Simultaneous Influence of Active and Inert Diluents ... - ACS Publications

Dec 7, 2005 - (p ) CHA/[HA]) differ significantly from the values of the overall distribution coefficient (m ) CHA/CHA) with the rise of extractant co...
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Ind. Eng. Chem. Res. 2006, 45, 503-510

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Simultaneous Influence of Active and “Inert” Diluents on the Extraction of Lactic Acid by Means of Tri-n-octylamine (TOA) and Tri-iso-octylamine (TIOA) George Kyuchoukov,*,† Abdallah Labbaci,‡ Joe1 l Albet,§ and Jacques Molinier§ Bulgarian Academy of Sciences, Institute of Chemical Engineering, Academician George BoncheV Street, Building 103, 1113 Sofia, Bulgaria, UniVersite´ de Blida, De´ partement de Chimie Industrielle, Laboratoire d’Analyse Fonctionnelle des Proce` des Chimiques, Route de soumea, BP 270, Blida, Alge´ rie, and Institut National Polytechnique de Toulouse, Ecole Nationale Superieure des Ingenieurs en Arts Chimiques et Technologiques, Laboratoire de Chimie Agro-Industrielle UMR 1010 INRA, Equipe Ge´ nie Chimique, 118, Route de Narbonne 31077 Toulouse, France

The extraction of lactic acid with tri-n-octylamine (TOA) or tri-iso-octylamine (TIOA) dissolved in a mixture of dodecane and a different alcohol was investigated under various experimental conditions. The influence of extractant, modifier, and diluent concentrations on the overall and overall particular distribution coefficients was determined. The obtained results and the observed phenomena were discussed by taking into consideration the mechanism of extraction and the concentration of the interaction product in the aqueous phase. Introduction Solvent extraction accompanied by chemical interaction is widely used for the removal of organic acids from their aqueous solutions. The solvent (the organic phase), as a rule, consists of an extractant and a diluent. The diluent has an important role when a long-chain tertiary amine is used as an extractant. There are two types of diluents: inert diluents (diluents) and active diluents (modifiers).1-4 The inert diluent improves the physical properties of the extraction system without affecting the extraction mechanism. It is nonpolar and provides for a very low solvation of the interaction product. Its presence in the organic phase has no effect on the solubility of the interaction product in the organic phase; however, it can extract the solute by physical extraction.5-7 The active diluent (modifier) has functional groups that favor the solvation of the interaction product and prevent the aggregation of the interaction product molecules in the organic phase. It was also supposed that the modifier enhances the solubility of complex.1,7-12 Inert diluents have no such effect. Using an amine extractant without modifier or at a very low modifier concentration, the polar acid-amine complex may form, in extreme cases, a separate phase or a precipitate.1 Single amines have very low extraction ability. The modifier addition results in up to a 100-fold increase in the distribution coefficient over the pure amine or amine diluted with a diluent.13-15 However, the increase is not proportional to the modifier concentration. In the absence of inert diluent and at relatively low amine concentration, the distribution coefficient decreases as the modifier concentration increases.6,13 Another observed phenomenon is the overloading of the extractant with the extracted acid (expressed as the ratio between the molar concentration of extracted acid and the initial molar concentration of extractant). To explain the experimental results, there are many publications where different complexes between p molecules of acid and n molecules of extractant are taken into consideration and the corresponding extraction constants are calculated.3,9,15-17 In all these contributions, both the * To whom correspondence should be addressed. Tel.: +(359)(2) 720230. Fax: +(359)(2) 8707523. E-mail: [email protected]. † Bulgarian Academy of Sciences. ‡ Universite´ de Blida. § Institut National Polytechnique de Toulouse.

