Experimental Isobaric Vapor Liquid Equilibrium for Binary Systems

Article pubs.acs.org/jced

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

Experimental Isobaric Vapor Liquid Equilibrium for Binary Systems Diethylene Glycol Dibenzoate + Diethylene Glycol, Diethylene Glycol Dibenzoate + Octyl Benzoate, and Ternary System Diethylene Glycol Dibenzoate + Diethylene Glycol + Octyl Benzoate at 1.0152 kPa

J. Chem. Eng. Data Downloaded from pubs.acs.org by WASHINGTON UNIV on 09/20/18. For personal use only.

Lu Li, Qiujie Wu, Kuanhuai Wu, Haitao Wang, Yanmei Zheng,* and Qingbiao Li Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People’s Republic of China ABSTRACT: Diethylene glycol dibenzoate (DEDB) is nowadays considered as one of the most promising environment-friendly plasticizers. Isobaric vapor−liquid equilibrium (VLE) data were measured for the binary systems diethylene glycol dibenzoate (DEDB) (1) + diethylene glycol (2), DEDB (1) + octyl benzoate (2) and ternary system DEDB (1) + diethylene glycol (2) + octyl benzoate (3) at 1.0152 kPa using a modified Othmer still, which enriched the basic data for DEDB. The UNIFAC model, Wilson model, and NRTL model were used to predict the VLE data of the binary and ternary systems. The comparison reveals that on average the most accurate VLE predictions are obtained with the NRTL model.

1. INTRODUCTION DEDB is a kind of environment-friendly plasticizer which can have direct contact with food as packaging materials, potential completely substituting dioctyl phthalate (DOP) and dibutyl phthalate (DBP) as primary plasticizer in terms of performance and safety.1−3 DEDB as a plasticizer is gradually receiving tremendous attention both from industry and academic because of its good compatibility, low volatility, good resistance to oil, water, light, pollution, and environmental friendliness.4 Much of the research in the last two decades has been carried out in the synthesis of DEDB plasticizer and the most common synthetic method is the transesterification of octyl benzoate with diethylene glycol.5−7 In this synthesis, octyl benzoate with diethylene glycol are usually used as solvents. Reactive distillation is a practical way of improving reaction rate and separating the reaction products. VLE data of the DEDB (1) + diethylene glycol (2) + octyl benzoate (3) system are vital for the simulation and design of a reactive distillation. Unfortunately, information related to VLE involving DEDB, diethylene glycol, and octyl benzoate are scarce in the open literature. In this work, the VLE data of DEDB (1) + diethylene glycol (2), DEDB (1) + octyl benzoate (2) and DEDB (1) + diethylene glycol (2) + octyl benzoate (3) was measured and the thermodynamic correlation model of the system was investigated, which provided a valuable calculation method for industrial design. © XXXX American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Experimental Chemicals. Apart from diethylene glycol dibenzoate (DEDB) and octyl benzoate, the other reagents are of analytical grade. The materials and reagents used in the experiment and the physical properties of the reagents are listed in Table 1 and Table 2, respectively. 2.2. Apparatus and Procedure. A modified Othmer still8 was used in the measurement of the isobaric VLE data. The equilibrium still was equipped with a temperature tube at the top and heat-conduction oil inside of it. The thermometer was Table 1. Experimental Materials and Reagents reagent

CAS No.

specification

diethylene glycol octyl benzoate

111-46-6

AR, ⩾99%

Xilong Chemical Co., Ltd.

manufacturer

94-50-8

standard, ⩾96%

diethylene glycol dibenzoate

120-55-8

standard, ⩾97%

Hubei Tuochukangyuan Pharmaceutical Chemical Co., Ltd. TCI (Shanghai) Development Co., Ltd.

