Using binary mixtures of dicationic ionic liquids for determination of activity coefficients at infinite dilution by gas–liquid chromatography

Fluid Phase Equilibria 353 (2013) 93–100

Contents lists available at SciVerse ScienceDirect

Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid

Using binary mixtures of dicationic ionic liquids for determination of activity coefficients at infinite dilution by gas–liquid chromatography Kourosh Tabar Heydar ∗ , Halime Gharehmoshk Gharavi, Mina Nazifi, Mojtaba Mirzaei, Ali Sharifi Chemistry and Chemical Engineering Research Center of Iran, PO Box 14335-186, Tehran, Iran

a r t i c l e

i n f o

Article history: Received 20 February 2013 Received in revised form 23 May 2013 Accepted 29 May 2013 Available online 12 June 2013 Keywords: Ionic liquid Activity coefficients at infinite dilution Gas chromatography Abraham solvation parameters Stationary phase

a b s t r a c t This work is the continuation of our investigation into using dicationic ionic liquids (ILs) as stationary phase in gas chromatography (Tabar Heydar K, Nazifi M, Sharifi A, Mirzaei M, Gharavi H, Ahmadi SH, J. Chromatographia 76 (2013) 165). In this work, the activity coefficients at infinite dilution of 23 various solutes (alkanes, aromatics, alcohols, aldehydes, ketones, amines, chloroalkanes, ethers) have been measured in the two binary mixtures of ILs: 1,12-di(N-methylpyrrolidinium)dodecane–bis(trifluoromethylsulfonyl)imide/1,12-di(3-methylimidazolium)dodecane–bis(trifluoromethylsulfonyl)imide (1:1), [C12(mpy)2]–[(NTf2)2]/[C12 (mim)2]–[(NTf2)2] and 1,12-di(N-methylpyrrolidinium)dodecane– bis(trifluoromethylsulfonyl)imide/1,12 di(3-methylimidazolium)dodecane–tetrafluoroborate (1:1), [C12(mpy)2]–[(NTf2)2]/[C12(mim)2]–[(BF4)2], by gas–liquid chromatography (GLC) in the temperature range from 313 to 343 K. The same operations were performed on the neat IL: 1, 12-di(N-methylpyrrolidinium)dodecane–bis(trifluoromethylsulfonyl)imide, [C12(mpy)2]–[(NTf2)2] at T = 313 and 323 K, in order to make a comparison between different ILs. These mixtures of dicationic ILs with different anions and the neat IL have been investigated in this study for the first time. Moreover, the solvation interactions between solvents and solute molecules at 313, 343 and 373 K have been determined via Abraham solvation parameter model (linear solvation free energy relationship [LSFER] model). The selectivities for the octane/linear alcohols, octane/polar compounds, cyclohexane/aromatics were obtained from experimental activity coefficient data at 313 K, and compared with other ILs from the literature. The result of this comparison confirms that these ILs are potentially excellent solvents for the separation of alkanes/alcohols, alkanes/polar compounds and aliphatic/aromatic mixtures. © 2013 Elsevier B.V. All rights reserved.

1. Introduction In recent years, the applications of ionic liquids (ILs) in various disciplines of science, particularly analytical chemistry, have greatly expanded. This rapid increase is mainly due to ILs’ environment-friendly behaviour, plus their tunable physiochemical properties. When ILs are served as stationary phase in gas–liquid chromatography (GLC), the retention data can be used for obtaining multiple solvation interaction between solvents and solutes. In addition, a wide range of thermodynamic parameters can be extracted from chromatographic data. There are three methods to determine multiple solvation interactions between ILs and solute molecules. In all three

∗ Corresponding author. Tel.: +989122973152. E-mail addresses: [email protected] (K. Tabar Heydar), st nazifi@ccerci.ac.ir (M. Nazifi). 0378-3812/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fluid.2013.05.038

methods ILs used as stationary phase for gas chromatography (GC) columns, with the probe molecules’ retention data being chromatographically obtained to understand the types and magnitudes of solute–solvent interactions. These methods include Rohrschneider–McReynolds classification system [2,3], solvation parameter model [4,5] and the measurement of IL’s thermodynamic parameters such as activity coefficients at infinite dilution [6–8]. Activity coefficients at infinite dilution of a solute i ( i ∞ ) are a key factor to determine quantity of solutes’ volatility and also give information about intermolecular energy between solvent and solute [6–9]. Values of  i ∞ are important in separation processes, in particular for the selection of solvents for extraction and extractive distillation. Activity coefficients at infinite dilution can be obtained from different techniques such as dilutor technique (DT) [10,11], inert gas stripping [10,11], differential ebulliometry [11], headspace [12] and dew point techniques [13]. However, there are drawbacks, in terms of cost and material, associated with each method. Because the inverse gas chromatography technique needs

94

K. Tabar Heydar et al. / Fluid Phase Equilibria 353 (2013) 93–100

Table 1 Purity, purification methods and methods of purity analysis for ionic liquids solvents. Solvent

Purity (%)

Purification methods

Methods of purity analysis

[C12(mpy)2][(NTf2)2]

98

[C12(mim)2]–[(NTf2)2]

98

[C12(mim)2]–[(BF4)2]

97

Removing impurities with water, filtration by a silica gel column, and solvent evaporation Removing impurities with water, filtration by a silica gel column, and solvent evaporation Extraction with acetone: acetonitrile (10:1), filtration by a silica gel column, and solvent evaporation

