Measurement and Correlation of Phase Equilibria in Aqueous Two

Article pubs.acs.org/jced

Measurement and Correlation of Phase Equilibria in Aqueous Two-Phase Systems Containing Polyoxyethylene Cetyl Ether and Potassium Salt at Different Temperatures Yang Lu,*,†,‡ Biao Cong,† Juan Han,‡ Yun Wang,‡ Zhenjiang Tan,*,† and Yongsheng Yan*,†,‡ †

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

‡

ABSTRACT: The aqueous two-phase system (ATPS) containing the polyoxyethylene(20) cetyl ether (C56H114O21, POELE20) and three potassium salts (KOH, K2CO3, and K3PO4) at the three temperatures (288.15, 298.15, and 308.15) K were designed. The binodal data of the studied systems were determined and correlated with three experience equations, and a satisfactory correlation effect was gained. The effect of the type of salt on the phaseforming ability of the system was discussed in the study of effective excluded volume (EEV), phase diagram, and Gibbs free energy of ionic hydration. It was found that the phase-forming ability of the system was enhanced with the increase in system EEV and anion valence, and it also increased with an increase in the absolute value of Gibbs free energy of ionic hydration. The binodal curves are influenced by the system temperature, and it was found that, with the increase in temperature, the binodal curves moved to the left and the two-phase areas expanded. Moreover, the effect of temperature on the slope of the tie line was studied, and we have drawn a conclusion that the value of the slope of the tie line increased with rising temperature.

1. INTRODUCTION Aqueous two-phase extraction is a new and green separation and enrichment technology, and it has some advantages, such as being simple, saving time, and being efficient, green, and ecofriendly, and it has been applied to the quantitative separation and extraction of metal ions, separation and purification of bioactivators, and extraction of natural products. The existent aqueous two-phase system (ATPS) included a polymer−polymer aqueous two-phase system,1,2 polymer−salt aqueous two-phase system,3,4 ionic liquid−salt aqueous two-phase system,5,6 and micromolecule organic solvent−salt aqueous two-phase system.7,8 Because organic solvent is volatile and instable, the price of ionic liquid is higher, and the viscosity of the system containing two polymers is larger, the application of these three types of aqueous two-phase systems in large-scale industrial production was affected. One polymer of the polymer−polymer aqueous two-phase system was replaced by salt, and it is a polymer−salt aqueous two-phase system. The cost of the polymer−salt aqueous two-phase system is cheaper, and it has the advantage of good biocompatibility. It is applied in the separation and enrichment of bioactivators, natural products, and antibiotics9−11 and has a high-exploited value and broad prospects on its application.12−16 Polyoxyethylene n-alkyl ethers can be an appropriate class of phase-forming polymers for ploymer−salt ATPS because they are composed of a hydrophilic polyoxyethylene domain and a hydrophobic alkyl tail. These ATPSs have a great application potential for the separation and purification of biological material. In our previous works,17−21 the liquid−liquid equilibrium © XXXX American Chemical Society

compositions of the ATPSs containing polyoxyethylene(10) lauryl ether (C32H66O11, POELE10) and eight kinds of inorganic salts (KOH, K2CO3, K3PO4, K2HPO4, (NH4)2HPO4, Li2SO4, MgSO4, and ZnSO4) / six kinds of organic salts (KC6H11O7, K 2 C 2 O 4 , K 2 C 4 H 4 O 6 , K 3 C 6 H 5 O 7 , (NH 4 ) 2 C 4 H 4 O 6 , and Na2C4H4O6) at different temperatures have been reported. Few studies on ATPS composed of POELE20 have been reported yet. In this work, the phase diagram data of ATPSs containing polyoxyethylene(20) cetyl ether (C56H114O21, POELE20) and three kinds of potassium salt (KOH, K2CO3, and K3PO4) will been given, and the effect of salt type and temperature on these systems also will be discussed.

2. EXPERIMENTAL SECTION 2.1. Materials. Potassium salts (KOH, K2CO3, and K3PO4) were obtained from the Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China), and they were analytical grade reagents (GR, minimum 99% by mass fraction). The quoted purity of nonionic surfactants POELE20 was greater than 99% mass fraction, which was purchased from Aladdin Reagent Co. (Shanghai, China). POELE20 was characterized as follows: the average molar mass is 1123.50 g·mol−1, the melting point is 311.15 K, the hydrophilic lipophilic balance (HLB) is 11.5, and the critical micelle concentration (cmc) is 0.07 mg·L−1. Received: December 25, 2014 Accepted: February 25, 2015

A

DOI: 10.1021/je501165h J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Sample Table

a

chemical name

CAS reg. no.

source

initial mole fraction purity

purification method

POELE20 KOH K2CO3 K3PO4

9004-95-9 1310-58-3 584-08-7 22763-03-7

Aladdin Reagent Co. Sinopharm Chemical Reagent Sinopharm Chemical Reagent Sinopharm Chemical Reagent

0.992 0.990 0.990 0.990

noa noa noa noa

Reagent was used without further purification.

