Experimental and Theoretical Investigations on the Reactive

Article pubs.acs.org/jced

Experimental and Theoretical Investigations on the Reactive Extraction of Itaconic (2-Methylidenebutanedioic) Acid Using Trioctylamine (N,N‑Dioctyloctan-1-amine) Hasan Uslu† and Dipaloy Datta*,‡ Beykent University, Engineering and Architecture Faculty, Chemical Engineering Department, Ayazağa, Iṡ tanbul 34433, Turkey Department of Chemical Engineering, Thapar University, Patiala, Punjab 147004, India

† ‡

ABSTRACT: The paper presents the equilibrium distribution study of itaconic acid (also known as 2-methylidenebutanedioic acid, 0.615 mol·kg−1) between water and trioctylamine (TOA, 0.374 mol·kg−1 to 1.946 mol·kg−1) at 298 ± 0.1 K. The extract phase is prepared by varying the concentration of TOA and dissolving the same in four categories of solvents (alkane, ester, ketone and alcohol). The batch equilibrium results are presented in the form of loading ratio (Z), extraction efficiency (% E), and distribution coefficient (KD). Maximum extraction efficiency of 94.80% with the value of KD equal to 18.20 is obtained at 1.946 mol·kg−1 of TOA in octan-1-ol. The extractability of TOA with different solvents is found to be in the order of alcohol > ketone > ester > alkane. The values of stoichiometric coefficient (1:m), overall equilibrium constant (KE) and individual equilibrium constants (K11, K21, and K12) are estimated using equilibrium data and employing mass action law. The acid molecules form 1:1 and 2:1 type of complexes (m < 1) with TOA dissolved in alkanes, and 1:1 and 1:2 solvates (m > 1) with TOA dissolved in alcohols, ketones, and esters. The estimated values of KE followed the same trend as the distribution coefficient (alcohol > ketone > ester > alkane).

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INTRODUCTION Itaconic acid (pKa1 = 3.65 and pKa2 = 5.13 at 298 K, log P = −0.43),1 an α-substituted acrylic acid is used in the production of synthetic resins, coatings, and other industrial products. Its addition to paints increases the durability of carpet fiber. The resins of itaconic acid with acrylic or methacrylic acid or their esters are used in coating like emulsion, leather, cars, refrigerators, and other electrical appliances to improve their physical properties. The polymer of itaconic acid shows special luster and transparency. Due to this, it is used to make synthetic cut stone and special lens. Due to the limitations of chemical synthesis path, itaconic acid may be produced by Aspergillus terreus in a fermentor but with a very low acid concentration.2−4 The fermentation route can be made efficient by employing a highly competent separation technique. Among several separation techniques, the recovery of carboxylic acids by reactive extraction is found to be a promising and efficient method of separation.5−10 Literature cited different studies1−4,11−13 on the reactive extraction of dicarboxylic acids from aqueous solutions by different categories of extractants [tributylphosphate (TBP), trioctylphosphine oxide (TOPO), di-2-ethylhexylphosphoric acid, Aliquat 336, tridodecylamine (TDDA), trioctylamine (TOA), Amberlite LA-2, etc.]. Kyuchoukov et al.1 studied extraction of six dicarboxylic acids like itaconic, maleic, malic, oxalic, tartaric, and succinic acids from aqueous solutions using TBP as extractant and dodecane as diluent. They investigated the effect of volume-phase ratio on the distribution of acid. © 2015 American Chemical Society

Mass action law had been employed to determine stoichiometry of extraction. They proposed formation of 1:1 and 1:2 acid−TBP complexes in the organic phase. Wasewar et al.3 performed extraction study on itaconic acid by Aliquat 336 using solvents like ethyl acetate, kerosene, toluene, and hexane. They anticipated 1:1 acid−amine solvates in the extract phase. In their study, they reported highest values of the distribution coefficient (KD) and degree of extraction (E) were found to be 2.65% and 72.66%, respectively, with Aliquat 336 + ethyl acetate system. The same research group also investigated the reactive extraction of itaconic acid using TBP and Aliquat 336 both dissolved in a biocompatible diluent (sunflower oil).4 They reported the highest values of the KD equal to 4 and 0.95 with TBP and Aliquat 336, respectively, in sunflower oil. In another study, Hano et al.11 showed that the hydrophobicity of the acids (acetic, glycolic, propionic, lactic, pyruvic, butyric, succinic, fumaric, maleic, malic, itaconic, tartaric, citric, and isocitric) mainly controls the extraction equilibrium constant when TOPO + hexane solvent system was used. Selective separation of itaconic acid was conducted by Bressler and Braun12 by water-immiscible amine extractants. They presented equilibrium results in the form of loading ratios, distribution coefficients, and FTIR and fluorescence spectra. Matsumoto et al.13 correlated the equilibrium constants with the hydrophobicity Received: December 14, 2014 Accepted: April 15, 2015 Published: April 22, 2015 1426

