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Jun 27, 2014 - The experimental VLE and LLE data were correlated using NRTL model, and ... (2-11) The phase equilibrium data are crucial in the design...
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Phase Equilibrium (VLE, LLE, and VLLE) Data of the Ternary System: Ionic Liquid [OMIM][PF6] + Butan-1-ol + Butyl Acetate Jialin Cai,† Shensheng Zhen,† Dengpan Gao,*,† and Xianbao Cui‡ †

Institute of Chemical Materials, China Academy of Engineering Physics, Mianyang, Sichuan 621900, China State Key Laboratory of Chemical Engineering (Tianjin University), Tianjin 300072, China

‡

ABSTRACT: Vapor−liquid equilibrium (VLE), liquid−liquid equilibrium (LLE), and vapor−liquid−liquid equilibrium (VLLE) data were measured for the ternary mixture of 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF6]), butan-1-ol, and butyl acetate. Results showed that the selectivity of butan-1-ol and butyl acetate can be enhanced by ionic liquid [OMIM][PF6]. The experimental VLE and LLE data were correlated using NRTL model, and the calculated values agreed well with the experimental values.

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INTRODUCTION Ionic liquids (ILs) are organic salts composed of cations and anions with a melting point lower than 373.15 K.1 In recent years, many scholars reported the separation of azeotropic mixtures using ILs as entrainers and solvents.2−11 The phase equilibrium data are crucial in the design of separation processes, but these data are still rare. Butyl acetate is an important intermediate in chemical industries, and it is used widely as a solvent in the production of lacquers. In the past decade, the production of butyl acetate has been growing fast because of its low toxicity and lower environmental impact compared with other esters.12−14 However, during the production of butyl acetate the azeotropic mixture butan-1-ol + butyl acetate is difficult to separate and enhanced distillation should be used.15,16 Ionic liquids might be used as a suitable solvent to separate the azeotropic mixture due to their particular properties. The COSMO-SAC model was used to calculate the infinite dilution activity coefficients of butan-1-ol and butyl acetate in hundreds of ILs,17,18 and we found that 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF6]) was a potential effective entrainer to separate butan-1-ol + butyl acetate. In our previous work, we have reported the vapor−liquid equilibrium (VLE) of methanol + methyl acetate + [OMIM][PF6].19 This paper focuses on the VLE and liquid−liquid equilibrium (LLE) of butan-1-ol + butyl acetate + [OMIM][PF6], and these data are essential for our research on producing butyl acetate and methanol from butan-1ol and methyl acetate using [OMIM][PF6] as an entrainer.19,20 We measured the VLE, LLE, and vapor−liquid−liquid equilibrium (VLLE) of butan-1-ol + butyl acetate + [OMIM][PF6], and the VLE and LLE data of the ternary mixture were correlated using the nonrandom two liquid (NRTL) model. Furthermore, the effects of entrainers [OMIM][PF6] © 2014 American Chemical Society

and 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([BMIM][NTf2]) on the separation of butan1-ol + butyl acetate were compared.21

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EXPERIMENTAL SECTION

Materials. Butan-1-ol and butyl acetate were supplied by Jiangtian Chemical Reagents Co., Tianjin (China), with a minimum mass fraction purity of 0.997, checked by gas chromatography. The water mass fractions of these chemicals were less than 0.001, checked by Karl Fischer titration. Entrainers. The [OMIM][PF6] was supplied by Chengjie Chemical Reagents Co., Shanghai (China), liquid chromatography was used to check the purity of the IL, and the minimum mass fraction of [OMIM][PF6] was 0.99. The water mass fraction of IL was less than 0.001, checked by Karl Fischer titration. The IL was used after being carefully degassed. Apparatus and Procedure. The solutions were weighed accurately by an electronic balance (Acculab Alc 210.4) whose standard uncertainty was 0.0001 g. The pressure was measured by a manometer (BY-2003P) whose standard uncertainty was 0.05 kPa. All the phase equilibrium temperature was measured by a precise and calibrated thermometer (BIMDTI1000) whose standard uncertainty was 0.05 K. The VLE was measured by a circulation equilibrium still with a stirrer. The details of the apparatus were given in our previous paper.22 The equilibrium state was observed by the constancy of boiling temperature. Samples were taken every 20 min and the standard deviation of the last five samples was less than Received: January 10, 2014 Accepted: June 19, 2014 Published: June 27, 2014 2171

