Separation of acetone: From a water miscible system to an efficient aqueous two-phase system

Accepted Manuscript Separation of acetone: From a water miscible system to an efficient aqueous two-phase system Shaoqu Xie, Wenli Song, Chuhan Fu, Conghua Yi, Xueqing Qiu PII: DOI: Reference:

S1383-5866(17)32594-7 https://doi.org/10.1016/j.seppur.2017.09.056 SEPPUR 14065

To appear in:

Separation and Purification Technology

Received Date: Revised Date: Accepted Date:

5 August 2017 17 September 2017 26 September 2017

Please cite this article as: S. Xie, W. Song, C. Fu, C. Yi, X. Qiu, Separation of acetone: From a water miscible system to an efficient aqueous two-phase system, Separation and Purification Technology (2017), doi: https://doi.org/ 10.1016/j.seppur.2017.09.056

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Separation of acetone: From a water miscible system to an efficient aqueous two-phase system Shaoqu Xie,a ǂ Wenli Song,a Chuhan Fu,b Conghua Yi*,a Xueqing Qiu*a a

School of Chemistry & Chemical Engineering, South China University of Technology,

No. 381 Wushan Road, Guangzhou P. R. China 510640 b

Guangdong TCM Key Laboratory for Metabolic Diseases, Guangdong Metabolic

Diseases Research Center of Integrated Chinese and Western Medicine, Guangdong Pharmaceutical University, Guangzhou Higher Education Mega Centre, Guangzhou 510006, China ǂ Current address: Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA.

AUTHOR INFORMATION Corresponding Authors * E-mail: [email protected]. Tel.: +86-20-87113806. * E-mail: [email protected]. Tel.: +86-20-87114722.

Highlights The liquid-liquid phase equilibria for acetone + water +salts system were studied. K4P2O7 was superior to K2CO3, K2HPO4, and K3PO4 in the separation of acetone.

The efficient aqueous two-phase system of water and acetone formed.

ABSTRACT: In view of the lower boiling point of acetone and no acetone/water azeotrope, it is a significant work to study the liquid-liquid phase equilibria for acetone + water + high-solubility inorganic electrolyte system. K4P2O7 was superior to K2CO3, K2HPO4, and K3PO4 in the separation of acetone from the aqueous solution. Both 600 g/kg of K2HPO4 and 550 g/kg of K4P2O7 drove the acetone recovery high into even 100.00 %. When the initial concentration of K4P2O7 was equal or greater than 400 g/kg, the desalination of the organic phase was satisfied. More than 96 % of water from the aqueous acetone solution was removed. The reported efficient aqueous two-phase system can be applied to recover acetoin and biobutanol from fermentation broths efficiently. KEYWORDS：Salting-out; acetone; aqueous two-phase system; recovery; solubility correlation; desalination of the organic phase 1. INTRODUCTION Acetone, a high polar solvent, can be mixed with water in any proportion to form a water miscible system. Separation of acetone from the aqueous solution and its dehydration is very important in biochemical process [1]. According to the differences in the volatility or boiling point of acetone and water, traditional distillation is often adopted to separate acetone from the acetone + water system[2,3,4]. Pervaporation is commercially used in

