Vapour-liquid equilibrium measurements and extractive distillation process design for separation of azeotropic mixture (dimethyl carbonate + ethanol)

Vapour-liquid equilibrium measurements and extractive distillation process design for separation of azeotropic mixture (dimethyl carbonate + ethanol)

Accepted Manuscript Vapor–liquid equilibrium measurements and extractive distillation process design for separation of azeotropic mixture (dimethyl ac...

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Accepted Manuscript Vapor–liquid equilibrium measurements and extractive distillation process design for separation of azeotropic mixture (dimethyl acetate + ethanol) Kai Liu, Zhaojie Wang, Yi Zhang, Dongmei Xu, Jun Gao, Zhun Ma, Yinglong Wang PII: DOI: Reference:

S0021-9614(18)31122-4 https://doi.org/10.1016/j.jct.2019.01.027 YJCHT 5702

To appear in:

J. Chem. Thermodynamics

Received Date: Revised Date: Accepted Date:

6 November 2018 19 January 2019 29 January 2019

Please cite this article as: K. Liu, Z. Wang, Y. Zhang, D. Xu, J. Gao, Z. Ma, Y. Wang, Vapor–liquid equilibrium measurements and extractive distillation process design for separation of azeotropic mixture (dimethyl acetate + ethanol), J. Chem. Thermodynamics (2019), doi: https://doi.org/10.1016/j.jct.2019.01.027

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Vapor–liquid equilibrium measurements and extractive distillation process design for separation of azeotropic mixture (dimethyl acetate + ethanol) Kai Liu a, Zhaojie Wang a, Yi Zhang a, Dongmei Xu a, Jun Gao* a, Zhun Ma a, Yinglong Wang b a

College of Chemical and Environmental Engineering, Shandong University of Science and

Technology, Qingdao 266590, China b

College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao

266042, China *Corresponding authors E-mail addresses: [email protected]

Abstract: Dimethyl carbonate and ethanol can form an azeotrope with the minimum boiling point. To separate the azeotrope (dimethyl carbonate + ethanol) by extractive distillation, p-xylene, butyl propionate, and isobutyl acetate were chosen as entrainers, and the isobaric vapor-liquid equilibrium (VLE) data for the binary systems of (dimethyl carbonate + p-xylene), (dimethyl carbonate + butyl propionate), (dimethyl carbonate + isobutyl acetate) and (ethanol + isobutyl acetate) were measured at 101.3kPa using a modified Rose type recirculating still. The thermodynamic consistency of the VLE experimental data for the four binary mixtures were tested by the Herington and van Ness methods. Furthermore, the measured VLE data were correlated by the NRTL, UNIQUAC and Wilson thermodynamic models and the binary interaction parameters of the three models were regressed. Based above, an extractive distillation process with the entrainer of p-xylene was proposed and simulated to separate the azeotrope (dimethyl carbonate + ethanol). Keywords: Vapor-liquid equilibrium; Azeotrope; Extractive distillation; Dimethyl acetate.

1

1. Introduction Dimethyl carbonate (DMC) is an environmentally benign chemical product [1], which is widely used in production of pesticides, medicines [2] and polymer synthesis, and can be used as fuel additives [3] and solvents [4]. Meanwhile, DMC is also an important raw material for preparation of a variety of high value-added special fine chemicals [5]. For synthesis of diethyl carbonate or methyl ethyl carbonate by transesterification, dimethyl carbonate and ethanol are used as raw materials [6]. However, since the reaction is reversible, the reactive distillation technology is required to improve the reaction yield. Therefore, the efficient separation of DMC and ethanol is involved in the process. DMC and ethanol can form the lowest azeotrope, which is difficult to separate by conventional distillation. Thus, special distillations are considered to separate such azeotropic mixture, such as extractive distillation [7], reactive distillation [8], azeotropic distillation [9]. In this work, the extractive distillation was applied for separation of the azeotropic mixture of DMC and ethanol. For separation of the azeotrope of DMC and ethanol by extractive distillation, a suitable solvent is needed to enhance the relative volatility [10] of DMC to ethanol. According to the standard for the selection of entrainers proposed by Gmehling and Möllmann [11], p-xylene, isobutyl acetate and butyl propionate were considered as the entrainer candidates for separation of the azeotropic mixture (DMC + ethanol). In the literatures, few researchers have reported the VLE data for the system of (DMC + ethanol). Oh et.al. [12] measured the isothermal VLE data for (DMC + ethanol) at 333.15 K by headspace gas chromatography (HSGC). Fukano et.al. [13] reported the boiling point data of three binary systems (methanol + ethanol + DMC) under different pressure. Zhao and Yang [14] determined the VLE data for (DMC + ethanol) at 100 kPa using a double cycle vapor-liquid equilibrium still. And the vapor-liquid equilibrium data for the binary system (DMC + ethanol) at 101.3 kPa were reported by Luo et. al. [15]. However, the isobaric VLE data for the binary systems of DMC with p-xylene, isobutyl acetate, butyl propionate and ethanol with isobutyl acetate have not been found in the NIST [16] and Dortmund Data Bank (DDB) [17]. 2

