Experimental Measurements of Vapor–Liquid Equilibrium Data for the

May 30, 2013 - Experimental Measurements of Vapor–Liquid Equilibrium Data for the Binary Systems of Methanol + 2-Butyl Acetate, 2-Butyl Alcohol + 2-...
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Experimental Measurements of Vapor−Liquid Equilibrium Data for the Binary Systems of Methanol + 2‑Butyl Acetate, 2‑Butyl Alcohol + 2‑Butyl Acetate, and Methyl Acetate + 2-Butyl Acetate at 101.33 kPa Hong-xing Wang,* Jing-jing Xiao, Yan-yi Shen, Chang-shen Ye, Ling Li, and Ting Qiu College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou 350108, Fujian, China ABSTRACT: The isobaric vapor−liquid equilibrium measurements for the systems of 2-butyl acetate with three chemicals (methanol, 2-butyl alcohol, methyl acetate) were determined respectively in a modified Rose still at 101.33 kPa. Thermodynamic consistency of the three binary vapor−liquid equilibrium data had been confirmed by Herington methods. The three groups of experimental data were all correlated with NRTL and Wilson models, respectively. The binary interaction parameters of both models had been obtained by the simplex method. The NRTL and Wilson equations showed low deviation with respect to the experimental data.

1. INTRODUCTION 2-Butyl alcohol is an important chemical raw material which is mainly used to produce methyl ethyl ketone. It also can be used in the production of pesticides, pharmaceutical intermediates, spices, dyes, wetting agents, flotation agents, polymerization additives, rubber additives, and the solubilizers of nitrocellulose lacquer and nitrocellulose lacquer thinner. The usual method of producing 2-butyl alcohol is the hydration of butylene, including indirect hydration under the catalysis of sulfuric acid and direct hydration. There are some drawbacks in these methods. Serious corrosion on equipment and high running costs are the main drawbacks of indirect hydration under the catalysis of sulfuric acid, while the conversion ratio of the feedstock is not high for direct hydration.1−3 Transesterification is known as an alcoholysis reaction where ester and alcohol react under acid or alkali catalyst and generate a new ester and alcohol. It is a reversible reaction.4 The Chemistry Industry Co., Ltd. in china hoped to use the byproduct, 2-butyl acetate (SBAC), to produce 2-butyl alcohol, which will be used to produce methyl ethyl ketone. Therefore, SBAC and methanol were used as raw materials to produce 2-butyl alcohol. In recent years, reactive distillation has been widely used in transesterification.5−7 Combining transesterification with reactive distillation, a new process for production of 2-butyl alcohol was proposed for which a patent had been sought (Chinese patent: CN102731250A) . Preliminary experiments indicated that using continuous reactive distillation to synthesize 2-butyl alcohol had some advantages such as it being a simple process, high conversion, low energy consumption, and noncorrosive, etc. The new synthetic technology of 2-butyl alcohol could be simulated by means of mathematical models before industrial application. An accurate model, based on systematic experiments, associated with accurate vapor−liquid equilibrium (VLE) measurements, can provide an experimental basis for optimizing, designing, © XXXX American Chemical Society

and revamping the separation processes and can effectively reduce the cost. Considering the incomplete reaction of the reactants, there will be SBAC and methanol in the reaction distillation column and separation column system. In open literature, there are isobaric VLE data for these two binary systems: methyl acetate + 2-butyl alcohol8 and methanol + methyl acetate.9−11 The isobaric VLE data of these systems methanol + SBAC, 2-butyl alcohol + SBAC, and methyl acetate + SBAC have not been reported in the literature. Thus, research on VLE data of this system became necessary. The aim of this paper is to measure VLE data for SBAC with methanol, 2-butyl alcohol, and methyl acetate at 101.33 kPa respectively.

