Isobaric Vapor–Liquid Equilibrium for Methanol + Dimethyl Carbonate

Article pubs.acs.org/jced

Isobaric Vapor−Liquid Equilibrium for Methanol + Dimethyl Carbonate + Trifluoromethanesulfonate-based Ionic Liquids at 101.3 kPa Qunsheng Li,† Shuang Zhang,† Bangqin Ding,‡ Ling Cao,† Panpan Liu,† Zilong Jiang,† and Baohua Wang*,§ †

State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China College of Chemical and Biological Engineering, Nantong Vocational University, Nantong 226007, China § College of Chinese Pharmacology, Beijing University of Chinese Medicine and Pharmacology, Beijing 100029, China ‡

ABSTRACT: Isobaric vapor−liquid equilibrium (VLE) data for the binary system methanol + dimethyl carbonate as well as the VLE data for the ternary systems methanol + dimethyl carbonate +1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][OTf]) and methanol + dimethyl carbonate + 1butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][OTf]) at 101.3 kPa have been obtained with a modified Othmer still. The results indicated that both [EMIM][OTf] and [BMIM][OTf] produced crossover effects. Due to the difference of polarity of the two ILs, [BMIM][OTf] eliminated the azeotropic point at mole fraction about 10%, whereas [EMIM][OTf] only pulled down the azeotropic point. The measured VLE data were fitted using the NRTL model with a good consistency.

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INTRODUCTION Extractive distillation is widely utilized in the industry and becomes an important separation method for azeotropic or close-boiling mixtures.1,2 In extractive distillation, the selection and design of suitable entrainer is a critical step before the distillation sequence is designed.3−5 It is feasible to use an ionic liquid (IL) as the entrainer for extractive distillation rather than only salts or liquid solvents.6 ILs have specific structure and ionic interactions, which lead to their unique properties: a negligible vapor pressure, a wide liquid range, good solubility for a wide range of materials, great potential to be reused and recycled, and high thermal and chemical stabilities. However, the thermodynamic data of IL-containing systems are still scarce.7,8 Dimethyl carbonate (DMC) is a nonirritant, nontoxic chemical.9 Its characteristics (high oxygen content, good solvency power, favorable distribution coefficients for gasoline/water two-phase systems, a low freeze point) determine that it can be applied in a wide range of fields, for example, as lithium rechargeable batteries, a blowing agent in polyurethane foam after CFC ban, a fuel additive, and an oxygenate additive.9−12 Nowadays, the production technology and application of DMC are becoming a hot topic.13 In the several kinds of synthesis methods of DMC, methanol is one of the raw materials.14,15 The separation of the methanol + DMC mixture is very difficult due to the formation of the methanol + DMC azeotrope.16 In order to obtain high-purity DMC from the mixture (DMC + methanol), various salts or reagents have been used as the entrainers in the extractive © 2014 American Chemical Society

distillation, such as tetramethylammonium bicarbonate, toluene, and ethylbenzene.17−19 Several ILs were reported to have broken the azeotrope of DMC and methanol, such as 1-octyl-3methylimidazolium tetrafluoroborate ([OMIM][BF4]),20 1methyl-3-methylimidazolium dimethylphosphate ([MMIM][DMP]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]),21 and 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]).22 The main purpose of this work is to determine if 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][OTf]) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][OTf]) can be applied as the entrainers to break the methanol + DMC azeotrope. In this work, the isobaric vapor−liquid equilibrium (VLE) data for the binary system methanol + DMC and the ternary systems methanol + DMC containing [EMIM][OTf] or [BMIM][OTf] were measured at 101.3 kPa, and the effects of [EMIM][OTf] and [BMIM][OTf] on the VLE of methanol + DMC system were discussed and compared with that of [OMIM][BF 4 ], [MMIM][DMP], [EMIM][DEP], and [BMIM][DBP].

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EXPERIMENTAL SECTION Chemicals. The solvents used were methanol, DMC, [EMIM][OTf], and [BMIM][OTf]. Methanol was obtained from Tianjin Siyou Fine Chemical Reagents Factory, China, Received: May 19, 2014 Accepted: October 17, 2014 Published: October 30, 2014 3488

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Table 1. Specifications of Chemical Samples chemical name

source

mass fraction purity

purification method

final water mass fraction

analysis method

0.999

none

0.00047

GCc, KFe

DMC [EMIM][OTf]a

Tianjin Siyou Fine Chemical Reagents Factory Suzhou Huntsman Chemical Co. Ltd. Shanghai Chengjie Chemical Co. Ltd.

