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Carbon-Based Nanoporous Networks as Media for the Separation of CO2/CH4 Mixtures: A Molecular Dynamics Approach Ioannis Skarmoutsos,* George Tamiolakis, and George E. Froudakis* Department of Chemistry, University of Crete, Voutes, Heraklion, 71003 Crete, Greece ABSTRACT: Molecular dynamics simulation techniques have been employed to investigate the separation of a CO2/CH4 equimolar mixture at ambient temperature, using a recently designed 3D-carbon-based nanostructured model material as a potential molecular sieve. The calculations performed have shown that the carbon dioxide molecules are preferentially adsorbed over the methane ones, yielding a very satisfactory selectivity for carbon dioxide. The residence time correlation functions and mean-square displacements of the CO2 and CH4 molecules adsorbed in the nanopores have also been calculated predicting higher diffusivities for the methane molecules inside the nanostructured material, but significantly lower than in the bulk gas mixture. The translational and reorientational dynamics of the CO2 and CH4 molecules have also been investigated, indicating that in the case of CO2 they are more sensitive upon confinement. The results obtained signify that the rational design of novel carbon-based nanostructured porous networks might lead to the development of promising candidates for the separation of CO2/CH4 mixtures, exhibiting important applications in natural gas technology.

I. INTRODUCTION The most prominent fuel gases nowadays, such as natural gas and biogas, primarily consist of methane and to a lesser extent carbon dioxide.1−6 Natural gas has been classified among the most important energy sources and the most efficient substitutes of environmental unfriendly fossil fuels. However, before using it on a commercial scale, it has to meet several specifications, mainly related to its heat content and flame temperature. It has been observed that the heat content of natural gas can be increased by reducing the amount of carbon dioxide.7 The existence of water and carbon dioxide impurities in natural gas could also lead to the formation of carbonic acid, which is extremely harmful for the equipment and media used to store and transport natural gas due to corrosion effects.8,9 Therefore, the development of efficient methods to separate carbon dioxide from natural gas mixtures has become an issue of crucial importance the past decade, in view also of the rapid decrease of fossil fuel resources. Several methods have been proposed so far to separate carbon dioxide from gas mixtures, including amine and ionic liquid absorption,10−12 chemical conversion,10 membrane separation,13 and adsorption by nanoporous materials.14 Physisorption-based separation methods, using porous materials as molecular sieves, are among the most environmental friendly and economically feasible methods to achieve efficient removal of carbon dioxide from CO2/CH4 mixtures. The most common types of porous materials which have been used as adsorbents so far are carbon-based molecular sieves,7,15−19 zeolites,20−23 polymeric membranes,24−26 metal−organic frameworks,27−32 covalent organic frameworks,33,34 and silicalite.35 The development of such types of porous materials is based upon the modification of their pore size, volume, and chemical functionality in order to increase not only their © 2013 American Chemical Society

selectivity during separation processes but also their adsorption capacity. Taking also into account that the synthesis of materials for these particular applications can be a difficult and time-consuming task, the use of computational modeling techniques in conjunction with experiment could significantly assist in the rational design of novel adsorbent materials. Carbon-based materials possess a superior structural stability to a wide range of processing conditions, keeping them in the race for commercial applications. Therefore, the key factor toward the rational design of carbon-based materials for storage and separation of gases is the development of novel architectures of large surface areas and pores. Such an approach could combine the superior stability and light framework of carbon-based materials with a larger surface area and high porosity, which is a missing requirement of carbon nanotubes.36,37 In this framework, in a previous study we designed a novel three-dimensional (3D) porous nanotube network (PNN),37 consisting of interconnected (8,8) single-walled carbon nanotubes forming a 3D orthogonal network (Figure 1). Using a multiscale modeling approach (density functional theory quantum calculations and classical Monte Carlo simulations), it was revealed that this model material exhibits an enhanced hydrogen storage capacity. The porosity in such novel carbon superstructures could also be appropriately tuned, yielding in this way several types of candidate materials for gas storage and separation. Note also that recently published synthetic strategies have revealed that the synthesis of 3D nanotube networks is possible,38−40 opening thus a new route Received: February 26, 2013 Revised: July 22, 2013 Published: August 27, 2013 19373