DOI: 10.1021/je501131j J. Chem. Eng. Data 2015, 60, 1426−1433

Journal of Chemical & Engineering Data

Article

Table 1. Extractant/Diluent System for the Recovery of Itaconic Acid by Reactive Extraction sl no

initial acid concentration

extractant used

mol·kg−1

extractant concentration

diluent used

mol·kg−1

maximum distribution coefficient

references

KD, max

1. 2.

0.0821−0.248 0.05−0.25

TBP Trin-octylamine (TOA)

0.372−2.97 0.115−0.229

3.

0.05−0.20

Aliquat 336

0.19−0.59

4.

0.05−0.20

5.

0.615

TBP Aliquat 336 TOA

0.37−1.1 0.19−0.59 0.374−1.946

dodecane heptane kerosene methylbenzene decan-1-ol 4-methylpentan-2-one dichloromethane ethyl acetate kerosene toluene hexane sunflower oil octane decane 2-heptanone 2-octanone ethyl acetate propyl acetate octan-1-ol nonan-1-ol decan-1-ol

9.11 0.082 0.313 2.188 16.855 15.739 32.478 1.93 0.832 1.26 1.30 4.0 0.95 2.73 2.20 12.09 8.32 6.41 5.28 18.20 16.08 15.62

ref 1 ref 2

ref3

ref4 present study

determine the stoichiometry (m:n), the values of the overall (KE) and the individual equilibrium constants (K11, K21, and K12) for 1:1, 2:1, and 1:2 complexes of reactive extraction.

of the acids (acetic, glycolic, propionic, lactic, succinic, fumaric, L-malic, and itaconic) with TOA or TBP in hexane. These studies suggested that the tertiary amines like TOA are best suited for the recovery of carboxylic acids from dilute aqueous solutions. They proposed that these weak carboxylic acids are efficiently extracted by using higher molecular weight, tertiary and quaternary amines such as N,N-dioctyloctan-1amine (TOA), trioctylmethylammonium chloride (Aliquat 336), Alamine 336 (trioctyl/decyl amine), Amberlite LA-2, and so forth from dilute aqueous solution.14−28 In Table 1, the reactive extraction study for itaconic acid was shown for comparison with the present equilibrium study. In the extraction, separation is facilitated because of the strong interaction between acid and extractant molecules in the presence of a diluting medium and due to the formation of acid−extractant solvates. Additionally, the extractant selectivity recovers acid from a mixture of nonacidic components. Also, the nature of the reaction is reversible, which enables easy recovery of the acid and recycling of the extractant−solvent system. It was found that the nature of acid, compositions of acid and amine, and polarity of diluents affect the equilibrium behavior of the carboxylic acids extraction process by amine.22 The physical and chemical interactions of highly hydrophilic acids with the water-solvent systems showed extremely nonideal behavior. It remained a challenging problem when modeling such type of systems.29 Since, polar diluents were found to be better solvating diluents and also enhanced the extractability of nonpolar extractants for the recovery of organic acids from aqueous solution.30 In the present study, the experimental and theoretical investigation is performed on the reactive extraction of itaconic acid with N,N-dioctyloctan-1-amine or trioctylamine (TOA) in wide range of solvents such as alkane (octane and decane), ester (ethyl acetate and propyl acetate), ketone (2-heptanone and 2-octanone), and alcohol (octan-1-ol, nona1-ol and decan-1-ol). The equilibrium data are used to

