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Fluid Phase Equilibria 325 (2012) 100– 104

Contents lists available at SciVerse ScienceDirect

Fluid Phase Equilibria

j o ur nal homep age: www.elsev ier .com/ locate / f lu id

iquid–liquid equilibria of water + 2,3-butanediol + isobutanol at severalemperatures

an-Yang Wu, De-Tao Pan, Jia-Wen Zhu ∗, Kui Chen, Bin Wu, Li-Jun Jihemical Engineering Research Center, East China University of Science & Technology, Shanghai 200237, China

r t i c l e i n f o

rticle history:eceived 27 January 2012eceived in revised form 5 April 2012ccepted 21 April 2012vailable online 28 April 2012

a b s t r a c t

(Liquid–liquid) equilibrium (LLE) data for the ternary system of water + 2,3-butanediol + isobutanol havebeen determined at 298.2, 308.2 and 318.2 K and atmospheric pressure. Solubility curves were obtainedby the cloud point method, while compositions of tie-lines were obtained by gas chromatography. Distri-bution coefficients and separation factors have been evaluated for the immiscibility region. The reliabilityof the experimental tie-lines has been confirmed by using Othmer–Tobias correlation. The LLE data of the

eywords:iquid–liquid equilibria,3-Butanediol

sobutanolNIQUAC

ternary systems have been correlated by both the NRTL model and UNIQUAC model. Root mean squaredeviations between experimental and calculated compositions were considered satisfactory.

© 2012 Elsevier B.V. All rights reserved.

RTL

. Introduction

The 2,3-butanediol (2,3-BD), whose combustion value is7.19 kJ/g [1], has been considered a potential and alternative fuel.t can be produced by chemical synthesis and microbial route. Thehemical synthesis of 2,3-BD is unambiguously more costly thanhe microbial route and therefore commercial production of thisompound would be limited to fermentation. Its microbial prepa-ation has been observed in several yeasts and bacteria from variousenera such as Klebsiella, Bacillus, Serratia and Pseudomonas since906 [2–5]. However, the separation of 2,3-butanediol from fer-entation broth, due to its high boiling point and hydrophilicity

nd the specialty of the fermentation broth [6,7], has always beenne of the bottlenecks to realize its commercial production.

Since the fermented liquors, obtained by Serratia marcescensrom our coorporated lab, contain the concentration of 2,3-utanediol which is below 15% (mass percent) along withomplicated impurities which cause difficulty in separation andince 2,3-butanediol has a much higher boiling point than that ofater and may not be distilled out directly, extraction from the

ermentation liquors by a suitable solvent seems to be a feasi-le method. Various organic solvents have been investigated and

eported for 2,3-butanediol extraction [8–10]. Isobutanol used inhis study may be a suitable solvent for extraction of 2,3-butanediol

∗ Corresponding author. Tel.: +86 21 64253003; fax: +86 21 64253914.E-mail addresses: jwzhu@ecust.edu.cn, wyywitty@163.com (J.-W. Zhu).

378-3812/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.fluid.2012.04.018

from water, being capable of forming azeotropic mixtures withwater to take it from 2,3-butanediol.

The aim of this work is to present the phase behavior of LLE forthe (water + 2,3-butanediol + isobutanol) ternary system at 298.2,308.2 and 318.2 K and atmospheric pressure, which is not availablein the literature. The experimental data were correlated by activ-ity coefficients expressions NRTL [11] and UNIQUAC [12]. Finally,the reliability of these models is tested by comparison with exper-imental results.

2. Experimental

2.1. Chemicals

All the chemicals used in this study were purchased fromcommercial sources. 2,3-Butanediol was supplied by Sino-pharmChemical Reagent Co., Ltd. with a minimum mass fraction purityof 99.2%. Isobutanol was provided by Shanghai Chemical ReagentCo., Ltd. with a minimum mass fraction purity of 99.5%. They wereused directly without further treatment in this study. Water wasdistilled twice before utilization.

