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Available online at www.sciencedirect.com

Fluid Phase Equilibria 265 (2008) 122–128

Liquid–liquid equilibria of the systems isobutyl acetate + isobutylalcohol + water and isobutyl acetate + isobutyl alcohol + glycerol

at different temperatures

A. Chafer ∗, J. de la Torre, J.B. Monton, E. LladosaDepartamento de Ingenierıa Quımica, Escuela Tecnica Superior de Ingenierıa, Universitat de Valencia, 46100 Burjassot, Valencia, Spain

Received 12 November 2007; received in revised form 14 January 2008; accepted 15 January 2008Available online 19 January 2008

bstract

In this work, experimental liquid–liquid equilibria (LLE) data of the isobutyl acetate + isobutyl alcohol + water and isobutyl acetate + isobutyllcohol + glycerol systems are presented. The LLE of both systems have been measured at 283.15 and 323.15 K. The NRTL and UNIQUAC models

ere applied to both ternary systems. The interaction parameters obtained from both models successfully correlated the equilibrium compositions.he experimental tie lines were compared to the values predicted by the UNIFAC method. Moreover, the solvent capabilities of water and glycerolere compared.2008 Elsevier B.V. All rights reserved.

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eywords: Liquid–liquid equilibria; Isobutyl acetate; Isobutyl alcohol; Water;

. Introduction

Isobutyl acetate is a widely solvent used in Chemical Indus-ry. It is used alone or in solvent blends in applications includingoatings, inks, adhesives, industrial cleaners and degreasers.he isobutyl acetate is produced by etherification of acetic acidith isobutyl alcohol. Final purification of acetate by traditional

echnologies is a relatively complex procedure due to the exis-ence of a minimum boiling point azeotrope in the isobutyllcohol + isobutyl acetate mixture at atmospheric pressure.

Azeotropes are non-ideal mixtures whose components areery difficult and, hence, expensive to separate. This can bevercome by several techniques including azeotropic and extrac-ive distillation [1–3], reactive distillation [4,5], liquid–liquidxtraction (LLE) [6], adsorption [7], membrane pervapora-ion [8], salt addition [9] and pressure-swing distillation (PSD)10].

This work is undertaken as a part of the thermodynamicesearch on the separation of isobutyl alcohol + isobutyl acetateixture using different techniques.

∗ Corresponding author. Tel.: +34 963544540; fax: +34 963544898.E-mail address: amparo.chafer@uv.es (A. Chafer).

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378-3812/$ – see front matter © 2008 Elsevier B.V. All rights reserved.oi:10.1016/j.fluid.2008.01.010

rol; UNIQUAC; NRTL

Firstly, the separation can be improved making a simplehange in pressure, provided that the azeotropic compositions sensitive to pressure. This possibility has been investigated inrevious work [11], showing that the azeotropic composition hasstrong dependency on pressure. This phenomenon is of great

mportance for the possibility of separation by pressure-swingistillation [11,12].

Another possibility of improving the separation can be addingn agent that alters the relative volatility of the componentsextractive distillation). To this aim, different entrainers werenvestigated [12–15]. The purpose of screening solvents forxtractive distillation is to determine whether this is a promisingeparation technique, and if so to select which of several solventsppears to be the most selective.

As a part of a continuing program, another technique ofeparation is explored in this work: liquid–liquid extraction.nfortunately, the study of the viability of this separation

echnique is limited by the lack of data related to the thermody-amic behaviour of ternary systems containing isobutyl acetate,sobutyl alcohol and different solvents which might be used to

eparate these compounds by liquid–liquid extraction.

Water was chosen as a first possible solvent because waters a green and cheap solvent. On the other hand, water is a sec-ndary product on the isobutyl acetate made from acetic acid

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A. Chafer et al. / Fluid Phas

nd isobutyl alcohol reaction. This can also be a good reasono obtain equilibria data of the ternary system. So the ternaryiquid–liquid equilibria of the system isobutyl acetate + isobutyllcohol + water has been measured at 283.15 and 323.15 K inrder to study the viability of water as a solvent and the influencef temperature on the equilibria.

