Energy-Saving Recovery of Acetone, Butanol, and Ethanol from a

Article pubs.acs.org/jced

Energy-Saving Recovery of Acetone, Butanol, and Ethanol from a Prefractionator by the Salting-Out Method Shaoqu Xie, Conghua Yi, and Xueqing Qiu* School of Chemistry&Chemical Engineering, South China University of Technology, No. 381 Wushan Road, Guangzhou 510640, P. R. China ABSTRACT: Thirty compounds including salts, saccharides, and alkalies have been investigated as possible salting-out agents to recover (acetone + butanol + ethanol) (ABE) from a prefractionator. The most promising salt is potassium carbonate. The mechanisms of salting-out by potassium carbonate are summarized as hydration and hydrogen-bond breaking. The thermodynamic study of salting-out by potassium carbonate has been investigated and shows that the salting-out process is endothermic and a process of entropy increment. The extractant of saturated potassium carbonate solution should be double that of the sketchy ABE solution. When the salting-out process is performed at 333.15 K instead of 298.15 K, equilibrium time is shortened from 9 to 3 min. Energy demand in an industrial application shows that salting-out produces 25.13 %, even 35.42 % less energy consumption than that of the conventional distillation process.

1. INTRODUCTION Biobutanol is a kind of clean, new-type energy which has been studied for about ninety years.1,2 As a main product, biobutanol can be produced with some byproducts of acetone and ethanol from corn fermentation.3 This traditional process is called (acetone + butanol + ethanol) (ABE) fermentation.4 Meanwhile, there are some other accessory byproducts produced, such as acetic acid, isoamyl alcohol, acetaldehyde, 1- hexanol which make the separation process complicated and challenging. The concentration of biobutanol in the fermentation broth is about (10 to 20) kg. m−3, and is not higher than 2.0 wt % to ensure it will not stop the fermentation process.5 Therefore, the conventional recovery process of the ABE is often related with distillation.6 Distillation is an energy-intensive unit operation, because the products need to be condensed again after heating and lots of heat can not be obtained for reuse, which leads to a higher price of biobutanol compared with synthetic butanol. The oil crisis has highlighted the advantages of biobutanol with the fast development of enzymic and fermentation-based processes and separation processes for biobutanol separation.7 In order to obtain rarefied biobutanol from fermentation broth, multidistillations are applied to separate most of the byproducts.8 The fermentation broth is added in prefractionator to obtain sketchy products of acetone (around 10%, mass fraction), biobutanol (around 26%, mass fraction), ethanol (around 4%, mass fraction) and water (around 60%, mass fraction). Then the above products will need at least six columns and one decanter to gain rarefied acetone (around 99.7%, mass fraction), 1-butanol (around 99.9%, mass fraction), ethanol (around 95%, mass fraction). So more and more other separation processes arise along with the high energy-consumption.9 Liquid−liquid extraction of biobutanol from water, as an efficient separation process employing nonfluorinated task-specific © 2013 American Chemical Society

ionic liquids (TSILs), had been evaluated by higher distribution coefficient and selectivity (DBuOH = 21, S = 274) than oleyl alcohol (DBuOH = 3.42, S = 192) against distillation and extraction with conventional solvents that required 73% less energy.10 Hybrid extraction−distillation process is another way to deal with the broth.11 Considering heat integration from the fermentation broth to cut costs of the process, mesitylene was used as a novel solvent with excellent properties for ABE extraction via computer-aided molecular design (CAMD). Because of low polarity in biobutanol molecules, the molecules can be adsorbed by resins (IRC-50, XAD-2, XAD-4, XAD-7, XAD-8, XAD-16, XD-41, H-511, and KA-I).12,13 Despite their quick sorption, high adsorptive capacity, low cost, ease of desorption and regeneration, the selectivity needs to be solved, and also the selectivity of liquid−liquid extraction. Pervaporation becomes a high-frequency word for biobutanol recovery because ABE are volatile liquids or substances matched to water as the improvement of membrane performance.14,15 Membrane material applied to the pervaporation includes organic membranes, inorganic membranes and hybrid membranes, such as organic membranes with polytetrafluoroethylene (PTFE) membrane, polypropylene (PP) membrane, polydimethylsiloxane (PDMS) membrane, poly(ether block amide) (PEBA2533) membranes, inorganic membranes with aluminosilicate crystals and hybrid membranes with silicalite-1/polydimethylsiloxane (PDMS) hybrid membranes.16−18 But pervaporation also needs to deal with severe problems, such as membrane permselectivity, high cost and membrane fouling. Membrane solvent extraction, which is different from conventional liquid−liquid extraction and use membrane as interphase boundary where alcohols is extracted Received: September 6, 2013 Accepted: October 14, 2013 Published: October 28, 2013 3297

