Reactive Extraction of Picolinic Acid Using Tri-n ... - ACS Publications

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Reactive Extraction of Picolinic Acid Using Tri‑n‑octylamine Dissolved in Different Diluents: Effect of Solvent Polarity Dipaloy Datta† and Sushil Kumar*,‡ †

Department of Chemical Engineering, Malaviya National Institute of Technology (MNIT), Jaipur, Rajasthan India Department of Chemical Engineering, Motilal Nehru National Institute of Technology (MNNIT), Allahabad, Uttar Pradesh, India

Downloaded by FLORIDA ATLANTIC UNIV on August 30, 2015 | http://pubs.acs.org Publication Date (Web): August 7, 2015 | doi: 10.1021/acs.jced.5b00387

‡

ABSTRACT: Picolinic acid is a useful intermediate for the synthesis of different pharmaceuticals, herbicides, and metal salts which is applied in the food supplements. Due to the rapid rise in the costs of fossil resources, efforts are made to synthesize this carboxylic acid from the renewable feedstock like biomass. The recovery of picolinic acid can be achieved by reactive extraction which is catching the attention of the researchers. For higher selectivity and efficient recovery of acid with high distribution, a proper combination and selection of extractant−diluent system is required. Therefore, the current study is focused on the reactive extraction of picolinic acid [(0.01 to 0.10) mol·kg−1] from aqueous solution by using tri-n-octylamine [TOA, (0.115 to 0.459) mol· kg−1] as extractant dissolved in five different diluents (cyclohexane, chlorobenzene, dichloromethane, 4-methylpentan-2-one, and octan-1-ol). The extraction results are interpreted and analyzed defining three terms like distribution coefficient (KD), degree of extraction (%E), and loading ratio (Z). Highest value of the KD (16.64) is obtained with 0.459 mol·kg−1 of TOA in DCM at 0.10 mol·kg−1 of picolinic acid concentration. The solvent’s ability to extract acid with TOA is observed as DCM ≥ MIBK > chlorobenzene > octan-1-ol > cyclohexane. The number of TOA molecules (n) in the acid−TOA complex formed at equilibrium and equilibrium complexation constants (KE) are estimated by developing a mathematical model using mass action law and regressing the experimental results.

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INTRODUCTION Picolinic acid (pyridine-2-carboxylic acid) appears white in color and solid-crystalline in nature. This pyridine acid has two active groups: a carboxyl group (−COOH) and a pyridinic nitrogen atom (−N). Therefore, the aqueous solution of this acid is weakly acidic.1 Picolinic acid shows efficient chelating activity for metals like Cu, Fe, Ni, Zn, Cd, Pb, Mn, Cr, and Mo inside the human body.2 Due to the ability of chelate formation with metals, these bioactive complexes are extensively used in the biological organisms. Especially, chromium picolinate as food supplementation facilitates carbohydrate and lipid metabolism inside human body which controls type 2 diabetes.3 Picolinic acid can be produced by liquid-phase oxidation and heterogeneous catalytic oxidation of 2-picoline4,5 or by enzymatic oxidization of 3-hydroxyanthranilic acid.6 The chemical synthesis of this acid is not advantageous as it depends on nonrenewable resources, its environment unfriendly production processes, its toxic byproducts, and waste. Therefore, biosynthesis (fermentation) route could be preferred to produce carboxylic acid, but the major challenge lies on the downstream processing (recovery) of the product from a very dilute solution.7 Therefore, to achieve good yield and productivity in the biochemical synthesis of picolinic acid, it is needed to make recovery technique stronger. Several separation techniques have been used in the chemical industries to recover many organic acids from aqueous solutions.8,9 Among the methods available, the reactive extraction is found © XXXX American Chemical Society

to be a better recovery step in the fermentative production of carboxylic acid from a dilute aqueous solution.9−11 Conventional extractants like aliphatics, aromatics, ketones, alcohols, and so forth, have almost no ability to extract acids from their aqueous solutions as they provide low distribution coefficients (≪ 1).10,11 An economical and affordable recovery of the acid will be ensured when relatively a high distribution coefficient is achieved. Reactive extraction with an extractant (organophosphoric or aminic) has been attaining considerable attention of the researchers to solve this setback. In this process of extraction, a reaction takes place between solute or acid molecules and extractant molecules to form various acid− extractant complexes in the organic phase. These complexes gets dissolved into the organic phase by a suitable extractant− diluent system, and then the acid molecules are back-extracted to get the final product, i.e., acid. The extractant is usually diluted with an organic (conventional) solvent to achieve suitable physical properties such as viscosity, density, surface tension, and so forth of the organic phase.12 Extensive literature is available on the reactive extraction of different carboxylic acids from aqueous streams but limited on the picolinic acid recovery. Senol13 performed reactive extraction of picolinic acid from aqueous solution by using Received: May 5, 2015 Accepted: July 28, 2015

