MetalâOrganic Framework Composites for H2S Removal

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Ionic Liquid/Metal-Organic Framework Composites for HS Removal from Natural Gas: A Computational Exploration Zhengjie Li, Yuanlong Xiao, Wenjuan Xue, Qingyuan Yang, and Chongli Zhong J. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 02 Feb 2015 Downloaded from http://pubs.acs.org on February 3, 2015

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The Journal of Physical Chemistry

Ionic Liquid/Metal-Organic Framework Composites for

H2 S

Removal

from

Natural

Gas:

A

Computational Exploration Zhengjie Li, Yuanlong Xiao, Wenjuan Xue, Qingyuan Yang*, and Chongli Zhong* State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China

ACS Paragon Plus Environment

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ABSTRACT The separation of H2S/CH4 mixture was computationally examined in the composites of ionic liquids (ILs) supported on metal-organic frameworks (MOFs) at room temperature. Cu-TDPAT was selected as supporter for four types of ILs combined from identical cation [BMIM]+ with different anions ([Cl]-, [Tf2N]-, [PF6]- and [BF4]-). The results show that introducing ILs into CuTDPAT can greatly enhance the adsorption affinity towards H2S compared to the pristine MOF, and the strongest enhancement occurs in the composite containing the anion [Cl]- with the smallest size. The H2S/CH4 adsorption selectivities of each composite are significantly higher than those of the pristine Cu-TDPAT within the pressure range examined, and the selectivity generally shows an increasing trend with increasing the loading of the IL. By further taking the H2S working capacity into account, this work also reveals that the [BMIM][Cl]/Cu-TDPAT composite exhibits the best separation performance in both VSA and PSA processes. These findings may provide useful information for the design of new promising IL/MOF composites applied for H2S capture from natural gas.


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1. INTRODUCTION As a cleaner energy source than oil and coal, natural gas is believed to occupy a vital role in worldwide energy supply in the next few decades for industrial and domestic utilizations.1-3 However, besides the main component CH4, acid gases such as CO2 and H2S usually also present as the impurities in the low-quality natural gas including biogas and landfill gas. These undesirable impurities will decrease the energy content and lead to pipeline corrosion. Moreover, H2S is a highly toxic gas and will release SO2 into the atmosphere after combustion.4-6 Thus, considering the requirements of efficient energy utilization and environmental protection, highefficient desulfurization has become an area of growing interest in the industrial upgrading of natural gas.7-10 At the moment, one strategy commonly used for the removal of H2S from natural gas is the liquid-phase chemical scrubbing with amines.11,12 Nonetheless, this method suffers from several drawbacks such as the amine loss, excessive corrosion and inherently high regeneration cost.13-15 Considerable efforts have been devoted to proposing other solvents for H2S capture and separation. During the past years, ionic liquids (ILs), formed by a combination of various organic cations and inorganic/organic anions,16,17 have received widespread attention in many fields.18-21 Because of their attractive features such as negligible volatility, good thermal stability and tunable functionality, many experimental and theoretical studies have been performed to explore the properties of diverse ILs towards the removal of H2S.22,23 For example, Jalili et al.24,25 reported a plenty of solubility data of H2S in a variety of imidazolium-based ILs in a wide range of temperature and pressure, and found that H2S solubility in 1-butyl-3-methylimidazoliumbased ILs follows the order: [Tf2N]->[PF6]->[BF4]-. Sakhaeinia et al.26 showed that the solubilities of H2S in 1-(2-hydroxyethyl)-3-methyl-imidazolium-based ILs are greater than those


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of CO2 and the number of trifluoromethyl (-CF3) groups can affect the solubility of both gases. Huang et al.27 demonstrated that 1-alkyl-3-methylimidazolium carboxylate ILs have significantly larger absorption capacities for H2S than those common ILs reported in the literature. They also found that H2S solubility is strongly affected by the alkalinity of the anions while is slightly influenced by the length of the alkyl chains in the cations. Chen and co-workers28 computationally explored the effects of different combinations of imidazolium cations and nonfluorous anions for selective adsorption of H2S from CH4. It was suggested that the hydroxyl groups in cations are essential in governing the absorption properties. Mortazavi-Manesh et al.29 developed semi-empirical models to rank the performance of more than 400 possible ILs in terms of the selectivities of CO2 and H2S over CH4 and C2H6. It was claimed that the best promising ILs are those containing anions [BF4]-, [NO3]- and [CH3SO4]- and cations [N4111]+, [PMG]+ and [TMG]+. Although ILs can act as a promising candidate for H2S capture, the high cost and viscosity are the two major disadvantages that hinder their practical applications.30 To overcome these drawbacks, a new strategy named supported ILs (SILs) has been proposed,31,32 where ILs were encapsulated into porous solids to improve separation efficiency.33 During the past decades, metal-organic frameworks (MOFs) have attracted tremendous attention due to their many unique properties such as high surface area, large pore volume and designable structure.34-38 Some experimental and theoretical studies have shown that MOFs could be used as potential porous supporter for ILs.39-46 Jiang and co-workers42 first investigated the IL/IRMOF-1 composites for CO2/N2 separation by molecule simulation, showing that the selectivity can be enhanced when introducing ILs into the pores of IRMOF-1. Later, this group further computationally explored the capabilities of MOF-supported IL membranes for CO2/N2 separation in which the effect of


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anions of ILs and the role of hydrophobic/hydrophilic framework were examined.43,44 Calero and co-workers45 examined several IL/Cu-BTC composites for CO2 separation with the focus paid on the influence of the type of anions and the amount of ILs. Tzialla et al.46 found that the CO2 selectivity and permeability of a [omim][TCM]/ZIF-69 composite membrane are higher than those of pure ZIF-69 membrane and the bulk IL. Thus, these results indicate that introducing ILs into MOFs can be a feasible approach to create promising adsorbents for gas separation. Motivated by the observations described above, we conducted a computational investigation to explore the performance of IL/MOF composites for the removal of H2S from natural gas. Although other components also coexist with CH4 in crude natural gas, only the binary gas mixture of H2S and CH4 was chosen as the model system in the current preliminary study. Such a treatment would give a better understanding of the separation behavior of IL/MOF composites for H2S/CH4 mixture by eliminating the influences of other impurities.