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0.0015 (mole fraction). The sampling process could ascertain the mixture was in the equilibrium state. Most of the samples in the liquid phase were transparent, only a few samples in the liquid phase were muddy, and these samples were considered to be in VLLE. In the case of VLLE, the compositions of the two liquid phases are difficult to obtain. The initial composition of the solution added to the still was considered as the liquid composition and the condensed vapor in vapor phase sampling point (about 0.5% of the total solution) was neglected. The sampling procedure of the vapor phase for VLLE is the same as VLE. A self-designed apparatus was used to measure the LLE data.10 The samples were settled at constant temperature for about 24 h. After that, the system separated into two liquid phases that became transparent with a well-defined interface and the system was considered to be in equilibrium state. Eight samples were taken from the extract phase and raffinate phase, respectively. Because the total sample volume was less than 0.8 % of the total solution, the interference of sampling to equilibrium was neglected. The standard deviations of the samples were less than 0.0015 (mole fraction) for both phase and raffinate phase. Sample Analysis. A high-performance liquid chromatography (HPLC) was used to analyze these samples. The HPLC (Waters 490E) was equipped with a refractive index detector (BIO-RAD 1770) and the column we used was C18 (250 mm × 4.6 mm × 5 μm). The operating conditions were the following: mobile phase, methanol + water (v/v = 1:1); injection volume, 5 μL; flow rate, 1.0 mL·min−1. The compositions of butan-1-ol, butyl acetate, and [OMIM][PF6] in the sample were calculated using the area normalization method. The method was evaluated by measuring five samples of known composition. It showed that the standard deviation between the HPLC measurements and the known compositions was below 0.002 (mole fraction). The expanded uncertainty in the mole fraction was below 0.008 with 95 % confidence.

Table 1. Experimental VLE Data for Butan-1-ol (1) + Butyl Acetate (2)a T/K

P/kPa

x1

y1

σy1

399.15 395.56 394.31 392.53 391.37 390.69 390.38 390.20 390.20 390.48 390.48

101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30

0.000 0.122 0.180 0.302 0.420 0.531 0.612 0.699 0.792 0.901 1.000

0.000 0.211 0.272 0.410 0.491 0.582 0.652 0.711 0.791 0.881 1.000

0.000 0.005 0.005 0.008 0.006 0.001 0.008 0.001 0.006 0.002 0.000

σy1 = |y1exp − y1cal|; standard uncertainties u are u(T) = 0.08 K, u(P) = 0.07 kPa; expanded uncertainty Uc are Uc(x1) = Uc(y1) = 0.007 (95 % level of confidence); the purity of butan-1-ol, butyl acetate, and IL are all greater than 0.99 (mass fraction). a

Figure 1. Absolute deviation σy1 = yexp − ycal between the calculated and experimental values (mole fraction) of butan-1-ol in the vapor phase for the system of butan-1-ol (1) + butyl acetate (2) at 101.30 kPa: ■, this work with error bars representing the expanded uncertainty.

