Grand Canonical Monte Carlo Method Research Articles

Chemical reaction process and dynamic characteristics of urea pyrolysis products in inhibiting gas explosion

During the coal mining process, gas explosions pose significant hazards, causing casualties and property losses. In order to develop new types of inhibitors for gas explosions, this paper explores the reaction mechanisms of urea pyrolysis products NH3 and HNCO inhibiting gas explosions based on density functional theory (DFT), transition state theory, and grand canonical ensemble Monte Carlo method (GCMC). It analyzes the reaction processes and kinetic characteristics of urea pyrolysis products with key radicals and gas molecules involved in explosions from a microscopic dynamic perspective. The results show that urea pyrolysis products exhibit good inhibition effects on active radicals involved in explosion reactions·NH3 and HNCO show stronger van der Waals forces in electrostatic attraction towards O2 and *H, respectively, and faster rate advantages in reaction rate constants. The lower Gibbs free energy barrier indicates higher reaction activity of pyrolysis products, thereby diluting the concentration of key radicals involved in explosion reactions and effectively inhibiting explosion key elementary reactions (R32, R38, R53, R57, R156, and R170). This study provides new insights into the microscopic inhibition mechanism of urea pyrolysis products on gas explosions, offering a new approach for designing more targeted modified inhibitors, which helps reduce the hazards of gas explosions during coal mining and provides scientific support and technical guidance for safe coal mining production.

Molecular simulation of competitive adsorption of CO2/N2/O2 gas in bituminous coal

The main cause of coal spontaneous combustion is the oxidation and temperature rise of coal. Injecting composite inert gas for fire prevention and extinguishing is one of the important methods to prevent coal spontaneous combustion. A large number of studies have macroscopically investigated the fire prevention and extinguishing effects of CO2/N2 and their synergistic actions. However, there is currently a lack of research at the molecular level on the competitive adsorption mechanism between mixed inert gases (CO2, N2) and O2 molecules in coal. Therefore, this study conducted adsorption experiments using Qian Yingzi(QYZ) bituminous coal and compared them with the simulation data of the Wiser coal model to verify the reliability of the Wiser model. Subsequently, employing grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) methods, the competitive adsorption behavior of different proportions of binary mixed component gases (CO2/O2, CO2/N2, O2/N2) at a temperature of 303.15 K was investigated from five perspectives: adsorption capacity, adsorption selectivity coefficient, potential energy distribution, competitive adsorption heat, and interaction energy. The results indicate that among the competitive component gases, CO2 exhibits the strongest adsorption effect on the entire system, which is closely correlated with the distribution range of adsorption energy sites. The adsorption heat and adsorption amount of CO2 consistently exhibit a negative correlation, whereas the relationship between the adsorption heat of N2 and O2 and the adsorption amount shows a positive correlation. Their adsorption capacities depend on the pressure and the proportion of the two gases. Based on the isothermal adsorption curve of CO2/N2, it is recommended that the gas pressure during actual inert gas injection be less than 2.5 MPa. Under this pressure, the competitive adsorption effect is no longer significant, providing a certain theoretical basis for high-pressure injection. Moreover, the preliminary determination of the optimal injection ratio range is from 4:6–3:7. Furthermore, a systematic logical framework for selecting underground inert gas composition is proposed, and an underground mobile inert gas infusion process is adopted. The actual gas composition for infusion is determined based on cost factors in practical engineering. The research results can provide guidance for the selection of gas injection parameters for mixed inert gas fire prevention and extinguishing in goaf.