Potentiometric titration,1 H and 13 C NMR spectra Potentiometric titration, 1 H and 13 C NMR spectra Potentiometric titration, 1 H and 13 C NMR spectra

less than 1 g of ILs, it can be considered as a cost-efficient method. In this work, values of  i ∞ for 23 polar and non-polar compounds in the two following binary mixtures of ILs with different anions and neat [C12 (mpy)2]–[(NTf2)2] have been determined at various temperatures (313, 323 and 373 K). 2. Experimental 2.1. Solvents and solutes All ILs were synthesized in CCEII1 . Table 1 describes the purity, purification methods and methods of purity analysis for ionic liquids solvents. N-Methylpyrrolidine, N-Methylimidazole and 1, 12-dibromododecane were purchased from Merck (Munich, Germany). Lithiumbis(trifluoromethylsulfonyl)imide was purchased from Acros and sodiumtetrafluoroborate was purchased from Sigma-Aldrich (Munich, West Germany). The solutes were purchased from Merck and Fluka. Table 2 describes the sources and purity of compounds. Since GC separates any impurities on the columns, no further purification was performed. Chromosorb W/AW (mesh 60/80) was purchased from Fluka. The purity of ILs is 98% for [C12(mpy)2][(NTf2)2] and [C12(mim)2]–[(NTf2)2] and 97% for [C12(mim)2]–[(BF4)2]. 2.2. Analysis method A Varian CP-gas chromatograph 3800 (Middelburg—Netherlands) was used in all gas chromatography experiments. The gas chromatograph is equipped with a thermal conductivity detector (TCD) and a 1041 injector, with the temperatures being constant at 523 K through all experiments. Helium was used as carrier gas and its flow rate was adjusted to reach the optimum level. The dead time was determined by air injection. A personal computer equipped with Galaxie software directly recorded detector signals and corresponding chromatograms.

Table 2 Sources and purity of compounds. Solute

Company

Purity (%)

Hexane Octane Decane Dodecane Tridecane Cyclohexane Benzene Toluene o-Xylene m-Xylene p-Xylene Methanol Ethanol Propanol 1-Pentanol 2-Propanol Cyclohexanol Butyraldehyde Octyl aldehyde Benzaldehyde 2-Pentanone Cyclopentanone Cyclohexanone Cycloheptanone Acetophenone Aniline N-Methylaniline Pyridine 1,2-Dichloroethane 1,4-Dioxane Acetonitrile Benzonitrile Ethylacetate Acetic acid Propionic acid Dimethylformamide 1-Chlorooctane 1-Bromooctane Nitrobenzene [C12(mpy)2]–[(NTf2)2] [C12(mpy)2]–[(NTf2)2] [C12(mim)2]–[(BF4)2]

Merck Merck Sigma-Aldrich Fluka Fluka Merck Merck Merck Merck Merck Merck Merck Merck Fluka Fluka Merck Sigma-Aldrich Fluka Aldrich Fluka Sigma-Aldrich Aldrich Sigma-Aldrich Aldrich Fluka Sigma-Aldrich Aldrich Sigma-Aldrich Fluka Fluka Merck Fluka Merck Fluka Sigma-Aldrich Merck Aldrich Aldrich Fluka Synthesized in CCERCIa Synthesized in CCERCIa Synthesized in CCERCIa

95 ≥99 99.5 ≥99.5 ≥99.5 99.8 ≥99 99.8 ≥99 ≥99 ≥99 99.9 ≥99 ≥99 ≥99.5 99.7 99 ≥99 99 ≥99 99.8 ≥99 99.5 99 98 99.5 98 99.8 ≥99 ≥98 ≥99 98 99 ≥99 ≥99.5 99.9 99 99 ≥99 98 98 97

2.3. Stationary phase preparation and sample injection condition Column packing, containing from 10%, 15% and 18% of stationary phase (IL) on Chromosorb W-AW (mesh 60/80), was prepared using the rotary evaporator technique. After evaporation of the dichloromethane under vacuum, the support was equilibrated at 323 K for 18 h. The solid support material was filled in a stainless steel column with an inner diameter of 1/8 in. and a length of 1 m. The weight of the packing material was calculated from the weights of the packed and empty column. In order to be in infinite dilution conditions, 0.1–0.5 ␮l of headspace vapor of samples was injected into the columns. No differences in retention times tR were found by injecting individual pure components or their mixtures. The measurements were carried out at 313, 323 and 343 K. At any temperature, each experiment was repeated at least three times in

1

Chemistry and Chemical Engineering Research centre of Iran.

order to check the reproducibility. The differences of the retention times of the three measurements were reproducible within 0.01 to 0.1 min. Under mentioned conditions, 23 organic solutes were injected into 7GC columns at different temperatures (313, 323 and 343 K), with the retention data using for calculation of activity coefficients at infinite dilution, selectivity and Abraham solvation parameters. 2.4. Calculation Rohrschneider–McReynolds classification system: The Rohrschneider–McReynolds system is the foremost classification system that codifies stationary phases based on the retention behaviour of five probe molecules: benzene, butanol, 2-pentanone, nitropropane, and pyridine. Each probe molecule is used to represent a distinct or a combination of interactions between solutes

K. Tabar Heydar et al. / Fluid Phase Equilibria 353 (2013) 93–100

95

[C12(mpy)2][(NTf2)2]

[C12(mim)2]-[ (NTf2)2]

[C12(mim)2]-[(BF4)2] Fig. 1. Structures of ionic liquids.

and the stationary phases. The Rohrschneider–McReynolds system is defined in Eq. (1) in terms of the five probes and their corresponding phase constants; namely, benzene (X ), butanol (Y ), 2-pentanone (Z ), nitropropane (U ), and pyridine (S ) with the overall difference in the Kovats retention index (I). I = ax + bY  + cZ  + dU  + eS 