The main contents of this work are as follows: (1) the isobaric VLE data for four binary systems (DMC + p-xylene), (DMC + butyl propionate), (DMC+ isobutyl acetate) and (ethanol + isobutyl acetate) under pressure of 101.3 kPa were determined using a modified Rose type recirculating still; (2) two thermodynamic consistency tests of Herington [18] and van Ness [19] were adopted to check the consistency of the measured VLE data; (3) the VLE data were correlated by the NRTL [20], UNIQUAC [21] and Wilson [22] activity coefficient models and the binary interaction parameters of the three models were regressed; (4) the excess Gibbs energy of the four binary systems were calculated based on the measured VLE data and (5) an extractive distillation process for separating the azeotrope (DMC + ethanol) was developed. 2. Experimental 2.1. Chemicals DMC, ethanol, p-xylene, isobutyl acetate and butyl propionate used in this work were analytical reagents and purchased commercially. The boiling temperatures of the pure component were measured and compared with the literature data. The CAS numbers, suppliers, mass fraction, boiling temperatures are listed in Table 1. Table 1 The CAS numbers, mass fraction purity and boiling temperature (Tb) of the chemicals. Tb/K b

Mass Component

CAS

DMC

616-38-6

Ethanol

64-17-5

P-xylene

106-42-3

Isobutyl acetate 110-19-0

Butyl propionate 590-01-2

Suppliers Shandong Xiya Chemical Co., Ltd. Yantai Far Eastern Fine Chemical Co., Ltd. Tianjin Kemiou Chemical Reagent Co., Ltd. Shandong Xiya Chemical Co., Ltd. Aladdin reagent (Shanghai) Co., Ltd.

3

Analysis

fraction

exp

lit

method

≥0.995

363.35

363.24 [23] 363.35 [24] 363.39 [13]

GCa

≥0.997

351.45

351.44 [13] 351.45 [25] 351.41 [26]

GCa

≥0.990

411.45

411.51 [27] 411.23 [28] 411.45 [9]

GCa

≥0.990

389.55

389.75 [29] 389.85 [30] 389.37 [31]

GCa

>0.990

418.35

418.69 [32] 418.07 [33] 418.69 [34]

GCa

a

Gas chromatograph. The experimental pressure for the measurement of boiling temperature is 101.3 kPa, the standard uncertainties u of P and T are u(P)=0.12 kPa, u(T)=0.12 K. b

2.2. Apparatus and procedure The VLE data for the binary systems (DMC + p-xylene), (DMC + isobutyl acetate), (DMC + butyl propionate) and (ethanol + isobutyl acetate) were measured at pressure of 101.3 kPa using a modified Rose type recirculating equilibrium still [35]. During the measurement, Both the vapor and liquid phases were consecutively recycled which made the two phases fully contact intimately. To reach the equilibrium state, the temperature of the system was kept constant for 60 min. Meanwhile, the vapor and liquid samples were withdrawn by syringe for analysis, respectively. The detailed descriptions of the apparatus can be found in the previous literatures [36-38]. 2.3. Analysis The compositions of the samples from the vapor and liquid phases were analyzed by GC (Lunan Rui Hong SP6890), which was connected to a thermal conductivity detector (TCD). A packed column (PorapaQ, 3mm × 2 m) was used. The carrier gas was high purity hydrogen (99.999 wt%) and the flow rate was 50 mL·min-1. The temperatures of the detector, injector and column were set at 473.15 K, 473.15 K, and 463.15 K, respectively. The compositions of the samples were determined by the area correction normalization method [39]. Before analyzing the compositions of the samples, the GC was calibrated by the standard samples prepared by a AR1140 electronic balance (Ohaus Corporation) with a precision of ± 0.0001 g. The equilibrium temperature was measured by a mercury thermometer with a precision of ± 0.1 K. 3. Results and discussion 3.1. Experimental results In this work, the isobaric VLE data for binary systems (DMC + p-xylene), (DMC + isobutyl acetate), (DMC + butyl propionate) and (ethanol + isobutyl acetate) were determined at 101.3 kPa. The experimental VLE data, the calculated activity coefficients and excess Gibbs energy (GE) for four binary mixtures are listed in Tables 4

2-5. The T-x-y phase diagrams for four binary systems are plotted in Figures 1-4. For the system (DMC + p-xylene), the measured VLE data at 101.3 kPa were compared with those reported by Yadav et al. at 93.13 kPa [40] as shown in Figure 1. From Figure 1, the reference data at 93.13 kPa show deviations from the measured VLE data at 101.3 kPa in this work, which may be due to the difference of the VLE apparatus. In the meantime, the reference data at 93.13 kPa were predicted by the NRTL, UNIQUAC and Wilson models with the binary parameters regressed from the measured VLE data in this work. Also, for the system (ethanol + isobutyl acetate), the measured VLE data at 101.3 kPa were compared with those reported by Susial et al. at 600 kPa [41] as shown in Figure 4. In Figure 4, the reference data at 600 kPa show deviations from the measured VLE data at 101.3 kPa in this work, which may be due to the difference of the VLE apparatus and pressure. Meanwhile, the VLE data reported by Susial et al. at 600 kPa were predicted by the NRTL, UNIQUAC and Wilson models with the binary parameters regressed from the measured VLE data in this work. The results showed that the Wilson model could correlate well the reference data at 600 kPa compared to the NRTL and UNIQUAC models. Table 2 Experimental VLE data for the binary system of DMC (1) + p-xylene (2), liquid mole fraction (x), vapor mole fraction (y), activity coefficient (γ) and Gibbs energy (GE) at 101.3 kPa a.

a

T/K

x1

y1

γ1

γ2

GE/J·mol-1

366.65 370.05 372.95 377.25 380.65 384.45 387.65 391.05 394.65 398.25 401.05 403.25 405.65 407.95

0.8276 0.7037 0.6075 0.4878 0.4007 0.3192 0.2637 0.2102 0.1608 0.1197 0.0897 0.0675 0.0429 0.0240

0.9399 0.8899 0.8517 0.7909 0.7355 0.6730 0.6160 0.5532 0.4728 0.3880 0.3157 0.2542 0.1831 0.1129

1.0242 1.0267 1.0427 1.0617 1.0893 1.1241 1.1397 1.1705 1.1889 1.1929 1.2052 1.2205 1.3024 1.3569

1.3767 1.3053 1.2024 1.1262 1.0906 1.0517 1.0339 1.0114 1.0087 1.0051 1.0032 1.0029 1.0012 1.0009

228.25 300.02 303.11 282.51 273.08 229.12 190.33 136.67 115.19 84.77 65.40 54.19 42.12 27.77

Standard uncertainties u of T, P, x and y are u(T) = 0.12 K, u(P) = 0.12 kPa, u(x) = 0.0026, u(y) = 5

0.0025.

