Reactive Extraction of o-, m-, and p-Chlorophenol from Aqueous

Feb 21, 2013 - Reactive extractions of o-, m-, and p-chlorophenol (o-, m-, and p-CP) from aqueous solutions using tri-n-butyl phosphate (TBP) dissolve...
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Reactive Extraction of o-, m-, and p‑Chlorophenol from Aqueous Solution Using Tri‑n‑butyl Phosphate in Kerosene De-Liang Li,* Yuan-Yuan Guo, Zhi-Xian Chang, Fei Yu, and Xiao-Li Feng Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, China ABSTRACT: Reactive extractions of o-, m-, and p-chlorophenol (o-, m-, and p-CP) from aqueous solutions using tri-n-butyl phosphate (TBP) dissolved in kerosene were studied. The influences of equilibrium aqueous pH (pHeq) and initial TBP concentrations on distribution ratio (D) were discussed. Effective extractions of CP were observed only under pHeq lower than 7.0. D values increased with the increase of initial TBP concentration. TBP mainly reacted with the neutral form of CP by forming 1:1 (TBP:CP) complex through a hydrogen-bond between phosphoryl in TBP and hydroxyl in CP. The apparent reaction extraction equilibrium constant (K) for o-, m-, and p-CP was found in good linear relationship with the addition of dissociation constant (pKa) and the hydrophobic parameter (Log P) of CP, namely, log K = −0.1171 × pKa + 0.0680 × Log P + 2.5848, suggesting pKa plays a much more important role that affects K than Log P. Back-extraction experiments supported > 95 % CP could be recovered using 0.5 mol·L−1 NaOH as stripping agent. The work put forward a potential green process for treatment of CP effluents with great importance.

1. INTRODUCTION As a type of the most important chemical raw materials and intermediates, chlorophenols, including o-, m-, and p-chlorophenol (o-, m-, and p-CP), have been widely used in fields of synthetic dyes, medicine, and pesticide. Chlorophenols are considered as toxic compounds and widely exist in wastewaters and sewages. Owing to the high stability of the aromatic ring, chlorophenols are not easily degraded by light, oxygen, and microorganism. Chlorophenols also tend to accumulate in the food chain resulting in seriously effects on the growth and reproduction of aquatic organisms. They have been included in the 129 kinds of Critical Control Point pollutants by the U.S. Environmental Protection Agency and have been listed in 76/464/EEC Directive of the European Union, aiming at the control of dangerous substances discharge. Removal of chlorophenols from effluents has always been a focus for researchers. Investigations consisted of conventional processes like adsorption,1−4 advanced oxidation,5−8 biochemical9,10 and so on. The adsorption process has advantages of simple equipment, easy operation, high efficiency, and selectivity, but its use is mainly for the treatment of chlorophenols under low levels of concentration; moreover, the regeneration of adsorbent is difficult. Advanced oxidation processes like photocatalytic oxidation and chemical oxidation are of great efficiency, quick response, and complete degradation; however, they are usually accompanied with high costs and long terms or exhausting large amounts of chemicals. Owing to the toxicity of chlorophenols, the biochemical process often requires characterized microorganism as well as rigorous operating conditions, leading to high running costs. Thus, the economical and © 2013 American Chemical Society

efficient approaches to removing chlorophenols from aqueous solutions are highly desired. In the 1980s, King proposed a method for separating polar organics from aqueous solutions,11 namely reactive extraction. The method is based upon the reversible reaction of the specific functional groups of solute and extractant, showing high efficiency and selectivity. Recently, this method has been widely used for separating carboxylic acids,12−17 amines,18 phenols,19,20 alcohol21,22 and amphoteric compounds23−26 and a series of encouraging results have been received. As typical polar organic compounds, chlorophenols have a functional group of −OH, which makes them can react with Lewis-base extractants thus being extracted into organic phases. Therefore, it has great potential to separate chlorophenols from aqueous solutions using a reactive extraction technique. However, as far as our knowledge, there are few works reported on separating chlorophenols using such technique. In the present work, Lewis base tri-n-butyl phosphate (TBP) dissolved in kerosene was employed as extractant for separating o-, m-, and p-CP from aqueous solutions. The factors that affected distribution ratio (D), such as equilibrium pH and initial TBP concentrations, were investigated. An expression of D was proposed and the related parameters were calculated. The effects of characteristic parameters of o-, m-, and p-CP, like dissociation constant and hydrophobic parameter, were also discussed. Finally, the loading organic phases were carried out by back-extraction using NaOH and Na2CO3 as stripping Received: November 17, 2012 Accepted: February 12, 2013 Published: February 21, 2013 731