Investigation of the microscopic mechanism of H2O adsorption by low-rank coal slit pores through GCMC and MD simulations

This study investigates the influence of pore structure on H2O adsorption in low-rank coal (LRC) models at a molecular level, employing variously sized LRC slit-pore models·H2O adsorption behavior is analyzed across different pore sizes ranging from 0.001 to 100 kPa fugacity, by employing the Grand canonical Monte Carlo (GCMC) method and molecular dynamics (MD) simulations to explore saturated adsorption kinetics. The findings indicate a positive correlation between H2O adsorption levels and both fugacity and pore diameter. Furthermore, at constant pore diameter, the adsorption heat increases exponentially with increasing adsorption levels. Notably, H2O adsorption in LRC slit pores exhibits multilayer adsorption characteristics. First, adsorption occurs as monomolecular layers on the LRC surface, transitioning to secondary adsorption sites formed by previously adsorbed H2O molecules with increasing fugacity, ultimately saturating the pores. This adsorption process exhibits a correlation with a shift in potential energy distribution from high to low potential energy directions. Moreover, the ordering of H2O molecule arrangements between hydrogen atoms, oxygen atoms, and H2O molecules decreases with increasing pore diameters. Larger pore diameters correspond to increased H2O molecule diffusion, the stronger interaction between the LRC slit pores and H2O molecules but reduced interaction with individual H2O molecules. Overall, this study establishes a theoretical foundation for further studies on coal pore wetting and offer valuable insights for studies aimed at reducing dust and preventing gas outbursts.

Macromolecular insight into the adsorption and migration properties of CH4/CO2/N2 in bituminous coal matrix under uniaxial strain loading

Gas adsorption–migration in coal is of crucial importance for coalbed methane (CBM) recovery; however, the effect of coal deformation on it is not yet very clear, especially at the molecular level. In this study, the effects of uniaxial tension–compression strains on the CH4/CO2/N2 adsorption–migration characteristics in bituminous coal matrix were investigated by integrating the grand canonical Monte Carlo and molecular dynamics methods. The results show that the dual-mode equation fits the isothermal adsorption results, and the adsorption concentration and Langmuir volume are positively correlated with strain. Tension strain has a small effect on a thermodynamic factor but a large effect on Henry constant. In addition, the swelling resistance of coal matrix is positively correlated with tension strain which has a greater impact on the shear resistance of coal matrix containing CO2. The average mass density of the gas is linearly positively correlated with strain that has a large impact on N2 stability. More significantly, the self-diffusion coefficient (Ds) of CH4 is larger than that of CO2/N2, and the relationship between Fick diffusion coefficient and strain is roughly similar to that between Ds and strain. Also, the mass transfer of CO2 permeation is more significant compared to N2, especially for tension strain. These research results provide a basis for the optimization design of CBM recovery in deformed coal reservoirs.

Investigation of water adsorption characteristics of MgCl2 salt hydrates for thermal energy storage: Roles of hydrogen bond networks and hydration degrees

Thermochemical energy storage holds great promise in solar energy applications, and MgCl2 hydrate salt is considered a promising material for medium and low-temperature thermochemical energy storage. Understanding the adsorption behavior of water molecules in MgCl2 hydrate salts and uncovering the underlying mechanisms are crucial for designing efficient thermochemical energy storage systems. This paper investigated the water adsorption characteristics of MgCl2 hydrate salt utilizing the Grand Canonical Monte Carlo (GCMC) method and captured the adsorption isotherm and concentration distributions of water molecules in MgCl2 hydrate salts pores at various temperatures. The results demonstrate that at low temperatures, particularly when the pore size is small (D < 0.8 nm), the interconnected hydrogen bond network plays a crucial role in enhancing the water adsorption capacity of pure MgCl2. As the temperature increases, the influence of hydrogen bond networks diminishes, and their impact on the water adsorption capacity becomes negligible. Moreover, the hydration degrees of MgCl2 salt significantly influence their water adsorption capacity. MgCl2·6H2O exhibits the best water-uptake performance, followed by MgCl2·4H2O, while MgCl2·2H2O displays the worst water-uptake performance. These findings shed light on the adsorption behavior of water molecules in MgCl2 hydrate salt and offer valuable insights into the design and optimization of efficient thermochemical energy storage systems. Such knowledge is essential for advancing the utilization of thermochemical energy storage in solar energy applications.

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.