Moreover, as an alternative to water, it was chosen an alco-ol with higher molecular weight than isobutyl alcohol. Thislcohol can be able to achieve the separation between isobutylcetate and isobutyl alcohol. The behaviour of several alcoholss possible solvents was been investigated by means of ASPENPLIT V2006-Aspentech software [16]. Between all the alco-ols studied, only glycerol has shown an appropriate behaviouro be considered. Finally, glycerol can be considered as a solventnvironmentally friendly and relatively cheap. So the LLE dataf the system isobutyl acetate + isobutyl alcohol + glycerol haseen obtained at 283.15 and 323.15 K.

The LLE data were correlated using the NRTL and UNI-UAC activity coefficient models. The experimental tie linesere compared to the values predicted by the UNIFAC method.he influence of the temperature on the LLE has been studied

or both systems. Finally the solvent capability of both solventsas been compared.

. Experimental

.1. Chemicals

Ethanol (>99.5 mass%, analytical grade) was purchased fromanreac. Isobutyl acetate (≥98.5% (GC)) was supplied by Fluka;

sobutyl alcohol (99.5%) was purchased from Sigma–Aldrich;nd finally, glycerol (99.6% for analysis ACS) was supplied bycros organics. Water from NANO pure was used. The reagentsere used without further purification after chromatography

ailed to show any significant impurities. The refractive indexesf the pure components were measured at 298.15 K using anbbe refractometer Atago 3T, and the densities were measured

t 298.15 K using an Anton Paar DMA 58 densimeter. Tem-erature was controlled to ±0.01 K with a thermostated bath.

he uncertainly in refractive index and density measurementsre ±0.0002 and ±0.01 kg m−3, respectively. The experimen-al values of these properties are given in Table 1 togetherith those given in the literature. Appropriate precautions were

cuih

able 1ensities ρ, refractive indexes nD, and UNIQUAC structural parameters of the used p

ompound ρ (298.15 K) (kg m−3) nD (29

Experimental Literaturea Exper

sobutyl acetate 866.12 867.70 1.3876sobutyl alcohol 797.83 797.80 1.3938

ater 997.06 997.05 1.3325lycerol 1258.5 1257.9 1.4726

a Taken from TRC tables [17].b DECHEMA [18].c Daubert and Danner [19].

ilibria 265 (2008) 122–128 123

aken when handling the reagents in order to avoid hydra-ion.

.2. Equilibrium measurements

LLE measurements for the ternary systems were made atwo temperatures. Equilibrium data were obtained by preparing

ixtures with a bulk composition in the immiscibility regionhich were placed inside of test tubes which were filled almost

ompletely. The reason for this is to prevent the appearance ofn additional vapour phase, liable to happen when working atigh temperatures. The tested tubes were followed by intensetirring at least 5 h and setting for at least 24 h at constant tem-erature. The temperature was controlled with a thermostatedath (UNITRONIC ORBITAL from SELECTA with an incor-orated stirring system). The accuracy of the temperatureeasurements was ±0.1 K. At the end of the setting period,

amples were taken from both phases and analyzed by gashromatography. This analysis provides the tie data of ternaryystems. The time necessary to attain equilibrium, no varia-ion of composition with time, was established in preliminaryxperiments.

.3. Analysis

The composition of the sampled liquid phases were deter-ined using a HP 6890 Series chromatograph equipped withthermal conductivity detector (TCD), an HP3395 integrator

nd a 2 m × 1/8 in. column packed with Porapack Q-S 80/100.etector temperature was 533 K for both systems, whereas the

njector and column temperatures were 483 K for the isobutylcetate + isobutyl alcohol + water system, and 523 and 513 Kespectively for isobutyl acetate + isobutyl alcohol + glycerol.ery good peak separation was achieved under these condi-

ions and calibration analyses were carried out to convert theeak areas ratio on the mass composition of the sample. In ordero obtain miscible mixtures of the standards, 1 mL of ethanolas been added to calibration vials. Like this, the mixtures of

hromatograph. The standard deviation in the mole fraction wassually less than 0.002. Ethanol was also added to samples ofmmiscible phases previously to analysis, in order to ensure aomogeneous phase at room temperature.

