n-Hexane with Ester-Functionalized

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Selective Separation of Benzene/n-hexane with Ester-Functionalized Ionic Liquids Zhongqi Ren, Mengyao Wang, Yong Li, Zhiyong Zhou, Fan Zhang, and Wei Liu Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 25 May 2017 Downloaded from http://pubs.acs.org on May 28, 2017

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Energy & Fuels

Selective Separation of Benzene/n-hexane with

1 2

Ester-Functionalized Ionic Liquids

3

Zhongqi Ren, Mengyao Wang, Yong Li, Zhiyong Zhou, Fan Zhang*, Wei Liu*

4

College of Chemical Engineering, Beijing University of Chemical Technology, Beijing, 100029, P.R. China

5

Abstract

6

The designer nature of ionic liquids (ILs) has driven their exploration and application in countless

7

fields because of their unique phisco-chemical properties. In this work, two ester-functionalized ionic

8

liquids (ILs), N-ethylacetate-N-methylimidazole bis(trifluoromethylsulfonyl)imide ([Eamim][NTf2])

9

and N-ethylacetate-N-methylimidazole sulfocyanide([Eamim][SCN]), were prepared. Two ternary

10

systems, benzene-hexane-[Eamim][NTf2] and benzene-hexane-[Eamim][SCN], were investigated in

11

terms of both quantum chemical calculation and liquid-liquid extraction experiment. Quantum

12

chemical calculation results showed that the interaction between ILs and benzene was larger than

13

that between ILs with n-hexane. The liquid-liquid extraction results showed that the selectivity

14

reached 29.55 with [Eamim][NTf2], while the selectivity reached 61.44 with [Eamim][SCN] at 25 °C.

15

Vapor permeation process was conducted through supported membrane with ILs. The influences of

16

operating temperature and the feed concentration of benzene were investigated. With the increase of

17

temperature, the selectivity of benzene increased at first and then decreased. When the concentration

18

of benzene was 0.5 and the temperature was 35 °C, the selectivity of benzene reached 16.05, while

19

the flux was 22.14 g·h-1·m-2. The stability of the membrane in the vapor permeation was also tested

20

and could remain steady for 60 hours.

21

Key words: ester-functionalized ionic liquid, liquid-liquid extraction, vapor permeation, membrane

22

separation

23 1

ACS Paragon Plus Environment

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1

1. Introduction

2

The separation of aromatic hydrocarbons is one of the most difficult problems in petrochemical

3

refinery process, which will cause a huge energy consumption.1-3 It is extremely important to

4

develop energy efficient technologies to separate aromatics from alkanes. Absorption,

5

crystallization, liquid-liquid extraction and membrane separation have been applied to separate

6

aromatic hydrocarbons. Among them, liquid-liquid extraction process is the most promising one

7

due to its simple operation, high efficiency, and low energy cost. 4-7 The most commonly used

8

solvent in industrial process is sulfolane (UOP/Shell Process). The applications of other solvents,

9

including polyethylene glycols (UDEX Process), tetraethylene glycol (Union Carbide Process),

10

dimethyl sulfoxide, N-methylpyrrolidone (Arosolvan Process), and N-formylmorpholine

11

(Uhde/Formex Process), are also developed. Compared with those volatile organic solvents, ILs

12

were getting more and more attention in aromatic separation process because of their unique

13

physico-chemical properties. Some of them present negligible vapor pressure at room temperature

14

and normal pressure condition. So the regeneration of ILs could be achieved by flash distillation.

15

The properties of ILs also could be designed by selecting different chemical structures of cations

16

and anions.8,9 In recent years, many functional ILs were designed by changing anions or cations.

17

They have been reported in various fields, such as separation10-12, catalysis13, functional materials14

18

and electrochemistry15-17.

19

Many researchers have done a lot of work in the separation of aromatic hydrocarbons with ILs.

20

Requejo et al., investigated the extraction of benzene from octane and decane by using IL

21

tributylmethylammonium bis(trifluoromethylsulfonyl) imide ([N4441][NTf2]) at atmospheric

22

pressure when the temperature was 25 °C.18 The distribution coefficient and selectivity showed 2


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that this IL could be used as a suitable solvent. The extraction of benzene was greatly affected

2

when both aliphatic hydrocarbons were present in the mixture and especially when the

3

compositions of octane in the initial feed was high. The experimental liquid-liquid extraction (LLE)

4

data were satisfactorily correlated by the nonrandom two-liquid thermodynamic model (NRTL)

5

model. Sandra et al., studied the separation of heptane, cyclohexane and toluene with

6

1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) at 25 °C, and the results were correlated with

7

NRTL model.19 Corderi et al., studied the separation performance of heptane and toluene with

8

1-ethyl-3-methylimidazolium

9

sulfocyanide([SCN]−), mesylate([CH3SO3]−), and dicyanamide ([DCA]−) anions showed better performance

([Emim])

than

IL.20

The

sulfolane.

results

The

showed

that

selectivities

of

ILs

with

10

separation

toluene

11

with1-ethyl-3-methylimidazolium sulfocyanide ([Emim][SCN]) and 1-ethyl-3-methylimidazolium

12

dicyanamide ([Emim][DCA]) were over four times than that with sulfolane. The ILs with

13

tricyanomethanide ([TCM]−), bis(trifluoromethylsulfonyl)imide ([NTf2]−), and dicthylphosphate

14

([DEP]−) anions showed the best distribution coefficient. Mobin et al., studied the separation of

15

heptane and benzene with two pyridinium based IL, and the influence of temperature was also

16

investigated.21 The results showed that the selectivity of benzene with N-butylpyridinium

17

nitrate([BPy][NO3]) was higher than that with N-hexylpyridinium nitrate ([HPy][NO3]), and the

18

separation performance at low temperature was higher than that at high temperature.

