Article pubs.acs.org/jced
Isobaric Vapor−Liquid Equilibrium for Methanol + Dimethyl Carbonate + 1‑Butyl-3-methylimidazolium Dibutylphosphate Xiaochun Chen, Fufeng Cai, Xinying Wu, Charles Asumana, and Guangren Yu* Beijing Key Laboratory of Membrane Science and Technology & College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, P. R. China S Supporting Information *
ABSTRACT: Isobaric vapor−liquid equilibrium at 101.3 kPa for the ternary system methanol + dimethyl carbonate +1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]) and their binary systems are determined using a modified Othmer still. By adding [BMIM][DBP] into the azeotropic system of methanol + dimethyl carbonate, the relative volatility of dimethyl carbonate is increased, which might be ascribed to the saltingout effect of [BMIM][DBP]. The relative volatility α21 increases with increasing molar fraction of [BMIM][DBP]. The azeotropic point disappears when the molar fraction of [BMIM][DBP] is above 0.150. The equilibrium data are well fitted by the electrolyte nonrandom two-liquid model.
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INTRODUCTION Dimethyl carbonate (DMC) is an environmentally benign solvent, which is widely used as a substitute for dimethyl sulfate, methyl halides, and phosgene in methylation and carbonylation reactions.1−3 DMC is prepared from the catalytic oxidative carbonylation of methanol. In this process, the separation of DMC and methanol is challenging because they form an azeotrope. Low temperature crystallization,4 high pressure distillation,5 azeotropic distillation,6 extractive distillation,7,8 membrane separation,9,10 and absorption11 were studied for separating DMC from methanol; among these, extractive distillation is a very promising technology.12−14 The selection of entrainer is key in extractive distillation. Ionic liquids (ILs) are a new class of solvents with some desirable properties such as nonvolatility, excellent capacity for dissolving organic/nonorganic compounds, and high thermal stability; therefore, they are generating a great deal of interest. The use of ILs as entrainer in extractive distillation for the separation of an azeotropic mixture was first reported by Arlt et al.15−17 ILs have some advantages over classical entrainers or inorganic salts. The ILs do not enter into the distillate stream thanks to their nonvolatility; they also do not corrode the column and pipeline as opposed to inorganic salts. ILs can be regenerated by flash distillation of the column bottom stream. The vapor−liquid equilibrium (VLE) data are essential for the analysis and design of extractive distillation. ́ Martinez-Andreu and co-workers studied the effect of various ILs on the azeotropic systems of ethanol + water,18,19 acetone + methanol,20−22 1-propanol + water,23 and methyl acetate + methanol.24 Zhang et al.25−27 reported isobaric VLE data for the systems containing imidazolium-based ILs with water +1-propanol, water +2-propanol, and water + ethanol +ethyl acetate. Zhao et al.28,29 presented isobaric VLE data of ethanol + methanol + IL and ethanol + water + IL. The effect of 1-ethyl-3-methylimidazolium © 2013 American Chemical Society
ethyl sulfate ([EMIM][EtSO4]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) on the VLE data of methanol + DMC at T = 333.15 K was outlined by Kim et al.30 Isobaric VLE data for methanol + DMC + 1-octyl-3-methylimidazolium tetrafluoraborate ([OMIM][BF4]) was provided by Li et al.31 The ILs with fluorine-containing anions such as [BF4]¯easily decompose and release corrosive hydrogen fluoride. In this work, isobaric VLE data for methanol + DMC + 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]) and their binary systems are determined at 101.3 kPa, and the effect of [BMIM][DBP] on VLE of methanol + DMC is discussed.
