Grand Canonical Monte Carlo Method Research Articles

Molecular simulation on carbon dioxide capture performance for carbons doped with various elements

Among the different types of CO2 capture technologies for post-combustion, sorption CO2 capture technology with carbon-based sorbents have been extensively explored with the purpose of enhancing their sorption performance by doping hetero elements due to the rapid reaction kinetics and low costs. Herein, sorption capacity and selectivity for CO2 and N2 on carbon-based sorbents doped with elements such as nitrogen, sulfur, phosphorus, and boron, are evaluated and compared using the grand canonical Monte Carlo (GCMC) method, the universal force field (UFF), and transferable potentials for phase equilibria (TraPPE). The sorption capacities of N-doped porous carbons (PCs) at 50 °C were 76.1%, 70.7%, 50.6%, and 35.7% higher than those of pure PCs, S-doped PCs, P-doped PCs, and B-doped PCs, respectively. Its sorption selectivity at 50 °C was approximately 14.0, nearly twice that of pure PCs or other hetero-element-doped PCs. The N-doped PCs showed the largest sorption heat at 50 °C among all the PCs, approximately 20.6 kJ·mol−1, which was 9.7%−25.5% higher than that of the pure PCs under post-combustion conditions. Additionally, with the product purity of 41.7 vol.%−75.9 vol.% for vacuum pressure swing sorption, and 53.4 vol.%−83.6 vol.% for temperature swing sorption, the latter is more suitable for post-combustion conditions than pressure-swing sorption.

Grand canonical Monte Carlo simulation of the adsorption and separation of carbon dioxide and methane using functionalized Mg-MOF-74

Grand canonical Monte Carlo (GCMC) simulations were used to analyse the effect of -O-Li, -NH2, -SH, -F, -COOH, and -NO2 functional groups on the adsorption and separation of pure CO2 and a mixture of CO2 and CH4. The metal–organic framework (MOF) skeleton was structurally optimized using the Forcite and Dmol 3 modules. First, the GCMC method was employed to simulate the adsorption of pure CO2 by functionalized Mg-MOF-74 at 298 K and 10–3000 kPa. The results illustrated that -O-Li, -NH2, and -SH groups increased the CO2 adsorption below 101 kPa and followed the order Li-O-Mg-MOF-74 > NH2-Mg-MOF-74 > SH-Mg-MOF-74. When the pressure was >101 kPa, the adsorption capacity of Mg-MOF-74 was higher than that of functionalized Mg-MOF-74. Then, the adsorption capacity and selectivity of functionalized Mg-MOF-74 in the CO2/CH4 mixture were investigated at 298 K and 10–3000 kPa. The results showed that the introduction of -O-Li, -NH2, and -SH groups increased the CO2 selectivity of Mg-MOF-74 within the range of 10–1440 kPa and followed the order Li-O-Mg-MOF-74 > NH2-Mg-MOF-74 > SH-Mg-MOF-74.

Screening of Hypothetical Metal–Organic Frameworks for Xylene Isomers and Ethylbenzene Separation

A database of hypothetical metal–organic frameworks (hMOFs) was investigated in search of top-performing adsorbents for the separation process of xylene isomers and ethylbenzene mixture. The structural properties of individual hMOF are calculated to understand the correlation between the properties with adsorption capacity or selectivity. The high-throughput staged screening of the hMOF database is performed and screened. The simulations of hMOF with a gas mixture were conducted at 373 K and 30 kPa using a multicomponent grand canonical Monte Carlo method to obtain the para-xylene selectivity. The top five hMOFs showed significantly better performance of all and compared to previously discovered materials. The top hMOFs were further simulated at different pressures to obtain the adsorption isotherms. Further, the energetic contribution of organic linkers and inorganic metal nodes toward competitive adsorption was studied to further understand the enhanced interaction between hMOF and para-xylene.