0.999 0.990

0.00036 0.00054

GCc, KFe LCd, KFe

[BMIM][OTf]b

Shanghai Chengjie Chemical Co. Ltd.

0.990

none rotary evaporation under a vacuum rotary evaporation under a vacuum

0.00048

LCd, KFe

methanol

a

[EMIM][OTf] = 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. b[BMIM][OTf] = 1-butyl-3-methylimidazolium trifluoromethanesulfanate. cGC = gas chromatography. dLC = liquid chromatography. eKF = Karl Fischer titration.

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RESULTS AND DISCUSSION Experimental VLE Results. The VLE data for binary system methanol + DMC were measured at 101.3 kPa, and the results are listed in Table 2 and compared with the literature

and the purity was not less than 99.9% (weight ratio). DMC was purchased from Suzhou Huntsman Chemical Co., Ltd., China, and the purity was not less than 99.9% (weight ratio). The ILs ([EMIM][OTf] and [BMIM][OTf]) were supplied by Shanghai Chengjie Chemical Reagents Factory and their mass fraction purities were both not less than 99.0%, and the water mass fraction contents for [EMIM][OTf] and [BMIM][OTf] were less than 0.054% and 0.048%, respectively, which were determined by Karl Fischer titration. The pretreatment and recovery of ILs were carried by the rotary evaporation for 48 h at 383 K under a vacuum condition in order to remove trial water and volatile components. The specifications of all reagents were summarized in Table 1. Apparatus and Procedure. All VLE data were measured at atmospheric pressure (101.3 kPa) using the modified Othmer still, which was described in a previous paper.23 This apparatus was connected to a constant pressure system to maintain the value of pressure at 101.3 kPa, and the pressure was measured by a barometer with an uncertainty of 0.1 kPa. The equilibrium temperature was measured with a calibrated mercury thermometer and its standard uncertainty was 0.1 K. Every experimental point of the binary system methanol + DMC and the ternary systems methanol + DMC + [EMIM][OTf] and methanol + DMC + [BMIM][OTf] was obtained from a gas chromatograph (SP7800, China) equipped with a TCD detector and a Porapak-Q column. The chromatographic column was 3 m long and the external diameter was 3 mm. Hydrogen was used as the carrier gas with a flow rate of 50 cm3· min−1. When the VLE temperature maintained at a constant value for at least 30 min, the feed (≈ 1 μL) was directly injected into the gas chromatograph without any pretreatment. The operating conditions were as follows: the injector temperature of 443 K, the oven temperature of 403 K, and the detector temperature of 453 K. For the liquid phase samples of ternary systems, the ILs were trapped by the glass wool, which was putted in the glass liner. The glass liner located between the injector and the chromatographic column, and it was periodically cleaned. A calibration curve, which can be used to quantify the amounts of methanol and DMC, was obtained from a set of gravimetrically prepared standard solutions by an electronic balance with an uncertainty of 0.1 mg. The combined standard uncertainty of mole fraction of methanol and DMC was 0.002. The amount of the feed was so small that the concentration of ionic liquid could be considered unchanged during the VLE measurements. By measuring the mass difference of liquid phase with and without IL, the mole fraction of IL in the liquid phase was determined, and the combined standard uncertainty of mole fraction of the ILs were 0.002.

Table 2. Vapor−Liquid Equilibrium Data for Temperature T, Liquid-Phase Mole Fraction x, and Gas-Phase Mole Fraction y for the Methanol (1) + DMC (2) System at 101.3 kPaa T

x1

y1

0.000 0.086 0.123 0.181 0.227 0.284 0.354 0.464 0.558 0.649 0.718 0.797 0.862 0.902 0.944 1.000

0.000 0.350 0.426 0.511 0.570 0.613 0.673 0.717 0.740 0.776 0.804 0.824 0.865 0.887 0.933 1.000

K 363.2 352.5 350.0 346.5 344.0 342.7 340.4 338.9 338.0 337.3 337.0 336.7 336.6 336.8 337.0 337.9

a Standard uncertainties u are u(T) = 0.1 K, u(P) = 0.10 kPa, and the combined standard uncertainties are uc(x1) = uc(y1) = 0.002.