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DOI: 10.1021/acs.jced.5b00387 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Reagents Used in the Equilibrium Study specific gravity

viscosity

dipole moment C·m (× 1030)

s. no.

reagent name

supplier

purity, w

kg·mol−1

kg·m−3

mPa·s

1 2 3 4 5 6 7

picolinic acid N,N-dioctyloctan-1-amine (TOA) cyclohexane chlorobenzene dichloromethane (DCM) 4-methylpentan-2-one (MIBK) octan-1-ol

Himedia, India Fluka, USA S. D. Fine Chem Ltd., India RFCL, India Fisher Scientific, India Spectrochem, India Spectrochem, India

0.995 0.98 0.99 0.99 0.995 0.998 0.99

123.11 353.68 84.16 112.56 84.93 100.16 130.23

809 779 1106 1330 801 825

8.325a 0.98a 0.8a 0.406a 0.58b 8.925a

a


mol. wt

298 K. b293 K.

relative permittivity

14.74 0 5.14 5.34 9.314 5.74

2.02 5.62 8.93 13.1 10.3

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EXPERIMENTAL SECTION Reagents. The chemicals with their physical properties used in the present equilibrium study are listed in Table 1. Aqueous solution of sodium hydroxide (98 %; Merck, Germany) is used as a titrant and phenolphthalein solution (pH range of 8.2 to 10.0, CDH, India) as an indicator for titration. Ultra pure water (conductivity < 0.02 S·m−1 at 298 K, Millipore Milli-Q Water System, India) is utilized in the experiment to prepare the aqueous solutions of picolinic acid (in different concentrations) and sodium hydroxide. Procedure. The aqueous solutions of picolinic acid were prepared in the concentration ranges of (0.01 to 0.10) mol· kg−1. The organic extract phase were prepared by dissolving TOA [(0.115 to 0.459) mol·kg−1] in different diluents. Equal volumes (0.02 dm3) of organic and aqueous phases were placed in 0.1 dm3 of conical flask and equilibrated for 8 h at 298 ± 1 K in a constant temperature water shaker bath (Remi Laboratories, HS 250, India). After reaching equilibrium, the phases were allowed to settle for 2 h to have a clear separation of the phases. The aqueous phase is sampled by a pipet. This aqueous solution was titrated with freshly prepared NaOH solution of 0.008 N to determine the picolinic acid concentration in the aqueous phase at equilibrium. Acid concentration in the organic phase is calculated by a mass balance. The initial and equilibrium pH values of aqueous solutions were noted using a digital pH-meter (ArmField Instruments, PCT-40, UK) with ± 0.01 uncertainty in the pH measurement. This uncertainty for concentration measurement was found to be within ± 1 %. The uncertainty in the experimental results was found to be within ± 5 % error.

Alamine 336 as an extractant dissolved in various diluents. The equilibrium data were interpreted by calculating distribution ratio (KD), degree of extraction (%E), overall (total) loading factor (Zt), stoichiometric loading factor (Zs), and modified separation factor (sf). A maximum KD of 1.948 was obtained with Alamine 336 in cyclopentanol. Tuyun and Uslu14 extracted picolinic acid by tridodecylamine dissolved in acetates (ethyl acetate and propyl acetate), alcohols (1-octanol and 1-decanol), and ketones (2-heptanone and 2-octanone). Alamine 336 in 1octanol showed a maximum KD of 4.121. The same group reported results on the reactive extraction of picolinic acid using TOA dissolved in various diluents such as n-octane, ndecane, octan-1-ol, decan-1-ol, diisobutyl ketone, and 2octanone.15 The highest synergistic extraction efficiency was found to be 89.2% (KD = 8.26) with the TOA + isoamyl alcohol extractant system. In another study by Waghmare et al.,16 picolinic acid was recovered by using TBP in nontoxic diluents (sunflower oil and castor oil). With sunflower oil and castor oil, the maximum values of KD were found to be 0.65 (E = 42.9%) and 0.9 (E = 74.6%), respectively, using the phosphorus-based extractant, TBP. This shows a greater scope to study and investigate the equilibrium distribution of picolinic acid between aqueous and organic phase by various diluent systems comprising tri-n-octylamine (TOA) as an extractant. The objective of the present study is to investigate the reactive extraction of picolinic acid from dilute aqueous solutions by using trin-octylamine (N,N-dioctyloctan-1-amine, TOA) as an extractant dissolved in different categories of organic solvents (aliphatic hydrocarbon, chlorinated hydrocarbon, ketone, aromatic, and alcohol) and to get the extraction data at equilibrium for the process intensification of the recovery of picolinic acid production through an enzymatic path. The solvents like cyclohexane, chlorobenzene, dichloromethane (DCM), 4-methylpentan-2-one (MIBK), and octan-1ol are used with (reactive or chemical extraction) and without (physical extraction) TOA to investigate their solvation ability and to improve the extractive efficiency of TOA. Also, the effects of diluent polarity, initial acid concentration, and composition of extractant (TOA) on the distribution of acid are deliberated. Mass action law is applied to derive an equilibrium model, and this developed model is used to determine the equilibrium extraction constants (KE) and the number of extractant molecules per acid molecule (n) by using two methods (i) a graphical method and (ii) an optimization procedure.