2. EXPERIMENTAL SECTION 2.1. Materials. In this paper, all the chemicals were highpurity grade. SBAC had been purified by distillation in order to eliminate the organic impurities. The sources of the materials, purification methods, and final purities were listed in Table 1. The purities of all components were determined by gas chromatography. 2.2. Apparatus and Procedure. The VLE experiments equipment was a modified Rose still in which both gaseous and liquid phases were refluxed. The instrument had been successfully applied in other systems.12,13 A digital thermometer with accuracy of ± 0.05 K was used to measure the equilibrium temperatures. A mercury barometer was used to determinate the pressure in the still. In each experiment, the pressure was controlled at 101.33 kPa which has a small fluctuation, and the maximal absolute deviation was 0.02 kPa. The system was kept at the boiling point for at least 1 h to ensure that equilibrium Received: March 7, 2013 Accepted: May 8, 2013

A

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Table 1. Mass Fraction Purities of Chemical Samples chemical name

source

methanol 2-butyl alcohol methyl acetate 2-butyl acetate ethanol a

Guangzhou Guangzhou Guangzhou Guangzhou Guangzhou

Jinhuada Jinhuada Jinhuada Jinhuada Jinhuada

initial mass fraction

purification method

final mass fraction

analysis methoda

0.997 0.997 0.997 0.986 0.997

none none none distillation none

0.997 0.997 0.997 0.996 0.997

GC GC GC GC GC

Chemistry Chemistry Chemistry Chemistry Chemistry

GC: gas chromatography.

Table 3. Experimental VLE Data for System of 2-Butyl Alcohol (1) + SBAC (2)a at 101.33 kPab

Figure 1. Experimental data and literature data for ethanol (1) + water (2) system at 101.33 kPa: ○, literature data; ■, experimental data.

Table 2. Experimental VLE Data for System of Methanol (1) + SBACa (2) at 101.33 kPab x1,exp

y1,exp

Texp/K

0 0.0079 0.0101 0.0153 0.0285 0.0481 0.0731 0.0897 0.0989 0.1555 0.2520 0.2812 0.3420 0.4395 0.5153 0.5720 0.6450 0.7339 0.7706 0.8422 0.8831 0.9186 1

0 0.0898 0.1299 0.1785 0.2905 0.4089 0.5257 0.5783 0.6125 0.7085 0.7805 0.7951 0.8163 0.8490 0.8647 0.8850 0.8936 0.9075 0.9150 0.9325 0.9485 0.9581 1

385.25 382.35 381.45 379.30 375.05 370.35 365.60 362.85 361.30 355.70 349.15 348.05 346.25 344.53 343.33 342.03 341.10 340.50 339.80 339.45 338.97 338.35 337.65

γ1 2.2324 2.6351 2.5715 2.5939 2.5535 2.5616 2.5372 2.5835 2.3441 2.0489 1.9539 1.7721 1.5399 1.4054 1.3677 1.2728 1.1659 1.1529 1.0928 1.0831 1.0802 1

γ2 1 0.9620 0.9712 0.9931 1.0101 1.0188 1.0030 1.0096 0.9954 1.0004 1.1223 1.1432 1.2122 1.2613 1.3789 1.4078 1.6383 1.9526 2.1495 2.5188 2.6511 3.1848

x1,exp

y1,exp

Texp/K

0 0.1023 0.1305 0.2132 0.2334 0.2583 0.3217 0.3363 0.3768 0.4116 0.4485 0.4974 0.5743 0.5973 0.6499 0.6914 0.7431 0.7701 0.7996 0.8377 0.9100 0.9270 0.9561 0.9766 1

0 0.1867 0.2260 0.3355 0.3562 0.3835 0.4520 0.4638 0.4979 0.5291 0.5603 0.6015 0.6623 0.6788 0.7221 0.7516 0.7902 0.8109 0.8316 0.8641 0.9222 0.9361 0.9611 0.9794 1

385.25 382.05 381.30 379.45 379.05 378.55 377.60 377.45 376.90 376.50 376.05 375.55 374.95 374.70 374.25 373.95 373.65 373.60 373.35 373.10 372.90 372.80 372.70 372.65 372.35

γ1

γ2

1.2105 1.1868 1.1721 1.1570 1.1508 1.1393 1.1263 1.1068 1.0977 1.0896 1.0810 1.0630 1.0600 1.0601 1.0532 1.0472 1.0416 1.0413 1.0468 1.0432 1.0452 1.0474 1.0490

1 1.0249 1.0301 1.0320 1.0386 1.0433 1.0409 1.0451 1.0587 1.0627 1.0717 1.0791 1.0944 1.1075 1.1133 1.1359 1.1583 1.1648 1.1967 1.1970 1.2336 1.2499 1.2634 1.2444 1

a SBAC = 2-butyl acetate. bUncertainties u of pressure p, composition x1,y1, and temperature T are u(p) = ± 0.02 kPa, u(x1) = u(y1) = ± 0.0002, and u(T) = ± 0.05 K.