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TBP/kerosene concentrations under different pHeq values. The results are presented in Tables 1, 2, and 3 and Figures 2, 3, and 4. As shown in Tables 1−3 and Figures 2−4, D values increase with the increase of TBP concentration, regardless of o-, m-, or p-CP. As known, CP possesses a typical Lewis acid group hydroxyl, which makes it react with the Lewis base group phosphoryl of the TBP through a hydrogen bond to form a complex. The reaction can be considered as a reversible balance. As the extractant concentration increases, the extraction equilibrium moves toward the direction that forms the extraction complex. Thus, the increase of TBP concentration leads to an increase in D values. By taking Le Chatelier’s principle into account, the results can be easily understood. From Tables 1−3 and Figures 2−4, it can also be seen that D values are highly dependent on the values of pHeq. High D values are observed under lower pHeq (< 6.0), while medium D values appear under intermediate pHeq (6−10), and low D values close to 0 are received at high pHeq (> 10). The change trend of D is similar to that of the mole fraction of neutral CP in aqueous solution, indicating that efficient extraction of CP using TBP mainly occurs between TBP and a neutral CP molecule, which further suggested the reaction between TBP and CP occurs at the sites of the phosphoryl of TBP and the hydroxyl of CP. As the dissociation constants (pKa) of hydroxyl are 8.55, 9.10, and 9.43 corresponding to o-, m- and p-CP,27 the significant decreases of D values are expected appearing at pHeq > 7.5 like the decrease of mole fraction of neutral CP. However, the pHeq that the D values appear to decrease obviously is around 6.0 in the present work. This deviation might be resulted from the errors in experiments. Even so, the approximate consistency of D values obtained under pH < 6.0 indicates that these data could be employed for exploring the extraction regularity of CP using TBP. The phenomenon of D changing with pHeq also suggests an approach to recovering CP from organic loading by adjusting the pHeq. 3.2. Extraction Mechanism. The extraction of CP with TBP in kerosene could be governed by the mass action law.28 The overall extraction consists of a reactive extraction by TBP and physical extraction by kerosene. The reactive extraction occurs by means of forming a hydroxyl-bond between hydroxyl in CP and phosphoryl in TBP at the interface between the aqueous and organic phases. If the activities of all species are assumed to be proportional to their concentrations, and the reactive extraction and physical extraction are accorded with simple addition, then the reactive extraction of CP (marked as HA in following equations) by TBP is

agents. The results obtained from this work could provide preliminary experimental data and a theoretical basis for the separation of o-, m-, and p-CP from aqueous solutions, as well as their recoveries from effluents.

2. EXPERIMENTAL SECTION 2.1. Materials. O-Chlorophenol (o-CP) and p-chlorophenol (p-CP) were furnished by Tianjin Guangfu Fine Chemical Research Institute (China). M-Chlorophenol (m-CP) was purchased from Xi’an Chemical Reagent Factory (China). They are all analytical grade with purities > 99 % and are used as received. Tri-n-butyl phosphate (TBP) was supplied by Luoyang Aoda Chemical Reagent Co., Ltd. (Henan, China). It is a colorless liquid with an average molecular weight of 266 g·mol−1, a density of 0.976 kg·dm−3 (25 °C) and a viscosity of 3.32 mPa·s (25 °C). The structures of CPs and TBP are shown in Figure 1.

Figure 1. Structures of o-CP (A), m-CP (B), p-CP (C), and TBP (D).

