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Measurement and Correlation of Phase Equilibria in Aqueous Two-Phase Systems Containing Polyoxyethylene Lauryl Ether and Three Kinds of Potassium Salts at Different Temperatures Yang Lu,†,‡ Juan Han,† Zhenjiang Tan,*,‡ and Yongsheng Yan*,† †

School of Chemistry and Chemical Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang, 212013, China School of Computer Science, Jilin Normal University, 1301 Haifeng Street, Siping, 136000, China

‡

ABSTRACT: The binodal curves of the aqueous two-phase system (ATPS) containing the polyoxyethylene (10) lauryl ether (POELE10, C32H66O11) and three potassium salts (KOH/ K2CO3/K3PO4) were determined at the temperatures (288.15, 293.15, 303.15, and 308.15) K. The three experience equations were used to fit the binodal data for the studied systems, and a satisfactory correlation effect was obtained. The effect of salts on the binodal curves for the investigated systems was discussed by the effective excluded volume (EEV), and we found that the salting-out effect is mainly influenced by valence of anion of salts. The salt containing the higher valence of anion has a stronger phase-forming ability than that with a lower charge of anion. The liquid−liquid equilibrium (LLE) data for the investigated systems were determined and correlated by the Othmer−Tobias and Bancroft equations. The effect of the change of temperature on the binodal curves and tie-lines was also studied through the analysis of the EEV values and cloud point (CP) figure. The increase in temperature leads to the strengthening hydrophobicity of POELE10 that drive more water transferring from the top phase to the bottom phase, which means the phase-forming ability of the whole systems was strengthened. Thus, the critical concentration of POELE10 and salts for forming ATPS decreases with the rising temperature.

1. INTRODUCTION The aqueous two-phase system (ATPS) is becoming more widely appreciated as a new type of green separation and extraction technology. Compared with the traditional liquid− liquid extraction technology, the ATPS has the advantages such as a simple device, mild operation condition, continuous operation, and easy scale up. When two mutually incompatible materials, such as two water-soluble polymers, one polymer and one salt, one ionic liquid and one salt, and one water-soluble micromolecule alcohol and one salt, are dissolved in water above a critical concentration, the aqueous two-phase systems (ATPSs) are formed. The ATPS provides a benign environment for proteins,1−3 antibiotics,4−6 nucleic acids,7 viruses,8 and other biological9−12 molecules because of its high water content of both phases. At present, there are many studies reporting the successful extraction of the above-mentioned materials. Our research team focused our attention to study the determination of the trace residual antibiotics in the food and natural environment using the ATPSs.4,6,13−15 In light of the application of the ATPS, the extraction efficiency is strongly influenced by the attribute of the ATPS itself. Therefore, it is absolutely vital to determine the baseline data and discuss the effect of various factors on the ATPS. The further research on ATPS should be centered on the following three aspects, namely, completing the liquid−liquid equilibrium (LLE) data of exiting ATPSs, finding new properly polymer or ionic liquid or micromolecule alcohol used to form the ATPS, © XXXX American Chemical Society

and synthesizing the functional polymer or ionic liquid. On the basis of analyzing and selecting, we found that nonionic surfactant polyoxyethylene (10) lauryl ether (POELE10, C32H66O11) was an appropriate choice to form polymer−salt ATPS because of its structure containing the hydrophobic alkyl domain and hydrophilic polyoxyethylene tail. This conclusion was verified by comparing the forming-phase ability of POELE10 with that of other polymer.16 Differing from the previous work,16 which has discussed the ATPS composed of the POELE10 and three salts at same temperature, we have conducted the present experiment to further study the effect of temperature on binodal curves and tie-lines in this paper. The binodal data of POELE10-KOH/ K2CO3/K3PO4 ATPSs at the different temperatures (288.15, 293.15, 303.15, and 308.15) K were determined and correlated by the experience equations. The effect of the temperature and the type of salt on the binodal data were studied through the analysis of effective excluded volume and the diagram about dependence of cloud point (CP) on the mass fraction of salts. The LLE data of the above-mentioned systems were given and fit by using the Othmer−Tobias and Bancroft equations. The effect of the temperature on the tie-lines was discussed. Received: September 2, 2012 Accepted: November 13, 2012

A

dx.doi.org/10.1021/je300955p | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Table 1. Values of Parameters of eq 1 for Aqueous Solution of POELE10 + KOH/K2CO3/K3PO4 at 298.15 K system

n0

a1

a2

R2

POELE10 + KOH POELE10 + K2CO3 POELE10 + K3PO4

1.3329 1.3331 1.3330

0.1417 0.1378 0.1395

0.1823 0.1770 0.1891

0.9995 0.9997 0.9994

Table 3. Binodal Data for the POELE10 (1) + K2CO3 (2) + H2O (3) ATPSs at T = (288.15, 293.15, 303.15, and 308.15) K and Pressure p = 0.1 MPaa

Table 2. Binodal Data for the POELE10 (1) + KOH (2) + H2O (3) ATPSs at T = (288.15, 293.15, 303.15, and 308.15) K and Pressure p = 0.1 MPaa 100w1