with 0.5 m film thickness. Nitrogen was the carrier gas. The temperatures of injection port and detector was 523.15 K. The oven temperature was programmed at 333.15 K(for 1 min), then increased to 343.15 K at 2 K min−1, was maintained at 343.15 K for 2 min, and finally increased to 453.15 K at 15 K min−1. Isopropyl alcohol was used as the internal standard. The relationship between mass and peak area was determined for every binary mixture. Each vapor and liquid sample was analyzed at least three times to eliminate the error. The uncertainty of mole fraction was within ± 0.0002. 2.3. Reliability of the Instruments. The standard mixture of ethanol (1) + H2O (2) was selected to verify the reliability of apparatus and accuracy of the experimental method. The VLE data of ethanol + H2O was from Gmehling J.14 The experimental data and literature values for system ethanol + H2O were shown in Figure 1. As shown in Figure 1, the experimental data agreed with the literature values well. Therefore, the apparatus and experimental technique applied in this paper were credible and reliable.

a SBAC = 2-butyl acetate. bUncertainties u of pressure p, composition x1,y1, and temperature T are u(p) = ± 0.02 kPa, u(x1) = u(y1) = ± 0.0002, and u(T) = ± 0.05 K.

state was reached. Samples of equilibrium phases were taken at small volumes and were analyzed by a gas chromatograph. During the analyzing procedure, a flame ionization detector (FID) was used together with a TM-5 capillary column (0.32 mm × 50 m) B

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3. EXPERIMENTAL RESULTS AND DISCUSSION 3.1. Experimental Data. The isobaric VLE data for methanol + SBAC, 2-butyl alcohol + SBAC, and methyl acetate + SBAC at 101.33 kPa were listed in Table 2, Table 3 and Table 4, respectively. The activity coefficients γ for both chemicals were calculated by

j=1

y1,exp

Texp/K

0 0.0122 0.0150 0.0183 0.0263 0.0635 0.0923 0.1713 0.2266 0.3246 0.3275 0.3571 0.3767 0.4029 0.4196 0.4292 0.4814 0.4953 0.4976 0.5588 0.5886 0.6886 0.7438 0.8078 0.8811 0.9311 1

0 0.0769 0.0955 0.1135 0.1578 0.3215 0.4135 0.5911 0.6795 0.7792 0.7828 0.8035 0.8175 0.8286 0.8392 0.8485 0.8755 0.8805 0.8828 0.9065 0.9179 0.9455 0.9565 0.9700 0.9831 0.9905 1

385.25 383.05 382.80 382.10 381.05 376.00 372.50 364.95 360.80 354.75 354.55 353.10 352.05 350.75 349.90 349.30 347.10 346.30 346.25 343.65 342.65 338.90 337.20 335.25 333.20 331.70 329.95

γ1 1.3293 1.3509 1.3388 1.3292 1.2737 1.2338 1.1634 1.1350 1.0813 1.0830 1.0641 1.0589 1.0435 1.0413 1.0481 1.0316 1.0338 1.0331 1.0250 1.0173 1.0110 1.0014 0.9980 0.9940 0.9975 1

N

∑ ∑ yyi j Bij)p/RT ]

(2)

i=1 j=1

where the second virial coefficient of the pure gas Bii and the cross second virial coefficient Bij were calculated by Tsonopoulos.17 pis is the saturated vapor pressure of pure component, which is calculated by Antoine equation as follows:

Table 4. Experimental VLE Data for System of Methyl Acetate(1) + SBAC (2)a at 101.33 kPab x1,exp

N

ϕî = exp[(2 ∑ yj Bij −

log pis /kPa = A − B /(T /K + C)

γ2

(3)

The Antoine equation parameters A, B, C of methanol, 2butyl alcohol, and methyl acetate were listed in Table 5. The saturated vapor pressure of SBAC was obtained by an equation as follows:22

1 1.0049 0.9957 1.0022 0.9943 0.9903 0.9999 1.0104 0.9973 1.0060 1.0022 1.0080 1.0097 1.0467 1.0480 1.0306 1.0273 1.0500 1.0370 1.0601 1.0454 1.0942 1.1518 1.1661 1.1740 1.2366

ln ps = 38.7855 − 6098/T + 4.2398 ln T + 2.1506·10−18T 6

(4)

The application scope of temperature for this equation is from 174.15 K to 561 K. This paper employed a semiempirical method reported by Herington23 to examine the thermodynamic consistency of VLE data for the three systems. The criteria of consistency of this method is that the value of D − J Table 6. Thermodynamics Consistency Check system

D

J

D−J

methanol (1) + SBAC (2) 2-butyl alcohol (1) + SBAC (2) methyl acetate (1) + SBAC (2)

1.38 1.48 0.80

19.51 3.78 23.22

−18.12 −2.30 −22.42

a SBAC = 2-butyl acetate. bUncertainties u of pressure p, composition x1,y1 and temperature T are u(p) = ± 0.02 kPa, u(x1) = u(y1) = ± 0.0002, and u(T) = ± 0.05 K.