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EXPERIMENTAL SECTION Reagents. Itaconic acid (purity = 99% by weight) is a white crystalline powder and a dicarboxylic acid was procured from Sigma-Aldrich Co. Trioctylamine or N,N-dioctyloctan-1-amine (molar mass = 353.67 kg·kmol−1, purity = 98% by weight) procured from Sigma-Aldrich Co. was used as extractant in this study. Solvents from four different categories (alkane, ketone, ester and alcohol) were used as diluents. Alcohols (octan-1-ol, nonan-1-ol, and decan-1-ol), alkanes (octane, decane), esters (ethyl acetate and propyl acetate), and ketones (2-heptanone and 2-octanone) were supplied by Aldrich and Fluka. The purity of diluents used in this study was above 98% by weight and of technical grade. Sodium hydroxide used for titration was supplied by Merck. Phenolphthalein was used as an indicator for titration. Procedure. The initial concentration of itaconic acid (7.43% by weight) in the aqueous solution was 0.615 mol·kg−1 and prepared by using distilled water. The concentrations of trioctylamine (TOA) in the extract phase were considered between 0.374 and 1.946 mol·kg−1 to conduct equilibrium batch experiments. Same volumes (20 mL) of aqueous and organic phases were mixed in Erlenmeyer flask of 100 mL in volume. This flask was kept in a shaker maintained at 298 ± 0.1 K and at 40 rpm speed for 6 h. After equilibrium was achieved, this mixture was kept for at least 2 h at the same temperature in a digitally controlled incubator. Earlier tests showed that 6 h was the sufficient time to achieve equilibrium. A Mettler Toledo pH meter was used to measure the pH of aqueous phase before and after equilibrium. The uncertainty in the pH measurements was noted to be ± 0.01. The concentration of acid in the aqueous phase at equilibrium was determined by using sodium hydroxide (0.1 N) as titrant and phenolphthalein as an indicator 1427



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for titration. The relative uncertainty in the concentration measurement was found to be within ± 1%. The amount of extracted acid in the organic phase was determined by a complete mass balance.

The free TOA concentration (C̅ 0R3N) at equilibrium in the extract phase was estimated by eq 8.

THEORETICAL SECTION Mass Action Law Modeling. The solvents/extractants such as octane, decane, 2-heptanone, 2-octanone, ethyl acetate, propyl acetate, octan-1-ol, nonan-1-ol, decan-1-ol, and trioctylamine used in the present study have very poor solubility in water. Again, it was reported that organic acids carry small quantity of water with them in the extraction process by solvents and therefore coextraction of water in the extract phase by the solvents was neglected.15,30 In the extraction of itaconic acid using TOA in these solvents, a negligible change (0.5 mL) in the phase volume was observed after reaching equilibrium. In the calculation of KD using experimental values, it was found that KD values were affected by only ± 1% when the volume change of each phase at equilibrium was neglected. Therefore, the effect of solubility of solvents in the calculation of distribution coefficients and other parameters were ignored. The reactive extraction of itaconic acid (undissociated acid part, H2I) with amine (R3N) was a reaction taking place between aqueous and organic phase interface and given by eq 1

Now, for the estimation of equilibrium constant (KE) and the number of extractant molecules per acid molecule (n), the theoretical study based on mass action law was carried out. Equation 8 for m = 1 and with an assumption of C̅ 0R3N ≫ n[(H 2I)m (T)n] was used to find the values of KE and n. The validity of this assumption fails at higher acid concentration due to an increased extractant concentration in the acid−TOA complex in the organic phase. With these assumptions, eq 3 can be represented as eq 9

C̅ R3N = C̅ 0R3N − n[(H 2I)m (T)n ]

■

mH 2I + nT̅ ↔ (H 2I)m (T)n

KE =

[(H 2I)m (T)n ] [H 2I]m [T]̅ n

⎛ K a1 ⎞ 0 log KD + log⎜1 + ⎟ = log KE + n log C̅ R3N ⎝ [H+] ⎠

C̅ H2I C H 2I

=m

A plot of log KD + log(1 + (Ka1/[H ])) versus yielded a straight line with a slope of n and an intercept of log KE. The expressions of experimentally calculated degree of extraction (% E) and loading ratio (Z) were defined by the eqs 10 and 11, respectively

E=

(1)

Z= (2)

(3)

where, C̅ H2I and CH2I represent the total acid concentration in the organic and aqueous phase, respectively, and [(H 2I)m (T)n] is the concentration of acid−TOA solvates in the organic phase at equilibrium. The dissociation reactions of itaconic acid (first dissociation constant, Ka1, and second dissociation constant) in the aqueous phase at equilibrium take place by following eqs 4−5 H 2I ↔ H+ + HI−K a1 = HI− ↔ H+ + I2 −K a2 =