100w2

100w1

16.22 15.28 14.42 13.72 12.93 12.26 11.75 11.08 10.66

9.71 9.87 10.01 10.13 10.31 10.46 10.58 10.68 10.78

10.17 9.36 8.53 7.59 6.77 5.95 5.39 4.82 4.09

17.55 16.53 15.80 15.13 14.55 13.83 13.27 12.71 12.20

8.87 9.01 9.09 9.18 9.25 9.40 9.48 9.58 9.67

11.22 10.48 9.56 8.71 7.70 6.90 6.24 5.24 4.52

17.73 17.00 16.04 15.25 14.67 14.03 13.41 12.89

7.88 7.98 8.16 8.28 8.40 8.48 8.56 8.65

12.34 11.46 10.70 10.03 9.33 8.51 7.62 6.60

18.38 16.97 16.22 15.57 14.92 14.29 13.35 12.48 11.59

7.02 7.13 7.21 7.28 7.36 7.47 7.57 7.71 7.84

10.81 10.13 9.54 8.95 8.24 7.60 7.09 6.61 5.94

100w2

100w1

T = 288.15 K 10.88 3.36 11.03 2.73 11.21 1.97 11.41 1.56 11.60 1.14 11.80 0.79 11.98 0.43 12.12 0.19 12.30 0.11 T = 293.15 K 9.85 3.93 10.01 3.26 10.21 2.68 10.37 2.09 10.58 1.57 10.77 1.14 10.94 0.84 11.18 0.52 11.38 0.27 T = 303.15 K 8.78 5.60 8.91 4.58 9.07 3.86 9.18 3.26 9.35 2.52 9.49 1.96 9.69 1.40 9.90 0.64 T = 308.15 K 7.95 5.34 8.08 4.87 8.20 4.32 8.31 3.82 8.46 3.33 8.59 2.85 8.72 2.33 8.83 1.88 8.96 1.50

100w2

100w1

100w2

12.54 12.76 13.08 13.28 13.49 13.69 13.96 14.19 14.41

0.05 0.03 0.02 0.01

14.60 14.88 15.15 15.38

11.61 11.84 12.07 12.30 12.49 12.71 12.93 13.22 13.48

0.17 0.08 0.04 0.03 0.02

13.77 14.03 14.31 14.80 15.36

10.17 10.40 10.61 10.76 11.02 11.21 11.45 11.83

0.28 0.10 0.05 0.02 0.01

12.15 12.46 12.74 13.08 13.51

9.12 9.23 9.40 9.54 9.72 9.85 10.00 10.23 10.41

1.17 0.68 0.37 0.11 0.03 0.02 0.01

10.58 10.87 11.17 11.66 12.04 12.49 12.73

100w1

100w2

100w1

17.00 16.05 15.09 14.42 13.93 13.37 12.84 11.92 11.08

7.19 7.29 7.42 7.55 7.64 7.75 7.82 7.98 8.15

10.29 9.67 9.09 8.54 8.06 7.61 6.99 6.54 5.83

17.74 16.88 15.95 15.17 14.47 13.76 13.13 12.54 12.06

6.42 6.50 6.68 6.80 6.91 7.08 7.19 7.33 7.41

11.61 11.10 10.37 9.69 9.02 8.45 7.56 6.83 6.09

15.89 14.94 14.28 13.79 13.23 12.71 11.80 10.97 10.19

5.91 6.06 6.13 6.22 6.28 6.38 6.49 6.63 6.80

9.57 9.00 8.46 7.98 7.54 6.93 6.48 5.77 5.18

18.76 17.72 16.98 16.23 15.51 14.89 14.30 13.68 12.76

4.92 5.03 5.11 5.23 5.33 5.45 5.53 5.63 5.78

11.88 11.06 10.30 9.67 9.12 8.20 7.57 6.88 5.94

100w2

100w1

T = 288.15 K 8.30 5.23 8.42 4.37 8.53 3.69 8.67 2.98 8.80 2.33 8.92 1.82 9.05 1.43 9.15 1.08 9.37 0.80 T = 293.15 K 7.50 5.68 7.61 5.20 7.79 4.50 7.93 3.70 8.09 3.00 8.22 2.17 8.40 1.65 8.58 1.12 8.78 0.59 T = 303.15 K 6.94 4.32 7.06 3.56 7.19 2.95 7.30 2.31 7.39 1.80 7.54 1.42 7.65 1.07 7.81 0.79 7.95 0.36 T = 308.15 K 5.94 5.25 6.09 4.74 6.23 4.20 6.36 3.66 6.47 3.11 6.67 2.58 6.79 2.12 6.96 1.73 7.18 1.32

100w2

100w1

100w2

9.54 9.77 10.00 10.20 10.45 10.68 10.96 11.19 11.41

0.36 0.19 0.08 0.04 0.03 0.02 0.01

11.76 12.02 12.34 12.69 12.98 13.35 13.57

8.90 9.05 9.23 9.48 9.71 9.98 10.22 10.54 10.89

0.26 0.12 0.04 0.02 0.01

11.15 11.46 11.82 12.11 12.48

8.19 8.41 8.65 8.85 9.05 9.24 9.43 9.61 9.90

0.19 0.08 0.04 0.03 0.02 0.01

10.22 10.49 10.75 11.00 11.36 11.62

7.40 7.53 7.69 7.86 8.05 8.26 8.50 8.64 8.84

0.98 0.70 0.34 0.15 0.06 0.03 0.02 0.01

8.99 9.19 9.43 9.82 10.11 10.38 10.67 10.81

a

Standard uncertainties u are u(w) = 0.0001, u(T) = 0.05 K, and u(p) = 10 kPa.