concentration of interaction products and the concentration of extractant in the aqueous phase are neglected. But is there a reason to neglect these concentrations? Depending on the composition of the solvent, the volume ratio between the organic and aqueous phase and the concentration of acid, the aqueous phase often becomes cloudy or even opaque after the interaction with the solvent. It clarifies after dilution with water. This means that the aqueous phase is saturated with the interaction product. Another interesting question is why experimentally determined pH values are up to two pH units higher than the values expected on the basis of the aqueous acid concentration in the aqueous phase? This deviation is dependent not only on the extractant concentration but also on the composition of the solvent, the extracted acid, and the distribution coefficient. In some cases, an increase in the total concentration of acid in the aqueous phase leads to an increase in the pH. This fact cannot be explained with the presence of a small amount of a basic impurity.1 The aforementioned phenomena require that the extractant and interaction product be present in the aqueous phase, which was proven by Wardel and King.6 Consequently, the concentrations of extractant and interaction product must be taken into consideration for the interpretation of the experimental results. The aim of this work was, first, to compare the effects of modifier (active diluent) and diluent on the extraction ability of two amine extractants of the same chemical formula but of different chemical structure (tri-n-octylamine (TOA) and triiso-octylamine (TIOA)) in the case of lactic acid extraction and, second, to show that the presence of interaction products and extractant in the aqueous phase must be taken into consideration for the explanation of the obtained experimental results. Materials and Methods The model aqueous medium was prepared by dissolving acid (Sigma-Aldrich) in deionized water (Millipore Milli-Q Water System) without pH adjustment. The 85% (mass) lactic acid was distilled under total reflux for 8-10 h for breaking up the dimers. The presence or absence of dimers was controlled by high-performance liquid chromatography (HPLC). Pure (98% mass), crystalline L-(+)- lactic acid was used to prepare the standard solutions for the HPLC analyses.

L-(+)-lactic

10.1021/ie050912f CCC: $33.50 © 2006 American Chemical Society Published on Web 12/07/2005

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The tertiary amines tri-n-octylamine (98% mass TOA, Acros Organics) and tri-iso-octylamine (98% mass TIOA, SigmaAldrich) were used as extractants without further purification. The organic phase (solvent) consisted of the extractant dissolved in the active diluent (modifier) and/or the inert diluent (diluent). Hexanol (99% mass), octanol (99% mass), and decanol (99% mass) were used as active diluents. All diluents used were produced by Acros Organics. The experiments were performed in 125-cm3 separatory funnels. Equal volumes (20 cm3) of aqueous phase containing lactic acid and organic phase were shaken for 20 min at ambient temperature on the shaking machine IKA HS501 digital (IKA Labortechnik) with a frequency of 280 rpm. This mixing time was sufficient to reach the liquid-liquid equilibrium, because, after 10 min of shaking time, the concentration of lactic acid in the aqueous phase remains constant. After the phases were separated, the volume of each phase was measured. The pH of the aqueous phase before and after extraction was measured with a WTW Microprocessor pH-meter that was equipped with a temperature-compensating probe. The concentration of lactic acid was determined by HPLC, and the corresponding concentration in the organic phase was calculated by mass balance. The HPLC system was composed of a pump (Spectra Physics, model SP 8800), autosampler (Spectra Physics, model SP8875), UV-spectrophotometer (Spectra Physics, model 100UV-Vis Detector (wavelength of λ ) 210 nm)), integrator (Chromjet model SP4400), and column for organic acid analyses (BioRad Aminex Ion Exclusion HPX-87 H) operated at 35 °C. The mobile phase was 0.005 M H2SO4 with a flow rate of 0.6 cm3/min. Each sample was analyzed in triplicate under identical conditions, and the average value was reported. The analyses were made immediately after phase separation to avoid possible oxidation by air, evaporation, or eventual bacteriological degradation of the acid. Each experiment was performed in duplicate or triplicate, under identical experimental conditions. The experimental error was octanol > decanol. The same order of the influence of alcohols on the overall distribution coefficient m is observed for the extraction of lactic acid by means of TOA (Figure 2a). When the results are presented in terms of the influence of the extractant concentration on the overall particular (intrinsic) distribution coefficient (p) (Figure 2b), the shape of the curves is the same as that

Figure 1. Influence of the volume fraction of extractant (tri-iso-octylamine, TIOA) on (a) the overall distribution coefficient (m) and (b) the overall particular distribution coefficient (p) at a constant volume ratio between the extractant and the modifier (ratio ) 1). The organic phase is composed of TIOA, modifier (hexanol, octanol, or decanol), and diluent (dodecane). The initial lactic acid concentration in the aqueous phase is 7.33-8.20 g/L. (Figure legend: ([) hexanol modifier (curve 1), (9) octanol modifier (curve 2), and (2) decanol modifier (curve 3).)

