Macromolecular Structure Model Research Articles

Molecular simulation study of adsorption-diffusion of CH4, CO2 and H2O in gas-fat coal

In order to clarify the microscopic dynamics mechanism of CH4, CO2 and H2O adsorption and diffusion in coal, and to reveal the mechanism of the influence of different temperatures and pressures on the adsorption and diffusion characteristics of coal adsorbed CH4, CO2 and H2O molecules. In this paper, the macromolecular structure model of Jixi gas-fat coal was constructed, based on the Giant Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods. The adsorption-diffusion characteristics of CH4,CO2 and H2O single-component gases in the gas-fat coal macromolecule model at temperatures ranging from 273.15 K to 313.15 K and pressures ranging from 0.01 MPa to 15 MPa were investigated by using Material Studio software. The research results indicated that: The adsorption of three gases, CH4, CO2 and H2O, increased with the increase of equilibrium pressure, and the adsorption isotherms conformed to Langmuir type I isotherms. The amount of saturated adsorption of CH4 ranged from 11.18 to 14.37 ml/g, the saturated adsorption of CO2 ranged from 20.40 to 24.70 ml/g, and the saturated adsorption of H2O ranged from 66.61 to 84.21 ml/g. With the increase of temperature, the saturated adsorption of CH4 and CO2 both decreased, and the saturated adsorption of H2O firstly increased and then decreased, and the adsorption of H2O by low temperature and high temperature had both an inhibitory effect on the adsorption of H2O. The potential energy distributions of CH4, CO2 and H2O molecules are poisson distributed. The absolute values of the most available interaction energies are, from highest to lowest: H2O > CO2 > CH4; the activation energies for diffusion of CH4, CO2 and H2O are 12.20 kJ/mol, 3.36 kJ/mol, and 8.47 kJ/mol, respectively, and the diffusion of CO2 is the more likely to occur. The adsorption of CH4 and CO2 in coal is physical adsorption, while the adsorption process of H2O molecules is beyond the scope of physical adsorption. The absolute value of the interaction energy is H2O > CO2 > CH4 in descending order.

Molecular Structural Characteristics and 3D Model Reconstruction of Organic Matter in Longmaxi Formation Shale.

The establishment of molecular structure modeling is an important means to study the pore characteristics of shale organic matter and is significant for molecular-level simulations of gas storage and diffusion. Using 13C NMR, FTIR, and XPS combined with the split-peak fitting technique, the structural characteristics of the aromatic structure, aliphatic structure, and oxygen functional groups of kerogen from the shale of the Longmaxi Formation, Wuxi County, Chongqing Municipality, were quantitatively characterized. A macromolecular structure model of the kerogen was also constructed by using the 2D macromolecular structure model construction method in combination with elemental analysis experiments. The results showed that the 2D single-molecule structural model of the sample consisted of 2 benzenes, 2 naphthalenes, 1 anthracene, 5 pyrenes, 1 pyridine, and 1 pyrrole. The C skeleton types were 93 protonated arylons, 39 bridged arylons, 6 carboxylons, 5 alkyl-substituted carbons, 2 oxygen-substituted carbons, 4 methylene carbons, and 3 methylons. The established 2D molecular structure formula was C152H82O12N2. The final 3D macromolecular structure model consisted of 14 2D molecular structures (structural formula C2128H1148O168N28), with the density set to 1.77 cm3/g, compressed in a cubic cell with an edge length of 3.05 nm. Finally, the adsorption results showed that the experimental adsorption of CO2 adsorption was less than the simulated adsorption, completing the validation of the model. The above study provides a method for determining the molecular structure of kerogen in the Longmaxi Formation shale, which can guide the study of the pore structure characteristics of the Longmaxi Formation shale.

Quantitative Characterization and Macromolecular Structure Model Construction of Taixi Anthracite as Raw Material of Coal-Based Activated Carbon

Quantitative Characterization and Macromolecular Structure Model Construction of Taixi Anthracite as Raw Material of Coal-Based Activated Carbon

Structural Characteristics of the Yunnan Deashed Lignite and Construction of the Macromolecular Structure Model.

