Grand Canonical Monte Carlo Method Research Articles

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.

Effects of the ZSM-5 zeolites on hydrocarbon emission control of gasoline engine under cold start

The feasibility of ZSM-5 zeolite for controlling hydrocarbon (HC) emissions during cold start period of gasoline engine was studied by temperature programmed desorption (TPD) experiment and molecular simulation (MS). Acetylene, 1-butene, propylene, ethylene, acetaldehyde and benzene molecules were selected as representative HCs based on the HC emission components of gasoline engine cold start experiment. TPD experiment was carried on commercial ZSM-5, and desorption intensity curve of ZSM-5 zeolite for main cold start hydrocarbons was obtained. TPD results indicated that ZSM-5 zeolite can retain most of the hydrocarbons after 472 K, and the overall desorption intensity on ZSM-5 zeolite is acetaldehyde>1-butene > acetylene. Then adsorption and diffusion properties of the six main cold start hydrocarbon components on Na-ZSM-5 zeolite with different Si/Al ratio were studied by grand canonical Monte Carlo (GCMC) method and canonical ensemble Molecular Dynamics (MD) method. The results showed that the adsorption and diffusion of single-component hydrocarbons on ZSM-5 zeolite were affected by the number of exchange cations of zeolite, environment temperature, diameter of HC molecules and covalent bond types of HC molecules, and the adsorption capacity and diffusion coefficient were also affected by the competitive effect between the HC components. In competitive adsorption, molecules with large diameters such as acetaldehyde, 1-butene and benzene occupied the main adsorption sites of zeolite, so the adsorption capacity of these three HC molecules was large, while the adsorption capacity of smaller molecules such as ethylene, acetylene and propylene were small.

Occurrence Regularity of Methane Gas Molecules in Composite Nanopores: A Molecular Simulation Study

Abstract To understand the occurrence regularity of methane gas molecules in composite nanopores, the effects of temperature, pressure, size of nanopore, and burial depth on the occurrence state of methane were studied theoretically by using the grand canonical Monte Carlo and molecular dynamic simulation methods. By comparing the results available in the literature, the reasons for the difference in the occurrence states of methane molecules in nanopores were analyzed, and a reasonable occurrence regularity of methane was proposed, which provides corresponding suggestions for the actual exploitation of shale gas. The results indicated that the methane gas molecules existed in nanopore only in the adsorption and transition states under different environmental conditions. They were preferentially adsorbed at the strong adsorption sites on the nanopore surface to form a stable adsorption layer. After the adsorption layer reached saturation, a transition layer with higher density than that of bulk methane was formed at the nanopore center. The total adsorption capacity of methane decreased gradually with an increase in the internal temperature of shale reservoirs and increased with an increase in nanopore size. In addition, the average amount of methane stored in the nanopore increased at a deeper burial depth. The occurrence state of methane under different pressure ranges was controlled under different action mechanisms. Under low pressure (P<20 MPa), the adsorption of methane molecules was controlled by the number of strong adsorption sites on the nanopore surface, where the density peak intensity of the adsorption layer increased with the pressure. However, under high pressure (P>20 MPa), the adsorption was controlled by the diffusion process of methane molecules in the organic matter layer, where both the adsorption and transition layers reached the saturation state, and excessive methane molecules diffused deeper into the kerogen layer. The approach to effectively improve the recovery efficiency was to inject water or carbon dioxide into the shale reservoir where the water or carbon dioxide molecules occupy strong adsorption positions than the methane molecules adsorbed originally under the competitive adsorption effect, and the adsorbed methane molecules were transformed to a free state.