Kerosene, purchased from a local petrochemical plant, is reported as a mixture (C10−C16) of alkyl (68.4 %), naphthenic hydrocarbon (22.1 %), aromatic hydrocarbon (6.3 %), and alkene (3.2 %). It was pretreated with H2SO4 (98 %) (VH2SO4/ Vkerosene = 1:5), until the bottom became achromatically transparent, and then with water until the aqueous layer became neutral. The final product’s density is about 0.79 kg·dm−3, and the content of arene is less than 10 %. High-purity water was used throughout the experimental procedure. 2.2. Method. All extraction experiments were performed with 100 mL flasks at 25 ± 0.5 °C. The equal volume (20 mL) of initial aqueous (0.0078 mol·L−1 CP solutions) and organic aqueous (about 0.18, 0.37, 0.73, 1.10, 1.47, and 1.83 mol·L−1 TBP in kerosene) were agitated for a certain time (1.5 h for o-CP, 2 h for m-CP, and 1 h for p-CP) in a SHZ-B water bath oscillator (Jintan Instrument Manufacturing Co. Ltd., China) at 200 rpm, followed by settling for at least 2 h for separation. The initial aqueous pH (measured by a HI1200B composite electrode with a pH 211 Microprocessor pH meter, Hanna, Italy) was adjusted with a little saturated NaOH or diluent H2SO4 to desired pH. After separation, the same method was used to determine aqueous equilibrium pH (pHeq). The final aqueous phases were adjusted to pH = 1.50 ± 0.05 for o- and p-CP while pH = 3.00 ± 0.05 for m-CP, and analyzed at 274 nm for o- and m-CP and 280 nm for p-CP (maximum adsorption wavelengths of CP at corresponding pH) on an UV2000 spectrophotometer (Beijing Labtech, Ltd.). The loading CP in the organic phase was calculated by material balance. The deviation of this method was < 3 %.

K

HA + nTBP ↔ HA·TBPn

The physical extraction of CP by kerosene is m

HA ↔ HA

with the equilibrium constants: K=

[HA·TBPn ] [HA]·[TBP]n

(1)

m=

[HA ] [HA]

(2)

where K is the apparent reactive extraction equilibrium constant; m is the physical extraction equilibrium constant; n is the number of TBP molecule per complex; and, the overbar denotes species in the organic phase.

3. RESULTS AND DISCUSSION 3.1. Extraction Equilibrium Results. A concentration of 0.0078 mol·L−1 o-, m-, and p-CP was equilibrated with various 732

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Table 1. Extraction Equilibrium Results for o-CP + TBP/Kerosene System total concn of o-CP

total concn of o-CP initial concn of TBP

initial concn of TBP

× 10−3 mol·L−1

× 10−3 mol·L−1

mol·L−1

equil pH in aq phase

aq phase

org phase

D

mol·L−1

equil pH in aq phase

aq phase

org phase

D

0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.7338 0.7338 0.7338 0.7338 0.7338 0.7338 0.7338 0.7338 0.7338

1.66 2.04 3.21 4.30 4.41 4.77 7.54 9.51 10.28 10.99 2.02 3.33 4.54 4.68 4.84 6.12 6.52 9.18 10.95 11.25 2.28 3.42 3.93 4.40 4.96 5.07 5.18 6.38 9.56

0.469 0.486 0.490 0.515 0.529 0.547 0.898 1.80 4.01 5.00 0.316 0.312 0.323 0.327 0.330 0.423 0.479 1.44 3.17 4.09 0.198 0.192 0.187 0.190 0.193 0.203 0.221 0.305 1.06

7.33 7.31 7.31 7.29 7.27 7.25 6.90 6.00 3.79 2.80 7.48 7.49 7.48 7.47 7.47 7.38 7.32 6.36 4.63 3.71 7.60 7.61 7.61 7.61 7.61 7.60 7.58 7.50 6.74

15.6 15.0 14.9 14.1 13.7 13.2 7.67 3.33 0.945 0.560 23.6 23.9 23.1 22.8 22.6 17.4 15.2 4.41 1.45 0.907 38.3 39.5 40.7 40.1 39.4 37.4 34.3 24.5 6.37

0.7338 1.1008 1.1008 1.1008 1.1008 1.1008 1.1008 1.1008 1.1008 1.1008 1.1008 1.4677 1.4677 1.4677 1.4677 1.4677 1.4677 1.4677 1.4677 1.4677 1.8346 1.8346 1.8346 1.8346 1.8346 1.8346 1.8346 1.8346 1.8346