V

γi = [ϕî yp /(xiϕispis )] × exp[(p − pis )ViL /RT ] i

(1)

where xi and yi are equilibrium liquid and vapor phase mole fraction of species i, respectively. Liquid molar volumes VLi were calculated by the Rackett equation.15 The critical parameters for pure component used in the Rackett equation are listed in Table5. The Rackett parameter ZRA of a pure component was calculated by the method reported in the literature.16 Fugacity coefficients ϕ̂ Vi and ϕsi were calculated as follows:

Figure 2. Relationship between activity coefficients (ln γ1/γ2) and molar fractions in liquid phase (x1)L: ■, methanol (1) + SBAC (2); ○, 2-butyl alcohol (1) + SBAC (2); ▲, methyl acetate (1) + SBAC (2).

Table 5. Critical Parameters and Antoine’s Constants for Pure Components Antoine constants

a

compound

Tc/K

Pc/MPa

A

B

C

temperature range/K

methyl acetate methanol 2-butyl alcoholb SBAC

506.55a 512.5a 536.2a 561d

4.75a 8.084a 4.202a 3.2d

6.25449b 7.09498b 6.59921c

1189.608b 1521.23b 1314.19c

−50.035b −39.18b −86.6c

260 to 365 338 to 487 298.15 to 393.15

Reference 18. bReference 19. cReference 20. dReference 21. C

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Table 7. Correlated Model Parameters of Activity Coefficient Models and Deviations parameters Δg12a/J·mol−1

model

Δg21b/J·mol−1

NRTL Wilson

2734.7 5104.3

1285.5 −688.5

NRTL Wilson

−662.5 2641.3

1945.5 −1385.3

NRTL Wilson

−1930.9 3768.9

3218.6 −2637.5

deviations α1c

δ(y1)d

Methanol (1) + SBAC (2) 0.3 0.0066 0.0060 2-Butyl Alcohol (1) + SBAC (2) 0.3 0.0022 0.0027 Methyl Acetate (1) + SBAC (2) 0.3 0.0024 0.0022

RMSD(y1)e

δ(T)f

RMSD(T)g

0.0081 0.0071

0.25 0.26

0.29 0.31

0.0031 0.0037

0.05 0.04

0.06 0.05

0.0028 0.0028

0.12 0.10

0.15 0.12

Δg12, interaction parameters for NRTL and Wilson model. bΔg21, interaction parameters for NRTL and Wilson model. cReference 24. dδ(y1) = /n∑n1|y1,exp − y1,cal|. eRMSD(y1) = (∑i n= 1(y1,exp − y1,cal)2/n)1/2. fδ(T1) = 1/n∑n1|Texp − Tcal|. gRMSD(T) = (∑i n= 1(Texp − Tcal)2/n)1/2.

a

1

Figure 4. Experimental and calculated T−x1−y1 diagram for 2-butyl alcohol (1) + SBAC (2) at 101.33 kPa: ■, experimental data for T−x1; ●, experimental data for T−y1; solid blue line, calculated values from NRTL models; red dash dot line, calculated values from Wilson models.

Figure 3. Experimental and calculated T−x1−y1 diagram for methanol (1) + SBAC (2) at 101.33 kPa: ■, experimental data for T−x1; ●, experimental data for T−y1; solid blue line, calculated values from NRTL models; red dash dot line, calculated values from Wilson models.

can not be larger than 10. D and J were obtained by eq 5 and eq 6, respectively. x =1

D = 100

1

2

x1= 1

γ1

1

γ2

∫x = 0 ln J = 150

γ

∫x =1 0 ln γ1 dx1

Tmax − Tmin Tmin

dx1

(5)

(6)