dx.doi.org/10.1021/je400740z | J. Chem. Eng. Data 2013, 58, 3297−3303

Journal of Chemical & Engineering Data

Article

Table 1. Effect of Saturated Salts on Mutual Solubility of ABE System at 298.15 K solubility type

neutral salt

acid salt

basic salt

a

salt

(g/100 g water)

control LiCl CaCl2 KCl MgCl2 NaCl NaNO3 K2SO4

84. 87. 35. 55. 36 91. 12.

85 25 70 20

EDTA-2Na AlCl3 (NH4)2SO4 NH4Cl NaH2PO4 FeSO4 NaHSO4 Al2(SO4)3 MnSO4

10. 46. 76. 39. 96. 56 10. 38. 62.

80 20 70 30 95

K2C2O4 NaAc KAc NaNO2 K2CO3 Na2CO3 Na3PO4 HCOONa K3PO4 Na2SiO3

3. 55. 269. 84. 112. 30. 14. 91. 100. a

61 50 50 20 50 60 20 60 15

25 05

35 40 90

organic phase (wt %)

aqueous phase (wt %)

water

ethanol

acetone

1-butanol

water

ethanol

acetone

1-butanol

60.00 18.09 13.76 17.79 24.21 13.52 14.23 37.53

4. 00 6.36 5.9 6.09 4.2 6.85 6.86 4.43

10. 00 14.91 13.55 15.26 9.93 17.13 15.46 11.43

26. 00 60.64 66.79 60.86 61.66 62.5 63.46 46.61

60.00 84. 69 83. 95 88. 36 82. 91 91. 33 90. 92 76. 84

4.00 3. 37 3. 60 2. 45 3. 49 2. 05 1. 80 3. 50

10.00 9. 38 9. 82 6. 61 9. 23 5. 05 5. 80 8. 80

26.00 2. 56 2. 63 2. 58 4. 37 1. 57 1. 48 10. 86

41.65 23.74 14.09 15.44 16.37 35.54 20.45 23.81 23.54

4.55 5.12 7.76 5.65 7.6 4.87 7.26 6.4 6.82

11.81 13.95 21.22 14.58 19.65 12.91 17.54 17.9 18.89

42 57.19 56.93 64.33 56.38 46.69 54.76 51.88 50.75

73. 86. 98. 86. 98. 84.

3. 2. 0. 2. 0. 2.

23.12 14.63 14.58 10.66 4.91 20.72 34.37 6.98 7.11 26.89

6.22 6.51 5.6 7.36 9.44 7.98 4.76 8.24 9.3 6.22

16.73 18.34 18.27 17.31 23.59 19.21 12.44 22.4 22.33 16.64

53.93 60.52 61.56 64.67 62.05 52.08 48.44 62.38 61.26 50.25

92. 90. 81. 92. 100 98. 79. 95. 100 93.

54 34 03 79 19 38

96. 35 97. 48 32 65 37 54 79 70 72 13

62 67 77 85 64 94

9. 6. 0. 6. 1. 6.

37 27 85 89 17 72

1. 05 0. 65

1. 95 1. 58

2. 2. 2. 1. 0 0. 3. 1. 0 1.

4. 4. 5. 5. 0 0. 8. 2. 0 3.

01 33 68 09 41 43 46 97

04 63 87 42 66 33 82 18

13. 4. 0. 3. 0 5.

47 72 35 47 96

0. 65 0. 29 1. 2. 10. 0. 0 0. 8. 0 0 1.