CO2 adsorption and separation properties of M-MOF-74 materials determined by molecular simulation

This study simulated the adsorption and separation of CO2 by the metal-organic frameworks material M-MOF-74, established the skeleton model of M-MOF-74 series adsorbent, and calculated the adsorption of CO2 pure component gas and CO2/N2 mixed gas on MMOF- 74 series adsorbent by the grand canonical Monte Carlo method. Among the CO2 adsorption performances of MOF-74 materials with metal centers of Mg, Co, Ni, and Zn, Mg-MOF-74 had the highest CO2 adsorption capacity, adsorption selection coefficient and adsorption heat. When mixed gas was adsorbed, the law of CO2 adsorption was consistent with that of pure CO2 adsorption. The size law of adsorption heat on MOF-74 was similar to that of adsorption amount. Our findings demonstrated that the interaction between the metal-organic framework material and CO2 is greater than that between the material and N2. The interaction between the gas and the MOF-74 series adsorbent was the main factor affecting the adsorption amount, which reveals the strong influence of metal central atoms on the amount of gas adsorption. Our findings provide new ideas for the design of efficient adsorbent materials. Cited as: Deng, J., Zhao, G., Zhang, L., Ma, H., Rong, Y. CO2 adsorption and separation properties of M-MOF-74 materials determined by molecular simulation. Capillarity, 2023, 6(1): 13-18. https://doi.org/10.46690/capi.2023.01.02

Molecular Simulation of the Pore Structure and Adsorption Properties of Coal under Compression Stress

The deformation of the macromolecular structure of coal under compression stress may affect the pore structure and adsorption properties. In this study, the Grand Canonical Monte Carlo and molecular dynamics methods were used to investigate the effects of compression stress on the pore structure and adsorption properties of coal, and the coupling relationships between stress, strain, pore structure, and adsorption properties were explored. A macromolecular model of coal was constructed, and uniaxial compression simulation was conducted. The increase of compression stress reduces the pore volume, specific surface area, and connectivity of coal and concentrates the pore size distribution in pores with smaller sizes. The increase of stress leads to a different degree of reduction in the adsorption performance of coal on CH4 and CO2, and the stress sensitivity of CH4 is slightly stronger than that of CO2. The results of adsorption configurations in the pores under different strains indicate that the reduction of adsorption properties is controlled by the pore volume and pore connectivity. The adsorption performance of CH4 and CO2 in coal at different strains has a good linear relationship with the volume and specific surface area of the pores; the smaller the volume and specific surface area of the pores, the weaker the adsorption performance of coal. This study clarifies the control of the strain response under compression stress on the pore structure and adsorption properties of coal and provides guidance for the study of adsorption, desorption, and diffusion of CBM.

INVESTIGATION OF COMPETITIVE ADSORPTION AND DIFFUSION BEHAVIORS OF CO2/CH4/N2/H2O AFFECTED BY COAL RANKS IN SLIT STRUCTURES

In this work, different slit structures of coals (brown coal, bituminous coal, and anthracite coal) with various ranks are established at a molecular level. Based on the grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) methods, the effects of coal rank on CO<sub>2</sub>, CH<sub>4</sub>, N<sub>2</sub> and H<sub>2</sub>O multi-component gases adsorption and diffusion in slit structures are investigated. The influence of coal rank on the swelling ratio caused by adsorption and diffusion in different slit structures is discussed for the first time. It is shown that the adsorption capacity of CO<sub>2</sub>, CH<sub>4</sub>, N<sub>2</sub> and H<sub>2</sub>O in different slit structures follows the order of H<sub>2</sub>O > CO<sub>2</sub> > CH<sub>4</sub> > N<sub>2</sub>, whereas the diffusion coefficient follows H<sub>2</sub>O < CO<sub>2</sub> < CH<sub>4</sub> < N<sub>2</sub>. With the growth of coal rank, the adsorption capacity and diffusion coefficients of CO<sub>2</sub>, CH<sub>4</sub>, N<sub>2</sub> and H<sub>2</sub>O increase, meanwhile, the adsorption selectivity coefficients of CH<sub>4</sub>/CO<sub>2</sub>, N<sub>2</sub>/CH<sub>4</sub>, and CO<sub>2</sub>/H<sub>2</sub>O rise, following the order of anthracite coal > bituminous coal > brown coal. In addition, both the adsorption and diffusion swelling ratio reduce with the decrease of coal rank. The present molecular investigation of competitive adsorption and diffusion characteristics of multi-component gases can provide theoretical basis for efficient exploitation of coalbed methane.

