Isobaric VaporâLiquid Equilibria for Ethyl Acetate + Methanol + Ionic

Article pubs.acs.org/jced

Isobaric Vapor−Liquid Equilibria for Ethyl Acetate + Methanol + Ionic Liquids Ternary Systems at 101.3 kPa Zhigang Zhang, Fenjin Pan, Qinqin Zhang, Tao Zhang, Lin Zhang, Kaifang Wu, and Wenxiu Li* Liaoning Provincial Key Laboratory of Chemical Separation Technology, Shenyang University of Chemical Technology, Shenyang, 110142, China S Supporting Information *

ABSTRACT: Isobaric vapor−liquid equilibrium (VLE) data for the ethyl acetate + methanol +1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]) and ethyl acetate + methanol +1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]) ternary systems were measured at 101.3 kPa with an improved all-glass single-cycle still. They were correlated with the nonrandom two-liquid (NRTL) model and were in good agreement with the correlated data. The results showed that the two ionic liquids (ILs) produced an obvious effect on the VLE behavior. With the addition of them into the azeotropic system, the relative volatility of ethyl acetate to methanol was enhanced. Moreover, the azeotropic point was eliminated as the mole fractions of [EMIM][DEP] and [BMIM][DBP] in the liquid phase were equal to 0.05 and 0.1, respectively. As for salting-out effect on ethyl acetate, [EMIM][DEP] outperforms [BMIM][DBP].

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convenient recycling, tailorable structures, high solubility, etc.12,13 Thus, as a class of novel environmental friendly “green solvents”, ILs are recognized as promising alternatives to organic solvents and solid salts.14,15 Currently, imidazoles ionic liquids feature low-cost, a relatively simple preparation process, high chemical stability, etc. They have been widely used as entrainers for extractive distillation. As far as we know, there are several studies reporting the isobaric VLE data for the ester + alcohol + IL systems: Qunsheng Li et al.16 (methanol + dimethyl carbonate +1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][OTf]), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][OTf]) systems), Rui Li et al.17 (ethyl ecetate + ethanol +1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]) system), Qunsheng Li et al.18 (ethyl ecetate + ethanol +1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIM][BF4]) systems), Dohnal et al.19 (methyl acetate + methanol +1-butyl-1-methylpyrrolidinium dicyanamide ([BMIM][N(CN)2]), 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) systems), Cai et al.20 (methyl acetate + methanol + [EMIM][Ac], 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF6]) systems), etc. However, to date, we have not found isobaric VLE data for the ethyl acetate + methanol + ILs systems in literature. In this work, 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]) and 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]) were used to separate the ethyl acetate + methanol azeotropic mixture. The VLE data for the

INTRODUCTION Methanol is a very excellent raw material in the chemical industry, and is widely used in dye synthesis and the pharmaceutical and national defense industries. It is also a fine organic solvent and liquid fuel. Because of its excellent solubility and volatility, ethyl acetate is widely used in the fine chemical industry. A mixture of ethyl acetate and methanol is widely used in the manufacture of medicament as solvent. However, the separation of ethyl acetate and a methanol mixture is difficult, as a mixture can form a minimum azeotrope1,2 at an ethyl acetate mole fraction of 29.5% at atmospheric pressure, and the azeotropic temperature is 335.7 K. Several methods have been used to separate azeotropic systems: lower temperature crystallization, membrane separation, pressure-swing distillation, azeotropic distillation, and extractive distillation, etc. Among them, extractive distillation is a very efficient method which has been widely applied to the separation of azeotropic systems in industrial processes.3−5 The advantages of this method include low-energy, low-corrosion, and high-performance.6 Traditional entrainers of extractive distillation, that is, organic solvents7 and inorganic solid salts,8−10 have been used to separate the azeotropic systems. The search for environment-friendly extractive entrainers is very essential. However, the processes using organic solvents or inorganic solid salts, are often complicated, have recycling difficulties, and need a huge energy consumption. In recent years, ionic liquids11 (ILs) have been increasingly employed as entrainers to separate azeotropic systems, which are composed entirely of organic cations (including imidazole, pyridinium, pyrrolidinium, tetra-alkyl-phosphonium, quaternary ammonium, etc.) and inorganic or organic anions. In contrast to organic solvents and solid salts, ILs have many advantages: extremely low vapor pressure, high selectivity, nonflammability, © XXXX American Chemical Society