The structural characteristics and macromolecular model of lignite are important for its effective utilization. In this paper, Yunnan (YN) lignite was taken as the study object, and deashing pretreatment was carried out to remove the influence of minerals in lignite before spectroscopic analysis. Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and 13C nuclear magnetic resonance (NMR) spectroscopy of deashed lignite and gas chromatography and mass spectrometry (GC/MS) of methanol lignite extract were subsequently performed. Then, the lignite structural parameters were calculated, and lignite macromolecular models were constructed and optimized. The results showed that the aromatic carbon ratio and molar fraction of aromatics in YN lignite were 0.62 and 0.19, respectively. The numbers of benzene, naphthalene, phenanthrene, pyrrole and pyridine groups were calculated as 4, 4, 1, 1, and 4, respectively. Afterward, 2D and 3D macromolecular structure models of YN lignite were drawn and optimized by ChemDraw software, and the chemical shift regions of the predicted 13C NMR spectrum agreed well with the experimental spectrum, suggesting the reliability of the constructed macromolecular structure model of YN lignite.

Construction of macromolecular structure model of Luling coal and study on the dynamic mechanism of micro-wetting process

The physicochemical structure and energy composition of coal macromolecules are the major factors affecting coal wettability. This study thus employed 13C NMR, FTIR, and XPS to determine the chemical structure of coal in the No. 10 coal seam of the Luling coal mine and gain insights into the molecular mechanisms of coal wetting. The results showed that the molecular formula of the Luling 10 model was C290H223O25N5S. Through molecular dynamics simulation, upon the stable adsorption of sodium dodecyl sulfate (SDS) on the coal surface, both the mobility of water molecules and the water molecule content in the interfacial adsorption layer increased. After SDS was added, except for the hydrogen bond energy, the increase rate of each potential energy increased, and van der Waals energy and bond length energy changed the most. The reason for the decrease of hydrogen bond energy is that more atoms in coal macromolecules form hydrogen bonds with polar water molecules. The increase of SDS promoted the significant changes of bond length energy, bond angle energy and van der Waals force of coal, thus increasing the wettability of coal. Taken together, our findings provide important insights into the molecular mechanisms through which surfactants improve chemical wetting.

Molecular Dynamics Simulation of Methane Adsorption and Diffusion

To study the adsorption and diffusion mechanism of low-rank coal at the microscopic level, samples of Fukang low-rank coal were collected, and the elemental composition, carbon type distribution and functional group type of the Fukang low-rank coal structure were determined by elemental analysis (Ea), Fourier-transform interferometric radiometer (FTIR), X-ray photoelectron spectroscopy (XPS) and 13C nuclear magnetic resonance (13C NMR) experiments to construct a 2D molecular structure of the coal and a 3D macromolecular structure model. The adsorption and diffusion characteristics of methane were researched by giant regular Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods. The results showed that the excess adsorption amount of methane increased and then decreased with the increase in pressure. The diffusion of methane showed two stages with increasing pressure: a sharp decrease in the diffusion coefficient from 0.5 to 5.0 MPa and a slow decrease in the diffusion coefficient from 5.0 to 15.0 MPa. The lower the pressure, the larger the effective radius of the CH4 and C atoms, and the higher the temperature, the more pronounced the diffusion and the larger the effective radius.

Research on CO2/CH4/N2 competitive adsorption characteristics of anthracite coal from Shanxi Sihe coal mine.

