1944
Ind. Eng. Chem. Res. 1996, 35, 1944-1950
Comparison of Extraction Equilibria of Succinic and Tartaric Acids from Aqueous Solutions with Tri-n-octylamine Ruey-Shin Juang* and Ren-Hour Huang Department of Chemical Engineering, Yuan-Ze Institute of Technology, Nei-Li, Taoyuan 320, Taiwan, R.O.C.
A comparative study was made on the extraction equilibria of succinic and tartaric acids from aqueous solutions with tri-n-octylamine in xylene. It was shown that the extractability of tartaric acid was higher than succinic acid under comparable conditions. The compositions of the multiple-extracted complexes in the organic phase and the equilibrium constants for the formation of the complexes were numerically determined. Furthermore, the mole fractions of the species present in the organic phase were quantitatively obtained as a function of initial concentrations of the acids and amine. The effect of temperature on the extraction of acids was also examined and a change of complex composition with temperature was seen for succinic acid in the temperature range 293-323 K. Finally, the related thermodynamic data were calculated. Introduction A solvent extraction process can be considered as an alternative to the calcium salt precipitation techniques for the recovery of carboxylic acids from aqueous streams (Kertes and King, 1986; Schugerl and Degener, 1992; Su and Jiang, 1987; Wardell and King, 1978). The conventional solvents such as ketones and alcohols give rather low distribution ratios, making the extraction inefficient especially when applied to dilute acid solutions. In this case, a solvent giving a higher distribution ratio is needed. This leads to the use of specific extractants through reversible chemical complexation (Kertes and King, 1986). When phosphorus-based oxygen-containing extractants are used for recovering citric acid from a fermentation medium, a stable emulsion exists, which is difficult to break up (Schugerl and Degener, 1992). Amine-based extractants are thus suggested to be particularly suitable for the recovery of aliphatic carboxylic acids (King, 1992). In fact, the use of tertiary amines including trin-octylamine (TOA), triisooctylamine, trilaurylamine, and Alamine 336 for the extraction of succinic and tartaric acids from aqueous streams has been reported (Malmary et al., 1993, 1994; Manenok et al., 1979; Sato et al., 1985; Tamada et al., 1990; Tamada and King, 1990a,b; Vieux et al., 1974; Vieux and Rutagengwa, 1977). These acids are used in the food processing, chemical, and pharmaceutical industries (Berger, 1981; Kertes and King, 1986). Although the reaction stoichiometry of succinic acidamine extraction systems has been reviewed and studied (Tamada et al., 1990), there is no general agreement. The (1,1) acid-amine complex was often suggested (Manenok et al., 1979; Vieux et al., 1974; Vieux and Rutagengwa, 1977). In addition to this, the (2,1) or (1,2) complex, depending on the nature of organic solvents, has been proposed to fit the distribution data (Tamada et al., 1990). For tartaric acid, to our knowledge no such information is available in the literature, although several batch extraction equilibrium data have been recently presented (Malmary et al., 1993, 1994; Sato et al., 1985). Succinic acid is a dicarboxylic acid, and tartaric acid is a dihydroxyl-substituted succinic acid. Consequently, * To whom correspondence should be addressed.