Table 3 Experimental VLE data for the binary system of DMC (1) + isobutyl acetate (2), liquid mole fraction (x), vapor mole fraction (y), activity coefficient (γ) and Gibbs energy (GE) at 101.3 kPa a. T/K

x1

y1

γ1

γ2

GE/J·mol-1

365.25 366.85 368.25 370.25 371.85 374.35 376.25 378.45 380.35 382.75 384.20 385.55 387.55

0.8504 0.7411 0.6647 0.5568 0.4886 0.3901 0.3202 0.2420 0.1905 0.1208 0.0908 0.0657 0.0296

0.9203 0.8629 0.8190 0.7492 0.6963 0.6102 0.5401 0.4561 0.3834 0.2804 0.2250 0.1704 0.0861

1.0195 1.0434 1.0572 1.0858 1.0953 1.1156 1.1373 1.1916 1.2048 1.2978 1.3299 1.3407 1.4219

1.1698 1.0985 1.0676 1.0456 1.0401 1.0303 1.0249 1.0125 1.0115 1.0079 1.0033 1.0026 1.0005

121.15 170.33 180.34 201.87 199.70 189.45 181.09 163.06 141.53 122.24 92.41 69.51 34.98

a

Standard uncertainties u of T, P, x and y are u(T) = 0.12 K, u(P) = 0.12 kPa, u(x) = 0.0026, u(y) = 0.0025. Table 4 Experimental VLE data for the binary system of DMC (1) + butyl propionate (2), liquid mole fraction (x), vapor mole fraction (y), activity coefficient (γ) and Gibbs energy (GE) at 101.3 kPa a.

a

T/K

x1

y1

γ1

γ2

GE/J·mol-1

366.85 370.75 374.10 377.95 381.75 385.45 389.45 393.35 397.05 400.35 404.05 407.85 411.45 414.95

0.8550 0.7049 0.6041 0.5062 0.4216 0.3493 0.2738 0.2138 0.1629 0.1245 0.0882 0.0589 0.0360 0.0161

0.9649 0.9247 0.8901 0.8435 0.7941 0.7411 0.6751 0.6083 0.5381 0.4690 0.3901 0.2971 0.1999 0.0992

1.0113 1.0425 1.0586 1.0692 1.0835 1.0999 1.1451 1.1899 1.2536 1.3137 1.4053 1.4598 1.4728 1.5064

1.3249 1.2020 1.1536 1.1430 1.1213 1.1015 1.0809 1.0576 1.0389 1.0283 1.0110 1.0059 1.0045 1.0009

153.80 257.80 283.01 313.77 317.42 308.17 303.13 265.61 227.08 194.40 134.33 94.32 62.52 25.68

Standard uncertainties u of T, P, x and y are u(T) = 0.12 K, u(P) = 0.12 kPa, u(x) = 0.0026, u(y) = 0.0025. 6

Table 5 Experimental VLE data for the binary system of ethanol (1) + isobutyl acetate (2), liquid mole fraction (x), vapor mole fraction (y), activity coefficient (γ) and Gibbs energy (GE) at 101.3 kPa a. T/K

x1

y1

γ1

γ2

GE/J·mol-1

354.65 357.35 359.75 361.85 364.25 367.25 370.05 373.25 375.85 378.35 381.45 384.05 387.25

0.8254 0.7025 0.6051 0.5257 0.4451 0.3580 0.2762 0.2072 0.1500 0.1097 0.0671 0.0399 0.0153

0.9423 0.8922 0.8452 0.8001 0.7475 0.6767 0.6011 0.5159 0.4398 0.3647 0.2691 0.1865 0.0809

1.0082 1.0118 1.0167 1.0253 1.0365 1.0478 1.0932 1.1201 1.2074 1.2597 1.3724 1.4738 1.5084

1.0631 1.0543 1.0454 1.0418 1.0335 1.0306 1.0253 1.0206 1.0115 1.0101 1.0049 1.0020 1.0005

51.44 71.14 82.49 97.92 103.67 110.17 131.28 123.11 118.61 107.71 81.99 55.36 21.78

a

Standard uncertainties u of T, P, x and y are u(T) = 0.12 K, u(P) = 0.12 kPa, u(x) = 0.0026, u(y) = 0.0025.

FTGURE 1. T-x-y diagram for the binary system DMC (1) + p-xylene (2) at 101.3 kPa and 93.13 kPa; ●, T-x, experimental values; ○, T-y, experimental values; —, calculated by the NRTL model; ---, calculated by the UNIQUAC model; , calculated by the Wilson model; ▲, T-x, literature 7

values at 93.13kPa [40]; △, T-y, literature values at 93.13 kPa [40]; the red line, calculated by the NRTL model at 93.13 kPa with the regressed parameters; the green line, calculated by the UNIQUAC model at 93.13 kPa with the regressed parameters; the blue line, calculated by the Wilson model at 93.13 kPa with the regressed parameters.

