Phase Equilibrium Study of Binary and Ternary Mixtures of Ionic

Nov 6, 2014 - 20. Seiler , M. ; Jork , C. ; Schneider , W. ; Arlt , W. Ionic liquids and hyper-branched polymers. Promising new classes of selective e...
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Phase Equilibrium Study of Binary and Ternary Mixtures of Ionic Liquids + Acetone + Methanol Wenxiu Li, Dezhang Sun, Tao Zhang, Yanhong Huang, Lin Zhang, and Zhigang Zhang* Liaoning Provincial Key Laboratory of Chemical Separation Technology, Shenyang University of Chemical Technology, Shenyang 110142, China ABSTRACT: The vapor−liquid equilibrium (VLE) data for binary systems of acetone + 1-ethyl-3-methylimidazolebromine ([EMIM][Br]), methanol + 1-ethyl-3-methylimidazolebromine ([EMIM][Br]), acetone + 1-butyl-3-methylimidazolebromine ([BMIM][Br]), methanol + 1-butyl-3methylimidazolebromine ([BMIM][Br]), and ternary VLE data for systems of acetone + methanol + 1-ethyl-3methylimidazolebromine ([EMIM][Br]), acetone + methanol + 1-ethyl-3-butylimidazolebromine ([BMIM][Br]) were detected at 101.3 kPa in an all-glass dynamic recirculating still. With the addition of bromine−based ionic liquids, the relative volatility of acetone to methanol was enhanced and the azeotropy was eventually eliminated. As for the separating effect, [EMIM][Br] is better than [BMIM][Br]. The measured binary and ternary VLE data were correlated with the nonrandom twoliquid activity coefficient model, and the results demonstrated that the experimental data and the correlated data were in good agreement.

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INTRODUCTION Methanol and acetone are important organic chemical raw materials which both have extremely widespread application in the modern chemical industry. However, a separation problem occurs because acetone and methanol form a minimum azeotrope at a mole fraction of acetone of 78 %, and its azeotropic temperature is 328.65 K1 at 101.3 kPa. Therefore, some special distillation methods will be adopted to separate the acetone and methanol system, such as extractive distillation, pressure swing distillation, azeotropic distillation, and salt adding distillation, etc. In this article, the extractive distillation separation method is selected because of its advantages of less energy consumed, less corrosiveness, and flexible selection of the possible entrainers.2 In the process of extractive distillation, it is essential to select the extractive solvent with the properties of high selectivity and solubility, low toxicity, high stability, and so forth. Previously, organics like water,3 monoethanolamine,4 and chlorobenzene5 have been selected as extractive solvents to separate a methanol and acetone system by the method of extractive distillation, but in recent years ILs have been gradually replacing organic solvents in the extractive distillation process. As a new kind of green solvents, ionic liquids (ILs) are chemicals composed entirely of ions whose cations are mainly macromolecular organic such as imidazole, pyridinium, quaternary ammonium, tetra-alkyl-phosphonium, and the anions are mainly inorganic anions such as halide, tetrafluoroborate, alkyl-sulfate, acetate, trifluoromethanesulfonate and so forth.6 According to the structure of ILs, they exhibit many unique physical and chemical properties;7 for example, the cation and anion can be varied at will, they have no effective vapor pressure, they possess high selectivity and thermal © XXXX American Chemical Society

solubility, and they are liquid in a wide range of temperature, etc. All these unique physical and chemical properties are the ones which are needed a solvent material. At present, the ILs as extractive solvents used in the vapor−liquid equilibrium of acetone and methanol system are 1-ethyl-3-methylimidazolehydrogensulfate ([EMIM][HSO4]) and1-ethyl-3methylimidazolemethylsulfate ([EMIM][MeSO4]) by Liebert,8 1-ethyl-3-methylimidazoletrifluoromethanesulfonate ([EMIM][CF 3 SO 3 ]),1-butyl-3-methylimidazoletrifluoromethanesulfonate ([BMIM][CF3SO3]), 1-butyl-1-methylpyrrolidiniumtrifluoromethanesulfonate ([BMPYR][CF3SO3]) and 1-ethyl-3methylimidazolium dicyanamide ([EMIM][DCA]) by Orchilles9−11 and n-butylpyridiniumhexafluorophosphate ([BPY] [PF6]) by Kurzin et al.12 In this paper, we focus on the influence of bromine-based ILs on the vapor−liquid equilibrium of the methanol and acetone azeotropic system.