observed in Figure 2a. The difference is only between the calculated values of m and p, but not so manifested as in the case of TIOA. What is the reason for the differences between the performance of the two amines and between the two distribution coefficients? Our assumption is that this reason is the presence of both amine and interaction products in the aqueous phase, which significantly affects the pH of the solution. In absence of other cations, the acidity is directly proportional to the total acid concentration. Consequently, the concentration of undissociated molecules is also directly proportional to the total acid concentration. In that case, the shape of the curve m vs [E] and p vs [E] must be the same. In the observed case, the two amines are strong Lewis bases and the presence of molecules of the extractant or/and of the interaction product in the aqueous phase significantly influences the pH and the calculated concentration of undissociated molecules, respectively. Depending on the composition of the organic phase for a given total acid concentration in the aqueous phase, different pH values may be measured. From Figures 1a and 2a, we can conclude that the extraction ability of TIOA is weaker than that of TOA. However, if we compare Figures 1b and 2b, we shall see that the overall particular (intrinsic) distribution coefficient with

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Figure 2. Influence of the volume fraction of extractant (tri-n-octylamine, TOA) on (a) the overall distribution coefficient (m) and (b) the overall particular distribution coefficient (p) at a constant volume ratio between the extractant and the modifier (ratio ) 1. The organic phase is composed of TOA, modifier (hexanol, octanol, or decanol), and diluent (dodecane). The initial lactic acid concentration in the aqueous phase is 7.46-9.37 g/L. (Figure legend: ([) hexanol modifier (curve 1), (9) octanol modifier (curve 2), and(2) decanol modifier (curve 3).)

decanol as a modifier is higher for TIOA than for TOA. The reason is that TIOA reduces the acidity of the aqueous phase to a greater extent than TOA. The calculated values of the concentration of undissociated acid molecules are according to the measured pH, without taking into account the concentration of the interaction product. For the above observed case (VE ) VM), eq 8 transforms to

VE p ) (KEM + pM - 2pD) + pD V

(10)

which corresponds to a straight line. It follows from Figures 1 and 2 that the dependence (eq 10) is not a straight line. The experimental points can be fitted, assuming a set of equations as eqs 1 and 2, where n molecules of extractant interact with q molecules or ions of the acid; however, in that way, we can explain neither the difference between the measured and the theoretical pH value nor the influence of modifier or diluent on the extraction ability of the organic phase. Figures 1 and 2 do not provide real information about the modifier influence on the extraction ability of the extractant, because of the presence of diluent in the organic phase, which also influences the extraction. Therefore, our subsequent

Figure 3. Dependence of (a) the overall distribution coefficient (m) and (b) the overall particular distribution coefficient (p) on the volume fraction of extractant. The organic phase is composed of extractant TIOA or TOA and dodecane. Initial lactic acid concentration in the aqueous phase is 7.81 g/L. (Figure legend: ([) TIOA (curve 1), and (9) TOA (curve 2).)

investigations were performed at a constant concentration of a given component of the organic phase when it was composed of three components or it consisted of only two components. Decanol was chosen as the modifier, because of its lower solubility in water. Here, it must be mentioned that, because of the use of TIOA and alcohol in the absence of an inert diluent (dodecane), the aqueous phase is not completely transparent, which we attributed to the overloading of the aqueous phase with the interaction product. Our experiments showed that, when the volume ratio between the organic and aqueous phase increases, the cloudy aqueous phase becomes transparent and vice versa. If the alcohol is mixed with water, the aqueous phase is transparent but not in the presence of lactic acid. This is evidence for an interaction between the acid and the alcohol. In the presence of dodecane in appropriate concentration, however, the aqueous phase remains transparent. Hence, the diluent cannot be considered to be inert, because it also extracts the interaction product. When the organic phase consists of extractant and diluent, the extraction ability of the extractant is very low. Figure 3a illustrates the experimental results for the overall distribution coefficient m, as a function of the concentration of extractant (curve 1 for TIOA and curve 2 for TOA). As expected, the maximal efficiency is observed at 100% amine. In the absence of a modifier, TIOA better extracts lactic acid than TOA. There is no substantial difference between the values of m and p for TOA. For TIOA, the ratio between the values of m and p increases with the rise of amine concentration, because of the stronger pH change. When TIOA was used, the aqueous phase began to cloud at 70 and 90 vol % TIOA (30 and 10 vol %

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Figure 4. Dependence of (a) the overall distribution coefficient (m) and (b) the overall particular distribution coefficient (p) on the volume fraction of extractant. The organic phase is composed of extractant TIOA or TOA and decanol. Initial lactic acid concentration in the aqueous phase is 7.81 g/L. (Figure legend: (9) TOA (curve 1), and ([) TIOA (curve 2).)

dodecane, respectively). The dispersion of the organic phase is more stable at these concentrations. The observed dependences are curves rather than straight lines. For those experimental conditions (VM ) 0) , eq 8 transforms to

