Canonical Ensemble Monte Carlo Method Research Articles

Study on the Effect of H2S on the Adsorption of CH4, N2, and CO2 by Anthracite.

In order to study the effect of H2S on gas adsorption in a coal seam, the adsorption characteristics of single-component CO2, CH4, N2, and H2S and multicomponent H2S mixed with CO2, CH4, and N2 by anthracite were simulated by using the Grand Canonical Ensemble Monte Carlo (GCMC) method. The results show that the adsorption capacity of CO2, CH4, N2, and H2S in anthracite decreases with increasing temperature and increases with increasing pressure. The isothermal adsorption curves of CO2, CH4, N2, and H2S and different proportions of H2S/CH4, H2S/N2, and H2S/CO2 are highly consistent with the Langmuir equation, and the R 2 is above 0.99. Under different temperature and pressure conditions, the adsorption capacity of H2S and CO2 is stronger than that of coal for N2 and CH4, and the adsorption capacity difference is about 3 mmol/g. There is competitive adsorption among H2S, CO2, CH4, and N2, and H2S has a superior adsorption property. When H2S and other gases exist at the same time, the adsorption capacities of CH4, N2, and CO2 are reduced by 48-60%, 81-91%, and 51-66%, respectively.

Machine learning based screening of organic frameworks for separation of CF4/N2, C2F6/N2, and SF6/N2

Through molecular simulation, feature analysis and extraction, as well as the modeling and optimization of machine learning algorithms, we have developed exceptional regression prediction models for the high-throughput screening of organic framework materials in CF4/N2, C2F6/N2, and SF6/N2 separation. The Grand Canonical Ensemble Monte Carlo method was employed to simulate the adsorption behavior of these three gas mixtures in 603 organic framework materials at room temperature 298 K and different pressures, constructing a dataset suitable for subsequent machine learning studies. We analyzed the impact of six common structural features of adsorbents (PLD, LCD, Density, ASA, AVF, and AV) on separation performance, determining the optimal ranges of each structural feature for adsorption separation in different gas mixtures. Additionally, we introduced two custom descriptors (AVG_SIG, AVG_SQRT_EPS) to describe adsorbent force field parameters, revealing their significant correlation with adsorption separation performance. Using pressure, adsorbent structural features, and custom descriptors as features, and TSQ value representing adsorption separation performance as the target, we applied eight machine learning models based on linear regression (MLR, RR), decision tree (DT, RF, GBDT, XGBoost), and neural network (MLP, GN) principles to model and predict on three datasets. Results indicated that simple models struggle to reliably predict adsorption separation performance, while structurally complex machine models demonstrate significant potential. We utilized the Harris Hawks Optimization (HHO) algorithm to perform hyperparameter optimization on multiple machine learning models and introduced improvements to the GN network. The optimized models, especially XGBoost and GN, exhibited outstanding performance, significantly enhancing the accuracy of predicting adsorption separation.

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 Adsorption in Deep Marine Shale Gas Reservoirs

Deep marine shale gas reservoirs are extremely rich in the Sichuan basin in China. However, due to the in situ conditions with high temperature and high pressure (HTHP), in particular reservoir pressure being usually much higher than the test pressure, it is difficult to accurately clarify the adsorption behavior, as seepage theory plays an important role in shale gas reserves evaluation. Therefore, three kinds of sorbent, including illite, quartz and kerogen, and two simulation methods, containing the grand canonical ensemble Monte Carlo method and molecular dynamics method, are synthetically used to determine the methane adsorption behavior under HTHP. The results show that both absolute adsorption and excess adsorption decrease with the increase of temperature. When the pressure increases, the absolute adsorption increases quickly and then slowly, and the excess adsorption first increases and then decreases. The superposition of wall potential energy is strongest in a circular hole, second in a square hole, and weakest in a narrow slit. The effect of pore size increases with the decrease of the pore diameter. Under HTHP, multi-layer adsorption can occur in shale, but the timing and number of layers are related to the sorbent type.