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EXPERIMENTAL SECTION Material. The chemicals used in this work are acetone (Sinopharm Group, minimum wt 99.5 %), dried methanol (Sinopharm Group, minimum wt 99.5 %), and the ILs. Overviews of the chemicals used in this study are summarized in Table 1. The ILs13,14 were synthesized in our own laboratory. The ILs were dehydrated by Karl Fisher titration, and the mass fraction of the water was below 0.005. The acetone and methanol were both analyzed by gas chromatography and the ILs were detected using liquid chromatography, no impurities Received: May 12, 2014 Accepted: October 27, 2014

A

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deviation of 0.0001 g, and then the mass fraction of acetone or methanol can also be obtained. There were only two peaks observed in the analysis of vapor phase by chromatography since the IL had a negligible vapor pressure. For the VLE data in the liquid phase, the compositions of volatile solvents were also obtained by the gas−liquid chromatography with a headspace sampler which can retain the entire IL in a trap located between the injector and the capillary column. The content of IL was analyzed by the same way as the binary VLE data of IL + solvent. The maximum standard deviation of the composition in the samples is 0.001 mol fraction.

Table 1. Specifications of the Chemical Samples chemical name acetone methanol [EMIM] [Br] [BMIM] [Br]

source

purification method

purity

analysis method

Sinopharm Group Sinopharm Group Synthesizedown

0.995

none

GCa

0.995

none

GCa

0.990

LCc KFb

Synthesizedown

0.990

vacuum desiccation vacuum desiccation

LCc KFb

a

GC = gas chromatography. bKF = Karl Fisher titration. cLC = liquid chromatography.

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RESULT AND DISCUSSION Experimental Data. To check the reliability of the device used in this experiment, isobaric VLE data for the binary system

were detected. Densities of the pure components were measured at 298.15 K using a vibrating tube density meter (M196028, China), and boiling points with values15,16 from the corresponding literature are shown in Table 2. Table 2. Density ρ and Normal Boiling Point T of Pure Components ρ/(g·cm−3) (298.15 K)

T/K (101.3 kPa)

component

exptl

lit.

exptl

lit.

acetone methanol [EMIM][Br] [BMIM][Br]

0.7843 0.7897 1.3881 1.3023

0.7850 0.7913 1.3946 1.3001

329.38 337.81

329.27 337.66

Standard uncertainties u are u(ρ) = 0.1 kPa, u(T) = 0.15 K.

Apparatus and Procedure. Experiments of binary and ternary isobaric vapor−liquid equilibrium were conducted at atmospheric pressure in an all-glass dynamic recirculating still (NGW, Wertheim, Germany) which has been described in detail in the previous literature.17 The equilibrium temperature was determined using a Beckmann thermometer with a deviation of 0.01 K.The vapor−liquid equilibrium (VLE) data were detected using a headspace sampler (G1888 Network headspace sampler, Agilent Technologies) and a gas−liquid chromatography (model 7890A, Agilent Technologies) equipped with a 30 m in length, 2.5 mm in diameter, and 2.5 mm in thickness SP-1000 capillary column and a FID detector for which the carrier gas is N2. The operating conditions were as follows: the temperature of oven, injector, and detector was 308, 423, and 443 K, respectively. For the binary systems, every experimental data point was obtained by adding different amounts of solvent to the initial sample whose content of ILs is highest. For the ternary system, the VLE data point was obtained by adding different quantities of a mixture of IL and methanol to the mixture of certain content IL and acetone, so as to keep the content of IL in both acetone and methanol constant. Only when the temperature was constant and lasted for 30 min or longer was the equilibrium assumed. The sampling was conducted 2 h after the equilibrium was assumed. Sample Analysis. For the binary systems of solvent + IL, only the mass fraction of the IL in the liquid phase needs to be detected because an IL has no effective vapor pressure. The mass fraction content of IL in the liquid phase was gravimetrically determined after evaporating the volatile component from a mass-known sample (about 2.5 g) until the weight was constant at 393 K in a vacuum oven. The mass fraction of the IL can be weighed by an analytical balance with a

Figure 1. Isobaric VLE data for acetone (1) + methanol (2) system at 101.3 kPa: △,▽,○ literature data; solid line, experimental data.