the pharmaceutical industry for the selective recovery and dehydration of acetone from aqueous mixtures[5,6,7]. Moreover, the presence of an electrolyte can dramatically reduce the solubility parameters of polar solvents, such as methanol, ethanol, and 1-propanol due to the salting-out effect[8], and thus achieve the liquid-liquid phase splitting for the recoveries of these solvents. Seventy-nine compounds were used as the potential salting-out agents to separate the acetone +water system so that the liquid-liquid system could be applied to extract metal chelates [9]. Only three preferred salting-out agents, calcium chloride (CaCl2), magnesium chloride (MgCl2), and sucrose, are efficient for the recovery of acetone. After the phase equilibrium, the organic phase contained 0.321±0.011 % of water (v / v) and 212 ppm of salt(wt/v) under CaCl2-saturated conditions. But the authors failed to mention the composition of another phase which could show the salting-out effect of a salt. The effect of the addition of calcium chloride (CaCl2) on the liquid–liquid equilibrium data of the binary system water–acetone has been further studied [10]. The poor salting-out effects of CaCl2 was demonstrated. AlCl3, Al(NO3)3, Al2(SO4)3, NH4Cl, NH4NO3, (NH4)2SO4, CaCl2, Ca(NO3)2, CaSO4, MgCl2, Mg(NO3)2, MgSO4, KCl, KNO3, K2SO4, NaCl, NaNO3 or Na2SO4 was used to separate aqueous acetone solution. Only AlCl3、 NaCl、CaCl2、MgCl2 or NH4Cl showed potential properties for producing the salting-out of acetone from water to form the aqueous two-phase system. However, the recovery of acetone was lower than 40 % when these salts were introduced into the 65.5 wt% acetone aqueous solution [11]. Therefore, the selection of the proper salting-out agents which will

recover acetone efficiently is very essential for the application of the salting-out systems of acetone and water. The target of salting-out herein is to recover acetone. The efficient recovery of bio-based chemicals by using the aqueous two-phase system depends on the composition of the aqueous two-phase system. For instance, aqueous two-phase system composed of monosodium phosphate and ethanol exhibited excellent extraction efficiency for both butyric acid (∼99%) and acetic acid (∼90%)[12]. The recovery of acetoin fermentation broth reached 95.3% if the ethanol/K2HPO4 salting-out extraction system was conducted[13]. Methanol/ K2HPO4 or ethanol/ K2HPO4 salting-out extraction system can recover more than 90 % of the 1,3-propanediols from the fermentation broth under suitable conditions[ 14 , 15 ]. More than 90 % of 2,3-butanediols can be recovered, and more than 97 % of cells, 78 % of proteins and 80 % of sugars were removed when using the (methanol, ethanol)/(K3PO4, K2HPO4, K2CO3) salting-out extraction systems[ 16]. However, the unsuitable salt or the insufficient addition of the favorable salt led to the loss of the solvent, the failing recovery of target products, or the interfusion of the salt in the organic phase [17,18]. The target of the salting-out extraction is to recover the solvent and the target product. The same target of salting-out and salting-out extraction is to avoid the loss of the solvent. The boiling point of acetone is 56.53 °C, which is lower than that of methanol (64.7 °C) or ethanol (78 °C). Acetone has the advantage of not forming a new azeotrope with water whereas an ethanol/water azeotrope limits the ethanol/water salting-out extraction system. If the acetone/salt aqueous two-phase system is used to extract the

target products, acetone can then be scrubbed (removed) from the organic phase by evaporation. Thus the liquid-liquid equilibria for the acetone +water + salt system are worth studying. In the present study, we aim to provide the efficient aqueous two-phase system of acetone and water which is featured with the total recovery of acetone, the higher dehydration of organic phase and lower salt content of the organic phase. The combination of the separation of acetone from the aqueous solution and the efficient aqueous two-phase system was desired. 2. EXPERIMENTAL 2.1. Materials. The materials used in the salting-out experiments include potassium carbonate (K2CO3), tripotassium phosphate trihydrate (K3PO4·3H2O), dipotassium hydrogen phosphate

trihydrate

(K2HPO4·3H2O),

pyrophosphate

potassium

trihydrate

(K4P2O7·3H2O), and deionized water, as can be seen in Table 1. The other agents used in the analysis were of analytical grade. Table 1 Materials Materials

