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salts
Accepted Manuscript Extraction of Succinic Acid by Aqueous Two-Phase System Using Alcohols/ Salts and Ionic Liquids/Salts Aulia Indah Pratiwi, Takeyuki Yokouchi, Michiaki Matsumoto, Kazuo Kondo PII: DOI: Reference:
S1383-5866(15)30107-6 http://dx.doi.org/10.1016/j.seppur.2015.07.039 SEPPUR 12458
To appear in:
Separation and Purification Technology
Received Date: Revised Date: Accepted Date:
20 October 2014 3 July 2015 17 July 2015
Please cite this article as: A.I. Pratiwi, T. Yokouchi, M. Matsumoto, K. Kondo, Extraction of Succinic Acid by Aqueous Two-Phase System Using Alcohols/Salts and Ionic Liquids/Salts, Separation and Purification Technology (2015), doi: http://dx.doi.org/10.1016/j.seppur.2015.07.039
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Extraction of Succinic Acid by Aqueous Two-Phase System Using Alcohols/Salts and Ionic Liquids/Salts
(2nd Revised version)
by Aulia Indah Pratiwi, Takeyuki Yokouchi, Michiaki Matsumoto*, and Kazuo Kondo
Department of Chemical Engineering and Materials Science Doshisha University Kyotanabe, Kyoto 610-0321 JAPAN
* Corresponding author TEL/FAX +81-774-65-6655 E-mail; [email protected]
1
ABSTRACT Succinic acid is the important feedstock for several industrial products including biodegradable plastics. Production of a fermentation-derived succinic acid (bio-succinic acid) has recently emerged as a potential green technology. For bio-succinic acid production, 50 to 60% of processing costs are attributed to recovery and purification processes. In this paper, we examine aqueous two phase systems (ATPS) using water-miscible alcohols/salts and ionic liquids/salts to extract succinic acid. From binodal curves, the phase separation abilities of solvents are in the order t-butanol > 1-propanol > HmimBr > 2-propanol ≈ OmimBr > BmimBr > ethanol. Extractability of succinic acid was within 0 to 72.1 % in ATPSs with1-propanol using salt concentration of 20 g/100mL-water and depended on the pH of the salt solution. When salts, K2HPO4, K3PO4, K2CO3, KF, (NH4)2SO4, C6H5Na3O 7, Na2CO3, NaCl, MgSO4, and NH4NO3, were used, relatively high extractabilities were obtained by using the salt solutions which gave pH smaller than pKa1 of succinic acid. In the ATPS with ionic liquids, Extractability of succinic acid was within 16 to 85.5% and were affected by not pH but the salts used. An ATPS with an OmimBr and (NH4)2SO4 system gave highest extraction, 85.5%. Extracted succinic acid was quantitatively precipitated by adding sodium hydroxide to the extracted phase and recovered as crystallization of sodium succinate. Highlights We extracted succinic acid was extracted with OmimBr/(NH4)2SO4 ATPS system. Extraction of succinic acid with ATPS using aqueous alcohols was controlled by pH. 2
Extracted succinic acid was recovered as precipitation of sodium succinate.
Key words Ionic liquids, Extraction, Succinic acid, Aqueous two-phase system
1. Introduction Succinic acid is the important feedstock for several industrial products including tetrahydrofuran, adipic acid, 1,4-butanediol, aliphatic esters, and biodegradable plastics [1]. Succinic acid for industrial use is mainly produced petrochemically. Nowadays, production of a fermentation-derived succinic acid (bio-succinic acid) has potential as green technology because CO2 is consumed during the fermentation process [1]. Furthermore, bio-succinic acid has the potential to become a key building block for commodity chemicals [2]. Higher cost in production of fossil fuels results in a high market potential for bio-succinic acid because its production has a net fossil energy consumption of 30-40% less than petroleum-based succinic acid production [3]. A few companies and consortia have begun to develop industrial production of bio-succinic acid [2]. The global bio-based succinic acid market is expected to reach volume of 0.7 million tons by 2020 [4]. In bio-succinic acid production plants reported, membrane and ion exchange as separation processes from the neutralized broth were utilized to obtain the crude succinic acid [5]. In general, for bio-succinic acid production, 50 to 60% of processing costs are attributed to recovery and purification processes to obtain the final product [3] because succinic acid has relatively low product 3
concentration in the complex medium. Therefore, economical and efficient recovery and purification processes for bio-succinic acid are desired. Several separation methods for succinic acid recovery have been proposed: selective precipitation, adsorption, electrodialysis, extraction with solvents and/or amines, ion exchange, membrane separation and esterification [6,7]. Recently, we proposed liquid membrane systems containing ionic liquid for succinic acid separation [8,9]. Although considerably stable liquid membranes containing ionic liquid were obtained compared with conventional liquid membranes, membrane performance was gradually impaired over the long term. Sun et al. [10] reported an acetone/(NH4)2SO4 aqueous two-phase system (ATPS) for recovery of bio-succinic acid. The ATPS has been well known as one extraction technique for biomolecules [11]. Recent research has focused on ATPSs that were formed by water-miscible organic solvent or ionic liquid with salt [11,12]. Most of the polymers, used in ATPSs so far have high viscosity and tend to form a cloudy solution [13] by the slight external disturbance because of low interfacial tension. Therefore, a polymer/salt ATPS has difficulty isolating the extracted biomolecules from the viscous polymer phase by back-extraction. An ATPS composed of hydrophilic organic solvents and salts attracted much attention because of low extraction cost, easy solvent recovery by evaporation and easy scale up [11]. An ATPS composed of hydrophilic ionic liquids and salts was also interesting because of faster phase separation, reduction in viscosity, and tailoring of the polarity of the coexisting phase compared with ATPSs composed of polymers. [14]. In this study, we examined water-miscible alcohol/salt and ionic liquid/salt ATPSs for the extraction of succinic acid. As mentioned, water-miscible alcohol 4
is easily recovered by evaporation. 1-Alkyl-3-methylimidazolium bromide was used as ionic liquid. It is known that, because of the different Gibbs energies of hydration of Cl- (-340 kJ/mol) and Br- (-315 kJ/mol) [15], the ionic liquids with Clanion hydrate more water molecules than those with Br-, resulting in difficulty in phase formation as salt was added. Finally we recovered succinic acid from the extracted phase by direct precipitation with alkali hydroxide.