Received: June 4, 2018 Accepted: September 10, 2018

A

DOI: 10.1021/acs.jced.8b00460 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 2. Physical Properties of the Reagentsa molecular formula

M (g·mol−1)

ρ (g·cm−3)

Tb (K)

DEDB

C18H18O5

314.34

1.183

diethylene glycol octyl benzoate

C4H10O3

106.12

1.106

509.1 (0.667 kPa) 518.15

C15H22O2

234.33

0.9614

593.85

reagent

Table 3. Isobaric VLE Data for the Binary Systems of DEDB (1) + Diethylene Glycol (2) and DEDB (1) + Octyl Benzoate (2) at 1.0152 kPaa DEDB (1) + diethylene glycol (2)

a

Taken from SciFinder Scholar.

immersed in the heat-conduction oil with the mercury part submerged and the accuracy of the temperature measurement was 0.1 K. The still was in vacuum state inside and wrapped with absorbent cotton insulation outside. The still could be filled with 40 mL of liquid. However, because of the large viscosity of DEDB, bubble is difficult to leave the liquid, which often leads to a rush of the vapor−liquid mixture to the top of the equilibrium chamber. Therefore, only 30 mL of the liquid mixture was added to the still in the experiment to avoid the liquid entering the connecting pipe. The system was in vacuum state and the pressure was measured by a mercury-containing U-tube differential pressure gauge. During the heating process, the wire valve on the buffer tank was adjusted manually to maintain relative stability of the pressure. The system was connected to the vacuum pump, so two-stage condensation was used to avoid part of the vapor being drawn out of the system before being condensed. Otherwise, the materials will pollute the pump oil and shorten pump life. Whereas the loss of material from the system will also reduce the accuracy of experiment. Ice water was used as first-class condensate with a temperature of about 273.15 K, and the condenser was connected to the ground joint of equilibrium still. The second condenser was operated with cooling brine at a temperature of about 263.15−278.15 K. The data in the whole concentration range were difficult to be measured because of the particularity of the systems containing DEDB. When x1 < 0.9 (x1 being DEDB), serious bumping would occur, leading to inaccurate VLE data. On the other hand, the VLE data was measured to simulate the reactive distillation process for DEDB synthesis. The DEDB purity requirement in this process is 0.98, so the lack of data in the concentration range x1 < 0.9 has little effect on the usefulness of the data. 2.3. Sample Analysis. All the samples were analyzed with a gas chromatograph (GC-9160, Ohua, China) and the data were processed by the chromatographic workstation. The GC was equipped with a flame ionization detector (FID) and a SE-30 polar capillary column (30 m × 0.52 mm × 0.5 μm). Nitrogen was used as the carrier gas at a constant flow of 4 mL/min. The injection volume was 0.6 μL and split ratio was 50:1. The temperature of sample injector and detector were 553.15 and 573.15 K, respectively. The column temperature was 373.15 K, hold 2 min, 9 K/min increasing to 553.15 K, and maintained at 553.15 K for 2 min.

DEDB (1) + octyl benzoate (2)

T/K

x1

y1

x1

y1

506.93 507.68 508.28 508.82 509.35 509.55 509.76 509.95 510.38 510.85 511.35

0.9046 0.9243 0.9343 0.9470 0.9573 0.9637 0.9793 0.9842 0.9906 0.9992 1

0.1215 0.2834 0.3678 0.4826 0.5752 0.6375 0.7785 0.8277 0.8975 0.9827 1

0.9350 0.9466 0.9573 0.9652 0.9719 0.9757 0.9846 0.9925 0.9948 0.9971 1

0.08527 0.2354 0.3784 0.4915 0.5785 0.6398 0.7575 0.8724 0.9052 0.9462 1

a Standard uncertainties u are u(T) = 0.2 K, u(P) = 0.05 kPa, and u(x1) = u(y1) = 0.005.