Table 3. Vapor−Liquid Equilibrium Data for Temperature T, Liquid-Phase Mass Fraction w3 for the System Acetone (1), Methanol (2) + [EMIM][Br] (3) at 101.3 kPaa 1+3

a

2+3

w3

T/K

w3

T/K

0.0109 0.0117 0.0127 0.0147 0.0158 0.0170 0.0196 0.0207 0.0217 0.0230

329.61 329.63 329.65 329.69 329.73 329.78 329.82 329.85 329.88 329.93

0.0221 0.0488 0.0907 0.1375 0.1987 0.2828 0.3785 0.4484 0.5007 0.5580

337.42 337.58 337.94 338.26 338.77 339.70 341.47 342.86 344.52 346.87

Standard uncertainties u are u(w3) = 0.001, u(T) = 0.15 K.

of acetone (1) + methanol (2) at atmospheric pressure was measured and compared with the previous literature data8,18,19 as shown in Figure 1, and from the figure it can be seen that the experimental data and literature data are in good agreement. X presents the mole fraction of acetone in the liquid phase, Y presents the mole fraction of acetone in the vapor phase in Figure 1. The binaries for acetone (1) + [EMIM][Br] (3), methanol (2) + [EMIM][Br] (3), acetone (1) + [BMIM][Br] (3), B

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6. Since IL has no effective vapor pressure, the assumption that there is almost no IL in the vapor phase can be made. Therefore, the values of ys1 and ys2 are equal to y1 and y2. The ternary VLE data for the system of acetone and methanol containing [EMIM][Br] are obtained by keeping the IL mass fraction nearly constant in series at about X3 = 0.050, 0.150, and 0.300, and for the system of acetone (1) + methanol (2) + [BMIM][Br] (3) the ternary VLE data are obtained by keeping the IL mass fraction at about w3 = 0.060, 0.170, 0.340, respectively. In Tables 3 and 4, w3 is the mass fraction of ILs in the liquid phase and T is the equilibrium temperature. In Tables 5 to 6, w3 is the mass fraction of ILs in the liquid phase and x1 is the mole fraction of acetone in the liquid phase expressed on an IL-free basis. y1 is the mole fraction of acetone in the vapor phase, and T is the equilibrium temperature. Calculation of the Phase Equilibrium. In the fact that ILs as a new kind of organic salts show some characters of ions, the nonrandom two-liquid (NRTL) model has been selected to correlate the vapor−liquid equilibrium of IL+ solvent systems due to its previous application in electrolyte solutions byArlt,10−22 Heintz,23−25 and Gmehling.26 In this work, the ternary VLE data have also been correlated using the NRTL

Table 4. Vapor−Liquid Equilibrium Data for Temperature T, Liquid-Phase Mass Fraction w3 for the System Acetone (1), Methanol (2) + [BMIM] [Br] (3) at 101.3 kPaa 1+3

a

2+3

w3

T/K

w3

T/K

0.0156 0.0168 0.0182 0.0197 0.0213 0.0221 0.0244 0.0259 0.0271 0.0303

330.13 330.17 330.22 330.28 330.33 330.35 330.41 330.46 330.50 330.58

0.0416 0.1034 0.1774 0.2339 0.3025 0.3843 0.4392 0.5186 0.6037 0.6628

338.13 338.77 339.49 339.96 340.72 342.31 343.04 344.15 346.48 348.22

Standard uncertainties u are u(w3) = 0.001, u(T) = 0.15 K.

methanol (2) + [BMIM][Br] (3) at 101.3 kPa are listed in Tables 3 and 4, and ternary VLE data for acetone (1) + methanol (2) + [EMIM][Br] (3) and acetone (1) + methanol (2) + [BMIM][Br] (3) at 101.3 kPa are listed in Tables 5 and