dx.doi.org/10.1021/jp401978m | J. Phys. Chem. C 2013, 117, 19373−19381

The Journal of Physical Chemistry C

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the z-axis direction) two orthogonal parallelepiped boxes were placed, having the same x- and y-axis length with the cubic PNN and the double z-axis length. Each of the boxes was containing a well-equilibrated configuration of a mixture of 500 CO2 molecules and 500 CH4 ones at the aforementioned density of 0.375 g/cm3. These equilibrated configurations were obtained by performing a NVT-MD simulation of the bulk mixture for a time period of 1 ns. The calculated pressure for the equilibrated bulk mixture was 19.6 MPa. In order to avoid possible overlaps between the bulk mixtures and the PNN carbon atoms in the initial configurations, the two boxes were placed in a distance of 4 Å from the PNN, yielding in the end a simulation box with dimensions 41 Å × 41 Å × 213 Å and containing in total 1000 CO2 molecules, 1000 CH4 ones, and 3328 carbon atoms of the 3D PNN. The initial configuration of the system is depicted in the first snapshot of Figure 2. After building the initial configuration of the system, an equilibration simulation using periodic boundary conditions was performed at 300 K until the numbers of CO2 and CH4 molecules adsorbed in the PNN reach a constant value each one. It was observed that an equilibration time of about 3 ns was needed for the system to reach equilibrium. Some representative snapshots depicting the filling procedure of the PNN during this period are presented in Figure 2. After calculating the amount of adsorbed molecules in the nanopore, a subsequent 3 ns MD run was performed by putting at the center of the simulation box the nanopore with the adsorbed gas molecules and by placing again left and right of the nanopore + adsorbed gases system the boxes containing the bulk gas mixture, which were initially used in the first configuration (t = 0, Figure 2). From each simulation the amount of adsorbed molecules was calculated, and this procedure was repeated several times until the amount of adsorbed CO2 and CH4 reaches a constant value and saturation has been achieved. When saturation was achieved, a final MD simulation with 15 ns duration was performed, and the mole fraction profiles of each gas constituent were calculated, attaining in this way the bulk density and composition for the gas mixture outside the nanopore. This methodology has been also applied in recent studies of air, hydrogen, and methane adsorption in carbon nanotubes.41−43 As in our case, in these studies the authors had observed that this procedure of consecutive MD simulations until there is no net adsorption (i.e., the nanoporous material is saturated) can be seen as a stationary flux of gas flowing over a nanoporous material. In this sense the results obtained by this method can be considered as totally equivalent with the ones obtained with the commonly employed grand canonical Monte Carlo (GCMC), since in this method the main idea is to bring the material in equilibrium with a virtual gas reservoir and to insert (or delete) gas molecules until the value of the chemical potential inside the porous material becomes equal to that one of the bulk gas. In such a way this stationary flux is being achieved. Although the equilibrium in GCMC can be probably achieved faster than with this MD method, dynamic and kinetic effects as well as interfacial properties may also be calculated in a very straightforward manner. The potentials employed in the simulation to model the interactions between the species in the system were the 3-site rigid EPM2 model44 for CO2 and the 5-site rigid OPLS model45 for CH4. The intermolecular interactions in these models are represented as pairwise additive with site−site 12−6 Lennard-Jones plus Coulomb interactions. Previous studies in

Figure 1. Two representations of the structure of the threedimensional (3D) porous nanotube network (PNN). Different colors have been used just to depict more clearly the 3D orthogonal network formed.

toward the design of novel nanomaterials for various applications not only limited to gas storage and separation but also including nanoengineering, drug delivery, and many more. In view of all the above, the main aim of the present study was to investigate the separation of an equimolar CO2/CH4 mixture at ambient temperature in these porous nanotube networks by employing molecular dynamics simulation techniques. Such an investigation could be used as springboard toward the development and rational design of novel carbonbased nanomaterials as effective media for the separation of CO2/CH4 mixtures. This paper is organized as follows: the computational details are presented in section II, results and discussion are presented in section III, and general conclusions are presented in section IV.

II. SIMULATION DETAILS In this work, the results presented and discussed correspond to the separation of an equimolar CO2/CH4 mixture at 300 K and a density of 0.375 g/cm3. In order to perform this simulation study, the initial configuration of the system was built by initially placing the cubic 3D PNN in the center of the simulation box. Afterward, from both sides of the PNN (along 19374



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Figure 2. Representative snapshots depicting the filling procedure of the PNN with the CO2/CH4 mixture.

the value of 0.5 in the bulk phase. In order to present a quantitative measurement of the separation of the CO2−CH4 mixture, the adsorption selectivity was calculated by using the equation xCO2 yCH4 S= xCH4 yCO (1)

the literature have shown that these models are very accurate in predicting the structural, thermodynamic, transport, and dynamic properties of CO2 and CH4 as well as of their binary mixtures in a wide range of thermodynamic conditions.46,47 The C−C parameters for the Lennard-Jones interactions between the carbon atoms of the PNN and the atoms of the CO2 and CH4 molecules were also adopted by previous studies in the literature,48,49 and Lorentz−Berthelot combining rules were employed. The equations of motion were integrated using a leapfrog-type Verlet algorithm, and the integration time step was set to 1 fs. A Nose−Hoover thermostat with a temperature relaxation time of 0.2 ps was used to constrain the temperature during the simulations. The intramolecular geometry of CO2 and CH4 molecules was constrained using the quaternion formalism, and the PNN was kept frozen during the simulation. A cutoff radius of 12.0 Å has been applied for all Lennard-Jones interactions, and long-range corrections have been also taken into account. To account for the long-range electrostatic interactions, the standard Ewald summation technique has been used. The simulation runs were performed using the DL_POLY simulation code.50

