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Isobaric vapor–liquid equilibrium for methyl acetate + methanol system containing different ionic liquids at 101.3 kPa
Fluid Phase Equilibria 408 (2016) 20–26
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Fluid Phase Equilibria j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / fl u i d
Isobaric vapor–liquid equilibrium for methyl acetate + methanol system containing different ionic liquids at 101.3 kPa Zhigang Zhang, Angran Hu, Tao Zhang, Qinqin Zhang, Zeqiang Yang, Wenxiu Li* Liaoning Provincial Key Laboratory of Chemical Separation Technology, Shenyang University of Chemical Technology, Shenyang 110142, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 5 June 2015 Received in revised form 23 July 2015 Accepted 24 July 2015 Available online 30 July 2015
Isobaric vapor–liquid equilibrium (VLE) data for ternary systems of methyl acetate + methanol containing three ionic liquids (ILs) were measured at 101.3 kPa. The investigated ILs were 1-hexyl-3methylimidazolium chloride ([HMIM][Cl]), 1-benzyl-3-methylimidazolium chloride ([BzMIM][Cl]), and 1-hexyl-3-methylimidazolium bromide ([HMIM][Br]). The results indicate that the addition of ILs can give rise to the increase of the relative volatility of methyl acetate to methanol. Besides, the more ILs, the larger the relative volatility. All the three investigated ILs can eliminate the azeotropic point of methyl acetate and methanol, and the separation effect follows the order: [HMIM][Cl] > [BzMIM][Cl] > [HMIM] [Br]. Additionally, the measured VLE data are well correlated with NRTL model. ã 2015 Elsevier B.V. All rights reserved.
Keywords: Vapor–liquid equilibrium Ionic liquid Methyl acetate Methanol NRTL model
1. Introduction Extractive distillation is the most widely utilized technology to separate azeotropic or close-boiling point mixtures [1–3]. The selection of a suitable entrainer is of great importance before the separationprocess is designed [4,5]. In recent years, ionic liquids (ILs) have attracted impressive attention for potential applications as entrainers in extractive distillation [6]. ILs possess properties of negligible vapor pressure, high selectivity, low toxicity and corrosion, and good solubilities for various of chemicals [7,8]. Moreover, ILs as entertainers combine the advantages of a liquid solvent (easy operation) and a solid salt (high separation ability) [9]. However, the thermodynamic data of IL-containing systems are still scarce, which are essential for further design of extractive distillation process. Methyl acetate and methanol mixture is involved in industrial manufacturing process of poly (viny1 alcohol). It is difficult to separate them by conventional separation method since they form a minimum azeotrope at atmospheric pressure. Traditional organic solvents [10] and solid salts [11–14] have been used as entrainers to separate methyl acetate and methanol mixture in extractive distillation process. As environment-friendly solvents, ILs are compelling alternatives to volatile organic solvents and caustic solid salts. Up to now, several ILs have been investigated as entrainers to
* Corresponding author. Fax: +86 24 89383736. E-mail address: [email protected] (W. Li). http://dx.doi.org/10.1016/j.fluid.2015.07.045 0378-3812/ ã 2015 Elsevier B.V. All rights reserved.
break methyl acetate and methanol azeotrope, such as 1-ethyl-3methylimidazolium trifluoromethanesulfonate ([EMIM][Triflate]) [15], 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]) [16], 1octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF6]) [17], 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM][EtSO4]) [18], 1-butyl-1-methylpyrrolidinium dicyanamide ([BMPYR][DCA]), and 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) [19]. Besides, the separation effects of 1-butyl-3-methylimidazolium chloride ([C4MIM][Cl]), 1-(2-chloroethyl)-3-methylimidazolium chloride ([ClC2MIM][Cl]) and 1-butyl-3-methylimidazolium bromide ([C4MIM][Br]) on the azeotrope were explored in our previous work [20]. As a continuation of the previous study, one aim of this work is to determine if 1-hexyl-3-methylimidazolium chloride ([HMIM][Cl]), 1-benzyl-3-methylimidazolium chloride ([BzMIM] [Cl]), or 1-hexyl-3-methylimidazolium bromide ([HMIM][Br]), can eliminate the azeotropic point of methyl acetate and methanol mixture. In this work, isobaric VLE data of the ternary systems of methyl acetate + methanol containing three different ILs, namely [HMIM] [Cl], [BzMIM][Cl], and [HMIM][Br], were measured at 101.3 kPa. The separation effect of ILs on methyl acetate and methanol mixture was investigated and compared with that of the reported ILs. Furthermore, the separation effect produced by ILs was related to the intermolecular interactions between molecules of the investigated systems. Besides, the measured VLE data were correlated with the non-random two liquid (NRTL) model proposed by Renon and Prausnitz [21].
Z. Zhang et al. / Fluid Phase Equilibria 408 (2016) 20–26
Nomenclature
List of symbols Dgij binary energy parameter of NRTL model xi mole fraction of component i in the liquid phase x0 i mole fraction of component i in the liquid phase expressed on an IL-free basis yi mole fraction of solvent i in the vapor phase T equilibrium temperature N number of experimental data points m number of parameters for the model P total pressure in the equilibrium system Pi saturated vapor pressure of component i at equilibrium temperature Texptl equilibrium temperature measured by experimental data Tcalcd equilibrium temperature calculated with the NRTL model Tb normal boiling point of pure component yexptl mole fraction of solvent i in the vapor phase measured by experimental data ycalcd mole fraction of solvent i in the vapor phase calculated with the NRTL model Greek letters r density aij non-randomness parameter of NRTL model gi activity coefficient of component i g iexptl activity coefficient of component i measured by experimental data g icalcd activity coefficient of component i calculated with the NRTL model dy mean absolute deviation of the vapor phase mole fraction sy standard deviation of the vapor phase mole fraction dT mean absolute deviation of the equilibrium temperature sT standard deviation of the equilibrium temperature
reported methods in literature [22,23]. Their purities checked by liquid chromatography are 99% in mass fraction, and no major impurities were detected by ion chromatography. The ILs were placed in a vacuum drying oven at 343.15 K overnight before use to remove trace impurities. The final water content of ILs, determined by Karl Fischer titration, was less than 0.005 (mass fraction). The overall information of the chemicals were summarized in Table 1. The densities of the pure components were measured at 298.15 K using a vibrating tube density meter (M196028, China), and the standard uncertainty is 0.0002 g cm3. The boiling points of methyl acetate and methanol were determined at 101.3 kPa, and the standard uncertainty is 0.05 K. The measured densities of components and boiling points of methyl acetate and methanol as well as the values of the corresponding literature [23–25] are shown in Table 2. 2.2. Apparatus and procedure The VLE experiments were conducted in an all-glass equilibrium still (NGW, Wertheim, Germany), which have been described in detail in a previous literature [26]. The pressure was kept constant at 101.3 kPa by controlling a gas buffer connected with the still, and detected by a manometer with a standard uncertainty of 0.1 kPa. The temperature was determined with a standard and calibrated thermometer, and its standard uncertainty is 0.01 K. Each solution was gravimetrically prepared with the help of a digital balance (CAV264C OHAUS America) with a standard uncertainty of 0.0001 g. For the binary system of methyl acetate + methanol, some methyl acetate was added to the pure methanol until a very diluted solution was obtained. For each ternary system, the mixture of methanol and defined mole fraction of IL was prepared, where some other mixtures of methyl acetate and the same mole fraction of IL were added, trying to keep the scheduled mole fraction of IL in each series. Only when the temperature was
Table 2 Density r and the normal boiling point Tb of pure components. Component
Methyl acetate Methanol [HMIM][Cl] [BzMIM][Cl] [HMIM][Br]
2. Experimental 2.1. Materials Methyl acetate and methanol were provided by Sinopharm group with mass fraction purities higher than 99.5% examined by gas chromatography. The ILs, [HMIM][Cl], [BzMIM][Cl], and [HMIM][Br] were synthesized in our laboratory according to the
21
r/(g cm3) (298.15 K)
Tb (101.3 kPa)/K
Exptl
Lit.
Exptl
Lit.
