Effect of Ionic Liquids on the Binary VaporâLiquid Equilibrium of Ethyl

Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Effect of Ionic Liquids on the Binary Vapor−Liquid Equilibrium of Ethyl Acetate + Methanol System at 101.3 kPa Wenxiu Li, Liyue Zhang, Hongfan Guo, Jipeng Li, and Tao Zhang* Liaoning Provincial Key Laboratory of Chemical Separation Technology, Shenyang University of Chemical Technology, Shenyang 110142, China

J. Chem. Eng. Data Downloaded from pubs.acs.org by UNIV OF SOUTH DAKOTA on 12/20/18. For personal use only.

S Supporting Information *

ABSTRACT: Three ionic liquids (ILs) (1-ethyl-3-methylimidazolium bromide, [EMIM]Br; 1-ethyl-3-methylimidazolium chloride, [EMIM]Cl; and 1ethyl-3-methylimidazolium acetate, [EMIM][Ac]) were used for the separation of the ethyl acetate + methanol azeotropic mixture. The vapor− liquid equilibrium (VLE) data of ethyl acetate + methanol azeotropic mixtures containing ILs were measured at 101.3 kPa. The three ILs show significant salting-out effects on ethyl acetate. The azeotropic point of the ethyl acetate + methanol azeotropic system is eliminated when the mole content of IL reaches a special value. The separation abilities of the three ILs follow the order [EMIM][Ac] > [EMIM]Cl > [EMIM]Br. The experimental data are correlated well by the nonrandom two-liquid model.

1. INTRODUCTION Ethyl acetate and methanol are vital chemical raw materials. The mixture of ethyl acetate and methanol is common in fine chemical industry and pharmaceutical processes, such as the production process of gastrodine, gliclazide, and cafotaxime sodium. In order to reduce environmental pollution and recycle resources, it is necessary to separate them from their mixture. However, ethyl acetate and methanol can form a minimum azeotrope.1 It is impossible to obtain their pure products by common distillation. Some special distillation methods have been utilized to separate the close-boiling or azeotropic mixtures, such as extractive distillation, azeotropic distillation and pressure swing distillation.2−6 Extractive distillation is widely used because of its advantages of flexible selection of entrainers, simple operation, and high separation ability.7,8 In extractive distillation, the key point is to select a suitable entrainer.9 Traditional entrainers (organic solvents and solid salts) have a lot of defects, such as solvent loss, difficulty in recovery, high energy consumption, and equipment corrosion. At present, ionic liquids (ILs) have been increasingly studied as entrainers in extractive distillation because of their negligible vapor pressure, high selectivity, wide liquid temperature range, and good thermal and chemical stability.10−15 The vapor−liquid equilibrium (VLE) behavior of methanol + ethyl acetate containing traditional entrainer (organic solvent or solid salt) have been studied for design and development of the extractive distillation process.16−18 It can be seen from the VLE data of methanol + ethyl acetate containing chloroform that the azeotropic phenomena of the ethyl acetate−methanol binary mixture and the chloroform−methanol binary mixture were eliminated in the ternary system.16 The separation effect © XXXX American Chemical Society

of calcium chloride on the methanol−ethyl acetate binary mixture was reported by Ohe et al.17 The relative volatility of ethyl acetate to methanol was increased due to the formation of CaCl2·6CH3OH, but the azeotropic phenomenon of the ethyl acetate−methanol mixture was not completely eliminated in that work. However, there are very few reports on the use of ILs as entrainers to separate the ethyl acetate−methanol binary azeotropic system up to now. The separation effects of two phosphate-based ILs (1-ethyl-3-methylimidazolium diethylphosphate, [EMIM][DEP], and 1-butyl-3-methylimidazolium dibutylphosphate, [BMIM][DBP]) on the binary system have been investigated by this research group.19 The two ILs showed separation ability better than that of the traditional entrainers, and the azeotropic point was eliminated when the mole fractions of [EMIM][DEP] and [BMIM][DBP] were up to 0.05 and 0.10, respectively. Methylimidazolium-based ILs are the most widely studied IL entrainers in extractive distillation, and their good selectivity has been verified by a large number of experiments.20−26 Methylimidazolium-based ILs showed excellent separation effect on ester−alcohol azeotropic systems, such as the methyl acetate−methanol system,27,28 ethyl acetate−ethanol system,29 and ethyl acetate−2-propanol system.30 The shorter the alkyl substituent chain of methylimidazole ring, the stronger the separation effect of IL on the ester−alcohol azeotropic mixture. This work is a continuation of our studies on the separation of the ethyl acetate−methanol azeotropic mixture by ILs. 1Ethyl-3-methylimidazolium is selected as cation due to the Received: May 21, 2018 Accepted: December 6, 2018

A

DOI: 10.1021/acs.jced.8b00424 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Specifications of the Chemicals chemical name

CAS Reg. No.

source

mass fraction purity

purification method

analysis methoda

ethyl acetate methanol [EMIM]Brb [EMIM]Clc [EMIM][Ac]d

141-78-6 67-56-1 65039-08-9 65039-09-0 143314-17-4

Sinopharm Group Co. Ltd. Sinopharm Group Co. Ltd. Yulu Fine Chemical Co. Ltd. Yulu Fine Chemical Co. Ltd. Yulu Fine Chemical Co. Ltd.

