- Email: [email protected]
Selectivities at infinite dilution of xylene isomers in ionic liquids
Accepted Manuscript Title: Selectivities at infinite dilution of xylene isomers in ionic liquids Author: Li-Sheng Wang Xue-Yuan Wang PII: DOI: Reference:
S0378-3812(14)00236-2 http://dx.doi.org/doi:10.1016/j.fluid.2014.04.016 FLUID 10077
To appear in:
Fluid Phase Equilibria
Received date: Revised date: Accepted date:
12-11-2013 12-4-2014 16-4-2014
Please cite this article as: L.-S. Wang, X.-Y. Wang, Selectivities at infinite dilution of xylene isomers in ionic liquids, Fluid Phase Equilibria (2014), http://dx.doi.org/10.1016/j.fluid.2014.04.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
*Revised Manuscript
Selectivities at infinite dilution of xylene isomers in ionic liquids
Li-Sheng Wang,* Xue-Yuan Wang School of Chemical Engineering & the Environment, Beijing Institute of Technology, Beijing 100081, China
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Abstract: A database on activity coefficients of organic solutes at infinite dilution in ILs was collected from literature sources. The activity coefficient model with the combinatorial term
cr
represented by the Kikic et al. was used as a modification to Flory’s equation. The activity coefficients had been used to correlate the solubility parameter of ionic liquids. The obtained
us
solubility parameters of ionic liquids had been further correlated based on a concept of the group contribution method. Through the analysis of the database and the prediction results of
an
selectivities at infinite dilution of xylene isomers, we showed that higher selectivity can be
M
achieved by using ILs as working solvents for separation of xylene isomer mixtures.
ce pt
1. Introduction
ed
Keywords: activity coefficient, ionic liquid, selectivity, xylene isomers.
In the petrochemical industry, the separation of xylene isomers is of significant importance for production of chemicals such as terephthalic, phthalic, and isophthalic acids. Because of the close boiling points of these isomers, it is impractical to separate them by distillation. Processes
Ac
based on zeolitic adsorption have been developed. Room temperature ionic liquids (ILs) can be designed to special task and have been applied as replacement for conventional toxic, flammable and volatile organic solvents in the development of new separation process.1-4 The common organic solvents are remarkable similar in a relatively narrow liquidus region. They are all relatively volatile and easily becoming emissions into the atmosphere at the process conditions. The emissions of VOC have been linked to global climate change and human illness. It is the aim of chemical engineers to reduce the emissions of VOCs, and to find a new class of “green” solvents. In the direction of developing an efficient and environmentally benign chemical process, many scientists have concentrated their 1
Page 1 of 36
research activities using ILs as green solvents, because not only ILs have essentially no vapor pressure, and they do not evaporate, and so they cannot lead to fugitive emissions, but also they act much like good organic solvents, dissolving both polar and nonpolar species. An important example is the innovative application of ILs as working solvents in supported liquid membrane (SILM) for the separation gas mixtures conducted by vapor pervaporization.5 In the SILM
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technology, an ionic liquid can be impregnated in the pore in polymer support or hollow fiber module, the capability of ILs to separate solutes mixtures depends on the selectivity of the
cr
solutes in ILs.
us
The major driving force for selective separation of xylene isomer gas mixture by SILM is the solubility difference between these isomers in ionic liquid. Selectivity (Sij) can be calculated from the ratio of solubilities of the two solutes in one solvent. We have experimental
an
demonstrated that even though these xylene isomers have close boiling points, their solubilities in an ionic liquid can be evidently different.6 A separation factor, selectivity of the solutes at
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infinite dilution in an ionic liquid, can be calculated from the ratio of activity coefficients at infinite dilution (Sij∞, defined according to the equation: Sij∞ =γis∞/γjs∞, where subscript s denotes
ed
solvent).
Activity coefficients at infinite dilution of different organic solutes in ILs can be determined
ce pt
with an ionic liquid as the stationary phase using gas-liquid chromatography.7,8 In this work, we continue our research to establish a database of activity coefficient at infinite dilution of organic solutes in ILs from the open literatures.9 It is clear to find out from this database that how the
Ac
change of cations and anions affects the γi∞ and Sij∞ values. Based on the database, an activity coefficient model for regular solutions has been applied and developed. The objective of this paper is to predict the solubility parameter for the activity coefficient model for the ILs and to predict the selectivities when the activity coefficient data for xylene isomers/other solutes are not available. Through the analysis of the database and the predicted Sij∞ values and taking the advantage of ionic liquids as designable solvents, we will discuss the possibility for the further application of ILs in SILM technology for xylene isomer separation.
2
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2. Classification of ILs and database
To correlate the activity coefficients with a wide range representation of organic solutes and ILs, we need to build a database. Cations and anions were separated and then numbered by an ID code respectively. In our previously paper we published a database of activity coefficients of
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organic solutes at infinite dilution in ILs from literature sources.9 In this work, the database have
cr
been extended to include most of the recently published data of ionic liquids (as listed in Appendix) and from which 50 kinds of cations and 29 kinds of anions can be extracted and they
us
were listed in Table 1, as well as their abbreviations, chemical names, formulas, and molecular
3.1. Correlation with Flory’s equation
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3. Correlation of activity coefficients
an
weights.
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The activity coefficients at infinite dilution of different solutes in a given solvent can be used to estimate solubility parameters of the solvents when the solubility parameters of these
ce pt
solutes are known. This method provides a basis for the correlation of the activity coefficients at infinite dilution of solutes in ILs. The activity coefficient model can be represented by a two-term equation in which the combinatorial term can be represented by the Kikic et al. 10
Ac
modification to Flory’s equation, and the residual term is given by the regular solution theory:
ln i ln icomb ln ires
ln icomb ln(ri / rs )2/ 3 1 (ri / rs )2/ 3 ln ires (vi / RT )( i s )2
(1) (2) (3)
Where ri and rs are the van der Waals volumes of solute and solvent, respectively; vi is the solute molar volume; δi and δs are solubility parameters of solute and solvent, respectively. The solubility parameter of ILs can be correlated from the experimental γ∞ data. A residual function Y can be rearranged from Eq. 3 according to literature11
3
Page 3 of 36
Yi
ln ires i 2 2 s 2 i s vi RT RT RT
(4)
This equation shows that there is a linear relation between Yi and the solute solubility parameter δi for a given solvent and temperature T. The value of the solvent (i.e., ionic liquid) solubility parameter δs can be obtained from the slope of this line. The values of experimental γ∞
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were taken from the database. The values of ln γ∞comb were calculated by Eq. 2. According to Eq.
cr
1, with the ln i known (by experimental data), the value of ln ires can be calculated, and finally the values of Yi for different solutes in an ionic liquid were calculated according to Eq. 4.
us
Information on vi, δi, and ri were obtained from the literature.12 The van der Waals volumes of ILs were calculated by group contribution method.13 The dependence between Yi and δi (δi =
an
δsolute) can thus be plotted for different solutes with a specified ionic liquid and high accuracy of the linear correlation which was displayed by Fig. 1. The solubility parameters (δs) of 26 ionic
M
liquids calculated by this procedure were published in our previously paper.9 More solubility parameters of 33 ionic liquids obtained in this work were listed in Table 2 (the data sources for the correlation were listed in Table A1 in Appendix). Some of the results of van der Waals
ed
volumes of ionic liquids were listed in Table 3.
3.2. Group contribution of the solubility parameters
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From the idea that the total cohesive energy of a molecule is the sum of the individual cohesive energies (molar attraction constants) associated with each constituent group on the molecule, the solubility parameters of ionic liquids can be determined based on a group
Ac
contribution method.14 This method also assumes that molar attraction constants are considered constant regardless of the surrounding chemical environment. The following expression can be used to calculate the solubility parameter δs of an ionic liquid:
s
F j
vs
j
(5)
In Eq. 5, subscript s represents the solvent, j represents each substitute chemical group, F is the molar attraction constant of chemical group j, and vs is the molar volume of the solvent. With the solubility parameters of the ionic liquid known, F can be obtained for the sub-group j. The classification of the structure of an ionic liquid is shown with 1-R1-3-R2-imidazolium 4
Page 4 of 36
tetrafluoroborate as example, as shown in Fig. 2, in which the cationic imidazolium ring and tetrafluoroborate cation are defined together as one neutral group (ionic functional group, IFG), while the substitute R1 and R2 on the ring can be separated into methyl, methylene, etc. Molar attraction constants of several organic functional groups relevant to this study were taken from literature.15 Values for the IFG of ILs classified according to Fig. 2 were estimated from the
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values of solubility parameter using group contribution method, and the results of the FIFG values
cr
were summarized in Table 4.
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4. Selectivities of xylene isomers in ILs: results and discussions
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4.1. The results of analysis for the selectivity from the experimental data
In petrochemical industry, the development of production technology of terephthalic,
M
phthalic, and isophthalic acids are mainly limited by the separation technology of xylene isomers. Up to now, the researches for the separation of para-xylene from its bulkier meta- and orthoisomers by zeolite membrances via vapor permeation were successful,16,17 and satisfactory
ed
permselectivities were obtained. However, from a point of view of petrochemical production, the results for the separation of meta-xylene from its para- and ortho- isomer mixtures were not
ce pt
successful by using the same technique because the limit by the kinetic diameter.18 In a SILM apparatus, the separation factor depends on the difference in solubilities of the isomers in ionic liquid, but not on the boiling points. Therefore, the isomer mixture can be
Ac
theoretical separated by using SILM technology. Using the database and the group contribution activity coefficient model developed in this work, we can analyze the structure-property relationship for ILs, especially for the effect of molecular structure on the selectivity of the xylene isomers in the ionic liquid. The results of analysis for the selectivity from the experimental data19-35 of activity coefficients at infinite dilution of xylene isomers in ionic liquids calculated in this work were o
listed in Table 5. Because the kinetic diameters of both meta- and ortho- xylene equal to 6.8 A , it seems not possible to separate them with a zeolite membrance. From Table 5, it can be seen that the highest selectivity is obtained by using [MAOOMIM]Br to separate meta-xylene (1) and 5
Page 5 of 36
ortho-xylene (2), the result is S12 =2.070. Compared with the results of [C8MIM]Cl in Table 5, the introduction of an ester group improves selectivity greatly. 4.2. The prediction results: effect of alkyl chain of cations of ILs on the selectivity The γi∞ value and selectivity can also be calculated using the group contribution activity
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coefficient model correlated in this work. To explore the effect of carbon number in alkyl chain of cations on the selectivity, we calculated the solubility parameters, activity coefficients based
cr
on the group contribution activity coefficient model, and the results of solubility parameters for ionic liquids ([CnAOOMIM][Br], [CnMIM][CH3SO3], [CnMIM][SCN] and [CnMPYR][SCN])
us
were listed in Table 6.
Table 7 lists the prediction results at 313.15 K for the selectivity of [RAOOMIM][Br] for
an
meta- and ortho- xylene, in which the R represents alkyl chain. With the increase of alkyl chain length, the selectivity decreases.