0.9273 0.7871 1.0443 1.1928 1.2292
0.9275a 0.7869a 1.044202b 1.1930c 1.229168b
330.20 337.69
330.4a 337.7a
Standard uncertainties u are u(r) = 0.0002 g cm3,u(T) = 0.05 K. a From Ref. [24]. b From Ref. [23]. c From Ref. [25].
Table 1 Specifications of chemical samples. Chemical name
Source
Mass fraction purity
Purification method
Analysis method
Methyl acetate Methanol [HMIM][Cl]a [BzMIM][Cl]b [HMIM][Br]c
Sinopharm group Sinopharm group Synthesized own Synthesized own Synthesized own
0.995 0.995 0.990 0.990 0.990
None None Vacuum desiccation Vacuum desiccation Vacuum desiccation
GCd GCd LCe , KFf , ICg LCe , KFf , ICg LCe , KFf , ICg
a b c d e f g
[HMIM][Cl] = 1-hexyl-3-methylimidazolium chloride. [BzMIM][Cl] = 1-benzyl-3-methylimidazolium chloride. [HMIM][Br] = 1-hexyl-3-methylimidazolium bromide. GC = gas chromatography. LC = liquid chromatography. KF = Karl Fischer titration. IC = ion chromatography.
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Z. Zhang et al. / Fluid Phase Equilibria 408 (2016) 20–26
constant for more than half an hour (the deviation of temperature was 0.01 K), were the equilibrium conditions assumed. 2.3. Sample analysis
to the relative volatility of methyl acetate to methanol, which is calculated by the following equations based on the assumption of the ideal vapor phase due to the low total pressure in this work.
y i P ¼ xi g i P i
The condensed vapor and liquid phase samples were inserted into a headspace sampler (HS-sampler) (G1888 Network headspace sampler, Agilent Technologies) and then detected by a gas chromatograph (Model 7890A, Agilent Technologies) equipped with a SP-1000 capillary column (30 m in length, 2.5 mm in diameter, and 2.5 mm in thickness) and a FID detector. Nitrogen was used as carrier gas. The operating conditions were as follows: the temperatures of oven, injector, and detector were 335 K, 423 K, and 443 K, respectively. Since ILs have no detectable vapor pressure, only the peaks of methyl acetate and methanol were observed. The content of ILs was gravimetrically determined by the mass difference before and after vaporizing the volatile components. The standard uncertainty of ILs was 0.001 in mole fraction. Every sample was analyzed at least three times and the standard uncertainty of the volatile components in vapor and liquid phases was 0.001 in mole fraction. 3. Results and discussion 3.1. Experimental data The reliability of our apparatus has been validated by the VLE data of methyl acetate + methanol binary system at 101.3 kPa in our previous study [20]. The ternary VLE data of methyl acetate + methanol containing [HMIM][Cl], [BzMIM][Cl], and [HMIM][Br] were measured at 101.3 kPa by keeping the mole fractions of ILs nearly constant at 0.05, 0.10, and 0.15, respectively. The experimental data are orderly listed in Tables 3–5, where x3 represents the mole fraction of ILs in the liquid phase, T is the equilibrium temperature, x1 represents the mole fraction of methyl acetate in the liquid phase containing ILs, x0 1 refers to the mole fraction of methyl acetate in the liquid phase expressed on an IL-free basis, y1 is the mole fraction of methyl acetate in the vapor phase. a12 refers
ð1Þ
a12 ¼
g 1 P1 g 2 P2
ð2Þ
where yi and xi are the mole fractions of component i in the vapor phase and liquid phase, respectively, g i represents activity coefficient of component i, P is the total pressure (101.3 kPa in this work), Pi refers to the saturated pressure of component i at equilibrium temperature which is calculated by Antoine equation with the Antoine parameters taken from previous literature [24]. 3.2. Correlation of the phase equilibrium The NRTL model is commonly used for the correlation of the VLE data containing ILs since it often fits the experimental data well [27–30]. In this work, the NRTL model is also adopted for the correlation of the measured VLE data. To reproduce the VLE data, nine parameters should be determined for each ternary system, including six binary energy parameters and three non-random factors. The binary parameters for methyl acetate and methanol are taken from literature [20]. The other parameters are obtained from the ternary VLE data containing ILs. The model parameters are regressed with the help of Levenberg–Marquardt method through minimization of the following objective function: ARDð%Þ ¼
1X g i exptl g i calcd j j 100 n n g i exptl
ð3Þ
where n is the number of experiment points, g i is the activity coefficient of component i, and the superscripts “exptl” and “calcd” denote experimental and calculated values, respectively. Following this procedure, the binary interaction parameters of NRTL model and the average relative deviations (ARDs) of
Table 3 Vapor–liquid equilibrium data for methyl acetate (1) + methanol (2) + [HMIM][Cl] (3) at 101.3 kPa.a x3
T (K)
x1
x0 1
y1
0.050 0.051 0.049 0.050 0.052 0.050 0.051 0.052 0.050 0.051 0.050 0.049 0.050 0.052 0.050 0.051 0.050 0.101 0.100 0.100 0.101 0.100 0.099 0.100 0.101 0.102
341.01 339.01 334.67 332.04 330.12 329.03 328.36 327.83 327.71 327.74 327.90 328.26 328.57 329.30 330.12 331.01 331.61 346.73 342.28 336.76 333.66 331.78 330.47 329.31 328.71 328.46
0.000 0.021 0.083 0.142 0.208 0.267 0.322 0.404 0.451 0.531 0.587 0.657 0.703 0.778 0.854 0.913 0.950 0.000 0.032 0.093 0.147 0.195 0.243 0.309 0.371 0.427
0.000 0.022 0.087 0.149 0.219 0.281 0.339 0.426 0.475 0.560 0.618 0.691 0.740 0.821 0.899 0.962 1.000 0.000 0.036 0.103 0.164 0.217 0.270 0.343 0.413 0.476
0.000 0.102 0.304 0.422 0.512 0.570 0.613 0.665 0.691 0.733 0.761 0.796 0.821 0.865 0.917 0.965 1.000 0.000 0.195 0.414 0.528 0.598 0.650 0.705 0.745 0.776
a
a12 5.019 4.568 4.154 3.727 3.391 3.084 2.673 2.474 2.161 1.969 1.746 1.612 1.400 1.242 1.087
6.571 6.130 5.723 5.378 5.029 4.571 4.158 3.821
x3
T (K)
x1
x0 1
y1
a12
0.100 0.099 0.100 0.102 0.100 0.101 0.100 0.099 0.149 0.150 0.151 0.150 0.152 0.150 0.151 0.150 0.149 0.150 0.149 0.150 0.151 0.150 0.149 0.152 0.150
328.45 328.65 329.02 329.55 330.17 331.01 331.88 332.29 352.88 346.15 339.07 336.34 334.05 331.67 330.36 329.71 329.06 328.97 329.16 329.48 329.98 330.59 331.24 331.83 332.51
0.496 0.562 0.621 0.681 0.745 0.811 0.874 0.901 0.000 0.037 0.098 0.134 0.176 0.238 0.294 0.335 0.416 0.477 0.547 0.598 0.655 0.713 0.765 0.804 0.850
0.551 0.624 0.690 0.758 0.828 0.902 0.971 1.000 0.000 0.044 0.115 0.158 0.208 0.280 0.346 0.394 0.489 0.561 0.643 0.704 0.771 0.839 0.899 0.948 1.000
0.810 0.840 0.865 0.892 0.921 0.952 0.986 1.000 0.000 0.275 0.509 0.590 0.657 0.727 0.771 0.798 0.840 0.866 0.893 0.912 0.931 0.951 0.970 0.983 1.000
3.472 3.167 2.879 2.632 2.415 2.170 2.095
Standard uncertainties u are u(T) = 0.05 K, u(P) = 0.1 kPa, u(x3) = u(x1) = u(x0 1) = u(y1) = 0.001.