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THEORETICAL SECTION The reaction at equilibrium can be described for the extraction of a carboxylic acid with a tertiary amine dissolved in an organic solvent by the mass action law and proposed by Kertes and King (1986).10 The undissociated part of a carboxylic acid molecule present in the aqueous solution reacts with the tertiary amine molecule and can only be extracted by an suitable solvent. There are three steps in which a acid molecule is been extracted by an amine molecule: (i) partial dissociation of the acid molecule in the aqueous phase (HC), eq 1; (ii) distribution of the undissociated acid molecules between aqueous and organic phase, eq 2; and (iii) complex formation reaction between a acid molecule and n-tertiary amine (T) molecules in the organic phase, eq 3. HC ↔ H+ + C− B

(1) DOI: 10.1021/acs.jced.5b00387 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


Article

HC ↔ HC

(2)

HC + nT̅ ↔ (HC)(T)n

(3)

distribution coefficient about 0.301 for cyclohexane, 0.27 for chlorobenzene, 0.534 for dichloromethane, 0.334 for MIBK, and 0.867 for octan-1-ol as given in Table 2. These diluents

The equilibrium complexation constant (KE) can be estimated by using eq 4, and the experimental values of distribution coefficients are calculated by using eq 5. [(HC)(T)n ] [HC][T]̅ n

KE =


KD =

Table 2. Values of Partition (P) and Dimerization (D) Coefficients, Distribution Coefficient (Kdiluent ), and Degree D of Extraction (% Ediluent) for Picolinic Acid in Physical Extraction at 298 ± 1 K

(4)

[HC] [HC]

(5)

The acid concentration in the undissociated form in the aqueous phase is crucial as it is the only chemical species that can react with the amine molecule in the organic phase. The undissociated acid concentration be calculated with the Henderson−Hasselbach eq 6 from the known value of pH and total initial acid concentration in the aqueous phase. ⎛ [C−] ⎞ pH = pK a + log⎜ ⎟ ⎝ [HC] ⎠

(6)

[HC] [T]̅ o

(7)

Using eqs 4, 5, and 6, the following relation is obtained. KD =

KE[T̅ ]n

(1 +

Ka [H+]

)

D

range of Kdiluent D

range of % Ediluent

cyclohexane chlorobenzene DCM MIBK octan-1-ol

0.115 0.043 0.313 0.158 0.200

24.19 739.48 16.38 36.79 80.34

0.122−0.301 0.089−0.270 0.351−0.534 0.172−0.334 0.270−0.867

10.88−23.14 8.20−21.25 25.99−34.80 14.70−25.03 21.21−46.45

KDdiluent = P + 2DP 2[HC] (8)

(12)

Equation 12 was fitted linearly to the experimental values (Figure 1) to get the values of P from the intercept and D, from the slope. The values of P for picolinic acid in chlorobenzene, cyclohexane, MIBK, octan-1-ol, and DCM were found to be 0.043, 0.115, 0.158, 0.2, and 0.313, respectively.

Taking logarithm on both sides of eq 8, a linear expression is obtained (eq 9). ⎛ Ka ⎞ log KD + log⎜1 + ⎟ = log KE + n log[T]̅ ⎝ [H+] ⎠

P

(conventional) do not meet the standards of an ideal extractant and do not fulfill the requirements of higher distribution of acid. The reason may be the extent of dissociation and hydrophilicity of picolinic acid (pKa = 5.29; dipole moment, μ = 14.74·10−30 Cm; log P = −0.97) which affect the extraction capability of diluent and lead to the poor recovery of acid. Thus, to achieve a better recovery of acid in terms of high distribution coefficient and high selectivity, there is a requirement of an extractant which will contribute in the enhancement of extraction efficiency of reactive extraction. The physical extraction parameters (partition coefficient, P and dimerization constant, D) are estimated by using eq 12 for dilute concentration of acid in the aqueous phase and fitting the experimental data linearly between Kdiluent and [HC]. The D complete derivation of this equation can be found in ref 10.

