Simulations methane adsorption

It is difficult to determine the interpenetration in amorphous porous polymers. Haranczyk et al. set up some non-interpenetration and interpenetration models of porous polymer networks (PPNs) based on the ideal crystalline model with dia topology. They systematically compared the simulated pore diameter, framework density, simulated pore volume, and experimental pore diameter and pore volume of non-interpenetration and interpenetration models of PAF-1 (PPN-6), PPN-4 and other PPNs (PPN-2, PPN-3, PPN-5). The results indicated that for PPN-4, PPN-5 and PPN-6 (PAF-l), the simulated methane adsorption isotherm of the non-interpenetrated structure compared favourably with the experimental data. This strongly supports that the experimental strueture ean be well modeled by the non-interpenetrated dia net. On the eontrary, the experimental data of the pore... 

Fig. 2 shows the simulated methane adsorption isotherms for a variety of IRMOF materials. In order to judge the performance of the materials, both the amount adsorbed per volume and per mass are shown. The materials with the best volumetric performances are the ones with the smallest linker molecules and therefore the smallest cavities (see Fig. 1 and Table 1). Within the group of the smaller IRMOFs, materials that consist of linker molecules with more carbon atoms (e.g. the dicarboxylate naphthalene linka- of lRMOF-7 compared to the dicarboxylate benzene linker of IRMOF-1) show a better performance, as the additional carbon atoms result not only in an increased surface area but also in strongs interactions between the methane molecules and the cavities. Fig. 2 a also illustrates that the interpenetrated IRMOFs, which have comparable (in the case of IRMOF-15) or even smaller cavities (IRMOF-9), show a similar performance. At higji pressures the differences between the absolute and the excess amount adsorbed become apparent. Whereas the absolute adsorption isotherms start to level off, the excess adsorption isotherms show a maximum, which is expected for any gas above its critical temperature when the increase of the bulk gas density is larger than the increase in the density of the adsorbate (see Eq. (1)). 

Adsorption isotherms of methane in silicalite have also been predicted in a number of calculation studies (62, 155, 156). Goodbody et al. (62) predicted a heat of adsorption of 18 kJ/mol and simulated the adsorption isotherm up to 650 bar. From the adsorption isotherm, they found that the sinusoidal pore volume contains more methane molecules at all pressures. Snurr et al. (155) performed GC-MC and MD simulations over a wide range of occupancies at several temperatures. The intermolecular zeolite-methane potential parameters were taken from previous MD studies (11, 87) and the methane-methane parameters from MD simulations were adjusted to fit experimental results for liquid methane (157). Electrostatic contributions were neglected on account of the all-silica framework, and methane was represented by a rigid, five-center model. 

Kowalczyk P, Tanaka H, Kaneko K, Terzyk AP, and Do DD. Grand canonical Monte Carlo simulation study of methane adsorption at an open graphite surface and in slit like carbon pores at 273 K. Langmuir, 2005 21(12) 5639-5646. 

In relation to methane adsorption in active carbon, which as previously described is formed by slit pores (see Figure 2.21), several numerical simulations have revealed that the highest density of the adsorbed phase is achieved within slit pores of 1.12-1.14 nm of diameter [187,200], For slit pores of a width, L = 1.13 nm (see Figure 2.21), two facing methane molecule monolayers may be inserted between pore walls [203-205],... 

Molecular mechanics (MM), molecular dynamics (MD), and Monte-Carlo (MC) methods were employed to simulate the adsorption of methane, ethane, propane and isobutane on silicalite and HZSM-5. The silicalite was simulated using the same cluster-model adopted in the diffusion calculations. The H-ZMS-5 structure was constructed according to the procedure suggested by Vetrivel et al. [32], which consists in replacing one atom at the channel intersection by and protonating the oxygen atom bridging the Ta and Tg sites in order to preserve the lattice neutrality. 

Zhang X. and Wang W., Methane adsorption in single-walled carbon nanotubes arrays by molecular simulation and density fimctional theory. Fluid Phase Equilibria 194-197 (2002) pp 289-295. 

Figure 6 PSDs obtained for methane adsorption in square model carbon pores using molecular simulation to interpret an activated carbon isotherm. PSD results are shown for regularization smoothing parameter values of 1 (solid line), 10 (open circles), 100 (open diamonds), 600 (filled circles), and 800 (filled diamonds) [25].

