Article pubs.acs.org/jced
Phase behavior at Different Temperatures of an Aqueous Two-Phase Ionic Liquid Containing ([BPy] NO3 + Ammonium Sulfate and Sodium Sulfate + Water) Yuliang Li,*,†,‡ Rong Huang,† Qi Zhu,† Yonghong Yu,† and Jing Hu§ †
School of Environmental Science and Engineering, Chang’ an University, Xi’an, 710064, China Key Laboratory of Subsurface Hydrology and Ecological Effects in Arid Region, Ministry of Education, Xi’an, 710064, China § State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, 710075, China ‡
S Supporting Information *
ABSTRACT: Phase diagrams of aqueous two-phase systems composed of N-butylpyridinium nitrate + salt (ammonium sulfate and sodium sulfate) + water determined at (298.15, 308.15, 318.15 and 328.15) K. The binodal curves were associated with the Merchuk expression and another two empirical expressions. The influences of temperature and the type of cations were also studied, which demonstrated that lower temperature led to the expansion of the two-phase region, whereas the salting-out abilities of Na2SO4 exceeded that of (NH4)2SO4, which was proven by the Gibbs free energy of hydration of the ions.
1. INTRODUCTION Two different chemical substances mixed above a certain concentration and temperature will be separated into two no-miscibility phases, which is called aqueous two-phase systems (ATPSs). Aqueous two-phase systems usually consist of polymer−polymer or polymer−salt systems.1,2 An extraction based on ATPSs is a new separation method to enrich and purify bioactive substances,2 and has several advantages when compared with traditional extraction methods; it is more effective and can provide mild conditions, which helps to expand its application range to the purification of antibiotics,3−7 metal ions,8 and biomolecules9−12 Recently, various kinds of ATPSs have been formed. The IL-based ATPSs (ILATPSs), which were first found by Gutowski in 2003, have been the focus of recent research.13 Ionic liquids are usually considered as “green solvents”, they have plenty of advantages and properties, like negligible volatility, high thermal and chemical stability, and nonflammability under ambient conditions.14−16 ILATPSs have been used in purification, concentration, and separation of drugs,17,18 proteins,19,20 amino acids,21,22 and antibiotics.23,24 Unfortunately, in reality, the high cost of ILs and polymers prohibits the use of ATPSs, and encourages the development of low-cost ATPSs as an efficient way to solve this problem. Hydrophilic organic solvents have the advantage of low cost over the polymers and ILs. In addition, a hydrophilic organic solvent is easily reused and recycled. Some ILATPSs [Cnmim]X (X = Br and Cl) + salt (KOH, K2HPO4, © 2017 American Chemical Society
K2CO3, K3PO4, K3C6H5O7 and sucrose) + H2O have been formed.25−28 So far, there are no reports on ATPSs composed of N-butylpyridinium nitrate and salt sulfate. Therefore in this work, biphasic systems comprising N-butylpyridinium nitrate, salt, and water were determined. To analyze the nature of the salts, the salts used were ammonium sulfate and sodium sulfate. Equilibrium data at different temperaments were determined to investigate temperature responses. By the fitting approach, the regularity of the data was obtained. In addition, the factors of the type of salts and the temperature upon phase equilibrium were discussed in detail, since these results are not reported in the literature. These systems provide a novel and good purification method in the treatment of biomolecules.
2. EXPERIMENTAL SECTION 2.1. Materials. Table 1 summarizes the suppliers and purities of chemicals used in the study, and these products fulfill the high standards needed for an international research work. N-Butylpyridinium nitrate (shown in Figure 1) was provided by Chengjie Chemical Co., Ltd. (Shanghai, China) with a quoted purity of more than 0.99 mass fraction. Ammonium sulfate/ sodium sulfate were analytical grade reagents (GR, min. 99% by Received: September 29, 2016 Accepted: January 9, 2017 Published: January 23, 2017 796
DOI: 10.1021/acs.jced.6b00844 J. Chem. Eng. Data 2017, 62, 796−803
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Table 1. Sources and Purities of Chemicals Used in the Study chemical name
molar mass
supplier
final mass fraction purity
free water content
analysis methoda
[BPy]NO3 (NH4)2SO4 Na2SO4
198.22 132.14 142.06
Chengjie Chemical Reagent Co., Ltd. (Shanghai, China) Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China)
>0.99 >0.99 >0.99
not detcted NH4 + (ΔGhyd = −285 kJ/mol). This mean the order of the two-phase system ability of salt is Na2SO4 > (NH4)2SO4 in the investigated systems. The reason is that the salts containing Na+ exceed those with NH4+ in the terms of the salting-out ability. 2.3.3. The Effect of Temperature on Phase Diagram. The temperature is another important affecting factor besides the salt type for the phase diagram of many ATPSs.35−37 In this work, for the N-butylpyridinium nitrate−Na2SO4 ATPSs, the binodal curve at 298.15 K, 308.15 K, 318.15 K, and 328.15 K was shown in Figure 5. The region below the one curve refers to the homogeneous system, while that above denotes the two-phase region. Though it was found that temperature has a weak influence on phase-forming, an increase in the temperature causing a shrinking of the two-phase area28 can still be found in the Figure 5. A possible reason is that [BPy]NO3 becomes more hydrophobic as the temperature decreases. Studies on the [C4mim]BF4− Na 2 CO 3 /NaH 2 PO 4 16 and [C 4 mim]BF 4 −sucrose/maltose ATPSs38 also demonstrated that the two-phase area is larger at lower temperature.39 So, under increased temperatures, water is shift from the IL-rich phase to the other phase.
Figure 5. Phase diagram of [BPy] NO3 + Na2SO4 + H2O ATPS at T = 298.15 K, ■; T = 308.15 K, red ●; T = 318.15 K, blue ▲; T = 328.15 K, purple ▼.
3. CONCLUSIONS The binodal data of the systems containing [BPy]NO3, salt (Na2SO4 and (NH4)2SO4), and H2O were studied at different temperatures (from 298.15 K to 328.25 K) and were satisfactorily fitted by three empirical equations, among which Merchuk performed best. The Gibbs free energy of hydration illustrated that the salting-out ability follows the order Na2SO4 > (NH4)2SO4. Furthermore, the two-phase area becomes larger as temperature decreases, for both systems containing Na2SO4/(NH4)2SO4.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.6b00844. NMR spectra of the [BPy]NO3 (deuterated acetone) (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Yuliang Li: 0000-0002-7803-5073 Funding
This work was sponsored by the National Natural Science Foundation of China (Nos. 41472220 and 41202164), the
Figure 4. Effect of the type of salt on the binodal curves at T = 308.15 K (a) and 318.15 K (b): ■, (NH4)2SO4; red ●, Na2SO4. 801
DOI: 10.1021/acs.jced.6b00844 J. Chem. Eng. Data 2017, 62, 796−803
Journal of Chemical & Engineering Data
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Research and Development Project of Science and Technology for Shaanxi Province (No. 2015 KJXX-25), and the Fundamental Research Funds for the Central Universities (Nos. 310829153507, 31082916004, 310829161112, and 0009-2014G1291076). Project funded by China and Shaanxi Postdoctoral Science Foundation (No. 2014M552400), and the National Training Projects of the University Students’ Innovation and Entrepreneurship Program (Nos. 201610710078 and 201610710069). Notes
The authors declare no competing financial interest.
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DOI: 10.1021/acs.jced.6b00844 J. Chem. Eng. Data 2017, 62, 796−803
