Isobaric Vapor–Liquid Equilibria of Binary Systems (Propyl Acetate + 2

Article pubs.acs.org/jced

Isobaric Vapor−Liquid Equilibria of Binary Systems (Propyl Acetate + 2‑Methylbutan-1-ol), (Propyl Acetate + Hexan-1-ol), and (Propyl Acetate + Heptan-1-ol) at 101.3 kPa Ye Qi, Yulong Liu, Jingwei Xie, and Minqing Zhang* School of Chemical Engineering &Technology, Tianjin University, Tianjin 300072, P.R. China

ABSTRACT: Isobaric vapor−liquid equilibrium (VLE) data for the binary systems formed by (propyl acetate +2-methylbutan1-ol), (propyl acetate + hexan-1-ol), and (propyl acetate + heptan-1-ol) have been determined at the pressure of 101.3 kPa using an equilibrium still. The experimental data were checked through the semiempirical methods of Herington, and the thermodynamic consistency was satisfactory. The activity coefficients were correlated with the nonrandom two liquid (NRTL), Wilson, and universal quasichemical (UNIQUAC) models. In addition, the UNIQUAC functional-group activity coefficients (Do) model was used to correlate the VLE data. The NRTL model shows slightly better results compared with other three models among all three binary systems.

1. INTRODUCTION

2. EXPERIMENTAL SECTION 2.1. Apparatus and Procedure. We used an equilibrium still5 for the VLE measurement.5 To establish the vapor−liquid equilibrium rapidly, both vapor and liquid phases were continuously circulated in this still. For minimizing the sample loss, vapor and liquid phase sample connections were sealed with Teflon tape. Prior to each experiment, the entire system was thoroughly cleaned thereby eliminating any contaminants existing in the system. After cleaning, a certain amount of mixture of given content was supplied into the boiling chamber with an injector. The equilibrium, in every experiment, was reached after the temperature, the liquid composition, and the vapor composition were maintained constant for at least 90 min. We used a thermometer to measure the equilibrium temperature, and the accuracy of the thermometer was less than 0.1 K. The vapor and liquid compositions were determined by a gas chromatograph (GC, SP-3420A, Beifen Co.) equipped with a hydrogen flame ionization detector (FID). Two gas chromatographic columns were employed. The HJ-SE-54 column (30 m in length, 0.25 μm in film thickness, and 0.25 mm in diameter) was used to analyze the vapor and liquid composition of the binary systems (propyl acetate + hexan-1-ol, or heptan-1-ol). The CBP20 column (25 m in length, 0.25 μm in film thickness) was used to analyze the vapor and liquid composition of the

Increasing high global demand for fuels and the large consumption of fossil fuels have stimulated the renewable fuels research. Liquid fuels, including mixed-hydrocarbons and mixedalcohols, have abundant and sustainable sources.1 And the promising route for manufacture of mixed-alcohols from biomass has been researched.2 The main composition of mixed-alcohols includes low-carbon alcohols, small amounts of esters, and acids. To produce high purity alcohol compositions, establishment of the related vapor−liquid equilibrium (VLE) data are essential, and the VLE data are necessary for the development of separation processes. The VLE data for the system of (methanol + propyl acetate),3 (propyl acetate + ethanol, or propan-1-ol/1-methylethan-1-ol, or butan-1-ol/1-methylpropan-1-ol),4 and (propyl acetate + pentan-1-ol, or 1-methylbutan-1-ol/3-methylbutan-1-ol)5 have been reported. To improve the VLE data of binary systems including alcohol and propyl acetate, we have studied the vapor− liquid equilibrium of binary systems (propyl acetate + 2methylbutan-1-ol, or hexan-1-ol, or heptan-1-ol) experimentally, checked the thermodynamic consistency using semiempirical methods of Herington,6 and correlated the VLE data using nonrandom two liquid (NRTL),7 Wilson,8 and universal quasichemica (UNIQUAC)9 models. In the meantime, the UNIQUAC functional-group activity coefficients (UNIFAC) (Do) model10 was used to correlate the VLE data. © 2014 American Chemical Society

