Realistic molecular models of silica-templated CMK-1, CMK-3, and CMK-5 carbon materials have been developed by using carbon rods and carbon pipes that were obtained by adsorbing carbon in a model MCM-41 pore. The interactions between the carbon atoms with the silica matrix were described using the PN-Traz potential, and the interaction between the carbon atoms was calculated by the reactive empirical bond order (REBO) potential. Carbon rods and pipes with different thicknesses were obtained by changing the silica–carbon interaction strength, the temperature, and the chemical potential of carbon vapor adsorption. These equilibrium structures were further used to obtain the atomic models of CMK-1, CMK-3, and CMK-5 materials using the same symmetry as found in TEM pictures. These models are further refined and made more realistic by adding interconnections between the carbon rods and carbon pipes. We calculated the geometric pore size distribution of the different models of CMK-5 and found that the presence of interconnections results in some new features in the pore size distribution. Argon adsorption properties were investigated using GCMC simulations to characterize these materials at 77 K. We found that the presence of interconnection results greatly improves the agreement with available experimental data by shifting the capillary condensation to lower pressures. Adding interconnections also induces smoother adsorption/condensation isotherms, and desorption/evaporation curves show a sharp jump. These features reflex the complexity of the nanovoids in CMKs in terms of their pore morphology and topology.

The adsorption of pure N2/H2/CH4/CO2 along with the adsorption and separation of mixtures thereof in two metal organic frameworks (MOFs) of UMCM-1 and UMCM-2 have been extensively studied using a hybrid method of computer simulation and adsorption theory. It is found that the excess adsorption isotherms from grand canonical Monte Carlo (GCMC) simulations basically agree with the available experimental data of pure gases, except for H2 adsorption in UMCM-1 at 298 K. Moreover, the GCMC results show that both MOF materials exhibit an excellent storage capacity for pure CH4 and CO2 at room temperature. The excess uptakes of CH4 by UMCM-1 and UMCM-2 for at 5000 kPa are 12.53 and 15.06 mmol g−1, while those of CO2 at 4500 kPa are 30.13 and 36.04 mmol g−1, respectively, which approaches and even exceeds the 30.82 mmol g−1 of MOF-177. In addition, dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is also used to correlate the simulated adsorption isotherms of pure gases and further predict the separation of equimolar mixtures. IAST shows a good agreement with the GCMC results in most cases studied here. The selectivities of both MOF materials in CH4/H2 and CH4/N2 are insensitive to the pressure. The selectivities of both MOF materials for CH4/H2 are almost the same having a value of 4, while they are 2 for CH4/N2. By contrast, the selectivities for CO2/H2, CO2/N2 and CO2/CH4 apparently rely on the pressure, showing 16.4 and 26.9, 5.4 and 7.8, and 2.9 and 4.7 at 4000 kPa for UMCM-1 and UMCM-2, respectively. Compared with other MOFs materials, their separation ability is not prominent, but they are suitable for gas storage.

Adsorption of H2S and SO2 pure gases and their selective capture from the H2S-CH4, H2S-CO2, SO2-N2, and SO2-CO2 binary mixtures by the single-walled carbon nanotubes (SWNT) are investigated via using the grand canonical Monte Carlo (GCMC) method. It is found that the (20, 20) SWNT with larger diameter shows larger capacity for H2S and SO2 pure gases at T = 303 K, in which the uptakes reach 16.31 and 16.03 mmol/g, respectively. However, the (6,6) SWNT with small diameter exhibits the largest selectivity for binary mixtures containing trace sulfur gases at T = 303 K and P = 100 kPa. By investigating the effect of pore size on the separation of gas mixtures, we found that the optimized pore size is 0.81 nm for separation of H2S-CH4, H2S-CO2, and SO2-N2 binary mixtures, while it is 1.09 nm for the SO2-CO2 mixture. The effects of concentration and temperature on the selectivity of sulfide are also studied at the optimal pore size. It is found that the concentration (ppm) of sulfur components has little effect on selectivity of SWNTs for these binary mixtures. However, the selectivity decreases obviously with the increase of temperature. To improve the adsorption capacities, we further modify the surface of SWNTs with the functional groups. The selectivities of H2S-CO2 and SO2-CO2 mixtures are basically uninfluenced by the site density, while the increase of site density can improve the selectivity of H2S-CH4 mixture doubly. It is expected that this work could provide useful information for sulfur gas capture.