S0888-5885(95)00652-X CCC: $12.00
tartaric acid is more hydrophilic and behaves as a slightly stronger acid in the aqueous phase (pKa1 ) 3.01) than succinic acid (pKa1 ) 4.21). In this work, the extraction equilibria of the two acids with TOA in xylene were compared. First, the formulations of the acidTOA complexes were numerically determined by a modified LETAGROP-DISTR program (Huang and Tsai, 1989; Liem, 1971), and then the effect of the concentrations of amine and acid on the contribution of each species present in the organic phase was quantitatively investigated. The effect of temperature on the extraction of acids was also examined, and the apparent thermodynamic data including the enthalpy and entropy were obtained. Experimental Section Reagents and Solutions. Deionized water used in this work was produced by a Millipore Milli-Q water system. TOA was the product of Tokyo Chemical Industry Co., Ltd., Japan, which had a purity of about 98.5% and was used without further purification. Succinic acid, tartaric acid, xylene, and other inorganic chemicals were supplied by Merck Co. as analytical reagent grade and were used as received. The organic phase was prepared by diluting TOA in xylene. The initial concentration of TOA varied from 5 × 10-2 to 1.0 mol/dm3. The aqueous phase was prepared by dissolving acids in deionized water without pH adjustment. The initial concentration of acids ranged from 8 × 10-3 to 1.0 mol/dm3. In the extraction of acids with TOA (reactive extraction), the equilibrium pH values of the aqueous phase were located within 2.37-3.52 for succinic acid and 1.85-3.33 for tartaric acid. Procedures. For measuring the distribution ratio of acids, equal volumes (40 cm3) of the organic and aqueous solutions were mixed in glass flasks by a magnetic stirrer for at least 12 h. The two phases were separated after they had been allowed to settle for 1 h. After phase separation, the concentration of acids (all forms) in the aqueous phase was potentiometrically titrated with a known NaOH using Radiometer autotitrator Model RTS82. The concentration of acids in the organic phase was similarly determined but with an isopropyl alcohol solution of NaOH. The titration error was checked to be less than 1% under the acid concentration range measured (>0.01 mol/dm3). Experiments © 1996 American Chemical Society
Ind. Eng. Chem. Res., Vol. 35, No. 6, 1996 1945
were performed in the temperature range 293-323 K, and each run was duplicated under identical conditions. For the extraction of monocarboxylic acids with tertiary amines, the possibilities of the presence of an acetic acid salt of TOA (Wardell and King, 1978) and a hydrogen salt of Alamine 336 (Ju and Verma, 1994) in the aqueous phase have been reported. These types of salts were detected from the titration curve of the aqueous phase after extraction by amines with rather high concentrations, which exhibited two inflection points, one corresponding to the free acid and the other to the salt (Ju and Verma, 1994; Wardell and King, 1978). In the present systems (dicarboxylic acids), nevertheless, such behaviors were not observed for the described ranges. The distribution ratio of acids was calculated as the ratio of the molarity of acids in the organic phase to that in the aqueous phase. Mass balance closed within 2%. In some cases the mass balance of acids does not involve organic- and aqueousphase titrations; in such instances the data are based on only the aqueous-phase titration values. In such cases the errors do not exceed 5%. Results and Discussion
Figure 1. Extraction of succinic acid with TOA at 293 K.
Extraction of the Acids with Pure Diluent. It is known that carboxylic acids may exist as dimers in the organic phase due to the intermolecular hydrogen bonding, especially in nonpolar or low polar solvents like xylene (Kertes and King, 1986). In the aqueous phase, on the other hand, they mainly exist as monomers because the intermolecular hydrogen bonding between acids is destroyed due to their preferential hydrogen bonding with water molecules. As the aqueous pH is far less than the first dissociation constant of acids (this is the case here), we have the following reactions:
H2A S H2A; 2H2A S (H2A)2; H2A S H+ + HA-;
Kd
(1)
K2 Ka1
(2) (3)
where the overbar refers to the organic phase. As indicated in eqs 1-3, evidently, the dissociation of the second hydrogen ions in the aqueous phase is ignored (pKa2 ) 4.38 for tartaric acid and 5.64 for succinic acid). The total equilibrium concentrations of acids in the organic and aqueous phases, [H2A]t and [H2A]t, are obtained as follows:
[H2A]t ) [H2A] + 2[(H2A)2]
(4)
[H2A]t ) [H2A] + [HA-]
(5)
Thus, the distribution ratio of acids in the absence of TOA (i.e., physical extraction), D0, is given by
D0 ) [H2A]t/[H2A]t ) (Kd + 2Kd2K2[H2A])/ {1 + (Ka1/[H+])} (6) Here, the concentration of the undissociated acid in the aqueous phase, [H2A], can be obtained from eq 5 and the measured aqueous equilibrium pH, that is, [HA-] ) [H+], since no amine is present in the aqueous phase. The lowest data points in Figures 1 and 2 show the
Figure 2. Extraction of tartaric acid with TOA at 293 K.