Manufacturer

Purities

Acetone

Guangzhou Chemical Reagent Factory

99.5 %

K2HPO4·3H2O

Guanghua Chemical Plants Co. Ltd. ,

99.0 %

K3PO4·3H2O

Guangzhou Chemical Reagent Factory

99.0 %

K2CO3

Shanghai Lingfeng Chemical Reagent Co.,

99.0 %

Ltd.,

K4P2O7·3H2O

Tianjin Damao Chemical Plants Co. Ltd.,

Deionized water

Ultra Pure Water System

99.0 % （Electrical conductivity ＜1.5×10-4 S· m-1）

2.2. Partition Experiments Acetone stock solution was prepared by adding 200 g of acetone and 300 g of deionized water into a glass bottle that can be sealed. Then they were stirred with a magnetic stirrer until they are well-blended. 20 mL headspace bottles were employed to carry out the partition experiments by mixing a certain amount of K2CO3、K2HPO4·3H2O、 K3PO4·3H2O or K4P2O7·3H2O and an corresponding amount of the acetone stock solution to ensure they were in agreement with the expected initial salt concentration. The initial salt concentration (CI) having the unit of g/kg is given by,

in which msalt is the mass of salt, and mwater is the mass of water in the research system. The aluminum cap and tan PTFE/white silicone septa were used to seal the headspace bottles. The salting-out agents dissolved in the acetone stock solution to promote the liquid-liquid phase splitting. Then the sealed headspace bottles were shaken for 1 h and stood for 24 h at 25 oC before the GC measurements. Samples were carefully withdrawn

from both phases for gas chromatography (GC) analysis and flame atomic absorption spectrophotometer (FAAS) measurement. GC was used to determine the acetone and water contents, and FAAS was used to determine the salt content. 2.3. Analysis. The gas chromatography (Techcomp GC7900, China), equipped with a 2 m(L) × 3 mm(ID) × 5 mm(OD) Porapak Q 80 - 100 mesh packed column and a thermal conductivity detector (TCD) was employed to determine ethanol and water contents of each phase [19,20]. The column temperature was kept at 393.5 K for 10 minutes, and the injector and detector temperatures were 453.15 K. The salt content of the organic phase was determined by FAAS (Shimadzu AA-6800F, Japan) at the wavelength of 766.5 nm [21]. The salt content of the aqueous phase was calculated according to the mass balance. All the analytical experiments were duplicated. The uncertainty of the GC results was 0.005 wt%. Combining the GC and FAAS results, the compositions of the organic phase and aqueous phase were calculated. Thus the recovery of acetone (R) in the organic phase is obtained by,

in which m1 is the mass of the aqueous phase, m0 is the mass of the acetone stock solution, 21 is the mass fraction of acetone in the aqueous phase. The dehydration ratio (DR) is calculated as,

in which m2 is the mass of the organic phase, 12 is the mass fraction of water in the organic phase. 3. RESULTS AND DISCUSSION 3.1 The phase splits The experimental results in Table 2 show that the acetone + water + K2CO3 ternary system formed two phases as the initial K2CO3 concentration is greater than 100 g/kg. The light phase consists of water, acetone, and a small amount of K2CO3, while the heavy phase consists of water, K2CO3, and a small amount of acetone. Thus the light phase is called the organic phase and the heavy phase is called the aqueous phase. Table 2 Experimental Tie-line Data of (Water + Acetone + K2CO3) Ternary System at 298.15 K CI (g·kg-1)

organic phase water

acetone

aqueous phase K2CO3

ω12×100 ω22×100 ω32×100

water

acetone

K2CO3

ω11×100 ω21×100 ω31×100

control

60.00

40.00

0.00

60.00

40.00

0.00

100

51.72

46.30

1.98

73.06

4.82

22.11

150

45.58

53.49

0.93

70.89

2.97

26.14

200

39.31

60.34

0.35

68.73

1.89

29.38

250

31.43

68.42

0.15

66.97

1.27

31.76

300

23.85

76.12

0.03

64.44

0.81

34.75

350

16.92

83.07

0.01

61.38

0.44

38.18

400

11.67

88.32

0.01

57.66

0.22

42.13

a

450

7.49

92.51

0.01

53.58

0.09

46.33

500

4.87

95.13

0.01

49.12

0.03

50.85

550a

3.63

96.37

0.01

—

—

—

Saturation condition. Table 2 also shows that increasing the initial K2CO3 concentration enhances the