Received: July 3, 2015 Accepted: December 24, 2015

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DOI: 10.1021/acs.jced.5b00546 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Specifications of Chemical Samples chemical name

molecular formula

source

purity

purification method

analysis method

methanol ethyl acetate [EMIM][DEP]a [BMIM][DBP]b

CH4O C4H8O2 C10H21 N2O4P C16H33N2O4P

Sinopharm Group Sinopharm Group synthesized in this work synthesized in this work

0.995 0.995 0.990 0.990

none none vacuum desiccation vacuum desiccation

GCc GCc LCd, KFe LCc, KFe

a

[EMIM][DEP] = 1-Ethyl-3-methylimidazolium diethyl phosphate. b[BMIM][DBP] = 1-Butyl-3-methylimidazolium dibutyl phosphate. cGC = gas chromatography. dLC = liquid chromatography. eKF = Karl Fischer titration.

Table 2. Experimental VLE Data for Ethyl Acetate (1) + Methanol (2) at 101.3 kPaa T/K

x1

y1

337.68 337.12 336.49 335.87 335.59 335.64 335.50 335.58 335.81 336.02 336.26 337.05 337.53 338.29 339.65 341.59 343.71 346.22 348.74 350.35

0.000 0.030 0.072 0.145 0.211 0.244 0.303 0.365 0.419 0.487 0.531 0.610 0.672 0.734 0.801 0.865 0.913 0.952 0.983 1.000

0.000 0.058 0.114 0.195 0.246 0.265 0.311 0.332 0.361 0.391 0.410 0.447 0.483 0.522 0.580 0.653 0.734 0.826 0.932 1.000

Figure 2. T−x3 diagram for methanol (2) + [EMIM][DEP] (3) system at 101.3 kPa: □, this work; ■, data from ref 28. The agreement with the literature data is within 0.25%.

Standard uncertainties u are u(T) ≈ 2.5 K, u(P) = 0.3 kPa, and u(x1) = u(y1) = 0.005.

a

Figure 3. T−x3 diagram for methanol (2) + [BMIM][DBP] (3) system at 101.3 kPa: □, this work; ■, data from ref 29. The agreement with the literature data is within 0.38%.

our laboratory according to the method reported in the literature.21 The water mass fraction in the two ILs determined by Karl Fischer titration is below 0.005 for each. Their purities analyzed by liquid chromatography (LC) are higher than 99.0% in mass fraction. Before use, the ILs were dried under vacuum at 393 K for 48 h. The chemical specifications of the materials used are summarized in Table 1. Apparatus and Procedure. In the present study, all VLE measurements were made with an all-glass dynamic recirculating still (NGW, Wertheim, Germany) described by Hunsmann.22 The pressure of this apparatus was determined by a manometer with a deviation of 0.1 kPa and kept constant at 101.3 kPa by means of a pressure-controlling system. A Beckmann thermometer with a deviation of 0.01 K was used to measure the equilibrium temperature. For the ethyl acetate + methanol binary system, every experimental point was obtained from an initial sample of pure ethyl acetate in which different amounts of methanol were added

Figure 1. Isobaric VLE data for ethyl acetate (1) + methanol (2) system at 101.3 kPa: □, experimental data; ■, data from ref 2; , calculated by the NRTL model. The agreement with the literature data is within 0.6%.

ternary systems containing ILs were measured at 101.3 kPa with a dynamic recirculating still and were correlated with the nonrandom two liquid (NRTL) model. The effects of ILs on the ethyl acetate−methanol binary system were briefly discussed.