measured results at 293 K. It is found that D0 is greater for succinic acid than for tartaric acid, which is due to the fact that tartaric acid has two additional hydrophilic hydroxyl groups. As clearly indicated in eq 6, the values of K2 and Kd can be obtained from the slope and intercept of the plot of D0 vs [H2A], and in this way they are 9.01 × 10 dm3/mol and 5.74 × 10-3 for succinic acid and 2.72 × 102 dm3/mol and 1.82 × 10-3 for tartaric acid, respectively. Compared to succinic acid, the larger K2 for tartaric acid indicates the ease formation of an intermolecular hydrogen bond due to the presence of hydroxy groups (Tamada et al., 1990). Extraction of the Acids with TOA. Figures 1 and 2 also show the distribution ratio of acids extracted with TOA as a function of the initial acid and TOA concentrations. It is seen that the amount of tartaric acid extracted is greater than that of succinic acid under comparable conditions. This agrees with the previous
1946
Ind. Eng. Chem. Res., Vol. 35, No. 6, 1996
findings that the greater the ionizing acidity, as measured by pKa1, the more it is extracted (Tamada et al., 1990). For a given acid system, the distribution ratio increases with TOA concentration. Although the amount of the acid extracted in the organic phase smoothly increases with the initial acid concentration at a fixed TOA concentration (not shown), however, the distribution ratio has no certain trends with respect to the initial acid concentration, as is clearly seen in Figures 1 and 2. It is shown that tertiary amines (e.g., Alamine 336) extract only undissociated molecules of carboxylic acids (Yang et al., 1991). Therefore, the extraction of acids with TOA can be expressed by the following stoichiometric relation:
pH2A + qTOA S (H2A)p(TOA)q;
Kpq
(7)
For amine extraction of carboxylic acids, there may exist different extents of water coextraction in the organic phase, each of which strongly depends on the types of diluent and the nature of acids investigated (Bizek et al., 1992; Kertes and King, 1986; Tamada and King, 1990b). As is often done by many investigators (Fahim et al., 1992; Juang and Huang, 1994; Prochazka et al., 1994; Tamada et al., 1990), such an effect is not considered here for simplicity. In this case, the extraction equilibrium constant, Kpq, of eq 7 is given by
Kpq ) [(H2A)p(TOA)q]/{[H2A]p[TOA]q}
(8)
The total concentration of acids in the organic phase now becomes
[H2A]t ) [H2A] + 2[(H2A)2] +
∑p ∑q p[(H2A)p(TOA)q] ) Kd[H2A] + 2K2Kd2[H2A]2 +
∑p ∑q pKpq[H2A]p[TOA]q
(9)
Equation 9 means that the amount of acids complexed with TOA is corrected by subtracting that physically extracted by pure diluent from the measured [H2A]t. The term [TOA] in eqs 8 and 9 can be calculated by the following mass-balance equation because the solubility of TOA in acidic aqueous solution is negligibly small.
[TOA]0 ) [TOA] +
∑p ∑q q[(H2A)p(TOA)q] )
[TOA] +
∑p ∑q qKpq[H2A]p[TOA]q
(10)
The LETAGROP-DISTR computer program was originally developed to analyze the distribution data of a component between two phases using the least-squares error method (Liem, 1971). The “best” equilibrium constants for the formation of a set of complexes with up to four components can be calculated. This program was extended to five-component systems and was successfully used to treat equilibrium data in the extraction of metals with organophosphoric acids (Huang and Tsai, 1989; Juang and Lee, 1994). Here, we further modify this program to analyze the equilibrium data for the extraction of carboxylic acids with amines.