The purity of these materials was checked and assured by gaschromatography. The normal boiling point and refractive indexvalues were measured in this study and reported in Table 1 in com-parison with the literature data [13–16] so as to demonstrate the

purity of the compounds. Refractive indexes were measured by anAbbe refractometer (WZS-I model, made in Shanghai, China), withan accuracy of ±0.0001. The boiling points were determined byan Ebuillometer (DZBW model, made in Nanjing, China), with an

Y.-Y. Wu et al. / Fluid Phase Equilibria 325 (2012) 100– 104 101

Table 1Refractive indexes and densities at T = 293.2 K and boiling points at 101.3 kPa, of thecompounds.

2,3-Butanediolb Isobutanol Water

Refractive indexes Exp. 1.4375 1.3972 1.3325Lit.a 1.4366 1.3988 1.3325

Boiling points, K Exp. 454.21 372.87 373.3Lit.a 454.2 372.66 373.26

Densities, g cm−3 Exp. 1.0023 0.8065 0.8062Lit. 1.0033c 0.8063a 0.8058c

rd 3.756 3.45 0.92qd 3.32 3.05 1.4

a Taken from Ref. [13].

ado

2

ss

ptkCLmombis(po

a(otamtawtt

ibogat(f(tQrw

1.000.750.500.250.00

0.00

0.25

0.50

0.75

1.000.00

0.25

0.50

0.75

1.00

2,3-butanediol

Iso-butanol water

b Taken from Ref. [14].c Taken from Ref. [15].d Taken from Ref. [16].

ccuracy of ±0.01 K. And densities were measured by a DMA-4100ensimeter (Anton Paar GmbH model, Germany), with an accuracyf ±0.0001 g cm−3.

.2. Equilibrium measurements

Three different temperatures (298.2, 308.2 and 318.2 K) at atmo-pheric pressure were selected to study the ternary equilibriumystem to observe the evaluation of the binodal curves and tie-lines.

The binodal (solubility) curves were determined by the cloudoint method [17] in an equilibrium glass cell with a water jacketo maintain isothermal conditions. Temperature in the cell wasept constant by circulating water from a water bath (SUPER-ONSTANTTEP BATH, Shanghai Precision Science Instrument Co.,td.), which is equipped with a temperature controller capable ofaintaining the temperature within ±0.1 K. The major central part

f the solubility curves was obtained by titrating heterogeneousixtures of water + isobutanol with 2,3-butanediol until the tur-

idity had disappeared. For the water-side and solvent-side regionsn which the curve and the sides of the triangle are close and exhibitimilar slopes, binary mixtures of either (water + 2,3-butanediol) orisobutanol + 2,3-butanediol) were titrated against the third com-onent until the transition from homogeneity to heterogeneity wasbserved.

All mixtures were prepared by weighing with a Sartorius scaleccurate to within ±0.0001 g. Mutual solubility values of thewater + isobutanol) binary were measured using the method basedn the detection of the cloud point. The transition point betweenhe homogeneous and heterogeneous zones was determined visu-lly. The reliability of the method depends on the precision of theicro burette with an accuracy of ±0.01 cm3, and is limited by

he visual inspection of the transition across the apparatus. Theccuracy of the visual inspection of the transition is achieved byaiting approximately 5 min in the transition point and observing

he heterogeneity. All visual experiments were repeated at leasthree times in order to acquire high accuracy.

End-point determinations of the tie-lines were based upon thendependent analysis of the conjugate phases that were regarded aseing in equilibrium. For this purpose, mixtures of known massesf water, 2,3-butanediol, and isobutanol lying within the hetero-eneous zone were introduced into the equilibrium cell and weregitated for not less than 2 h with a magnetic stirrer vigorously, andhen left for 4 h to settle down into raffinate (aqueous) and extractsolvent) layers. The compositions of liquid samples withdrawnrom conjugate phases were analyzed by a gas chromatographGC9790) with a thermal conductivity detector (TCD), after calibra-

ion with gravimetrically prepared standard solutions. A PorapackS packed column (3 m × ̊ 3 mm × 0.5 mm) was used to sepa-

ate components. The oven, injector and detector temperaturesere 473.2, 473.2 and 493.2 K, respectively. High-purity hydrogen

Fig. 1. Ternary diagram for LLE of (water + 2,3-butanediol + isobutanol) at 298.2 K:(—) experimental solubility curve; (©) experimental tie-line data; (. . .) experimen-tal tie-line.

