Salting-Out Effect of Dipotassium Hydrogen Phosphate on the

Apr 4, 2014 - Salting-out effect of potassium pyrophosphate (K 4 P 2 O 7 ) on the separation of biobutanol from an aqueous solution. Shaoqu Xie , Cong...
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Salting-Out Effect of Dipotassium Hydrogen Phosphate on the Recovery of Acetone, Butanol, and Ethanol from a Prefractionator Conghua Yi, Shaoqu Xie, and Xueqing Qiu* School of Chemistry & Chemical Engineering, South China University of Technology, No. 381 Wushan Road, Guangzhou 510640, P. R. China ABSTRACT: Dipotassium hydrogen phosphate (K2HPO4) has been investigated as an excellent salting-out agent to recover (acetone + butanol + ethanol) (ABE) from a prefractionator. The increasing additions of K2HPO4·3H2O to the ABE system under unsaturated conditons show strong salting-out effects on the ABE. This favorable saltingout effect is based on the hydration of the charged ions. The HPO42− ions may destroy the “hydration shell”, but the crescent concentrations of K2HPO4 make positive salting-out effects on the ABE. More acetone, 1-butanol, and ethanol are recovered after higher-level concentrations of K2HPO4 solution are added to the ABE system. Meanwhile, the equilibrium time shortens. A higher temperature can also make the equilibrium time shorter. The smallest amount of K2HPO4 in the organic phase causes no trouble for the (salting-out + distillation) process in an industrial application.

1. INTRODUCTION The oil crisis has led to large-scale development of the renewable energy resources. Biofuel has become a hot field of research, especially the fuels obtained from liquid fermentation techniques. Bioethanol and biobutanol are outstanding outcomes of fermentation.1,2 Biobutanol is particularly more suitable for engines because of its highlighted properties such as higher energy content, lower vapor pressure, more stable combustion, and hydrophobicity.3,4 1-Butanol is an important chemical feedstock.5 Therefore, the production of biobutanol is more meaningful. 1-Butanol can be produced from the (acetone + butanol + ethanol) (ABE) fermentation of biomass.6,7 The total mass fraction of solvents (acetone, butanol, and ethanol) in the fermentation broth is around 2 wt % due to the effect of butanol toxicity.8 The production of 1-butanol by biological means lasts for more than one century.9 However, acetone, ethanol, and other byproducts make the separation complicated. Acetone, 1-butanol, and ethanol with low concentrations in the fermentation broth need multistep recovery and purification.8,9 So the conventional solvent recovery process is the distillation method.10 A series of distillers is established in a plant to recover acetone, 1-butanol, and ethanol according to the volatility difference of all solvents in the fermentation broth. But this fermentation process and the separation process are unattractive because of the large energy consumption.11,12 Research into other methods to recover ABE arise because of the high cost of distillation. According to the shortcoming of the ABE fermentation, the in situ recovery of ABE has received much attention.13 Adsorption or absorption,14 membrane technology (pervaporation),15 liquid−liquid extraction,16 and gas stripping17 have been evaluated as the alternative methods of solvent recovery. © 2014 American Chemical Society

Adsorption was considered as the most energy-efficient method to recover ABE.18,19 Different adsorbents such as resins (IRC50, XAD-2, XAD-4, XAD-7, XAD-8, XAD-16, XD-41, H-511, and KA-I) were tried to enhance the yield and concentration of 1-butanol.20 But it is hard to replace the distillation method in an industrial application because of the multicomponent outcomes. So the most practical job is the modification of distillation. The (salting-out + distillation) process may give us a surprise. According to Chen’s report,21 a prefractionator is an indispensable distiller. It aims to enrich the ABE fermentation broth. In the top of the prefractionator, the initial ABE solution is obtained. The mass fraction of water of the solution is around 60 % after the pretreatment of the prefractionator. The rest are mainly biobutanol (around 26 %, mass fraction), ethanol (around 4 %, mass fraction), and acetone (around 10 %, mass fraction). Then this stream is fed to the first butanol column. In the top of this column, acetone and ethanol are obtained. Acetone and ethanol are ultimately separated in the acetone column and the ethanol column, respectively. Water and 1butanol from the bottom of the first butanol column are separated in a two-column distillation system in conjunction with a decanter. The subsequent energy consumption mainly results from the binary heterogeneous azeotropic (1-butanol + water) system.22 So a salting-out operation to remove the water of the ABE system (acetone + 1-butanol + ethanol + water) from the prefractionator may cut down the energy consumption. Received: December 6, 2013 Accepted: March 27, 2014 Published: April 4, 2014 1507