(1) X ,

Y ,

Z ,

U ,

S )

The value of each phase constant (i.e., and is determined by subtracting the retention index of the probe on a Squalane stationary phase from the retention index of the probe on the stationary phase being characterized. 2.5. Abraham solvation parameter model: Abraham solvation parameter model works successfully as a powerful tool for characterizing liquid- or gas-phase interactions between solute molecules and liquid phases [4,14,15]. In addition, describing more than one polarity or phase constant, this model can provide further information about the solvation interactions originated from cation and anion in ionic solvents. This model can describe simultaneous interactions between solvent and solutes. LSFER equation is given in Eq. (2): Log KL = c + eE + sS + aA + bB + lL

(2)

where KL describes gas–liquid partition coefficient. The solute descriptors are defined as: E is the excess molar refraction, S is the solute dipolarity/polarizability index, A and B are the solute hydrogen-bond acidity and basicity, respectively, and L is the logarithm of the gas–hexadecane partition coefficient at T = 298 K. Solute descriptors are available for an extensive range of compounds [4]. The six regression coefficients (c, e, s, a, b and l) relate to the properties of the solvent phase and are determined by multiple linear regression analysis (MLRA) from experimental KL . MLRA and statistical computations were performed using the programme Analyze it (Microsoft, USA). The c coefficient is the model constant, e provides a measure of the solute–stationary phase interactions via ␲–␲ and n–␲ interactions, s is a measure of stationary phase dipolarity, a provides a measure of hydrogen bond basicity, b is a measure of hydrogen bond acidity, and l describes overall dispersive-type interactions. The gas–liquid partition coefficient is determined by linear regression using Eqs. (3) and (4) [16,17] with experimental data for a minimum of three column packing with different phase loadings (10%, 15%, 18%) (Fig. 1). VN∗

B = KL + VL VL

VN∗ =

 3  (2W )

(3)

 (tR − tM )F0

(P 2 − 1) (P 3 − 1) *

Fig. 2. Plot of VN * /VL versus 1/VL for solutes: 1: cyclopentanone, 2: 1,2dichloroethane, 3: benzene, 4:butyraldehyde, 5: methanol, 6: octane in ionic liquid [C12(mpy)2][(NTf2)2]/[C12(mim)2]–[(BF4)2] at 313 K.

integer containing terms characteristic of the magnitude of interfacial adsorption at the support and/or liquid interface. Two plots of VN * /VL versus 1/VL for six solutes (cyclopentanone, butyraldehyde, benzene, 1,2-dichloroethane, methanol and octane) at 313 K are given in Figs. 2 and 3. According to Eq. (4), tR the solute retention time, tM the column dead time, F0 the carrier gas flow-rate at the column outlet, P the column pressure drop Pi /P, Pi the column inlet pressure, P the ambient pressure and W the weight of column packing. The partition coefficient KL can be determined by plotting VN * /VL with 1/VL . 2.6. Measurement of ionic liquid thermodynamic parameters: Eq. (5) developed by Everett and Cruickshank et al. [9] has been broadly applied for determining the values of activity coefficients at infinite dilution. Ln i∞ = Ln(

2B12 − V∞ o B11 − V s nRT + JP ) − Ps RT RT V N Ps

(5)

In aforementioned equation, n is the mole number of the stationary phase component inside the column, R the ideal gas constant, T the temperature of the oven, VN is the standardized retention ◦ volume of the solute, P the column outlet pressure (equal to atmospheric pressure), Vs the saturated liquid molar volume of the solute at T and V∞ is the partial molar volume of the solute at infinite dilution in the solvent. B11 the second virial coefficient of the solute in the gaseous state at temperature T, B12 the mutual virial coefficient

VN*/VL 8000 7000 6000 5000 4000 3000 2000 1000

 (4)

According to Eq. (3), VN is the net retention volume per gram of column packing, VL is the volume of liquid phase per gram of column packing, KL is the gas–liquid partition coefficient, B is an

0 0

2

4

6

8

10

12

14

16

1/VL

Fig. 3. Plot of VN * /VL versus 1/VL for solutes: 1: cyclopentanone, 2: butyraldehyde, 3: benzene, 4: 1,2-dichloroethane, 5: methanol, 6: octane in ionic liquid [C12(mpy)2][(NTf2)2]/[C12(mim)2]–[(NTf2)2] at 313 K.

96

K. Tabar Heydar et al. / Fluid Phase Equilibria 353 (2013) 93–100

Table 3 Rohrschneider–McReynolds constants at 373 K. Stationary phase

Benzene

1-Buthanol

2-Pentanone

Nitropropane

Pyridine

Total coefficient

[C12(mpy)2][(NTf2)2]/[C12(mim)2]–[(NTf2)2] C12(mpy)2][(NTf2)2]/[C12(mim)2]–[(BF4)2] [C12(mpy)2][(NTf2)2] Squalane DB-5a OV-22b

331 394 401 0 27 160

574 885 598 0 66 188

557 607 582 0 71 191

758 886 750 0 93 283

679 777 657 0 63 253

2899 3549 2988 0 320 1075

a

Stationary phase of (5% phenyl)-methylpolysiloxane. Obtained from Ref. [26] Stationary phase of phenylmethyldiphenylpolysiloxane. Obtained from Ref. [26] Standard uncertainties u are u (total coefficient)  1%, u(T) = ±1 K. b

Table 4 The experimental gas–liquid partition coefficients KL for the solutes in ionic liquid[C12(mpy)2][(NTf2)2]/[C12(mim)2]–[(NTf2)2]. Solute