separation efficiency of the aqueous acetone solution at 298.15 K. The lower initial K2CO3 concentration resulted in the inefficient aqueous two-phase system which was embodied in the higher water content and salt content of the organic phase, and the acetone content of the aqueous phase. There are sharp declines in the water content and salt content of the organic phase, and the acetone content of the aqueous phase with increasing the initial K2CO3 concentration. The water content of the organic phase was 3.63 wt% and the acetone content of the aqueous phase was less than 0.03 wt% under K2CO3-saturated condition. The negligible amount of K2CO3 was detected when the initial K2CO3 concentration was greater than 350 g/kg. Table 3 Experimental Tie-line Data of (Water + Acetone + K2HPO4) Ternary System at 298.15 K CI (g·kg-1)

organic phase water

acetone

aqueous phase

K2HPO4

ω12×100 ω22×100 ω32×100

water

acetone

K2HPO4

ω11×100 ω21×100 ω31×100

control

60.00

40.00

0.00

60.00

40.00

0.00

100

54.89

43.81

1.31

67.22

1.93

30.85

150

51.14

47.97

0.89

66.06

1.58

32.36

200

47.29

52.09

0.61

64.13

1.23

34.64

a

250

42.84

56.83

0.34

62.19

0.87

36.94

300

37.29

62.52

0.18

60.33

0.61

39.06

350

31.64

68.31

0.05

57.83

0.42

41.75

400

24.27

75.71

0.01

55.37

0.26

44.37

450

18.07

81.93

0.00

52.05

0.14

47.80

500

12.37

87.63

0.00

48.30

0.06

51.64

550

8.44

91.55

0.01

44.03

0.02

55.95

600

5.37

94.62

0.01

39.51

0.00

60.49

650a

4.52

95.47

0.01

—

—

—

Saturation condition. The feasibility of using K2HPO4 to induce the efficient aqueous two-phase system of

acetone and water was studied at 298.15 K. The solubility of K2HPO4 in the aqueous acetone solution is surprisingly greater than that of K2CO3. The similar results can be obtained, as shown in Table 3. Significantly, the acetone content cannot be detected at the initial K2HPO4 concentration of 600 g/kg, suggesting that the performance of K2HPO4 is better than that of K2CO3. Meanwhile, the water content of the organic phase is 5.37 wt% which means that the aqueous acetone solution was much concentrated. The K2HPO4 content of the organic phase is hovering at 0.01 wt%. The solubility of the salting-out agents in pure water must be large so as to have maximum interaction with the water molecules from the aqueous acetone solution. K3PO4 and K4P2O7 also effected phase separation in the present investigation at 298.15 K. The salting-out of acetone from water with K3PO4 was showed in Table 4. To obtain Maximum separation efficiency, the initial concentration of K3PO4 was increased to 500

g/kg. The water content of the organic phase was declined to 5.24 wt%, but the acetone content of the aqueous phase less than 0.02 wt% which was close to 0.03 wt% as K2CO3 was used. The K3PO4 content of the organic phase was 0.03 wt%, indicating that K3PO4 was inferior to K2CO3 and K2HPO4.

