(liquid + liquid) equilibria of (water + ethanol + dimethyl glutarate) at several temperatures

J. Chem. Thermodynamics 35 (2003) 1671–1679

www.elsevier.com/locate/jct

(Liquid+ liquid) equilibriaof (water + ethanol + dimethyl glutarate)

at several temperatures

Erol _IInce, S�. _IIsmail Kırbas�lar*

Istanbul University, Engineering Faculty, Chemical Engineering Department, 34320,

Avcilar, Istanbul, Turkey

Received 30 September 2002; accepted 17 July 2003

Abstract

(Liquid+ liquid) equilibrium (LLE) data of (water + ethanol + dimethyl glutarate) have

been determined experimentally at T ¼ ð298:15; 308:15 and 318.15) K. The reliability of the

experimental tie-line data was ascertained by using the Othmer and Tobias correlation. The

LLE data of the ternary mixture were predicted by UNIFAC method. Distribution coefficients

and separation factors were evaluated for the immiscibility region.

� 2003 Elsevier Ltd. All rights reserved.

Keywords: (Liquid+ liquid) equilibria; Ethanol; Dimethyl glutarate; UNIFAC method

1. Introduction

In the scope of investigating more benign solvents as potential replacements for

chlorocarbons or aromatic hydrocarbons and as new solvents for separations, we

have studied the dibasic esters, which have excellent properties for industrial appli-

cations. They have low toxicity, great stability, rather high boiling temperatures (463to 573 K), viscosity and density that are close to those of water [1].

The separation of ethanol from dilute solutions resulting from fermentation

processes is industrially important. Because of the lower energy cost of the process,

* Corresponding author. Fax: +90-212-5911-997.

E-mail addresses: [email protected] (E. _IInce), [email protected] (S�:_II. Kırbas�lar).

0021-9614/$ - see front matter � 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/S0021-9614(03)00154-X

mail to: [email protected]

1672 E. _IInce, S�._II : Kırbas�lar / J. Chem. Thermodynamics 35 (2003) 1671–1679

(liquid+ liquid) extraction is an alternative method to distillation [2–7]. At the same

time, (liquid + liquid) extraction is a technique known to separate the ethanol from

aqueous solutions and many solvents have been tried for this purpose [8–13].

The UNIFAC (the universal quasichemical functional group activity coefficient)

is one of the best methods in the estimating activity coefficient that has been estab-lished to date [14]. This method was developed by Fredenslund et al. [15]. The real

behaviour of fluid mixtures can be calculated with the help of activity coefficients.

The mole fractions, X Ei and XR

i of LLE phases can be calculated using the following

equation:

TABL

Physic

Com

Wat

Eth

Dim

cEi XEi ¼ cRi X

Ri ; ð1Þ

where E, extract (solvent) phase; R, raffinate (aqueous) phase; c, activity coefficient

of the i component; i, component number.

This study is part of a research program on the recovery of ethanol from diluteaqueous solutions using environmentally friendly solvents with high boiling points.

Recently, _IInce and Kırbas�lar [16,17] studied (water + ethanol + dimethyl succinate)

and (water + ethanol + dimethyl adipate) ternary systems. In this paper, LLE results

were reported for the ternary system (water + ethanol + dimethyl glutarate), for

which no such data have previously been published.

2. Experimental

Ethanol and dimethyl glutarate purchased from Merck both with nominal mass

fraction purities of 0.999 and >0.99, respectively, are used in this study. The both

of substance purities were checked chromatographically and the compounds were

used without further purification. Mass fraction water contents of these substances

were measured with a Metrohm 701 KF Titrino as 7 � 10�4 and 6 � 10�4, respectively.

Deionised water was double distilled before use. Refractive indexes were measured

with Abb�ee–Hilger refractometer; its stated accuracy is �5 � 10�4. Densities were mea-sured using an Anton Paar DMA 4500 density meter. Boiling temperature measure-

ments were obtained by using a Fischer boiling temperature apparatus. The

estimated uncertainties in the density and boiling point measurements were �1 � 10�4

g � cm�3 and T ¼ 0:01 K, respectively. The measured physical properties are listed in

table 1, along with some values from the literature [18].