[H+][HI−] [H 2I] [H+][I2 −] [HI−]

(1 +

C̅ R03N

(11)

C̅ 11 [H 2I]C̅ R3N

K 21

2H 2I + R3N ← → (H 2I)2 (R3N)K 21 =

(4)

K12

H 2I + 2R3N ← → (H 2I)(R3N)2 K12 =

(12)

C̅ 21 [H 2I]2 C̅ R3N

(13)

C̅ 12 [H 2I]C̅ 2R3N

(14)

C̅ 11, C̅ 21, and C̅ 12 were the concentrations of the complexes such as 1:1, 2:1, and 1:2 in the organic phase at equilibrium, respectively. The values of C̅ H2I and C̅ R0 3N in the extract phase were represented by eqs 15 and 16, respectively

(5)

C̅ H2I = C̅ 11 + 2C̅ 21 + C̅ 12

(6)

=K11[H 2I]C̅ R3N + 2K 21[H 2I]2 C̅ R3N + K12[H 2I]C̅ 2R3N (15) C̅ R3N =

C̅ 0R3N

− (C̅ 11 + C̅ 21 + 2C̅ 12)

=C̅ 0R3N − (K11[H 2I]C̅ R3N + K 21[H 2I]2 C̅ R3N + 2K12[H 2I]C̅ 2R3N)

C H 2I K a1 [H+]

C̅ H2I

K11

In this work, the values of pH (in the range of 2.11 to 3.25) were found to be less than pKa2 (= 5.13) of the acid. Therefore, in the mathematical modeling, the dissociation of second carboxylic group in itaconic acid was neglected. Using eqs 4 and 6, eq 7 was deduced to find out the concentration of undissociated acid ([H2I]) [H 2I] =

(10)

H 2I + R3N ↔ (H 2I)(R3N)K11 =

Now, the expression for CH2I can be represented in terms of undissociated acid concentration ([H2I]), and dissociated acid concentration ([HI−], and [I2−]) as eq 6 C H2I = [H 2I] + [HI−] + [I2 −]

KD × 100 1 + KD

The determined values of n were useful in confirming the stoichiometry of reactive extraction. Hence, on the basis of this information, the formation of different types of complexes like 1:1, 2:1, and 1:2 between acid and TOA were considered. The stoichiometric equations were represented by eqs 12 to 14 with the corresponding individual equilibrium constants (K11, K21, and K12).

[(H 2I)m (T)n ] C H 2I

(9)

logC̅ 0R3N

+

The distribution coefficient (KD) can be calculated by eq 3 KD =

(8)

(16)

)

The eq 16 was used to determine the value of C̅ R3N and written in the following form, eq 17

(7) 1428



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Table 2. Results for the Extraction of Itaconic Acid with TOA + Alkane System solvents (alkane)

pHaq

C̅ 0R3N mol·kg

octane

2.12 2.19 2.31 2.52 2.64 2.11 2.17 2.29 2.50 2.59

decane

CH2I −1

mol·kg

0.374 0.772 1.166 1.517 1.946 0.374 0.772 1.166 1.517 1.946

KD

KD,pred

E

0.75 1.18 1.76 2.29 2.72 0.73 1.08 1.59 2.01 2.21

0.71 1.29 1.81 2.2 2.65 0.70 1.19 1.60 1.89 2.24

42.74 54.13 63.77 69.65 73.13 42.16 52.00 61.46 66.82 68.82

−1

Z

0.703 0.431 0.336 0.282 0.231 0.498 0.334 0.271 0.236 0.198

Table 5. Results for the Extraction of Itaconic Acid with TOA + Alcohol System

Table 3. Results for the Extraction of Itaconic Acid with TOA + Ester System solvents (ester)

pHaq

ethyl acetate

2.34 2.41 2.60 2.68 2.90 propyl acetate 2.34 2.40 2.59 2.68 2.87

C̅ R0 3N

C H2 I

mol·kg−1

mol·kg−1

0.374 0.772 1.166 1.517 1.946 0.374 0.772 1.166 1.517 1.946

0.329 0.254 0.197 0.144 0.083 0.337 0.264 0.204 0.144 0.098

KD

KD,pred

E

solvents (alcohol)