Molecular dynamics simulations of shale gas transport in rough nanopores

For the effective exploration and development of shale gas, it is important to understand the transport and adsorption mechanisms of methane, the main composition of shale gas. The wide variety of mineral components in shale matrices makes the pore surface complex, causing difficulty to understand the mass transport and adsorption behaviors within shale pores. Molecular dynamics (MD) have high fidelity to simulate the domains with complex geometries at nanoscale. However, most of the previous MD studies focused on the mechanisms of methane in slit nanopores, which could not reflect the real adsorption and transport behaviors of shale gas in nanopores with complex structures. This work studied the fluid properties in shale nanopores with high relative roughness and complex boundary geometries. The graphene sheets with different geometrical structures are used to characterize the complex boundary of shale pores. In addition, the effects of temperature, pressure, driving force, relative roughness, and absolute roughness on the adsorption and transport behaviors are investigated. In this study, shale gas diffusion is developed by the Einstein method to calculate the spatial diffusion coefficient D, planar diffusion coefficient Dxy, and vertical diffusion coefficient Dz of gas molecules to quantify and analyze the effects of temperature and pressure on shale gas diffusion. The results indicate that the main diffusion mechanism of methane is planar diffusion. Diffusion coefficients are sensitive to temperature and pressure changes for rarefied gases. Then, Grand Canonical Monte Carlo (GCMC) method is carried out to investigate the adsorption behavior. The simulation results show that the adsorption density increases with the increase of pressure and the decrease of temperature. The pressure-driven flow behavior of methane in nanopores is investigated by using non-equilibrium molecular dynamics (NEMD). The results indicate that the flow velocity of methane increases with the driving force. Moreover, the rough elements near wall dampen the transport of methane molecules.

Studying crack propagation along symmetric tilt grain boundary with H segregation in Ni by MD simulation

Hydrogen ingression in metals generally causes catastrophic failure. The H-induced fracture surface mostly exhibits intergranular feature, suggesting that grain boundary (GB) is the dominant crack propagation path. In this paper, the grand canonical Monte Carlo method was first performed to obtain equilibrated H distribution around various symmetric tilt grain boundaries (STGBs) in nickel. Then, atomistic simulations were conducted to study the influence of H segregation on the Mode I crack propagation behavior. In the absence of hydrogen, significant crack tip blunting and transgranular fracture are observed, implyinga tendency toward ductile transgranular fracture. However, in the case of H segregation, it is found that dislocation emission from the crack tip is enhanced but the crack tip still remains highly sharp. Moreover, crack propagation is dominated by alternate GB dislocation emission and GB cleavage, implying a tendency of ductile–brittle alternating intergranular fracture behavior. The H-inhibited GB migration and H-enhanced GB dislocation emission are believed to be the key mechanisms governing the H-assisted crack propagation along the GB.

Investigation of Competitive Adsorption Properties of CO/CO2/O2 onto the Kailuan Coals by Molecular Simulation.

To reveal the CO, CO2, and O2 adsorption properties of two bituminous coals at different pressures and temperatures, the molecular unit-cell structures of two types of bituminous coal are constructed (C1180H960O120N20 and C1160H860O80N20) by Fourier transform infrared (FTIR) spectroscopy. The bituminous coal molecular FTIR spectroscopic curve is calculated by quantum chemistry, and the results are consistent with the experimental curve. The isothermal adsorption curves of the single-component gases CO, CO2, and O2 conform to the Langmuir equation from 20 to 60 °C. The adsorption simulations are mainly performed using grand canonical Monte Carlo (GCMC) methods. The amount of adsorption decreases with increasing temperature at the same pressure, and CO2 can be the first to reach adsorption saturation at the same temperature. The CO2/CO adsorption selectivity for binary gas mixtures has apparent advantages in low-pressure or shallow buried coal seams. The adsorption selectivity of O2/CO varying under different pressures is not obvious. The high amount of CO inhibits the adsorption capacity of CO2 and O2. In other words, the effect of injecting CO2 to control fire extinguishing in bituminous coal seams with high abnormal CO concentrations is not significant.

