalification stages, there exist different factors influencing the VL and PL values. For low-rank coals (Ro,max<1.1%), the increase of VL values and decrease of PL values are mainly due to the abundant primary pore and fracture within coal. For middle-rank coals (1.1%o,max<2.1%), the moisture content, vitrinite content and total pore volume are all the factors influencing VL, and the reduction of PL is mainly attributed to the decrease of moisture content and inertinite content. Meanwhile, this result is also closely related to the pore shape. For high-rank coals (Ro,max>2.1%), VL values gradually increase and reach the maximum. When the coal has evolved into anthracite, liquid hydrocarbon within pore begins pyrolysis and gradually disappears, and a large number of macropores are converted into micropores, leading to the increase of specific surface area and total pore volume, corresponding to the increase of VL. In addition, the increase of vitrinite content within coal also contributes to the increase of VL. PL, reaches the minimum, indicating that the adsorption rate reaches the largest at the low pressure stage. The result is mainly controlled by the specific surface area and total pore volume of coal samples. This research results will provide a clearer insight into the relationship between adsorption parameters and coal rank, moisture content, maceral composition and pore structure, and it is of great significance for better assessing the gas adsorption capacity. [ABSTRACT FROM AUTHOR]

CO2 enhanced shale gas recovery (CO2-ESGR) draws worldwide attentions in recent years with having significant environmental benefit of CO2 geological storage and economic benefit of shale gas production. This paper is aimed at reviewing the state of experiment and model studies on gas adsorption, competitive adsorption of CO2/CH4, and displacement of CO2-CH4 in shale in the process of CO2-ESGR and pointing out the related challenges and opportunities. Gas adsorption mechanism in shale, influencing factors (organic matter content, kerogen type, thermal maturity, inorganic compositions, moisture, and micro/nano-scale pore), and adsorption models are described in this work. The competitive adsorption mechanisms are qualitatively ascertained by analysis of unique molecular and supercritical properties of CO2 and the interaction of CO2 with shale matrix. Shale matrix shows a stronger affinity with CO2, and thus, adsorption capacity of CO2 is larger than that of CH4 even with the coexistence of CO2-CH4 mixture. Displacement experiments of CO2-CH4 in shale proved that shale gas recovery is enhanced by the competitive adsorption of CO2 to CH4. Although the competitive adsorption mechanism is preliminary revealed, some challenges still exist. Competitive adsorption behavior is not fully understood in the coexistence of CO2 and CH4 components, and more experiment and model studies on adsorption of CO2-CH4 mixtures need to be conducted under field conditions. Coupling of competitive adsorption with displacing flow is key factor for CO2-ESGR but not comprehensively studied. More displacement experiments of CO2-CH4 in shale are required for revealing the mechanism of flow and transport of gas in CO2-ESGR. [ABSTRACT FROM AUTHOR]

The exploration and development of unconventional resources have been of growing interest in the industry in recent years. It is widely known that the adsorption and desorption mechanisms of unconventional gas have great significance for gas accumulation and exploration. However, major researches based on the mechanism of solid-gas interface have failed to reveal it completely, which introduce large discrepancies between actual and predicted production. In this paper, the mechanism of solid-liquid-gas adsorption and desorption interface is enlightened to describe the characteristics of unconventional gas. The validity of the proposal was verified preliminarily by building a conceptual model which redefines the gas-water distribution. Furthermore, the possibility of production of gas trapped in micropores was first investigated. The findings of this study can help for better understanding of the adsorption, desorption, and production mechanisms and in unconventional gas system. Accordingly, the explanation of variation between experiment result and actual production rate even with physical parameters was reasonable in theory. Therefore, this work should provide a basis for improving the accuracy of production predictions in actual reservoirs and should assist analysts in determining reasonable unconventional gas target. [ABSTRACT FROM AUTHOR]

In this paper, an experimental study of the variation of resistivity of coal samples in different bedding directions at 1 MHz frequency was performed by establishing an experimental system for resistivity testing of coal under triaxial stress. The low-pressure nitrogen gas adsorption (LP-N2GA) experiment and scanning electron microscopy (SEM) were obtained to analyze the pore-fracture structural characteristics of coal samples and the influence on resistivity anisotropy. Furthermore, the fundamental cause of anisotropy of coal resistivity is expounded systematically. The results show that the resistivity of loaded coal decreased first before increasing. The ionic conductance and the high degree of metamorphism slow down the decrease of resistivity. The distribution of pore and fracture structures is anisotropic. The connected pores and fractures are mainly distributed along the parallel bedding direction. The weak plane of bedding, diagenetic fractures, and plane fracture structures of parallel bedding result in the increase of fractures in the direction of vertical bedding, so increasing the potential barrier. Therefore, the resistivity in the vertical bedding direction is higher than that of the parallel bedding. Loading coal resistivity anisotropy degree is a dynamic change trend; the load increases anisotropy significantly under axial pressure, and the degree of anisotropy has a higher discreteness under confining pressure. It is mainly the randomness of the internal pore-fracture compaction, closure, and development of the heterogeneous coal under the confining pressure; the more rapid the decline in this stage, the larger the stress damage degree. [ABSTRACT FROM AUTHOR]

The phenomenon of coal swelling caused by gas adsorption is well known. For Enhanced Coal Bed Methane Recovery and carbon storage, coal swelling induced by gases adsorption may cause significant reservoir permeability change. In this paper, based on the assumption that the surface energy change caused by adsorption is equal to the change in elastic energy of the coal matrix, a theoretical model is derived to describe coal swelling induced by gas adsorption in the full pressure range. The Langmuir constant, coal density, solid elastic modulus, and Poisson's ratio are required in this model. These model parameters are easily obtained through laboratory testing. The developed model is verified by available experimental data. The results show that the presented model shows good agreement with the experimental observations of swelling. The model errors are within 14% for pure gas, and within 20% for mixed gas. It is shown that this model is able to describe coal swelling phenomena for full pressure range and different gas type including pure gas and mixed. In addition, it is also shown that the errors of the presented model and the Pan's model are almost the same, but the presented model is solved more easily. [ABSTRACT FROM AUTHOR]

Tectonic deformation can cause significant changes in the physical and chemical structures of coal by damaging the macrostructure and macromolecular composition. For thorough research on the coal tectonic deformation impacts on gas adsorption capacity, this paper collected and summarized the parameters of experimental adsorption isotherms and coal macerals, conducted proximate and ultimate analyses, and systematically discussed the adsorption properties of different structures of coals and the influence of temperature and pressure on coal adsorption. Furthermore, the semi-quantitative relationships between the structural parameters of coal and its methane adsorption capacity are explored. The results show that (1) due to different tectonic stresses, the molecular and porous structures of different types of tectonic coal exhibit significant differences (e.g. sample N25, which is in a fault zone, has the highest methane adsorption capacity), and (2) coal methane adsorption capacity decreases along with increasing temperature. At a pressure of 12 MPa, primary coal (N32) showed Langmuir volume (VL) values of 15.38, 9.58, and 7.86 cm3/g and Langmuir pressure (PL) values of 3.82, 2.07, and 1.81 MPa at temperatures of 30°C, 50°C, and 70°C, respectively. (3) The Langmuir volume appears to have a linear relationship with parameters ID1/IG, Al/OX, and A-factor, as well as a parabolic curve relationship with f a, thereby illustrating that increases of apparent aromaticity can raise CH4 adsorption on coal. [ABSTRACT FROM AUTHOR]