2. MODELS AND METHODS 2.1. Structures of MOF and ILs In this computational study, Cu-TDPAT, originally synthesized by Li and co-workers,47 was adopted as a representative of MOFs and used as the supporter for ILs. Previous studies have shown that this MOF exhibits an excellent capability for CO2 capture from CO2/CH4 and CO2/N2 mixtures.48,49 As a member of rht-type MOFs, this material is built up from the Cu2(COO)4 paddle-wheel units bounded to four 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine (TDPAT) linkers, leading to a three-dimensional porous framework shown in Figure 1. The tetragonal structure of Cu-TDPAT has three types of cages (truncated tetrahedral, cuboctahedral and octahedral cages) with diameters of 9.1, 12.0 and 17.2 Å, respectively.


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Figure 1. (a) Illustration of the crystal structure of Cu-TDPAT. Hydrogen atoms were omitted for clarity. The large yellow, light-purple and cyan spheres represent the void regions inside the truncated tetrahedral, cuboctahedral and truncated octahedral cages, respectively. (b) The atomic types used in this work (Cu, orange; O, red; C, gray; N, blue; H, white). The molecular structures of the ILs studied in this work are shown in Figure 2. These ILs have the identical cation, i.e., 1-n-butyl-3-methylimidazolium [BMIM]+. This cation is combined with the following four anions: bis[(trifluoromethyl)sulfonyl]imide [Tf2N]-, tetrafluoroborate [BF4]-, hexafluorophosphate [PF6]-, and chloride [Cl]-. [BMIM]+ and [Tf2N]- have a chain-like structure, while those of the anions [PF6]-, [Cl]- and [BF4]- are quasi-spherical.

Figure 2. Molecular structures of the cation [BMIM]+ and four anions for the ILs considered in this work.


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2.2. Force Fields In present work, the intermolecular interactions of H2S with Cu-TDPAT and the ILs were described by a combination of Lennard-Jones (LJ) and Coulombic potentials, while those for CH4 were only treated using a site-site LJ potential. A single LJ interacting-site model was used to depict a CH4 molecule with the potential parameters taken from the TraPPE forcefield.50 H2S was treated using the three-site model reported by Kamath et al.,51 where only S atom is the LJ interacting site while partial charges are centered on each atom. The H-S bond length is 1.34 Ǻ and the H-S-H angle is 92.5°. All the corresponding atomic partial charges and interatomic potential parameters are reported in Table S1 in the Supporting Information (SI). The two force fields have been successfully used to reproduce the experimental vapor-liquid phase equilibrium data of the respective gases. The LJ parameters for the MOF atoms were taken from the all-atom OPLS force field (OPLS-AA) of Jorgensen et al.52 with those for the Cu atom taken from the Universal force field (UFF),53 as shown in Table S2 in the SI. The partial charges for the framework atoms of MOFs were taken from the study of Zhang et al.48 All the LJ crossinteraction parameters were determined by using the Lorentz-Berthelot mixing rules. It should be noted that the OPLS-AA force field has been successfully used to reproduce the experimental adsorption properties of CO2, CH4 and N2 in Cu-TDPAT.48 Regarding to the considered ILs, a fully flexible representation was used to describe the cation [BMIM]+ and the anion [Tf2N]-, while a rigid model was used to treat the other anions. For all the flexible components, the intramolecular interactions consist of bonded stretching, bending, torsional potentials. The nonbonded interactions involved by the ILs are also described by a combination of LJ and Coulombic potentials. The LJ potential parameters and atomic partial charges for the anions [PF6]- and [BF4]- were taken from the work of Gupta et al., 43 while those


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for [Cl]- were adopted from the work of Liu et al.54 For the cation [BMIM]+ and anion [Tf2N]-, the force field parameters were taken from study of Xing et al.55 All the related parameters are listed in Table S3 in the SI. 2.3. Simulation Details To explore the properties of IL/Cu-TDPAT composites, different amounts of ILs were introduced into the pores of Cu-TDPAT using Monte Carlo (MC) simulations in the NVT ensemble. Molecular dynamics (MD) simulations in the NVT ensemble were then applied to equilibrate each composite system at 298 K. The velocity Verlet algorithm was used to integrate the Newton motion equations and the QUATERNION algorithm was applied for the rotational motion of the anions treated with rigid structure. The temperature was maintained using the Berendsen thermostat with a relaxation time of 1.0 ps. Periodic boundary conditions were considered in all three dimensions. The long-range electrostatic interactions were evaluated using the Ewald summation method, while all the LJ interactions were calculated with a cutoff radius of 14.0 Å. The time step used in the MD simulations was taken as 1.0 fs. The total duration of each MD run was 20 ns with the last 10 ns used for analysis. All the MD simulations were accomplished using DL_POLY 2.20 simulation package.56 On the basis of the equilibrated IL/Cu-TDPAT composites, grand canonical Monte Carlo (GCMC) simulations were performed at room temperature to examine the adsorption behaviors of H2S/CH4 mixture using our in-house code CADSS (Complex Adsorption and Diffusion Simulation

Suite).

The

bulk

molar

composition

of

the

mixture

was

taken

as

H2S:CH4=0.001:0.999 (i.e., 1000 ppm of H2S), which can represent a typical concentration of H2S in crude natural gas.59 As done by others,42,45 the structures of all the IL/Cu-TDPAT composites were treated as rigid during adsorption simulations. Actually, we have done some


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testing calculations by allowing the IL molecules to move and found that there are no significant differences in the results (Figure S1 in the SI). For each state point, the simulation used 2×107 steps to ensure the equilibration, followed by 2×107 steps to sample the desired thermodynamic properties. For the calculation of the isosteric heat of adsorption ( ) of H2S and CH4 at infinite

dilutions, configuration-bias Monte Carlo (CBMC) simulations in the canonical (NVT) ensemble were performed using the revised Widom’s test particle method.57 The radial distribution functions (RDFs) between the guest molecules and the framework atoms were calculated using NVT-MC simulations in which the loadings were taken from the GCMC simulation results. Each run consisted of 1×107 equilibration steps followed by 1×107 production steps where the configurations were sampled at an interval of 1000 steps. The adsorption selectivity for H2S over CH4 is defined by / = ( / )/( / ), where and are the mole fractions of H2S and CH4 in the adsorbed phase, respectively; and are corresponding mole fractions in the bulk mixture, respectively. − The working capacity ( ) of the targeted component H2S is evaluated by = , where and are the amounts of the gas in the adsorbed mixture under the corresponding adsorption and desorption conditions respectively, in units of mmol gas per g of the adsorbent. The above definitions can be found in the work of Bae and Snurr.1