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Table 1. Effects of Different Initial Dipotassium Hydrogen Phosphate Concentrations (concn) on Separation Efficiency of the ABE System from a Prefractionator at 298.15 K organic phase (wt %)

a

aqueous phase (wt %)

concn

water

ethanol

acetone

1-butanol

water

ethanol

acetone

1-butanol

g·kg−1

ω14·100

ω24·100

ω34·100

ω44·100

ω11·100

ω21·100

ω31·100

ω41·100

control 100.00 150.00 200.00 250.00 300.00 350.00 400.00 450.00 500.00 550.00 600.00 650.00a

60.00 28.29 25.97 24.82 22.45 20.70 17.98 15.41 12.92 10.62 8.43 6.34 5.50

4.00 5.58 6.10 6.47 6.95 7.36 7.79 8.19 8.49 8.85 9.12 9.35 9.51

10.00 14.64 16.05 16.93 18.00 18.77 19.58 20.36 20.83 21.72 22.00 22.41 22.59

26.00 51.49 51.88 51.77 52.60 53.17 54.64 56.05 57.76 58.80 60.45 61.91 62.40

60.00 88.61 92.09 95.04 97.04 98.27 99.07 99.45 99.78 99.92 99.96 100.00 100.00

4.00 2.50 1.96 1.39 0.98 0.67 0.41 0.28 0.15 0.07 0.04 0.00 0.00

10.00 5.28 3.84 2.57 1.50 0.86 0.42 0.23 0.07 0.01 0.00 0.00 0.00

26.00 3.61 2.11 1.01 0.48 0.20 0.10 0.05 0.01 0.00 0.00 0.00 0.00

Saturated condition.

chromatography. They were all in accord with the marked mass concentration. The electrical conductivity of deionized water at 293.15 K was lower than 1.5·10−4 S·m−1. 2.2. Analytical Method. The mass fractions of acetone, 1butanol, ethanol, and water under salt-free conditions in the organic phase and aqueous phase were measured by gas chromatography (GC). It is 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). The content analysis of four components (acetone, 1-butanol, ethanol, and water) from two phases was conducted by the peak area normalization method. The concentrations of the dipotassium hydrogen phosphate solution were analyzed at a subsensitive resonance line (404.5 nm) of potassium by flame atomic absorption spectrometry (AAS).31 The external standard method was adopted. The experiment was repeated for three times, always with corresponding blanks. The mass fraction of dipotassium hydrogen phosphate in the organic phase was measured at 766.5 nm by atomic absorption spectrometry analysis as well. Cesium nitrate was used as an ionization buffer. Lanthanum chloride was a releasing agent. 2.3. Salting-out Process. The initial ABE solution from a prefractionator (1-butanol, 26 wt %; acetone, 10 wt %; ethanol, 4 wt %) was prepared in an aqueous solution by referring to Chen’s report.21 The salting-out process was performed in a gas-tight vial with a sealing pad after the additions of K2HPO4· 3H2O or its solution. Then the ABE system will be divided into two phases. The salting-out system was shaken at the speed of 200 r.p.m. for 1 h and then settled for 2 h until phase equilibrium was obtained at the specified temperatures. After that, an amount of 0.5 μL of the organic phase was withdrawn by a microsyringe. An amount of 0.5 μL of the aqueous phase was withdrawn after the gas-tight vial was turned upside down. The recovery of the ABE is determined by the mass fractions of acetone, 1-butanol, and ethanol in the aqueous phase. The enrichment of the ABE depends on the mass fraction of water in the organic phase. The initial mass concentrations of K2HPO4 in the ABE system were determined only by the water as solvent when the separation efficiency was studied. K2HPO4 was added to the