data20,22 shown in Figure 1. The results in Figure 1 indicate that our experimental data were quite consistent with those of reported data,20,22 and the results also show that the maximum absolute deviations of the mole fraction of methanol in the vapor phase between the calculated values using NRTL model and measured values were less than 0.010. Hence, the experimental apparatus can be used to study the VLE of the systems containing ILs. The VLE data for the ternary systems of methanol (1) + DMC (2) + [EMIM][OTf] (3) and methanol (1) + DMC (2) + [BMIM][OTf] (3) were obtained at 101.3 kPa, and the IL mole fraction was kept constant in each of the three series at x3 ≈ 0.050, 0.100, 0.150. Our experimental values are listed in Tables 3 and 4, where x3 is the mole fraction of ILs in the liquid phase, x1 is the mole fraction of methanol in the liquid phase containing ILs, y1 is the mole fraction of methanol in the vapor phase, T is the equilibrium temperature, γ1 is the activity coefficient of methanol, γ2 is the activity coefficient of DMC, and α12 is the relative volatility of methanol to DMC. The 3489

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Table 4. Vapor−Liquid Equilibrium Data for Liquid-Phase Mole Fraction of [BMIM][OTf] x3, Temperature T, LiquidPhase Mole Fraction of Methanol x1a, Vapor-Phase Mole Fraction y, and Relative Volatility α12, for Ternary System Methanol (1) + DMC (2) + [BMIM][OTf] (3) at 101.3 kPab x3

T

x1

y1

α12

0.117 0.171 0.269 0.341 0.403 0.526 0.599 0.745 0.853 0.111 0.150 0.223 0.335 0.419 0.514 0.616 0.711 0.805 0.102 0.134 0.213 0.304 0.403 0.484 0.588 0.663 0.759

0.381 0.472 0.564 0.630 0.667 0.718 0.746 0.816 0.893 0.351 0.405 0.489 0.585 0.659 0.714 0.766 0.838 0.907 0.321 0.364 0.474 0.568 0.643 0.704 0.801 0.855 0.918

4.378 4.069 3.271 3.040 2.720 2.058 1.722 1.222 0.950 3.856 3.418 2.898 2.375 2.218 1.878 1.512 1.381 1.149 3.470 3.059 2.701 2.352 2.004 1.805 1.791 1.658 1.329

K 0.050 0.050 0.049 0.050 0.050 0.051 0.050 0.052 0.050 0.099 0.102 0.101 0.100 0.101 0.101 0.102 0.100 0.099 0.149 0.153 0.151 0.152 0.149 0.150 0.149 0.149 0.149

Figure 1. Absolute deviations Δ y1 = y(exptl) − y(calcd) between the calculated by NRTL model and measured mole fraction of methanol in the vapor phase for the binary system of methanol (1) + DMC (2) at 101.3 kPa: ■, this work with error bars representing the extended uncertainty; △, ref 20; ○, ref 22.

Table 3. Vapor−Liquid Equilibrium Data for Liquid-Phase Mole Fraction of [EMIM][OTf] x3, Temperature T, LiquidPhase Mole Fraction of Methanol x1a, Vapor-Phase Mole Fraction y, and Relative Volatility α12, for Ternary System Methanol (1) + DMC (2) + [EMIM][OTf] (3) at 101.3 kPab x3

T

x1

y1

α12

0.119 0.198 0.291 0.369 0.460 0.562 0.660 0.757 0.859 0.112 0.183 0.265 0.346 0.436 0.524 0.623 0.716 0.811 0.107 0.175 0.252 0.332 0.398 0.468 0.585 0.678 0.765

0.368 0.476 0.565 0.632 0.665 0.700 0.753 0.822 0.895 0.330 0.427 0.510 0.586 0.631 0.692 0.743 0.825 0.904 0.307 0.393 0.469 0.541 0.595 0.656 0.753 0.829 0.910

4.058 3.450 2.939 2.706 2.116 1.609 1.338 1.182 0.906 3.456 2.920 2.499 2.266 1.821 1.616 1.286 1.213 1.034 3.090 2.492 2.094 1.840 1.669 1.562 1.387 1.227 1.126

K 0.052 0.050 0.051 0.051 0.052 0.050 0.052 0.050 0.050 0.101 0.099 0.101 0.101 0.101 0.100 0.102 0.099 0.099 0.149 0.149 0.151 0.149 0.151 0.151 0.150 0.150 0.152

353.6 347.8 345.0 342.6 341.3 339.9 339.0 338.5 338.6 356.0 351.0 348.5 345.6 343.7 342.1 341.7 340.4 340.4 358.0 354.0 351.0 348.5 346.4 345.0 343.6 342.9 342.5

