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APPLIED CHEMISTRY Specific Influence of the Modifier (1-Decanol) on the Extraction of Tartaric Acid by Different Extractants Mariya Marinova,† Joe1 l Albet,‡ Jacques Molinier,‡ and George Kyuchoukov*,† Institute of Chemical Engineering, Bulgarian Academy of Sciences, Academician George Bonchev Street, Building 103, 1113 Sofia, Bulgaria, and Equipe Ge´ nie Chimique, Laboratoire de Chimie Agro-Industrielle UMR 1010 INRA, Ecole National Superieure des Ingenieurs en Arts Chimques et Technologiques, Institut National Polytechnique de Toulouse, 118, Route de Narbonne 31077 Toulouse, France
The effect of the modifier 1-decanol on the extraction of tartaric acid by the extractants tri-noctylamine (TOA), quaternary ammonium chloride (Aliquat 336), or their mixture in the diluent n-dodecane was studied at different pH values. The effect of the modifier was examined as a function of the initial pH value of the aqueous solution for the three extractants mentioned above. A positive, negative, or no effect of the modifier on the distribution coefficient of tartaric acid was observed in the different cases. Introduction There are a significant amount of data on the extraction of carboxylic acids in the literature. Various aspects have been considered, such as the influence of the type and concentration of extractant,1-15 the nature of the diluent,4,5,7,8,11,16-18 the composition of the aqueous phase,3,5-7,10,12,15,17,19-21 the effect of pH,1-3,6-8,20-23 and the effect of temperature.1,2,4,13,15,24,25 Tertiary amines and quaternary ammonium salts have been found to be efficient extractants for carboxylic acid recovery.1-4,6-8,10,19,20 Usually, they have been dissolved in inert diluents in order to improve the physical properties of the organic phase, and/or active diluents (modifiers) to prevent third phase formation and to improve the extraction. The use of binary diluents composed of an active and an inert diluent has been reported. Poposka et al.9 have studied the equilibrium and the kinetics of tartaric acid extraction with Hostarex A324 (commercial triisooctylamine) dissolved in isodecyl alcohol/kerosene mixtures as a function of acid, amine, and modifier concentrations. The increase in the isodecyl alcohol fraction in the solvent enhances the extraction mainly in the case of lower acid concentrations in the aqueous phase. A solvent composed of tri-n-octylamine (TOA) as an extractant, 1-decanol as a modifier, and n-dodecane as an inert diluent has been used by Marinova et al.10 to recover tartaric and lactic acids from their individual solutions and from their mixture. The influence of modifier concentration on the distribution coefficient of the acids has been studied. Depending on the organic phase composition, it has been possible to achieve a high extraction extent of both acids or to * To whom correspondence should be addressed. Tel.: +(359)(2) 720230. Fax: +(359)(2) 8707523. E-mail:
[email protected]. † Bulgarian Academy of Sciences. ‡ Institut National Polytechnique de Toulouse.
selectively extract tartaric acid. Yankov et al.11 have reported the recovery of lactic acid from aqueous solutions and simulated fermentation broth by TOA dissolved in a binary diluent. Various inert diluents and modifiers have been tested. As less toxic for the bacteria producing lactic acid, decanol has been selected as a modifier and n-dodecane as an inert diluent. A detailed study of the effect of the organic phase composition on the distribution coefficient of lactic acid has been carried out. The extraction of five monocarboxylic acids by TOA dissolved in 1-decanol and n-dodecane has been studied by Flores-Morales et al.12 The influence of inert and active diluent concentrations on the equilibrium extraction constant and the number of reacting extractant molecules in the case of formic, acetic, lactic, propionic, and butyric acids has been investigated. Prochazka et al. have studied the extraction of three hydroxycarboxylic acids, lactic, malic, and citric acids, with trialkylamine (TAA) in 1-octanol/n-heptane mixtures,15 and then the extraction of citric acid with the same extractant in a binary diluent consisting of chloroform or methyl isobutyl ketone (MIBK) in n-heptane.16 Recently, these authors have explored the extraction equilibria of dicarboxylic acids, oxalic, succinic, malic, and tartaric acids, with solutions of TAA in 1-octanol, MIBK, or chloroform or in their binary mixtures with n-heptane.17 In their studies, different mathematical models for correlating the experimental data have been proposed. Malmary et al.18 have investigated the extraction of some carboxylic acids, aconitic, citric, lactic, malic, and oxalic acids, with triisooctylamine (TIOA) dissolved in various diluents as chloroform, 1-octanol, and the binary diluent 1-hexanol/n-heptane. The extraction of tartaric acid with a solution of TAA in the binary diluent 1-octanol/n-heptane has been explored by Tomovska et al.23 The purpose of their study has been to investigate the effect of pH on the acid extraction, and they have concluded that only the free, undissociated acid can be extracted.