19

Both IL cations and anions could be selected among a huge diversity according to the specific

20

system in different applications. As a supplement to the experiment, quantum calculation could be

21

used to select specific IL and investigate the mechanism of dissolution by calculating the optimum

22

structure and interaction between IL and system compounds. Tsuzuki et al., studied the interaction 3


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1

in benzene and pyridinium cations and the results showed that it should be categorized into a

2

cation-π interaction. This was mainly because the electrostatic and induction interactions greatly

3

contribute to the attraction.22 Rogers et al., studied the solubility of benzene in fifteen ionic liquids

4

and the results showed that benzene interacted with IL cation primarily. The liquid clathrate

5

formation and benzene solubility were controlled by the strength of the cation-anion interactions.

6

23-24

7

Membrane separation is a promising method as it is low energy consumption and could be

8

carried out at mild condition.25 Combined with ILs and membrane could not only reduce the usage

9

amount of ILs but also enhance the stability of membrane process. Yamanouchi et al., studied the

10

separation performance of benzene and cyclohexane with vapor permeation process, and the

11

separation membrane was consisted of triglycol, water and salt solution.26 The effects on

12

separation performance of water and salt solution were investigated at 30 °C, and the results

13

showed that the addition of salt could increase the selectivity obviously. Wang et al., studied the

14

separation of benzene and cyclohexane with supported ionic liquid membrane.27 The results

15

showed that with the increasing of temperature, the selectivity was increased at first and then

16

decreased after 40 °C, and the selectivity ranged from 15 to 25 with different concentrations of

17

benzene. The stability of separation process was also tested and the results showed that the

18

membrane could keep excellent extraction performance for a long time.

19

In this paper, benzene and n-hexane as the representative of aromatic and alkane were selected

20

as the separation system and two ester-functionalized ionic liquids were chosen as extractants. The

21

quantum chemical calculations on the interactions of ILs with aromatic and alkane were also

22

conducted as a complementarity for experimental methods. Liquid-liquid extraction of aromatics 4


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(benzene) from alkane (n-hexane) using two ILs had been studied. For this purpose, liquid-liquid

2

extractions of two ternary systems, benzene-hexane-IL ([Eamim][NTf2] or [Eamim][SCN]), were

3

investigated at 25 °C and atmospheric pressure. The reliability of obtained LLE data had been

4

checked by using Othmer-Tobias correlation. The influence of the concentrations of benzene and

5

operating temperature were studied. The NRTL model was used to correlate the experimental LLE

6

data. Moreover, ILs and vapor permeation were combined to separate benzene from the mixture. In

7

vapor permeation process, the concentration of benzene, operating temperature, and the stability of

8

vapor permeation were investigated.

9

2. Experimental section

10

2.1 Materials

11

N-methylimidazole and potassium sulfocyanide were supplied by Energy Chemical, Beijing,

12

China. Ethyl chloroacetate and bis(trifluoromethane)sulfonimide lithium salt were purchased from

13

Aladdin, Shanghai, China. Benzene, hexane, cyclohexane, ethanol and acetone were supplied by

14

Beijing Chemical Plant, Beijing, China. All chemicals were at analytical grade and used without

15

any further purification.

16

2.2 Preparation of ILs

17

In this paper, both ILs were synthesized with two steps and their structures were shown in Figure

18

1.

19

Figure 1

20

The N-ethylacetate-N-methylimidazoium chloride was synthesized by mixing equimolar (0.1 mol)

21

quantities of N-methylimidazole and ethyl chloroacetate in ultrapure water with magnetic stirring

22

for 12 h. The reaction temperature was controlled by an ice-bath. Then 0.1 mol LiNTf2 was added 5


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1

into the mixture and stirred for another 12 h. The aqueous phase containing LiCl was removed and

2

the IL was washed with ultrapure water many times to remove chloride ion. 0.1 mol/L AgNO3

3

solution was used to test the residual halogen and no precipitation was observed. The IL was set in

4

vacuum oven at 80 °C for several days to remove possible traces of solvents and moisture.

5

Due to the hydrophilic of [Eamim][SCN], acetone was used as solvent to replace water when

6

N-ethylacetate-N-methylimidazoium chloride was synthesized. KSCN was added into the mixing

7

solution and stirred for 12 h at room temperature. The precipitated solid KCl was removed by

8

filtration. After that, anhydrous MgSO4 was used to remove water. Finally, the product was

9

obtained after evaporation of acetone under vacuum conditions by rotary evaporator. Both ILs

10

structures were analyzed by 1H-NMR, 13C-NMR and FT-IR.(Figure S1-4) Some other properties of

11

ILs were also measured. All these results were showed in Supporting Information. (Table S1-2)

12

2.3 Liquid-liquid extraction process

13

Liquid-liquid extraction was carried out at 25 °C and atmospheric pressure. Both 10 mL IL and the

14

mixture of benzene/n-hexane were added into a conical flask. The extractions were carried out

15

under vigorously stirring long enough to ensure the extractions were completed. Then the mixtures

16

were settled for 3 hours to get a complete phase split, and the samples of two layers were analyzed

17

by gas chromatography.

18 19 20 21 22

The distribution coefficient (Di) and selectivity (S) of liquid-liquid extraction process were calculated as follows: = /

(1)

/ = /

(2)

where xi is the mole fraction of component i, IL means ionic liquid phase while raf means the 6


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mixture of benzene and n-hexane.

2

2.4 Vapor permeation process

3

The separation membrane used in vapor permeation process were prepared by using infusion

4

method. IL entered into the membrane pore by capillary force. Firstly, the membrane was set in

5

drying oven for 3 hours at 45 °C. Then, the membrane was immersed in IL completely and placed

6

in drying oven at 50 °C for 12 hours. The separation membrane was obtained after another 12

7

hours at 30 °C. The flow diagram of experiment was showed in Figure 2. The prepared membrane

8

was put into membrane module. The vapor in feed phase could through the membrane by pressure

9

difference and was collected by cold trap. The collected samples were analyzed by gas

10

chromatography. Figure 2

11 12 13 14 15

The flux (J) and separation factor (α) were calculated as follows: = /

(3)

= (1 − )/ (1 − )

(4)

where means the mass of samples, s means active area, means time of the process, while

16

and mean the final and initial concentration of benzene respectively.