8.335 7.944 7.689 7.314 6.848 6.356 6.073 5.490 5.054 4.638 4.367 3.996 3.729 3.635 3.164
Z. Zhang et al. / Fluid Phase Equilibria 408 (2016) 20–26
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Table 4 Vapor–liquid equilibrium data for methyl acetate (1) + methanol (2) + [BzMIM][Cl] (3) at 101.3 kPa.a x3
T (K)
x1
x0 1
y1
0.049 0.050 0.051 0.050 0.049 0.050 0.052 0.050 0.049 0.051 0.051 0.050 0.051 0.050 0.049 0.051 0.050 0.100 0.101 0.100 0.102 0.100 0.101 0.100 0.099 0.100
341.37 339.73 335.33 333.07 331.65 330.24 329.34 328.61 328.15 327.97 327.88 327.84 328.02 328.34 328.86 330.35 331.52 348.17 343.56 339.23 336.15 333.88 332.52 331.63 331.22 330.73
0.000 0.016 0.079 0.124 0.162 0.218 0.273 0.327 0.381 0.437 0.485 0.549 0.613 0.694 0.773 0.888 0.950 0.000 0.037 0.085 0.141 0.196 0.252 0.298 0.324 0.383
0.000 0.017 0.083 0.131 0.170 0.229 0.288 0.344 0.401 0.460 0.511 0.578 0.646 0.731 0.813 0.936 1.000 0.000 0.041 0.094 0.157 0.218 0.280 0.331 0.360 0.426
0.000 0.080 0.294 0.389 0.451 0.517 0.568 0.607 0.640 0.671 0.695 0.726 0.757 0.797 0.843 0.932 1.000 0.000 0.208 0.373 0.492 0.567 0.627 0.663 0.682 0.717
a
a12 5.076 4.586 4.241 4.001 3.594 3.251 2.943 2.660 2.390 2.180 1.935 1.708 1.448 1.236 0.942
6.118 5.704 5.200 4.703 4.316 3.974 3.819 3.420
x3
T (K)
x1
x0 1
y1
a12
0.101 0.100 0.098 0.100 0.101 0.100 0.102 0.100 0.149 0.150 0.152 0.150 0.151 0.150 0.149 0.150 0.152 0.151 0.150 0.149 0.150 0.151 0.151 0.150 0.149
330.46 330.28 330.26 330.44 330.70 331.09 331.93 333.08 355.59 351.20 344.55 340.96 338.61 336.33 335.06 334.71 334.13 333.67 333.40 333.24 333.32 333.50 333.77 334.34 334.72
0.451 0.512 0.569 0.597 0.648 0.721 0.804 0.900 0.000 0.026 0.085 0.131 0.179 0.244 0.298 0.324 0.384 0.435 0.482 0.549 0.591 0.648 0.711 0.804 0.851
0.502 0.569 0.631 0.663 0.721 0.801 0.895 1.000 0.000 0.031 0.100 0.154 0.211 0.287 0.350 0.381 0.453 0.512 0.567 0.645 0.695 0.763 0.837 0.946 1.000
0.753 0.782 0.808 0.821 0.845 0.882 0.930 1.000 0.000 0.186 0.426 0.531 0.606 0.675 0.718 0.735 0.770 0.796 0.817 0.848 0.867 0.892 0.922 0.973 1.000
3.028 2.718 2.463 2.328 2.112 1.856 1.553
x3
T (K)
x1
x0 1
y1
a12
0.101 0.100 0.100 0.099 0.100 0.101 0.102 0.100 0.150 0.151 0.150 0.149 0.150 0.151 0.150 0.152 0.150 0.149 0.150 0.151 0.150 0.152 0.151 0.150 0.150
329.96 330.03 330.24 330.75 331.16 331.71 332.31 333.48 346.55 342.83 338.34 335.99 333.93 332.93 332.29 332.09 331.91 331.93 332.16 332.43 332.78 333.10 333.55 334.33 335.16
0.507 0.558 0.611 0.697 0.739 0.785 0.826 0.900 0.000 0.034 0.094 0.143 0.215 0.276 0.336 0.394 0.451 0.502 0.558 0.601 0.657 0.683 0.732 0.798 0.850
0.564 0.620 0.679 0.774 0.821 0.873 0.920 1.000 0.000 0.040 0.111 0.168 0.253 0.325 0.395 0.465 0.531 0.590 0.656 0.708 0.773 0.805 0.862 0.939 1.000
0.709 0.737 0.765 0.818 0.847 0.884 0.923 1.000 0.000 0.178 0.369 0.465 0.560 0.617 0.661 0.698 0.730 0.758 0.789 0.814 0.847 0.865 0.898 0.952 1.000
1.884 1.718 1.540 1.315 1.206 1.107 1.045
7.242 6.662 6.214 5.757 5.158 4.725 4.503 4.045 3.714 3.409 3.069 2.857 2.562 2.294 2.062
Standard uncertainties u are u(T) = 0.05 K, u(P) = 0.1 kPa, u(x3) = u(x1) = u(x0 1) = u(y1) = 0.001.
Table 5 Vapor–liquid equilibrium data for methyl acetate (1) + methanol (2) + [HMIM][Br] (3) at 101.3 kPa.a x3
T (K)
x1
x0 1
y1
0.049 0.050 0.051 0.050 0.051 0.052 0.050 0.049 0.050 0.052 0.050 0.052 0.050 0.051 0.050 0.049 0.050 0.101 0.100 0.101 0.100 0.099 0.100 0.102 0.100 0.101
339.54 336.96 333.16 331.45 329.97 329.38 328.79 328.39 328.27 328.34 328.43 328.71 328.86 329.24 329.67 330.22 331.92 342.70 339.63 335.86 333.82 332.00 330.95 330.43 330.05 329.95
0.000 0.036 0.115 0.171 0.248 0.296 0.358 0.433 0.504 0.563 0.636 0.686 0.725 0.772 0.818 0.864 0.950 0.000 0.033 0.094 0.143 0.210 0.276 0.336 0.394 0.452
0.000 0.038 0.121 0.180 0.261 0.312 0.377 0.455 0.531 0.594 0.669 0.724 0.763 0.813 0.861 0.909 1.000 0.000 0.037 0.105 0.159 0.233 0.307 0.374 0.438 0.503
0.000 0.136 0.323 0.405 0.486 0.528 0.566 0.609 0.646 0.679 0.717 0.746 0.771 0.806 0.843 0.889 1.000 0.000 0.149 0.326 0.417 0.503 0.565 0.609 0.645 0.678
a
a12 3.996 3.460 3.101 2.673 2.464 2.157 1.863 1.615 1.446 1.251 1.122 1.045 0.953 0.866 0.806
4.600 4.142 3.786 3.330 2.937 2.605 2.333 2.082
5.191 4.703 4.303 3.759 3.345 2.983 2.663 2.392 2.178 1.957 1.806 1.626 1.548 1.407 1.292
Standard uncertainties u are u(T) = 0.05 K, u(P) = 0.1 kPa, u(x3) = u(x1) = u(x0 1) = u(y1) = 0.001.
different systems are obtained and listed in Table 6. With the regressed parameters, the mole fraction of methyl acetate in the vapor phase and the equilibrium temperature can be calculated. Then the mean absolute deviations and standard deviations between experimental and calculated mole fractions of methyl acetate in the vapor phase (dy, s y) and that of the equilibrium temperatures (dT, s T) can be obtained. The results are presented in Table 7, which indicate that the NRTL model correlated the experimental data quite well.
Figs. 1–3 illustrate that the addition of a small quantity of ILs produces a remarkable salting-out effect, which makes the content of methyl acetate in the vapor phase increase, consistently, as shown in Figs. 4–6, the relative volatility of methyl acetate to methanol increase. Moreover, the more ILs, the greater the relative volatility of methyl acetate to methanol, which means, the easier the separation. It can be seen in Figs. 4–6 that [HMIM][Cl] gives the greatest of a12, followed by [BzMIM][Cl], and lastly [HMIM][Br]. Furthermore, the replacement of the azeotropic point is observed
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Z. Zhang et al. / Fluid Phase Equilibria 408 (2016) 20–26
Table 6 Parameters and correlation statistics for NRTL model. Component i
Component j
aij
Dgij (J mol)
Dgji (J mol)
ARD (%)
Methyl acetate Methyl acetate Methanol Methyl acetate Methanol Methyl acetate Methanol
Methanol [HMIM][Cl] [HMIM][Cl] [BzMIM][Cl] [BzMIM][Cl] [HMIM][Br] [HMIM][Br]
0.302a 0.040 0.773 0.680 0.710 0.745 0.321
1507.7a 12484.2 283.6 26120.7 9377.4 99.5 47.8
1626.3a 2820.7 5643.3 106979.6 6990.9 22274.0 -6653.8
1.57a 1.68 1.65
a
1.64
From Ref [20].
