Reactive Extraction of o-, m-, and p-Aminophenol Using

Jun 11, 2012 - Zhixian Chang†, Mei Xu‡, Ling Zhang†, and Deliang Li*† ... Mu-Hua Duan , Zhi-Xian Chang , Ling-Ling Su , Wen-Jing Liu , and De-...
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Reactive Extraction of o-, m-, and p-Aminophenol Using Trialkylphosphine Oxide/Kerosene Zhixian Chang,† Mei Xu,‡ Ling Zhang,† and Deliang Li*,† †

Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, China ‡ Pharmaceutical College of Henan University, Kaifeng 475004, China ABSTRACT: Reactive extractions of o-, m-, and p-aminophenol (OAP, MAP, and PAP) using trialkylphosphine oxide/kerosene (TRPO/kerosene) have been studied. The equilibrium aqueous pH (pHeq) and the concentrations of TRPO in organic phases were found to be of important effects on the distribution coefficient (D) of OAP, MAP, and PAP between TRPO/kerosene and water. Infrared spectra results suggested pHeq had no influence on the complexes' structures, and TRPO mainly reacted with neutral aminophenol through forming a hydrogen bond between its PO and aminophenol OH. An expression of D was proposed, and the apparent reactive extraction equilibrium constants (K) were calculated by fitting the experimental data. The dissociation constant of the OH group of aminophenol (namely, pKa2) played a vital role that affected K, while the hydrophobic parameter (log P) of aminophenol had little effect. K was statistically calculated to be in accordance with the equation of log K + pKa2 = 10.94 under all experimental test conditions. D values calculated from the model were in good agreement with experimental ones.

1. INTRODUCTION The separation of polar organic compounds from diluents is a hot research field in chemical engineering including purification, separation, and wastewater treatment, and so forth. In the early 1980s, King1 proposed a reversible reactive extraction method for the separation of these compounds. Recently, it has received increasing attention and has been widely used for the separation of carboxylic acids,2−10 phenols,11−14 amines,15,16 and amino acids17−20 and received a series of encouraging results. Especially, it has been successfully applied to the treatment of wastewaters those contain phenols or amines in China. With the development of applied technology, theories of reactive extraction were also continuously improved. King et al.2,3 considered that the formation of complexes with more than one acid per amine was a common behavior in carboxylic acid with amine extrantant systems. The author also drew a conclusion that the interactions between the first acid and amine involved ion pairs and hydrogen bonds, and the second acid formed hydrogen bonds to the carboxylate of the first acid from infrared spectroscopic investigations. Li et al.4,5 introduced the conception of specific basicity (pKa,B) of amine/dilutes to describe extraction of carboxylic acid with amine and discussed its influence on extraction equilibrium. Meanwhile a correlation of the apparent extraction equilibrium constant with pKa,B, hydrophobic constant (log P), and acidic constant (pKa) of acid was proposed. Liu et al.17−19 conducted extraction equilibrium experiments of amino acids (such as Lphenylalanine, L-isoleucine, and L-tryptophan) using di(2© 2012 American Chemical Society

ethylhexyl)phosphoric acid (D2EHPA). The interaction mechanism between amino acids and D2EHPA was found to be consisted of proton-transfer and ion-exchange reactions, which provided an important theoretical support for the separation of amino acids. The studies on extraction of amphiprotic compounds like aminobenzoic acid,21,22 aminobenzenesulfonic acid, 23 aminophenol,24−28 and pyridine carboxylic acid,29−36 and so forth, have also been reported. Results suggested that these amphiprotic compounds could be extracted by Lewis acid and/or basic extractants, and generally, Lewis acid extractants reacted with a Lewis basic functional group of amphiprotic compounds, while Lewis basic extractants reacted with a Lewis acid functional group. For example, tributyl phosphate (TBP) and trioctylamine (TOA) reacted with OH of aminophenol, while D2EHPA reacted with NH2 of aminophenol.24,25,27 Nevertheless, there is still no very deep understanding of extraction mechnism of amphiprotic compounds with various extractants and diluents. More efforts are expected. Aminophenols, including o-aminophenol (OAP), m-aminophenol (MAP), and p-aminophenol (PAP), a kind of typical amphiprotic compounds, have been widely used as raw materials or intermediates in the fields of pharmaceuticals, dyes, and pesticides, and so forth. In the past decades, a few works on extraction of aminopenols have been reported. Yang Received: March 14, 2012 Accepted: May 31, 2012 Published: June 11, 2012 2030