353.5 350.0 345.8 343.6 342.0 340.8 340.0 338.1 338.5 355.5 353.0 350.5 346.0 343.6 342.1 341.4 340.9 340.6 357.3 355.5 352.3 349.5 347.0 346.4 344.8 343.9 342.8

a Containing IL. bStandard uncertainties u are u(T) = 0.1 K, u(P) = 0.1 kPa, and the combined standard uncertainties uc are uc(x1) = uc(y1) = 0.002, uc(x3) = 0.002.

activity coefficient of methanol and DMC, γi, and the relative volatility of methanol to DMC, α12, in the Tables 3 and 4 are calculated based on the assumption of a nonideal behavior of liquid phase and an ideal behavior of the vapor phase during the experimental process due to the pressure is at 101.3 kPa, and the equations are as follows: yP γi = i S xiPi (1) α12 =

γ1P1S γ2P2S

(2)

in which xi is the mole fraction of components i in the liquidphase containing ILs, yi is the mole fraction of components i in the vapor-phase, P is the total pressure of the whole system (101.3 kPa), and PiS presents the vapor pressure of pure component i at equilibrium temperature and can be calculated by Antoine equation. The Antoine constants of methanol and DMC were obtained from literature.24,25 Modeling Results. The NRTL model was proposed by Renon and Prausnitz (1968),26 and it was reported to have reproduced various VLE data containing ILs properly.27−31

a Containing IL. bStandard uncertainties u are u(T) = 0.1 K, u(P) = 0.1 kPa, and the combined standard uncertainties uc are uc(x1) = uc(y1) = 0.002, uc(x3) = 0.002.

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Therefore, the experimental VLE data for methanol + DMC and methanol + DMC + ILs systems were also correlated by the NRTL model. In the NRTL model, the Levenberg−Marquardt method was used to regress the model parameters, the objective function (average relative deviation, ARD) was defined as ARD(%) =

1 n

∑

γiexptl − γicalcd

n

γiexptl

× 100 (3)

in which the indices “exptl” and “calcd” represented experimental and calculated values, respectively; n was the number of data points; γi was the activity coefficient of solvent i (1 and 2). In this work, α12 is set as 0.30, which is taken from the Aspen Plus, and the other parameters were obtained when the above function reached a minimum. The correlated results are listed in Table 5. The binary interaction parameters of Table 5. Calculated Values of Binary Parameters Δgij and Δgji in the NRTL Model i component

j component

αij

Δgij J·mol

methanol (1) methanol (1) DMC (2) methanol (1) DMC (2)

Δgji

−1

Figure 2. Isobaric VLE diagram for methanol (1) + DMC (2) + [EMIM][OTf] (3) system at 101.3 kPa: ○, x3 = 0; ●, x3 ≈ 0.050; ■, x3 ≈ 0.100; ▲, x3 ≈ 0.150; solid lines, correlated using the NRTL model.

ARD

−1

J·mol

%

DMC (2)

0.300

3710.93

217.68

1.37

[EMIM][OTf] (3) [EMIM][OTf] (3) [BMIM][OTf] (3) [BMIM][OTf] (3)

0.290

14280.31

−9247.66

3.03

0.100

32568.64

−16735.86

2.66

0.450

10097.50

−7018.55

0.100

33810.52

−18664.38

methanol and DMC components in the NRTL model was obtained from the VLE data of methanol + DMC system first, and the others were calculated from the ternary VLE data of ILs containing systems. The mole fraction of methanol in the vapor-phase and the equilibrium temperature were calculated by NRTL model combined with the regressed parameters. The mean absolute deviations between experimental and calculated mole fraction of methanol in the vapor-phase δy and that of the equilibrium temperature δT are listed in Table 6. The y−x′ diagram of the measured and calculated VLE data of the ternary systems methanol + DMC + [EMIM][OTf] and methanol + DMC + [BMIM][OTf] were presented in Figures 2 and 3, respectively. The relative volatilities of methanol to DMC are shown in Figure 4. It can be seen that the separation capacity of [BMIM][OTf] is stronger than that of [EMIM]-

Figure 3. Isobaric VLE diagram for methanol (1) + DMC (2) + [BMIM][OTf] (3) system at 101.3 kPa: ○, x3 = 0; ●, x3 ≈ 0.050; ■, x3 ≈ 0.100; ▲, x3 ≈ 0.150; solid lines, correlated using the NRTL model.