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RESULTS AND DISCUSSION Experimental Data. To evaluate the accuracy of the VLE/ VLLE apparatus, the measurement for the VLE of butan-1-ol (1) + butyl acetate (2) was conducted at 101.30 kPa. The experimental values and the calculated values obtained from ChemCAD (by the NRTL model) were compared. The absolute deviations between experimental and calculated results of butan-1-ol in the vapor phase are given in Table 1 and Figure 1. It shows that our experimental data agree well with those calculated by ChemCAD. The maximum absolute deviation between the calculated and experimental values of butan-1-ol in the vapor phase is 0.008 (mole fraction), it indicates that the VLE/VLLE apparatus are reliable. The isobaric VLE of butan-1-ol (1) + butyl acetate (2) + [OMIM][PF6] (3) was measured at 101.30 kPa. The mole fractions of ionic liquid in the liquid phase were kept approximately at x3 = 0.1, 0.2, and 0.3, respectively. The experimental data are shown in Table 2. In Table 2, x1′ is the mole content of butan-1-ol in the liquid phase excluding ionic liquid, y1 represents the mole content of butyl acetate in vapor phase, x3 is the mole content of ionic liquid in the liquid phase, α12 represents the selectivity of butan-1-ol (1) and butyl acetate (2), and T represents the equilibrium temperature. There is no ionic liquid in the vapor phase, because the vapor pressure of ionic liquid is negligible. The ternary system of butan-1-ol (1) + butyl acetate (2) + [OMIM][PF6] (3) can form VLLE in some cases. However, at

the measurement temperature, only a few data points formed VLLE. In Table 2, the VLLE data points are labeled. Table 3 gives the LLE data of butan-1-ol (1) + butyl acetate (2) + [OMIM][PF6] (3) measured at 288.15 K. In Table 3, distribution coefficient (β) and selectivity (S) were defined as β=

S=

x 2E x 2R

(1)

x 2Ex1R x 2R x1E

x1E,

(2)

E

E

where x2 , and x3 represent the mole fractions of butan-1ol, butyl acetate, and [OMIM][PF6] in the extract phase, respectively; x1R, x2R, and x3R represent the mole fractions of butan-1ol, butyl acetate, and [OMIM][PF6] in the raffinate phase, respectively. Correlation of the Phase Equilibrium. Many scholars used the NRTL model in the correlation of liquid−liquid equilibrium and vapor−liquid equilibrium with ILs.23,24 Here, the NRTL model was also used in the correlation of the experimental data. The NRTL model is in the following: ln γi =

∑j τjiGjixj ∑k Gkixk

⎡

+

⎛ ∑ τ G x ⎞⎤ ⎜⎜τij − k ki kj k ⎟⎟⎥ ∑k Gkjxk ⎠⎥⎦ ⎣ ∑k Gkjxk ⎝

∑ ⎢⎢ j

xjGij

(3) 2172

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Pyi = γixiPsat i . In the case of VLLE, because the compositions of the two liquid phases were not obtained, the four VLLE data were not used in the correlation. The binary parameters for butan-1-ol (1) and butyl acetate (2) of the NRTL model (B12, B21, and α12) were obtained from the ChemCAD. The binary interaction parameters (B13, B23, B31, and B32) and nonrandomness parameters (α13 and α23) were correlated from ternary experimental VLE and LLE data. The objective function is given by eq 6:25

Table 2. Experimental VLE Data for Butan-1-ol (1) + Butyl Acetate (2) + [OMIM][PF6] (3)a x3

T/K

P/kPa

x1′

y1

α12

0.102 0.101 0.099 0.098 0.102 0.103 0.098 0.100 0.098 0.200 0.198 0.203 0.202 0.199 0.202 0.202 0.201 0.198 0.300 0.302 0.297 0.301 0.297 0.299 0.301 0.298 0.301

398.72 396.63 395.42 393.64 392.95 392.77 392.66 392.95 393.25 400.67 398.09 395.97 395.26 394.32 393.97 393.56 393.57 393.77 403.52 399.42 396.41 395.76 394.48 394.17 393.56 393.64 393.66

101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30 101.30

0.090 0.201 0.288 0.412 0.502 0.612 0.705 0.822 0.906 0.120 0.211 0.302 0.411 0.486 0.595 0.705 0.812b 0.903b 0.105 0.211 0.302 0.395 0.498 0.612 0.704 0.814b 0.903b

