ZIF-8-porous ionic liquids for the extraction of 2,2,3,3-tetrafluoro-1-propanol and water mixture

Article abstract of DOI:10.1039/d1nj01053k

The design of stable ionic liquids (ILs) has become crucial for efficient liquid-liquid extraction (LLE) of alcohol and water. Porous ionic liquids (PILs), as a special class of ILs, have attracted attention by virtue of their unique porous structure and IL characteristics. In this research, a series of zeolitic imidazolate framework-8 based porous ionic liquids (ZIF-8-PILs) were synthesized by simply mixing a solution of zeolitic imidazolate framework-8 (ZIF-8) and rationally designed ILs. The introduction of ZIF-8 resulted in a unique liquid porous structure and molecular sieve for ZIF-8-PILs. The improved extraction properties endowed ZIF-8/[Bpy][NTf2] with more efficiency for the separation of 2,2,3,3-tetrafluoro-1-propanol (TFP) and water with 88.1% TFP extraction rate and steady reuse. The excellent extraction performance of ZIF-8-PILs is discussed in relation to their textural property and unique intermolecular interaction.

Full text of DOI:10.1039/d1nj01053k

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ZIF-8-porous ionic liquids for the extraction of
2,2,3,3-tetrafluoro-1-propanol and water mixture†
Cite this: DOI: 10.1039/d1nj01053k
ab
a
Zenghui Wang,a Pingping Zhao,
*
Jimin Wu,a Jun Gao,
Lianzheng Zhanga
and Dongmei Xu*a
The design of stable ionic liquids (ILs) has become crucial for efficient liquid–liquid extraction (LLE) of
alcohol and water. Porous ionic liquids (PILs), as a special class of ILs, have attracted attention by virtue
of their unique porous structure and IL characteristics. In this research, a series of zeolitic imidazolate
framework-8 based porous ionic liquids (ZIF-8-PILs) were synthesized by simply mixing a solution of
zeolitic imidazolate framework-8 (ZIF-8) and rationally designed ILs. The introduction of ZIF-8 resulted
in a unique liquid porous structure and molecular sieve for ZIF-8-PILs. The improved extraction
properties endowed ZIF-8/[Bpy][NTf2] with more efficiency for the separation of 2,2,3,3-tetrafluoro-1-
propanol (TFP) and water with 88.1% TFP extraction rate and steady reuse. The excellent extraction
performance of ZIF-8-PILs is discussed in relation to their textural property and unique intermolecular
interaction.
Received 3rd March 2021,
Accepted 12th April 2021
DOI: 10.1039/d1nj01053k
rsc.li/njc
structure of ILs can be task-specifically designed at the molecular
level according to the characteristics of the system. Therefore, IL
1. Introduction
2,2,3,3-Tetrafluoro-1-propanol (TFP, C3H4F4O), as a valuable systems are considered to be promising environmentally friendly
fluoride alcohol, has been extensively applied in industry.1–3 green solvents for the separation of alcohol–water.12,13 Very
Especially, TFP is adopted as a solvent and cleaning reagent recently, we have prepared a series of ILs for obtaining pure
due to the high solubility and gasification speed as well as the TFP by separation from aqueous solution by LLE.14,15 However,
low toxicity, but it is inevitable that it forms aqueous solutions conventional ILs, even hydrophobic 1-butyl-3-methylimidazolium
with different TFP contents. Owing to the pollution and cost,4 hexafluorophosphate ([Bmim][PF6]) and 1-decyl-3-methylimid-
the recycling of TFP from wastewater is profound and extra- azolium bis(trifluoromethane)sulfonamide ([Dmim][NTf2]), usually
ordinary. Meanwhile, TFP tends to form an azeotropic mixture have certain solubility in water. Therefore, it is difficult to use these
with water at 365.7 K,5,6 so the distillation operation is not a ILs as effective extractants to gain high separation efficiency in
worthwhile method to obtain highly purified TFP. Liquid–liquid fluoroalcohol–water azeotropic systems.