Gas transport through porous coal contains gas laminar flow in the cleat network and gas adsorption/diffusion in the matrix block. Since permeable capacity of the cleat is greater than that of the matrix, change of the matrix pressure readily lags behind change in the cleat pressure. Such unsynchronized pressure changes can result in a complex compatible deformation of a cleat-matrix system, significantly affecting the coal permeability. In this paper, we investigated the cleat-matrix interaction on coal permeability by using a modified pressure pulse decay method integrated with numerical analysis. The experimental results indicate that the bulk volume of the coal sample rapidly expanded at the beginning of gas injection, and then the volume expansion rate of the coal sample slowed down as the downstream pressure of the coal sample gradually equilibrated with the upstream pressure. During this process, the coal permeability was observed to gradually decrease with time. Numerical analysis results indicate that gas transport from the cleat to the matrix can attenuate the differential pressure between the cleat and the matrix. A smaller ratio of initial matrix permeability to initial cleat permeability can prolong decay duration of the differential pressure inside the cleat-matrix system. Although the coal sample is subjected to a stress-controlled condition, the coal permeability response to gas diffusion is closer to the case using a constant volume boundary. The dynamic change of coal permeability is significantly affected by the cleat-matrix interaction, in cases where the short-term change is mainly attributable to the cleat network and the long-term change is controlled by matrix swelling/shrinkage. [ABSTRACT FROM AUTHOR]

The parameters of pore-fracture structure and permeability have a controlling effect on the behaviors of gas adsorption/desorption and transportation in coal reservoir. A mathematic model for coal seams is of great significance to evaluate the mass migration within the coal fracture-matrix system. In this paper, the hydraulic-mechanical coupling model considering both dual-porosity dual-permeability and anisotropy characteristics is first established by using the methods of theoretical analysis, nuclear magnetic resonance (NMR) test, and numerical simulation. Then, this model is applied to simulate the gas migration characteristics of No. 3 coal seam in Changping Mine, China. Results show that the pore structure of No. 3 coal seam is characterized by small radius of pores and pore throats, which is determined by the NMR test, verifying the dual-permeability dual-porosity of coal seams. Both matrix permeability and fracture permeability increase approximately linearly with the process of mine gas extraction. The increased magnitude of the matrix permeability is greater than that of the fracture permeability. The permeability is inversely proportional to the anisotropy coefficient. The pressure gradient within the coal matrix and fracture increases first and then decreases with the extraction time. This pressure gradient is proportional to the anisotropy coefficient at the early stage of extraction and is inversely proportional to the anisotropy coefficient at the later stage. The seepage and diffusion flux are proportional to the anisotropy coefficient. The proportion of matrix-to-fracture seepage flux to the total flux increases first and then decreases to a certain value. The proposed model provides a guide for accurate designation of gas extraction from coal seams. [ABSTRACT FROM AUTHOR]

In the present paper, the Nonlinear Frequency Response (NFR) analysis is applied for theoretical study of kinetics of adsorption governed by pore-surface diffusion. The concept of higher-order frequency response functions (FRFs) is used. Based on a nonlinear mathematical model for adsorption of pure gas and spherical adsorbent particles, the theoretical first- and second-order FRFs, which relate the adsorbate concentration in the particle to the surrounding pressure (F1(ω) and F2(ω,ω)), have been derived. The obtained FRFs have been simulated for different steady-state pressures and different ratios (between zero and one) of surface to pore diffusion coefficients. The results show that, unlike F1(ω), F2(ω,ω) exhibits features which unambiguously distinguish the pore-surface diffusion model from pure pore diffusion and micropore diffusion. Based on the characteristic features of F1(ω) and F2(ω,ω), a new methodology for direct estimation of the separate values of the pore and surface diffusion coefficients has been established. [ABSTRACT FROM AUTHOR]

The adsorption of methane in coal depends on both pressure and temperature, and the adsorption gas content decreases as the temperature rises while increases as the pressure increases. When the gas molecule switches between the free state and adsorbed state, energy exchange is accompanied. To study the thermodynamic characteristics (adsorption heat, adsorption content, and adsorption time) of the methane adsorption of coal, the isothermal methane adsorption experiments of coal with different initial free gas pressures at different temperatures (30–90°C) were conducted. In this paper, a well-defined mathematical function of the adsorption heat was established on the basis of the actual gas state equation, Boltzmann energy distribution theory, and the two-state energy model, and the function was verified by the experimental data. The results show that the mathematical function of the adsorption heat can well describe the relationship among the adsorption heat, temperature, and initial free gas pressure in the closed adsorption system, and the adsorption heat involves the initial free gas pressure. The greater the initial free gas pressure, the less the adsorption heat is. In the adsorption process with different initial free gas pressures at different temperatures, the real-time free gas content increases with time and the adsorption system shows desorption process generally. For the adsorption process with the same initial free gas pressure, the adsorption time increases with the rising temperature. For the adsorption process with different initial free gas pressures at the same temperature, the greater the initial free gas pressure, the shorter the adsorption time it takes to reach an equilibrium state. The results help to understand the thermodynamic characteristics and the heat and mass transfer of methane in coal adsorption. [ABSTRACT FROM AUTHOR]

Adsorption energy distributions from experimental gas adsorption isotherms are capable to characterize the energetic heterogeneity of a solid surface. Unfortunately, they can only be computed by the adsorption integral equation, which represents an ill-posed problem, i.e., the solution is highly sensitive to errors in the input data. Ill-posed problems are usually solved by means of regularization, but general regularization schemata do not provide useful criteria to estimate the approximation quality. In this paper, a former presented solution strategy tailor-made for the Langmuir kernel of the adsorption integral equation is extended to Fourier transform. This yields a simple and effective cut-off criterion for the Fourier cosine transform of the adsorption energy distribution. The cut-off criterion is applied to calculate adsorption energy distributions from synthetic and experimental adsorption isotherms. [ABSTRACT FROM AUTHOR]

The pore-fracture structure of deep coal reservoirs is highly important for evaluating, exploring, and developing coalbed methane (CBM) resources. This study considers three coal samples from the DJ57 well in the Benxi Formation in the Daning–Jixian block on the eastern margin of the Ordos Basin as the research object. Based on the coal quality parameters of the coal samples, field emission scanning electron microscopy (FE-SEM), gas adsorption experiments, high-pressure mercury intrusion porosimetry (MIP), and microcomputed tomography (micro-CT) scanning were used to quantitatively characterize the nanoscale pores and microscale fractures in deep coal reservoirs and to evaluate the pore-fracture structure at different scales. The results reveal that the pore types in the Benxi Formation coal samples are diverse and include mainly organic matter (OM) pores, inorganic pores (intraparticle and interparticle pores), and microfractures. The organic pores are diverse in shape and mainly exhibit round, oval, and wedge shapes, while the microfractures exhibit slender stripes or serrated curves. The multiscale quantitative characterization of deep coal reservoir pores and fractures is based on a variety of pore characterization methods, and the pore and fracture volume distributions are mainly U-shaped, revealing the coexistence of micropores and microfractures. The volumes of micropores (0.3–2 nm), mesopores (2–50 nm), macropores (50 nm to 10 μm), and microfractures (>10 μm) account for 78.00%, 6.78%, 2.08%, and 13.14%, respectively, of the total pore volume (PV). Based on a full-scale pore-fracture splicing calculation, the total permeability of the Benxi Formation coal samples ranges from 5.77 to 28.22 mD. The observation results indicate that the microfractures are connected to each other, forming a network structure with strong connectivity. The microfractures are mainly associated with pore diameters > 100 μm, accounting for approximately 95% of the total permeability. Moreover, micropores in deep coal reservoirs provide a large space for CBM adsorption, and microfractures enhance the seepage capacity of CBM. [ABSTRACT FROM AUTHOR]