Table 7 Mean absolute deviations, dy and dT, and standard deviations, s y and s T, between experimental and calculated values of the vapor-phase mole fractions and the equilibrium temperatures. System Methyl Methyl Methyl Methyl
acetate + methanol acetate + methanol + [HMIM][Cl] acetate + methanol + [BzMIM][Cl] acetate + methanol + [HMIM][Br]
dya
s yb
dTc (K)
s Td (K)
0.003 0.007 0.006 0.005
0.004 0.009 0.008 0.007
0.02 0.33 0.27 0.26
0.03 0.42 0.39 0.37
Fig. 2. Isobaric VLE diagram for the ternary system of methyl acetate (1) + methanol (2) + [BzMIM][Cl] (3) at 101.3 kPa: dotted line, IL-free system; &, x3 = 0.05; ~, x3 = 0.10; !, x3 = 0.15; solid line, correlated using NRTL model.
N is the number of experimental points, and m is the number of parameters for the model. P a dy = (1/N) |yexptl ycalcd|. P b s y = [ (yexptl ycalcd)2/(N m)]1/2. P c dT = (1/N) |Texptl Tcalcd|. P d s T = [ (Texptl Tcalcd)2/(N m)]1/2.
Fig. 3. Isobaric VLE diagram for the ternary system of methyl acetate (1) + methanol (2) + [HMIM][Br] (3) at 101.3 kPa: dotted line, IL-free system; &, x3 = 0.05; ~, x3 = 0.10; !, x3 = 0.15; solid line, correlated using NRTL model.
Fig. 1. Isobaric VLE diagram for the ternary system of methyl acetate (1) + methanol (2) + [HMIM][Cl] (3) at 101.3 kPa: dotted line, IL-free system; &, x3 = 0.05; ~, x3 = 0.10; !, x3 = 0.15; solid line, correlated using NRTL model.
with increasing the amounts of ILs in Figs. 1–3. Note that the elimination of the azeotropic point takes place when the mole fractions of [HMIM][Cl], [BzMIM][Cl] and [HMIM][Br] are up to 0.05, 0.10 and 0.15, respectively. According to the NRTL model, the minimum mole fractions of [HMIM][Cl], [BzMIM][Cl], and [HMIM] [Br] needed to break the azeotrope are 0.047, 0.069, and 0.122, respectively. Therefore, it can be concluded that [HMIM][Cl] outperforms the other two investigated ILs. The separation effect of ILs produced on methyl acetate and methanol system can be ascribed to the intermolecular interactions between molecules, which mainly consist of electrostatic interactions, hydrogen bonding and van der Waals interactions [31]. Hydrogen bonding and van der Waals interactions are discussed here. Methyl acetate is hydrogen bonding acceptor while methanol is both hydrogen bonding acceptor and hydrogen
Fig. 4. Relative volatility of methyl acetate (1) to methanol (2) with different mole fractions of [HMIM][Cl] (3) at 101.3 kPa: dotted line, IL-free system; &, x3 = 0.05; ~, x3 = 0.10; !, x3 = 0.15; solid line, correlated using NRTL model.
Z. Zhang et al. / Fluid Phase Equilibria 408 (2016) 20–26
Fig. 5. Relative volatility of methyl acetate (1) to methanol (2) with different mole fractions of [BzMIM][Cl] (3) at 101.3 kPa: dotted line, IL-free system; &, x3 = 0.05; ~, x3 = 0.10; !, x3 = 0.15; solid line, correlated using NRTL model.
25
ILs, which results in greater relative volatility of methyl acetate to methanol. As chloride atom has stronger electronegativity than bromine atom, hydrogen bond between [HMIM][Cl] and methanol is stronger than that between [HMIM][Br] and methanol, leading to the better separation effect of [HMIM][Cl]. When comparing [BzMIM][Cl] with [HMIM][Cl], the differences lie in alky groups on imidazole ring. The bulky steric hindrance group of [BzMIM][Cl] makes the cation difficult to access methanol [34], leading to weaker interactions with methanol, hence [BzMIM][Cl] produces relatively weaker separation effect. When comparing to the ILs in our previous work, it was found that the separation effect is [HMIM][Cl] > [BzMIM][Cl] > [HMIM][Br] > [C4MIM][Cl] > [ClC2MIM] [Cl] > [C4MIM][Br]. This indicates that hydrogen bonding between the anions and methanol becomes less significant when van der Waals interactions between the cation and methanol increase in importance [35]. The separation effect of [HMIM][Cl] on the methyl acetate and methanol mixture is also compared with the ILs that reported by other groups. The minimum mole fraction of [BzMIM][Cl] to break the azeotrope is 0.045 calculated by NRTL model at 327.31 K. As shown in Table 8, the azeotrope breaking capacity of [HMIM][Cl] is similar to that of [BMPYR][DCA] but superior to all the other reported ILs. Hence, [HMIM][Cl] may be a potential entrainer for the separation of the azeotropic mixture of methyl acetate and methanol. 4. Conclusions
Fig. 6. Relative volatility of methyl acetate (1) to methanol (2) with different mole fractions of [HMIM][Br] (3) at 101.3 kPa: dotted line, IL-free system; &, x3 = 0.05; ~, x3 = 0.10; !, x3 = 0.15; solid line, correlated using NRTL model.
The VLE data of methyl acetate and methanol containing [HMIM][Cl], [BzMIM][Cl], and [HMIM][Br], were measured at 101.3 kPa. The ternary VLE data were correlated using NRTL model with good accuracy. The addition of ILs produced a notable saltingout effect on methyl acetate, enhancing the relative volatility of methyl acetate to methanol, and could eventually eliminate the azeotropic point. The separation effects of the three ILs is [HMIM] [Cl] > [BzMIM][Cl] > [HMIM][Br]. The IL [HMIM][Cl] outperforms the other two investigated ILs and can break the azeotrope when its mole fraction is up to 0.047 at 101.3 kPa according to NRTL model. Acknowledgments
Table 8 The minimum mole fractions of ILs (3) to break the methyl acetate (1) + methanol (2) azeotrope at 327.31 K. Ionic liquid
x3,min
Reference
[HMIM][Cl] [EMIM][Triflate] [EMIM][Ac] [OMIM][PF6] [BMPYR][DCA] [EMIM][SCN] [C4MIM][Cl]
0.045 0.125a 0.096 0.343 0.043 0.087 0.123
This work [19] [19] [19] [19] [19] [20]
a
Electrolyte NRTL (eNRTL).
bonding donator because of the hydroxy group. Methanol can form hydrogen bond with the anions and the acidic protons in imidazolium cations of ILs [32,33], whereas methyl acetate can only form hydrogen bond with imidazolium cations of ILs. Besides, as the polarity of methanol is stronger than that of methyl acetate, the van der Waals interactions of ILs between methanol is also stronger than that between ILs and methyl acetate. Therefore, the affinities between methanol and ILs are stronger than that between ILs and methyl acetate, thus making methyl acetate more volatile compared to the IL-free system. With the content of ILs increase, more and more methanol molecules are “bonded” by
This work is financially supported by the National Science Foundation of China (Project No. 21076126), Program for Liaoning Excellent Talents in University (Project No. 2012013) and Liaoning Province Science Foundation of China (Project No. 2014020140). References [1] Z. Lei, H. Wang, R. Zhou, Z. Duan, Influence of salt added to solvent on extractive distillation, Chem. Eng. J. 87 (2002) 149–156. [2] Z. Lei, C. Li, B. Chen, Extractive distillation: a review, Sep. Purif. Rev. 32 (2003) 121–213. [3] Z. Lei, B. Chen, Z. Ding, Special Distillation Processes, Elsevier, Amsterdam, 2005. [4] W.L. Luyben, Effect of solvent on controllability in extractive distillation, Ind. Eng. Chem. Res. 47 (2008) 4425–4439. [5] Z. Zhang, D. Huang, M. Lv, P. Jia, D. Sun, W. Li, Entrainer selection for separating tetrahydrofuran/water azeotropic mixture by extractive distillation, Sep. Purif. Technol. 122 (2014) 73–77. [6] A.B. Pereiro, J.M.M. Araújo, J.M.S.S. Esperança, I.M. Marrucho, L.P.N. Rebelo, Ionic liquids in separations of azeotropic systems—a review, J. Chem. Thermodyn. 46 (2012) 2–28. [7] J.G. Huddleston, H.D. Willauer, R.P. Swatloski, A.E. Visser, R.D. Rogers, Room temperature ionic liquids as novel media for ‘clean’ liquid–liquid extraction, Chem. Commun. 176 (1998) 5–1766. [8] A.B. Pereiro, A. Rodriguez, Purification of hexane with effective extraction using ionic liquid as solvent, Green Chem. 11 (2009) 346–350. [9] Z. Lei, C. Dai, J. Zhu, B. Chen, Extractive distillation with ionic liquids: a review, AIChE J. 60 (2014) 3312–3329.