M
Table 8 lists the prediction results of selectivity of para-xylene /ortho-xylene in ionic liquids. From Table 8 it can be seen that the selectivity of para-xylene /ortho-xylene in different
ed
type of ionic liquids can be increased with the reduction of carbon number in alkyl chain (the Cn groups) of cations.
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Fig. 3 shows the selectivity of the meta-xylene (1)/ortho-xylene (2), and para-xylene(1) /ortho-xylene (2) in ionic liquids [MAOOCnMIM][TCB]. From Fig. 3 it can be seen that the selectivity of meta-xylene/ortho-xylene and para-xylene/ortho-xylene in ionic liquids [MAOCnMIM] [TCB] can be increased with the reduction of carbon number in alkyl chain (the
Ac
Cn groups) of cations. Satisfactory results of [MAOOC1MIM][TCB] obtained at 333.15 K were 1.802 and 2.548, respectively. From the results of Tables 6 – 8 and Fig.3, it can be summarized that with the increase of alkyl chain length of cation of ionic liquids, their selectivity for xylene isomers will decrease. It is reasonable because the homogeneous of two different ionic liquids will be increased with the increase of alkyl chain of cations. 4.3. Prediction results: effect of anions of ILs on the selectivity Table 9 lists the predicted selectivities S12∞ of aromatic (1)/aromatic (2) hydrocarbon at infinite
dilution
in
the
ionic
liquids
when
the
cation
[MAOOMIM] 6
Page 6 of 36
(1-methacryloyloxyhexyl-1-methylimidazolium) combines with eight different anions, i.e., [NTf2], [SCN], [NO3], [MDEGSO4], [TCB], [MeSO4], [OSO4], [(CH3)2PO4].
From Table 9, it can be seen that the selectivity in ionic liquids can be changed by the choice of anions. In addition, it can be seen that the highest selectivity ( S12 =1.377) was obtained
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by using [TCB], the result was not better than the result ( S12 =2.070) by using [MAOOMIM]Br (as listed in Table 5) to separate meta-xylene (1) and ortho-xylene (2). Pal et al. demonstrated the
cr
blue-shifting measurement from FTIR for the cation [C4mim] with different anions in ethylene glycol.36 They indicated that very weaker interactions between [C4mim]+ and Br ,which were
us
even weaker than interactions between [C8OSO3] and [C4mim]+. The magnitude of interaction for these ionic liquids with xylenes is more for [TCB] as compared to Br anion,
an
it implies that weaker interaction between ionic liquid and xylene isomers will be more sensitive for the selectivity.
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Satisfactory selectivities were obtained for [MAOOMIM][TCB], the results with comparison for different mixtures were: for meta-xylene (1) /ortho-xylene (2), S12 =1.377; for
ed
para-xylene (1)/ortho-xylene (2), S12 =1.690) and for para-xylene (1)/ meta-xylene (2),
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S12 =1.227. The above results showed that it is possible to use only one ionic liquid as working solvent to separate these three isomers.
4.4. Uncertainty of the prediction results
Equation 4 provides a way to calculate the solubility parameter of an ionic liquid from the
Ac
slope of the equation based on the activity coefficient data at infinite dilution. The solubility parameter can also be computed from the intercept of
Eq. 4. In our previously
paper (literature: Feng et al.,21 see Table 5 of Feng el al.), we compared the solubility parameter
of an ionic liquid when values of were correlated from the slope, or from the intercept. We calculated the values of at different temperatures, the results indicated that would approach a constant in the range of temperature studied. The average value of at different temperatures was more close to the results from slope, than from the intercept. To correlate the solubility parameters, the average uncertainty for the activity coefficients based on the linear relation of Eq. 4 were less than 5%. The results calculated from the group 7
Page 7 of 36
contribution (Eq. 5) for the solubility parameter were compared with the values directly from the slope. The uncertainty is within 2%. Moreover, the prediction results of selectivities based the obtained solubility parameters of this work and the activity coefficient model (Eq. 1) were compared with the results of selectivity data directly derived from the experimental data, and the
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results were satisfactory. Average deviations were less than 5%.
cr
5. Conclusion
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The activity coefficients at infinite dilution of xylene in ionic liquids can be used to study their selectivity. The establishment of the database will promote the application of ionic liquids
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in the design of separation process. In this work, we established a database and found that ILs showed good selectivity for these separation problems. The activity coefficients can be
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represented by the regular solution theory. In this paper, the activity coefficients at infinite dilution data of different organic solutes in a given solvent have been used to estimate the solubility parameter of ionic liquids. The solubility parameters of ionic liquids have been
ed
correlated based on a concept of group contribution. This paper shows that based on the designable nature of ILs, there is a significant potential for exploiting how the variation of
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substitute, cation and anion influences the solubility of the xylene isomers in ILs. A traditional measurement method for the activity coefficient of solutes at infinite dilutions with an ionic liquid as the stationary phase using GLC and a classical thermodynamic model can be used to
Ac
analyze this possibility. By a combination of ILs with supported liquid membrane technology, the restriction from thermodynamic and dynamic diameter can be eliminated. The effectiveness of SILM process relies on the permeabilities of the solutes in the liquid membrane as well. Most probably, there are some differences in diffusivities between different xylene isomers in an ionic liquid. In this case, the selectivity of ionic liquid for the isomers will be strengthened. Further work should be done in this area, to measure the molecular diffusion and viscosity of the xylene isomers with ionic liquids. The results of this paper provide a basis for the selection of ionic liquids towards this purpose. *To whom correspondence should be addressed. E-mail: [email protected] 8
Page 8 of 36
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Ac
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[18] Kinetic diameter para-xylene = 5.8 A ; kinetic diameter meta- and ortho- xylene = 6.8 A . [19] F. Mutelet, J.N. Jaubert, M. Rogalski, J. Phys. Chem. B., 112 (2008) 3773-3785. 9
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[48] Y. Li, L.S. Wang, M.Y. Li, J. Chem. Eng. Data, 56 (2011) 1704-1708. [49] A. Bondi, Physical Properties of Molecular Crystals, Liquids and Glasses. New York: Wiley, 1968.
Ac
ce pt
ed
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an
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cr
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Appendix Table A1
11
Page 11 of 36
Table 1 Cations and anions of the ionic liquids included in the database. ID
Abbreviation
Name
M/g·mol −1
Formula
ip t
Anions Cl
chloride
Cl
2
Br
bromide
Br
3
BF4
tetrafluoroborate
BF4
86.80
4
PF6
hexafluorophosphate
PF6
144.96
5
TfO
trifluoromethanesulfonate
CF3SO3
149.07
6
NTf2
bis(trifluoromethylsulfonyl)imide
8
ESO4
9
OSO4
M0SO4
11
E0SO4
12
TOS
M
an
us
79.90
O F3C S O
280.16
O
N S CF3 O
CH3SO4
111.10
ethylsulfate
C2H5SO4
125.12
octylsulfate
C8H17SO4
209.28
methoxyethylsulfate
Ac
10
methylsulfate
ed
MeSO4
ce pt
7
35.45
cr
1
CH3O C2H5SO4
ethoxyethylsulfate
156.16
170.16 C2H5O C2H5SO4
tosylate
171.20 SO3H
13
MDEGSO4
diethyleneglycolmonomethylethersulfate
O O
O SO3
199.20
12
Page 12 of 36
14
(CH3)2PO4
dimethylphosphate
125.04 O H 3C O P O CH3 O
15
FAP
tris(pentafluoroethyl) trifluorophosphate
F
F C2F5
445.01 C2F 5
P
F
NO3
nitrate
NO3
62.00
17
N(CN)2
dicyanamide