Table 2. Values of Parameters of Equation 1 for Aqueous Solution of POELE20 + KOH/K2CO3/K3PO4 at 298.15 K system

n0

a1

a2

POELE20 + KOH POELE20 + K2CO3 POELE20 + K3PO4

1.3340 1.3330 1.3351

0.1476 0.1395 0.1359

0.2018 0.1891 0.2109

Table 3. Binodal Data for the POELE20 (1) + KOH (2) + H2O (3) ATPSs at T = (288.15, 298.15, and 308.15) K and Pressure p = 0.1 MPaa 100 w1

The water used in experiments was double distilled. All reagents were used without further purification. Sample description and purity are given in Table 1. 2.2. Apparatus and Procedure. Following the cloud point method, a 50 mL glass vessel was used to determine the binodal data in these systems. The system temperature was kept at the desired temperature through equipping a coat for the vessel, and the water temperature was regulated using a DC-2008 water thermostat (Shanghai Hengping Instrument Factory, China). A certain amount of POELE20 solution was put into the vessel, and the salt solution was dropped into it until the solution became cloudy. At this time, the mass fractions of POELE20 and salt were calculated by weighting method. In this process one analytical balance (BS124S, Beijing Sartorius Instrument Co., China) with an uncertainty of ± 1.0·10−7 kg was used. Then, one drop of water was added into the solution to determine the next cloud point. The POELE20, salt, and water were added into the vessel in proportion and oscillated for 15 min. The sample temperature was controlled at constant temperature by using the thermostat water bath. When the liquid−liquid equilibrium was achieved, the volume and mass of the two phases were determined. The mass fractions of salt in the top and bottom phases were determined by flame photometry (TAS-968, Beijing Purkinje General Instrument Co., Ltd., China). The precision of the mass fractions of salts using this method was better than 0.0002. The mass fractions of POELE20 in the top and bottom phases were determined by a refractometer (WZS-I 811639, Shanghai, China) with a precision of ± 0.0001. The following equation (eq 1) represented the relationships between the mass fractions of POELE20 (w1), the mass fractions of salt (w2), and the index of refraction of the mixed solution (nD). The precision of this method was 0.0005. nD = n0 + a1w1 + a 2w2 (1)

100 w2

100 w1

11.73 10.88 10.29 9.60 8.85 7.92 7.38 6.93

11.89 11.98 12.05 12.17 12.34 12.54 12.65 12.79

6.51 5.90 5.34 4.88 4.49 4.04 3.52 3.06

12.87 11.66 11.05 10.39 9.44 8.55 8.04 7.54

10.20 10.40 10.51 10.61 10.80 10.95 11.08 11.18

6.84 6.27 5.51 4.95 4.41 3.88 3.10 2.62

14.37 13.43 12.19 11.21 10.33 9.84 9.21 8.44

8.42 8.51 8.63 8.73 8.85 8.92 9.02 9.14

7.69 7.19 6.70 6.19 5.75 5.23 4.65 4.01

100 w2

100 w1

T = 288.15 K 12.87 2.64 13.03 2.25 13.17 1.88 13.29 1.29 13.39 1.06 13.54 0.85 13.69 0.64 13.83 0.46 T = 298.15 K 11.31 2.17 11.46 1.79 11.61 1.48 11.73 1.05 11.90 0.81 12.00 0.56 12.20 0.42 12.34 0.31 T = 308.15 K 9.26 3.39 9.37 2.80 9.47 2.32 9.58 1.82 9.66 1.37 9.78 1.06 9.90 0.80 10.09 0.54

100 w2

100 w1

100 w2

13.98 14.13 14.25 14.53 14.69 14.89 15.08 15.33

0.34 0.22 0.17 0.09 0.06 0.05

15.58 15.89 16.14 16.29 16.56 16.78

12.49 12.64 12.79 12.98 13.13 13.31 13.52 13.76

0.15 0.08 0.07 0.05 0.04 0.02 0.01

14.00 14.36 14.69 14.87 15.16 15.49 15.79

10.28 10.47 10.64 10.81 11.03 11.18 11.35 11.56

0.23 0.14 0.09 0.05 0.03

11.90 12.09 12.37 12.62 12.91

a

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

has been obtained. These existing empirical equations were used to fit the investigated binodal data, and it was found that the following equations (eqs 2− to 4) have a nice correlation effect. w1 = exp(a + bw2 0.5 + cw2 + dw2 2)

(2)

w1 = aw2 3 + bw2 2 + cw2 + d

(3)

w1 = a exp(bw2

where n0, a1, and a2 are constants; the values of the three parameters for the investigated systems are given in Table 2.