In this calculation, the computer searches for the best set of equilibrium constants for a given model that would minimize the error squares sum defined by:
U)
∑(log Dexpt - log Dcalc)2
(11)
where Dexpt is the measured distribution ratio of acids and Dcalc is the distribution ratio calculated by the program considering the above mass-balance equations (eqs 5, 9, and 10) and the measured equilibrium pH. Now, the effect of Ka2 is taken into account for calculating the value of Dcalc. This program also calculates the standard deviation σ(log D) defined by
σ(log D) ) (U/Np)1/2
(12)
where Np is the degree of freedom, that is, the difference between the total number of experimental data points and the total number of equilibrium constants to be calculated. The values tried here are p ) 1-4 and q ) 1-2, which is inferred from the literature results for succinic acid (Tamada et al., 1990). The calculation shows that for succinic acid the simultaneous formation of (1,1) and (3,1) complexes can fit the distribution data best at 293 K, whereas for tartaric acid the best-fit model contains (1,1), (1,2), and (3,1) complexes. The minimum standard deviations σ(log D), an indication for the difference between the experimental data and model predictions, in these two cases are found to be 0.206 and 0.253, respectively. The equilibrium constants calculated are K11 ) 0.34 dm3/mol and K31 ) 0.47 (dm3/mol)3 for succinic acid and K11 ) 0.14 dm3/mol, K12 ) 11.2 (dm3/ mol)2, and K31 ) 1.4 × 10-4 (dm3/mol)3 for tartaric acid at 293 K. It is apparent that overloading, i.e., the complexes with more than one acid per amine, occurs for both acids. Although previous researchers (Manenok et al., 1979; Vieux et al., 1974; Vieux and Rutagengwa, 1977) indicated that dicarboxylic acid forms only (1,1) complexes with tertiary amines, the present results for succinic acid are somewhat similar to those obtained for its extraction by Alamine 336 in methyl isobutyl ketone and nitrobenzene (Tamada et al., 1990), in which the formation of (1,1) and (2,1) complexes is suggested. Tamada et al. also found that the formation of a strong (1,1) complex and a minor, if any, (2,1) complex is consistent with the data obtained in chloroform and methylene chloride media. The overloaded complex (3,1) rather than (2,1) obtained in this work for succinic and tartaric acids may be understood from the findings of Chaikhorskii et al. (1966) for the extraction of acetic acid with tridecylamine in carbon tetrachloride. They studied the infrared spectra of the complexes and proposed that an additional acid is hydrogen bonded to the (2,1) complex to form a cyclic arrangement around the nitrogen atom in the amine, with the proton associated with the two oxygen atoms near it. This would lead to a more stable (3,1) complex compared to the (2,1) complex. In addition to the (1,1) and (3,1) stoichiometries observed for succinic acid, a multiamine complex (1,2) is obtained for tartaric acid. On a semiquantitative basis by the slope analysis technique, Sato et al. (1985) proposed the formation of a (p,q) complex with p ) 1 and q ) 1-2 for the extraction of succinic and tartaric acids with TOA in xylene. Also, it is reported that in
Ind. Eng. Chem. Res., Vol. 35, No. 6, 1996 1947
Figure 3. Mole fraction of the species present in the organic phase for succinic acid at 293 K.
Figure 4. Mole fraction of the species present in the organic phase for tartaric acid at 293 K.
some organic diluents dicarboxylic acids such as bisuccinate, bimalonate, bimaleate, and biphthalate can undergo appreciable intramolecular hydrogen bonding between the carboxyl and carboxylate groups (Evans and Goldstein, 1969; Kolthoff and Chantooni, 1975). For example, the bisuccinate ions can orient themselves to form internal hydrogen bonds through rotation about the central C-C bond. On the other hand, spectroscopic data showed that in the bifumarate anion the carboxyl groups are fixed on the opposite side of the double bond and cannot form intramolecular hydrogen bonds (Tamada and King, 1990a). In the case of bitartarate ions, the carboxyl groups are likely separated to a certain distance due to their repulsive interactions with hydroxyl groups and therefore cannot easily form internal hydrogen bonds. The larger K2 value obtained here for tartaric acid, in contrast to succinic acid, may primarily reflect that tartaric acid has a greater tendency to form intermolecular hydrogen bonds. About the effect of hydroxyl groups, Tamada and King (1990a) observed that octanol diluent allows for significant (1,2) complex formation with succinic acid and Alamine 336. In addition, Gusakova et al. (1986) showed that malonic acid and triethylamine in methanol form a (1,2) complex, whereas in dioxane, chloroform and acetonitrile do not, which is explained by the fact that the alcohol hydroxyl group interferes with the intramolecular hydrogen bond of malonic acid. Figures 3 and 4 show the mole fraction of species present in the organic phase as a function of the concentration of acids. These results are obtained by solving eqs 9 and 10, coupled with the measured distribution ratios. For succinic acid at low TOA concentration, the complex (1,1) and the acid dimer dominate under the whole [H2A]0 ranges examined. At high TOA concentration the dominant species are the (1,1) and (3,1) complexes. In the case of tartaric acid (Figure 4), on the other hand, the (1,2) and (1,1)