Received: April 10, 2014 Accepted: July 16, 2014 Published: July 25, 2014 2541

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ensure the accuracy, we analyzed each sample at least three times. 2.2. Chemicals. Propyl acetate (GR grade, + 99 %), hexan-1ol (GR grade, + 99 %) and heptan-1-ol (GR grade, + 99 %) were purchased from Alfa Aesar, 2-methylbutan-1-ol (GR grade, + 99 %) was purchased from Adamas-beta. We checked the purity of all chemicals with gas chromatography analysis, and the results are indicated in Table 1.

Table 1. Chemical Sample Specifications chemical name

supplier

mole fraction purity as determined by GC

propyl acetate 2-methylbutan-1-ol hexan-1-ol heptan-1-ol

Alfa Aesar Adamas-beta Alfa Aesar Alfa Aesar

0.998 0.997 0.999 0.997

Table 2. VLE Data for Binary System of (Propyl Acetate (1) + 2-Methylbutan-1-ol (2)) at P = 101.3 kPaa no.

T/K

x1

y1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

401.15 399.25 398.05 396.55 394.45 392.85 391.45 389.75 388.65 387.35 386.15 384.75 383.45 381.95 380.95 379.85 378.55 377.65 376.85

0.0355 0.0813 0.1121 0.1461 0.2047 0.2439 0.2910 0.3450 0.3865 0.4348 0.4799 0.5322 0.5829 0.6451 0.6870 0.7429 0.8043 0.8584 0.9179

0.0988 0.1922 0.2497 0.3103 0.4018 0.4583 0.5203 0.5755 0.6172 0.6605 0.6973 0.7404 0.7727 0.8116 0.8393 0.8709 0.9065 0.9298 0.9587

3. RESULTS AND DISCUSSION 3.1. Binary System. The isobaric VLE data of the three binary systems were measured using the equilibrium still. The experimental results of VLE data (T, xi, yi) are shown in Table 2, Table 3, and Table 4, respectively. The corresponding phase Table 4. VLE Data for Binary System of (Propyl Acetate (1) + Heptan-1-ol (2)) at P = 101.3 kPaa

a

x1 is the mole fraction of propyl acetate in the liquid phase; y1 is the mole fraction of propyl acetate in the vapor phase. Standard uncertainties u are u(T) = 0.05 K and u(x1) = u(y1) = 0.001.

Table 3. VLE Data for Binary System of (Propyl Acetate (1) + Hexan-1-ol (2)) at P = 101.3 kPaa no.

T/K

x1

y1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

427.05 421.85 418.10 412.95 409.85 405.19 402.55 399.35 396.35 393.55 391.95 388.95 387.25 385.35 383.57 381.79 380.25 378.52 376.95

0.0345 0.0760 0.1102 0.1640 0.2064 0.2633 0.3071 0.3563 0.4080 0.4626 0.5053 0.5706 0.6255 0.6787 0.7240 0.7878 0.8333 0.8803 0.9512

0.1677 0.3263 0.4270 0.5550 0.6290 0.7018 0.7323 0.7758 0.8148 0.8494 0.8657 0.8936 0.9136 0.9273 0.9418 0.9565 0.9675 0.9773 0.9917

no.

T/K

x1

y1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

445.05 437.05 430.15 424.95 416.98 413.15 406.95 402.43 398.85 395.95 393.15 390.37 388.25 387.85 385.15 382.35 380.45 378.45 376.85

0.0260 0.0695 0.1171 0.1547 0.2109 0.2487 0.3164 0.3778 0.4234 0.4790 0.5360 0.5985 0.6420 0.6506 0.7195 0.7968 0.8416 0.8996 0.9526

0.1905 0.4119 0.5706 0.6576 0.7508 0.7941 0.8472 0.8815 0.9020 0.9223 0.9397 0.9517 0.9599 0.9601 0.9711 0.9801 0.9857 0.9916 0.9964

a

x1 is the mole fraction of propyl acetate in the liquid phase; y1 is the mole fraction of propyl acetate in the vapor phase. Standard uncertainties u are u(T) = 0.05 K and u(x1) = u(y1) = 0.001.

