Research Article pubs.acs.org/journal/ascecg
Effect of Cations in Ionic Liquids on the Extraction Characteristics of 1,3-Propanediol by Ionic Liquid-based Aqueous Biphasic Systems Woo Yun Lee,† Ki-Sub Kim,† Jong Kyun You,*,‡ and Yeon Ki Hong*,† †
Department of Chemical and Biological Engineering, Korea National University of Transportation, Daehak-ro 50, Chungju, Chungbuk 380-702, Republic of Korea ‡ Green Energy Process Laboratory, Korea Institute of Energy Research, Gajeong-ro 152, Yuseong-gu, Daejeon 341-129, Republic of Korea ABSTRACT: Separation of 1,3-propanediol (1,3-PDO) from fermentation broths becomes a bottleneck in biological production due to its high hydrophilicity and low concentration. Aqueous biphasic systems (ABS) composed of piperidinium-based ionic liquids (ILs) and K2HPO4 could be an alternative to extract 1,3-propanediol from fermentation broths. In this study, the ability of piperidinium-based ILs to form ABS with aqueous K2HPO4 solution was investigated. Binodal curves and tie-lines and tie-line length were evaluated by three parameter equation and mass balances for each components in top and bottom phases. The piperidiniumbased ILs was effective on promoting ABS formation in the presence of K2HPO4 and the forming ability of ABS increased with alkyl chain length of cations in ILs. The volume ratio to top and bottom phase decreased with K2HPO4 concentration and alkyl chain length of cations in ILs. However, above 20 wt % of K2HPO4, the partitioning of water into top phase is dominant, resulting in low phase volume ratio. The extraction efficiency of 1,3-PDO reached up to 95%. It is expected that piperidinium IL-based ABS is a prospective extraction media for the separation and concentration of 1,3-PDO. KEYWORDS: Aqueous biphasic system, Piperidinium, Extraction, 1,3-Propanediol, Phase volume ratio
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INTRODUCTION 1,3-Propanediol (1,3-PDO) is a promising chemical that has various applications such as laminates, solvents, moldings, adhesives, cosmetics, and other uses. Currently, 1,3-PDO is used as a monomer of poly(trimethylene terephthalate) (PTT). PTT derived from 1,3-PDO has excellent physical properties in the fiber and textile industry such as better stretching and stretch-recovering, lower dyeing temperature, and higher light stability than other polyesters.1 The production of 1,3propanediol is growing rapidly and achieving 100 million pounds annually. The growth of the 1,3-propanediol market is highly related to the increasing market demand of its derivatives into highly valuable products.2 So far, most of 1,3-PDO has been mainly produced by the conventional chemical synthesis through hydration of acrolein and hydroformylation of ethylene oxide. In the past decade, the biological production of 1,3-PDO from crude and pure glycerol has been developed because the price of petroleum is unstable and demand for biopolymer is rapidly increased. For economic biological production of 1,3PDO, the efficient separation process for 1,3-PDO is needed because of its low concentration in fermentation broth and impurities. Furthermore, its high boiling point and strong hydrophilicity is a bottleneck for the development of an © 2015 American Chemical Society
efficient separation process. The application of evaporation for the primary recovery of 1,3-PDO is not attractive due to the large energy requirement and low product yield.3 For the removal of salts from 1,3-PDO fermentation broth, electrodialysis with bipolar membranes was applied. Under optimum conditions, 1,3-PDO recovery and conversion rate of salts were 96.0% and 85.1%, respectively.4 In spite of high recovery rate by electrodialysis process, there are several disadvantages such as membrane contamination and high cost of bipolar membrane. Liquid−liquid extraction process is an alternative for the recovery of 1,3-PDO from its aqueous solution because of its proper selectivity, simplicity and low operating cost. In spite of these advantages the most of organic solvents used in extraction are highly volatile and toxic. Malinowski (2000) attempted extraction based on the reaction between 1,3-PDO and acetealdehyde. However, the selectivity of reaction was Special Issue: Ionic Liquids at the Interface of Chemistry and Engineering Received: August 18, 2015 Revised: October 15, 2015 Published: November 13, 2015 572
DOI: 10.1021/acssuschemeng.5b00893 ACS Sustainable Chem. Eng. 2016, 4, 572−576
Research Article
ACS Sustainable Chemistry & Engineering
Agilent HP5 19091S-433UI, and operated with N2 as the carrier gas at flow rate of 1 mL/min, detector temperature 325 °C, and column temperature 100 °C).