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EXPERIMENTAL SECTION Material. Methanol and ethyl acetate used in this work were obtained from Sinopharm Group Co. Ltd. Their purity was higher than 99.5 wt %, checked by gas chromatography (GC). [EMIM][DEP] and [BMIM][DBP] were synthesized in B



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Table 3. Experimental Vapor−Liquid Equilibrium Data, Temperature T, Liquid-Phase Mole Fraction of [EMIM][DEP] x3, Liquid-Phase Mole Fraction of Ethyl Acetate x′1 (Based on IL-Free), Gas-Phase Mole Fraction y1 for Ternary Systems Ethyl Acetate (1) + Methanol (2) + [EMIM][DEP] (3) at 101.3 kPaa

a

x3

T/K

x′1

y1

x3

T/K

x′1

y1

0.031 0.029 0.029 0.032 0.030 0.031 0.029 0.028 0.031 0.030 0.032 0.029 0.029 0.031 0.030 0.033 0.032 0.031 0.030 0.031 0.050 0.051 0.049 0.052 0.050 0.051 0.049 0.050 0.048 0.050

341.60 339.68 338.41 337.31 337.51 338.11 338.61 338.88 339.62 340.07 341.02 341.85 342.53 343.89 344.77 345.34 346.20 347.46 349.37 351.30 346.00 345.00 344.50 343.90 343.60 343.40 343.60 344.19 344.66 345.10

0.000 0.043 0.084 0.126 0.178 0.236 0.303 0.357 0.415 0.477 0.548 0.610 0.672 0.741 0.789 0.820 0.861 0.909 0.947 1.000 0.000 0.050 0.094 0.150 0.211 0.289 0.336 0.389 0.440 0.489

0.000 0.108 0.167 0.209 0.282 0.352 0.385 0.424 0.481 0.536 0.578 0.609 0.639 0.698 0.743 0.762 0.807 0.843 0.916 1.000 0.000 0.125 0.202 0.279 0.373 0.437 0.530 0.572 0.600 0.642

0.051 0.051 0.052 0.049 0.049 0.051 0.050 0.052 0.048 0.049 0.100 0.101 0.101 0.102 0.099 0.098 0.099 0.010 0.101 0.103 0.100 0.100 0.098 0.099 0.100 0.099 0.102 0.100 0.098 0.100

345.51 345.90 346.47 347.00 347.79 348.56 349.33 350.20 350.92 351.80 348.60 347.99 347.56 347.04 346.72 346.45 345.76 345.81 346.07 346.35 346.83 347.36 347.99 348.35 348.95 349.73 350.43 351.28 352.19 352.90

0.539 0.585 0.633 0.682 0.743 0.801 0.851 0.902 0.947 1.000 0.000 0.035 0.078 0.124 0.168 0.213 0.288 0.338 0.388 0.421 0.463 0.527 0.598 0.658 0.716 0.770 0.820 0.874 0.938 1.000

0.678 0.709 0.737 0.769 0.807 0.845 0.882 0.919 0.958 1.000 0.000 0.125 0.202 0.279 0.373 0.437 0.530 0.572 0.600 0.642 0.673 0.723 0.756 0.785 0.832 0.851 0.882 0.915 0.955 1.000

Standard uncertainties u are u(T) ≈ 2.5 K, u(P) = 0.3 kPa, u(x3) = 0.002, and u(x′1) = u(y1) = 0.005.

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until a very diluted solution was achieved. For the each ternary system, the mixture of methanol and IL with a defined mole fraction of IL was taken, and the mixture of ethyl acetate + IL with the same mole fraction of IL was added, trying to keep the scheduled IL mole fraction in each series. Only when the temperature was constant for 30 min or longer time, were the equilibrium conditions assumed. Sample Analysis. Ethyl acetate and methanol contained in the liquid and condensed vapor phases were analyzed by a gas chromatography (7890A, Agilent Technologies) with a headspace sampler (G1888 Network headspace sampler, Agilent Technologies). The GC is equipped with an Agilent 19091J-413 capillary column (30 m in length, 0.32 mm in diameter, and 2.5 μm in thickness) and a thermal conductivity cell detector (TCD) for which the carrier gas is H2. The operating conditions were as follows: the temperatures of injector, oven, and detector were 473, 323, and 473 K, respectively. As ILs have negligible vapor pressure, only the peaks of ethyl acetate and methanol were observed. In this way, the analysis results were not affected by the presence of the IL. The mass fraction content of IL in the liquid phase was gravimetrically determined by an analytical balance with a deviation of 0.0001 g, after evaporating the volatile solvents from a mass-known sample at 393 K until the weight was constant. Each sample was analyzed at least three times with an absolute deviation in mole fraction of 0.002, that is, u(x) = 0.002.