2

In eq 1, xi and yi are the mole fractions of each component i in the adsorbed and bulk phases, respectively. The value of the adsorption selectivity has been estimated to be 3.02, signifying that the composition of the CO2/CH4 mixture inside the PNN is about 3:1. Such a finding indicates that the PNN could be used as a suitable candidate material to tune the composition of CO2/CH4 mixtures via adsorption. Another issue that is of significant importance in gas separation is the estimation of the diffusivities of the binary mixture constituents in the bulk phases and inside the adsorbent material. To estimate the self-diffusion coefficients of the CO2 and CH4 molecules inside the PNN, an additional NVT-MD simulation was performed. In this simulation the initial configuration in the central simulation box was consisting of the PNN containing the average number of CO2 and CH4 molecules which were adsorbed and were calculated from the previous simulations. The estimated average numbers of adsorbed CO2 and CH4 molecules in the PNN were 493 and 163, respectively. Periodic boundaries for this central simulation box have also been taken into account. Starting from this configuration, an equilibration run of 2 ns was performed, followed by a 5 ns productive run. An additional MD run for the bulk mixture was also performed to estimate the self-diffusion coefficients in the bulk phase as well. The selfdiffusion coefficients of CO2 and CH4 were estimated from the

III. RESULTS AND DISCUSSION The calculated average number density profiles along the z-axis of the simulation box as well as the mole fraction profiles of CO2 and CH4 are presented in Figure 3. From this figure it may be observed that the number density and mole fraction of CO2 molecules inside the PNN are much higher than those corresponding to CH4, indicating that this material exhibits an enhanced storage capacity of CO2 in comparison to CH4. The average mole fraction of CO2 inside the PNN is about 0.75, a value which is significantly higher than 19375



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it may be observed that the CH4 molecules diffuse faster than the CO2 ones inside the nanoporous material. The calculated self-diffusion coefficients inside the PNN are DCO2 = 5.7 × 10−9 m2/s, and DCH4 = 6.9 × 10−9 m2/s, whereas in the bulk phase the corresponding values are DCO2 = 41.7 × 10−9 m2/s and DCH4 = 53.9 × 10−9 m2/s. Note however that although the selfdiffusion coefficients decrease by about an order of magnitude inside the nanoporous network, the fraction DCH4/DCO2 in the bulk phase and in the adsorbent material is not significantly altered; their values are 1.21 and 1.29 in the adsorbed and bulk phases, respectively. In order to investigate deeper the interactions between the PNN and the CO2 and CH4 molecules inside the nanopores, the local structure and corresponding dynamics have also been studied in the present work. The radial distribution functions (rdf) for the CO2−PNN and CH4−PNN atom pairs are presented in Figure 5.

Figure 3. Calculated average number density and mole fraction profiles of CO2 and CH4 along the z-axis of the simulation box.

calculated mean-square displacements of the molecules using the well-known Einstein relation: 1 1 D= lim ⟨| ri (0) − ri (⃗ t )|2 ⟩ ⃗ (2) 6 t →∞ t The calculated mean-square displacements of the CO2 and CH4 molecules in the PNN are depicted in Figure 4. From this figure

Figure 5. Calculated radial distribution functions for the CO2−PNN and CH4−PNN atom pairs.

From the shape of the C−C rdfs, the radius of the first coordination shell was estimated to be 6.05 and 5.95 Å for the PNN−CO2 and PNN−CH4 rdfs. Using these distances as radial cutoffs, the residence dynamics of CO2 and CH4 close to the carbon atoms of the PNN were investigated by calculating the appropriate residence time correlation functions. The pair

Figure 4. Calculated mean-square displacements of the CO2 and CH4 molecules inside the PNN. 19376



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residence dynamics time correlation function (tcf) for a pair of atoms i and j is defined as follows: Cres(t ) =

⟨nij(0) ·nij(t )⟩t * ⟨nij(0)2 ⟩

(3)

where nij(t) = 1 if a specific atom j is within a predefined cutoff distance of a second atom i at times 0 and t, and the atom j has only left the cutoff sphere for a period shorter than t*; otherwise nij(t) = 0. The corresponding residence time is defined according to the relation τres =

∫0

∞

Cres(t ) dt

(4)

