Separation and Purification Technology 37 (2004) 199–207

Separation of tartaric and lactic acids by meansof solvent extraction

Maria Marinova a, George Kyuchoukov a,∗, Joël Albet b,Jacques Molinier b, Guy Malmary b

a Institute of Chemical Engineering, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl.103, 1113 Sofia, Bulgariab Ecole Nationale Supérieure des Ingénieurs en Arts Chimiques et Technologiques, Equipe Génie Chimique, Laboratoire de ChimieAgro-Industrielle UMR 1010 INRA, Institut National Polytechnique de Toulouse, 118 Route de Narbonne, 31077 Toulouse, France

Received 11 November 2002; received in revised form 2 July 2003; accepted 30 July 2003

Abstract

A study of the possibilities for separating tartaric and lactic acids from winery wastewaters was conducted. Some principalextractants were tested. The organic phase containing TBP, dodecane or TOA, 1-decanol, dodecane permits a selective extractionof one of the acids. The distribution coefficients of both acids with solution of tertiary amine, modifier and diluent were determined.The same organic phase was tested to remove tartaric and lactic acids from a mixture. Taking into account the selective extraction,it was concluded that the most appropriate solvent composition corresponds to 15% (v/v) TOA, 15% (v/v) 1-decanol, and 70%(v/v) dodecane. This solvent was applied in a system of countercurrent extraction which permits to separate successfully tartaricfrom lactic acid.© 2003 Elsevier B.V. All rights reserved.

Keywords: Separation; Extraction equilibrium; Tartaric acid; Lactic acid; Tertiary amine

1. Introduction

The development of agroindustrial productionprocesses with alimentary or not alimentary appli-cations is connected with several problems of pol-lution. All these industries produce a great volumeof aqueous streams containing different compounds,which sometimes are released directly in rivers. Thewinemaking process generates a great amount ofindustrial wastewaters rich in diverse by-products

∗ Corresponding author. Tel.: +359-2-720-230;fax: +359-2-707-523.

E-mail address: gdkyuch@bas.bg (G. Kyuchoukov).

obtained from sugar fermentation, like polyphenols,glycerol and carboxylic acids. In order to reduceenvironmental pollution, the wastewaters are treatedin biological reactors where organic materials aretransformed in methane and carbon dioxide. Thepresence of carboxylic acids can disturb this processof transformation, which operates at pH value nearthe neutrality.

Wastewaters from wineries contain tartaric and lac-tic acids. These acids are used in food processing andpharmaceutical industry. The wastewaters from thewinemaking process are the only industrial source fortartaric acid production [1]. Lactic and tartaric acidscan be valorized if it is possible to obtain them with

1383-5866/$ – see front matter © 2003 Elsevier B.V. All rights reserved.doi:10.1016/S1383-5866(03)00218-1

200 M. Marinova et al. / Separation and Purification Technology 37 (2004) 199–207

Nomenclature

A− anions of monocarboxylicacid

A2− anions of dicarboxylic acidfrom second dissociation

C total concentration of the acidCHA monocarboxylic acidCH2A dicarboxylic acidE organic phase at equilibriumE (%) extent of extractionExtr extractantF fresh aqueous phaseHA undissociated molecules of

monocarboxylic acidHA− anions of dicarboxylic acid

from first dissociationH2A undissociated molecules of

dicarboxylic acidKa dissociation constant of acidKE extraction constantm distribution coefficientn number of the extractant

molecules associated with onemolecule of acid

Over bar organic phaseP (%) purity of the acidR aqueous phase at equilibriumS fresh organic phaseSquare brackets molar concentrationV volume of the phase

Greek letterβ solvent selectivity

Indicesin initial solution1 monoacid2 diacid

great purity. The most advanced process for this pur-pose studied in recent years is solvent extraction withappropriate solvent [2].