T (K) 313

Hexane Heptane Octane Decane Dodecane Cyclohexane Benzene Toluene Ethylbenzene o-Xylene m-Xylene p-Xylene Methanol Ethanol Propanol 1-Pentanol 1-Octanol 1-Decanol 2-Propanol Cyclohexanol Butyraldehyde Octyl aldehyde Benzaldehyde 2-Pentanone Cyclopetanone Cyclohexanone Cycloheptanone Acetophenone Aniline N-Methylaniline Pyridine 3-Methylpyridine Carbontetrachloride 1,2-Dichloroethane 1,4-Dioxane Acetonitrile Benzonitrile Ethylacetate Acetic acid Propionic acid Dimethylformamide Nitropropane 1-Chlorooctane 1-Bromooctane

323

373

KL

R2 a

KL

R2

KL

R2

78.89 – 136.14 – – 78.89 530.88 1109.17 2152.78 3698.28 2728.98 2540.97 198.61 283.79 827.94 3953.67 – – 346.74 – 559.76 – – – 6208.69 – – – – – 3380.65 – 191.87 461.32 1499.68 897.43 – 512.86 3047.89 – – – 3741.11 6280.58

0.97 – 0.98 – – 0.99 0.97 0.95 0.98 0.96 0.99 0.97 1 0.98 0.92 0.92 – – 1 – 0.99 – – – 0.99 – – – – – 0.97 – 1 1 0.96 0.97 – 0.97 0.97 – – – 0.93 0.95

37.15 – 60.26 – – 40.74 191.87 367.28 571.48 853.10 650.13 625.17 87.90 125.60 225.42 810.96 4864.07 – 143.55 3083.19 190.11 1927.52 6456.54 469.89 1618.08 3006.08 6456.50 2060.63 – – 1051.96 2079.69 75.86 171.79 521.19 332.66 – 176.10 928.97 1713.96 – – 722.77 1250.26

0.99 – 1 – – 1 1 0.98 0.98 0.99 0.99 0.99 1 0.99 0.98 0.98 1 – 1 0.99 1 0.97 0.95 0.99 0.97 0.97 0.99 0.96 – – 0.96 0.97 1 1 0.98 1 – 1 1 1 – – 0.98 0.99

28.71 26.24 41.59 74.99 143.55 25.41 83.37 145.88 215.28 303.39 222.33 213.30 42.85 62.37 96.83 254.68 1066.59 2890.68 61.94 931.11 82.04 575.44 – 164.44 535.80 948.42 1659.59 623.73 4954.50 4875.28 367.28 751.62 41.78 83.37 167.49 158.12 2415.46 81.47 338.06 576.77 3301.44 419.76 248.31 387.56

0.99 1 0.92 0.99 0.93 0.94 0.93 0.98 0.99 1 0.92 0.93 0.98 1 1 1 0.97 0.97 0.99 1 1 0.99 – 0.97 0.97 0.99 0.97 0.98 0.98 0.97 0.96 0.97 1 0.98 0.98 1 0.98 0.99 1 0.98 0.97 0.92 1 0.98

a Statistical correlation coefficient. Standard uncertainties u are u(KL )  3%, u(T) = ±1 K

between the solute 1 and the carrier gas helium 2 and Pς is the probe vapor pressure at temperature T. The second and third terms in Eq. (5) are correction terms that results from the non-ideality of the mobile gaseous phase. The molar volume of the solute Vs was determined by experimental densities, and the partial molar volumes of the solutes at infinite dilution V∞ were assumed to be equal to Vς . The vapor pressure values were calculated via Antoine

equation [18,19]. The standardized retention volume, VN , can be calculated with the following equation: V N = JUo t  R

(6)

The adjusted retention time, tR , calculated from the difference between retention time of a solute and that of air. U0 , the flow rate of the carrier gas, measured at the room temperature. The factor J

K. Tabar Heydar et al. / Fluid Phase Equilibria 353 (2013) 93–100

97

Table 5 The experimental gas–liquid partition coefficients KL for the solutes in ionic liquid[C12(mpy)2][(NTf2)2]/[C12(mim)2]–[(BF4)2]. Solute

T (K) 313

Hexane Octane Decane Dodecane Tridecane Cyclohexane Benzene Toluene o-Xylene m-Xylene p-Xylene Methanol Ethanol Propanol 1-Pentanol 2-Propanol Cyclohexanol Butyraldehyde Octyl aldehyde Benzaldehyde 2-Pentanone Cyclopetanone Cyclohexanone Cycloheptanone Acetophenone Aniline N-Methylaniline Pyridine 3-Methylpyridine 1,2-Dichloroethane 1,4-Dioxane Acetonitrile Benzonitrile Ethylacetate Acetic acid Propionic acid Dimethylformamide 1-Chlorooctane 1-Bromooctane Nitrobenzene

323 2a

373 2

KL

R

KL

R

KL

R2

48.42 69.50 261.82 622.30 595.66 46.77 395.37 835.60 2360.48 1682.67 1674.94 255.86 377.57 790.68 – 454.99 – 183.65 – – 981.75 4466.84 – – – – – 2600.16 – 469.89 1355.19 870.96 – 325.09 – – – 1798.87 3758.37 –

0.96 0.99 0.99 1 0.99 0.98 0.99 0.99 0.99 0.92 0.92 0.99 0.99 0.93 – 0.92 – 0.97 – – 0.99 0.97 – – – – – 0.93 – 0.99 1 0.97 – 0.93 – – – 0.95 0.99 –

