Liquid–Liquid Equilibria for the Ternary System 2-Methoxy-2

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Liquid−Liquid Equilibria for the Ternary System 2‑Methoxy-2methylpropane + Phenol + Water Yong Lei, Yun Chen,* Xiuxi Li, Yu Qian, Siyu Yang, and Chufen Yang School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, P. R. China ABSTRACT: Liquid−liquid equilibria data for the ternary system 2-methoxy-2-methylpropane (methyl tert-butyl ether) + phenol + water were measured at temperatures of (298.15, 313.15, and 323.15) K at atmosphere pressure. The distribution coefficient and selectivity were used to evaluate the extraction performance of the 2-methoxy-2-methylpropane. The reliability of the experimental tie-line data was verified by the Hand and Bachman equations. The experimental data were correlated with the NRTL and UNIQUAC models. The binary interaction parameters of these two models were reported. Both models correlated the experimental data successfully. In comparison, the NRTL model presents a better prediction than the UNIQUAC model.

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INDRODUCTION Phenol is a common organic water pollutant. It is probably produced by many industrial processes, such as refineries, coking operations, coal processing, manufacture of petrochemicals, and coal gasification. For its high toxicity and hazardous character, phenol could be recycled from wastewaters before their discharge. For treatment of high concentrated phenol wastewater (over 3000 mg·L−1), solvent extraction is a preferable method.1,2 Until now, there have been many solvents developed for extraction, such as benzene, heavy benzene, benzol, ethyl ethanoate, isopropyl ethanoate, etc. Currently, the extraction solvents used in industry are 2,2′oxybis(propane) (diisopropyl ether) and 4-methylpentan-2-one (methyl isobutyl ketone), and much research has been reported on the application of the two solvents.3,4 However, these two solvents have several limitations in practical application. For 2,2′-oxybis(propane), the subsequent treatment becomes difficult due to the low efficiency. In contrast, 4-methylpentan-2-one has been broadly accepted as an effective solvent, and its application, however, is limited by the high energy consumption. Thus, in this paper we select 2-methoxy-2methylpropane (methyl tert-butyl ether), a fuel additive, as the extraction solvent because of its high distribution coefficient5 and low energy consumption of recovery. Liquid−liquid equilibria (LLE) data are essential for a proper understanding and design of the solvent extraction process.6 Various studies have been carried out on the LLE data of the ternary solvent−phenol−water system. Yang et al.7 studied the extraction of phenol with 4-methylpentan-2-one. Martin et al.8,9 reported the experimental data for the aromatic hydrocarbons (toluene or ethylbenzene) + phenols + water system and the aliphatic hydrocarbons (heptane or octane) + phenols + water system. Hwang et al.10 researched the LLE data of the dimethyl carbonate + phenol + water and diphenyl carbonate + phenol + water systems. However, the LLE data of 2-methoxy-2© XXXX American Chemical Society

methylpropane + phenol + water has not been reported until now. To obtain reliable data for the simulation of phenol recovery from wastewater, we investigated the LLE data for the 2methoxy-2-methylpropane + phenol + water system at temperatures of (298.15, 313.15, and 323.15) K under atmosphere pressure. The LLE data were determined in low concentrations of phenol (the mass fraction ranging from 0.000053 to 0.002521) in the raffinate. The NRTL11 and UNIQUAC12 models were applied to correlate the LLE data to obtain the binary interaction parameters of these components.

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EXPERIMENTAL SECTION Chemicals. The supplier and the mass fraction of the chemical reagents used in this work are shown in Table 1. The purity of the materials was checked by gas chromatography. All of the chemicals in the study were used without further purification. Deionized and distilled water was used in all experiments.

Table 1. Suppliers and Mass Fraction of the Chemical Reagents supplier

mass fraction

Sinpharm Chemical reagent Co., Ltd.

0.99

GuangZhou Chemical reagent Factory ShangHai LingFeng Chemical reagent Co., Ltd. TianJin Kemiou Chemical reagent Co.,Ltd.