The relative excess of the extractant may be quantified by the term loading ratio (Z) and given by eq 7. A plot of the Z against the concentration of acid or amine gives an estimate of the stoichiometry and the types of complexes formed in the organic phase during the reactive extraction of the acid. Z=

diluent

(9)

The remaining amount of TOA ([T̅ ]) in the organic phase can be represented as [T]̅ = [T]̅ 0 − n[(HC)(T)n ]

(10)

Substituting the value of [T̅ ] from eq 10 into eq 9, eq 11 is derived. ⎛ Ka ⎞ log KD + log⎜1 + ⎟ ⎝ [H+] ⎠ = log KE + n log([T]̅ 0 − n[(HC)(T)n ])

(11)

This eq 11 can be solved to estimate the parameters (n and KE) considering two approaches: (i) a graphical method with an assumption that [T̅ ]0 ≫ n[(HC)(T)n], i.e., initial extractant concentration is higher than the complex concentration at equilibrium; and (ii) an optimization procedure due to the apparition of n under logarithm.

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RESULTS AND DISCUSSION Physical Extraction. The solubility of picolinic acid in pure diluents alone is remarkably small with a maximum value of

Figure 1. Determination of P and D for the physical extraction of picolinic acid using different diluents. Symbols: + , cyclohexane; △, chlorobenzene; *, MIBK; ■, DCM; □, octan-1-ol; −, linear fit lines. C




Article

constant TOA concentration. With an increase in the picolinic acid concentration from (0.01 to 0.1) mol·kg−1, the distribution coefficients were found to be increased for cyclohexane, DCM and MIBK, and to be deceased for chlorobenzene and octan-1ol with TOA. The polarity of solvent is a vital factor that controls the distribution, and the performance of the reactive extraction process has a direct correlation with the polarity of the solvent. In the reaction, through dipole−dipole interaction or H-bonding, there forms ion pairs which are polar in nature. The main role of these diluents is to solvate these polar ion-pair into the organic phase by favoring the formation of one or simultaneously at least two acid-amine complexes. Therefore, the diluents not only improve the physical properties of organic phase consisting amine extractant but also enhance the solvation efficiency of the acid-extractant complex. Here in the current study, two types of diluents from active (DCM, MIBK, chlorobenzene, and octan-1-ol) and inactive (cyclohexane) category were used. DCM (μ = 5.34·10−30 Cm; ε = 8.93) and chlorobenzene (μ = 5.14·10−30 Cm; ε = 5.62) both have a chlorinated (both proton acceptor and donor) group. Octan-1-ol [dipole moment, μ = 5.74·10−30 Cm; dielectric constant, ε = 10.3] is having − OH, a proton donor group, and MIBK (μ = 9.314·10−30 Cm; ε = 13.1) a = CO (proton acceptor) group. The presence of these active groups in the solvent is responsible for improving the extracting capability of an extractant used. Cyclohexane (μ = 0; ε = 2.02) being an inactive or nonpolar diluent does not contribute much in the extraction process. The solvation ability of diluents are found (in terms of KD) to be in the order of: DCM ≥ MIBK > chlorobenzene > octan-1-ol > cyclohexane. Among these diluents, DCM showed a higher extraction efficiency with TOA. This is because of the DCM affects the diluent−complex aggregation more instantaneously through hydrogen bonding and ion pair formation than the diluent−acid association in the absence of extractant. The maximum removal of picolinic acid (0.1 mol·dm−3) was 94.33 % with TOA (0.456 mol·kg−1) in DCM. Therefore, DCM with TOA can be a better extractive

Figure 2. Physical equilibria for extraction of picolinic acid at 298 ± 1 K. Symbols: +, cyclohexane; △, chlorobenzene; *, MIBK; ■, DCM; □, octan-1-ol.

Chemical Extraction. It was observed that the physical extraction of picolinic acid only with organic solvents was not suitable for the efficient recovery of this acid. The hydrophilic nature of picolinic acid (dipole moment, μ = 14.74·10−30 Cm; log P = −0.97) makes it poorly extractable by common organic solvents. Hence, there was a need to use an extractant to enhance the extraction efficiency of this acid. Therefore, the recovery of picolinic acid were also carried out with TOA [(0.115 to 0.459) mol·kg−1] dissolved in different diluents and taking five different initial concentrations of the acid [(0.01 to 0.1) mol·kg−1]. The equilibrium results are presented in Tables 3 to 7. An improvement in the extraction efficiency in terms of KD was observed when TOA was used with diluents as compared to that of pure diluent alone. Initial acid concentration has an effect on the extraction efficiency at