10.1021/ie050159q CCC: $30.25 © 2005 American Chemical Society Published on Web 07/20/2005
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However, the investigations that have been conducted in the case of an extractant dissolved in a binary diluent are associated with a mathematical modeling of the extraction equilibrium or a comparison between various active diluents and their effects on the distribution coefficients of carboxylic acids. The aim of this work was to investigate the influence of the modifier on the extraction efficiency in a broad pH range in the case of tartaric acid recovery by means of different extractants. Experimental Section Chemicals. Aqueous solutions were prepared by dissolving 99% (m/m) D-(-) tartaric acid (Acros Organics) in deionized water (Millipore, Milli-Q system). The initial acid concentration was about 5 g/L. The various initial pH values were adjusted by addition of solid NaOH (VWR International). Three extractants were tested: Aliquat 336 (quaternary alkylammonium salt), 98% (m/m) TOA, and a mixture of both extractants. The 99% (m/m) n-dodecane and 99% (m/m) 1-decanol were used as diluent and modifier, respectively. All constituents of the organic phase were purchased from Acros Organics. Procedure. The experiments were carried out in 125 mL separatory funnels. Equal volumes (20 cm3) of the aqueous phase and the organic phase were shaken for 30 min at ambient temperature on the shaking machine IKA HS 501 Digital (IKA Labortechnik). Our preliminary studies had shown that 30 min of mixing time are sufficient to reach equilibrium.3 After settling, the phases were separated, the volume of each phase was determined, and the pH value of the aqueous phase was measured with the pH 320 (WTW) pH meter. The tartaric acid concentration in the initial and equilibrium aqueous phases was determined by HPLC using a column for organic acid analysis, Aminex HPX-87H (BioRad) kept at 35 °C, with a mobile phase of 0.005 M H2SO4 with a flow rate of 0.6 cm3/min and PHD 206 (ICS) detector at a wavelength of 210 nm. The acid concentration in the organic phase was calculated by the mass balance. The extraction ability was represented by the distribution coefficient:
m)
C h VinCin - VC ) C V hC
where the overbar refers to the organic phase, V is the volume of the phase, C is the total concentration of tartaric acid, subscript “in” is the initial solution, and the absence of subscript indicates solution after reaching equilibrium. Results and Discussion The effect of 1-decanol concentration on the distribution coefficient of tartaric acid extracted by the three different extractants at two pH values of the initial aqueous solution was first studied. The organic phase was composed of extractant, modifier, and inert diluent. The extractant concentration was fixed at 15% (v/v) Aliquat 336 and 15% (v/v) TOA, used individually or as a mixture called mixed extractant. Figure 1a illustrates the study at pH 2.52, which is the initial pH of the aqueous solution. Curve 1 depicts the results of tartaric acid extraction with Aliquat 336. The available literature data imply that the extraction
Figure 1. (a) Influence of modifier concentration on distribution coefficient m at initial pH 2.52 ( 0.06 and tartaric acid concentration ) 4.99 ( 0.103 g/L. Composition of the organic phase: curve 1 ([) 15% (v/v) Aliquat 336, 1-decanol, n-dodecane; curve 2 (9) 15% (v/v) TOA, 1-decanol, n-dodecane; curve 3 (2) 15% (v/v) Aliquat 336, 15% (v/v) TOA, 1-decanol, n-dodecane. (b) Influence of modifier concentration on distribution coefficient m at initial pH 5.01 ( 0.04 and tartaric acid concentration ) 5.08 ( 0.0825 g/L. Composition of the organic phase: curve 1 ([) 15% (v/v) Aliquat 336, 1-decanol, n-dodecane; curve 2 (9) 15% (v/v) TOA, 1-decanol, n-dodecane; curve 3 (2) 15% (v/v) Aliquat 336, 15% (v/v) TOA, 1-decanol, n-dodecane.