21.13 33.19 – – 173.38 22.54 123.88 249.46 599.79 433.51 441.57 90.99 116.68 232.27 979.49 118.03 2018.37 128.82 1224.62 5984.12 293.09 1091.44 1936.42 3854.78 1663.41 – – 814.70 1721.87 161.81 385.48 292.42 – – 1145.51 1442.12 5407.54 430.53 760.33 –

1 0.99 – – 1 0.97 0.99 0.96 0.93 0.97 0.92 0.99 0.99 1 0.99 1 1 1 0.99 0.99 0.96 1 1 1 0.99 – – 0.99 0.98 0.97 0.99 1 – – 0.99 0.99 0.92 0.94 0.99 3396.25

13.89 23.12 43.85 62.52 – 17.62 65.01 98.40 180.30 138.36 146.89 48.08 65.61 110.92 254.06 58.48 544.51 63.39 338.84 1465.55 104.71 345.94 562.34 963.83 449.78 5495.41 4216.97 266.07 496.59 63.09 147.23 140.93 2032.36 – 279.25 651.63 1448.77 131.83 213.32 0.97

0.99 0.98 0.99 0.94 – 0.96 1 1 1 0.99 0.92 0.95 0.99 0.99 0.98 0.99 0.99 1 0.92 0.98 0.99 0.98 0.92 1 0.92 0.99 0.97 0.93 0.96 1 0.99 0.97 0.95 – 1 0.93 0.97 0.99 0.98 –

a Statistical correlation coefficient Standard uncertainties u are u(KL )  3%, u(T) = ±1 K

Table 6 Interaction parameters obtained from the [C12(mpy)2][(NTf2)2]/[C12(mim)2]–[(BF4)2].

solvation

parameter

model

for

two

binary

mixture

of

ILs

[C12(mpy)2][(NTf2)2]/[C12(mim)2]–[(NTf2)2]and

Solvent

T (K)

c

e

s

a

b

l

na

R2 b

C12 (mpy)2–NTf2 /C12 (mim)2–NTf2

313

0.05 (0.11) 0.14 (0.11) 0.11 (0.09) 0.14 (0.15) 0.12 (0.13) 0.39 (0.22) −2.83 (0.12) −2.85 – −2.99 (0.1)

0.06 (0.14) 0.01 (0.16) 0.07 (0.12) 0.37 (0.19) 0.16 (0.16) 0.19 (0.27) 0.27 (0.10) 0.34 (0.09) 0.23 (0.09)

1.78 (0.17) 1.46 (0.19) 1.40 (0.14) 1.90 (0.27) 1.62 (0.19) 1.44 (0.31) 1.71 (0.12) 1.52 (0.11) 1.49 (0.10)

1.81 (0.17) 1.42 (0.17) 1.32 (0.15) 2.13 (0.35) 1.61 (0.20) 1.39 (0.34) 1.98 (0.10) 1.65 (0.08) 1.48 (0.08)

0.33 (0.19) 0.40 (0.22) 0.14 (0.19) 0.17 (0.32) 0.33 (0.25) −0.15 (0.41) 0.32 (0.15) 0.35 (0.13) 0.15 (0.14)

0.60 (0.03) 0.47 (0.02) 0.38 (0.02) 0.47 (0.03) 0.38 (0.03) 0.28 (0.05) 0.62 (0.03) 0.48 (0.03) 0.42 (0.03)

24

0.97

35

0.95

42

0.95

24

0.95

32

0.95

38

0.95

30

0.99

32

0.99

30

0.99

343 373 C12 (mpy)2–NTf2 /C12 (mim)2–BF4

313 343 373

C9 (mpy)2–NTf2 c

313 343 373

a

Number of probe molecules subjected to multiple linear regression analysis Statistical correlation coefficient. c Obtained from Ref. [27]. The figures in parenthesis refer to the standard uncertainty. b

98

K. Tabar Heydar et al. / Fluid Phase Equilibria 353 (2013) 93–100

Table 7 The experimental activity coefficients at infinite dilution  i ∞ for solutes in the two binary mixture of ILs [C12(mpy)2][(NTf2)2]/[C12(mim)2]–[(NTf2)2] and [C12(mpy)2][(NTf2)2]/[C12(mim)2]–[(BF4)2] at different temperatures. C12 (mpy)2–NTf2 /C12 (mim)2–NTf2

C12 (mpy)2–NTf2 /C12 (mim)2–BF4

T (K)