In the available literature, there is a significantamount of data on the extraction of carboxylicacids. The phosphorus-bonded oxygen donor ex-

tractants and aliphatic amine extractants were pro-posed as most efficient. Recently Ingale and Ma-hajani have studied some aspects of extractionof C2–C6 carboxylic acids with tributylphosphate(TBP) as extractant [3,4]. Wang et al. [5] investi-gated the extraction equilibria of monocarboxylicacids (formic, acetic, propionic, butyric, caproic,monochloroacetic, dichloroacetic, trichloroacetic andlactic) with trialkylphosphine oxide (TRPO). Thefeasibility of extraction and recovery of acetic andformic acids with such phosphate-containing extrac-tants as TRPO and TBP was explored by Cai et al.[6].

The use of tertiary amines was reported too. Vari-ous aspects of this subject were considered, such asthe influence of amine and acid concentration, the na-ture of acid, amine and diluent, the effect of temper-ature on the extraction process. Tertiary amines withlong aliphatic chains were most often suggested assuitable extractants for tartaric acid. Poposka et al. [7]have studied the equilibrium and the kinetics of tar-taric acid extraction with tri-iso-octylamine (TIOA)dissolved in iso-decanol/kerosene mixtures as a func-tion of acid, amine, and modifier concentrations. Thedependence of tartaric acid extraction on pH of theaqueous phase was explored by Tomovska et al. [8].The organic phase was a solution of trialkylamine(TAA) in binary diluent (n-octanol and n-heptane).The recovery of tartaric acid by trioctylamine (TOA)in binary diluent was explored by Yankov et al. [9].The extraction equilibria of succinic and tartaric acidswith TOA in xylene were compared by Juang andHuang [10]. The effect of pure diluent, amine con-centration in the solvent and temperature was exam-ined. Different solvents for lactic acid extraction weretested by Siebold et al. [11]. Phosphate-containing ex-tractants (TOPO and TBP) were compared with sec-ondary (Amberlite LA2) and tertiary (Hostarex A 327)amines, the best results were obtained with aliphaticamines dissolved in modifier and diluent. Choudhuryet al. [12] have studied the extraction of lactic acid withTOA and Aliquat 336 in many diluents, the influenceof pH of the aqueous phase was investigated. TOA,di(2-ethylhexyl) phosphoric acid (D2EHPA), and xy-lene in organic mixture or individually were appliedby Juang and Huang [13] for lactic acid recovery. Theinfluence of the organic phase composition and thetemperature on the extraction was explored. A mixed

M. Marinova et al. / Separation and Purification Technology 37 (2004) 199–207 201

extractant for lactic acid extraction containing TOA,Aliquat 336 and 1-decanol was developed by Kyu-choukov et al. [14]. The influence of pH, aqueousand organic phase compositions on the efficiency ofthe process was studied. A comparison with individ-ual extractants was made. Malmary et al. [15] haveinvestigated the extraction of some carboxylic acids(aconitic, citric, lactic, malic, and oxalic) with TIOAdissolved in various diluents as chloroform, 1-octanol,and binary diluent 1-hexanol/hexane. Extraction equi-libria of lactic, malic and citric acids with TAA inmixtures of 1-octanol/n-heptane as functions of sol-vent composition and temperature were explored byProchazka et al. [16]. Matsumoto et al. [17] have stud-ied the extraction equilibrium of acetic, glycolic, pro-pionic, lactic, succinic, fumaric, malic and itaconicacids with TOA and TBP alone and with a mixtureof both extractants observing their synergistic effect.TOA in chloroform was used by Kirsch and Mau-rer [18] for a study of the competitive partitioning ofbinary mixtures of citric, acetic and oxalic acids be-tween water and organic phase. The authors have con-cluded that the amine preferably extracts the strongeracid.

A large amount of work has been done on the re-covery of single organic acids, such as tartaric andlactic, but we did not find the studies referring to theirseparation.

The aim of this study is to select an appropriatesolvent composition for separation of tartaric and lac-tic acids from aqueous solution containing both acidsin concentrations corresponding to these of winerywastewaters.