2. Experimental 2.1. Chemicals 1-Butyl-3-methylimidazolium bromide [BmimBr] was purchased from Merck, 1-hexy-3-methylimidazolium bromide [HmimBr] and 1-octyl-3-methylimidazolium bromide [OmimBr] were purchased from Tokyo Chemical Industries, Ltd, and these were used as received. K2HPO4, K3PO4, K2CO3, KF, (NH4)2SO4, C6H5Na3O7.2H2O, Na2CO3, NaCl, MgSO4, and NH4NO3 of G.R. grade were used as salts. 1-Propanol (1-ProOH), 2-propanol (2-ProOH), t-butanol (t-BuOH) and ethanol (EtOH) were used as water-miscible organic solvents. 2.2. Preparation of phase diagram The binodal curves were determined by turbidimetric titration as described in a previous paper on an ATPS using water-miscible organic solvent and salt [16]. A K2HPO4 solution of known concentration was placed in a 100 mL conical flask, and ionic liquids (BmimBr, HmimBr and OmimBr) were added drop-wise to the flask until the clear solution turned turbid or two-phase systems were formed at 25ºC. Then, de-ionized water was added drop-wise to the flask to obtain a clear one-phase system, and more ionic liquids were added again to
5
produce two-phase systems. The composition of this mixture was noted and the experiments were repeated to obtain the binodal curve. The tie lines were measured by the following procedure. A series of ATPSs with three or four different composition were prepared in graduated glass tubes. These solutions were mixed thoroughly and left standing for more than 1 h in a thermostated bath at 25ºC. To ensure the complete phase separation, these solutions were centrifuged for 10 min at 5000 rpm at 25ºC. After that, visual estimation of volumes of top and bottom phase. The concentrations of organic solvents or ionic liquids were analyzed by HPLC or UV at 211nm (UV2500, Shimadzu, Kyoto, Japan), respectively, and the water content in both phases were determined by Karl Fischer’s method (AQ-300, Hiranuma, Kyoto, Japan). The salt concentration was calculated by subtracting total weight from weights of water and organic solvent (ionic liquid). 2.3. Extraction of succinic acid using ATPS Solid inorganic salts and 5 mL of water-miscible organic solvents or ionic liquids were added into the 5 mL solution including succinic acid (20 g/L) to form the ATPS consisting of 25-150 g-salt/100 g-water in a calibrated test tube with a stopper. The solution was mixed thoroughly and left standing for more than 6 h in a thermostated bath at 25ºC. The volumes of the top and bottom phases were recorded. The concentrations of succinic acid and the water content in both phases were analyzed by HPLC as described in previous papers [8,9] and Karl Fischer’s method. The pHs of the aqueous solutions before and after equilibration were determined by a Horiba F-71 pH meter. The extractability (E) and distribution ratio (D) of succinic acid was defined as,
6
[%] =
× 100
=
(1) (2)
where C and V are the concentration of succinic acid and the solution volume and subscripts T, B and 0 denote the top and bottom phases and initial state. 2.4. Precipitation of succinate from extracted phase After succinic acid was extracted by ATPS containing ammonium sulfate of 20 g/100mL, the aliquot of the solvent-rich phase was taken from the test tube for extraction into the flask tube. The precipitants, NaOH, NH4OH and Ca(OH)2, were added until the precipitate formed. Precipitates were filtered. The amounts of unrecovered succinic acid in the filtrate were measured with HPLC.
3. Results and discussion 3.1 Phase diagram for ATPS consisting of water-miscible organic solvent or ionic liquid, and dipotassium hydrogen phosphate Figure 1 shows the effects of water-miscible solvents on the binodal curves of the K2HPO4/solvent ATPS at 25ºC plotted as mass fractions. The closer the binodal curves are to the coordinate origin, the less solvent is required for the formation of the ATPS under the same concentration of salt. From the figure, the phase separation abilities of solvents are in the order t-BuOH > 1-ProOH > HmimBr > 2-ProOH ≈ OmimBr > BmimBr > EtOH. The phase separation abilities of ionic liquids and alcohols with K2HPO4 were almost the same as the previous data [15, 24]. Pei et al. [15] reported that HmimBr has the best phase-forming ability among the 1-alkyl-3-methylimidazolium bromides. The unusual behaviors of Hmim+ were observed in the melting points, the
7
polarity and partition coefficients of 1-alkyl-3-methylimidazolium ionic liquids [23, 25, 26]. This is because the increase in the alkyl side chain leads to a decrease in coulombic and polar interactions and an increase in the dispersive interaction between the ionic liquids [25]. In this paper, the phase-forming ability of HmimBr was relatively high among the solvents used. The polarity of HmimBr (ETN =0.59 [17]) exists between those of 1-ProOH (0.62) and 2-ProOH (0.55). A relatively small polarity of HmimBr may lead to good phase-forming ability. The data of tie lines are summarized in Table 1, along with their tie line length (TLLs). An example of the tie lines for HmimBr-K2HPO4-H2O aqueous biphasic systems is presented in Fig. 2. These data obtained for ionic liquids were almost the same as previous data [15]. 3.2 Extraction of succinic acid with ATPS containing water-miscible alcohol Table 2 shows the extractability of succinic acid by ATPS using water-miscible alcohol and (NH4)2SO4. In Table 2, the top and bottom phases were alcohol-rich and salt rich phases, respectively. The extractability and the water content in the top phase decreased with increasing salt concentrations in all cases, although increases in salt concentration result in increases in distribution ratio of succinic acid (acetone/ammonium sulfate system) [10] and biomacromolecules (polymer/salt system) [11] in top phase due to salting-out. The volume of top phase using EtOH was much higher than those with other solvents, suggesting that EtOH has lower phase-forming ability. The highest extractability except EtOH in this paper was 78.7 %. Sun et al. [10] reported 90 % recovery of succinic acid with ATPS using 30% acetone and 20% ammonium sulfate. However, direct comparison of their data with ours was difficult because composition of the top phase was not described in their paper 8