0.5

3

− cw2 )

(4)

where w1 and w2 are the mass fractions of POELE20 and salts and a, b, c, and d are the fitting parameters. Wang et al.7,22 used eq 2 to fit the binodal data of micromolecule organic solvents− salt ATPSs and obtained satisfactory effect. The binodal data of poly(ethylene glycol)−salt (PEG−salt) ATPSs23 and inoic liquid−salt ATPSs24,25 were correlated by the third-order polynomial equation (eq 3). The binodal curves of many polymer−salt ATPSs26−28 and inoic liquid−salt ATPSs29 were correlated with eq 4. The fitting parameters a, b, c, and d of eqs 2 to 4 for the investigative systems were determined through

3. RESULTS AND DISCUSSION 3.1. Binodal Data and Correlation. The binodal data of ATPS containing POELE20 and three salts (KOH, K2CO3, and K3PO4) at temperature T = (288.15, 298.15, and 308.15) K were determined and have been shown in Tables 3−5. The binodal curves of the studied systems are given in Figures 1−3. In recent years, there are many empirical equations for the correlation of the binodal data of ATPS, and a desirable effect B



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Table 4. Binodal Data for the POELE20 (1) + K2CO3 (2) + H2O (3) ATPSs at T = (288.15, 298.15, and 308.15) K and Pressure p = 0.1 MPaa 100 w1

100 w2

100 w1

14.70 13.56 12.14 10.68 9.86 8.91 8.10 7.77

7.46 7.60 7.84 8.11 8.29 8.51 8.71 8.82

7.16 6.65 6.23 5.47 4.60 4.19 3.70 3.17

13.64 12.75 11.58 10.91 10.28 9.69 9.04

6.93 7.09 7.27 7.41 7.55 7.68 7.80

8.24 7.62 6.90 6.44 5.76 5.22 4.78

11.70 10.84 10.10 9.53 8.58 8.06 7.64 7.23

6.63 6.76 6.87 6.97 7.13 7.21 7.29 7.37

6.76 6.13 5.69 5.07 4.43 4.07 3.68 3.23

100 w2

100 w1

T = 288.15 K 8.99 2.71 9.13 2.23 9.24 1.78 9.44 1.28 9.69 0.90 9.81 0.61 9.97 0.38 10.16 0.25 T = 298.15 K 7.96 4.22 8.11 3.65 8.23 3.07 8.35 2.58 8.50 1.84 8.63 1.33 8.75 0.79 T = 308.15 K 7.46 2.83 7.59 2.40 7.70 2.06 7.84 1.76 7.97 1.50 8.07 1.12 8.19 0.82 8.31 0.52

100 w2

100 w1

100 w2

10.29 10.44 10.61 10.83 11.02 11.21 11.45 11.65

0.11 0.09 0.06 0.04 0.02

11.96 12.28 12.69 12.99 13.39

8.94 9.09 9.28 9.45 9.71 9.92 10.15

0.45 0.21 0.13 0.07 0.06 0.04 0.02

10.42 10.76 10.96 11.48 11.87 12.17 12.61

8.40 8.53 8.66 8.80 8.90 9.09 9.21 9.43

0.27 0.15 0.08 0.06 0.03 0.01

9.68 10.01 10.28 10.46 10.68 10.85

Figure 1. Binodal curves of the POELE20 (1) + KOH (2) + H2O (3) ATPSs at (288.15, 298.15, and 308.15) K: □, 288.15 K; ○, 298.15 K; △, 308.15 K; solid line, reproduced by eq 3.