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Contents lists available at ScienceDirect
Fluid Phase Equilibria j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / fl u i d
Isobaric vapor–liquid equilibrium for methyl acetate + methanol system containing different ionic liquids at 101.3 kPa Zhigang Zhang, Angran Hu, Tao Zhang, Qinqin Zhang, Zeqiang Yang, Wenxiu Li* Liaoning Provincial Key Laboratory of Chemical Separation Technology, Shenyang University of Chemical Technology, Shenyang 110142, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 5 June 2015 Received in revised form 23 July 2015 Accepted 24 July 2015 Available online 30 July 2015
Isobaric vapor–liquid equilibrium (VLE) data for ternary systems of methyl acetate + methanol containing three ionic liquids (ILs) were measured at 101.3 kPa. The investigated ILs were 1-hexyl-3methylimidazolium chloride ([HMIM][Cl]), 1-benzyl-3-methylimidazolium chloride ([BzMIM][Cl]), and 1-hexyl-3-methylimidazolium bromide ([HMIM][Br]). The results indicate that the addition of ILs can give rise to the increase of the relative volatility of methyl acetate to methanol. Besides, the more ILs, the larger the relative volatility. All the three investigated ILs can eliminate the azeotropic point of methyl acetate and methanol, and the separation effect follows the order: [HMIM][Cl] > [BzMIM][Cl] > [HMIM] [Br]. Additionally, the measured VLE data are well correlated with NRTL model. ã 2015 Elsevier B.V. All rights reserved.
Keywords: Vapor–liquid equilibrium Ionic liquid Methyl acetate Methanol NRTL model
1. Introduction Extractive distillation is the most widely utilized technology to separate azeotropic or close-boiling point mixtures [1–3]. The selection of a suitable entrainer is of great importance before the separationprocess is designed [4,5]. In recent years, ionic liquids (ILs) have attracted impressive attention for potential applications as entrainers in extractive distillation [6]. ILs possess properties of negligible vapor pressure, high selectivity, low toxicity and corrosion, and good solubilities for various of chemicals [7,8]. Moreover, ILs as entertainers combine the advantages of a liquid solvent (easy operation) and a solid salt (high separation ability) [9]. However, the thermodynamic data of IL-containing systems are still scarce, which are essential for further design of extractive distillation process. Methyl acetate and methanol mixture is involved in industrial manufacturing process of poly (viny1 alcohol). It is difficult to separate them by conventional separation method since they form a minimum azeotrope at atmospheric pressure. Traditional organic solvents [10] and solid salts [11–14] have been used as entrainers to separate methyl acetate and methanol mixture in extractive distillation process. As environment-friendly solvents, ILs are compelling alternatives to volatile organic solvents and caustic solid salts. Up to now, several ILs have been investigated as entrainers to
* Corresponding author. Fax: +86 24 89383736. E-mail address: [email protected] (W. Li). http://dx.doi.org/10.1016/j.fluid.2015.07.045 0378-3812/ ã 2015 Elsevier B.V. All rights reserved.
break methyl acetate and methanol azeotrope, such as 1-ethyl-3methylimidazolium trifluoromethanesulfonate ([EMIM][Triflate]) [15], 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]) [16], 1octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF6]) [17], 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM][EtSO4]) [18], 1-butyl-1-methylpyrrolidinium dicyanamide ([BMPYR][DCA]), and 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) [19]. Besides, the separation effects of 1-butyl-3-methylimidazolium chloride ([C4MIM][Cl]), 1-(2-chloroethyl)-3-methylimidazolium chloride ([ClC2MIM][Cl]) and 1-butyl-3-methylimidazolium bromide ([C4MIM][Br]) on the azeotrope were explored in our previous work [20]. As a continuation of the previous study, one aim of this work is to determine if 1-hexyl-3-methylimidazolium chloride ([HMIM][Cl]), 1-benzyl-3-methylimidazolium chloride ([BzMIM] [Cl]), or 1-hexyl-3-methylimidazolium bromide ([HMIM][Br]), can eliminate the azeotropic point of methyl acetate and methanol mixture. In this work, isobaric VLE data of the ternary systems of methyl acetate + methanol containing three different ILs, namely [HMIM] [Cl], [BzMIM][Cl], and [HMIM][Br], were measured at 101.3 kPa. The separation effect of ILs on methyl acetate and methanol mixture was investigated and compared with that of the reported ILs. Furthermore, the separation effect produced by ILs was related to the intermolecular interactions between molecules of the investigated systems. Besides, the measured VLE data were correlated with the non-random two liquid (NRTL) model proposed by Renon and Prausnitz [21].
Z. Zhang et al. / Fluid Phase Equilibria 408 (2016) 20–26
Nomenclature
List of symbols Dgij binary energy parameter of NRTL model xi mole fraction of component i in the liquid phase x0 i mole fraction of component i in the liquid phase expressed on an IL-free basis yi mole fraction of solvent i in the vapor phase T equilibrium temperature N number of experimental data points m number of parameters for the model P total pressure in the equilibrium system Pi saturated vapor pressure of component i at equilibrium temperature Texptl equilibrium temperature measured by experimental data Tcalcd equilibrium temperature calculated with the NRTL model Tb normal boiling point of pure component yexptl mole fraction of solvent i in the vapor phase measured by experimental data ycalcd mole fraction of solvent i in the vapor phase calculated with the NRTL model Greek letters r density aij non-randomness parameter of NRTL model gi activity coefficient of component i g iexptl activity coefficient of component i measured by experimental data g icalcd activity coefficient of component i calculated with the NRTL model dy mean absolute deviation of the vapor phase mole fraction sy standard deviation of the vapor phase mole fraction dT mean absolute deviation of the equilibrium temperature sT standard deviation of the equilibrium temperature
reported methods in literature [22,23]. Their purities checked by liquid chromatography are 99% in mass fraction, and no major impurities were detected by ion chromatography. The ILs were placed in a vacuum drying oven at 343.15 K overnight before use to remove trace impurities. The final water content of ILs, determined by Karl Fischer titration, was less than 0.005 (mass fraction). The overall information of the chemicals were summarized in Table 1. The densities of the pure components were measured at 298.15 K using a vibrating tube density meter (M196028, China), and the standard uncertainty is 0.0002 g cm3. The boiling points of methyl acetate and methanol were determined at 101.3 kPa, and the standard uncertainty is 0.05 K. The measured densities of components and boiling points of methyl acetate and methanol as well as the values of the corresponding literature [23–25] are shown in Table 2. 2.2. Apparatus and procedure The VLE experiments were conducted in an all-glass equilibrium still (NGW, Wertheim, Germany), which have been described in detail in a previous literature [26]. The pressure was kept constant at 101.3 kPa by controlling a gas buffer connected with the still, and detected by a manometer with a standard uncertainty of 0.1 kPa. The temperature was determined with a standard and calibrated thermometer, and its standard uncertainty is 0.01 K. Each solution was gravimetrically prepared with the help of a digital balance (CAV264C OHAUS America) with a standard uncertainty of 0.0001 g. For the binary system of methyl acetate + methanol, some methyl acetate was added to the pure methanol until a very diluted solution was obtained. For each ternary system, the mixture of methanol and defined mole fraction of IL was prepared, where some other mixtures of methyl acetate and the same mole fraction of IL were added, trying to keep the scheduled mole fraction of IL in each series. Only when the temperature was
Table 2 Density r and the normal boiling point Tb of pure components. Component
Methyl acetate Methanol [HMIM][Cl] [BzMIM][Cl] [HMIM][Br]
2. Experimental 2.1. Materials Methyl acetate and methanol were provided by Sinopharm group with mass fraction purities higher than 99.5% examined by gas chromatography. The ILs, [HMIM][Cl], [BzMIM][Cl], and [HMIM][Br] were synthesized in our laboratory according to the
21
r/(g cm3) (298.15 K)
Tb (101.3 kPa)/K
Exptl
Lit.