A detailed molecular dynamics simulation and experimental investigation of CO2 adsorption on graphene oxide-polyaniline nanocomposite

The study investigated the sorption and diffusion of carbon dioxide on Graphene oxide-polyaniline (GO-PANI) using volumetric method and molecular dynamics simulations. The experimental results showed that GO-PANI was more effective at adsorbing CO2 than either of the individual materials alone. Simulations supported this trend in CO2 adsorption and provided additional insights into the structural information of the adsorbents and the dynamics of CO2 molecules. The Langmuir adsorption model was employed to fit sorption isotherms computed using Grand Canonical Monte Carlo (GCMC) method. The GO-PANI nanocomposite compound exhibited a superior adsorption rate compared to pure structures. The isosteric heat for CO2 adsorption was 27.59 kJ/mol. The interaction energy of single molecules of CO2 on GO-PANI surface was −38.075 kcal/mol. Diffusion coefficient value for CO2 was 41.2 × 10 −9 m2/s, lower than that of the pure polymer. FT-IR, FE-SEM, and BET techniques were used to analyze synthesized GO-PANI structure. The highest CO2 adsorption was observed at a temperature of 283 K. Isosteric heat adsorption decreased with uniform surface charge. This research provides critical microscopic information on gas adsorption in polymer nanocomposites and demonstrates the effectiveness of GO-PANI as an efficient adsorbent for carbon dioxide, which could be useful in various industrial applications.

Transport property of hydrogen sulfide in amorphous polyethylene using grand canonical Monte Carlo and molecular dynamics simulations

H2S corrosion poses a significant hurdle to safely transporting sulfur-containing natural gas through metal gathering pipes. Reinforced thermoplastic composite pipes have emerged as a solution, using the polyethylene inner lining layer that resists H2S corrosion. However, the permeation of H2S in the polyethylene may lead to the failure of reinforced thermoplastic composite pipes, resulting in natural gas leakage and environmental pollution. Therefore, it is crucial to investigate the gas transport properties of H2S in polyethylene materials to ensure the reliable functioning of gathering pipes. In this study, the dissolution behavior of H2S for pure H2S and H2S/CH4 mixture in amorphous PE is investigated using the grand canonical Monte Carlo method in conjunction with the NPT, with consideration given to the swelling effect. In addition, the diffusion characteristic is explored through the NVT on the amorphous PE adsorbing H2S. Subsequently, the permeability coefficient is calculated based on the obtained data. The findings reveal that with as the temperature increases, the solubility coefficient decreases, while both the diffusion and permeability coefficients increase. With increasing pressure, both the diffusion and permeability coefficients increase. Additionally, the above three coefficients all increase with increasing H2S mole fraction. The relationships between solubility, diffusion, and permeability coefficients & temperature all conform to the Arrhenius law. Finally, the diffusion mechanism of H2S in amorphous PE is revealed at the microscopic level as the “jumping” mechanism by tracking the diffusion pathway of H2S molecule.

Competitive sorption of CO2/CH4 and CO2 capture on modified silica surfaces: A molecular simulation

The effect of functionalization of modified silica (FMS) surfaces on the adsorption behaviors for CH4, CO2 and the mixture have been studied by combining a grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) methods. The isotherms, gas distribution, sorption sites, isosteric heat, interaction energy and adsorption selectivity for CO2/CH4 mixture are computed and discussed. And the effects of pressure and temperature on adsorption behavior are also studied. The adsorption capacity (C) of surface with various functional groups for CH4 is as follows: C(SiO2-COOH) > C(SiO2-SH) > C(SiO2-OH) > C(SiO2-CH3) > C(SiO2-NH2) > C(SiO2-H) and for CO2 is as follows: C(SiO2-COOH) > C(SiO2-SH) > C(SiO2-NH2) > C(SiO2-OH) > C(SiO2-CH3) > C(SiO2-H). Increasing temperature is not advantageous for gas adsorption on all FMS surfaces. The CO2/CH4 selectivity (S) for FMS surfaces decrease in the following order of S(SiO2-COOH) > S(SiO2-NH2) > S(SiO2-OH) > S(SiO2-SH) > S(SiO2-CH3) > S(SiO2-H). As the pressure increase, the CO2/CH4 selectivity decrease early and then flatten out to a constant value. The isosteric heat of adsorption (Qst) for gas adsorbed on each FMS surface are also calculated, the value of isosteric heat for CO2 is much higher than that for CH4 due to the stronger interaction between CO2 molecules and functional groups of FMS surface. The result of the smallest self-diffusion coefficients of gas in SiO2-COOH slit pores is consistent with the adsorption capacity in the slit pore with corresponding functional group. The electronegative atoms in the functional group act as basic adsorption sites for gas adsorbate molecules, which generates a larger electrostatic contribution on the selectivity of CO2 over CH4.