(99.9999% purity) dehydrated with silica gel was used as the car-rier gas at a constant flow rate of 30 mL min−1. Each sample wasanalyzed at least three times to ensure accuracy. The uncertaintyin mass fractions was within ±0.003.

3. Results and discussion

The LLE measurements were made for the ternary system of(water + 2,3-butanediol + isobutanol) at 298.2, 308.2 and 318.2 Kand atmospheric pressure. The experimental binodal curves for thisternary system at each temperature are listed in Table 2, for whichWi refers to the mass fraction of ith component. The experimen-tal tie-line compositions of the equilibrium phases are shown inTable 3, for which Wi1 and Wi3 refer to the mass fractions of the ithcomponent in the aqueous and solvent phases, respectively.

The experimental equilibrium data of the ternary system atT = 298.2 K are plotted in Fig. 1. As can be seen from Fig. 1,the system exhibited type 1 phase behavior [18,19], having onlyone liquid pair of partially miscible (isobutanol + water) and twopairs of completely miscible (water + 2,3-butanediol) and (2,3-butanediol + isobutanol). Also, similar results are observed atT = 308.2 K and T = 318.2 K in Figs. 2 and 3.

The effectiveness of 2,3-butanediol extraction by isobutanol isgiven by its separation factor, which is a measure of the ability ofisobutanol to separate the 2,3-butanediol from water. To show theselectivity and extraction strength of the solvent to extract 2,3-butanediol, the distribution coefficients, Di, for water (i = 1) and2,3-butanediol (i = 2), and the separation factors, S, are calculatedaccording to the following equations:

Di = Wi3

Wi1(1)

S = distribution coefficient of 2,3-butanedioldistribution coefficient of water

= D2

D1(2)

where Wi3 and Wi1 are the mass concentrations of component i insolvent-rich and water-rich phases; D1 and D2 are the distributioncoefficients of water and 2,3-butanediol, respectively.

The distribution coefficients and separation factors for eachtemperature are given in Table 4. Separation factors was found tobe greater than 1.5, for the systems reported here, which meansthat the extraction of 2,3-butanediol by isobutanol is possible. The

102 Y.-Y. Wu et al. / Fluid Phase Equilibria 325 (2012) 100– 104

Table 2Experimental binodal curve data (mass fraction) of [water (1) + 2,3-buatanediol (2) + isobutanol (3)] at different temperatures.

T/K W1 W2 W3 W1 W2 W3 W1 W2 W3

298.2 0.9184 0.0000 0.0816 0.6915 0.1575 0.1510 0.3336 0.1481 0.51830.8400 0.0734 0.0866 0.6612 0.1621 0.1767 0.2923 0.1309 0.57680.8300 0.0808 0.0892 0.6306 0.1632 0.2062 0.2708 0.1203 0.60880.8063 0.1013 0.0924 0.5983 0.1660 0.2357 0.2561 0.1035 0.64040.7726 0.1243 0.1031 0.5611 0.1650 0.2739 0.2369 0.0873 0.67580.7561 0.1317 0.1122 0.5128 0.1659 0.3213 0.2150 0.0690 0.71600.7429 0.1400 0.1171 0.4536 0.1622 0.3842 0.1889 0.0466 0.76450.7247 0.1448 0.1305 0.4255 0.1621 0.4124 0.1745 0.0300 0.79550.7109 0.1528 0.1363 0.3518 0.1529 0.4953 0.1566 0.0000 0.8434

