Isobaric LiquidâLiquid Equilibrium Measurements and

Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Isobaric Liquid−Liquid Equilibrium Measurements and Thermodynamics Modeling for Systems: Benzene + Cyclohexane + DESs at 303.15 and 323.15 K Lanyi Sun,* Fei Luo, Rui Liu, Hao Yang, Liguo Huang, and Jun Li State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, China

J. Chem. Eng. Data Downloaded from pubs.acs.org by UNIV OF NEW ENGLAND on 02/18/19. For personal use only.

S Supporting Information *

ABSTRACT: In this work, three deep eutectic solvents (DESs), which are sulfolane + tetrabutylammonium bromide 3:1 (molar ratio, ST3:1), sulfolane + tetrabutylammonium bromide 7:1 (molar ratio, ST7:1), and ethylene glycol + trimethylamine hydrochloride 5:1 (molar ratio, ET5:1), were prepared and used as extractants for the separation of benzene and cyclohexane mixture by liquid−liquid extraction. Liquid− liquid equilibrium (LLE) data for the three ternary systems of benzene + cyclohexane + DESs were measured at 303.15 and 323.15 K under atmospheric pressure. The Othmer−Tobias equation was used to validate the consistency of the experimental tie-lines data and the regression coefficients R2 were all close to 1. Meanwhile, distribution coefficient (β), selectivity (S), and performance index (PI) were used to evaluate the performance of the three DESs, and the result indicates that the DESs ST3:1 and ST7:1 as extractants are more feasible for the separation of benzene and cyclohexane mixture compared to ET5:1. In addition, the nonrandom two-liquid (NRTL) model was used to correlate the LLE data of the ternary systems, and the binary interaction parameters of the NRTL model were obtained.

1. INTRODUCTION Benzene and cyclohexane are important chemical raw materials in which benzene is feedstock for the production of styrene, phenol, aniline, and so forth, and cyclohexane is mainly used to produce resins, cyclohexanone, and Nylon precursors.1 Currently, industrial cyclohexane is mostly produced by catalytic hydrogenation of benzene. Nonconverted benzene is entrained into the cyclohexane product. To obtain high purity benzene and cyclohexane, it is necessary to separate benzene and cyclohexane mixture.2−4 However, the separation of aromatic and aliphatic compounds has been one of the most challenging and important separation tasks in the petrochemical industry, in which benzene and cyclohexane is the most representative of the two substances due to their close boiling points (only 0.6 K).5 The common methods used to separate benzene and cyclohexane include extractive distillation, azeotropic distillation, and liquid−liquid extraction.6,7 Among these methods, liquid− liquid extraction is the most widely used in the industry because of simple operation, low equipment cost, and low energy consumption.8 The key to liquid−liquid extraction is the selection of extractant. At present, the solvents used for separation of benzene and cyclohexane are mainly organic solvents and ionic liquids. Industrial organic solvents, such as ethylene glycol, tetraethylene glycol, sulfolane, and N-methylpyrrolidone,9−11 have disadvantages of being volatile, toxic, and flammable. In contrast, different types of ionic liquids (ILs) with characteristics of © XXXX American Chemical Society

negligible vapor pressure, high thermal stability, and high solution capacity have been reported as an extractant for benzene and cyclohexane separation,12 such as [bmpy][BF4],13 [C4mim][AlCl4],14 and [C2mim][Ac]15 have been reported for benzene and cyclohexane separation. However, they have disadvantage of toxicity, poor biodegradability, difficulty in synthesis, high cost, which limit their application.16,17 In 2003, Abbott et al.18 proposed a new solvent called deep eutectic solvents (DESs). They have advantages of low cost, simple preparation and good biodegradable and are expected to replace ILs as new solvents.19−21 Salleh et al.22 reported five DESs as extractants in the separation of benzene and cyclohexane in the liquid−liquid extraction at 298.15 K and verified the feasibility of DESs as extractants for the separation. Until now, rare literatures about the liquid−liquid equilibrium (LLE) for the systems of benzene + cyclohexane + DESs at different temperature have been reported. In this work, three DESs, namely sulfolane + tetrabutylammonium bromide 3:1 (molar ratio, ST3:1), sulfolane + tetrabutylammonium bromide 7:1 (molar ratio, ST7:1), and ethylene glycol + trimethylamine hydrochloride 5:1 (molar ratio, ET5:1) were used as extractants for the separation of benzene + cyclohexane mixture. First, LLE data were measured Received: November 2, 2018 Accepted: January 31, 2019