decreased due to deactivation of catalyst by impurities in fermentation broth.5 To overcome this limitation, aqueous biphasic systems (ABS) for selective separation of 1,3-PDO has been studied. Li et al. used ABS composed of ethanol/ammonium sulfate for extraction of 1,3-PDO from its fermentation broth. In their study, the highest partition coefficient (4.77) and recovery (93.7%) of 1,3-PDO was obtained with ethanol and saturated ammonium sulfate.6 They have also reported that a higher partition coefficient (38.3) of the system composed of methanol and phosphate salt gave a recovery (94.7%).7 Recently, ionic liquids (ILs) are promising alternatives to polymers or conventional organic solvents to develop a suitable aqueous biphasic extraction process. The usage of ILs leads to easy control of hydrophilicity by functional tuning, low viscosity of aqueous phases, and rapid phase separation.8 Their physical properties strongly depend both on the alkyl chain length of cation and a specifically designed cation and anion. Gutowski et al. reported that aqueous solutions of imidazolium-based ILs can form aqueous biphasic systems (ABS) with the addition of appropriate inorganic salts.9 Muller et al. investigated the structure of cation such as 1-butyl-3-methylmorpholinium, 1butyl-3-methylpyrrolidinium, 1-ethyl-3-methylimidazolium, and 1-methoxyethyl-3-methylimidazolium and the type of anion including dicyanamide, thiocyanate, and methysulfate on ABS formation and extraction characteristics of 1,3-PDO from its aqueous solution.10 This study aims at evaluating the influence of the alkyl chain length of IL cation on ABS formation and especially, water distribution ratio between top and bottom phases for overcoming limitation of 1,3-PDO separation such as high energy requirement of water evaporation process. The corresponding concentrations of ILs and salts in each phases were calculated by using three-parameter equations. These results suggested that piperidinium IL-based ABS has the potential for the recovery of 1,3-propanediol.
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RESULTS AND DISCUSSION Phase Diagram and Tie-Lines. The experimental binodal curves fitted by least-squares regression according to following equation:11
Figure 1. Effect of alkyl chain length of cations in piperidinium-based ILs on aqueous biphasic formation in the presence of K2HPO4 solution at 298 K and atmospheric pressure.