(Shanghai, China). The trade name of POELE10 is Brij35. The average molar mass, the critical micelle concentration (CMC), the hydrophilic lipophilic balance (HLB), and the melting point of the POELE10 are 626.86 g·mol−1, 0.09 mg·L−1, 16.9, and 300.15 K, respectively. All reagents were used without further purification, and the water used in experiments was doubledistilled. 2.2. Apparatus and Procedure. According to the cloud point method, a 50 mL glass vessel was used to determine the binodal data. The POELE10 solution was put into the vessel which was equipped with a coat in which the water was kept at the desired temperature using a DC-2008 water thermostat (Shanghai Hengping Instrument Factory, China). Then the salt solution was dropped into the vessel until the solution becomes cloudy. The mass fraction of POELE10 and salt was noted

a


2. EXPERIMENTAL SECTION 2.1. Materials. Three types of potassium salts (KOH, K2CO3, and K3PO4) were obtained from the Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China), which were analytical grade reagents (GR, min. 99 % by mass fraction). Nonionic surfactants POELE10 with a quoted purity of greater than 0.99 mass fraction was purchased from Aladdin Reagent Company B



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Table 4. Binodal Data for the POELE10 (1) + K3PO4 (2) + H2O (3) ATPSs at T = (288.15, 293.15, 303.15, and 308.15) K and Pressure p = 0.1 MPaa 100w1

100w2

100w1

17.57 16.20 15.45 14.86 14.19 13.59 12.97 12.50

5.91 6.11 6.23 6.36 6.51 6.66 6.82 6.96

12.04 11.39 10.77 10.07 9.48 8.92 8.06 7.31

18.53 17.63 16.77 16.02 15.38 14.80 14.21 13.65

5.86 6.04 6.22 6.36 6.49 6.59 6.72 6.85

13.11 12.55 11.76 10.95 10.00 9.24 8.47 7.83

17.41 15.98 14.86 14.32 13.56 12.77 12.00 11.33 10.64

5.51 5.69 5.89 5.99 6.11 6.22 6.37 6.48 6.62

10.09 9.56 9.05 8.50 7.83 7.20 6.33 5.59 4.74

18.60 17.64 16.94 16.10 15.18 14.31 13.40 12.66

4.58 4.78 4.90 5.01 5.11 5.26 5.43 5.56

11.79 10.81 10.06 9.08 8.44 7.89 6.83 5.59

100w2

100w1

T = 288.15 K 7.08 6.53 7.29 5.63 7.48 4.85 7.66 4.06 7.82 3.27 8.02 2.47 8.26 1.80 8.49 1.21 T = 293.15 K 7.00 7.17 7.12 6.23 7.30 5.56 7.48 4.82 7.72 3.81 7.91 3.07 8.09 2.43 8.29 1.79 T = 303.15 K 6.75 4.06 6.88 3.21 7.01 2.37 7.12 1.74 7.28 1.23 7.46 0.74 7.65 0.32 7.84 0.16 8.10 0.07 T = 308.15 K 5.69 4.81 5.91 3.67 6.06 3.08 6.25 2.50 6.42 1.93 6.56 1.40 6.87 0.93 7.21 0.55

100w2

100w1

100w2

8.72 9.06 9.32 9.62 9.89 10.21 10.55 10.88

0.78 0.51 0.23 0.11 0.04 0.02 0.01

11.10 11.35 11.71 12.01 12.32 12.80 13.22

8.45 8.72 8.94 9.15 9.44 9.66 9.90 10.18

1.20 0.64 0.38 0.15 0.06 0.02 0.01

10.41 10.69 11.07 11.38 11.71 12.21 12.91

8.32 8.60 8.89 9.16 9.40 9.72 10.02 10.30 10.64

0.03 0.02 0.01

10.97 11.29 11.64

7.45 7.91 8.10 8.38 8.63 8.86 9.15 9.44

0.24 0.05 0.02 0.01

9.83 10.28 10.61 11.14

Figure 1. Binodal curves of the POELE10 (1) + KOH (2) + H2O (3) ATPSs at (288.15, 293.15, 298.15, 303.15, and 308.15) K. △, 288.15 K; ○, 293.15 K; □, 298.15 K;16 ▽, 303.15 K; ×, 308.15 K; solid line, reproduced by eq 2.