A

DOI: 10.1021/acs.jced.8b01029 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

to stand for 3 h so that the solution in the tank was sufficiently layered. Hence, the phase interface was clearly visible. Finally, the upper and lower balance solutions were separately extracted with a disposable syringe and injected into a small vial for immediate analysis of their composition. 2.3. Analysis. The composition of samples was tested using GC to obtain the mass content of the two liquid phases in the liquid−liquid equilibrium. Since the DESs cannot be analyzed by GC owing to the negligible vapor pressure, it was collected in a precolumn (5 m × 0.25 mm, uncoated fused silica).30 After determining the mass fraction of benzene and cyclohexane in the extract phase and raffinate phase by GC, respectively, the mass fraction of the DESs was determined by the sample mass difference before and after vaporizing the solvents in a drying oven at 373.15 K (±0.1 K).21 Finally, based on the measured results above, the mass fraction of benzene, cyclohexane, and DESs in the extract phase and the raffinate phase can be calculated. Each sample was tested at least 3 times, and the average of the similar data was taken as the final result. Before analyzing the samples, GC was calibrated by an external standard calibration method and the calibration curve was made. Hence, the mass fraction of benzene and cyclohexane was determined using the standard equation. The standard uncertainty in temperature and pressure were 0.1 K and 0.3 kPa, respectively, and the standard uncertainty for the GC analysis for mass fraction of each component was 0.001. The detection conditions of the benzene + cyclohexane + DESs system are shown in Table 2.

at 303.15 and 323.15 K under atmospheric pressure, respectively. Afterward, the Othmer−Tobias equation was used to verify the consistency of the experimental tie-lines data.23,24 Then, the extraction performance of the three extractants were analyzed by the distribution coefficient (β), selectivity (S), and performance index (PI).25,26 Finally, the nonrandom two-liquid (NRTL) thermodynamic model was used to correlate the experimental data.27,28

2. EXPERIMENTAL SECTION 2.1. Chemicals. The chemicals used in this work were benzene, cyclohexane, sulfolane, tetrabutylammonium bromide, ethylene glycol, and trimethylamine hydrochloride that are of high purity (>99 wt %). The detailed information about the chemicals is listed in Table 1. The purity of benzene, Table 1. Reagents Used in Experiment name benzene

CAS no. 71-43-2

cyclohexane

110-82-7

sulfolane

126-33-0

tetrabutylammonium bromide ethylene glycol trimethylamine hydrochloride

1643-19-2 107-21-1 593-81-7

source Shanghai Macklin Biochemical Co., Ltd. Shanghai Macklin Biochemical Co., Ltd. Shanghai Macklin Biochemical Co., Ltd. Shanghai Macklin Biochemical Co., Ltd. Shanghai Macklin Biochemical Co., Ltd. Shanghai Macklin Biochemical Co., Ltd.

purity (wt %) 99.5 99.7 99.4 99.0 99.0 99.0

Table 2. Gas Chromatography Detection Conditions Employed for Benzene + Cyclohexane- DESs System

cyclohexane, sulfolane, and ethylene glycol was checked by gas chromatography (GC, GC9790II, Zhejiang Fuli Analytical Instrument Co., Ltd., China). The results confirmed that the purity of used chemicals was higher than 99 wt %. All chemicals were used without further purification. 2.2. Apparatus and Procedure. The detailed apparatus and methods applied in this work have been presented in previous works,29 and the reliability of the experimental system had been evaluated in the literature.29 A Mettler AX205 balance with precision of ±0.0001 g was used. Both the hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA) were introduced into a closed round-bottom flask at the specified molar ratio. Then, the mixture was heated and stirred at 343.15 K (±0.1 K) for 1 h using a thermostatic oil bath with a temperature controller to form a colorless and transparent liquid. The purity of the three prepared DESs was analyzed using the spectra of 1H NMR, and the results are provided in Figures S1−S3 in the Supporting Information. As seen in Figures S1− S3, no obvious impurity peaks appear, and molar fraction of impurities in the ST3:1, ST7:1, and ET5:1 is less than 0.008. Finally, the prepared DESs were dried in a vacuum oven for 12 h before use to remove the residual volatile impurities of the DESs, and the mass fraction of water in the three DESs was measured by the Karl Fischer titration technique, which is less than 0.0005. Experimental LLE data of the ternary systems benzene + cyclohexane + DESs were experimentally determined at different temperatures under atmospheric pressure. First, 30 g of mixed solution of benzene + cyclohexane at different mass compositions and 30 g of prepared DESs were weighed using the electronic balance and introduced into the liquid−liquid equilibrium tank. The mixed solution was stirred under constant temperature 303.15 and 323.15 K (±0.1 K) for 2 h and allowed