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EXPERIMENTAL SECTION Materials. Methanol (HPLC grade, 100 w ≥ 99.9) and DMC (AR grade, 100 w ≥ 99.0) are supplied by Tianjin Guangfu Technology Development Co. Ltd., China. The purity is verified by GC (GC112A-1, China). [BMIM][DBP] is synthesized as per the published procedure;32 it is dried by heating at T = 393 K under high vacuum (0.2 kPa) for 48 h prior to use; the mass fraction of water in the IL, determined by Karl Fischer titration, is xw < 0.0005. After using the liquid mixtures in the VLE apparatus, the solvents are removed by heating and stirring under vacuum (368 K, 0.2 kPa) by a rotary evaporator to recover the used IL. Apparatus and Procedures. The VLE for methanol (1) + DMC (2) + [BMIM][DBP] (3) is measured by a circulation VLE still (a modified Othmer still) at 101.3 kPa. A detailed description of the equilibrium still has been described.33 The equilibrium temperature of Othmer still is measured with a precised and Received: December 7, 2012 Accepted: March 27, 2013 Published: April 8, 2013 1186
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Table 1. Vapor−Liquid Equilibrium Data for Methanol (1) + DMC (2) at 101.3 kPaa
Table 2. Vapor-Liquid Equilibrium Data for Methanol (1) + [BMIM][DBP] (3) at 101.3 kPaa
T/K
x1
y1
x3
T/K
357.0 353.1 349.5 347.5 345.1 343.6 341.7 340.5 339.7 338.9 338.4 337.8 337.4 337.1 337.0 337.0 336.9 337.2 337.4
0.038 0.074 0.119 0.150 0.197 0.235 0.307 0.365 0.426 0.471 0.530 0.569 0.631 0.687 0.731 0.793 0.839 0.898 0.947
0.212 0.319 0.422 0.472 0.533 0.571 0.624 0.662 0.693 0.711 0.729 0.741 0.761 0.784 0.798 0.818 0.842 0.880 0.925
0.025 0.028 0.034 0.038 0.043 0.048 0.052 0.056 0.063 0.066 0.066 0.074 0.079 0.085 0.092 0.099 0.105 0.113 0.120 0.127 0.133 0.137 0.142 0.148 0.151 0.156 0.160 0.163 0.165 0.168 0.170 0.176 0.182 0.191 0.206 0.222 0.254
338.9 339.1 339.5 339.8 340.2 340.6 340.9 341.3 342.0 342.2 342.3 343.2 343.8 344.5 345.4 346.2 347.1 348.2 349.3 350.2 351.2 351.9 352.7 353.7 354.2 355.0 355.9 356.5 356.7 357.5 357.8 358.9 360.1 361.8 364.9 368.2 374.9
a
Standard uncertainties u are u(x1) = 0.001, u(y1) = 0.001, u(T) = 0.1 K, u(p) = 0.1 kPa.
calibrated thermometer with a standard uncertainty of 0.1 K. The pressure is measured by a manometer whose standard uncertainty is 0.1 kPa. When a given liquid solution is put into the equilibrium still and heated, equilibrium is attained in about 40 min which is indicative of the constant boiling temperature. Each experimental point of the binary solvent + IL systems is obtained from an initial sample of solvent + IL where IL concentration is highest at which different quantities of solvent are added. For the ternary system, several methanol + IL mixtures of known composition are prepared, and different quantities of another mixture of DMC + IL are added, making sure to maintain the same mole fraction of IL in each series. Sample Analysis. For solvent + IL binary systems, IL molar fraction in liquid phase is gravimetrically determined after distilling the volatile solvents at vacuum (393 K, 0.2 kPa) until a constant mass is reached. An analytical balance with a standard uncertainty of 0.001 g is used to weigh the samples. For ternary system, IL molar fraction in liquid phase is gravimetrically determined. The compositions of the condensed vapor and the concentration of methanol + DMC in the liquid phase are analyzed by gas chromatography. The gas chromatograph (GC112A-1, China) is equipped with a FID detector, and the column is SE-30 (30 m × 0.32 mm). The operating conditions are as follows: the temperature of both the injector and detector is 423 K, and that of the oven is 338 K. In the Supporting Information, we describe a detailed procedure for obtaining the equilibrium composition of vapor phase and liquid phase of the ternary mixture. For the samples of the liquid phase, the entire IL is retained by a trap located between the injector and the chromatographic column. The trap is periodically cleaned to prevent the IL from coming into the column. A calibration curve is obtained from a set of gravimetrically prepared standard solutions, which permits the quantification of methanol and DMC in the samples. The maximum deviation found between the measured and real composition in the samples is 0.001 molar fraction.
a
Standard uncertainties u are u(x3) = 0.001, u(T) = 0.1 K, u(p) = 0.1 kPa.