Figure 2. Binodal curves of the POELE10 (1) + K2CO3 (2) + H2O (3) ATPSs at (288.15, 293.15, 298.15, 303.15, and 308.15) K. △, 288.15 K; ○, 293.15 K; □, 298.15 K;16 ▽, 303.15 K; ×, 308.15 K; solid line, reproduced by eq 2.

a


to represent the relationships between the index of refraction of the mixed solution (nD), the mass fractions of POELE10 (w1), and the mass fractions of salt (w2). nD = n0 + a1w1 + a 2w2 (1)

using an analytical balance (BS124S, Beijing Sartorius Instrument Co., China) with an uncertainty of ± 1.0·10−7 kg. To determine the next cloud point, one drop of water was added, and the above process was repeated. The appropriate amounts of POELE10, salt, and water were added into the vessel to determine the tie-line data. After the mixed solution kept stirring for 0.5h, it was placed in the thermostat water bath whose temperature was controlled at the constant temperature. The two phases were completely separated after 48 h, then, the mass fractions of POELE 10 and salt in both phases were determined. The mass fraction of salt in two phases was determined using flame photometry (TAS-968, Beijing Purkinje General Instrument Co., Ltd., China). The uncertainty in the measurement of the mass fraction of the salts was 0.0003. The mass fraction of POELE10 in the top and bottom phases was determined by a refractometer17 (WZS-I 811639, Shanghai, China) with a precision of ± 0.0001. The following equation (eq 1) is used

where n0, a1, and a2 are constants, the values of which for the investigated systems are given in Table 1. The precision of the mass fraction of POELE10 using this method was better than 0.0002.

3. RESULTS AND DISCUSSION 3.1. Binodal Data and Correlation. The binodal data of the systems containing POELE10 and three salts (KOH, K2CO3, and K3PO4) at the different temperatures (288.15, 293.15, 303.15, and 308.15) K were determined and listed in Tables 2 to 4. The binodal curves of the investigated systems were shown in Figures 1 to 3. In recent years, many empirical equations were used to correlate the binodal data of ATPSs, we C



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applied these equations to the investigated systems and found that the following three equations (eqs 2 to 4) showed a satisfactory fitting effect. w1 = exp(a + bw20.5 + cw2 + dw22)

(2)

w1 = aw23 + bw22 + cw2 + d

(3)

w1 = a exp(bw20.5 − cw23)

(4)

where w1 represents the mass fraction of POELE10, w2 represents the mass fraction of salts, and a, b, c, and d are fitting parameters. Through the regression analysis of experimental binodal data shown in Tables 2 to 4, the fitting parameters a, b, c, and d of eqs 2 to 4 were determined and listed in Tables 5 to 7, in which the square of correlation coefficients (R2) and the corresponding standard deviations (sd) for the investigative systems are shown. The binodal data of alcohol−citrate ATPS18 were correlated by using eq 2 at 298.15 K. The third-order polynomial equation (eq 3) was used to fit the binodal data for the systems containing PEG and satls.19 Equation 4 was used for the correlation of the binodal

Figure 3. Binodal curves of the POELE10 (1) + K3PO4 (2) + H2O (3) ATPSs at (288.15, 293.15, 298.15, 303.15, and 308.15) K. △, 288.15 K; ○, 293.15 K; □, 298.15 K;16 ▽, 303.15 K; ×, 308.15 K; solid line, reproduced by eq 2.

Table 5. Values of Parameters of eq 2 for the POELE10 (1) + KOH/K2CO3/K3PO4 (2) + H2O (3) ATPSs at T = (288.15, 293.15, 303.15, and 308.15) K T/K

a

b

c

288.15 293.15 303.15 308.15

42.9374 70.7387 48.1179 77.0181

−421.5704 −632.7006 −476.9693 −734.6344

288.15 293.15 303.15 308.15

74.6481 83.3231 76.4515 42.8112

−710.9939 −828.5511 −792.3902 −474.8019

288.15 293.15 303.15 308.15

75.6647 55.7227 43.4311 37.3931

−743.3757 −574.8016 −460.6159 −419.1393

POELE10 + KOH + H2O 1135.5370 1591.3320 1316.9646 1969.9518 POELE10 + K2CO3 + H2O 1895.5416 2298.0419 2292.1383 1453.7805 POELE10 + K3PO4 + H2O 2032.6136 1639.9346 1351.0369 1286.8709

d

R2

100sda

−2509.9565 −3204.3538 −3178.4589 −4541.0258

0.9992 0.9995 0.9991 0.9995

0.15 0.13 0.17 0.12

−4269.4111 −5496.7439 −6046.3722 −4416.3588

0.9997 0.9998 0.9997 0.9997

0.09 0.08 0.09 0.11

−4733.4548 −4179.0872 −3785.2803 −3943.6438

0.9998 0.9994 0.9993 0.9985

0.09 0.14 0.14 0.22

a exp 2 exp cal 0.5 sd = (∑ni=1(wcal 1 − w1 ) /n) , where w1 is the experimental mass fraction of POELE10 in Tables 2 to 4, w1 is the corresponding data calculated using eq 2. n represents the number of binodal data.