Table 3. Equilibrium Results for the Extraction of Picolinic Acid Using TOA Dissolved in Cyclohexane at 298 ± 1 K Cin mol·kg

Caq

[T]0 −1

0.010

0.025

0.050

0.075

0.100

mol·kg

−1

0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459

mol·kg

Corg −1

0.0067 0.0061 0.0057 0.0054 0.0172 0.0164 0.0161 0.0157 0.0404 0.0351 0.0294 0.0238 0.0555 0.0478 0.0432 0.0394 0.0539 0.0476 0.0471 0.0466

mol·kg−1

KD

Kmodel eq11 D

%E

Z

pHeq

0.0033 0.0039 0.0043 0.0046 0.0078 0.0086 0.0089 0.0093 0.0096 0.0149 0.0206 0.0262 0.0195 0.0272 0.0318 0.0356 0.0461 0.0524 0.0529 0.0534

0.493 0.639 0.754 0.852 0.453 0.524 0.553 0.592 0.238 0.425 0.701 1.101 0.351 0.569 0.736 0.904 0.855 1.101 1.123 1.146

0.483 0.642 0.759 0.853 0.453 0.518 0.560 0.592 0.178 0.442 0.744 1.073 0.352 0.565 0.743 0.900 0.898 1.031 1.117 1.182

33.06 38.80 42.63 46.45 31.15 34.21 35.74 37.27 19.22 29.79 41.11 52.44 26.05 36.25 42.37 47.47 46.14 52.44 52.91 53.38

0.029 0.017 0.013 0.010 0.068 0.038 0.026 0.020 0.084 0.065 0.060 0.057 0.170 0.119 0.092 0.078 0.402 0.229 0.154 0.116

3.74 3.76 3.77 3.79 3.53 3.54 3.55 3.55 3.34 3.37 3.41 3.46 3.27 3.31 3.33 3.35 3.28 3.31 3.31 3.31

D



Article

Table 4. Equilibrium Results for the Extraction of Picolinic Acid Using TOA Dissolved in Chlorobenzene at 298 ± 1 K Cin

[T]0

Caq

Corg

mol·kg−1

mol·kg−1

mol·kg−1

mol·kg−1

KD

Kmodel eq11 D

%E

Z

pHeq

0.010

0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459

0.0028 0.0023 0.0020 0.0017 0.0073 0.0065 0.0054 0.0046 0.0438 0.0385 0.0347 0.0313 0.0634 0.0589 0.0532 0.0476 0.0712 0.0662 0.0621 0.0583

0.0072 0.0077 0.0080 0.0083 0.0177 0.0185 0.0196 0.0204 0.0062 0.0115 0.0153 0.0187 0.0116 0.0161 0.0218 0.0274 0.0288 0.0338 0.0379 0.0417

2.571 3.348 4.000 4.882 2.425 2.846 3.630 4.435 0.142 0.299 0.441 0.597 0.183 0.273 0.410 0.576 0.404 0.511 0.610 0.715

2.527 3.457 4.137 4.696 2.230 3.112 3.755 4.287 0.145 0.293 0.443 0.595 0.152 0.294 0.429 0.559 0.391 0.526 0.623 0.702

72.46 77.05 80.11 82.79 70.93 73.99 78.58 81.64 12.42 22.99 30.54 37.34 15.44 21.48 29.03 36.58 28.81 33.85 37.95 41.73

0.063 0.034 0.023 0.018 0.154 0.081 0.057 0.044 0.054 0.050 0.044 0.041 0.101 0.070 0.063 0.060 0.251 0.147 0.110 0.091

3.93 3.97 4.01 4.04 3.72 3.74 3.79 3.82 3.33 3.35 3.38 3.40 3.25 3.26 3.28 3.31 3.22 3.24 3.25 3.26

0.025

0.050


0.075

0.100

Table 5. Equilibrium Results for the Extraction of Picolinic Acid Using TOA Dissolved in Dichloromethane at 298 ± 1 K Cin mol·kg

Caq

[T]0 −1

0.010

0.025

0.050

0.075

0.100

mol·kg

−1

0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459

mol·kg

Corg −1

0.0055 0.0042 0.0038 0.0034 0.0145 0.0111 0.0103 0.0096 0.0302 0.0106 0.0083 0.006 0.0472 0.0170 0.0132 0.0098 0.0309 0.0106 0.0079 0.0057

mol·kg−1

KD

Kmodel eq11 D

%E

Z

pHeq

0.0045 0.0058 0.0062 0.0066 0.0105 0.0139 0.0147 0.0154 0.0198 0.0394 0.0417 0.0440 0.0278 0.0580 0.0618 0.0652 0.0691 0.0894 0.0921 0.0943