308.2 0.9208 0.0000 0.0792 0.6958 0.1416 0.1626 0.3491 0.1392 0.51170.8704 0.0466 0.0830 0.6605 0.1487 0.1908 0.3169 0.1305 0.55260.8521 0.0590 0.0889 0.6282 0.1503 0.2215 0.2876 0.1179 0.59450.8153 0.0918 0.0929 0.5576 0.1556 0.2868 0.2608 0.0967 0.64250.7995 0.1001 0.1004 0.5168 0.1543 0.3289 0.2389 0.0776 0.68350.7710 0.1166 0.1124 0.4742 0.1531 0.3727 0.2111 0.0517 0.73720.7563 0.1227 0.1210 0.4018 0.1494 0.4488 0.1919 0.0316 0.77650.7186 0.1375 0.1439 0.3754 0.1438 0.4808 0.1788 0.0000 0.8212

318.2 0.9138 0.0000 0.0862 0.6106 0.1386 0.2508 0.3787 0.1305 0.49080.8624 0.0466 0.0910 0.5736 0.1396 0.2868 0.3456 0.1228 0.53160.8431 0.0610 0.0959 0.5489 0.1396 0.3115 0.3067 0.1077 0.58560.8177 0.0818 0.1005 0.5188 0.1403 0.3409 0.2796 0.0938 0.62660.7814 0.1001 0.1185 0.4990 0.1413 0.3597 0.2563 0.0768 0.6669

sa

at

l

wWattid

f

TE

0.7413 0.1171 0.1416 0.4790

0.7053 0.1279 0.1668 0.4456

0.6536 0.1357 0.2107 0.4164

eparation factor is not constant over the whole two-phase regionnd its uncertainty is within ±0.1.

The reliability of experimentally measured tie-line data can bescertained by applying the Othmer–Tobias correlation [20] at eachemperature as below:

n(

1 − W11

W11

)= a + b ln

(1 − W33

W33

)(3)

here W11 is the mass fraction of water in the water-rich phase;33 is the mass fraction of isobutanol in the solvent-rich phase; a

nd b are the constants of Eq. (3). The parameters of this correla-ion are listed in Table 5 and the correlation is shown in Fig. 4 forhe temperatures studied. The correlation factor (R2) being approx-

mately unity indicates the degree of consistency of the relatedata.

Suitable thermodynamic models for activity coefficients areundamental to accurate correlation of the experimental data for

able 3xperimental tie-line data in mass fractions for water (1) + 2,3-buatanediol (2) + isobutan

T/K Organic phase

W13 W23 W33

298.2 0.2738 0.1189 0.6073

0.2352 0.0814 0.6834

0.2096 0.0584 0.7320

0.1968 0.0475 0.7557

0.1897 0.0383 0.7720

0.2179 0.0655 0.7166

308.2 0.2051 0.0443 0.7506

0.2111 0.0518 0.7371

0.2247 0.0632 0.7121

0.2282 0.0685 0.7033

0.2550 0.0910 0.6540

0.2735 0.1086 0.6179

0.2601 0.0960 0.6439

318.2 0.2200 0.0389 0.7411

0.2275 0.0524 0.7201

0.2503 0.0662 0.6835

0.2623 0.0795 0.6582

0.2798 0.0954 0.6248

0.3047 0.1074 0.5879

0.3302 0.1201 0.5497

0.1423 0.3787 0.2344 0.0560 0.70960.1395 0.4149 0.2152 0.0336 0.75120.1375 0.4461 0.1932 0.0000 0.8068

ternary liquid–liquid equilibrium. The most widely utilized modelsin liquid–liquid equilibrium are based on the local composition con-cept, such as NRTL, UNIQUAC, in which the properties of the liquidmixture are considered to be related to the interactions betweenthe components rather than random mixing. In this work, bothof the models were used to correlate the LLE data for the systemof (water + 2,3-butanediol + isobutanol) and a comparison betweenthe two models was made. In fitting the UNIQUAC interactionparameters, the structural parameters (ri and qi) recommended byDECHEMA [21] were used for the pure components and are listedin Table 1. The non-randomness parameter (˛ij) of the NRTL modelwas set to 0.2.

There are two effective binary interaction parameters for a pair

of substances. Therefore, six effective binary interaction param-eters are required for a ternary system. The corresponding setsof binary interaction parameters were determined by minimiz-ing the differences between the experimental and calculated mole

ol (3) ternary system.