This study aims to solve the problem of unsatisfactory development and utilization of coalbed methane and CO2 storage efficiency. It is focused on the adsorption behavior of CO2, CH4, and N2 in the macromolecular structure model of Shanxi Sihe coal mine anthracite, as well as the competitive adsorption behavior of CO2/CH4 and CH4/N2 binary gas mixtures with different ratios. Experimental analysis such as elemental analysis, solid 13C nuclear magnetic resonance (13C NMR), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis were used to construct the Shanxi Sihe coal mine model of the macromolecular structure of anthracite coal. The Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods were used to study the adsorption capacity and heat characteristics of CO2, CH4, and N2 at different temperatures using a molecular model of anthracite coal from Shanxi Sihe coal mine, as well as the competitive adsorption characteristics of CO2/CH4 and CH4/N2 binary mixtures. The mechanism of the influence of temperature and gas properties on the adsorption capacity and heat of adsorption was revealed from a microscopic perspective. The results indicated that the aromatic carbon content of anthracite in the Sihe coal mine, Shanxi is 81.19%, and the ratio Xbp of aromatic bridgehead carbon to surrounding carbon is 0.489. The aromatic structure is mainly composed of pyrene and anthracene. The molecular formula of the macromolecular structure model of anthracite in Shanxi Sihe coal mine is C233H157O13N2. The adsorption capacity and equivalent adsorption heat of the macromolecular model for adsorbing single-component gas CO2/CH4/N2 decrease with the increase in temperature. The temperature has the greatest impact on CO2 adsorption capacity and adsorption heat, followed by CH4 and N2. Under the competitive adsorption conditions of CO2/CH4 and CH4/N2 binary mixtures, the higher the partial pressure of a single-component gas in the mixture, the greater the adsorption capacity of the gas. The difference in the adsorption heat of CH4 and N2 is smaller than that of CH4 and CO2. The conclusions obtained from the study can provide technical and theoretical support for formulating reasonable drainage methods for coalbed methane wells.

Structural characterization and macromolecular structure construction of non-caking coal in Chicheng Mine

Given that coal is not a homogeneous substance, it is of great significance to identify and quantify the structural characteristics thereof for comprehensive analysis. In this paper, the non-caking coal in Chicheng Coal Mine was selected as the research object. The C, H, O, N, and S contents in the coal samples were obtained by proximate/ultimate analysis experiments. The structural characteristics of aromatic, aliphatic hydrocarbons, and oxygen-containing functional groups in the experimental coal samples were obtained by Fourier transform infrared spectroscopy (FT-IR) experiments. X-ray photoelectron spectroscopy (XPS) experiments were performed to obtain the occurrence state of N and S elements in coal samples. Nuclear magnetic resonance (13C NMR) experiments provided the carbon skeleton structural information of the coal samples. The macromolecular structure model of non-caking coal in the Chicheng Coal Mine was established on this basis. The molecular formula of non-caking coal in Chicheng Coal Mine was determined to be C207H181O32N3S.The13C NMR-predicted spectrum of the model showed good consistency with the 13C NMR-experimental spectrum obtained from the experiments, providing researchers with reference to the construction ideas and methods of molecular structure models of different coal samples.

Structural characterization analysis and macromolecular model construction of coal from Qinggangping coal mine

Understanding the molecular structure characteristics of coal at the molecular level is of great significance to realize the rational utilization and efficient conversion of coal. This paper gives insights into the acquisition of characterization parameters of coal molecular microstructure by testing and analyzing the long flame coal from Qinggangping (QGP) Coal Mine through proximate analysis, ultimate analysis, vitrinite reflectance determination, fourier transform infrared Spectroscopy test (FTIR), X-ray photoelectron epectroscopy test (XPS), carbon nuclear magnetic resonance (13C-NMR) and X-ray diffraction (XRD). The results show that benzene rings in the QGP coal are mainly connected in a disubstituted way, accounting for 36.48%. Oxygen atoms mainly exist in the oxygen-containing functional groups such as the ether C–O, C=O and –COO. Aliphatic hydrocarbons in the aliphatic group are mainly of symmetrical -CHx stretching vibration. Hydroxyl groups are mainly composed of OH–OH and OH–O hydrogen bonds, accounting for 29.21% and 21.53%, respectively. Nitrogen atoms exist in the form of C4H5N. The coal molecular is mainly of aromatic carbon structure, where the ratio of bridge aromatic carbon to peripheral carbon is 0.198. There are benzene, naphthalene and anthracene in the coal molecular structure, and the former two chemicals play a dominating role. According to the analysis results, the molecular formula of the QGP coal is finally determined as C205H181O29N3S. On this basis, the two-dimensional and three-dimensional macromolecular models are constructed with the assistance of simulation software. In addition, the 13C-NMR spectra and densities of the constructed molecular models are calculated, which verifies the rationality of the models. The macromolecular structure model of bituminous coal constructed in this study provides a theoretical model basis for the optimal surfactant.