63 39 08 95 14 54

72

Saturation condition.

ethanol and biobutanol from prefractionator. In addition, the superior salts were selected for further study in order to get energy-saving industrial technology.

with a water-soluble solvent on the other side, is aimed to evaluate the practical applicability of liquid−liquid extraction and membrane solvent extraction in butanol fermentations.19 Unfortunately this method will cause solvent reverse osmosis. Gas stripping is an effective way to solve the inhibition of butanol for fermenters using nitrogen or fermentation gas from itself (H2 and CO2).20,21 N2 can improve the conversion rate of glucose and yield and yield rate of ABE without negative effects on fermentation process.22,23 Gas stripping has great potential for biobutanol recovery. Nevertheless, the conventional distillation process still plays a leading role in industrial application. It is well-known that water in organic solvent can be removed by salting-out method rapidly so that the useful organic compound can be concentrated.24−26 Salts such as LiCl, NaBr, KI showed a strong salting-out effect for 1-butanol from the aqueous phase.27 When butanol with water and propionic acid was treated by addition of CaCl2, a more important salting-out effect performed, which was better than that of NaCl.28 Seventynine compounds were investigated as salting-out agents for the separation of acetone, but only CaCl2, MgCl2 and sucrose showed relatively better performance among them.29 When ethanol was separated by salting-out, the strength of the investigated salts was ordered as following: K3PO4 > Na3C6H5O7 > K3C6H5O7.30 So the salting-out effect can make a difference on the partially separated products of ABE from prefractionator, which has been rarely reported yet. Therefore, as much as possible salting-out agents with stability and nontoxicity were investigated to separate water, acetone,

2. EXPERIMENTAL SECTION Materials. Acetone, 1-butanol, ethanol, alkalies, saccharides and all salts were supplied by Guanghua Chemical Plants Co. Ltd., (Guangzhou, China). Acetone, 1-butanol, ethanol were measured with purities of at least 99.5% (mass fraction) through gas chromatography. Potassium carbonate was measured with purity of at least 99.0% (mass fraction) by atomic absorption spectrometry(AAS) analysis. Water was deionized and its electrical conductivity at 293.15 K was lower than 1.5 × 10−4 S. m−1. Other compounds with purities of at least 99.0% (mass fraction) were of analytical grade without further purification. Procedure. The initial ABE system was prepared according to Chen’s report.8 The phase equilibrium of ABE system was performed in a gastight vial with a sealing pad by adding enough single-salt, alkali or saccharide until saturated condition formed. This system was stirred at 298.15 K at the speed of 200 r. min−1 for 1 h and then settled for 2 h until phase equilibrium was reached. After equilibrium, some of the liquid in two separated phases were withdrawn by microsyringe. The mass fractions of four components (acetone, 1-butanol, ethanol and water) in the two phases were analyzed by the withdrawn liquid through gas chromatography. Three or more analytical duplicates were carried out and the results were averaged. Moreover, the effect 3298



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3. RESULTS AND DISCUSSION Salting-Out Agents. The compounds tested as salting-out agents can be separated into three classes. (1) Salt compounds obtained by acid−base interaction. The agents in this category are shown in Table 1. (2) Alkali compounds including NaOH and KOH. The agents in this category are shown in Table 2. (3) Saccharide compounds including sucrose and glucose.29 The agents in this category are shown in Table 3. All compounds could cause phase separation and exhibited different influences on the ABE system. Salts used in the salting-out process can be sorted into neutral salt, acid salt, and basic salt. There is a general relationship between dehydration and the solubility of salt, because both cation and anion can form a hydration shell with water molecules.32 According to Table 1, water content in the organic phase decreased from 60 % to 4. 91 % after the addition of salts. Both neutral salt and acid salt had a salting-out effect on the ABE system. NaCl was the best neutral salt and (NH4)2SO4 was the best acid salt. However, they could not be selected as the final salting-out agents because of the high content of organic compounds in the aqueous phase. Some basic salts, especially potassium carbonate, potassium phosphate, and sodium formate, played a good role in dehydration. Considering the water content in the organic phase and the organics content in the aqueous phase, the best salt selected for salting-out of the ABE system was potassium carbonate. Besides salts, sucrose is an efficient agent for salting-out.29 Two kinds of saccharides including sucrose and glucose were used for salting-out. Sucrose and glucose had strong hydrophilic effects which led to repelling biobutanol, but far less than some salts. Strong alkalies had stronger hydrophilic effects than salts because hydroxyl ions could break the hydrogen bonds which formed among the water molecules and the organic compounds, repelling organic compounds. Compared with KOH, the water content of the organic phase after the same addition of NaOH was less, as shown in Table 2. The molar mass of NaOH (0.04 kg·mol−1) is less than that of KOH (0.056 kg·mol−1), and NaOH ionizes more sodium ions and hydroxyl ions than KOH if the same dosages are used. As a result, the effect of NaOH on salting-out was better than that of KOH. The pH of the aqueous phase increased with the concentration of the alkali that caused the polymerization of acetone, leading to the yellow color of the solution. Even if the additional amount of KOH or NaOH was less than K2CO3, they showed a better salting-out effect. This was because they ionized more hydroxyl ions than K2CO3 which effectively broke the hydrogen bonds. Hydration and breaking hydrogen bonds are two important factors for salting-out. K2CO3 had strong hydrophilic effects and hydrolytic hydroxyl ions so that K2CO3 showed a great salting-out effect for the ABE system. K2CO3 Salting-Out for ABE System. K2CO3 was the best salting-out agent for the ABE system, so it had the potential to perform well at higher temperatures.