extraction (LLE) is considered to be an extremely important
Porous ionic liquids (PILs), as Type III porous liquids,
industrial process for separating azeotropic mixtures.7 At present, recently have been successfully developed and recognized as a
feasible works have been investigated for the systems involving promising new type of porous materials.16 It refers to a porous
fluoride alcohol by LLE,8,9 but only a few works have been reported frame material uniformly dispersed in ILs, where ILs are held
due to the absence of an appropriate extracting solvent.10,11 In this out of the pore structure frame. Such porous materials combine
context, task-specific design of new efficient solvent systems play a the classic characteristics of porous solids, such as permanent
crucial role in TFP extraction from aqueous solution.
multistage pores and molecular sieving, with the tunable
Ionic liquids (ILs) have been used in the alcohol–water structure and good solubility of ILs. As a result, PILs attract
separation system due to their wide liquid range, relatively low great attention due to their unique and fascinating physico-
melting point, good solvation performance, excellent thermal chemical properties and provide unique possibilities for storage
stability and other characteristics.12 More importantly, the and adsorption, homogeneous catalysis and separation fields.16–21
However, so far, only a few successful examples of PILs have
a College of Chemical and Biological Engineering, Shandong University of Science
and Technology, Qingdao 266590, China. E-mail: zhaopingping@sdust.edu.cn,
xudongmei@sdust.edu.cn
b Shandong Key Laboratory of Biochemical Analysis, College of Chemistry and
Molecular Engineering, Qingdao University of Science and Technology, Qingdao
266042, P. R. China. E-mail: zhaopingping@sdust.edu.cn
been reported,19–21 and they have not been used in liquid–liquid
extraction separations.
It is worth noting that zeolitic imidazolate framework-8
(ZIF-8), a kind of metal organic porous framework, has been used
as a novel adsorption material for many chemical separation with
the advantages of enhanced stability and improved molecular
† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1nj01053k
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and collected by centrifugation (10 000 rpm, 5 min), and then
dried in vacuum at 343.15 K for 1 h to give ZIF-8 nanocrystals.
2.2.2. Synthesis of the ionic liquids. The IL N-butylpyridinium
bromide ([Bpy]Br) was prepared according to a previous literature.19
Pyridine (1.5820 g, 20 mmol) and 1-bromobutane (2.7404 g,
20 mmol) were added to 40 ml ethanol, and the mixture was
refluxed under vigorous stirring at 343.15 K for 12 h. Then, the
ethanol was removed by a rotary evaporator at 333.15 K,
followed by washing with acetone (3 ꢂ 30 ml) and vacuum
drying at 353.15 K for 12 h to give white solid N-butylpyridinium
bromide ([Bpy]Br). Then, with a 1 : 1 molar ratio of IL [Bpy]Br
Fig. 1 The synthesis of ZIF-8-PILs (ZIF-8/[Bpy][NTf2]).
sieving.22,23 Actually, as a thermally and chemically stable porous
framework material, ZIF-8 has been adopted as the porous host
of PILs, which can cause significant improvements in gas
separation.18,19 Taking account of the good alcohol-water separation
performance and tunable structure of ILs as well as the improved
molecular sieving of ZIF-8, we think that it is rational to try a ZIF-8-
PIL solvent system for obtaining pure TFP by separation from
aqueous solution, which has not been reported yet. Herein, we
report a series of ZIF-8-PILs that can be synthesized by a simple
mixture of ZIF-8 and specially designed ILs (Fig. 1 illustrates the
formation of ZIF-8/[Bpy][NTf2] porous ionic liquids). The resulting
PILs were fairly stable over reasonably long periods of time, and no
accumulation was observed. They were used as the extractants to
separate TFP aqueous solutions by LLE, showing an improved
separation performance and good recyclability. A possible
extraction mechanism for getting TFP from the aqueous
solution by ZIF-8-PILs is proposed.