complexes dominate at low TOA concentration. At high TOA concentration, the acid dimer becomes the second abundant species at [H2A]0 > 0.7 mol/dm3. It is worth noting from Figure 4 that at both TOA concentrations, unlike succinic acid, the amount of 3:1 tartaric acid-TOA complex formed is negligibly small for the described acid concentration ranges. Moreover, the mole fraction of the (1,1) complex is rather smaller for tartaric acid than succinic acid under comparable conditions. As clearly shown in Figure 3, the greater amount of the overloaded succinic acid-TOA complex (3,1) exists at high [TOA]0 compared to low [TOA]0. Such behaviors are likely effected by reaching an equivalent TOA loading, defined as the total acid concentration in the organic phase divided by the initial TOA concentration (Tamada et al., 1990). Effect of Temperature on Acid Extraction with TOA. The effect of temperature on the extraction of acids is shown in Figures 5 and 6. As indicated earlier (Tamada and King, 1990b), the complexation reactions of acids and amines in the organic phase involve proton transfer or hydrogen-bond formation and are therefore expected to be exothermic. Formation of a complex makes the system more ordered and therefore decreases the entropy. Thus, as the temperature is increased, the amount of acids extracted decreases. Similar computer calculations are performed to treat the data obtained at different temperatures. The temperature corrections of Kd, K2, Ka1, and Ka2 are not considered here, and those values obtained at 293 K are used. This would be acceptable because the temperature range is rather narrow. This action could slightly change the values of Kpq; however, the complex formulations determined are not affected. It is found that the complex formulations for tartaric acid are unaltered with temperature. For succinic acid, however, the (1,1) composition is rejected in the best-fit model and is replaced by (1,2) at temperatures equal and greater
1948
Ind. Eng. Chem. Res., Vol. 35, No. 6, 1996
Figure 5. Effect of temperature on the extraction of succinic acid with TOA.
Figure 6. Effect of temperature on the extraction of tartaric acid with TOA.
than 303 K. That is, now the simultaneous formation of (1,2) and (3,1) complexes is suggested. To our knowledge, such types of findings are scarcely reported in the literature. It is possibly a result of the destruction of intramolecular hydrogen bonds formed in bisuccinate ions due to the stronger thermal motion at higher temperatures. A similar behavior has been recently observed by Prochazka et al. (1994) for the extraction of citric acid by trialkylamine in mixtures of 1-octanol/ n-heptane at temperatures 298, 323, and 348 K. They found that the complexes consist of (1,1) and (1,2), and (2,3) at 298 K, and the formation of the (2,3) complex can be neglected at elevated temperatures. In order to understand how the contribution of organic species would change with temperature, the mole fractions of those species at 313 K and [TOA]0 ) 0.2 mol/ dm3 are shown in Figures 7 and 8. For succinic acid,
Figure 7. Mole fraction of the species present in the organic phase for succinic acid at 313 K.
Figure 8. Mole fraction of the species present in the organic phase for tartaric acid at 313 K.
as indicated above, the complex (1,1) formed at 293 K is gone at 313 K and is replaced by the (1,2) complex, but it is still dominant. It follows from Figure 8 that the distribution type is essentially similar to that observed at 293 K for tartaric acid, except a sharp increase in the amount of the (3,1) complex at higher [H2A]0. In contrast to 293 K (Figure 4), the mole fraction of the (1,2) complex is largely reduced and that of the (1,1) complex is increased. The preferential formation of the overloaded (3,1) complex over the (1,2) or (1,1) complex at high [H2A]0 (>0.7 mol/dm3) could be similarly effected by an equivalent organic loading. Finally, it should be noted that for succinic acid at 313 K the second abundant species is the acid monomer rather than the (3,1) complex at 293 K or the acid dimer. This is attributed to the lower organic loading (distribution ratio) at higher temperature and the relatively small K2 value.