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RESULTS AND DISCUSSION Experimental Data. VLE data at 101.3 kPa for the binary systems of methanol (1) + DMC (2), methanol (1) + [BMIM][DBP] (3), DMC (2) + [BMIM][DBP] (3) are shown in Tables 1 to 3. In these tables, x1 and y1, respectively, represent the molar fraction of methanol in the liquid phase and in the vapor phase, x3 is the molar fraction of IL in the liquid phase, and T is the equilibrium temperature. VLE data at 101.3 kPa for methanol (1) + DMC (2) + [BMIM][DBP] (3) are obtained at IL molar fraction of x3 ≈ 0.050, 0.150, and 0.200. The results are shown in Table 4 where x3 is the molar fraction of IL in the liquid phase, x1′ represents the molar fraction of methanol in the liquid phase expressed on an IL-free basis, y1 represents the molar fraction of methanol in the vapor phase, T is the equilibrium temperature. Calculation of Phase Equilibrium. The electrolyte nonrandom two-liquid (e-NRTL) model is used to correlate the VLE of methanol (1) + DMC (2) + [BMIM][DBP] (3). The e-NRTL model is an extension of the nonrandom twoliquid local composition proposed by Renon and Prausnitz34 1187
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Table 3. Vapor−Liquid Equilibrium Data for DMC (2) + [BMIM][DBP] (3) at 101.3 kPaa
a
Table 4. Vapor−Liquid Equilibrium Data for Methanol (1) + DMC (2) + [BMIM][DBP] (3) at 101.3 kPaa
x3
T/K
x3
x1′
y1
T/K
0.021 0.022 0.027 0.031 0.036 0.039 0.044 0.050 0.053 0.059 0.066 0.072 0.074 0.087 0.091 0.093 0.104 0.115 0.124 0.127 0.141 0.143 0.148 0.160 0.173 0.187 0.204 0.214 0.222 0.239 0.266 0.281 0.323
362.9 362.9 363.0 363.0 363.0 363.0 363.0 363.0 363.0 363.0 363.1 363.1 363.1 363.1 363.2 363.2 363.3 363.3 363.4 363.4 363.5 363.7 363.7 363.9 364.1 364.2 364.5 364.9 365.1 365.2 365.8 366.2 367.7
0.049 0.050 0.050 0.049 0.048 0.048 0.048 0.048 0.049 0.048 0.048 0.151 0.148 0.149 0.148 0.150 0.149 0.149 0.150 0.150 0.150 0.152 0.202 0.199 0.199 0.199 0.201 0.202 0.202 0.202 0.202 0.200 0.201
0.055 0.110 0.212 0.315 0.414 0.513 0.616 0.714 0.800 0.894 0.932 0.101 0.164 0.257 0.357 0.456 0.551 0.641 0.725 0.816 0.906 0.939 0.100 0.185 0.285 0.385 0.461 0.562 0.657 0.753 0.841 0.921 0.954
0.104 0.199 0.357 0.473 0.565 0.629 0.691 0.746 0.802 0.878 0.915 0.065 0.117 0.195 0.287 0.367 0.454 0.546 0.630 0.724 0.844 0.894 0.049 0.101 0.169 0.241 0.300 0.384 0.478 0.585 0.704 0.835 0.898
361.3 358.4 353.5 349.3 346.3 343.9 342.1 340.9 340.3 339.9 340.2 363.3 362.3 360.6 358.5 357.1 355.7 354.5 353.8 353.4 353.0 353.5 364.2 363.7 362.8 361.9 361.4 360.9 360.7 360.5 360.7 361.1 361.6
a
Standard uncertainties u are u(x3) = 0.001, u(T) = 0.1 K, u(p) = 0.1 kPa.