2. Experimental

2.1. Materials

The aqueous medium was prepared by dissolv-ing 98% l(+) lactic acid (Sigma Aldrich) and/or99% d(−) tartaric acid (Sigma Aldrich) in deionizedwater (Millipore, Milli-Q-system). The initial con-centrations were 5 g/l tartaric acid and 8 g/l lacticacid.

The organic phase was a solution of the extrac-tant in n-dodecane (99%) as inert diluent and 1-decanol (99%) as modifier, both products of Acros

Organics. Three extractants were tested: 98% TOA(tri-n-octylamine, Acros Organics), 98% TBP (tri-n-butylphosphate, Sigma Aldrich) and 99% Aliquat336 (quaternary C8- and C10-alkyl ammonium salt,Acros Organics).

For the stripping operation, aqueous solutionsof H2SO4 (Sigma Aldrich) or (NH4)2CO3 (SigmaAldrich) were used.

2.2. Procedure

The experiments were carried out in 125 ml sepa-ratory funnels. Equal volumes of aqueous and organicphases were shaken for 20 min at ambient temper-ature on the shaking machine IKA HS 501 Digital(IKA Labortechnik). A preliminary study has shownthat the mixing time was sufficient to obtain equi-librium. After phase separation, pH of the aqueousphase was measured with the WTW MicroprocessorpH meter. The tartaric and lactic acids concentra-tions were determined by high-performance liquidchromatography (HPLC) using a column for or-ganic acid analysis Aminex HPX-87H (Bio-Rad),0.005 M H2SO4 as a mobile phase, and Spectra100 UV-Vis Detector (Spectra-Physics) at 210 nmwavelength. The initial concentration of tartaricand lactic acids and pH of the aqueous phasewere also determined. The concentration of acidin the organic phase was calculated by mass bal-ance.

3. Definition of the characteristic parameters

The extraction efficiency is represented by extentof extraction, distribution coefficient, purity of lacticacid in the aqueous phase, and purity of tartaric acidin the organic phase:

E = VinCin − VC

VinCin× 100 (1)

m = C̄

C= VinCin − VC

V̄C(2)

P = CHA

CHA + CH2A× 100 and

P̄ = C̄H2A

C̄H2A + C̄HA× 100 (3)

202 M. Marinova et al. / Separation and Purification Technology 37 (2004) 199–207

where

CHA = [HA] + [A−] (4)

CH2A = [H2A] + [HA−] + [A2−] (5)

The solvent selectivity is used to assess the efficiencyand ease of separation of two solutes and it is definedby:

β = m2

m1(6)

4. Theory

The extraction equilibria of carboxylic acids can bedescribed by a set of equations.

The following reactions take place:

- the dissociation of the acid in the aqueous solution;- the formation of reaction product “acid-solvent”.

In the case of monocarboxylic acid:

HA ↔ H+ + A−, Ka1 = [H+][A−]

[HA](7)

HA + n1Extr ↔ HA.Extrn1 (8)

with extraction constant:

KE1 = [HA.Extrn1]

[HA][Extr]n1= m1(Ka1 + [H+])

[Extr]n1[H+](9)

The distribution coefficient of monoacid (m1) ex-presses the ratio between the total concentrations ofacid in all of its possible forms in the organic and theaqueous phases:

m1 = C̄HA

CHA= [HA.Extrn1]

[HA] + [A−]

= KE1[HA][Extr]n1

[HA] + Ka1[HA]/[H+]

= KE1[Extr]n1 [H+]

Ka1 + [H+](10)

In the case of dicarboxylic acid:

H2A ↔ HA− + H+, Ka2,1 = [HA−][H+]

[H2A](11)

HA− ↔ H+ + A2−, Ka2,2 = [H+][A2−]

[HA−](12)

H2A + n2Extr ↔ H2A.Extrn2 (13)

with extraction constant:

KE2 = [H2A.Extrn2]

[H2A][Extr]n2

= m2([H+]2 + Ka2,1[H+] + Ka2,1Ka2,2)

[Extr]n2[H+]2(14)