a

b

288.15 293.15 303.15 308.15

18.6511 −374.6466 −137.4447 −595.4221

50.1131 194.0812 108.8465 251.5659

288.15 293.15 303.15 308.15

−200.1671 172.0714 −172.0742 −167.7814

119.2024 4.8066 110.9715 104.4356

288.15 293.15 303.15 308.15

92.4570 188.8103 −156.3235 −284.9193

16.6510 −11.9126 96.5998 120.7406

c POELE10 + KOH + H2O −16.3927 −32.8423 −21.7111 −34.8984 POELE10 + K2CO3 + H2O −20.6773 −8.5523 −18.0770 −16.2989 POELE10 + K3PO4 + H2O −8.6813 −5.6507 −15.8074 −16.2790

d

R2

100sda

1.2660 1.8219 1.2817 1.5941

0.9991 0.9995 0.9989 0.9992

0.15 0.13 0.19 0.15

1.1125 0.6582 0.8737 0.7538

0.9996 0.9996 0.9994 0.9998

0.10 0.11 0.12 0.08

0.6418 0.5194 0.7763 0.7077

0.9989 0.9990 0.9994 0.9995

0.18 0.18 0.13 0.13

exp 2 exp cal 0.5 sd = (∑ni=1(wcal 1 − w1 ) /n) , where w1 is the experimental mass fraction of POELE10 in Tables 2 to 4, w1 is the corresponding data calculated using eq 3. n represents the number of binodal data. a

D



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a

288.15 293.15 303.15 308.15

0.0001 0.0163 0.0040 0.5775

288.15 293.15 303.15 308.15

0.0940 0.0633 0.1255 0.4952

288.15 293.15 303.15 308.15

0.0702 0.0905 0.2652 0.9872

b

c

POELE10 + KOH + H2O 33.9836 2869.5479 13.6215 2440.9974 19.4662 3456.3588 −0.5814 2963.5915 POELE10 + K2CO3 + H2O 6.1839 2937.9135 7.4652 3373.5307 4.6468 4436.8132 −2.2670 4131.1677 POELE10 + K3PO4 + H2O 6.5847 2906.0402 5.4027 3057.6309 0.7866 3765.1665 −6.3139 3246.9596

R2

100sda

0.9990 0.9989 0.9988 0.9983

0.16 0.19 0.20 0.22

0.9989 0.9983 0.9983 0.9990

0.18 0.23 0.20 0.19

0.9976 0.9977 0.9983 0.9988

0.27 0.29 0.22 0.21

Figure 5. Diagram about the dependence of the cloud point (CP) on the mass fraction of salts in the presence of POELE10. △, K3PO4; ○, K2CO3; □, KOH; dot (red), wp = 0.2; dash (blue), wp = 0.15; solid (black), wp = 0.1; dash dot dot (green), wp = 0.05.

exp 2 exp 0.5 sd = (∑ni=1(wcal 1 − w1 ) /n) , where w1 is the experimental mass fraction of POELE10 in Tables 2 to 4, wcal 1 is the corresponding data calculated using eq 4. n represents the number of binodal data. a

Table 8. Values of Parameters of eq 5 for the POELE10 (1) + KOH/K2CO3/K3PO4 (2) + H2O (3) ATPSs at T = (288.15, 293.15, 303.15, and 308.15) K T/K 288.15 293.15 303.15 308.15 288.15 293.15 303.15 308.15 288.15 293.15 303.15 308.15

V*213/g·mol−1

R2

POELE10 + KOH + H2O 436.6765 0.9585 468.4118 0.9448 520.3226 0.9537 581.9118 0.9719 POELE10 + K2CO3 + H2O 555.5882 0.9715 599.1515 0.9785 656.6364 0.9736 719.4857 0.9836 POELE10 + K3PO4 + H2O 579.9688 0.9720 613.0000 0.9711 657.2813 0.9673 731.4828 0.9777

sda 0.17 0.18 0.16 0.13 0.16 0.16 0.14 0.15 0.18 0.18 0.17 0.18

Figure 4. Binodal curves of the POELE10 (1) + KOH/K2CO3/K3PO4 (2) + H2O (3) ATPSs at 288.15 K. ▲, K3PO4; ●, K2CO3; ■, KOH; solid line, reproduced by eq 2.

exp 2 exp 0.5 sd = (∑ni=1(wcal 1 − w1 ) /n) , where w1 is the experimental mass fraction of POELE10 in Tables 2 to 4, wcal 1 is the corresponding data calculated using eq 5. n represents the number of binodal data.