VE p ) (KEM - pD) + pD V

(11)

According to eq 11, a plot of p vs VE/V should be a straight line. The positive deviation from the straight line implies a negative influence of the inert diluent on the extraction ability of the organic phase. These experimental results do not prove the supposition that the concentration of extractant and that of interaction product in the aqueous phase can be neglected. Figure 4, which presents the experimental results in the absence of dodecane in the organic phase, poses an interesting question. Why does the weaker extractant become stronger in the presence of decanol (see Figure 4a)? The effect of the modifier is evident, if one compares Figures 3 and 4. This effect is explained by other authors by the increase in the solubility of the complex between the amine and the acid, which is caused by its solvation by the modifier.2,9-13,26 In this way, the precipitation or second-layer formation in the organic phase is avoided. The increase in the distribution coefficient that is due to the modifier cannot be explained without taking into account the presence of extracted species in the aqueous phase. A competitive complexation/solvation theory of solvent extraction

has been developed to explain quantitatively the influence of active diluent on acid solvent extraction by amine based extractants.27,28 This theory predicts a synergistic or an antagonistic distribution effect of the active solvent on the basic amine extractant. However, if the organic phase contains only extractant and modifier, the dependence of the distribution coefficient on the concentration of extractant should have a maximum at 50 vol % of extractant, because of the positive effect of the modifier, or it should be shifted to the higher concentration of extractant (>50 vol % of extractant) in the presence of a negative effect of the modifier. Our experiments on the influence of the modifier on the extraction ability of the extractant, in the absence of an inert diluent, and the results of other publications show that the maximum is always shifted to the lower extractant concentrations.6,13,18,29,30 This suggests more than one positive effect of the modifier. The modifier solvates the lactic acid molecules in the aqueous phase. As shown by Tamada et al., the active diluent stabilizes the amine-acid complex, forming an amine-acid-active diluent complex or, in the present case, an amine-acid-alcohol complex.2 Consequently, the concentration of this extraction product is dependent on the concentration of modifier. This is the first positive modifier effect. The extraction product is characterized by a higher distribution coefficient for the composition of the solvent, and the distribution coefficient is highest for the modifier. Thus, the increase in modifier concentration will enhance the concentration of extracted species in the organic phase. This is the second positive modifier effect. The modifier also affects the basicity of the amine,6 which is the third positive effect of the modifier. The modifier may also affect the equilibrium dissociation constant of the acid. The main factor for the decrease in the acidity of the aqueous solution is the protonation of the extractant (amine in the observed case). In Figure 4a, the distribution coefficient of lactic acid for TOA (curve 1) and for TIOA (curve 2) passes through a maximum, which appears at ∼20 vol % amine and ∼80 vol % decanol. The favorable concentration interval for both amines is large: from 10 vol % to 50 vol % for the amine and from 90 vol % to 50 vol % for decanol, respectively. The ratio between the corresponding volume fractions in the organic phase significantly changes (from 9 to 1) but not the distribution coefficient. An increase in amine concentration of >20 vol % does not enhance the extraction, in the absence of dodecane. In that interval, a synergistic modifier effect is observed. For both amines, the maximum overall distribution coefficient appears at an extractant concentration of ∼20 vol %. Figure 4b illustrates the dependence of the overall particular distribution coefficient (p) on the extractant concentration in the presence of decanol. The shapes of the curves are the same but not their positions. For the extraction with TOA in the presence of decanol, the corresponding values of the overall and overall particular distribution coefficient do not significantly differ and the maximum remains located at 20 vol % TOA. In regard to TIOA, there is a large difference between the two coefficients in the region of maximal extraction ability. The ratio of the overall to the particular distribution coefficient is >2 at 30 vol % TIOA. The maximal value of p is shifted to the right (at 30 vol % TIOA. The influence of TIOA on the acidity of the aqueous phase (the difference between theoretical and measured pH values) is larger than that of TOA. Therefore, the divergence between the values of the overall and particular coefficients will be larger. The next experiments were performed at various concentrations of modifier (decanol). The obtained results are shown in Figures 5 and 6, for TIOA and TOA, respectively. These figures