According to this definition, τres is dependent on the selection of the parameter t*, and two limiting cases arise: (a) t* = 0, which corresponds to atom j remaining in the solvation cutoff sphere of i continuously for the whole time interval [0, t]. In this case we define the continuous residence tcf CCres(t) and the corresponding continuous residence lifetime τCres. (b) t* = ∞, where the intermittent presence of atom j in the solvation cutoff sphere of i at time t is investigated, regardless of the number of exits and entrances of this atom into the cutoff sphere during the time interval [0, t]. In this case we define I (t)and the corresponding intermittent residence tcf Cres I intermittent residence lifetime τres. The calculated continuous and intermittent residence tcfs for the carbon−carbon CO2−PNN, and CH4−PNN atom pairs inside a radial cutoff equal to the first coordination shell of the corresponding radial distribution functions. are depicted in Figure 6. From this figure it may be observed that the CO2 molecules exhibit stronger interactions with the PNN carbon atoms, and as a result of this they stay for a longer time close to them. This is more clearly observed by the calculated residence times. For the CO2−PNN C−C pairs the calculated residence times are τCres = 3.0 ps and τIres = 10.1 ps, whereas for the CH4−PNN C− C pairs the corresponding lifetimes are τCres = 2.1 ps and τIres = 8.1 ps. The larger residence lifetimes obtained for the CO2− PNN carbon−carbon pairs indicate that there is a stronger interaction between the PNN and the carbon dioxide molecules, which could possibly be the reason for the higher CO2 concentration in the nanoporous network. Recent studies51 have also revealed that the stronger interaction of CO2 with the carboxyl and hydroxyl groups of activated graphite sheets promotes the adsorption of CO2, a result which also points out the importance of the CO2-sorbent interactions on gas storage and separation. Interestingly, in the present study the fraction of the intermittent residence lifetimes (τIres)CO2/(τIres)CH4 and of the diffusion coefficients of methane and carbon dioxide molecules DCH4/DCO2 are almost similar. Such a finding indicates a possible quantitative way of tuning the diffusivities of confined molecules, by appropriately adjusting the interactions between the sorbent material and the molecules of the gas mixture, and could lead toward a much more efficient rational design of novel sorbent materials. However, a more detailed analysis for several different thermodynamic conditions, compositions, and different gas mixtures is required in order to reveal any possible interrelation between these phenomena and their effect on the separation of

Figure 6. Calculated continuous and intermittent residence time correlation functions for the carbon−carbon CO2−PNN and CH4− PNN atom pairs.

the gas mixtures, with particular emphasis on the CO2/CH4 ones. In order to have a clearer picture about the confinement effects on the dynamics of the CO2 and CH4 molecules, the reorientational dynamics of the confined molecules were calculated and compared with the results obtained for the bulk mixture. In general, the reorientational dynamics for specified intramolecular vectors are investigated by means of the Legendre reorientational tcfs: C (t ) = ⟨P (⇀ u (0) ·⇀ u (t ))⟩, S = 1, 2 (5) SR

S

⇀

In this equation, u is a unit vector along a specified direction inside a molecule and PS is a Legendre polynomial (P1(x) = x, P2(x) = 1/2(3x2 − 1)). The corresponding reorientational times τSR (S = 1, 2) are defined as follows: τSR =

∫0

∞

CSR(t ) dt

(6)

The calculated first- and second-order Legendre reorientational tcfs for the C−H vector of methane and for the bond axis vector CO2 are presented for the adsorbed and bulk phases in Figures 7 and 8. From these figures it may be clearly that confinement affects significantly the reorientational dynamics of the molecules. Especially in the case of the confined CO2 molecules, the decay 19377



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Figure 7. Legendre reorientational tcfs for the C−H of methane molecules confined in the PNN and in the bulk CO2/CH4 mixture.

Figure 8. Legendre reorientational tcfs for the CO2 molecules confined in the PNN and in the bulk CO2/CH4 mixture.

of the calculated reorientational tcfs is significantly slower and corresponds to the behavior of bulk CO2 at much denser environments than the bulk density investigated at the present study. In the case of the confined methane molecules, although the decay is similar to the one observed for the bulk phase, there is a clear minimum observed for the molecules in the bulk phase at about 0.2 ps. This minimum is usually observed for low-density methane, and this observation can be attributed to the fact that the methane molecules inside the PNN “sense” a denser environment around them. The significant confinement effects upon the reorientational dynamics of CO2 molecules are also clearly reflected on the calculated reorientational correlation times, presented in Table 1. From Table 1 it may be observed that the first- and second-order Legendre reorientational correlation times of CO2 are significantly increased in the case of the confined molecules, whereas in the case of methane they remain almost the same. The calculated reorientational correlation times of confined CO2 molecules are similar to the ones corresponding to high-density (liquid-like) bulk CO2 fluid.52 The fact that the shape and decay of the reorientational tcfs of CO2 are significantly affected in more condensed environments is probably related to the linear shape of the CO2 molecules which strongly affects their rotational and translational motions, as well as their coupling,53 in comparison to the more “spherically” shaped methane molecules.