curves of many ATPSs.20−25 In accordance with the obtained square of correlation coefficients and standard deviations, it has been concluded that eq 2 is more suitable to correlate the binodal curves for the investigated ATPSs. 3.2. Effect of the Salt Type on the Binodal Curves. We have discussed the effect of three salts (KOH, K2CO3, K3PO4) on the binodal curves at 298.15 K in the previously published article.16 It was found that the two phase area expanded with increasing the salting-out strength of salts that mainly depended on the charge of the anion of the salt. The salting-out strength of salts containing anions with a higher valence is more powerful than that with a lower valence; namely, the order of phase-forming ability for the investigated salts is K3PO4 > K2CO3 > KOH. This conclusion has already been demonstrated by the effective excluded volume and the salting-out coefficient. In this paper, the binodal data of the systems containing the POELE10 and KOH/K2CO3/K3PO4 at the temperatures (288.15, 293.15, 303.15, and 308.15) K is shown

in Tables 2 to 4. The data showed the same conclusion at every temperature as that in the article reported by Lu et al.,16 which further testified the reliability of the conclusion. We take the POELE10-KOH/K2CO3/K3PO4 ATPSs at the 288.15 K, for instance, and their binodal curves are presented in Figure 4. 3.3. Effect of the Temperature on the Binodal Curves. Figures 1 to 3 showed a general trend that the binodal curve is moving toward the coordinate with the increase in temperature, which means that raising the temperature will benefit the formation of ATPSs. The main reason for this is that the increase in temperature caused the hydrophobicity of POELE10 to be enhanced, which results in more water transfers to the bottom phase from the top phase, where two phases are easily formed. To closely explain this question, we drew a diagram (Figure 5) of the dependence of the cloud point (CP)26 on the mass fraction of salts, from which we can see that the disparities between the salting-out strength of all kinds of salts are large at the lower temperature, but these

a

E



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Table 9. Tie-Line Data for the POELE10 (1) + KOH (2) + H2O (3) ATPSs at T = (288.15, 293.15, 303.15, and 308.15) K and Pressure p = 0.1 MPaa total system 100w1

a

POELE10-rich phase

100w2

100wt1

100wt2

8.54 8.53 8.49

11.49 11.99 12.51

15.61 19.51 23.65

9.83 9.32 8.87

8.51 8.48 8.46

10.99 11.51 12.02

19.38 23.95 27.28

8.57 8.03 7.71

8.49 8.49 8.48

10.02 10.49 11.01

27.53 32.61 36.02

6.43 5.95 5.71

8.49 8.45 8.50

9.510 10.01 10.55

31.79 35.80 39.37

6.09 5.93 5.81

salt-rich phase 100wb1 T= 1.82 0.62 0.15 T= 1.63 0.65 0.27 T= 1.90 0.84 0.34 T= 1.31 0.57 0.21

100wb2

TLL

slope (k)

average of slope

13.10 13.88 14.49

14.17 19.43 24.17

−4.2171 −4.1342 −4.1777

−4.1763

12.61 13.30 13.93

18.20 23.89 27.72

−4.4011 −4.4239 −4.3465

−4.3905

11.28 11.95 12.59

26.09 32.33 36.34

−5.2897 −5.2990 −5.1895

−5.2594

10.57 11.20 11.83

30.81 35.62 39.62

−6.8050 −6.6877 −6.5086

−6.6671

288.15 K

293.15 K

303.15 K

308.15 K


Table 10. Tie-Line Data for the POELE10 (1) + K2CO3 (2) + H2O (3) ATPSs at T = (288.15, 293.15, 303.15, and 308.15) K and Pressure p = 0.1 MPaa total system 100w1

a

POELE10-rich phase

100w2

100wt1

100wt2

8.50 8.48 8.49

9.01 9.51 10.01

15.38 20.07 22.63

7.40 6.81 6.57

8.97 9.02 8.99

8.53 8.97 9.53

24.29 27.91 31.44

5.16 4.86 4.54

9.00 8.96 9.00

8.02 8.48 9.01

26.43 29.74 33.64

5.11 4.97 4.83

8.99 9.01 9.01

7.52 7.99 8.49

29.13 33.63 37.05

4.21 4.03 3.92


100wb2

TLL

slope (k)

average of slope

10.49 11.30 12.00

13.43 19.66 22.93

−4.2297 −4.2637 −4.1058

−4.1997

9.86 10.73 11.45

22.19 27.47 31.75

−4.6023 −4.5755 −4.4891

−4.5556

9.32 9.81 10.51

25.49 29.59 33.94

−5.9725 −6.0095 −5.8935

−5.9585

8.77 9.35 9.93

28.10 33.42 37.29

−6.0827 −6.2058 −6.1270

−6.1385

288.15 K

293.15 K

303.15 K

308.15 K


systems containing two types of polymers. In the paper, we applied this model to the aqueous surfactant−salt systems, and the corresponding equation is written as

disparities become small with the increasing temperature. When the temperature is low, the hydrophobicity of POELE10 is weak, at the moment, the main driver of the formation of two phases was the salting-out effect, and the effect of the hydrophobicity of POELE10 on forming two phase was very small. However, with the increase in the temperature the hydrophobicity of POELE10 enhanced,27 and then the formation of the ATPS was jointly driven by the salting-out effect of salt and the hydrophobicity of POELE10. Thus the phase-forming ability of whole systems enhanced and the critical concentrations of POELE10 and salt decreased with the increasing temperature, which is consistent with the other polymer−salt ATPSs.19,28−33 3.4. Effective Excluded Volume. The effective excluded volume (EEV) is calculated with the binodal model that was developed by Guan et al. based on the statistical geometry methods.34 This binodal model was originally used in the