Exptl
Lit.
0.9273 0.7871 1.0443 1.1928 1.2292
0.9275a 0.7869a 1.044202b 1.1930c 1.229168b
330.20 337.69
330.4a 337.7a
Standard uncertainties u are u(r) = 0.0002 g cm3,u(T) = 0.05 K. a From Ref. [24]. b From Ref. [23]. c From Ref. [25].
Table 1 Specifications of chemical samples. Chemical name
Source
Mass fraction purity
Purification method
Analysis method
Methyl acetate Methanol [HMIM][Cl]a [BzMIM][Cl]b [HMIM][Br]c
Sinopharm group Sinopharm group Synthesized own Synthesized own Synthesized own
0.995 0.995 0.990 0.990 0.990
None None Vacuum desiccation Vacuum desiccation Vacuum desiccation
GCd GCd LCe , KFf , ICg LCe , KFf , ICg LCe , KFf , ICg
a b c d e f g
[HMIM][Cl] = 1-hexyl-3-methylimidazolium chloride. [BzMIM][Cl] = 1-benzyl-3-methylimidazolium chloride. [HMIM][Br] = 1-hexyl-3-methylimidazolium bromide. GC = gas chromatography. LC = liquid chromatography. KF = Karl Fischer titration. IC = ion chromatography.
22
Z. Zhang et al. / Fluid Phase Equilibria 408 (2016) 20–26
constant for more than half an hour (the deviation of temperature was 0.01 K), were the equilibrium conditions assumed. 2.3. Sample analysis
to the relative volatility of methyl acetate to methanol, which is calculated by the following equations based on the assumption of the ideal vapor phase due to the low total pressure in this work.
y i P ¼ xi g i P i
The condensed vapor and liquid phase samples were inserted into a headspace sampler (HS-sampler) (G1888 Network headspace sampler, Agilent Technologies) and then detected by a gas chromatograph (Model 7890A, Agilent Technologies) equipped with a SP-1000 capillary column (30 m in length, 2.5 mm in diameter, and 2.5 mm in thickness) and a FID detector. Nitrogen was used as carrier gas. The operating conditions were as follows: the temperatures of oven, injector, and detector were 335 K, 423 K, and 443 K, respectively. Since ILs have no detectable vapor pressure, only the peaks of methyl acetate and methanol were observed. The content of ILs was gravimetrically determined by the mass difference before and after vaporizing the volatile components. The standard uncertainty of ILs was 0.001 in mole fraction. Every sample was analyzed at least three times and the standard uncertainty of the volatile components in vapor and liquid phases was 0.001 in mole fraction. 3. Results and discussion 3.1. Experimental data The reliability of our apparatus has been validated by the VLE data of methyl acetate + methanol binary system at 101.3 kPa in our previous study [20]. The ternary VLE data of methyl acetate + methanol containing [HMIM][Cl], [BzMIM][Cl], and [HMIM][Br] were measured at 101.3 kPa by keeping the mole fractions of ILs nearly constant at 0.05, 0.10, and 0.15, respectively. The experimental data are orderly listed in Tables 3–5, where x3 represents the mole fraction of ILs in the liquid phase, T is the equilibrium temperature, x1 represents the mole fraction of methyl acetate in the liquid phase containing ILs, x0 1 refers to the mole fraction of methyl acetate in the liquid phase expressed on an IL-free basis, y1 is the mole fraction of methyl acetate in the vapor phase. a12 refers
ð1Þ
a12 ¼
g 1 P1 g 2 P2
ð2Þ
where yi and xi are the mole fractions of component i in the vapor phase and liquid phase, respectively, g i represents activity coefficient of component i, P is the total pressure (101.3 kPa in this work), Pi refers to the saturated pressure of component i at equilibrium temperature which is calculated by Antoine equation with the Antoine parameters taken from previous literature [24]. 3.2. Correlation of the phase equilibrium The NRTL model is commonly used for the correlation of the VLE data containing ILs since it often fits the experimental data well [27–30]. In this work, the NRTL model is also adopted for the correlation of the measured VLE data. To reproduce the VLE data, nine parameters should be determined for each ternary system, including six binary energy parameters and three non-random factors. The binary parameters for methyl acetate and methanol are taken from literature [20]. The other parameters are obtained from the ternary VLE data containing ILs. The model parameters are regressed with the help of Levenberg–Marquardt method through minimization of the following objective function: ARDð%Þ ¼
1X g i exptl g i calcd j j 100 n n g i exptl
ð3Þ
where n is the number of experiment points, g i is the activity coefficient of component i, and the superscripts “exptl” and “calcd” denote experimental and calculated values, respectively. Following this procedure, the binary interaction parameters of NRTL model and the average relative deviations (ARDs) of
Table 3 Vapor–liquid equilibrium data for methyl acetate (1) + methanol (2) + [HMIM][Cl] (3) at 101.3 kPa.a x3
T (K)
x1
x0 1
y1
0.050 0.051 0.049 0.050 0.052 0.050 0.051 0.052 0.050 0.051 0.050 0.049 0.050 0.052 0.050 0.051 0.050 0.101 0.100 0.100 0.101 0.100 0.099 0.100 0.101 0.102
341.01 339.01 334.67 332.04 330.12 329.03 328.36 327.83 327.71 327.74 327.90 328.26 328.57 329.30 330.12 331.01 331.61 346.73 342.28 336.76 333.66 331.78 330.47 329.31 328.71 328.46
0.000 0.021 0.083 0.142 0.208 0.267 0.322 0.404 0.451 0.531 0.587 0.657 0.703 0.778 0.854 0.913 0.950 0.000 0.032 0.093 0.147 0.195 0.243 0.309 0.371 0.427
0.000 0.022 0.087 0.149 0.219 0.281 0.339 0.426 0.475 0.560 0.618 0.691 0.740 0.821 0.899 0.962 1.000 0.000 0.036 0.103 0.164 0.217 0.270 0.343 0.413 0.476
0.000 0.102 0.304 0.422 0.512 0.570 0.613 0.665 0.691 0.733 0.761 0.796 0.821 0.865 0.917 0.965 1.000 0.000 0.195 0.414 0.528 0.598 0.650 0.705 0.745 0.776
a
a12 5.019 4.568 4.154 3.727 3.391 3.084 2.673 2.474 2.161 1.969 1.746 1.612 1.400 1.242 1.087
6.571 6.130 5.723 5.378 5.029 4.571 4.158 3.821
x3
T (K)
x1
x0 1
y1
a12
0.100 0.099 0.100 0.102 0.100 0.101 0.100 0.099 0.149 0.150 0.151 0.150 0.152 0.150 0.151 0.150 0.149 0.150 0.149 0.150 0.151 0.150 0.149 0.152 0.150
328.45 328.65 329.02 329.55 330.17 331.01 331.88 332.29 352.88 346.15 339.07 336.34 334.05 331.67 330.36 329.71 329.06 328.97 329.16 329.48 329.98 330.59 331.24 331.83 332.51
0.496 0.562 0.621 0.681 0.745 0.811 0.874 0.901 0.000 0.037 0.098 0.134 0.176 0.238 0.294 0.335 0.416 0.477 0.547 0.598 0.655 0.713 0.765 0.804 0.850
0.551 0.624 0.690 0.758 0.828 0.902 0.971 1.000 0.000 0.044 0.115 0.158 0.208 0.280 0.346 0.394 0.489 0.561 0.643 0.704 0.771 0.839 0.899 0.948 1.000
0.810 0.840 0.865 0.892 0.921 0.952 0.986 1.000 0.000 0.275 0.509 0.590 0.657 0.727 0.771 0.798 0.840 0.866 0.893 0.912 0.931 0.951 0.970 0.983 1.000
3.472 3.167 2.879 2.632 2.415 2.170 2.095
Standard uncertainties u are u(T) = 0.05 K, u(P) = 0.1 kPa, u(x3) = u(x1) = u(x0 1) = u(y1) = 0.001.