C2N3
66.04
18
CF3COO
trifluoroacetate
C2F3O2
19
SCN
thiocyanate
SCN
20
CoBr4
tetrabromidocobaltate(ii)
CoBr4
21
FeCl4
tetrachloridoferrate(iii)
22
(C8H17)2PO2
bis- (2,4,4-trimethylpentyl) -phosphinate
TCB
DBP 26
27
cr
us
378.55
an M
dibutylphosphate
diethylphosphate
Ac
DEP
methanesulfonate
ce pt
25
58.08
197.66
289.41
O C8 H17
C8 H17
P
O
tetracyanoborate
24 CH3SO3
113.02
FeCl4
ed
23
ip t
16
SbF6
hexafluoroantimonate
TS
thiosalicylate
114.88 B(CN)4 95.1 CH3SO3 209.21
O C4 H9
O
P
O
C4H9
O
153.1
O C 2H 5 O P O C 2H 5 O
235.75 SbF6
28
153.18
HS O O
29
O
BOB
bis(oxalato)borate
O B O O O
O
122.85
O
O
31
C1MIM
1-methyl-3-methylimidazolium
97.14
N
N
13
Page 13 of 36
32
33
34
C2MIM
C4MIM
C6MIM
1-ethyl-3-methylimidazolium
N
N
N
N
111.15
C2H5
1-butyl-3-methylimidazolium
139.21
C4H9
1-hexyl-3-methylimidazolium
167.27
N NC H 6 13 C8MIM
1-octyl-3-methylimidazolium
195.33
N
N C10MIM
1-decyl-3-methylimidazolium
223.38
N
N C16MIM
1-hexadecyl-3-methylimidazolium
307.54
N
N
38
M4B-PY
C10H21
us
37
C8H17
cr
36
ip t
35
4-methyl-n-butylpyridinium
C16H33 150.24
42
43
44
45
46
HydEMIM
BMPYR
HMPYR
OMPYR
PPeMIM
PPeOIM
M
C6H13
C6H13
P
139.22 N
N C H 3 7
1-(2-hydroxyethyl)-3-methylimidazolium
127.16
N
N C H OH 2 4
1-butyl-1-methyl-pyrrolidinium
142.25 C4H9
N
1-hexyl-1-methyl-pyrrolidinium N
C6H13
1-octyl-1-methyl-pyrrolidinium N
198.37
N
1-propenyl-3-octylimidazolium
221.36
N
1-propenyl-3-decylimidazolium
249.41 C10H21
PPeDoIM
170.31
123.18 N
N
48
C8H17
1-propenyl-3-methylimidazolium
C8H17 PPeDeIM
483.86
C6H13
N 47
C14H29
1-propyl-2,3-dimethylimidazolium
ed
41
PDMIM
trihexyl(tetradecyl)-phosphonium
ce pt
40
THTD-P
Ac
39
an
N C4H9
N
1-propenyl-3-dodecylimidazolium
277.47 N C12H25
N
14
Page 14 of 36
49
PBAMIM
1-propyl boronicacid-3-methylimidazolium
141.00
(HO)2BC3H6 50
PBAOIM
N
N
1-propyl boronicacid-3-octylimidazolium
239.18 N
N
C8H17
(HO)2BC3H6
51
PBADeIM
1-propyl boronicacid-3-decylimidazolium
267.24
N
N
C10H21
(HO)2BC3H6
PBADoIM
1-propyl boronicacid-3-dodecylimidazolium
N
N
C12H25
(HO)2BC3H6
MAOOMIM
1-methacryloyloxyhexyl-1-methylimidazolium
251.39
N
N
(CH2)6O
cr
53
295.29
ip t
52
O
54
AOOMIM
1-acryloyloxypropyl-1-methylimidazolium
197.21
58
59
60
61
DMEIM
1,2-dimethyl-3- ethyl-imidazolium
C2PY
Me3BuN
P
C4H9
C4H9
80.11 NH+
128.22
N
N
C2H5 108.16
N+
C2H5
136.21 N+ C H 4 9
n-amylpyridinium
150.24 N+
triethylsulphonium
63
C6H13OCH2MIM
1-hexyloxymethyl-3-methyl-imidazolium
117.23 N+
C4H9
Et3S
119.25
197.30
N (C6H13OCH2)2IM
N
CH2OC6H13
1,3-dihexyloxymethylimidazolium
381.53
C6H13OH2C
(OC1)2IM
C5H11
trimethyl-butylammonium
Et3S
65
217.35
n-butylpyridinium
62
64
O
n-ethylpyridinium
C4PY
C5PY
an
pyridinium
M
PY
(CH2)3O
C4H9
ed
57
tributylmethylphosphonium
N
ce pt
56
TBMeP
Ac
55
us
N
N N CH OC H 2 6 13
1,3-dimethoxyimidazolium
129.14 N
N
OCH3
H3CO
15
Page 15 of 36
66
C2OC1MIM
1-(methylethylether)-3-methylimidazolium C2H5OH2C
67
C2OHMIM
N
N
1-ethanol-3-methylimidazolium
141.19
127.16 N
N
HOC2H4
68
C3CNMIM
1-(3-cyanopropyl)-3-methylimidazolium
N
NCC3H6 OMA
C8H17
trioctylmethylammonium
148.19
368.70
ip t
69
N
N
C8H17
C8H17
70
BMPY
1-butyl 4-methyl-pyridinium
150.23
P1,4,4,4
tri-iso-butylmethylphosphonium
CH(CH3) 2
us
71
cr
N C4H9
P
217.35
CH(CH3) 2
CH(CH3) 2
72
PMPIP
1-propyl-1-methylpiperidinium
an
73
1-(2-methoxyethyl)-1-methylpyrrolidinium
COC2mMOR
4-(2-methoxyethyl)-4-methylmorpholinium
COC2mPIP
1-(2-methoxyethyl)-1-methypiperidinium
N-C3OHPY
1-(3-hydroxypropyl)pyridinium
M
COC2mPYR 74
ed
75
77 N1,1,2,2OH 78
79
ethyl(2-hydroxyethyl)dimethyl-ammonium
N-octylisoquinolinium
Ac
C8iQuin
ce pt
76
C6iQuin
N-hexylisoquinolinium
BMPIP
1-butyl-1-methyl-piperidinium
N
128.23
C3H7
N
140.2 (CH2)2OCH3
160.23 H3CO(H2C) 2
N
O
158.26
N
(CH2)2OCH3
138.19
N (CH2 )3OH 118.2
C2H5
N
C2H4 OH
N
257.41 (CH2)7CH3
N
229.36 (CH2)5CH3
80
156.29 N
C4H9
16
Page 16 of 36
Table 2 Solubility parameters (δs) of ionic liquids used in Eq. 3. δs /MPa1/2
[C16MIM][BF4] [DMEIM][NTf2]
298.15 298.15
19.94 26.36
[Me3BuN][NTf2] [C6MIM][NTf2] [BMPY][NTf2] [THTDP][NTf2] [TBMeP][MeSO4] [P,1,4,4,4][TOS] [C8MIM][MDEGSO4] [C2MIM][DEP] [C4MIM][SCN] [PY][EOSO4] [C6MIM][TfO] [C2MIM][TCB] [C4PY][NTf2] [C5PY][NTf2] [HMPYR][NTf2]
298.15
Ac
[BMPY][TfO]
[C2MIM][NO3] [C4MIM][NO3] [C0C2mMOR][NTf2] [N1,1,2,2OH][DEP] [COC2MMOR][FAP] [N-C3OHPY][NTf2] [C4MIM]BOB [C6MIM]BOB
21.60 21.10 21.82 19.46 20.58 26.99 24.69 22.12 26.30 21.98 22.39 22.12 21.01 21.18 13.35
cr us
an
M ed
ce pt
[OMPYR][NTf2] [PMPIP][NTf2] [Me3BuN][BF4] [C2MIM][FAP] [C8MIM][Cl] [AOOMIM][Br] [C2MIM][TfO]
298.15 298.15 298.15 298.15 298.15 298.15 298.15 298.15 298.15 298.15 298.15 303.15 303.15 303.15
ip t
T/K
Ionic Liquid
303.15
14.31
308.15 308.15 313.15 313.15 313.15 313.15 308.15 323.15 303.15 328.15 323.15 328.15 328.15 328.15 328.15
21.55 20.14 20.10 27.46 27.97 24.53 23.04 25.24 26.68 22.03 28.96 19.68 23.13 21.31 21.57
17
Page 17 of 36
Table 3 The van der Waals volumes (rs ) of ionic liquids estimated according to literature49 used in Eq. 2. rs/ cm3mol-1
Ils
172.83 183.06 193.29 203.52
cr
ip t
[C2AOOMIM][Br] [C3AOOMIM][Br] [C4AOOMIM][Br] [C5AOOMIM][Br]
an ed
ce pt
73.24 86.91 97.14 107.37 117.60 127.83 20.43 34.10 44.33 54.56 64.79 75.02
Ac
[MPYR][SCN] [C1MPYR][SCN] [C2MPYR][SCN] [C3MPYR][SCN] [C4MPYR][SCN] [C5MPYR][SCN]
M
[MIM][SCN] [C1MIM][SCN] [C2MIM][SCN] [C3MIM][SCN] [C4MIM][SCN] [C5MIM][SCN]
85.41 99.08 109.31 119.54 129.77 140.00
us
[MIM][CH3SO3] [C1MIM][CH3SO3] [C2MIM][CH3SO3] [C3MIM][CH3SO3] [C4MIM][CH3SO3] [C5MIM][CH3SO3]
18
Page 18 of 36
Table 4 Estimated molar attraction constants of ionic functional group (IFG) by group contribution used
ip t
in Eq. 5.
FIFG MPa1/2cm3mol-1 6068.46 3100.65 3381.58 5378.46 5353.57 3882.65 4850.02 4273.49 4345.99 3905.39 4324.72 5629.20 4907.05 5379.25 4262.82 6074.24 1523.04 2789.11 4135.24 5249.28 5319.13 2724.19 6674.45 3654.73 2354.88 3947.19 3425.66 3651.77 3798.81 3850.76
us an M ed ce pt
Ac
[IM][Br] [IM][BF4] [IM][PF6] [IM][NTf2] [PY][NTf2] [IM][(CH3)2PO4] [IM][ESO4] [IM][MOSO4] [IM][MeSO4] [PYR][TfO] [IM][TfO] [IM][MDEGSO4] [IM][NTf2] [IM][NTf2] [S][NTf2] [IM][OSO4] [N][BF4] [PYR][NTf2] [N][NTf2] [P][NTf2] [PIP][NTf2] [P][MeSO4] [P][TOS] [IM][(C2F5)3PF3] [IM][NO3] [IM][TCB] [IM][SCN] [PY][SCN] [PYR][SCN] [IM][CH3SO3]
cr
ILs
19
Page 19 of 36
Table 5
Ionic Liquid
o-xylene
[MAOOMIM][Br]
m-xylene
o-xylene
[C8MIM][Cl]
p-xylene
ce pt
Ac
p-xylene
p-xylene [C2MIM][N(CN)2]
1.351
1.162
p-xylene m-xylene
1.257
0.740
20
0.860
21
1.066 0.938 0.885
22
1.038 0.963 0.795
1.173
19
an 0.807
1.173
o-xylene
19
0.929
0.853
1.130
Ref
1.077
1.239
o-xylene m-xylene
0.688
1.455
o-xylene
m-xylene
[HMIM][NO3]
1.732
ed
m-xylene
0.577
M
m-xylene
[C4MIM][NO3]
2.070
o-xylene
[AOOMIM][Br]
p-xylene
us
o-xylene
m-xylene 0.483
cr
experimental data of activity coefficients.
ip t
Selectivities S12∞ (Sij∞ =γis∞/γjs∞) of ionic liquids for xylene isomers at infinite dilution from
0.852
23
0.933 1.072
20
Page 20 of 36
m-Xylene p-Xylene [C4MIM][TOS]
p-xylene
1.308
1.005
1.000
0.855
0.860
1.170 1.162
0.994 0.901
1.110 1.062
m-xylene
[N1,1,2,2OH][DEP]
o-xylene
ce pt
m-xylene p-xylene
1.191
p-xylene
p-xylene o-xylene
1.072
0.839
28
1.070 0.952
29
1.048 0.954 0.872
1.147 1.096
27
0.935
1.102
o-xylene m-xylene
0.898
0.908
1.051
0.950
0.933
1.113
o-xylene
m-xylene
Ac
1.052
ed
p-xylene
1.128
26
0.957 0.886
o-xylene
0.942 1.045
M
[C2MIM][DEP]
25
us
p-xylene
24
1.006
o-xylene m-xylene
[C2MIM][TCB]
0.765 0.995
an
[P1,4,4,4][TOS]
[BMPYR][TCB]
0.769 1.000
o-xylene m-xylene
[C4MIM][DBP]
1.000 1.301
ip t
o-Xylene
cr
[C2MIM][CH3SO3]
0.913
30
1.047 0.955 0.851
0.899
31
21
Page 21 of 36
1.174
p-xylene
1.112
p-xylene
0.899
1.097
0.986 0.853
p-Xylene
1.140
o-xylene
ed
[C4MIM][SCN]
m-xylene
ce pt
p-xylene
Ac
1.194
p-xylene
p-xylene
0.986
0.838
34
0.940 0.835
35
1.055 0.948 0.791
1.265 1.208
33
1.064
1.263
o-xylene m-xylene
0.787
0.792
1.197
0.877
1.014
1.271
o-xylene
m-xylene
0.978 0.890
1.124
33
1.022
1.146
o-Xylene m-Xylene
cr
1.172
M
[C6MIM][BOB]
0.872
us
p-xylene
32
1.015
o-xylene m-xylene
0.912
1.113
an
[C4MIM][BOB]
[BMPYR][SCN]
0.947
o-xylene m-xylene
[BMPY][SCN]
1.056
ip t
[DMIM][TCB]
m-xylene
0.828
35
1.047 0.956
22
Page 22 of 36
ip t cr us an M
Table 6
ed
Predicted solubility parameters (δs) of ionic liquids [CnAOOMIM][Br], [CnMIM][CH3SO3], [CnMIM][SCN] and [CnMPYR][SCN] used in Eq. 3.