The distribution coefficient of diacid (m2) is given bythe following expression:

m2 = C̄H2A

CH2A= [H2A.Extrn2]

[H2A] + [HA−] + [A2−]

= KE2[H2A][Extr]n2

[H2A](1 + Ka2,1/[H+] + Ka2,1Ka2,2/[H+]2)

= KE2[Extr]n2 [H+]2

[H+]2 + Ka2,1[H+] + Ka2,1Ka2,2

(15)

Taking into account expressions (10) and (15) theratio between both distribution coefficients will be:

m2

m1= KE2

KE1[Extr]n2−n1

× [H+](Ka1 + [H+])

[H+]2 + Ka2,1[H+] + Ka2,1Ka2,2(16)

As can be seen from expression (16) for any givenpair of diacid and monoacid the ratio between theirdistribution coefficients will depend on their extractionconstants, respectively composition of the solvent (ex-tractant, diluent and modifier), extractant concentra-tion, dissociation constants and pH of aqueous phase.

5. Solvent selection

Our objective was to separate tartaric and lacticacids and in order to choose the best solvent forthis a preliminary study was carried out. Differentsolvents were tested, the acids were recovered fromindividual solutions containing tartaric or lactic acid.The obtained results are presented in Table 1. Inrespect of studied solutes two solvents have shownbest selectivity—TOA dissolved in dodecane with1-decanol as modifier and TBP dissolved in dodecane.

M. Marinova et al. / Separation and Purification Technology 37 (2004) 199–207 203

Table 1Extent of extraction and ratio between the distribution coefficientsof both acids depending on used solvent

Solvent E (%) m2/m1

Tartaric acid Lactic acid

100% (v/v) 1-Decanol 5.81 11.61 0.47070% (v/v) TBP, 30%

(v/v) dodecane21.22 40.29 0.399

30% (v/v) Aliquat 336,70% (v/v) 1-decanol

28.31 39.40 0.607

30% (v/v) TOA, 70%(v/v) 1-decanol

98.06 94.78 2.650

15% (v/v) Aliquat 336,15% (v/v) TOA,70% (v/v) 1-decanol

100 97.11 �1

15% (v/v) Aliquat 336,15% (v/v) 1-decanol,70% (v/v) dodecane

18.07 14.72 1.323

30% (v/v) Aliquat 336,40% (v/v) TBP, 30%(v/v) dodecane

57.13 48.71 1.340

15% (v/v) TOA, 15%(v/v) TBP, 70% (v/v)dodecane

31.68 19.19 2.035

15% (v/v) TOA, 15%(v/v) 1-decanol, 70%(v/v) dodecane

92.93 53.42 11.459

Initial acid concentrations in the aqueous phase: tartaric acid =4.728 ± 0.621 g/l; lactic acid = 8.206 ± 0.406 g/l.

6. Results and discussion

6.1. Distribution coefficients of tartaric and lacticacids with the system TOA–1-decanol–dodecane

Several experiments with TOA as extractant,1-decanol as modifier and dodecane as inert diluentwere carried out in order to determine the most appro-priate composition of the organic phase which allowsthe separation of the acids under consideration fromwinery wastewaters. Individual solutions containingabout 5 g/l of tartaric acid or 8 g/l of lactic acid wereused to determine the distribution coefficients. Theeffect of the concentrations of modifier and extractantwas investigated. All experiments were performed atvolume ratio of 1.

First the concentration of TOA was fixed at 5% (v/v)and the influence of 1-decanol was examined at a sig-nificantly large interval. Fig. 1 shows the results ofthis study. The increase of modifier concentration in-

0

20

40

60

80

100

0 20 40 60 80 100

1-decanol (v/v %)

m 1

2

Fig. 1. Influence of modifier concentration on the distributioncoefficient of tartaric and lactic acids. Initial acid concentrationsin the aqueous phase: tartaric acid = 4.733 ± 0.097 g/l; lacticacid = 7.461 ± 0.003 g/l. Composition of the organic phase: 5%(v/v) TOA, 1-decanol, dodecane. Curve 1: (�) individual solutionof tartaric acid. Curve 2: (�) individual solution of lactic acid.

fluences the dissolution of “amine acid” complex andconsequently, the distribution of both acids betweenorganic and aqueous phases. High concentrations ofalcohol involve an important extent of extraction, butthe purity decreases.