17

2.5 Analytical methods

18

Gas chromatography (Agilent 7890A with a hydrogen flame ionization detector, 0.25 mm × 30 m

19

DB-FFAP capillary column) with an internal standard method was used to analyze the

20

concentration of benzene and n-hexane. Cyclohexane was added into the samples as internal

21

standard while acetone was added as solvent to dilute the samples. The conditions were as follows:

22

programmed temperature, injection and detector temperature were 230 °C and 250 °C. To ensure 7


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1

enough accuracy, all experiments were carried out in triplicate.

2

3. Results and discussion

3

3.1 Interactions of ILs with benzene and n-hexane

4

The interaction between IL and the system compounds could be used to select specific cation

5

and anion of IL. In this section, the interaction between both ILs (cation and anion) and

6

aromatic/alkane was calculated by quantum chemistry calculation. The optimized geometries were

7

calculated and performed on isolated benzene, n-hexane, ILs (cation and anion) and their

8

complexes. The initial geometries of all compounds were first constructed and pre-optimized at

9

semiempirical level with the Chem3D Ultra package. Then the obtained geometry with the lowest

10

energy was further optimized with Gaussian 09 software.28 The hybrid density functional theory

11

(DFT), which incorporates Becke’s three-parameter exchange with Lee, Yang, and Parr’s (B3LYP)

12

correlation functional method, was employed together with 6-311++G** basis set 29, 30.

13

The binding energy was calculated as follows:

14

opt opt BE =EIL-system − [ EILopt + Esystem ]

15

opt where BE means binding energy, EILopt , Esystem means the energy of IL and system compound at the

16

opt optimized structure, EIL-system means the energy of IL and system compound at the optimized

17

structure, respectively.

18

Both cation and anion played significant roles in the separation of aromatic compounds from

19

alkanes. For each kind of interaction between IL and aromatic/alkane, more than three different

20

initial geometries of each pair were optimized, which meant aromatics or alkanes were located at

21

different positions around IL. The optimized geometry with the lowest energy was used as global

22

minimum for the subsequent calculation. No imaginary frequency appeared in the calculated

23

vibrational frequencies of the optimized structures, which ensured obtained structures stable. The 8


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optimized geometries between ILs (cation and anion) and benzene/n-hexane were shown in Figure

2

3. The interaction energies between ILs (cation and anion) and benzene/n-hexane were also

3

calculated and summarized in Table 1.

4

Figure 3

5

Table 1

6

The binding energy between [Eamim]+ and benzene was -28.09 kJ/mol, while the value was -13.45

7

kJ/mol between [Eamim]+ and n-hexane. As showed in Figure 3, the interaction between [Eamim]+

8

and benzene should be categorized into a CH-π interaction. The binding energy between [NTf2] and

9

benzene was -18.50 kJ/mol, while the value was -15.02 kJ/mol between [NTf2] and n-hexane. When

10

the anion was [SCN] , the interaction with n-hexane was almost the same, while the value was

11

-20.58 kJ/mol with benzene. The calculated binding energy differences between benzene and

12

n-hexnae was -14.64 kJ/mol, while the values were -14.51 kJ/mol (N-Benzyl-N-methyl imidazoium

13

cation) and -15.38 kJ/mol (N-benzyl-N-vinyl imidazolium) in our previous work.5 Both anion and

14

cation showed stronger interaction with benzene rather than that with n-hexane. So these two ILs

15

could be used as extractants to separate benzene and n-hexane.

16

3.2 Liquid-liquid extraction

17

3.2.1 Experimental LLE Data

18

Most ILs remain liquid at a wide range around room temperature and this makes them can be used as

19

extractants in liquid-liquid extraction process. They are used as novel extractants to replace

20

traditional volatile organic solvents. In this section, experimental compositions of alkane-rich

21

(raffinate) and IL-rich (extract) phases in equilibrium for ternary systems {n-hexane (1) + benzene (2)

-

-

-

9


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1

+ IL (3)} at 25 °C and atmospheric pressure were investigated and the results were plotted in Figure

2

4. Figure 4

3 4

To verify the reliability of the experimental LLE data, Othmer-Tobias equation was applied：

5

 1 − wⅡ   1 − wⅠ1  3 ln   = a + bln  Ⅰ  Ⅱ  w1   w3 

6

where wⅡ is the mass fraction of ionic liquid in IL-rich phase (lower layer), wⅠ is the mass fraction 3 1

7

of alkane in alkane-rich phase (upper layer), a and b are the fitting parameters of the Othmer-Tobias

8

correlation. The results were very close to unity and showed in Supporting Information (Table S3).

9

To compare with the separation performance of ILs in this work, some other ILs in literatures were

10

listed in Table 2 below.28-29 The synthesized ILs in this work showed good performance in both

11

distribution coefficient and selectivity. When the cation was [Eamim]+, the IL with [NTf2] could

12

dissolve more benzene than that with [SCN] . This should contribute to the increase of the anion size.

13

When the anion was [NTf2] , more benzene was dissolved in the IL with alkyl and benzyl group. The

14

zwitterionic also could be used to enhance the separation performance. At the same time, this also

15

improved the solubility of n-hexane. As a result, the selectivity of IL on benzene decreased. In this

16

research, the group of ethyl acetate was introduced in IL to improve the separation performance. The

17

distribution coefficient of n-hexane was more sensitive when ethyl acetate group was introduced, so

18

the selectivity of ILs maintained high level. The selectivity of two IL synthesized was 29.55

19

([Eamim][NTf2]) and 61.44([Eamim]SCN]) and the distribution coefficient of n-hexane was 0.035

20

and 0.009, respectively.