Table 5. Binodal Data for the POELE20 (1) + K3PO4 (2) + H2O (3) ATPSs at T = (288.15, 298.15, and 308.15) K and Pressure p = 0.1 MPaa 100 w1

100 w2

100 w1

14.02 12.47 11.54 10.62 9.51 8.62 7.70

8.33 8.51 8.68 8.84 9.03 9.17 9.37

6.94 6.44 5.89 5.45 4.88 4.30 3.72

14.10 13.29 12.69 11.91 11.13 10.44 9.84 9.19

6.68 6.78 6.89 7.05 7.24 7.39 7.51 7.64

8.73 8.33 7.52 6.60 5.94 5.50 4.98 4.42

12.25 11.53 10.68 10.01 9.36 8.77 8.17 7.71

6.03 6.14 6.29 6.43 6.55 6.67 6.80 6.88

7.31 6.97 6.43 5.94 5.48 5.01 4.42 3.78

100 w2

100 w1

T = 288.15 K 9.53 3.06 9.64 2.41 9.76 1.92 9.86 1.48 10.02 1.06 10.15 0.70 10.31 0.37 T = 298.15 K 7.73 3.78 7.84 3.20 8.01 2.68 8.25 2.22 8.41 1.57 8.51 1.14 8.62 0.72 8.77 0.53 T = 308.15 K 6.97 3.14 7.06 2.66 7.19 2.14 7.31 1.68 7.41 1.29 7.52 0.90 7.68 0.59 7.88 0.36

100 w2

100 w1

100 w2

10.47 10.66 10.82 10.99 11.18 11.37 11.60

0.22 0.14 0.08 0.05 0.02

11.90 12.19 12.53 12.91 13.53

8.98 9.17 9.33 9.51 9.74 9.97 10.17 10.35

0.31 0.23 0.11 0.08 0.06 0.04 0.02

10.59 10.88 11.11 11.47 11.84 12.01 12.35

8.08 8.23 8.45 8.65 8.81 9.01 9.25 9.46

0.18 0.09 0.06 0.05 0.04 0.03 0.01

9.78 10.04 10.28 10.40 10.28 10.53 10.81

Figure 2. Binodal curves of the POELE20 (1) + K2CO3 (2) + H2O (3) ATPSs at (288.15, 298.15, and 308.15) K. □, 288.15 K; ○,298.15 K; △, 308.15 K; solid line, reproduced by eq 3.

Figure 3. Binodal curves of the POELE20 (1) + K3PO4 (2) + H2O (3) ATPSs at (288.15, 298.15, and 308.15) K. □, 288.15 K; ○, 298.15 K; △, 308.15 K; solid line, reproduced by eq 3. C



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Table 6. Values of Parameters of Equation 2 for the POELE20 (1) + KOH/K2CO3/K3PO4 (2) + H2O (3) ATPSs at T = (288.15, 298.15, and 308.15) K T/K

a

b

288.15 298.15 308.15

5.403 −3.095 9.000

−85.58 −71.32 −110.4

288.15 298.15 308.15

−14.04 57.89 63.54

288.15 298.15 308.15

62.78 59.36 56.16

74.91 −604.1 −681.3 −631.3 −620.8 −610.6

c POELE20 + KOH + H2O 299.8 398.9 372.3 POELE20 + K2CO3 + H2O −58.93 1753 2042 POELE20 + K3PO4 + H2O 1768 1803 1845

d

R2

100 sda

−969.4 −1621 −1451

0.9964 0.9972 0.9983

0.21 0.19 0.17

−715.8 −4652 −5838

0.9949 0.9983 0.9996

0.30 0.15 0.07

−4299 −4777 −5384

0.9983 0.9985 0.9997

0.17 0.16 0.06

exp 2 exp cal 0.5 sd = (Σni=1 (wcal 1 − w1 ) /n) , where w1 is the experimental mass fraction of POELE20 in Tables 3 to 5, w1 is the corresponding data calculated using eq 2. n represents the number of binodal data. a

Table 7. Values of Parameters of Equation 3 for the POELE20 (1) + KOH/K2CO3/K3PO4 (2) + H2O (3) ATPSs at T = (288.15, 298.15, and 308.15) K

a

T/K

a

b

288.15 298.15 308.15

−364.6 −519.3 −1383

222.9 272.4 538.2

288.15 298.15 308.15

60.56 −108.2 −445.1

37.30 96.59 207.2

288.15 298.15 308.15

−207.8 155.2 −60.20

167.1 16.59 84.96

c POELE20 + KOH + H2O −43.52 −46.38 −70.05 POELE20 + K2CO3 + H2O −12.18 −18.05 −28.57 POELE20 + K3PO4 + H2O −29.26 −9.904 −15.52

d

R2

100 sda

2.750 2.579 3.048

0.9982 0.9978 0.9990

0.12 0.18 0.13

0.8198 0.9608 1.231

0.9983 0.9988 0.9997

0.17 0.14 0.06

1.574 0.6817 0.7623

0.9986 0.9988 0.9998

0.15 0.15 0.06

See footnote a of Table 6.