of the salting-out process was evaluated by the mass fraction of water in organic phase. Meanwhile, the mass fractions of acetone, biobutanol, ethanol in the aqueous phase were also taken into account. After the most favorable salt was determined, its potential for salting-out at successively high temperature was investigated because the temperature of the mixture from prefractionator was higher than 355.15 K after condensation at the top of the column. The solubility of potassium carbonate in water at temperatures from 273.15 to 353.15 K increases, which can make salting-out perform better.31 Potassium carbonate in the aqueous phase was always kept saturated as the temperature increased, ranging from 298.15 to 333.65 K. Meanwhile, the study on thermodynamics of salting-out with the most favorable salt was carried out as salting-out temperature increased. The thermodynamic properties of salting-out in different potassium carbonate concentrations were investigated by increasing the temperature, ranging from 295.55 to 333.35 K. The addition of potassium carbonate (35%, 45%, 55%, respectively, mass fraction) was determined by the whole mass of water in two phases. The salting-out factor, which was defined as the volume ratio of saturated potassium carbonate solution to the sketchy ABE solution, was studied at 298.15 and 333.15 K. The best saltingout factor was selected according to the energy conservation from energy demand. Moreover, phase equilibrium time was given. Analytical Methods. The mass fractions of water, acetone, 1-butanol, ethanol under salt-free condition were determined by gas chromatography which was equipped with a 2m(L) × 3 mm(ID) × 5 mm(OD) Porapak Q 80 - 100 mesh packed column and a thermal conductivity detector. The column temperature was kept at 393.15 K for 5 min and then soared to 433.15 K at a rate of 40 K/min. The injector and detector temperatures were fixed at 453.15 K. The content analysis of four components (acetone, 1-butanol, ethanol and water) from two phases was conducted by the peak area normalization method. Table 2. Effect of Different Addition of Alkalies on Mutual Solubility of ABE System at 298.15 K organic phase (wt %) salt

addition (g/15 g water)

water

ethanol

acetone

1-butanol

2.00 5.00 7. 50 10.00 2.00 5.00 7.00 10.00 15.00 18.00

60.00 16.51 7.38 4.75 4.24 18.69 11.91 8.09 6.09 4.81 3.72

4. 00 6.80 8.54 9.44 9.54 6.08 7.15 8.04 8.58 9.14 9.85

10. 00 19.74 23.32 24.23 22.97 17.60 20.94 22.47 23.30 24.21 24.63

26. 00 56.95 60.76 61.58 63.26 57.64 60.01 61.41 62.03 61.85 61.81

control NaOH

KOH

Table 3. Effect of Saturated Saccharides on Mutual Solubility of ABE System at 298.15 K solubility saccharide control sucrose glucose


aqueouse phase (wt %)

(g/100 g water)

water

ethanol

acetone

1-butanol

water

ethanol

acetone

1-butanol

209. 30 83.00

60.00 14.27 20.80

4. 00 5.56 5.35

10. 00 15.38 14.55

26. 00 64.89 59.30

60.00 83.72 83.73

4. 00 2.03 2.78

10. 00 7.77 7.64

26. 00 6.47 5.85

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4.91 % at 298.15 K, and the ratio of ABE was 23.59:62.05:9.44 which was approximately to 10:26:4 as shown in Table 5 simply to prove that most organic compounds had been separated. When the temperatures increased, the solubility of potassium carbonate increased resulting in a greater salting-out effect on dehydration, as shown in Table 5. Obviously, at a higher temperature of 333.65 K, more potassium ions and hydroxyl ions were involved with dehydration. Temperature changes of salting-out for the ABE system have a great influence on the distribution coefficient. The distribution coefficient has a relationship with temperature as shown in the following formula,

Table 4. Effect of Potassium Carbonate Concentration (concn) on Separation Efficiency at 298.15 K concn

a


kg·kg−1

water

ethanol

acetone

1-butanol

35.00 40.00 45.00 50.00 55.00 58.00a

13.32 11.46 8.84 6.83 5.31 4.91

8.24 8.54 8.92 9.14 9.36 9.44

21.28 21.81 22.53 23.11 23.46 23.59

57.16 58.20 59.71 60.91 61.88 62.05

Saturation condition.