Table 1. Parameters A, B, and C of Equation 1 For the Piperidinium-based ILs+K2HPO4+Water Systems at 298 K [EMPip][Br] [BMPip][Br] [HMPip] [Br] [OMPip] [Br]
EXPERIMENTAL SECTION
Materials. To make simulated aqueous mixture of 1,3-PDO (Sigma-Aldrich, 98%), it was dissolved in deionized water as a concentration of 80 g/L. All ionic liquids were purchased from CTRI(Korea). Piperidinium ionic liquids used in this study were Nethyl-N-methylpiperidinium bromide ([EMPip][Br]), N-butyl-Nmethylpiperidinium bromide ([BMPip][Br]), N-hexyl-N-methylpiperidinium bromide ([HMPip][Br]), and N-octyl-N-methylpiperidinium bromide ([OMPip][Br]). K2HPO4(98 wt %) were obtained from Sigma-Aldrich. All chemicals were used without further purification. Experimental Procedure. The phase diagram of the ILs/salt/ water system was obtained by a turbidity titration method. K2HPO4 dissolved in deionized water was added into a vial, and IL was then added dropwise to the vial placed on an analytical balance for measuring the amount of added IL. After each drop, the mixture was vortexed for 5 min. The point where phase separation first was the turbid point. The total amount of added IL was precisely measured by weighting, and the mass fractions of each component were determined by weight quantification. The experimental procedure for the partition of 1,3-PDO in piperidinium ILs based ABS was as follows. A ternary mixture was prepared within the biphasic region based on phase diagram of ILs/ salt/water systems. In this biphasic region, ILs, K2HPO4 and aqueous solution of 1,3-PDO were vigorously vortexed with a magnetic stirrer and then held for 12 h at room temperature. Samples were taken with a syringe from top and bottom layers, respectively. Concentration Analysis. The concentration of 1,3-PDO was analyzed by gas chromatography (Agilent 6890N, FID-detector,
A±σ
B±σ
105(C ± σ)
R2
92.91 ± 3.30 108.18 ± 3.34 192.21 ± 3.59
−0.36 ± 0.12 −0.44 ± 0.13 −0.65 ± 0.19
3.57 ± 1.07 4.21 ± 1.05 4.40 ± 1.48
0.9955 0.9968 0.9959
243.90 ± 3.67
−0.74 ± 1.97
4.99 ± 1.61
0.9961
wtotal,IL = A exp[(B × wtotal,salt 0.5) − (C × wtotal,salt 3)]
(1)
where wtotal,IL and wtotal,salt are the ionic liquid and the inorganic salt mass fraction percentages, respectively, and A, B, and C are fitted parameters obtained by the regression of the phase equilibrium data. For the concentration determination of ILs and salts in each phase, the following system of four eqs (eqs 2, 3, 5, and 6) and four unknown values was solved.8 wtop,IL = A exp[(B × wtop,salt 0.5) − (C × wtop,salt 3)]
(2)
wbot,IL = A exp[(B × w bot,salt 0.5) − (C × wbot,salt 3)]
(3)
where subscripts “top” and “bot” designate the top phase and the bottom phase. From the mass balance for IL. αwtop,IL = wtotal,IL − (1 − α)w bot,IL
(4)
where α is the ratio between the mass of the top phase and the total mass of the mixture. Rearranging the eq 4 for wtop,IL gives wtotal,IL 1−α − wbot,IL wtop,IL = (5) α α 573
DOI: 10.1021/acssuschemeng.5b00893 ACS Sustainable Chem. Eng. 2016, 4, 572−576
Research Article
ACS Sustainable Chemistry & Engineering
Table 2. Compositions (Mass Fraction) For the Piperidinium-based ILs+K2HPO4+Water Systems at 298 K, Respective Values of TLL 100 (mass fraction composition ±2−4)a
a
IL
α
wtop,IL
wtop,salt
wtotal,IL
wtotal,salt
wbot,IL
wtop,salt
TLL ± 0.22a
[C2mpip][Br] [C2mpip][Br] [C2mpip][Br] [C2mpip][Br] [C4mpip][Br] [C4mpip][Br] [C4mpip][Br] [C4mpip][Br] [C6mpip][Br] [C6mpip][Br] [C6mpip][Br] [C6mpip][Br] [C8mpip][Br] [C8mpip][Br] [C8mpip][Br] [C8mpip][Br]
0.20 0.22 0.24 0.26 0.20 0.22 0.24 0.26 0.20 0.22 0.24 0.26 0.20 0.22 0.24 0.26
36.71 29.38 38.64 44.33 27.98 36.78 43.35 48.38 47.62 46.69 53.93 58.56 46.78 53.55 61.68 67.56
6.62 9.81 5.94 4.27 9.02 5.91 4.29 3.33 4.54 4.67 3.78 3.31 5.01 4.23 3.49 3.04
24.24 18.13 19.48 20.65 16.76 18.21 19.45 20.65 23.64 18.27 19.54 20.93 16.87 18.18 19.55 20.85
15.15 18.01 19.33 20.63 16.64 17.99 19.33 20.63 15.27 17.98 19.31 20.56 16.63 18.00 19.31 20.58
7.59 9.81 5.77 3.63 8.55 5.13 3.39 2.21 4.33 3.84 2.77 1.85 5.15 3.49 2.51 1.75
26.54 24.07 28.89 32.39 22.24 26.51 29.44 32.14 23.92 24.74 26.89 29.31 21.18 23.72 25.71 27.75
35.27 24.22 40.09 49.47 23.50 37.76 47.21 54.42 47.43 47.31 56.14 62.38 44.66 53.72 63.21 70.30
Expanded uncertainty at the 0.95 confidence level from the standard deviation and applying a converge factor k = 0.2.