Table 8. Values of Parameters of Equation 4 for the POELE20 (1) + KOH/K2CO3/K3PO4 (2) + H2O (3) ATPSs at T = (288.15, 298.15, and 308.15) K

a

T/K

a

288.15 298.15 308.15

0.0003 0.0001 0.2525

288.15 298.15 308.15

0.0073 0.0021 0.0026

288.15 298.15 308.15

0.0003 0.0032 0.0150

b

c

POELE20 + KOH + H2O 27.78 2161 47.69 3767 4.834 3329 POELE20 + K2CO3 + H2O 16.42 3671 22.42 5265 22.85 7170 POELE20 + K3PO4 + H2O 30.38 4540 20.35 5086 14.09 6263

R2

100 sda

0.9977 0.9976 0.9985

0.17 0.19 0.17

0.9960 0.9987 0.9992

0.27 0.14 0.10

0.9977 0.9987 0.9992

0.18 0.16 0.11


Figure 4. Effect of type of salt on the binodal curves plotted in molality fraction for the ATPSs at 288.15 K: ▲, POELE20 + K3PO4 + H2O; ●, POELE20 + K2CO3 + H2O; ■, POELE20 + KOH + H2O.

the regression analysis of experimental binodal data that were respectively given in Tables 6 to 8, which also give the square of correlation coefficients (R2) and the corresponding standard deviations (sd). It was found that eq 3 is satisfactorily used to fit the binodal data of investigated systems through comparing the correlation coefficients and standard deviations shown in Tables 6 to 8.

3.2. Effect of the Salt Type on the Binodal Curves. Salt types have important influence on liquid−liquid phase equilibria; therefore, the form-phase abilities of three potassium salts were discussed from the anion perspective. The binodal curves of ATPS containing POELE20 and potassium salts D



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calculated with the binodal model. The EEV model was used to calculate the bimodal data of ATPS consisted of two polymers, and then this binodal model was applied to fit the binodal data of polymer−salt ATPS. The corresponding equation is as follows:

Table 9. Values of Parameters of Equation 5 for the POELE20 (1) + KOH/K2CO3/K3PO4 (2) + H2O (3) ATPSs at T = (288.15, 298.15, and 308.15) K V*231/(g·mol−1)

T/K

POELE20 + KOH + H2O 398.4 0.9594 444.9 0.9436 541.1 0.9711 POELE20 + K2CO3 + H2O 1314 0.9877 1433 0.9879 1565 0.9941 POELE20 + K3PO4 + H2O 1891 0.9962 2150 0.9953 2400 0.9956

288.15 298.15 308.15 288.15 298.15 308.15 288.15 298.15 308.15 a

R2

sda

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

0.25 0.27 0.19

(5)

where w1 and M1 represent the mass fraction and molecular mass of POELE20, w2 and M2 represent the mass fraction and molecular mass of salt, and V231 * is the scaled EEV of the salt. The EEV values along with R2 and sd values are shown in Table 9, and the order of the EEV values in the investigated systems is found to be KOH < K2CO3 < K3PO4 when the temperature of system is the same. This agrees with the conclusion drawn from the binodal curves on the basis of former statements. There are two conclusions to take away from all of this. First, the valence of the cation has an impact on the phase-forming ability, namely, the phase-forming ability of salt enhanced with the increase in the valence of cation. The higher the valence of the cations of the salt is, the stronger the phase-forming ability of salt is. Second, the phase-forming ability of the salt is related to EEV, which means that the higher the EEV of the system is, the stronger the phase-forming ability of the salt is. Rogers et al.32 proposed that the salting-out ability of the salt is relevant with the Gibbs free energy of hydration of the ions. Because the salts in the studied systems have the same cation (K+), the correlation between the Gibbs free energy of

0.10 0.09 0.07 0.04 0.05 0.05


(KOH/K2CO3/K3PO4) at 288.15 K are given in Figure 4. The concentrations of two matters (POELE20 and salts) are shown in the molality fraction (w1/M1 and w2/M2) in Figure 4 in order to exactly show the relationship between the molecules in the systems.8,30 It was found that when the salts have the same cation, the phase-forming ability of salt increased with the rising valence of the anion; namely, the order of the phase-forming ability of these three salts is KOH < K2CO3 < K3PO4. On the basis of statistical geometry methods, Guan et al.31 developed the effective excluded volume (EEV) that is

Table 10. VE of the Aqueous Solutions of POELE20 for Different POELE20 Mass Fractions (w1) at the Temperatures T = (283.15 to 313.15) Ka T/K = 283.15 VE/(mL·g−1) VE/(mL·g−1) a