Some salts showed strong salting-out effects for the (1butanol + water) system, the (acetone + water) system, and the (ethanol + water) system, respectively.23−26 So salts can also show strong salting-out effects for the ABE system from the prefractionator. The ABE can be recovered from the fermentation broth by the salting-out method.27,28 But the addition of extra organic solvent challenge the subsequent distillation. The in situ salting-out process is difficult to achieve the ends. The ex situ salting-out process is more suitable for an industrial application. Potassium carbonate was investigated to recover the ABE from the prefractionator at our previous work.29 More than 25.16 % energy will be saved in the separation process. But the high salting-out factor of 2:1 plagues the regenerate potassium carbonate considering the evaporation of the salting-out raffinate. The salting-out factor is defined as the volume of electrolyte solution divided by that of the initial ABE solution from the prefractionator (volume ratio). So the research into less salting-out extractant (electrolyte solution without extra organic solvent) to reduce the mass fraction of water in the ABE system from the prefractionator is meaningful. The objective of this study is to investigate the dipotassium hydrogen phosphate with great solubility to recover acetone, 1butanol, and ethanol. The dipotassium hydrogen phosphate is alkalescent in water. The salting-out effect of dipotassium hydrogen phosphate will be shown in great detail. The ABE fermentation industry has recently been re-established in China.30 The recovery of acetone, 1-butanol, and ethanol by salting-out method avails the distillation process, so as to get energy-saving industrial technology.

2. EXPERIMENTAL SECTION 2.1. Materials. Acetone (99.5 wt %) was purchased from Guangzhou Chemical Reagent Factory, (Guangzhou, China). 1-Butanol (99.5 wt %) was obtained from Shanghai Lingfeng Chemical Reagent Co., Ltd. (Shanghai, China). Ethanol (99.7 wt %) and dipotassium hydrogen phosphate trihydrate (K2HPO4·3H2O) (99.0 wt %) were supplied by Guangdong Guanghua Sci-Tech Co., Ltd., (Guangzhou, China). They were all analytical grade without further purification. The purities of acetone, 1-butanol, and ethanol were checked by gas 1508

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ABE system gradually (from 10 wt % to saturated condition at 298.15 K). K2HPO4 is a hydrophilic agent. So the greater solubility of K2HPO4 at higher temperatures may enhance the dehydration effect. K2HPO4 was kept under saturated conditions in the ABE system at different temperatures (298.15 K to 333.15 K) to enrich the ABE to the extreme. An amount of 0.5 mL of the organic phase was withdrawn to check the residues of K2HPO4. The salting-out factors were studied at 298.15 K and 333.15 K. The suitable volume ratios were 1:2, 2:2, 3:2, 4:2, and 5:2. The extractants were saturated K2HPO4 solution at 298.15 K and 333.15 K. The salting-out process was performed at 298.15 K or 333.15 K. Then the recoveries of 1-butanol, acetone, and ethanol were calculated. Moreover, the phase equilibrium time with the salting-out factors of 2:2 and 4:2 were given. The mass fraction of water in organic phase was analyzed by gas chromatography after the shaking process was stopped, with a residence time of different minutes. It showed us the mass transfer rate indirectly. Figure 1. Residues of K2HPO4 (ω54) in the organic phase as a function of the initial concentrations (concn) of K2HPO4 at 298.15 K.

3. RESULTS AND DISCUSSION The salting-out effects of different initial dipotassium hydrogen phosphate concentrations on separation efficiency of the ABE system from a prefractionator at 298.15 K are shown in Table 1 (ω14 = mass fraction of water in the organic phase, ω24 = mass fraction of ethanol in the organic phase, ω34 = mass fraction of acetone in the organic phase, ω44 = mass fraction of 1-butanol in the organic phase, ω11 = mass fraction of water in the aqueous phase, ω21 = mass fraction of ethanol in the aqueous phase, ω31 = mass fraction of acetone in the aqueous phase, ω41 = mass fraction of 1-butanol in the aqueous phase). K2HPO4 showed great repulsive interaction with the ABE, especially 1butanol. With the increasing K2HPO4 concentration, the mass fraction of 1-butanol in the organic phase increased gradually, and the mass fraction of 1-butanol in the aqueous phase decreased dramatically. 1-Butanol was totally recovered if the addition of K2HPO4 was greater than 500.00 g·kg−1. Water content in the organic phase decreased from 60.00 wt % to 5.50 wt % under the saturated condition of K2HPO4 at 298.15 K. The ABE was further enriched. K2HPO4 showed salting-out effects at lower concentrations and enrichment functions at higher concentrations. The salting-out ease of ABE was ordered as following: 1-butanol > acetone > ethanol. The result is consistent with the polarity indexes: water (9.0) > ethanol (5.2) > acetone (5.1) > 1-butanol (4.0).32 If the polarity level of one compound is lower, the salting-out effect of K2HPO4 for this compound is better. As a strong electrolyte, K2HPO4 can ionize cations (K+) and anions (HPO42−). Water molecules with a high polarity index will form a “hydration shell” around K+.33 The “hydration shell” repels the molecules of acetone, 1-butanol, and ethanol, so the salting-out process is performed. More cations (K+) were ionized, and more water molecules were attracted. More molecules of acetone, 1-butanol, and ethanol were repelled. So the mass fraction of water in organic phase decreased with the increase of the initial concentration of K2HPO4. Figure 1 shows the residues of K2HPO4 in the organic phase as a function of the initial concentrations of K2HPO4 at 298.15 K. K2HPO4·3H2O was added to the ABE system as the extractant. The water from K2HPO4·3H2O and the ABE system was used as solvent of K2HPO4. The residues of K2HPO4 in the organic phase decreased when more K2HPO4 was added to the ABE system because the concentrated ABE repelled the ions in