[10]. Extractabilities were found to be roughly correlated with water content in the top phase. This might be caused by succinic acid being co-extracted with water to the alcohol-rich phase. Table 3 shows the effect of salt on the extractability and volumes of both phases. Volumes of both phases were almost identical, suggesting that the phase-forming ability of each salt is similar. Figure 3 shows the relation between the equilibrium pH of the bottom phase and the extractability. Evidently, lower pH caused the high extractability and, neutral and acidic salts were found to be favorable to the extraction of succinic acid. Because the pKa values of succinic acid were 4.2 and 5.6, extracted species in the alcohol-rich phase were undissociated forms of succinic acid. Undissociated succinic acid may be integrated in the hydrogen-bonding network [18] in the alcohol-rich phase. 3.3 Extraction of succinic acid with ATPS containing water-miscible ionic liquids Table 4 shows the extractability of succinic acid by ATPS using water-miscible ionic liquids and K2HPO4. In Table 4, the top and bottom phases were ionic liquid-rich and salt rich phases, respectively. From Table 4, BmimBr gave the highest extractability among the solvents, although BmimBr had a relatively small phase forming ability as mentioned above. Extractability was independent of water contents unlike ATPS with alcohol and water contents generally were higher than those with alcohols. Table 5 shows the effect of salt on the extractability and volumes of both phases. In the cases of using MgSO4, NH4NO3, Na2CO3 and NaCl, ATPS was not formed under the condition of 20 g-salt/100mL-water. Two salts, (NH4)2SO 4 and K2CO3, had high extractability, while for volume change of both phases between before and after equilibrium, (NH4)2SO4 had a largest effect. These 9
extractabilities (85.5% and 82.8%) were comparable to those with two-phase extraction using phosphonium-based hydrophobic ionic liquids (73 – 90%) [19]. Figure 4 shows the relation between the equilibrium pH of the bottom phase and the extractability for BmimBr, HmimBr and OmimBr. Unlike ATPS with alcohols, extractability depended on not pH but salt used. Over pH 6, succinate di-anion was also distributed to ionic liquid phase. Water aggregation in non-polar solvent such as reversed micelle was influenced by the water activity, which was determined by the salt used. Therefore, we guess the formation of water pool in ionic liquid and the distribution of succinic acid and succinate to the water pool. ATPSs with ionic liquids had higher extractabilities compared with those with alcohols. Lateef et al [20] reported that lactic acid and HmimBr was miscible in all proportions and HmimBr was excellent solvent to extract lactic acid from wine, suggesting that HmimBr solvate lactic acid well. Therefore, HmimBr may also have high solvating capacity for succinic acid. 3.3 Precipitation of succinate from extracted phase The recovery of succinic acid from loaded organic solvents was important for process development. In the reactive extraction with a water-immiscible solvent and an extractant like alkylamine, succinic acid was back-extracted by pH-swing [21]. In ATPS with acetone, acetone was recovered by vacuum distillation and then succinic acid was crystallized at a pH of 2.0 and a temperature of 4 ºC [10]. In ATPS with ionic liquid, organic acid in ionic liquid phase was stripped by 10 wt% Na2CO3 solution [14]. In this paper, in order to recover the directly succinic acid from the extracted phase, we added the hydroxides, NH4OH, NaOH and Ca(OH)2 to the extracted phase and the results were listed in Table 6. It was found that sodium hydroxide 10
was effective as the precipitant. Quantitative recovery, which is larger than 85 % with crystallization of succinic acid in ATPS with acetone [10], was accomplished with crystallization of sodium succinate in the case of 1-propanol/ammonium sulfate ATPS. For comparison, in the method of traditional calcium precipitation with ion-exchange adsorption the yield obtained was only 52% [22]. In the cases of ionic liquids/ ammonium sulfate ATPS, recoveries were lower than that of 1-propanol because ionic liquid-ATPS had the larger water content that 1-propanol-ATPS. In further investigation, recovery may be improved by the optimization of extraction and crystallization processes.
4. Conclusion In this paper, we examined ATPS with water-miscible alcohols/salts and ionic liquids/salts to extract succinic acid. From binodal curves, the phase separation abilities of solvents are in the order t-BuOH > 1-ProOH > HmimBr > 2-ProOH ≈ OmimBr > BmimBr > EtOH. Succinic acid was successfully extracted in both ATPSs. In ATPS with alcohols, extractability of succinic acid with ATPS consisted of 1-propanol/NaCl using salt concentration of 20 g/100mL water was 72.1 %. And it was found that undissociated succinic acid was extracted, suggesting that undissociated succinic acid may be integrated in the hydrogen bonding network in the alcohol-rich phase. In ATPS with ionic liquids, extractability of succinic acid with ATPS consisted of HmimBr/(NH4)2SO4 using salt concentration of 20 g/100mL water was 85.5 %.
And the extraction
behaviors of succinic acid are affected by the salts used, suggesting that the formation of water pool in ionic liquid and the distribution of succinic acid and succinate to the water pool. Extracted succinic acid in 1-propanol was 11
quantitatively precipitated by adding sodium hydroxide to the extracted phase and recovered as crystallization of sodium succinate.
Acknowledgements The present work was supported by a Grant-in-Aid for Scientific Research (C) (No. 25420813) from the Japan Society for the Promotion of Science.
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ionic liquid influence on propagation rate coefficients in methyl methacrylate radical polymerization based on Kamlet-Taft solvatochromic parameters, Macromolecules, 42 (2009) 8801. [18] A. Wakisaka, T. Ohki, Phase separation of water-alcohol binary mixtures induced by the microheterogeneity, Faraday Discuss., 129 (2005) 231. [19] F. S. Oliveira, J. M. M. Araújo, R. Ferreira, L. P. N. Rebelo, I. M. Marrucho, Extraction of L-lactic, L-malic, and succinic acids using phosphonium-based ionic liquids, Separ. Purif. Technol., 85 (2012) 137. [20] H. Lateef, A. Gooding, S. Grimes, Use of 1-hexyl-3-methylimidazolium bromide ionic liquid in the recovery of lactic acid, J. Chem. Tech. Biotechnol., 87 (2012) 1066. [21] E. Z. Lee, Y. S. Huh, Y. S. Jun, H. J. Won, Y. K. Hong, W. H. Hong, Effect of operating variables on back-extraction characteristics of succinic acid from organic phase, Biotechnol. Bioproc. Eng., 13 (2008) 342. [22] Q. Li, D. Wang, Y. Wu, W. Li, Y. Zhang, J. Xing, Z. Su, One step recovery of succinic acid from fermentation broths by crystallization, Separ. Purif. Technol., 72 (2010) 294. [23]
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tartrate) aqueous two-phase systems, J. Mol. Liq., 193 (2014) 23. [26] Q. Li, X. Jiang, H. Zou, Z. Cao, H. Zhang, M. Xian, Extraction of short-chain organic acids using imidazolium-based ionic liquids from aqueous media, J. Chem. Pharm. Sci., 6 (2014) 374.