Aqueous phase

W11 W21 W31

0.7405 0.1418 0.11770.8001 0.1061 0.09380.8291 0.0847 0.08620.8399 0.0734 0.08670.8565 0.0593 0.08420.8209 0.0931 0.08600.8675 0.0503 0.08220.8451 0.0651 0.08980.8276 0.0809 0.09150.8103 0.0933 0.09640.7648 0.1186 0.11660.6977 0.1405 0.16180.7463 0.1278 0.12590.8601 0.0467 0.09320.8346 0.0680 0.09740.7989 0.0907 0.11040.7683 0.1080 0.12370.7335 0.1187 0.14780.6996 0.1289 0.17150.6576 0.1388 0.2036

Y.-Y. Wu et al. / Fluid Phase Equilibria 325 (2012) 100– 104 103

1.000.750.500.250.00

0.00

0.25

0.50

0.75

1.000.00

0.25

0.50

0.75

1.00

Isobutanol water

2,3-butanediol

F(t

fo

O

wk

rtia

R

F(t

Table 4Distribution coefficients (Di) of water (i = 1) and 2,3-butanediol (i = 2) and separationfactors (S).

T/K D1 D2 S

298.2 0.3697 0.8382 2.270.2940 0.7669 2.610.2528 0.6895 2.730.2343 0.6472 2.760.2215 0.6462 2.920.2654 0.7030 2.65

308.2 0.2364 0.8816 3.730.2498 0.7962 3.190.2715 0.7817 2.880.2816 0.7348 2.610.3335 0.7673 2.300.3921 0.7724 1.970.3485 0.7510 2.16

318.2 0.2557 0.8321 3.250.2725 0.7708 2.830.3133 0.7300 2.330.3413 0.7356 2.160.3815 0.8039 2.110.4356 0.8336 1.910.5021 0.8650 1.72

Table 5Constants of Othmer–Tobias equation for the water + 2,3-butanediol + isobutanolternary system (R2: regression coefficient).

T/K a b R2

298.2 0.7225 1.0936 0.9934

ig. 2. Ternary diagram for LLE of (water + 2,3-butanediol + isobutanol) at 308.2 K:—) experimental solubility curve; (©) experimental tie-line data; (. . .) experimen-al tie-line.

ractions for each of the components over all the tie-lines. Thebjective function (OF) used is expressed as:

F =N∑k

∑j

∑i

(Wexpijk

− Wcalijk )

2(4)

here Wijk is the composition of component i in phase j on tie-line. N is the number of the tie-lines.

Two different kinds of correlations were made. First the cor-elation of experimental data was carried out separately at eachemperature. The parameters (�i,j) calculated in this way are givenn Table 6. Also included in this table is the root-mean-square devi-tion (RMSD) in the phase composition as shown in Eq. (5).

MSD = 100 ×[∑N

k

∑j

∑i(W

expijk

− Wcalijk

)2

6N

]1/2

(5)

1.000.750.500.250.00

0.00

0.25

0.50

0.75

1.000.00

0.25

0.50

0.75

1.00

Isobutanol water

2,3-butanediol

ig. 3. Ternary diagram for LLE of (water + 2,3-butanediol + isobutanol) at 318.2 K:—) experimental solubility curve; (©) experimental tie-line data; (. . .) experimen-al tie-line.

308.2 0.0749 0.6631 0.9885318.2 0.2572 0.7378 0.9946

The RMSD is a measure of the agreement between the experi-mental and calculated data. In Table 6, it can be observed that theNRTL model provides a slightly better correlation of the experimen-tal tie-lines than UNIQUAC based on RMSD values. And althougha good fit is obtained for all temperatures, the parameters deter-mined for each temperature have no relation between them. So, asimultaneous correlation of all the experimental LLE data of thissystem was carried out in order to obtain a unique set of param-eters valid for the range of temperatures studied. Table 7 liststhe optimized UNIQUAC and NRTL interaction parameters (�i,j)

obtained in a simultaneous correlation of all data assuming tem-perature independent parameters. As was expected, the RMSDvalues were higher than when the individual correlation at each

0.50.0-0.5-1.0-1.5-2.0-2.5-3.0-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

ln((1-W

33)/W

33)

ln((1- W11)/W

11)

Fig. 4. Othmer–Tobias plots of the (water + 2.3-butanediol + isobutanol) ternary sys-tems: (�) 298.2 K; (©) 308.2 K; (�) 318.2 K.