Table 1. Calculated Legendre Reorientational and Velocity Correlation Times of CO2 and CH4 Molecules Confined in the PNNa correlation times (ps) τ1R τ2R τv τv∥ τv⊥

CO2 1.15 0.73 0.11 0.16 0.08

(0.42) (0.25) (0.73) (0.41) (0.51)

CH4 0.17 (0.16) 0.09 (0.07) 0.05 (0.35)

a

The values in parentheses correspond to the results obtained for the bulk 1:1 CO2/CH4 mixture.

In order to further investigate the effect of confinement on the motions of CO2 molecules, the molecular center-of-mass velocity normalized tcfs of CO2 and CH4, together with the normalized tcfs of the parallel and perpendicular projections of the molecular center of mass velocity vector to the CO2 intramolecular axis were calculated: ⟨⇀ v (0) ·⇀ v (t ) ⟩ ⟨⇀ v (0) ·⇀ v (t ) ⟩ , , C v (t ) = 2 ⇀ ⇀ ⟨ v (0) ⟩ ⟨ v (0)2 ⟩ ⟨⇀ v ⊥(0) ·⇀ v ⊥(t )⟩ C v⊥(t ) = ⟨⇀ v ⊥(0)2 ⟩

Cv(t ) =

19378

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The parallel and perpendicular components at each time t are expressed as ⇀ v (t ) = [⇀ v (t ) ·u ⃗(t )]·u ⃗(t ),

⇀ v ⊥(t ) = ⇀ v (t ) − ⇀ v (t ) (8)

⇀

In this equation, u is a unit vector along the longitudinal bond axis of CO2. This definition has been systematically examined by Singer et al.54 in extensive studies of the translational and rotational dynamics of linear molecules and expresses implicitly the coupling between translational and rotational motions, as also pointed out in previous studies in the literature.53 The obtained time correlation functions for the bulk and confined mixtures and are presented in Figure 9 and 10, and the

Figure 10. Normalized correlation functions of the parallel and perpendicular projections of the molecular center-of-mass velocity vector to the CO2 longitudinal axis.

exhibits a slightly negative part, which is a characteristic of hindered translational motions (Figure 10). The different confinement effect upon the transverse and longitudinal translation modes of CO2 is also reflected on the calculated correlation times, presented in Table 1. Such a finding indicates that the confinement effects upon the different translational modes of the CO2 molecules are substantially different.

IV. CONCLUDING REMARKS In the present study classical molecular dynamics simulations have been performed to investigate the separation of a CO2/ CH4 equimolar mixture at ambient temperature, using a recently designed 3D-carbon-based nanostructured model material as a potential molecular sieve. The calculations performed in this present study have shown that the carbon dioxide molecules are preferentially adsorbed over the methane ones in the 3D porous nanotube network, yielding a very satisfactory selectivity for carbon dioxide. The continuous and intermittent residence dynamics for the carbon−carbon CO2− PNN and CH4−PNN have been also investigated and the larger residence lifetimes obtained for the CO2−PNN carbon− carbon pairs indicate that there is a stronger interaction between the PNN and the carbon dioxide molecules, which could possibly be the reason for the higher CO2 concentration in the nanoporous network. Interestingly, the fraction of the

Figure 9. Normalized correlation functions of the molecular center-ofmass velocities of CO2 and CH4.

corresponding correlation times are presented in Table 1. From Figure 9, it might be observed that the overall center-of-mass translational dynamics of CO2 and CH4 molecules are quite similarly affected when going from the bulk to the confined environment. Note also here that the obtained self-diffusion coefficients obtained by the well-known Green−Kubo relation are similar to the ones obtained by the mean-square displacement of the molecules. However, in the case of CO2, the correlation function associated with the transverse velocity component is more strongly affected under confinement in comparison to the one corresponding to the parallel one, and it 19379



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intermittent residence lifetimes (τIres)CO2/(τIres)CO4 has been found to be the inverse of the fraction of the diffusivities of CO2 and methane DCO2/DCH4. Such a finding indicates a possible quantitative way of tuning the diffusivities of confined molecules, by appropriately adjusting the interactions between the sorbent material and the molecules of the gas mixture, and could lead toward a much more efficient rational design of novel sorbent materials. The translational and reorientational dynamics of the CO2 and CH4 molecules have also been investigated for the confined and bulk mixtures, indicating that these are more sensitive upon confinement in the case CO2. Motivated by these results, we are currently studying the separation of several gas mixtures at a wide range of thermodynamic conditions using the PNN as a separation media. The effect of the geometrical characteristics, as well as of the functionalization of 3D PNN materials is also currently investigated in order to achieve the maximum storage and separation capacity particularly for CO2/CH4 mixtures. The results of this ongoing research will be the subject of a forthcoming publication.