Ind. Eng. Chem. Res., Vol. 35, No. 6, 1996 1949
Figure 9. Temperature dependence of the equilibrium constants, Kpq. Table 1. Apparent Enthalpies and Entropies for the Formation of the Complex (H2A)p(TOA)q in the Temperature Range 293-323 K succinic acid
tartaric acid
complex (p,q)
∆H (kJ/mol)
∆S (J/mol‚K)
∆H (kJ/mol)
∆S (J/mol‚K)
(1,1) (1,2) (3,1)
-36.4 -83.9
-53.4 ( 2.7 -127.0 ( 3.8
-236.2 58.2 174.6
-338.6 ( 6.8 78.4 ( 3.2 225.5 ( 6.1
Figure 9 illustrates the temperature dependence of the equilibrium constants Kpq. It is surprising to find that under the temperature ranges studied the dependencies of K11 and K12 are reversed for tartaric acid at 293 K. If we ignore the two data points, the apparent enthalpies and entropies for the formation of each complex can be calculated as follows (Juang and Huang, 1994; Tamada and King, 1990b).
d(log Kpq)/d(1/T) ) -∆H/(2.303R)
(13)
∆G ) -RT ln Kpq
(14)
∆S ) (∆H - ∆G)/T
(15)
The calculated results are listed in Table 1. There are important differences between succinic and tartaric acids for the same stoichiometries. The cause leading to such great discrepancies remains unclear at this stage because Kpq is an overall equilibrium constant in nature. As shown in Table 1, 1:1 complexation is much more exothermic and involves a much greater loss of entropy for tartaric acid than for succinic acid. It is known that either the partial molar enthalpy of mixing of the complex in the diluent, the partial molar enthalpy of mixing of the acid in the aqueous phase, or the intrinsic enthalpy of formation reaction must differ between the two acids (Tamada and King, 1990b). The partial molar enthalpies of mixing of dilute succinic and tartaric acids in water have been determined to be 28.7 and 15.7 kJ/ mol, respectively, at 298.15 K (Apelblat, 1986). Such a small difference suggests that this factor is not an important contribution to the variation in the apparent
enthalpy of complex formation with acid under the concentration ranges studied, as was also concluded by Tamada and King (1990b) for the comparison between succinic and lactic acids. Furthermore, the information on the organic-phase enthalpy of mixing can be obtained from the temperature dependence of distribution ratios of acids extracted by pure diluent, i.e., D0 (Tamada and King, 1990b). Because the difference in enthalpies of transfer of lactic and succinic acids from the aqueous phase to an organic phase of methyl isobutyl ketone is found to be about 11.7 kJ/mol (Tamada and King, 1990b), it is considered that the enthalpy of mixing of the complex in the diluent, which can be related to the enthalpy of mixing of the acid in the diluent, is also not a significant factor for the present systems. In this respect, the intrinsic enthalpy of complexation with acids thus plays an important role in determining apparent thermodynamic data. It is seen from Table 1 that for tartaric acid the 1:2 and 3:1 complexation reactions give positive enthalpies and entropies. As indicated above, there may exist a different extent of water coextraction in the organic phase, which strongly depends on the nature of acids under consideration. It is reported that water coextraction at low acid concentrations decreases in the dicarboxylic acid order fumaric > malonic> maleic ≈ succinic (Tamada and King, 1990b). Tartaric acid may give more water coextraction than succinic acid because of the smaller extent of internal self-association, as in the case of fumaric acid (Tamada and King, 1990a). In this regard, the complex formation of tartaric acid and TOA might release more water molecules than the case of succinic acid, thus leading to an increase in the system entropy. Such an effect is expected to be more apparent for the formation of overloaded complex (3,1). Conclusions The extraction equilibria of succinic and tartaric acids from aqueous solutions by TOA in xylene have been examined and compared. Multiple complexes with a general composition (H2A)p(TOA)q are simultaneously formed in the organic phase. In the temperature range 293-323 K, the values of (p,q) are (1,1), (1,2), and (3,1) for tartaric acid, and for succinic acid they are (1,1) and (3,1) at 293 K but become (1,2) and (3,1) at higher temperatures (g303 K). The apparent thermodynamic data for the formation of these complexes are listed in Table 1. It is deduced that the intrinsic enthalpy of complex formation is an important factor in determining these functions. With regard to the contribution of complexes in the organic phase at 293 K, under the whole acid concentration ranges (0.01-1 mol/dm3) the dominant complex is (1,1) at low TOA concentration and becomes (1,1) and (3,1) at high TOA concentration for succinic acid. For tartaric acid, the (1,2) and (1,1) complexes dominate. At higher temperature (313 K), the dominant species is the (1,2) complex for succinic acid. In addition, for tartaric acid the distribution type is basically similar to that observed at 293 K, except a sharp increase in the amount of the (3,1) complex at higher [H2A]0. For both acids, the greater amount of the overloaded complex (3,1) formed at higher [H2A]0 or higher [TOA]0 is probably affected by reaching an equivalent organic loading.