313

323

343

Solute Heptane Octane Cyclohexane

4.144 18.695 2.311

3.350 12.105 2.070

2.470 4.297 1.630

Benzene Toluene o-Xylene m-Xylene p-Xylene

0.308 0.417 0.521 0.585 0.584

0.318 0.433 0.552 0.612 0.614

0.334 0.472 0.604 0.670 0.674

Methanol Ethanol Propanol 2- Propanol

0.471 0.588 0.710 0.641

– 0.552 0.664 0.599

– 0.488 0.584 0.525

Butyraldehyde

0.246

0.253

0.272

313

323

343

7.493 34.541 3.735

6.611 21.316 3.392

5.199 8.171 2.807

0.423 0.606 0.806 0.653 0.898

0.444 0.636 0.843 0.771 0.938

0.490 0.695 0.916 1.039 1.021

0.422 0.574 0.721 0.625

– 0.543 0.670 0.589

– 0.486 0.582 0.522

0.375

0.387

0.414

0.403 0.307

0.424 0.319

0.465 0.345

2.783 0.241 Chloride alkanes – 0.456 Ethers 0.306 Other solutes 0.206 0.482 –

2.030 0.247

1.126 0.265

– 0.452

– 0.448

0.324

0.352

0.209 – –

0.222 – 0.136

Alkanes

Aromatics

Alcohols

Aldehydes Ketones 2- Pentanone Cyclopentanone

0.246 0.197

0.258 0.205

0.287 0.224

Triethylamine Pyridine

0.452 0.167

0.440 0.175

0.244 0.190

Carbontetrachloride 1,2-Dichloroethane

0.763 0.397

0.744 0.396

0.709 0.394

1,4-Dioxane

0.224

0.233

0.250

Acetonitrile Ethylacetate Acetic acid

0.191 0.293 –

0.188 0.302 –

0.186 0.323 0.239

Amines

Standard uncertainties u are u( i ∞ )  3%, u(T) = ±1 K Table 8 The experimental activity coefficients at infinite dilution  i ∞ for solutes in [C12(mpy)2]–[(NTf2)2] at different temperatures.

B = 0.430 − 0.886 Vc

T (K) 313 Solute Heptane Octane Cyclohexane

323

Methanol Ethanol Propanol

4.764 6.667 2.216

5.649 9.181 2.490

0.259 0.346 Alcohols 0.385 0.496 0.656

Carbontetrachloride 1,2-Dichloroethane trichloroethylene

0.464 0.166 0.261

Acetonitrile

0.156

0.310 0.417 0.445 0.537 0.647 0.656 0.246 0.300 Other solutes 0.179

Standard uncertainties u are u( i ∞ )  3%, u(T) = ±1 K

corrects the influence of the pressure drop along the column. The correction factor of J depends on the pressure at the column outlet and inlet. This factor is defined by Eq. (7). 3 (pi − po )2 − 1 2 (pi − po )3 − 1

c

T

 T 2

− 0.694

c

T

 T 4.5

− 0.0375(n − 1)

c

T (8)

Chloride alkanes

J=

T 

Alkanes

Aromatics Benzene Toluene

The values of B11 and B12 were calculated using the McGlashan and Pottere equation (8):

(7)

where n denotes the number of carbon atoms. In the above equation, the critical properties of the pure component (Tc 11 and Vc 11 ) were extracted from the literature [20–24] and the critical data Tc 12 , Vc 12 were calculated using the Hudson and McCoubrey combining rule [22,25]. The selectivity Sij ∞ is the ratio of the activity coefficients at infinite dilution and is given by Eq. (9) [26]: Sij∞ =

ILi∞ ILj∞

(9)

The selectivity factor Sij ∞ demonstrates the suitability of a solvent for separating mixtures of components i and j, where i and j refer to the liquids to be separated. The selectivity values are especially important to determine the potential of the ionic solvent for extractive distillation in the separation of aromatic compounds from aliphatic compounds. To achieve an effective and economic separation the selectivity should be greater than one. 3. Result and discussion Rohrschneider–McReynolds coefficients were determined for the two binary mixtures of ILs and neat [C12(mpy)2]–[(NTf2)2] at 373 K. The final results are presented in Table 3 and compared with Rohrschneider–McReynolds coefficients taken from other literature [27]. It can be seen that the polarity of mixture solvents

K. Tabar Heydar et al. / Fluid Phase Equilibria 353 (2013) 93–100

99

Table 9 Selectivities Sij ∞ for different ILs for alkane/alcohol separation at T = 313 K. Solvent

Octane/Methanol

Octane/Ethanol

Octane/Propanol

Octane/2-Propanol

Reference

[C12(mpy)2][(NTf2)2]/[C12(mim)2]–[(NTf2)2] [C12(mpy)2][(NTf2)2]/[C12(mim)2]–[(BF4)2] [C12(mpy)2]–[(NTf2)2] [C12(methylmorpholine)2]-[(NTf2)2] [C9(methylmorpholine)2]–[(NTf2)2] 1-Buthyl-3-methylimidazolium–CF3 SO3 1-Buthyl-3-methylimidazolium–BF4 1-Buthyl-3-methylimidazolium–FeCl4

39.7 81.8 17.32 21.48 33.63 118.4 189.9 22.2

31.8 60.2 13.44 15.53 24.68 73.6 97.8 18.9

26.3 47.9 10.15 10.75 16.63 57.0 54.8 15.7

29.2 55.4 – – – 58.3 61.2 –

This work This work This work [1] [1] [28,29] [30,31] [32]

Table 10 Selectivities Sij ∞ for different ILs for alkane/polar compound separation at T = 313 K. Solvent

Octane/1,4-dioxane

Octane/ethylacetate

Octane/acetonitrile

Reference

[C12(mpy)2]–[(NTf2)2]/[C12(mim)2]–[(NTf2)2] [C12(mpy)2][(NTf2)2]/[C12(mim)2]–\[(BF4)2] [C12(mpy)2]–[(NTf2)2] 1-Buthyl-3-methylimidazolium–CF3 SO3 1-Buthyl-3-methylimidazolium–BF4