10.52 2.25 3.56 4.61 5.10 5.14 5.18 5.48 5.81 8.00 10.78 2.14 3.45 4.18 4.94 5.20 5.60 7.40 9.86 10.81 1.87 3.40 3.75 4.44 5.05 5.11 5.52 10.16 11.07

2.01 0.124 0.123 0.129 0.135 0.133 0.132 0.155 0.159 0.478 1.51 0.095 0.093 0.092 0.096 0.097 0.131 0.274 1.23 1.24 0.0729 0.0682 0.0625 0.0704 0.0802 0.0803 0.0802 0.739 1.20

5.79 7.68 7.68 7.67 7.67 7.67 7.67 7.65 7.64 7.32 6.29 7.71 7.71 7.71 7.70 7.70 7.67 7.53 6.57 6.56 7.73 7.73 7.74 7.73 7.72 7.72 7.72 7.06 6.60

2.87 61.7 62.2 59.2 56.6 57.4 57.8 49.3 47.9 15.3 4.15 80.8 82.3 83.4 80.3 78.8 58.3 27.4 5.32 5.26 105.4 116.9 120.8 104.0 94.3 96.3 96.1 9.53 5.47

Thus the plot of log[D(1 + 10pH−pKa)] versus log B0 would yield a straight line with a slope of n, as shown in Figure 5. The slopes, n, for o-, m-, and p-CP are calculated to be 0.84, 0.92, and 0.86, which are close to 1, indicating one TBP molecule reacts with one CP molecule in the extraction process. To determine K values, n = 1 was put into eq 5. Figure 6 shows the results that K values are calculated to be 54.07, 48.68, and 44.33 L·mol −1 for o-, m-, and p-CP, respectively. It is obvious that K values are shown as a declining order of o→m→p-CP, which are in the same order of dissociation constant (pKa) of CP. Taking the same extrantant into account, K values for o-, m- and p-CP were thought to be possibly in a relationship with characteristic parameters of CP themselves, such as dissociation constant (pKa) and hydrophobic parameter (Log P, 2.19, 2.47, and 2.44 for o-, m- and for p-CP,27 respectively). Thus, log K values were first plotted against pKa and Log P (Figure 7). From Figure 7, we could conclude that pKa plays a much more important role on log K than does Log P: as pKa increases, log K decreases; namely, the stronger is the acidity of CP (the smaller pKa is), the greater is log K, while there is no apperent regularity between log K and Log P. This result further confirms TBP has reacted with CP at −OH by forming a hydrogen-bond with phosphoryl. For further study, the least-squares method was used to solve the parameters of log K fitting with pKa and Log P. Then, eq 7 was obtained as follows:

CP dissociates in aqueous phase given as follows, Ka

HA ↔ A− + H+

where the dissociation balance constant is Ka =

[H+][A−] [HA]

(3)

with pKa values are 8.55, 9.10, and 9.43 for o-, m-, and p-CP, respectively. So, the experimentally accessible distribution coefficient, D, can be deduced from eqs 1 to eq 3 as given in eq 4: D=

[HA·TBPn ] + [HA ] = (K[TBP ]n + φm)/(1 + 10 pH − pKa) [HA] + [A−] (4)

where φ is the volume fraction of kerosene in organic phase. Since m values for o-, m-, and p-CP are close to 0, they can be neglected. In addition, suppose the initial TBP concentration is B0, which is far higher that that of CP, and we can consider that TBP concentration has no change before and after extraction. So, eq 4 can be revised as follows D = KB0n /(1 + 10 pH − pKa)

(5)

Linearizing eq 5 by taking logarithm on both sides, we get eq 6. log[D(1 + 10 pH − pKa)] = log K + n log B0

log K = − 0.1171 × pK a + 0.0680 × Log P + 2.5848

(6) 733

(7)

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Table 2. Extraction Equilibrium Results for m-CP + TBP/ Kerosene System

Table 3. Extraction Equilibrium Results for p-CP + TBP/ Kerosene System

total concn of m-CP initial concn of TBP

total concn of p-CP × 10−3 mol·L−1

initial concn of TBP

× 10−3 mol·L−1

mol·L−1

equil pH in aq phase

aq phase

org phase

D

0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.7338 0.7338 0.7338 0.7338 0.7338 0.7338 0.7338 0.7338 0.7338 0.7338 1.1008 1.1008 1.1008 1.1008 1.1008 1.1008 1.1008 1.1008 1.4677 1.4677 1.4677 1.4677 1.4677 1.4677 1.4677 1.8346 1.8346 1.8346 1.8346 1.8346 1.8346