ce pt
ILs
δs /MPa1/2 31.04 30.11 29.23 28.38
[MIM][CH3SO3] [C1MIM][CH3SO3] [C3MIM][CH3SO3] [C4MIM][CH3SO3] [C5MIM][CH3SO3]
31.00 29.57 27.52 26.58 25.67
[MIM][SCN] [C1MIM][SCN] [C2MIM][SCN] [C3MIM][SCN] [C5MIM][SCN]
31.54 29.59 28.16 26.86 24.55
Ac
[C2AOOMIM][Br] [C3AOOMIM][Br] [C4AOOMIM][Br] [C5AOOMIM][Br]
23
Page 23 of 36
30.24 28.39 27.05 25.82 23.59
M
an
us
cr
ip t
[MPYR][SCN] [C1MPYR][SCN] [C2MPYR][SCN] [C3MPYR][SCN] [C5MPYR][SCN]
Table 7
ILs
ce pt
[AOOMIM][Br]
ed
Predicted selectivites S12∞ of m/o-xylene at infinite dilution in ionic liquids. Selectivity of m/o-xylene in ILs 1.732
2.070
[C2AOOMIM][Br]
1.774
[C3AOOMIM][Br]
1.686
[C4AOOMIM][Br]
1.608
[C5AOOMIM][Br]
1.539
Ac
[MAOOMIM][Br]*
*from experimental data
24
Page 24 of 36
ip t cr us an M ed ce pt
Table 8
Predicted selectivites (S12∞) of p/o-xylene at infinite dilution in ionic liquids. Selectivity of p/o-xylene in ILs
Ac
ILs
[MIM][CH3SO3] [C1MIM][CH3SO3] [C2MIM][CH3SO3]* [C3MIM][CH3SO3] [C4MIM][CH3SO3] [C5MIM][CH3SO3]
2.386 2.133 1.308 1.828 1.706 1.600
[MIM][SCN] [C1MIM][SCN] [C2MIM][SCN] [C3MIM][SCN] [C4MIM][SCN]* [C5MIM][SCN]
2.386 2.133 1.828 1.706 1.194 1.600 25
Page 25 of 36
[MPYR][SCN] [C1MPYR][SCN] [C2MPYR][SCN] [C3MPYR][SCN] [C4MPYR][SCN]* [C5MPYR][SCN]
2.246 1.949 1.766 1.617 1.208 1.390
Table 9
ce pt
ed
M
an
us
cr
ip t
*from experimental data
Selectivity (S12∞) of m/o, p/o-xylene in [MAOOMIM]-type ILs: predicted results for the effect of anion.
Ac
Ionic Liquid
[MAOOMIM][NTf2] 363.15K [MAOOMIM][SCN] 363.15K [MAOOMIM][NO3] 363.15K
[MAOOMIM][MDEGSO4]
S12∞
o-xylene o-xylene m-xylene p-xylene o-xylene m-xylene p-xylene o-xylene m-xylene p-xylene o-xylene
1.113 1.203 1.090 1.163 0.993 0.994
m-xylene 0.898 1.081 0.917 1.067 1.007 1.001 0.895
p-xylene 0.831 0.925 0.860 0.937 1.006 0.999 0.826 26
Page 26 of 36
m-xylene p-xylene o-xylene m-xylene p-xylene o-xylene m-xylene p-xylene o-xylene m-xylene p-xylene o-xylene m-xylene p-xylene
[MAOOMIM][MeSO4] 363.15K [MAOOMIM][OSO4] 333.15K
1.084 0.726
1.377 1.690
1.227 0.841
1.189 1.339
1.126 0.974
1.027 1.054 1.110 1.198
0.592 0.815 0.747 0.888 0.949 0.975
1.026 0.901
0.834 0.926
1.080
ed
M
an
us
[MAOOMIM][(CH3)2PO4] 333.15K
0.923
ip t
[MAOOMIM][TCB] 333.15K
1.118 1.211
cr
363.15K
Table A1
ce pt
Experimental data and literatures used in this work to derive the solubility parameters of ionic liquids with their identification defined in Table 1. Ref.
33-19 70-19 42-19 32-24 73-6 76-6 74-15 75-6 74-6 78-6 42-15 42-23 36-23
34 35 35 24 37 38 39 40 41 42 30 32 25
Ac
ID
27
Page 27 of 36
ip t
43 23 22 29 28 44 45 46 47 48 27 27 33 33
Ac
ce pt
ed
M
an
us
cr
33-12 75-15 32-17 34-16 33-25 77-26 39-6 33-27 69-28 39-3 36-3 32-26 33-29 34-29
Figure Captions 28
Page 28 of 36
Fig. 1. Residual function Y versus solute solubility parameters δi of ionic liquids Fig. 2. The classification of the structure of an ionic liquid.
Ac
ce pt
ed
M
an
us
cr
ip t
Fig. 3. Selectivity of m(1)/o(2) and p(1)/o(2) xylene in ionic liquids [MAOOCnMIM][TCB].
29
Page 29 of 36
cyclohexane methylcyclohexane 1-hexene cyclohexene benzene toluene acetone methanol ethanol 1-propanol Isopropyl alcohol
Yi
0.25 0.20 0.15
A
cr
0.30
0.10 0.05 18
0.30
1-hexene 1-hexyne benzene toluene ethylbenzene
Yi
0.20
0.15
ce pt
0.10
22
i
24
26
0.05
Ac
14
0.30 0.28 0.26 0.24
16
28
18
20
30
B
thiophene pyridine methanol ethanol tertbutyl alcohol THF 1,4-dioxane acetone acetonitrile
ed
0.25
20
an
16
M
14
us
0.35
ip t
0.40
22
24
26
28
30
i
R-methylstyrene thiophene pyridine methanol ethanol 1-propanol
C
Yi
0.22
2-butanol tertbutyl alcohol methyl propanoate methyl butanoate 1,4-dioxane acetone acetonitrile styrene
0.20 0.18 0.16 0.14 0.12 0.10 16
18
20
22
24
26
28
30
i
30
Page 30 of 36
0.35
0.25
methanol ethanol 1-propanol 1-butanol thiophene THF 1,4-dioxane acetone 2-pentanone
Yi
0.20
0.15
0.10
0.05 14
16
18
20
22
24
26
28
30
us
cr
i
ip t
D
cycloheptane 1-hexene cyclohexene 1-heptyne benzene toluene ethylbenzene
0.30
n-hexane cyclohexane methylcyclohexane 1-hexene 1-hexyne benzene toluene ethylbenzene methanol ethanol 1-propanol
0.25
Yi
0.20
M
0.15
E
an
0.30
0.10
0.05 14
16
18
20
22
24
26
28
30
ce pt
ed
i
n-hexane cyclohexane methylcyclohexane 1-hexene 1-heptyne benzene toluene ethylbenzene methanol ethanol 1-propanol
0.30
0.25
Yi
0.20
Ac
0.15
F
0.10
0.05 14
16
18
20
22
24
26
28
30
i
31
Page 31 of 36
G
n-pentane n-decane cyclopentane 1-pentene 1-octene 1-pentyne benzene p-xylene methanol THF thiophene
0.35
0.30
0.25
Yi
0.20
0.15
0.10
ip t
0.05
0.00 14
16
18
20
22
24
26
28
30
H
0.20
an
n-pentane n-octane cyclopentane cycloheptane 1-hexene 1-heptyne benzene methanol
0.25
Yi
us
0.35
0.30
0.15
18
20
22
i
24
26
28
n-pentane n-hexane n-heptane n-nonane n-decane cyclohexane methylcyclohexane 2,2,4-trimethylpentane cyclohexene styrene benzene toluene
30
I
ce pt
0.12
16
ed
14
M
0.10
0.05
cr
i
Yi
0.10
0.08
0.06
Ac
0.04
14
15
16
i
17
18
19
20
32
Page 32 of 36
n-hexane n-heptane n-decane cyclohexane cycloheptane 1-hexene 1-hexyne benzene toluene ethylbenzene methanol ethanol thiophene THF
0.30
0.25
Yi
0.20
0.15
0.10
J
0.05
0.00 14
16
18
20
22
24
26
28
30
cr
i
ip t
0.35
us
Fig. 1. Residual function Y versus solute solubility parameters δi of ionic liquids. A: [N1,1,2,2OH][DEP]; B: [COC2mMOR][NTf2]; C: [COC2MMOR][FAP]; D: [N-C3OHPY][NTf2]; E: [C4MIM][BOB]; F: [C6MIM][BOB]; G: [P,1,4,4,4][TOS]; H:
Ac
ce pt
ed
M
an
[C8MIM][MDEGSO4]; I: [C2MIM][DEP]; J: [C4MIM][SCN]
33
Page 33 of 36
IF
N
R2
BF4-
ip t
N
cr
R1
Ac
ce pt
ed
M
an
us
Fig. 2. The classification of the structure of an ionic liquid.
34
Page 34 of 36
2.6
m/0 p/o
2.5 2.4
ip t
2.3 2.2 2.1
S12
2.0 1.9 1.8
cr
1.7 1.6 1.5
1.3 1
2
3
4
n
5
us
1.4 6
Ac
ce pt
ed
M
an
Fig. 3. Selectivity of m(1)/o(2) and p(1)/o(2) xylene in ionic liquids [MAOOCnMIM][TCB].
35
Page 35 of 36
1. We collect a database on activity coefficients of organic solutes at infinite dilution in ionic liquids.
ip t
2. We model activity coefficients to correlate the solubility parameter of ionic liquids.
Ac ce p
te
d
M
an
us
cr
3. Higher selectivity is achieved when using ionic liquids to separate xylene isomers.
Page 36 of 36
S0378-3812(14)00236-2 http://dx.doi.org/doi:10.1016/j.fluid.2014.04.016 FLUID 10077
To appear in:
Fluid Phase Equilibria
Received date: Revised date: Accepted date:
12-11-2013 12-4-2014 16-4-2014
Please cite this article as: L.-S. Wang, X.-Y. Wang, Selectivities at infinite dilution of xylene isomers in ionic liquids, Fluid Phase Equilibria (2014), http://dx.doi.org/10.1016/j.fluid.2014.04.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
*Revised Manuscript
Selectivities at infinite dilution of xylene isomers in ionic liquids
Li-Sheng Wang,* Xue-Yuan Wang School of Chemical Engineering & the Environment, Beijing Institute of Technology, Beijing 100081, China
ip t
Abstract: A database on activity coefficients of organic solutes at infinite dilution in ILs was collected from literature sources. The activity coefficient model with the combinatorial term
cr
represented by the Kikic et al. was used as a modification to Flory’s equation. The activity coefficients had been used to correlate the solubility parameter of ionic liquids. The obtained
us
solubility parameters of ionic liquids had been further correlated based on a concept of the group contribution method. Through the analysis of the database and the prediction results of
an
selectivities at infinite dilution of xylene isomers, we showed that higher selectivity can be
M
achieved by using ILs as working solvents for separation of xylene isomer mixtures.
ce pt
1. Introduction
ed
Keywords: activity coefficient, ionic liquid, selectivity, xylene isomers.