3. RESULTS AND DISCUSSIONS 3.1. Structures of the IL/ Cu-TDAPT Composites Prior to exploring the separation properties of IL/Cu-TDPAT composites, it is necessary to examine their structural features. For this purpose, we investigated the preferential locations and structures of the ILs confined in the MOF. To clearly illustrate the preferential location of the


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anions in Cu-TDPAT, Figure S2 shows the RDFs of the geometric center-of-mass (COM) of the anions around various framework atoms of Cu-TDPAT in the four IL/Cu-TDPAT composites with the lowest loading considered in this work (that is, 5 IL molecules per unit cell for each composite system). By comparing the distances for the occurrence of first peaks, it can be found that the anions are preferentially located around the metal sites. Figure 3a presents the RDFs of the four anions around the Cu atoms for comparison. Obviously, the distances for the first peak follow an order of [Cl]-< [BF4]-< [PF6]-< [Tf2N]-, which is in line with the sizes of the anions. The quasi-spherical structures of the former three anions make them fit more closely to the Cu metal center than [Tf2N]- with a chain-like structure. In addition, the anion [Cl]- exhibits the highest height in the first peak, indicating that this smallest anion with a negative charge interacts most favorably with the positively charged Cu atom. For comparison, we also examined the RDFs of the geometric COM of the cation [BMIM]+ around the MOF atoms in the same IL/CuTDPAT composites. The results indicate that the cations paired with [Cl]-, [PF6]- or [Tf2N]- in the ILs are preferentially distributed near the N1 atoms (see the notation in Figure 1b) in the organic linkers, as shown in Figure 3b. With regard to the IL containing [BF4]-, the cations [BMIM]+ are more preferentially located near the N2 atom of Cu-TDPAT, which can be reflected from the positions of the first peaks shown in Figures 3b and c. These observations reveal that the anions are more energetically distributed around the Cu atoms while the cations are located closer to the organic linkers.


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(a)

7

-

[Tf2N] -Cu

+

(b)

4.0

+

[BF4] -Cu

6

-

3.5

[BMIM] ([BF4] )-N1

3.0

[BMIM] ([PF6] )-N1

-

+

[PF6] -Cu -

5

-

[BMIM] ([Tf2N] )-N1

-

[Cl] -Cu

-

+

-

[BMIM] ([Cl] )-N1 2.5

4

g (r)

g (r)

3

1.0

1 0

2.0 1.5

2

0.5 0

2

4

6

8

10

0.0

12

0

2

4

6

r (Å)

r (Å) 4.0

8

10

12

(c) +

-

[BMIM] ([BF4] )-N2

3.5 3.0 2.5

g (r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2.0 1.5 1.0 0.5 0.0

0

2

4

6

8

10

12

r (Å)

Figure 3. Radial distribution functions of (a) anions around the Cu atom, (b) cations around N1 atom, and (c) cations in the IL containing [BF4]- around the N2 atom of Cu-TDPAT. The loading of IL in each composite is 5 molecules per unit cell of Cu-TDPAT. Figure 4a and Figure S3 in the SI show the MD-simulated structures of the above four IL/CuTDPAT composites. Obviously, the molecules of the ILs [BMIM][Tf2N], [BMIM][BF4] and [BMIM][PF6] appear in the three type cages of Cu-TDPAT or in the intersection regions between these cages (Figure S3), while [BMIM][Cl] molecules dominantly occupy the tetrahedral cages with the smallest pore size (Figure 4a). This can be explained by the reason that the large sizes of the anions of the former three ILs result in the difficult accommodation of all the molecules in the tetrahedral cages. These observations indicate that the size of the anions can affect the distribution of the ILs in the pores of Cu-TDPAT. As a result, it can be speculated that small IL


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molecules will have more distinct filling sequence in Cu-TDPAT with increasing the loading. To give an evidence for this speculation, Figure 4 also presents the MD-simulated snapshots for the structures of the [BMIM][Cl]/Cu-TDPAT composites with other two different loadings of the IL. Clearly, with increasing the loading, [BMIM][Cl] molecules start to appear in the cuboctahedral cages, followed by the filling of the octahedral cages. In addition, we also found that the heights of the first peaks in the RDFs of the anions around the Cu atoms shown in Figure 3a will decrease with increasing the loading of ILs in the composites. These results indicate that adding more ILs into the MOF will induce a more uniform distribution of the ILs in the composites. Such a trend has also been found in the study of IL/IRMOF-1 composites.43

Figure 4. Snapshots for the structures of the [BMIM][Cl]/Cu-TDPAT composites with three different loadings of the IL: (a) 5 IL molecules per unit cell of the MOF, (b) 10 IL molecules per unit cell of the MOF, and (c) 15 IL molecules per unit cell of the MOF. Figure 5 compares the RDFs of the cation-anion pairs in the respective IL/Cu-TDPAT composites with a loading of 5 IL molecules per unit cell. Clearly, the [BMIM]+-[Tf2N]- pair exhibits the highest peak at r = 3.8 Å, while the pronounced peaks are observed at r = 4.3, 4.5 and 4.9 Å for the pairs of [BMIM]+-[BF4]-, [BMIM]+-[Cl]- and [BMIM]+-[PF6]-, respectively.