1950
Ind. Eng. Chem. Res., Vol. 35, No. 6, 1996
Acknowledgment This work was supported by the ROC National Science Council under Grant No. NSC85-2214-E-155003, which is greatly appreciated. Nomenclature D ) distribution ratio of the acids with TOA D0 ) distribution ratio of the acids by pure xylene diluent H2A ) succinic or tartaric acid ∆G ) apparent free energy change, kJ/mol ∆H ) apparent enthalpy change, kJ/mol Ka1 ) first dissociation constant of acids in the aqueous phase, mol/dm3 Ka2 ) second dissociation constant of acids in the aqueous phase, mol/dm3 Kd ) distribution constant of monomeric acids defined in eq 1 K2 ) dimerization constant of acids in the organic phase defined in eq 2, dm3/mol Kpq ) overall equilibrium constant defined in eq 8, (mol/ dm3)1-p-q Np ) degree of freedom defined in eq 12 p ) number of the acids involved in the extracted complex q ) number of TOA involved in the extracted complex R ) universal gas constant, J/mol‚K ∆S ) apparent entropy change, J/mol‚K T ) absolute temperature, K TOA ) tri-n-octylamine U ) error square sum defined in eq 11 [ ] ) molar concentration of species in the brackets, mol/ dm3 Greek Letter σ ) standard deviation defined in eq 12 Superscript (overbar) ) species in the organic phase Subscript 0 ) initial
Literature Cited Apelblat, A. Enthalpy of Solution of Oxalic, Succinic, Adipic, Maleic, Malic, Tartaric, and Citric Acids, Oxalic Acid Dihydrate, and Citric Acid Monohydrate in Water at 298.15 K. J. Chem. Thermodyn. 1986, 18, 351-357. Berger, S. E. Hydroxy Dicarboxylic Acids. In Encyclopedia of Chemical Technology, 3rd ed.; Kirk, R., Othmer, D. F., Eds.; John Wiley: New York, 1981; Vol. 13, pp 103-121. 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, 1554-1562. Chaikhorskii, A. A.; Nikolskii, B. P.; Mikhailov, B. A. Complex Formation in Nonaqueous Solutions. X. Interaction of Tridecylamine with Acetic Acid. Sov. Radiochem. 1966, 8, 152-158. Evans, H. G.; Goldstein, J. H. An Investigation of Intramolecular Hydrogen Bonding in Some Malonic Acid Using NMR Techniques. Spectrochim. Acta 1969, 24A, 73-79. Fahim, M. A.; Qader, A.; Hughes, M. A. Extraction Equilibria of Acetic and Propionic Acids from Dilute Aqueous Solution by Several Solvents. Sep. Sci. Technol. 1992, 27, 1809-1821. Gusakova, G. V.; Denisov, G. S.; Smloyanskii, A. L. Infrared Spectra and Structures of Complexes Formed for Dibasic Carboxylic Acids with Amines in Nonaqueous Solvents: Malonic Acid. J. Gen. Chem. USSR 1986, 56, 531-536. Huang, T. C.; Tsai, T. H. Extraction of Nickel(II) from Sulfate Solutions by Bis(2-ethylhexyl)phosphoric Acid Dissolved in Kerosene. Ind. Eng. Chem. Res. 1989, 28, 1557-1562. Ju, L. K.; Verma, A. Characteristics of Lactic Acid Transport in Supported Liquid Membranes. Sep. Sci. Technol. 1994, 29, 2299-2315.