21

(3)

-

-

-

Table 2 10


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3.2.2 The concentration of benzene

2

In order to study the influence of the content of benzene, a set of extraction experiments were

3

carried out with the content of benzene range from 0.1 to 0.9 at room temperature. The results

4

were plotted in Figure 5 and listed in Table S4.

5

Figure 5

6

The results showed that the selectivity of benzene with two ILs decreased with the increasing of

7

benzene. This was mainly because that the concentration difference was the driving force of the

8

extraction process. With the increasing of mole fraction of benzene, the distribution coefficient of

9

benzene decreased while the distribution coefficient of hexane increased quickly, which would

10

lead to a decrease of the selectivity of benzene. Compared the two ILs, the selectivity of benzene

11

with [Eamim][SCN] was better than that with [Eamim][NTf2], which was due to the concentration

12

of n-hexane in [Eamim][SCN] was lower. The similar trend was observed in quantum calculation

13

result, the difference of binding energy between benzene and n-hexane with the anion [SCN] was

14

bigger than that with [NTf2] . The best selectivity was more than 61 while the distribution

15

coefficient of benzene was over 0.5 when [Eamim][SCN] was used. The selectivity was high at

16

low benzene concentration and this would lead to a greener process. The remove of low

17

concentration of benzene by liquid-liquid extraction process with IL could be done with low

18

energy cost. Both ILs could be regenerated by using vacuum distillation because of their excellent

19

chemical and thermal stability.

20

3.2.3 Operating temperature

21

In thermodynamic equilibrium process, the operating temperature was important to the separation

22

performance. In this section, the separation of benzene/n-hexane with two ILs were carried out at

-

11


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1

different temperatures (25 °C, 30 °C, 35 °C and 40 °C). The initial mole concentration of benzene

2

was 0.3. The results were showed in Table 3.

3

Table 3

4

When [Eamim][NTf2] was used as extractant, the distribution coefficient of benzene changed from

5

0.824 to 0.921 with the increasing of operating temperature, while the selectivity of benzene

6

decreased from 26.85 to 21.74. When [Eamim][SCN] was used, the distribution coefficient of

7

benzene changed from 0.451 to 0.529 with the increasing of operating temperature, while the

8

selectivity of benzene decreased from 42.20 to 23.78. This was mainly because the solubility of

9

hexane in both ILs was more sensitive to the operating temperature than that of benzene. The

10

distribution coefficient and selectivity of benzene was at high level when the operating temperature

11

was 25 °C. So the separation process with these two ILs would lead to less energy consumption.

12

3.2.4 Benzene-cyclohexane system

13

The system consisted of benzene and cyclohexane was also tested in this research. The experiment

14

was carried out under room temperature and the initial mole fraction of benzene was 0.1. The results

15

were exhibited in Table 4.

16

Table 4

17

The distribution coefficients of both compounds in benzene/cyclohexane system were higher than

18

that in benzene/n-hexane system. In benzene/cyclohexane system, the distribution coefficients of

19

benzene were more than twice the value of benzene in benzene/hexane system. The distribution

20

coefficients of cyclohexane were triple the value of hexane. As a result, the selectivity of benzene in

21

benzene/cyclohexane system was lower than that in benzene/hexane system. This was mainly

22

because the cyclic structure of cyclohexane made it easily to dissolve into ILs, which also could 12


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improve the solubility of benzene in ILs.

2

3.2.5 Thermodynamic correlation

3

A further study of the experimental data was performed by using NRTL model.33 The NRTL model

4

has been successfully implemented for the prediction of the phase behavior of several systems

5

containing ILs by several researchers.34-39 The binary interaction parameters ∆gij and ∆gji were

6

optimized and the third nonrandomness parameter (αij) of the NRTL equation was fixed to 0.30. The

7

parameters were adjusted to minimize the difference between the experimental and the calculated

8

mole fractions defined as:

9

,& '& ,& '& ,& '& & '& O. F. = ∑, − ) − ) ( + #) ( + + ∑, ( + #) ( + -$ "#$ − $ -$ "#$ − $

)

)

)

)

(6)

10

,& '& ,& & ,& &'& ,& '& where $ ，) ，$ ，) are the experimental mole fraction, $ ，) ，$ ，) are

11

the calculated mole fraction, respectively.

12

The fitting parameters associated with the estimation deviations were summarized in Table 5. The

13

root means square deviation of the composition, σx, was defined as the following expression:

14 15

? ? F ∑BCD23 6,789 : 6,; @3 66,789 : 66,; A E 45 45 45 45

∑4 σx = 1001

),G

(7)

where M is the number of connecting lines, N is the number of components, respectively.

16

Table 5

17

The best correlation was found when α was fixed to 0.3. The rmsd value was 0.0829 with

18

[Eamim][NTf2] and 0.0653 with [Eamim][SCN], respectively. The result showed that the NRTL

19

model could correlate the experimental LLE data of these studied ternary systems adequately. The

20

experimental and calculated tie-lines data were plotted in Figure 4 and agreed relatively well.

21

3.3 Vapor permeation

22

In this part, the hydrophobic PVDF membrane was used as supported material when [Eamim][NTf2] 13


Energy & Fuels

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1

was used as membrane phase. Hydrophilic PAN membrane was selected when [Eamim][SCN] was

2

used as membrane phase.

3

3.3.1 Operating temperature

4

With the increasing of operating temperature, the vapor pressure of benzene and hexane in feed

5

phase increased and the mass transfer driving force in membrane process would increase. The

6

viscosity of ILs decreased with the increasing of operating temperature, which would reduce the

7

mass transfer resistance. In this section, the experiments were carried out from 25 °C to 65 °C. The

8

concentration of benzene was 0.5 and the vacuum degree was 735 mmHg. Figure 6

9 10

In Figure 6, with the increasing of temperature, the flux of benzene decreased at first and then

11

increased, while the selectivity was on the contrary. At 25 °C, the evaporation of benzene and hexane

12

might be not sufficient in feed phase. When the temperature was over 35 °C, the mass transfer

13

driving force increased and mass transfer resistance reduced as the viscosity of ILs decreased, so the

14

flux of benzene was increased. More benzene solved in membrane phase would also promote the

15

dissolution of hexane. So the selectivity of benzene was decreased.