Thermodynamics of liquid and fluid mixtures from the kinetic Monte Carlo viewpoint.

In this study a binary mixture is modelled in a uniform simulation cell at various temperatures using an extended version of the grand canonical kinetic Monte Carlo (GC-kMC) method. The main goal of this study is to consider the thermodynamic properties of binary liquids, gases, and gas-liquid mixtures from a more general point of view than that applied to the particular case of vapour-liquid equilibrium when the pressure and partial chemical potentials in coexisting phases are the same. Particular attention is paid to thermodynamic functions such as chemical potentials, Gibbs free energy and entropy. For the pair potential of unlike molecules a more universal scheme is proposed in comparison with the Lorentz-Berthelot combining rule. The approach is tested on an Ar-Kr mixture in a wide range of temperatures. In all cases, the obtained values of chemical potentials, pressure and internal energy for the entire set of component densities and temperature fully satisfy the Gibbs-Duhem equation with a high degree of accuracy. For the case of vapour-liquid equilibrium, the developed approach made it possible to reproduce the experimental pressure-composition diagrams with the highest accuracy ever achieved in the literature. Despite the fact that the Ar-Kr mixture, according to Raoult's law, is close to an ideal system, it was found that the partial pressures in the liquid phase or in a dense supercritical gas mixture are non-linear functions of the composition, and the partial pressure of the heavier component (Kr) can even be negative.

Identifying pathways to metal-organic framework collapse during solvent activation with molecular simulations.

Metal-organic framework (MOF) materials are a vast family of nanoporous solids with potential applications ranging from drug delivery to environmental remediation. Application of MOFs in these scenarios is hindered, however, by difficulties in MOF 'activation' after initial synthesis - removal of the synthesis solvent from the pores to make the pore space accessible - often leading to framework collapse if improperly performed. While experimental studies have correlated collapse to specific solvent properties and conditions, the mechanism of activation-collapse is currently unknown. Developing this understanding would enable researchers to create better activation protocols for MOFs, accelerating discovery and process intensification. To achieve this goal, we simulated solvent removal using grand-canonical Monte Carlo and free energy perturbation methods. By framing activation as a fluid desorption problem, we investigated activation processes in the isoreticular metal organic framework (IRMOF) family of MOFs for different solvents. We identified two pathways for solvent activation - the solvent either desorbs uniformly from each individual pore or forms coexisting phases during desorption. These mesophases in turn lead to large capillary stresses within the framework, corroborating experimental hypotheses for the cause of activation-collapse. Finally, we found that the activation energy of solvent removal increased with pore size and connectivity due to the increased stability of solvent mesophases, matching experimental findings. Using these simulations, it is possible to screen MOF activation procedures, enabling rapid identification of ideal solvents and conditions and thus enabling faster development of MOFs for practical applications.

Molecular simulation on the effect of formation depth on methane adsorption by clay minerals

Shale gas is an unconventional natural gas with large reserves. Recently, its production has increased rapidly, significantly impacting the international gas market and global energy landscape. In addition to organic matter and quartz, clay minerals constitute the majority of shale, and their production activities are effectively guided by evaluating their shale gas adsorption capabilities. To explore shale gas reserves and model their distribution, the variation in shale gas content with formation depth should be investigated. Currently, experimental methods are used to evaluate the effect of formation depth on shale gas adsorption, the data are substituted into a theoretical model, and the resulting mathematical model is used to estimate the variation in methane adsorption with formation depth, considering only temperature and pressure. However, the experimental method is flawed, and the true adsorption content cannot be obtained. The absolute methane adsorption amount was calculated using molecular dynamics and the grand-canonical Monte Carlo method for the corresponding temperature and pressure conditions. The supercritical Dubinin–Radushkevich (SDR) equation was fitted, yielding a temperature-dependent equation for the SDR parameter. Shale gas adsorption can be predicted using the developed mathematical model based on formation depth and temperature–pressure gradient.