Study on Molecular Model Construction and Gas Adsorption Simulation of Anthracite in the Qinshui Basin.

Uncovering gas adsorption characteristics of coal at the molecular scale is of great theoretical significance for the study of gas occurrence, coalbed methane exploitation, and carbon dioxide sequestration. In this study, based on proximate analysis, ultimate analysis, 13C nuclear magnetic resonance, and Fourier-transform infrared spectroscopy experiments, the existence forms and relative contents of elements of anthracite in the Qinshui Basin were tested and analyzed, and a macromolecular structure model was constructed. Besides, three types of acidic oxygen-containing functional groups, namely, carboxyl groups, phenolic hydroxyl groups, and lactone groups, were added to the molecular model. Furthermore, CH4 adsorption simulation was conducted on the original molecular model of anthracite and models with three types of acidic functional groups added. The following research results were obtained. The molecular formula of the constructed macromolecular model of anthracite in the Qinshui Basin is C193H138N2O7. The molecular structure of coal becomes more compact and curved after structural optimization and annealing optimization. For the four models, the CH4 adsorption characteristics of coal molecules all conform to the Langmuir equation under the same simulation conditions. Among them, the original model has the largest CH4 adsorption capacity, while the addition of oxygen-containing functional groups reduces the CH4 adsorption capacity to varying extents. The reduction of CH4 adsorption capacity follows the order: adding carboxyl groups > adding phenolic hydroxyl groups > adding lactone groups, which is mainly attributed to the different adsorption heats and adsorptive potential wells triggered by the addition of acidic functional groups in molecules.

Construction and optimization of macromolecular structure model of Tiebei lignite.

Mastering the molecular structure of coal is important for the effective utilization of coal. For a detailed study of the microstructural characteristics of Tiebei lignite, its molecular structure was characterized by elemental analysis, solid 13C nuclear magnetic resonance (13C NMR), Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The results showed that the aromatic carbon content of Tiebei lignite was 51.98%, the aromatic carbon structure was mainly composed of benzene and naphthalene, and the ratio of aromatic bridgehead carbon to surrounding carbon Xbp was 0.14. Oxygen existed in phenol, ether, carbonyl, and carboxyl; nitrogen-containing structures mainly existed in the form of pyrrole and pyridine; sulfur mainly existed in thiophene sulfur; and aromatic substitution was mainly in the form of trisubstitution. The molecular formula of the macromolecular structure model of Tiebei lignite was C190H161O57N2, and the 13C NMR spectrum of the model was in good agreement with the experimental results, which fully verified the accuracy of the macromolecular structure model of Tiebei lignite. The construction of a macromolecular structure model of Tiebei lignite is essential to intuitively understand the molecular structure characteristics of Tiebei lignite and to provide theoretical support and guidance for the micromechanism research and prevention of lignite spontaneous combustion and other disasters.

Simulation Study on Molecular Adsorption of Coal in Chicheng Coal Mine.

To study the importance of the adsorption mechanism of methane (CH4) and carbon dioxide (CO2) in coal for coalbed methane development, we aimed to reveal the influence mechanism of adsorption pressure, temperature, gas properties, water content, and other factors on gas molecular adsorption behavior from the molecular level. In this study, we selected the nonsticky coal in Chicheng Coal Mine as the research object. Based on the coal macromolecular model, we used the molecular dynamics (MD) and Monte Carlo (GCMC) methods to simulate and analyze the conditions of different pressure, temperature, and water content. The change rule and microscopic mechanism of the adsorption amount, equal adsorption heat, and interaction energy of CO2 and CH4 gas molecules in the coal macromolecular structure model establish a theoretical foundation for revealing the adsorption characteristics of coalbed methane in coal and provide technical support for further improving coalbed methane extraction.