⎛ w ⎞ w * 2 ⎟ + V 213 * 1 =0 ln⎜V 213 M2 ⎠ M1 ⎝

(5)

where V213 * is the scaled EEV of salt, w and M represent the mass fraction and molecular mass, the subscripts “1” and “2” express POELE10 and salts, respectively. The EEV values along with the square of correlation coefficients (R2) and standard deviations (sd) for the investigated systems are given in Table 8. Through analyzing the values of EEV in the table, we found that at the same temperature the EEV values rise with the increase in the charge of the anion of the salts, which lives up to the above-mentioned ideas. The salt containing the higher valence anion has a stronger salting-out ability, and it can F



Article

Table 11. Tie-Line Data for the POELE10 (1) + K3PO4 (2) + H2O (3) ATPSs at T = (288.15, 293.15, 303.15, and 308.15) K and Pressure p = 0.1 MPaa total system 100w1

a

POELE10-rich phase

100w2

100wt1

100wt2

8.50 8.42 8.47

9.01 9.61 10.02

19.76 22.42 24.92

6.23 6.01 5.79

8.39 8.37 8.48

8.86 9.18 9.49

24.52 26.86 29.34

5.05 4.80 4.68

8.51 8.48 8.48

7.99 8.52 9.01

25.12 29.05 32.94

4.84 4.62 4.45

8.50 8.49 8.489

7.51 8.00 8.53

27.28 30.91 34.39

3.99 3.82 3.69


100wb2

TLL

slope (k)

average of slope

10.82 11.62 12.06

19.03 22.78 25.59

−4.0244 −3.9296 −3.9453

−3.9664

10.55 10.99 11.42

23.87 26.80 29.68

−4.2257 −4.2143 −4.2962

−4.2454

9.33 10.03 10.55

23.99 28.90 33.20

−5.2521 −5.2518 −5.3514

−5.2851

8.85 9.47 10.04

26.38 30.75 34.65

−5.3350 −5.3563 −5.3619

−5.3511

288.15 K

293.15 K

303.15 K

308.15 K


Figure 6. Tie-lines of the POELE10 (1) + KOH (2) + H2O (3) ATPSs at (288.15, 293.15, 298.15, 303.15, and 308.15) K. ▲, dot, red, 288.15 K; ●, dash, green, 293.15 K; ■, solid, blue, 298.15 K;16 ★, dash dot, magenta, 303.15 K; ▼, dash dot dot, cyan, 308.15 K.

Figure 7. Tie-lines of the POELE10 (1) + K2CO3 (2) + H2O (3) ATPSs at (288.15, 293.15, 298.15, 303.15, and 308.15) K. ▲, dot, red, 288.15 K; ●, dash, green, 293.15 K; ■, solid, blue, 298.15 K;16 ★, dash dot, magenta, 303.15 K; ▼, dash dot dot, cyan, 308.15 K.

⎛ wb ⎞ ⎛ w3t ⎞r 3 ⎜⎜ b ⎟⎟ = k 2⎜ t ⎟ ⎝ w1 ⎠ ⎝ w2 ⎠

exclude a more effective volume. The EEV values increase with rising temperature at the same POELE−salt ATPS, because that the increase in temperature made the hydrophobicity of POELE10 stronger, and then it indirectly strengthened the salting-out effect of salts. 3.5. Liquid−Liquid Equilibrium Data and Correlation. The LLE experimental data of the aqueous systems composed of the POELE10 and KOH/K2CO3/K3PO4 at the different temperatures T = (288.15, 293.15, 303.15, and 308.15) K are given in Tables 9 to 11, respectively. Meanwhile, the tie-lines for the studied ATPSs at different temperatures are respectively shown in Figures 6 to 8. The LLE data were correlated by the empirical correlation equations given by Othmer−Tobias and Bancroft35 (eqs 6 and 7) for the studied systems. ⎛ 1 − w b ⎞n ⎛ 1 − w1t ⎞ 2 ⎟⎟ k = ⎟ ⎜ ⎜ 1⎜ t b ⎝ w1 ⎠ ⎝ w2 ⎠

(7)

In the equations, wt1 is the mass fraction of the POELE10 in the top phase; wb2 is the mass fraction of the salt in the bottom phase; wt3 and wb3 are the mass fraction of water in the top and bottom phases, respectively; and k1, n, k2, and r are the fit parameters. The Othmer−Tobias and Bancroft equations have been successfully used to correlate the tie-lines compositions of the types of ATPSs.24,25,36,37 For the investigated systems, the values of the parameters in Othmer−Tobias and Bancroft equations along with the square of correlation coefficient values (R2) and standard deviations (sd) are listed in Table 12, which indicated that the fitting effect is satisfactory. 3.6. Effect of Temperature on the Tie-Line. Two important parameters used to measure the nature of the tie-lines

(6) G



Article

the STL increases with decreasing the absolute value of ΔX and increasing the absolute value of ΔY. We concluded that the increase in temperature leads to the increasing absolute value of STL, which is intuitively observed in Figures 6 to 8.