RESULTS AND DISCUSSION

Experimental Data. To verify the reliability of the device used in this work, the isobaric VLE data for the ethyl acetate (1) + methanol (2) system were measured at 101.3 kPa, and the results for this binary system are listed in Table 2. Figures 1−3 illustrate that the VLE data of ethyl acetate (1) + methanol (2), methanol (2) + ILs (3) systems measured in this work agree well with data reported in the literature.2,28,29 Hence, the experimental apparatus is reliable. The ternary VLE data for ethyl acetate (1) + methanol (2) + [EMIM][DEP] (3) and ethyl acetate (1) + methanol (2) + [BMIM][DBP] (3) systems at 101.3 kPa are listed in Tables 3 and 4, where x3 is the mole fraction of IL in the liquid phase, x1′ is the mole fraction of ethyl acetate in the liquid phase on an IL-free basis, y1 is the mole fraction of ethyl acetate in the vapor phase, and T is the equilibrium temperature. The mole fractions of [EMIM][DEP] were kept constant at x3 ≈ 0.03, 0.05, and 0.1. For the ethyl acetate (1) + methanol (2) + [BMIM][DBP] (3) system, the mole fractions of [BMIM][DBP] were fixed at x3 ≈ 0.05, 0.1, and 0.15. Calculation of the Phase Equilibrium. Nowadays, many researchers select the NRTL model to predict the vapor−liquid equilibrium data of the IL-containing systems since it often fits the experimental data well.23 Here the NRTL model is also used to correlate the experimental VLE data. The NRTL model is as follow: C



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Table 4. Experimental Vapor−Liquid Equilibrium Data, Temperature T, Liquid-Phase Mole Fraction of [BMIM][DBP] x3, Liquid-Phase Mole Fraction of Ethyl Acetate x′1 (Based on IL-Free), Gas-Phase Mole Fraction y1 Ternary Systems Ethyl Acetate (1) + Methanol (2) + [BMIM][DBP] (3) at 101.3 kPaa

a

x3

T/K

x′1

y1

x3

T/K

x′1

y1

0.050 0.051 0.049 0.052 0.050 0.051 0.049 0.050 0.048 0.050 0.051 0.052 0.049 0.048 0.051 0.049 0.049 0.051 0.050 0.052 0.100 0.101 0.101 0.102 0.099 0.098 0.099 0.010 0.101 0.102

340.35 338.98 338.34 337.92 337.65 337.65 337.54 337.65 337.92 338.61 338.90 339.61 340.84 341.95 343.33 344.42 345.61 347.04 348.90 351.10 344.60 342.92 342.16 341.88 341.92 342.45 343.01 343.39 344.25 345.01

0.000 0.062 0.110 0.166 0.205 0.246 0.283 0.351 0.406 0.460 0.517 0.572 0.637 0.698 0.760 0.809 0.852 0.900 0.950 1.000 0.000 0.046 0.080 0.122 0.155 0.204 0.265 0.315 0.385 0.456

0.000 0.137 0.210 0.279 0.313 0.341 0.371 0.416 0.458 0.500 0.528 0.558 0.597 0.645 0.701 0.757 0.799 0.857 0.924 1.000 0.000 0.120 0.193 0.249 0.313 0.363 0.430 0.486 0.556 0.618

0.100 0.100 0.098 0.099 0.101 0.099 0.102 0.100 0.098 0.100 0.151 0.152 0.150 0.151 0.149 0.149 0.148 0.150 0.151 0.149 0.151 0.148 0.149 0.151 0.152 0.150 0.150 0.152 0.149 0.150

345.77 346.53 347.10 347.63 348.09 348.62 349.33 349.99 350.52 351.30 348.41 347.21 346.00 345.00 344.50 343.99 343.84 344.34 344.90 345.65 346.26 346.75 347.41 348.22 348.76 349.27 350.03 350.78 351.73 352.80

0.540 0.607 0.646 0.691 0.745 0.799 0.847 0.900 0.950 1.000 0.000 0.035 0.070 0.116 0.155 0.211 0.265 0.321 0.371 0.438 0.502 0.552 0.607 0.668 0.718 0.770 0.828 0.884 0.938 1.000

0.681 0.726 0.744 0.773 0.815 0.849 0.877 0.919 0.955 1.000 0.000 0.115 0.196 0.256 0.329 0.405 0.472 0.539 0.592 0.648 0.692 0.720 0.756 0.796 0.826 0.854 0.888 0.933 0.970 1.000

Standard uncertainties u are u(T) ≈ 2.5 K, u(P) = 0.3 kPa, u(x3) = 0.002, and u(x′1) = u(y1) = 0.005.