T/K = 288.15

T/K = 293.15

T/K = 298.15

T/K = 303.15

T/K = 308.15

T/K = 313.15

−0.0221

−0.0209

−0.0198

−0.0190

−0.0194

−0.0184

−0.0172

−0.0153

w1 = 0.1 −0.0254

−0.0242

−0.0230 w1 = 0.2

−0.0225

−0.0213

−0.0201

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

Table 11. Tie-Line Data for the POELE20 (1) + KOH (2) + H2O (3) ATPSs at T = (288.15, 298.15, and 308.15) K and Pressure p = 0.1 MPaa total system 100 w1

a

POELE20-rich phase 100 w2

100 wt1

salt-rich phase

100 wt2

7.01 7.00 7.00 6.99

12.75 13.00 13.25 13.50

10.83 18.37 22.97 26.15

12.01 10.89 10.35 10.02

6.99 7.00 6.99 7.03

11.51 11.75 12.00 12.25

19.96 23.42 26.62 30.37

9.35 8.98 8.68 8.35

7.01 7.00 6.99 7.00

9.75 10.00 10.25 10.52

23.95 26.96 30.92 33.73

7.46 7.27 6.97 6.87

100 wb1 T = 288.15 K 6.57 3.70 2.36 1.23 T = 298.15 K 3.68 2.64 1.31 0.95 T = 308.15 K 3.36 2.10 1.41 0.82

100 wb2

slope (k)

av of slope

12.84 13.62 14.11 14.51

−5.155 −5.380 −5.485 −5.538

−5.390

12.06 12.51 12.97 13.28

−6.009 −5.897 −5.903 −5.972

−5.945

10.24 10.68 11.01 11.36

−7.402 −7.294 −7.303 −7.332

−7.333

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



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Table 12. Tie-Line Data for the POELE20 (1) + K2CO3 (2) + H2O (3) ATPSs at T = (288.15, 298.15, and 308.15) K and Pressure p = 0.1 MPaa total system 100 w1

a


100 wt1

salt-rich phase

100 wt2

7.00 7.00 7.00 7.00

9.50 9.75 10.00 10.25

21.90 24.20 26.81 29.19

6.16 5.89 5.56 5.24

7.00 7.00 7.00 7.00

8.74 8.99 9.24 9.51

23.36 25.63 28.07 30.63

5.40 5.22 5.07 4.84

7.01 7.00 6.99 7.00

8.00 8.25 8.50 8.76

25.07 27.81 30.89 33.81

5.07 4.85 4.61 4.39

100 wb1

100 wb2

slope (k)

av of slope

10.61 11.10 11.49 11.80

−4.455 −4.455 −4.453 −4.426

−4.447

9.66 10.16 10.61 10.87

−4.971 −4.969 −5.014 −5.065

−5.004

8.85 9.21 9.58 9.90

−6.189 −6.155 −6.146 −6.122

−6.153

T = 288.15 K 2.08 1.00 0.43 0.13 T = 298.15 K 2.08 1.03 0.36 0.09 T = 308.15 K 1.65 0.91 0.35 0.10


Table 13. Tie-Line Data for the POELE20 (1) + K3PO4 (2) + H2O (3) ATPSs at T = (288.15, 298.15, and 308.15) K and Pressure p = 0.1 MPaa total system 100 w1

a


100

wt1

100

salt-rich phase wt2

7.01 6.99 7.00 6.99

9.74 9.99 10.24 10.50

17.11 20.14 22.98 25.57

7.71 7.35 7.02 6.75

7.00 7.02 7.00 7.00

8.50 8.74 8.99 9.26

24.84 27.88 30.52 33.59

4.99 4.64 4.38 4.06

7.00 6.98 7.00 7.00

7.75 8.00 8.25 8.50

27.83 30.96 34.09 37.16

3.95 3.61 3.29 3.01

100

wb1

T = 288.15 K 3.29 1.70 0.96 0.32 T = 298.15 K 2.75 1.64 0.61 0.13 T = 308.15 K 1.44 0.89 0.30 0.07

100 wb2

slope (k)

av of slope

10.47 11.04 11.41 11.80

−5.000 −4.995 −5.007 −4.991

−4.998

9.33 9.80 10.26 10.59

−5.087 −5.088 −5.090 −5.122

−5.097

8.77 9.08 9.41 9.69

−5.478 −5.487 −5.505 −5.535

−5.501


liquid−salt ATPSs24,35,36 was moving toward to the left when temperature decreased; namely, the temperature reduction is beneficial to form two phases. However, the temperature hardly has any influence on the binodal curves of ATPSs7,22,37 containing micromolecule organic solvent and salt, and the binodal curve moved to the left slightly when the temperature increased. The binodal curves of the investigated system at different temperatures are shown in Figures 1 to 3 to study the influences of temperature on the binodal curves of POELE20− salts (KOH/K2CO3/K3PO4) ATPSs. It was found that the increase in temperature results in the binodal curves moving to the left for these three systems. It shows that the rising temperature benefits the phase separation for the studied systems. It might be because the hydrophobicity of POELE20 strengthens with the rising temperature, and that causes the decrease of polymer hydration power. Therefore, the change of hydrophobicity of POELE20 with temperature is discussed as follows.