Fig. 2 presents the effect of extractant concentra-tion on the distribution coefficient when a 1-decanolconcentration was fixed at 15% (v/v). The increase ofamine concentration causes improvement of the distri-bution coefficient of lactic acid (curve 2). In the caseof tartaric acid the distribution coefficient increases,reaching a maximum value which corresponds to 30%(v/v) of TOA, and then begins to decrease (curve 1).This maximum was found in other investigations con-cerning the extraction of carboxylic acids by tertiaryamine and alcohol as modifier [15,19] or ketone [12].

In the case of constant ratio between the extractantand the modifier, the increase of their concentrationsameliorates the value of the distribution coefficientof lactic acid. The distribution coefficient of tartaricacid passes again through a maximum at 30% (v/v)of amine as is shown in Fig. 3. Taking into accountthe extents of extraction of both acids, we can con-clude that high concentrations of TOA and 1-decanolfavour their removal. Consequently, the solvent con-taining 30% (v/v) of TOA can be used for unselec-

204 M. Marinova et al. / Separation and Purification Technology 37 (2004) 199–207

0

5

10

15

20

25

0 20 40 60 80 100

TOA (v/v %)

m

2

1

Fig. 2. Influence of extractant concentration on the distributioncoefficient of tartaric and lactic acids. Initial acid concentrationsin the aqueous phase: tartaric acid = 4.813 ± 0.041 g/l; lacticacid = 7.726±0.074 g/l. Composition of the organic phase: TOA,15% (v/v) 1-decanol, dodecane. Curve 1: (�) individual solutionof tartaric acid. Curve 2: (�) individual solution of lactic acid.

tive recovery of solutes from aqueous streams in orderto purify them. The obtained results were applied todraw the curves representing the tartaric acid purityin the organic phase and the ratio between the distri-

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60TOA (v/v %)

m

2

1

Fig. 3. Influence of extractant concentration on the distributioncoefficient of tartaric and lactic acids. Initial acid concentrations inthe aqueous phase: tartaric acid = 4.636 g/l; lactic acid = 7.458 g/l.Composition of the organic phase: TOA, 1-decanol, dodecane;volume ratio extractant/modifier = 1. Curve 1: (�) individualsolution of tartaric acid. Curve 2: (�) individual solution of lacticacid.

35

40

45

50

55

60

65

5 10 15 20 25 30 35 40 45 50TOA (v/v %)

P (

%)

2

4

6

8

10

12

14

16

m2 /m

1

1

2

Fig. 4. Influence of TOA concentration on the tartaric acid purityin the organic phase and on the ratio between the distribution co-efficients of both acids. Initial acid concentrations in the aqueousphase: tartaric acid = 4.636 g/l; lactic acid = 7.458 g/l. Composi-tion of the organic phase: TOA, 1-decanol, dodecane; volume ratioextractant/modifier = 1. Curve 1: (�) P̄ . Curve 2: (�) m2/m1.

bution coefficients of tartaric and lactic acids shownin Fig. 4. The extraction process is more efficient forhigher distribution coefficients. On the other hand, dueto the low influence of high distribution coefficient onthe extent of extraction, the purity of tartaric acid de-creases. In this case we think that the best conditionsfor the selectivity are in the cross point between bothcurves.