ure components

8.15 K) UNIQUAC parameters

imental Literature rib qi

b

1.3880a 4.8266 4.19181.3938a 3.4535 3.0481.3325a 0.9200 1.39901.4730c 3.5857 3.0599

1 e Equilibria 265 (2008) 122–128

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Table 3Liquid–liquid equilibrium experimental data of the system isobutyl acetate(1) + isobutyl alcohol (2) + glycerol (3)

T (K) Isobutyl acetate rich phase Glycerol rich phase

x1 x2 x1 x2

283.15 1.000 0.000 0.007 0.0000.935 0.065 0.006 0.0090.875 0.125 0.007 0.0170.816 0.184 0.006 0.0260.767 0.233 0.005 0.0280.688 0.299 0.006 0.0350.620 0.359 0.006 0.0430.577 0.399 0.005 0.0420.531 0.435 0.005 0.0490.460 0.498 0.005 0.0590.395 0.552 0.005 0.064

24 A. Chafer et al. / Fluid Phas

. Results and discussion

.1. Experimental data

The determination of composition of the equilib-ium liquid phases for the ternary mixtures of isobutylcetate + isobutyl alcohol + water and isobutyl acetate + isobutyllcohol + glycerol were carried out at 283.15 and 323.15 Kt atmospheric pressure and are presented in Tables 2 and 3,espectively. All concentrations are expressed in mole fractions.

The liquid–liquid phase diagrams for isobutylcetate + isobutyl alcohol + water system are type II accordingo Sorensen and Artl [20] where two pairs of partially miscibleiquids are formed. On the other hand, the general shape ofhe ternary diagrams for the system isobutyl acetate + isobutyl

lcohol + glycerol are type I, where only one liquid pair hasery low partially miscibility and two liquid pairs are miscible20].

able 2iquid–liquid equilibrium experimental data of the system isobutyl acetate

1) + isobutyl alcohol (2) + water (3)

(K) Isobutyl acetate rich phase Water rich phase

x1 x2 x1 x2

83.15 0.935 0.000 0.001 0.0000.808 0.090 0.002 0.0050.720 0.149 0.002 0.0080.616 0.204 0.001 0.0100.508 0.276 0.001 0.0120.450 0.314 0.001 0.0130.397 0.342 0.003 0.0150.368 0.359 0.001 0.0150.250 0.424 0.002 0.0180.230 0.428 0.001 0.0170.204 0.442 0.001 0.0180.233 0.429 0.001 0.0180.095 0.502 0.001 0.0220.090 0.508 0.001 0.0220.091 0.511 0.002 0.0220.054 0.528 0.000 0.0240.037 0.535 0.000 0.0250.020 0.544 0.000 0.0260.000 0.557 0.000 0.027

23.15 0.903 0.000 0.002 0.0000.768 0.098 0.003 0.0030.678 0.155 0.003 0.0040.590 0.210 0.001 0.0050.474 0.280 0.001 0.0070.434 0.319 0.001 0.0080.376 0.342 0.001 0.0090.346 0.355 0.001 0.0090.236 0.416 0.000 0.0110.217 0.417 0.001 0.0110.194 0.428 0.001 0.0120.308 0.382 0.000 0.0090.085 0.474 0.000 0.0150.154 0.446 0.001 0.0130.050 0.486 0.000 0.0160.034 0.493 0.000 0.0170.000 0.510 0.000 0.019

0.351 0.587 0.006 0.0730.316 0.618 0.005 0.0720.284 0.639 0.005 0.0760.262 0.651 0.005 0.0770.220 0.684 0.006 0.0950.187 0.702 0.005 0.0900.152 0.718 0.005 0.1040.095 0.720 0.005 0.1190.059 0.709 0.005 0.149