Table 5. Thermodynamics Consistency Test for Three Binary Mixtures at 101.3 kPa mixture

D

J

D − J < 10

propyl acetate + 2-methylbutan-1-ol propyl acetate + hexan-1-ol propyl acetate + heptan-1-ol

19.9 0.9 28.0

10.8 22.2 29.7

9.1 −21.3 −1.7

diagrams are presented in Figure 1 panels a, b, and c, successively. According to Figure 1, it can be obtained that there is no azeotropic behavior in any binary mixtures involved in this study. 3.2. Thermodynamics Consistency Verification. To ensure the thermodynamics consistency of the three binary systems, all experimental binary VLE data were tested for thermodynamic consistency by the method of Herington.6 Rules state that if (D − J) < 10, then the experimental data would be regarded as thermodynamically consistent.

a

x1 is the mole fraction of propyl acetate in the liquid phase; y1 is the mole fraction of propyl acetate in the vapor phase. Standard uncertainties u are u(T) = 0.05 K and u(x1) = u(y1) = 0.001.

1

D = 100 ×

propyl acetate + 2-methylbutan-1-ol system. The carrier gas was high-purity nitrogen with a flow rate of 30 mL·min−1. To

∫0 ln(γ1/γ2) dx1 1

∫0 |ln(γ1/γ2)| dx1 2542

(1)

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Figure 1. Temperature−vapor and liquid composition relationships: ■, experimental T−x1; and □, experimental T−y1; red solid line, NRTL; green dash dot line, Wilson; and black dotted line, UNIQUAC. (a) (propyl acetate (1) + 2-methylbutan-1-ol (2)) at 101.3 kPa; (b) (propyl acetate (1) + hexan-1-ol (2)) at 101.3 kPa; (c) (propyl acetate (1) + heptan-1-ol (2)) at 101.3 kPa.

T − Tmin J = 150 × max Tmin

Figure 2. Plot of ln(γ1/γ2) versus x1. Red line, calculated value of Herington test: (a) (propyl acetate + 2-methylbutan-1-ol); (b) (propyl acetate + hexan-1-ol); (c) (propyl acetate + heptan-1-ol).

heptan-1-ol, Tmax/K and Tmin/K are the highest and lowest temperature in the system, respectively. The results of thermodynamics consistency verification are shown in Table 5 and Figure 2 panels a, b, c, which clearly demonstrate that the experimental VLE data conformed to the Herington test.

(2)

where γ1 is the activity coefficient of propyl acetate, γ2 represents the activity coefficient of 2-methylbutan-1-ol or hexan-1-ol or 2543

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Table 6. Antoine Equation Parametersa temperature units pressure units C1i C2i C3i C4i C5i C6i C7i C8i C9i a

propyl acetate

2-methylbutan-1-ol

hexan-1-ol

heptan-1-ol

K kPa 108.2522 −8433.9 0 0 −13.934 1.03·10−05 2 178.15 549.73

K kPa 112.3322 −10738 0 0 −13.522 1.4271·10−17 6 195 575.4

K kPa 128.5122 −12288 0 0 −15.732 1.2701·10−17 6 228.55 611.3

K kPa 140.5022 −13466 0 0 −17.353 1.1284·10−17 6 239.15 632.3

Taken from Aspen property databank.