8.335 7.944 7.689 7.314 6.848 6.356 6.073 5.490 5.054 4.638 4.367 3.996 3.729 3.635 3.164
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23
Table 4 Vapor–liquid equilibrium data for methyl acetate (1) + methanol (2) + [BzMIM][Cl] (3) at 101.3 kPa.a x3
T (K)
x1
x0 1
y1
0.049 0.050 0.051 0.050 0.049 0.050 0.052 0.050 0.049 0.051 0.051 0.050 0.051 0.050 0.049 0.051 0.050 0.100 0.101 0.100 0.102 0.100 0.101 0.100 0.099 0.100
341.37 339.73 335.33 333.07 331.65 330.24 329.34 328.61 328.15 327.97 327.88 327.84 328.02 328.34 328.86 330.35 331.52 348.17 343.56 339.23 336.15 333.88 332.52 331.63 331.22 330.73
0.000 0.016 0.079 0.124 0.162 0.218 0.273 0.327 0.381 0.437 0.485 0.549 0.613 0.694 0.773 0.888 0.950 0.000 0.037 0.085 0.141 0.196 0.252 0.298 0.324 0.383
0.000 0.017 0.083 0.131 0.170 0.229 0.288 0.344 0.401 0.460 0.511 0.578 0.646 0.731 0.813 0.936 1.000 0.000 0.041 0.094 0.157 0.218 0.280 0.331 0.360 0.426
0.000 0.080 0.294 0.389 0.451 0.517 0.568 0.607 0.640 0.671 0.695 0.726 0.757 0.797 0.843 0.932 1.000 0.000 0.208 0.373 0.492 0.567 0.627 0.663 0.682 0.717
a
a12 5.076 4.586 4.241 4.001 3.594 3.251 2.943 2.660 2.390 2.180 1.935 1.708 1.448 1.236 0.942
6.118 5.704 5.200 4.703 4.316 3.974 3.819 3.420
x3
T (K)
x1
x0 1
y1
a12
0.101 0.100 0.098 0.100 0.101 0.100 0.102 0.100 0.149 0.150 0.152 0.150 0.151 0.150 0.149 0.150 0.152 0.151 0.150 0.149 0.150 0.151 0.151 0.150 0.149
330.46 330.28 330.26 330.44 330.70 331.09 331.93 333.08 355.59 351.20 344.55 340.96 338.61 336.33 335.06 334.71 334.13 333.67 333.40 333.24 333.32 333.50 333.77 334.34 334.72
0.451 0.512 0.569 0.597 0.648 0.721 0.804 0.900 0.000 0.026 0.085 0.131 0.179 0.244 0.298 0.324 0.384 0.435 0.482 0.549 0.591 0.648 0.711 0.804 0.851
0.502 0.569 0.631 0.663 0.721 0.801 0.895 1.000 0.000 0.031 0.100 0.154 0.211 0.287 0.350 0.381 0.453 0.512 0.567 0.645 0.695 0.763 0.837 0.946 1.000
0.753 0.782 0.808 0.821 0.845 0.882 0.930 1.000 0.000 0.186 0.426 0.531 0.606 0.675 0.718 0.735 0.770 0.796 0.817 0.848 0.867 0.892 0.922 0.973 1.000
3.028 2.718 2.463 2.328 2.112 1.856 1.553
x3
T (K)
x1
x0 1
y1
a12
0.101 0.100 0.100 0.099 0.100 0.101 0.102 0.100 0.150 0.151 0.150 0.149 0.150 0.151 0.150 0.152 0.150 0.149 0.150 0.151 0.150 0.152 0.151 0.150 0.150
329.96 330.03 330.24 330.75 331.16 331.71 332.31 333.48 346.55 342.83 338.34 335.99 333.93 332.93 332.29 332.09 331.91 331.93 332.16 332.43 332.78 333.10 333.55 334.33 335.16
0.507 0.558 0.611 0.697 0.739 0.785 0.826 0.900 0.000 0.034 0.094 0.143 0.215 0.276 0.336 0.394 0.451 0.502 0.558 0.601 0.657 0.683 0.732 0.798 0.850
0.564 0.620 0.679 0.774 0.821 0.873 0.920 1.000 0.000 0.040 0.111 0.168 0.253 0.325 0.395 0.465 0.531 0.590 0.656 0.708 0.773 0.805 0.862 0.939 1.000
0.709 0.737 0.765 0.818 0.847 0.884 0.923 1.000 0.000 0.178 0.369 0.465 0.560 0.617 0.661 0.698 0.730 0.758 0.789 0.814 0.847 0.865 0.898 0.952 1.000
1.884 1.718 1.540 1.315 1.206 1.107 1.045
7.242 6.662 6.214 5.757 5.158 4.725 4.503 4.045 3.714 3.409 3.069 2.857 2.562 2.294 2.062
Standard uncertainties u are u(T) = 0.05 K, u(P) = 0.1 kPa, u(x3) = u(x1) = u(x0 1) = u(y1) = 0.001.
Table 5 Vapor–liquid equilibrium data for methyl acetate (1) + methanol (2) + [HMIM][Br] (3) at 101.3 kPa.a x3
T (K)
x1
x0 1
y1
0.049 0.050 0.051 0.050 0.051 0.052 0.050 0.049 0.050 0.052 0.050 0.052 0.050 0.051 0.050 0.049 0.050 0.101 0.100 0.101 0.100 0.099 0.100 0.102 0.100 0.101
339.54 336.96 333.16 331.45 329.97 329.38 328.79 328.39 328.27 328.34 328.43 328.71 328.86 329.24 329.67 330.22 331.92 342.70 339.63 335.86 333.82 332.00 330.95 330.43 330.05 329.95
0.000 0.036 0.115 0.171 0.248 0.296 0.358 0.433 0.504 0.563 0.636 0.686 0.725 0.772 0.818 0.864 0.950 0.000 0.033 0.094 0.143 0.210 0.276 0.336 0.394 0.452
0.000 0.038 0.121 0.180 0.261 0.312 0.377 0.455 0.531 0.594 0.669 0.724 0.763 0.813 0.861 0.909 1.000 0.000 0.037 0.105 0.159 0.233 0.307 0.374 0.438 0.503
0.000 0.136 0.323 0.405 0.486 0.528 0.566 0.609 0.646 0.679 0.717 0.746 0.771 0.806 0.843 0.889 1.000 0.000 0.149 0.326 0.417 0.503 0.565 0.609 0.645 0.678
a
a12 3.996 3.460 3.101 2.673 2.464 2.157 1.863 1.615 1.446 1.251 1.122 1.045 0.953 0.866 0.806
4.600 4.142 3.786 3.330 2.937 2.605 2.333 2.082
5.191 4.703 4.303 3.759 3.345 2.983 2.663 2.392 2.178 1.957 1.806 1.626 1.548 1.407 1.292
Standard uncertainties u are u(T) = 0.05 K, u(P) = 0.1 kPa, u(x3) = u(x1) = u(x0 1) = u(y1) = 0.001.
different systems are obtained and listed in Table 6. With the regressed parameters, the mole fraction of methyl acetate in the vapor phase and the equilibrium temperature can be calculated. Then the mean absolute deviations and standard deviations between experimental and calculated mole fractions of methyl acetate in the vapor phase (dy, s y) and that of the equilibrium temperatures (dT, s T) can be obtained. The results are presented in Table 7, which indicate that the NRTL model correlated the experimental data quite well.