0.173 0.326 0.425 0.542 0.598 0.692 0.762 0.841 0.912 0.236 0.384 0.486 0.585 0.658 0.719 0.815 0.878 0.928 0.252 0.433 0.545 0.638 0.712 0.785 0.841 0.910 0.945

2.115 1.935 1.827 1.689 1.476 1.424 1.340 1.145 1.075 2.265 2.345 2.185 2.020 2.035 1.742 1.843 1.666 1.385 2.872 2.856 2.768 2.699 2.492 2.315 2.224 2.310 1.846

⎛ C ⎛ cal exp ⎞2 ⎛ cal exp ⎞2 ⎜ ⎜ yj , i − yj , i ⎟ ⎜ T j − T j ⎟ F = ∑ ⎜∑ + ⎟ ⎜ ⎟ ⎜ σy σT ⎝ ⎠ j=1 ⎜ i=1 ⎝ ⎠ ⎝ N

⎛ x cal,R − x exp,R ⎞2 C ⎛ x cal,E − x exp,E ⎞2 ⎞ j,i j,x j,x ⎟ + ∑ ⎜ j,i ⎟⎟ + ∑ ⎜⎜ ⎟ ⎜ ⎟ ⎟⎟ σ σ x x ⎠ i=1 ⎝ ⎠⎠ i=1 ⎝ C

(6)

where C is the number of experimental components; N is the number of experimental data points; T represents the temperature of VLE; R denotes the raffinate phase; E denotes the extract phase; x is the mole content in LLE; y is the mole content in vapor phase of VLE; σT, σx, and σy are estimated standard deviations of T, x, and y, respectively (σT = 0.06 K, σx = 0.002, σy = 0.002); cal denotes the calculated values and exp denotes the experimental values. All the binary parameters for butan-1-ol (1) + butyl acetate (2) + [OMIM][PF6] (3) of the NRTL model are listed in Table 4. Table 4. Binary Parameters of the NRTL Model

a

Standard uncertainties u are u(T) = 0.08 K, u(P) = 0.07 kPa; expanded uncertainty Uc are Uc(x1) = Uc(x3) = Uc(y1) = 0.007 (95 % level of confidence); x′1, the mole fraction of butan-1-ol excluding IL. b Vapor−liquid−liquid equilibrium.

Gji = exp( −αjiτji)

(4)

τji = Bji /T

(5)

i component

j component

αij

Bij/K

Bji/K

butan-1-ol butan-1-ol butyl acetate

butyl acetate [OMIM][PF6] [OMIM][PF6]

0.301 0.135 0.223

105.906 687.352 1192.526

89.1323 638.231 −586.246

The ternary VLE, VLLE, and LLE diagrams are plotted in Figures 2 to 4, and in the figures the experimental and correlated results are compared. As seen from these figures, the calculated values agree well with the experimental values. The mean absolute deviation σy, and standard deviation δy of vapor-phase mole fractions (σy = (1/N)Σ|yexp − ycal|; δy = [(1/ N)Σ(yexp − ycal)2]1/2) are 0.012 and 0.015 respectively. The mean

where αij is a nonrandomness parameter; Bij is the binary interaction parameter, K; and T is the temperature, K. In the correlation, the thermodynamic criteria for LLE is γiExiE = γiRxiR, and the thermodynamic criteria for VLE is

Table 3. Experimental LLE Data, Solute Distribution Ratio (β) and Selectivity (S) for the Ternary Mixture Butan-1-ol (1) + Butyl Acetate (2) + [OMIM][PF6] (3) at 288.15 Ka raffinate phase

a

extract phase

T/K

x1R

x2R

x3R

x1E

x2E

x3E

β

S

288.15 288.15 288.15 288.15 288.15 288.15 288.15 288.15 288.15 288.15 288.15 288.15