Molecular Mechanisms of the Effect of Water on CO2/CH4 Mixture Adsorption in Slitlike Carbon Pores

The grand canonical ensemble Monte Carlo method has been used to study adsorption of carbon dioxide, methane, and their mixtures with different compositions in slitlike carbon pores at a temperature of 318 K and pressures below 60 atm. The data obtained have been used to show the effect of fixed amounts of pre-adsorbed water (19, 37, and 70 vol %) on the adsorption capacity and selectivity of carbon micro- and mesopores. The presence of water reduces the adsorption capacity throughout the studied pressure range upon adsorption of gaseous mixtures containing less than 50% CO2, as well as in narrow micropores (with widths of 8−12 A). Upon adsorption of mixtures with CO2 contents higher than 50%, the adsorption capacity of pores with low water contents appears, in some region of the isotherm, to be higher than that in dry pores. In the case of wide pores (16 and 20 A), this region is located at low and moderate pressures, while for mesopores it is located at high pressures. The analysis of the calculated data has shown that the molecular mechanism of the influence of preadsorbed water on the adsorption capacity is based on the competition between the volume accessible for adsorption (decreases the capacity) and the strength of the interaction between carbon dioxide molecules and water molecules (increases the capacity). Therewith, the larger the surface area of the water–gas contact, the stronger the H2O–CO2 interactions.

Microcanonical-ensemble computer simulation of the high-temperature expansion coefficients of the Helmholtz free energy of a square-well fluid

ABSTRACTThe microcanonical-ensemble computer simulation method (MCE) is used to evaluate the perturbation terms Ai of the Helmholtz free energy of a square-well (SW) fluid. The MCE method offers a very efficient and accurate procedure for the determination of perturbation terms of discrete-potential systems such as the SW fluid and surpass the standard NVT canonical ensemble Monte Carlo method, allowing the calculation of the first six expansion terms. Results are presented for the case of a SW potential with attractive ranges 1.1 ≤ λ ≤ 1.8. Using semi-empirical representation of the MCE values for Ai, we also discuss the accuracy in the determination of the phase diagram of this system.

Directing the Self-Assembly of Tripod Molecules on Solid Surfaces: A Monte Carlo Simulation Approach

Directing the self-assembly of organic molecules toward low-dimensional superstructures has been an attractive method of fabrication of functional materials with programmable architecture. In this contribution, using theoretical modeling, we demonstrate how fine-tuning of directional intermolecular interactions which are encoded in a simple organic building block allows for the creation of surface-confined assemblies with largely diversified morphology. To that end, the self-assembly of a model tripod-shaped molecule adsorbed on a triangular lattice was simulated using the canonical ensemble Monte Carlo method. The simulations were performed for flat, rigid building blocks built of four discrete segments (core plus three arm segments) and equipped with adjustable peripheral interaction centers providing directional intermolecular bonds. The simulated results revealed that changes in the directionality of interactions imposed on the centers are responsible for the emergence of different molecular structure...

Influences of lithium doping and fullerene impregnation on hydrogen storage in metal organic frameworks

Using the grand canonical ensemble Monte Carlo method, two similar metal organic frameworks (isoreticular MOFs [IRMOF]-12 and -14) and their modified structures by doping lithium (Li) atoms above the organic units and/or impregnating with fullerenes in their cavities have been employed to investigate the capacities of H2 storage. Our simulations show that the H2 uptakes of Li-C60@Li-IRMOF-12 and Li-C60@Li-IRMOF-14 achieve the U.S. Department of Energy targets before 2017 both in gravimetric density and in volumetric density at 243 K and 100 bar. Combining the results of IRMOF-10-based structures, we further study the relationships between the H2 uptakes and the physical properties of the materials to identify the influence factors on the H2 storage at room temperature.

Study on the Adsorption of Carbonized Micron Wood Fiber Filter for the Nanoparticle Emissions of Diesel Engine

Carbonized Micron Wood Fiber (CMWF) has many merits of high filtration efficiency, low cost, green environmental protection and so on. Besides, it also has the properties of activated carbon, which makes its adsorption ability for nanoparticles emitted by a diesel engine much stronger. In this paper, the adsorption number density of the nonoparticles in the CMWF filter under the different conditions is simulated based on Grand Canonical Ensemble Monte Carlo Method (GCEMC). Moreover, the result of simulation is validated by a engine bench experiment. Theoretical deduction and experiment results both prove the simulation method can be applied to simulate the adsorption process of the nanopaticles.