Insight into the effect of biaxial compression strain on adsorption structure of bituminous coal matrix as well as gas diffusion and permeability properties by macromolecule simulation

The concentrated stress induced by mining activities leads to deformation of the coal, especially the coal matrix, which affects the production of coalbed methane (CBM). Therefore, grand canonical Monte Carlo and molecular dynamics methods were used to study the effect of biaxial compression strain on the adsorption structure of the bituminous coal matrix as well as the CH4/CO2/N2 diffusion and permeability properties based on the constructed macromolecular coal model. The results show that the dual-mode equation fits the gas adsorption isotherm and the order of influence of adsorption concentration on the model structure is N2 > CO2 > CH4. For the diffusion models, the orders of swelling rate and specific volume are CH4 > N2 > CO2, while those of the fractional free volume and pore volume are opposite. Compression (negative) strain (0.00 ∼ −0.20) reduces the bulk modulus but has a negligible effect on the shear modulus and wave velocity. Also the Poisson’s ratio of the CH4 diffusion model is smaller compared to the CO2/N2 diffusion model. The cohesive energy density (CED) order is CO2 > N2 > CH4 and its van der Waals component accounts for the major part. The mean square displacement distribution of gases successively increases in the power function and linearity with time. The self-diffusion coefficient of CH4 is larger than that of CO2/N2, which is greatly affected by strain. The (negative) interaction energy order between gas and coal matrix is CH4 > N2 > CO2, and the order of intermolecular interaction distance of gases is N2 > CO2 > CH4. Most importantly, the solubility order of gases is CO2 > CH4 > N2, and the strain has the dual effect of promoting and inhibiting the permeability of the coal matrix. The research results provide molecular-level insights into CBM recoveries in coal reservoirs with different strain degrees, with some technical value and theoretical importance.

In Silico Screening of Metal-Organic Frameworks and Zeolites for He/N2 Separation.

In silico screening of 10,143 metal-organic frameworks (MOFs) and 218 all-silica zeolites for adsorption-based and membrane-based He and N2 separation was performed. As a result of geometry-based prescreening, structures having zero accessible surface area (ASA) and pore limiting diameter (PLD) less than 3.75 Å were eliminated. So, both gases can be adsorbed and pass-through MOF and zeolite pores. The Grand canonical Monte Carlo (GCMC) and equilibrium molecular dynamics (EMD) methods were used to estimate the Henry's constants and self-diffusion coefficients at infinite dilution conditions, as well as the adsorption capacity of an equimolar mixture of helium and nitrogen at various pressures. Based on the obtained results, adsorption, diffusion and membrane selectivities as well as membrane permeabilities were calculated. The separation potential of zeolites and MOFs was evaluated in the vacuum and pressure swing adsorption processes. In the case of membrane-based separation, we focused on the screening of nitrogen-selective membranes. MOFs were demonstrated to be more efficient than zeolites for both adsorption-based and membrane-based separation. The analysis of structure-performance relationships for using these materials for adsorption-based and membrane-based separation of He and N2 made it possible to determine the ranges of structural parameters, such as pore-limiting diameter, largest cavity diameter, surface area, porosity, accessible surface area and pore volume corresponding to the most promising MOFs for each separation model discussed in this study. The top 10 most promising MOFs were determined for membrane-based, vacuum swing adsorption and pressure swing adsorption separation methods. The effect of the electrostatic interaction between the quadrupole moment of nitrogen molecules and MOF atoms on the main adsorption and diffusion characteristics was studied. The obtained results can be used as a guide for selection of frameworks for He/N2 separation.