hydration of the anion and the salting-out ability of salt will be discussed. The Gibbs free energy of the investigated anions is as follows: PO4 3 − (− 2765 kJ· mol−1) > CO32 − (− 1315 kJ ·mol−1) > OH− (− 430 kJ· mol−1)

As seen in the preceding statistics, the salt possesses stronger salting-out abilities if the Gibbs free energy of its anion is more negative when the salts have the same cation. 3.3. Effect of the Temperature on the Binodal Curves. The system temperature has an important influence on the mechanism of phase forming, which has attracted researchers’ attention. There are reports33,34 that the temperature has a significant effect on the binodal curves of ATPS composed of two polymers or polymer and salt ATPS, namely, the binodal curves moved to the left with the increase in temperature, which means rising temperature was conducive to the ATPS forming. On the contrary, the binodal curves of the ionic F



Article

The excess specific volume (VE) is determined as the following equation (eq 6) according to Zafarani-Moattar et al.38 VE =

⎛w w ⎞ 1 − ⎜⎜ 1 + 2 ⎟⎟ ρ ⎝ ρ1 ρ2 ⎠

(6)

where ρ represents the density of the aqueous solutions of POELE20 and w is the mass fraction, the subscripts “1” and “2” standing for POELE20 and water. VE of the aqueous solutions of POELE20 at temperatures T = (283.15 to 313.15) K were given in Table 10. Zafarani-Moattar thought that the VE is closely related to the intermolecular interacting forces between the oxygen atoms of the polymer and the hydrogen atom of the water. The hydrogen bond interactions between polymer and water are stronger at the low temperatures, which show up as the more negative value of VE. Instead, when it is at the higher temperatures, the hydrogen bond interactions are weakened and less negative values of VE are obtained. From the data in Table 10, we conclude that POELE20 becomes more hydrophobic when the temperature is increased. 3.4. Liquid−Liquid Equilibrium Data and Correlation. The tie-lines data of POELE20−salts (KOH/K2CO3/K3PO4) ATPSs were determined at different temperatures and given in Tables 11 to 13, and the tie-lines composition are shown in Figures 5 to 7. The Othmer-Tobias and Bancroft39 empirical

Figure 6. Tie lines of the POELE20 (1) + K2CO3 (2) + H2O (3) ATPSs at (288.15, 298.15, and 308.15) K: --△--, 288.15 K; ···○···, 298.15 K; −□−, 308.15 K.

Figure 7. Tie lines of the POELE20 (1) + K3PO4 (2) + H2O (3) ATPSs at (288.15, 298.15, and 308.15) K: --△--, 288.15 K; ···○···, 298.15 K; −□−, 308.15 K.

3.5. Effect of the Temperature on the Tie Lines. The tie lines of POELE20−salts (KOH/K2CO3/K3PO4) ATPSs at three different temperatures were respectively plotted in Figures 5 to 7, and the following equation was used to express the slope of the tie line (STL).

Figure 5. Tie lines of the POELE20 (1) + KOH (2) + H2O (3) ATPSs at (288.15, 298.15, and 308.15) K: --△--, 288.15 K; ···○···, 298.15 K; −□−, 308.15 K.

correlation equations (eqs 7 and 8) widely used in the correlation of the tie lines of many systems,24,35,40 were used to fit the tie-lines data of the studied systems. ⎛ 1 − w b ⎞n ⎛ 1 − w1t ⎞ 2 ⎟⎟ k = ⎟ ⎜ ⎜ 1⎜ t b ⎝ w1 ⎠ w ⎝ ⎠ 2

(7)

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

(8)

wt1

STL = ΔY /ΔX

(9)

where ΔX is the concentration of salt in the top phase minus that of salt in the bottom phase and ΔY presents the concentration of POELE20 in the top phase minus that in the bottom phase. By analyzing the data in Tables 11 to 13 and studying Figures 5 to 7, we found that the absolute value of STL of investigated systems increased with the temperature rising. When the temperature of studied systems increased, the binodal curves moved to the left and the absolute value of STL increased. The enhancing of the hydrophobicity of POELE20 with rising temperature was the major factor causing this phenomenon. When the system temperature increased, the hydrophobicity of POELE20 heightened, which led to the water coming into the bottom phase from the top phase. While the concentration of salt in the bottom phase decreased, the

wt3

where and are the mass fractions of POELE20 and water at the top phase, respectively; wb2 and wb3 are the mass fractions of salt and water at the bottom phase, respectively; and k1, k2, n, and r are the fitting parameters. The values of the fitting parameters along with R2 and sd values are given in Table 14 for the investigated systems. G