Boron-substituted graphyne as a versatile material with high storage capacities of Li and H2: a multiscale theoretical study

Based on density functional theory (DFT), first-principles molecular dynamics (MD), and the grand canonical ensemble Monte Carlo (GCMC) method, we investigated the boron substitution in aromatic rings of graphyne in terms of geometric and electronic structures as well as its bifunctional application including Li and H2 storage. The calculated binding energies of B-doped graphyne (BG) are significantly enhanced at two adsorptive sites compared to pristine graphyne, leading to high lithiation potentials of 2.7 V in 6Li@1BG, and even higher with 3.0 V in 6Li@3BG. Thus, 6Li@1BG with a capacity of 1125 mA h g(-1), which is much larger than other carbon materials, is proposed to be a good anode material in lithium-ion batteries. For further hydrogen storage in 6Li@nBG, the results show that it can steadily adsorb at least 8H2 in DFT, MD and GCMC computations, and the excess gravimetric H2 uptake is 7.4 wt% at ambient conditions, exceeding the 2017 DOE target. Our multiscale simulations demonstrate that chemical modifications in two-dimensional carbon structures are very promising for high lithium storage and hydrogen uptake.

Optimaization of Single-Walled Carbon Nanotube for Adsorption of Methane

In this paper, methane adsorption in single-walled carbon nanotube (SWNT) has been simulated by using the grand canonical ensemble Monte Carlo (GCMC) method. Lennard-Jones (LJ) potential is used to represent the fluid-fluid interaction, Lennard-Jones potential and integral method are used to calculation of the potential between fluid molecules and carbon atoms, respectively. In the simulation, two methods of calculation of potential between fluid molecules and SWNT are compared. The potential calculated by the two methods are almost the same. Then the influence of diameter of SWNT on the usable capacity ratio (UCR) is analyzed, and the parameters of the SWNT which has the best adsorption performance at 300K is recommended under certain pressure.

Computer Simulation in Actived Carbon Pores for Methane Storage

In this paper, adsorption of methane in actived carbon pores has been simulated by using the grand canonical ensemble Monte Carlo (GCMC) method. In the simulation, Lennard-Jones (LJ) potential is used for represent the fluid-fluid interaction, and the 10-4-3 potential is used for represent the interaction between fluid molecules and a slit carbon wall. Firstly, the adsorption isotherms of methane in actived carbon pores and local density profiles of methane in slit pore are obtained. Then, the interaction energy of methane in slit carbon pores with nine different pore sizes is obtained. Finally, the temperature, pressures, pore sizes affect the adsorption amount was studied, respectively.

Computational Simulation of Methane Adsorption in Single-Walled Carbon Nanotube

In this paper, methane adsorption in single-walled carbon nanotube (SWNT) has been simulated by using the grand canonical ensemble Monte Carlo (GCMC) method. Lennard-Jones (LJ) potential is used to represent the fluid-fluid interaction, and integral method is used to calculation of the potential between fluid molecules and carbon atoms. In the simulation, adsorption isotherms of methane in the (15, 15), (20, 20), (25, 25) and (30, 30) SWNT are simulated.

A molecular modeling study on small molecule gas transportation in poly (chloro-p-xylylene)

Results of molecular dynamics (MD) and Monte Carlo (MC) simulations on transport process of small molecules in poly (chloro-p-xylylene) membranes are discussed. Diffusion coefficients have been obtained by MD combined with Einstein fluid equation. Solubility coefficients have also been calculated by the transition state Great Canonical ensemble Monte Carlo (GCMC) method. Then permeability has been derived by diffusion coefficient and solubility. The agreement between calculated and experimental data for diffusion coefficient, solubility factors and permeability can be considered acceptable. Therefore, atomistic simulations techniques have proven to be a useful tool for the understanding of structure–property relationships of materials and in particular MD can be used for detailed descriptions of the complex morphologies and transport mechanisms associated with rigid glassy structures.