323.15 1.000 0.000 0.007 0.0000.933 0.067 0.006 0.0080.862 0.125 0.006 0.0130.806 0.183 0.011 0.0210.754 0.230 0.007 0.0290.678 0.294 0.008 0.0360.610 0.351 0.007 0.0440.568 0.391 0.008 0.0510.516 0.423 0.009 0.0600.448 0.481 0.009 0.0640.380 0.525 0.008 0.0740.335 0.555 0.009 0.0790.299 0.579 0.009 0.0900.265 0.596 0.011 0.0990.247 0.611 0.009 0.1020.198 0.613 0.011 0.124

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0.164 0.614 0.010 0.1320.122 0.586 0.012 0.154

.2. Data correlation

The NRTL [21] and UNIQUAC [22] models were used to cor-elate the experimental data for the ternary systems discussedere. To fit the UNIQUAC interaction parameters, the struc-ural parameters (ri and qi) recommended by DECHEMA [18]ere used for the pure components and are listed in Table 1.he non-randomness parameter (αij) of the NRTL equation wasetermined as the best set the values between 0.2 and 0.3 andhe results are given in Table 4.

There are two effective binary interaction parameters for ainary subsystem. Therefore, six effective binary interactionarameters are required for a ternary system. The corresponding

ets of binary interaction parameters were determined by mini-izing the differences between the experimental and calculatedole fractions for each of the components over all the tie lines

same global initial mixture). The objective function (OF) used

A. Chafer et al. / Fluid Phase Equilibria 265 (2008) 122–128 125

Table 4UNIQUAC and NRTL binary interaction parameters for the systems isobutyl acetate (1) + isobutyl alcohol (2) + water (3) and isobutyl acetate (1) + isobutyl alcohol(2) + glycerol (3) systems

T (K) i–j UNIQUAC parameters rmsd (%) NRTL parameters rmsd (%)

Aij (J mol−1) Aji (J mol−1) α Aij (J mol−1) Aji (J mol−1)

Isobutyl acetate (1) + isobutyl alcohol (2) + water (3)

283.15

1–2 −2075.15 2494.330.30

0.3 5088.08 −3106.430.211–3 4850.83 188.66 0.3 5185.77 12526.06

2–3 980.51 990.68 0.3 234.22 8451.50

323.15

1–2 3548.86 −1793.210.29

0.3 −562.80 3370.990.201–3 4160.09 1060.39 0.3 4875.07 13607.93

2–3 −239.23 2737.25 0.3 −343.97 11052.50

Isobutyl acetate (1) + isobutyl alcohol (2) + glycerol (3)

283.15

1–2 338.88 −243.710.33

0.3 −1697.63 2411.840.351–3 4538.24 935.88 0.2 11388.32 8048.67

2–3 260.88 1724.71 0.2 1668.12 4532.43

3

1–2 −2550.01 4527.868

0.3 3158.06 −2767.86

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3.3. Prediction

The experimental data were compared with those predictedby the UNIFAC group contribution method [23]. The interac-

23.15 0.31–3 3740.82 1227.902–3 515.73 1482.55

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k=1

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3∑i=1

(xijk − xijk)2 (1)

here M is the number of tie lines, x indicates the experimentalole fraction, x the calculated mole fraction, and subscripts i, j

nd k denote, respectively, component, phase and tie line.Two different kinds of correlations were made. First, the cor-

elation of experimental data was carried out separately at eachemperature. The binary interaction parameters calculated in thisay are given in Table 4. Also the root-mean-square deviation

rmsd) of the phase composition is included in this table:

msd = 100 ×⎛⎝

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(2)

The rmsd is a measure of the agreement between the exper-mental and calculated data. In Table 4 it can be observedhat both models were found to properly correlate the dataor the two systems studied, but the NRTL model led to theest results for isobutyl acetate + isobutyl alcohol + water sys-em and the UNIQUAC model led to the best results for isobutylcetate + isobutyl alcohol + glycerol system. In Figs. 1 and 2,xperimental data at 283.15 and 323.15 K have been plottedor isobutyl acetate + isobutyl alcohol + water system togetherith binodal curves calculated using NRTL model and some

xperimental and calculated tie lines. In Figs. 3 and 4 exper-mental data at 283.15 and 323.15 K have been plotted forsobutyl acetate + isobutyl alcohol + glycerol system togetherith binodal curves calculated using UNIQUAC model and

ome experimental and calculated tie lines.