Table 6. Nonrandom Factors and Binary Energy Parameters for NRTL Modela

Table 5. Antoine Constants for Pure Components

a

component

A

B

C

temp range (K)

methanola ethyl acetateb

16.4847 14.228

3563.73 2799.54

−37.42 −58.92

315−345 310−359

From ref 24. bFrom ref 25.

ln γi =

∑j τijGjixj ∑k Gkixk

+

∑ i

⎡ ∑ τ x G ⎤ ⎢τij − m mj m mj ⎥ ∑k xkGkj ⎥⎦ ∑k xkGkj ⎢⎣ xjGij

a

(1)

Gij = exp( −αijτij)

Δgij = τijRT

Δgij

component i

j

αij

methanol methanol ethyl acetate methanol ethyl acetate

ethyl acetate [EMIM][DEP] [EMIM][DEP] [BMIM][DBP] [BMIM][DBP]

0.300 0.301 0.030 0.448 0.460

ARD(%) =

where γi is the activity coefficient of component i, αij is the nonrandomness parameter, Δgij is the binary interaction parameter, and T is the temperature. In this work, the nonrandomness parameter (α12) and binary interaction parameters (Δg12, Δg21) were obtained from the VLE data for the binary system of ethyl acetate + methanol. The other nonrandomness parameters (α13, α23) and other binary interaction parameters (Δg13, Δg31, Δg23, Δg32) were obtained from the ternary VLE data containing ILs with Levenberg−Marquardt method by minimizing the following objective function:

1513.7 5047.5 6491.6 4379.8 6651.2

Δgji −1

J·mol

1710.6 −13771.1 −11345.2 −6587.4 2246.1

ARD % 1.78 3.21 2.26

Δgij = gij − gjj, gij = gji, τij = (gij − gjj)/(RT).

(2) (3)

J·mol

−1

1 n

∑ n

γi exptl − γi calcd γi exptl

× 100 (4)

where n is the number of experimental date point, γi is the activity coefficient of component i, and the indices exptl and calcd denote the experimental and calculated values, respectively. Because the experiment was carried out at 101.3 kPa, the assumption of ideal behavior of the vapor phase could be made. The equilibrium conditions are expressed by the following equation: γi = D

Pyi Pi 0xi

(5) DOI: 10.1021/acs.jced.5b00546 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


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Figure 5. T−(x1′ , y1) diagrams of ternary system for ethyl acetate (1) + methanol (2)+ [BMIM][DBP] (3) at different mole fraction of [BMIM][DBP]: dash lines, x3 = 0; ■, x1′ (x3 ≈ 0.05); □, y1 (x3 ≈ 0.05); ●, x′1 (x3 ≈ 0.1); ○, y1 (x3 ≈ 0.1); ▲, x′1 (x3 ≈ 0.15); △, y1 (x3 ≈ 0.15); solid lines, calculated by the NRTL model.

Figure 4. T−(x1′ , y1) diagrams of ternary system for ethyl acetate (1) + methanol (2) + [EMIM][DEP] (3) at different mole fraction of [EMIM][DEP]: dash lines, x3 = 0; ■, x1′ (x3 ≈ 0.03); □, y1 (x3 ≈ 0.03); ●, x1′ (x3 ≈ 0.05); ○, y1 (x3 ≈ 0.05); ▲, x1′ (x3 ≈ 0.1); △, y1 (x3 ≈ 0.1); solid lines, calculated by the NRTL model.