Adsorption behaviors for clathrate hydrates of CO2 with mixed gases

Here, the preference and adsorption capacities of guest molecules in the sI and sII hydrate of water cages when CO2 + H2S, CO2 + SO2 and CO2 + N2O gas mixture form hydrates are simulated by using grand canonical Monte Carlo and molecular dynamics hybrid simulations method. The results indicate that SO2 prefers to occupy large cages, H2S prefers small cages for CO2 + H2S and CO2 + SO2 and N2O exhibits little preference between small or large or cages of CO2 + N2O sI hydrates, respectively. The abundance ratio shows hydrate can effectively achieve the separation of flue gases. Moreover, the thermodynamics calculation results show that the impurity gases H2S, SO2 and N2O favors the formation of CO2 hydrate. The stability CO2 + H2S, CO2 + SO2 and CO2 + N2O sI hydrates is higher compared to the stability of sII hydrates. The phase equilibrium analysis provides clear evidence that enclathration of H2S and SO2 molecules into the water cages of the hydrate structure plays a crucial role in stabilizing the hydrate lattices. The findings of this study suggest that removal of certain flue gas impurities is not required during the replacement of CH4 in hydrate form with the CO2 gas. The current investigation provides theoretical background for executing replacement of CH4 in hydrate form with the CO2 gas.

Adsorption performance of the functional COFs for removal of bisphenol A: Molecular dynamic simulations

The inherent structural features of the covalent organic frameworks (COFs) play a crucial role in determining their adsorption performances for bisphenol A (BPA). The computational methods were advantageous in unraveling intrinsic molecular properties about their performances. Herein, some COFs with different functional groups (–COOH, –NH2, –NO2 and –CF3) were designed to demonstrate the efficacy of the functional COFs for adsorbed BPA in gas phase and aqueous solution. The density functional theory (DFT) and Grand Canonical Monte Carlo (GCMC) methods were used to analyze the interaction energy between COFs and BPA, structure properties, and adsorption performances etc.. The results indicated that the addition of strong electronegative functional groups in COFs increased these COFs’ isosteric heat of adsorption (Qst) (TpBD-(COOH)2 > TpBD-(CF3)2 > TpBD-(NH2)2 > TpBD-(NO2)2 > TpBD) for gas phase BPA, but their introduction also reduced the pore size of COFs (TpBD > TpBD-(COOH)2 > TpBD-(NH2)2 > TpBD-(CF3)2 > TpBD-(NO2)2). However, these functional COFs demonstrated the stronger the adsorption capacity for gas phase BPA (At 298 K and 1 bar, the BPA uptake of TpBD-(COOH)2, TpBD-(NH2)2, TpBD, TpBD-(NO2)2 and TpBD-(CF3)2 was 242.52, 232.43, 219.31, 206.64 and 197.73 mg/g, respectively.). The amount of BPA adsorbed by functional COFs was the result of the synergistic effect of the electronegativity of functional groups and the pore size. Molecular dynamic (MD) simulation performed the same phenomenon for BPA in aqueous solution. In addition, the higher temperature will decrease the adsorption amount of BPA by COF, but increase its desorption ability.