return. When the initial concentrations of K2HPO4 were beyond 400 g·kg−1, the residues of K2HPO4 were relatively stable and less than 200 ppm. So higher concentrations of K2HPO4 availed the salting-out process. The actual concentrations of K2HPO4 in the aqueous phase are shown in Table 2. They are a little higher than the initial concentrations because some water with niggardly K2HPO4 was in the organic phase. Table 2. Actual Concentrations of K2HPO4 (concnA) in the Aqueous Phase and the Average Numbers (no.) of Water Molecules around Two K+ Ions and One HPO42− Ion with the Initial Concentrations (concn) of K2HPO4 concn

concnA

g·kg−1

g·kg−1

no.

100.00 150.00 200.00 250.00 300.00 350.00 400.00 450.00 500.00 550.00 600.00

110.12 167.44 225.80 278.73 330.03 376.93 422.62 468.07 513.65 559.34 605.74

69.22 44.27 31.50 24.28 19.29 15.83 13.14 10.96 9.15 7.61 6.29

The numbers of water molecules around two K+ ions and one HPO42− ion can be calculated according to the following formula, no. =

[(1 − w51) ·w11]/18.016 w51/174.17

(1)

where no. is the numbers of water molecules around two K+ ions and one HPO42− ion, ω15 is the mass fraction of K2HPO4 in the aqueous phase (related with the actual concentrations of K2HPO4), ω11 is the mass fraction of water in the aqueous phase under salt-free conditions, 18.016 is the molar mass of water (18.016 g·mol−1), and 174.17 is the molar mass of K2HPO4 (174.17 g·mol−1). 1509

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Figure 2. Salting-out process of the (1-butanol + acetone + ethanol + water + K2HPO4) system at 298.15 K, ∼ is a molecule of ABE, ● is a water molecule.

The numbers of water molecules around two K+ ions and one HPO42− ion decreased when more K2HPO4 was added to the ABE system, as shown in Table 2. There is a bridging configuration of water molecules between adjacent cations and anions. The anions will remove the “hydration shell” largely, so HPO42− ions have negative effects on salting-out.34 The “hydration shell” of ions includes the first shell (chemical shell) and the second shell (physical shell).35 The first shell is relatively stable, but the second shell is variable. A HPO42− ion destroyed the second shell gradually, and these water molecules were attracted by an extra K+ ion. So the numbers of water molecules around two K+ ions and one HPO42− ion decreased with the crescent concentrations of K2HPO4. The chemical hydration number of K+ ion is 2,36 or doubtfully 3. So the second shell was destroyed mostly at high concentrations of K2HPO4. The salting-out process of the (1-butanol + acetone + ethanol + water + K2HPO4) system at 298.15 K is shown in Figure 2. Figure 2a shows the ABE system. The first shell and the second shell are formed after a small amount of K2HPO4 is added to the ABE system, as shown in Figure 2b, so the ABE is salted out. The K+ ions do not show linear relation with the attracted water molecules because the HPO42− ions destroys the second shell, as shown in Figure 2c. The water molecules in the organic phase make a balance with the relatively free water molecules in the aqueous phase. So the mass fraction of water in the organic phase decreased. All in all, the crescent concentrations of K2HPO4 make positive salting-out effects for the ABE system. The salting-out process will be more energy-saving if it is performed at high temperatures. The temperature of the initial ABE solution from the prefractionator was higher than 333.15 K after two stages of condensation.21 The higher solubility of K2HPO4 at higher temperatures will ionize more available ions to attract the water molecules, which may show stronger salting-out effects and enrichment functions. This is verified in Table 3. The mass fractions of water in the organic phase decreased gradually under the saturated conditions of K2HPO4 at the higher temperatures. It was 3.23 wt % at 333.15 K, as shown in Table 3. The ABE was further enriched with higher solubility of K2HPO4 at the higher temperature of 333.15 K, which availed the more energy-saving salting-out process. The K2HPO4 solutions have priority to be used as extractants in an industrial application if the salting-out method is used as an important unit operation for the separation of the ABE system from the prefractionator. The salting-out cases were carried out with saturated K2HPO4 solutions at 298.15 K and 333.15 K, respectively. The ABE was extracted by saturated K2HPO4 solution (59.54 %, mass fraction; 1.65 g·mL−1) with the salting-out factors of 1:2, 2:2, 3:2, 4:2, and 5:2 at 298.15 K. The mass fraction of