Standard uncertainties u are u(x3) = 0.001, u(x′1) = 0.001, u(y1) = 0.001, u(T) = 0.1 K, u(p) = 0.1 kPa.
from which Chen et al.35 derived a model for single-solvent + electrolyte systems for liquid phase activity coefficients. Following that, Mock et al.36,37 extended it to mixed-solvent + electrolyte systems by neglecting the long-range interaction contribution term. In this way, the e-NRTL model produces expressions for the liquid-phase activity coefficients of methanol (1) and DMC (2) in a binary or ternary system containing IL of [BMIM][DBP] (3). These equations have been described elsewhere.38 According to the proposed method, nine binary adjustable parameters are needed for all of the solvent + solvent and solvent + IL pairs in the systems to represent the phase equilibrium of mixed-solvent + electrolyte systems. The 1−2 binary parameters are obtained from the VLE data in Table 1 using the e-NRTL model. The 1−3 and 2−3 binary parameters are obtained by using the VLE ternary data in Table 4 through the minimization of the objective function (OF) 2 2 ⎛ γ1 ⎞ ⎛ γ2 ⎞ OF = ∑ ⎜1 − calcd ⎟ +⎜1 − calcd ⎟ ⎜ γ1 ⎟⎠ ⎜⎝ γ2 ⎟⎠ N ⎝ exptl exptl
Table 5. Antoine Coefficients for the Pure Componentsa methanolb DMCc
A
B
C
temp range/K
7.14736 6.4338
1544.804 1413.00
−37.235 −44.25
335 to 376 273.15 to 548.0
Antoine equation: log(P/kPa) = A − B/(T/K + C). bReference 39. Reference 40.
a c
Table 6. Estimated Values of Nonrandomness Factors, αij, and Energy Parameters, Δgij and Δgji, for the e-NRTL Model Δgij
Δgji
i component
j component
αij
J·mol−1
J·mol−1
methanol (1) methanol (1) DMC (2)
DMC (2) [BMIM][DBP] (3) [BMIM][DBP] (3)
0.300 −0.017 0.161
3115.6 13133.8 22551.7
833.1 −26879.7 −8832.0
Because of the low total pressure, the vapor phase is assumed to be ideal, and the fugacity coefficients and the Poynting correction are neglected. Following this procedure, the binary parameters 1−3 and 2−3 are obtained by iteratively solving the equilibrium conditions expressed in eq 2 for the solvent.
(1)
where γi is the activity coefficient of solvent i; the indices calcd and exptl respectively denote the calculated and experimental values; N is the number of experimental data points; and the summations are extended to the whole range of data points.
yP = XiγiPis i 1188
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Table 7. 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 system
δya
σyb
δTc/K
σTd/K
methanol + DMC methanol + [BMIM][DBP] DMC + [BMIM][DBP] methanol + DMC + [BMIM][DBP]
0.007
0.002
0.004
0.001
0.15 0.29 0.31 0.40
0.04 0.06 0.07 0.08
δy = (1/N) ∑|yexptl − ycalcd|. bσy = [1/(N-1)][∑(yexptl − ycalcd)2]1/2. δT = (1/N) ∑|Texptl − Tcalcd|. dσT = [1/(N-1)][∑(Texptl − Tcalcd)2]1/2. a c
Figure 1. Isobaric VLE diagram for the binary system of methanol (1) + DMC (2) at 101.3 kPa: □, this work; ●, Li et al.;31 ▲, Yang et al.;41 ⧫, Luo et al.;42 solid lines, correlated using the e-NRTL model.