(1.0806 g,
5 mmol) and bis(trifluoromethane)sulfonimide
lithium Li[NTf2] (1.4355 g, 5 mmol), the 10 ml acetonitrile
solution of [Bpy]Br was drop-wise added into 10 ml acetonitrile
solution of Li[NTf2] under vigorous stirring at room temperature
for 24 h. The acetonitrile was removed by a rotary evaporator at
333.15 K, followed by washing with methylene chloride (3 ꢂ 50 ml),
and dried to obtain colorless transparent IL N-butylpyridinium
bis(trifluoromethane)sulfonimide ([Bpy][NTf2]). 1H NMR
(500 MHz, D6-DMSO, TMS); d0.91 (t, 3 H), 1.33 (m, 2 H),
1.92 (m, 2 H), 4.60 (t, J = 7.4 Hz, 2 H), 8.15 (m, 2 H), 8.59 (m,
1 H), 9.08 (m, 2 H). (Fig. S1, ESI†)
The other two ILs with varying carbon chains, N-ethyl-
pyridinium bis(trifluoromethane)sulfonimide ([Epy][NTf2]) and
N-hexylpyridinium bis(trifluoromethane)sulfonimide ([Hpy][NTf2]),
were prepared accordingly. The analogues of ILs, N-ethyl-
methylimidazole bis(trifluoromethane)sulfonimide ([Emim][NTf2]),
N-butylmethylimidazole bis(trifluoromethane)sulfonamide ([Bmim]-
[NTf2]) and N-hexylmethylimidazole bis(trifluoromethane)-
sulfonimide ([Hmim][NTf2]) were prepared following a similar
process using the corresponding IL precursors. Moreover, the
synthesis scheme of [Bpy][NTf2] and various counterparts is
illustrated in Scheme S1 (ESI†).
2.2.3. Synthesis of ZIF-8-PILs. The ZIF-8-PILs were synthe-
sized according to the literature with minor changes.19,20 The
synthesis of ZIF-8/[Bpy][NTf2] is shown here as an example. In a
10 ml round-bottom flask, ZIF-8 powder (2 mg) was added to
0.75 g [Bpy][NTf2], and then the mixture was ultrasonically
treated for 2 h at room temperature to obtain homogeneous
ZIF-8/[Bpy][NTf2]. The resulting solution was vacuum-dried at
353.15 K overnight for further use. The other ZIF-8-PILs used in
this work were synthesized by similar procedures with consistent
mass ratios of ZIF-8 to ILs.
2. Experimental
2.1. Materials and methods
All chemicals were commercially available and used without
further purification. The reagents were AR grade. The purity of
TFP was checked by gas chromatography (GC, SP6890). The
deionized water was prepared in our laboratory using an ultra-
pure water machine (CSR-1D, Beijing Aisitaike Technology
Development Co., Ltd.).
X-Ray diffraction (XRD) patterns were collected on a Bruker
D8 Advance powder diffractometer using a Ni-filtered Cu Ka
radiation source at 40 kV and 200 mA in the 2 range of 51–501 at a
scan rate of 21 minꢀ1. Thermogravimetric (TG) analysis was
implemented using a STA409 instrument in dry air at a heating
rate of 10 1C minꢀ1. A Hitachi S-4800 field-emission scanning
electron microscope was used to obtain the scanning electron
microscopy (SEM) images. Elemental analyses were performed on 2.3. Extraction experiment
a CHN elemental analyzer (FlashEA 1112). A Thermo Elemental
X7 ICP-MS equipped with a laser unit Thermo New Wave UP/213
was used for the Zn element analyses in ZIF-8.
The standard solution of TFP and water mixture was selected
based on the azeotrope composition of 72.5/27.5 (TFP/water by
weight) at 365.7 K and atmospheric pressure.14,15 The LLE
experiments were performed as follows: a suitable amount of
TFP and water standard solution and ZIF-8-PILs were blended
2.2. Preparation of extractant
2.2.1. The preparation of ZIF-8 nanocrystals. The prepara- in a customized thermostatic glass container with a magnetic
tion of ZIF-8 nanocrystals was carried out based on previous stirrer for 10 min. Then, the stirring was ceased and the mixture
literatures.20,24 Typically, Zn(NO3)2ꢁ6H2O (0.738 g, 2.48 mmol) was motionless for some time at the same temperature. The typical
and 2-methylimidazole (1.643 g, 19.99 mmol) were dissolved in extraction temperature and time were 298.15 K and 10 min,
methanol (100 ml) at 323.15 K for 1 h with stirring at 500 rpm. respectively. During the settlement process, external interference
The formed precipitate was washed with methanol three times was avoided until the phase equilibrium state was reached.