15
Table 1 Phase composition and the tie line length (TLL) for solvent (1) + K2HPO 4 (2) + H2O (3) aqueous biphasic systems at T= 298.15K. Total w1
w2
0.250 0.280 0.320 0.350
0.250 0.280 0.320 0.350
0.320 0.350
0.320 0.350
0.250 0.280
0.250 0.280
0.250 0.280 0.320 0.350
0.250 0.280 0.320 0.350
0.250
0.250
0.250 0.280 0.320 0.350
0.250 0.280 0.320 0.350
0.250 0.280 0.320 0.350
0.250 0.280 0.320 0.350
Salt-rich phase w1 w2 Ethanol 0.0022 0.5971 0.0012 0.6712 0.0011 0.7784 0.0009 0.8839 1-Propanol 0.0022 0.4992 0.0015 0.5696 2-Propanol 0.0055 0.4357 0.0021 0.4735 t-Butanol ~0 0.7518 ~0 0.8562 ~0 0.9172 ~0 0.9352 BmimBr 0.0052 0.4270 HmimBr 0.0032 0.4076 0.0007 0.4773 0.0006 0.5544 0.0005 0.5820 OmimBr 0.0018 0.4203 0.0012 0.4455 0.0005 0.5342 0.0004 0.6112
16
Solvent-rich phase w1 w2
TLL
0.4190 0.4711 0.5484 0.5795
0.0307 0.0197 0.0110 0.0076
0.7032 0.8033 0.9426 1.0501
0.8576 0.8726
0.0041 0.0058
0.9883 1.0376
0.6587 0.7609
0.0024 0.0005
0.7838 0.8942
0.3656 0.4229 0.4978 0.5804
0.0347 0.0208 0.0116 0.0052
0.8049 0.9363 1.0334 1.0963
0.6206
0.0298
0.7324
0.6112 0.6767 0.7550 0.8443
0.0163 ~0 0.0005 ~0
0.7230 0.8275 0.9359 1.0250
0.6779 0.7658 0.8139 0.8421
0.0003 0.0002 0.0001 0.0001
0.7959 0.8848 0.9731 1.0344
Table 2 Effect of water-miscible alcohol on extractability of succinic acid by ATPS with (NH4)2SO4
Alcohol
Salt concentration [g/100mL-water]
w1**
w2**
20
0.408
0.099
6.2
40
0.393
0.101
20
0.405
40
1-ProOH
2-ProOH
t-BuOH
EtOH
Top Bottom phase* phase* [mL] [mL]
Water content [%]
E [%]
D [-]
3.8
24.4
70.8
1.49
5.8
4.1
18.2
64.8
1.30
0.099
6.8
3.2
33.0
78.7
1.74
0.390
0.102
6.0
4.0
23.8
68.1
1.42
20
0.402
0.100
6.2
3.8
25.8
76.3
1.97
40
0.386
0.102
5.6
4.4
17.3
67.5
1.63
60
0.378
0.104
5.5
4.5
13.0
65.0
1.52
20
0.407
0.099
8.0
2.0
42.6
86.9
1.66
*Initial volumes of both phases were 5 mL. **Values are weight fraction compositions of initial state.
Table 3 Effect of salt on extractability of succinic acid by ATPS with 1-propanol
Salts [20 g /100mL-water]
w1**
w2**
Top
Bottom
phase*
phase*
[mL]
[mL]
pH
E [%]
D [-]
K2HPO4
0.401
0.100
6.2
3.8
7.47
3.6
0.02
(NH4)2SO4
0.408
0.099
5.8
4.2
3.39
70.8
1.76
MgSO4
0.396
0.101
6.4
3.6
2.95
36.8
0.33
K3PO4
0.399
0.100
6.0
4.0
12.3
0.0
0.00
K2CO3
0.399
0.100
6.0
4.0
10.6
1.4
0.01
KF
0.397
0.100
5.6
4.4
6.27
0.9
0.01
NH4NO3
0.414
0.098
6.2
3.8
2.75
35.3
0.33
C6H5Na3O7·2H2O
0.403
0.099
6.5
3.5
5.88
8.7
0.05
Na2CO3
0.395
0.100
6.0
4.0
10.2
1.4
0.01
2.66
72.1
2.20
NaCl 0.406 0.099 5.4 4.6 *Initial volumes of both phases were 5 mL. **Values are weight fraction compositions of initial state.
17
Table 4 Effect of water-miscible ionic liquids on extractability of succinic acid by ATPS with K2HPO4 Ionic liquid
Salt concentration [g/100mL-water]
w1**
w2**
Top phase* [mL]
Bottom phase* [mL]
Water content [%]
E [%]
D [-]
40
0.111
0.254
1.6
4.2
56.5
37.4
1.57
60
0.105
0.336
1.4
4.4
55.7
48.1
2.91
80
0.099
0.400
1.2
4.6
54.8
47.7
3.50
100
0.094
0.453
1.0
4.8
35.5
36.2
2.72
40
0.128
0.249
1.5
4.3
46.3
32.3
1.37
60
0.121
0.330
1.2
4.6
35.2
33.4
1.92
80
0.114
0.394
1.0
4.8
28.9
29.1
1.97
100
0.108
0.446
1.0
4.8
23.2
23.7
1.49
40
0.123
0.251
1.4
4.4
41.0.
37.4
1.88
60
0.116
0.332
1.2
4.6
30.0
42.7
2.86
80
0.110
0.396
1.0
4.8
24.7
36.8
2.79
100
0.103
0.448
1.0
4.8
21.4
32.5
2.31
BmimBr
HmimBr
OmimBr
*Initial volumes of water and ionic liquid phases were 5 mL and 0.8 mL, respectively. **Values are weight fraction compositions of initial state.
Table 5 Effect of salt on extractability of succinic acid by ATPS with HmimBr
Salts [20 g/100mL-water]
Top w1**
w2**
pH
E [%]
D [-]
[mL]
Bottom phase* [mL]
phase*
K2HPO4
0.391
0.101
6.3
2.0
7.40
58.7
0.45
(NH4)2SO4
0.398
0.100
7.2
1.3
3.43
85.5
1.06
K3PO4
0.390
0.102
6.0
2.4
11.6
60.3
0.61
K2CO3
0.390
0.102
5.8
2.5
10.5
82.8
2.07
KF
0.388
0.102
5.0
3.0
6.97
16.0
0.11
C6H5Na3O7·2H2O
0.394
0.101
6.5
1.9
5.72
58.6
0.41
*Initial volumes of water and ionic liquid phases were 5 mL and 3.1 mL, respectively. **Values are weight fraction compositions of initial state.
18
Table 6 Recovery of succinate from top phase in ATPS Alkali
HmimBr
OmimBr
1-propanol
NH4OH
0
0
0
NaOH
71.1%
31.2%
100%
Ca(OH)2*
≈0
≈0
84.9%
* Two–phase formation was not observed.
FIGURE CAPTIONS Fig. 1 Binodal curves of solvent (alcohol and ionic liquid) + K2HPO4 aqueous two phase system Fig. 2 Phase diagram for HmimBr + K2HPO4 + H2O system: binodal curve (circle) and tie lines (triangles) Fig. 3
Relationship between equilibrium pH of bottom phase and extractablity for alcohol + salt aqueous two phase system
Fig. 4
Relationship between equilibrium pH of bottom phase and extractablity for ionic liquid + salt aqueous two phase system. Symbols are as follows; circle: K2HPO4, hexagonal: (NH4)2SO4, square: K3PO4, triangle: K2CO3, diamond: KF, and open: BmimBr, right half black and +: HmimBr, filled: OmimBr.