0.964 0.955 0.942 0.921 0.886 0.862 0.831 0.785 0.718 0.635 0.535 0.468

0.000 0.008 0.021 0.040 0.070 0.095 0.122 0.161 0.214 0.286 0.349 0.394

0.036 0.037 0.037 0.039 0.044 0.043 0.047 0.054 0.068 0.079 0.116 0.138

0.043 0.048 0.053 0.064 0.075 0.085 0.098 0.127 0.135 0.179 0.234 0.262

0.000 0.033 0.065 0.110 0.173 0.210 0.234 0.285 0.351 0.392 0.440 0.453

0.957 0.919 0.882 0.826 0.752 0.705 0.668 0.588 0.514 0.429 0.326 0.285

4.13 3.09 2.75 2.47 2.21 1.92 1.77 1.64 1.37 1.26 1.15

82.07 55.01 39.57 29.20 22.41 16.26 10.94 8.72 4.86 2.88 2.05

Standard uncertainties u(T) = 0.08 K; expanded uncertainty Uc are Uc(xR) = Uc(xE) = 0.007 (95 % level of confidence). 2173

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Figure 2. Vapor−liquid equilibrium diagram for butan-1-ol (1) + butyl acetate (2) + [OMIM][PF6] (3) system at 101.30 kPa (in the case of VLLE, x1′ is the mole fraction of butan-1-ol excluding ionic liquid considering the two liquids as a whole): □, x3 = 0; ■, x3 = 0.1; ●, x3 = 0.2; ▲, x3 = 0.3; solid lines, calculated by the NRTL model.

Figure 4. LLE of butan-1-ol (1) + butyl acetate (2) + [OMIM][PF6] (3) at 288.15 K: ●, experimental value; ○, correlated by NRTL model.

absolute deviation σT, and standard deviation δT of equilibrium temperatures (σT = (1/N)Σ|Texp − Tcal|; δT = [(1/N)Σ(Texp − Tcal)2]1/2) are 0.184 and 0.216 K, respectively. The mean absolute deviation and standard deviation of the extract phase and the raffinate phase σxE, δxE, σxR, and δxR (σxE = (1/NC) Σj=1N Σi=1C|xj,iE,cal − xj,iE,exp|; δxE = [(1/NC) Σj=1N Σi=1C (xj,iE,cal −xj,iE,exp)2]1/2; σxR = (1/NC) Σj=1N Σi=1C|xj,iR,cal − xj,iR,exp|; δxR = [(1/NC) Σj=1N Σi=1C (xj,iR,cal − xj,iR,exp)2]1/2) are 0.014, 0.021, 0.012, and 0.018, respectively. The LLE data of butan-1-ol (1) + butyl acetate (2) + [OMIM][PF6] (3) at 375 K, 385 K and 395 K are calculated using the NRTL model, and the values are plotted in Figure 5. As shown in Figure 5, the area of the two-phase region increases with the decreasing temperature.

Figure 5. LLE of butan-1-ol (1) + butyl acetate (2) + [OMIM][PF6] (3) at different temperatures (calculated by the NRTL model): ▼, 395.00 K; ▲, 385.00 K; ■, 375.00 K.

Figure 2 shows that the mole fraction of butan-1-ol in the vapor phase increases with the mole fraction of [OMIM][PF6] in liquid phase. The T, x, y diagram (Figure 3) demonstrates that the equilibrium temperatures increase with the concentration of [OMIM][PF6] in liquid phase. Figures 2 and 3 show that the IL [OMIM][PF6] can enhance the selectivity of butan-1-ol and butyl acetate greatly. The interactions between the two organic solvents and IL are different. Butyl acetate is miscible in [OMIM][PF6] but butan1-ol is partially miscible in [OMIM][PF6]. We can infer that the interaction between butan-1-ol and [OMIM][PF6] is less than that between butyl acetate and [OMIM][PF6], so the selectivity of butan-1-ol and butyl acetate can be enhanced by [OMIM][PF6].