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et al.24 discussed the influences of extractants, diluents, and aqueous pH on the extraction equilibrium of PAP using TOA, TBP, and D2EHPA as extractants and 1-octanol and kerosene as diluents. Our group25−28 carried out systematical studies on extractions of OAP, MAP, and PAP using TBP, D2EHPA, or TRPO in different diluents. The results are very useful for the separation of aminophenol from their diluent solutions. However, all studies remained in the aspect of extraction equilibrium; the interaction mechanism of extractant with aminophenol has been rarely reported. In the present work, experimental studies were conducted systematically, using OAP, MAP, and PAP as solutes, TRPO as extractant, and kerosene as diluent. The effects of TRPO concentration, equilibrium aqueous pH, electric parameters (pKa), and hydrophobic parameter (log P) of aminophenols were discussed, and the extraction mechanisms were analyzed from infrared spectra. Especially an expression of D was proposed, through which D values were predicted in agreement with experimental results very well.

material balance. The deviation of this method was less than 3 %. Infrared spectra (IR) were recorded on an AVATAR 30 Fourier transformation infrared spectrometer (Nicolet, America). The organic phase was first centrifuged under 4000 rpm for 20 min to completely eliminate water and then was injected into the sample cell (a thickness of 0.05 mm between two CaF2 plates) to record IR spectra.

3. RESULTS AND DISCUSSION 3.1. Extraction Equilibrium Results. Tables 1 to 3 list the extraction equilibrium data of OAP, MAP, and PAP with Table 1. Extraction Equilibrium Results for the OAP + TRPO/Kerosene System init. conc. of TRPO

2. EXPERIMENTAL SECTION 2.1. Chemicals. OAP and PAP were purchased from Fluka (Seelze, Germany). MAP was furnished by China Medicine (Group) Shanghai Chemical Reagent Corporation. The purities of these chemicals are higher than 99 %. TRPO, an industrial product from CYTEC Canada Incorporation, is a C8 to C10 saturated straight-chain trialkylphosphine oxide mixture (purity ≥ 93 %) with average molecular weight of 350 g·mol−1 and density of 0.88 g·cm−3. Before being used, it was washed with 5 % NaOH solution (VNaOH/VTRPO = 1:5) first and then with water until the aqueous layer became neutral. Kerosene was obtained from a local chemical plant. It was first washed with H2SO4 (98 %; VH2SO4/Vkerosene = 1:5) until the bottom became achromatism transparent, and then with water until the aqueous layer became neutral. High-purity water was used throughout the experimental procedure. 2.2. Experimental Procedure. Aminophenols were dissolved in 0.01 mol·L−1 H2SO4 solutions to prepare 250 mg·L−1 (2.291·10−3 mol·L−1) phenol solutions. The organic phases were pure kerosene, TRPO in kerosene with concentrations of (0.2338, 0.4676, 0.7014, and 1.169) mol·L−1, and pure TRPO (2.238 mol·L−1). All extraction experiments were conducted with 100 mL flasks at 25 ± 0.5 °C. Equal volumes (20 mL) of aqueous and organic phases were shaken in a constant temperature water bath-vibrator (SHZ-B, Shanghai Yuejin Medical Instruments Factory) at 200 rpm for 90 min, which preliminary tests demonstrated to be a sufficient time for equilibrium, and then the mixtures were left to settle for 5 h at fixed temperature (25 ± 0.5 °C) to reach full separation. Before extraction process, the aqueous pH, which was measured by a HI1200B composite electrode with a pH meter (pH211 Microprocessor pH meter, HANNA, Italy), was adjusted with saturated NaOH to a desirable pH. After the two phases are separated, the same procedure was performed to measure aqueous pH. Then the aqueous phase was adjusted to pH ≤ 2.0 and finally analyzed on a UV-2000 spectrometer (Beijing Labtech, Ltd.) at (271, 272, and 273) nm, corresponding to the maximum adsorption wavelengths of OAP, MAP, and PAP. The concentrations of OAP, MAP, and PAP in organic phases were calculated by