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Separation of Methane and Carbon Dioxide. Sep. Purif. Technol. 2010, 74, 280−287. (8) Carlson, H. A. Corrosion in Natural Gas−Condensate Wells−pH and Carbon Dioxide Content of Well Waters at Wellhead Pressure. Ind. Eng. Chem. 1949, 41, 644−645. (9) Bae, Y.-S.; Mulfort, K. L.; Frost, H.; Ryan, P.; Punnathanam, S.; Broadbelt, L. J.; Hupp, J. T.; Snurr, R. Q. Separation of CO2 from CH4 Using Mixed-Ligand Metal−Organic Frameworks. Langmuir 2008, 24, 8592−8598. (10) D’Alessandro, D. M.; Smit, B.; Long, J. R. Carbon Dioxide Capture: Prospects for New Materials. Angew. Chem., Int. Ed. 2010, 49, 6058−6082. (11) Yu, C.-H.; Huang, C.-H.; Tan, C.-S. A Review of CO2 Capture by Absorption and Adsorption. Aerosol Air Qual. Res. 2012, 12, 745− 769. (12) Karadas, F.; Atilhan, M.; Aparicio, S. Review on the Use of Ionic Liquids (ILs) as Alternative Fluids for CO2 Capture and Natural Gas Sweetening. Energy Fuels 2010, 24, 5817−5828. (13) Aaron, D.; Tsouris, C. Separation of CO2 from Flue Gas A Review. Sep. Sci. Technol. 2005, 40, 321−348. (14) Bae, Y.-S.; Snurr, R. Q. Development and Evaluation of Porous Materials for Carbon Dioxide Separation and Capture. Angew. Chem., Int. Ed. 2011, 50, 11586−11596. (15) Mantzalis, D.; Asproulis, N.; Drikakis, D. Enhanced Carbon Dioxide Adsorption Through Carbon Nanoscrolls. Phys. Rev. E 2011, 84, 066304. (16) Peng, X.; Cao, D.; Wang, W. Adsorption and Separation of CH4/CO2/N2/H2/CO Mixtures in Hexagonally Ordered Carbon Nanopipes CMK-5. Chem. Eng. Sci. 2011, 66, 2266−2276. (17) Sanip, S. M.; Ismail, A. F.; Goh, P. S.; Soga, T.; Tanemura, M.; Yasuhiko, H. Gas Separation Properties of Functionalized Carbon Nanotubes Mixed Matrix Membranes. Sep. Purif. Technol. 2011, 78, 208−213. (18) Peng, X.; Cao, D.; Wang, W. Computational Study on Purification of CO2 from Natural Gas by C60 Intercalated Graphite. Ind. Eng. Chem. Res. 2010, 49, 8787−8796. (19) Kowalczyk, P. Molecular Insight into the High Selectivity of Double-Walled Carbon Nanotubes. Phys. Chem. Chem. Phys. 2012, 14, 2784−2790. (20) Palomino, M.; Corma, A.; Rey, F.; Valencia, S. New Insights on CO2-Methane Separation Using LTA Zeolites with Different Si/Al Ratios and a First Comparison with MOFs. Langmuir 2010, 26, 1910− 1917. (21) Krishna, R.; van Baten, J. M. Using Molecular Simulations for Screening of Zeolites for Separation of CO2/CH4 Mixtures. Chem. Eng. J. 2007, 133, 121−131. (22) Leyssale, J.-M.; Papadopoulos, G. K.; Theodorou, D. N. Sorption Thermodynamics of CO2, CH4, and their Mixtures in the ITQ-1 Zeolite as Revealed by Molecular Simulations. J. Phys. Chem. B 2006, 110, 22742−22753. (23) Li, S.; Alvarado, G.; Noble, R. D.; Falconer, J. L. Effects of Impurities on CO2/CH4 Separations through SAPO-34 Membranes. J. Membr. Sci. 2005, 251, 59−66. (24) Shilton, S. J.; Ismail, A. F.; Gough, P. J.; Dunkin, I. R.; Gallivan, S. L. Molecular Orientation and the Performance of Synthetic Polymeric Membranes for Gas Separation. Polymer 1997, 38, 2215− 2220. (25) Blinova, N. V.; Svec, F. Functionalized Polyaniline-Based Composite Membranes with Vastly Improved Performance for Separation of Carbon Dioxide from Methane. J. Membr. Sci. 2012, 423, 514−521. (26) Uchytil, P.; Schauer, J.; Petrychkovych, R.; Setnickova, K.; Suen, S. Y. Ionic Liquid Membranes for Carbon Dioxide-Methane Separation. J. Membr. Sci. 2011, 383, 262−271. (27) Sumida, K.; Rogow, D. L.; Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.; Bae, T.-H.; Long, J. R. Carbon Dioxide Capture in Metal-Organic Frameworks. Chem. Rev. 2012, 112, 724− 781.

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (I.S.). *E-mail [email protected] (G.E.F.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research has been cofinanced by the European Union (European Social Fund − ESF) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework (NSRF) - Research Funding Program: THALES. Funding by the Air Force Office of Scientific Research/European Office of Aerospace Research & Development (AFOSR/EOARD) under grant number FA8655-12-1-2014 is also acknowledged.

