Supporting Information for
Capture of H2S from Binary Gas Mixture by Imidazolium-Based Ionic Liquids
with Non-Fluorous Anions: A Theoretical Study
Jie-Jie Chen, Wen-Wei Li, and Han-Qing Yu*
Department of Chemistry, University of Science & Technology of China, Hefei,
230026, China
Xue-Liang Li*
School of Chemical Engineering, Hefei University of Technology, Hefei, 230009,
China
*Corresponding authors:
Prof. Xue-Liang Li, E-mail: lixuel987@163.com; Prof. Han-Qing Yu, E-mail:
hqyu@ustc.edu.cn
1
Interaction energy of ion-H2S
In the geometry optimization, the positions of all the atoms were fully relaxed by
using DMol3 code. To say, the structure with the most negative energy was
investigated to compare with the other system. The true minima in the potential
energy surface were confirmed in details. For example, the geometry structures of the
possible local minimums for the [bmim]-H2S system are shown in Figure S1(a-1~a-4).
The structure in Figure S1(a-4) with the strongest interaction energy was used to
analyze the topological characteristics in this study. The changing trend of the values
of ΔEI-S, PW91/DNP, ΔEI-S, PW91/TNP and ΔEI-S, PBE/TNP in Table S1 separately based on
basis levels of PW91/DNP, PW91/TNP and PBE/TNP is identical to each other. Thus,
the most stable structure (i.e., most negative energy) of each cation-H2S system has
been obtained and is shown in Figure S1.
The negative values of the cation-H2S interaction energy shown in Table S1
indicate that the systems tend to be stable with the absorption of H2S. These suggest
that the H2S molecule prefers to approach from the S atom toward the C2H hydrogen
for the cation of [bmim] and [hbmim] correspondingly shown in Figure S1(a-4) and
(c-4). But the most stable interaction site of [bhmim] and H2S is between the H2S and
hydroxyl group on methyl of imidazolium. The C2H hydrogen, which is the hydrogen
attached to the carbon atom positioned between the two nitrogen atoms of the
imidazolium ring, carries the most positive charge in the cation.
Gas solubility calculations
2
Many reported results show that the imidazolium-based ILs have a considerable
solubility capacity of H2S, even greater than that of CO2.1-4 The solubility of gases in
solvents is quantified by using Henry’s law. For instance, Henry’s law constant (KH)
for the solubilities of H2S and CO2 in a common IL, [bmim][PF6], are 0.1435 and
5.176 MPa at 298.15 K, respectively. This large difference in Henry’s law constant
suggests that it may be possible to selectively capture and separate these gases using
ILs. Higher KH values of H2S in the imidazolium-based ILs reported by Karadas et
al.7 prove the capacity of imidazolium ILs for absorbing H2S.
The gas solubilities in these six ILs have been calculated by conductor-like
screening model for real solvents (COSMO-RS) method.8 The COSMO-RS
developed by Klamt et al.9 provides an alternative approach to predict the
thermodynamic properties of fluids for various systems, including ILs.10-11 All
COSMO-RS calculations were computed at the BP/TZP level. The available studies
on the predictive ability of the COSMO-RS model for gas solubilities in ILs have
proven to be successful. For instance, the calculated KH of CO2 in [bmim][PF6] and
[bmim][BF4] around ambient temperature reported by Zhang et al.12 agree with the
experimental data well. Therefore, the COSMO-RS method can be used to predict the
H2S solubility in these ILs at ambient temperature.
The calculated KH of H2S and CO2 in these six ILs separately in Table 2 and
Table S2 indicate that the solubility of H2S is higher than that of CO2 in
imidazolium-based ILs. If we know the density of ILs, the calculated KH in the unit of
3
mol/(L·atm) can be transferred to that in pressure (MPa, bar, atm) as described in the
following equation:
0.1 cIL (mol/L )
100   IL (g/cm 3 )
K H (MPa ) 

K H (mol/L  atm ) K H (mol/L  atm )  M IL (g/mol )
(S1)
Then, the calculated KH values in Table 2 and Table S2 can be compared with
those in pressure from some references.5-6,12 For example, the density of
[bmim]MeSO4 is 1.21 g/cm3, and the KH for H2S and CO2 in this IL are 0.470 and
5.983 MPa, respectively, from Equation S1. The magnitude order is the same with the
experimental data5-6 in [bmim][PF6].