Adsorption behavior of H2 in quartz silt-pores at high temperature and pressure

To understand the storage and transport of H2 in the Earth’s interior, the adsorption behaviors of H2 in the slit-like pore of quartz under different conditions were calculated by the grand canonical Monte Carlo method. The Poisson distributions of interaction energy show unimodal, indicating that the adsorption behavior is mainly affected by van der Waals interaction between molecular H2 and quartz, the adsorption potential energy increases, and when the pressure increases, the temperature and pore size decrease. Isosteric heat of adsorption is in the range of −5.0 to −1.7 kJ/mol, which indicates that the adsorption behavior belongs to physical adsorption. The results of isosteric heat of adsorption show that strong energy exchange occurs in the H2-quartz system at the initial stage of adsorption, which may affect the stability of quartz. The average isosteric heat of adsorption linearly increases with temperature. However, the increasing rate of average isosteric heat of adsorption decreases with the increase in the pore size. Adsorption snapshots show most of the H2 distributed randomly and there is no obvious adsorption layer of H2 in the pores. Excess adsorption amount increases with the decrease in temperature and the increase in pressure and pore size. The change rate of excess adsorption amount with temperature increases with the increase in pressure. Similarly, with the increase in pressure, the change rate of excess adsorption amount with pore size decreases slowly at first, then increases rapidly, and finally decreases. The results are helpful to reveal the migration and formation of H2 reservoirs in the Earth’s interior.

Distribution of ions between different dielectric media: Direct simulation of the Donnan equilibrium in the grand canonical ensemble

A modification of the original Grand Canonical Monte Carlo (GCMC) method to handle Donnan equilibrium is proposed that provides an equilibrium between two implicit-solvent bath electrolytes with different dielectric constants. A solvation energy penalty (described by the Born theory) and an electrical potential difference (Donnan potential) exist between the two baths, the ‘system’ under investigation and the ‘reservoir’. These terms are deducted from the chemical potential of the ‘reservoir’, and the resulting chemical potential is used in the ‘system’. The simulation performed with this chemical potential in the acceptance probabilities of the ion insertion/deletions is called Donnan GCMC and provides a thermodynamic state in the ‘system’ that is in equilibrium with the electrolyte in the ‘reservoir’. The simulation provides the distribution of ions between the two baths (concentrations in both media) from a single run instead of a numerical procedure that requires several GCMC runs. Using individual ion insertion/deletions, the Donnan potential can be determined.

Prediction of Carbon Dioxide and Methane Adsorption on UiO-66 Metal–Organic Framework via Molecular Simulation

The adsorption equilibrium of methane (CH4) and carbon dioxide (CO2) on the metal–organic framework (MOF) UiO-66 is studied via molecular simulation. UiO-66 is a versatile MOF with vast potential for various adsorption processes, such as biogas upgrading, CO2 capture, and natural gas storage. The molecular simulations employ the grand canonical Monte Carlo (GCMC) method, covering a temperature range of 298–343 K and pressures up to 70 bar for CH4 and 30 bar for CO2. The accuracy of different forcefields in describing the adsorption equilibria is evaluated. Two modelling approaches are explored: (i) lumping each hydrogen atom in the MOF framework to the heavy atom it is bonded to (united atom approximation) and (ii) considering explicit hydrogen atoms. Additionally, the influence of electrical charges on CO2 adsorption is also evaluated. The findings indicate that the most effective forcefield to describe the adsorption equilibrium is a united atom forcefield based on the TraPPE parametrization. This approach also yields an accurate calculation of the isosteric heat of adsorption. In the case of CO2, it is observed that the use of electrical charges enhances the prediction of the heat of adsorption, especially in the low-coverage region.