6.2. Extraction of tartaric and lactic acids by thesystem TBP–dodecane

Taking into account the possibility of selectiveextraction with the system TBP–dodecane, a lot ofexperiments with this solvent were carried out forthe mixture of tartaric and lactic acids and for theindividual solutions of acids. Fig. 5 shows that therise of TBP concentration leads to an increase ofboth acids extraction. When organophosphorus com-pound is used as extractant, lactic acid is recoveredin greater quantities than tartaric acid. Lactic acid ispreferentially extracted in presence of both acids andwhen it is dissolved alone in the aqueous solution.The maximum extent of extraction is 56% for lacticacid and 42% for tartaric acid at 100% TBP. The sol-vent TBP–dodecane extracts selectively both solutesbut the result is less satisfying than the result ob-

M. Marinova et al. / Separation and Purification Technology 37 (2004) 199–207 205

0

10

20

30

40

50

60

0 20 40 60 80 100

TBP (v/v %)

E (

%)

1

2

3

4

Fig. 5. Influence of TBP concentration on the extent of extrac-tion. Initial acid concentrations in the aqueous phase: tartaricacid in the individual solution = 5.349 g/l; lactic acid concen-tration in the individual solution = 7.950 g/l; tartaric acid in themixture = 4.946 g/l; lactic acid in the mixture = 8.007 g/l. Com-position of the organic phase: TBP, dodecane. Curve 1: (�) indi-vidual solution of tartaric acid. Curve 2: (�) tartaric acid in themixture. Curve 3: (�) individual solution of lactic acid. Curve 4:(�) lactic acid in the mixture.

tained with the solvent containing amine, alcohol andhydrocarbon.

6.3. Extraction of tartaric and lactic acids from amixture by the system TOA–1-decanol–dodecane

The amine influence on the simultaneous extractionof both solutes at constant concentration of modifier(15% (v/v)) is shown in Fig. 6. The difference betweenFigs. 2 and 6 is obvious. The influence of extractantconcentration on the distribution coefficient of lacticacid is weaker when both acids were present in theaqueous solution and stronger for tartaric acid. Themaximum ratio between the distribution coefficientsof tartaric and lactic acids observed at higher concen-trations of extractant was not the optimum conditionfor the separation of both solutes as can be seen inFig. 7. This Fig. 7 shows the purity of tartaric acidin the organic phase (curve 1) and the ratio betweenthe distribution coefficients of tartaric and lactic acids(curve 2) as a function of the concentration of TOAin the solvent. Two opposite curves were obtained, infact the optimum composition of the organic phase is

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35TOA (v/v %)

m

2

1

Fig. 6. Influence of TOA concentration on the distribution coef-ficient of tartaric and lactic acids. Initial aqueous phase: mixtureof 4.565 g/l tartaric acid and 7.448 g/l lactic acid. Composition ofthe organic phase: TOA, 15% (v/v) 1-decanol, dodecane. Curve1: (�) tartaric acid. Curve 2: (�) lactic acid.

a compromise between both curves, because this is acompromise between the extent of extraction and theselectivity. The best solvent composition correspondsto 15% (v/v) TOA, 15% (v/v) 1-decanol, 70% (v/v)dodecane which permit to recover 90% of tartaric acidand 40% of lactic acid. When the organic acids are

50

53

56

59

62

65

5 10 15 20 25 30TOA (v/v %)

P (

%)

0

5

10

15

20

25

30

m2 /m

1

2 1

Fig. 7. Influence of TOA concentration on the tartaric acid purityin the organic phase and on the ratio between the distribution co-efficients of both acids. Initial aqueous phase: mixture of 4.565 g/ltartaric acid and 7.448 g/l lactic acid. Composition of the organicphase: TOA, 15% (v/v) 1-decanol, dodecane. Curve 1: (�) P̄ .Curve 2: (�) m2/m1.

206 M. Marinova et al. / Separation and Purification Technology 37 (2004) 199–207

IE IIE IIIE S

F IR IIR IIIR

IIIIII

Fig. 8. Flow diagram of countercurrent extraction.

extracted from a mixture they have a specific behaviorwhich is different when they are recovered from indi-vidual solution. However, the determined concentra-tion is not far from the selected optimum compositionof solvent in the case of single acid solution.