∂K ΔH 0 = ∂T RT 2

Table 5. Effect of Potassium Carbonate Concentration on Separation Efficiency at Different Temperatures (T/K)

where K is the distribution coefficient, T is the absolute scale of temperature, R is the universal gas constant, and ΔH0 is the molar enthalpy change. If salting-out is exothermic, the distribution coefficient K decreases with the increase of temperature. Conversely, constant K rises with the increase of temperature. We took ABE as one compound, then K = Corg/Caq. Changing the concentration of K2CO3 and fixing other extraction conditions, a series of distribution coefficient values were measured at different temperatures. The ln K mapped 1/(RT), and after linear regression the slopes were obtained. The results are shown in Figure 1. When the concentration of K2CO3 was 35 % (mass fraction), ΔH = 28.0 kJ·mol−1, 45 % (mass fraction), ΔH = 36.5 kJ·mol−1, and 55 % (mass fraction), ΔH = 49.7 kJ·mol−1, respectively. So the salting-out of K2CO3 was endothermic. Elevated temperatures and increasing solution concentration of potassium carbonate availed salting-out. So 333.15 K close to the boiling point of acetone was a good choice. We calculated the values of ΔG and ΔS according to the following two formulas.


a

T (K)

water

ethanol

acetone

1-butanol

298.15a 304.35a 313.35a 323.25a 333.65a

4.91 4.53 4.48 4.44 4.42

9.44 9.49 9.49 9.44 9.52

23.59 23.61 23.65 23.45 23.81

62.05 62.37 62.38 62.67 62.26

(1)

Saturation conditions.

ΔG = −RT ln K

(2)

ΔH = ΔG + T ΔS

(3)

where ΔG is the Gibbs energy change and ΔS is the entropy change. With the increase of K2CO3 solution concentration, ΔG decreased and was less than zero, and ΔS increased. So the salting-out extraction was a spontaneous process; meanwhile, the process of entropy increased, as shown in Table 6. Table 7 and Table 8 showed different salting-out factors between the saturated aqueous solution of K2CO3 and the sketchy ABE solution from the prefractionator. The water content of the organic phase decreased along with the increase of the salting-out factor at 298.15 K. But the higher salting-out factor involves more energy to evaporate water for recovery of the saturated aqueous solution of K2CO3. So the best outcome was 4/2 as shown in Table 7. The salting-out factor data at 333.15 K was different from that at 298.15 K. The water

Figure 1. Relationship between ln K and 1/(R × T) on a salt-free basis for the system water + acetone +1-butanol + ethanol with ■, 35 %; ●, 45 %; ▲, 55 % (mass fraction) of K2CO3 using only the water of the ABE system as solvent.

With the increase of concentration of K2CO3, more potassium ions with hydrated shells contributed to the water decrease of the organic phase, and more hydroxyl ions rooting in the hydrolysis of carbonate ions broke the hydrogen bonds of ABE system for decreasing organic residues in aqueous phase. This change of concentration is evident in Table 4. The water content of the organic phase reached a minimum of

Table 6. The Thermodynamics Properties of Salting-Out at Different Temperatures (T/K) concn of K2CO3 (35 %, mass fraction)

concn of K2CO3 (45 %, mass fraction)

concn of K2CO3 (55 %, mass fraction)