0.995 0.995 0.980 0.980 0.980

none none vacuum desiccation vacuum desiccation vacuum desiccation

GC GC LC KF LC KF LC KF

a

GC = gas chromatography; LC = liquid chromatography; KF = Karl Fischer titration. b[EMIM]Br = 1-ethyl-3-methylimidazolium bromide. [EMIM]Cl = 1-ethyl-3-methylimidazolium chloride. d[EMIM][Ac] = 1-ethyl-3-methylimidazolium acetate.

c

and liquid phase were taken out from the corresponding sampling ports using 5 mL sealed syringes and analyzed. 2.3. Sample Analysis. The vapor and liquid phase samples were placed into a headspace sampler (G1888 Network headspace sampler, Agilent Technologies), and the mole fractions of ethyl acetate and methanol were analyzed by gas chromatography (GC; Model 7890A, Agilent Technologies). The GC is equipped with a capillary column (SP-1000, 30 m × 0.25 mm × 0.25 μm) and a FID detector with nitrogen as carrier gas. The temperatures of the oven, injector, and detector were 323, 423, and 443 K, respectively. The mole fraction of IL was gravimetrically measured by the mass difference after evaporating the volatile ethyl acetate and methanol from a known mass of sample until constant mass. Every sample was analyzed at least three times.

short chain length of the ethyl substituent. Bromide anion, chloride anion, and acetic acid anion are three common anions. Synthesis methods of chloride-based or bromide-based ILs are mature and simple. Acetate-based ILs have high separation abilities for alcohol-containing systems due to their abilities to form strong hydrogen bonds with alcohols as hydrogen bond acceptors. The distinct difference of hydrogen bonding ability among chloride anion, bromine anion, and acetic acid anion makes it possible to further study the influence of anion bonding ability on IL separation ability. In addition, the physical parameters of the three ILs, [EMIM]Br, [EMIM]Cl, and [EMIM][Ac], have been extensively studied.31−36 Further research on the data related to the separation performance of the three ILs will help them to be industrialized as soon as possible. A large number of studies on the three ILs have also shown that the stabilities of them are reliable. The isobaric VLE data of ethyl acetate + methanol containing ILs were measured at 101.3 kPa. The nonrandom two-liquid (NRTL) model was used to correlate the VLE data. The separation abilities of the three ILs for the ethyl acetate−methanol system were discussed.

3. RESULT AND DISCUSSION 3.1. Experimental Data. The binary VLE data for the ethyl acetate (1) + methanol (2) system were measured at 101.3 kPa to test the reliability of the apparatus used in this work. The experimental data and literature data are shown in Table 2, where T is the equilibrium temperature and x1 and y1 represent the mole fractions of ethyl acetate in the liquid phase and vapor phase, respectively. The superscript “L” denotes the literature value.19 The experimental data are also compared with the literature data in Figure 1. The experimental data for the binary mixture are in good agreement with the literature data. Hence, the apparatus is reliable. The isobaric VLE data of the ethyl acetate (1) + methanol (2) system containing IL ([EMIM]Br, [EMIM]Cl, or [EMIM][Ac]) were measured at 101.3 kPa, and the mole fraction of the three ILs were maintained nearly constant at x3 = 0.10, 0.15, 0.20; x3 = 0.05, 0.10, 0.15; and x3 = 0.02, 0.05, 0.10, respectively. The experimental data were shown in Tables 3−5, where T is the equilibrium temperature, x3 is the mole fraction of IL in liquid phase, x1’ is the mole fraction of ethyl acetate in liquid phase excluding IL, y1 is the mole fraction of ethyl acetate in vapor phase, α12 is the relative volatility of ethyl acetate to methanol, and γ1 and γ2 are the activity coefficients of ethyl acetate and methanol, respectively. 3.2. Correlation of the Phase Equilibrium. The NRTL model38 is used to correlate the VLE data and depicted as follows: ÄÅ ÉÑ ∑j τijGjixj ∑m τmjxmGmj ÑÑÑ xjGij ÅÅÅ ÅÅÅτij − ÑÑÑ ln γi = +∑ ∑k xkGkj ÑÑÑ ∑k Gkixk ∑k xkGkj ÅÅÅ i Ç Ö