Table 5. Vapor−Liquid Equilibrium Data for Liquid-Phase Mass Fraction of [EMIM][Br] w3, Temperature T, Liquid-Phase Mole Fraction (IL-free) x1, and Gas-Phase Mole Fraction y1, for the Ternary System Acetone (1) + Methanol (2) + [EMIM][Br] (3) at 101.3 kPaa

a

w3

x1

y1

T/K

x3

x1

y1

T/K

0.054 0.047 0.052 0.051 0.052 0.051 0.053 0.050 0.053 0.046 0.047 0.054 0.050 0.052 0.048 0.054 0.048 0.052 0.049 0.053 0.049 0.051 0.154 0.149 0.154 0.146 0.148 0.151 0.149 0.152 0.152 0.151 0.154

0.000 0.045 0.081 0.131 0.169 0.217 0.264 0.319 0.370 0.422 0.475 0.534 0.583 0.632 0.690 0.748 0.794 0.850 0.882 0.926 0.964 1.000 0.000 0.042 0.066 0.109 0.147 0.192 0.242 0.291 0.344 0.408 0.451

0.000 0.088 0.151 0.234 0.289 0.347 0.398 0.453 0.495 0.540 0.583 0.621 0.655 0.685 0.724 0.767 0.812 0.857 0.894 0.900 0.954 1.000 0.000 0.080 0.122 0.192 0.251 0.315 0.385 0.445 0.505 0.570 0.613

338.68 337.46 336.70 335.62 334.95 334.14 333.39 332.65 332.07 331.46 330.95 330.42 330.12 329.79 329.51 329.24 329.05 328.88 329.03 329.24 329.49 329.73 339.72 338.74 338.17 337.23 336.56 335.79 334.96 334.26 333.54 332.89 332.44

0.151 0.149 0.147 0.152 0.148 0.149 0.150 0.151 0.153 0.301 0.299 0.302 0.305 0.296 0.305 0.299 0.302 0.304 0.303 0.295 0.302 0.296 0.303 0.300 0.301 0.303 0.296 0.301 0.297 0.298 0.304

0.495 0.557 0.631 0.717 0.761 0.813 0.846 0.884 1.000 0.000 0.021 0.030 0.052 0.071 0.092 0.120 0.144 0.208 0.285 0.356 0.396 0.434 0.465 0.503 0.564 0.644 0.741 0.823 0.882 0.956 1.000

0.638 0.684 0.739 0.776 0.824 0.888 0.900 0.944 1.000 0.000 0.043 0.063 0.116 0.140 0.171 0.215 0.280 0.348 0.420 0.486 0.575 0.626 0.666 0.688 0.741 0.818 0.885 0.916 0.927 0.984 1.000

332.15 331.76 331.47 331.37 331.33 331.30 331.26 331.20 331.16 340.20 339.49 339.01 338.22 337.92 337.55 337.07 336.33 335.67 334.94 334.17 333.76 333.30 333.13 332.91 332.68 332.55 332.25 332.20 332.14 332.12 332.08

Standard uncertainties u are u(x1) = u(y1) = 0.01, u(T) = 0.15 K, u(w3) = 0.001. C

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Table 6. Vapor−Liquid Equilibrium Data for Liquid-Phase Mass Fraction of [EMIM][Br] w3, Temperature T, Liquid-Phase Mole Fraction (IL-free) x1, and Gas-Phase Mole Fraction y1, for the Ternary System Acetone (1) + Methanol (2) + [BMIM][Br] (3) at 101.3 kPaa

a

x3

x1

y1

T/K

x3

x1

y1

T/K

0.062 0.057 0.063 0.059 0.065 0.066 0.061 0.059 0.059 0.068 0.061 0.063 0.058 0.062 0.066 0.052 0.058 0.062 0.060 0.063 0.055 0.167 0.174 0.169 0.172 0.176 0.168 0.171 0.169 0.172

0.000 0.033 0.072 0.114 0.166 0.214 0.261 0.314 0.366 0.420 0.480 0.538 0.608 0.659 0.720 0.774 0.832 0.882 0.927 0.974 1.000 0.000 0.036 0.081 0.134 0.174 0.213 0.265 0.299 0.341