are the slope of the tie-line (STL) and the tie-line length (TLL) that were described as STL = ΔY /ΔX TTL =

(8)

ΔX2 + ΔY 2

(ΔX = w2t − w2b ,

ΔY = w1t − w1b)

4. CONCLUSION The binodal data and liquid−liquid equilibria data of ATPSs containing POELE10 and KOH/K2CO3/K3PO4 at the different temperatures T = (288.15, 293.15, 303.15, and 308.15) K were determined. The experience formulas for extensively practicing operation were used to fit the binodal data for the investigated systems and have achieved satisfactory results. The tie-line data were satisfactorily correlated with Othmer−Tobias and Bancroft for the studied systems. In light of the effect of type of salt on the binodal curves, we found that the ATPSs are more likely to form for the investigated systems when the valence of anion of the salt is higher, which is correspondent with the values of EEV obtained by eq 5. Furthermore, the effect of the temperature on the binodal curves and liquid− liquid equilibrium compositions were discussed. With the increase in temperature, the critical concentration of POELE10 and salt for forming two phases will decrease. With the rising temperature, the hydrophobicity of POELE10 increases, and that leads to the rise in absolute value of the slope of the tieline.

(9)

where wt1 and wb1 are the mass fraction of POELE10 in the top and bottom phases, and similarly, wt2 and wb2 are the mass fraction of salt in the top and bottom phases. The values of TLL and STL (slope) were given in Tables 9 to 11, from which it was found that the values of TLL and STL increase as temperatures go up. The rising temperature made the hydrophilicity of the POELE10 weaken and its hydrophobicity strengthen. The decrease in the amount of water in the POELE10-rich phase caused the values of wt1 and wt2 to increase. On the contrary, the values of wb1 and wb2 decrease with increasing the water in the salt-rich phase. The absolute value of

■

AUTHOR INFORMATION

Corresponding Author

*Z.T.: E-mail: [email protected]. Tel.: +86-434-3291953. Fax: +86-434-3291953. Y.Y.: E-mail: [email protected]. Tel.: +86511-88790683. Fax: +86-511-88791800. Funding

This work was supported by the National Natural Science Foundation of China (No. 21076098), the Natural Science Foundation of Jiangsu Province (Nos. BK2010349 and BK2011529), China Postdoctoral Science Foundation funded project (No. 20110491352), Ph.D. Innovation Programs Foundation of Jiangsu Province (No. CXLX12_0645), Jiangsu Postdoctoral Science Foundation funded project (No.

Figure 8. Tie-lines of the POELE10 (1) + K3PO4 (2) + H2O (3) ATPSs at (288.15, 293.15, 298.15, 303.15, and 308.15) K. ▲, dot, red, 288.15 K; ●, dash, green, 293.15 K; ■, solid, blue, 298.15 K;16 ★, dash dot, magenta, 303.15 K; ▼, dash dot dot, cyan, 308.15 K.

Table 12. Values of Parameters of eqs 6 and 7 for the POELE10 (1) + KOH/K2CO3/K3PO4 (2) + H2O(3) ATPSs at T = (288.15, 293.15, 303.15, and 308.15) K T/K

10−3k1

n

288.15 293.15 303.15 308.15

1.3730 2.2031 3.8444 8.0081

4.3786 3.8914 3.1600 2.6167

288.15 293.15 303.15 308.15

6.0264 28.0815 7.9724 5.1787

3.1712 2.1300 2.5707 2.6235

288.15 293.15 303.15 308.15

27.0957 8.5481 5.4831 9.8467

2.3790 2.7544 2.7726 2.4022

k2

r

POELE10 + KOH + H2O 0.1898 0.2196 0.2671 0.3369 POELE10 + K2CO3 + H2O 5.4538 0.2637 5.7752 0.4028 6.9059 0.3484 7.7500 0.3403 POELE10 + K3PO4 + H2O 4.9776 0.3682 5.9306 0.3247 6.8615 0.3206 7.1385 0.3805 4.8239 5.1103 6.1122 6.6625

R12

R22

100 sd1a

100 sd2a

0.9942 0.9860 0.9778 0.9979

0.9991 0.9730 0.9652 0.9948

0.3389 0.8487 1.0806 0.4030

0.57 2.53 2.30 0.71

0.9585 0.9964 0.9929 0.9875

0.9407 0.9996 0.9849 0.9819

1.5872 0.2498 0.7337 0.8747

4.40 0.24 1.41 1.54

0.9635 0.9993 0.9892 0.9998

0.9740 0.9997 0.9932 1.0000

0.9344 0.0853 0.6117 0.0481

1.73 0.14 1.04 0.03

top 2 bot bot 2 0.5 sd = [∑Ni=1((wtop i,j,cal − wi,j,exp) + (wi,j,cal − wi,j,exp) )/2N] , where N is the number of tie lines and j = 1 and j = 2, sd1 and sd2 represent the mass percent standard deviations for POELE10 and salt, respectively. a

H



Article

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1101036C), and the Programs of Senior Talent Foundation of Jiangsu University (No. 11JDG029). Notes

The authors declare no competing financial interest.

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