We perform a molecular simulation study on methane and carbon dioxide storage in carbon nanoscrolls. The effects of temperature and pressure, interlayer spacing, VDW gap and innermost radius on the gas storage have been examined extensively. It is found that the adsorption of gases on pristine carbon nanoscrolls is relatively low. However, once the interlayer spacing is expanded, both adsorption capacities of methane and carbon dioxide exhibit a significant improvement. In particular, the excess uptake of methane reaches 13 mmol/g at p = 6.0 MPa and T = 298.15 K and VDW gap Δ = 1.1 nm, which is about 3.5 times of uptake of the pristine carbon nanoscrolls; while the uptake of carbon dioxide could also be raised by 294.9% at T = 298.15 K and p = 3.0 MPa and Δ = 1.5 nm, reaching 30.21 mmol/g at 6.0 MPa. This work demonstrates that carbon nanoscrolls with an expansion of interlayer spacing may be a suitable material for methane storage and carbon dioxide capture.

By combining grand canonical Monte Carlo (GCMC) simulations with adsorption theory, we perform a computational study on adsorption of CH4 and CO2 gases and purification of CO2 from the CH4−CO2 and N2−CO2 binary mixtures by the C60 intercalated graphite. The adsorption isotherms, isosteric heats and snapshots of pure gases have been examined extensively. It is found that the maximum excess uptakes at 298 K are relatively low, only giving 4.04 and 4.96 mmol/g for CH4 and CO2, respectively, due to a low porosity of 0.45 and a large crystal density of 1.57 g/cm3 of this material. It indicates that the pristine material is not suitable for gas storage. However, this material provides excellent selectivity for CO2, and the selectivity at ambient condition can reach 8 and 50 for the CH4−CO2 and N2−CO2 mixture, respectively. Furthermore, the selectivity of CO2 is almost independent of the bulk gas composition for P > 0.1 MPa. The dual-site Langmuir−Freundlich (DSLF) equation is used to fit the adsorption isotherms of pure gases from GCMC simulations, and the corresponding parameters are obtained. Moreover, we further predicted the adsorption behavior of binary mixtures by the DSLF-based ideal adsorption solution theory (IAST). Although the IAST theory slightly overestimates the selectivity, compared to GCMC results, the uptakes and selectivity from both methods are basically consistent. To improve the adsorption capacities, we further tailor the structural parameter “g” of the C60 intercalated graphite by GCMC simulations. For equimolar gas composition, at the condition of g = 1.4 nm and 6 MPa, the CO2 uptakes could be raised by 200%, approaching 12 mmol/g for both mixtures, without loss of the selectivity for CO2. In summary, this work demonstrates that the C60 intercalated graphite is an excellent material for CO2 purification, especially for N2−CO2 system at room temperature.

Grand canonical Monte Carlo (GCMC) simulations were carried out to investigate the adsorption of CH4 and CO2 mixture on an ordered carbon material CMK-1. In the simulation, the fluid molecules are both modeled as Lennard–Jones spheres, and the CMK-1 adsorbent is characterized by the rod-aligned slitlike (RSP) pore model to emphasize its textural and grooved structure. The effects of temperature, pressure, pore width, and bulk composition on adsorption have been conducted in details. Adsorption amounts, local density profiles, snapshots and the solid–fluid potential curves are also extensively analyzed to provide deep insight into the separation mechanism. We finally investigate the adsorption behavior in the real CMK-1, with a pore size distribution (PSD) to characterize the heterogeneity of adsorbent. The optimum operating condition is obtained at T = 308 K, P = 7.0 MPa and the bulk composition yCO2=0.2yCO2=0.2, corresponding to the greatest selectivity of 3.55. Our results show that CMK-1 might be a promising adsorbent for the separation of a rich CH4 natural gas.

We performed grand canonical Monte Carlo (GCMC) simulations to characterize the hexagonally ordered carbon nanopipes CMK-5 and further investigated the adsorptive properties of this material for H2. The geometrical model from Solovyov et al. was used to characterize the hexagonal structure of the CMK-5 adsorbent. The interactions between a fluid molecule inside and outside the nanopipe and a single layer were calculated by the potential models proposed by Tjatjopoulos et al. and Gordon et al. When the calculated results were fitted to the experimental isotherm of N2 adsorption at 77 K, the structural parameters of the CMK-5-S material were obtained. To improve H2 adsorption, we also optimized the structural parameters of CMK-5 material. The maximum excess gravimetric and volumetric uptakes of H2 in the CMK-5 material with the optimized structural parameters at T = 77 K are 5.8 wt % and 41.27 kg/m3, which suggest that the CMK-5 material with an optimized structure is a promising adsorbent for gas adsorption.