CO2 solubility in terpenoid-based hydrophobic deep eutectic solvents: An experimental and theoretical study

This research deals with the experimental measurement and molecular dynamics simulations of the CO2 capture in hydrophobic-based natural deep eutectic solvents (NADESs). First, Thymol and Menthol based NADESs were prepared in the appropriate mole ratios. The CO2 capture in the NADESs was evaluated using Henry’s law constant at 298 K under the pressure up to 600 kPa. The best CO2 capture result was obtained for the eutectic mixture of Thymol:Camphor with the mole ratio of 4:6. The effects of the temperature, pressure, and the mole ratio of Thymol:Camphor on the capacity of the CO2 absorption were evaluated using the Response Surface Methodology/Central Composite Design (RSM/CCD) method. The obtained results using the RSM/CCD method presented the appropriate temperature and gas pressure for the optimized conditions of the CO2 capture. The molecular interactions in the DESs were analyzed using the investigation of the H NMR and FTIR spectroscopy and Thermogravimetric analysis. The molecular dynamic simulations, using the COMPASS force field and grand canonical Monte Carlo methods, were performed to examine the microscopic behavior of Thymol and Camphor with the CO2 molecule in three different molar ratios of the DES components. Radial distribution functions, mean square displacement analysis, and self-diffusion coefficients were also applied to interpret the solvent-solvent and solute-solvent interactions during the dissolving of the CO2 in the solvents.

Molecular simulation study on the effect of coal metamorphism on the competitive adsorption of CO2/CH4 in binary system

To explore the competitive adsorption characteristics of a CO2/CH4 binary gas in coal with different metamorphic degrees, macromolecular-structure coal models with different metamorphic degrees (anthracite coal, coking coal, and long-flame coal) were constructed based on elemental analysis, X-ray photoelectron spectroscopy (XPS), and carbon-13 nuclear magnetic resonance (13C NMR) results. Then, the competitive adsorption behaviors of CO2 and CH4 molecules in the different coal molecular models were simulated using molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) methods, and the changes of the competitive adsorption capacity, density distribution, adsorption selectivity, adsorption heat, and energy distribution were investigated. The results showed that the variation characteristics of the total adsorption of mixed gas were similar to those of pure gases, and the increase in the pressure led to an increase in the total adsorption, which also increased with the increase in the coal deterioration degree. The distribution ranges of the gas adsorption sites in coal with different metamorphic degrees were significantly different, with anthracite coal being the most widely distributed and long-flame coal being the least widely distributed. With the increase in the coal rank, the competitive adsorption selectivity of any proportion of CO2/CH4 binary mixed gas increased. The difference in the equivalent adsorption heat of single-component gases CO2 and CH4 in the mixed gas increased with the increase in the coal metamorphism and decreased with the increase in the CO2 gas proportion coefficient. This paper provides a theoretical basis for the application of CO2 enhanced coal bed methane in coal seams with different metamorphic degrees.

Adsorption characteristic analysis of PAHs on activated carbon with different functional groups by molecular simulation.

As widespread organic pollutants in the environment, polycyclic aromatic hydrocarbons (PAHs) greatly threaten human health. The adsorption technology has become one of the main methods to deal with PAHs because of its low cost, simple design, and no secondary pollution. Among them, solid media have strong adsorption capacities for PAHs and are widely used. In this work, activated carbon was chosen as the solid adsorbent. The adsorption behavior of three PAHs (naphthalene, anthracene, and phenanthrene) on activated carbon was investigated at the molecular level by Grand Canonical Monte Carlo (GCMC) method. The effects of different functional groups (amino, carboxyl, hydroxyl, carbonyl, and hydrogen groups) and temperature effect on the adsorption isotherms and heat of adsorption of PAHs on activated carbon were calculated. The results showed that the carbonyl functional group increased the adsorption of PAH molecules by the most considerable amount among all the functional groups. Acid functional groups were more favorable to the adsorption of PAHs than alkali functional groups. The adsorption capacity and heat of adsorption of PAHs decreased when the temperature increased. The adsorption performance of bicyclic aromatic hydrocarbons was more influenced by temperature than that of tricyclic aromatic hydrocarbons.