Table 4. Isobaric VLE Data for the Ternary System of DEDB (1) + Diethylene Glycol (2) + Octyl Benzoate (3) at 1.0152 kPaa T/K

x1

x2

y1

y2

506.27 506.78 507.34 507.53 507.82 508.14 508.22 508.39 508.41 508.62 508.66 508.87 509.27 509.47 509.76 509.91 510.48 510.74

0.9253 0.9162 0.9283 0.9362 0.9435 0.9579 0.9489 0.9548 0.9584 0.9627 0.9622 0.9742 0.9727 0.9763 0.9825 0.9847 0.9926 0.9957

0.0286 0.0694 0.0584 0.0472 0.0431 0.0033 0.0351 0.0329 0.0312 0.0282 0.0311 0.0041 0.0249 0.0217 0.0145 0.0117 0.0053 0.0032

0.0427 0.1134 0.2253 0.2744 0.3725 0.3902 0.3947 0.4826 0.5026 0.5498 0.5766 0.6158 0.6925 0.7466 0.7965 0.7996 0.9054 0.9365

0.3085 0.6821 0.5894 0.4890 0.4176 0.0162 0.3468 0.3296 0.3430 0.3256 0.3222 0.0419 0.2657 0.2390 0.1698 0.1349 0.0626 0.0377

a

Standard uncertainties u are u(T) = 0.2 K, u(P) = 0.05 kPa, and u(x1) = u(y1) = u(x2) = u(y2) = 0.005.

3.2. Data Processing. The experimental VLE data is shown in Figure 1. The tie-lines for the ternary system of DEDB (1) + diethylene glycol (2) + octyl benzoate (3) (1.1052 kPa) are presented in Figure 2. The reliability test is needed for the experimental data because of the errors caused by many reasons.9,10 According to the chemical thermodynamics, the variables of T, P, x, y of any system are restricted by the phase rule and the activity coefficient can be linked to them. Therefore, the reliability of experimental data can be checked by the general formula of thermodynamics and the basic formula is activity coefficient form of the Gibbs− Duhem equation.11 This method is the thermodynamic consistency test of VLE. The semiempirical method recommended by Herington12 is generally used to test the thermodynamic consistency of binary isobaric experimental data. The data in the whole concentration range were difficult to

3. EXPERIMENTAL DATA AND DISCUSSION 3.1. Experimental Data. The isobaric VLE data of binary systems DEDB (1) + diethylene glycol (2), DEDB (1) + octyl benzoate (2) and ternary system DEDB (1) + diethylene glycol (2) + octyl benzoate (3) were measured at 1.0152 kPa with the modified Othmer still. Because the intersolubility of the three components was poor, the VLE data below 506 K cannot be measured. All the experimental data are mole fractions, which are given in Tables 3 and 4. B



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Figure 1. T−x−y phase equilibrium diagram for (a) DEDB (1) + diethylene glycol (2) system, (b) DEDB (1) + octyl benzoate (2) system.

Table 7. Binary Parameters of Wilson Model λmn − λmm/J·mol−1

component m

n

DEDB (1) diethylene glycol (2) octyl benzoate (3)

Table 5. Group Volume Rk and Area Qk Parameters group numbers k in component i

group

DEDB

ACH AC CH2 COO CH2O OH CH3

10 2 3 2 1 0 0

0 0 3 0 1 2 0

octyl benzoate

volume parameter Rk

area parameter Qk

5 1 7 1 0 0 1

0.5313 0.3652 0.6744 1.38 0.9183 1 0.9011

0.4 0.12 0.54 1.2 0.78 1.2 0.848

diethylene glycol (2)

octyl benzoate (3)