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Compared with the result obtained for the IL in bulk phase,43 [BMIM]+ and [Tf2N]- become much closer to each other in the composite (first-peak position in bulk phase: 5.0 Å), together with a significantly higher height. In contrast, the first-peak positions in the RDFs of [BMIM]+[BF4]-, [BMIM]+-[PF6]- and [BMIM]+-[Cl]- pairs are similar to those in the corresponding bulk phases but with significantly elevated heights.43,54,58 These observations demonstrate that the pores of Cu-TDPAT have a significant confinement effect on the structural arrangements of the ILs in the composites. 40 +

[BMIM] -[Tf2N]

35

+

-

+

-

[BMIM] -[BF4]

30

[BMIM] -[PF6] +

25

g (r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-

-

[BMIM] -[Cl]

20 15 10 5 0

0

2

4

6

8

10

12

r (Å)

Figure 5. Radial distribution functions of anion-cation pairs in the respective IL/Cu-TDPAT composites with a loading of 5 IL molecules per unit cell of Cu-TDPAT. 3.2. Separation of H2S/CH4 mixture in IL/Cu-TDAPT composites Figure 6a shows the calculated isosteric heats of adsorption at infinite dilution ( ) of H2S in Cu-TDPAT and IL/Cu-TDPAT composites with different IL loadings. Clearly, the value of

exhibits a large increase with the presence of each IL in the pores of Cu-TDPAT, indicating that the IL/Cu-TDPAT composites have stronger adsorption affinity towards H2S compared to the pristine MOF. Figure S4 (see the SI) illustrates the corresponding results for CH4, showing that there is also an increase trend in the by incorporating ILs into the MOF but the values are

much lower than those of H2S in all the respective composites. These phenomena may be


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partially explained according to the “like dissolves like” principle: H2S can be “dissolved” more easily than CH4 in the IL/Cu-TDPAT composites due to the highly polar nature of both H2S and the ILs. Furthermore, at the same loading of the ILs, Figure 6a shows that H2S has the highest heat of adsorption in the [BMIM][Cl]/Cu-TDPAT composite compared to those in the composites containing other three types of anions.

Figure 6. (a) Isosteric heats of adsorption at infinite dilution ( ) for H2S in Cu-TDPAT and

IL/Cu-TDPAT composites at 298 K. (b) H2S/CH4 selectivities of Cu-TDPAT and IL/Cu-TDPAT composites at 298 K and 1 bar. The results for the composites with loadings of 5, 10 and 15 IL molecules per unit cell of Cu-TDPAT are shown for comparison. Figure 6b presents the simulated adsorption selectivities of H2S over CH4 at 1.0 bar in the IL/Cu-TDPAT composites. One can observe that the selectivity can be significant enhanced with the presence of ILs in the pores of the MOF. Among the composites considered, the systems containing the anion [Cl]- exhibits the best separation performance for H2S/CH4 mixture in terms of selectivity. Figure 6b also shows that the selectivity increases with increasing the loading of [BMIM][BF4], [BMIM][PF6] and [BMIM][Tf2N] in their respective composites. However, the selectivity of the [BMIM][Cl]/Cu-TDPAT composite shows a decrease when the loading of the IL exceeds 10 molecules per unit cell of the MOF. Figure 7 shows the RDFs of the adsorbed H2S


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molecules around some atoms of Cu-TDPAT framework and [BMIM][Cl] in the composite with a loading of 10 IL molecules per unit cell. Obviously, there is a well-developed first peak in the RDF of H2S around the N1 atoms of the MOF framework, which occurs at a distance of 2.3 Å (Figure 7a). At the same time, a very sharp peak with large height is observed at a distance of r = 2.3 Å for H2S around the anions [Cl]- (Figure 7b). These results reveal that the anions [Cl]- and the N1 atoms can be regarded as the most preferential adsorption sites for H2S in the [BMIM][Cl]/Cu-TDPAT composites. Similar results can also be found in the composites with other IL loadings, as shown in Figures S5 and S6 in the SI. 25

(a)

5

(b)

SH S-Cu of Cu-TDPAT

HH S-Cl of [Cl]

HH S-N1 of Cu-TDPAT

20

2

4

-

2

2

HH S-N3 of [BMIM]

+

HH S-N1 of [BMIM]

+

2

HH S-N2 of Cu-TDPAT 2

2

15 3

g (r)

g ( r)

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1 0

10

0

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12

0

0

2

4

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8

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r (Å)

r (Å)

Figure 7. Radial distribution functions of the adsorbed H2S molecules at 1.0 bar around some atoms of the MOF framework (a) and the IL (b) in the [BMIM][Cl]/Cu-TDPAT composite with a loading of 10 IL molecules per unit cell of the MOF. With respect to the [BMIM][Cl]/Cu-TDPAT composite, additional simulations were performed by incorporating more ILs into the system. The selectivities obtained at 1.0 bar are shown in Figure 8, as a function of the loading of the IL in the composite. It can be found that there is an oscillating trend in the selectvity, which shows a first increasing trend when the loading of the IL increases from 0 to 10 molecules per unit cell of the MOF and then decreases at the loading of 15 molecules per unit cell. With further increasing the loading of the IL up to 25


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molecules per unit cell, the selectivity exhibits a second increasing trend. Figure 9 shows the snapshots for H2S/CH4 mixture adsorbed at 1.0 bar in the composites with different loadings of [BMIM][Cl]. Obviously, H2S molecules are preferentially located in the tetrahedral cages around the N1 atoms in the pristine Cu-TDPAT (Figure 9a). After introducing the IL into the MOF, the anions [Cl]- become the most favorable adsorption sites. For the composite with 10 IL molecules per unit cell, most of the adsorbed H2S molecules appear in the tetrahedral cages (Figure 9b), which is consistent with the locations of the ILs in the composite shown in Figure 4b. At even higher loadings, H2S molecules are also adsorbed around the anions [Cl]- in the large cages (Figures 9c and d) due to the contribution of the IL molecules distributed in these regions.

Figure 8. H2S/CH4 adsorption selectivity of the [BMIM][Cl]/Cu-TDPAT composite at 298 K and 1.0 bar, as a function of the loading of the IL per unit cell of the MOF. The first increasing trend in the selectivity shown in Figure 8 can be ascribed to the fact that IL can act as favorable sites for H2S adsorption (see Figure 7b) and more such sites are available when incorporating more IL molecules into the pores of Cu-TDPAT. For the composite with 15 IL molecules per unit cell, many anions [Cl]- located in the tetrahedral cages are enclosed by the cations [BMIM]+ and the MOF framework atoms (Figure 4c). This steric effect hinders the accessibility of H2S to these preferential adsorption sites, as can be seen from the local view of


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the snapshot shown in Figure S7 (see the SI). In contrast, for the composite with 10 IL molecules per unit cell, the tetrahedral cages still can provide enough space for H2S adsorbed around the anions (Figure 4b). Consequently, the selectivity shows a decrease when the loading of the IL increases from 10 to 15 molecules per unit cell. With further increasing the loading, the IL molecules distributed in the larger cages provide more free favorable sites for H2S adsorption, leading to the second increasing trend in the selectivity. When the loading increases to 30 IL molecules per unit cell, the pores of the MOF are heavily filled, and thus the final decease in the selectivity is attributed to the significant reduction of free void in the composite.