16

3.3.2 The concentration of benzene

17

Different concentrations of benzene would cause the change of mass transfer driving force in

18

membrane process. In this section, the concentration of benzene varied from 0.1 to 0.9. The

19

operating temperature was 35 °C and the vacuum degree was 735 mmHg. The result was showed in

20

Figure 7.

21 22

Figure 7 In Figure 7, with the increasing of benzene, the flux increased while the selectivity declined 14


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Energy & Fuels

1

gradually. When [Eamim][SCN] was used as membrane phase, the flux of benzene increased from

2

35.30 to 70.67 g·h-1·m-2 while the selectivity changed from 16.42 to 2.85. When [Eamim][NTf2] was

3

used as membrane phase, the flux increased from 16.49 to 36.98 g·h-1·m-2 while the selectivity

4

changed from 24.56 to 6.68. The trend was similar with the selectivity when ILs were used as

5

extraction solvents. The mass transfer driving force of benzene would increase with the increasing of

6

benzene in feed phase. More benzene was solved in membrane phase and transported through the

7

membrane. As a result, more hexane was solved in membrane phase and this would lead to reduce

8

the selectivity of benzene.

9

3.3.3 Long-term experiment

10

The long-term stability of membrane is an important factor in vapor permeation process. In this part,

11

continuous separation of benzene and hexane was carried out to investigate the stability of separation

12

process. The experiments were performed at 35 °C and the vacuum degree was 735 mmHg. The flux

13

and selectivity of benzene were showed in Figure 8. Figure 8

14 15

The selectivity of benzene ranged from 10.07 to 13.60, while the flux changed from 17.7 to 21.2

16

g·h-1·m-2. These two parameters changed in a small scale. This was mainly because the capillary

17

force and molecular interaction between IL and base membrane was strong. The results showed that

18

the ionic liquids separation membrane had excellent stability in separation of benzene and hexane.

19

Ionic liquid was able to maintain in membrane pores for a long time.

20

4. Conclusions

21

Two ester-functionalized ionic liquids(ILs) were synthesized and confirmed by NMR and FT-IR.

22

Quantum chemical calculation, liquid-liquid extraction and vapor permeation with two ionic liquids 15


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1

were studied. Quantum chemical calculations results showed that the interactions between ILs and

2

benzene were larger than that between ILs and hexane. The planar five-member heterocycle of

3

imidazole modified with ester group could attract benzene more strongly. In liquid-liquid extraction

4

process, both ILs showed excellent separation performance to benzene in both distribution

5

coefficient and selectivity. The selectivity was more than 61 while the distribution coefficient of

6

benzene was over 0.5 when [Eamim][SCN] was used. The distribution coefficient and selectivity of

7

benzene were at high level when the operating temperature was 25 °C. The system consisted of

8

benzene and cyclohexane also could be separated by these two ILs. Both Othmer-Tobias equation

9

and NRTL model could correlate the experimental LLE data adequately. In vapor permeation process,

10

PVDF and PAN were used as base membrane. The selectivity could reach 16.05, while the flux

11

reached 22.14 g·h-1·m2 at room temperature. With the increasing of benzene, the flux increased while

12

the selectivity decreased gradually. The selectivity and flux had no valid difference when the

13

membrane were operated for 60 hours continuously.

14

AUTHOR INFORMATION

15

Corresponding Author

16

Tel: +86-10-6442-3628; Fax: +86-10-6442-3628;

17

E-mail: [email protected], [email protected].

18

Notes

19

The authors declare no competing financial interest.

20

ACKNOWLEDGMENTS

21

This work was supported by the National Natural Science Foundation of China (21276012 and

16


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Energy & Fuels

1

21576010), National Science and Technology Major Project of the Ministry of Science and

2

Technology of China (2013ZX09202005 and 2014ZX09201001-006-003), Fundamental Research

3

Funds for the Central Universities (BUCTRC-201515), BUCT Fund for Disciplines Construction and

4

Development (XK1508) and Higher Education and High-quality and World-class Universities

5

(PY201607). The authors gratefully acknowledge these grants.

6

Reference

7 8

(1) Meindersma, G. W.; de Haan, A. B. Conceptual process design for aromatic/aliphatic separation with ionic liquids. Chem. Eng. Res. Des. 2008, 86, 745-752.

9

(2) Zhou, T.; Wang, Z. Y.; Ye, Y. M.; Chen, L. F.; Xu, J.; Qi, Z. W. Deep Separation of Benzene

10

from Cyclohexane by Liquid Extraction Using Ionic Liquids as the Solvent. Ind. Eng. Chem. Res.

11

2012, 51, 5559-5564.

12 13

(3) Sholl, D. S.; Lively, R. P. Seven chemical separation to change the world. Nature 2016, 532, 435-437.

14

(4) Fang, W. J.; Shao, D. B.; Lu, X. X.; Guo, Y. S.; Xu, L. Extraction of Aromatics from

15

Hydrocarbon Fuels Using N-Alkyl Piperazinium-Based Ionic Liquids. Energy Fuels 2012, 26,

16

2154-2160.

17

(5) Zhang, F.; Li, Y.; Zhang, L.; Zhou, Z.; Sun, W.; Ren, Z. Benzyl- and Vinyl-Functionalized

18

Imidazoium Ionic Liquids for Selective Separating Aromatic Hydrocarbons from Alkanes. Ind. Eng.

19

Chem. Res. 2016, 55, 747-756.

20

(6) Larriba, M.; Navarro, P.; Garcia, J.; Rodriguez, F. Liquid-Liquid Extraction of BTEX from

21

Reformer Gasoline Using Binary Mixtures of [4empy][Tf2N] and [emim][DCA] Ionic Liquids.