1.95 2.90 3.07 4.35 4.40 5.39 9.79 10.85 2.36 3.07 3.33 4.84 5.18 5.82 5.99 8.98 2.06 3.05 4.10 4.29 4.60 4.87 5.04 5.37 7.24 9.64 1.59 2.93 3.47 4.90 5.27 5.56 6.36 9.57 2.15 4.24 4.99 5.21 5.58 6.69 8.62 2.23 3.17 4.99 5.38 7.42 8.47

0.617 0.638 0.640 0.660 0.673 0.766 2.06 3.92 0.405 0.390 0.390 0.416 0.422 0.443 0.477 1.40 0.225 0.224 0.230 0.241 0.245 0.258 0.257 0.274 0.422 1.55 0.142 0.146 0.156 0.166 0.183 0.184 0.240 1.33 0.115 0.109 0.120 0.119 0.123 0.174 0.786 0.0709 0.0681 0.0801 0.0803 0.172 0.617

7.18 7.16 7.16 7.14 7.13 7.03 5.74 3.88 7.40 7.41 7.41 7.38 7.38 7.36 7.32 6.40 7.58 7.58 7.57 7.56 7.56 7.54 7.54 7.53 7.38 6.25 7.66 7.65 7.65 7.63 7.62 7.62 7.56 6.47 7.73 7.62 7.68 7.68 7.68 7.62 7.04 7.73 7.73 7.72 7.72 7.63 7.18

11.6 11.2 11.2 10.8 10.6 9.16 2.78 0.990 18.2 19.0 19.0 17.7 17.5 16.6 15.3 4.56 33.6 33.7 32.9 31.3 30.7 29.2 29.3 27.4 17.5 4.03 53.9 52.2 49.1 45.9 41.5 41.4 30.9 4.83 68.7 70.7 63.7 64.6 62.5 42.8 8.90 109.1 113.5 94.7 92.8 44.1 11.6

It is obvious that the absolute value of coefficient before pKa is about two folds than that before Log P, indicating pKa plays a much more important role than Log P in affecting K values. It further confirmed that the extraction process mainly followed the reactive extraction. Through eq 7, K values were calculated as 54.02, 48.66, and 44.31 L·mol−1 for o-, m- and p-CP, which are in good

mol·L−1

equil pH in aq phase

aq phase

org phase

D

0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.1835 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.3669 0.7338 0.7338 0.7338 0.7338 0.7338 0.7338 0.7338 1.1008 1.1008 1.1008 1.1008 1.1008 1.1008 1.1008 1.1008 1.1008 1.4677 1.4677 1.4677 1.4677 1.4677 1.4677 1.4677 1.4677 1.8346 1.8346 1.8346 1.8346 1.8346 1.8346 1.8346 1.8346

1.75 2.06 3.15 4.04 4.30 4.51 4.61 4.63 6.01 6.37 1.50 2.38 3.32 4.31 4.60 4.72 5.27 6.47 6.68 7.74 1.56 3.28 4.25 4.40 7.55 10.25 11.79 1.72 2.25 3.31 4.13 4.27 4.40 4.45 4.92 6.32 1.52 1.95 3.18 3.89 4.23 4.48 4.67 6.65 1.60 2.00 3.08 4.09 4.20 4.45 6.56 8.18

0.608 0.607 0.612 0.623 0.642 0.644 0.648 0.658 0.843 0.950 0.379 0.372 0.389 0.407 0.418 0.421 0.414 0.728 0.865 1.33 0.264 0.248 0.264 0.272 0.966 2.08 2.86 0.156 0.144 0.157 0.159 0.155 0.168 0.166 0.172 0.345 0.111 0.106 0.118 0.124 0.128 0.131 0.148 0.508 0.0801 0.0792 0.0793 0.0797 0.0968 0.105 0.315 0.899