FTGURE 2. T-x-y diagram for the binary system DMC (1) + butyl propionate (2) at 101.3 kPa: ●, T-x experimental values; ○, T-y experimental values; —, calculated by the NRTL model; ---, calculated by the UNIQUAC model; , calculated by the Wilson model.

8

FIGURE 3. T-x-y diagram for the binary system DMC (1) + isobutyl acetate (2) at 101.3 kPa: ●, T-x experimental values; ○, T-y experimental values; —, calculated by the NRTL model; ---, calculated by the UNIQUAC model; , calculated by the Wilson model.

FIGURE 4. T-x-y diagram for the binary system ethanol (1) + isobutyl acetate (2) at 101.3 kPa and 600 kPa; ●, T-x, experimental values; ○, T-y, experimental values; —, calculated by the NRTL model; ---, calculated by the UNIQUAC model; , calculated by the Wilson model; ▲, T-x, literature values at 600 kPa [41]; △, T-y, literature values at 600 kPa [41]; the red line, calculated 9

by the NRTL model at 600 kPa with the regressed parameters; the green line, calculated by the UNIQUAC model at 600 kPa with the regressed parameters; the blue line, calculated by the Wilson model at 600 kPa with the regressed parameters.

3.2. VLE calculation The VLE relationship can be expressed as follows [42]: (1) where P and T represent the system pressure (101.3 kPa) and temperature;

is the

saturated vapor pressure of pure component i at the equilibrium temperature T; the fugacity coefficient of component i in the vapor phase mixture;

is the fugacity

coefficient at the equilibrium temperature and the saturation vapor pressure; activity coefficient of component i; i;

and

is

is the

is the liquid molar volume of pure component

stand for the mole fraction of component i in the liquid phase and in the

vapor phase, respectively; R is the universal gas constant and its value is 8.314 JK-1mol-1. Since the pressure of the VLE experiment is 101.3 kPa, which belongs to low pressure, the vapor phase can be regarded as an ideal gas, so the Poynting factor and

are approximately equal to 1. Thus, Eq. (1) is simplified as [43]: (2)

where the value of

can be calculated by the following extended Antoine

expression: (3) For pure component i, the Antoine parameters from

to

are listed in Table

6, which were obtained directly from the Aspen databank [44]. Table 6. Parameters of the extended Antoine equation a Component

C1i

C2i

C3i

C4i

C5i

C6i (×10-6)

C7i

C8i/K

C9i/K

DMC

46.5201

-5991.3

0

0

-5.097

1.340×10-11

6.0

0

274.9

10

a

ethanol

61.7911

-7122.3

0

0

-7.142

2.885

2.0

-114. 1

240.9

butyl propionate

59.7151

-7709.8

0

0

-6.842

6.359×10-12

6.0

-89.5

321.5

p-xylene

77.2071

-7741.2

0

0

-9.869

6.077

2.0

13.3

343.1

Isobutyl acetate

60.7971

-6944.3

0

0

-7.298

3.789

2.0

-98.9

287.7

Taken from Aspen Property Databank [44].

The activity coefficient

for four binary systems can be calculated by Eq. (2),

and the values are given in Tables 2-5. Meanwhile, the relative volatility (α) for four binary mixtures (DMC + p-xylene), (DMC + isobutyl acetate), (DMC + butyl propionate) and (ethanol + isobutyl acetate) were calculated using the following equation [45]: (4) where x represents the mole fraction in the liquid phase and y represents the mole fraction in the vapor phase. The relative volatilities of the binary systems are shown in Figure 5. As illustrated in Figure 5, the values of relative volatility of the systems (DMC + p-xylene), (DMC + butyl propionate) and (DMC + isobutyl acetate) are all greater than 1, which indicates that DMC and the entrainers can be separated by conventional distillation. Meanwhile, the relative volatility values of the binary system (DMC + butyl propionate) are greater than those of the systems (DMC + p-xylene), (DMC + isobutyl acetate), which means that butyl propionate is a suitable entrainer compared with p-xylene and isobutyl acetate.

11

FIGURE 5. Diagram of

vs.

for the binary systems at 101.3 kPa: ○, DMC (1) + ethanol

(2), the data from the literature [46]; ▼, DMC (1) + p-xylene (2); ●, DMC (1) + butyl propionate (2); ▲, DMC (1) + isobutyl acetate (2); ■, ethanol (1) + isobutyl acetate (2); the solid line is the trend line.

To assess the non-ideality of the binary systems, the excess Gibbs energy (GE) was calculated as follows: (5) where the activity coefficients

was calculated based on the NRTL model. The

calculation results of excess Gibbs energy (GE) for four binary systems are listed in Tables 2-5 and plotted in Figure 6. As shown in Figure 6, the values of GE of the binary systems (DMC + p-xylene), (DMC + butyl propionate), (DMC + isobutyl acetate), and (ethanol + isobutyl acetate) are positive and show a maximum point. Thus, the four binary systems present positive deviations from Raoult’s law.

12

FIGURE 6. Experimental excess Gibbs energy for the four binary systems at 101.3 kPa: ■, DMC (1) + p-xylene (2); ●, DMC (1) + butyl propionate (2); ▽, DMC (1) + isobutyl acetate (2); △, ethanol (1) + isobutyl acetate (2), the solid line is the trend line.