T

ΔH

ΔG

ΔS

ΔH

ΔG

ΔS

ΔH

ΔG

ΔS

K

kJ·mol−1

J·mol−1·K−1

J·mol−1

kJ·mol−1

J·mol−1·K−1

J·mol−1

kJ·mol−1

J·mol−1·K−1

J·mol−1

299.6 306.7 313.9 322.2 333.4

28.0 28.0 28.0 28.0 28.0

−11058 −11824 −12613 −14018 −15368

130 130 130 131 130

36.5 36.5 36.5 36.5 36.5

−11088 −12037 −13352 −15171 −16158

159 158 159 160 158

49.7 49.7 49.7 49.7 49.7

−12664 −13919 −15221 −16835 −19792

208 207 207 206 208

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content of the organic phase increased and then decreased when the salting-out factor increased. When the salting-out factor was higher than 4/2, the water content of organic phase increased because thermal movement of hydration ions intensified and it destroyed the physical hydrated shell to release more free water molecules. Extractant brought several times more water than extractive that inhibited the salting-out process. So the salting-out factor of 4/2 was selected, referring to Table 8. Taking the content of ABE in the aqueous phase into account (not given), about 98.3 % biobutanol, 99.0 % acetone, and 98.0,% ethanol can be recovered. With salting-out factor of 4/2, liquid−liquid equilibrium (LLE) time was measured at 298.15 K and 333.15 K, respectively. Figure 2 shows that equilibrium time is about 9 min at 298.15 K; however, it is less than 3 min at 333.15 K. Diffused mass transfer is the only way for salting-out, so the higher temperature of 333.15 K intensified the thermal motion of molecules, which made the phase equilibrium time shorter than that at 298.15 K. Energy Consumption in Industrial Application. Because the heat required to evaporate water (2258 kJ·kg−1) is much higher than that for 1-butanol (592 kJ·kg−1),33 salting-out of biobutanol is suggested to split most of the water efficiently. Figure 3 shows the conventional process of the ABE system distillation. Three distillation columns are indispensable to purify only biobutanol, while one column with a side withdrawal is recommended after salting-out, as shown in Figure 4. Acetone and ethanol can be recovered easily in the improved process. Compared with the conventional process, an extraction column and a flash separator are additional. Less water with biobutanol from the decanter will return to the prefractionator so that 7.0 % energy is saved, as shown in Table 9. Compared with three columns, just one column for recovering biobutanol will save 89.6 % energy and 73.3 % energy for acetone. Extra energy is needed for the evaporator. The heat to recover water in the potassium carbonate solution will be reutilized for the fermentation process or separation process. Salting-out leads to a reduction in the energy demand that more than 25.16 % energy will be saved in the separation process. If the abovementioned heat can be recovered totally, 35.42 % energy is saved at most.

Table 7. Salting-out Factor Data of Organic Phase at 298.15 K organic phase (wt %) salting-out factor

water

ethanol

acetone

1-butanol

2/2 3/2 4/2 5/2 6/2 7/2

10.33 8.10 7.53 6.70 6.32 6.08

8.50 8.75 8.78 8.82 8.80 8.75

20.77 22.09 22.33 22.34 22.29 22.53

60.40 61.06 61.36 62.14 62.59 62.65

Table 8. Salting-out Factor Data of Organic Phase at 333.15 K organic phase (wt %) salting-out factor

water

ethanol

acetone

1-butanol

2/2 3/2 4/2 5/2 6/2

10.15 8.07 7.16 7.46 7.44

8.45 8.77 8.78 9.03 9.54

21.97 22.52 22.64 23.85 25.47

59.42 60.65 61.42 59.66 57.55

Figure 2. Salting-out equlilibrium time for mass fraction of water (ω1) in the system water + acetone +1-butanol + ethanol + K2CO3 with salting-out factor of 4/2 at ●, 298.15 K; ■, 333.15 K.

Figure 3. Conventional process of ABE system distillation. 3301



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Figure 4. Improved process of ABE system distillation.

Table 9. Energy Demand between the Conventional Process and the Improved Process energy demand (kJ/kg BuOH) unit prefractionator butanol columns evaporator acetone columns ethanol column in total a

conventional process 24.16 11.54 0 2.07 0.26 38.03

×103 × 103

improved process

energy saving (%)

× × × × × ×

7.02 89.56 a 73.33 6.67 25.16 (or 35.42)

22.52 1.18 3.92 0.56 0.28 28.46

× 103 ×103 × 103

103 103 103 (or 0.02 × 103) 103 103 103(or 24.56 × 103)

Not given.