83.4 112.9 – 70.6 88.5

63.8 71.8 – 41.2 40.7

97.9 167.7 42.7 103.6 183.3

This work This work This work [28,29] [30,31]

are considerably higher than common solvents used in gas chromatography. Also, the polarity of ILs doesn’t change radically with adding of IL with different cation (imidazolium) into the neat IL, whereas the polarity of the mixture of ionic liquids with the different anion (BF4 − ) and cation increase remarkably. Thus, anions play an important role in the polarity of the ILs. In second part of the experiment, in order to study the different interactions between the solutes and the solvents, the Abraham solvation parameters were computed for the two mixtures of ILs with the stationary phase loadings of 10%, 15% and 18%. Tables 4 and 5 present the gas–liquid partition coefficients for all compounds that are used in Abraham solvation parameter model. High values of KL for polar compounds anticipate good solubility of solute in ionic liquid and comport with the low values of  i ∞ . Low values of KL for alkanes bespeak that these non-polar compounds dissolve in ionic liquids poorly, and it is connected with high values of  i ∞ . Abraham parameters have been calculated for the two mixtures of ILs at 313, 343 and 373 K. The final results are presented in Table 6 and compared with Abraham parameters taken from other literature [28]. The terms of e, a measure of the solute–stationary phase interactions via ␲–␲ and n–␲ interactions, a, the hydrogen bond basicity term, and s, the dipolarity term for mixture of ILs with different anions NTf2 − /BF4 − are larger than the mixture of ILs with similar anions NTf2 − /NTf2 − . The weak basicity of NTf2 − anion is due to delocalized negative charge. The ability of mixture of ionic liquids with NTf2 − /NTf2 − anions for separating of homologues, the term of l, is larger than other mixture of ionic liquids with NTf2 − /BF4 − anions. The results show that anion in ionic liquids has a profound effect on different interactions between the solutes and the solvents. The activity coefficients at infinite dilution of 23 either polar or non-polar organic solutes in the two binary mixtures of ILs inclusive of [C12(mpy)2]–[(NTf2)2]/[C12(mim)2]–[(NTf2)2],[C12(mpy)2]– [(NTf2)]/[C12(mim)2]–[(BF4)2] and neat [C12(mpy)2]–[(NTf2)2]

at different temperatures have been measured and Tables 7 and 8 report the final results of calculation, respectively. The stationary phase loading of all columns is 18 percent. Logically, the high values of  i ∞ for non-polar indicate their low solubility in the ILs. Small values of  i ∞ portend strong interactions between solvents and solutes. It can be seen that in linear hydrocarbons the values of  i ∞ rise with the increase in the length of carbon chain. In aromatic compounds, the values of  i ∞ are noticeably small. This is mainly due to the presence of delocalized ␲ electrons which can interact strongly with the highly polar cations and anions in ionic liquids. The values of  i ∞ for aromatic compounds increase with the addition of alkyl substitutions to the aromatic rings, which results in lower polarity. However, the position of alkyl substitutions in xylene has a small effect on the measures of  i ∞ . The trend of changes in the values of  i ∞ in linear alcohols is similar to those for linear alkanes. Carbon tetrachloride has a relatively small value of  i ∞ in comparison to other non-polar compounds; it is because of the presence of 24 polarizable electrons which can interact with polar solvent. In amine group, the values of  i ∞ for pyridine, aromatic amine, are smaller than aliphatic ones. The values of selectivities were calculated directly from experimental values of  i ∞ at 313 K. The values of selectivities for octane/methanol, octane/ethanol, octane/propanol and octane 2propanol are presented in Table 9, the values of selectivities for octane/1,4-dioxane, octane/ethyl acetate and octane/acetonitrile are presented in Table 10 and the values of selectivities for cyclohexane/benzene and cyclohexane/toluene are presented in Table 11. All the values of selectivities were compared to those values taken from the literature [29–35]. The values of selectivity in [C12(mpy)2]–[(NTf2)2]/[C12(mim)2]–[(BF4)2] for the separation of alkanes/alcohols and alkanes/polar compounds are very great, in compared to those for the mixture of [C12(mpy)2]–[(NTf2)2]/[C12(mim)2]–[(NTf2)2], and the

Table 11 Selectivities Sij ∞ for different ionic liquids for aliphatic/aromatic separation at T = 313 K. Solvent

Cyclohexane/benzene

Cyclohexane/toluene

Reference

[C12(mpy)2]–[(NTf2)2]/[C12(mim)2]–[(NTf2)2] [C12(mpy)2]–[(NTf2)2]/[C12(mim)2]–[BF4] [C12(mpy)2]–[(NTf2)2] [C12(methylmorpholine)]–[(NTf2)2] [C9(methylmorpholine)]–[(NTf2)2] 1-Hexyl-3-methylimidazolium–CF3 SO3 Trihexyltetradecylphosphonium-bis-(2,4,4-trimethylpentyl)–phosphinate

7.5 8.8 8.4 4.3 9.60 7.3 1.1

5.5 6.2 6.4 3.4 7.62 5.4 –

This work This work This work [1] [1] [33] [34]