0.995 0.999

component 2-methoxy-2methylpropane phenol methanol 1-octanol

0.995

Received: March 27, 2013 Accepted: May 10, 2013

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Table 2. Experimental LLE Data (Mass Fraction) for the Ternary System 2-Methoxy-2-methylpropane (1) + Phenol (2) + Water (3)a at 0.1 MPa T

aqueous phase

w1

w2

w3

w1

w2

w3

298.15

0.899062 0.925163 0.933380 0.943459 0.947898 0.952325 0.955085 0.960075 0.964525 0.966073 0.969241 0.979750 0.9826 0.987450 0.826316 0.848179 0.863480 0.884214 0.889632 0.895459 0.928051 0.932464 0.949825 0.958355 0.967305 0.980730 0.981854 0.9853 0.893503 0.901230 0.931592 0.936545 0.950582 0.955787 0.957841 0.963599 0.966550 0.968970 0.973767 0.975389 0.980776 0.9842

0.058800 0.044137 0.039882 0.033194 0.031339 0.028353 0.026593 0.022899 0.020206 0.019417 0.017496 0.006998 0.004728 0.000000 0.124193 0.108730 0.097855 0.079007 0.074668 0.069793 0.045649 0.041993 0.029327 0.024115 0.016341 0.003779 0.002664 0 0.068453 0.063375 0.039306 0.035212 0.026394 0.021375 0.020150 0.015957 0.013874 0.012295 0.008940 0.008346 0.003239 0

0.042138 0.025333 0.025788 0.023347 0.020763 0.019322 0.018322 0.017026 0.015269 0.014510 0.013263 0.013252 0.012672 0.012550 0.049491 0.043091 0.038665 0.036779 0.035700 0.034748 0.026300 0.025543 0.020848 0.017530 0.016354 0.015491 0.015482 0.0147 0.038044 0.035396 0.029103 0.028244 0.023025 0.022838 0.022009 0.020444 0.019576 0.018735 0.017293 0.016265 0.015917 0.0158

0.025091 0.025333 0.025788 0.026201 0.026213 0.026535 0.026712 0.027509 0.029113 0.029934 0.030255 0.030402 0.0315 0.032906 0.018146 0.019200 0.019308 0.020718 0.020839 0.020971 0.021545 0.023352 0.023969 0.024127 0.024504 0.024751 0.024847 0.025 0.012435 0.013177 0.014344 0.014671 0.014874 0.014966 0.015160 0.015250 0.016120 0.016328 0.016413 0.017002 0.017570 0.019

0.001085 0.000925 0.000673 0.000602 0.000564 0.000553 0.000533 0.000433 0.000383 0.000330 0.000275 0.000131 0.000076 0.000000 0.002521 0.002384 0.001916 0.001551 0.001491 0.001404 0.000852 0.000816 0.000678 0.000415 0.000291 0.000110 0.000053 0 0.001711 0.001665 0.001037 0.000890 0.000626 0.000523 0.000492 0.000390 0.000367 0.000310 0.000218 0.000190 0.000118 0

0.973824 0.973742 0.973539 0.973197 0.973223 0.972912 0.972755 0.972058 0.970504 0.969736 0.96947 0.969467 0.968424 0.967094 0.979333 0.978416 0.978776 0.977731 0.977670 0.977625 0.977603 0.975832 0.975353 0.975458 0.975205 0.975139 0.9751 0.975 0.985854 0.985159 0.984619 0.984440 0.984500 0.984510 0.984347 0.984360 0.983513 0.983362 0.983369 0.982809 0.982312 0.981

313.15

323.15

a

organic phase

K

Standard uncertainties u are u(T) = 0.1 K, u(w) = 0.0019.

Procedure. The experimental LLE data were carried out by using a 100 mL glass equilibrium cell equipped with a heating jacket to keep the temperature constant. The cell temperature was controlled by a thermostatic bath with an uncertainty of ± 0.1 K. The mixture of solvent and wastewater was fed into the glass cell and vigorously agitated by a magnetic stirrer for at least 2 h and then left to settle for at least 10 h to reach phase equilibrium. After the mixture was split into two liquid phases, the samples of both phases were collected by a syringe. The analysis was performed by using a gas chromatograph (GC6820, Agilent Technologies) equipped with a flame ionization detector (FID) and a DB-5MS capillary column (30 m × 0.32 mm × 0.25 μm). The determination of the composition is based on the internal standard. Methanol was

selected as the internal standard of 2-methoxy-2-methylpropane and 1-octanol as the internal standard of phenol. Water concentration was obtained by mass balance. The injector and detector were set at (533.15 and 523.15) K. The initial temperature of oven was kept at 303.15 K for 2 min and then increased at a rate of 30 K·min−1 to reach 433.15 K. The carrier gas was nitrogen with a rate of 30 mL·min−1 throughout the column. Each sample was analyzed at least three times, and the mean value was used.