Adsorption behavior of molecular hydrogen in forsterite

Recent experimental studies have already discussed the existence of molecular hydrogen in mantle minerals. Here, we investigate the adsorption behavior of molecular hydrogen in forsterite with 0–15 Å intercrystalline pore at 0–519 MPa and 300–1800 K by using the Grand Canonical Monte Carlo (GCMC) method. Molecular hydrogen fills the interstitial positions of nonporous forsterite in an adsorbed state, whereas the filling of intercrystalline pore includes the adsorbed and free states. The adsorption of molecular hydrogen on the crystal surface of forsterite intercrystalline pore belongs to physisorption. The interaction between the adsorbate molecular hydrogen and the adsorbent forsterite framework weakens with pressure and strengthens with temperature, which is a crucial factor, and intercrystalline pore size. The adsorption capacity of molecular hydrogen in the intercrystalline pore of forsterite increases with pressure and intercrystalline pore size and decreases with temperature. By contrast, the adsorption capacity of molecular hydrogen in nonporous forsterite is controlled by pressure above 1200 K. Variations in intercrystalline pore size above 5 Å have a negligible effect on the capacity of adsorbed state molecular hydrogen at a given temperature and pressure. The adsorption of molecular hydrogen on different crystal faces of forsterite is anisotropic, with stronger adsorption on (001) and (100) than on (010) crystal faces. The adsorption capacity of molecular hydrogen in the intercrystalline pore decreases with the increase in oxygen fugacity at a given pressure, temperature, or intercrystalline pore sizes. The significant amount of molecular hydrogen stored in forsterite can provide a rich material basis for the short-term seismic precursor anomaly of hydrogen concentration and the formation of water through the reaction of silica with molecular hydrogen in the mantle.

Effect analysis of initial water content and temperature on the adsorption of VOCs by activated carbon based on molecular simulation

To analyse the effects of initial water content (IWC) and temperature on the adsorption behaviour of VOCs on activated carbon (AC), the grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) methods were used. Benzene and acetone are regarded as two representative components of VOCs, and their adsorption properties in AC models with four different IWC at 298.15 K were investigated. Their adsorption properties at four different temperatures (278.15, 288.15, 298.15, and 308.15 K) were also investigated. The simulated pressures were set in the range of 3 × 10−4 to 3 kPa (benzene) and 10 × 10−4 to 10 kPa (acetone). The results show that water molecules can impede the adsorption of benzene and acetone, decreasing the saturated adsorption capacity, the isosteric heat, and monomolecular interaction energy. However, the pre-loaded water molecules can enhance the electrostatic interaction at low pressure, which affects the isosteric heat and monomolecular interaction energy, but the pore volume is still the main influencing factor. Before reaching the saturated adsorption capacity, the higher the temperature, the lower the adsorption capacity, and the monomolecular interaction energy follows the same trend. The results provide mechanistic insights into how the IWC and temperature affect the adsorption properties of AC for VOCs.

A molecular level based parametric study of transport behavior in different polymer composite membranes for water vapor separation

The membrane dehumidification technology has great energy-saving potential compared to traditional methods. However, the design of composite membrane depends mostly on trial tests. To understand the mechanisms dominating material properties and quantitatively predict the air dehumidification performance of the composite membranes in practical applications, various models combined with different polymeric materials and porous support membranes were developed and investigated by using grand canonical Monte Carlo (GCMC) and Molecular dynamics (MD) simulation methods. The interfacial interactions between the selective layer and the support membrane were analyzed in detail to explore the interface stability and compatibility of various composite membranes. The physical characteristics (density, fractional free volume, solubility parameter and cohesive energy density) and transport properties (solubility, diffusivity, permeability and selectivity) of various composite membranes were parametrically evaluated. The polydimethylsiloxane (PDMS) composite membranes exhibited stronger interfacial interaction in comparison to the PVA composite membranes. The hydrophilicity and polarity of polyvinyl alcohol (PVA) polymer resulted in a stronger interaction between the gas molecules and the PVA membrane. According to the solution–diffusion mechanism, the PVA-PVDF membrane presented the optimal H2O permeability of 3121.38 Barrer among all composite membranes. Generally, polyvinylidene fluoride (PVDF) or polyacrylonitrile (PAN) as the materials of support membrane had good fiber forming characteristics and low gas diffusion resistance, which significantly affects the performance of selective layers. The microscopic mechanisms revealed in this work would lay a solid theoretical foundation for the design of high performance composite membrane for air dehumidification.