3.3. Thermodynamic consistency test In this work, the Herington and van Ness methods were applied to test the consistency of the measured VLE data for four binary systems. The Herington test [18] method can be defined as follows: (6) (7) where

is the algebraic sum of the surface area contained in the curve vs

which is plotted in Figure 7;

contained in the curve

vs. ;

and

is the total surface area are the highest and lowest

boiling points of the system, respectively; 150 is the empirical constant, which was obtained by Herington after analyzing the typical mixed data of organic solutions. The values of

for the binary systems (DMC + p-xylene), (DMC + butyl

propionate), (DMC + isobutyl acetate) and (ethanol + isobutyl acetate) are listed in 13

Table 7, which are all less than 10. All results show that the experimental VLE values are consistent thermodynamically. Table 7 Thermodynamic consistency check by the Herington test (D and J defined variables in the test). Binary system

D

J

|D-J| < 10

DMC (1) + p-xylene (2)

27.9643

19.6092

8.3551

DMC (1) + butyl propionate (2)

17.8438

22.7054

4.8616

DMC (1) + isobutyl acetate (2)

20.4276

10.8161

9.6115

Ethanol (1) + isobutyl acetate (2)

18.5895

16.2612

2.3283

FIGURE 7.

γ γ

vs. x1 plot: □, DMC (1) + p-xylene (2); ▲, DMC (1) + butyl propionate

(2); ●, DMC (1) + isobutyl acetate (2); ▽, ethanol (1) + isobutyl acetate (2).

The van Ness test [19,35] is defined as: (8) (9) where N is the point of the experimental values, fraction of component i in vapor phase,

refers to the experimental mole

refers to the calculated mole fraction of 14

component i in the vapor phase by the NRTL model, pressure,

refers to experimental

refers to the calculated pressure by the NRTL models. If the

calculated values of Δy and ΔP are both less than 1, the determined VLE data are able to pass the thermodynamic consistency test. All results of the thermodynamic consistency test are presented in Table 8. As illustrated in Table 8, the calculated values of Δy and ΔP the systems are less than 1, indicating that the determined VLE data are consistent thermodynamically. Table 8 Thermodynamic consistency check by the van Ness test (ΔP and Δy defined variables in the test). Binary System DMC (1) + p-xylene (2) DMC (1) + butyl propionate (2) DMC (1) + isobutyl acetate (2) Ethanol (1) + isobutyl acetate (2)

ΔP

Δy

0.0545 0.0382 0.0201 0.0214

0.3579 0.2637 0.1423 0.1299

3.4 VLE data correlation The measured experimental VLE data for four binary mixtures (DMC + butyl propionate), (DMC + p-xylene), (DMC + isobutyl acetate) and (ethanol + isobutyl acetate) were correlated by the NRTL [20], UNIQUAC [21]and Wilson [22] activity coefficient models. The non-randomness parameter (

) was set at 0.3 for the NRTL

model as recommended by Renon and Prausnitz [47]. For the UNIQUAC model, the structural parameters r (van der Waals volume of molecular) and q (van der Waals surface area of molecular) are listed in Table 9. Table 9 Van der Waals volume (r) and surface area (q) of the components for the UNIQUAC equation. a Component DMC Ethanol Butyl propionate Isobutyl acetate P-xylene a

r

q

3.048 2.105 5.502 4.827 4.658

2.816 1.972 4.736 4.192 3.536

Taken from Aspen property databank [44]. 15

To correlate the measured VLE data and optimize the binary interaction parameters of the three models, the objective function is defined as follows: (10) where N refers to the experimental data points,

refers to the standard deviation; T

and P stand for the equilibrium temperature and pressure, respectively; the superscripts “exp” represents the experimental values, the superscripts “cal” represents the calculated values;

and

represent the liquid and vapor phase

mole fraction of component i, respectively. To evaluate the difference between the experimental and the calculated results, the root-mean-square deviations (RMSD) [48] of vapor phase mole fraction and temperature were calculated, which are defined as follows: (11) (12) The regressed interaction parameters of the NRTL, UNIQUAC, Wilson models for four binary mixtures and the values of RMSD are listed in Table 10. As illustrated in Table 10, the values of

and

are less than 0.0064 and 0.29,

respectively, which indicates that the NRTL, UNIQUAC and Wilson activity coefficient models can be applied to correlate the VLE data for four binary mixtures.

16

Table 10 Binary interaction parameters of the NRTL, UNIQUAC and Wilson models, and root-mean-square deviations (RMSD) of vapor mole fraction ( ) and boiling temperature (T) for the four binary systems. Model

a

NRTL UNIQUAC b Wilson c

NRTL UNIQUAC Wilson

NRTL UNIQUAC Wilson

NRTL UNIQUAC Wilson a

NRTL,

b

UNIQUAC,

c

Wilson,

Parameters

RMSD

0.8583 22.2738 7.1908

DMC (1) + p-xylene (2) -4.7936 -235.59 1822.83 -5.7356 -2119.74 1768.10 7.3182 2855.85 -2594.78

0.0039 0.0052 0.0064

0.17 0.16 0.19

-3.8053 22.4079 -28.9897

DMC (1) + butyl propionate (2) -3.9679 1538.60 1886.11 -6.4884 -2226.66 2125.43 4.0197 3156.39 -1382.43

0.0033 0.0052 0.0047

0.18 0.29 0.24

-0.9686 20.2739 12.6938

DMC (1) + isobutyl acetate (2) 4.6822 530.74 -1706.22 -2.4290 -1784.27 1020.48 5.2966 1412.00 -2391.47

0.0018 0.0045 0.0039

0.11 0.15 0.14

-0.5858 22.2330 10.9896

Ethanol (1) + isobutyl acetate (2) 6.5265 320.21 -2492.05 -7.8770 -2144.65 2596.73 1.4095 1123.04 -364.43

0.0019 0.0034 0.0022

0.12 0.22 0.13

, the value of

was set at 0.3 for the four binary systems.

. .