Spontaneous segregation on a hybrid chiral surface

Segregation of enantiomers in two-dimensional adsorbed layers is a process that is usually controlled by anisotropic directional interactions between adsorbed molecules. In this contribution, we propose a simple theoretical model in which the chiral segregation occurs even though the lateral interactions are neglected. In particular, we consider a solid surface composed of two domains with different patterns of active sites being mirror images of each other. The domains of opposite handedness represent crystal facets of a composite chiral material which are adjoined to form a heterochiral adsorbing surface. To explore equilibrium properties of the system, we use Canonical Ensemble Monte Carlo method for a square lattice. The influence of factors such as energetic properties of the surface and density of the adsorbed layer on the extent of separation is examined. The obtained results indicate that effective two-dimensional separation on the hybrid chiral surface assumed in our model can be achieved only at sufficiently low adsorbate densities. The results also suggest that the segregation on the hybrid surface would be a promising method of enantiodiscrimination for those chiral molecules which do not exhibit strong lateral interactions.

Structure of polymer solutions at interfaces: a Monte Carlo simulation study

The canonical ensemble Monte Carlo method is applied to study the structure of polymer solutions confined between surfaces. The polymer molecules are modeled as fused-sphere freely rotating chains with fixed bond length and bond angles and the solvent as hard spheres. The simulation results for the configurational and conformational properties of the chains are presented with varying interfacial distances, chain concentrations, and chain lengths. The chains are depleted at the wall at lower density, which, however, becomes less at higher density. With an increase in the interfacial distance, the enhancement/depletion of the chains at the wall becomes more marked. At all interfacial distances and chain lengths, increasing the concentration of the solvent makes the oscillation in the density profile of the chains more pronounced. Conformational properties provide important indications regarding the behaviour of chains as they approach surfaces.

Connectivity effects for slit pores linked by a channel

This paper describes a Monte Carlo computer simulation study of connectivity effects in a system of two parallel slit pores and a quasi-one-dimensional joint. A numerical method for evaluation of accessible volume in computer simulation studies of adsorption in pores is presented and applied to simple slit pores and systems of interconnected pores. A local version of the grand canonical ensemble Monte Carlo method is used to study adsorption under conditions mimicking mass transfer limitations.

Effect of micropore on hydrogen adsorption of single walled carbon nanotubes

Using grand canonical ensemble Monte Carlo method,the effect of micropores,mainly the hollow cores of single-walled carbon nanotubes(SWNTs) and the interstitial channel among SWNTs,on the hydrogen adsorption of SWNTs was studied.Comparing with experimental observations,it was found that the hollow cores of SWNTs are the dominant sites for hydrogen adsorption,The overlap and efficiency of the adsorption potential inside a SWNT were analyzed,and it was found that the hydrogen adsorption capacity of the SWNTs is improved when the diameter of the SWNTs is around 2nm.The calculation also showed that the interstitial channel among SWNTs can become effective sites for hydrogen adsorption when the gap between two SWNTs increases.

In-Layer Structuring of Like-Charged Macroions in a Thin Film

A thin liquid film formed from similarly charged macroions dissolved in an electrolyte solution is modeled using the canonical ensemble Monte Carlo method. Simulation studies are performed within a one-component fluid approach; i.e., the model system is composed of the macroions only but using an effective pairwise interaction that incorporates contributions from both the electrostatic nature of the supporting electrolyte and the discrete nature of a polar solvent. The layering phenomenon and in-layer ordering of the macroions in a thin macroion film are analyzed, and the role of electrostatics and excluded volume forces is discussed. We find that the electrostatic forces enhance the overall phenomenon of macroion layering while the excluded volume forces are important for the formation of the surface monolayers and contribute to the macroion structuring within monolayers.

Correlation of stress and structure in a simple fluid confined to a pore with furrowed walls

A Lennard-Jones (12,6) film confined between two furrowed walls was simulated by the grand canonical ensemble Monte Carlo method. The walls are constructed by gouging triangular grooves in planar substrates that are structureless on the molecular scale. The furrows are infinitely long in one transverse direction (y) and of nanoscopic width (s(x)) and depth (D). The furrows in the two walls are maintained parallel and in register. The diagonal components of the stress tensor (T(alphaalpha), alpha=x,y,z) are computed as functions of D and the separation between the substrates (s(z)) at fixed temperature, chemical potential, and s(x). The T(alphaalpha) for the film between the furrowed walls are strongly shifted from their counterparts for the film between flat (i.e., planar) walls. The shifts are rationalized in terms of the structure of the film, which becomes more ordered as the furrows deepen and the packing of film molecules becomes more restricted in the two dimensions normal to the y direction. The results demonstrate the profound impact of the coupling between molecular and nanoscopic scales on the properties of geometrically constrained fluids.