Table 3. Salting-out Effect of Dipotassium Hydrogen Phosphate Concentrations (concn) on the Enrichment of the Organic Phase in the ABE System from a Prefractionator at Different Temperatures (T/K) organic phase (wt %)

a

water

ethanol

acetone

1-butanol

T/K

ω14·100

ω24·100

ω34·100

ω44·100

control 298.15a 303.35a 307.55a 313.15a 317.65a 323.25a 327.75a 333.15a

60.00 5.50 5.17 4.74 4.45 4.30 3.90 3.27 3.23

4.00 9.51 9.55 9.60 9.60 9.65 9.62 9.78 9.68

10.00 22.59 22.78 22.43 22.41 22.51 22.53 22.63 22.31

26.00 62.40 62.49 63.23 63.54 63.54 63.95 64.32 64.78

Saturated condition.

water in the organic phase decreased from 17.65 wt % to 9.47 wt % when the salting-out factors ranged from 1:2 to 5:2, and it was always higher than that of ethanol, as shown in Figure 3. Figure 4 shows the ABE left in the aqueous phase after the extractions at 298.15 K. The losses of ABE were ordered as follows: ethanol > acetone > 1-butanol.

Figure 3. Mass fractions of water (■, ω14), ethanol (●, ω24), acetone (▲, ω34), and 1-butanol (▼, ω44) in the organic phase with different salting-out factors: the salting-out process with a saturated solution of K2HPO4 at 298.15 K. 1510

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ethanol. So K2HPO4 with a higher solubility at 333.15 K was another choice. The saturated K2HPO4 solution at 333.15 K (69.01 %, mass fraction; 1.80 g·mL−1) was used to recover the ABE with the salting-out factors of 1:2, 2:2, 3:2, 4:2, and 5:2 at 333.15 K. Figure 6 shows that the ABE was further enriched. The mass

Figure 4. Mass fractions of water (■, ω11), ethanol (●, ω21), acetone (▲, ω31), and 1-butanol (▼, ω41) in the aqueous phase with different salting-out factors: the salting-out process with a saturated solution of K2HPO4 at 298.15 K.

After the mass fractions of four components (1-butanol, acetone, ethanol, and water) in both phases were measured, the recovery of 1-butanol, acetone, or ethanol was calculated by the following formula, mc Ri = 1 i m0ci0 (2)

Figure 6. Mass fractions of water (■, ω14), ethanol (●, ω24), acetone (▲, ω34), and 1-butanol (▼, ω44) in the organic phase with different salting-out factors: the salting-out process with a saturated solution of K2HPO4 at 333.15 K.

fraction of water in the organic phase with salting-out factor of 2:2 was 8.88 wt %, which is lower than that with a salting-out factor of 5:2 at 298.15 K. K2HPO4 showed a much better enrichment performance than K2CO3 with the same salting-out factors at 333.15 K.29 So the salting-out process was performed at 333.15 K with the saturated K2HPO4 solution, which also reduced the losses of the ABE largely, as shown in Figure 7.

where Ri is the recovery of acetone, 1-butanol, or ethanol, m1 is the mass of the organic phase, ci is the mass fraction of each component in the organic phase, m0 is the mass of the initial ABE system, ci0 is the mass fraction of each component in the initial ABE system. m1 is determined according to the conservation of mass. Figure 5 shows the recovery of ethanol, acetone, or 1butanol. It was difficult to recover ABE totally because of the

Figure 7. Mass fractions of water (■, ω11), ethanol (●, ω21), acetone (▲, ω31), and 1-butanol (▼, ω41) in the aqueous phase with different salting-out factors: the salting-out process with a saturated solution of K2HPO4 at 333.15 K.