104 Y.-Y. Wu et al. / Fluid Phase Equilibria 325 (2012) 100– 104

Table 6UNIQUAC and NRTL binary interaction parameters and RMSD for the system water (1) + 2,3-buatanediol (2) + isobutanol (3).a

Model T/K �12 �21 �13 �31 �23 �32 RMSD (%)

NRTL(˛ = 0.2) 298.2 −17.61 −2668.30 1172.31 −9.56 332.66 −1282.54 0.47308.2 −1197.65 −574.46 1222.51 1.21 −456.97 8347.25 0.51318.2 −6466.80 −740.74 1249.61 −9.39 −556.10 −6487.36 0.38

UNIQUAC 298.2 694.74 250.92 −281.66 8.11 −102.84 981.67 0.75308.2 −660.83 342.18 −295.24 5.74 182.80 −429.79 0.43318.2 −956.40 1181.42 −308.23 14.01 270.39 −553.12 0.34

a The interaction parameters for models are as follows: NRTL, �i,j = (gi,j − gj,i)/R (K); UNIQUAC, �i,j = (ui,j − uj,i)/R (K).

Table 7Optimized temperature independent binary interaction parameters and RMSD for the system water (1) + 2,3-buatanediol (2) + isobutanol (3) fitted to all isotherms.a

Model T(K) �12 �21 �13 �31 �23 �32 RMSD (%)

NRTL(˛ = 0.2) 1386.89 −835.40 1217.42 −2.96 218.39 −165.70 1386.89 0.77−13

K); UN

tvatctt

4

tadcgtrssaIts

LaDNRRSTWqrO

G˛�

[

[[[

[

[

[

[

UNIQUAC 3168.33 −78.41 −273.69

a The interaction parameters for models are as follows: NRTL, �i,j = (gi,j − gj,i)/R (

emperature was made. In any case, the overall magnitude of RMSDalues suggests that the NRTL and UNIQUAC models provide andequate representation of the phase behavior of the ternary sys-em water + 2,3-butanediol + isobutanol at all temperatures. Theseorrelated parameters of models are recommended to be used inhe simulation and design of the liquid–liquid separation for thisernary system.

. Conclusions

The liquid–liquid equilibrium data of the ternary mix-ures water + 2,3-butanediol + isobutanol have been presentedt 298.2, 308.2, 318.2 K and atmospheric pressure. The LLEata were correlated using the NRTL and UNIQUAC activityoefficient models. The correlation with the NRTL equationives better results than the UNIQUAC equation and fitshe experimental data satisfactorily. The simultaneous cor-elation of the three isothermal data sets gives a uniqueet of parameters in the range of the temperature con-idered. Separation factor is found to be greater than 1.5nd it is not constant over the whole two-phase region.t is concluded that isobutanol may serve as a alterna-ive solvent to extract 2,3-butanediol from its dilute aqueousolutions.

ist of symbols, b Othmer–Tobias correlation constants

distribution coefficient number of tie-linesMSD root mean square deviation2 Othmer–Tobias correlation coefficients

separation factor temperature (K)

concentration in mass fraction surface parameter of the UNIQUAC model

size parameter of the UNIQUAC modelF objective function

reek letters non-randomness parameter of the NRTL model

parameters of solution models

[[[[

.74 134.61 2657.02 3168.33 0.93

IQUAC, �i,j = (ui,j − uj,i)/R (K).

Subscriptsi componentj phasek tie-line

Superscriptscal calculatedexp experimental

Acknowledgment

The financial support of the National Natural Science Foundationof China (Grant No. 21106039) is gratefully acknowledged.

References

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