0 11500 1258.6

−1238.1 0 −2041.5

1135.6 6866.4 0

be measured because of the particularity of the system. Therefore, diethylene glycol (1) + octyl benzoate (2) in the system were used to carry out the phase equilibrium experiment in this work and all the experimental data pass the thermodynamic consistency test. 3.3. Models and Predictions. The VLE data of the binary systems DEDB (1) + diethylene glycol (2), DEDB (1) + octyl benzoate (2) and ternary system DEDB (1) + diglycol (2) + octyl benzoate (3) were correlated with UNIFAC, Wilson, and NRTL models by Aspen Plus V7.2. (1) UNIFAC model The volume parameters Rk and area parameters Qk of all the groups13−15 are listed in Table 5 and the interaction parameters are shown in Table 6.16 The activity coefficients of the ternary system calculated by UNIFAC model were compared with the experimental data. The relative deviation of activity coefficient is expressed

Figure 2. Tie-lines for the ternary system of DEDB (1) + diethylene glycol (2) + octyl benzoate (3) at 1.1052 kPa.

diethylene glycol

DEDB (1)

cal exp jij γ1 − γ1 zyz jj z jj γ exp zzz × 100 1 k { (2) Wilson model

(1)

Table 6. Group Interaction Parameters m ACH AC CH2 COO CH2O OH CH3

n

ACH

AC

CH2

COO

CH2O

OH

CH3

0 0 61.13 317.6 52.13 89.6 61.13

0 0 61.13 317.6 52.13 89.6 61.13

−11.12 −11.12 0 529 83.36 156.4 0

103.5 103.5 387.1 0 417 190.3 387.1

32.14 32.14 251.5 −247.8 0 28.06 251.5

636.1 636.1 986.5 88.63 237.7 0 986.5

−11.12 −11.12 0 529 83.36 156.4 0

C



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Table 8. Binary Interaction Parameters of NRTL Model i

gji − giib/J·mol−1

αjia

component j

DEDB (1) diethylene glycol (2) octyl benzoate (3)

DEDB (1)


octyl benzoate (3)

DEDB (1)


octyl benzoate (3)

0 −1.5546 −1.0178

−1.5546 0 −0.5985

−1.0178 −0.59847 0

0 4609.8 1266.1

1013.2 0 806.3843

825.55 2431.9732 0

αji represents the ordered characteristic parameter when component j and component i are mixed. bgji, gjj, gii represent the interaction energy between the molecules on j−i, j−j, and i−i, respectively. a

Figure 3. T versus x1, y1 diagram for (a) DEDB (1) + diethylene glycol (2) system, (b) DEDB (1) + octyl benzoate (2) system.

Table 9. Comparison of Experimental γ Data with Calculated Results for DEDB (1) + Diethylene Glycol (2) + Octyl Benzoate (3) System γ1cal

Figure 4. Comparison of experimental γ data with calculated results for DEDB (1) + diethylene glycol (2) + octyl benzoate (3) system.

The Wilson parameters (λ12 − λ11) and (λ21 − λ22) were gained by regression of the binary VLE data. The nonlinear leastsquares method was used to set the objective function F and made it the minimum value.17 F is described as following equation 2

F=

n

∑ ∑ (ykical k=1 i=1

− ykiexp )2

T/K

γ1exp

UNIFAC

Wilson

NRTL

506.27 506.78 507.34 507.53 507.82 508.14 508.22 508.39 508.41 508.62 508.66 508.87 509.27 509.47 509.76 509.91 510.48 510.74

0.9252 0.9427 0.9676 0.9718 0.9829 0.9563 0.9625 0.9715 0.9792 0.9844 1.0182 1.0015 1.0061 1.0283 1.0219 0.9928 1.0083 0.9996

1.0012 1.0039 1.0028 1.0018 1.0015 1.0007 1.0010 1.0008 1.0008 1.0006 1.0008 1.0002 1.0005 1.0004 1.0002 1.0001 1.0000 1.0000

1.0153 1.0245 1.0220 1.0298 1.0252 1.0041 1.0266 1.0242 1.0223 1.0291 1.0221 1.0044 1.0255 1.0221 1.0147 1.0118 1.0053 1.0032