which γi represents the activity coefficient of component i obtained from the electrolyte NRTL model, yi and xi are the mole fraction of components i in the vapor phase and liquid phase, respectively, P is the total pressure of the equilibrium system at about 101.3 kPa, and Pi0 represents the saturated vapor pressure of pure component i at equilibrium temperature which can be calculated by Antoine equation: Bi ln Pi 0 = Ai − T + Ci (6) where Pi0 is the saturated vapor pressure in kPa, Ai, Bi, Ci are the Antoine parameters of i, and T is the equilibrium temperature in K. The Antoine constants of ethyl acetate and methanol are listed in Table 5. With the NRTL model and the experimental ternary VLE data, the regressed parameters and the average absolute deviations (ARD) were listed in Table 6. Then using the NRTL model and the regressed parameters, the mole fraction of ethyl acetate in the vapor phase and the equilibrium temperature were calculated.

Figure 6. Isobaric y1−x′1 diagram for ethyl acetate (1) + methanol (2) + [EMIM][DEP] (3) system at 101.3 kPa: dash lines, x3 = 0; ■, x3 ≈ 0.03; ●, x3 ≈ 0.05; ▲, x3 ≈ 0.1; solid lines, calculated by the NRTL model.

In Figures 4 and 5, the experimental and calculated VLE of ethyl acetate (1) + methanol (2) + [EMIM][DEP] (3) and E



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Figure 7. Isobaric y1−x1′ diagram for ethyl acetate (1) + methanol (2) + [BMIM][DBP] (3) system at 101.3 kPa: dash lines, x3 = 0; ■, x3 ≈ 0.05; ●, x3 ≈ 0.1; ▲, x3 ≈ 0.15; solid lines, calculated by the NRTL model.

Figure 10. Activity coefficient of ethyl acetate, γ1, and methanol, γ2, in relation with the mole fraction of ethyl acetate (based on IL-free) for the mixtures containing [EMIM][DEP] at 101.3 kPa: dash lines, γ1, γ2 (x3 = 0); ■, γ1, γ2 (x3 ≈ 0.03); ●, γ1, γ2 (x3 ≈ 0.05); ▲, γ1, γ2 (x3 ≈ 0.1); solid line, calculated by the NRTL model.

Figure 8. Relative volatility of ethyl acetate (1) to methanol (2) with the ethyl acetate mole fraction(based on IL-free) for different mole fraction of [EMIM][DEP] at 101.3 kPa: dash lines, x3 = 0; ■, x3 ≈ 0.03; ●, x3 ≈ 0.05; ▲, x3 ≈ 0.1; solid lines, calculated by the NRTL model.

The y1−x1′ diagrams of the ethyl acetate (1) + methanol (2) + [EMIM][DEP] (3) and ethyl acetate (1) + methanol (2) + [BMIM][DBP] (3) ternary systems are shown in Figures 6 and 7, respectively. As can be seen, both [EMIM][DEP] and [BMIM][DBP] significantly increase the mole fraction of ethyl acetate in the vapor phase, and the azeotropic point of the ethyl acetate + methanol binary system shifts upward with the addition of IL. The azeotrope of ethyl acetate and methanol is broken as the mole fractions of [EMIM][DEP] and [BMIM][DBP] are equal to 0.05 and 0.1, respectively. α12 =

y1 /x1 y2 /x 2

=

γ1P10 γ2P2 0

(7)

The relative volatility (α12) of ethyl acetate to methanol is shown in Figures 8 and 9, which was obtained from the eq 7, where xi and yi are the mole fractions of component i in the liquid and vapor phase, respectively. γi represents the activity coefficient of component i obtained from the experiment. From Figures 8 and 9, it can be seen that both ILs effectively improve the relative volatility of ethyl acetate to methanol, which indicates that the ILs produce a salting-out effect on ethyl acetate. Furthermore, [EMIM][DEP] produces more significant effect than [BMIM][DBP] on the enhancement of the relative volatilities at the same mole fraction. In this work, the range of the ratio P10/P20 is 0.62−0.65. So the value of α12 depends on the ratio of γ1/γ2 according to eq 7. As shown in Figures 10 and 11, with the addition of ILs, the activity coefficient of ethyl acetate γ1 increases while the activity coefficient of methanol γ2 decreases in the whole liquid concentration range. This phenomenon shows