[OTf]. The T−x′−y diagrams were presented in Figures 5 and 6. Those figures showed that the NRTL model properly fit the experimental VLE data. As shown in Figures 2 to 4, both [EMIM][OTf] and [BMIM][OTf] produced crossover effects between salting-out and salting-in on the VLE of methanol + DMC system. When the methanol content was above 0.65, both [EMIM][OTf] and [BMIM][OTf] showed salting-out effects for methanol, so the values of relative volatility of methanol to DMC increased. With the increase of the ILs content, the salting-out effect became more obvious and followed the order 15% > 10% > 5%. In addition, [EMIM][OTf] can shift upward the azeotropic point but [BMIM][OTf] can totally eliminate the azeotropic phenomenon of methanol and DMC when its mole fraction in liquid phase is up to 0.100. Thus, the effect of [BMIM][OTf] for separating the methanol−DMC azeotrope is better than that of [EMIM][OTf].

Table 6. Mean Absolute Deviations, δy and δT, Between Experimental and Calculated Values of the Vapor-Phase Mole Fractions and the Equilibrium Temperature system

δya

δTb

methanol + DMC methanol + DMC + [EMIM][OTf] methanol + DMC + [BMIM][OTf]

0.005 0.007 0.006

0.2 0.4 0.6

K

δy = (1/N)∑|yexptl − ycalcd|, where N is the number of experimental points. bδT = (1/N)∑|Texptl − Tcalcd|, where N is the number of experimental points..

a

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Figure 6. T−x1′−y diagram for the ternary system methanol (1) + DMC (2) + [BMIM][OTf] (3) at different contents of IL at 101.3 kPa: ●, x1 (x3 = 0); ○, y1 (x3 = 0); ■, x1 (x3 ≈ 0.050); □, y1 (x3 ≈ 0.050); ▲, x1 (x3 ≈ 0.100); △, y1 (x3 ≈ 0.100); ★, x1 (x3 ≈ 0.150); ☆, y1 (x3 ≈ 0.150); solid lines, correlated using the NRTL model.

Figure 4. Relative volatilities of methanol (1) to DMC (2) at different mole fractions of [EMIM][OTf] (3) and [BMIM][OTf] (3) at 101.3 kPa: ○, x3 = 0 (IL-free); □, x3 ≈ 0.050 ([EMIM][OTf]); ■, x3 ≈ 0.050 ([BMIM][OTf]); △, x3 ≈ 0.100 ([EMIM][OTf]); ▲, x3 ≈ 0.100 ([BMIM][OTf]); ☆, x3 ≈ 0.150 ([EMIM][OTf]); ★, x3 ≈ 0.150 ([BMIM][OTf]); solid lines, correlated using the NRTL model.

[OTf] and DMC, so the effect of [BMIM][OTf] on the VLE of the methanol + DMC system is significantly greater than that of [EMIM][OTf], as shown in Figures 4, 7, and 8. However, when

Figure 5. T−x1′−y diagram for the ternary system methanol (1) + DMC (2) + [EMIM][OTf] (3) at different contents of IL at 101.3 kPa: ●, x1 (x3 = 0); ○, y1 (x3 = 0); ■, x1 (x3 ≈ 0.050); □, y1 (x3 ≈ 0.050); ▲, x1 (x3 ≈ 0.100); △, y1 (x3 ≈ 0.100); ★, x1 (x3 ≈ 0.150); ☆, y1 (x3 ≈ 0.150); solid lines, correlated using the NRTL model.

Figure 7. Experimental and calculated activity coefficients of methanol, γ1, and DMC, γ2, in relation with methanol mole fraction on an IL-free basis for the mixture methanol (1) + DMC (2) + [EMIM][OTf] (3) at 101.3 kPa: ●, γ1 (x3 = 0); ○, γ2 (x3 = 0); ■, γ1 (x3 ≈ 0.050); □, γ2 (x3 ≈ 0.050); ▲, γ1 (x3 ≈ 0.100); △, γ2 (x3 ≈ 0.100); ★, γ1 (x3 ≈ 0.150); ☆, γ2 (x3 ≈ 0.150); solid lines, correlated using the NRTL model.