In the petrochemical industry, the separation of xylene isomers is of significant importance for production of chemicals such as terephthalic, phthalic, and isophthalic acids. Because of the close boiling points of these isomers, it is impractical to separate them by distillation. Processes
Ac
based on zeolitic adsorption have been developed. Room temperature ionic liquids (ILs) can be designed to special task and have been applied as replacement for conventional toxic, flammable and volatile organic solvents in the development of new separation process.1-4 The common organic solvents are remarkable similar in a relatively narrow liquidus region. They are all relatively volatile and easily becoming emissions into the atmosphere at the process conditions. The emissions of VOC have been linked to global climate change and human illness. It is the aim of chemical engineers to reduce the emissions of VOCs, and to find a new class of “green” solvents. In the direction of developing an efficient and environmentally benign chemical process, many scientists have concentrated their 1
Page 1 of 36
research activities using ILs as green solvents, because not only ILs have essentially no vapor pressure, and they do not evaporate, and so they cannot lead to fugitive emissions, but also they act much like good organic solvents, dissolving both polar and nonpolar species. An important example is the innovative application of ILs as working solvents in supported liquid membrane (SILM) for the separation gas mixtures conducted by vapor pervaporization.5 In the SILM
ip t
technology, an ionic liquid can be impregnated in the pore in polymer support or hollow fiber module, the capability of ILs to separate solutes mixtures depends on the selectivity of the
cr
solutes in ILs.
us
The major driving force for selective separation of xylene isomer gas mixture by SILM is the solubility difference between these isomers in ionic liquid. Selectivity (Sij) can be calculated from the ratio of solubilities of the two solutes in one solvent. We have experimental
an
demonstrated that even though these xylene isomers have close boiling points, their solubilities in an ionic liquid can be evidently different.6 A separation factor, selectivity of the solutes at
M
infinite dilution in an ionic liquid, can be calculated from the ratio of activity coefficients at infinite dilution (Sij∞, defined according to the equation: Sij∞ =γis∞/γjs∞, where subscript s denotes
ed
solvent).
Activity coefficients at infinite dilution of different organic solutes in ILs can be determined
ce pt
with an ionic liquid as the stationary phase using gas-liquid chromatography.7,8 In this work, we continue our research to establish a database of activity coefficient at infinite dilution of organic solutes in ILs from the open literatures.9 It is clear to find out from this database that how the
Ac
change of cations and anions affects the γi∞ and Sij∞ values. Based on the database, an activity coefficient model for regular solutions has been applied and developed. The objective of this paper is to predict the solubility parameter for the activity coefficient model for the ILs and to predict the selectivities when the activity coefficient data for xylene isomers/other solutes are not available. Through the analysis of the database and the predicted Sij∞ values and taking the advantage of ionic liquids as designable solvents, we will discuss the possibility for the further application of ILs in SILM technology for xylene isomer separation.
2
Page 2 of 36
2. Classification of ILs and database
To correlate the activity coefficients with a wide range representation of organic solutes and ILs, we need to build a database. Cations and anions were separated and then numbered by an ID code respectively. In our previously paper we published a database of activity coefficients of
ip t
organic solutes at infinite dilution in ILs from literature sources.9 In this work, the database have
cr
been extended to include most of the recently published data of ionic liquids (as listed in Appendix) and from which 50 kinds of cations and 29 kinds of anions can be extracted and they
us
were listed in Table 1, as well as their abbreviations, chemical names, formulas, and molecular
3.1. Correlation with Flory’s equation
M
3. Correlation of activity coefficients
an
weights.
ed
The activity coefficients at infinite dilution of different solutes in a given solvent can be used to estimate solubility parameters of the solvents when the solubility parameters of these
ce pt
solutes are known. This method provides a basis for the correlation of the activity coefficients at infinite dilution of solutes in ILs. The activity coefficient model can be represented by a two-term equation in which the combinatorial term can be represented by the Kikic et al. 10
Ac
modification to Flory’s equation, and the residual term is given by the regular solution theory:
ln i ln icomb ln ires
ln icomb ln(ri / rs )2/ 3 1 (ri / rs )2/ 3 ln ires (vi / RT )( i s )2
(1) (2) (3)
Where ri and rs are the van der Waals volumes of solute and solvent, respectively; vi is the solute molar volume; δi and δs are solubility parameters of solute and solvent, respectively. The solubility parameter of ILs can be correlated from the experimental γ∞ data. A residual function Y can be rearranged from Eq. 3 according to literature11
3
Page 3 of 36
Yi
ln ires i 2 2 s 2 i s vi RT RT RT
(4)
This equation shows that there is a linear relation between Yi and the solute solubility parameter δi for a given solvent and temperature T. The value of the solvent (i.e., ionic liquid) solubility parameter δs can be obtained from the slope of this line. The values of experimental γ∞
ip t
were taken from the database. The values of ln γ∞comb were calculated by Eq. 2. According to Eq.
cr
1, with the ln i known (by experimental data), the value of ln ires can be calculated, and finally the values of Yi for different solutes in an ionic liquid were calculated according to Eq. 4.
us
Information on vi, δi, and ri were obtained from the literature.12 The van der Waals volumes of ILs were calculated by group contribution method.13 The dependence between Yi and δi (δi =
an
δsolute) can thus be plotted for different solutes with a specified ionic liquid and high accuracy of the linear correlation which was displayed by Fig. 1. The solubility parameters (δs) of 26 ionic
M
liquids calculated by this procedure were published in our previously paper.9 More solubility parameters of 33 ionic liquids obtained in this work were listed in Table 2 (the data sources for the correlation were listed in Table A1 in Appendix). Some of the results of van der Waals
ed
volumes of ionic liquids were listed in Table 3.
3.2. Group contribution of the solubility parameters
ce pt
From the idea that the total cohesive energy of a molecule is the sum of the individual cohesive energies (molar attraction constants) associated with each constituent group on the molecule, the solubility parameters of ionic liquids can be determined based on a group
Ac
contribution method.14 This method also assumes that molar attraction constants are considered constant regardless of the surrounding chemical environment. The following expression can be used to calculate the solubility parameter δs of an ionic liquid:
s
F j
vs
j
(5)
In Eq. 5, subscript s represents the solvent, j represents each substitute chemical group, F is the molar attraction constant of chemical group j, and vs is the molar volume of the solvent. With the solubility parameters of the ionic liquid known, F can be obtained for the sub-group j. The classification of the structure of an ionic liquid is shown with 1-R1-3-R2-imidazolium 4
Page 4 of 36
tetrafluoroborate as example, as shown in Fig. 2, in which the cationic imidazolium ring and tetrafluoroborate cation are defined together as one neutral group (ionic functional group, IFG), while the substitute R1 and R2 on the ring can be separated into methyl, methylene, etc. Molar attraction constants of several organic functional groups relevant to this study were taken from literature.15 Values for the IFG of ILs classified according to Fig. 2 were estimated from the
ip t
values of solubility parameter using group contribution method, and the results of the FIFG values
cr
were summarized in Table 4.
us
4. Selectivities of xylene isomers in ILs: results and discussions
an
4.1. The results of analysis for the selectivity from the experimental data
In petrochemical industry, the development of production technology of terephthalic,
M
phthalic, and isophthalic acids are mainly limited by the separation technology of xylene isomers. Up to now, the researches for the separation of para-xylene from its bulkier meta- and orthoisomers by zeolite membrances via vapor permeation were successful,16,17 and satisfactory
ed
permselectivities were obtained. However, from a point of view of petrochemical production, the results for the separation of meta-xylene from its para- and ortho- isomer mixtures were not
ce pt
successful by using the same technique because the limit by the kinetic diameter.18 In a SILM apparatus, the separation factor depends on the difference in solubilities of the isomers in ionic liquid, but not on the boiling points. Therefore, the isomer mixture can be
Ac
theoretical separated by using SILM technology. Using the database and the group contribution activity coefficient model developed in this work, we can analyze the structure-property relationship for ILs, especially for the effect of molecular structure on the selectivity of the xylene isomers in the ionic liquid. The results of analysis for the selectivity from the experimental data19-35 of activity coefficients at infinite dilution of xylene isomers in ionic liquids calculated in this work were o
listed in Table 5. Because the kinetic diameters of both meta- and ortho- xylene equal to 6.8 A , it seems not possible to separate them with a zeolite membrance. From Table 5, it can be seen that the highest selectivity is obtained by using [MAOOMIM]Br to separate meta-xylene (1) and 5
Page 5 of 36
ortho-xylene (2), the result is S12 =2.070. Compared with the results of [C8MIM]Cl in Table 5, the introduction of an ester group improves selectivity greatly. 4.2. The prediction results: effect of alkyl chain of cations of ILs on the selectivity The γi∞ value and selectivity can also be calculated using the group contribution activity
ip t
coefficient model correlated in this work. To explore the effect of carbon number in alkyl chain of cations on the selectivity, we calculated the solubility parameters, activity coefficients based
cr
on the group contribution activity coefficient model, and the results of solubility parameters for ionic liquids ([CnAOOMIM][Br], [CnMIM][CH3SO3], [CnMIM][SCN] and [CnMPYR][SCN])
us
were listed in Table 6.
Table 7 lists the prediction results at 313.15 K for the selectivity of [RAOOMIM][Br] for
an
meta- and ortho- xylene, in which the R represents alkyl chain. With the increase of alkyl chain length, the selectivity decreases.
M
Table 8 lists the prediction results of selectivity of para-xylene /ortho-xylene in ionic liquids. From Table 8 it can be seen that the selectivity of para-xylene /ortho-xylene in different
ed
type of ionic liquids can be increased with the reduction of carbon number in alkyl chain (the Cn groups) of cations.
ce pt
Fig. 3 shows the selectivity of the meta-xylene (1)/ortho-xylene (2), and para-xylene(1) /ortho-xylene (2) in ionic liquids [MAOOCnMIM][TCB]. From Fig. 3 it can be seen that the selectivity of meta-xylene/ortho-xylene and para-xylene/ortho-xylene in ionic liquids [MAOCnMIM] [TCB] can be increased with the reduction of carbon number in alkyl chain (the
Ac
Cn groups) of cations. Satisfactory results of [MAOOC1MIM][TCB] obtained at 333.15 K were 1.802 and 2.548, respectively. From the results of Tables 6 – 8 and Fig.3, it can be summarized that with the increase of alkyl chain length of cation of ionic liquids, their selectivity for xylene isomers will decrease. It is reasonable because the homogeneous of two different ionic liquids will be increased with the increase of alkyl chain of cations. 4.3. Prediction results: effect of anions of ILs on the selectivity Table 9 lists the predicted selectivities S12∞ of aromatic (1)/aromatic (2) hydrocarbon at infinite
dilution
in
the
ionic
liquids
when
the
cation
[MAOOMIM] 6
Page 6 of 36
(1-methacryloyloxyhexyl-1-methylimidazolium) combines with eight different anions, i.e., [NTf2], [SCN], [NO3], [MDEGSO4], [TCB], [MeSO4], [OSO4], [(CH3)2PO4].