with Aliquat 336 is mainly determined by its concentration and not by the diluent.7,8 Similarly, the present experimental results show that, upon extraction with Aliquat 336 diluted with an active or an inert diluent at a low pH, the active diluent concentration slightly affects the distribution coefficient. In the case of TOA as an extractant (curve 2), the higher modifier concentrations lead to an increase in the distribution coefficient of tartaric acid. The extraction ability of the mixed extractant is depicted by curve 3. There is a very strong modifier effect on the distribution coefficient, whose values significantly exceed those obtained with the individual extractants. The volumes of the organic phase and the aqueous phase after their separation are shown in Tables 1 and 2. The change in the volume of the organic phase, due to the coextraction of water, does not exceed 4%. Consequently, that strong effect cannot be explained by coextraction of water. As no experimental data were available in the literature on the influence of the modifier on the extraction of carboxylic acids at high pH values, it was interesting
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Table 1. pH of Aqueous Phase and Volumes of Organic and Aqueous Phases after Reaching Equilibrium: pHin 2.52 ( 0.06 and Initial Tartaric Acid Concentration ) 4.99 ( 0.103 g/L 1-decanol (% v/v)
V (cm3)
V h (cm3)
pH
15% (v/v) Aliquat 336, 1-Decanol, n-Dodecane 5 19.75 20.00 10 20.00 20.00 20 19.75 20.00 30 19.75 20.25 40 19.75 20.00 50 19.75 20.50 60 19.50 20.25 70 20.00 20.50
2.26 2.27 2.30 2.32 2.32 2.33 2.33 2.34
15% (v/v) TOA, 1-Decanol, n-Dodecane 19.50 20.00 19.75 20.25 19.75 20.25 19.50 20.00 19.50 20.00 19.50 20.50 19.50 20.50 19.50 20.75
2.69 2.86 3.12 3.33 3.49 3.57 3.71 3.81
5 10 20 30 40 50 60 70
15% (v/v) Aliquat 336, 15% (v/v) TOA, 1-Decanol, n-Dodecane 5 19.25 20.00 2.86 10 19.50 20.50 3.00 20 19.50 20.25 3.25 30 19.75 20.25 3.47 40 19.75 20.25 3.64 50 19.50 20.25 3.79 60 19.00 20.75 3.87 70 19.50 20.50 4.05 Table 2. pH of Aqueous Phase and Volumes of Organic and Aqueous Phases after Reaching Equilibrium: pHin 5.01 ( 0.04 and Initial Tartaric Acid Concentration ) 5.08 ( 0.0825 g/L 1-decanol (% v/v)
V (cm3)
V h (cm3)
pH
15% (v/v) Aliquat 336, 1-Decanol, n-Dodecane 5 19.50 20.25 10 19.75 20.25 20 19.75 20.50 30 19.50 20.00 40 19.50 20.00 50 19.50 20.00 60 19.50 20.50 70 19.50 20.50
4.70 4.70 4.72 4.74 4.75 4.77 4.79 4.80
15% (v/v) TOA, 1-Decanol, n-Dodecane 20.00 20.25 19.75 20.00 20.00 20.00 19.50 20.00 19.50 20.00 19.75 20.25 20.00 20.50 20.00 20.50
5.06 5.13 5.30 5.44 5.58 5.69 5.81 5.91
5 10 20 30 40 50 60 70
15% (v/v) Aliquat 336, 15% (v/v) TOA, 1-Decanol, n-Dodecane 5 19.75 20.25 5.17 10 19.75 20.25 5.31 20 19.50 20.00 5.60 30 19.50 20.00 5.88 40 19.50 20.00 6.11 50 19.50 20.00 6.31 60 19.50 20.00 6.44 70 19.50 20.00 6.63
to perform this investigation. The pH value of the tartaric acid solution was adjusted close to 5 by means of NaOH. The obtained results are presented in Figure 2. It is obvious that at high pH values the extraction with Aliquat 336 depends on the modifier concentration. Upon increasing the 1-decanol concentration in the organic phase up to 30% (v/v), the distribution coefficient decreases (curve 1), but it remains almost constant at
Figure 2. Effect of initial pH of aqueous solution on distribution coefficient m. Initial tartaric acid concentration ) 5.08 ( 0.0755 g/L. Composition of the organic phase: curve 1 (]) 15% (v/v) Aliquat 336, 5% (v/v) 1-decanol, 80% (v/v) n-dodecane; curve 2 ([) 15% (v/v) Aliquat 336, 50% (v/v) 1-decanol, 35% (v/v) n-dodecane. Table 3. Effect of Initial pH on Ratio between Distribution Coefficients for Two Modifier Concentrations: Initial Tartaric Acid Concentration ) 5.08 ( 0.0825 g/L; Composition of Organic Phase ) 15% (v/v) Aliquat 336, 1-Decanol, n-Dodecane pHin
m1/m2a
3.53 3.91 4.41 5.03
1.34 1.44 1.57 1.62
a Subscript 1, 5% (v/v) 1-decanol; subscript 2, 50% (v/v) 1-decanol.