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Figure 5. Dependence of (a) the overall distribution coefficient (m) and (b) the particular distribution coefficient (p) on the volume fraction of extractant (TIOA) at different constant concentrations of modifier (decanol) in the presence of diluent (dodecane). Volume fraction of decanol: ([) 3 vol %, (9) 5 vol %, (2) 15 vol %, (×) 30 vol %, (*) 50 vol %, (b) 70 vol %, (+) and 80 vol %. The initial lactic acid concentration is 8.30-9.40 g/L.

provide useful information for the simultaneous influence of the active and inert diluent on the extraction ability of the organic phase. When TIOA was used as the extractant, the overall distribution coefficient (Figure 5a) passes through a maximum with the rise of extractant concentration for modifier concentrations up to 30 vol %. This effect cannot be explained with the change in modifier concentration, because the latter remains constant. The concentration of the inert diluent decreases and consequently, the extraction of lactic acid also decreases. This means that the amine-acid-modifier complex is more soluble in the inert diluent than in the extractant. At low modifier concentration and high extractant concentration, the extracted complex reaches its solubility in the modifier but not in the extractant and inert diluent. The same shape of the curves for low modifier concentrations ( diluent > extractant. (6) The distribution coefficient of the interaction product (amine-acid) has the following order: extractant > diluent.

CHA ) total acid concentration in the aqueous phase; CHA ) [HA] + [A-] m ) overall distribution coefficient, given by the ratio between the total acid concentration in the organic phase and its total (analytical) concentration in the aqueous phase; m ) CHA/CHA m(E:HA), m(EH+A-) ) partial distribution coefficients that represent the ratio between the concentration of the corresponding interaction product in the organic phase and the total acid concentration in the aqueous phase; m(E:HA) ) [E:HA]/CHA

Nomenclature KE(EH+A-) ) partial equilibrium extraction constants for ionpair formation KE(E:HA) ) partial equilibrium extraction constants for hydrogen-bond formation Ka ) dissociation constant of monocarboxylic acid R ) molar fraction of dissociated molecules; R ) Ka/(Ka + [H+])

and m(EH+A-) ) [EH+A-]/CHA mE ) sum of the partial distribution coefficients of the interaction products, given by the ratio between the total concentration of interaction products in the organic phase and the total acid concentration in the aqueous phase; mE ) ([EH:A] + [EH+A-])/CHA p(E:HA) ) particular (intrinsic) distribution coefficient of the interaction product with hydrogen-bond formation, expressed by the ratio between the concentration of interaction product with hydrogen-bond formation in the organic phase and the concentration of undissociated molecules in the aqueous phase; p(E:HA) ) [E:HA]/[HA] p(EH+A-) ) particular (intrinsic) distribution coefficient of the interaction product with ion pair formation, given by the ratio between the concentration of the interaction product with ion pair formation in the organic phase and the concentration of

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undissociated molecules in the aqueous phase; p(EH+A-) ) +

-

[EH A ]/[HA] pe ) sum of particular (intrinsic) distribution coefficients of the interaction products, given by the ratio between the total concentration of interaction products in the organic phase and the concentration of undissociated molecules in the aqueous phase; pe ) p(EH+A-) + p(E:HA) ) ([EH+A-] + [E:HA])/[HA] mM, mD ) distribution coefficients presenting the ratio between the concentration of removed acid in the volume fraction of modifier and diluent, respectively, and the total acid concentration in the aqueous phase; mM ) [HA]M/CHA, mD ) [HA]D/CHA pM, pD ) particular (intrinsic) distribution constants that represent the ratio between the concentration of removed acid molecules in the volume fraction of modifier and diluent, respectively, and the concentration of undissociated acid in the aqueous phase; pM ) [HA]M/[HA], pD ) [HA]D/[HA] p ) overall particular (intrinsic) distribution coefficient that expresses the ratio between the total concentration of extracted acid in all forms in the organic phase and the concentration of undissociated acid in the aqueous phase; p ) p(E:HA) + p(EH+A-) + pM + pD M ) molar concentration of pure extractant V ) volume of the organic phase Acknowledgment A.L. gratefully acknowledges financial support from the Ministries of Education and Research of France and Algeria, and from CROUS. Literature Cited (1) Tamada, J. A.; Kertes, A. S.; King, C. J. Extraction of Carboxylic Acids with Amine Extractants. Equilibria and Law of Mass Action Modelling. Ind. Eng. Chem. Res. 1990, 29, 1319. (2) 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. (3) 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. (4) Poposka, F. A.; Prochazka, J.; Tomovska, R.; Nikolovski, K.; Grizo, A. Extraction of tartaric acid from aqueous solutions with triisooctylamine (Hostarex A 324). Equilibrium and kinetics. Chem. Eng. Sci. 2000, 55, 1591. (5) 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. (6) Wardell, J. M.; King, C. J. Solvent equilibria for extraction of carboxylic acids from water. J. Chem. Eng. Data 1978, 23, 144. (7) Kertes, A. S.; King, C. J. Extraction chemistry of fermentation product carboxylic acids. Biotechnol. Bioeng. 1986, 28, 269. (8) Wang, M.; Qin, W.; Dai, Y. Extraction mechanism and behavior of malic acid with trioctylamine (TOA). Sep. Sci. Technol. 2004, 39, 185. (9) Bizek, V.; Horacek, J.; Kousova, M. Amine extraction of citric acid: effect of diluent. Chem. Eng. Sci. 1993, 48, 1447. (10) Senol, A. Effect of Diluent on Amine Extraction of Acetic Acid: Modeling Considerations. Ind. Eng. Chem. Res. 2004, 43, 6496. (11) Qin, W.; Li, Z.; Dai, Y. Extraction of Monocarboxylic Acids with Trioctylamine: Equilibria and Correlation of Apparent Reactive Equilibrium Constant. Ind. Eng. Chem. Res. 2003, 42, 6196.