4
Table S1. Interaction energy (EI-S, kcal/mol) of ions in NIILs and H2S calculated at
different basis levels of PW91/DNP, PW91/TNP and PBE/TNP according to the
geometry structures of the possible local minimums for the ion-H2S systems in Figure
S1
Ions
ΔEI-S,PW91/DNP
ΔEI-S,PW91/TNP
ΔEI-S,PBE/TNP
(a-1)
[bmim]-H2S-1
-11.585
-5.977
-4.822
(a-2)
[bmim]-H2S-2
-12.344
-8.423
-7.242
(a-3)
[bmim]-H2S-3
-12.734
-8.732
-6.826
(a-4)
[bmim]-H2S-4
-13.359
-9.277
-8.488
(b-1)
[bhmim]-H2S-1
-17.420
-12.929
-11.592
(b-2)
[bhmim]-H2S-2
-14.146
-9.235
-8.052
(b-3)
[bhmim]-H2S-3
-11.883
-7.962
-6.680
(b-4)
[bhmim]-H2S-4
-16.382
-12.318
-8.649
(c-1)
[hbmim]-H2S-1
-12.580
-8.346
-7.988
(c-2)
[hbmim]-H2S-2
-14.107
-9.592
-8.594
(c-3)
[hbmim]-H2S-3
-16.357
-11.778
-8.268
(c-4)
[hbmim]-H2S-4
-16.529
-11.986
-9.168
(c-5)
[hbmim]-H2S-5
-12.783
-8.265
-6.759
(e)
LAC-H2S
-21.181
-17.328
-16.658
(f)
MeSO4-H2S
-13.241
-10.248
-10.079
5
Table S2. The Henry’s law constants of CO2 in the imidazolium-based ILs predicted
by COSMO-RS at 298.15 K
ILs
KH
(mol/(L·atm))
[bmim]MeSO4
0.0808
[bmim]LAC
0.0567
[bhmim]MeSO4
0.0451
[bhmim]LAC
0.0507
[hbmim]MeSO4
0.0512
[hbmim]LAC
0.0591
6
Table S3. Interaction energy (EA-C, kcal/mol) of cation and anion in NIILs
calculated at different basis levels of PW91/DNP, PW91/TNP and PBE/TNP for
different anion sites relative to cation according to Figure S2
NIILs
ΔEA-C,PW91/DNP
ΔEA-C,PW91/TNP
ΔEA-C,PBE/TNP
(a-1)
[bmim]LAC-1
-89.584
-94.866
-89.236
(a-2)
[bmim]LAC-2
-97.327
-99.419
-97.032
(b-1)
[bmim]MeSO4-1
-87.361
-86.802
-85.864
(b-2)
[bmim]MeSO4-2
-94.192
-93.424
-91.763
(c-1)
[bhmim]LAC-1
-96.390
-97.313
-91.399
(c-2)
[bhmim]LAC-2
-118.823
-120.032
-110.627
(d-1)
[bhmim]MeSO4-1
-90.095
-89.478
-85.372
(d-2)
[bhmim]MeSO4-2
-104.966
-102.331
-102.775
(e-1)
[hbmim]LAC-1
-93.155
-93.349
-91.388
(e-2)
[hbmim]LAC-2
-101.752
-101.573
-99.743
(f-1)
[hbmim]MeSO4-1
-92.336
-91.224
-89.114
(f-2)
[hbmim]MeSO4-2
-100.480
-98.946
-97.539
7
Table S4. Interaction energy (EIL-S, kcal/mol) between NIIL and H2S with hydrogen
bonding calculated at different basis levels of PW91/DNP, PW91/TNP and PBE/TNP
for different H2S sites relative to NIIL according to Figure 2
NIIL-H2S
ΔEIL-S,PW91/DNP
ΔEIL-S,PW91/TNP
ΔEIL-S,PBE/TNP
(a-1)
[bmim]LAC-H2S-1