From Table 9, it can be seen that the selectivity in ionic liquids can be changed by the choice of anions. In addition, it can be seen that the highest selectivity ( S12 =1.377) was obtained
ip t
by using [TCB], the result was not better than the result ( S12 =2.070) by using [MAOOMIM]Br (as listed in Table 5) to separate meta-xylene (1) and ortho-xylene (2). Pal et al. demonstrated the
cr
blue-shifting measurement from FTIR for the cation [C4mim] with different anions in ethylene glycol.36 They indicated that very weaker interactions between [C4mim]+ and Br ,which were
us
even weaker than interactions between [C8OSO3] and [C4mim]+. The magnitude of interaction for these ionic liquids with xylenes is more for [TCB] as compared to Br anion,
an
it implies that weaker interaction between ionic liquid and xylene isomers will be more sensitive for the selectivity.
M
Satisfactory selectivities were obtained for [MAOOMIM][TCB], the results with comparison for different mixtures were: for meta-xylene (1) /ortho-xylene (2), S12 =1.377; for
ed
para-xylene (1)/ortho-xylene (2), S12 =1.690) and for para-xylene (1)/ meta-xylene (2),
ce pt
S12 =1.227. The above results showed that it is possible to use only one ionic liquid as working solvent to separate these three isomers.
4.4. Uncertainty of the prediction results
Equation 4 provides a way to calculate the solubility parameter of an ionic liquid from the
Ac
slope of the equation based on the activity coefficient data at infinite dilution. The solubility parameter can also be computed from the intercept of
Eq. 4. In our previously
paper (literature: Feng et al.,21 see Table 5 of Feng el al.), we compared the solubility parameter
of an ionic liquid when values of were correlated from the slope, or from the intercept. We calculated the values of at different temperatures, the results indicated that would approach a constant in the range of temperature studied. The average value of at different temperatures was more close to the results from slope, than from the intercept. To correlate the solubility parameters, the average uncertainty for the activity coefficients based on the linear relation of Eq. 4 were less than 5%. The results calculated from the group 7
Page 7 of 36
contribution (Eq. 5) for the solubility parameter were compared with the values directly from the slope. The uncertainty is within 2%. Moreover, the prediction results of selectivities based the obtained solubility parameters of this work and the activity coefficient model (Eq. 1) were compared with the results of selectivity data directly derived from the experimental data, and the
ip t
results were satisfactory. Average deviations were less than 5%.
cr
5. Conclusion
us
The activity coefficients at infinite dilution of xylene in ionic liquids can be used to study their selectivity. The establishment of the database will promote the application of ionic liquids
an
in the design of separation process. In this work, we established a database and found that ILs showed good selectivity for these separation problems. The activity coefficients can be
M
represented by the regular solution theory. In this paper, the activity coefficients at infinite dilution data of different organic solutes in a given solvent have been used to estimate the solubility parameter of ionic liquids. The solubility parameters of ionic liquids have been
ed
correlated based on a concept of group contribution. This paper shows that based on the designable nature of ILs, there is a significant potential for exploiting how the variation of
ce pt
substitute, cation and anion influences the solubility of the xylene isomers in ILs. A traditional measurement method for the activity coefficient of solutes at infinite dilutions with an ionic liquid as the stationary phase using GLC and a classical thermodynamic model can be used to
Ac
analyze this possibility. By a combination of ILs with supported liquid membrane technology, the restriction from thermodynamic and dynamic diameter can be eliminated. The effectiveness of SILM process relies on the permeabilities of the solutes in the liquid membrane as well. Most probably, there are some differences in diffusivities between different xylene isomers in an ionic liquid. In this case, the selectivity of ionic liquid for the isomers will be strengthened. Further work should be done in this area, to measure the molecular diffusion and viscosity of the xylene isomers with ionic liquids. The results of this paper provide a basis for the selection of ionic liquids towards this purpose. *To whom correspondence should be addressed. E-mail: [email protected] 8
Page 8 of 36
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ip t
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[4] J.F. Brennecke, E.J. Maginn, AIChE J. 47 (2001) 2384-2389.
cr
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M
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ed
[10] I. Kikic, P. Alessi, P. Rasmussen, A. Fredenslund, Can. J. Chem. Eng., 58 (1980) 253-258.
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ce pt
[11] G.M. Foco, S.B. Bottini, N. Quezada, J.C. Fuente, C.J. Peters, J. Chem. Eng. Data, 51 (2006)
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Ac
[14] T.K. Carlisle, J.E. Bara, R.D. Noble, C.J. Gabriel, D.L. Gin, Ind. Eng. Chem. Res., 47 (2008) 7005-7012.
[15] J. Brandrup, E.H. Immergut, E.A.Grulke, Polymer handbook, 4th ed., Wiley, New York, 1999. [16] G. Xomeritakis, Z. Lai, M. Tsapatsis, Ind. Eng. Chem. Res., 40 (2001) 544-552. [17] T.Y.Yan, Ind. Eng. Chem. Res., 28 (1989) 572-576. o
o
[18] Kinetic diameter para-xylene = 5.8 A ; kinetic diameter meta- and ortho- xylene = 6.8 A . [19] F. Mutelet, J.N. Jaubert, M. Rogalski, J. Phys. Chem. B., 112 (2008) 3773-3785. 9
Page 9 of 36
[20] F. Mutelet, V. Butet, J. N. Jaubert, Ind. Eng. Chem. Res., 44 (2005) 4120-4127. [21] Y.X. Feng, L.S. Wang, Y. Li, J. Chem. Eng. Data, 56 (2011) 2730-2736. [22] K. Jiang, L.S. Wang, X.X. Wang, Ind. Eng. Chem. Res., 51 (2012) 12479-12487. [23] L.N. Ma, W.R Ji, J.B. Ji, J. Chem. Eng. Chin. Univ., 22 (2008) 547-552. [24] U. Domanska, M. Krolikowski, J. Chem.Thermodyn., 54 (2012) 20-27.
ip t
[25] U. Domanska, , M. Krolikowski, J. Chem. Eng. Data, 55 (2010) 4817-4822.
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cr
[26] U. Domanska, K. Paduszynski, J. Chem. Thermodyn., 42 (2010) 707-711.
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us
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M
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ce pt
[35] U. Domanska, M. Krolikowska, J. Phys. Chem. B., 114 (2010) 8460-8466. [36] A. Pal, B. Kumar, T.S. Kang, Fluid Phase Equilibr., 358(2013) 241-249. [37] A. Marciniak, M. Wlazlo, J. Chem. Thermodyn, 54 (2012) 90-96. [38] A. Marciniak, J. Chem. Thermodyn, 43 (2011) 1446-1452.
Ac
[39] M. Wlazlo, A. Marciniak, J. Chem.Thermodyn, 54 (2012) 366-372 . [40] A. Marciniak, M. Wlazlo, J. Chem.Thermodyn, 49 (2012) 137-145. [41] U. Domanska, M. Zawadzki, M. Krolikowska, J. Chem. Thermodyn, 43 (2011) 499-504. [42] U. Domanska, E.V. Lukoshko, M. Krolikowski, Chem. Eng. J., 183 ( 2012) 261-270. [43] A. Marciniak, M. Wlazlo, J. Chem. Thermodyn, 57 (2012) 97-202. [44] K. Tumba, T.M. Letcher, J. Chem. Thermodyn, 49 (2012) 46-53. [45] E. Olivier, T.M. Letcher, P. Naidoo, J. Chem. Thermodyn, 43 (2011) 829-833. [46] P. Reddy, N.V. Gwala, N. Deenadayalu, J. Chem. Thermodyn, 43 (2011) 754-758. [47] K. Tumba, P. Reddy, P. Naidoo, J. Chem. Thermodyn, 43 (2011) 670-676. 10
Page 10 of 36
[48] Y. Li, L.S. Wang, M.Y. Li, J. Chem. Eng. Data, 56 (2011) 1704-1708. [49] A. Bondi, Physical Properties of Molecular Crystals, Liquids and Glasses. New York: Wiley, 1968.