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RESULTS AND DISCUSSION LLE Experimental Data. The LLE data of the ternary system 2-methoxy-2-methylpropane + phenol + water at (298.15, 313.15, and 323.15) K are listed in Table 2. All

B

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concentrations are expressed in mass fraction. The phase behaviors for the studied system at different temperatures were also plotted in the quadrilateral diagrams as shown in Figure 1.

Table 3. Distribution Coefficient (D) and Selectivity (S) at Three Different Temperatures T = 298.15 K

T = 313.15 K

T = 323.15 K

D

S

D

S

D

S

54.19 47.72 59.26 55.14 55.57 51.27 49.89 52.88 52.76 58.84 63.62 53.42 62.21

1252.43 1834.08 2237.16 2298.44 2604.52 2581.64 2648.93 3019.31 3353.27 3932.37 4650.49 3908.00 4754.27

49.26 45.61 51.07 50.94 50.08 49.71 53.58 51.46 43.26 58.11 56.15 34.35 50.26

974.83 1035.57 1292.86 1354.17 1371.45 1398.58 1991.58 1966.03 2023.65 3233.45 3348.56 2162.58 3165.78

40.01 38.07 37.92 39.56 42.15 40.84 40.93 40.92 37.80 39.73 40.95 44.00 27.45

1036.88 1059.71 1282.76 1379.00 1802.12 1760.70 1830.48 1970.08 1899.23 2085.19 2328.48 2658.91 1693.98

⎛ w ⎞W ⎛ w ⎞O ln⎜ 2 ⎟ = a1 + b1 ln⎜ 2 ⎟ ⎝ w1 ⎠ ⎝ w3 ⎠

(3)

⎛ wO ⎞ w1O = a 2 + b2⎜ 1W ⎟ ⎝ w3 ⎠

(4)

where a1,b1 and a2,b2 are the parameters of the Hand and Bachman equations. The straight lines plotted by these two equations are shown in Figures 2 and 3, respectively. The

Figure 1. LLE data for the system 2-methoxy-2-methylpropane + phenol + water at different temperatures: (a) 298.15 K, (b) 313.15 K, and (c) 323.15 K; ■, experimental data.

To estimate the ability of 2-methoxy-2-methylpropane to separate phenol from wastewater, the distribution coefficient (D) and selectivity (S) are determined as follows: D=

S=

Figure 2. Hand plots of the system 2-methoxy-2-methylpropane (1) + phenol (2) + water (3) at different temperatures: -■-, 298.15 K; −▲, 313.15 K; ·●·, 323.15 K.

w2O w2W

(1)

parameters together with the regression coefficients are given in Table 4. All of the regression coefficients (R2) close to 1 represent a high consistency of the experimental data. Data Correlation. The experimental LLE data were correlated by using the NRTL and UNIQUAC equations. For the UNIQUAC correlation, the structural parameters (r and q) are derived from the literature15,16 as shown in Table 5. The nonrandomness parameter (αij) for the NRTL correlation was fixed, and the values are given in Table 6. The binary interaction parameters of the NRTL and UNIQUAC models for the studied system are listed in Table 6. The six binary interaction parameters (Aij and Aji) were obtained by minimizing the objective function (OF) given in the following equation:

(w2 /w3)O (w2 /w3)W

(2)

where the superscripts O and W are the organic phase and the aqueous phase, respectively. The distribution coefficient and selectivity at each temperature are calculated and presented in Table 3. The results indicate that 2-methoxy-2-methylpropane is a good solvent for removal of phenol. It could be found that the extraction performance of the 2-methoxy-2-methylpropane slightly decreases with the increasing temperature. The reliability of the experimental tie-line data was evaluated by using the Hand13 and Bachman14 equations, given by eqs 3 and 4, respectively. C

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agreement between the experimental data and the calculated data. The RMSD value is defined as ⎡ ∑3 ∑2 ∑n (w exp − w cal)2 ⎤1/2 ijk ijk i=1 j=1 k=1 ⎥ RMSD = ⎢ ⎢ ⎥ 6 n ⎣ ⎦

(6)

The RMSD values of the two models are shown in Table 7. It can be seen that both models show good representation of the Table 7. RMSD Values for the Studied System

Figure 3. Bachman plots of the system 2-methoxy-2-methylpropane (1) + phenol (2) + water (3) at different temperatures: -■-, 298.15 K; −▲, 313.15 K; ·●·, 323.15 K.