Metal-organic coordination networks on a titanium carbide MXene: DFT based grand canonical Monte Carlo simulation

The self-assembly of 2D metal–organic networks comprising 1,3,5-tris (pyridyl)benzene (TPyB) molecules and copper atoms on the oxygen-terminated titanium carbide MXene surface was theoretically investigated. We have developed a lattice model of the TPyB-Cu networks on the energetically heterogeneous Ti2CO2(0001) surface. The model based on DFT calculations of the structure and energy of key adsorption complexes and metal–organic structures. Using the grand canonical Monte Carlo method, we have calculated and analyzed adsorption isotherms, structure, potential energy, and heat capacity of the adlayer. Due to steric hindrances in the three-fold Cu-TPyB junction, metal–organic structures consisting of only two-fold Cu-TPyB coordination motifs predominantly emerge on the Ti2CO2(0001) surface: honeycomb (HON), honeycomb filled with Cu3TPyB (HON + Cu3TPyB) and zigzag (ZZ) phases. These phases differ in the local environment of the copper adatoms. Thermal stability of the phases decreases in the following series: ZZ, HON + Cu3TPyB and HON. Self-assembly of these structures offers the opportunity to stabilize and “tune” properties of the single-atom Cu/Ti2CO2(0001) catalyst. We hope that our results will stimulate further experimental studies of hybrid “metal–organic network/MXene” catalysts.

Influences of gas permeation with adsorption effect on the transient thermal insulation performance of silica aerogel at pressure and temperature differences

Silica aerogel is a thermal protective material for an outer space launch under aerodynamic heating, significant temperature difference, and pressure gradient conditions. This paper proposes a gas permeation model by considering the gas adsorption effect for silica aerogel under pressure differences. The gas (N2) adsorption behavior of silica aerogel is simulated by the grand canonical Monte Carlo method. This simulation provides the concentration of the adsorbate gas layer and the average thickness of adsorbate gas in the nanopore. An unsteady-state heat transfer model within silica aerogel, coupling with the acquired gas diffusion effect, heat conduction, and thermal radiation, is developed to study the thermal insulation performance. The gas permeation with the gas adsorption inside silica aerogel exerts a prominent influence on the dynamic temperature response of the hot surface. At the temperature of 77–90 K, the gas adsorption has a remarkable impact on the gas permeation within silica aerogel, which would finally affect the energy migration. The order of the coefficient changes from 10−14 to 10−10 m2. In contrast, the adsorption effect is negligible at the temperature of 298–1300 K. When the gas diffusion and heat transfer directions are opposite, gas diffusion will impede heat transfer, and thus the thermal insulation performance will be improved up to 88.94% and 25.65% at unsteady- and steady-state, respectively.

Investigation on the influence of modified zeolite molecular sieve on the hydrocarbon adsorbent and adsorption performance during cold-start conditions based on Monte Carlo simulation and grey relational analysis

To discover adsorbents with promising adsorption capability for hydrocarbon catcher, this study numerically investigated the adsorption process of modified MOR, MFI, and CON zeolites utilized in hydrocarbon catcher of hydrocarbon (HC) molecules for hydrocarbon emission control during cold-start. Ethylene (C2H4) and benzene (C6H6) were used as probe molecules in the single-component adsorption simulation. The mixture of methane (CH4), C2H4, propylene (C3H6), propane (C3H8), water (H2O) and C6H6 was used as adsorbate in the multicomponent adsorption simulation. The Grand Canonical Monte Carlo (MC) method was used in the adsorption simulation. Grey Relational Analysis (GRA) method was used to determine the influence degree of zeolite molecular sieve type and environmental conditions on the adsorption capacity of hydrocarbons. The adsorption isotherms of hydrocarbon single component and multicomponent molecules on different silicon-aluminum (Si/Al) ratios and different ion exchange zeolites were studied at various low temperatures and pressures. Results of adsorption simulation present that the best adsorption effect on C2H4 was obtained for the magnesium ion (Mg2+) modified MFI molecular sieve at a Si/Al ratio of 3. The adsorption of C6H6 was better for the Na+ modified molecular sieve at Si/Al ratios of 15 and 7. Mg2+ modified MOR molecular sieve can be given priority when the overall control of hydrocarbon mixture content is required, which has adsorption for all kinds of hydrocarbon molecules and more uniform adsorption performance. The calcium ion (Ca2+) modified MFI molecular sieve is suitable for the condition when exhaust gas contains more C3H6, while Mg2+ modified MFI molecular sieve can be used when there are more C3H8. In GRA, the factors with the greatest influence on the adsorption of the C2H4 component are the type of molecular sieve and the porosity. The most important factors on the adsorption of the C6H6 component are the molecular sieve type and temperature, followed by the porosity. In the adsorption of multicomponent hydrocarbons, porosity has the greatest effect on the adsorption amount, followed by molecular sieve type and Si/Al ratio. In addition, the total adsorption of hydrocarbon molecules will be increased with the Si/Al ratio of the molecular sieve.