Molecular Dynamics Simulation of Methane Adsorption and Diffusion: A Case Study of Low-Rank Coal in Fukang Area, Southern Junggar Basin

Adsorption and diffusion are the key factors affecting coalbed methane (CBM) accumulation, resource assessment and production prediction. To study the adsorption and diffusion mechanism of Fukang low-rank coal at the microscopic level, samples of Fukang low-rank coal were collected, and the elemental composition, carbon type distribution and functional group type of the Fukang low-rank coal structure were determined by elemental analysis (Ea), Fourier-transform interferometric radiometer (FTIR), X-ray photoelectron spectroscopy (XPS) and 13C nuclear magnetic resonance (13C NMR) experiments to construct a 2D molecular structure of the coal and a 3D macromolecular structure model. The adsorption and diffusion characteristics of methane were researched by giant regular Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods. The results showed that the excess adsorption amount of methane increased and then decreased with the increase in pressure. The diffusion of methane showed two stages with increasing pressure: a sharp decrease in the diffusion coefficient from 0.5 to 5.0 MPa and a slow decrease in the diffusion coefficient from 5.0 to 15.0 MPa. The lower the pressure, the larger the effective radius of the CH4 and C atoms, and the higher the temperature, the more pronounced the diffusion and the larger the effective radius.

Structural Model Construction and Optimal Characterization of High-Volatile Bituminous Coal Molecules

The structural characteristics of coal at the molecular level are important for its efficient use. Bituminous coal from the Baozigou Coal Mine is investigated, using elemental analysis, 13C nuclear magnetic resonance, X-ray photoelectron spectroscopy, and Fourier transform infrared. The molecular structure was determined. The aromatic compounds of bituminous coal molecules are primarily two- and three-ring structures, and the aliphatic structures are primarily in the form of methyl, ethyl side chains, and naphthenic hydrocarbons. The ratio of aromatic bridge carbon to peripheral carbon in the molecular structure is 0.279. Oxygen atoms in the form of carbonyl, phenolic hydroxyl and C–O, and nitrogen atoms in pyrroles. Thus, the average structure model of bituminous coal macromolecules was constructed; the molecular formula was C169H128O10N2S, and the molecular weight was 2378. The aromatic structural units in the macromolecular structure of coal include four naphthalenes, three anthracenes, two tetracenes, and heteroatoms in the form of three carbonyl groups, one phenolic hydroxyl group, one pyrrole, and one pyridine. The structure optimization and annealing kinetic simulation of a single macromolecular structure model were performed. Chemical bonds such as bridge bonds and aliphatic bonds were found to be twisted, and π–π interactions between the aromatic sheets in the molecule produced adjacent aromatic sheets. This arrangement tends to be approximately parallel, and the total energy decreases from 6713.401 to 2667.595 kJ/mol, among which the bond stretching energy and van der Waals energy dominate. We used 20 bituminous coal macromolecular models to construct aggregated structural models. After optimization by molecular dynamics simulation, the macromolecules were constrained by the surrounding molecules, and the sheet-like aromatic carbon structures that were originally approximately parallel were distorted. The macromolecular structure model of bituminous coal constructed in this study provides a theoretical model basis for the optimal surfactant.