Figure 3. T, x, y diagram for butan-1-ol (1) + butyl acetate (2) + [OMIM][PF6] (3) at different contents of [OMIM][PF6] (in the case of VLLE, x1′ is the mole fraction of butan-1-ol excluding ionic liquid considering the two liquids as a whole): ■, x′1 (x3 = 0.1); □, y1 (x3 = 0.1); ●, x1′ (x3 = 0.2); ○, y1 (x3 = 0.2); ▲, x1′ (x3 = 0.3); Δ, y1 (x3 = 0.3); dashed lines, calculated by the NRTL model for an IL-free system; solid lines, calculated by the NRTL model. 2174

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Funding

We would like to thank Innovation Fund of Tianjin University for financial support of this work. Notes

The authors declare no competing financial interest.

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(1) Rogers, R. D.; Voth, G. A. Ionic Liquids. Acc. Chem. Res. 2007, 40, 1077−1078. (2) Han, X.; Armstrong, D. W. Ionic Liquids in Separations. Acc. Chem. Res. 2007, 40, 1079−1086. (3) Beste, Y.; Eggersmann, M.; Schoenmakers, H. Extractive Distillation with Ionic Fluids. Chem. Ing. Technol. 2005, 77, 1800− 1808. (4) Lei, Z.; Arlt, W.; Wasserscheid, P. Separation of 1-Hexene and nHexane with Ionic Liquids. Fluid Phase Equilib. 2006, 241, 290−299. (5) Jork, C.; Seiler, M.; Beste, Y. A.; Arlt, W. Influence of Ionic Liquids on the Phase Behavior of Aqueous Azeotropic Systems. J. Chem. Eng. Data 2004, 49, 852−857. (6) Shiflett, M. B.; Yokozeki, A. Binary Vapor-Liquid and Vapor− Liquid−Liquid Equilibria of Hydrofluorocarbons (HFC-125 and HFC-143a) and Hydrofluoroethers (HFE-125 and HFE-143a) with Ionic Liquid [emim][Tf2N]. J. Chem. Eng. Data 2008, 53, 492−497. (7) Li, Q.; Zhang, J.; Lei, Z.; Zhu, J.; Wang, B.; Huang, X. Isobaric Vapor-Liquid Equilibrium for (Propan-2-ol + Water + 1-Butyl-3methylimidazolium Tetrafluoroborate). J. Chem. Eng. Data 2009, 54, 2785−2788. (8) Martin, M. C.; Mato, R. B. Isobaric Vapor−Liquid Equilibrium for Methyl Acetate + Methanol + Water at 101.3 kPa. J. Chem. Eng. Data 1995, 40, 326−327. (9) Orchilles, A. V.; Miguel, P. J.; Vercher, E.; Martinez-Andreu, A. Isobaric Vapor−Liquid Equilibria for Methyl Acetate + Methanol + 1Ethyl-3-methylimidazolium Trifluoromethanesulfonate at 100 kPa. J. Chem. Eng. Data 2007, 52, 915−920. (10) Cai, J. L.; Cui, X. B.; Zhang, Y.; Li, R.; Feng, T. Y. Vapor−Liquid Equilibrium and Liquid−Liquid Equilibrium of Methyl Acetate + Methanol + 1-Ethyl-3-methylimidazolium Acetate. J. Chem. Eng. Data 2011, 56, 282−287. (11) Kato, R.; Krummen, M.; Gmehling, J. Measurement and Correlation of Vapor−Liquid Equilibria and Excess Enthalpies of Binary Systems Containing Ionic Liquids and Hydrocarbons. Fluid Phase Equilib. 2004, 224, 47−54. (12) Bożek-Winkler, E.; Gmehling, J. Transesterification of Methyl Acetate and n-butanol Catalyzed by Amberlyst 15. Ind. Eng. Chem. Res. 2006, 45, 6648−6654. (13) Kroschwitz, J. I. Ed. Kirk-Othmer Encyclopedia of Chemical Technology. 4. Bearing Materials To Carbon, 4th ed.; Wiley Interscience: New York, 1992. (14) Ruiz, D. A. Fuel Additive. Patent Application 11/972860, 2009. (15) Jimenez, L.; Garvin, A.; Costa-Lopez, J. The Production of Butyl Acetate and Methanol via Reactive and Extractive Distillation. I. Chemical Equilibrium, Kinetics, and Mass-Transfer Issues. Ind. Eng. Chem. Res. 2002, 41, 6663−6669. (16) Jimenez, L.; Costa-Lopez, J. The Production of Butyl Acetate and Methanol via Reactive and Extractive Distillation. II. Process Modeling, Dynamic Simulation, and Control Strategy. Ind. Eng. Chem. Res. 2002, 41, 6735−6744. (17) Mullins, E.; Oldland, R.; Liu, Y. A.; Wang, S.; Sandler, S. I.; Chen, C. C.; Zwolak, M.; Seavey, K. C. Sigma-Profile Database for Using COSMO-Based Thermodynamic Methods. Ind. Eng. Chem. Res. 2006, 45, 4389−4415. (18) Lin, S. T.; Sandler, S. I. A Priori Phase Equilibrium Prediction from a Segment Contribution Solvation Model. Ind. Eng. Chem. Res. 2002, 41, 899−913. (19) Cai, J. L.; Cui, X. B.; Zhang, Y.; Li, R.; Feng, T. Y. Isobaric Vapor−Liquid Equilibrium for Methanol + Methyl Acetate + 1-Octyl3-methylimidazolium Hexafluorophosphate at 101.3 kPa. J. Chem. Eng. Data 2011, 56, 2884−2888.