2. EXPERIMENTAL SECTION 2.1. Material. The chemicals used were ethyl acetate, methanol, and ILs ([EMIM]Br, [EMIM]Cl, and [EMIM][Ac]). Ethyl acetate and methanol were purchased from Sinopharm Group Co. Ltd. Their mass fractions checked by gas chromatography (GC) were not less than 99.5%. [EMIM]Br, [EMIM]Cl, and [EMIM][Ac] were provided by Lanzhou Yulu Fine Chemical Co. Ltd. Before each experiment, the ILs were dried for 48 h (373 K, 2 kPa) to remove the volatile impurities. The mass fraction of ILs was at least 98% checked by liquid chromatography (LC). The water content in IL was determined using Karl Fischer titration, and the mole fraction of water was below 0.005. The assumption is made that the effect of water (0.5 mol %) of IL on VLE data is negligible. The specifications of the chemicals are illustrated in Table 1. 2.2. Apparatus and Procedure. In this work, an all glass dynamic recirculating still described in our previous literature was used to conduct the VLE experiment.37 An electronic balance (CAV264C OHAUS America) with a standard uncertainty of 0.0001 g was used to prepare the experimental samples. The pressure of the apparatus was kept constant by a pressure control system and measured by a manometer with a standard uncertainty of 0.1 kPa. The equilibrium temperature was determined through a mercury thermometer with a standard uncertainty of 0.01 K. The system equilibrium was assumed when the system temperature was fixed for 30 min, and the vapor phase composition did not change with the decrease in the condensate flow. Then the samples of vapor

(1)

Gij = exp( −αijτij) B

(2) DOI: 10.1021/acs.jced.8b00424 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


Article

Table 2. Experimental and Literature VLE Data: Equilibrium Temperature (T), Liquid Phase Mole Fraction of Ethyl Acetate (x1), and Vapor Phase Mole Fraction of Ethyl Acetate (y1) for the Binary System of Ethyl Acetate (1) + Methanol (2) at 101.3 kPaa,b T/K

x1

y1

TL/K

xL1

yL1

337.45 337.29 336.85 336.49 336.12 335.80 335.62 335.45 335.50 335.70 336.26 337.48 339.95 343.06 346.80 349.95

0.000 0.023 0.049 0.077 0.113 0.158 0.198 0.266 0.322 0.428 0.540 0.673 0.809 0.898 0.961 1.000

0.000 0.039 0.080 0.116 0.159 0.199 0.233 0.275 0.314 0.354 0.413 0.485 0.589 0.715 0.857 1.000

337.68 337.12 336.49 335.87 335.59 335.64 335.5 335.58 335.81 336.02 336.26 337.05 337.53 338.29 339.65 341.59 343.71 346.22 348.74 350.35

0 0.03 0.072 0.145 0.211 0.244 0.303 0.365 0.419 0.487 0.531 0.61 0.672 0.734 0.801 0.865 0.913 0.952 0.983 1

0 0.058 0.114 0.195 0.246 0.265 0.311 0.332 0.361 0.391 0.41 0.447 0.483 0.522 0.58 0.653 0.734 0.826 0.932 1

Table 3. Experimental VLE Data: Equilibrium Temperature (T), Liquid Phase Mole Fraction of IL (x3), Liquid Phase Mole Fraction of Ethyl Acetate Based on IL-Free (x1′), Vapor Phase Mole Fraction of Ethyl Acetate (y1), Relative Volatility of Ethyl Acetate to Methanol (α12), Activity Coefficient of Ethyl Acetate (γ1), and Activity Coefficient of Methanol (γ2) for the Ethyl Acetate (1) + Methanol (2) System Containing [EMIM]Br at 101.3 kPaa

a

Standard uncertainties of experimental data u(T) = 0.01 K, u(P) = 0.1 kPa, and u(x1) = u(y1) = 0.001. bAverage relative deviations: between the correlated curve and the literature data, ARD(%) = 1.78; between the correlated curve and the experimental data, ARD(%) = 0.75.

Figure 1. Isobaric VLE data for the binary system of ethyl acetate (1) + methanol (2) at 101.3 kPa: ■, experimental data; ○, data from ref 1; △, data from ref 19; solid line, correlated by the NRTL model.

T/K

x3

x 1′

y1

α12

γ1

γ2

340.40 339.41 339.04 339.01 339.13 339.54 340.22 340.90 341.68 342.56 343.50 344.60 346.50 344.32 342.91 342.02 341.48 341.36 341.45 341.86 342.45 343.15 343.85 344.85 345.79 348.20

0.102 0.103 0.103 0.103 0.101 0.101 0.102 0.103 0.101 0.102 0.100 0.098 0.099 0.153 0.153 0.152 0.151 0.152 0.152 0.151 0.150 0.150 0.151 0.150 0.149 0.149

0.076 0.149 0.211 0.273 0.330 0.391 0.456 0.509 0.570 0.627 0.688 0.754 0.836 0.055 0.106 0.154 0.205 0.252 0.301 0.365 0.426 0.490 0.548 0.618 0.685 0.820

0.164 0.272 0.343 0.400 0.441 0.485 0.525 0.560 0.597 0.635 0.673 0.718 0.782 0.151 0.255 0.328 0.395 0.445 0.483 0.532 0.576 0.615 0.655 0.700 0.743 0.830