0.818 1.381 1.632 1.941 0.724 1.252 1.427 1.604 0.656 3.717 5.024 7.333 0.589 3.412 4.682 6.653 2.236 8.434 11.658 16.544

0.849 1.294 1.657 1.970 0.797 1.147 1.421 1.651 1.406 3.035 5.145 7.334 1.358 2.768 4.722 6.720 3.023 7.454 12.167 16.612

44.54 57.93 61.75 66.34 41.86 55.63 58.69 61.75 39.60 78.86 83.39 87.92 37.08 77.35 82.38 86.91 69.13 89.45 92.13 94.33

0.039 0.025 0.018 0.014 0.092 0.061 0.043 0.034 0.173 0.172 0.121 0.096 0.242 0.253 0.180 0.142 0.603 0.390 0.268 0.206

3.78 3.84 3.86 3.89 3.57 3.63 3.64 3.66 3.41 3.64 3.69 3.76 3.31 3.53 3.59 3.65 3.40 3.64 3.70 3.77

two above reactions shown in eq 13 and eq 14 are dependent on the pH and the pKa of acid, the acid and extractant concentration, and the basicity of the extractant with respect to the acid. TOA extracts acids by following both mechanisms. The pH of the aqueous solution shows a considerable influence on the distribution of acid and complex formation reaction. When TOA extracts acid, the maximum ionization of pyridine group in acid takes place at strong acidic pH domain (pKa1 = 1.01) which inhibits the extraction efficiency. Further, an increase in pH induces dissociation of the −COOH group (pKa2 = 5.29), which also reduces the extraction efficiency. Thus, as the result of the two contrary effects generated by the change of pH, an optimum pH of aqueous solution should lie

system for the recovery of picolinic acid from dilute aqueous solution. The interfacial interactions between the picolinic acid molecule and the TOA molecule could be of two types: (i) one through H-bonding of undissociated acid molecule as given by eq 13, and (ii) second is by ion pair formation as given by eq 14. HC + T̅ ↔ (HC)(T)

(13)

H+ + C− + T̅ ↔ H+C−T

(14)

where HC, H+, and C− represent the undissociated picolinic acid, hydrogen ion and dissociated acid ion, respectively. These E



Article

Table 6. Equilibrium Results for the Extraction of Picolinic Acid Using TOA Dissolved in 4-Methyl-2-pentanone at 298 ± 1 K Cin

[T]0

Caq

Corg

mol·kg−1

mol·kg−1

mol·kg−1

mol·kg−1

KD

Kmodel eq11 D

%E

Z

pHeq

0.010

0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459

0.0065 0.0051 0.0046 0.0042 0.0168 0.0134 0.0122 0.0111 0.0117 0.0102 0.0098 0.0094 0.0181 0.0159 0.0155 0.0147 0.0107 0.0095 0.0079 0.0069

0.0035 0.0049 0.0054 0.0058 0.0082 0.0116 0.0128 0.0139 0.0383 0.0398 0.0402 0.0406 0.0569 0.0591 0.0595 0.0603 0.0893 0.0905 0.0921 0.0931

0.538 0.961 1.174 1.381 0.488 0.866 1.049 1.252 3.274 3.902 4.102 4.319 3.144 3.717 3.839 4.102 8.346 9.526 11.658 13.493

0.581 0.902 1.167 1.400 0.523 0.813 1.053 1.264 3.328 3.801 4.107 4.335 3.186 3.622 3.899 4.103 7.887 10.284 11.831 13.025

34.98 48.75 54.10 57.93 32.68 46.45 51.04 55.63 76.60 79.62 80.37 81.13 75.84 78.86 79.36 80.37 89.29 90.55 92.13 93.07

0.031 0.021 0.016 0.013 0.072 0.051 0.037 0.030 0.334 0.174 0.117 0.089 0.496 0.258 0.173 0.131 0.779 0.395 0.268 0.203

3.74 3.80 3.82 3.84 3.54 3.59 3.61 3.63 3.62 3.65 3.65 3.66 3.52 3.55 3.55 3.57 3.64 3.66 3.70 3.73

0.025

0.050


0.075

0.100

Table 7. Equilibrium Results for the Extraction of Picolinic Acid Using TOA Dissolved in Octan-1-ol at 298 ± 1 K Cin mol·kg