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After that, the two layers were presented clearly and each phase 3.2. Influences of extraction conditions
was analyzed accurately by a gas chromatography (GC, SP-6890)
For the purpose of a high TFP extraction efficiency, influences
of the extraction temperature and extraction time were investi-
gated with a mass ratio of 2 [ZIF-8/[Bpy][NTf2]: (TFP + water)],
which are shown in Fig. 2. The results proved that both were
significant extraction parameters, which influenced the extraction
performance of ZIF-8/[Bpy][NTf2]. As shown in Fig. 2(a), the
viscosity of ZIF-8/[Bpy][NTf2] decreased and the solubility increased
as the temperature increased, making it easier for TFP to be
separated from its aqueous solution, and eventually the extraction
efficiency gradually increased. Furthermore, the low viscosity was
beneficial to increase the mass transfer rate, which was the other
key factor of the extraction efficiency increase. However, consider-
ing the actual situation of industrial production and the idea of
energy conservation, 25 1C was selected as the optimal extraction
temperature with a relatively satisfying TFP extraction efficiency.
Fig. 2(b) shows that the length of the extraction time had only a
little influence on the extraction efficiency. The extraction could
reach equilibrium in 10 min, which was supposed to arise from
the strong electrostatic interaction and hydrogen bonding between
ZIF-8/[Bpy][NTf2] and TFP.14,15 Therefore, 10 min was used as the
optimal extraction time.
instrument equipped with a thermal conductivity detector
(TCD). The detailed analysis conditions are listed in Table S1
(ESI†). All samples were tested at least three times, and the
average was considered as the final result. The TFP extraction
rate was calculated by eqn (1).
ꢀ
ꢁ
C0 ꢀ Cf
R ¼
ꢂ 100%
(1)
C0
where C0 is the concentration of TFP in the standard solution of
(TFP + water), and Cf refers to the concentration of TFP in the
upper phase after the extraction.
Extraction time, extraction temperature, mass ratio of
extractant to (TFP + water) and ZIF-8 content in ZIF-8-PILs were
changed to investigate the influences of the conditions. In
order to test the extraction recyclability of ZIF-8-PILs, the
extractant was separated by a separating process and dried in
vacuum at 373.15 K for 24 h. The recovered extractant was
charged into the next run for a reuse.
In addition, ZIF-8/[Bpy][NTf2] and [Bpy][NTf2] were surveyed
separately for the extraction of TFP and water, and the results
are shown in Fig. 3. Whatever kind of extractant was used, the
increase in the mass ratio of extractant to (TFP + water) from
0 to 3 led to a remarkable increase in the TFP extraction
efficiency. It showed that [Bpy][NTf2] could separate TFP from
3. Results and discussion
3.1. Extractant characterization
The XRD pattern of ZIF-8 (Fig. S2, ESI†) displayed strong diffrac-
tions at 71, 101, 121 and 181, similar to the pattern simulated by
known structural data, which suggested a high-purity crystal
structure. Table S2 (ESI†) shows the CHNS and ICP elemental
analysis results of ZIF-8. It could be seen that the element mass
percentages in the prepared ZIF-8 sample were almost consistent
with the calculated values. The ratio between N and Zn was
approximately 4, pointing to a formula of Zn(C4H5N2)2, a
coordination composed of one Zn and two imidazole rings.
Fig. S3 (ESI†) shows the adsorption–desorption isotherms of
ZIF-8, which exhibited a combination of type I and type IV
adsorption isotherms. The high N2 adsorption capacity at very
low relative pressure revealed the microporous property of
ZIF-8. The small hysteresis loop at high relative pressure indicated
the existence of ZIF-8 intergranular large accumulated pores.
Based on the desorption branch of the isotherms, ZIF-8 showed
a rather high BET surface area of 1228 m2 gꢀ1. The implication
of these results was that ZIF-8 could be a good porous frame of
PILs. The SEM image in Fig. S4(A) (ESI†) illustrated the regular
morphology of ZIF-8 nanoparticles, which were hexagonal
blocks with uniform particle size. Based on the SEM image of
ZIF-8/[Bpy][NTf2] (Fig. S4(B), ESI†), ZIF-8 nanoparticles had low
polymerization and distinct edge, and the elemental mapping
images disclosed homogeneous dispersions of Zn across the
image area. It indicated that ZIF-8 probably has a high and
stable dispersion energy in [Bpy][NTf2]. Fig. S5 (ESI†) shows
the TGA curves of ZIF-8/[Bpy][NTf2] and [Bpy][NTf2]. It could be
seen from the measured data that the sharp decomposition
temperatures of [Bpy][NTf2] and ZIF-8/[Bpy][NTf2] both began at
365 1C, suggesting an excellent thermal stability.