Several techniques (such as scanning electron microscopy (SEM) and gas adsorption systems) have been used to study the pore features and structures of shale reservoirs. The available methods and techniques have restricted the specific research on micropores, and the morphology, genesis, volume, and main factors controlling pore characteristics are yet to be analyzed. Currently, there is no systematic understanding of the role that these spaces play in gas storage and flow. As such, our understanding of the spatial connectivity of pores and reserves of shale reservoirs is limited. In this study, the pores of the Fuling shale gas reservoir in the Sichuan Basin were systematically observed by SEM and transmission electron microscopy. Images of pores smaller than 2 nm were captured for the first time, and their morphology and genesis were analyzed by combining these images with the rock mineralogy theory. The pore size distribution characteristics of the reservoir were analyzed by the adsorption-mercury injection method and nuclear magnetic resonance, and the main factors controlling the distribution of different pore sizes were analyzed. The results show that large numbers of micropores were distributed between the mesopores and macropores in the shale reservoir, which mainly consisted intergranular pores, intermolecular pores, interlamellar pores of clay minerals, and organic matter skeleton pores. The development of pores smaller than 1 nm was mainly controlled by the clay mineral content, and the development of pores with a size of approximately 1-2 nm was related to the contents of clay minerals and organic matter. These pores could connect the macropores and mesopores well, which is important for gas storage and flow. In this paper, the types, distribution, and main controlling factors of micropores were studied, and our understanding of the reservoir space was improved from the nanometer level to the Angstrom level, which is important for gas storage and flow process analysis. [ABSTRACT FROM AUTHOR]

Summary: Injecting carbon dioxide for shale gas recovery enhancement (CO2‐ESGR) is an effective method to improve gas production and also realize the CO2 geosequestration. In the CO2‐ESGR system, there are two‐component gases (TCG) coexisted. The gas transport and adsorption mechanisms are different from the single‐component gas system. However, most of current work is still focused on single‐component gas (ie, methane). Many mechanisms have not been considered in the study of CO2‐ESGR study. In order to conduct reliable numerical simulation for CO2‐ESGR, a clear understanding of the transport and adsorption mechanisms for TCG system is necessary. In this review, we focused on two key issues regarding CO2‐ESGR: the fluid transport and competitive adsorption. The fundamental mechanisms and models for pure gas and TCG transport have been comprehensively summarized. The adsorption models for TCG system have been reviewed and analyzed. Models such as extended Langmuir model, ideal adsorption solution model, and lattice density functional model have been compared. Also, the factors affecting the competitive adsorption of TCG in shale have been illustrated. The main factors include organic matter content, shale composition, pore structure, water content, and pressure. At last, the problems existed in current research of transport and adsorption models for TCG have been analyzed. The issues that are necessary to be considered in CO2‐ESGR technology have been proposed so that more accurate numerical simulation and more reliable production prediction can be achieved. [ABSTRACT FROM AUTHOR]

The various modes of acid gas storage in aquifers, namely structural, residual, and local capillary trapping, are effective only if the rock remains water-wet. This paper reports an evaluation, by means of the captive-bubble method, of the water-wet character in presence of dense acid gases (CO2, H2S) of typical rock-forming minerals such as mica, quartz, calcite, and of a carbonate-rich rock sampled from the caprock of a CO2 storage reservoir in the South-West of France. The method, which is improved from that previously implemented with similar systems by Chiquet et al. ( Geofluids 2007; 7: 112), allows the advancing and receding contact angles, as well as the adhesion behavior of the acid gas on the mineral substrate, to be evaluated over a large range of temperatures (up to 140°C), pressures (up to 150 bar), and brine salinities (up to NaCl saturation) representative of various geological storage conditions. The water-receding (or gas-advancing) angle that controls structural and local capillary trapping is observed to be not significantly altered in the presence of dense CO2 or H2S. In contrast, some alteration of the water-advancing (or gas-receding) angle involved in residual trapping is observed, along with acid gas adhesion, particularly on mica. A spectacular wettability reversal is even observed with mica and liquid H2S. These results complement other recent observations on similar systems and present analogies with the wetting behavior of crude oil/brine/mineral systems, which has been thoroughly studied over the past decades. An insight is given into the interfacial forces that govern wettability in acid gas-bearing aquifers, and the consequences for acid gas geological storage are discussed along with open questions for future work. [ABSTRACT FROM AUTHOR]

This paper describes an investigation of argon adsorption into carbon nanotubes at temperatures below the triple point, using a grand canonical Monte Carlo simulation to study the effects of confinement and surface strength on the 2D transition. In large pores, it was found that 2D transitions can occur in more than one layer, but are absent in higher layers for small pores. The 2D critical temperature of the first layer for a small pore (R = 1.2 nm) was found to be ca. 66 K (MWCNT) and 65 K (SWCNT), compared to 55-59 K observed experimentally for a flat graphite surface. This is because of the overlapping effects due to the surface curvature or the confinement in a carbon nanotube. Assuming a weaker carbon surface by reducing the graphene surface strength by 40% for SWCNT, the 2D critical temperature was only modestly reduced to 63 K. This suggests that the experimental data at 59 K might be attributed to other factors, other than confinement effects. An imperfect surface is suggested and, employing 5% defects on this surface, the 2D critical temperature has been determined as 58 K which is in better agreement with the experimental value of 59 K. [ABSTRACT FROM AUTHOR]

Due to the insufficient accurate evaluation model of gas resources in abandoned mines, the development and utilization of abandoned mine gas resources in China are still in the preliminary exploration stage. To this end, in response to the problem of imprecise assessment of gas resource reserves in the adsorbed state of residual coal, the No. 3 coal seam in Jincheng mine was used as the research object, by analyzing the evolution of the ambient gas pressure and temperature of the residual coal in the abandoned mine, and simulating the pressure and temperature environment in which the residual coal is located, the gas adsorption experiment of the residual coal was carried out in this environment, and a gas storage model of the residual coal was constructed with the combination of the adsorption theory. The results show that pressure has a positive effect on gas adsorption by residual coal, while temperature has a negative effect on it. The adsorption potential gradually decreases with increasing pressure and increases with increasing temperature, while the adsorption space increases with increasing pressure and decreases with increasing temperature. The adsorption characteristic curves obtained by the two methods are temperature independent and polynomial in shape, and the fitted correlation coefficient of method 1 is generally higher than that of method 2. The adsorption characteristic curves of two methods are best fitted at k = 2.5 , so the value of k is most appropriately taken as 2.5 when calculating the virtual saturation vapour pressure. The average relative errors between the predicted and measured values of method 1 and 2 were 2.98% and 7.13%, respectively. The prediction effect of method 1 was significantly better than that of method 2 and met the requirements of engineering applications; therefore, method 1 was used to establish a model for the adsorbed gas storage capacity of residual coal in abandoned mines. [ABSTRACT FROM AUTHOR]