Molecular simulation of shale gas adsorption in type III kerogen organic matter

Type III kerogen play an important role in coal-bearing shale gas generation and occurrence. The physical and structural properties and the adsorption mechanism of kerogen are difficult to be analyzed comprehensively by experiments. Molecular simulation provides technical support to the investigation of the adsorption and enrichment mechanisms of shale gas at molecular level. Using the Grand Canonical Monte Carlo (GCMC) and Molecular Dynamic (MD) methods, type III kerogen model was constructed, and the adsorption behaviors of methane were investigated. The effects of temperature and gas composition on shale gas adsorption, and the adsorption selectivity of mixed gas C2H6/CH4 and the radial distribution function (RDF) were also discussed. The results show that the adsorption capacity of C2H6 decreases with the increase of temperature and pressure. The adsorption capacity of C2H6 increases first, then decreases, and finally tends to be stable. The adsorption experiment and molecular simulation results show that Type III kerogen has a stronger adsorption capacity for C2H6 than CH4. C2H6 in smaller nano-scale pores are more difficult to desorption under the lower pressure. The carbon atoms in kerogen interact strongly with the gas molecule of CH4 and C2H6.

Separation of SO2 and NO2 with the Zeolite Membrane: Molecular Simulation Insights into the Advantageous NO2 Dimerization Effect.

NO2 and SO2, as valuable chemical feedstock, are worth being recycled from flue gases. The separation of NO2 and SO2 is a key process step to enable practical deployment. This work proposes SO2 separation from NO2 using chabazite zeolite (SSZ-13) membranes and provides insights into the feasibility and advantages of this process using molecular simulation. Grand canonical ensemble Monte Carlo and equilibrium molecular dynamics methods were respectively adopted to simulate the adsorption equilibria and diffusion of SO2, NO2, and N2O4 on SSZ-13 at varying Si/Al (1, 5, 11, 71, +∞), temperatures (248-348 K), and pressures (0-100 kPa). The adsorption capacity and affinity (SO2 > N2O4 > NO2) demonstrated strong competitive adsorption of SO2 based on dual-site interactions and significant reduction in NO2 adsorption due to dimerization in the ternary gas mixture. The simulated order of diffusivity (NO2 > SO2 > N2O4) on SSZ-13 demonstrated rapid transport of NO2, strong temperature dependence of SO2 diffusion, and the impermeability of SSZ-13 to N2O4. The membrane permeability of each component was simulated, rendering a SO2/NO2 membrane separation factor of 26.34 which is much higher than adsorption equilibrium (6.9) and kinetic (2.2) counterparts. The key role of NO2-N2O4 dimerization in molecular sieving of SO2 from NO2 was addressed, providing a facile membrane separation strategy at room temperature.

Study on the effects of H on the plastic deformation behavior of grain boundaries in nickel by MD simulation

It is generally believed that the influence of hydrogen on plastic deformation of grain boundaries should be considered when analyzing hydrogen-induced intergranular fracture in polycrystalline metals. In this paper, the equilibrated H distribution around GBs was firstly investigated by employing the grand canonical Monte Carlo method. Then, MD simulations were performed to study the plastic response of GBs under uniaxial tensile loads in different directions, with various bulk H concentrations considered. The results indicate that the influence of H on dislocation nucleation from GB depends on both tensile directions and characteristics of GB structures. Specifically, two dislocation nucleation mechanisms, called dislocation dissociation nucleation (DDN) and heterogeneous dislocation nucleation (HDN), are identified. Careful analyses show that H segregation can increase the energy barrier of DDN, which results in H-inhibited dislocation nucleation. In contrast, the HDN mechanism involves H-enhanced or H-insensitive dislocation nucleation, which mainly depends on the influence of H on GB stress.