Juang, R. S.; Lee, S. H. Extraction Equilibria of Lead(II) from Nitrate Solutions with Acidic Organophosphorus Compounds. J. Chem. Technol. Biotechnol. 1994, 60, 61-66. Juang, R. S.; Huang, W. T. Equilibrium Studies on the Extraction of Citric Acid from Aqueous Solutions with Tri-n-octylamine. J. Chem. Eng. Jpn. 1994, 27, 498-405. Kertes, A. S.; King, C. J. Extraction Chemistry of Fermentation Product Carboxylic Acids. Biotechnol. Bioeng. 1986, 28, 269282. King, C. J. Amine-Based Systems for Carboxylic Acid Recovery. CHEMTECH 1992, 22, 285-291. Kolthoff, I. M.; Chantooni, M. K. Intramolecular Hydrogen Bonding in Monoanions of o-Phthalic Acid and the Homologous Oxalic Acid Series in Acetonitrile. J. Am. Chem. Soc. 1975, 97, 1376-1381. Liem, D. H. High Speed Computers as a Supplement to Graphical Methods. 12. Application of LETAGROP-DISTR to Data for Liquid-Liquid Distribution Equilibria. Acad. Chem. Scand. 1971, 25, 1521-1534. Malmary, G. H.; Mourgues, J. F.; Bakti, J.; Conte, T. S.; Achour, D.; Smagghe, F. J.; Molinier, J. R. Partition Coefficients of Tartaric and Malic Acids between Dilute Aqueous Solutions and Amine Extractants Dissolved in Various Diluents. J. Chem. Eng. Data 1993, 38, 537-539. Malmary, G. H.; Vezier, A.; Robert, A.; Mourgues, J.; Conte, T.; Achour, D.; Molinier, J. Recovery of Tartaric and Malic Acids from Dilute Aqueous Effluents by Solvent Extraction Technique. J. Chem. Technol. Biotechnol. 1994, 60, 67-71. Manenok, G. S.; Korobanova, V. I.; Yudina, T. N.; Soldatov, V. S. Influence of the Nature of the Solvent on Extraction of Certain Mono- and Dicarboxylic Acids by Amines. Russ. J. Appl. Chem. 1979, 52, 156-160. 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, 1565-1573. Sato, T.; Watanabe, H.; Nakamura, H. Extraction of Lactic, Tartaric, Succinic, and Citric Acids by Trioctylamine. Bunseki Kagaku 1985, 34, 559-563. Schugerl, K.; Degener, W. Recovery of Low-Molecular-Weight Compounds from Complex Aqueous Mixtures by Extraction. Int. Chem. Eng. 1992, 32, 29-40. Su, Y.; Jiang, Y. Process for Recovery of Organic Acids from Aqueous Solutions. U.S. Patent 4,705,894, 1987. Tamada, J. A.; King, C. J. Extraction of Carboxylic Acids with Amine Extractants. 2. Chemical Interactions and Interpretation of Data. Ind. Eng. Chem. Res. 1990a, 29, 1327-1333. Tamada, J. A.; King, C. J. Extraction of Carboxylic Acids with Amine Extractants. 3. Effect of Temperature, Water Coextraction, and Process Considerations. Ind. Eng. Chem. Res. 1990b, 29, 1333-1338. Tamada, J. A.; Kertes, A. S.; King, C. J. Extraction of Carboxylic Acids with Amine Extractants. 1. Equilibria and Law of Mass Action Modeling. Ind. Eng. Chem. Res. 1990, 29, 1319-1326. Vieux, A. S.; Rutagengwa, N. Extraction of Glutaric and Succinic Acids by Tri-isooctylamine. Anal. Chim. Acta 1977, 91, 359363. Vieux, A. S.; Rutagengwa, N.; Rulinda, J. B.; Balikungeri, A. Extraction of Some Dicarboxylic Acids by Tri-isooctylamine. Anal. Chim. Acta 1974, 68, 415-424. Wardell, J. M.; King, C. J. Solvent Equilibria for Extraction of Carboxylic Acids from Water. J. Chem. Eng. Data 1978, 23, 144-148. 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, 1335-1342.
Received for review October 23, 1995 Revised manuscript received March 19, 1996 Accepted March 21, 1996X IE950652+
Abstract published in Advance ACS Abstracts, May 1, 1996. X