Z

0.72 1.69 2.70 3.64 4.61 0.70 1.59 2.49 3.3 4.18

46.45 58.68 67.93 76.59 86.53 45.27 57.02 66.83 76.64 84.12

octan-1-ol 0.764 0.467 0.358 0.311 0.273 0.744 0.454 0.353 0.311 0.266

nonan-1-ol

decan-1-ol

2K12[H 2I]C̅ 2R3N + (1 + K11[H 2I] + K 21[H 2I]2 )C̅ R3N − C̅ 0R3N = 0 (17)

This value of C̅ R3N was substituted in eq 15 to calculate the total acid concentration in the extract phase. The values of the individual equilibrium constants (K11, K21, and K12) were estimated based on the values of CH2I, and minimizing the error between the experimental and predicted values of C̅ H2I ∑1 (C̅ H2I,exp − C̅ H2I,pred)2 N−1

C̅ R0 3N

C H2 I

2.43 2.59 2.72 2.88 3.25 2.42 2.57 2.72 2.86 3.23 2.41 2.56 2.71 2.85 3.22

mol·kg 0.374 0.772 1.166 1.517 1.946 0.374 0.772 1.166 1.517 1.946 0.374 0.772 1.166 1.517 1.946

KD

KD,pred

E

Z

1.53 2.30 3.44 6.55 18.20 1.36 2.09 3.15 5.65 16.20 1.10 1.94 2.93 4.25 15.60

1.08 3.11 5.62 7.97 9.69 0.97 2.78 4.96 7.04 8.57 0.81 2.40 4.37 6.30 7.78

% 60.52 69.74 77.46 86.75 94.80 57.65 67.63 75.91 84.95 94.21 52.28 65.95 74.58 80.96 93.98

0.995 0.556 0.409 0.352 0.300 0.948 0.539 0.400 0.344 0.298 0.860 0.525 0.393 0.328 0.297

−1

mol·kg 0.243 0.186 0.139 0.081 0.032 0.260 0.199 0.148 0.093 0.036 0.293 0.209 0.156 0.117 0.037

the calculated values of the distribution coefficient (KD), degrees of extraction (% E), and loading ratio (Z). It can be seen from Figure 1 that the extraction power of the (TOA + diluent) mixture changes with increasing initial concentration of TOA in the organic phase. According to Tables 2 to 5 and Figure 2, the distribution coefficients of itaconic acid between aqueous and TOA + solvent phase had been obtained in the following orders in terms of maximum distribution coefficient (KD,max). Alcohols: octan-1-ol (KD,max = 18.2) > nonan-1-ol (KD,max = 16.2) > decan-1-ol (KD,max = 15.6)

N

rmsd =

pHaq

−1

% 0.87 1.42 2.12 3.27 6.42 0.83 1.33 2.02 3.28 5.30

RESULTS AND DISCUSSION

The reactive extraction of itaconic acid (0.615 mol·kg−1) using trioctylamine (0.374 mol·kg−1 to 1.946 mol·kg−1) from aqueous solution was performed by using nine different solvents. They were alkanes (octane and decane), ketones (heptanone and octanone), esters (ethyl acetate and propyl acetate), and alcohols (octan-1-ol, nonan-1-ol, and decan-1-ol). They were used to dilute the extractant and to give proper physical properties of the organic phase. The diluents have different polarity and also effect the distribution of acid between water (aqueous phase) and extractant−diluent (organic phase) in different ways. The results of the equilibrium experiments for the recovery of itaconic acid by using an aminic extractant, TOA (a tertiary amine) were presented in Tables 2 to 5 with

%

0.352 0.282 0.223 0.187 0.165 0.356 0.295 0.237 0.204 0.192

Article

(18)

where N is the number of data points.