(12) 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. (13) 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. (14) 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. (15) Juang, R. Sh.; Huang, R. H. Equilibrium studies on reactive extraction of lactic acid with an amine extractant. Chem. Eng. J. 1997, 65, 47. (16) Bizek, V.; Horacek, J.; Kousova, M.; Heyberger, A.; Prochazka, J. Mathematical model of extraction of citric acid with amine. Chem. Eng. Sci. 1992, 47, 1433. (17) Bizek, V.; Horacek, J.; Rericha, R.; Kousova, M. Amine Extraction of Hydroxycarboxylic Acids. 1. Extraction of Citric Acid with 1-Octanol/ n-Heptane Solutions of Trialkylamine. Ind. Eng. Chem. Res. 1992, 31, 1554. (18) 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. (19) 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. (20) Canari, R.; Eyal, A. M. Selectivity in the Extraction of Lactic, Malic, Glutaric, and Maleic Acids from Their Binary Solutions Using an AmineBased Extractant: Effect of pH. Ind. Eng. Chem. Res. 2003, 42, 1308. (21) Canari, R.; Eyal, A. M. Selectivity in Monocarboxylic Acids Extraction from Their Mixture Solutions Using an Amine-Based Extractant: Effect of pH. Ind. Eng. Chem. Res. 2003, 42, 1301. (22) Kirsch, T.; Maurer, G. Distribution of binary mixtures of citric, acetic, and oxalic acid between water and organic solutions of tri-noctylamine. Part II: Organic solvent methylisobutyl ketone. Fluid Phase Equilib. 1998, 142, 215. (23) Choudhury, B.; Basha, A.; Swaminathan, T. Study of lactic acid extraction with higher molecular weight aliphatic amines. J. Chem. Technol. Biotechnol. 1998, 72, 111. (24) 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. (25) Morales, A. F.; 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. (26) Senol, A. Extraction equilibria of nicotinic acid using alamine 336 and conventional solvents: Effect of diluent. Chem. Eng. J. 2001, 83, 155. (27) Kislik, V.; Eyal, E. Competitive complexation/ solvation theory of solvent extraction: general statements, acid extraction by amines, influence of active solvents and temperature. J. Chem. Technol. Biotechnol. 2003, 78, 358. (28) Kislik, V.; Eyal, A.; Hazan, B. Competitive complexation/solvation theory of solvent extraction. III. Influence of active solvents on acid solvent extraction by amine based extractants. Sep. Sci. Technol. 2003, 38, 1681. (29) Bakti, J. Re´cupe´ration d’acides malique et tartrique par extraction liquide-liquide. Application a la de´pollution d’effluents agro-industriels. The`se de Doctorat, Institut National Polytechnique de Toulouse (INPT), Toulouse, France, 1993. (30) Achour, D. Contribution a l’e´tude du traitement d’effluents agroindustriels par extraction liquide-liquide. Mise au point d’un proce´de´ continu de se´paration des acides tartrique et lactique. The`se de Doctorat, Institut National Polytechnique de Toulouse (INPT), Toulouse, France, 1994.

ReceiVed for reView August 5, 2005 ReVised manuscript receiVed November 4, 2005 Accepted November 4, 2005 IE050912F