total conc. of phenols/ mg·L−1

mol·L−1

equil. pH in aq. phase

in aq. phase

in org. phase

D

0 0 0 0 0 0 0.2338 0.2338 0.2338 0.2338 0.2338 0.4676 0.4676 0.4676 0.4676 0.4676 0.7014 0.7014 0.7014 0.7014 0.7014 1.169 1.169 1.169 1.169 1.169 2.338 2.338 2.338 2.338 2.338

4.60 5.51 6.48 6.88 7.62 8.26 4.81 5.43 6.18 6.93 7.17 4.74 5.25 5.94 6.48 6.95 4.75 5.35 5.93 6.24 6.59 4.68 5.25 5.72 6.27 6.47 4.57 4.79 5.17 5.58 6.10

209.2 203.6 198.3 193.3 188.4 188.4 76.60 60.68 53.55 46.63 44.74 50.09 37.72 27.96 24.28 22.67 30.28 22.72 17.21 15.19 14.57 18.54 13.14 10.43 9.449 9.197 11.63 9.418 6.718 5.732 5.233

40.80 46.42 51.74 56.65 61.61 61.61 173.4 189.3 196.5 203.4 205.3 199.9 212.3 222.0 225.7 227.3 219.7 227.3 232.8 234.8 235.4 231.5 236.9 239.6 240.6 240.8 238.4 240.6 243.3 244.3 244.8

0.195 0.228 0.261 0.293 0.327 0.327 2.27 3.12 3.67 4.36 4.59 3.99 5.63 7.94 9.30 10.0 7.26 10.0 13.5 15.5 16.2 12.5 18.0 23.0 25.5 26.2 20.5 25.5 36.2 42.6 46.8

different concentrations of TRPO/kerosene under different equilibrium pH (pHeq). The data are also clearly plotted in Figures 1 to 3. As shown in Tables 1 to 3 and Figures 1 to 3, it is observed that the distribution coefficients (D) increase with the increase of TRPO concentration in kerosene. This phenomenon could be easily explained by taking into account Le Chatelier’s principle. It could also be seen from Tables 1 to 3 and Figures 1 to 3 that D values change with pHeq for a certain concentration of TRPO in kerosene. The effects of pHeq on extraction 2031

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Table 2. Extraction Equilibrium Results for the MAP + TRPO/Kerosene System init. conc. of TRPO

Table 3. Extraction Equilibrium Results for the PAP + TRPO/Kerosene System

total conc. of phenols/ mg·L−1

init. conc. of TRPO

total conc. of phenols/ mg·L−1

mol·L−1

equil. pH in aq. phase

in aq. phase

in org. phase

D

mol·L−1

equil. pH in aq. phase

in aq. phase

in org. phase

D

0 0 0 0 0 0.2338 0.2338 0.2338 0.2338 0.4676 0.4676 0.4676 0.4676 0.4676 0.7014 0.7014 0.7014 0.7014 0.7014 1.169 1.169 1.169 1.169 2.338 2.338 2.338 2.338

4.34 5.15 5.74 6.28 6.76 4.35 4.79 5.36 5.91 4.43 4.88 5.01 5.45 5.86 4.56 4.88 5.10 5.48 5.72 4.31 4.84 5.29 5.65 4.51 4.72 5.04 5.27

218.7 209.4 206.8 206.8 203.7 101.2 87.72 75.53 72.05 56.95 48.92 46.73 41.88 40.26 37.54 34.44 31.77 29.17 27.62 25.85 20.37 17.78 16.90 13.18 11.10 10.39 9.881