Table 4. Results for the Extraction of Itaconic Acid with TOA + Ketone System solvents (ketone)

pHaq

C̅ R0 3N mol·kg

2-heptanone

2-octanone

2.39 2.50 2.68 2.81 3.19 2.37 2.48 2.64 2.75 3.10

C H2 I −1

0.374 0.772 1.166 1.517 1.946 0.374 0.772 1.166 1.517 1.946

mol·kg

KD

KD,pred

E

0.97 1.64 2.50 4.03 11.90 0.94 1.54 2.35 3.82 8.26

0.72 2.08 3.72 5.32 6.55 0.74 1.91 3.2 4.41 5.38

49.14 62.16 71.45 80.11 92.30 48.45 60.63 70.12 79.25 89.21

−1

0.313 0.233 0.176 0.122 0.047 0.317 0.242 0.184 0.128 0.066 1429

Z

% 0.808 0.495 0.377 0.325 0.292 0.797 0.483 0.370 0.321 0.282



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distribution of the acid compared to other solvents in the organic phase. Octan-1-ol was having low carbon number and promoted extraction of acid by providing a good solvation media for the acid−amine ion pair complex. The strength of attraction of the −OH group is higher in case of the first three alcohols (methanol, ethanol, and propanol) and, hence, they are completely miscible in water. They dissolve in water in any proportion. But with an increase in the carbon number the solubility of alcohols starts to decrease. The polarity (or polarizability) of octan-1-ol accounted for the better solubility of acid molecules in the organic phase and confirmed higher distribution coefficient (KD = 18.2) and removal efficiency (% E = 94.80%). The maximum values were observed at 1.946 mol·kg−1 of TOA concentration and at constant concentration of itaconic acid (0.615 mol·kg−1). The acid concentration in the organic phase increases with increasing concentration of TOA from 0.374 mol·kg−1 to 1.946 mol·kg−1. It was also seen from Tables 2 to 5 that the increase of TOA concentration brings about a gradual increase in the extraction efficiency. A maximum of 73.13%, 86.53%, 92.30%, and 94.80% of itaconic acid had been extracted in the vicinity of 1.946 mol·kg−1 of TOA concentration with octane, ethyl acetate, 2-heptanone, and octan-1-ol, respectively. Now, the values of KE and n were estimated using a graphical method. The plots between the values of log KD + log(1 + (Ka1/[H+])) and log[T̅ ]0 were drawn and shown in Figure 2a to d. The values of KE and n for individual solvents were presented in Table 6. The estimated values of m less than one for octane (0.84) and decane (0.74) confirmed the formation of 1:1 and 2:1 acid−TOA complexes in the extract phase. The values of m greater than one for all other solvents (1.49 for 2-heptanone, 1.32 for 2-octanone, 1.20 for ethyl acetate, 1.15 for propyl acetate, 1.50 for octan-1-ol, 1.48 for nonan-1-ol, and 1.53 for decan-1-ol) suggested that the TOA made both types of 1:1 and 1:2 solvates with itaconic acid molecules in the organic phase. The apparent value of equilibrium constant (KE) was found to be highest for octan-1-ol (KE = 4.989) > nonan-1-ol (KE = 4.416) > decan-1-ol (KE = 3.855) > 2-heptanone (KE = 3.273) > 2-octanone (KE = 2.864) > ethyl acetate (KE = 2.443) > propyl acetate (KE = 2.265). The values were in accordance with the observed values of KD and % E. The values of KD were predicted using model eq 9 and presented in Tables 2 to 4. The model prediction showed a good match with the experimental values having maximum SD = 0.2423. Therefore, with the assumption of 1:1, 1:2, and 2:1 complex formation in the organic phase, the values of the individual equilibrium constants (K11, K21, and K12) were determined by minimizing the error between experimental and predicted values of C̅ H2I using eq 18, and their values were presented in Table 6. The values of individual equilibrium constants (K11 = 11.732 and K12 = 6.501) were also found highest with octan-1-ol in TOA for the extraction of itaconic acid. The concentrations of itaconic acid−TOA complexes (C̅ 11,C̅ 21, and C̅ 12) in the organic phase at equilibrium and amount of amine used in the extraction were also determined using eqs 12, 13, 14, and 16 respectively, and their profiles were drawn in Figures 3a−d. Figure 3a, b, and c showed that the concentration of 1:1 types of complexes (C̅ 11) was increased with an increase in the TOA concentration up to 1.166 mol·kg−1 with 2-heptanone, ethyl acetate, and octan-1-ol and then decreased. This was because that the acid molecules were being extracted by TOA molecule by forming 1:2 solvates, which consumed more amine molecule per acid molecule in the

Figure 1. Plot of distribution coefficients KD against concentration of TOA. Symbols: ■, decane; ○, octane; *, propyl acetate; × , ethyl acetate; +, 2-octanone; ●, 2-heptanone; △, decan-1-ol; ▲, nonan-1-ol; □, octan-1-ol.