Swelling Characteristics and Interaction Mechanism of High-Rank Coal during CO2 Injection: A Molecular Simulation Study.

In CO2-enhanced coalbed methane (CO2-ECBM) engineering, accurate knowledge of the interaction mechanism of CO2 and coal matrix is crucial for improving the recovery of CH4 and contributing to the geological sequestration of CO2. This study is performed to prove the accuracy of molecular simulation and calculate the variation characteristics of pore structure, volumetric strain, mechanical properties, Fourier transform infrared (FT-IR) spectra, and the system free energy by molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) methods. According to the obtained results, a relationship between pore structure, swelling strain, mechanical properties, chemical structure, and surface free energy was established. Then, the correlation of various coal change characteristics was analyzed to elucidate the interaction mechanism between CO2 and coal. The results showed that (1) the molecular simulation method was able to estimate the swelling mechanism of CO2 and coal. However, because the adsorption capacity of the molecular simulate is greater than that of the experiment and the raw coal is softer than the macromolecular structure, the molecular results are slightly better than the experimental results. (2) As pressure increased from 0 to 4 MPa, the intramolecular pores and sorption-induced strain changed significantly, whereas when the pressure increased from 4 to 8 MPa (especially at 6–8 Mpa), there was an increase of the intermolecular pores and mechanical properties and transition from elastic to plastic. In addition, when the pressure was >8 MPa, the coal matrix changed slightly. ScCO2 with a higher adsorption capacity results in greater damage and causes larger alterations of coal mechanical properties. (3) The change of the coal matrix is essentially controlled by the surface free energy of the molecular system. Evalence affects the aromatic structure and changes the volume of the intramolecular pores, thus affecting the sorption-induced strain change rate. Enon affects the length of side chains and the disorder degree of coal molecules and changes the volume of the intramolecular pores, thus affecting the mechanical property change rate. Our findings shed light on the dynamic process of coal swelling and provide a theoretical basis for CO2 enhancing the recovery of CH4 gas in coal.

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.

Molecular simulation to analyze the influence of ultrafine particles on activated carbon adsorbing low concentration toluene

Adsorption is an effective technology to remove the gaseous pollutants. In the actual implementation, the particulate matters (PMs) are firstly filtered to guarantee the adsorption performance of absorbent. However, the PMs cannot be completely removed based on the current state of the art, especially the ultrafine particles. Therefore, in this work, taking activated carbon as an example, the influence of ultrafine particles on its gaseous adsorption performance was detailed investigated. The nanoporous carbon model was proposed and the adsorption of toluene with/without NaCl particles was simulated based on the GCMC (Grand Canonical Monte Carlo) method and MD (Molecular Dynamics) method. The results showed that, with the existence of NaCl, the diffusion coefficient of toluene in the activated carbon was reduced by 27%, the amount of toluene absorbed was reduced by 20.8%–28.6%, and the van der Waals energy was varied in a relative wider range. The favorable adsorption sites were 4.4 Å away from the graphite slices of activated carbon, which was not affected by NaCl particles. This was also verified by the analysis of energy distribution. This study revealed the mechanism of gas-solid coupling mass transfer in the porous materials and would help master the actual adsorption performance of adsorbent.