1.0003 1.0196 1.0230 1.0257 1.0247 1.0039 1.0152 1.0232 1.0226 1.0265 1.0219 1.0037 1.0242 1.0213 1.0135 1.0111 1.0045 1.0026

(3) NRTL model αji, gji − gii, and gij − gjj18,19 were gained by the regression of the binary VLE data and the objective function F was the same equation used for Wilson model (eq 2). The binary interaction parameters are listed in Table 8. (4) Comparison of three models

(2)

After the two parameters are obtained, the Wilson equation is complete, which can be used to calculate the VLE data. The parameters of the Wilson equation are shown in Table 7. D



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Table 10. Comparison of the Maximum and Average of Relative Deviation of the Temperature UNIFAC model system

Wilson model

NRTL model

maximum relative deviation /%

average of relative deviation /%





−0.13

0.07

−0.12

0.07

−0.12

0.07

−0.11

0.05

−0.10

0.05

0.10

0.05

DEDB (1) + diethylene glycol (2) DEDB (1) + octyl benzoate (2)

Table 11. Comparison of the Maximum and Average of Relative Deviation of the Vapor Composition UNIFAC model system

Wilson model

NRTL model







−1.85

3.37

−5.05

1.01

−4.64

0.99

−3.15

1.44

3.19

1.08

9.43

1.76

DEDB (1) + diethylene glycol (2) DEDB (1) + octyl benzoate (2)

glycol (2) and DEDB (1) + octyl benzoate (2) system. The maximum relative deviation and the average of relative deviation of temperature are small and the results of Wilson model are close to that of NRTL model. Compared comprehensively, NRTL model is optimal for these three systems.

Table 12. Comparison of the Maximum and Average of Relative Deviation of the γ Data for Dedb (1) + Diethylene Glycol (2) + Octyl Benzoate (3) System model

maximum relative deviation/%

average of relative deviation/%

UNIFAC Wilson NRTL

8.21 9.74 8.16

2.65 3.71 3.48

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +86 592 2189595. Fax: +86 592 2183088.

The experimental data and the calculated data are shown in Figures 3 and 4 and Table 9. In order to determine the most appropriate model to correlate experimental data from the perspective of relative deviation, the maximum relative deviation and average of relative deviation for temperature and vapor phase composition of the two binary systems are shown in Tables 10 and 11 and that for activity coefficient of the ternary system are shown in Table 12. According to the tables above, it can be seen that the maximum relative deviation and average of relative deviation of temperature in the three systems are the largest when correlated with UNIFAC model. Also, that of vapor phase composition in the two binary systems are the largest when correlated with NRTL model but the deviation is not large. On the basis of the results of the three systems, NRTL model is optimum and the calculated results are consistent with the experimental data. The idea of UNIFAC model is to use the interaction between groups to calculate the activity coefficient of system, which has ignored the interaction between molecules. For DEDB (1) + diethylene glycol (2) + octyl benzoate (3) system, results predicted by all three models are in good agreement with experimental values, but not as good as the binary systems. That probably results from the complexity of ternary system, which leads to more factors that affect the interaction between substances. By comparing the maximum relative deviation and average of relative deviation of the system, the deviation of UNIFAC and NRTL model are similar, which are better than Wilson model.

ORCID

Yanmei Zheng: 0000-0002-0869-1809 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Fundamental Research Funds for the Central Universities (20720170049)

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REFERENCES

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4. CONCLUSION The isobaric VLE data of binary systems DEDB (1) + diethylene glycol (2), DEDB (1) + octyl benzoate (2) and ternary system DEDB (1) + diethylene glycol (2) + octyl benzoate (3) were measured at 1.0152 kPa using a modified Othmer still. All the isobaric VLE data were predicted and correlated with UNIFAC model, Wilson model, and NRTL model. The three models have great predictions and correlations of DEDB (1) + diethylene E



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Experimental Isobaric Vapor Liquid Equilibrium for Binary Systems

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