In the ternary systems methanol + DMC + [EMIM][OTf] and methanol + DMC + [BMIM][OTf], the attractive interaction between solvent molecules and ILs causes the crossover effects. The ILs can be treated as weak electrolyte in a solution of highly dielectric solvent. The polarity of methanol is greater than that of DMC. Therefore, the attractive interaction between ILs and DMC is stronger than that of ILs and methanol according to the principle of “like dissolves like”. When the methanol content was above 0.65, with the increase of the ILs contents, more and more DMC molecules are “bonded” by ILs, which leads to the relative volatility of methanol to DMC increases. Compared with [EMIM][OTf], [BMIM][OTf] has a longer carbon chain, and thus the polarity of [BMIM][OTf] is smaller. The attractive interaction between [BMIM][OTf] and DMC is stronger than that of [EMIM]-

the methanol content is below 0.65, the solubility of the ILs in methanol and DMC mixed solution may be limited, which causes the relative volatility of methanol to DMC decreases, as shown in Figure 4. The relative volatility of methanol to DMC was calculated by α12 = (γ1/γ2)(P1S/P2S). The variation range of the ratio P1S/P2S was from 2.44 to 2.52 in our experiment, so the effect of ILs on α12 depends on the ratio of activity coefficients (γ1/γ2). As shown in Figures 7 and 8, with the increase of ILs, the activity coefficient of methanol (γ1) decreases over the whole range of 3492

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CONCLUSIONS The VLE data for methanol + DMC systems containing [EMIM][OTf] or [BMIM][OTf] were obtained at 101.3 kPa. The results indicated that both [EMIM][OTf] and [BMIM][OTf] showed crossover effects on the VLE of methanol + DMC system, and lead to a higher equilibrium temperature. The addition of the ILs also caused an enhancement of the relative volatility of methanol to DMC in the methanol-rich domain. Especially, [BMIM][OTf] can even totally eliminated the azeotropic phenomenon when its concentration in liquid phase was up to 0.100, whereas [EMIM][OTf] pulled down the azeotropic point. The VLE data were correlated using the NRTL model, and the modeling results can reproduce both binary and the ternary systems well. Compared with [EMIM][OTf], [BMIM][OTf] has a stronger impact on the VLE of methanol and DMC. Also, the extractive capacity of [BMIM][OTf] is greater than that of [OMIM][BF4], [MMIM][DMP], [EMIM][DEP], and [BMIM][DBP].

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Figure 8. Experimental and calculated activity coefficients of methanol, γ1, and DMC, γ2, in relation with methanol mole fraction on an IL-free basis for the mixture methanol (1) + DMC (2) + [BMIM][OTf] (3) at 101.3 kPa: ●, γ1 (x3 = 0); ○, γ2 (x3 = 0); ■, γ1 (x3 ≈ 0.050); □, γ2 (x3 ≈ 0.050); ▲, γ1 (x3 ≈ 0.100); △, γ2 (x3 ≈ 0.100); ★, γ1 (x3 ≈ 0.150); ☆, γ2 (x3 ≈ 0.150); solid lines, correlated using the NRTL model.

AUTHOR INFORMATION

Corresponding Author

* Tel.: + 86 10 6444 6523. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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the liquid concentrations, the activity coefficient of DMC (γ2) decreases more apparently when the methanol content is greater than 0.65 but increases in the rest of the range. So in the methanol-rich domain, the effect of lowering γ2 causes the relative volatility of methanol to DMC to increase with the addition of ILs. The results in Figures 5 and 6 indicate that the equilibrium temperature of both the ternary methanol + DMC + [EMIM][OTf] and methanol + DMC + [BMIM][OTf] systems rises with the increasing concentration of ILs in the liquid phase. Moreover, when the ILs’ contents are at the same level, the extent of temperature elevation of methanol + DMC + [EMIM][OTf] is higher than that of methanol + DMC + [BMIM][OTf]. So the energy demand for distillation with [BMIM][OTf] is lower compared with [EMIM][OTf]. [BMIM][OTf] may be a promising extrainer for the extractive distillation to separate the methanol + DMC azeotropic mixture. Besides, the effect of [BMIM][OTf] on separating the methanol + DMC azeotrope was compared with that of [OMIM][BF 4 ], [MMIM][DMP], [EMIM][DEP], and [BMIM][DBP].20−22 The results indicate that the extractive capacities of these ILs follow the order of [BMIM][OTf] > [MMIM][DMP] > [EMIM][DEP] > [BMIM][DBP] > [OMIM][BF4]. When the concentration of the ILs in the same level, the equilibrium temperature of the ternary systems methanol + DMC + ILs follows the order of [BMIM][DBP] > [EMIM][DEP] > [MMIM][DMP] > [OMIM][BF4] > [BMIM][OTf], thus the system methanol + DMC + [BMIM][OTf] needs less energy to achieve equilibrium. Therefore, [BMIM][OTf] may be a more potential entrainer for separating the methanol + DMC azeotropic mixture compared with [OMIM][BF4], [MMIM][DMP], [EMIM][DEP], and [BMIM][DBP].