4. Extractive distillation process design 4.1 Comparison of the entrainer effects The effect of the entrainers (p-xylene, butyl propionate and isobutyl acetate) added into the azeotrope system (DMC + ethanol) is shown in Figure 8. As shown in Figure 8, after adding the entrainers, the azeotropic point of (DMC + ethanol) can be effectively eliminated. Compared with the three entrainers, the deviation degree of p-xylene from diagonal line is the greatest, indicating that the azeotrope system is easier to be separated after adding p-xylene. Hence, p-xylene was chosen to be an entrainer to design an extractive distillation process for separating the azeotrope 17

(DMC + ethanol).

FIGURE 8. Influence on VLE data for the system of DMC (1) + ethanol (2) with different entrainers: -▲-, experimental value without entrainers; —, calculated by the NRTL model with p-xylene; , calculated by NRTL model with butyl propionate; ---, calculated by NRTL model with isobutyl acetate.

4.2 Extractive distillation process design The flow diagram of separating azeotrope (DMC + ethanol) by extractive distillation with p-xylene as an entrainer is shown in Figure 9, which was simulated by Aspen Plus. The separation process consists of an extractive distillation column (EDC) and a solvent recovery column (SRC). The mixture (DMC + ethanol) was fed into the EDC at the stage 51, while the entrainer (p-xylene) was added into the EDC at the stage 27. Ethanol (stream D1) with the purity of 99.9% was obtained from the top of the EDC. The mixture (DMC + p-xylene) from the bottom of EDC were fed into the SRC. In the SRC, DMC (stream D2) was separated from the top with the purity of 99.9%. The entrainer p-xylene was recovered from the bottom of the SRC and recycled to the EDC after being cooled. A fresh p-xylene stream was applied to make up the minor loss of p-xylene in the EDC and SRC. The simulated results of all 18

the streams are presented in Table 11. From Table 11, the azeotrope (DMC + ethanol) can be separated by extractive distillation using p-xylene as the entrainer.

FIGURE 9. Flow diagram for the separation process of the mixture (DMC + ethanol) by adding p-xylene as entrainer.

Table 11 The information of all the streams for the extractive distillation process. Streams F S D1 B1 D2 R M

Mole flow/(kmol·h-1)

Mole fraction

DMC

Ethanol

P-xylene

DMC

Ethanol

P-xylene

50.000 0.020 0.013 50.007 49.987 0.020 0.000

50.000 trace 49.970 0.003 0.030 trace 0.000

0.000 200.000 0.037 199.963 0.020 199.942 0.058

0.5000 100 PPM 252 PPM 0.2000 0.9990 100 PPM 0.0000

0.5000 trace 0.9990 119 PPM 593 PPM trace 0.0000

0.0000 0.9999 748 PPM 0.7999 407 PPM 0.9999 1.0000

5. Conclusions In this work, p-xylene, butyl propionate and isobutyl acetate were chosen as the entrainers to separate the azeotrope (DMC + ethanol). The isobaric experimental VLE data for the binary mixtures of (DMC+ p-xylene), (DMC + butyl propionate), (DMC + isobutyl acetate) and (ethanol + isobutyl acetate) were determined at 101.3 kPa by a 19

modified Rose-type still. Both the Herington and van Ness tests were used to test the thermodynamic consistency of the experimental data. The calculated results show that the binary VLE data are consistent thermodynamically. Meanwhile, the experimental isobaric VLE data for four binary mixtures were correlated by the three activity coefficient models of NRTL, UNIQUAC and Wilson. The values of RMSD for the temperature and the vapor-phase compositions are less than 0.29 K and 0.0064, respectively. The three selected entrainers had significant effect on the phase behavior of the azeotropic mixture (DMC + ethanol). The relative volatility of DMC to ethanol was enhanced with the addition of the entrainers. The three entrainers can break the azeotropic point of the mixture (DMC + ethanol). Compared to the entrainers of butyl propionate and isobutyl acetate, p-xylene is the best entrainer for separating the azeotrope (DMC + ethanol) by extractive distillation. Based on above, the extractive distillation process for the separation of the azeotrope (DMC + ethanol) was proposed and simulated.

Acknowledgement This work was supported by the National Natural Science Foundation of China (Grant 21878178),

Shandong

Provincial

Key

Research

&

Development

Project

(2018GGX107001) and the Project of Shandong Province Higher Educational Science and Technology Program (J18KA072).

20

References: [1]

A.K.

Das,

B.N.

Rajasekhar,

Experimental

and

computational

VUV

photoabsorption study of dimethyl carbonate: A green solvent. J. Quant. Spe. Ra. 217 (2018) 116-125. [2] P. Tundo, M. SELVA, The Chemistry of Dimethyl Carbonate. Acc. Chem. Res. 35 (2002) 706-716. [3] S.H. Pyo, J.H. Park, T.S. Chang, Dimethyl carbonate as a green chemical. C. O. G. Sus. Chem. 5 (2017) 61-66. [4] X.W. Liu, D.M. Xu, J. Gao, L.Z. Zhang, Separation of Dimethyl Carbonate and Methanol by Deep Eutectic Solvents: Liquid−Liquid Equilibrium Measurements and Thermodynamic Modeling. J. Chem. Eng. Data 63 (2018) 1234-1239. [5] P. Wang, D.M. Xu, J Gao, L.Z Zhang, Separation of azeotrope (ethanol and ethyl methyl carbonate) by different imidazolium-based ionic liquids: Ionic liquids interaction analysis and phase equilibrium measurements. J. Mol. Liq. 261 (2018) 89-95. [6] I. Z. Nadolska, K. Warmuzinski, J. Richter, Zeolite and other heterogeneous catalysts for the transesterification reaction of dimethyl carbonate with ethanol. Catal. Today 114 (2006) 226–230. [7] J.Y. Wu, D.M. Xu, P.Y. Shi, J. Gao, L.Z. Zhang, Separation of azeotrope (allyl alcohol + water): Isobaric vapour-liquid phase equilibrium measurements and extractive distillation. J. Chem. Thermodynamics. 118 (2018) 139-146. [8] M. Banchero, G. Gozzelino, Reactive distillation in the intensification of oleic acid esterification with methanol - A simulation case-study. J. Ind. Eng. Chem. 20 (2014) 4242-4249. [9]

P.Y.