Simulation Study of the Air Separation Performance of Cr-MIL-101 in High-Altitude Environments

The most severe challenge for troops in a high-altitude environment is hypoxia. Pressure swing adsorption coupled with membrane separation is an ideal solution for oxygen production in high-altitude areas, but the molecular sieve membranes and organic membranes used in this technique are greatly affected by the ambient temperature, humidity, and pressure. Compared with traditional porous materials, metal-organic frameworks (MOFs) have outstanding features such as low densities, large specific surface areas, high crystallinities, and flexible structures. Cr-MIL-101 (MIL: Matérial Institut Lavoisier) and its derivatives are MOFs with high nitrogen adsorption capacities and can be used for oxygen production by air separation. However, since the plateau climate is complex, the applicability of Cr-MIL-101 for oxygen production in high-altitude environments awaits clarification. Therefore, this study constructed a molecular model of Cr-MIL-101, simulated the adsorption equilibrium of N2 and O2 molecules on this material using the grand canonical Monte Carlo (GCMC) method, and obtained their adsorption isotherms and densities. At 298 K and 100 kPa, the maximum adsorption capacities of Cr-MIL-101 for N2 and O2 were 0.94 per cell and 0.23 per cell, respectively. While at 238 K and 100 kPa, the maximum adsorption amounts of Cr-MIL-101 for N2 and O2 were 5.10 and 1.07 per cell, respectively. The thermodynamic parameters and adsorption equilibrium parameters during the adsorption process were analyzed. The conclusion of this study provides theoretical support for optimizing the N2/O2 separation performance of Cr-MIL-101 in high-altitude environments.

Changes in the three-dimensional molecular structure of coal during methane adsorption induced swelling

Methane (CH4) adsorption-induced swelling is one of the critical factors controlling the permeability of coalbed methane (CBM). CH4 adsorption alters the molecular structure of coal so as to induce coal swelling, and many uncertainties still exist in the process. In this study, the change in the molecular structures of different chemical structures by CH4 adsorption was investigated using the Grand Canonical Monte Carlo method to simulate the alteration of bond lengths and bond angles during swelling. The results demonstrate that the alteration of chemical structure is more extensive than a chemical bond, which is the critical factor causing the swelling behavior. Owing to the complex molecular structure of coal, among the different types of chemical structures, the C-O-C (-O-) chemical structure showed the most significant change in bond angle, with the largest degree of change is 12.89%. Compared with other chemical structures, the C-C-C (aromatic -C-) chemical structures are more stable and the largest degree of change is 0.65%. For the different types of chemical bonds, the C-C chemical bonds showed the most significant change in bond lengths, with the largest degree of change is 2.94%. And the O-H chemical bond showed the smallest change, with the largest degree of change is 0.79%. Considering the structure evolution of coal, the C-O-C (-O-) chemical structure decreases with increasing maturity and changes to the greatest after the adsorption of methane. The aromatic structure increases and the degree of deformation decreases, which is consistent with the previous experimental values for swelling. These results reveal the details of different types of chemical group deformation, providing a molecular-level insight into adsorption swelling and permeability changes.

3D porous polymers for selective removal of CO2 and H2 storage: experimental and computational studies.

In this article, newly designed 3D porous polymers with tuned porosity were synthesized by the polycondensation of tetrakis (4-aminophenyl) methane with pyrrole to form M1 polymer and with phenazine to form M2 polymer. The polymerization reaction used p-formaldehyde as a linker and nitric acid as a catalyst. The newly designed 3D porous polymers showed permanent porosity with a BET surface area of 575m2/g for M1 and 389m2/g for M2. The structure and thermal stability were investigated by solid 13C-NMR spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). The performance of the synthesized polymers toward CO2 and H2 was evaluated, demonstrating adsorption capacities of 1.85mmol/g and 2.10mmol/g for CO2 by M1 and M2, respectively. The importance of the synthesized polymers lies in their selectivity for CO2 capture, with CO2/N2 selectivity of 43 and 51 for M1 and M2, respectively. M1 and M2 polymers showed their capability for hydrogen storage with a capacity of 66cm3/g (0.6wt%) and 87cm3/g (0.8wt%), respectively, at 1bar and 77K. Molecular dynamics (MD) simulations using the grand canonical Monte Carlo (GCMC) method revealed the presence of considerable microporosity on M2, making it highly selective to CO2. The exceptional removal capabilities, combined with the high thermal stability and microporosity, enable M2 to be a potential material for flue gas purification and hydrogen storage.