Table 4 Experimental Tie-line Data of (Water + Acetone + K3PO4) Ternary System at 298.15 K CI (g·kg-1)

organic phase water

acetone

aqueous phase K3PO4

ω12×100 ω22×100 ω32×100

water

acetone

K3PO4

ω11×100 ω21×100 ω31×100

control

60.00

40.00

0.00

60.00

40.00

0.00

100

54.47

43.76

1.77

68.49

2.96

28.55

150

49.90

49.18

0.92

67.48

2.10

30.41

200

44.08

55.32

0.60

66.77

1.48

31.76

250

36.77

62.92

0.31

65.61

1.01

33.38

300

28.88

71.03

0.09

63.64

0.61

35.75

350

21.26

78.70

0.04

60.93

0.30

38.77

400

15.75

84.23

0.02

57.29

0.14

42.58

450

10.27

89.71

0.02

53.43

0.05

46.51

a

500

6.00

93.97

0.03

49.19

0.02

50.79

550 a

5.24

94.74

0.03

—

—

—

Saturation condition. The ideal aqueous two-phase system was made up of an organic phase with no water

and salt, and an aqueous phase with no acetone. When K4P2O7 was introduced into the aqueous acetone solution, the organic phase with no salt and the aqueous phase with no acetone were obtained at the initial concentration K4P2O7 of 550 g/kg, as shown in Table 5. The water content of the organic phase was 4.05 wt% which would not affect the nature of acetone too much. When the initial concentration of K4P2O7 was equal or greater than 400 g/kg, no K4P2O7 content was detected in the organic phase. Table 5 Experimental Tie-line Data of (Water + Acetone + K4P2O7) Ternary System at 298.15 K CI (g·kg-1)

organic phase water

acetone

aqueous phase K4P2O7

ω12×100 ω22×100 ω32×100

water

acetone

K4P2O7

ω11×100 ω21×100 ω31×100

control

60.00

40.00

0.00

60.00

40.00

0.00

100

53.17

45.92

0.91

70.44

1.83

27.74

150

48.97

50.47

0.55

68.17

1.36

30.47

200

43.59

56.08

0.33

66.74

0.96

32.30

250

38.19

61.67

0.14

64.46

0.68

34.86

300

31.20

68.76

0.04

62.46

0.44

37.09

350

24.30

75.69

0.01

59.80

0.24

39.96

400

16.83

83.17

0.00

56.83

0.13

43.04

450

10.92

89.08

0.00

53.15

0.05

46.80

a

500

6.80

93.19

0.00

48.95

0.01

51.03

550

4.05

95.94

0.00

44.44

0.00

55.56

600a

3.29

96.71

0.00

—

—

—

Saturation condition. Figure 1 shows the ternary diagram of water + acetone+ salt at 298.15 K. It can be

seen that the liquid-liquid phase equilibria were influenced by the effect of the salt presence greatly. All the results demonstrate that K4P2O7 is superior to K2CO3, K2HPO4, and K3PO4 in the separation of acetone from the aqueous solution. The water content of the organic phase was 3.29 wt% under K4P2O7-saturated condition. This value was lower than those under K2CO3, K2HPO4, or K3PO4 saturated condition. The total recovery of acetone, and the organic phase with no salt and a very small amount of water were very crucial factors for the application of the acetone + water + K4P2O7 system. 0.00 0.00

0.25

0.50

0.75

0.75

0.25

0.25

1.00

0.00 0.25

0.50

Water

0.75

1.00

Acetone

4

HP O

0.50

2

0.50

K

0.50

Acetone

3

0.75

0.75

2

K

CO

0.25

0.00

1.00

1.00

1.00 0.00

0.00 0.25

0.50

Water

0.75

1.00

0.00

0.25

2

7

PO

0.50

0.50

4

0.50

K

0.50

Acetone

4

0.75

0.75

3

K

PO

0.25

0.75

0.75

0.25

0.25

1.00 0.00

1.00

1.00

1.00

0.00 0.25

0.50

0.75

Acetone

0.00

0.00

0.00

1.00

0.25

0.50

0.75

1.00

Water

Water

Figure 1 Ternary system of water + acetone+ salt system at 25 oC, and solid line, experimental tie lines. The reliability of the experimental tie-line data of (water + acetone + salt) ternary system at 298.15 K can be ascertained by applying the Othmer-Tobias correlation [22],

where  is the mass fraction of acetone in the organic phase, 31 is the mass fraction of salt in the aqueous phase,  andare constants. Table 6 Parameters of the Othmer-Tobias Equation for the (water + acetone + salt) ternary system at 298.15 K salt