the higher 1-decanol concentrations. The same trend was found for the extraction with the mixed extractant (curve 3); however, the distribution coefficient slightly surpasses that obtained with Aliquat 336. The extraction with TOA (curve 2) is not efficient and does not depend on the modifier concentration. There is a very interesting modifier effect on the distribution coefficient of tartaric acid extracted with the mixed extractant as a function of pH of the aqueous solution. This effect is positive at a low pH value and negative at a high (∼5) pH value. To elucidate the influence of pH, comparative experiments were carried out with the individual and the mixed extractant, dissolved in a binary diluent, at fixed extractant concentrations and two modifier concentrations. The initial pH was adjusted to the desired value with NaOH. Figure 2 shows the dependence of the distribution coefficient on the initial pH of the aqueous solution using Aliquat 336 as an extractant. Curve 1 refers to the organic phase composed of 15% (v/v) Aliquat 336, 5% (v/v) 1-decanol, and 80% (v/v) ndodecane, whereas curve 2 is for 15% (v/v) Aliquat 336, 50% (v/v) 1-decanol, and 35% (v/v) n-dodecane. A high concentration of 1-decanol in the organic phase decreases the efficiency of the quaternary ammonium salt; hence, the distribution coefficient obtained with 5% (v/ v) 1-decanol exceeds that obtained with 50% (v/v). Moreover, with the rise of the initial pH, the ratio between the distribution coefficients for the two modifier concentrations also increases (Table 3); i.e., the efficiency of Aliquat 336 is favored by the high pH values at a low concentration of 1-decanol.
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Figure 3. Dependence of distribution coefficient m on initial pH of the aqueous solution. Initial tartaric acid concentration ) 5.08 ( 0.0820 g/L. Composition of the organic phase: curve 1 (0) 15% (v/v) TOA, 5% (v/v) 1-decanol, 80% (v/v) n-dodecane; curve 2 (9) 15% (v/v) TOA, 50% (v/v) 1-decanol, 35% (v/v) n-dodecane.
Figure 4. Influence of initial pH of the aqueous solution on distribution coefficient m. Initial tartaric acid concentration ) 5.08 ( 0.0750 g/L. Composition of the organic phase: curve 1 (4) 15% (v/v) Aliquat 336, 15% (v/v) TOA, 5% (v/v) 1-decanol, 65% (v/v) n-dodecane; curve 2 (2) 15% (v/v) Aliquat 336, 15% (v/v) TOA, 50% (v/v) 1-decanol, 20% (v/v) n-dodecane.
Table 4. Effect of Initial pH on Ratio between Distribution Coefficients for Two Modifier Concentrations: Initial Tartaric Acid Concentration ) 5.08 ( 0.0825 g/L; Composition of Organic Phase ) 15% (v/v) TOA, 1-Decanol, n-Dodecane pHin
m2/m1a
3.53 3.91 4.41 4.97
3.33 3.58 4.39 15.7
a Subscript 1, 5% (v/v) 1-decanol; subscript 2, 50% (v/v) 1-decanol.
In Figure 3 the distribution coefficient is shown as a function of the initial pH for the following organic phase compositions: 15% (v/v) TOA, 5% (v/v) 1-decanol, 80% (v/v) n-dodecane (curve 1); 15% (v/v) TOA, 50% (v/v) 1-decanol, 35% (v/v) n-dodecane (curve 2). In the case of extraction with amine, the distribution coefficient is higher at the higher alcohol concentration. For both modifier concentrations, the extraction decreases with the pH increase but the ratio between the distribution coefficients increases (Table 4). The dependence of the distribution coefficient on the initial pH when tartaric acid is extracted with the mixed extractant is given in Figure 4. The composition of the mixed extractant was 15% (v/v) Aliquat 336 and 15% (v/v) TOA, dissolved in 5% (v/v) (curve 1) or 50% (v/v) (curve 2) 1-decanol and a corresponding concentration of n-dodecane. When the pH of the aqueous solution lies below the average value between the two pKa values of tartaric acid (pKa1 ) 3.01, pKa2 ) 4.38),26 TOA is the active constituent of the mixed extractant and the distribution coefficient is higher for the higher concentration of 1-decanol. When the pH of the aqueous solution exceeds the above-mentioned value, the extraction by Aliquat 336 predominates and the distribution coefficient decreases with the increase in modifier concentration. In the crossing point of the curves no influence of modifier concentration on the extraction is expected. This assumption was confirmed by the experimental results shown in Figure 5 depicting the influence of 1-decanol concentration on the distribution coefficient of tartaric acid extracted by the mixed extractant consisting of 15% (v/v) Aliquat 336 and 15% (v/v) TOA,
Figure 5. Effect of modifier concentration on distribution coefficient m at initial pH 3.90 and tartaric acid concentration ) 4.92 g/L. Composition of the organic phase: 15% (v/v) Aliquat 336, 15% (v/v) TOA, 1-decanol, n-dodecane.