Occurrence mode and molecular structure model of unburned carbon in coal gasification fine slags

Coal gasification fine slag (CGFS) is a kind of solid waste produced in the process of coal gasification, in which unburned carbon (UC) severely restricts its resource utilization. The study of physical/chemical properties, occurrence state and molecular structure of UC is of great significance to the utilization of CGFS. The characterization results show that the carbon content of particles increases with the increase of particle size, which is enriched to concentrate in particle size above 125 μm. UC is loose and porous, which leads to the wrapping and covering with inorganic ash particles. The molecular formula of the UC is determined to be C178H73O46N1S1, with a molecular weight of 2991. The average macromolecular structure model of UC is established by computer simulation. It is basically consistent with the infrared results of the simulation experiment. From the perspective of structure, UC has a high degree of aromatization and abundant oxygen-containing functional groups, which may increase the difficulty of decarbonization by enhancing hydrophilicity. This work provides a comprehensive understanding of UC structure at the atomic level, which is conducive to the efficient decarbonization of CGFS.

Monte Carlo and molecular dynamics simulations of CH4 molecules adsorption behavior in bituminous coal

Abstract In this study, we established a macromolecular structure model of the Wiser bituminous coal (C192H166N4O19S9) to study the adsorption characteristics of CH4 molecules in bituminous coal. We then combined the grand canonical Monte Carlo and molecular dynamics simulation methods to study the adsorption behavior of CH4 molecules in coal at different temperatures and moisture contents with fugacity values of 0–12 MPa. The simulation results showed that the adsorption isotherms of CH4 gas are consistent with those of the Langmuir model, and the adsorption of CH4 molecules is negatively correlated with temperature and positively correlated with fugacity. The adsorption amount and rate of CH4 molecules in bituminous coal decreased as the moisture content in the coal molecules increased. The presence of H2O molecules in coal reduced the interaction between the coal and CH4 molecules. H2O molecules exhibited a stronger interaction with the heteroatomic groups in coal molecules than that of the CH4 molecules. Finally, the main factors causing a linear negative correlation between moisture content and the adsorption of CH4 molecules were the preferential occupation of H2O molecules in effective adsorption sites in coal molecules and the linear reduction of free volume in coal.

Construction of a Macromolecular Structure Model for Zhundong Subbituminous Coal

Understanding the coal molecular structure is of paramount importance for the effective utilization of coal. In this paper, the molecular structure of Zhundong coal (ZD) was characterized by physical detection techniques, such as solid state 13C nuclear magnetic resonance spectroscopy (13C-NMR), fourier transform infrared resonance spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The occurrence and distribution of aromatic carbocyclic frameworks were analyzed by 13C-NMR. Based on the FTIR and XPS analysis, the existing forms and the length of the aliphatic chain, the substitution forms of aromatic carbocyclic rings, and different types of functional groups were confirmed. The aliphatic chains and functional groups were introduced into these aromatic carbocyclic frameworks, and the 2D molecular structures model of ZD with the molecular chemical formula as C179H124O21N4 were constructed. The simulated 13C-NMR spectra of which were consistent with the experimental spectra, indicating the accuracy of the 2D ZD molecular structure model. Efforts were made to obtain the energy-minimum conformation of the 3D molecular structure by molecular mechanics (MM) and molecular dynamics (MD). The simulated FTIR spectra of the model were in good agreement with the experimental results, which fully verified the accuracy of the ZD molecular structure. The molecular structure provides a deep reference to understand the structural characteristics of ZD coal at the molecular micro-scale, which would be helpful to understand the reactivity of ZD coal.

Stress degradation mechanism of coal macromolecular structure: Insights from molecular dynamics simulation and quantum chemistry calculations

The shear action caused by tectonic stresses deforms and destroys the coal macrostructure and significantly affects the coal macromolecular structure. To study the degradation mechanism of the macromolecular structure of low-rank coal during shearing, the macromolecular structure model of Wender coal was selected in this study. Forty molecules of this structure were used to construct a polymer cell. Shearing simulations were performed using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) software, and bond strength was determined using Gaussian software. Two chemical bond breakage types were observed: tensile break and shear break. The former is controlled by the bond's position and strength, while the latter is controlled by the bond's position and angle strength. The mechanism of tensile break is different from that of shear break. The former tends to occur when the bond rotates clockwise around the point of action, towards the shear action direction (X axis positive direction), and the rotation angle is between 0° and 90°. The latter easily occurs when the bond rotates clockwise around the point of action, towards the shear action direction (X axis positive direction), and the rotation angle is between 90° and 180°. Small molecules, such as CH4, are produced by the shear action, partially revealing the excess coalbed methane eruption mechanism of coal and gas outburst. The shear action increases the order degree and stratification of the coal molecular structure by breaking and cutting side chains and bridge bonds, promoting the evolution of the coal rank.