benzene + cyclohexane + DESs systems detection type capillary column column temperature injection temperature detector temperature carrier gas purity flow

FID PEG-20 M 30 m*0.32 mm*0.33 μm 308.15 K 373.15 K 373.15 K N2 99.999 wt % 30 mL/min

3. RESULTS AND DISCUSSION 3.1. Experimental LLE Data. The LLE data for the ternary systems of benzene (1) + cyclohexane (2) + DESs (3) were measured at 303.15 and 323.15 K under 101.32 kPa, which were expressed as mass fraction and listed in Tables 3, 4, and 5. Meanwhile, the ternary phase diagrams of benzene + cyclohexane + DESs at two temperatures are shown in Figures 1, 2, and 3. According to Tables 3, 4,and 5, the prepared DESs were almost exclusively present in the extract phase and no DESs were detected in the raffinate phase, which means that there was no solvent crossing. No additional separation steps is required and the extractants can be recovered by simply evaporating the extract phase, leading to simplify the extraction process. As seen in Figures 1, 2, and 3, there are two miscibility regions in every ternary phase diagram. Also, the slope of the tie-lines for every ternary systems are negative, which indicates that benzene shows a much higher solubility in the extract phase than cyclohexane, and the selectivity of ET5:1 to benzene is larger than that to cyclohexane compared to ST3:1 and ST7:1. Moreover, the widely spaced miscible region demonstrated that B



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Table 3. Experimental Isobaric LLE Data (Mass Fraction) and the Distribution Coefficient (β), Selectivity (S) and Performance Index (PI) for the Ternary System Benzene (1) + Cyclohexane (2) + ST3:1 (3) at Temperature T = 303.15 and 323.15 K under Pressure P = 101.32 kPaa raffinate phase

extract phase

T/K

wI1

wI2

wI3

wII1

wII2

wII3

β

S

PI

303.15

0.0631 0.1346 0.2109 0.2970 0.3859 0.4694 0.5270 0.5675 0.0569 0.1440 0.2151 0.2956 0.3687 0.4609 0.5178 0.5661

0.9369 0.8654 0.7891 0.7030 0.6141 0.5306 0.4730 0.4325 0.9431 0.8560 0.7849 0.7044 0.6313 0.5391 0.4822 0.4339

0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

0.0282 0.0630 0.0996 0.1444 0.1825 0.2375 0.2676 0.3050 0.0231 0.0537 0.0903 0.1300 0.1765 0.2313 0.2691 0.3077

0.0327 0.0371 0.0437 0.0507 0.0561 0.0697 0.0747 0.0828 0.0301 0.0404 0.0498 0.0543 0.0669 0.0837 0.0891 0.0962

0.9391 0.8999 0.8567 0.8048 0.7614 0.6928 0.6577 0.6122 0.9468 0.9060 0.8599 0.8157 0.7566 0.6850 0.6419 0.5961

0.4472 0.4678 0.4722 0.4864 0.4728 0.5060 0.5078 0.5374 0.4066 0.3728 0.4199 0.4398 0.4786 0.5019 0.5196 0.5435

12.8251 10.8974 8.5189 6.7383 5.1763 3.8507 3.2148 2.8074 12.7347 7.9071 6.6168 5.7060 4.5178 3.2344 2.8127 2.4518

5.7353 5.0976 4.0228 3.2774 2.4476 1.9485 1.6326 1.5087 5.1780 2.9475 2.7782 2.5095 2.1624 1.6234 1.4615 1.3326

323.15

a

The superscript I represents the raffinate phase; II represents the extract phase, and the subscripts 1, 2, and 3 represent benzene, cyclohexane, and ST3:1, respectively. Standard uncertainties: u(T) = 0.1 K, u(P) = 0.3 kPa, and u(w) = 0.001.