Article

Table 14. Values of Parameters of Equations 7 and 8 for the POELE20 (1) + KOH/K2CO3/K3PO4 (2) + H2O (3) ATPSs at T = (288.15, 298.15, and 308.15) K T/K

103k1

n

k2

288.15 298.15 308.15

0.0034 0.2279 0.3236

7.642 4.923 4.239

5.482 5.844 7.020

288.15 298.15 308.15

3.882 7.418 1.044

3.208 2.731 3.414

6.055 6.522 7.805

288.15 298.15 308.15

1.324 3.722 0.3066

3.827 2.949 3.861

6.160 7.117 8.365

R21

r

POELE20 + KOH + H2O 0.0706 0.9814 0.1407 0.9881 0.1736 0.9849 POELE20 + K2CO3 + H2O 0.2559 0.9859 0.2984 0.9669 0.2528 0.9989 POELE20 + K3PO4 + H2O 0.1960 0.9951 0.2694 0.9892 0.2260 0.9992

R22

100 sd1a

100 sd2a

0.9605 0.9975 0.9882

1.32 0.63 0.89

3.42 1.09 2.11

0.9941 0.9760 0.9999

0.59 1.13 0.15

1.20 2.37 0.05

0.9974 0.9933 0.9996

0.44 0.68 0.19

1.12 1.34 0.34

t t b sd = [ΣNi=1 ((wi,j,cal − wi,j,exp )2 + (wi,j,cal − wbi,j,exp)2)/2N]0.5, where N is the number of tie lines and j = 1 and j = 2, sd1 and sd2 represent the mass percent standard deviations for POELE20 and salt, respectively. a

Foundation of Jilin Province (Grant Nos. 20150520062JH, 20140101206JC, and 20130101179JC), and Science and Technology Research Foundation of Jilin Province Department of Education (Grant No. 2014_158).

concentration of salt in the top phase increased, which caused the decrease in the value of ΔX with the temperature increasing. Instead, the value of ΔY increased because of the increase in the concentration of POELE20 of the top phase and the decrease in the concentration of POELE20 of the bottom phase. And then the absolute value of STL will increase with the increase in the value of ΔY and decrease in the value of ΔX.

Notes

The authors declare no competing financial interest.

■ ■

ACKNOWLEDGMENTS We are grateful to the Computing Center of Jilin Province for essential support.

4. CONCLUSION The binodal data and tie-line data of POELE20−salts (KOH/ K2CO3/K3PO4) ATPSs at three temperatures T = (288.15, 298.15, and 308.15) K were determined. Three experience formulas were used to fit the binodal data for the investigated systems and achieved satisfactory results. The tie-line data of the studied systems was correlated with Othmer-Tobias and Bancroft equations. In the investigated systems, three conclusions were drawn from discussing the effect of the type of salt on the binodal curves through phase diagram, the EEV, and Gibbs free energy of hydration of the ions (ΔGhyd). First, the phase-forming ability of salt was enhanced with the increase in valence of anion when the cation of the salt was same. Second, the phase-forming ability of the salt was enhanced with the system EEV rising in the investigated systems. Third, when the salts have the same cation, the salt containing the more negative Gibbs free energy of anion has stronger phase-forming ability than other salts. The effect of the system temperature change on ATPS forming was discussed, and it was found that the higher temperature was advantageous to ATPS forming than lower temperature in the investigated systems.

■

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AUTHOR INFORMATION

Corresponding Authors

*(Z.T.) E-mail:[email protected]. Tel.: +86-04343291953. Fax: +86-0434-3291953. *(Y.Y.) E-mail: [email protected]. Tel.: +86-04343291953. Fax: +86-0434-3291953. *(Y.L.) E-mail: [email protected]. Funding

This work was supported by the National Natural Science Foundation of China (Grant Nos. 31470434, 21406090, 21206059, and 21407058), the Natural Science Foundation of Jiangsu Province (Grant Nos. BK20141289 and BK20131258), China Postdoctoral Science Foundation funded project (Project No. 2013M531284), the Natural Science H



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Measurement and Correlation of Phase Equilibria in Aqueous Two

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