2.385 2.134 1.952 1.775 1.602 1.467 1.319 1.228 1.118 1.035 0.933 0.831 0.704 3.056 2.887 2.681 2.532 2.380 2.170 1.978 1.830 1.663 1.566 1.442 1.329 1.072

3.363 2.950 2.662 2.402 2.176 1.991 1.806 1.687 1.559 1.463 1.365 1.277 1.177 3.957 3.641 3.321 3.058 2.818 2.552 2.283 2.072 1.877 1.747 1.598 1.480 1.273

0.908 0.893 0.882 0.875 0.879 0.877 0.882 0.883 0.894 0.904 0.932 0.975 1.054 0.823 0.805 0.793 0.775 0.760 0.755 0.739 0.724 0.720 0.710 0.702 0.703 0.744

349.00 346.79 345.21 344.38 344.12 344.17 344.56 345.15 345.92 346.74 347.45 348.50 350.60

0.202 0.203 0.203 0.202 0.202 0.201 0.201 0.200 0.201 0.200 0.200 0.199 0.199

0.046 0.101 0.165 0.225 0.287 0.343 0.402 0.463 0.515 0.568 0.612 0.676 0.795

0.156 0.287 0.396 0.474 0.535 0.587 0.630 0.667 0.705 0.733 0.758 0.795 0.865

3.833 3.583 3.318 3.104 2.858 2.722 2.533 2.323 2.251 2.088 1.986 1.859 1.652

4.429 4.001 3.566 3.216 2.872 2.628 2.375 2.137 1.980 1.813 1.699 1.556 1.343

0.722 0.703 0.681 0.658 0.639 0.614 0.595 0.583 0.556 0.547 0.538 0.524 0.505

a

τij =

Standard uncertainties u(T) = 0.01 K, u(P) = 0.1 kPa, and u(x3) = u(x1′) = u(y1) = 0.001.

Δgij RT

(3)

Levenberg−Marquardt method by the minimization of the average relative deviation (ARD):

where αij and Δgij are the binary nonrandomness parameter and binary interaction energy parameter between component i and component j. For the system, nine parameters are included in this model. The binary parameters (α12, Δg12, and Δg21) of the ethyl acetate and methanol system are obtained from their binary experimental data, and the remaining binary parameters (α13, α23, Δg13, Δg31, Δg23,and Δg32) are obtained from the experimental data which are shown in Tables 3−5 using the

ARD/% =

1 n

∑∑ n

i

γiexptl − γicalcd γiexptl

× 100 (4)

γexptl i

where n represents the number of experimental points. and γicalcd are the experimental and calculated activity coefficients of component i, respectively. The parameters of the NRTL model and ARD (%) are shown in Table 6. A good C



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Table 4. Experimental VLE Data: Equilibrium Temperature (T), Liquid Phase Mole Fraction of IL (x3), Liquid Phase Mole Fraction of Ethyl Acetate Based on IL-Free (x1′), Vapor Phase Mole Fraction of Ethyl Acetate (y1), Relative Volatility of Ethyl Acetate to Methanol (α12), Activity Coefficient of Ethyl Acetate (γ1), and Activity Coefficient of Methanol (γ2) for the Ethyl Acetate (1) + Methanol (2) System Containing [EMIM]Cl at 101.3 kPaa

Table 5. Experimental VLE Data: Equilibrium Temperature (T), Liquid Phase Mole Fraction of IL (x3), Liquid Phase Mole Fraction of Ethyl Acetate Based on IL-Free (x1′), Vapor Phase Mole Fraction of Ethyl Acetate (y1), Relative Volatility of Ethyl Acetate to Methanol (α12), Activity Coefficient of Ethyl Acetate (γ1), and Activity Coefficient of Methanol (γ2) for the Ethyl Acetate (1) + Methanol (2) System Containing [EMIM][Ac] at 101.3 kPaa

T/K

x3

x1′

y1

α12

γ1

γ2

T/K

x3

x 1′

y1

α12

γ1

γ2

339.45 338.90 338.42 337.70 337.45 337.55 337.85 338.35 338.85 339.97 340.98 342.25 343.85

0.053 0.053 0.052 0.053 0.052 0.051 0.052 0.052 0.051 0.051 0.050 0.050 0.049

0.049 0.091 0.135 0.213 0.285 0.346 0.403 0.474 0.534 0.618 0.687 0.758 0.824

0.105 0.178 0.237 0.323 0.382 0.425 0.456 0.504 0.535 0.588 0.625 0.685 0.741

2.277 2.163 1.990 1.763 1.551 1.397 1.242 1.128 1.004 0.882 0.759 0.694 0.611

3.275 3.049 2.781 2.469 2.199 2.006 1.830 1.689 1.561 1.425 1.313 1.248 1.173

0.929 0.912 0.906 0.910 0.922 0.934 0.957 0.971 1.007 1.041 1.111 1.150 1.222

338.46 337.74 337.02 336.55 336.28 336.19 336.20 336.37 336.88 337.55 339.45 342.55 345.25