Table 4. Experimental Isobaric LLE Data (Mass Fraction) and the Distribution Coefficient (β), Selectivity (S) and Performance Index (PI) for the Ternary System Benzene (1) + Cyclohexane (2) + ST7:1 (3) at Temperature T = 303.15 and 323.15 K under Pressure P = 101.32 kPaa raffinate phase

extract phase

T/K

wI1

wI2

wI3

wII1

wII2

wII3

β

S

PI

303.15

0.0619 0.1334 0.2152 0.2987 0.3816 0.4643 0.4931 0.5408 0.0657 0.1374 0.2181 0.2888 0.3778 0.4700 0.5185 0.5662

0.9381 0.8666 0.7848 0.7013 0.6184 0.5357 0.5069 0.4592 0.9343 0.8626 0.7819 0.7112 0.6222 0.5300 0.4815 0.4338

0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

0.0278 0.0619 0.0993 0.1552 0.1838 0.2352 0.2658 0.2990 0.0282 0.0620 0.0962 0.1403 0.1712 0.2232 0.2366 0.2506

0.0220 0.0290 0.0385 0.0501 0.0543 0.0643 0.0699 0.0772 0.0355 0.0389 0.0463 0.0549 0.0600 0.0755 0.0785 0.0765

0.9502 0.9090 0.8622 0.7947 0.7620 0.7004 0.6643 0.6237 0.9363 0.8990 0.8575 0.8048 0.7688 0.7013 0.6849 0.6729

0.4492 0.4642 0.4614 0.5196 0.4816 0.5067 0.5389 0.5530 0.4291 0.4512 0.4412 0.4858 0.4532 0.4748 0.4563 0.4425

19.1658 13.8532 9.4128 7.3915 5.4894 4.2194 3.9074 3.4530 11.3045 9.9953 7.4479 6.2955 5.3590 3.3333 2.7990 2.5089

8.6088 6.4305 4.3427 3.8404 2.6437 2.1378 2.1057 1.9095 4.8511 4.5102 3.2864 3.0584 2.4288 1.5826 1.2772 1.1103

323.15

a

The superscript I represents the raffinate phase; II represents the extract phase, and the subscripts 1, 2, and 3 represent benzene, cyclohexane, and ST7:1, respectively. Standard uncertainties: u(T) = 0.1 K, u(P) = 0.3 kPa, and u(w) = 0.001.

and b are adjustable parameters. The diagrams plotted by the Othmer−Tobias equation for the ternary systems (benzene + cyclohexane + DESs) at 303.15 and 323.15 K are presented in Figure 4. The whole of regression coefficients R2 shown in Figure 4 are more than 0.98, and both plots show nearly linear correlations for every temperature, indicating that the experimental LLE data give a good reliability. The parameters and correlation factors are listed in Table 6. 3.3. Extraction Performance. The feasibility of using a solvent in liquid−liquid extraction are evaluated by the distribution coefficient (β), selectivity (S), and performance index (PI). The β determines the solvent usage for the extraction process and the S determines the product purity and the size of

DESs is suitable for benzene extraction at low benzene mass fraction. In addition, the temperature has a slight effect on the three ternary systems. 3.2. Consistency Test. To confirm the reliability of the ternary LLE data at different temperature in this work, the Othmer−Tobias equation was applied to test the consistency of the experimental tie-lines data, which is shown as follows II y i ij 1 − w2I yz zz = a + b lnjjj 1 − w3 zzz lnjjj zz j z I II j w j w z 2 3 k { { k

(1)

where wI2 and wII3 represent the mass fractions of cyclohexane in the raffinate phase and DESs in the extract phase, respectively. a C



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Table 5. Experimental Isobaric LLE Data (Mass Fraction) and the Distribution Coefficient (β), Selectivity (S) and Performance Index (PI) for the Ternary System Benzene (1) + Cyclohexane (2) + ET5:1 (3) at Temperature T = 303.15 and 323.15 K under Pressure P = 101.32 kPaa raffinate phase

extract phase

T/K

wI1

wI2

wI3

wII1

wII2

wII3

β

S

PI

303.15

0.0936 0.1940 0.2867 0.3925 0.5154 0.6010 0.6438 0.6884 0.0898 0.1911 0.2780 0.3822 0.4851 0.5952 0.6345 0.6954