31.28 40.62 43.22 43.22 46.25 148.8 162.3 174.5 178.0 193.1 201.1 203.3 208.1 209.7 212.5 215.6 218.2 220.8 222.4 224.1 229.6 232.2 233.1 236.8 238.9 239.6 240.1

0.143 0.194 0.209 0.209 0.227 1.47 1.85 2.31 2.47 3.39 4.11 4.35 4.97 5.21 5.66 6.26 6.87 7.57 8.05 8.67 11.3 13.1 13.8 18.0 21.5 23.1 24.3

0 0 0 0 0 0.2338 0.2338 0.2338 0.2338 0.4676 0.4676 0.4676 0.4676 0.4676 0.7014 0.7014 0.7014 0.7014 0.7014 1.169 1.169 1.169 1.169 1.169 2.338 2.338 2.338 2.338

4.72 5.08 5.86 6.31 6.71 5.02 5.46 6.01 6.27 4.92 5.25 5.75 5.93 6.30 5.06 5.37 5.77 6.10 6.30 4.93 5.22 5.46 5.76 6.22 5.20 5.61 5.67 6.02

238.5 236.1 231.2 226.7 218.2 189.1 162.8 129.9 127.2 148.5 126.5 93.63 88.65 71.84 109.6 93.28 72.46 60.53 55.19 84.75 69.64 58.96 49.31 39.18 33.78 25.99 24.06 21.42

11.50 13.86 18.81 23.35 31.85 60.89 87.24 120.1 122.8 101.5 123.5 156.4 161.3 178.2 140.4 156.7 177.5 189.5 194.8 165.3 180.4 191.0 200.7 210.8 216.2 224.0 225.9 228.58

0.0482 0.0587 0.0814 0.103 0.146 0.322 0.536 0.925 0.965 0.684 0.977 1.67 1.82 2.48 1.28 1.68 2.45 3.13 3.53 1.95 2.59 3.24 4.07 5.38 6.40 8.62 9.39 10.7

equilibrium of OAP, MAP, and PAP with TRPO have been completely discussed in our previous works,25,26,28 with the pHeq ranging from 2.0 to 11.0. The changes of D values versus pHeq support that aminopheols mainly react with TRPO by their neutral forms. Thus, all experiments in present work were performed under pHeq in the range of 4.0 to 7.0, in which the neutral aminophenol dominated. The effects of pHeq on D in present work were obtained in good agreement with the previous works (refs 25, 26, and 28). As a result of comparing Tables 1 and 2 with 3, as well as Figures 1 and 2 with 3, D values versus various aminophenol are observed in the order of OAP > MAP > PAP, which is in the same order of hydrophobic parameter (log P) with 0.62 for OAP, 0.15 for MAP, and 0.04 for PAP,37 and in the inverse order of electrical parameter (pKa2) with 9.66 for OAP, 9.87 for MAP, and 10.30 for PAP.38 The effects of log P and pKa2 on extraction equilibrium will be discussed subsequently. 3.2. IR Spectra Analysis. To investigate the interactions between TRPO and OAP, MAP, or PAP, IR spectra of loading organic phase (aminophenol + 30 % (v/v) TRPO/n-heptane) under acidic, near-neutral, and weak alkaline conditions were recorded, as well as pure OAP, MAP, and PAP, original organic phase TRPO/n-heptane. (For obtained much more clear features, n-heptane here was used to replace kerosene.) Figures 4, 5, and 6 demonstrate IR spectra of loading organic phases for OAP, MAP, and PAP, respectively. As shown in Figure 4, IR spectra of OAP + TRPO/n-heptane display no significant difference either pHeq at acidic, neutral ,or alkaline

Figure 1. D vs pHeq for the OAP + TRPO/kerosene system. ■, kerosene; ●, 0.2338; ▲, 0.4676; ▼, 0.7014; ◀, 1.169, ▶, 2.338 TRPO/kerosene (in mol·L−1).