Figure 2. Ternary phase diagram for [EMPip][Br]+K2HPO4+water at 298 K and atmospheric pressure.
Figure 3. Effect of alkyl chain length of cations in piperidinium-based ILs and concentration of K2HPO4 on volume ratio of top to bottom phase (R).
Similarly, wtop,salt can be represented as follows wtotal,salt 1−α − wbot,salt wtop,salt = (6) α α The system solution results in the mass fraction of the IL and inorganic salt in each phase, and thus the tie-line length (TLL) can be simply represented. TLL =
(wtop,salt − w bot,salt)2 + (wtop,IL − w bot,IL)2
[BMPip][Br] > [EMPip][Br]. The decrease in the solubility of ILs in water with cation alkyl chain length increase is driven by a decrease in the entropy of solution. Therefore, ILs with longer alkyl chains require less amount of salt for salting-out and are more easily excluded from the salt-rich phase (bottom phase) to the IL-rich phase (top phase).12,13 Especially, self-aggregation can be possible in aqueous solution of ILs having longer than C8 alkyl chain length of their cations. The formation of aggregates increases the solubility of ILs in water and thus decreases the ability of aqueous biphase-formation.14 In the case of imidazolium ILs, it was reported that [C6min][Br] has the best phase forming ability, which is not in accordance with the hydrophobicities of imidazolium ILs.15 Similar results was also reported in case of ABS by morpholinium ILs and K2HPO4.16 The experimental binodal curves were fitted using eq 1. The parameters in eq 1 along with the correlation coefficients (R2) are given in Table 1. The TL compositions and the tie-line
(7)
In the present study, the top phase is the IL-rich phase, whereas the bottom phase is the K2HPO4-rich phase. Effect of Cation Chain Length in ILs on ABS Formation. The binodal curves determined at 25 °C for the piperidinium ILs/K2HPO4 systems are shown in Figure 1. These curves provide information about the concentration of phase forming components in order to form ABS. As seen in Figure 1, all piperidinium ILs used in this study were effective on the ABS formation and the ability of the ILs for biphasic separation follows the order: [OMPip][Br] > [HMPip][Br] > 574
DOI: 10.1021/acssuschemeng.5b00893 ACS Sustainable Chem. Eng. 2016, 4, 572−576
Research Article
ACS Sustainable Chemistry & Engineering
Figure 3 shows the volume ratio of top to bottom volume after aqueous two phase extraction of 1,3-propanediol by piperidinium ILs and K2HPO4. It can be found that the amount of water distributed into top phase decreased as the alkyl chain length of cations in ILs and as the concentration of K2HPO4 increases. The increase in alkyl chain length of cation decreases the hydrophilicity and enhanced the ability of the ILs to form ABS. It is distinct that, below about 20 wt % of K2HPO4, the volume of [EMPip][Br]-rich phase overwhelmed those of the other IL-rich phases. However, in the case of [HMPip][Br] and [OMPip][Br], the volume ratios of top to bottom phase were less than 0.3 over the entire concentration range of K2HPO4. In piperidinium ILs and K 2HPO 4 aqueous systems, extraction efficiency of 1,3-PDO