Figure 5. Recovery of ethanol (■), acetone (●), and 1-butanol (▲) from the prefractionator with different salting-out factors: the saltingout process with a saturated solution of K2HPO4 at 298.15 K. 1511

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while that with the salting-out factor of 4:2 was about 15 min. More extractant shortened the equilibrium time from 25 min to 15 min because of the high density of the K2HPO4 solution. Figure 10 shows that the equilibrium time was shortened from

If the salting-out factor is higher than 2:2, 1-butanol and acetone are totally recovered, as shown in Figure 8. The

Figure 8. Recovery of ethanol (■), acetone (●), and 1-butanol (▲) from the prefractionator with different salting-out factors: the saltingout process with a saturated solution of K2HPO4 at 333.15 K.

Figure 10. Salting-out equilibrium time (t) for mass fraction of water (ω14) in the water + acetone + 1-butanol + ethanol + K2HPO4 system with salting-out factors of ■, 4:2; ●, 2:2 at 333.15 K.

extractant with a higher salting-out factor means that more energy will be needed to evaporate the salting-out raffinate for recycling. The lower mass fraction of water in organic phase means less energy will be needed to separate the ABE system from the prefractionator. So the salting-out factors of 2:2, 3:2, and 4:2 are the objective selections. The salting-out process of the ABE system from the prefractionator with less extractant is achieved in this study. The more energy-saving process (salting-out + distillation) will be performed in an industrial application. With the salting-out factors of 2:2 and 4:2, the liquid−liquid equilibrium (LLE) time was measured at 298.15 K and 333.15 K, respectively. Figure 9 shows that the equilibrium time with the salting-out factor of 2:2 at 298.15 K was about 25 min,

5 min to 3 min when more extractant was used at 333.15 K. The equilibrium time with the salting-out factor of 2:2 at 333.15 K was shorter than that with a salting-out factor of 4:2 at 298.15 K, which predicted that higher temperature accelerated the mass transfer rate. The density of the K2HPO4 solution with the electrostatic repulsion of charged ions and the temperature are the primary mass transfer driving forces. Figure 11 shows the residues of K2HPO4 in the organic phase with different salting-out factors at 298.15 K and 333.15 K. It decreased with the higher salting-out factor, just like the results ahead. The mass fractions of K2HPO4 in the organic phase with salting-out factors of 2:2, 3:2, and 4:2 at 333.15 K were less

Figure 9. Salting-out equilibrium time (t) for mass fraction of water (ω14) in the water + acetone + 1-butanol + ethanol + K2HPO4 system with salting-out factors of ■, 4:2; ●, 2:2 at 298.15 K.

Figure 11. Mass fraction of K2HPO4 in the organic phase with different salting-out factors: the salting-out process with a saturated K2HPO4 solution at ■, 298.15 K; ●, 333.15 K. 1512

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than 140 ppm. So the residues of K2HPO4 in the organic phase can be ignored.

4. CONCLUSIONS In this study, K2HPO4 was investigated as an outstanding salting-out agent for the salting-out process of the ABE system from a prefractionator. More K2HPO4 dissolved in the ABE system to attract more water molecules and repel the ABE molecules. So the ABE was salted out and enriched. The salting-out theory is the hydration of the charged ions. The HPO42− ions destroyed the “hydration shell”, so the K+ ions did not show a linear relation with the attracted water molecules. But the crescent concentrations of K2HPO4 make positive salting-out effects for the ABE system. So K2HPO4 with higher solubility at higher temperatures showed greater salting-out effects and enrichment functions for the ABE system. There were less losses of acetone, 1-butanol, and ethanol if they were extracted from the ABE system by the saturated K2HPO4 solution at 333.15 K instead of that at 298.15 K. The ABE in the organic phase was further enriched as well. About 100.0 % 1-butanol, 100.0 % acetone, and 98.2 % ethanol can be recovered if the salting-out process is performed with the salting-out factor of 2:2 at 333.15 K in an industrial application. This process makes the equilibrium time shorter than 5 min. Less extractant to extract the ABE from a prefractionator has been realized. The smallest amount of K2HPO4 in the organic phase causes no trouble for the (salting-out + distillation) process of the ABE system.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +86-20-87114722; +86-2087113806. Funding

The authors greatly acknowledge the financial support by National High-tech Research and Development Projects (863) (no. 2012AA021202). Notes

The authors declare no competing financial interest.

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