Hand

Bachman 2

K

a1

b1

R

298.15 313.15 323.15

0.9734 1.0689 1.0790

3.8204 4.4585 4.3004

0.9890 0.9903 0.9861

a2

b2

R2

0.8983 0.9515 0.9495

0.0718 0.0237 0.0333

0.9981 0.9999 0.9994

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Table 5. UNIQUAC Structural (Area and Volume) Parameters component

r

q

water 2-methoxy-2-methylpropane phenol

0.9200 4.0678 3.5517

1.4000 3.6320 2.6800

3

OF =

2

n

⎡

∑ ∑ ∑ ⎢⎢ i=1 j=1 k=1

(Tkexp − Tkcal)2 σT 2

⎣

+

NRTL

UNIQUAC

298.15 313.15 323.15 average

0.001577 0.001706 0.001127 0.001470

0.004220 0.001375 0.010994 0.005530

tie-line data for the studied system. However, the NRTL model is more accurate than the UNIQUAC model according to the average RMSD. The experimental and calculated data (NRTL model) of phenol at each temperature are shown in Figure 4. The calculated data is in good agreement with the experimental data. It indicates that the NRTL model is suitable for simulation of phenol extraction.

Table 4. Hand and Bachman Equations Parameters for the 2-Methoxy-2-methylpropane + Phenol + Water System T

T/K

CONCLUSIONS

LLE data for the ternary system 2-methoxy-2-methylpropane + phenol + water were measured at (298.15, 313.15, and 323.15) K at atmosphere pressure. The distribution coefficients and selectivity values reflect the possibility of recovering phenol from wastewater by using 2-methoxy-2-methylpropane. The effect of temperature on the extraction performance of 2methoxy-2-methylpropane was investigated. The Hand and Bachman equations were used to check the reliability of the experimental tie-line data. The experimental results were correlated with the NRTL and UNIQUAC models. The good match between the experimental data and the calculated data denote that the NRTL prediction is satisfactory. The work is important for process simulation and development of phenol extraction and solvent recovery from phenol-containing industrial wastewater.

exp cal 2 ⎤ (wijk ) − wijk ⎥ 2 ⎥⎦ σw

(5)

where n is the number of the tie-lines, wexp and Texp are the experimental mass fraction and temperature, and wcal and Tcal are the calculated mass fraction and temperature, respectively. The subscripts i, j, and k refer to the component, the phase, and the tie-line, respectively. σT and σw denote the standard deviation of the temperature and the mass fraction. The rootmean-square-deviation (RMSD) was used to check the

Table 6. Binary Interaction Parameters of NRTL and UNIQUAC Model for the 2-Methoxy-2-methylpropane (1) + Phenol (2) + Water (3) System T

components

NRTL

UNIQUAC

K

i-j

Aij/K

Aji/K

αij

Aij/K

Aji/K

298.15

1−2 1−3 2−3 1−2 1−3 2−3 1−2 1−3 2−3

1445.42346 430.903538 −1477.81163 −308.915085 351.694891 −932.724732 2183.69889 −672.366806 −1831.98945

−1106.40983 1225.61151 3562.38334 −406.354464 1406.43675 2386.53906 −1277.46292 1578.67186 2775.21544

0.3 0.2 0.2 0.3 0.2 0.2 0.3 0.2 0.2

1244.4875 −704.847408 998.804963 −685.464555 −574.235699 1431.69887 −1125.85858 −860.297235 1794.28464

509.566513 −48.037 2111.9301 411.080058 −102.214069 −1018.06426 677.906717 −48.037 −1527.54565

313.15

323.15

D

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Figure 4. Experimental data and the calculated data of phenol at (a) 298.15 K, (b) 313.15 K, (c) 323.15 K; −, calculated data by NRTL model; ■, experimental data.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: 86-20-87112046. Fax: 86-20-87112046. E-mail: [email protected]. Funding

Financial support from Project of the Science & Technology New Star of Pearl River in Guangzhou (2011J2200056) and National Science Foundation of China (Nos. 20906028, 21136003, 21176089, and 21106021) are gratefully acknowledged. Notes

The authors declare no competing financial interest. E

dx.doi.org/10.1021/je400295z | J. Chem. Eng. Data XXXX, XXX, XXX−XXX