Ac
ce pt
ed
M
an
us
cr
ip t
Appendix Table A1
11
Page 11 of 36
Table 1 Cations and anions of the ionic liquids included in the database. ID
Abbreviation
Name
M/g·mol −1
Formula
ip t
Anions Cl
chloride
Cl
2
Br
bromide
Br
3
BF4
tetrafluoroborate
BF4
86.80
4
PF6
hexafluorophosphate
PF6
144.96
5
TfO
trifluoromethanesulfonate
CF3SO3
149.07
6
NTf2
bis(trifluoromethylsulfonyl)imide
8
ESO4
9
OSO4
M0SO4
11
E0SO4
12
TOS
M
an
us
79.90
O F3C S O
280.16
O
N S CF3 O
CH3SO4
111.10
ethylsulfate
C2H5SO4
125.12
octylsulfate
C8H17SO4
209.28
methoxyethylsulfate
Ac
10
methylsulfate
ed
MeSO4
ce pt
7
35.45
cr
1
CH3O C2H5SO4
ethoxyethylsulfate
156.16
170.16 C2H5O C2H5SO4
tosylate
171.20 SO3H
13
MDEGSO4
diethyleneglycolmonomethylethersulfate
O O
O SO3
199.20
12
Page 12 of 36
14
(CH3)2PO4
dimethylphosphate
125.04 O H 3C O P O CH3 O
15
FAP
tris(pentafluoroethyl) trifluorophosphate
F
F C2F5
445.01 C2F 5
P
F
NO3
nitrate
NO3
62.00
17
N(CN)2
dicyanamide
C2N3
66.04
18
CF3COO
trifluoroacetate
C2F3O2
19
SCN
thiocyanate
SCN
20
CoBr4
tetrabromidocobaltate(ii)
CoBr4
21
FeCl4
tetrachloridoferrate(iii)
22
(C8H17)2PO2
bis- (2,4,4-trimethylpentyl) -phosphinate
TCB
DBP 26
27
cr
us
378.55
an M
dibutylphosphate
diethylphosphate
Ac
DEP
methanesulfonate
ce pt
25
58.08
197.66
289.41
O C8 H17
C8 H17
P
O
tetracyanoborate
24 CH3SO3
113.02
FeCl4
ed
23
ip t
16
SbF6
hexafluoroantimonate
TS
thiosalicylate
114.88 B(CN)4 95.1 CH3SO3 209.21
O C4 H9
O
P
O
C4H9
O
153.1
O C 2H 5 O P O C 2H 5 O
235.75 SbF6
28
153.18
HS O O
29
O
BOB
bis(oxalato)borate
O B O O O
O
122.85
O
O
31
C1MIM
1-methyl-3-methylimidazolium
97.14
N
N
13
Page 13 of 36
32
33
34
C2MIM
C4MIM
C6MIM
1-ethyl-3-methylimidazolium
N
N
N
N
111.15
C2H5
1-butyl-3-methylimidazolium
139.21
C4H9
1-hexyl-3-methylimidazolium
167.27
N NC H 6 13 C8MIM
1-octyl-3-methylimidazolium
195.33
N
N C10MIM
1-decyl-3-methylimidazolium
223.38
N
N C16MIM
1-hexadecyl-3-methylimidazolium
307.54
N
N
38
M4B-PY
C10H21
us
37
C8H17
cr
36
ip t
35
4-methyl-n-butylpyridinium
C16H33 150.24
42
43
44
45
46
HydEMIM
BMPYR
HMPYR
OMPYR
PPeMIM
PPeOIM
M
C6H13
C6H13
P
139.22 N
N C H 3 7
1-(2-hydroxyethyl)-3-methylimidazolium
127.16
N
N C H OH 2 4
1-butyl-1-methyl-pyrrolidinium
142.25 C4H9
N
1-hexyl-1-methyl-pyrrolidinium N
C6H13
1-octyl-1-methyl-pyrrolidinium N
198.37
N
1-propenyl-3-octylimidazolium
221.36
N
1-propenyl-3-decylimidazolium
249.41 C10H21
PPeDoIM
170.31
123.18 N
N
48
C8H17
1-propenyl-3-methylimidazolium
C8H17 PPeDeIM
483.86
C6H13
N 47
C14H29
1-propyl-2,3-dimethylimidazolium
ed
41
PDMIM
trihexyl(tetradecyl)-phosphonium
ce pt
40
THTD-P
Ac
39
an
N C4H9
N
1-propenyl-3-dodecylimidazolium
277.47 N C12H25
N
14
Page 14 of 36
49
PBAMIM
1-propyl boronicacid-3-methylimidazolium
141.00
(HO)2BC3H6 50
PBAOIM
N
N
1-propyl boronicacid-3-octylimidazolium
239.18 N
N
C8H17
(HO)2BC3H6
51
PBADeIM
1-propyl boronicacid-3-decylimidazolium
267.24
N
N
C10H21
(HO)2BC3H6
PBADoIM
1-propyl boronicacid-3-dodecylimidazolium
N
N
C12H25
(HO)2BC3H6
MAOOMIM
1-methacryloyloxyhexyl-1-methylimidazolium
251.39
N
N
(CH2)6O
cr
53
295.29
ip t
52
O
54
AOOMIM
1-acryloyloxypropyl-1-methylimidazolium
197.21
58
59
60
61
DMEIM
1,2-dimethyl-3- ethyl-imidazolium
C2PY
Me3BuN
P
C4H9
C4H9
80.11 NH+
128.22
N
N
C2H5 108.16
N+
C2H5
136.21 N+ C H 4 9
n-amylpyridinium
150.24 N+
triethylsulphonium
63
C6H13OCH2MIM
1-hexyloxymethyl-3-methyl-imidazolium
117.23 N+
C4H9
Et3S
119.25
197.30
N (C6H13OCH2)2IM
N
CH2OC6H13
1,3-dihexyloxymethylimidazolium
381.53
C6H13OH2C
(OC1)2IM
C5H11
trimethyl-butylammonium
Et3S
65
217.35
n-butylpyridinium
62
64
O
n-ethylpyridinium
C4PY
C5PY
an
pyridinium
M
PY
(CH2)3O
C4H9
ed
57
tributylmethylphosphonium
N
ce pt
56
TBMeP
Ac
55
us
N
N N CH OC H 2 6 13
1,3-dimethoxyimidazolium
129.14 N
N
OCH3
H3CO
15
Page 15 of 36
66
C2OC1MIM
1-(methylethylether)-3-methylimidazolium C2H5OH2C
67
C2OHMIM
N
N
1-ethanol-3-methylimidazolium
141.19
127.16 N
N
HOC2H4
68
C3CNMIM
1-(3-cyanopropyl)-3-methylimidazolium
N
NCC3H6 OMA
C8H17
trioctylmethylammonium
148.19
368.70
ip t
69
N
N
C8H17
C8H17
70
BMPY
1-butyl 4-methyl-pyridinium
150.23
P1,4,4,4
tri-iso-butylmethylphosphonium
CH(CH3) 2
us
71
cr
N C4H9
P
217.35
CH(CH3) 2
CH(CH3) 2
72
PMPIP
1-propyl-1-methylpiperidinium
an
73
1-(2-methoxyethyl)-1-methylpyrrolidinium
COC2mMOR
4-(2-methoxyethyl)-4-methylmorpholinium
COC2mPIP
1-(2-methoxyethyl)-1-methypiperidinium
N-C3OHPY
1-(3-hydroxypropyl)pyridinium
M
COC2mPYR 74
ed
75
77 N1,1,2,2OH 78
79
ethyl(2-hydroxyethyl)dimethyl-ammonium
N-octylisoquinolinium
Ac
C8iQuin
ce pt
76
C6iQuin
N-hexylisoquinolinium
BMPIP
1-butyl-1-methyl-piperidinium
N
128.23
C3H7
N
140.2 (CH2)2OCH3
160.23 H3CO(H2C) 2
N
O
158.26
N
(CH2)2OCH3
138.19
N (CH2 )3OH 118.2
C2H5
N
C2H4 OH
N
257.41 (CH2)7CH3
N
229.36 (CH2)5CH3
80
156.29 N
C4H9
16
Page 16 of 36
Table 2 Solubility parameters (δs) of ionic liquids used in Eq. 3. δs /MPa1/2
[C16MIM][BF4] [DMEIM][NTf2]
298.15 298.15
19.94 26.36
[Me3BuN][NTf2] [C6MIM][NTf2] [BMPY][NTf2] [THTDP][NTf2] [TBMeP][MeSO4] [P,1,4,4,4][TOS] [C8MIM][MDEGSO4] [C2MIM][DEP] [C4MIM][SCN] [PY][EOSO4] [C6MIM][TfO] [C2MIM][TCB] [C4PY][NTf2] [C5PY][NTf2] [HMPYR][NTf2]
298.15
Ac
[BMPY][TfO]
[C2MIM][NO3] [C4MIM][NO3] [C0C2mMOR][NTf2] [N1,1,2,2OH][DEP] [COC2MMOR][FAP] [N-C3OHPY][NTf2] [C4MIM]BOB [C6MIM]BOB
21.60 21.10 21.82 19.46 20.58 26.99 24.69 22.12 26.30 21.98 22.39 22.12 21.01 21.18 13.35
cr us
an
M ed
ce pt
[OMPYR][NTf2] [PMPIP][NTf2] [Me3BuN][BF4] [C2MIM][FAP] [C8MIM][Cl] [AOOMIM][Br] [C2MIM][TfO]
298.15 298.15 298.15 298.15 298.15 298.15 298.15 298.15 298.15 298.15 298.15 303.15 303.15 303.15
ip t
T/K
Ionic Liquid
303.15
14.31
308.15 308.15 313.15 313.15 313.15 313.15 308.15 323.15 303.15 328.15 323.15 328.15 328.15 328.15 328.15
21.55 20.14 20.10 27.46 27.97 24.53 23.04 25.24 26.68 22.03 28.96 19.68 23.13 21.31 21.57
17
Page 17 of 36
Table 3 The van der Waals volumes (rs ) of ionic liquids estimated according to literature49 used in Eq. 2. rs/ cm3mol-1
Ils
172.83 183.06 193.29 203.52
cr
ip t
[C2AOOMIM][Br] [C3AOOMIM][Br] [C4AOOMIM][Br] [C5AOOMIM][Br]
an ed
ce pt
73.24 86.91 97.14 107.37 117.60 127.83 20.43 34.10 44.33 54.56 64.79 75.02
Ac
[MPYR][SCN] [C1MPYR][SCN] [C2MPYR][SCN] [C3MPYR][SCN] [C4MPYR][SCN] [C5MPYR][SCN]
M
[MIM][SCN] [C1MIM][SCN] [C2MIM][SCN] [C3MIM][SCN] [C4MIM][SCN] [C5MIM][SCN]
85.41 99.08 109.31 119.54 129.77 140.00
us
[MIM][CH3SO3] [C1MIM][CH3SO3] [C2MIM][CH3SO3] [C3MIM][CH3SO3] [C4MIM][CH3SO3] [C5MIM][CH3SO3]
18
Page 18 of 36
Table 4 Estimated molar attraction constants of ionic functional group (IFG) by group contribution used
ip t
in Eq. 5.
FIFG MPa1/2cm3mol-1 6068.46 3100.65 3381.58 5378.46 5353.57 3882.65 4850.02 4273.49 4345.99 3905.39 4324.72 5629.20 4907.05 5379.25 4262.82 6074.24 1523.04 2789.11 4135.24 5249.28 5319.13 2724.19 6674.45 3654.73 2354.88 3947.19 3425.66 3651.77 3798.81 3850.76
us an M ed ce pt
Ac
[IM][Br] [IM][BF4] [IM][PF6] [IM][NTf2] [PY][NTf2] [IM][(CH3)2PO4] [IM][ESO4] [IM][MOSO4] [IM][MeSO4] [PYR][TfO] [IM][TfO] [IM][MDEGSO4] [IM][NTf2] [IM][NTf2] [S][NTf2] [IM][OSO4] [N][BF4] [PYR][NTf2] [N][NTf2] [P][NTf2] [PIP][NTf2] [P][MeSO4] [P][TOS] [IM][(C2F5)3PF3] [IM][NO3] [IM][TCB] [IM][SCN] [PY][SCN] [PYR][SCN] [IM][CH3SO3]
cr
ILs
19
Page 19 of 36
Table 5
Ionic Liquid
o-xylene
[MAOOMIM][Br]
m-xylene
o-xylene
[C8MIM][Cl]
p-xylene
ce pt
Ac
p-xylene
p-xylene [C2MIM][N(CN)2]
1.351
1.162
p-xylene m-xylene
1.257
0.740
20
0.860
21
1.066 0.938 0.885
22
1.038 0.963 0.795
1.173
19
an 0.807
1.173
o-xylene
19
0.929
0.853
1.130
Ref
1.077
1.239
o-xylene m-xylene
0.688
1.455
o-xylene
m-xylene
[HMIM][NO3]
1.732
ed
m-xylene
0.577
M
m-xylene
[C4MIM][NO3]
2.070
o-xylene
[AOOMIM][Br]
p-xylene
us
o-xylene
m-xylene 0.483
cr
experimental data of activity coefficients.