Molecular simulation of CH4 adsorption characteristics in bituminous coal after different functional group fractures

To explore the effect of different functional group fractures in coal on the adsorption characteristics of CH4, molecular models of bituminous coal (Wiser) with fractured oxygen-containing functional groups (W–O5), sulfur-containing functional groups (W–S5), and nitrogen-containing functional groups (W–N5) were constructed. The microscopic mechanism by which the fracture of different functional groups in bituminous coal molecules affects CH4 adsorption was analyzed using Density Functional Theory (DFT), Molecular Dynamics (MD), and Grand Canonical Monte Carlo (GCMC) methods. The results show that functional groups facilitated the polarization of CH4 during the adsorption process, with the following influence relationship: oxygen-containing functional groups > sulfur-containing functional groups > nitrogen-containing functional groups; Fracturing functional groups in bituminous coal molecules weakened the adsorption capacity and reduced adsorption sites of CH4, the sequence of CH4 adsorption was Wiser > W–N5 > W–S5 > W–O5. High temperature reduced the effect of nitrogen-containing functional group fractures on CH4 adsorption, but had no obvious effect on sulfur-containing and oxygen-containing functional groups. The interaction between CH4 and the coal molecule decreased after functional group fractures, causing the enhanced diffusion of CH4 on bituminous coal molecules, and the order was W–O5 > W–S5 > W–N5 > Wiser. Additionally, the fracture of functional groups decreased the pore size of the bituminous coal molecules, which inhibited CH4 adsorption but facilitated its diffusion. The research provides theoretical support for enhancing CH4 desorption and improving the recovery rate of coalbed CH4.

Role of site–site interaction on the phase equilibria of multiple-site associating fluids in a functionalized slit pore

Vapor–liquid phase equilibria for multiple sites associating fluids with different associating strengths are investigated in a slit pore using grand-canonical transition matrix Monte Carlo method. The increase of critical temperature from two-site to four-site associating fluids at constant site strength is quite significant as compared to that of the one-site to two-site associating fluids, which is more pronounced at higher associating strength (ϵ* = 6). Monomer fraction and cluster size distribution are used to investigate the association of fluid particles in coexistence phases. The monomer fraction for both phases decreases with increased associating sites on the fluid particles due to more site–site interaction with neighboring fluid particles and forming a larger cluster. Therefore, the number of associating sites and their distribution play a vital role in the association of fluid particles. Moreover, the saturation chemical potential changes with the arrangement of the sites. For two-site associating fluids, we observe early vapor–liquid transition when the sites are oppositely placed, and when the sites are placed at 90°, the vapor–liquid transition is observed at the higher chemical potential. Moreover, four-site associating fluids with a square arrangement show early vapor–liquid phase transition, mainly because these arrangements of sites effectively interact with surface sites and the molecules in the next layer.

Computational Study of Metal‐Organic Frameworks for Hydrogen Sulfide Adsorption: Grand Canonical Monte Carlo and Molecular Dynamics Simulations

AbstractHydrogen sulfide (H2S) is a highly toxic, and flammable acid gas that is widely present in confined spaces. However, conventional adsorption materials are inefficient and have poor reuse properties. Metal‐organic frameworks (MOFs) show potential viability as novel materials in gas adsorption. Herein, mainstream MOFs were investigated based on molecular simulation techniques to explore the differences contributing to H2S adsorption. The adsorption process of H2S in MOFs was simulated by Grand Canonical Monte Carlo (GCMC) method, and the diffusion behavior was investigated based on molecular dynamics (MD) simulations. The results showed that the interaction energy and isosteric heat of adsorption were important criteria for determining the adsorption performance of H2S. The regulation of open metal sites could help to further enhance the adsorption of H2S, and the pore structure of MOFs affected the capture of H2S. A higher self‐diffusion rate implies faster H2S capture. Hydrogen bonds affect the trapping efficiency of MOFs for H2S and the relative positions of ligands in the benzene ring cause subtle differences in adsorption. This study provides design strategies for the improvement of new high‐performing MOFs for H2S adsorption in confined spaces.