The value of D−J for the three binary system were listed in Table 6. The relationship between the activity coefficients (ln γ1/γ2) and molar fractions in liquid phase (x1) are shown in Figure 2. The figure demonstrates that all the VLE data had passed the thermodynamic consistency test. 3.2. Correlation of VLE Data. In this work, the experimental VLE data were correlated by means of NRTL and Wilson models.24,25 The saturated vapor pressure of pure component were calculated by equation 3 and equation 4, respectively. The binary interaction parameters of both models were obtained by the simplex method based on minimization of the objective function F as follows:26

Figure 5. Experimental and calculated T−x1−y1 diagram for methyl acetate (1) + SBAC (2) at 101.33 kPa: ■, experimental data for T−x1; ●, experimental data for T−y1; solid blue line, calculated values from NRTL models; red dash dot line, calculated values from Wilson models. D

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Figure 8. Experimental and calculated y1−x1 diagram for methyl acetate (1) + SBAC (2) at 101.33 kPa: ■, experimental data; solid blue line, calculated values from NRTL models; red dash dot line, calculated values from Wilson models.

Figure 6. Experimental and calculated y1−x1 diagram for methanol (1) + SBAC (2) at 101.33 kPa: ■, experimental data; solid blue line, calculated values from NRTL models; red dash dot line, calculated values from Wilson models.

calculated values of both models coincide well with the experimental data. The average absolute deviations δ and root-mean-square deviations (RMSD) of the boiling temperature and vapor phase mole fraction are exhibited in Table 7. It is observed that deviations in boiling temperature and vapor phase composition of NRTL and Wilson models are small for the three binary systems; average absolute deviations of both models satisfactorily correlate with the isobaric VLE data. From Figure 3 and Figure 5 we can see that there are no azeotropes for these two binary systems (methanol + SBAC and methyl acetate + SBAC) . Therefore, it is easy to separate methanol and SBAC and methyl acetate and SBAC by distillation. Figure 7 shows that the difference between the gas and liquid phase mole fraction of 2-butyl alcohol becomes reasonably small especially when the liquid mole fraction of 2-butyl alcohol reaches 0.9. These reveal that the separation for 2-butyl alcohol and SBAC will become difficult when the mixture is in high alcohol concentration.

Figure 7. Experimental and calculated y1−x1 diagram for 2-butyl alcohol (1) + SBAC (2) at 101.33 kPa: ■, experimental data; solid blue line, calculated values from NRTL models; red dash dot line, calculated values from Wilson models.

4. CONCLUSIONS Experimental VLE data have been obtained at normal pressure for the three binary systems: methanol + SBAC, 2-butyl alcohol + SBAC, methyl acetate + SBAC. All three binary systems had been demonstrated to satisfy thermodynamic consistency by Herington’s test. Wilson and NRTL equations were selected to correlate the experimental data. For methanol + SBAC, calculated results of Wilson and NRTL equation were basically the same. The calculated results corresponded to the experimental data to a large extent. There were no azeotrope behaviors found in the methanol + SBAC and methyl acetate + SBAC systems. It will be difficult to obtain a high concentration for 2-butyl alcohol from a mixture of 2-butyl alcohol + SBAC system by distillation.

N

F=

∑ (Mi ,exp − Mi ,cal)2 /M2i ,exp i=1

(Mi = T , y)

(7)

The subscript “cal” and “exp” represent the calculated and experimental values, respectively. The correlated binary interaction parameters from experimental data are shown in Table7. α is the constant characteristic of the nonrandomness for the binary systems. We recommend α = 0.3 for the three binary systems as these systems belong to type I according to the definition in the literature.24 Comparison of the experimental data with calculated values for T−x1−y1 are shown in Figure 3, Figure 4, and Figure 5. The equilibrium curves are shown in Figure 6, Figure 7, and Figure 8. In these figures, black solid points represent experimental data, solid blue lines represent calculated data by NRTL model, while red dash dot represent the calculated value by the Wilson model. From Figure 3, Figure 4, Figure 5, Figure 6, Figure 7 and Figure 8, we can see that values calculated by the NRTL model and Wilson model almost totally overlap each other, and



AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] Funding

The authors would like to thank the National Undergraduate Training Programs for Innovation and Entrepreneurship for the financial support (201210386011). E

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Notes

(25) Wilson, G. M. A new expression for the excess free energy of mixing. J. Am. Chem. Soc. 1964, 86, 127−130. (26) Nelder, J.; Mead, R. A simple method for function minimization. Comput. J. 1967, 7, 308−313.

The authors declare no competing financial interest.



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