Figure 6. Salting-out effect of [OMIM][PF6] and [BMIM][NTf2] on the VLE of butan-1-ol (1) + butyl acetate (2) system at 101.30 kPa for an IL mole fraction of x3 = 0.2: □, IL-free system; ▲, [BMIM][NTf2] (ref 21); ■, [OMIM][PF6]; solid lines, calculated by NRTL model.

Figure 7. Salting-out effect of [OMIM][PF6] and [BMIM][NTf2] on the VLE of butan-1-ol (1) + butyl acetate (2) system at 101.30 kPa for an IL mass fraction of x3 = 0.5 (calculated by NRTL model): ▲, [BMIM][NTf2] (ref 21); ■, [OMIM][PF6]; □, IL-free system.

Tian et al. used [BMIM][NTf2] as an entrainer to separate butan-1-ol (1) + butyl acetate (2), and the minimum concentration of [BMIM][NTf2] to eliminate the azeotropic point is 0.125 in mole fraction and 0.447 in mass fraction at 101.30 kPa.21 We used [OMIM][PF6] as an entrainer to separate butan-1-ol (1) + butyl acetate (2). The minimum concentration of [OMIM][PF6] to eliminate the azeotropic point is estimated to be 0.087 in mole fraction and 0.302 in mass fraction at 101.30 kPa, which is less than that of [BMIM][NTf2]. In addition, [OMIM][PF6] is also very stable in the mixture and it is much cheaper than [BMIM][NTf2]. The effects of [OMIM][PF6] and [BMIM][NTf2] are compared in Figure 6 (on mole basis) and Figure 7 (on mass basis).

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CONCLUSIONS The ternary VLE, LLE, and VLLE for butan-1-ol + butyl acetate + [OMIM][PF6] were measured. Results indicate that [OMIM][PF6] can enhance the selectivity of butan-1-ol and butyl acetate greatly. It can eliminate the azeotropic point of butan-1-ol + butyl acetate if the concentration of [OMIM][PF6] in the liquid phase is larger than 0.087 (mole fraction) at 101.30 kPa. The LLE data and VLE data were correlated by NRTL model simultaneously, and the calculated results agreed well with the experimental results. The [OMIM][PF6] is an effective entrainer to separate butan-1ol + butyl acetate. It is a promising entrainer for the production of butyl acetate and methanol from butan-1-ol and methyl acetate.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-0816-2492400. E-mail: [email protected]. 2175

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dx.doi.org/10.1021/je5000296 | J. Chem. Eng. Data 2014, 59, 2171−2176