0.000 0.060 0.141 0.224 0.306 0.373 0.428 0.482 0.532 0.574 0.615 0.653 0.694 0.728 0.766 0.800 0.836 0.886 0.930 0.977 1.000 0.000 0.074 0.151 0.217 0.265 0.326 0.389 0.446 0.500

339.19 338.25 337.09 336.03 334.86 333.97 333.19 332.47 331.88 331.32 330.82 330.39 329.95 329.72 329.47 329.28 329.12 329.18 329.27 329.38 329.49 341.51 340.37 339.33 338.44 337.67 336.73 335.67 334.97 334.34

0.174 0.175 0.169 0.167 0.172 0.168 0.169 0.171 0.174 0.173 0.169 0.339 0.342 0.345 0.336 0.335 0.339 0.342 0.344 0.338 0.345 0.342 0.336 0.343 0.339 0.341 0.333 0.338 0.341 0.347

0.399 0.449 0.497 0.579 0.647 0.701 0.764 0.805 0.869 0.947 1.000 0.000 0.083 0.128 0.159 0.219 0.263 0.342 0.429 0.468 0.515 0.569 0.608 0.649 0.694 0.737 0.791 0.840 0.907 1.000

0.558 0.603 0.641 0.699 0.750 0.793 0.837 0.872 0.920 0.982 1.000 0.000 0.131 0.190 0.264 0.354 0.424 0.486 0.524 0.561 0.619 0.678 0.719 0.763 0.808 0.850 0.907 0.964 0.998 1.000

333.61 333.09 332.65 332.01 331.55 331.21 330.85 330.65 330.36 330.06 329.94 346.81 344.62 343.07 341.85 340.42 339.56 338.32 337.34 336.62 335.83 335.12 334.65 334.20 333.74 333.33 332.90 332.51 332.27 331.79

Standard uncertainties u are u(x1) = u(y1) = 0.01, u(T) = 0.15 K, u(w3) = 0.001.

model. And according to the formula of the NRTL model function, every one of the nine parameters should be determined for the binary systems of acetone + methanol, [EMIM][Br] (3) + acetone (1), [EMIM][Br] (3) + methanol (2) and for the binary systems of [BMIM][Br] (3) + acetone (1) and [BMIM][Br] (3) + methanol (2). Then the ternary VLE data for the system of acetone (1) + methanol (2) containing [EMIM][Br] (3) or [BMIM][Br] (3) can be predicted. Among the nine parameters, six of them are binary energy parameters (G12, G13, G23, G21, G31, G32); the rest are parameters called nonrandomness factors (α12, α13, α23). In the previous literature9 G12, G21, and α12 are cited and the parameters for [EMIM][Br] (3) + acetone (1), [EMIM][Br] (3) + methanol (2), [BMIM][Br] (3) + acetone (1), and [BMIM][Br] (3) + methanol (2) are measured using the

Table 7. Antoine’s Parameter for Pure Components

a

componentsa

A

B

C

acetonea methanola

6.3565 7.0224

1277.0 1474.1

−35.920 −44.020

Parameter obtained from ref 3.

Table 8. Nonrandom Factor αi,j and Binary Energy Parameter Δgi,j, Δgj,i for the NRTL Model component i acetone acetone methanol acetone methanol a

component j methanol [EMIM][Br] [EMIM][Br] [BMIM][Br] [BMIM][Br]

αi,j 0.300 0.400 0.076 0.315 0.226

Δgi,j/(J/mol) a

924.2 −14502.9 −9427.2 −1744.4 −1133.9

a

Δgj,i/(J/mol) 863.1a 2316.3 10758.3 278.6 1294.0

From Orchillés, Δgi,j = gi,j − gi,i , τij = (gi,j − gi,i)/RT.

Table 9. Mean Absolute Deviations, δy and δT, and Standard Deviations, σy and σT, between Experimental and Calculated Values of the Vapor-Phase Mole Fractions and the Equilibrium Temperatures systems

δya

σyb

δTc/K

σTd/K

acetone + methanol + [EMIM][Br] acetone + methanol + [BMIM][Br]

0.006 0.004

0.007 0.003

0.47 0.51

0.34 0.38

a δy = (1/N)∑|yexptl − ycalcd|. bσy = [∑(yexptl − ycalcd)2/(N−m)]1/2. cδT = (1/N)∑|Texptl − Tcalcd|. dσT=[∑(Texptl − Tcalcd)2/(N − m)]1/2. N is the number of experimental points, and m is the number of parameters for the model.