Figs. 1–3 illustrate that the addition of a small quantity of ILs produces a remarkable salting-out effect, which makes the content of methyl acetate in the vapor phase increase, consistently, as shown in Figs. 4–6, the relative volatility of methyl acetate to methanol increase. Moreover, the more ILs, the greater the relative volatility of methyl acetate to methanol, which means, the easier the separation. It can be seen in Figs. 4–6 that [HMIM][Cl] gives the greatest of a12, followed by [BzMIM][Cl], and lastly [HMIM][Br]. Furthermore, the replacement of the azeotropic point is observed
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Z. Zhang et al. / Fluid Phase Equilibria 408 (2016) 20–26
Table 6 Parameters and correlation statistics for NRTL model. Component i
Component j
aij
Dgij (J mol)
Dgji (J mol)
ARD (%)
Methyl acetate Methyl acetate Methanol Methyl acetate Methanol Methyl acetate Methanol
Methanol [HMIM][Cl] [HMIM][Cl] [BzMIM][Cl] [BzMIM][Cl] [HMIM][Br] [HMIM][Br]
0.302a 0.040 0.773 0.680 0.710 0.745 0.321
1507.7a 12484.2 283.6 26120.7 9377.4 99.5 47.8
1626.3a 2820.7 5643.3 106979.6 6990.9 22274.0 -6653.8
1.57a 1.68 1.65
a
1.64
From Ref [20].
Table 7 Mean absolute deviations, dy and dT, and standard deviations, s y and s T, between experimental and calculated values of the vapor-phase mole fractions and the equilibrium temperatures. System Methyl Methyl Methyl Methyl
acetate + methanol acetate + methanol + [HMIM][Cl] acetate + methanol + [BzMIM][Cl] acetate + methanol + [HMIM][Br]
dya
s yb
dTc (K)
s Td (K)
0.003 0.007 0.006 0.005
0.004 0.009 0.008 0.007
0.02 0.33 0.27 0.26
0.03 0.42 0.39 0.37
Fig. 2. Isobaric VLE diagram for the ternary system of methyl acetate (1) + methanol (2) + [BzMIM][Cl] (3) at 101.3 kPa: dotted line, IL-free system; &, x3 = 0.05; ~, x3 = 0.10; !, x3 = 0.15; solid line, correlated using NRTL model.
N is the number of experimental points, and m is the number of parameters for the model. P a dy = (1/N) |yexptl ycalcd|. P b s y = [ (yexptl ycalcd)2/(N m)]1/2. P c dT = (1/N) |Texptl Tcalcd|. P d s T = [ (Texptl Tcalcd)2/(N m)]1/2.
Fig. 3. Isobaric VLE diagram for the ternary system of methyl acetate (1) + methanol (2) + [HMIM][Br] (3) at 101.3 kPa: dotted line, IL-free system; &, x3 = 0.05; ~, x3 = 0.10; !, x3 = 0.15; solid line, correlated using NRTL model.
Fig. 1. Isobaric VLE diagram for the ternary system of methyl acetate (1) + methanol (2) + [HMIM][Cl] (3) at 101.3 kPa: dotted line, IL-free system; &, x3 = 0.05; ~, x3 = 0.10; !, x3 = 0.15; solid line, correlated using NRTL model.
with increasing the amounts of ILs in Figs. 1–3. Note that the elimination of the azeotropic point takes place when the mole fractions of [HMIM][Cl], [BzMIM][Cl] and [HMIM][Br] are up to 0.05, 0.10 and 0.15, respectively. According to the NRTL model, the minimum mole fractions of [HMIM][Cl], [BzMIM][Cl], and [HMIM] [Br] needed to break the azeotrope are 0.047, 0.069, and 0.122, respectively. Therefore, it can be concluded that [HMIM][Cl] outperforms the other two investigated ILs. The separation effect of ILs produced on methyl acetate and methanol system can be ascribed to the intermolecular interactions between molecules, which mainly consist of electrostatic interactions, hydrogen bonding and van der Waals interactions [31]. Hydrogen bonding and van der Waals interactions are discussed here. Methyl acetate is hydrogen bonding acceptor while methanol is both hydrogen bonding acceptor and hydrogen
Fig. 4. Relative volatility of methyl acetate (1) to methanol (2) with different mole fractions of [HMIM][Cl] (3) at 101.3 kPa: dotted line, IL-free system; &, x3 = 0.05; ~, x3 = 0.10; !, x3 = 0.15; solid line, correlated using NRTL model.
Z. Zhang et al. / Fluid Phase Equilibria 408 (2016) 20–26
Fig. 5. Relative volatility of methyl acetate (1) to methanol (2) with different mole fractions of [BzMIM][Cl] (3) at 101.3 kPa: dotted line, IL-free system; &, x3 = 0.05; ~, x3 = 0.10; !, x3 = 0.15; solid line, correlated using NRTL model.
25
ILs, which results in greater relative volatility of methyl acetate to methanol. As chloride atom has stronger electronegativity than bromine atom, hydrogen bond between [HMIM][Cl] and methanol is stronger than that between [HMIM][Br] and methanol, leading to the better separation effect of [HMIM][Cl]. When comparing [BzMIM][Cl] with [HMIM][Cl], the differences lie in alky groups on imidazole ring. The bulky steric hindrance group of [BzMIM][Cl] makes the cation difficult to access methanol [34], leading to weaker interactions with methanol, hence [BzMIM][Cl] produces relatively weaker separation effect. When comparing to the ILs in our previous work, it was found that the separation effect is [HMIM][Cl] > [BzMIM][Cl] > [HMIM][Br] > [C4MIM][Cl] > [ClC2MIM] [Cl] > [C4MIM][Br]. This indicates that hydrogen bonding between the anions and methanol becomes less significant when van der Waals interactions between the cation and methanol increase in importance [35]. The separation effect of [HMIM][Cl] on the methyl acetate and methanol mixture is also compared with the ILs that reported by other groups. The minimum mole fraction of [BzMIM][Cl] to break the azeotrope is 0.045 calculated by NRTL model at 327.31 K. As shown in Table 8, the azeotrope breaking capacity of [HMIM][Cl] is similar to that of [BMPYR][DCA] but superior to all the other reported ILs. Hence, [HMIM][Cl] may be a potential entrainer for the separation of the azeotropic mixture of methyl acetate and methanol. 4. Conclusions
Fig. 6. Relative volatility of methyl acetate (1) to methanol (2) with different mole fractions of [HMIM][Br] (3) at 101.3 kPa: dotted line, IL-free system; &, x3 = 0.05; ~, x3 = 0.10; !, x3 = 0.15; solid line, correlated using NRTL model.
The VLE data of methyl acetate and methanol containing [HMIM][Cl], [BzMIM][Cl], and [HMIM][Br], were measured at 101.3 kPa. The ternary VLE data were correlated using NRTL model with good accuracy. The addition of ILs produced a notable saltingout effect on methyl acetate, enhancing the relative volatility of methyl acetate to methanol, and could eventually eliminate the azeotropic point. The separation effects of the three ILs is [HMIM] [Cl] > [BzMIM][Cl] > [HMIM][Br]. The IL [HMIM][Cl] outperforms the other two investigated ILs and can break the azeotrope when its mole fraction is up to 0.047 at 101.3 kPa according to NRTL model. Acknowledgments
Table 8 The minimum mole fractions of ILs (3) to break the methyl acetate (1) + methanol (2) azeotrope at 327.31 K. Ionic liquid
x3,min
Reference
[HMIM][Cl] [EMIM][Triflate] [EMIM][Ac] [OMIM][PF6] [BMPYR][DCA] [EMIM][SCN] [C4MIM][Cl]
0.045 0.125a 0.096 0.343 0.043 0.087 0.123
This work [19] [19] [19] [19] [19] [20]
a
Electrolyte NRTL (eNRTL).
bonding donator because of the hydroxy group. Methanol can form hydrogen bond with the anions and the acidic protons in imidazolium cations of ILs [32,33], whereas methyl acetate can only form hydrogen bond with imidazolium cations of ILs. Besides, as the polarity of methanol is stronger than that of methyl acetate, the van der Waals interactions of ILs between methanol is also stronger than that between ILs and methyl acetate. Therefore, the affinities between methanol and ILs are stronger than that between ILs and methyl acetate, thus making methyl acetate more volatile compared to the IL-free system. With the content of ILs increase, more and more methanol molecules are “bonded” by
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