1-decanol, and n-dodecane. The initial pH of the aqueous solution was adjusted to 3.90, a value near the crossing point of the two curves in Figure 4. At this pH, the increase in the active diluent concentration slightly affects the extraction of tartaric acid. Conclusions The effect of 1-decanol on the extraction of tartaric acid by Aliquat 336, TOA, or their mixture dissolved in a binary diluent was studied at various pH values of the aqueous solution. The experimental results permit the following conclusions: (i) At low pH values, the increase in the modifier concentration insignificantly affects the extraction of tartaric acid with Aliquat 336, favors the distribution coefficient with TOA as an extractant, and manifests a very strong positive effect in the case of the mixed extractant. (ii) At high pH values, the extraction with Aliquat 336 decreases at the higher modifier concentration; the same trend is observed for the mixed extractant. The extrac-
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tion of tartaric acid with TOA does not depend on modifier concentration. There is a specific effect of 1-decanol concentration on the distribution coefficient of tartaric acid extracted with the mixed extractant. When the pH of the aqueous solution is below the average value between the two pKa values of tartaric acid, this effect is positive, while for pH above this value the effect is negative. At the average value there is no influence of the modifier concentration on the extraction. Studies with other acids and extraction systems are in progress with a view to elucidate the mechanism of the modifier effect. Acknowledgment This work was supported by the National Council for Scientific Research-Ministry of Education and Science of Bulgaria (Project No. Rila 13/2003), and the Ministry of Foreign Affairs of France (Project No. 06258TC). M.M. gratefully acknowledges financial support from the Agence Universitaire de la Francophonie for her postdoctoral fellowship. Literature Cited (1) Siebold, M.; Frieling, P. v.; Joppien, R.; Rindfleisch, D.; Schu¨gerl, K.; Ro¨per, H. Comparison of the Production of Lactic Acid by Three Different Lactobacilli and its Recovery by Extraction and Electrodialysis. Process Biochem. 1995, 30, 81. (2) Frieling, P. v.; Schu¨gerl, K. Recovery of Lactic Acid from Aqueous Model Solutions and Fermentation Broths. Process Biochem. 1999, 34, 685. (3) Kyuchoukov, G.; Marinova, M.; Molinier, J.; Albet, J.; Malmary, G. Extraction of Lactic Acid by Means of a Mixed Extractant. Ind. Eng. Chem. Res. 2001, 40, 5635. (4) Han, D. H.; Hong, Y. K.; Hong, W. H. Separation Characteristics of Lactic Acid in Reactive Extraction and Stripping. Korean J. Chem. Eng. 2000, 17, 528. (5) Jung, M.; Schierbaum, B.; Vogel, H. Extraction of Carboxylic Acids from Aqueous Solutions with the Extractant System Alcohol/ Tri-n-Alkylamines. Chem. Eng. Technol. 2000, 23, 70. (6) Lazarova, Z.; Peeva, L. Solvent Extraction of Lactic Acid from Aqueous Solution. J. Biotechnol. 1994, 32, 75. (7) Yang, S. T.; White, S. A.; Hsu, S. T. Extraction of Carboxylic Acids with Tertiary and Quaternary Amines: Effect of pH. Ind. Eng. Chem. Res. 1991, 30, 1335. (8) Choudhury, B.; Basha, A.; Swaminathan, T. Study of Lactic Acid Extraction with Higher Molecular Weight Aliphatic Amines. J. Chem. Technol. Biotechnol. 1998, 72, 111. (9) Poposka, F. A.; Prochazka, J.; Tomovska, R.; Nikolovski, K.; Grizo, A. Extraction of Tartaric Acid from Aqueous Solutions with Tri-iso-octylamine (Hostarex A 324). Equilibrium and Kinetics. Chem. Eng. Sci. 2000, 55, 1591. (10) Marinova, M.; Kyuchoukov, G.; Albet, J.; Molinier, J.; Malmary, G. Separation of Tartaric and Lactic Acids by Means of Solvent Extraction. Sep. Purif. Technol. 2004, 37, 199.