Figure 3. T−x′1−y1 diagram for methanol (1) + DMC (2) + [BMIM][DBP] (3) at 101.3 kPa for different IL molar fractions: ■, x′1 experimental for x3 = 0, □, y1 experimental for x3 = 0; ▲, x′1 experimental for x3 ≈ 0.050, Δ, y1 experimental for x3 ≈ 0.050; ●, x1′ experimental for x3 ≈ 0.150, ○, y1 experimental for x3 ≈ 0.150; ⧫, x′1 experimental for x3 ≈ 0.200, ◇, y1 experimental for x3 ≈ 0.200; solid lines, correlated using the e-NRTL model.
Figure 2. x′1−y1 diagram at 101.3 kPa for methanol (1) + DMC (2) + [BMIM][DBP] (3) and methanol (1) + DMC (2) + tetramethylammonium bicarbonate (TMAB): □, x3 = 0; Δ, x3 ≈ 0.050; ○, x3 ≈ 0.150; ◇, x3 ≈ 0.200; ●, xTMAB = 0.04, from ref 41; ⧫, xTMAB = 0.07, from ref 41; ▼, xTMAB = 0.10, from ref 41; solid lines, correlated using the e-NRTL model.
i obtained from the e-NRTL model; and Psi is the vapor pressure of pure solvent i at equilibrium temperature which is calculated using the Antoine equation. Table 5 lists the parameters of Antoine equation. Results of the optimized binary parameters are summarized in Table 6. The mean absolute deviations between
In eq 2, yi is the vapor phase molar fraction of solvent i; P is the total pressure in the system; Xi is the liquid phase molar fraction of component i based on the assumption of total dissociation of IL; γi is the activity coefficient of component 1189
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stant value of above 2.0. It can also be seen from Figure 4 that the ability of increasing the relative volatility of DMC from [BMIM][DBP] is larger than that from TMAB. The activity coefficients and boiling temperature of methanol and DMC in their binary mixture with [BMIM][DBP], against the IL molar fraction are shown in Figure 5. As shown in Figure 5
the experimental and calculated values of vapor-phase molar fractions and the equilibrium temperature are given in Table 7. Table 7 reveals that the e-NRTL model is able to properly correlate the experimental VLE data. The comparison of the VLE data for the binary system of methanol + DMC with the literatures is shown in Figure 1. It can be seen that our experimental data agree well with those reported in the literature. For a visual understanding, the VLE data of methanol (1) + DMC (2) + [BMIM][DBP] (3) is represented in Figures 2 (x′1 −y1) and 3 (T−x′1 −y1), where scattered points are obtained from the experiment and solid lines from the e-NRTL model. As indicated in Figures 2 and 3, the addition of [BMIM][DBP] increases the relative volatility of DMC to methanol, which might be ascribed to a salting-out effect for DMC.41 It was observed that [BMIM][DBP] is miscible in methanol while it is partially miscible in DMC. Therefore, following the principle of “like-dissolves-like”, the “attractive interaction” between [BMIM][DBP] and DMC is weaker than that between [BMIM][DBP] and methanol. From this, an increase of the relative volatility of DMC to methanol can be understood. As shown in Figure 2, the azeotropic point disappears when the [BMIM][DBP] mole fraction is above 0.150; while the addition of tetramethylammonium bicarbonate (TMAB) with different molar fractions of 0.04, 0.07, and 0.10 cannot eliminate the azeotropic point.41 From the e-NRTL model, it can be calculated that the disappearance of the azeotropic point for methanol + DMC system at 101.3 kPa takes place at x3 = 0.096 for [BMIM][DBP]. 1-Octyl-3methylimidazolium tetrafluoroborate can eliminate the azeotropic phenomena for methanol + the DMC system at x3 = 0.20.31 Figure 4 gives the effect of IL molar fraction on the relative volatility, α21, which is obtained using eq 3. α21 =
γ2P2s γ1P1s
(3)
As shown in Figure 4, α21 increases along with the molar fraction of [BMIM][DBP]. When the molar fraction of [BMIM][DBP] increases to 0.200, α21 presents a nearly con-
Figure 4. Variation of the relative volatility α21 between methanol (1) and DMC (2) with the methanol molar fraction x1′ for different [BMIM][DBP] (3) or TMAB molar fraction: □, x3 = 0; Δ, x3 ≈ 0.050; ○, x3 ≈ 0.150; ◇, x3 ≈ 0.200; ●, xTMAB = 0.04, from ref 41; ▼, xTMAB = 0.10, from ref 41; solid lines, correlated using the e-NRTL model.