Caq

[T]0 −1

0.010

0.025

0.050

0.075

0.100

mol·kg

−1

0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459 0.115 0.229 0.344 0.459

mol·kg

Corg −1

0.0042 0.0030 0.0024 0.0019 0.0111 0.0077 0.0065 0.0054 0.0359 0.0310 0.0298 0.0291 0.0544 0.0472 0.0453 0.0442 0.0674 0.0655 0.0650 0.0646

mol·kg−1

KD

Kmodel eq11 D

%E

Z

pHeq

0.0058 0.0070 0.0076 0.0081 0.0139 0.0173 0.0185 0.0196 0.0141 0.0190 0.0202 0.0209 0.0206 0.0278 0.0297 0.0308 0.0326 0.0345 0.0350 0.0354

1.381 2.333 3.167 4.263 1.252 2.247 2.846 3.630 0.393 0.613 0.678 0.718 0.379 0.589 0.656 0.697 0.484 0.527 0.538 0.548

1.325 2.362 3.304 4.173 1.288 2.173 2.943 3.634 0.430 0.566 0.666 0.746 0.412 0.546 0.643 0.722 0.487 0.519 0.538 0.552

57.93 70.17 76.29 80.88 55.63 69.40 74.00 78.58 28.28 38.09 40.36 41.87 27.52 37.08 39.60 41.11 32.60 34.48 34.95 35.43

0.051 0.031 0.022 0.018 0.121 0.075 0.054 0.043 0.123 0.083 0.059 0.046 0.180 0.121 0.086 0.067 0.284 0.150 0.102 0.077

3.84 3.92 3.96 4.02 3.63 3.71 3.74 3.79 3.37 3.40 3.41 3.42 3.28 3.31 3.32 3.32 3.23 3.24 3.24 3.24

in between the pKa’s of the acid with TOA. In this work, the values of equilibrium pH (3.22 to 4.04) were observed in between the pKa’s of the acid. Therefore, the first and second dissociation of acid could be neglected, and it could also be assumed that only undissociated acid molecules transfer from the aqueous to the organic phase. The estimation of the equilibrium parameters (n and KE) were obtained by two approaches: (i) in the graphical method and with an assumption of [T̅ ]0 ≫ n[(HC)(T)n], the plots between log[KD·(1 + 10 pH − pKa)] and log[T̅ ]0 were drawn and best fitted to determine log KE from the intercept, and n from the slope. The obtained results are presented in Table 8 for different solvents and initial concentration of acid; (ii) in

the second approach an error function was defined (root-meanmodel 2 square deviation, rmsd = [(∑(Kexp ) )/(N − 1)]1/2) to D − KD minimize the difference between experimental and predicted values of KD. The estimated values of KE and n by eq 11 are listed in Table 8 with rmsd. These values of KE and n were used to calculate the values of KD. The different values of KE and n for the same acid in different diluents indicated different solvation ability of the diluent and various associations between acid and amine molecules which could be critical factors in the reactive extraction of the picolinic acid. The higher value of KE (39.23) was found for DCM with TOA which also showed that DCM is better solvating agent for acid. So, DCM with TOA F



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Table 8. Values of Equilibrium Constants (KE) and Number of Reacting Extractant Molecules (n) per Acid Molecule with TOA in Different Diluents at 298 ± 1 K Cin diluent cyclohexane

chlorobenzene


DCM

MIBK

octan-1-ol

optimization KE

n

rmsd

KE

n

R2

0.010 0.025 0.050 0.075 0.100 0.010 0.025 0.050 0.075 0.100 0.010 0.025 0.050 0.075 0.100 0.010 0.025 0.050 0.075 0.100 0.010 0.025 0.050 0.075 0.100

1.21 0.69 3.15 1.54 1.38 6.64 6.17 1.36 1.20 0.97 3.16 2.49 19.78 18.13 39.23 2.30 2.08 5.02 4.72 16.98 7.95 6.50 1.02 1.00 0.59

0.41 0.19 1.26 0.65 0.19 0.44 0.45 1.01 0.91 0.40 0.60 0.52 1.11 1.05 0.88 0.63 0.63 0.19 0.17 0.31 0.81 0.72 0.39 0.39 0.10

0.0147 0.0028 0.0474 0.0052 0.0521 0.1202 0.2193 0.0044 0.0262 0.0156 0.0595 0.0786 0.5935 0.5804 0.7889 0.0406 0.0391 0.0707 0.0745 0.5317 0.0626 0.0828 0.0385 0.0350 0.0053

1.20 0.70 2.37 1.54 1.42 6.89 6.08 1.35 1.02 0.97 3.42 2.72 33.87 31.42 57.9 2.52 2.24 5.18 4.85 17.43 8.20 6.86 1.09 1.05 0.60

0.40 0.19 1.09 0.68 0.21 0.43 0.43 1.03 0.82 0.41 0.64 0.58 1.73 1.75 1.45 0.68 0.68 0.20 0.19 0.35 0.81 0.77 0.44 0.45 0.09

0.993 0.998 0.979 0.999 0.862 0.985 0.931 0.999 0.972 0.989 0.985 0.960 0.944 0.943 0.969 0.987 0.985 0.973 0.965 0.951 0.998 0.994 0.938 0.945 0.966

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can be successfully applied for the extraction of picolinic acid from dilute aqueous solution as well as a fermentation medium.