conditions, as well as those of MAP + TRPO/n-heptane in Figure 5 and PAP + TRPO/n-heptane in Figure 6. It indicates that pHeq has an ignorable influence on the interaction forms between TRPO and aminophenol; namely, the same structure complexes are formed under different pHeq. Figures 7, 8, and 9 show the comparison results of IR spectra of original and loading organic phases with pure aminophenol, respectively. The characteristic deformation vibration of OH, in OAP at 1403 cm−1, MAP at 1392 cm−1, and PAP at 1387 cm−1, disappeared in the corresponding loading organic phase. At the same time, the band at 1157.1 cm−1, which could be attributed 2032

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Figure 5. IR spectra of MAP + TRPO/n-heptane. pHeq: 1, 2.44; 2, 5.31; 3, 8.28.

Figure 2. D vs pHeq for the MAP + TRPO/kerosene system. ■, kerosene; ●, 0.2338; ▲, 0.4676; ▼, 0.7014; ◀, 1.169, ▶, 2.338 TRPO/kerosene (in mol·L−1).

Figure 6. IR spectra of PAP + TRPO/n-heptane. pHeq: 1, 2.39; 2, 5.66; 3, 8.56.

Figure 3. D vs pHeq for the PAP + TRPO/kerosene system. ■, kerosene; ●, 0.2338; ▲, 0.4676; ▼, 0.7014; ◀, 1.169, ▶, 2.338 TRPO/kerosene (in mol·L−1).

Figure 7. IR spectra of 1, OAP; 2, TRPO/n-heptane, and 3, OAP + TRPO/n-heptane (pHeq: 5.59). Figure 4. IR spectra of OAP + TRPO/n-heptane. pHeq: 1, 2.38; 2, 5.59; 3, 9.13.

to the characteristic stretching of PO, was shown with slight shifts toward lower wavenumbers at (1144.5, 1150.0, and 1150.5) cm−1, in loading OAP, MAP, or PAP TRPO/n-heptane systems, respectively. Generally, the characteristic asymmetry and symmetry stretching of NH2 on the benzene ring are commonly near the bands at 1620 cm−1, which would disappear or shift to lower wavenumbers after forming intramolecular or intermolecular hydrogen bonds. The asymmetry and symmetry stretching of NH2 of OAP, MAP, and PAP were tested to be at (1604.8, 1610.5, and 1614.9) cm−1, respectively. The new bands at (1617.8 and 1607.5) cm−1 and the wide band at 1636.2 cm−1 in loading OAP, MAP, and PAP organic phases suggested that NH2 did not participate in the interaction with

Figure 8. IR spectra of 1, MAP; 2, TRPO/n-heptane, and 3, MAP + TRPO/n-heptane (pHeq: 5.31).

2033

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H 2+A ← → HA + H+ K a2

HA ← → A− + H+

where the dissociation balance constants are K a1 =

[HA][H+] [H 2+A]

(3)

K a2 =

[A−][H+] [HA]

(4)

with pKa1 = 4.74 and pKa2 = 9.66 of OAP, pKa1 = 4.17 and pKa2 = 9.87 of MAP, and pKa1 = 5.29 and pKa2 = 10.30 of PAP,38 respectively. So, the distribution coefficient, D, can be deduced from eqs 1 to 4 and written as:

Figure 9. IR spectra of 1, PAP; 2, TRPO/n-heptane, and 3, PAP + TRPO/n-heptane (pHeq: 5.66).