22

Energy Fuels 2014, 28, 6666-6676. 17


Energy & Fuels

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

1

(7) Zhang, J.; Huang, C. P.; Chen, B. H.; Ren, P. J.; Lei, Z. G. Extraction of aromatic

2

hydrocarbons from aromatic/aliphatic mixtures using chloroaluminate room-temperature ionic

3

liquids as extractants. Energy Fuels 2007, 21, 1724-1730.

4 5 6 7

(8) Plechkova, N. V.; Seddon, K. R. Applications of ionic liquids in the chemical industry. Chem. Soc. Rev. 2008, 37, 123-150. (9) Weingaertner, H. Understanding ionic liquids at the molecular level: Facts, problems, and controversies. Angew. Chem. Int. Ed. 2008, 47, 654-670.

8

(10) Gjineci, N.; Boli, E.; Tzani, A.; Detsi, A.; Voutsas, E. Separation of the ethanol/water

9

azeotropic mixture using ionic liquids and deep eutectic solvents. Fluid Phase Equilib. 2016, 424,

10

1-7.

11

(11) Blahut, A.; Dohnal, V. Ionic liquid 1-ethyl-3-methylimidazolium tetracyanoborate：An

12

efficient entrainer to separate methanol dimethyl carbonate azetropic mixture. Fluid Phase Equilib.

13

2016, 423, 120-127.

14

(12) Meindersma, G.; W., Haan, A. B. Cyano-containing ionic liquids for the extraction of

15

aromatic hydrocarbons from an aromatic/aliphatic mixture, Sci. China: Chem. 2012, 55,

16

1488-1499.

17 18 19 20 21 22

(13) Bideau, J. Le.; Viau, L.; Vioux, A. Ionogels, ionic liquid based hybrid materials. Chem. Soc. Rev. 2011, 40, 907-925. (14) Villagrán, C.; Banks, C, E.; Hardacre, C.; Compton R. G. Electroanalytical determination of trace chloride in room-temperature ionic liquids. Anal. Chem. 2004, 76, 1998-2003. (15) Hardacre, C.; Holbrey, J. D.; McMath, S. E. J. A highly efficient synthetic procedure for deuteriating imidazoles and imidazolium salts. Chem. Commun. 2001, 4, 367-368. 18


Page 18 of 37

Page 19 of 37

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

Energy & Fuels

1

(16) Kay, N. J.; Higgins, S. J.; Jeppesen, J. O.; Leary, E.; Lycoops, J.; Ulstrup, J.; Nichols, R. J.

2

Single-Molecule Electrochemical Gating in Ionic Liquids. J. Am. Chem. Soc. 2012, 134,

3

16817-16826.

4

(17) Yoshida, K.; Nakamura, M.; Kazue, Y.; Tachikawa, N.; Tsuzuki, S.; Seki, S.; Dokko, K.;

5

Watanabe,

M.

Oxidative-Stability

Enhancement

and

Charge

Transport

Mechanism

6

Glyme-Lithium Salt Equimolar Complexes. J. Am. Chem. Soc. 2011, 133, 13121-13129.

in

7

(18) Requejo, P. F.; Calvar, N.; Domínguez, A.; Gómez, E. Application of the ionic liquid

8

tributylmethylammonium bis(trifluoromethylsulfonyl)imide as solvent for the extraction of benzene

9

from octane and decane at T = 298.15 K and atmospheric pressure. Fluid Phase Equilib. 2016, 417,

10

137-143.

11

(19) Sandra, C.; Elena, G.; Noelia, C.; Angeles, D. Measurement and Correlation of Liquid-Liquid

12

Equilibria for Ternary and Quaternary Systems of Heptane, Cyclohexane, Toluene, and [EMim][OAc]

13

at 298.15 K. Ind. Eng. Chem. Res., 2014, 53, 9471-9477.

14 15

(20) Canales, R. I.; Brennecke, J. F. Comparison of ionic liquids to conventional organic solvents for extraction of aromatics from aliphatics. J. Chem. Eng. Data. 2016, 61, 1685-1699.

16

(21) Enayati, M.; Mokhtarani, B.; Shariﬁ, A.; Mirzaei, M. Extraction of benzene from heptane

17

with pyridinium based ionic liquid at (298.15, 308.15 and 318.15) K. Fluid Phase Equilib. 2016, 411,

18

53-58.

19

(22) Tsuzuki, S.; Mikami, M.; Yamada, S. Origin of attraction, magnitude, and directionality of

20

interactions in benzene complexes with pyridinium cations. J. Am. Chem. Soc. 2007, 129,

21

8656-8662.

22

(23) Holbrey, J. D.; Reichert, W. M.; Nieuwenhuyzen, M.; Sheppard, O.; Hardacre, C.; Rogers, R. 19


Energy & Fuels

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

1

D. Liquid clathrate formation in ionic liquid-aromatic mixtures. Chem. Commun. 2003, 4, 476-477.

2

(24) Pereira, J. F. B.; Flores, L. A.; Wang, H.; Rogers, R. D. Benzene Solubility in Ionic Liquids:

3

Working Toward an Understanding of Liquid Clathrate Formation. Chem.-Eur. J. 2014, 20,

4

15482-15492.

5

(25) Zarca, G.; Home, W. J.; Ortiz, I.; Urtiaga, A.; Bara, J. E. Synthesis and gas separation

6

properties of poly(ionic liquid)-ionic liquid composite membranes containing a copper salt. J. Membr.

7

Sci. 2016, 515, 109.

8 9

(26) Yamanouchi, N.; Ito, A.; Yamagiwa, K. Separation of benzene/cyclohexane by vapor permeation through triethylene glycol liquid membrane. J. Chem. Eng. Jpn. 2003, 36, 1070-1075.