REFERENCES

(1) Lei, Z.; Li, C.; Chen, B. Extractive Distillation: A Review. Sep. Purif. Rev. 2003, 32, 121−213. (2) Stichlmair, J.; Fair, J. R.; Brovo, J. L. Separation of Azeotropic Mixtures via Enhanced Distillation. Chem. Eng. Prog. 1989, 85, 63−69. (3) Wahnschafft, O. M.; Westerberg, A. W. The Product Composition Regions of Azeotropic Distillation Columns. 2. Separability in Two-Feed Columns and Entrainer Selection. Ind. Eng. Chem. Res. 1993, 32, 1108−1120. (4) Laroche, L.; Bekiaris, N.; Andersen, H. W.; Morari, M. The Curious Behavior of Homogeneous Azeotropic Distillation-Implications for Entrainer Selection. AIChE J. 1992, 38, 1309−1328. (5) Foucher, E. R.; Doherty, M. F.; Malone, M. F. Automatic Screening of Entrainers for Homogeneous Azeotropic Distillation. Ind. Eng. Chem. Res. 1991, 30, 760−772. (6) Lei, Z.; Chen, B.; Ding, Z. Special Distillation Process; Elsevier: Amsterdam, 2005. (7) Orchillés, A. V.; Miguel, P. J.; Vercher, E.; Martínez-Andreu, A. Isobaric Vapor−Liquid Equilibria for Ethyl Acetate + Ethanol + 1Ethyl-3-methylimidazolium Trifluoromethanesulfonate at 100 kPa. J. Chem. Eng. Data 2007, 52, 2325−2330. (8) Li, Q.; Zhang, J.; Lei, Z.; Zhu, J.; Zhu, J.; Huang, X. Selection of Ionic Liquids as Entrainers for the Separation of Ethyl Acetate and Ethanol. Ind. Eng. Chem. Res. 2009, 48, 9006−9012. (9) Tundo, P.; Selva, M. The Chemistry of Dimethyl Carbonate. Acc. Chem. Res. 2002, 35, 706−716. (10) Pacheco, M. A.; Marshall, C. L. Review of Dimethyl Carbonate (DMC) Manufacture and Its Characteristics as a Fuel Additive. Energy Fuels 1997, 11, 2−29. (11) Rounce, P.; Tsolakis, A.; Leung, P.; York, A. P. E. A Comparison of Diesel and Biodiesel Emissions Using Dimethyl Carbonate as an Oxygenated Additive. Energy Fuels 2010, 24, 4812−4819. (12) Hellier, P.; Ladommatos, N.; Allan, R.; Rogerson, J. Influence of Carbonate Ester Molecular Structure on Compression Ignition Combustion and Emissions. Energy Fuels 2013, 27, 5222−5245. (13) Delledonne, D.; Rivetti, F.; Romano, U. Developments in the Production and Application of Dimethylcarbonate. Appl. Catal., A 2001, 221, 241−251. (14) Yang, B.; Wang, D.; Lin, H.; Sun, J.; Wang, X. Synthesis of Dimethyl Carbonate from Urea and Methanol Catalyzed by the 3493