Although a good fit is obtained for each temperature, the

arameters determined have no relation between them. There-ore, for each system, a simultaneous correlation of all thexperimental LLE data for the two temperatures was carried

F(pNm

0.440.2 13379.03 8423.730.2 859.71 5404.11

ut in order to obtain a unique set of parameters (global param-ters), valid for the range of temperatures studied, increasing inhis way their application. Nonetheless the residuals obtainedre higher. Table 5 lists the optimized interaction parametersor simultaneous correlation obtained using UNIQUAC for thesobutyl acetate + isobutyl alcohol + water system and NRTL forhe isobutyl acetate + isobutyl alcohol + glycerol system.

ig. 1. Liquid–liquid equilibria of isobutyl acetate (1) + isobutyl alcohol2) + water (3) system at 283.15 K. Experimental data: (�) isobutyl acetate richhase, (©) aqueous phase and (—) experimental tie lines. Calculated usingRTL model: (– ·· –) binodal curve and (· · ·) tie lines. Predicted by UNIFACethod: binodal curve (- - -).

126 A. Chafer et al. / Fluid Phase Equilibria 265 (2008) 122–128

Fig. 2. Liquid–liquid equilibria of isobutyl acetate (1) + isobutyl alcohol(2) + water (3) system at 323.15 K. Experimental data: (�) isobutyl acetate richpN

tooiiFp

(at

F(ruU

Fig. 4. Liquid–liquid equilibria of isobutyl acetate (1) + isobutyl alcohol(2) + glycerol (3) system at 323.15 K. Experimental data: (�) isobutyl acetaterich phase, (©) glycerol rich phase and (—) experimental tie lines. Calculatedusing UNIQUAC model: (– ·· –) binodal curve and (· · ·) tie lines.

Table 5Global binary interaction parameters (temperature independent) for the isobutylacetate (1) + isobutyl alcohol (2) + water (3) and isobutyl acetate (1) + isobutylalcohol (2) + glycerol (3) systems

Pair i–j UNIQUAC parameters rmsd (%)

Aij (J mol−1) Aji (J mol−1)

Isobutyl acetate (1) + isobutyl alcohol (2) + water (3)1–2 620.48 139.88

0.4221–3 4054.20 1004.412–3 −1.63 2351.52

Pair i–j NRTL parameters rmsd (%)

hase, (©) aqueous phase and (—) experimental tie lines. Calculated usingRTL model: (– ·· –) binodal curve and (· · ·) tie lines.

ion and structural parameters required for the implementationf the method were taken from Hansen et al. [24]. The valuesf the UNIFAC parameters for LLE prediction are summarisedn Tables 6 and 7. The quality of the prediction can be observedn Figs. 1 and 3, were the binodal curve predicted by UNI-AC together with experimental and correlated tie line areresented.

For the system isobutyl acetate + isobutyl alcohol + waterFig. 1) a good prediction can be observed. However for isobutyl

cetate + isobutyl alcohol + glycerol system (Fig. 3) the predic-ion is very poor.

ig. 3. Liquid–liquid equilibria of isobutyl acetate (1) + isobutyl alcohol2) + glycerol (3) system at 283.15 K. Experimental data: (�) isobutyl acetateich phase, (©) glycerol rich phase and (—) experimental tie lines. Calculatedsing UNIQUAC model: (– ·· –) binodal curve and (· · ·) tie lines. Predicted byNIFAC method: binodal curve (- - -).