10

(27) Wang, B. G.; Lin, J.; Wu, F.; Peng, Y. Stability and selectivity of supported liquid

11

membranes with ionic liquids for the separation of organic liquids by vapor permeation. Ind. Eng.

12

Chem. Res. 2008, 47, 8355-8360.

13

(28) Gaussian 09, Revision D.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.

14

Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M.

15

Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M.

16

Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.

17

Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N.

18

Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S.

19

Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken,

20

C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C.

21

Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J.

22

J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and 20


Page 20 of 37

Page 21 of 37

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

1 2 3 4 5

Energy & Fuels

D. J. Fox, Gaussian, Inc., Wallingford CT, 2009. (29) Lee, C.; Yang, W.; Parr, R. G., Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B. 1988, 37, 785. (30) Becke, A. D., Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648.

6

(31) Arce, A.; Earle, M. J.; Rodriguez, H.; Seddon, K. R. Separation of benzene and hexane by

7

solvent extraction with 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide ionic

8

liquids: Effect of the alkyl-substituent length. J. Phys. Chem. B. 2007, 111, 4732-4736.

9

(32) Sakal, S. A.; Lu, Y. Z.; Jiang, X. C.; Shen, C.; Li, C. X. A promising ionic liquid

10

[BMIM][FeCl4] for the extractive separation of aromatic and aliphatic hydrocarbons. J. Chem. Eng.

11

Data. 2014, 59, 533-539.

12 13

(33) Renon, H.; Prausnitz, J. M. Local compositions in thermodynamic excess functions for liquid mixtures. AIChE J. 1968, 14, 135-144.

14

(34) Simoni, L. D.; Lin, Y.; Brennecke, J. F.; Stadtherr, M. A. Modeling liquid−liquid equilibrium

15

of ionic liquid systems with NRTL, Electrolyte-NRTL, and UNIQUAC. Ind. Eng. Chem. Res. 2008,

16

47, 256-272.

17

(35) Kaminski, W.; Gorak, A.; Kubiczek, A., Modeling of liquid-liquid equilibrium in the quinary

18

system of water, acetone, n-butanol, ethanol, and ionic liquid. Fluid Phase Equilib. 2014, 384,

19

114-121.

20

(36) Zuo, G. L.; Zhao, Z. C.; Yan, S. H.; Zhang, X. D. Thermodynamic properties of a new

21

working pair: 1-Ethyl-3-methylimidazolium ethylsulfate and water. Chem. Eng. J. 2010, 156,

22

613-617. 21


Energy & Fuels

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

1

(37) Requejo, P. F.; Gómez, E.; Calvar, N.; Domínguez, Á. Application of pyrrolidinium-based

2

ionic liquid as solvent for the liquid extraction of benzene from its mixtures with aliphatic

3

hydrocarbons. Ind. Eng. Chem. Res. 2015, 54, 1342-1349.

4

(38) Pereiro, A. B.; Rodriguez, A. An ionic liquid proposed as solvent in aromatic hydrocarbon

5

separation by liquid extraction. AIChE J. 2010, 56, 381-386.

6

(39) Kuramochi, H.; Osako, M.; Kida, A.; Nishimura, K.; Kawamoto, K.; Asakuma, Y.; Fukui, K.;

7

Maeda, K. Determination of ion-specific NRTL parameters for predicting phase equilibria in

8

aqueous multielectrolyte solutions. Ind. Eng. Chem. Res. 2005, 44, 3289-3297.

9

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Energy & Fuels

1

List of Figures

2

Figure 1. Structure of [Eamim][NTf2] and [Eamim][SCN]

3

Figure 2. Vapor permeable membrane separation flowchart

4

Figure 3. The optimized geometries between IL (both cation and anion) and aromatic/alkanes. (a.

5

[Eamim] and benzene, b. [Eamim] and hexane, c. [NTf2] and benzene, d. [NTf2] and hexane, e.

6

[SCN] and benzene, f. [SCN] and hexane)

7

Figure 4. Tie-lines for the ternary mixtures {hexane + benzene + [Eamim][NTf2]}, {hexane +

8

benzene + [Eamim][SCN]}, at T= 25 °C and atmospheric pressure. Solid lines and full points

9

indicate experimental tie-lines, and dashed lines and empty circles indicate calculated data from the

+

-

-

+

-

-

10

NRTL model.

11

Figure 5. The selectivity of both ILs on benzene in both ternary systems

12

Figure 6. (a) The effect of operating temperature on membrane flux, (b) The effect of operating

13

temperature on membrane selectivity

14

Figure 7. (a) The effect of different benzene concentrations on membrane flux; (b) The effect of

15

different benzene concentrations on membrane selectivity

16

Figure 8. (a) The flux of benzene in long-term stability experiment; (b) The selectivity of benzene in

17

long-term stability experiment.

18

23


Energy & Fuels

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Page 24 of 37

1 2 3

cation

anion

Figure 1. Structure of [Eamim][NTf2] and [Eamim][SCN]

4

24


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Energy & Fuels

1 2

Figure 2. Vapor permeable membrane separation flowchart

3

25


Energy & Fuels

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 37

1

a

2

b

3 4

c

d

5 6

e

f

7

Figure 3. The optimized geometries between IL (both cation and anion) and aromatic/alkanes. (a.

8

[Eamim] and benzene, b. [Eamim] and hexane, c. [NTf2] and benzene, d. [NTf2] and hexane, e.

9

[SCN] and benzene, f. [SCN] and hexane)

+

-

+

-

-

26


-

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Energy & Fuels

benzene 0.0

1.0

0.1

0.9

0.2

0.8

0.3

0.7

0.4

0.6

0.5

0.5

0.6

0.4

0.7

0.3

0.8

0.2

0.9

hexane

0.1

1.0

0.0

1

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.0 [Eamim][NTf ] 2

benzene 0.0

1.0

0.1

0.9

0.2

0.8

0.3

0.7

0.4

0.6

0.5

0.5

0.6

0.4

0.7

0.3

0.8

0.2

0.9

hexane

0.1

1.0 0.0

0.0 [Eamim][SCN] 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

2 3

Figure 4. Tie-lines for the ternary mixtures {hexane + benzene + [Eamim][NTf2]}, {hexane +

4

benzene + [Eamim][SCN]}, at T= 25 °C and atmospheric pressure. Solid lines and full points

5

indicate experimental tie-lines, and dashed lines and empty circles indicate calculated data from the

6

NRTL model.