0.022 0.022 0.021 0.022 0.022 0.023 0.024 0.023 0.022 0.022 0.021 0.022 0.021

0.018 0.052 0.106 0.158 0.211 0.257 0.312 0.381 0.452 0.518 0.663 0.808 0.894

0.038 0.099 0.176 0.233 0.283 0.321 0.350 0.395 0.437 0.465 0.557 0.682 0.788

2.155 2.003 1.801 1.619 1.476 1.367 1.187 1.061 0.941 0.809 0.638 0.509 0.441

3.237 2.996 2.679 2.422 2.225 2.081 1.870 1.716 1.569 1.422 1.242 1.120 1.065

0.974 0.972 0.969 0.977 0.985 0.995 1.029 1.056 1.087 1.144 1.257 1.405 1.530

342.55 341.65 340.85 340.15 339.75 339.65 339.80 340.45 341.70 343.22 344.35 345.30 346.40

0.103 0.104 0.104 0.102 0.103 0.102 0.103 0.103 0.102 0.100 0.099 0.098 0.100

0.047 0.112 0.173 0.237 0.288 0.336 0.392 0.446 0.523 0.609 0.675 0.728 0.782

0.125 0.254 0.345 0.413 0.465 0.503 0.545 0.582 0.628 0.681 0.719 0.755 0.798

2.897 2.700 2.518 2.265 2.149 2.000 1.858 1.730 1.540 1.371 1.232 1.151 1.098

3.848 3.390 3.066 2.740 2.578 2.396 2.216 2.032 1.788 1.576 1.442 1.357 1.289

0.849 0.805 0.783 0.780 0.774 0.773 0.770 0.757 0.744 0.733 0.743 0.747 0.740

348.15 346.85 345.55 344.55 343.75 343.25 343.27 343.62 344.25 345.30 346.45 347.83 349.36

0.152 0.152 0.151 0.150 0.150 0.149 0.150 0.151 0.151 0.150 0.151 0.150 0.149

0.041 0.079 0.124 0.174 0.242 0.309 0.355 0.403 0.470 0.552 0.615 0.682 0.747

0.136 0.234 0.325 0.402 0.487 0.555 0.595 0.633 0.678 0.728 0.763 0.806 0.843

3.682 3.561 3.401 3.191 2.973 2.789 2.669 2.555 2.374 2.172 2.015 1.937 1.819

4.194 3.912 3.614 3.292 2.948 2.674 2.496 2.314 2.079 1.832 1.659 1.507 1.366

0.714 0.692 0.672 0.655 0.631 0.611 0.596 0.577 0.556 0.534 0.519 0.488 0.469

348.95 339.95 339.12 338.50 338.15 338.05 338.20 338.79 339.30 339.95 340.75 342.05 343.42 344.68 347.75

0.020 0.049 0.051 0.052 0.051 0.051 0.050 0.051 0.051 0.052 0.053 0.053 0.052 0.052 0.052

0.970 0.043 0.098 0.151 0.205 0.251 0.315 0.406 0.461 0.513 0.563 0.641 0.718 0.778 0.893

0.924 0.102 0.202 0.279 0.337 0.383 0.438 0.499 0.537 0.569 0.606 0.655 0.708 0.755 0.863

0.376 2.528 2.330 2.176 1.971 1.852 1.695 1.457 1.356 1.253 1.194 1.063 0.952 0.877 0.755

1.015 3.547 3.181 2.919 2.627 2.447 2.215 1.919 1.786 1.664 1.571 1.425 1.310 1.234 1.108

1.687 0.905 0.883 0.869 0.865 0.858 0.848 0.853 0.851 0.856 0.846 0.858 0.877 0.892 0.921

344.16 343.48 342.76 342.18 342.05 342.03 342.31 343.05 343.85 345.25 346.45 347.46 348.45 350.20

0.099 0.100 0.101 0.102 0.102 0.103 0.102 0.101 0.100 0.101 0.102 0.101 0.102 0.101

0.083 0.121 0.170 0.238 0.289 0.342 0.412 0.483 0.541 0.618 0.684 0.737 0.786 0.873

0.227 0.303 0.380 0.469 0.522 0.572 0.625 0.673 0.708 0.754 0.796 0.827 0.860 0.918

3.244 3.158 2.992 2.828 2.687 2.571 2.379 2.203 2.057 1.895 1.803 1.706 1.672 1.629

3.726 3.497 3.204 2.885 2.657 2.464 2.211 1.977 1.804 1.605 1.471 1.370 1.293 1.171

0.730 0.705 0.684 0.653 0.633 0.614 0.595 0.573 0.558 0.536 0.515 0.504 0.484 0.448

a

Standard uncertainties u(T) = 0.01 K, u(P) = 0.1 kPa, and u(x3) = u(x1′) = u(y1) = 0.001. a

Standard uncertainties u(T) = 0.01 K, u(P) = 0.1 kPa, and u(x3) = u(x1′) = u(y1) = 0.001.