4. CONCLUSIONS In this study, the best salt for salting-out of the ABE system from a prefractionator is K2CO3. According to the LLE data reported in great detail, the mechanisms of salting-out by K2CO3 are summarized as hydration and hydrogen-bond breaking. Neutral salts, acid salts, and saccharides do not involve the factors mentioned above, so that they show a general salting-out effect while basic salts and alkalies show a great salting-out effect due to the ionized cation and hydroxyl ions. But alkalies will catalyze the polymerization of acetone that leave basic salts as an exclusive choice. The feasibility of K2CO3 for salting-out at 333.15 K is confirmed by a thermodynamic study about the equilibrium system. Salting-out is an endothermic process with an entropy increment. Elevated temperatures and the increasing solution concentration of potassium carbonate avail salting-out. No matter at 298.15 K or 333.15 K, the salting-out factor of 4/2 is the best option. Results indicate that higher temperature speeds up phase equilibrium because of the thermal motion of molecules. The efficient separation of the ABE system is the salting-out of K2CO3 with a salting-out factor of 2/1 at 333.15 K if this salting-out method is applied to the recovery of acetone, biobutanol, and ethanol (ABE) from the prefractionator. The salting-out unit as a preferred plug-in unit exhibits good energy-saving performance (25.16 %, even 35.42 % in total) in the improved process.

■

Notes

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

■

REFERENCES

(1) Arthur, L. D. Acetone, Butanol, And Ethanol in Gas from the Butyric Fermentation of Corn. Ind. Eng. Chem. 1923, 15, 631−632. (2) Chang, H. P.; Martin, R. O.; Phillip, C. W. Acetone−Butanol− Ethanol (Abe) Fermentation and Simultaneous Separation in a Trickle Bed Reactor. Biotechnol. Prog. 1991, 7, 185−194. (3) Liu, J. H.; Wu, M.; Wang, M. Simulation of the Process for Producing Butanol from Corn Fermentation. Ind. Eng. Chem. Res. 2009, 48, 5551−5557. (4) Awang, G. M.; Jones, G. A.; Ingledew, W. M.; Kropinski, A. M. B. The Acetone−Butanol−Ethanol Fermentation. Crit. Rev. Microbiol. 1988, 15, S33. (5) Quresh, I. N.; M Eagher, M. M.; Hutkins, R. W. Recovery of Butanol from Model Solutions and Fermentation Broth Using a Silicalite−Silicone Membrane. J. Membr. Sci. 1999, 158, 115−125. (6) Parveen, K.; Diane, M. B.; Michael, J. D.; Pieter, S. Methods for Pretreatment of Lignocellulosic Biomass for Efficient Hydrolysis and Biofuel Production. Ind. Eng. Chem. Res. 2009, 48, 3713−3729. (7) Mahmoud, M. Biocatalysis: The Road Ahead. Org. Process Res. Dev. 2011, 15, 173−174. (8) Chen, T. S. Production Technology of Acetone and Butanol Fermentation; Chemical Industry Press: Beijing, 1991. (9) Ezeji, T. C.; Qureshi, N.; Karcher, P.; Minteer, S. D. Butanol Production from Corn. Alcoholic Fuels: Fuels for Today and Tomorrow; Taylor Francis: NewYork, 2006.