19
Fig. 1
80 t-BuOH 1-ProOH 2-ProOH EtOH BmimBr HmimBr OmimBr
Salts [wt %]
60
40
20
0 0
20
40
60
Solvents [wt%]
20
80
100
Fig. 2
80
Salt [wt%]
60
40
20
0 0
20
40
60
HmimBr [wt%]
21
80
100
Fig. 3
100
E [%]
80
60
40
20
0 2
4
6
8 pH
22
10
12
Fig. 4
100
E [%]
80
60
40
20
0 2
4
6
8 pH
23
10
12
14
Highlights We extracted succinic acid was extracted with OmimBr/(NH4)2SO4 ATPS system. Extraction of succinic acid with ATPS using aqueous alcohols was controlled by pH. Extracted succinic acid was recovered as precipitation of sodium succinate.
24
S1383-5866(15)30107-6 http://dx.doi.org/10.1016/j.seppur.2015.07.039 SEPPUR 12458
To appear in:
Separation and Purification Technology
Received Date: Revised Date: Accepted Date:
20 October 2014 3 July 2015 17 July 2015
Please cite this article as: A.I. Pratiwi, T. Yokouchi, M. Matsumoto, K. Kondo, Extraction of Succinic Acid by Aqueous Two-Phase System Using Alcohols/Salts and Ionic Liquids/Salts, Separation and Purification Technology (2015), doi: http://dx.doi.org/10.1016/j.seppur.2015.07.039
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Extraction of Succinic Acid by Aqueous Two-Phase System Using Alcohols/Salts and Ionic Liquids/Salts
(2nd Revised version)
by Aulia Indah Pratiwi, Takeyuki Yokouchi, Michiaki Matsumoto*, and Kazuo Kondo
Department of Chemical Engineering and Materials Science Doshisha University Kyotanabe, Kyoto 610-0321 JAPAN
* Corresponding author TEL/FAX +81-774-65-6655 E-mail; [email protected]
1
ABSTRACT Succinic acid is the important feedstock for several industrial products including biodegradable plastics. Production of a fermentation-derived succinic acid (bio-succinic acid) has recently emerged as a potential green technology. For bio-succinic acid production, 50 to 60% of processing costs are attributed to recovery and purification processes. In this paper, we examine aqueous two phase systems (ATPS) using water-miscible alcohols/salts and ionic liquids/salts to extract succinic acid. From binodal curves, the phase separation abilities of solvents are in the order t-butanol > 1-propanol > HmimBr > 2-propanol ≈ OmimBr > BmimBr > ethanol. Extractability of succinic acid was within 0 to 72.1 % in ATPSs with1-propanol using salt concentration of 20 g/100mL-water and depended on the pH of the salt solution. When salts, K2HPO4, K3PO4, K2CO3, KF, (NH4)2SO4, C6H5Na3O 7, Na2CO3, NaCl, MgSO4, and NH4NO3, were used, relatively high extractabilities were obtained by using the salt solutions which gave pH smaller than pKa1 of succinic acid. In the ATPS with ionic liquids, Extractability of succinic acid was within 16 to 85.5% and were affected by not pH but the salts used. An ATPS with an OmimBr and (NH4)2SO4 system gave highest extraction, 85.5%. Extracted succinic acid was quantitatively precipitated by adding sodium hydroxide to the extracted phase and recovered as crystallization of sodium succinate. Highlights We extracted succinic acid was extracted with OmimBr/(NH4)2SO4 ATPS system. Extraction of succinic acid with ATPS using aqueous alcohols was controlled by pH. 2
Extracted succinic acid was recovered as precipitation of sodium succinate.
Key words Ionic liquids, Extraction, Succinic acid, Aqueous two-phase system
1. Introduction Succinic acid is the important feedstock for several industrial products including tetrahydrofuran, adipic acid, 1,4-butanediol, aliphatic esters, and biodegradable plastics [1]. Succinic acid for industrial use is mainly produced petrochemically. Nowadays, production of a fermentation-derived succinic acid (bio-succinic acid) has potential as green technology because CO2 is consumed during the fermentation process [1]. Furthermore, bio-succinic acid has the potential to become a key building block for commodity chemicals [2]. Higher cost in production of fossil fuels results in a high market potential for bio-succinic acid because its production has a net fossil energy consumption of 30-40% less than petroleum-based succinic acid production [3]. A few companies and consortia have begun to develop industrial production of bio-succinic acid [2]. The global bio-based succinic acid market is expected to reach volume of 0.7 million tons by 2020 [4]. In bio-succinic acid production plants reported, membrane and ion exchange as separation processes from the neutralized broth were utilized to obtain the crude succinic acid [5]. In general, for bio-succinic acid production, 50 to 60% of processing costs are attributed to recovery and purification processes to obtain the final product [3] because succinic acid has relatively low product 3
concentration in the complex medium. Therefore, economical and efficient recovery and purification processes for bio-succinic acid are desired. Several separation methods for succinic acid recovery have been proposed: selective precipitation, adsorption, electrodialysis, extraction with solvents and/or amines, ion exchange, membrane separation and esterification [6,7]. Recently, we proposed liquid membrane systems containing ionic liquid for succinic acid separation [8,9]. Although considerably stable liquid membranes containing ionic liquid were obtained compared with conventional liquid membranes, membrane performance was gradually impaired over the long term. Sun et al. [10] reported an acetone/(NH4)2SO4 aqueous two-phase system (ATPS) for recovery of bio-succinic acid. The ATPS has been well known as one extraction technique for biomolecules [11]. Recent research has focused on ATPSs that were formed by water-miscible organic solvent or ionic liquid with salt [11,12]. Most of the polymers, used in ATPSs so far have high viscosity and tend to form a cloudy solution [13] by the slight external disturbance because of low interfacial tension. Therefore, a polymer/salt ATPS has difficulty isolating the extracted biomolecules from the viscous polymer phase by back-extraction. An ATPS composed of hydrophilic organic solvents and salts attracted much attention because of low extraction cost, easy solvent recovery by evaporation and easy scale up [11]. An ATPS composed of hydrophilic ionic liquids and salts was also interesting because of faster phase separation, reduction in viscosity, and tailoring of the polarity of the coexisting phase compared with ATPSs composed of polymers. [14]. In this study, we examined water-miscible alcohol/salt and ionic liquid/salt ATPSs for the extraction of succinic acid. As mentioned, water-miscible alcohol 4
is easily recovered by evaporation. 1-Alkyl-3-methylimidazolium bromide was used as ionic liquid. It is known that, because of the different Gibbs energies of hydration of Cl- (-340 kJ/mol) and Br- (-315 kJ/mol) [15], the ionic liquids with Clanion hydrate more water molecules than those with Br-, resulting in difficulty in phase formation as salt was added. Finally we recovered succinic acid from the extracted phase by direct precipitation with alkali hydroxide.