Figure 9. Snapshots extracted from GCMC simulations for H2S/CH4 mixture adsorbed in (a) pristine Cu-TDPAT and the [BMIM][Cl]/Cu-TDPAT composites with 10 IL molecules (b), 15 IL molecules (c), and 25 IL molecules (d) per unit cell of the MOF. For clarity, the cations are removed and CH4, H2S, and Cl are represented using the ball and stick model (Cu, orange; O, red; C, gray; N, blue; S, yellow; H, white; Cl, aquamarine, CH4, lime green).


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Page 18 of 32

Figure 10 shows the calculated selectivities of H2S over CH4 in the [BMIM][Cl]/Cu-TDPAT composites with different loadings of the IL, as a function of pressure. It can be found that the selectivity of the pristine MOF almost remains unchanged within the pressure range examined. In contrast, the changing tendency becomes more complicated with the presence of the IL, where the selectivities of all the composites exhibit a dramatic decrease in the low-pressure range and then gradually decrease with further increasing pressure. The reason is that the adsorption sites in the composites are inhomogeneous and adsorption occurs on less favorable sites with increasing pressure. Generally, the selectivity increases with increasing the loading of the IL. In addition, at high pressures, the composites with 25 and 30 IL molecules per unit cell have similar H2S/CH4 selectivities. Similar behaviors can also be observed for other IL/Cu-TDAPT composites considered in this work. Figure 10 also indicates that the [BMIM][Cl]/Cu-TDPAT composite with a loading of 25 IL molecules per unit cell exhibits the best performance for H2S/CH4 separation in terms of the selectivity over the whole pressure range. The selectivity can reach about 1302 and 715 at 1.0 and 10.0 bar, respectively, which are much higher than those reported in the literature for some other materials as shown in Table1. It should be noted that for the materials (such as NaY and [BMIM][BF4]) with calculated selectivities, good agreements have been found between the simulated pure-gas isotherms/solubilities and experimental data, and thus the calculation results can be regarded as reliable.


18

4

3

10

(a)

(b)

3

10 4

Cu-TDPAT Cu-TDPAT-5 ILs Cu-TDPAT-10 ILs Cu-TDPAT-15 ILs Cu-TDPAT-20 ILs Cu-TDPAT-25 ILs Cu-TDPAT-30 ILs

2

2

SH S/CH

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


SH S/CH

Page 19 of 32

2

2

10

0

10

20

30

40

P (bar)

10

50

0.0

0.2

0.4

0.6

0.8

P (bar)

1.0

Figure 10. (a) H2S/CH4 adsorption selectivity of the [BMIM][Cl]/Cu-TDPAT composites with different loadings of the IL at 298 K, as a function of pressure. (b) Enlarged view of the selectivities in low-pressure range. Table 1. Comparison of the H2S/CH4 selectivities of the [BMIM][Cl]/Cu-TDPAT composite with 25 IL molecules per unit cell of the MOF with those reported for some other materials.

Materials

T (K)

P (bar)

Bulk H2S content (ppm)

Si-CHA

298

1.0

-

NaY

298

1.0

NC100 AC

298

[C4mim][CH3SO3]

/ Refs. 6

59a

1000

235

60b

10.0

1000

75

61a

353

1.0

-

40

62a

MIL-125(Ti)-NH2

303

10.0

1000

70

2a

[BMIM][Tf2N]

333

-

-

24

63a

[BMIM][BF4]

298

20.0

-

63

29b

[BMIM][PF6]

303

-

-

40

24,64a

[BMIM][Cl]

298

20.0

-

66

29b

[BMIM][Cl]/Cu-TDPAT

298

1.0

1000

1302

This workb

[BMIM][Cl]/Cu-TDPAT

298

10.0

1000

715

This workb

a b

Experimental results. Simulation results.


19


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3.3. H2S Working capacity of IL/Cu-TDPAT composites For practical applications, working capacity for the gas of interest is an important parameter to evaluate the separation performance of materials. Thus, it would be helpful to examine the H2S working capacity of the IL/Cu-TDPAT composites. For this purpose, we investigated both the VSA and PSA working capacities, where the former was calculated between the adsorption amounts of H2S in the adsorbed mixtures at 0.1 and 1.0 bar, while the latter was obtained between those at 1.0 and 30 bar. The results obtained for the [BMIM][Cl]/Cu-TDPAT composites with different loadings of the IL are listed in Table 2, together with the selectivities calculated under the corresponding adsorption conditions. Table 2. H2S working capacity ( ) and H2S/CH4 adsorption selectivity ( / ) of the [BMIM][Cl]/Cu-TDPAT composites

Materials Cu-TDPAT [BMIM][Cl]/Cu-TDPAT

IL loading (molecules/u.c.)

/

/

(mmol/g)

(1.0 bar)

(mmol/g)

(30.0 bar)

-

0.20

141

1.25

131

5

0.59

611

1.32

241

10

0.71

890

1.45

350

15

0.58

745

1.46

371

20

0.67

866

1.24

431

25

0.71

1302

1.11

615

30

0.71

1116

0.98

603

Clearly, compared to pristine Cu-TDPAT, all the composites have a higher VSA working capacity, and the one with a loading of 25 IL molecules exhibits the best separation performance. From viewpoint of PSA working capacity, the composite with a loading of 15 IL molecules has the highest value; however, the selectivity of this composite is much lower than the one with a loading of 25 IL molecules and the H2S working capacity of the latter composite is just slightly


20

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smaller. As a result, taking the working capacity and selectivity into account, it can be concluded that the [BMIM][Cl]/Cu-TDPAT composite with a loading of 25 IL molecules has the best properties for H2S/CH4 separation in both the VSA and PSA processes.