The coal matrix can expand after gas adsorption, thus reducing the permeability of coal reservoirs and further affecting the coalbed methane production. Whether the heat released by coal adsorbing gas is a cause of the coal expansion has not yet been determined. Therefore, the anthracite coal with high gas adsorption capacity was used; under the conditions of 35°C and 1-6 MPa, the adsorption capacity and the adsorption heat of coal adsorbing CO2 and CH4 were tested. The specific heat capacity and thermal expansion coefficient of coal at 35°C were tested. The temperature change of the coal after being heated was calculated by combining the absorption heat and specific heat capacity; also, the thermal expansion rate was calculated by combining the temperature change and expansion coefficient. In addition, the cube law was used to calculate the permeability change of coal before and after the adsorption expansion. The results show that the changes in the gas adsorption capacity and adsorption heat of the coal obey the Langmuir equation, and those to CO2 are both higher than to CH4. The temperature of coal increases after the heat is released in the process of CO2 and CH4 adsorption, and the temperature change of coal adsorbing CO2 and CH4 reaches 102°C and 72°C, respectively, at 6 MPa. The thermal expansion rate of coal adsorbing CO2 and CH4 reaches 5.40% and 3.81%, at 6 MPa, respectively. It is found that a higher gas pressure could lead to a higher temperature change, a higher thermal expansion rate, as well as a higher thermal expansion and coal deformation. After the adsorption of CO2 and CH4, the coal permeability is reduced by 20.43% and 14.66%, respectively, at 6 MPa. Both the thermal expansion rate and the permeability change with the gas adsorption pressure obey the Langmuir equation. Therefore, the adsorption expansion of coal may be thermal expansion caused by the heat released by coal adsorbing gas. [ABSTRACT FROM AUTHOR]

Herein, we report a simple and scalable synthesis route to prepare Ag-functionalized porous ZnO sheets and their enhanced NO2 gas sensing properties. Porous ZnO sheets functionalized with well-dispersed submicron Ag particles were prepared by using a hydrothermal method-based one-pot synthesis route from Zn and Ag precursors. NO2 gas sensing performance (response, selectivity, response time, and recovery time) was optimized at 200°C in the gas sensor fabricated with 3 at% Ag-functionalized porous ZnO sheets. We demonstrated a response ( R g / R a ) of 17.18 to 10 ppm NO2 gas and also obtained a high response of 14.05 even at 60% relative humidity due to the synergetic effect of improved NO2 gas adsorption in the presence of Ag particles and increased resistance by the formation of Schottky barrier at Ag-ZnO heterojunctions. [ABSTRACT FROM AUTHOR]

The Ziehl-Neelsen stain is a mixture of Basic Fuchsin (BF), phenol (Ph), and methylene blue. It is used to stain the cell walls of Mycobacterium species. In this study, Basic Fuchsin was efficiently removed from synthetic wastewater using natural clay of Gankawa (GC) from Sulaimanyah city, and the effect of the presence of high concentrations of phenol in the adsorption mixture is demonstrated. In addition, X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 gas adsorption analyzer, and field-emission scanning electron microscopy (FESEM) were used to characterize the natural clay. The clay was found to be mostly calcite, with a minor percentage of smectite, and contaminated with low percentages of illite. The adsorption kinetics show a relatively fast equilibration time (60-70 minutes). A second-order pseudokinetic model better fits the experimental kinetic data. The effect of the initial pH of the solution mixture was negligible at the experimental concentration range of the study. Freundlich and Langmuir's adsorption isotherm models were applied to the equilibrium experimental data using nonlinear regression curve fitting. Both kinetics and isotherm studies point to a chemical adsorption mechanism for the process. For adsorption in the mixture, phenol molecules were found to compete with BF molecules for the active adsorption sites, while a synergetic effect of BF exists on phenol adsorption. As a naturally abundant cheap material, GC shows a superior adsorption capacity toward BF (287.0 mg g-1) over all natural materials and most of the synthetic or modified materials found in the literature. [ABSTRACT FROM AUTHOR]

Pore structure and methane adsorption of coal reservoir are closely correlated to the coalbed gas occurrence and outburst. Full-scale pore structure and its fractal heterogeneity of coal samples were quantitatively characterized using low-pressure N2 gas adsorption (LP-N2GA) and high-pressure mercury intrusion porosimetry (HP-MIP). Fractal pore structure and adsorption capacities between outburst and nonoutburst coals were compared, and their geological significance to gas occurrence and outburst was discussed. The results show that pore volume (PV) is mainly contributed by macropores (>1000 nm) and mesopores (100–1000 nm), while specific surface area (SSA) is dominated by micropores (<10 nm) and transition pores (10–100 nm). On average, the PV and SSA of outburst coal samples are 4.56 times and 5.77 times those of nonoutburst coal samples, respectively, which provide sufficient place for gas adsorption and storage. The pore shape is dominated by semiclosed pores in the nonoutburst coal, whereas open pores and inkbottle pores are prevailing in the outburst coal. The pore size is widely distributed in the outburst coal, in which not only micropores are dominant, but also, transition pores and mesopores are developed to a certain extent. Based on the data from HP-MIP and LP-N2GA, pore spatial structure and surface are of fractal characteristics with fractal dimensions D m 1 (2.81–2.97) and D n (2.50–2.73) calculated by Menger model and Frenkel–Halsey–Hill (FHH) model, respectively. The pore structure in the outburst coal is more heterogeneous as its D n and D m 1 are generally larger than those of the nonoutburst coal. The maximum methane adsorption capacities ( V L : 15.34–20.86 cm3/g) of the outburst coal are larger than those of the nonoutburst coal ( V L : 9.97–13.51cm3/g). The adsorptivity of coal samples is governed by the micropores, transition pores, and D n because they are positively correlated with the SSA. The outburst coal belongs to tectonically deformed coal (TDC) characterized by weak strength, rich microporosity, complex pore structure, strong adsorption capacity, but poor pore connectivity because of inkbottle pores. Therefore, the area of TDC is at high risk for gas outburst as there is a high-pressure gas sealing zone with abundant gas enrichment but limited gas migration and extraction. [ABSTRACT FROM AUTHOR]

In order to study the effect of different rank coals on the displacement of CH4 by CO2 and prevent the gas-related disasters, a series of experiments were carried out. For this purpose, we selected low-rank lignite raw from Datong coalfield of Shanxi Province, medium-rank bituminous coal raw from Xutuan coalfield of Anhui Province, and high-rank anthracite raw coal from Yangquan coalfield of Shanxi Province. The results showed that (1) the shape of the displacement adsorption curve of the mixed gas and the shape of the single-dimensional adsorption curve of the pure gas are both steep at the beginning, with the increase of the pressure, the curve becomes more and more gentle. The difference is that it is lower than the single-dimensional gas adsorption curve. (2) The separation factor in the coal samples used in the experiment shows a trend of first decreasing and then increasing with the decrease of coal rank. The displacement factor has the same trend as the separation factor of each coal rank, which is Z i j anthracite > Z i j lignite > Z i j bituminous coal . (3) The amount of displaced CH4 in the displacement/adsorption process has enhanced with the increase in pressure, and the trend for different coals is Q Z bituminous coal > Q Z anthracite > Q Z lignite . In addition, displacement showed the order ƞ lignite > ƞ anthracite > ƞ bituminous coal . The injection ratio of bituminous coal and anthracite decrease with the increase in pressure, while that of lignite increase first and later decreased. (4) In gas injection displacement, on the long time, the displacement effect of high coal rank is better than that of low coal rank. [ABSTRACT FROM AUTHOR]