2. Experimental 2.1. Chemicals 1-Butyl-3-methylimidazolium bromide [BmimBr] was purchased from Merck, 1-hexy-3-methylimidazolium bromide [HmimBr] and 1-octyl-3-methylimidazolium bromide [OmimBr] were purchased from Tokyo Chemical Industries, Ltd, and these were used as received. K2HPO4, K3PO4, K2CO3, KF, (NH4)2SO4, C6H5Na3O7.2H2O, Na2CO3, NaCl, MgSO4, and NH4NO3 of G.R. grade were used as salts. 1-Propanol (1-ProOH), 2-propanol (2-ProOH), t-butanol (t-BuOH) and ethanol (EtOH) were used as water-miscible organic solvents. 2.2. Preparation of phase diagram The binodal curves were determined by turbidimetric titration as described in a previous paper on an ATPS using water-miscible organic solvent and salt [16]. A K2HPO4 solution of known concentration was placed in a 100 mL conical flask, and ionic liquids (BmimBr, HmimBr and OmimBr) were added drop-wise to the flask until the clear solution turned turbid or two-phase systems were formed at 25ºC. Then, de-ionized water was added drop-wise to the flask to obtain a clear one-phase system, and more ionic liquids were added again to
5
produce two-phase systems. The composition of this mixture was noted and the experiments were repeated to obtain the binodal curve. The tie lines were measured by the following procedure. A series of ATPSs with three or four different composition were prepared in graduated glass tubes. These solutions were mixed thoroughly and left standing for more than 1 h in a thermostated bath at 25ºC. To ensure the complete phase separation, these solutions were centrifuged for 10 min at 5000 rpm at 25ºC. After that, visual estimation of volumes of top and bottom phase. The concentrations of organic solvents or ionic liquids were analyzed by HPLC or UV at 211nm (UV2500, Shimadzu, Kyoto, Japan), respectively, and the water content in both phases were determined by Karl Fischer’s method (AQ-300, Hiranuma, Kyoto, Japan). The salt concentration was calculated by subtracting total weight from weights of water and organic solvent (ionic liquid). 2.3. Extraction of succinic acid using ATPS Solid inorganic salts and 5 mL of water-miscible organic solvents or ionic liquids were added into the 5 mL solution including succinic acid (20 g/L) to form the ATPS consisting of 25-150 g-salt/100 g-water in a calibrated test tube with a stopper. The solution was mixed thoroughly and left standing for more than 6 h in a thermostated bath at 25ºC. The volumes of the top and bottom phases were recorded. The concentrations of succinic acid and the water content in both phases were analyzed by HPLC as described in previous papers [8,9] and Karl Fischer’s method. The pHs of the aqueous solutions before and after equilibration were determined by a Horiba F-71 pH meter. The extractability (E) and distribution ratio (D) of succinic acid was defined as,
6
[%] =
× 100
=
(1) (2)
where C and V are the concentration of succinic acid and the solution volume and subscripts T, B and 0 denote the top and bottom phases and initial state. 2.4. Precipitation of succinate from extracted phase After succinic acid was extracted by ATPS containing ammonium sulfate of 20 g/100mL, the aliquot of the solvent-rich phase was taken from the test tube for extraction into the flask tube. The precipitants, NaOH, NH4OH and Ca(OH)2, were added until the precipitate formed. Precipitates were filtered. The amounts of unrecovered succinic acid in the filtrate were measured with HPLC.
3. Results and discussion 3.1 Phase diagram for ATPS consisting of water-miscible organic solvent or ionic liquid, and dipotassium hydrogen phosphate Figure 1 shows the effects of water-miscible solvents on the binodal curves of the K2HPO4/solvent ATPS at 25ºC plotted as mass fractions. The closer the binodal curves are to the coordinate origin, the less solvent is required for the formation of the ATPS under the same concentration of salt. From the figure, the phase separation abilities of solvents are in the order t-BuOH > 1-ProOH > HmimBr > 2-ProOH ≈ OmimBr > BmimBr > EtOH. The phase separation abilities of ionic liquids and alcohols with K2HPO4 were almost the same as the previous data [15, 24]. Pei et al. [15] reported that HmimBr has the best phase-forming ability among the 1-alkyl-3-methylimidazolium bromides. The unusual behaviors of Hmim+ were observed in the melting points, the
7
polarity and partition coefficients of 1-alkyl-3-methylimidazolium ionic liquids [23, 25, 26]. This is because the increase in the alkyl side chain leads to a decrease in coulombic and polar interactions and an increase in the dispersive interaction between the ionic liquids [25]. In this paper, the phase-forming ability of HmimBr was relatively high among the solvents used. The polarity of HmimBr (ETN =0.59 [17]) exists between those of 1-ProOH (0.62) and 2-ProOH (0.55). A relatively small polarity of HmimBr may lead to good phase-forming ability. The data of tie lines are summarized in Table 1, along with their tie line length (TLLs). An example of the tie lines for HmimBr-K2HPO4-H2O aqueous biphasic systems is presented in Fig. 2. These data obtained for ionic liquids were almost the same as previous data [15]. 3.2 Extraction of succinic acid with ATPS containing water-miscible alcohol Table 2 shows the extractability of succinic acid by ATPS using water-miscible alcohol and (NH4)2SO4. In Table 2, the top and bottom phases were alcohol-rich and salt rich phases, respectively. The extractability and the water content in the top phase decreased with increasing salt concentrations in all cases, although increases in salt concentration result in increases in distribution ratio of succinic acid (acetone/ammonium sulfate system) [10] and biomacromolecules (polymer/salt system) [11] in top phase due to salting-out. The volume of top phase using EtOH was much higher than those with other solvents, suggesting that EtOH has lower phase-forming ability. The highest extractability except EtOH in this paper was 78.7 %. Sun et al. [10] reported 90 % recovery of succinic acid with ATPS using 30% acetone and 20% ammonium sulfate. However, direct comparison of their data with ours was difficult because composition of the top phase was not described in their paper 8