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REFERENCES

(1) Tuyun, A. F.; Uslu, H. Extraction Equilibria of Picolinic Acid from Aqueous Solution by Tridodecylamine (TDA). Desalination 2011, 268, 134−140. (2) Suzuki, K.; Yasuda, M.; Yamasaki, K. Stability Constants of Picolinic and Quinaldic Acid Chelates of Bivalent Metals. J. Phys. Chem. 1957, 61, 229−231. (3) Broadhurst, C. L.; Domenico, P. Clinical Studies on Chromium Picolinate Supplementation in Diabetes Mellitus - A Review. Diabetes Technol. Ther. 2006, 8, 677−687. (4) Chumakov, Y. I. Pyridine Bases (in Russian); Tekhnika Press: Kiev, 1965. (5) Alkaeva, E. M.; Andrushkevich, T. V.; Zenkovets, G. A.; Babushkin, D. E. Studies on the Conditions of Synthesis of Picolinic Acid by Heterogeneous Catalytic Oxidation of 2-Picoline. Catal. Lett. 1998, 54, 149−152. (6) Smith, A. J.; Stone, T. W.; Smith, R. A. Neurotoxicity of Tryptophan Metabolites. Biochem. Soc. Trans. 2007, 35, 1287−1289. (7) Kenealy, W. R.; Cao, Y.; Weimer, P. J. Production of Caproic Acid by Cocultures of Ruminal Cellulolytic Bacteria and Clostridium Kluyveri Grown on Cellulose and Ethanol. Appl. Microbiol. Biotechnol. 1995, 44, 507. (8) Cascaval, D.; Oniscu, C.; Dumitru, I. F.; Galaction, A. I. New Separation Techniques in Biotechnology. Roum. Biotechnol. Lett. 2001, 6, 207−232. (9) Wasewar, K. L. Separation of Lactic Acid: Recent Advances. Chem. Biochem. Eng. Q. 2005, 19, 159−172. (10) Kertes, A. S.; King, C. Extraction Chemistry of Fermentation Product Carboxylic Acids. Biotechnol. Bioeng. 1986, 28, 269−282. (11) Datta, D.; Kumar, S. Reactive Extraction of Glycolic Acid Using Tri-n-Butyl Phosphate and Tri-n-Octylamine in Six Different Diluents: Experimental Data and Theoretical Predictions. Ind. Eng. Chem. Res. 2011, 50, 3041−3048.

CONCLUSIONS Intensification of the recovery of picolinic acid using reactive extraction with tri-n-octylamine (TOA) as an extractant dissolved in five different diluents like DCM, MIBK, chlorobenzene, octan-1-ol, and cyclohexane is studied extensively in this paper. In the physical extraction of acid lower values of distribution coefficients (Kdiluent ≪ 1) are observed. D The maximum values of KD and %E for reactive extraction of picolinic acid are found to be 16.64 % and 94.33 %, with TOA (0.459 mol·kg−1) in DCM at 0.10 mol·kg−1 initial acid concentration. The equilibrium parameters such as number of TOA molecules (n) in the acid−TOA complex formed at equilibrium, and equilibrium complexation constants (KE) are determined by graphical as well as using optimization method. The data obtained and the correlations established in this study will be useful in designing a continuous extraction system.

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graphical method

mol·kg−1

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Authors would like to thank the Department of Chemical Engineering, Birla Institute of Technology & Science, Pilani, Rajasthan, India to provide the necessary laboratory and infrastructure facility to carry out the experiments. G



Article


(12) 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. (13) Senol, A. Influence of conventional diluents on amine extraction of picolinic acid. Sep. Purif. Technol. 2005, 43, 49−57. (14) Tuyun, A. F.; Uslu, H. Extraction Equilibria of Picolinic Acid from Aqueous Solution by Tridodecylamine (TDA). Desalination 2011, 268, 134−140. (15) Tuyun, A. F.; Uslu, H. Investigation of Picolinic Acid Extraction by Trioctylamine. Int. J. Chem. React. Eng. 2011, 9, A29. (16) Waghmare, M. D.; Wasewar, K. L.; Sonawane, S. S.; Shende, D. Z. Natural Nontoxic Solvents for Recovery of Picolinic Acid by Reactive Extraction. Ind. Eng. Chem. Res. 2011, 50, 13526−13537.

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