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(10) Lesly, Y. G.-C.; Christian, M. G.; Boelo, S.; André, B. Biobutanol Recovery Using Nonfluorinated Task-Specific Ionic Liquids. Ind. Eng. Chem. Res. 2012, 51, 8293−8301. (11) Kraemer, K.; Harwardt, A.; Bronneberg, R.; Marquardt, W. Separation of Butanol from Acetone−Butanol−Ethanol Fermentation by a Hybrid Extraction−Distillation Process. Comput. Chem. Eng. 2011, 35, 949−963. (12) Das, K.; Soni, B.; Ghose, T. Static and Column Studies on Selective Adsorption−Desorption of Butanol. Proceedings of the 4th European Congress onn Biotechnology; Elsevier: Amsterdam: The Netherlands, 1985. (13) Lin, X. Q.; Wu, J. L. Selective Separation of Biobutanol from Acetone−Butanol−Ethanol Fermentation Broth by Means of Sorption Methodology Based on a Novel Macroporous Resin. AIChE Biotechnol. Prog. 2012, 28, 962−972. (14) Peng, F. B.; Lu, L. Y.; Sun, H. L.; Wang, Y. Q.; Liu, J. Q.; Jiang, Z. Y. Hybrid Organic−Inorganic Membrane: Solving the Tradeoff between Permeability and Selectivity. Chem. Mater. 2005, 17, 6790− 6796. (15) Huang, J. C.; Meagher, M. M. Pervaporative Recovery of nButanol from Aqueous Solutions and ABE Fermentation Broth Using Thin-Film Silicalite-Filled Silicone Composite Membranes. J. Membr. Sci. 2001, 192, 231−242. (16) Qureshi, N.; Blaschek, H. P. Butanol Recovery from Model Solution/Fermentation Broth by Pervaporation: Evaluation of Membrane Performance. Biomass Bioenergy 1999, 17, 175−184. (17) Liu, F. F.; Liu, L.; Feng, X. S. Separation of Acetone−Butanol− Ethanol (ABE) from Dilute Aqueous Solutions by Pervaporation. Sep. Purif. Technol. 2005, 42, 273−282. (18) Zhou, H. L.; Sua, Y.; Chena, X. R.; Wana, Y. H. Separation of Acetone, Butanol and Ethanol (ABE) from Dilute Aqueous Solutions by Silicalite-1/PDMS Hybrid Pervaporation Membranes. Sep. Purif. Technol. 2011, 79, 375−384. (19) Groot, W. J.; Soedjak, H. S.; Donck, P. B.; Lans, R. G. J. M.; Luyben, K. Ch. A. M.; Timmer, J. M. K. Butanol Recovery from Fermentations by Liquid−Liquid Extraction and Membrane Solvent Extraction. Bioproc. Biosyst. Eng. 1990, 5, 203−216. (20) Ezeji, T. C.; Qureshi, N.; Blaschek, H. P. Butanol Fermentation Research: Upstream and Downstream Manipulations. Chem. Rec. 2004, 4, 305−314. (21) Ezeji, T. C.; Qureshi, N.; Blaschek, H. P. Bioproduction of Butanol from biomass: From Genes to Bioreactors. Curr. Opin. Biotechnol. 2007, 18, 220−227. (22) Qureshi, N.; Li, X. L.; Hughes, S. Butanol Production from Corn Fiber Xylan Using Clostridium Acetobutylicum. Biotechnol. Prog. 2006, 22, 673−680. (23) Maddox, I. S.; Qureshi, N.; Roberts, T. K. Production of Acetone−Butanol−Ethanol from Concentrated Substrates Using Clostridium Acetobutylicum in an Integrated Fermentation-Product Removal Process. Process Biochem. 1995, 30, 209−215. (24) Meissner, H. P.; Stokes, C. A. Solvent Dehydration by Salting Out. Ind. Eng. Chem. 1944, 36, 816−820. (25) Gross, P. M. The “Salting Out” of Non-electrolytes from Aqueous Solutions. Chem. Rev. 1933, 13, 91−101. (26) Yano, Y. F.; Uruga, T.; Tanida, H.; Terada, Y.; Yamada, H. Protein Salting Out Observed at an Air−Water Interface. J. Phys. Chem. Lett. 2011, 2, 995−999. (27) Taher, A. A.; Emina, K. Salt Effects of Lithium Chloride, Sodium Bromide, or Potassium Iodide on Liquid−Liquid Equilibrium in the System Water + 1-Butanol. J. Chem. Eng. Data 1997, 42, 74−77. (28) José, L. Z.; Mónica, B. G. de D.; Carlos, M. B.; Horacio, N. S. Effect of Addition of Calcium Chloride on the Liquid−Liquid Equilibria of the Water + Propionic Acid + 1-Butanol System at 303.15 K. J. Chem. Eng. Data 1998, 43, 1039−1042. (29) Charles, E. M.; Gary, D. C. Salting-out of Acetone from Water. Basis of a New Solvent Extraction System. Anal. Chem. 1973, 45, 1915−1921. (30) Wang, Y.; Mao, Y. L.; Han, J.; Liu, Y.; Yan, Y. S. Liquid−Liquid Equilibrium of Potassium Phosphate/Potassium Citrate/Sodium

Citrate + Ethanol Aqueous Two-Phase Systems at (298.15 and 313.15) K and Correlation. J. Chem. Eng. Data 2010, 55, 5621−5626. (31) Robert, C. M.; Robert, E. M.; John, M. S. Solubility of Potassium Carbonate in Water between 384 and 529 K Measured Using the Synthetic Method. J. Chem. Eng. Data 1997, 42, 1078−1081. (32) Villegas, I.; Weaver, M. J. Infrared Spectroscopy of Model Electrochemical Interfaces in Ultrahigh Vacuum: Evidence for Coupled Cation−Anion Hydration in the Pt(111)/K+, Cl− System. J. Phys. Chem. 1996, 100, 19502−19511. (33) Zhong, L.; Wu, Q.; Ma, S. P. Principles of Chemical Engineering; Beijing, 2008.

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