Figure 9. Relative volatility of ethyl acetate (1) to methanol (2) with the mole fraction of ethyl acetate (based on IL-free) for different mole fraction of [BMIM][BMIM] at 101.3 kPa: dash lines, x3 = 0; ■, x3 ≈ 0.05; ●, x3 ≈ 0.1;▲, x3 ≈ 0.15; solid lines, calculated by the NRTL model.

ethyl acetate (1) + methanol (2) + [BMIM][DBP] (3) systems are plotted on T−(x′1, y1) diagrams. As show in Figures 4 and 5, the NRTL model is in good agreement with the experimental data. It is also obvious that the addition of IL leads to an elevation of the equilibrium temperature. The more IL that is added, the higher is the equilibrium temperature. Besides, the energy consumption of [EMIM][DEP] is less than that of [BMIM][DBP] at the same separation condition. F



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(2) + [BMIM][DBP] (3) ternary systems were obtained at 101.3 kPa in this work. The results indicated that both [EMIM][DEP] and [BMIM][DBP] presented a high selectivity in separating the system of ethyl acetate and methanol and caused an enhancement of the relative volatility of ethyl acetate to methanol. The separation effect of [EMIM][DEP] is stronger than that of [BMIM][DBP], and the minimum mole fractions of [EMIM][DEP] and [BMIM][DBP] needed to break the azeotropy are 0.05 and 0.1, respectively. The experimental data were well correlated with the NRTL model. Both [EMIM][DEP] and [BMIM][DBP] are promising entrainers to separate the azeotropic system of ethyl acetate + methanol.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.5b00546. NMR spectra of 1-ethyl-3-methylimidazolium diethylphosphate and 1-butyl-3-methylimidazolium dibutylphosphate (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Fax: 86-24-89383736. E-mail: [email protected]. Funding

This work is financially supported by National Science Foundation of China (Project No. 21076126), Program for Liaoning Excellent Talents in University (LR2012013) and Liaoning Province Science Foundation of China (Project No. 2014020140).

Figure 11. Activity coefficient of ethyl acetate, γ1, and methanol, γ2, in relation with the mole fraction of ethyl acetate (based on IL-free) for the mixtures containing [BMIM][DBP] at 101.3 kPa: dash lines, γ1, γ2 (x3 = 0); ■, γ1, γ2 (x3 ≈ 0.05); ●, γ1, γ2 (x3 ≈ 0.1); ▲, γ1, γ2 (x3 ≈ 0.15); solid line, calculated by the NRTL model.

Notes

The authors declare no competing financial interest.

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that ILs have a stronger attraction to methanol than ethyl acetate, thus increasing the relative volatility of ethyl acetate. Moreover, when the mole fractions of ILs are at the same level, the value of γ1 in the ethyl acetate + methanol + [EMIM][DEP] ternary system is greater than in the ternary system containing [BMIM][DBP]. But the γ2 is just the opposite. This can show that the interaction between ILs and components follows the order: [EMIM][DEP] > [BMIM][DBP]. The influences of [EMIM][DEP] and [BMIM][DBP] on the VLE behavior of the ethyl acetate + methanol system may be attributed to affinity difference between ILs and different solvent molecules. The intermolecular interactions between solvents and ILs mainly contain electrostatic interaction, hydrogen bonding, and van der Waals forces.26 Methanol is a strong hydrogenbonding acceptor character and hydrogen-bonding donator, also the polarity of which is greater than ethyl acetate. ILs can be regarded as organic molten salts, and their polarities are also large. This leads to the electrostatic interaction and hydrogen bonding between ILs and methanol being stronger than that between ILs and ethyl acetate. The short side chain leads to a higher polarity27 of [EMIM][DEP] compared with [BMIM][DBP]. So the interaction between the methanol and [EMIM][DEP] is greater than that of methanol and [BMIM][DBP]. Thus, [EMIM][DEP] shows a better extraction performance than [BMIM][DBP]. Above all, [EMIM][DEP] can be selected as a suitable extractive solvent to separate the ethyl acetate and methanol system.

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CONCLUSION Isobaric VLE data for the ethyl acetate (1) + methanol (2) + [EMIM][DEP] (3) and ethyl acetate (1) + methanol G



Article

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Isobaric VaporâLiquid Equilibria for Ethyl Acetate + Methanol + Ionic

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