[10]. Extractabilities were found to be roughly correlated with water content in the top phase. This might be caused by succinic acid being co-extracted with water to the alcohol-rich phase. Table 3 shows the effect of salt on the extractability and volumes of both phases. Volumes of both phases were almost identical, suggesting that the phase-forming ability of each salt is similar. Figure 3 shows the relation between the equilibrium pH of the bottom phase and the extractability. Evidently, lower pH caused the high extractability and, neutral and acidic salts were found to be favorable to the extraction of succinic acid. Because the pKa values of succinic acid were 4.2 and 5.6, extracted species in the alcohol-rich phase were undissociated forms of succinic acid. Undissociated succinic acid may be integrated in the hydrogen-bonding network [18] in the alcohol-rich phase. 3.3 Extraction of succinic acid with ATPS containing water-miscible ionic liquids Table 4 shows the extractability of succinic acid by ATPS using water-miscible ionic liquids and K2HPO4. In Table 4, the top and bottom phases were ionic liquid-rich and salt rich phases, respectively. From Table 4, BmimBr gave the highest extractability among the solvents, although BmimBr had a relatively small phase forming ability as mentioned above. Extractability was independent of water contents unlike ATPS with alcohol and water contents generally were higher than those with alcohols. Table 5 shows the effect of salt on the extractability and volumes of both phases. In the cases of using MgSO4, NH4NO3, Na2CO3 and NaCl, ATPS was not formed under the condition of 20 g-salt/100mL-water. Two salts, (NH4)2SO 4 and K2CO3, had high extractability, while for volume change of both phases between before and after equilibrium, (NH4)2SO4 had a largest effect. These 9
extractabilities (85.5% and 82.8%) were comparable to those with two-phase extraction using phosphonium-based hydrophobic ionic liquids (73 – 90%) [19]. Figure 4 shows the relation between the equilibrium pH of the bottom phase and the extractability for BmimBr, HmimBr and OmimBr. Unlike ATPS with alcohols, extractability depended on not pH but salt used. Over pH 6, succinate di-anion was also distributed to ionic liquid phase. Water aggregation in non-polar solvent such as reversed micelle was influenced by the water activity, which was determined by the salt used. Therefore, we guess the formation of water pool in ionic liquid and the distribution of succinic acid and succinate to the water pool. ATPSs with ionic liquids had higher extractabilities compared with those with alcohols. Lateef et al [20] reported that lactic acid and HmimBr was miscible in all proportions and HmimBr was excellent solvent to extract lactic acid from wine, suggesting that HmimBr solvate lactic acid well. Therefore, HmimBr may also have high solvating capacity for succinic acid. 3.3 Precipitation of succinate from extracted phase The recovery of succinic acid from loaded organic solvents was important for process development. In the reactive extraction with a water-immiscible solvent and an extractant like alkylamine, succinic acid was back-extracted by pH-swing [21]. In ATPS with acetone, acetone was recovered by vacuum distillation and then succinic acid was crystallized at a pH of 2.0 and a temperature of 4 ºC [10]. In ATPS with ionic liquid, organic acid in ionic liquid phase was stripped by 10 wt% Na2CO3 solution [14]. In this paper, in order to recover the directly succinic acid from the extracted phase, we added the hydroxides, NH4OH, NaOH and Ca(OH)2 to the extracted phase and the results were listed in Table 6. It was found that sodium hydroxide 10
was effective as the precipitant. Quantitative recovery, which is larger than 85 % with crystallization of succinic acid in ATPS with acetone [10], was accomplished with crystallization of sodium succinate in the case of 1-propanol/ammonium sulfate ATPS. For comparison, in the method of traditional calcium precipitation with ion-exchange adsorption the yield obtained was only 52% [22]. In the cases of ionic liquids/ ammonium sulfate ATPS, recoveries were lower than that of 1-propanol because ionic liquid-ATPS had the larger water content that 1-propanol-ATPS. In further investigation, recovery may be improved by the optimization of extraction and crystallization processes.
4. Conclusion In this paper, we examined ATPS with water-miscible alcohols/salts and ionic liquids/salts to extract succinic acid. From binodal curves, the phase separation abilities of solvents are in the order t-BuOH > 1-ProOH > HmimBr > 2-ProOH ≈ OmimBr > BmimBr > EtOH. Succinic acid was successfully extracted in both ATPSs. In ATPS with alcohols, extractability of succinic acid with ATPS consisted of 1-propanol/NaCl using salt concentration of 20 g/100mL water was 72.1 %. And it was found that undissociated succinic acid was extracted, suggesting that undissociated succinic acid may be integrated in the hydrogen bonding network in the alcohol-rich phase. In ATPS with ionic liquids, extractability of succinic acid with ATPS consisted of HmimBr/(NH4)2SO4 using salt concentration of 20 g/100mL water was 85.5 %.
And the extraction
behaviors of succinic acid are affected by the salts used, suggesting that the formation of water pool in ionic liquid and the distribution of succinic acid and succinate to the water pool. Extracted succinic acid in 1-propanol was 11
quantitatively precipitated by adding sodium hydroxide to the extracted phase and recovered as crystallization of sodium succinate.
Acknowledgements The present work was supported by a Grant-in-Aid for Scientific Research (C) (No. 25420813) from the Japan Society for the Promotion of Science.
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15
Table 1 Phase composition and the tie line length (TLL) for solvent (1) + K2HPO 4 (2) + H2O (3) aqueous biphasic systems at T= 298.15K. Total w1
w2
0.250 0.280 0.320 0.350
0.250 0.280 0.320 0.350
0.320 0.350
0.320 0.350
0.250 0.280
0.250 0.280
0.250 0.280 0.320 0.350
0.250 0.280 0.320 0.350
0.250
0.250
0.250 0.280 0.320 0.350
0.250 0.280 0.320 0.350
0.250 0.280 0.320 0.350
0.250 0.280 0.320 0.350
Salt-rich phase w1 w2 Ethanol 0.0022 0.5971 0.0012 0.6712 0.0011 0.7784 0.0009 0.8839 1-Propanol 0.0022 0.4992 0.0015 0.5696 2-Propanol 0.0055 0.4357 0.0021 0.4735 t-Butanol ~0 0.7518 ~0 0.8562 ~0 0.9172 ~0 0.9352 BmimBr 0.0052 0.4270 HmimBr 0.0032 0.4076 0.0007 0.4773 0.0006 0.5544 0.0005 0.5820 OmimBr 0.0018 0.4203 0.0012 0.4455 0.0005 0.5342 0.0004 0.6112
16
Solvent-rich phase w1 w2
TLL
0.4190 0.4711 0.5484 0.5795
0.0307 0.0197 0.0110 0.0076
0.7032 0.8033 0.9426 1.0501
0.8576 0.8726
0.0041 0.0058
0.9883 1.0376
0.6587 0.7609
0.0024 0.0005
0.7838 0.8942
0.3656 0.4229 0.4978 0.5804
0.0347 0.0208 0.0116 0.0052
0.8049 0.9363 1.0334 1.0963
0.6206
0.0298
0.7324
0.6112 0.6767 0.7550 0.8443
0.0163 ~0 0.0005 ~0
0.7230 0.8275 0.9359 1.0250
0.6779 0.7658 0.8139 0.8421
0.0003 0.0002 0.0001 0.0001
0.7959 0.8848 0.9731 1.0344
Table 2 Effect of water-miscible alcohol on extractability of succinic acid by ATPS with (NH4)2SO4
Alcohol
Salt concentration [g/100mL-water]
w1**
w2**
20
0.408
0.099
6.2
40
0.393
0.101
20
0.405
40
1-ProOH
2-ProOH
t-BuOH
EtOH
Top Bottom phase* phase* [mL] [mL]
Water content [%]
E [%]
D [-]
3.8
24.4
70.8
1.49
5.8
4.1
18.2
64.8
1.30
0.099
6.8
3.2
33.0
78.7
1.74
0.390
0.102
6.0
4.0
23.8
68.1
1.42
20
0.402
0.100
6.2
3.8
25.8
76.3
1.97
40
0.386
0.102
5.6
4.4
17.3
67.5
1.63
60
0.378
0.104
5.5
4.5
13.0
65.0
1.52
20
0.407
0.099
8.0
2.0
42.6
86.9
1.66
*Initial volumes of both phases were 5 mL. **Values are weight fraction compositions of initial state.