R2

K4P2O7·3H2O

2.9417 -2.4412 0.9922

K3PO4·3H2O

3.1486

-2.655

0.9964

K2HPO4·3H2O 2.5864 -1.7381 0.9958 K2CO3

2.5449 -2.8216 0.9885

The parameters of the Othmer-Tobias Equation for the (water + acetone + salt) ternary system at 298.15 K were obtained through linear regression analysis and showed in Table 6, together with the coefficients of determination (R2). The linearity of the plot

(R2≥0.9885) shows that eq 4 can satisfactorily correlate the organic phase with the aqueous phase, and showed a good agreement with the experimental data. 3.2 Acetone recovery The efficient aqueous two-phase system must be guaranteed to minimize the loss of acetone. Thus the recovery of acetone is the most intuitive expression, as shown in Figure 2. Low salt concentrations are not favorable for creating the aqueous two-phase system because of the lower recovery of acetone and the labile liquid-liquid phase equilibrium. Most of water retained in the organic phase at the lower salt concentrations so that the mass fraction of salt in the aqueous phase was much higher than the corresponding initial concentration of salt. Thus a smaller amount of aqueous phase was obtained. That’s why the recovery of acetone was relatively higher at the lower salt concentrations. The recovery of acetone firstly decreased collectively but increased with the increase in the initial concentration of salt. The salting-out of acetone was more obvious at the higher initial concentration of salt because more water is bounded with ions[23]. At the initial salt concentration of 500 g/kg, the recovery of acetone from the 40 wt% acetone aqueous solution reached 99.91 %, 99.74 %, 99.94 %, and 99.95 % respectively when K2CO3, K2HPO4, K3PO4, and K4P2O7 were used. Both 600 g/kg of K2HPO4 and 550 g/kg of K4P2O7 drove the acetone recovery high into even 100.00 %. Compared with AlCl3、NaCl、CaCl2、MgCl2 or NH4Cl that recovered only 40 % of acetone from the 65.5 wt% acetone aqueous solution [11], K2HPO4 or K4P2O7 showed much better performance. Hence, the extraction condition with the salting out effect of K2HPO4 or K4P2O7 is prior

to be used to recover value-added chemicals or fuels from biomass.

1.00

40 wt% acetone

0.99

R

K2CO3 K2HPO4 K3PO4

0.98

K4P2O7

0.97 100

200

300

400

500

600

CI (g/kg)

Figure 2 Recovery of acetone vs. the initial concentration of salt

3.3 Dehydration ratio

1.0

40 wt% acetone 0.8

0.6

DR

K2CO3 K2HPO4

0.4

K3PO4 K4P2O7

0.2

0.0 100

200

300

400

CI (g/kg)

500

600

Figure 3 Dehydration ratio vs. the initial concentration of salt One target of this study is to create the acetone phase in the presence of water. Thus the dehydration ratio is a key factor in affecting the efficient aqueous two-phase system. As seen in Figure 3, the water content of the organic phase declined with increasing the initial salt concentration so as to obtain the increasingly high dehydration ratio. A larger amount of salting-out agent dissolved in the aqueous acetone solution and is highly ionized to attract more water molecules. Among these salting-out agents, K2CO3 showed the highest dehydration ratio at the same initial salt concentration. However, the higher solubility of K2HPO4 or K4P2O7 made up for the limitation of the relatively lower dehydration ratio. More than 96 % of water from the aqueous acetone solution was removed by the salting-out effect of K2CO3, K2HPO4 or K4P2O7. The dehydration ratio could be even as high as 97 % for K4P2O7.