Figure 9.1 Simulation of adsorption of methane at 159.88 K and 0.05 bar on monodisperse and polydisperse distributions of nanotubes within bundles. (Adapted from Ref. [11].)...

Density profiles of the hydrocarbon mixture components are calculated by MD simulations. The examples of the profiles are presented in Fig. 1 for temperature 330 K at two pressures. The liquid phase is butane-rich the vapor phase is methane-rich. The density profiles turn out to be non-typical for a liquid film. Absolute value of the methane density does not change remarkably at the transition from vapor to liquid phase. Moreover, the absolute methane density is lower in liquid phase with respect to vapor at some conditions. It is interesting to note that there is a maximum of the methane density near the phase boundary at 40 atm. It points to the methane adsorption on the interface. Similar phenomena are observed at the modeling of the liquid in a contact with solid walls [15-17, 20], as well as in Coulomb clusters [45, 46]. 

Aukett PN, Quirke N, Riddifird S, Tennison SR. Methane adsorption on microporous carbons -comparison of experiment, theory, and simulation. Carbon 1992 30(6) 913-924. 

Grand canonical Monte Carlo simulations performed for natural gas adsorbed on carbon have demonstrated that the optimum pore size is 0.76 nm, as mentioned earlier (methane adsorption (capillary condensation) does not takes place at room temperature) thus, a further increase of the slit width would lower the particle density without a significant increase in amounts adsorbed. These calculations predict that the theoretical maximum methane storage capacity of carbon at 3.5 MPa is 209 VA for a monolithic carbon that fills the vessel and contains a minimum amount of macropore volume and no external... 

In this paper, we use molecular simulations to study methane adsorption in different IRMOFs. Molecular simulations provide a powerful tool to investigate adsorption as they not only allow quantitative predictions of mefriane adsorption in IRMOFs as we have shown before [7] but they also give a detailed picture on the molecular scale that allows, for example, a thorou analysis of the siting of the methane molecules in the cavities. 

In this paper, molecular simulations were used to study methane adsorption in IRMOF materials and to examine which properties of the materials influence methane uptake. The materials were carefully characterised using Monte Carlo methods to get pore size distributions, accessible surface areas and pore volumes. Depending on the pressure, three distinct regimes can be distinguished. At low loading (10 kPa), the amount adsorbed is proportional to the isosteric heat of adsorption which is a measure for the strength of the interaction between the methane molecules and the framework. Here, the methane molecules are located preferentially in the energetically favourable comer sites of the materials. Materials with... 

In general, we have shown that molecular simulations are a powerful tool to analyse adsorption in MOFs. Althou the results presented here are for methane adsorption in one particular group of MOFs, namely IRMOFs, these results can be extended to other materials and guide the choice of the linker molecule. 

Fig. I. Absolute isotherms for methane adsorption on DAY (( ) simulation (O) experiment) and NaX (simulation Vitale s Structure-model 1 (A), Zhu s structure- model 2 (V) experiment (O)) at 300 K in the range of pressure 0-35 bars.

Adsorption of hard sphere fluid mixtures in disordered hard sphere matrices has not been studied profoundly and the accuracy of the ROZ-type theory in the description of the structure and thermodynamics of simple mixtures is difficult to discuss. Adsorption of mixtures consisting of argon with ethane and methane in a matrix mimicking silica xerogel has been simulated by Kaminsky and Monson [42,43] in the framework of the Lennard-Jones model. A comparison with experimentally measured properties has also been performed. However, we are not aware of similar studies for simpler hard sphere mixtures, but the work from our laboratory has focused on a two-dimensional partly quenched model of hard discs [44]. That makes it impossible to judge the accuracy of theoretical approaches even for simple binary mixtures in disordered microporous media. 

Development of Advanced Reservoir Characterisation and Simulation Tools for Improved Coalbed Methane Recovery. Led by Imperial College of Science Technology and Medicine, the main objective of this project is to develop technology and tools to more accurately assess the potential for improved methane recovery and COj sequestration by investigating the basic scientific phenomena of COj coal injection and retention. The researchers primary objective is to achieve a more comprehensive understanding of the fundamental mechanisms of water and CO2-CH4 adsorption/desorption, diffusion/counter diffusion, and 2-phase flow under simulated reservoir conditions (stress, pore pressure, and temperature). The results of these studies will then be applied to design of a CO2-ICBM recovery and COj sequestration simulator for the European industry. 

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