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REFERENCES

(1) Cavenati, S.; Grande, C. A.; Rodrigues, A. E. Removal of Carbon Dioxide from Natural Gas by Vacuum Pressure Swing Adsorption. Energy Fuels 2006, 20, 2648−2659. (2) Baxter, J.; Bian, Z.; Chen, G.; Danielson, D.; Dresselhaus, M. S.; Fedorov, A. G.; Fisher, T. S.; Jones, C. W.; Maginn, E.; Kortshagen, U.; et al. Nanoscale Design to Enable the Revolution in Renewable Energy. Energy Environ. Sci. 2009, 2, 559−588. (3) Dhingra, R.; Christensen, E. R.; Liu, Y.; Zhong, B.; Wu, C.-F.; Yost, M. G.; Remais, J. V. Greenhouse Gas Emission Reductions from Domestic Anaerobic Digesters Linked with Sustainable Sanitation in Rural China. Environ. Sci. Technol. 2011, 45, 2345−2352. (4) Lee, H.-H.; Ahn, S.-H.; Nam, B.-U.; Kim, B.-S.; Lee, G.-W.; Moon, D.; Shin, H. J.; Han, K. W.; Yoon, J.-H. Thermodynamic Stability, Spectroscopic Identification, and Gas Storage Capacity of CO2-CH4-N2 Mixture Gas Hydrates: Implications for Landfill Gas Hydrates. Environ. Sci. Technol. 2012, 46, 4184−4190. (5) Himeno, S.; Komatsu, T.; Fujita, S. High-Pressure Adsorption Equilibria of Methane and Carbon Dioxide on Several Activated Carbons. J. Chem. Eng. Data 2005, 50, 369−376. (6) Li, J. R.; Kuppler, R. J.; Zhou, H. C. Selective Gas Adsorption and Separation in Metal−Organic Frameworks. Chem. Soc. Rev. 2009, 38, 1477−1504. (7) Zhang, X.; Shao, X.; Wang, W.; Cao, D. Molecular Modeling of Selectivity of Single-Walled Carbon Nanotube and MCM-41 for 19380



Article

(28) Li, J.-R.; Ma, Y.; McCarthy, M. C.; Sculley, J.; Yu, J.; Jeong, H.K.; Balbuena, P. B.; Zhou, H.-C. Carbon Dioxide Capture-Related Gas Adsorption and Separation in Metal-Organic Frameworks. Coord. Chem. Rev. 2011, 255, 1791−1823. (29) Xiang, Z.; Peng, X.; Cheng, X.; Li, X.; Cao, D. CNT@ Cu3(BTC)2 and Metal-Organic Frameworks for Separation of CO2/ CH4 Mixture. J. Phys. Chem. C 2011, 115, 19864−19871. (30) Peng, X.; Cheng, X.; Cao, D. Computer Simulations for the Adsorption and Separation of CO2/CH4/H2/N2 Gases by UMCM-1 and UMCM-2 Metal Organic Frameworks. J. Mater. Chem. 2011, 21, 11259−11270. (31) Cabrales-Navarro, F. A.; Gomez-Ballesteros, J. L.; Balbuena, P. B. Molecular Dynamics Simulations of Metal-Organic Frameworks as Membranes for Gas Mixtures Separation. J. Membr. Sci. 2013, 428, 241−250. (32) Eguchi, R.; Uchida, S.; Mizuno, N. Highly Selective Sorption and Separation of CO2 from a Gas Mixture of CO2 and CH4 at Room Temperature by a Zeolitic Organic−Inorganic Ionic Crystal and Investigation of the Interaction with CO2. J. Phys. Chem. C 2012, 116, 16105−16110. (33) Zhu, Y.; Zhou, J.; Hu, J.; Liu, H.; Hu, Y. Computer Simulation of Adsorption and Separation of CO2/CH4 in Modified COF-102. Chin. J. Chem. Eng. 2011, 19, 709−716. (34) Furukawa, H.; Yaghi, O. M. Storage of Hydrogen, Methane, and Carbon Dioxide in Highly Porous Covalent Organic Frameworks for Clean Energy Applications. J. Am. Chem. Soc. 2009, 131, 8875−8883. (35) Babarao, R.; Jiang, J. Diffusion and Separation of CO2 and CH4 in Silicalite, C168 Schwarzite, and IRMOF-1: A Comparative Study from Molecular Dynamics Simulation. Langmuir 2008, 24, 5474− 5484. (36) Dimitrakakis, G. K.; Tylianakis, E.; Froudakis, G. E. Pillared Graphene: A New 3-D Network Nanostructure for Enhanced Hydrogen Storage. Nano Lett. 2008, 8, 3166−3170. (37) Tylianakis, E.; Dimitrakakis, G. K.; Melchor, S.; Dobado, J. A.; Froudakis, G. E. Porous Nanotube Network: a Novel 3-D Nanostructured Material with Enhanced Hydrogen Storage Capacity. Chem. Commun. 2011, 47, 2303−2305. (38) Hashim, D. P.; Narayanan, N. T.; Romo-Herrera, J. M.; Cullen, D. A.; Hahm, M. G.; Lezzi, P.; Suttle, J. R.; Kelkhoff, D.; MuñozSandoval, E.; Ganguli, S.; et al. Covalently Bonded Three-Dimensional Carbon Nanotube Solids via Boron Induced Nanojunctions. Sci. Rep. 2012, 2, 363. (39) Fan, Z.; Yan, J.; Zhi, L.; Zhang, Q.; Wei, T.; Feng, J.; Zhang, M.; Qian, W.; Wei, F. A Three-Dimensional Carbon Nanotube/Graphene Sandwich and Its Application as Electrode in Supercapacitors. Adv. Mater. 2010, 22, 3723−3728. (40) Lalwani, G.; Kwaczala, A. T.; Kanakia, S.; Patel, S. C.; Judex, S.; Sitharaman, B. Fabrication and Characterization of Three-Dimensional Macroscopic All-Carbon Scaffolds. Carbon 2013, 53, 90−100. (41) Huarte-Larrañaga, F.; Alberti, M. A Molecular Dynamics Study of the Distribution of Molecular Hydrogen Physisorbed on Single Walled Carbon Nanotubes. Chem. Phys. Lett. 2007, 445, 227−232. (42) Cervellera, V. R.; Alberti, M.; Huarte-Larrañaga, F. A Molecular Dynamics Simulation of Air Adsorption in Single-Walled Carbon Nanotube Bundles. Int. J. Quantum Chem. 2008, 108, 1714−1720. (43) Vela, S.; Huarte-Larrañaga, F. A Molecular Dynamics Simulation of Methane Adsorption in Single Walled Carbon Nanotube Bundles. Carbon 2011, 49, 4544−4553. (44) Harris, J. G.; Young, K. H. Carbon Dioxide’s Liquid-Vapor Coexistence Curve and Critical Properties as Predicted by a Simple Molecular Model. J. Phys. Chem. 1995, 99, 12021−12024. (45) Jorgensen, W. L.; Maxwell, D. S.; Tirado-Rives, J. Development and Testing of the OPLS All-Atom Force Field on Conformational Energetics and Properties of Organic Liquids. J. Am. Chem. Soc. 1996, 118, 11225−11236. (46) Skarmoutsos, I.; Kampanakis, L. I.; Samios, J. Investigation of the Vapor−Liquid Equilibrium and Supercritical Phase of Pure Methane via Computer Simulations. J. Mol. Liq. 2005, 117, 33−41.