Figure 5. Variation of the activity coefficient of solvent γi and boiling temperature with the mole fraction of IL x3 in solvent + [BMIM][DBP] binary systems at 101.3 kPa. Δ, methanol (1) + [BMIM][DBP] (3); □, DMC (2) + [BMIM][DBP] (3). Solid lines, correlated using the e-NRTL model. 1190
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panels a and b, γ1 decreases along with the molar fraction of [BMIM][DBP] while γ2 increases, thus the quotient γ2/γ1 becomes larger, which is in agreement with the result in Figure 4, that is, α21 increases along with the molar fraction of [BMIM][DBP]. As shown in Figure 5c, the addition of [BMIM][DBP] increases the boiling points of methanol and DMC; but [BMIM][DBP] increases the boiling points of methanol much more than that of DMC.
(8) Wang, S. J.; Yu, C. C.; Huang, H. P. Plant-Wide Design and Control of DMC Synthesis Process via Reactive Distillation and Thermally Coupled Extractive Distillation. Comput. Chem. Eng. 2010, 34, 361−373. (9) Won, W.; Feng, X.; Lawless, D. Separation of Dimethyl Carbonate/Methanol/Water Mixtures by Pervaporation Using Crosslinked Chitosan Membranes. Sep. Purif. Technol. 2003, 31, 129−140. (10) Wang, L.; Li, J.; Lin, Y.; Chen, C. Crosslinked Poly(vinyl alcohol) Membranes for Separation of Dimethyl Carbonate/Methanol Mixtures by Pervaporation. Chem. Eng. J. 2009, 146, 71−78. (11) Janisch, I.; Landscheidt, H.; Struver, W.; Klausener, A. US Parent No. 5455368, 1995. (12) Lei, Z.; Li, C.; Chen, B. Extractive Distillation: A Review. Sep. Purif. Rev. 2003, 32, 121−213. (13) Lei, Z.; Chen, B.; Ding, Z. Special Distillation Processes; Elsevier: Amsterdam, 2005. (14) Lei, Z.; Chen, B.; Li, C.; Liu, H. Predictive Molecular Thermodynamic Models for Liquids, Solid Salts, Polymers, and Ionic Liquids. Chem. Rev. 2008, 108, 1419−1455. (15) Arlt, W.; Seiler, M.; Jork, C.; Schneider, T. DE Patent No. 10136614, 2001. (16) Arlt, W.; Seiler, M.; Jork, C.; Schneider, T. Ionic Liquids as Selective Additives for the Separation of Close-Boiling or Azeotropic Mixtures. PCT Int. Appl. WO 02/074718 A2, 2002. (17) 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. (18) Orchillés, A. V.; Mifuel, P. J.; Vercher, E.; Martínez-Andreu, A. Using 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate as an Entrainer for the Extractive Distillation of Ethanol + Water Mixtures. J. Chem. Eng. Data 2010, 55, 1669−1674. (19) Orchillés, A. V.; Miguel, P. J.; Llopis, F. J.; Vercher, E.; MartínezAndreu, A. Isobaric Vapor−Liquid Equilibria for the Extractive Distillation of Ethanol + Water Mixtures Using 1-Ethyl-3-methylimidazolium Dicyanamide. J. Chem. Eng. Data 2011, 56, 4875−4880. (20) Orchillés, A. V.; Miguel, P. J.; Vercher, E.; Martínez-Andreu, A. Ionic Liquids as Entrainers in Extractive Distillation: Isobaric Vapor− Liquid Equilibria for Acetone + Methanol + 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate. J. Chem. Eng. Data 2007, 52, 141− 147. (21) Orchillés, A. V.; Miguel, P. J.; Llopis, F. J.; Vercher, E.; MartínezAndreu, A. Influence of Some Ionic Liquids Containing the Trifluoromethanesulfonate Anion on the