Shi,

Y.C.

Gao,

D.M.

Xu,

J.

Gao,

Separation

of

azeotrope

(2,2,3,3-tetrafluoro-1-propanol + water): Isobaric vapour-liquid phase equilibrium measurements and azeotropic distillation. J. Chem. Thermodynamics. 115 (2017) 19-26. [10] Y.C. Dong, C.N. Dai, Z.G. Lei, Extractive distillation of methylal/methanol mixture using ethylene glycol as entrainer. Fluid Phase Equilib. 462 (2018) 172-180. [11] J. Gmehling, C. Möllmann, Synthesis of Distillation Processes Using Thermodynamic Models and the Dortmund Data Bank. Ind. Eng. Chem. Res. 37 (1998) 3112-3123. [12] J.H. Oh, S.J. Park, Measurement and Correlation of Vapor-Liquid Equilibria at T = 333.15 K and Excess Molar Volumes at T = 298.15 K for Ethanol + Dimethyl 21

Carbonate (DMC), DMC + 1-Propanol, and DMC + 1-Butanol. J. Chem. Eng. Data 51 (2006) 1852-1855. [13] M. Fukano, K. Kurihara, K. Ochi, Ebulliometric Determination of Vapor-Liquid Equilibria for Methanol + Ethanol + Dimethyl Carbonate. J. Chem. Eng. Data 51 (2006) 1458-1463. [14] X. Zhao, Y. Yang, R. Guo, Isobaric vapor-liquid equilibrium of dimethyl carbonate-ethanol system. Chem. Eng. 38 (2010) 54-56. [15] H.P. Luo, J.H. Zhou, W.D. Xiao, Isobaric Vapor-Liquid Equilibria of Binary Mixtures Containing Dimethyl Carbonate under Atmospheric Pressure. J. Chem. Eng. Data 46 (2002) 842-845. [16] The NIST Bank, the National Institute of Standards and Technology, NIST. http://trc.nist.gov/thermolit/main/home.html [17] J. Gmehling, U. Onken. Dortmund Data Bank (DDB), the University of Dortmund. http://www.ddbst.com/ddb.html [18] E.F.G. Herington, Tests for the consistency of experimental isobaric vapour-liquid equilibrium data. J. Inst. Petrol. 37 (1951) 457-470. [19] H.C. van Ness, S.M. Byer, R.E. Gibbs, Vapour-liquid equilibrium: Part I. An appraisal of data reduction methods. AIChE J. 19 (1973) 238-244. [20] H. Renon, J.M. Prausnitz, Local Compositions in thermodynamic excess functions for liquid mixtures. AIChE J. 14 (1968) 135-144. [21] D.S. Abrams, J.M. Prausnitz, Statistical thermodynamics of liquid mixtures: a new expression for the excess Gibbs energy of partly or completely miscible systems. AIChE J. 21 (1975) 116-128. [22] G.M. Wilson, Vapour-liquid equilibrium. XI. A new expression for the excess free energy of mixing. J. Am. Chem. Soc. 86 (1964) 127-130. [23] E. Romano, J.L. Trenzado, E. González, J.S. Matos, Thermophysical properties of four binary dimethyl carbonate + 1-alcohol systems at 288.15-313.15 K. Fluid Phase Equilib. 211 (2003) 219-240. [24] Y.H. Shi, H.L. Liu, K. Wang, Measurements of isothermal vapor–liquid equilibrium of binary methanol/dimethyl carbonate system under pressure. Fluid Phase Equilib. 234 (2005) 1-10. [25] E. Gonzhlez, J. Ortega, Densities and Isobaric Vapor-Liquid Equilibria of Butyl Esters (Methanoate to Butanoate) with Ethanol at 101.32 kPa. J. Chem. Eng. Data 40(1995) 1178-1183. [26] Z.P. Xing, Y.J. Gao, H. Ding, Isobaric vapor–liquid equilibrium for ternary 22

system of ethanol, ethylropionate and para-xylene at 101.3 kPa. Chin. J. Chem. Eng. 26(2018) 560-565. [27] B.M. Yang, H. Wan, G.F. Guan, Investigation on Isobaric Vapour-Liquid Equilibrium for 1-Butanol + Ethylbenzene + o-Xylene + m-Xylene + p-Xylene. J. Chem. Eng. Data 57 (2012) 18-25. [28] M.C. Sa´nchez-Russinyol, A. Aucejo, S. Loras, Isobaric Vapor-Liquid Equilibria for Binary and Ternary Mixtures of Ethanol, Methylcyclohexane, and p-Xylene. J. Chem. Eng. Data 49(2004) 1258-1262. [29] Y.C. Gao, L. Xu, D.M. Xu, J. Gao, Measurement and Correlation of Isobaric Vapor-Liquid Equilibrium for Binary Systems of Allyl Alcohol with Isobutyl Acetate, Butyl Acetate, and Butyl Propionate at 101.3 kPa. J. Chem. Eng. Data 63 (2018) 845-852. [30] J.B. Mont´on, R. Mu˜noz, M.C. Burguet, Isobaric vapor–liquid equilibria for the binary systems isobutyl alcohol + isobutyl acetate and tert-butyl alcohol + tert-butyl acetate at 20 and 101.3 kPa. Fluid Phase Equilib. 227(2005) 19-25. [31] C. . S nchez,