3.4 The salting-out effects of different salts Salting-out effect is reflected by a decline in the solubility of the nonelectrolyte after the salt addition, whereas there are some special cases in which an increase in the solubility of the nonelectrolyte occurs after the addition of a certain amount of salts that is the salting-in effect. It is demonstrated that K2CO3, K2HPO4, K3PO4 and K4P2O7 showed salting-out effects on the aqueous acetone solution at the studied salt concentrations. It appeared that the solubility of acetone in the aqueous phase was mostly determined

by the initial salt concentration. The mass fractions of the salting-out agents in both phases differed greatly. The salt content of the organic phase is much smaller than that of the aqueous phase, especially at the higher initial salt concentrations. Thus it is verified that the solubility of acetone in the aqueous phase depends on the salt content of the same phase. Several empirical equations have been proposed to determine the salting-out effects of electrolytes on nonelectrolytes by correlating the solubility of the nonelectrolyte and the corresponding salt concentration. Setschenow equation seems to fit the data very well and has been most frequently employed [24,25]. To be specific, the logarithm of the solubility of nonelectrolyte and the added salt concentration showed a linear relationship within the range of certain salt concentration. The absolute value of the slope of the Setschenow equation expresses the salting-out effect of one electrolyte on one nonelectrolyte. The solubility of acetone (s21) with the units of g per 100 g water in the aqueous phase is defined as,

in which21 is the acetone content of the aqueous phase, and 11 is the water content of the aqueous phase. The salt concentration has been expressed as molality of salt (b, units: mol per 1 kg water) by solving the equation relating the salt content of the aqueous phase (31) to the water content of the aqueous phase ( 11) and the molar mass of a salt (M),

in which

is the molar mass of a salt (K2HPO4,

g/mol; K2CO3,

=138.21 g/mol; K3PO4,

= 174.18 g/mol; K4P2O7,

= 330.33

= 212.27 g/mol).

After fitting of the experimental results, the natural logarithm of the solubility of acetone in the aqueous phase has a linear relation with the molality of a salt in the same phase, as shown in Figure 4 and Table 7. In general, it can be seen that the solubility of acetone in the aqueous phase decreased rapidly with increasing the molality of a salt. In addition, Figure 4 further illustrates a general regularity in the salting-out data, that of the effect of salt type. After the linear regression, the salting-out effect of 4 salting-out agents can be expressed as,

l n s21   b  

(7)

in which  andare constants.  is the Setschenow constant, the larger absolute value of which characterises stronger salting-out effect of the electrolyte on the nonelectrolyte. Upon examining the  values in Table 7, it can see that the salting-out effects of 4 electrolytes on acetone were generally in the order K4P2O7 ＞ K3PO4 ＞ K2HPO4 ＞ K2CO3. There is no phase equilibrium data in the literature, so the order of the salting-out cannot be compared exactly. But according to the recovery of acetone, the salting-out effects of the salts used in this work were much stronger than those in the literature.

2

K4P2O7 K3PO4

1

K2HPO4 K2CO3

ln (s21)

0

-1

-2

-3

-4 1

2

3

4

5

6

7

8

Molality of salt (mol/kg)

Figure 4 Salting-out effects of different salting-out agents on the aqueous acetone solution

Table 7 Constantsand the coefficients of determination R2, obtained in the fittings of Figure 4 System

salt





R2

K4P2O7·3H2O

-2.3123 3.7846 0.9992

K3PO4·3H2O

-1.6763 4.5404 0.9919

40 wt% acetone K2HPO4·3H2O -0.8866 3.3624 0.9995 K2CO3

-0.8837 3.7314 0.9980

Combining ,constants and the molality of salt provides a simple approach to calculate the solubility of acetone in the aqueous phase, (8)

(9) (10) (11) Eqs. (8) ~ (11) mathematically represent the salting-out effects of K4P2O7, K3PO4, K2HPO4, and K2CO3 on acetone respectively. 3.5 Application of the efficient aqueous two-phase system The reported efficient salting-out system should be applied to the challenging matrices, in which chemicals of interest cannot be effectively extracted. The efficient aqueous two-phase system of acetone and water induced by phosphate was used to extract acetoin from fermentation broth [26].