TRPO (or diluent). Thus, it confirms that the interactions between TRPO and aminophenol are based upon the hydrogen bond between PO of TRPO and OH of aminophenol. 3.3. Description of Extraction Equilibrium. The extraction equilibrium is governed by the mass action law,2 and the diluents' physical extraction is also taken into account. It is also under the following assumptions: the systems studied are dilute solutions, so the activities of the interests (OAP, MAP, and PAP, denoted as HA) and the complexes are proportional to their concentrations; the concentrations of TRPO are far higher than that of HA, so TRPO mainly reacts with HA to form (1:1) complexes; and the reactive extraction and physical extraction accord with simple addition. Thus,The reactive extraction of TRPO with HA:

D = (K[TRPO] + φm)/(10 pKa1− pH + 1 + 10 pH − pKa2) (5)

where φ is the volume fraction of kerosene in the organic phase. Define the initial concentration of TRPO as B0, and ignore the solubility of TRPO in water, then: B0 = [TRPO] + [TRPO·HA]

(6)

Because B0 is far higher than the initial concentration of aminophenol, [TRPO·HA] could be neglected, and B0 is approximately equal to [TRPO]. So, D could be revised as: D = (KB0 + φm)/(10 pKa1− pH + 1 + 10 pH − pKa2)

(7)

According to the experimental results and eqs 2 to 4, m could be easily calculated, and then K was calculated using an equivalent eq 8 of eq 7.

K

TRPO + HA ↔ TRPO·HA

The physical extraction by kerosene:

K = [D(10 pKa1− pH + 1 + 10 pH − pKa2) − φm]/B0

m

HA ↔ HA with the equilibrium constants:

K=

[TRPO·HA] [TRPO]·[HA]

(1)

m=

[HA] [HA]

(2)

(8)

Table 4 lists the fitted results of m and K for every system. K is shown with some deviation at different TRPO concentrations for OAP, MAP, or PAP, respectively, which might result from deviations in the experimental procedure. TRPO mainly reacts with the OH functional group of aminophenol (confirmed in the IR spectra analysis part); thus K should be in relationship with the electric parameter, namely, pKa2, of aminophenol. To show a more intuitive effect of pKa2 on K, logK were plotted linearly against pKa2 in Figure 10. It is shown that log K are well linearly fitted versus pKa2, and all slopes are close to −1, indicating that pKa2 is a factor that affects log K. It also suggests that the smaller pKa2 (namely stronger acidity) of aminophenol is, the greater log K is. Another factor that affects K might be the log P of aminophenol. When the effects of log P were discussed, the result that log K was approximately in linearity versus pKa2 with

where K is the apparent reactive extraction equilibrium constant (L·mol−1); m is the physical extraction equilibrium constant of diluent; and the overbar denotes species in the organic phase. Aminophenol is a kind of amphoteric compound. There are three forms, namely, the charged cation (H2+A), neutral molecule (HA), and charged anion (A−), in aqueous solution. Two dissociation balances exist in aqueous solutions as follows:

Table 4. All Model Parameters for Various Aminophenol + TRPO/Kerosene Systems OAP, m = 0.30

init. conc. of TRPO

a

mol·L−1

φ

K/L·mol−1

0.2338 0.4676 0.7014 1.169 2.338

0.9 0.8 0.7 0.5 0

16.6 18.0 20.7 21.9 21.1

MAP, m = 0.22 K/L·mol−1

(n, s)a (5, (5, (5, (5, (5,

1.60) 2.38) 2.22) 1.13) 0.42)

9.53 10.6 11.0 12.1 11.4

PAP, m = 0.15

(n, s) (4, (5, (5, (4, (4,

0.41) 0.39) 0.43) 0.46) 0.30)

K/L·mol−1 3.69 4.68 4.78 4.89 5.67

(n, s) (4, (5, (5, (5, (4,

0.44) 0.53) 0.44) 0.36) 0.31)

n is the number of the values of K, and s is the standard deviation of the values of K. 2034

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Figure 12. Dexp vs Dcal (the error bar shows the deviation of Dcal at the 10 % level).

Figure 10. log K vs pKa2.

the slope −1 was also considered. Thus, plots of logK + pKa2 versus log P were fitted linearly in Figure 11. As shown, good

that described the extraction equilibrium has been proposed; and, the corresponding parameters, like the apparent reactive extraction constant (K), and so forth, were obtained by fitting experimental data. log K was found to be closely related to the electric parameter (pKa2) of aminophenol. But there was no effect of aminophenol's hydrophobic parameter (log P) on log K. The comparison between Dcal and Dexp supported good fitness of the proposed reaction extraction model. The results obtained in the present investigation were of potential use for studies on extraction of other homologous compounds and would provide supporting information for the development and improvement of reactive extraction.