agreement between the correlated results and the experimental data is shown in Figures 1−7. Since the vapor phase pressure of the experiment is low (101.3 kPa), the assumption of ideal vapor phase is made. The VLE equation can be simplified as eq 5. The relative volatility (α12) is calculated by eq 6. Py γi = s i Pi xi (5)

α12 =

y1 /x1 y2 /x 2

=

γ1P1s γ2P2s

(6)

where xi and yi represent mole fractions of component i in the liquid phase and the vapor phase, respectively. Presents the total vapor phase pressure and Psi calculated by eq 7 is the D



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Table 6. Parameters of NRTL Model and Average Relative Deviations component i

component j

aij

Δgij/(J/mol)

Δgji/(J/mol)

ARD/%

ethyl acetate ethyl acetate methanol ethyl acetate methanol ethyl acetate methanol

methanol [EMIM]Br [EMIM]Br [EMIM]Cl [EMIM]Cl [EMIM][Ac] [EMIM][Ac]

0.300 0.085 0.164 0.195 0.151 0.267 0.272

1710.6 −5085.4 −11209.6 1155.6 −6598.2 585.4 −8089.6

1513.7 2061.2 −6589.3 −3090.2 −11980.2 −3371.2 −11839.4

0.75 1.80 1.61 1.27

Figure 2. y1−x1′ diagram of ethyl acetate (1) + methanol (2) system containing [EMIM]Br at 101.3 kPa: dashed line, x3 = 0; ■, x3 ≈ 0.10; ▲, x3 ≈ 0.15; ●, x3 ≈ 0.20; solid lines, correlated by the NRTL model.

Figure 4. y1−x1′ diagram of ethyl acetate (1) + methanol (2) system containing [EMIM][Ac] at 101.3 kPa: dashed line, x3 = 0; ■, x3 ≈ 0.02;▲, x3 ≈ 0.05; ●, x3 ≈ 0.10; solid lines, correlated by the NRTL model.

Figure 3. y1−x1′ diagram of ethyl acetate (1) + methanol (2) system containing [EMIM]Cl at 101.3 kPa: dashed line, x3 = 0; ■, x3 ≈ 0.05;▲, x3 ≈ 0.10; ●, x3 ≈ 0.15; solid lines, correlated by the NRTL model.

Figure 5. Relative volatility of ethyl acetate (1) to methanol (2) at different mole fractions of [EMIM]Br at 101.3 kPa: dashed line, x3 = 0; ■, x3 ≈ 0.10;▲, x3 ≈ 0.15; ●, x3 ≈ 0.2; solid lines, correlated by the NRTL model.

three ILs calculated by the NRTL model to eliminate the azeotropic point of the binary mixture are 0.167, 0.119, and 0.074, respectively. And the relevant temperature ranges of the three mixtures containing IL at the minimum breaking azeotropic mole fraction are 347.27−356.67 K ([EMIM]Br), 346.06−354.58 K ([EMIM]Cl), and 344.07−352.86 K ([EMIM][Ac]), respectively. It can be concluded that all three ILs can effectively separate the ethyl acetate−methanol binary azeotropic mixture, and the separation abilities of the three ILs follow the order [EMIM][Ac] > [EMIM]Cl > [EMIM]Br. The relative volatilities of ethyl acetate to methanol (α12) for the mixtures containing IL are shown in Figures5−7. The α12 values increase with the increase in IL content. The α12 values

saturated vapor pressure of pure component i at equilibrium temperature. Bi ln(Pis/kPa) = Ai − (T /K) + Ci (7) where Ai, Bi, and Ci are the Antoine parameters of component i. The parameters of ethyl acetate and methanol are obtained from the literature39,40 and listed in Table 7. The y1−x1′ diagrams of the ethyl acetate + methanol system containing IL ([EMIM]Br, [EMIM]Cl, or [EMIM][Ac]) are illustrated in Figures 2−4. The azeotropic point of the ethyl acetate−methanol binary system is shifted upward with the increase in the IL content. The minimum mole fractions of the E



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attractive interaction for the systems containing the same IL follows the order IL−methanol> ethyl acetate−methanol > ethyl acetate−IL. And that for the systems containing different IL follows the order [EMIM][Ac]−methanol > [EMIM]Cl− methanol > [EMIM]Br−methanol and [EMIM][Ac]−ethyl acetate < [EMIM]Cl−ethyl acetate < [EMIM]Br−ethyl acetate. The separation abilities of the three ILs for the ethyl acetate and methanol may be attributed to the hydrogen bonds between them. The azeotropic phenomenon of the ethyl acetate−methanol mixture is produced by the formation of the hydrogen bond between the hydroxyl group of methanol and the carbonyl group of ethyl acetate, where methanol and ethyl acetate are hydrogen bond donator and acceptor, respectively. All three ILs can act as hydrogen bond acceptors to form hydrogen bonds with the hydroxyl group of methanol, and all the hydrogen bonds between the ILs and the hydroxyl group of methanol are stronger than that between the carbonyl group of ethyl acetate and the hydroxyl group of methanol. When the IL is added to the ethyl acetate−methanol binary system, the hydrogen bond between ethyl acetate and methanol is broken because of the formation of the stronger hydrogen bond between the IL and methanol. Hence the azeotropic phenomenon of the ethyl acetate−methanol binary mixture can be totally eliminated when the mole fraction of IL is increased to a certain value. The intensity of the hydrogen bond between the IL and methanol is determined by anions due to their same cation. The hydrogen bond acceptor ability for the three anions follows [Ac]− > Cl− > Br− which have been reported in previous literature.41,42 Thus, the separation abilities of the three ILs follow the order [EMIM][Ac] > [EMIM]Cl > [EMIM]Br.