(47) Skarmoutsos, I.; Samios, J. Local Intermolecular Structure and Dynamics in Binary Supercritical Solutions. A Molecular Dynamics Simulation Study of Methane in Carbon Dioxide. J. Mol. Liq. 2006, 125, 181−186. (48) Darkrim, F.; Levesque, D. Monte Carlo Simulations of Hydrogen Adsorption in Single-Walled Carbon Nanotubes. J. Chem. Phys. 1998, 109, 4981−4984. (49) Lithoxoos, G. P.; Labropoulos, A.; Peristeras, L. D.; Kanellopoulos, N.; Samios, J.; Economou, E. G. Adsorption of N2, CH4, CO and CO2 Gases in Single Walled Carbon Nanotubes: A Combined Experimental and Monte Carlo Molecular Simulation Study. J. Supercrit. Fluids 2010, 55, 510−523. (50) Smith, W.; Forester, T. R. DL_POLY_2.0: A General-Purpose Parallel Molecular Dynamics Simulation Package. J. Mol. Graphics 1996, 14, 136−141. (51) Lithoxoos, G. P.; Peristeras, L. D.; Boulougouris, G. C.; Economou, I. G. Monte Carlo Simulation of Carbon Monoxide, Carbon Dioxide and Methane Adsorption on Activated Carbon. Mol. Phys. 2012, 110, 1153−1160. (52) Saharay, M.; Balasubramanian, S. Evolution of Intermolecular Structure and Dynamics in Supercritical Carbon Dioxide with Pressure: An Ab Initio Molecular Dynamics Study. J. Phys. Chem. B 2007, 111, 387−392. (53) Idrissi, A.; Longelin, S.; Damay, P.; Krishtal, S.; Kiselev, M. Analysis of the Transverse and the Longitudinal Pseudodiffusion of CO2 in Sub- and Supercritical States: A Molecular-Dynamics Analysis. J. Chem. Phys. 2006, 125, 224501. (54) Singer, K.; Singer, J. V. L.; Taylor, A. J. Molecular Dynamics of Liquids Modelled by ‘2-Lennard-Jones Centres’ Pair Potentials II. Translational and Rotational Autocorrelation Functions. Mol. Phys. 1979, 37, 1239−1262.

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