Summary: Design of advanced highly porous heteroatom‐doped carbon is desirable for their wide presence in applications like electrochemical energy storage systems, gas adsorption, and separation processes. In this work, porous nitrogen‐doped carbon was developed from ethylenediamine via an in situ self‐doping solvothermal process followed by pyrolysis and KOH activation under high temperature. Micropore‐rich nitrogen‐containing carbon materials were prepared through variation of the KOH/C ratio during activation and their electrochemical performance in alkaline electrolyte as well as CO2 sorption behaviour was evaluated. The porous carbon developed using KOH/C ratio of 2 delivered highest supercapacitor performance in 6 M KOH achieving high specific capacitance of 353 F g−1 with 1 A g−1 of current due to its high pore volume and micropore rich surface. The functionalized carbon delivered CO2 uptake capacities of 4.48 and 3.0 mmol g−1 under temperatures of 273 and 298 K, respectively, at 1 bar pressure with a good CO2/N2 selectivity of 20.58 and CO2/CH4 selectivity of 3.83. The existence of nitrogen functional groups, high surface area, and micropore‐rich porous structures may be the essential reasons behind superior electrode performance and CO2 capture capacity of the material. This work hopefully offers a simple development of N‐doped carbon for effective energy storage and CO2 adsorption systems. [ABSTRACT FROM AUTHOR]

The characteristics of pores in anthracite from Guhanshan Coal Mine in the Jiaozuo mining area were tested by the mercury injection method. According to the pore size, pores in the coal sample were classified into gas seepage pores and gas adsorption pores which were in line with the stochastic fractal model and the dendric fractal model, respectively. Besides, the fractal characteristics of adsorption pores were analyzed by using a dendric fractal model, and the influence law of the tortuosity fractal dimension D t on the gas adsorption capacity was obtained. The research results show that the amount of mercury injected into each experimental coal sample is directly proportional to its porosity, but has no obvious correlation with specific surface area. Seepage pores with sizes over 65 nm fit the stochastic fractal model, and their fractal dimension D increases with the increase of specific surface area. Adsorption pores with sizes of below 65 nm fit the dendric fractal model, and their tortuosity fractal dimension D t is positively correlated with the specific surface area. Through the gas adsorption experiment on coal samples, it is found that a larger D t corresponds to a stronger gas adsorption capacity. The research results can provide a theoretical basis for elucidating the gas adsorption characteristics of anthracite from a microscopic point of view. [ABSTRACT FROM AUTHOR]

The Triassic Zhangjiatan shale in the Ordos basin, recognized as one of most promising shale oil and gas resources in China, is one example of medium-low-maturity lacustrine shale reservoirs wherein the pore network has been proven to be different from those of both conventional and high-maturity marine shale reservoirs. Here, we examine the quantitative characterization of pore size and movable fluid distribution of the Zhangjiatan shale reservoir. Eight shale core plugs were measured in a series of nuclear magnetic resonance (NMR) experiments to determine the pore structure and pore fluid transport during the processes of centrifuging and heating. The complete pore size distribution was obtained from the T 2 spectrum by integrating NMR, high-pressure mercury intrusion, and nitrogen gas adsorption. The results show that the movable fluid saturation of Zhangjiatan shale is 19.47–33.02% and the capillary-bound fluid saturation is 14.53–27.62%, whereas the unrecoverable fluid saturation was 43.51–65.26%. The movable fluids are mainly detected in macropores and mesopores with a minimum pore size of 50.5–121.2 nm, while capillary-bound fluids are mainly found in small pores and some mesopores with a minimum size of 25.8–67.5 nm. Almost all unrecoverable fluids are in micropores and small pores. In contrast to high-maturity shale reservoirs, the Zhangjiatan shale shows a poor correlation between total organic carbon content and unrecoverable fluid saturation but a good correlation between clay minerals and unrecoverable fluid saturation, showing that most micropores are associated with clay minerals and the organic matter pores are less developed. This study provides an accurate determination of the pore size distribution and pore fluid typing of Zhangjiatan shale, which is of great significance for the development of high-quality but medium-low-maturity shale reservoirs in China. [ABSTRACT FROM AUTHOR]

This paper addresses durability and shrinkage performance of the self-compacting concretes (SCCs) in which natural coarse aggregate (NCA) and/or natural fine aggregate (NFA) were replaced by recycled coarse aggregate (RCA) and/or recycled fine aggregate (RFA), respectively. A total of 16 SCCs were produced and classified into four series, each of which included four mixes designed with two water to binder (w/b) ratios of 0.3 and 0.43 and two silica fume replacement levels of 0 and 10%. Durability properties of SCCs were tested for rapid chloride penetration, water sorptivity, gas permeability, and water permeability at 56 days. Also, drying shrinkage accompanied by the water loss and restrained shrinkage of SCCs were monitored over 56 days of drying period. Test results revealed that incorporating recycled coarse and/or fine aggregates aggravated the durability properties of SCCs tested in this study. The drying shrinkage and restrained shrinkage cracking of recycled aggregate (RA) concretes had significantly poorer performance than natural aggregate (NA) concretes. The time of cracking greatly prolonged as the RAs were used along with the increase in water/binder ratio. [ABSTRACT FROM AUTHOR]

The influence of gas adsorption and desorption on the volumetric strain of coal was measured by a self-designed, fluid–solid coupling triaxial coal adsorption deformation experimental system. The experimental results show that coal deformation has a threshold value with an increase in gas content. Before the gas content reaches the threshold value, coal deformation is not obvious. When the gas content reaches the threshold value, the deformation will increase sharply. At the same time, coal volume strain changes with coal gas content in accordance with exponential law ε = ε0(eϒc-1). Based on the experimental results, considering the coupling effects of heat transfer, water seepage, coal and rock mass deformation, and coalbed methane desorption and seepage, a mathematical model of heat transfer–deformation–seepage coupling coalbed methane migration was established, and a numerical simulation study was carried out on the heat injection-enhanced coalbed methane mining project. The results show that (1) With continuous heat injection, the gas in the coal seam is rapidly desorbed, and the adsorbed gas content forms an elliptical funnel that extends from the extraction hole to the deep part of the coal body and takes the fracturing crack as the center to the upper and lower boundaries of the coal seam. At day 30, the adsorbed gas content in the whole drainage area has decreased to 0.1 m3/t within 2m from the fracture zone. (2) On the basis of considering the gas adsorption expansion effect, the strain of the coal body decreases from roof to floor. With the increase in the heat injection time, the strain value will also increase, and the strain increase will decrease. When the heat injection is 30 days, the maximum strain at the roof is 0.015. The research results have important guiding significance for predicting coal rock deformation and determining gas extraction efficiency in the process of heat injection-enhanced coalbed methane extraction. [ABSTRACT FROM AUTHOR]

In order to improve efficiency of gas drainage, the reasonable layout parameters for borehole on roadway head are investigated. Assuming that the coal mass has a dual pore structure with fractures and pores, a multiphysical field coupling mathematical model is proposed for gas drainage. The governing equations of gas adsorption, seepage, and diffusion are considered. The process of gas preextraction and excavating-extraction collaboration on roadway heading face in 2606 haulage roadway of Zhangcun mine is modeled by finite element (FE) method. The effects of gas drainage under different drilling arrangements are analyzed. The results show that the fastest decreasing rate of gas content occurs at the beginning of drainage, and decreasing rate of gas content tends to be stable in the later stage. After removing the predraining on roadway head, the gas content at the center of coal wall on the roadway heading face will rebound. The included angle between the borehole and the roadway middle line determines the spatial area of gas drainage. Too small included angle will reduce the area of gas content reduction, while too large included angle will result in a blind area on both sides of the roadway. The change in borehole spacing affects the decreasing rate of gas content in the rock and coal around the roadway. Large spacing may cause an inadequate decreasing rate in the middle of the roadway, while small spacing may cause an inadequate decreasing rate in both sides of the roadway. In the field application, the pure gas flow and gas concentration of drainage show a downward trend in whole. The gas concentration decreased from 13.2% to 10.8%, and the pure gas flow decreased from 10.6 m3/min to 8.15 m3/min. Research achievements can provide a basis for gas drainage in underground roadway. [ABSTRACT FROM AUTHOR]