■

Figure 11. log K + pKa2 vs log P.

*Phone/fax: +86 378 3881589. E-mail address: lideliang@ henu.edu.cn (D. Li).

linear relationships are obtained with all slopes are close to 0. It indicates that log P has little effect on reactive extraction equilibrium. Generally, log P is a parameter which can be used to describe physical extraction process. The small effects of log P on the systems studied in present work suggest the processes mainly dominated with reactive extraction, not a physical one. The log K + pKa2 are also calculated to be a constant, which is expressed as eq 9. log K + pK a2 = 10.94

AUTHOR INFORMATION

Corresponding Author

(n = 15, s = 0.054)

Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) King, C. J. Separation process based upon reversible chemical complexation. In Handbook of separation process technology; Rousseau, R. W., Ed.; John Wiley & Sons: New York, 1987; Chapter 15, pp 760− 774. (2) Tamada, J. A.; Kertes, A. S.; King, C. J. Extraction of carboxylic acids with amine extractants. 1. Equilibria and law of mass action modeling. Ind. Eng. Chem. Res. 1990, 29, 1319−1326. (3) Tamada, J. A.; King, C. J. Extraction of carboxylic acids with amine extractants. 2. Chemical interactions and interpretation of data. Ind. Eng. Chem. Res. 1990, 29, 1327−1333. (4) Li, Z. Y.; Qin, W.; Dai, Y. Y. Extraction equilibria behavior of monocarboxylic acids by trioctylamine (I) Extraction equilibria. J. Chem. Ind. Eng. (China) 2004, 55, 54−58. (5) Li, Z. Y.; Qin, W.; Dai, Y. Y. Extraction equilibria behavior of monocarboxylic acids by trioctylamine (II) Apparent extraction equilibrium constant and correlation. J. Chem. Ind. Eng. (China) 2004, 55, 59−64. (6) Keshav, A.; Wasewar, K. L.; Chand, S. Extraction of propionic acid with tri-n-octyl amine in different diluents. Sep. Purif. Technol. 2008, 63, 179−183. (7) Keshav, A.; Chand, S.; Wasewar, K. L. Recovery of propionic acid from aqueous phase by reactive extraction using quarternary amine (Aliquat 336) in various diluents. Chem. Eng. J. 2009, 152, 95−102. (8) Asci, Y. S.; Inci, I. Extraction equilibria of acrylic acid from aqueous solutions by Amberlite LA-2 in various diluents. J. Chem. Eng. Data 2010, 55, 2385−2389. (9) Marchitan, N.; Cojocaru, C.; Mereuta, A.; Duca, G.; Cretescu, I.; Gonta, M. Modeling and optimization of tartaric acid reactive

(9)

where n is the number of the values of log K + pKa2, and s is the standard deviation of the values of log K + pKa2. Through eq 9, K values for TRPO reacting with OAP, MAP, or PAP were predicted as three constants of 19.05, 11.75, or 4.37, respectively. Substituting K, m, and experimental pHeq, D values for all systems suddenly were calculated, marked as Dcal. Figure 12 shows a good fitness between Dcal and Dexp (experimental D values), indicating the proposed model in the present work is satisfactory.

4. CONCLUSIONS The systematical reactive extractions of OAP, MAP, and PAP using TRPO/kerosene have been experimentally studied. D was found to be highly dependent on equilibrium pH values and the initial concentrations of TRPO in kerosene in the organic phase. For the same TRPO/kerosene, its extraction ability to three aminophenols was in the order of OAP > MAP > PAP. pHeq did not affect the complexes' structures, and TRPO reacted with aminophenol through hydrogen bond action between its PO and OH of aminophenol. An expression of D 2035

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dx.doi.org/10.1021/je300329h | J. Chem. Eng. Data 2012, 57, 2030−2036