7.19 7.19 7.19 7.18 7.16 7.16 7.15 7.14 6.96 6.85 7.42 7.43 7.41 7.39 7.38 7.38 7.39 7.07 6.94 6.47 7.54 7.55 7.54 7.53 6.83 5.72 4.94 7.64 7.65 7.64 7.64 7.65 7.63 7.63 7.63 7.46 7.69 7.69 7.68 7.68 7.67 7.67 7.53 7.29 7.72 7.72 7.72 7.71 7.70 7.67 7.49 6.90

11.8 11.8 11.7 11.5 11.1 11.1 11.0 10.8 8.23 7.19 19.5 19.9 19.0 18.1 17.6 17.5 17.8 9.69 8.00 4.84 28.7 30.4 28.5 27.7 7.06 2.75 1.72 48.9 52.7 48.6 48.0 49.2 45.3 45.9 44.3 21.6 69.2 72.3 64.8 61.9 59.7 58.6 55.2 14.3 95.8 97.4 97.8 86.5 79.9 73.2 23.7 7.66

agreement with the experimental ones. According to eqs 5 and 6, B0, and pHeq, D values for all systems could be calculated, marked as Dcal. The solid lines in Figures 2−4 plotted with Dcal vs pHeq demonstrated an acceptable deviation range from 734

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Figure 2. D or Dcal vs pHeq of o-CP + TBP/kerosene systems.

Figure 6. D(1 + 10pH−pKa) vs B0.

Figure 3. D or Dcal vs pHeq of m-CP + TBP/kerosene systems.

Figure 7. Symbols: ■, log K vs pKa; □, Log P.

experimental D values, indicating that the proposed model is feasible and validated to the discussed extraction systems.

4. BACK-EXTRACTION The effect of pHeq on D allows us to recover solutes (o-, m-, and p-CP) and regenerate extractant (TBP/kerosene mixture) by controlling aqueous pHeq. Thus NaOH and Na2CO3 solutions with various concentrations were selected as stripping agents to attempt to recover o-, m-, and p-CP. The backextraction experiments were conducted after extraction of 0.0078 mol·L−1 CP by pure TBP and the results were shown in Figure 8, given as the plots of the recovery ratios of o-, m-, and

Figure 4. D or Dcal vs pHeq of p-CP + TBP/kerosene systems.

Figure 8. Influence of initial stripping agent concentrations on the back-extraction rate: ■, o-CP; ●, m-CP; ▲, p-CP.

p-CP against concentration of stripping agents. NaOH is shown as a superior stripping agent to Na2CO3. It might be attributed

Figure 5. log D(10pH−pKa) vs log B0. 735

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to the stronger alkalinity of NaOH than that of Na2CO3. NaOH could supply a much higher concentration of OH−, which not only could react with CP to from negative ions that transfer from the organic phase to the aqueous phase but also could react with the phosphoryl of TBP via its H terminal resulting in a positive effect on back-extraction, while CO32− could not. Figure 8 shows that 75 % CP can be recovered by using 0.2 mol·L−1 NaOH, and more than 95 % CP can be recovered with a NaOH concentration amount to 0.5 mol·L−1.

5. CONCLUSIONS Reactive extractions of o-, m-, and p-CP from an aqueous solution using tri-n-butyl phosphate (TBP) dissolved in kerosene have been experimentally studied. Aqueous equilibrium pH (pHeq) and TBP concentrations were found to be the key factors that affected the distribution ratios. The efficient extraction occurs at pHeq < 7. TBP mainly reacts with neutral CP by forming a 1:1 complex through a hydrogen-bond between phosphoryl in TBP and hydroxyl in CP. Apparent reactive extraction equilibrium constants (K) was well expressed by the addition of dissociation constant (pKa) and hydrophobic parameter (Log P). The pKa plays a much more important role than Log P in affecting K values. Moreover, the back-extraction supported > 95 % CP could be recovered by NaOH under suitable conditions. The results will provide an important theoretical foundation and reference data for the wastewater treatment of CP, and will provide supporting information for the development and improvement of reactive extractions.

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AUTHOR INFORMATION

Corresponding Author

*Tel./Fax: +86 378 3881589. E-mail: [email protected]. Funding

The work is supported by Major Project of Science and Technology, Education Department of Henan Province, China (No. 12A610001). Notes

The authors declare no competing financial interest.

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REFERENCES

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dx.doi.org/10.1021/je3012315 | J. Chem. Eng. Data 2013, 58, 731−736