D

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Figure 2. Experimental and calculated T−X−Y diagrams for acetone (1) + methanol (2) + [EMIM][Br] (3) at 101.3 kPa: dotted lines, T−X−Y experimental IL-free system;▼, T−X experimental for X3 = 0.050; ▽, T−Y experimental for X3 = 0.05; ●, T−X experimental for X3 = 0.150; ○, T−Y experimental for X3 = 0.150; ▲, T−X experimental X3 = 0.300; △, T−Y experimental for X3 = 0.300; solid line, correlated using the NRTL model.

Figure 3. Experimental and calculated T−X−Y diagrams for acetone (1) + methanol (2) + [BMIM][Br] (3) at 101.3 kPa: dotted lines, T−X−Y experimental IL-free system; ▼, T−Y experimental for X3 = 0.060; ▽, T−X experimental for X3 = 0.060; ●, T−Y experimental for X3 = 0.170; ○, T−X experimental for X3 = 0.170;▲, T−Y experimental X3 = 0.340; △, T−X experimental for X3 = 0.340; solid line, correlated using the NRTL model.

Figure 5. Isobaric VLE X,Y diagram for acetone (1) + methanol (2) + [BMIM][Br] (3) system at 101.3 kPa: □, X3 = 0.060; ○, X3 = 0.170; △, X3 = 0.340; solid line, correlated using NRTL model.

Figure 4. Isobaric VLE X,Y diagram for acetone (1) + methanol (2) + [EMIM][Br] (3) system at 101.3 kPa: □, X3 = 0.050; ○, X3 = 0.150; △, X3 = 0.300; solid line, correlated using NRTL model.

ternary VLE data listed in Table 5 and Table 6 and the NRTL model by minimizing the objective function:

(1)

phase as ideal behavior is given and the equilibrium conditions are expressed in the equation as follow: Py γi = 0 i Pi xi (2)

in which γi is the activity coefficient of the solvent i, the indices exptl and calcd denote the experimental and calculated values, respectively, N is the number of experimental data point, and the summations are extended to the whole range of data points. To get these parameters, the assumption of treating the vapor

where γi is the activity coefficient of component i obtained from the NRTL model, xi presents the mole fraction of component i in the liquid phase, and yi presents the mole fraction of component i in the vapor phase, P is the total pressure of the system at about 101.3 kPa, P0i represents the vapor pressure of

OF =

∑ (1 − γ1calcd/γ1explt)2 + ∑ (1 − γ2calcd/γ2explt)2 N

N

E

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(3) for X3 = 0.060, 0.170, 0.340 are plotted on T−X−Y diagrams, respectively. All these results are presented in Figure 2 and Figure 3. Where X is the mole fraction of acetone in the liquid phase, Y is the mole fraction of acetone in the vapor phase; T presents the equilibrium temperature in K. In Figure 2 and Figure 3, what can be seen is that a small content of [EMIM][Br] or [BMIM][Br] produces a displacement of the azeotropic point toward X values higher than 0.78 until the azeotrope disappears, and the effect is more noticeable as the amount of IL increase. When the mass fraction is 0.150 for [EMIM][Br] and 0.170 for [BMIM][Br], the azeotropic point of the acetone and methanol system is totally broken and the calculated contents of component i in the vapor and liquid phase by NRTL model are in good agreement with the experimental data. At the same time, the effect of [EMIM][Br] and [BMIM][Br] on the relative volatility of acetone to methanol is illustrated in Figure 4 and Figure 5.Where X presents the mole fraction of acetone in liquid phase, Y presents the mole fraction of acetone in vapor phase. The figures show that, with the addition of both ILs, the relative volatility of acetone to methanol is enhanced and growing higher as the ILs content increases. The relative volatility is measured by the equation described below:

Figure 6. Relative volatility of acetone (1) to methanol (2) with the acetone mole fraction for different [EMIM][Br] at 101.3 kPa. ▼, X3 = 0.050; ●, X3 = 0.150; ▲, X3 = 0.300.