. . S nchez, I.D. Gil, Vapor−Liquid Equilibrium for Binary

Mixtures of Acetates in the Direct Esterification of Fusel Oil. J. Chem. Eng. Data 62(2017) 11-19. [32] E. Lladosa, J.B. Monton, M.C. Burguet, R. Mu oz, Isobaric vapor-liquid equilibria for binary and ternary mixtures of dipropyl ether, 1-propyl alcohol, and butyl propionate. J. Chem. Eng. Data 51 (2006) 2233-2238. [33] J. Ortega, F. Espiau, M. Postigo, Vapor-Liquid Equilibria at 101.32 kPa and Excess Properties of Binary Mixtures of Butyl Esters + tert-Butyl Alcohol. J. Chem. Eng. Data 50(2005) 444-454. [34] R. Mu˜noz, J.B. Mont´on, M.C. Burguet, Vapor–liquid equilibria in the ternary system isobutyl alcohol + isobutyl acetate + butyl propionate and the binary systems isobutyl alcohol + butyl propionate, isobutyl acetate + butyl propionate at 101.3 kPa. Fluid Phase Equilib. 238(2005) 65-71. [35] J. Gao, L.W. Zhao, L.Z. Zhang, D.M. Xu, Isobaric vapour-liquid equilibrium for binary

systems

of

2,2,3,3-tetrafluoro-1-propanol

+

2,2,3,3,4,4,5,5-octafluoro-1-pentanol at 53.3, 66.7, 80.0 kPa. J. Chem. Eng. Data 61 (2016) 3371-3376. [36] Z.Y. Zhu, Y.X. Ma, J. Gao, Isobaric vapour-liquid equilibria for binary systems of acetic acid + benzene, chloroacetic acid + benzene, and dichloroacetic acid + benzene at 101.33kPa, J. Chem. Eng. Data 55 (2010) 3387-3390. 23

[37] J. Gao, H. Li, D.M. Xu, L.Z. Zhang, Isobaric vapour–liquid equilibrium for binary systems of thioglycolic acid with water, butyl acetate, butyl formate, and isobutyl acetate at 101.3 kPa. J. Chem. Eng. Data 62 (2017) 355-361. [38] X.J. Huang, S.Q. Xia, P.S. Ma, S. Song, B.J. Ma, Vapour-liquid equilibrium of N-formyl morpholine with toluene and xylene at 101.33 kPa. J. Chem. Eng. Data 53 (2008) 252-255. [39] J. Gao, D.R. Guan, D.M. Xu, L.Z. Zhang, Z.S. Zhang, Measurement and modeling of liquid-liquid equilibrium for the systems vinyl acetate + acetic acid / ethanol + water at 298.15 and 308.15 K. J. Chem. Eng. Data 62 (2017) 1240-1246. [40] S.S. Yadav, N. . Mali, S.S. Joshi, Isobaric Vapor−Liquid Equilibrium Data for the Binary Systems of Dimethyl Carbonate with Xylene Isomers at 93.13 kPa. J. Chem. Eng. Data 62 (2017) 2436-2442. [41] P. Susial, J.C. Apolinario, Isobaric VLE at 0.6 MPa for binary systems Isobutyl Acetate + Ethanol, + 1-Propanol or + 2-Propanol. Fluid Phase Equilib. 331 (2012) 12-17. [42] J.M. Smith, N.H.C. Van, M.M. Abbott, Introduction to Chemical Engineering Thermodynamics, sixth ed., McGraw-Hill, New York, 2001. [43] Y.X. Ma, J. Gao, M Li, Z.Y. Zhu, Isobaric vapour–liquid equilibrium measurements and extractive distillation process for the azeotrope of (N, N-dimethylisopropylamine + acetone). J. Chem. Thermodynamics. 122 (2018) 154-161. [44] Aspen Plus Software, Version 7.3; Aspen Technology, Inc.: Burlington, MA, 2001. [45] Y.C. Dong, C.N. Dai, Z.G. Lei, Extractive distillation of methylal / methanol mixture using the mixture of dimethylformamide (DMF) and ionic liquid as entrainers. Fuel 216 (2018) 503-512. [46] A. Rodriguez, J. Canosa, J. Tojo, Vapour–liquid equilibria of dimethyl carbonate with linear alcohols and estimation of interaction parameters for the UNIFAC and ASOG method. Fluid Phase Equilib. 201 (2002) 187-201. [47] H. Renon, J.M. Prausnitz, Local compositions in thermodynamic excess functions for liquid mixtures. AIChE J. 14 (1968) 135-144. [48] L. Xu, D.M. Xu, P.Y. Shi, J. Gao, Salts effect on isobaric vapor-liquid equilibrium for separation of the azeotropic mixture allyl alcohol + water, Fluid Phase 24

Equilib. 457 (2018) 11-17.

25

Highlights 1. The entrainers P-xylene, butyl propionate and isobutyl acetate were selected for separation of the azeotrope DMC and ethanol. 2. The VLE data for the systems (DMC + p-xylene), (DMC + butyl propionate), (DMC + isobutyl acetate) and (ethanol + isobutyl acetate) were measured. 3. The measured VLE data were correlated by the NRTL, UNIQUAC and Wilson models. 4. The extractive distillation process for separating the azeotrope DMC and ethanol was proposed.

26