6.4. Experiments for separation of tartaric and lacticacids from a mixture by countercurrent extraction

The obtained results of tartaric and lactic acids ex-traction with an amine were applied to create a processfor separation of both solutes. The organic phase 15%(v/v) TOA, 15% (v/v) 1-decanol, 70% (v/v) dode-cane, chosen to separate tartaric and lactic acids froma mixture was used for the realization of countercur-rent extraction. The simulation of this type of processwas achieved with three separatory funnels accordingto Fig. 8. In the beginning, the funnels were chargedwith equal volumes of fresh solvent and fresh aqueoussolution containing both solutes in concentrations cor-responding to their amounts in winery wastewaters.After mixing and separation the aqueous phase ob-tained in a third separatory funnel was analysed, on theother hand the solvent from the first separatory funnelwas stripped. In the second level, a fresh aqueous so-lution was introduced in a first funnel and mixed withthe solvent from the second funnel. A fresh solventwas introduced in a third funnel and mixed with theaqueous phase from second funnel. The second funnelwas charged with the aqueous solution from the firstfunnel and organic phase from the third one. It wasconsidered that every new portion of initial aqueoussolution and fresh solvent introduced in the systemdesigns a new process level. Several extractions (sixlevels) were effectuated according to this flow dia-gram. The results presented in Table 2 prove that afterthe third contact tartaric acid was completely recov-ered by the solvent. The aqueous phases coming fromthe system and containing pure lactic acid were sub-mitted to new extractions. The organic phases 50%

Table 2Composition of the aqueous phases coming from the system ofcountercurrent extraction

No. of level

I II III IV V VI

C2 (g/l) 0.484 0.032 0.042 0 0 0C1 (g/l) 4.533 2.476 2.611 3.016 3.011 2.993P1 (%) 90.35 98.71 98.41 100 100 100

Initial aqueous phase: mixture of 4.484 g/l tartaric acid and7.471 g/l lactic acid. Solvent: 15% (v/v) TOA, 15% (v/v) 1-decanol,70% (v/v) dodecane.

(v/v) TOA, 50% (v/v) 1-decanol or 15% (v/v) TOA,15% (v/v) Aliquat 336, 70% (v/v) 1-decanol permitto recover, respectively 87 and 94% of lactic acid. Onthe other hand, the aqueous phases still containingboth acids can be re-introduced in the system untiltotal separation.

The countercurrent extraction was applied also toextract preferentially one of both solutes after thestripping of the organic phases. The aqueous solutionsobtained from the stripping were submitted to new ex-tractions with the same solvent. After several contactsan aqueous phase containing one acid was obtained.

6.5. Regeneration of the solvent TOA–1-decanol–dodecane

The experiments carried out in order to regener-ate the solvent prove that three stripping with 0.1N(NH4)2CO3 solution permit to recover the acids fromthe organic phase. All the same, the solutes can berecuperated by one stripping with higher carbon-ate concentration, 1N (NH4)2CO3. The regenerationof the organic phases coming from the system ofcountercurrent extraction is feasible also with 0.2 MH2SO4 solution.

7. Conclusions

The organic phase including TOA as extractant,1-decanol as modifier, and dodecane as inert diluentpermits to obtain an important extent of extractionof both acids and in the same time to extract selec-tively tartaric acid. High concentrations of TOA and1-decanol favour the removal of both solutes, conse-quently the solvent containing 30% (v/v) of TOA can

M. Marinova et al. / Separation and Purification Technology 37 (2004) 199–207 207

be used for unselective recovery of acids from aque-ous streams in order to purify them. Taking into ac-count the selective extraction of tartaric acid, the bestsolvent composition corresponds to 15% (v/v) TOA,15% (v/v) 1-decanol, 70% (v/v) dodecane which per-mits to remove 90% of tartaric acid and 40% of lacticacid. A simulation of a countercurrent extraction usingthis solvent leads to selective recovery of tartaric acid.

Acknowledgements

Maria Marinova gratefully acknowledges the finan-cial support from the Centre Culturel Français in Bul-garia for her co-supervised Ph.D. thesis.

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