3.3. Data Correlation. Assuming that the vapor phase sample behaves as an ideal gas under low or medium pressure, the activity coefficients of each component were calculated by the following eq 3: γi =

yp /(xipis ) i

Table 8. UNIFAC-Dortmund Groups compound propyl acetate

(3) 2-methylbutan-1-ol

where psi is the saturated vapor pressure of pure solvent i at the equilibrium temperature. The value can be calculated with the seven parameters Antoine equation (eq 4). The specific parameters derived from Aspen property databank are shown in Table 6, where yi is the vapor phase mole fraction, xi is the liquid phase mole fraction, and P is the total pressure. The vapor pressure of pure component i was obtained by the following:

hexan-1-ol

heptan-1-ol

C 2i ln pis = C1i + + C4iT + C5i ln T + C6iT C7i T + C 3i C 8i ≤ T ≤ C 9i

RTci ti Zci , Pci

ti = 1 + (1 − T /Tci)2/7 ,

T /Tci ≤ 0.75

main group CH210

(5)

CCOO10 OH10

where Tci, Pci, and Zci are indicated in Table 7.

a

compound

Tc/K

Pc/kPa

Zc

r

q

549.73 575.4 611.3 632.3

3360 3940 3446 3085

0.254 0.271 0.259 0.261

4.153 4.285 4.803 5.477

3.656 3.394 4.132 4.672

1 2 1 2 2 1 1 1 5 1 1 6 1

subgroup

Rk

Qk

CH CH2 CH3 CH3COO OH

0.6325 0.6325 0.6325 1.2700 1.2302

0.3554 0.7081 1.0608 1.6286 0.8927

⎡⎛ exp cal ⎞2 ⎛ T exp − T cal ⎞2 ⎤⎥ ⎢⎜ yij − yij ⎟ j j ⎟⎥ OF = ∑ ∑ ⎢ + ⎜⎜ ⎟ ⎜ ⎟ σ σ y T ⎝ ⎠ ⎥⎦ N i ⎢ ⎝ ⎠ ⎣

(7)

where y represents the mole fraction of the pure chemical in the vapor phase, i represents each pure chemical in the binary systems, N is the number of the lines in Table 2, Table 3, and Table 4, respectively, and σ represents the standard deviation of the measured experimental values. The average absolute deviations (AAD)11,12 in boiling temperatures were used to measure the agreement between the experimental results and the calculated values. The AAD was defined by the following form:

Taken from Aspen property databank.

For the UNIQUAC model, q (the area parameters) and r (the molar volume parameters) are shown in Table 7. For the UNIFAC (Do) model equations, the interaction between groups is given by ⎛ a + b T + c T2 ⎞ nm nm ⎟ ψnm = exp⎜ − nm T ⎝ ⎠

CH3 CH2 CH3COO CH3 CH2 CH OH CH3 CH2 OH CH3 CH2 OH

The group interaction parameters were obtained from the literature.10 The groups for the compounds are shown in Table 8. All of the parameters Rk and Qk are shown in Table 9. The calculation of the objective function OF can be obtained from

Table 7. Physical Parameters and Properties of the Pure Componentsa propyl acetate 2-methylbutan-1-ol hexan-1-ol heptan-1-ol

group no.

Table 9. Volume Parameters (Rk) and Area Parameters (Qk) of Groups

(4)

The nonrandomness parameter αij in the NRTL model was set at 0.3. The molar volumes needed for the Wilson equation were calculated with eq 5: Vi =

group type

(6)

where ψnm represents the interaction between groups, anm, bnm, and cnm are the interaction parameters, and T represents the equilibrium temperature.