-24.102
-19.245
-12.736
(a-2)
[bmim]LAC-H2S-2
-23.296
-17.124
-12.179
(b-1)
[bmim]MeSO4-H2S-1
-21.342
-18.393
-15.020
(b-2)
[bmim]MeSO4-H2S-2
-19.371
-16.235
-13.834
(c-1)
[bhmim]LAC-H2S-1
-12.753
-6.689
-9.745
(c-2)
[bhmim]LAC-H2S-2
-11.382
-6.278
-9.322
(d-1)
[bhmim]MeSO4-H2S-1
-19.286
-17.718
-13.154
(d-2)
[bhmim]MeSO4-H2S-2
-18.372
-17.595
-7.320
(e-1)
[hbmim]LAC-H2S-1
-25.376
-19.213
-15.805
(e-2)
[hbmim]LAC-H2S-2
-22.225
-11.803
-11.376
(f-1)
[hbmim]MeSO4-H2S-1
-17.646
-14.707
-9.912
(f-2)
[hbmim]MeSO4-H2S-2
-16.029
-9.483
-8.143
8
Table S5. Interaction energy (EIL-M, kcal/mol) between NIIL and CH4 with hydrogen
bonding calculated at different basis levels of PW91/DNP, PW91/TNP and PBE/TNP
for different CH4 sites relative to NIIL
NIIL-CH4
ΔEIL-M,PW91/DNP
ΔEIL-M,PW91/TNP
ΔEIL-M,PBE/TNP
(a-1)
[bmim]LAC-CH4-1
-13.623
-13.095
-4.765
(a-2)
[bmim]LAC-CH4-2
-11.373
-7.788
-2.198
(b-1)
[bmim]MeSO4-CH4-1
-18.327
-18.677
-10.381
(b-2)
[bmim]MeSO4-CH4-2
-15.651
-15.572
-9.902
(c-1)
[bhmim]LAC-CH4-1
-9.477
-8.181
-3.797
(c-2)
[bhmim]LAC-CH4-2
-5.170
0.245
-2.613
(d-1)
[bhmim]MeSO4-CH4-1
-14.147
-10.463
-2.565
(d-2)
[bhmim]MeSO4-CH4-2
-4.285
-6.861
-2.462
(e-1)
[hbmim]LAC-CH4-1
-13.205
-15.604
-4.846
(e-2)
[hbmim]LAC-CH4-2
-6.209
-9.483
-3.545
(f-1)
[hbmim]MeSO4-CH4-1
-9.668
-10.471
-4.954
(f-2)
[hbmim]MeSO4-CH4-2
-7.237
-7.675
-3.665
9
Figure S1. Geometry structures of the possible local minimums for the ion-H2S
systems and with the interaction energy in Table S1
10
Figure S2. Geometry structures of NIILs for different anion sites relative to cation
and with the interaction energy in Table S3
11
Figure S3. Geometry structures of NIILs for different CH4 sites relative to NIILs and
with the hydrogen bond length in Angstrom and the interaction energy shown in
Table S5
12
Figure S4. Relationship between log(MSD) and log(t) for the NIIL-H2S-CH4 systems:
(a) [bmim]MeSO4; (b) [bmim]LAC; (c) [bhmim]MeSO4; (d) [bhmim]LAC; (e)
[hbmim]MeSO4; and (f) [hbmim]LAC
13
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15
Table of Contents (TOC) art
A computational investigation into the interactions between H2S and NIILs with
different combinations of imidazolium cations and non-fluorous anions for effective
H2S capture from H2S-CH4 mixture.
16