7

27


Energy & Fuels

70 [Eamim][NTf2] [Eamim][SCN]

60 50 40

S

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 37

30 20 10 0 0.0

0.2

0.4

0.8

1.0

x

1 2

0.6

Figure 5.

The selectivity of both ILs on benzene in both ternary systems

28


Page 29 of 37


J/(g·m-2·h-1)

60

40

20

0 20

30

40

50

T/°C

1

60

70

a

2


18

S

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

Energy & Fuels

12

6

0

20

30

40

50

3

T/°C

4

b

60

70

5

Figure 6. (a) The effect of operating temperature on membrane flux, (b) The effect of operating

6

temperature on membrane selectivity

29


Energy & Fuels

80 [Eamim][SCN] [Eamim][NTf2]

J/(g.m-1.h-1)

60

40

20

0 0.0

0.2

0.4

0.6

1

x

2

a

0.8

1.0

30

[Eamim][SCN] [Eamim][NTf2]

24

18

S

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 37

12

6

0 0.0

0.2

0.4

0.6

0.8

1.0

3

x

4

b

5

Figure 7. (a) The effect of different concentrations on membrane flux; (b) The effect of different

6

concentrations on membrane selectivity.

30


Page 31 of 37

60

J/(g·cm-2·h-1)

50 40


30 20 10 0 0

10

20

30

1

t/h

2

a

40

50

60

30 25


20

S

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

Energy & Fuels

15 10 5 0

0

10

20

30

3

t/h

4

b

40

50

60

5

Figure 8. (a) The flux of benzene in long-term stability experiment; (b) The selectivity of benzene in

6

long-term stability experiment.

7 8 31


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1

List of Tables

2

Table 1. Binding energies between ILs and benzene and n-hexane

3

Table 2. The influence of different ionic liquids on separation performance

4

Table 3. Values of the distribution coefficient (D) and selectivity (S) for the ternary system (hexane +

5

benzene + IL ([Eamim][NTf2] or [Eamim][SCN]) when mole fraction was 0.3 at different

6

temperatures

7

Table 4. The influence of different system on separation performance

8

Table 5. Values of NRTL parameters

9

32


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1

Energy & Fuels

Table 1. Binding energies between ILs and benzene and n-hexane

systems

∆E/kJ/mol

[Eamim]+-benzene

-28.09

[Eamim]+-hexane

-13.45

[NTf2] -benzene

-18.50

[NTf2] -hexane

-15.02

[SCN] -benzene

-20.58

[SCN] -hexane

-14.86

2

33


Energy & Fuels

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1

Page 34 of 37

Table 2. The influence of different ionic liquids on separation performance IL

Dhexane

Dbenzene

S

[Eamim][NTf2]

0.035

1.034

29.55

[Eamim][SCN]

0.009

0.523

61.44

[Bmim] [NTf2] [31]

0.104

1.660

15.89

[Omim] [NTf2] [31]

0.258

1.900

7.35

[Bzmim] [NTf2] [5]

0.072

2.226

30.87

[Bzvim] [NTf2] [5]

0.074

1.748

23.64

[Bmim][FeCl4][32]

0.171

2.270

13.26

2

*1. [Bmim][NTf2]: N-buthyl -N-methylimidazolium bis(trifluoromethylsulfonyl)imide

3

2. [Omim][NTf2]: N-octyl-N-methylimidazolium bis(trifluoromethylsulfonyl)imide

4

3. [Bzmim] [NTf2]: N-Benzyl-N-methyl imidazoium bis(trifluoromethylsulfonyl)imide

5

4. [Bzvim] [NTf2]: N-benzyl-N-vinyl imidazolium bis(trifluoromethylsulfonyl)imide

6

5. [Bmim][FeCl4]: N-butyl-N-methylimidazolium tetrachloroferrate

7 8

34


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Energy & Fuels

1

Table 3. Values of the distribution coefficient (D) and selectivity (S) for the ternary systems (hexane

2

+ benzene + IL) when the mole fraction of benzene was 0.3 at different temperatures IL

temperature

D benzene

D hexane

S

25 °C

0.824

0.031

26.85

30 °C

0.902

0.039

22.90

35 °C

0.921

0.041

22.47

40 °C

0.91

0.042

21.74

25 °C

0.451

0.011

42.20

30 °C

0.482

0.016

30.81

35 °C

0.529

0.022

24.49

40 °C

0.482

0.02

23.78

[Eamim][NTf2]

[Eamim][SCN]

3

35


Energy & Fuels

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1

Page 36 of 37

Table 4. The influence of different system on separation performance IL

Dalkane

system

Dbenzene

S

[Eamim][NTf2]

benzene/cyclohexane

0.105

2.382

22.70

[Eamim][SCN]

benzene/cyclohexane

0.029

1.108

38.26

2

36


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Energy & Fuels

Table 5. Values of NRTL parameters

1

i-j

∆g J (KLMN :$` )

∆g J (KLMN :$` )

αJ

σx

hexane(1)+benzene(2)+[Eamim][NTf2](3) 1-2

-0.7099

1.7550

1-3

7.1292

3.2048

2-3

5.8090

-0.8313

0.3

0.0829

hexane(1)+benzene(2)+[Eamim][SCN](3) 1-2

-0.2800

2.3423

1-3

4.8270

4.0231

2-3

4.9880

0.3777

2

37


0.3

0.0653

n-Hexane with Ester-Functionalized

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