α Aij (J mol−1) Aji (J mol−1)

Isobutyl acetate (1) + isobutyl alcohol (2) + glycerol (3)1–2 0.3 2999.75 −2015.66

0.5781–3 0.2 9666.40 8421.912–3 0.2 1632.70 4718.01

Table 6UNIFAC Rk and Qk parameters [24]

Sub group (k) Main group no. Rk Qk

CH3 1 0.9011 0.848CH2 1 0.6744 0.540CH 1 0.4469 0.228CH3COO 11 1.9031 1.728OH 5 1.0000 1.200H2O 7 0.9200 1.400

Table 7UNIFAC group interaction parameters [24]

m n am n an m

CH3,CH2,CH CH3COO 232.1 114.8CH3,CH2,CH OH 986.5 156.4CH3,CH2,CH H2O 1318 300CH3COO OH 245.4 101.1CH3COO H2O 200.8 72.87H2O OH −229.1 353.5

A. Chafer et al. / Fluid Phase Equ

Fig. 5. Distribution of isobutyl alcohol between the extract and raffinate phases.I(t

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sobutyl acetate (1) + isobutyl alcohol (2) + water (3) system: (�) 283.15 K and�) 323.15 K and isobutyl acetate (1) + isobutyl alcohol (2) + glycerol (3) sys-em: (�) 283.15 K and (©) 323.15 K.

.4. Comparative study of solvents

A comparative study of water and glycerol as solvents in theeparation of the azeotropic mixture (isobutyl acetate + isobutyllcohol) by liquid–liquid extraction was made. In Fig. 5 theffect of the solvent in the distribution of isobutyl alcohol inoth liquid phases is visualized; it can be observed, for bothystems, that the solubility of isobutyl alcohol in the extractwater or glycerol rich phase) is much lower than in the raffinateisobutyl acetate rich phase), which is according to the slope ofhe tie lines. Therefore, it can be concluded that both, water andlycerol, would not good solvents.

. Conclusions

Liquid–liquid equilibria of isobutyl acetate + isobutyl alco-ol + water and isobutyl acetate + isobutyl alcohol + glycerolave been measured at 283.15 and 323.15 K. The temperatureas practically no effect on the size of immiscibility region in thenvestigated temperature range. The LLE data were correlatedsing the NRTL and UNIQUAC activity coefficient models.he correlation with the NRTL equation gives better results for

he system isobutyl acetate + isobutyl alcohol + water and theNIQUAC equation fits the experimental data for the system

sobutyl acetate + isobutyl alcohol + glycerol better. The simul-aneous correlation of all the experimental LLE data for thewo temperatures gives a unique set of parameters in the rangef the temperature considered, which allows to describe thehase equilibrium behaviour appropriately. Experimental dataere finally compared to those predicted by the UNIFAC group

ontribution method. It was found that this method gives a rel-tively good prediction of the (liquid–liquid) equilibrium forhe isobutyl acetate + isobutyl alcohol + water system, but prob-

bly not enough for many practical purposes. However, for thesobutyl acetate + isobutyl alcohol + glycerol system this methodives a liquid–liquid behaviour very different to those experi-entally obtained. The effect of the solvent in the distribution

[

[

ilibria 265 (2008) 122–128 127

f isobutyl alcohol in both liquid phases shows that as water aslycerol could be not good solvents.

ist of symbolsUNIFAC group interaction parameterinteraction parametersnumber of tie lines

D refractive indexF objective function

area parameter in UNIQUAC equationk UNIFAC parameter

volume parameter in UNIQUAC equationk UNIFAC parameter

msd root-mean-square deviationcomposition of liquid phase, mole fraction

reek lettersnon-randomness factor in NRTL equationdensity

uperscriptcalculated

ubscriptcomponent icomponent jcomponent kgroup mgroup n

cknowledgments

Financial support from the Ministerio de Ciencia y Tec-ologıa of Spain, through project CTQ2007-61400/PPQ,EDER European Program and the Conselleria de Cultura,ducacio i Esport (Generalitat Valenciana) of Valencia (Spain)re gratefully acknowledged. One of the authors (E. Lladosa)as been funded by a grant from the Ministerio de Ciencia yecnologıa of Spain.

eferences

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1 e Equ

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[

[

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[

[

[

28 A. Chafer et al. / Fluid Phas

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[[[[

ilibria 265 (2008) 122–128

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