dx.doi.org/10.1021/je500443v | J. Chem. Eng. Data 2014, 59, 3488−3494

Journal of Chemical & Engineering Data

Article

Metallic Compounds at Atmospheric Pressure. Catal. Commun. 2006, 7, 472−477. (15) Sakakura, T.; Choi, J. C.; Saito, Y.; Sako, T. Synthesis of Dimethyl Carbonate from Carbon Dioxide: Catalysis and Mechanism. Polyhedron 2000, 19, 573−576. (16) Won, W.; Feng, X. Lawless, D. Pervaporation with Chitosan Membranes: Separation of Dimethyl Carbonate/Methanol/Water Mixtures. J. Membr. Sci. 2002, 209, 493−508. (17) Yang, C.; Yin, X.; Ma, S. Organic Salt Effect of Tetramethylammonium Bicarbonate on the Vapor−Liquid Equilibrium of the Dimethyl Carbonate + Methanol System. J. Chem. Eng. Data 2012, 57, 66−71. (18) Zhang, L.; Zhong, Y.; Wang, S.; Zhao, M. Study on Extractive Distillation of Dimethyl Carbonate from Its Azeotrope with Methanol Using Toluene as Extracting Agent. Natural. Gas.Chemical. Industry 2005, 30, 51−54. (19) Zhang, L.; Wang, S.; Zhong, Y.; Li, X. Study on Extractive Distillation of Dimethyl Carbonate from Its Azeotrope with Methanol Using Ethyl Benzene. Chem. Eng. Oil. Gas. 2005, 34, 522−524. (20) Li, Q.; Zhu, W.; Fu, Y.; Wang, H.; Li, L.; Wang, B. Isobaric Vapor-Liquid Equilibrium for Methanol + Dimethyl Carbonate + 1Octyl-3-methylimidazolium Tetrafluoroborate. J. Chem. Eng. Data 2012, 57, 1602−1606. (21) Cai, F.; Wu, X.; Chen, C.; Chen, X.; Asumana, C.; Haque, M. R.; Yu, G. Isobaric Vapor-Liquid Equilibrium for Methanol + Dimethyl Carbonate + Phosphoric-based Ionic Liquids. Fluid Phase Equilib. 2013, 352, 47−53. (22) Chen, X.; Cai, F.; Wu, X.; Asumana, C.; Yu, G. Isobaric VaporLiquid Equilibrium for Methanol + Dimethyl Carbonate + 1-Butyl-3methylimidazolium Dibutylphosphate. J. Chem. Eng. Data 2013, 58, 1186−1192. (23) Li, Q.; Liu, P.; Cao, L.; Wen, F.; Zhang, S.; Wang, B. VaporLiquid Equilibrium for Tetrahydrofuran + Methanol + Tetrafluoroborate-based Ionic Liquids at 101.3 kPa. Fluid Phase Equilib. 2013, 360, 439−444. (24) Stephenson, R. M.; Malanowski, S. Handbook of the Thermodynamics of Organic Compounds; Elsevier: New York, 1978. (25) Steele, W. V.; Chirico, R. D.; Knipmeyer, S. E.; Nguyen, A.; Smith, N. K. Thermodynamic Properties and Ideal-Gas Enthalpies of Formation for Dicyclohexyl Sulfide, Diethylenetriamine, Di-n-octyl Sulfide, Dimethyl Carbonate, Piperazine, Hexachloroprop-1-ene, Tetrakis (dimethylamino)ethylene, N,N′-bis-(2-hydroxyethyl)ethlenediamine, and 1,2,4-Triazolo[1,5-a]pyrimidine. J. Chem. Eng. Data 1997, 42, 1037−1052. (26) Renon, H.; Prausnitz, J. M. Local Compositions in Thermodynamic Excess Functions for Liquid Mixtures. AIChE J. 1968, 14, 135−144. (27) Li, Q.; Cao, L.; Sun, X.; Liu, P.; Wang, B. Isobaric Vapor−Liquid Equilibrium for Ethyl Acetate + Acetonitrile + 1-Butyl-3-methylimidazolium Hexafluorophosphate at 101.3 kPa. J. Chem. Eng. Data 2013, 58, 1112−1116. (28) Li, Q.; Zhu, W.; Wang, H.; Ran, X.; Fu, Y.; Wang, B. Isobaric Vapor−Liquid Equilibrium for the Ethanol + Water + 1,3Dimethylimidazolium Dimethylphosphate System at 101.3 kPa. J. Chem. Eng. Data 2012, 57, 696−700. (29) Jiang, X.; Wang, J.; Li, C.; Wang, L.; Wang, Z. Vapor Pressure Measurement for Binary and Ternary Systems Containing Water Methanol Ethanol and an Ionic Liquid 1-Ethyl-3-ethylimidazolium Diethylphosphate. J. Chem. Thermodyn. 2007, 39, 841−846. (30) Calvar, N.; González, B.; Gómez, E.; Domínguez, Á . Vapor− Liquid Equilibria for the Ternary System Ethanol + Water + 1-Butyl-3methylimidazolium Chloride and the Corresponding Binary Systems at 101.3 kPa. J. Chem. Eng. Data 2006, 51, 2178−2181. (31) Simoni, L. D.; Ficke, L. E.; Lambert, C. A.; Stadtherr, M. A.; Brennecke, J. F. Measurement and Prediction of Vapor−Liquid Equilibrium of Aqueous 1-Ethyl-3-methylimidazolium-based Ionic Liquid Systems. Ind. Eng. Chem. Res. 2010, 49, 3893−3901.

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