4. CONCLUSIONS Molecular simulations have been performed to investigate the performance of IL/Cu-TDPAT composites for the separation of H2S/CH4 mixture. The ILs considered in this work are composed of identical cation [BMIM]+ and four types of anions ([Cl]-, [Tf2N]-, [PF6]- and [BF4]-) with a large diversity in chemical property, shape and size. The results show that the anions of the ILs are preferentially located near the Cu atoms of the MOF framework, while the cations are located near the organic linkers. The adsorption affinity towards H2S is significantly enhanced by incorporating each IL into the pores of Cu-TDPAT, with the highest heat of adsorption in the composite containing the anion [Cl]- with the smallest size. In addition, this work demonstrates that the [BMIM][Cl]/Cu-TDPAT composite exhibits the best separation performance in both VSA and PSA processes, by taking both the adsorption selectivity and working capacity into account. On the basis of the results obtained in current study, it can be expected that the use of MOFs as the supporter for ILs is an alternative efficient strategy to generate new promising adsorbents for practical H2S separation related to natural gas purification.

ASSOCIATED CONTENT Supporting Information. Details of the force field parameters, structures of some IL/CuTDPAT composites, and some simulation results. This material is available free of charge via the Internet at http://pubs.acs.org.


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Page 22 of 32

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]; [email protected]

ACKNOWLEDGMENT This work was supported by the National Key Basic Research Program of China (“973”) (No. 2013CB733503) and Natural Science Foundation of China (Nos. 21136001, 21276009 and 21322603).

REFERENCES (1) 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. (2) Vaesen, S.; Guillerm, V.; Yang, Q.; Wiersum, A. D.; Marszalek, B; Gil, B; Vimont, A.; Daturi, M.; Devic, T.; Llewellyn, P. L.; et al. A Robust Amino-functionalized Titanium (IV) Based MOF for Improved Separation of Acid Gases. Chem. Commun. 2013, 49, 10082-10084. (3) Grande, C. A.; Rodrigues, A. E. Layered Vacuum Pressure-Swing Adsorption for Biogas Upgrading. Ind. Eng. Chem. Res. 2007, 46, 7844-7848. (4) Selene, C.-H.; Chou, J. Hydrogen Sulfide: Human Health Aspects. Concise International Chemical Assessment Document 53, World Health Organization, Geneva, 2003. (5) Lambert, T. W.; Goodwin, V. M.; Stefani, D.; Strosher, L. Hydrogen Sulfide (H2S) and Sour Gas Effects on the Eye. A Historical Perspective. Sci. Total Environ. 2006, 367, 1-22.


22

Page 23 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(6) Koech, P. K.; Rainbolt, J. E.; Bearden, M. D.; Zheng, F.; Heldebrant, D. J. Chemically Selective Gas Sweetening without Thermal-Swing Regeneration. Energy Environ. Sci., 2011, 4, 1385-1390. (7) Barea, E.; Montoro, C.; Navarro, J. A. R. Toxic Gas Removal-Metal-Organic Frameworks for the Capture and Degradation of Toxic Gases and Vapours. Chem. Soc. Rev. 2014, 43, 54195430. (8) Maghsoudi, H.; Soltanieh, M. Simultaneous Separation of H2S and CO2 from CH4 by A High Silica CHA-type Zeolite Membrane. J. Membr. Sci. 2014, 470, 159-165. (9) Sidi-Boumedine, R.; Horstmann, S.; Fischer, K.; Provost, E.; Fürst, W.; Gmehling J. Experimental Determination of Hydrogen Sulfide Solubility Data in Aqueous Alkanolamine Solutions. Fluid Phase Equilib. 2004, 218, 149-155. (10) Dhage, P.; Samokhvalov, A.; Repala, D.; Duin, E. C.; Tatarchuk, B. J. Regenerable Fe-MnZnO/SiO2 Sorbents for Room Temperature Removal of H2S from Fuel Reformates: Performance, Active Sites, Operando Studies. Phys. Chem. Chem. Phys. 2011, 13, 2179-2187. (11) Li, Y.-G.; Mather, A. E. Correlation and Prediction of the Solubility of CO2 and H2S in Aqueous Solutions of Methyldiethanolamine. Ind. Eng. Chem. Res. 1997, 36, 2760-2765. (12) Pani, F.; Gaunand, A.; Richon, D.; Cadours, R.; Bouallou, C. Absorption of H2S by an Aqueous Methyldiethanolamine Solution at 296 and 343 K. J. Chem. Eng. Data 1997, 42, 865870.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 32

(13) 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, 58175828. (14) Shiflett, M. B.; Niehaus, A. M. S.; Yokozeki, A. Separation of CO2 and H2S Using RoomTemperature Ionic Liquid [bmim][MeSO4]. J. Chem. Eng. Data 2010, 55, 4785-4793. (15) Kumar, S.; Cho, J. H.; Moon, I. Ionic Liquid-Amine Blends and CO2BOLs: Prospective Solvents for Natural Gas Sweetening and CO2 Capture Technology-A Review. Int. J. Greenh. Gas Con. 2014, 20, 87-116. (16) Rahmati-Rostami, M.; Ghotbi, C.; Hosseini-Jenab, M.; Ahmadi, A. N.; Jalili, A. H. Solubility of H2S in Ionic Liquids [hmim][PF6], [hmim][BF4], and [hmim][Tf2N]. J. Chem. Thermodyn. 2009, 41, 1052-1055. (17) Plechkova, N. V.; Seddon, K. R. Applications of Ionic Liquids in the Chemical Industry. Chem. Soc. Rev. 2008, 37, 123-150. (18) Aparicio, S.; Atilhan, M. Computational Study of Hexamethylguanidinium Lactate Ionic Liquid: a Candidate for Natural Gas Sweetening. Energy Fuels 2010, 24, 4989-5001. (19) Zhang, X.; Zhang, X.; Dong, H.; Zhao, Z.; Zhang, S.; Huang, Y. Carbon Capture with Ionic Liquids: Overview and Progress. Energy Environ. Sci. 2012, 5, 6668-6681. (20) Ju, Y.-J.; Lien, C.-H.; Chang, K.-H.; Hu, C.-C.; Wong, D. S.-H. Deep Eutectic SolventBased Ionic Liquid Electrolytes for Electrical Double-Layer Capacitors. J. Chin. Chem. Soc. 2012, 59, 1280-1287.