Construction of Buertai Coal Macromolecular Model and GCMC Simulation of Methane Adsorption in Micropores.

With the increase in high gas mines in the low coal rank mining area in the northwestern part of China, high gas mines in the low-rank coal mining area have caused many gas emission accidents. Coal is a porous material, containing a large number of micropores (<2 nm), which can absorb large amounts of methane, so it is necessary to explore methane adsorption in micropores of low-rank coal. In this work, FTIR, HRTEM, and 13C-NMR were used to test the macromolecular structural parameters of Buertai coal, which was a kind of low-rank Jurassic coal in northwestern China. The results showed that the aromatic structural units in the Buertai coal structure mainly consist of naphthalene, anthracene, and phenanthrene. The fat structure mainly occurs in the form of aliphatic side chains, cycloalkanes, and other compounds. The oxygen atoms are present in the form of carbonyl groups, ether bonds, and phenol groups with a ratio of about 6:4:9. The nitrogen atoms are present in the form of pyrrole and pyridine compounds. Finally, the macromolecular structure model of Buertai coal was built, and the calculated NMR spectrum from the model was very consistent with the experimental NMR spectrum of Buertai coal. The relationship between the macromolecular density and energy of Buertai coal was explored using the Amorphous Cell module in the simulation software, Materials Studios 8.0 (MS 8.0), and the density value at the lowest energy was determined to be about 1.23 g/cm3. The pore structure parameters of Buertai coal were also calculated. It was found that both pore volume and void fraction decreased evenly as the diameter of the probe molecule increased, but the surface area decreased rapidly when the diameter of the probe molecule was 3.46 Å. All pore sizes were found to be smaller than 10 Å from the pore size distribution (PSD) curve of Buertai coal, which provided a lot of adsorption sites for methane (CH4). The results of the CH4 adsorption simulation from Grand Canonical Monte Carlo (GCMC) showed that CH4 is adsorbed inside the micropores of coal, and the adsorption capacity of CH4 depends on the diameters of micropores when the micropores are less than 8.5 Å. There are many micropores where CH4 did not appear because these micropores are closed and did not provide a channel for CH4 to enter. The results of experimental methane adsorption indicate that the excess adsorption capacity from the GCMC simulation was very close to the experimental results of Buertai coal. This work provides a new perspective to study the methane adsorption behavior in micropores of coal.

Research on adsorption characteristics of H2S, CH4, N2 in coal based on Monte Carlo method

In order to study the adsorption characteristics of H2S, CH4 and N2 by coal under different conditions, the new macromolecular structure model of Dongqu No. 2 was constructed, and the grand canonical Monte Carlo (GCMC) method was used to simulate the adsorption process of three types of gases in coal. The dependence of adsorption capacity of coal on its temperature, pressure and moisture content was analyzed. The results show that with the increase of pressure and temperature, adsorption isotherms of all the three gases follow Langmuir model. For pressure greater than 2 MPa, the influence of temperature on adsorption capacity was greater than that of pressure. With rise in temperature, the decrease in rate of H2S adsorption was least and drops in the heat of adsorption of H2S most. This indicates that the adsorption of H2S on coal is more stable than those of CH4 and N2. As the water content of coal increased, its adsorption capacity for the present three gases decreased linearly, and the capacity for H2S (1.77 mmol/g) changed the most. The reduction of free volume linearly and preferential occupation of adsorption sites by water molecules are the main reasons for the highest change in the adsorbed amount of H2S gas.