The system containing 30% (w/w)

acetone and 35% (w/w) K2HPO4 recovered 96.4 % and 94.3 % of acetoin from the filtered and unfiltered fermentation broth respectively. Hydrophilic solvents namely acetone, 1-butanol, ethanol, and salting-out agents such as (NH4)2SO4, Na2CO3, K2HPO4 were employed to form aqueous two-phase systems to recover acetone-butanol-ethanol (ABE) from the simulated fermentation broth[27]. As can be seen in Table 8, comparing the partition coefficient of products and recovery of products by using three salting-out agents with the same solvent demonstrated that K2HPO4 appeared to be more favorable for the recovery of biobutanol. Considering the cost and boiling point, the efficient aqueous two-phase system consisted of acetone, water and K2HPO4 was effective to recover 98.10 % of biobutanol from the fermentation broth. Table 8 Partitions of ABE in different organic solvent/salt systems[27].

Salt/solvent

Partition coefficient of products (K)

Recovery of products (Y, %)

1-Butanol

Acetone

Ethanol

1-Butanol

Acetone

Ethanol

(NH4)2SO4/butanol

–

10.3

3.9

–

86.39

70.49

(NH4)2SO4/acetone

73.5

–

4.8

99.1

–

80.67

(NH4)2SO4/ethanol

14.9

20.5

–

93.58

95.25

–

Na2CO3/butanol

–

7.22

2.69

–

81.78

62.56

Na2CO3/acetone

80.13

–

2.66

99.14

–

79.38

Na2CO3/ethanol

60.1

26.7

–

98.96

97.69

–

K2HPO4/butanol

–

19.21

3.4

–

92.44

68.38

K2HPO4/acetone

92.42

–

3.84

99.2

–

77.89

K2HPO4/ethanol

134.42

120.25

–

99.54

99.29

–

Note: Simulated ABE fermentation broth contain 16.00 g/L of butanol, 8.04 g/L of acetone, and 2.75 g/L of ethanol. Salt concentration was saturated. Solvent concentration was 25% w/w. 4.

CONCLUSIONS The lower boiling point of acetone and no acetone/water azeotrope made the

salting-out extraction system of acetone and water more attractive. Thus the liquid-liquid phase equilibria for acetone + water + high-solubility inorganic electrolytes system were investigated at 25 oC. K4P2O7 is superior to K2CO3, K2HPO4, and K3PO4 in the separation of acetone from the aqueous solution. Both 600 g/kg of K2HPO4 and 550 g/kg of K4P2O7 drove the acetone recovery high into even 100.00 %. When the initial concentration of K4P2O7 was equal or greater than 400 g/kg, no K4P2O7 content was detected in the organic phase. More than 96 % of water from the aqueous acetone solution was removed by the

salting-out effect of K2CO3, K2HPO4 or K4P2O7. The solubility of acetone in the aqueous phase depends on the salt type and salt content of the same phase. The logarithm of the solubility of nonelectrolyte and the molality of salt showed a linear relationship within the range of certain salt concentration. The salting-out effects of 4 electrolytes on acetone were generally in the order K4P2O7 ＞ K3PO4 ＞ K2HPO4 ＞ K2CO3. The salt from the aqueous phase can be recycled for the purpose of reuse by evaporation[28].

Notation Abbreviations and symbols

b=molality, CI = initial salt concentration, DR=dehydration ratio, R = recovery, = molar mass of salt, m1 = mass of the aqueous phase, m2 = mass of the organic phase, m0 = mass of the aqueous acetone solution, s = solubility of acetone,

ij = mass fraction of one component in one phase (subscript i=1,2,3 represent water, acetone, and salt, respectively; subscript j=1,2 represent the aqueous phase and organic phase, respectively), , = constants.

Notes The authors declare no competing financial interest.

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