24

Page 25 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(21) Zhao, Y.; Zhang, J.; Han, B.; Song, J.; Li, S.; Wang, Q. Metal-Organic Framework Nanospheres with Well-Ordered Mesopores Synthesized in an Ionic Liquid/CO2/Surfactant System. Angew. Chem. Int. Ed. 2011, 50, 636-639. (22) Jou, F.-Y.; Mather, A. E. Solubility of Hydrogen Sulfide in [bmim][PF6]. Int. J. Thermophys. 2007, 28, 490-495. (23) Pomelli, C. S.; Chiappe, C.; Vidis, A.; Laurenczy, G.; Dyson, P. J. Influence of the Interaction between Hydrogen Sulfide and Ionic Liquids on Solubility: Experimental and Theoretical Investigation. J. Phys. Chem. B 2007, 111, 13014-13019. (24) Jalili, A. H.; Rahmati-Rostami, M.; Ghotbi, C.; Hosseini-Jenab, M.; Ahmadi, A. N. Solubility of H2S in Ionic Liquids [bmim][PF6], [bmim][BF4], and [bmim][Tf2N]. J. Chem. Eng. Data 2009, 54, 1844-1849. (25) Jalili, A. H.; Mehdizadeh, A.; Shokouhi, M.; Ahmadi, A. N.; Hosseini-Jenab, M.; Fateminassab, F. Solubility and diffusion of CO2 and H2S in the ionic liquid 1-ethyl-3methylimidazolium ethylsulfate. J. Chem. Thermodyn. 2010, 42, 1298-1303. (26) Sakhaeinia, H.; Jalili, A. H.; Taghikhani, V.; Safekordi, A. A. Solubility of H2S in Ionic Liquids 1-Ethyl-3-methylimidazolium Hexafluorophosphate ([emim][PF6]) and 1-Ethyl-3methylimidazolium Bis(trifluoromethyl)sulfonylimide ([emim][Tf2N]). J. Chem. Eng. Data 2010, 55, 5839-5845. (27) Huang, K.; Cai, D.-N.; Chen, Y.-L.; Wu, Y.-T.; Hu, X.-B.; Zhang, Z.-B. Thermodynamic Validation of 1-Alkyl-3-methylimidazolium Carboxylates as Task-Specific Ionic Liquids for H2S Absorption. AIChE J. 2013, 59, 2227-2235.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 32

(28) Chen, J.-J.; Li, W.-W.; Y, H.-Q.; Li, X.-L. Capture of H2S from Binary Gas Mixture by Imidazolium-Based Ionic Liquids with Nonfluorous Anions: A Theoretical Study. AIChE J. 2013, 59, 3824-3833. (29) Mortazavi-Manesh, S.; Satyro, M. A.; Marriott, R. A. Screening Ionic Liquids as Candidates for Separation of Acid Gases: Solubility of Hydrogen Sulfide, Methane, and Ethane. AIChE J. 2013, 59, 2993-3005. (30) Zheng, J.; Li, S.; Wang, Y.; Li, L.; Su, C.; Liu, H.; Zhu, F.; Jiang, R.; Ouyang, G. In Situ Growth of IRMOF-3 Combined with Ionic Liquids to Prepare Solid-phase Microextraction Fibers. Anal. Chim. Acta 2014, 829, 22-27. (31) Lozano, L. J.; Godínez, C.; de los Ríos, A. P.; Hernández-Fernández, F. J.; SánchezSegado, S.; Alguacil, F. J. Recent Advances in Supported Ionic Liquid Membrane Technology. J. Membr. Sci. 2011, 376, 1-14. (32) Selvam, T.; Machoke, A.; Schwieger, W. Supported Ionic Liquids on Non-porous and Porous Inorganic Materials-A Topical Review. Appl. Catal., A 2012, 445-446, 92-101. (33) Yu, Y.; Mai, J.; Wang, L.; Li, X.; Jiang, Z.; Wang, F. Ship-in-a-bottle Synthesis of Amine-Functionalized Ionic Liquids in NaY Zeolite for CO2 Capture. Sci. Rep. 2014, 4, 59976005. (34) Li, J.; Sculley, J.; Zhou, H. Metal-Organic Frameworks for Separations. Chem. Rev. 2012, 112, 869-932. (35) Gurdal, Y.; Keskin, S. Predicting Noble Gas Separation Performance of Metal Organic Frameworks using Theoretical Correlations. J. Phys. Chem. C 2013, 117, 5229-5241.


26

Page 27 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(36) Castillo, J. M.; Vlugt, T. J. H.; Calero, S. Understanding Water Adsorption in Cu-BTC Meta-Organic Frameworks. J. Phys. Chem. C 2008, 112, 15934-15939. (37) Nasalevich, M. A.; van der Veen, M.; Kapteijn, F.; Gascon, J. Metal-Organic Frameworks as Heterogeneous Photocatalysts: Advantages and Challenges. CrystEngComm 2014, 16, 49194926. (38) Devautour-Vinot, S.; Diaby, S.; da Cunha, D.; Serre, C.; Horcajada, P.; Maurin, G. Ligand Dynamics of Drug-Loaded Microporous Zirconium Terephthalates-Based Metal-Organic Frameworks: Impact of the Nature and Concentration of the Guest. J. Phys. Chem. C 2014, 118, 1983-1989. (39) Fujie, K.; Yamada, T.; Ikeda, R.; Kitagawa, H. Introduction of an Ionic Liquid into the Micropores of a Metal-Organic Framework and Its Anomalous Phase Behavior. Angew. Chem. Int. Ed. 2014, 53, 11302-11305. (40) Khan, N. A.; Hasan, Z.; Jhung, S. H. Ionic Liquids Supported on Metal-Organic Frameworks: Remarkable Adsorbents for Adsorptive Desulfurization. Chem. Eur. J. 2014, 20, 376-380. (41) Luo, Q.; Song, X.; Ji, M.; Park, S.-E.; Hao, C.; Li, Y. Molecular Size- and ShapeSelective Knoevenagel Condensation over Microporous Cu3(BTC)2 Immobilized AminoFunctionalized Basic Ionic Liquid Catalyst. Appl. Catal., A 2014, 478, 81-90. (42) Chen, Y.; Hu, Z.; Gupta, K. M.; Jiang, J. Ionic Liquid/Metal-Organic Frameworks Composite for CO2 Capture: A Computational Investigation. J. Phys. Chem. C 2011, 115, 21736-21742.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 32