Ketones: 2-heptanone (KD,max = 11.9) > 2-octanone (KD,max = 8.26) Esters: ethyl acetate (KD,max = 6.42) > propyl acetate (KD,max = 5.3) Alkane: octane (KD,max = 2.72) > decane (KD,max = 2.21) Polarity of the solvent is the most critical factor which facilitates the solvation of acid−amine complex in the organic phase from the aqueous solution. Generally, the polar nature of solvent decreases with an increase in the number of carbons present in it. Similar kinds of trends were observed in the current study in the distribution coefficients, that is, with an increase in the carbon number, the values of KD were found to decrease. Alkanes used in the current study being nonpolar gave low solvation of the polar complexes and, hence, provided low 1430



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Figure 2. Determination of n and KE for itaconic acid reactive extraction by using TOA in (a) alkane, (b) ester, (c) ketone, and (d) alcohol. Symbols: ■, decane; ○, octane; *, propyl acetate; × , ethyl acetate; +, 2-octanone; ●, 2-heptanone; △, decan-1-ol; ▲, nonan-1-ol; □, octan-1-ol; −, linear fit lines.

Table 6. Values of Number of Amine Molecules, n, Reacting with One Acid Molecule, and Equilibrium Constants, KE, K11, K21, and K12, in Different TOA + Solvent Systems diluents

n

KE

R2

SD

K11

K21

octane decane 2-heptanone 2-octanone ethyl acetate propyl acetate octan-1-ol nonan-1-ol decan-1-ol

0.84 0.74 1.49 1.32 1.20 1.15 1.50 1.48 1.53

1.663 1.486 3.273 2.864 2.443 2.265 4.989 4.416 3.855

0.988 0.985 0.831 0.878 0.907 0.934 0.808 0.812 0.807

0.0303 0.0301 0.2177 0.1603 0.1243 0.1002 0.2372 0.2309 0.2423

0.549 0.289 6.845 4.640 3.276 2.723 11.732 9.989 9.098

3.533 2.619

organic phase. In case of octane, the trend found was almost linear and increasing. With octane, a lesser amount of amines

K12

rmsd

3.408 3.009 2.575 2.460 6.501 5.404 4.374

0.0278 0.0567 0.0707 0.0609 0.0606 0.0570 0.0823 0.0798 0.0861

were being spent for the extraction, as there were more formation of 2:1 solvates in the extract phase. Though, octane 1431



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Figure 3. Concentration profiles of acid−amine complex formation (a) C̅ 11, (b) C̅ 21, (c) C̅ 12, and (d) the percentage amine used at equilibrium of itaconic acid (0.615 mol·kg−1) with TOA (0.374 to 1.946 mol·kg−1) dissolved in different solvents. Symbols: ■, decane; ○, octane; *, propyl acetate; × , ethyl acetate; +, 2-octanone; ●, 2-heptanone; △, decan-1-ol; ▲, nonan-1-ol; □, octan-1-ol.

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CONCLUSIONS The extraction capacity of TOA in different solvents for the extraction of itaconic acid from aqueous solution had been investigated. The equilibrium experimental data were presented in terms of distribution coefficients, loading ratios, and extraction efficiency. The diluents with −OH group, the alcohols showed better synergism with TOA. The highest recovery was observed with octan-1-ol (KD = 18.20, % E = 94.80%). The values of equilibrium constant (overall and individual) and the number of extractant molecules per acid molecule were estimated using mass action law. In the extraction, the inactive diluents (octane and decane) with TOA extracted acid molecules by forming 1:1 and 2:1 acid−amine complex where with active diluents mainly by making 1:1 and 1:2 solvates. The values of KD are also predicted and compared with the experimental

gave lower extraction efficiency but may facilitate easy recovery of itaconic acid from the organic phase. Figure 3d showed the profiles of TOA consumption (i.e., the amount of unused amine) in the extraction process by individual solvents from each category. At lower concentration of TOA (0.374 mol·kg−1), the maximum amount of TOA molecules (octane = 37.53%, 2-heptanone = 69.35%, ethyl acetate = 56.35%, and octan-1-ol = 74.81%) was being used in the acid extraction process, but at higher side (TOA = 1.946 mol·kg−1) these values were 13.97% for octane, 35.05% for 2-heptanone, 39.65% for ethyl acetate, and 38.46% for octan-1-ol. This may be due to the fact that at higher TOA concentrations, the solvents became more active and provided good solvating medium for the acid−TOA complexes. 1432