0.9064 0.8060 0.7133 0.6075 0.4846 0.3990 0.3562 0.3116 0.9102 0.8089 0.7220 0.6178 0.5149 0.4048 0.3655 0.3046

0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

0.0109 0.0147 0.0196 0.0254 0.0287 0.0311 0.0327 0.0381 0.0221 0.0356 0.0404 0.0465 0.0505 0.0598 0.0660 0.0687

0.0039 0.0036 0.0029 0.0028 0.0023 0.0020 0.0017 0.0017 0.0115 0.0073 0.0058 0.0048 0.0037 0.0033 0.0035 0.0030

0.9851 0.9817 0.9775 0.9718 0.9690 0.9669 0.9656 0.9601 0.9664 0.9571 0.9538 0.9488 0.9458 0.9370 0.9305 0.9283

0.1169 0.0758 0.0683 0.0648 0.0557 0.0517 0.0508 0.0554 0.2460 0.1864 0.1453 0.1215 0.1040 0.1004 0.1040 0.0987

27.0001 17.1382 16.9302 14.2288 11.6650 10.3167 10.6746 9.9235 19.4591 20.7880 17.9600 15.7774 14.5033 12.4577 10.7185 9.9236

3.1554 1.2997 1.1564 0.9221 0.6493 0.5334 0.5425 0.5499 4.7875 3.8756 2.6092 1.9176 1.5090 1.2510 1.1144 0.9799

323.15

a

The superscript I represents the raffinate phase; II represents the extract phase, and the subscripts 1, 2, and 3 represent benzene, cyclohexane, and ET5:1, respectively. Standard uncertainties: u(T) = 0.1 K, u(P) = 0.3 kPa, and u(w) = 0.001.

Figure 1. Ternary phase diagrams for benzene + cyclohexane + ST3:1: (■−■), experimental tie-lines data; (△--△), correlated results using the NRTL model. (a) T = 303.15 K, (b) T = 323.15 K.

where w1 and w2 represent the mass fractions of benzene and cyclohexane, respectively, and superscripts I and II indicate the raffinate phase and extract phase, respectively. The calculated values of the β, S, and PI are listed in Tables 3, 4, and 5. The β, S, and PI versus the benzene mass content in the raffinate phase are shown in Figures 5, 6, and 7. As seen in Figure 5, the values of the distribution coefficient for every ternary systems are less than 1, which implies only a small amount of benzene is extracted from the mixture of benzene and cyclohexane. Thus, this will lead to larger amount of the DESs needs for the separation of benzene and cyclohexane. It is worth noting that the distribution coefficients of the ternary systems benzene + cyclohexane + ST3:1 and benzene + cyclohexane + ST7:1 increase with the increase of

the extractor. In addition, the PI is introduced and defined as the product of the distribution coefficient and selectivity, which indicates the overall extraction efficiency of a solvent. The β, S, and PI are expressed as follows β=

w1II w1I

(2)

w1II

S=

w2II w1I w2I

PI = β*S

(3) (4) D



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Figure 2. Ternary phase diagrams for benzene + cyclohexane + ST7:1: (■−■), experimental tie-lines data; (△--△), correlated results using the NRTL model. (a) T = 303.15 K, (b) T = 323.15 K.

Figure 3. Ternary phase diagrams for benzene + cyclohexane + ET5:1: (■−■), experimental tie-lines data; (△--△), correlated results using the NRTL model. (a) T = 303.15 K, (b) T = 323.15 K.

finding is the differences in interaction of benzene and the DESs sulfolane + tetrabutylammonium bromide and ethylene glycol + trimethylamine hydrochloride. Benzene have polar surface segments because of electron density both above and below the plane of benzene ring, which can interact with the many polar surface segments in DES,6 and temperature affects the hydrogen bonding interaction between the hydrogen bond donor and the hydrogen bond acceptor in DESs.31,32 Therefore, the electrostatic interaction of the ET5:1 with benzene may be increased relative to hydrogen bonding interaction at higher temperature when the concentration of benzene in the raffinate phase is greater than 0.16 compared to the ST3:1 and ST7:1. For the separation of benzene and cyclohexane, a high distribution coefficient for benzene and a reasonable selectivity are key factors in selecting a suitable extractant. Therefore, from Figures