Vapor−Liquid Equilibria of the Acetone + Methanol System. J. Chem. Eng. Data 2011, 56, 4430− 4435. (22) Orchillés, A. V.; Miguel, P. J.; González-Alfaro, V.; Vercher, E.; Martínez-Andreu, A. 1-Ethyl-3-methylimidazolium Dicyanamide as a very Efficient Entrainer for the Extractive Distillation of the Acetone + Methanol System. J. Chem. Eng. Data 2012, 57, 394−399. (23) Orchillés, A. V.; Miguel, P. J.; González-Alfaro, V.; Vercher, E.; Martínez-Andreu, A. Isobaric Vapor−Liquid Equilibria of 1-Propanol + Water + Trifluoromethanesulfonate-Based Ionic Liquid Ternary Systems at 100 kPa. J. Chem. Eng. Data 2011, 56, 4454−4460. (24) Orchillés, A. V.; Miguel, P. J.; Vercher, E.; Martínez-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. (25) Zhang, L. Z.; Deng, D. S.; Han, J. Z.; Ji, D. X.; Ji, J. B. Isobaric Vapor−Liquid Equilibria for Water + 2-Propanol + 1-Butyl-3methylimidazolium Tetrafluoroborate. J. Chem. Eng. Data 2007, 52, 199−205. (26) Zhang, L.; Yuan, X.; Qiao, B.; Qi, R.; Ji, J. Isobaric Vapor− Liquid Equilibria for Water + Ethanol +Ethyl Acetate + 1-Butyl-3methylimidazolium Acetate at Low Water Mole Fractions. J. Chem. Eng. Data 2008, 53, 1595−1601. (27) Zhang, L. Z.; Han, J. Z.; Wang, R. J.; Qiu, X. Y.; Ji, J. B. Isobaric Vapor−Liquid Equilibria for Three Ternary Systems: Water + 2Propanol + 1-Ethyl-3-methylimidazolium Tetrafluoroborate, Water + 1-Propanol + 1-Ethyl-3-methylimidazolium Tetrafluoroborate, and
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CONCLUSIONS In this work, the isobaric VLE data at 101.3 kPa for methanol (1) + DMC (2), methanol (1) + [BMIM][DBP] (3), DMC (2) + [BMIM][DBP] (3), and methanol (1) + DMC (2) + [BMIM][DBP] (3) is determined with a circulation still, and the electrolyte nonrandom two-liquid (e-NRTL) model is used to correlate the data. Diagrams of x′1 −y1, T−x′1 −y1, α21−x′1 and variations of γ1 and γ2 along with the molar fraction of [BMIM][DBP] are obtained. It is observed that the addition of [BMIM][DBP] into the azeotropic system of methanol + DMC enhances the relative volatility of DMC, which might be ascribed to the salting-out effect of [BMIM][DBP]. By increasing the molar fraction of [BMIM][DBP], α21 and γ2 increases while γ1 decreases; the azeotropic point disappears when the molar fraction of [BMIM][DBP] is above 0.150. The VLE data are well fitted by the e-NRTL model. This work shows that [BMIM][DBP] is a potential entrainer for the separation of methanol and DMC using extractive distillation.
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ASSOCIATED CONTENT
S Supporting Information *
Procedure for obtaining the equilibrium composition of vapor phase and liquid phase of the ternary mixture methanol (1) + dimethyl carbonate (2) + ionic liquid (3). This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Tel./Fax: +86 10 6443 3570. E-mail:
[email protected]. Funding
This work was financially supported by National Natural Science Foundation of China (Grants 20806002, 20976005, 21176021, 21276020). Notes
The authors declare no competing financial interest.
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