ip t
Selectivities S12∞ (Sij∞ =γis∞/γjs∞) of ionic liquids for xylene isomers at infinite dilution from
0.852
23
0.933 1.072
20
Page 20 of 36
m-Xylene p-Xylene [C4MIM][TOS]
p-xylene
1.308
1.005
1.000
0.855
0.860
1.170 1.162
0.994 0.901
1.110 1.062
m-xylene
[N1,1,2,2OH][DEP]
o-xylene
ce pt
m-xylene p-xylene
1.191
p-xylene
p-xylene o-xylene
1.072
0.839
28
1.070 0.952
29
1.048 0.954 0.872
1.147 1.096
27
0.935
1.102
o-xylene m-xylene
0.898
0.908
1.051
0.950
0.933
1.113
o-xylene
m-xylene
Ac
1.052
ed
p-xylene
1.128
26
0.957 0.886
o-xylene
0.942 1.045
M
[C2MIM][DEP]
25
us
p-xylene
24
1.006
o-xylene m-xylene
[C2MIM][TCB]
0.765 0.995
an
[P1,4,4,4][TOS]
[BMPYR][TCB]
0.769 1.000
o-xylene m-xylene
[C4MIM][DBP]
1.000 1.301
ip t
o-Xylene
cr
[C2MIM][CH3SO3]
0.913
30
1.047 0.955 0.851
0.899
31
21
Page 21 of 36
1.174
p-xylene
1.112
p-xylene
0.899
1.097
0.986 0.853
p-Xylene
1.140
o-xylene
ed
[C4MIM][SCN]
m-xylene
ce pt
p-xylene
Ac
1.194
p-xylene
p-xylene
0.986
0.838
34
0.940 0.835
35
1.055 0.948 0.791
1.265 1.208
33
1.064
1.263
o-xylene m-xylene
0.787
0.792
1.197
0.877
1.014
1.271
o-xylene
m-xylene
0.978 0.890
1.124
33
1.022
1.146
o-Xylene m-Xylene
cr
1.172
M
[C6MIM][BOB]
0.872
us
p-xylene
32
1.015
o-xylene m-xylene
0.912
1.113
an
[C4MIM][BOB]
[BMPYR][SCN]
0.947
o-xylene m-xylene
[BMPY][SCN]
1.056
ip t
[DMIM][TCB]
m-xylene
0.828
35
1.047 0.956
22
Page 22 of 36
ip t cr us an M
Table 6
ed
Predicted solubility parameters (δs) of ionic liquids [CnAOOMIM][Br], [CnMIM][CH3SO3], [CnMIM][SCN] and [CnMPYR][SCN] used in Eq. 3.
ce pt
ILs
δs /MPa1/2 31.04 30.11 29.23 28.38
[MIM][CH3SO3] [C1MIM][CH3SO3] [C3MIM][CH3SO3] [C4MIM][CH3SO3] [C5MIM][CH3SO3]
31.00 29.57 27.52 26.58 25.67
[MIM][SCN] [C1MIM][SCN] [C2MIM][SCN] [C3MIM][SCN] [C5MIM][SCN]
31.54 29.59 28.16 26.86 24.55
Ac
[C2AOOMIM][Br] [C3AOOMIM][Br] [C4AOOMIM][Br] [C5AOOMIM][Br]
23
Page 23 of 36
30.24 28.39 27.05 25.82 23.59
M
an
us
cr
ip t
[MPYR][SCN] [C1MPYR][SCN] [C2MPYR][SCN] [C3MPYR][SCN] [C5MPYR][SCN]
Table 7
ILs
ce pt
[AOOMIM][Br]
ed
Predicted selectivites S12∞ of m/o-xylene at infinite dilution in ionic liquids. Selectivity of m/o-xylene in ILs 1.732
2.070
[C2AOOMIM][Br]
1.774
[C3AOOMIM][Br]
1.686
[C4AOOMIM][Br]
1.608
[C5AOOMIM][Br]
1.539
Ac
[MAOOMIM][Br]*
*from experimental data
24
Page 24 of 36
ip t cr us an M ed ce pt
Table 8
Predicted selectivites (S12∞) of p/o-xylene at infinite dilution in ionic liquids. Selectivity of p/o-xylene in ILs
Ac
ILs
[MIM][CH3SO3] [C1MIM][CH3SO3] [C2MIM][CH3SO3]* [C3MIM][CH3SO3] [C4MIM][CH3SO3] [C5MIM][CH3SO3]
2.386 2.133 1.308 1.828 1.706 1.600
[MIM][SCN] [C1MIM][SCN] [C2MIM][SCN] [C3MIM][SCN] [C4MIM][SCN]* [C5MIM][SCN]
2.386 2.133 1.828 1.706 1.194 1.600 25
Page 25 of 36
[MPYR][SCN] [C1MPYR][SCN] [C2MPYR][SCN] [C3MPYR][SCN] [C4MPYR][SCN]* [C5MPYR][SCN]
2.246 1.949 1.766 1.617 1.208 1.390
Table 9
ce pt
ed
M
an
us
cr
ip t
*from experimental data
Selectivity (S12∞) of m/o, p/o-xylene in [MAOOMIM]-type ILs: predicted results for the effect of anion.
Ac
Ionic Liquid
[MAOOMIM][NTf2] 363.15K [MAOOMIM][SCN] 363.15K [MAOOMIM][NO3] 363.15K
[MAOOMIM][MDEGSO4]
S12∞
o-xylene o-xylene m-xylene p-xylene o-xylene m-xylene p-xylene o-xylene m-xylene p-xylene o-xylene
1.113 1.203 1.090 1.163 0.993 0.994
m-xylene 0.898 1.081 0.917 1.067 1.007 1.001 0.895
p-xylene 0.831 0.925 0.860 0.937 1.006 0.999 0.826 26
Page 26 of 36
m-xylene p-xylene o-xylene m-xylene p-xylene o-xylene m-xylene p-xylene o-xylene m-xylene p-xylene o-xylene m-xylene p-xylene
[MAOOMIM][MeSO4] 363.15K [MAOOMIM][OSO4] 333.15K
1.084 0.726
1.377 1.690
1.227 0.841
1.189 1.339
1.126 0.974
1.027 1.054 1.110 1.198
0.592 0.815 0.747 0.888 0.949 0.975
1.026 0.901
0.834 0.926
1.080
ed
M
an
us
[MAOOMIM][(CH3)2PO4] 333.15K
0.923
ip t
[MAOOMIM][TCB] 333.15K
1.118 1.211
cr
363.15K
Table A1
ce pt
Experimental data and literatures used in this work to derive the solubility parameters of ionic liquids with their identification defined in Table 1. Ref.
33-19 70-19 42-19 32-24 73-6 76-6 74-15 75-6 74-6 78-6 42-15 42-23 36-23
34 35 35 24 37 38 39 40 41 42 30 32 25
Ac
ID
27
Page 27 of 36
ip t
43 23 22 29 28 44 45 46 47 48 27 27 33 33
Ac
ce pt
ed
M
an
us
cr
33-12 75-15 32-17 34-16 33-25 77-26 39-6 33-27 69-28 39-3 36-3 32-26 33-29 34-29
Figure Captions 28
Page 28 of 36
Fig. 1. Residual function Y versus solute solubility parameters δi of ionic liquids Fig. 2. The classification of the structure of an ionic liquid.
Ac
ce pt
ed
M
an
us
cr
ip t
Fig. 3. Selectivity of m(1)/o(2) and p(1)/o(2) xylene in ionic liquids [MAOOCnMIM][TCB].
29
Page 29 of 36
cyclohexane methylcyclohexane 1-hexene cyclohexene benzene toluene acetone methanol ethanol 1-propanol Isopropyl alcohol
Yi
0.25 0.20 0.15
A
cr
0.30
0.10 0.05 18
0.30
1-hexene 1-hexyne benzene toluene ethylbenzene
Yi
0.20
0.15
ce pt
0.10
22
i
24
26
0.05
Ac
14
0.30 0.28 0.26 0.24
16
28
18
20
30
B
thiophene pyridine methanol ethanol tertbutyl alcohol THF 1,4-dioxane acetone acetonitrile
ed
0.25
20
an
16
M
14
us
0.35
ip t
0.40
22
24
26
28
30
i
R-methylstyrene thiophene pyridine methanol ethanol 1-propanol
C
Yi
0.22
2-butanol tertbutyl alcohol methyl propanoate methyl butanoate 1,4-dioxane acetone acetonitrile styrene
0.20 0.18 0.16 0.14 0.12 0.10 16
18
20
22
24
26
28
30
i
30
Page 30 of 36
0.35
0.25
methanol ethanol 1-propanol 1-butanol thiophene THF 1,4-dioxane acetone 2-pentanone
Yi
0.20
0.15
0.10
0.05 14
16
18
20
22
24
26
28
30
us
cr
i
ip t
D
cycloheptane 1-hexene cyclohexene 1-heptyne benzene toluene ethylbenzene
0.30
n-hexane cyclohexane methylcyclohexane 1-hexene 1-hexyne benzene toluene ethylbenzene methanol ethanol 1-propanol
0.25
Yi
0.20
M
0.15
E
an
0.30
0.10
0.05 14
16
18
20
22
24
26
28
30
ce pt
ed
i
n-hexane cyclohexane methylcyclohexane 1-hexene 1-heptyne benzene toluene ethylbenzene methanol ethanol 1-propanol
0.30
0.25
Yi
0.20
Ac
0.15
F
0.10
0.05 14
16
18
20
22
24
26
28
30
i
31
Page 31 of 36
G
n-pentane n-decane cyclopentane 1-pentene 1-octene 1-pentyne benzene p-xylene methanol THF thiophene
0.35
0.30
0.25
Yi
0.20
0.15
0.10
ip t
0.05
0.00 14
16
18
20
22
24
26
28
30
H
0.20
an
n-pentane n-octane cyclopentane cycloheptane 1-hexene 1-heptyne benzene methanol
0.25
Yi
us
0.35
0.30
0.15
18
20
22
i
24
26
28
n-pentane n-hexane n-heptane n-nonane n-decane cyclohexane methylcyclohexane 2,2,4-trimethylpentane cyclohexene styrene benzene toluene
30
I
ce pt
0.12
16
ed
14
M
0.10
0.05
cr
i
Yi
0.10
0.08
0.06
Ac
0.04
14
15
16
i
17
18
19
20
32
Page 32 of 36
n-hexane n-heptane n-decane cyclohexane cycloheptane 1-hexene 1-hexyne benzene toluene ethylbenzene methanol ethanol thiophene THF
0.30
0.25
Yi
0.20
0.15
0.10
J
0.05
0.00 14
16
18
20
22
24
26
28
30
cr
i
ip t
0.35
us
Fig. 1. Residual function Y versus solute solubility parameters δi of ionic liquids. A: [N1,1,2,2OH][DEP]; B: [COC2mMOR][NTf2]; C: [COC2MMOR][FAP]; D: [N-C3OHPY][NTf2]; E: [C4MIM][BOB]; F: [C6MIM][BOB]; G: [P,1,4,4,4][TOS]; H:
Ac
ce pt
ed
M
an
[C8MIM][MDEGSO4]; I: [C2MIM][DEP]; J: [C4MIM][SCN]
33
Page 33 of 36
IF
N
R2
BF4-
ip t
N
cr
R1
Ac
ce pt
ed
M
an
us
Fig. 2. The classification of the structure of an ionic liquid.
34
Page 34 of 36
2.6
m/0 p/o
2.5 2.4
ip t
2.3 2.2 2.1
S12
2.0 1.9 1.8
cr
1.7 1.6 1.5
1.3 1
2
3
4
n
5
us
1.4 6
Ac
ce pt
ed
M
an
Fig. 3. Selectivity of m(1)/o(2) and p(1)/o(2) xylene in ionic liquids [MAOOCnMIM][TCB].
35
Page 35 of 36
1. We collect a database on activity coefficients of organic solutes at infinite dilution in ionic liquids.
ip t
2. We model activity coefficients to correlate the solubility parameter of ionic liquids.
Ac ce p
te
d
M
an
us
cr
3. Higher selectivity is achieved when using ionic liquids to separate xylene isomers.
Page 36 of 36