Fig. 2 Influence of (a) extraction temperature and (b) extraction time on
the extraction of TFP and water.
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the aqueous solution by LLE, consistent with the proposal that
ionic liquids are excellent extractants for the separation of
water–ethanol mixture.25–27 Further analysis also demonstrated
that ZIF-8/[Bpy][NTf2] maintained the excellent extraction property
of ionic liquids. It was of interest to note that when the mass ratio
of the extractant to (TFP + water) increased above 0.25, ZIF-8/
[Bpy][NTf2] caused a higher TFP extraction efficiency than
[Bpy][NTf2]. It verified that ZIF-8 had some effects on the
improvement of TFP extraction efficiency, which were supposed
to arise from a combination of the stable porous architecture of
ZIF-8/[Bpy][NTf2] and the strong intermolecular interaction
among [Bpy][NTf2], ZIF-8 and TFP.14,15 The maximum rate of
92.3% could be obtained at the mass ratio of 3.0. However,
considering the economics of extraction, the mass ratio of 2.0
was verified as the optimum condition in this study.
Fig. 4 Influence of ZIF-8 content in 10 min at 25 1C and at the mass ratio
of 2.0 (ZIF-8/[Bpy][NTf2]: (TFP + water)) for the extraction of TFP and
water.
3.3. Extraction mechanism
of ZIF-8-PILs to (TFP + water). This suggested that the ZIF-8-PIL
content played an important role during the extraction process,
which was consistent with the results of previous reports.14,15,25,28
Table 1 displays the extraction results over various function-
alized pyridine and imidazole ZIF-8-PILs for comparison. It was
observed that increasing the length of the carbon chain in
cations could improve the efficiency of TFP extraction (entries
1–3). This could be attributed to the increase of acting force
between anions and cations as well as the improvement of the
electrostatic attraction between TFP molecules and cations. In
addition, this was most likely due to the fact that ionic liquids
with longer alkyl chains were more hydrophobic,29–31 which
was preserved in ZIF-8-PILs and functioned as excellent hydro-
phobic interaction. Furthermore, the extraction efficiency of
imidazolyl-PILs was slightly lower than that of pyridinyl-PILs
(entries 1–6). It could be seen from the structures of imidazole
and pyridine that the nitrogen atoms in pyridine had some
enhancement in the polarity of ILs. When pyridinyl-PILs inter-
acted with TFP, the stronger polarization generated some effect
on the extraction efficiency.
On the basis of the above experiments, we deduced that the
effected TFP extraction efficiency probably stemmed from several
factors. First, the ZIF-8 material in PILs possessed a multistage
pore structure, high specific microporous surface area character-
istics and a large micropore volume, which could make huge
improvements on the physical adsorption of PILs, so that could
affect the extraction efficiency of TFP. Second, the combination of
strong electrostatic interaction among ZIF-8, [Bpy][NTf2] and TFP
was one of the biggest factors in reaching an excellent extraction
efficiency.
To verify the above speculation, ZIF-8 content in ZIF-8/
[Bpy][NTf2] was also surveyed and displayed in Fig. 4. The TFP
extraction efficiency slightly rose with the changing of ZIF-8 content
in ZIF-8/[Bpy][NTf2], where a maximum extraction efficiency of
89.5% was achieved. Actually, the content of ZIF-8 was so little
in ZIF-8/[Bpy][NTf2], and a higher ZIF-8 content caused serious
aggregation of nanoparticles in the practical experiment. There-
fore, the adsorption capacity of ZIF-8 played little part in the
extractive separation of TFP.