α12 =

Y1/X1 Y2/X 2

(4)

The conclusion that [EMIM][Br] shows a better separating effect than [BMIM][Br] can be drawn. On one hand, it can be clearly seen by comparing the enhancement of relative volatilities in Figure 6 and Figure 7. The higher is the relative volatility, the better the effect is. On the other hand, the addition of IL also causes the elevation of boiling point at atmospheric pressure, as shown in Figures 2 and 3, the equilibrium temperature increasing with increasing amount of IL. Therefore less energy will be consumed at the same separation effect for [EMIM][Br] than for [BMIM][Br]. This can be explained in that the shorter side chain leads to a higher polarity of [EMIM][Br] compared with the polarity of [BMIM][Br]. That is to say, the higher polarity [EMIM][Br] has the greater difference of solubility and interaction with acetone and methanol. Meanwhile, the lower the polarity that [BMIM][Br] has, the less difference there is. The effect of ILs used in this paper is also compared with other ILs in the binary acetone + methanol system. Relative volatility can be an indicator of the separation effect. The relative volatility of acetone with respect to methanol in the presence of [EMIM][BF4]19 at x3 = 0.5 does not come up to 2, a value that is much less than that of [EMIM][Br] or [BMIM][Br]. Meanwhile, the value of ILs mass fraction is 0.300 (0.157 in mole fraction) for [EMIM][Br] and 0.340 (0.155 in mole fraction) for [BMIM][Br] when a total break of the azeotrope is produced, while the value of that for [BMIM][CF3SO3] and [BMPYR][CF3SO3]8 is about 0.23. Thus, [EMIM][Br] or [BMIM][Br] can be selected as a potential entrainer to separate the system.

Figure 7. Relative volatility of acetone (1) to methanol (2) with the acetone mole fraction for different [BMIM][Br] at 101.3 kPa.: ▼ X3 = 0.060; ●, X3 = 0.170; ▲, X3 = 0.340.

component i at equilibrium temperature which can be calculated by Bi log Pi0 = Ai − T + Ci (3) The equation is called the Antoine equation in which P0 is the equilibrium pressure of pure solvent in kPa and T is equilibrium temperature in K, which is obtained in the same recirculating still. The Antoine parameters Ai, Bi, and Ci are listed in Table 7. A combination of the ternary VLE data for the system of acetone (1) + methanol (2) containing [EMIM][Br] (3) or [BMIM][Br] (3) with the NRTL model gives the binary energy parameters by the method of iteration. These are shown in Table 8. Subsequent to that, with the parameters calculated from the VLE data above and the NRTL model, each composition in the vapor phase and temperature corresponding to each composition in the liquid phase can be worked out and compared with the experimental data. Thus, the mean absolute deviation between the calculated and experimental values of the mole fraction in the vapor phase and the equilibrium temperature is listed in Table 9. The calculated and experimental VLE data for systems of acetone (1) + methanol (2) + [EMIM][Br] (3) for X3 = 0.050, 0.150, 0.300 and acetone (1) + methanol (2) + [BMIM][Br]

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CONCLUSION The isobaric VLE data for acetone (1) + [EMIM][Br] (3), methanol (2) + [EMIM][Br] (3), acetone (1) + methanol (2) + [EMIM][Br] (3), and acetone (1) + [BMIM][Br] (3), methanol (2) + [BMIM][Br] (3), and acetone (1) + methanol F

dx.doi.org/10.1021/je500418f | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

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(2) + [BMIM][Br] (3) were determined in a dynamic recirculating still at 101.3 kPa. From Figures 2 and 3, it can be seen that both ILs can break the azeotropy in the acetone and methanol azeotropic system for [EMIM][Br] at mass fraction of 0.150 and for [BMIM][Br] at mass fraction of 0.170. It can be seen that the relative volatility of acetone to methanol increases significantly with decreasing length of side chain. That is to say, the better separating effect belongs to [EMIM][Br]. The VLE data are well fitted by the NRTL model. The results of this work show that ILs may replace the conventional solvents as entrainer for an extractive distillation process.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: 86-024-89384726. Funding

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

The authors declare no competing financial interest.

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REFERENCES

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