benzene mass content in raffinate phase, which is opposite to that of benzene + cyclohexane + ET5:1 system. This may be due to the differences in affinity of DESs to the benzene/ cyclohexane. Figure 5 also shows that the lower temperature can lead to the increase of the distribution coefficient of the two ternary systems containing ST3:1 and ST7:1. Figure 6 shows that the values of the selectivity are greater than 1, which indicates the feasibility of the three DESs as solvents for the separation of benzene and cyclohexane. It is worth noting that when the mass fraction of benzene in the raffinate phase is less than 0.16, the selectivity of ET5:1 at 303.15 K is greater than that at 323.15 K, which is consistent with ST3:1 and ST7:1. But when the concentration of benzene in the raffinate phase is greater than 0.16, the selectivity of ET5:1 at 303.15 K is less than that at 323.15 K. The reason for this E



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Figure 5. Distribution coefficient (β) for the three ternary systems: benzene + cyclohexane + ST3:1 (■, 303.15 K; □, 323.15 K), benzene + cyclohexane + ST7:1 (●, 303.15 K; ○, 323.15 K), and benzene + cyclohexane + ET5:1 (▲, 303.15 K; △, 323.15 K).

Figure 6. Selectivity (S) for the three ternary systems: benzene + cyclohexane + ST3:1 (■, 303.15 K; □, 323.15 K), benzene + cyclohexane + ST7:1 (●, 303.15 K; ○, 323.15 K), and benzene + cyclohexane + ET5:1 (▲, 303.15 K; △, 323.15 K).

Figure 4. Othmer−Tobias plots of the ternary systems: (a) benzene + cyclohexane + ST3:1 (■, 303.15 K; ●, 323.15 K), (b) benzene + cyclohexane + ST7:1 (■, 303.15 K; ●, 323.15 K), and (c) benzene + cyclohexane + ET5:1 (■, 303.15 K; ●, 323.15 K).

Table 6. Adjustable Parameters of the Othmer−Tobias Equation and Regression Coefficients for the Ternary Systems system

T/K

a

b

R2

benzene + cyclohexane + ST3:1

303.15 323.15 303.15 323.15 303.15 323.15

−0.7375 −0.6784 −0.6912 −0.8413 −3.4744 −2.7817

0.7657 0.8301 0.8454 0.7065 0.3226 0.2495

0.996 0.991 0.9966 0.9946 0.9841 0.9834

benzene + cyclohexane + ST7:1 benzene + cyclohexane + ET5:1

Figure 7. Performance index (PI) for the three ternary systems: benzene + cyclohexane + ST3:1 (■, 303.15 K; □, 323.15 K), benzene + cyclohexane + ST7:1 (●, 303.15 K; ○, 323.15 K), and benzene + cyclohexane + ET5:1 (▲, 303.15 K; △, 323.15 K).

F



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Table 7. Binary Interaction Parameters of NRTL Model and RMSD Values for the Benzene (1) + Cyclohexane (2) + DESs (3) Ternary Systems binary interaction parameters T/K

i-j

303.15

323.15

303.15

323.15

303.15

323.15

aij

1−2 1−3 2−3 1−2 1−3 2−3

−32.9205 41.7213 40.8832 −30.4923 39.3376 38.9197

1−2 1−3 2−3 1−2 1−3 2−3

−32.6063 41.3746 40.9548 −30.6111 39.4519 38.8822

1−2 1−3 2−3 1−2 1−3 2−3

51.7722 −20.1664 20.9204 −28.0843 −22.5068 −18.3555

aji

bij

Benzene (1)−Cyclohexane (2)−ST3:1 (3) 33.0613 10000 −32.4833 −10000 −29.6407 −10000 30.6869 10000 −30.1772 −10000 −27.4216 −10000 Benzene (1)−Cyclohexane (2)−ST7:1 (3) 32.8256 10000 −32.4627 −10000 −29.2612 −10000 31.3006 10000 −39.7339 −10000 −27.5712 −10000 Benzene (1)−Cyclohexane (2)−ET5:1 (3) −31.9106 −10000 35.5591 8260.96 38.04 −3863.91 −32.1837 −10000 31.9269 10000 34.3272 8290.13