Figure 6. Relative volatility of ethyl acetate (1) to methanol (2) at different mole fractions of [EMIM]Cl at 101.3 kPa: dashed line, x3 = 0; ■, x3 ≈ 0.05;▲, x3 ≈ 0.10; ●, x3 ≈ 0.15; solid lines, correlated by the NRTL model.

4. CONCLUSION The VLE experiments of the ethyl acetate + methanol binary mixture containing ILs ([EMIM]Br, [EMIM]Cl, and [EMIM][Ac]) were conducted at 101.3 kPa using a recirculating still to study the effect of ILs on the VLE of the binary system. The result shows that all three ILs produce a notable salting-out effect on ethyl acetate, and the relative volatility of ethyl acetate to methanol increases with the increase in IL concentration. The minimum mole fractions of [EMIM]Br, [EMIM]Cl, and [EMIM][Ac] to eliminate the azeotropic point of the binary mixture are 0.167, 0.119, and 0.074, respectively. The experimental VLE data were correlated with the NRTL model, and the correlated data are in good agreement with the experimental data.

Figure 7. Relative volatility of ethyl acetate (1) to methanol (2) at different mole fractions of [EMIM][Ac] at 101.3 kPa: dashed line, x3 = 0; ■, x3 ≈ 0.02;▲, x3 ≈ 0.05; ●, x3 ≈ 0.10; solid lines, correlated by the NRTL model.

Table 7. Antoine Parameters for Pure Components Antoine constant component

A

B

C

temp range/K

ethyl acetatea methanolb

14.228 16.485

2799.54 3563.73

−58.92 −37.42

310−359 315−345

a

Parameters were obtained from ref 39. bParameters were obtained from ref 40.

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are higher than 1 when the mole fractions of [EMIM]Br, [EMIM]Cl, and [EMIM][Ac] reach 0.20, 0.15, and 0.10, respectively. All of the three ILs show excellent separation effect on the ethyl acetate + methanol binary mixture, and their separation abilities follow the order [EMIM][Ac] > [EMIM] Cl > [EMIM]Br. The activity coefficients of ethyl acetate (γ1) and methanol (γ2) are listed in Tables 3−5 to show the effect of IL on the solution nonideality. The γ1 value increases, while the γ2 value decreases with the increase in IL content. The γ1 values of the mixtures containing different ILs follow the order [EMIM][Ac] > [EMIM]Cl > [EMIM]Br, but the γ2 values are just the opposite. The greater the γi value is and the higher the volatility of component i is according to eq5, the weaker the intensity of intermolecular attractive interaction in liquid phase is. So it can be concluded that the intensity of intermolecular

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b00424.

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T−x1′−y1 diagrams and σ profiles (PDF)