Molecular Simulation Comparison of Two Ultrafine Coal-Based Activated Carbons for the Removal of Methylene Blue from Water

Coal-based activated carbons (CACs) have excellent valuable applications, and have been industrially produced. However, ultra-fine coal-based activated carbons (UCACs) and their removal of methylene blue (MB) have rarely been reported in the present literature. Two kinds of UCACs were obtained in this paper and the adsorption test of MB was carried out. The adsorption performance of MB on UCAC was simulated by Grand Canonical Monte Carlo (GC-MC) method. The experimental results were validated by molecular simulation, and the adsorption mechanism was investigated. The adsorption amount of MB, the d50, and specific surface area values of the UCACnew (obtained by the new method) and UCACcm (obtained by the conventional chemical method) were 746.95 mg/g, 12.54 μm, 1225.36 m2/g and 652.77 mg/g, 12.10 μm, 713.76 m2/g, respectively. The results of the molecular simulation calculations were consistent with the pattern of magnitude of the experimental results. The peak of the adsorption concentration occurred near 6 Å on the pore surface. The interaction energy of MB molecules with carboxyl groups was much larger than with hydroxyl groups. Van der Waals forces dominated the adsorption process, with a contribution of >60% in both cases.

Removing ionic and organic mercury from light hydrocarbon liquids by ordered zeolite-templated carbon doped with sulphur

Sulphur-doped, β-zeolite-templated carbons (S-β-ZTCs) were synthesized by chemical vapor co-deposition of hydrogen sulfide (H2S) and acetylene (C2H2) to remove ionic (Hg2+) and organic mercury (Hgorg) from gasoline. In situ doping of sulphur introduced aromatic thiols and thiophenes into the ZTC's framework that removed the mercury by forming Hg–S bonds. Notably, these covalently bonded sulphur groups exhibited better stability than physically deposited elemental sulphur, yielding less than 10% material loss after repeated adsorption-desorption tests. Thanks to these unique chemical properties, the adsorption capacity of S-β-ZTCs for Hg2+ in the gasoline (2660 μg/g) was at least an order of magnitude larger than that of common adsorbents. Moreover, simultaneous adsorption of Hg2+ and Hgorg on S-β-ZTCs proceeded independently when the total mercury concentration was in the range applicable to most natural gas condensate samples. Finally, Grand Canonical Monte Carlo (GCMC) method and Density Functional Theory (DFT) study were used to reveal the adsorption mechanism of ZTCs on Hg2+ and Hgorg. These findings provided a better understanding of the mercury sorption mechanism of S-β-ZTCs and have important practical significance for the clean production of the condensate processing industry.

Molecular Simulation on Permeation Behavior of CH4/CO2/H2S Mixture Gas in PVDF at Service Conditions.

Reinforced thermoplastic composite pipes (RTPs) have been widely used for oil and gas gathering and transportation. Polyvinylidene fluoride (PVDF) has the greatest potential as a thermoplastic liner of RTPs due to its excellent thermal and mechanical properties. However, permeation of gases is inevitable in the thermoplastic liner, which may lead to blister failure of the liner and damage the safe operation of the RTPs. In order to clarify the permeation behavior and obtain the permeation mechanism of the mixture gas (CH4/CO2/H2S) in PVDF at the normal service conditions, molecular simulations were carried out by combining the Grand Canonical Monte Carlo (GCMC) method and the Molecular Dynamics (MD) method. The simulated results showed that the solubility coefficients of gases increased with the decrease in temperature and the increase in pressure. The adsorption isotherms of all gases were consistent with the Langmuir model. The order of the adsorption concentration for different gases was H2S > CO2> CH4. The isosteric heats of gases at all the actual service conditions were much less than 42 kJ/mol, which indicated that the adsorption for all the gases belonged to the physical adsorption. Both of the diffusion and permeation coefficients increased with the increase in temperature and pressure. The diffusion belonged to Einstein diffusion and the diffusion coefficients of each gas followed the order of CH4 > CO2 > H2S. During the permeation process, the adsorption of gas molecules in PVDF exhibited selective aggregation, and most of them were adsorbed in the low potential energy region of PVDF cell. The mixed-gas molecules vibrated within the hole of PVDF at relatively low temperature and pressure. As the temperature and pressure increase, the gas molecules jumped into the neighboring holes occasionally and then dwelled in the holes, moving around their equilibrium positions.