In order to explore the change characteristics of the adsorption and desorption performance of coal under high gas pressure, low-field nuclear magnetic resonance (LFNMR) technology was used to conduct experimental research on coal adsorption and desorption. The results show that (1) the T 2 spectrum distribution diagram shows adsorption peaks ( T 2 = 0.01 ms ~ 1 ms) and free peaks ( T 2 = 5 ms ~ 1000 ms); (2) with the increase of equilibrium pressure, the peak area of adsorbed methane gradually increased at first and then tended to equilibrium. The initial increase rate of free methane was slower than that of adsorbed methane, and the increase rate of free methane was faster in the later stage; (3) the relationship between the amount of adsorbed gas in the adsorption state of coal and the gas pressure conforms to the Langmuir equation. Taking the equilibrium pressure P = 8.7 MPa as the critical hysteresis pressure, it can be divided into two stages which are higher gas pressure (0.5~8.7 MPa) and high gas pressure (8.7~10.33 MPa); the amount of adsorbed gas in the free state has a linear relationship with the gas pressure, and there is no obvious hysteresis; (4) comparative analysis under the same experimental conditions, the mass of the adsorbed gas in the desorption process is greater than the mass of the adsorbed gas in the adsorption process, and there is basically no difference in the mass of the free gas. [ABSTRACT FROM AUTHOR]

In this paper the results of the experimental studies on a relationship between pore volume of hard coals and their tendency to spontaneous combustion are presented. Pore volumes were determined by the gas adsorption method and spontaneous combustion tendencies of coals were evaluated by determination of the spontaneous combustion indexes Sza and Sza on the basis of the current Polish standards. An increase in the spontaneous combustion susceptibility of coal occurs in the case of the rise both in micropore volumes and in macropore surfaces. Porosity of coal strongly affects the possibility of oxygen diffusion into the micropores of coal located inside its porous structure. The volume of coal micropores determined on the basis of the carbon dioxide adsorption isotherms can serve as an indicator of a susceptibility of coal to spontaneous combustion. [ABSTRACT FROM AUTHOR]

This paper describes the effects of igneous intrusions on pore structure and adsorption capacity of the Permian coals in the Huaibei Coalfield, China. Twelve coal samples were obtained at different distances from a ~120m extremely thick sill. Comparisons were made between unaltered and heat-affected coals using geochemical data, pore-fracture characteristics, and adsorption properties. Thermal alteration occurs down to ~1.3 × sill thickness. Approaching the sill, the vitrinite reflectance (R°) increased from2.30% to 2.78%, forming devolatilization vacuoles and a fine mosaic texture. Volatile matter (VM) decreased from 17.6% to 10.0% and the moisture decreased from 3.0% to 1.6%. With decreasing distance to the sill, the micropore volumes initially increased from 0.0054 cm³/g to a maximum of 0.0146 cm³/g and then decreased to 0.0079 cm³/g.The results show that the thermal evolution of the sill obviously changed the coal geochemistry and increased the micropore volume and adsorption capacity of heat-affected coal (60-160m from the sill) compared with the unaltered coals. The trap effect of the sill prevented the high-pressure gas from being released, forming gas pocket.Mining activities near the sill created a low pressure zone leading to the rapid accumulation of methane and gas outbursts in the Haizi Mine. [ABSTRACT FROM AUTHOR]

The pore characteristics of coal have an important influence on the coal adsorption of methane. The liquid nitrogen adsorption method was used to study the pore structure of low- and middle-rank coal samples from two aspects: pore specific surface area and pore shape. Low-field nuclear magnetic resonance (NMR) technology was used to study the difference in methane adsorption of coal samples under the same adsorption conditions. The influence and mechanism of the pore structure of middle- and low-rank coal samples on gas adsorption are discussed and analyzed. The results show the following: (1) There are differences in the adsorption capacity of medium- and low-rank coal samples. Within 1 h of methane inflation, the methane adsorption capacity of middle-rank coals such as Henan Pingdingshan (PDS) and Shanxi Wangzhuang (WZ) and Xinjiang low-rank coals (XJ) increases by 36.4%, 31.7%, and 35.8%, respectively, and as the inflation time is extended to the cumulative inflation of 10 h, the order of the increase in methane adsorption capacity is still PDS>XJ>WZ. (2) The pore types of the experimental coal samples are mostly wedge-shaped pores and ink bottle-shaped pores. The order of the BET specific surface area of the coal samples is in the order of WZ>PDS> XJ, which means that the WZ samples can provide more adsorption sites for gas molecule adsorption, but under the same adsorption conditions, the WZ sample has the least amount of gas adsorbed. Further analysis shows that the order of the tortuosity of the coal sample is WZ>XJ>PDS, which means that the WZ sample has a large pore tortuosity, a long channel for methane molecules to diffuse into the internal pores of the coal sample, and large diffusion resistance. It is the main reason why the methane adsorption capacity of WZ coal samples is less than that of PDS and XJ coal samples in the same adsorption conditions. [ABSTRACT FROM AUTHOR]

Summary: Ionic liquids (ILs) are promising solvents for catalytic and electrolyte applications, gas absorption, and extractions in electrochemical systems due to their useful features, such as high conductivity and good thermal, chemical, and electrical stability. This review focuses on incorporating ILs into fuel cell (FC) systems, specifically into two main components of FC (ie, polymer electrolyte membrane and electrocatalyst). In FC, a polymer electrolyte membrane with excellent conductivity and deprived of humidity even at high temperatures must be created for effective early commercialization of this technology. Electrocatalyst performance can also be enhanced with additive materials, such as ILs, thus further improving the entire achievement of FCs. This work discusses the most important reasons for ongoing studies and outlines the current progress in using ILs as a revolutionary form of polymer electrolyte membrane and electrocatalyst. [ABSTRACT FROM AUTHOR]

Summary: Heteroatom‐doped porous carbon materials have great potential for both capacitive energy storage and gas sorption applications. This article reports the synthesis of highly porous sulfur‐doped carbon from thiophene using an in situ self‐doping strategy followed by KOH activation. A series of highly porous sulfur‐containing carbon materials with high surface area and pore volume were prepared through variation of activation temperature from 600°C to 900°C and applied as supercapacitor electrodes in alkaline as well as neutral electrolyte and also as adsorbent for CO2, H2 adsorption. The material prepared at 800°C presented the highest electrochemical performance with a specific capacitance of 300 F g−1 at 1 A g−1 in 6 M KOH because of its high surface area and pore volume. The presence of oxidized sulfur functionality, high surface area, and micro‐mesoporous structure were the responsible factors for enhanced storage of gases like CO2 and H2. The functionalized carbon showed a good H2 uptake value of 2.8 wt% under 1 bar pressure at 77 K. CO2 uptake capacities were found to be 5.6 and 3.3 mmol g−1 at 1 bar pressure under the temperature of 273 and 298 K, respectively with a good CO2/N2 selectivity of 14.36 and CO2/CH4 selectivity of 2.53. This report presents a promising porous sulfur‐doped carbon material for cost‐effective and efficient gas adsorption and energy storage systems. [ABSTRACT FROM AUTHOR]