Grand-canonical Monte Carlo (GCMC) simulations were performed to investigate the adsorption behavior of methane and hydrogen on a highly ordered carbon molecular sieve CMK-1 material. The rod-aligned slitlike pore (RSP) model was used to emphasize the grooved structure of the material, and the pore size distribution (PSD) was introduced to characterize the geometrical heterogeneity of the materials quantitatively. The PSD determined from adsorption isotherms of N2 at 77 K indicates that the CMK-1 adsorbent is a mesoporous material. By combining the GCMC and PSD techniques, adsorption isotherms of CH4 at 303 K and H2 at 303 and 77 K in the CMK-1 materials were obtained. The simulated isotherms are in an excellent agreement with experimental data, suggesting that it is necessary and efficient to use the PSD to characterize the materials. The GCMC predictions demonstrate that gravimetric uptakes of CH4 and H2 in the CMK-1 material at 30 MPa and 303 K are 31.23 and 1.19 wt %, respectively. Although a greater loading of 4.58 wt % for H2 is favored at 77 K and the same pressure, it does not reach the U.S. Department of Energy target of 6.5 wt %. By analyzing isosteric heats, we found that the adsorptions of CH4 at 303 K and H2 at 77 K exhibit an evidently energetic heterogeneous behavior in CMK-1 materials, with a broad range of isosteric heats of 10−27 kJ/mol for CH4 and 2.73−9.9 kJ/mol for H2. However, the adsorption behavior tends to be energetically homogeneous for H2 at 303 K, because the isosteric heat mainly centers on the range 4.82−6.65 kJ/mol. In addition, by exploring the relationship between the pore width and the surface excess, we found that, for CH4 at 303 K, the optimal operating conditions corresponding to the maximum surface excess are w = 1.2422 nm and P = 6 MPa, whereas for H2 at 77 K, they are w = 1.0647 nm and P = 3 MPa.

Adsorption and separation of N2, CH4, CO2, H2 and CO mixtures in CMK-5 material at room temperature have been extensively investigated by a hybrid method of grand canonical Monte Carlo (GCMC) simulation and adsorption theory. The GCMC simulations show that the excess uptakes of pure CH4 and CO2 at 6.0 MPa and 298 K can reach 13.18 and 37.56 mmol/g, respectively. The dual-site Langmuir–Freundlich (DSLF) model was also utilized to fit the absolute adsorption isotherms of pure gases from molecular simulations. By using the fitted DSLF model parameters and ideal adsorption solution theory (IAST), we further predicted the adsorption separation of N2–CH4, CH4–CO2, N2–CO2, H2–CO, H2–CH4 and H2–CO2 binary mixtures. The effect of the bulk gas composition on the selectivity of these gases is also studied. To improve the storage and separation performance, we finally tailor the structural parameters of CMK-5 material by using the hybrid method. It is found that the uptakes of pure gases, especially for CO2, can be enhanced with the increase of pore diameter Di, while the separation efficiency is apparently favored in the CMK-5 material with a smaller Di. The selectivity at Di=3.0 nm and 6.0 MPa gives the greatest value of 8.91, 7.28 and 27.52 for SCO2/N2, SCH4/H2 and SCO2/H2, respectively. Our study shows that CMK-5 material is not only a promising candidate for gas storage, but also suitable for gas separation.

The adsorption of pure N2/H2/CH4/CO2 along with the adsorption and separation of mixtures thereof in two metal organic frameworks (MOFs) of UMCM-1 and UMCM-2 have been extensively studied using a hybrid method of computer simulation and adsorption theory. It is found that the excess adsorption isotherms from grand canonical Monte Carlo (GCMC) simulations basically agree with the available experimental data of pure gases, except for H2 adsorption in UMCM-1 at 298 K. Moreover, the GCMC results show that both MOF materials exhibit an excellent storage capacity for pure CH4 and CO2 at room temperature. The excess uptakes of CH4 by UMCM-1 and UMCM-2 for at 5000 kPa are 12.53 and 15.06 mmol g−1, while those of CO2 at 4500 kPa are 30.13 and 36.04 mmol g−1, respectively, which approaches and even exceeds the 30.82 mmol g−1 of MOF-177. In addition, dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is also used to correlate the simulated adsorption isotherms of pure gases and further predict the separation of equimolar mixtures. IAST shows a good agreement with the GCMC results in most cases studied here. The selectivities of both MOF materials in CH4/H2 and CH4/N2 are insensitive to the pressure. The selectivities of both MOF materials for CH4/H2 are almost the same having a value of 4, while they are 2 for CH4/N2. By contrast, the selectivities for CO2/H2, CO2/N2 and CO2/CH4 apparently rely on the pressure, showing 16.4 and 26.9, 5.4 and 7.8, and 2.9 and 4.7 at 4000 kPa for UMCM-1 and UMCM-2, respectively. Compared with other MOFs materials, their separation ability is not prominent, but they are suitable for gas storage.