AAD =

1 N

N

∑ |Ciexp − Cical| k=1

(8)

where Ci is an independent variable of the pure component i. 2544

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absolute deviations of the temperature for (propyl acetate +2methylbutan-1-ol), (propyl acetate + hexan-1-ol), and (propyl acetate + heptan-1-ol) are 0.2551 K, 0.4419 K, and 0.5791 K, respectively. The average absolute deviations of the vapor phase compositions of propyl acetate for (propyl acetate +2-methylbutan-1-ol), (propyl acetate + hexan-1-ol), and (propyl acetate + heptan-1-ol) are 0.0013, 0.0119, and 0.0162, respectively. The correlated VLE data for the binary systems are compared with the experimental VLE data in Figure 3 panels a, b, and c. According to the binary parameters and the AAD of the three systems, as listed in Table 10, the prediction accuracy using the NRTL model is Table 10. Binary Parameters Calculated from the NRTLa, Wilson, and UNIQUAC Models and Average Absolute Deviations for the Temperature and Vapor Mole Fraction of Propyl Acetate for the Mixtures of (Propyl Acetate (1) + 2-Methylbutan-1-ol (2)), (Propyl Acetate (1) + Hexan-1-ol (2)), and (Propyl Acetate (1) + Heptan-1-ol (2)) at 101.3 kPa 2-methylbutan-1-ol A12 A21 B12 B21 deviations AAD y1 AAD T/K A12 A21 B12 B21 deviations AAD y1 AAD T/K A12 A21 B12 B21 deviations AAD y1 AAD T/K a

hexan-1-ol

NRTL Parameters (τij = Aij + Bij/T) −10.24 24.51 16.25 5.50 3762.70 −8306.21 −5973.00 −2769.23 0.0049 0.0178 0.1680 0.2397 Wilson Parameters (lnΛij = Aij + Bij/T) −10.32 2.71 5.90 −7.44 3732.35 −868.99 −2138.65 2568.17

heptan-1-ol 35.34 6.89 −12400.09 −3385.23 0.0163 0.3285 −19.73 7.75 7540.08 −2913.33

0.0051 0.0126 0.0186 0.1710 0.3526 0.3452 UNIQUAC Parameters (τij = exp(Aij + Bij/T)) 2.44 −13.19 5.31 −3.88 1.18 −11.23 −787.90 4526.54 −1907.04 1295.88 −121.18 4153.18 0.0047 0.1690

0.0166 0.2572

0.0203 0.3285

NRTL model: α12 = α21 = 0.3.

lightly better than that with the Wilson and UNIQUAC models. For example, in the binary system of (propyl acetate + heptan-1-ol), the NRTL correlation presents the best deviation of T = 0.1680, compared with the WILSON deviation (T = 0.1710) and UNIQUAC deviation (T = 0.1690). And the NRTL deviation (T = 0.1680) is also better than the UNIFAC (Do) deviation (T = 0.2551).

Figure 3. Temperature−vapor and liquid composition relationships: ■, experimental T−x1; □, experimental T−y1; , UNIFAC (Do). (a) (propyl acetate (1) + 2-methylbutan-1-ol (2)) at 101.3 kPa; (b) (propyl acetate (1) + hexan-1-ol (2)) at 101.3 kPa; (c) (propyl acetate (1) + heptan-1-ol (2)) at 101.3 kPa.

4. CONCLUSIONS The isobaric VLE data of the binary mixtures {(propyl acetate +2-methylbutan-1-ol), (propyl acetate + hexan-1-ol), and (propyl acetate + heptan-1-ol)} have been measured at P = 101.3 kPa. In this study, all experimental binary VLE data were examined for thermodynamic consistency by the semiempirical method of Herington.6 Compared to the other three models, the NRTL model shows slightly better results in these three binary systems.

Temperature−vapor and liquid composition relationships (T−xy) for three binary systems at P = 101.3 kPa are shown in Figure 1 panels a, b, and c, successively, with the curve fitting by NRTL, Wilson, and UNIQUAC equations.13 The UNIFAC (Do) model correlates the experimental data well. The average 2545

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AUTHOR INFORMATION

Corresponding Author

*Tel: +86 022 27890643. E-mail: [email protected]. Funding

The authors are grateful to the financial support from National High-tech R&D Program of China (2012AA062901, 2012AA03A609) and Program for Changjiang Scholars and Innovative Research Team in University (IRT1161). Notes

The authors declare no competing financial interest.

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REFERENCES

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