Gas adsorption and atom doping usually present when preparing carbon nanotubes (CNTs) and can affect the field emission properties of carbon nanotubes. H2O molecule and boron atom are the most important adsorbates, respectively. Using ab-initio calculations, we have investigated the electron field emission performance of CNTs simultaneously adsorbed with one H2O molecule and doped with one boron atom (BCNT+H2O) in this paper. The results indicate that the electrons localize at the top of BCNT+H2O and the electronic density of states (DOS) around the Fermi level is enhanced obviously. It is expected that BCNT+H2O will be more propitious to the field emission of electrons based on the calculations of DOS, HOMO/LUMO, and Mulliken charge population. [ABSTRACT FROM AUTHOR]

This paper focuses on polymers that demonstrate microporosity without possessing a network of covalent bonds--the so-called polymers of intrinsic microporosity (PIM). PIMs combine solution processability and microporosity with structural diversity and have proven utility for making membranes and sensors. After a historical account of the development of PIMs, their synthesis is described along with a comprehensive review of the PIMs that have been prepared to date. The important methods of characterising intrinsic microporosity, such as gas absorption, are outlined and structure-property relationships explained. Finally, the applications of PIMs as sensors and membranes for gas and vapour separations, organic nanofiltration, and pervaporation are described. [ABSTRACT FROM AUTHOR]

Phthalates are typical air pollutants in vehicular environment since numerous synthetic materials that might contain phthalates are widely used to fabricate vehicle interiors (e.g., seat cushions, floor mats and dashboards). Hitherto, the importance of phthalate pollution in vehicular environment is not well‐recognized because people spend only a small portion (around 8%) of their time in vehicles. In this study, the mass fractions of six phthalates in nine materials commonly used in Chinese vehicles (floor mats and seat cushions) were measured. Two phthalates, di‐n‐butyl phthalate (DnBP) and di‐2‐ethylhexyl phthalate (DEHP), were identified in most materials (the other phthalates were not detected). The emission characteristics of DnBP and DEHP from these materials were further investigated. The measured emission parameters were used as input for a mass‐transfer model to estimate DnBP and DEHP concentrations in cabin air. Finally, the ratios between human exposures (via inhalation and dermal absorption from the gas phase) in vehicular environment and the total exposures in typical indoor environments (e.g., residences and offices) were estimated to be up to 110% and 20% for DnBP and DEHP, respectively. Based on these results, the vehicular environment might be a considerable site for human exposure to airborne phthalates. [ABSTRACT FROM AUTHOR]

To understand the pore structure and heterogeneity of pore size distribution (PSD) is essential for revealing fluid mechanics and evaluating the utilization of unconventional resources. In this study, there are multiple shale examples collected from the Chang 7 section in the Ordos Basin for the investigation was conducted on the basis of various experiments on total organic carbon (TOC), X-ray diffraction (XRD), and nitrogen gas adsorption, through scanning electron microscopy (SEM) and multifractal method. The multifractal characteristic parameters, including the width of singularity spectra (Δ α), Hurst exponent (H), D 1 / D 0 , and nitrogen gas adsorption, were used to find out about the characteristics of pore development and to quantify the complexity and heterogeneity of pore structure. Depending on the exact mineral composition, the Yanchang Formation of Chang 7 shales is classified into either silty mudstone (SM) or muddy siltstone lithofacies (MS). According to the investigative results, the Chang 7 lacustrine shale features a complex pore system with the pores ranging from 1.5 to 10 nm in diameter. Besides, mesopores contribute significantly to the total pore volume (TPV) and total surface area (TSA). As for TPV and TSA of the SM lithofacies in the samples under investigation, they are nearly 1.09–1.78 and 0.80–1.72 times greater as compared to the MS lithofacies samples. The dominant types of reservoir spaces include organic matter (OM) pore and interparticle pore which are related to inorganic minerals. The value of Δ α is higher for MS lithofacies than for SM lithofacies, indicating a greater heterogeneity of PSD in the MS lithofacies. The pore structure of MS lithofacies is determined mainly by TOC and siliceous mineral content, whereas the influencing factors for SM lithofacies are TOC and clay mineral content. There is a significant relationship between multifractal parameters and pore structure parameters for both SM and MS lithofacies. The TOC of SM and MS lithofacies exhibits a close correlation with Δ α , suggesting that the pores in organic matter are dominated by those nanopores with a complex and heterogeneous pore structure. The rock composition of the lithofacies can affect Δ α to a varying extent, which means that the minerals have an evident impact on the heterogeneity of MS and SM lithofacies. [ABSTRACT FROM AUTHOR]

To study the role of the effective pressure on the percolation rate of coal, the effect of gas pressure, gas adsorption, and temperature on coal is taken into consideration comprehensively. Starting from the research direction of effective pressure and porosity, the coal body percolation rate and effective pressure equations considering the influence of temperature and gas pressure are established. The experiments on the percolation characteristics of raw coal are implemented under different effective pressure by using the independently developed thermos-solid-gas linking triaxial servosystem. The theoretical equation of the effective pressure and percolation rate of coal is calculated with the finite element software COMSOL, and the results obtained from the theoretical equation agree well with the experimental results. The results show that the percolation rate of coal gradually decreases with the growth of the effective pressure when the gas pressure and temperature are kept unchanged. Therefore, the results of the research are of certain reference value for the effective prevention of gas disaster. [ABSTRACT FROM AUTHOR]

Methane adsorption capacity is an important parameter for coalbed methane (CBM) exploitation and development. Traditional examination methods are mostly time-consuming and could not detect the dynamic processes of adsorption. In this study, a modified low-field nuclear magnetic resonance (NMR) method that compensates for these shortcomings was used to quantitatively examine the methane adsorption capacity of seven medium-rank coals. Based on the typical T 2 amplitudes obtained from low-field NMR measurement, the volume of adsorbed methane was calculated. The results indicate that the Langmuir volume of seven samples is in a range of 18.9–31.85 m3/t which increases as the coal rank increases. The pore size in range 1-10 nm is the main contributor for gas adsorption in these medium-rank coal samples. Comparing the adsorption isotherms of these coal samples from the modified low-field NMR method and volumetric method, the absolute deviations between these two methods are less than 1.03 m3/t while the relative deviations fall within 4.76%. The absolute deviations and relative deviations decrease as vitrinite reflectance ( R o ) increases from 1.08% to 1.80%. These results show that the modified low-field NMR method is credible to measure the methane adsorption capacity and the precision of this method may be influenced by coal rank. [ABSTRACT FROM AUTHOR]

Geological factors are key elements to control shale gas enrichment and influence the accurate estimation of shale gas reserve. However, the impact of the main geological factors, such as porosity, mineralogy, and organic matter, on marine shale gas enrichment and reserve calculation has not yet been fully clarified. Herein, we measured gas adsorption, porosity, mineralogical composition, and total organic carbon content of the marine shale samples from the Jiaoshiba area of Fuling gas field in Sichuan Basin, South China, and investigate the relationships between the geological factors and the adsorbed gas content. The results show that adsorbed gas content is positively correlated with total organic carbon and porosity; the larger specific surface area of samples with more clay minerals essentially contributes to shale gas enrichment. Additionally, the sealing of faults imposes a significant impact on shale gas accumulation. The probability volume method was applied to calculate the shale gas reserve. The reserves of P90 (the most pessimistic reserve), P50 (the most likely reserve), and P10 (the most optimistic reserve) were calculated, respectively, which provides useful information to reduce the risk in shale gas development. [ABSTRACT FROM AUTHOR]