∑j τjiGjixj ∑k Gkixk

τij = aij +

bij T

+

∑ j

ij y jjτ − ∑l τljGljxl zzz jj ij z ∑k Gkjxk zz ∑k Gkjxk j k {

2

(5)

(6)

0.0024

0.31

0.0024

0.3

0.0023

0.3

0.0033

0.3

0.0026

0.2

0.0045

(8)

4. CONCLUSIONS In this work, three DESs (ST3:1, ST7:1, and ET5:1) were studied as extractants for the separation of benzene and cyclohexane. The experimental LLE tie-lines data for the ternary systems were measured at 303.15 and 323.15 K under 101.32 kPa and tested by the Othmer−Tobias equation. The experimental data successfully passed the thermodynamic consistency test. In addition, the extraction performance for the three ternary systems were evaluated by distribution

3

exp cal 2 OF = min ∑ ∑ ∑ (wijk − wijk ) k=1 j=1 i=1

10000 −10000 −10000 10000 −10000 −10000

0.29

where w is the mass fraction and n is the number of tie-lines. Table 7 shows the binary interaction parameters for benzene− cyclohexane−DESs ternary system and the values of RMSD at two temperatures. The values of the mass-based RMSD between the experimental and calculated are no more than 0.0045, which indicates the NRTL model was successfully applied to correlate the experimental LLE data for benzene−cyclohexane−DESs. Therefore, the binary interaction parameters of the NRTL model can be used for the extraction process simulation at different temperatures. Figures 1, 2 and 3 show the ternary phase diagrams for benzene + cyclohexane + DESs at two temperatures, which were used to compare the experimental data and the calculated results obtained by the NRTL model, indicating that the calculated results by the NRTL model are in good agreement with the experimental LLE data.

where xi represents mole fraction of the component; aij and bij are the binary interaction parameters needed to be regressed; The nonrandom parameter αij is in the range of 0.2 to 0.5.27 By adjusting the quantity of the nonrandom parameter (αij), the value of the root-mean-square deviation (RMSD) was minimized,33,34 and the binary interaction parameter was predicted. To reflect the difference between the experimental and calculated equilibrium data, the objective function (OF) is defined as follows n

−10000 10000 10000 −10000 1619.85 10000

RMSD

1/2 l n 2 3 (w exp − w cal)2 | o o o o ijk ijk o o RMSD = m } ∑∑∑ o o o o 6n ok=1 j=1 i=1 o n ~

Gijxj

Gij = exp( −αijτij)

−100000 10000 10000 −10000 10000 10000

α

where n represents the number of tie-lines, wexp and wcal are the experimental mass fraction and the calculated mass fraction, respectively. The subscripts k, j, and i are the component, the phase and the tie-line, respectively. The root-mean-square deviation (RMSD) value was adopted to evaluate the quality of correlation, which is as follows

5 and 6, the ST3:1 and ST7:1 as extractants are better than ET5:1. From Figure 7, the performance indexes of the two ternary systems containing ST3:1 and ST7:1 are greater than that of the benzene + cyclohexane + ET5:1. Furthermore, when the benzene mass fraction in the raffinate phase is less than 20%, the values of the performance index for every ternary system increase dramatically with the decrease of benzene in raffinate phase, especially for the ternary system benzene + cyclohexane + ST7:1 at 303.15 K. Therefore, solvents have better separation for benzene of low concentrations. 3.4. Data Correlation. In this work, the NRTL activity coefficient model was used to correlate the experimental LLE data of the benzene-cyclohexane- DESs ternary system, which is expressed as follows ln γi =

bji

(7) G



Article

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coefficient (β), selectivity (S), and performance index (PI), which indicates that the DESs ST3:1 and ST7:1 as extractants are more feasible for the separation of benzene and cyclohexane mixture compared to ET5:1. In addition to the DES ET5:1, low temperature is beneficial to the extraction process. Meanwhile, the NRTL model was applied to correlate experimental LLE data and the binary interaction parameters were obtained successfully.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b01029.

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Additional figures(PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +86 13854208340. Fax: +86 0532 86981787. ORCID

Lanyi Sun: 0000-0002-3158-6388 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grant 21878333 and Grant 21676299). Finally the authors are grateful to the editor and the anonymous reviewers.

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REFERENCES

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