AUTHOR INFORMATION

Corresponding Author

*Tel.: +86 024 89381082. E-mail: [email protected]. ORCID

Wenxiu Li: 0000-0002-4749-7259 Tao Zhang: 0000-0002-4637-7482 F



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(19) Zhang, Z.; Pan, F.; Zhang, Q.; Zhang, T.; Zhang, L.; Wu, K.; Li, W. Isobaric Vapor−Liquid Equilibria for Ethyl Acetate + Methanol + Ionic Liquids Ternary Systems at 101.3 KPa. J. Chem. Eng. Data 2016, 61 (2), 772−779. (20) Zhang, Z.; Zhang, L.; Zhang, Q.; Sun, D.; Pan, F.; Dai, S.; Li, W. Separation of 2-Propanol and Water Azeotropic System Using Ionic Liquids as Entrainers. Fluid Phase Equilib. 2016, 412, 94−100. (21) Ge, Y.; Zhang, L.; Yuan, X.; Geng, W.; Ji, J. Selection of Ionic Liquids as Entrainers for Separation of (Water+ethanol). J. Chem. Thermodyn. 2008, 40 (8), 1248−1252. (22) Zhang, L.; Qiao, B.; Ge, Y.; Deng, D.; Ji, J. Effect of Ionic Liquids on (Vapor+liquid) Equilibrium Behavior of (Water+2Methyl-2-Propanol). J. Chem. Thermodyn. 2009, 41 (1), 138−143. (23) Tsanas, C.; Tzani, A.; Papadopoulos, A.; Detsi, A.; Voutsas, E. Ionic Liquids as Entrainers for the Separation of the Ethanol/Water System. Fluid Phase Equilib. 2014, 379, 148−156. (24) Li, W.; Sun, D.; Zhang, T.; Huang, Y.; Zhang, L.; Zhang, Z. Phase Equilibrium Study of Binary and Ternary Mixtures of Ionic Liquids + Acetone + Methanol. J. Chem. Eng. Data 2014, 59 (12), 3975−3981. (25) Zhang, Z.; Xu, H.; Zhang, Q.; Zhang, A.; Li, Y.; Li, W. Separation of Methanol + Dimethyl Carbonate Azeotropic Mixture Using Ionic Liquids as Entrainers. Fluid Phase Equilib. 2017, 435, 98− 103. (26) Li, Q.; Zhu, W.; Liu, B.; Fan, Z.; Zhu, Y.; Gao, Z. Measurement and Correlation of the Vapor−liquid Equilibrium for Methanol + Acetonitrile + Imidazolium-Based Ionic Liquids at 101.3 KPa. J. Chem. Thermodyn. 2016, 101, 25−30. (27) Zhang, Z.; Hu, A.; Zhang, T.; Zhang, Q.; Sun, M.; Sun, D.; Li, W. Separation of Methyl Acetate+methanol Azeotropic Mixture Using Ionic Liquids as Entrainers. Fluid Phase Equilib. 2015, 401, 1−8. (28) Cai, J.; Cui, X.; Zhang, Y.; Li, R.; Feng, T. Vapor−Liquid Equilibrium and Liquid−Liquid Equilibrium of Methyl Acetate + Methanol + 1-Ethyl-3-Methylimidazolium Acetate. J. Chem. Eng. Data 2011, 56 (2), 282−287. (29) Zhang, Z.; Wu, K.; Zhang, Q.; Zhang, T.; Zhang, D.; Yang, R.; Li, W. Separation of Ethyl Acetate and Ethanol Azeotrope Mixture Using Dialkylphosphates-Based Ionic Liquids as Entrainers. Fluid Phase Equilib. 2017, 454, 91−98. (30) Zhang, Z.; Zhang, A.; Wu, K.; Zhang, Q.; Hu, A.; Li, W. Separation of Ethyl Acetate and 2-Propanol Azeotropic Mixture Using Ionic Liquids as Entrainers. Fluid Phase Equilib. 2016, 429, 331−338. (31) Fröba, A. P.; Rausch, M. H.; Krzeminski, K.; Assenbaum, D.; Wasserscheid, P.; Leipertz, A. Thermal Conductivity of Ionic Liquids: Measurement and Prediction. Int. J. Thermophys. 2010, 31 (11−12), 2059−2077. (32) Fendt, S.; Padmanabhan, S.; Blanch, H. W.; Prausnitz, J. M. Viscosities of Acetate or Chloride-Based Ionic Liquids and Some of Their Mixtures with Water or Other Common Solvents. J. Chem. Eng. Data 2011, 56 (1), 31−34. (33) Nazet, A.; Sokolov, S.; Sonnleitner, T.; Makino, T.; Kanakubo, M.; Buchner, R. Viscosities, and Conductivities of the Densities, Viscosities, and Conductivities of the Imidazolium Ionic Liquids [Emim][Ac], [Emim][FAP], [Bmim][BETI], [Bmim][FSI], [Hmim][TFSI], and [Omim][TFSI]. J. Chem. Eng. Data 2015, 60 (8), 2400−2411. (34) Mac Dowell, N.; Llovell, F.; Sun, N.; Hallett, J. P.; George, A.; Hunt, P. A.; Welton, T.; Simmons, B. A.; Vega, L. F. New Experimental Density Data and Soft-SAFT Models of Alkylimidazolium ([CnC1im]+) Chloride (Cl−), Methylsulfate ([MeSO4]−), and Dimethylphosphate ([Me2PO4]−) Based Ionic Liquids. J. Phys. Chem. B 2014, 118 (23), 6206−6221. (35) Vila, J.; Fernández-Castro, B.; Rilo, E.; Carrete, J.; DomínguezPérez, M.; Rodríguez, J. R.; García, M.; Varela, L. M.; Cabeza, O. Liquid−solid−liquid Phase Transition Hysteresis Loops in the Ionic Conductivity of Ten Imidazolium-Based Ionic Liquids. Fluid Phase Equilib. 2012, 320, 1−10. (36) Paulechka, Y. U.; Kabo, G. J.; Blokhin, A. V.; Shaplov, A. S.; Lozinskaya, E. I.; Vygodskii, Y. S. Thermodynamic Properties of 1-

This work is financially supported by the National Science Foundation of China (Project 21576166) and the Program for Liaoning Excellent Talents in University (Project LR2012013). Notes

The authors declare no competing financial interest.

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