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(17) Hong, Y. K.; Hong, W. H.; Chang, Y. C. Effect of pH on Extraction Characteristics of Succinic and Formic Acids with Tri-nOctylamine Dissolved in 1-Octanol. Biotechnol. Bioprocess Eng. 2001, 6, 347−351. (18) Ince, E.; Kirbaslar, S. I.; Sahin, S. Liquid−Liquid Equilibria for Ternary Systems of Water + Formic Acid + Dibasic Esters. J. Chem. Eng. Data 2007, 52, 1889−1893. (19) Keshav, A.; Wasewar, K. L.; Chand, S. Extraction of Propionic Acid using Different Extractants (Tri-n-Butylphosphate, Tri-n-Octylamine, and Aliquat 336). Ind. Eng. Chem. Res. 2008, 47, 6192−6196. (20) Sahin, S.; Bayazit, S. S.; Bilgin, M.; Inci, I. Investigation of Formic Acid Separation from Aqueous Solution by Reactive Extraction: Effects of Extractant and Diluent. J. Chem. Eng. Data 2010, 55, 1519−1522. (21) Tuyun, A. F.; Uslu, H.; Gokmen, S.; Yorulmaz, Y. Recovery of Picolinic Acid from Aqueous Streams Using a Tertiary Amine Extractant. J. Chem. Eng. Data 2011, 56, 2310−2315. (22) Datta, D.; Kumar, S. Reactive Extraction of Picolinic Acid Using Nontoxic Extractant and Diluent Systems. J. Chem. Eng. Data 2011, 59, 1540−1548. (23) Datta, D.; Kumar, S. Equilibrium and Kinetic Studies on Reactive Extraction of Nicotinic Acid with Tri-n-octylamine Dissolved in MIBK. Ind. Eng. Chem. Res. 2013, 52, 14680−14686. (24) Uslu, H. Reactive Extraction of Formic Acid by Using Tri Octyl Amine (TOA). Sep. Sc. Technol. 2009, 44, 1784−1798. (25) Uslu, H.; Inci, I. (Liquid + Liquid) Equilibria of the (Water + Propionic Acid + Aliquat 336 + Organic Solvents) at T 298.15. J. Chem. Thermodyn. 2007, 39, 804−809. (26) Uslu, H.; Bayat, C.; Gokmen, S.; Yorulmaz, Y. Reactive Extraction of Formic Acid by Amberlite LA-2 Extractant. J. Chem. Eng. Data 2009, 54, 48−53. (27) Vogel, H.; Starr, J. N.; King, C. J. Extraction of Carboxylic Acids from Aqueous Solutions with the Extractant System Alcohol/Tri-nAlkylamines. Chem. Eng. Technol. 2000, 23, 70−74. (28) Datta, D.; Kumar, S. Intensification of Recovery of Formic Acid from Aqueous Stream Using Reactive Extraction with N,NDioctyloctan-1-Amine: Effect of Diluent and Temperature. Chem. Eng. Commun. 2013, 200, 678−700. (29) Senol, A. Extraction Equilibria of Valeric Acid Using (Alamine 336/Diluent) and Conventional Solvent Systems. Modeling Considerations. Chem. Eng. Process. 2002, 41, 681−692. (30) Kumar, S.; Datta, D.; Babu, B. V. Experimental Data and Theoretical (Chemodel Using the Differential Evolution Approach and Linear Solvation Energy Relationship Model) Predictions on Reactive Extraction of Monocarboxylic Acids Using Tri-n-Octylamine. J. Chem. Eng. Data 2010, 55, 4290−4300.

values. The equilibrium data and the equations obtained in the present study will be helpful in designing an equilibrium extractor. The experimental results infer that the octan-1-ol is a suitable solvent and can be used with 1.946 mol·kg−1 of TOA for the efficient extraction of itaconic acid from a dilute aqueous solution.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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Experimental and Theoretical Investigations on the Reactive

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