(43) Gupta, K. M.; Chen, Y.; Hu, Z.; Jiang, J. Metal-Organic Frameworks Supported Ionic Liquid Membranes for CO2 Capture: Anion Effects. Phys. Chem. Chem. Phys. 2012, 14, 57855794. (44) Gupta, K. M.; Chen, Y.; Jiang, J. Ionic Liquid Membranes Supported by Hydrophobic and Hydrophilic Metal-Organic Frameworks for CO2 Capture. J. Phys. Chem. C 2013, 117, 57925799. (45) Vicent-Luna, J. M.; Gutierrez-Sevillano, J. J.; Anta, J. A.; Calero, S. Effect of RoomTemperature Ionic Liquids on CO2 Separation by a Cu-BTC Metal-Organic Framework. J. Phys. Chem. C 2013, 117, 20762 -20768. (46) Tzialla, O.; Veziri, C.; Papatryfon, X.; Beltsios, K. G.; Labropoulos, A.; Iliev, B.; Adamova, G.; Schubert, T. J. S.; Kroon, M. C.; Francisco, M.; et al. Zeolite Imidazolate Framework-Ionic Liquid Hybrid Membranes for Highly Selective CO2 Separation. J. Phys. Chem. C 2013, 117, 18434-18440. (47) Li, B.; Zhang, Z.; Li, Y.; Yao, K.; Zhu, Y.; Deng, Z.; Yang, F.; Zhou, X.; Li, G.; Wu, H.; et al. Enhanced Binding Affinity, Remarkable Selectivity, and High Capacity of CO2 by Dual Functionalization of a rht-Type Metal-Organic Framework. Angew. Chem. Int. Ed. 2012, 51, 1412-1415. (48) Zhang, Z.; Li, Z.; Li, J. Computational Study of Adsorption and Separation of CO2, CH4, and N2 by an rht-Type Metal-Organic Framework. Langmuir 2012, 28, 12122-12133. (49) Wu, H.; Yao, K.; Zhu, Y.; Li, B.; Shi, Z.; Krishna, R.; Li, J. Cu-TDPAT, an rht-Type Dual-Functional Metal-Organic Framework Offering Significant Potential for Use in H2 and


28

Page 29 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Natural Gas Purification Processes Operating at High Pressures. J. Phys. Chem. C 2012, 116, 16609-16618. (50) Martin, M. G.; Siepmann, J. I. Transferable Potentials for Phase Equilibria. 1. UnitedAtom Description of n-alkanes. J. Phys. Chem. B 1998, 102, 2569-2577. (51) Kamath, G.; Lubna, N.; Potoff, J. J. Effect of Partial Charge Parametrization on the Fluid Phase Behavior of Hydrogen Sulfide. J. Chem. Phys. 2005, 123, 124505-124511. (52) 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. (53) Rappé, A. K.; Casewit, C. J.; Colwell, K. S.; Goddard III, W. A.; Skiff, W. M. UFF, a Full Periodic Table Force Field for Molecular Mechanics and Molecular Dynamics Simulations. J. Am. Chem. Soc. 1992, 114, 10024-10039. (54) Liu, Z.; Huang, S.; Wang, W. A Refined Force Field for Molecular Simulation of Imidazolium-Based Ionic Liquids. J. Phys. Chem. B 2004, 108, 12978-12989. (55) Xing, H.; Zhao, X.; Yang, Q.; Su, B.; Bao, Z.; Yang, Y.; Ren, Q. Molecular Dynamics Simulation Study on the Absorption of Ethylene and Acetylene in Ionic Liquids. Ind. Eng. Chem. Res. 2013, 52, 9308-9316. (56) Smith, W.; Forester, T. R. DL_POLY_2.0: A General-Purpose Parallel Molecular Dynamics Simulation Package. J. Mol. Graphics 1996, 14, 136-141.


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 32

(57) Vlugt, T. J. H.; García-Pérez, E.; Dubbeldam, D.; Ban, S.; Calero, S. Computing the Heat of Adsorption using Molecular Simulations: The Effect of Strong Coulombic Interactions. J. Chem. Theory. Comput. 2008, 4, 1107-1118. (58) Zhang, S.; Shi, R.; Ma, X.; Lu, L.; He, Y.; Zhang, X.; Wang, Y.; Deng, Y. Intrinsic Electric Fields in Ionic Liquids Determined by Vibrational Stark Effect Spectroscopy and Molecular Dynamics Simulation. Chem. Eur. J. 2012, 18, 11904-11908. (59) Maghsoudi, H.; Soltanieh, M.; Bozorgzadeh, H.; Mohamadalizadeh, A. Adsorption Isotherms and Ideal Selectivities of Hydrogen Sulﬁde and Carbon Dioxide over Methane for the Si-CHA Zeolite: Comparison of Carbon Dioxide and Methane Adsorption with the all-silica DD3R Zeolite. Adsorption 2013, 19, 1045-1053. (60) Cosoli, P.; Ferrone, M.; Pricl, S.; Fermeglia, M. Hydrogen Sulphide Removal from Biogas by Zeolite Adsorption: Part I. GCMC Molecular Simulations. Chem. Eng. J. 2008, 145, 86-92. (61) Hamon, L.; Frère, M.; Weireld, G. Development of a New Apparatus for Gas Mixture Adsorption Measurements Coupling Gravimetric and Chromatographic Techniques. Adsorption 2008, 14, 493-499. (62) Carvalho, P. J.; Coutinho, J. A. P. The Polarity Effect upon the Methane Solubility in Ionic Liquids: A Contribution for the Design of Ionic Liquids for Enhanced CO2/CH4 and H2S/CH4 Selectivities. Energy Environ. Sci. 2011, 4, 4614-4619. (63) Ramdin, M.; Balaji, S. P.; Vicent-Luna, J. M.; Gutiérrez-Sevillano J. J.; Calero, S.; W. de Loos, T.; Vlugt, T. J. H. Solubility of the Precombustion Gases CO2, CH4, CO, H2, N2, and H2S


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in the Ionic Liquid [bmim][Tf2N] from Monte Carlo Simulations. J. Phys. Chem. C 2014, 118, 23599 −23604. (64) Jou, F. Y.; Mather, A. E. Solubility of Hydrogen Sulfide in [bmim][PF6]. Int. J. Thermophys. 2007, 28, 490-495.


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MetalâOrganic Framework Composites for H2S Removal

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