100

K. Tabar Heydar et al. / Fluid Phase Equilibria 353 (2013) 93–100

selectivity values for the separation of aliphatic/aromatic mixture in the two mixtures of ILs are considerably close together. The results indicate that BF4 − anion play an important role in the separation of alcohols and polar compounds from alkanes. References [1] K. Tabar Heydar, M. Nazifi, A. Sharifi, M. Mirzaei, H. Gharavi, S.H. Ahmadi, J. Chromatogr. 76 (2013) 165–175, http://dx.doi.org/10.1007/ s10337-012-2385-3. [2] L. Rohrschneider, J. Chromatogr. A 22 (1966) 6–22. [3] M.B. Evans, J.K. Haken, J. Chromatogr. A 406 (1987) 105–115, http://dx.doi.org/10.1016/S0021-9673(00)94021-4. [4] M.H. Abraham, Chem. Soc. Rev. 22 (1993) 73–83. [5] T.O. Kollie, C.F. Poole, M.H. Abraham, G.S. Whiting, Anal. Chim. Acta 259 (1992) 1–13, http://dx.doi.org/10.1016/0003-2670(92)85067-g. [6] A. Heintz, D.V. Kulikov, S.P. Verevkin, J. Chem. Eng. Data 46 (2001) 1526–1529, http://dx.doi.org/10.1021/je0101348. [7] A. Heintz, D.V. Kulikov, S.P. Verevkin, J. Chem. Eng. Data 47 (2002) 894–899, http://dx.doi.org/10.1021/je0103115. [8] A. Heintz, D.V. Kulikov, S.P. Verevkin, J. Chem. Thermodyn. 34 (2002) 1341–1347, http://dx.doi.org/10.1006/jcht.2002.0961. [9] A.J.B. Cruickshank, M.L. Windsor, C.L. Young, Proc. R. Soc. London, Ser. A 295 (1966) 271–287, http://dx.doi.org/10.1098/rspa.1966.0240. [10] J.-C. Lerol, J.-C. Masson, H. Renon, J.-F. Fabries, Sannier H, AlChE J. 16 (1977) 139–144, http://dx.doi.org/10.1021/i260061a609. [11] C.A. Eckert, B.A. Newman, G.L. Nicolaides, T.C. Long, AIChE J. 27 (1981) 33–40, http://dx.doi.org/10.1002/aic.690270107. [12] S.C. Anand, J.P.E. Grolier, O. Kiyohara, C.J. Halpin, G.C. Benson, J. Chem. Eng. Data 20 (1975) 184–189, http://dx.doi.org/10.1021/je60065a020. [13] D.B. Trampe, C.A. Eckert, AIChE J. 39 (1993) 1045–1050, http://dx.doi.org/10.1002/aic.690390613. [14] J.L. Anderson, J. Ding, T. Welton, D.W. Armstrong, J. Am. Chem. Soc. 124 (2002) 14247, http://dx.doi.org/10.1021/ja028156h. [15] N.K. Sharma, M.D. Tickell, J.L. Anderson, J. Kaar, V. Pino, B.L. Wicker, D.W. Armstrong, J.H. Davis, A.J. Russell, Chem. Commun. (2006) 646. [16] R.N. Nikolov, J. Chromatogr. 241 (1982) 237–256, http://dx.doi.org/10.1016/ S0021-9673(00)81750-1.

[17] S.K. Poole, C.F. Poole, J. Chromatogr. 500 (1990) 329–348, http://dx.doi.org/10.1016/S0021-9673(00)96075-8. [18] J.A. Riddick, W.B. Bunger, T.K. Sakano, Organic Solvents: Physical Properties and Methods of Purification, Wiley Interscience, New York, 1986. [19] Thermodynamics Research Centre, TRC Thermodynamic Tables, The Texas A&M University System, College Station, TX, 1990. [20] R.C. Reid, J.M. Prausnitz, T.K. Sherwood, The Properties of Gases and Liquids, in: Chemical Engineering Series, McGraw-Hill, New York, 1977. [21] J.M. Prausnitz, R.N. Lichtenthaler, E.G. Azevedo, Molecular Thermodynamics of Fluid Phase Eqilibria, Prentice Hall, New York, 1986. [22] A.J.B. Cruickshank, M.L. Windsor, C.L. Young, Proc. Roy. Soc. A (1966), 295, 271. [23] Thermodynamics Research Center, Texas Engineering Experiment Station, The Texas A. and M. University System, College Station, TX, 1987. [24] R.C. Reid, J.M. Prausnitz, T.K. Sherwood, Chemical Engineering Series, third ed., McGraw-Hill, New York, 1977. [25] G.H. Hudson, J.C. McCoubrey, Trans. Faraday Soc. 56 (1960) 761–766. [26] B. Kolbe, J. Gmehling, U. Onken, Selection of Solvents for Extractive Rectification by means of Predicted Equilibria Data, Ber. Bunsenges. Phys. Chem. 83 (1979) 1133–1136. [27] D.W. Armstrong, L. He, Y.S. Lio, Anal. Chem. 71 (1999) 3873–3876, http://dx.doi.org/10.1021/ac990443p. [28] J.L. Anderson, R. Ding, A. Ellem, D.W. Armstrong, J. AM. Chem. Soc. 127 (2005) 593–604, http://dx.doi.org/10.1021/ja046521u. [29] M.L. Ge, L.S. Wang, M.Y. Li, J.S. Wu, J. Chem. Eng. Data 52 (2007) 2257–2260, http://dx.doi.org/10.1021/je700282w. [30] M.L. Ge, L.S. Wang, J. Chem. Eng. Data 53 (2008) 846–849, http://dx.doi.org/10.1021/je700560s. [31] Q. Zhou, L.S. Wang, J. Chem. Eng. Data 51 (2006) 1698–1701, http://dx.doi.org/10.1021/je060142u. [32] M.L. Ge, L.S. Wang, M.Y. Li, J.S. Wu, Q. Zhou, J. Chem. Eng. Data. 53 (2008) 1970–1974, http://dx.doi.org/10.1021/je800218g. [33] S.A. Kozlova, S.P. Verevkin, A. Heintz, T. Peppl, M. Kockerling, J. Chem. Thermodyn. 41 (2009) 330–333, http://dx.doi.org/10.1016/j.jct.2008.09.004. [34] X.J. Yang, J.S. Wu, M.L. Ge, L.S. Wang, M.Y. Li, J. Chem. Eng. Data 53 (2008) 1220–1222, http://dx.doi.org/10.1021/je800043a. [35] T.M. Letcher, D. Ramjugernath, M. Laskowska, M. Krolikowski, P. Naidoo, U. Domanska, J. Chem. Thermodyn. 40 (2008) 1243–1247, http://dx.doi.org/10.1016/j.jct.2008.04.002.