is shown in Figure 4. Although 1,3-PDO has high affinity to water, most of 1,3-PDO is partitioned into the top IL-rich phase. As indicated in Figure 4, the extraction efficiency of 1,3-PDO was decreased with the increase of K2HPO4 concentration. Below 20 wt % of K2HPO4, it was shown that the extraction efficiency is proportional to the alkyl chain length of cations in ILs. Above 20 wt % of K2HPO4, there is little difference of extraction efficiency with the alkyl chain length of cations in ILs due to the low distribution of water into top phase. When the concentration of K2HPO4 increased, the salting-out effect increased and the distribution of 1,3-PDO into top phase increased. However, the water distribution into top phase decreased with the concentration of K2HPO4, resulting in little variation of extraction efficiency. The separation of 1,3-PDO with ABSs has been reported by several research groups, and their results are summarized in Table 3. Distribution coefficients can be influenced not only by initial concentration of 1,3-PDO in its solution and by products but also by ABS. In this study, distribution coefficients for 1,3PDO reached from 14.6 to 60.9. Because this high distribution coefficients was obtained from artificial solution, further investigation on fermentation broth will be essential. In summary, the removal of the excess amount of water is important for the economic separation of 1,3-PDO from its fermentation broth. Therefore, piperidinium ILs having long alkyl chain in cations is appropriate for simultaneous in removal of water and separation of 1,3-propanediol from its aqueous solution.
Figure 4. Extraction efficiency of 1,3-PDO by piperidinium ILs-based ABS in the presence of K2HPO4 solution.
lengths are presented in Table 2. An example of the fitting of the experimental binodal data of [EMPip][Br]+K2HPO4+water system using eq 1 is provided in Figure 2. In Figure 2, it can be found that the empirical equation correlates satisfactorily with the experimental data for the [EMPip][Br]+K2HPO4+water system. The similar results of correlation occurs for the other piperidinium ILs. From these results, eq 1 can be useful in determining the compositions in each phase. The tie-lines for each ternary system were obtained by the gravimetric method.8 As can be seen in Figure 2, the slope of the TLs is slightly increases as the distance from origin to α point decreases. Because the tie-line length represents the difference the IL and K2HPO4 concentrations in the top and bottom phases, the higher the TLL, the higher is the IL concentration in the top phase and the K2HPO4 concentration in the bottom phase. Effect of Cation Chain Length in ILs on Phase Volume Ratio and Extraction Efficiency. After phase separation in ABS, volume ratio of top to bottom phase (R) is represented as follows: R=
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Vtop Vbot
CONCLUSION Binodal curves of ABS for several piperidinium-based ILs and K2HPO4 were determined by the cloud point titration method.
(8)
where Vtop and Vbot are the volume of top and bottom phase after phase separation, respectively.