Table 3 Effect of salt on extractability of succinic acid by ATPS with 1-propanol
Salts [20 g /100mL-water]
w1**
w2**
Top
Bottom
phase*
phase*
[mL]
[mL]
pH
E [%]
D [-]
K2HPO4
0.401
0.100
6.2
3.8
7.47
3.6
0.02
(NH4)2SO4
0.408
0.099
5.8
4.2
3.39
70.8
1.76
MgSO4
0.396
0.101
6.4
3.6
2.95
36.8
0.33
K3PO4
0.399
0.100
6.0
4.0
12.3
0.0
0.00
K2CO3
0.399
0.100
6.0
4.0
10.6
1.4
0.01
KF
0.397
0.100
5.6
4.4
6.27
0.9
0.01
NH4NO3
0.414
0.098
6.2
3.8
2.75
35.3
0.33
C6H5Na3O7·2H2O
0.403
0.099
6.5
3.5
5.88
8.7
0.05
Na2CO3
0.395
0.100
6.0
4.0
10.2
1.4
0.01
2.66
72.1
2.20
NaCl 0.406 0.099 5.4 4.6 *Initial volumes of both phases were 5 mL. **Values are weight fraction compositions of initial state.
17
Table 4 Effect of water-miscible ionic liquids on extractability of succinic acid by ATPS with K2HPO4 Ionic liquid
Salt concentration [g/100mL-water]
w1**
w2**
Top phase* [mL]
Bottom phase* [mL]
Water content [%]
E [%]
D [-]
40
0.111
0.254
1.6
4.2
56.5
37.4
1.57
60
0.105
0.336
1.4
4.4
55.7
48.1
2.91
80
0.099
0.400
1.2
4.6
54.8
47.7
3.50
100
0.094
0.453
1.0
4.8
35.5
36.2
2.72
40
0.128
0.249
1.5
4.3
46.3
32.3
1.37
60
0.121
0.330
1.2
4.6
35.2
33.4
1.92
80
0.114
0.394
1.0
4.8
28.9
29.1
1.97
100
0.108
0.446
1.0
4.8
23.2
23.7
1.49
40
0.123
0.251
1.4
4.4
41.0.
37.4
1.88
60
0.116
0.332
1.2
4.6
30.0
42.7
2.86
80
0.110
0.396
1.0
4.8
24.7
36.8
2.79
100
0.103
0.448
1.0
4.8
21.4
32.5
2.31
BmimBr
HmimBr
OmimBr
*Initial volumes of water and ionic liquid phases were 5 mL and 0.8 mL, respectively. **Values are weight fraction compositions of initial state.
Table 5 Effect of salt on extractability of succinic acid by ATPS with HmimBr
Salts [20 g/100mL-water]
Top w1**
w2**
pH
E [%]
D [-]
[mL]
Bottom phase* [mL]
phase*
K2HPO4
0.391
0.101
6.3
2.0
7.40
58.7
0.45
(NH4)2SO4
0.398
0.100
7.2
1.3
3.43
85.5
1.06
K3PO4
0.390
0.102
6.0
2.4
11.6
60.3
0.61
K2CO3
0.390
0.102
5.8
2.5
10.5
82.8
2.07
KF
0.388
0.102
5.0
3.0
6.97
16.0
0.11
C6H5Na3O7·2H2O
0.394
0.101
6.5
1.9
5.72
58.6
0.41
*Initial volumes of water and ionic liquid phases were 5 mL and 3.1 mL, respectively. **Values are weight fraction compositions of initial state.
18
Table 6 Recovery of succinate from top phase in ATPS Alkali
HmimBr
OmimBr
1-propanol
NH4OH
0
0
0
NaOH
71.1%
31.2%
100%
Ca(OH)2*
≈0
≈0
84.9%
* Two–phase formation was not observed.
FIGURE CAPTIONS Fig. 1 Binodal curves of solvent (alcohol and ionic liquid) + K2HPO4 aqueous two phase system Fig. 2 Phase diagram for HmimBr + K2HPO4 + H2O system: binodal curve (circle) and tie lines (triangles) Fig. 3
Relationship between equilibrium pH of bottom phase and extractablity for alcohol + salt aqueous two phase system
Fig. 4
Relationship between equilibrium pH of bottom phase and extractablity for ionic liquid + salt aqueous two phase system. Symbols are as follows; circle: K2HPO4, hexagonal: (NH4)2SO4, square: K3PO4, triangle: K2CO3, diamond: KF, and open: BmimBr, right half black and +: HmimBr, filled: OmimBr.
19
Fig. 1
80 t-BuOH 1-ProOH 2-ProOH EtOH BmimBr HmimBr OmimBr
Salts [wt %]
60
40
20
0 0
20
40
60
Solvents [wt%]
20
80
100
Fig. 2
80
Salt [wt%]
60
40
20
0 0
20
40
60
HmimBr [wt%]
21
80
100
Fig. 3
100
E [%]
80
60
40
20
0 2
4
6
8 pH
22
10
12
Fig. 4
100
E [%]
80
60
40
20
0 2
4
6
8 pH
23
10
12
14
Highlights We extracted succinic acid was extracted with OmimBr/(NH4)2SO4 ATPS system. Extraction of succinic acid with ATPS using aqueous alcohols was controlled by pH. Extracted succinic acid was recovered as precipitation of sodium succinate.
24