To get a deeper insight into the extraction mechanism of the
ZIF-8-PILs, different ZIF-8-PILs were prepared; the extraction
performances are listed in Table 1. It can be seen that all
extraction rates were reduced with the decrease in the mass ratio
In addition, ZIF-8/[Hmim][NTf2] still exhibited a lower TFP
extraction rate as compared to ZIF-8/[Emim][NTf2] and ZIF-8/
[Bmim][NTf2] (entries 4–6). It was most likely that the introduction
Table 1 Comparison of different ZIF-8-PILs for the extraction separation
of TFPa
Extraction capacity of different mass
ratio [ZIF-8-PILs: (TFP + water)]
Entry
ZIF-8-PILs
2
0.2
1
2
3
4
5
6
7
8
9
ZIF-8/[Epy][NTf2]
ZIF-8/[Bpy][NTf2]
ZIF-8/[Hpy][NTf2]
ZIF-8/[Emim][NTf2]
ZIF-8/[Bmim][NTf2]
ZIF-8/[Hmim][NTf2]
[Emim][NTf2]
84.1
88.1
88.0
83.7
87.5
79.1
76.6
82.1
86.5
43.1
63.8
65.9
46.7
60.3
37.9
40.3
54.8
57.5
[Bmim][NTf2]
[Hmim][NTf2]
a
Fig. 3 Influence of ZIF-8/[Bpy][NTf2] and [Bpy][NTf2] in 10 min at 25 1C for
the extraction of TFP and water.
Extraction conditions: the separation of TFP and water at 25 1C and
the ZIF-8-PILs mass ratio of 1.3 ꢂ 10ꢀ3 (ZIF-8: [Bpy][NTf2]) for 10 min.
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The unique liquid porous structure and ionic liquid characteristics
enabled ZIF-8/[Bpy][NTf2] to be very efficient in the extraction
separation of TFP with a TFP extraction rate of 88%. ZIF-8-PILs
also showed a simple preparation, an easy recoverability, and good
reusability. The unique liquid pore property and intermolecular
interaction were proposed to understand the extraction separation
of TFP and water using ZIF-8-PILs. This work may be helpful in the
optimization and design of effective functional PILs for the
separation of TFP and water.
Author contributions
Zenghui Wang: data curation, writing – original draft. Pingping
Zhao: writing – review & editing, supervision. Jimin Wu: software,
validation, data curation. Jun Gao: writing – review & editing,
resources. Lianzheng Zhang: supervision, resources. Dongmei Xu:
funding acquisition, supervision.
Fig. 5 Extraction recycling of ZIF-8/[Bpy][NTf2] for the extraction separa-
tion of TFP and water for 10 min at 25 1C. (a) Recovery and drying, (b)
without any further treatment, (c) recovery after the fifth recycle and dried.
of ZIF-8 increased the viscosity of ZIF-8/[Hmim][NTf2] and reduced
the extraction efficiency. Based on this speculation, the extraction
performances of the corresponding ionic liquids were surveyed
under similar extraction conditions (entries 7–9). The results
showed that the extraction efficiency improved with the increase
of the alkyl chains. These results verified the previous speculation
that the pore structure of PILs played an important role in the
extraction process. That was to say, the excellent extraction
performances of ZIF-8-PILs were closely correlated with their
liquid pore and intermolecular interaction.
Conflicts of interest
The authors declare no competing financial interest.
Acknowledgements
The authors thank the National Natural Science Foundation
of China (No. 21978155) and the Open Project of Qingdao
University of Science and Technology Chemistry Department
(No. QUSTHX202009).
3.4. Recycling test
To test the repeatability and durability of ZIF-8-PILs, the
recycling tests of ZIF-8/[Bpy][NTf2] for the extraction separation
of TFP and water were carried out, as shown in Fig. 5. After each
cycle, the used ZIF-8/[Bpy][NTf2] was recovered by a separation
process. Afterwards, the recovered ZIF-8/[Bpy][NTf2], without
any further treatment, was taken directly to next recycle run
(Fig. 5(b)). The extraction rate of TFP decreased slowly from 88.1%
to 76.0% after five recycle runs. To give an insight into the reasons
for the decline in the extraction efficiency, the recovered ZIF-8/
[Bpy][NTf2] for the fifth cycle was dried in vacuum at 373.15 K for
24 h, and then reused for the sixth run. As shown in Fig. 5(c), the
extraction rate of TFP was nearly back to the first test value. These
results indicated that the slow decrease of the extraction efficiency
was mainly due to ZIF-8/[Bpy][NTf2] adsorbed and saturated by TFP
during the recovery rather than the distortion of the ZIF-8/
[Bpy][NTf2] structure. Furthermore, as shown in Fig. 5(a), when
ZIF-8/[Bpy][NTf2] from each run was dried and then reused, the
extraction rate remained basically unchanged. This suggested that
ZIF-8/[Bpy][NTf2] was a reusable extractant for the extraction
separation of TFP and water.
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