Table 3. Aqueous Biphasic Systems and Distribution Coefficient Reported in the Literature for the Extraction of 1,3-PDO reference
aqueous biphasic systems
17
a
6 7
IM4,1 CF3SO3 /phosphate salts IM4,1 CH3SO4b/phosphate salts IM4,1 SCNc/phosphate salts IM2,1 CF3SO3d/phosphate salts MO4,1 CF3SO3e/phosphate salts ethanol/ammonium sulfate methanol/phosphate salts
distribution coefficients
composition of 1,3-PDO solution
3.4
artificial aqueous solution of 5 wt % 1,3-PDO in the presence of 0.5 wt % acetic acid and 0.5 wt % butylic acid
16.5 8.3 6.0 3.0 4.77 38.3
50−150 g/L 1,3-PDO fermentation broth of 65.06 g/L 1,3-PDO in the presence of 2,3-BD, glycerol
a
1-Butyl-3-methylimidazolium trifluoromethanesulfonate. b1-Butyl-3-methylimidazolium methylsulfonate. c1-Butyl-3-methylimidazolium thiocyanate. d1-Ethyl-3-methylimidazolium trifluoromethanesulfonate. e1-Butyl-1-methylmorpholinium trifluoromethanesulfonate. 575
DOI: 10.1021/acssuschemeng.5b00893 ACS Sustainable Chem. Eng. 2016, 4, 572−576
Research Article
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(10) Muller, A.; Gorak, A. Extraction of 1,3-propanediol from aqueous solutions using different ionic liquid-based aqueous two-phase systems. Sep. Purif. Technol. 2012, 97, 130−136. (11) Merchuk, J. C.; Andrews, B. A.; Asenjo, J. A. Aqueous two-phase systems for protein separation: Studies on phase inversion. J. Chromatogr., Biomed. Appl. 1998, 711, 285−293. (12) Freire, M. G.; Claudio, A. F. M.; Araujo, J. M. M.; Coutinho, J. A. P.; Marrucho, I. M.; Lopes, J. N. C.; Rebelo, L. P. N. Aqueous biphasic systems: a boost brought about by using ionic liquids. Chem. Soc. Rev. 2012, 41, 4966−4995. (13) Zafarani-Moattar, M. T.; Hamzehzadeh, S. Salting-out effect, preferential exclusion, and phase separation in aqueous solutions of chaotropic water-miscible ionic liquids and kosmotropic salts: Effects of temperature, anions, and cations. J. Chem. Eng. Data 2010, 55, 1598−1610. (14) Li, Z.; Pei, Y.; Wang, H.; Fan, J.; Wang, J. Ionic liquid-based aqueous two-phase systems and their applications in green separation processes. TrAC, Trends Anal. Chem. 2010, 29, 1336−1346. (15) Pei, Y.; Wang, J.; Wu, K.; Xuan, X.; Lu, X. Ionic liquid-based aqueous two-phase extraction of selected proteins. Sep. Purif. Technol. 2009, 64, 288−295. (16) Lee, Y. H.; Lee, W. Y.; Kim, K.-S.; Hong, Y. K. Extraction equilibrium of acrylic acid by aqueous two-phase systems using hydrophilic ionic liquids. Hwahak Konghak 2014, 52, 627−631. (17) Muller, A.; Schulz, R.; Wittmann, J.; Kaplanow, I.; Gorak, A. Investigation of a phosphate/1-butyl3-methylimidazolium trifluoromethanesulfonate/water system for the extraction of 1,3-propanediol from fermentation broth. RSC Adv. 2013, 3, 148−156.
The effect of alkyl chain length of cation in piperidinium-based ILs on the ability of forming ABS was investigated. It was observed that the longer the alkyl chain length of cations in ILs, the greater the ability of forming ABS in the presence of K2HPO4. It is mainly due to the increase of hydrophobicity with their alkyl chain length of cations in ILs. The tie-line compositions and the tie-line length of biphasic systems were determined by using three-parameter equation and mass balances for each components. The capacity of piperidiniumbased ABS as prospective extraction media for the separation of 1,3-PDO was demonstrated by low partition of water in top phase as well as high extraction efficiency. It is advantaged for this method when applied to obtaining higher concentration of 1,3-PDO from its fermentation broth.
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AUTHOR INFORMATION
Corresponding Authors
*Y. K. Hong. E-mail:
[email protected]. Tel: 82-43-841-5231. Fax: 82-43-841-5220. *J. K. You. E-mail:
[email protected]. Tel: 82-42-860-3088. Fax: 82-43-861-6224. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
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REFERENCES
This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education (NRF2013R1A1A2058483) and the framework of Research and Development Program of the Korea Institute of Energy Research(KIER)(B5-2436)
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DOI: 10.1021/acssuschemeng.5b00893 ACS Sustainable Chem. Eng. 2016, 4, 572−576