Insights into the heat contributions and mechanism of CO2 adsorption on metal–organic framework MIL-100 (Cr, Fe): Experiments and molecular simulations

Metal–organic frameworks (MOFs) MIL-100 (Cr, Fe) synthesized by the hydrothermal method were subjected to heat treatment under an H2 flow. The MIL-100 (Cr) samples had specific surface areas and pore volumes approximately-two times higher than those of the MIL-100 (Fe) samples. The H2 heat treatment enhanced the crystallinity, especially for MIL-100 (Fe). The resulting adsorbents exhibited a superior CO2 adsorption capacity. Furthermore, the grand canonical Monte Carlo method was used to examine the adsorption mechanism at a molecular level. The heat contribution of each atom type of MOFs was demonstrated. The highest heat was found at low loadings (Henry’s law region) among other regions owing to CO2 adsorption inside the supertetrahedron. The most active atoms were C atoms (CO > CC > CH), followed by the O atom (COunsaturated metal), the unsaturated metal site, the other O atom (COsaturated metal), the saturated metal site, the H atom of the ligands, and the O atom of the metal cluster, respectively. This study can provide insights into the determination of the atomic heat contributions of other adsorbents for a better understanding of material design and the mechanism of adsorption.

Simulation study on the effect of pore structure and surface curvature of activated carbon on the adsorption and separation performance of CO2/N2

In this paper, the grand canonical Monte Carlo (GCMC) method was used to explore the effects of four pore structures (disordered pore, wedge pore, carbon nanotube, and slit pore structures) and surface curvature of activated carbon on the adsorption and separation of CO2/N2. On the whole, carbon nanotubes have the greatest selectivity for CO2, followed by disordered pores, wedge pores, and slit pores. The effect of pore structure on the interaction energy of gas molecules is similar to that of selectivity, in which the fluid–solid potential energy between adsorbates and adsorbents plays an important role. Due to the different affinity between adsorbate molecules and activated carbon, CO2 with high affinity is more sensitive to the change of pore size. Therefore, under high pressure, the density of CO2 in the slit pore is greater than that in the wedge pore. However, N2 with poor affinity is limited by the surface area, resulting in the density of it in the wedge pore is always higher than that in the slit pore. Although the existence of non-six membered corannulene rings in activated carbon can’t always cause the increase of specific surface area, the surface curvature of activated carbon caused by it can increase strong energetically adsorption sites. Hence, the surface curvature plays a positive role in the adsorption density, interaction energy, and CO2 selectivity. The discovery of CO2/N2 adsorption and separation at the molecular level is expected to provide valuable insights.

Vapor-liquid phase equilibrium of n-pentane in quartz nanopores by grand canonical Monte Carlo calculation

As the main basis for calculating other physical property data, the critical temperature and pressure of fluid are important parameters in the process of oil and gas field development. In unconventional reservoirs, crude oil fluid generally exists in nanopores. The interaction between fluid molecules and the pore wall leads to the deviation of fluid properties. Pore size is an important parameter affecting the phase state of reservoir fluid. The phase state laws of alkanes in different nanopore sizes are quite different. We studied the effect of the pore size of quartz nanopores on the vapor–liquid phase equilibrium using the grand canonical Monte Carlo method. The quantitative relationship between the nanopore size and the adsorption amount, density profile, and phase diagram of n-pentane was obtained, and its micromechanism was analyzed. The results showed that the critical temperature and critical pressure of n-pentane increased with an increase in the nanopore size. The critical temperature was consistent with the bulk phase after the pore size reached 10 nm, and the critical pressure could be treated with the bulk phase after the pore size reached 30 nm. The van der Waals force between the fluid and the pore wall was the main factor leading to the phase change of the system. These findings suggest that the aperture of nanopores was significant for alkane phase change, which might provide a reference for understanding the phase transformation law behavior of alkanes in nanopores of tight reservoirs.