(11) Yankov, D.; Molinier, J.; Albet, J.; Malmary, G.; Kyuchoukov, G. Lactic acid Extraction from Aqueous Solutions with Tri-n-octylamine Dissolved in Decanol and Dodecane. Biochem. Eng. J. 2004, 21, 63. (12) Flores-Morales, A.; Albet, J.; Kyuchoukov, G.; Malmary, G.; Molinier, J. Influence of Extractant (TBP and TOA), Diluent, and Modifier on Extraction Equilibrium of Monocarboxylic Acids. J. Chem. Eng. Data 2003, 48, 874. (13) Sabolova, E.; Schlosser, S.; Martak, J. Liquid-Liquid Equilibria of Butyric Acid in Water + Solvent Systems with Trioctylamine as Extractant. J. Chem. Eng. Data 2001, 46, 735. (14) Wasewar, K. L.; Heesink, A. B. M.; Versteeg, G. F.; Pangarkar, V. G. Reactive Extraction of Lactic Acid using Alamine 336 in MIBK: Equilibria and Kinetics. J. Biotechnol. 2002, 97, 59. (15) Prochazka, J.; Heyberger, A.; Bizek, V.; Kousova, M.; Volaufova, E. Amine Extraction of Hydroxycarboxylic Acids. 2. Comparison of Equilibria for Lactic, Malic, and Citric Acids. Ind. Eng. Chem. Res. 1994, 33, 1565. (16) Prochazka, J.; Heyberger, A.; Volaufova, E. Amine Extraction of Hydroxycarboxylic Acids. 3. Effect of Modifiers on Citric Acid Extraction. Ind. Eng. Chem. Res. 1997, 36, 2799. (17) Prochazka, J.; Heyberger, A.; Volaufova, E. Extraction Equilibrium of Dicarboxylic Acids with Tertiary Amine in Single and Binary Diluents. Sep. Sci. Technol. 2004, 39, 1073. (18) Malmary, G.; Albet, J.; Putranto, A.; Hanine, H.; Molinier, J. Measurement of Partition Coefficients of Carboxylic Acids between Water and Triisooctylamine Dissolved in Various Diluents. J. Chem. Eng. Data 1998, 43, 849. (19) Matsumoto, M.; Takagi, T.; Nakaso, T.; Kondo, K. Extraction Equilibria of Organic Acids with Tri-n-octylmethylammonium chloride. Solvent Extr. Res. Dev. Jpn. 1999, 6, 144. (20) Kyuchoukov, G.; Marinova, M.; Albet, J.; Molinier, J. New Method for the Extraction of Lactic Acid by Means of a Modified Extractant (Aliquat 336). Ind. Eng. Chem. Res. 2004, 43, 1179. (21) Yankov, D.; Molinier, J.; Kyuchoukov, G. Extraction of Tartaric Acid by Trioctylamine. Bulg. Chem. Commun. 1999, 31, 446. (22) Tung, L. A.; King, C. J. Sorption and Extraction of Lactic and Succinic Acids at pH > pKa1. 1. Factors Governing Equilibria. Ind. Eng. Chem. Res. 1994, 33, 3217. (23) Tomovska, R.; Poposka, F.; Heyberger, A.; Prochazka, J. pH Dependence of Tartaric Acid Extraction. Chem. Biochem. Eng. Q. 1999, 13, 185. (24) San-Martin, M.; Pazos, C.; Coca, J. Liquid-Liquid Extraction of Lactic Acid with Alamine 336. J. Chem. Technol. Biotechnol. 1996, 65, 281. (25) Juang, R. S.; Huang, R. H. Equilibrium Studies on Reactive Extraction of Lactic Acid with an Amine Extractant. Chem. Eng. J. 1997, 65, 47. (26) Kertes, A. S.; King, C. J. Extraction Chemistry of Fermentation Product Carboxylic Acids. Biotechnol. Bioeng. 1986, 28, 269.
Received for review February 9, 2005 Revised manuscript received June 16, 2005 Accepted June 18, 2005 IE050159Q