Coal adsorption/desorption gas can cause temperature changes. Moreover, the pressure difference between the high gas pressure area and the low gas pressure area in the coal may affect the coal adsorption/desorption gas thermal effect. To study the effect of adsorption/desorption thermal effect on the evolution law of coal and gas outburst precursor information under different pressure differences, the adsorption/desorption thermal effect experiments were carried out. And the thermo-hydro-mechanical coupling model was established, which reflects the interaction between coal and gas. Under the action of ground stress, pore pressure, adsorption expansion stress, and thermal expansion stress, the model includes the dynamic evolution of coal porosity and permeability, gas adsorption-desorption-diffusion-seepage, and energy accumulation and dissipation. Using the coupling model, the mechanism of adsorption/desorption thermal effect on the evolution of outburst precursor information and the mutual coupling relation between coal and gas is analyzed. The experimental results show that the relation between pressure difference and coal sample temperature variation is linear, and the pressure difference has a quadratic parabolic relation with the temperature accumulation of coal sample. As the pressure difference increases, the temperature variation of the coal sample gradually increases, but the temperature accumulation gradually decreases. Numerical simulation results show that as the pressure difference increases, the changes in coal temperature and gas pressure gradually decrease, and the thermal expansion strain caused by the adsorption/desorption thermal effect decreases, and the permeability increases. Comparing the calculation results with or without the adsorption/desorption thermal effect, the volumetric strain, temperature, and permeability of the coal have significant changes when the adsorption/desorption thermal effect is considered, and the gas drainage volume increases as the pressure difference increases. The effect of thermal expansion strain caused by adsorption/desorption thermal effect on gas seepage is greater than the effect of temperature change on gas seepage. [ABSTRACT FROM AUTHOR]

Gas occurrence in coal seams shows zonation, and the outburst risk prediction index is significantly affected by coal seam gas. For different coal mine, the sensitivity of prediction index of outburst risk is inconsistent, and the different area of the same coal mine can present different sensitivities to the same index. In this study, we measured the industrial analysis of coals and determined the degree of outburst risk of each coal seam using coal samples with the particle size of 1 ∼ 3 mm. The relationships between the equilibrium gas pressure and gas desorption index of drill cuttings, between the desorption index of drill cuttings and the adsorption pressure, and between the critical values of the indexes of drill cuttings were also analyzed using the fuzzy clustering method. Based on the analysis of the particle size distribution of coal samples, the influence of grain size on the critical value of the drill cuttings desorption index was studied. The results showed that the critical values of the desorption index of drill cuttings were different under different adsorption equilibrium gas pressures, and those critical values increased with increasing adsorption equilibrium gas pressure. The desorption index of drill cuttings and adsorption equilibrium gas pressure had a linear relationship, and the higher the degree of outburst risk was, the greater the slope of the fitting function and the smaller the intercept; under the same gas pressure of adsorption equilibrium, there was a linear relationship between Δh2 and K 1, and the higher the outburst risk of coal seam was, the smaller the slope of the fitting function and the greater the intercept. The drill cuttings desorption index Δh2 was more sensitive than the index K 1. Under the same test pressure, the smaller the particle size of the coal samples was, the greater the value of desorption index of drill cuttings and the higher the outburst risk of coal seam. The research results have significant theoretical importance and practical value for the prediction and prevention of coal and gas outbursts in coal mines with similar occurrence conditions of coal seams. [ABSTRACT FROM AUTHOR]

The pore structure of marine-continental transitional shales from the Longtan Formation in Guizhou, China, was investigated using fractal dimensions calculated by the FHH (Frenkel-Halsey-Hill) model based on low-temperature N2 adsorption data. Results show that the overall D 1 (fractal dimension under low relative pressure, P / P 0 ≤ 0.5) and D 2 (fractal dimension under high relative pressure, P / P 0 > 0.5) values of Longtan shales were relatively large, with average values of 2.7426 and 2.7838, respectively, indicating a strong adsorption and storage capacity and complex pore structure. The correlation analysis of fractal dimensions with specific surface area, average pore size, and maximum gas absorption volume indicates that D 1 can comprehensively characterize the adsorption and storage capacity of shales, while D 2 can effectively characterize the pore structure complexity. Further correlation among pore fractal dimension, shale organic geochemical parameters, and mineral composition parameters shows that there is a significant positive correlation between fractal dimensions and organic matter abundance as well as a complex correlation between fractal dimension and organic matter maturity. Fractal dimensions increase with an increase in clay mineral content and pyrite content but decrease with an increase in quartz content. Considering the actual geological evaluation and shale gas exploitation characteristics, a lower limit for D 1 and upper limit for D 2 should be set as evaluation criteria for favorable reservoirs. Combined with the shale gas-bearing property test results of Longtan shales in Guizhou, the favorable reservoir evaluation criteria are set as D 1 ≥ 2.60 and D 2 ≤ 2.85. When D 1 is less than 2.60, the storage capacity of the shales is insufficient. When D 2 is greater than 2.85, the shale pore structure is too complicated, resulting in poor permeability and difficult exploitation. [ABSTRACT FROM AUTHOR]

Summary: Spin‐polarized density functional theory (DFT) is employed to study the adsorption of H2 gas molecules on zinc oxide nanotubes (ZnO‐NTs) with intrinsic defects (oxygen and zinc vacancies) and dopants (Pd and Pt). Results indicate that defects lead to a strong chemisorption process, associated with strong splitting of the H2 molecule, rendering an irreversible process; that is, desorption is not possible. Such strong chemisorption process results in large adsorption energy and charge transfer between the defective‐ZnO‐NTs and H2 molecules. On the other hand, a weaker chemisorption process, associated with weak splitting of H2 molecule, takes place in the case of Pd or Pt dopants. The chemisorption of H2 on defective sites and dopants changes the energy gap to a large extent, resulting in major changes in the electrical conductivity of the ZnO‐NTs and consequently revealing their relevance for gas sensing applications with an enhancement of sensor response. From a different perspective, Pd ought to be a good dopant for ZnO‐NT based hydrogen storage material as it weakens the adsorption strength between H2 and ZnO‐NT. [ABSTRACT FROM AUTHOR]

The permeability of coal is an indispensable parameter for predicting the coalbed methane (CBM) and enhanced CBM (ECBM) production. Considering the low permeability characteristics of coal, the permeability is usually measured by the transient technique in the laboratory. Normally, it is assumed that the calculated permeability will not greatly vary if the pulse pressure applied in the experiment is small (less than 10% of pore pressure) and previous studies have not focused on the effect of the pulse pressure on the measurement permeability. However, for sorptive rock, such as coals and shales, the sorption effect may cause different measurement results under different pulse pressures. In this study, both nonadsorbing gas (helium) and adsorbing gas (carbon dioxide) were used to investigate the adsorption effect on the gas permeability of coal measurement with the pulse-decay technique. A series of experiments under different pore pressures and pulse pressures was performed, and the carbon dioxide permeability was calculated by both Cui et al.'s and Jones' methods. The results show that the carbon dioxide permeability calculated by Jones' method was underestimated because the adsorption effect was not considered. In addition, by comparing the helium and carbon dioxide permeabilities under different pulse pressures, we found that the carbon dioxide permeability of coal was more sensitive to the pulse pressure due to the adsorption effect. Thus, to obtain the accurate permeability of coal, the effect of adsorption should be considered when measuring the permeability of adsorptive media with adsorbing gas by the transient technique, and more effort is required to eliminate the effect of the pulse pressure on the measured permeability. [ABSTRACT FROM AUTHOR]