E 1

al properties of the pure components at T ¼ 298:15 K and p ¼ 101:325 kPa [18]

pound q/kg �m�3 nD Tb/K

Exp. Lit. Exp. Lit. Exp. Lit.

er 1000.0 997.04 1.3324 1.3325 373.2 373.25

anol 785.1 784.93 1.3593 1.35941 351.5 351.44

ethyl glutarate 1087.4 1087.6 1.4215 1.42151 498.2 498

E. _IInce, S�._II: Kırbas�lar / J. Chem. Thermodynamics 35 (2003) 1671–1679 1673

Three different temperatures were chosen to study the ternary equilibrium system

in order to observe the change of the tie-lines. At each temperature, T¼ (298.15,

308.15 and 318.15) K, tie-line data were obtained by preparing (water + ethanol + di-

methyl glutarate) mixtures of known overall compositions lying within the two phase

region and after being stirred vigorously for at least 2 h jacked cell [19] and then leftto stand for at least 6 h (the time necessary to attain equilibrium was established in

preliminary experiments). After the complete separation of the phases, a suitable

amount of each layer was removed from the cell for analysis.

The mutual solubilities of the (water + dimethyl glutarate) system were deter-

mined by using cloud-point method [16]. A weighted amount of one component

was placed in the cell; then the other component added until a permanent heteroge-

neity was observed.

Temperature was controlled using water bath with a thermostat and the watertemperature was measured with a thermometer having precision of T ¼ �0:01 K.

All mixtures were prepared by weighing with a Mettler scale accurate to within

�10�4 g. The solvent was added by a Metrohm microburet with an accuracy of

5 � 10�3 cm3.

The liquid samples were analysed using a gas chromatograph (Hewlett Packard

GC, Model 6890 Series), equipped with a thermal conductivity detector (TCD) for

the quantitative determination of water, ethanol and dimethyl glutarate. A 15 m long

HP Plot Q column (0.32 lm i.d., 0.2 lm film thickness) was used with a temperatureprogrammed analysis. The oven temperature was fixed at T ¼ 523:15 K. The detec-

tor temperature was kept T ¼ 523:15 K, while injection port temperature was held at

T ¼ 473:15 K. The carrier gas was nitrogen, with a flow rate of 6 cm3/min.

3. Results and discussion

The experimental tie-line data of (water + ethanol + dimethyl glutarate) ternariesat each temperature, were given in table 2. The experimental and predicted tie-lines

at each temperature were plotted and shown in figures 1 to 3. As can be seen figures 1

to 3, it was found that dimethyl glutarate was slightly soluble in water, but miscible

with ethanol.

Distribution coefficients, Di, for water (i ¼ 1) and ethanol (i ¼ 2) and separation

factors, S, were determined as follows:

Di ¼ wi3=wi1; ð2Þ

S ¼ D2=D1; ð3Þ

where D2 and D1: distribution coefficients of ethanol (w23=w21) and distribution co-

efficients of water (w13=w11), respectively. The distribution coefficients and separation

factors for the each temperature are given in table 3.

The extraction power of the solvent at each temperature, plots of D2 vs. w21 areshown in figure 4. The effectiveness of extraction of ethanol by dimethyl glutarate

is given by its separation factor (S), which is an indication of the ability of dimethyl

TABLE 2

Experimental tie-line data for the (water+ ethanol + dimethyl glutarate) ternary system

Water-rich phase (mass fraction) Solvent-rich phase (mass fraction)

Water Ethanol Dimethyl glutarate Water Ethanol Dimethyl glutarate

T ¼ 298:15 K

0.8515 0.0605 0.0880 0.0450 0.0197 0.9353

0.7881 0.1171 0.0948 0.0635 0.0422 0.8943

0.7359 0.1586 0.1055 0.0884 0.0724 0.8392

0.6974 0.1807 0.1219 0.1107 0.0920 0.7973

0.6417 0.2022 0.1561 0.1484 0.1200 0.7316

0.5998 0.2119 0.1883 0.1781 0.1346 0.6873

0.5433 0.2182 0.2385 0.2281 0.1650 0.6069

T ¼ 308:15 K

0.8549 0.0584 0.8670 0.0513 0.0198 0.9289

0.8174 0.0776 0.1050 0.0506 0.0267 0.9227

0.7773 0.1011 0.1216 0.0626 0.0386 0.8988

0.7267 0.1338 0.1395 0.0786 0.0597 0.8617

0.6651 0.1537 0.1812 0.0942 0.0747 0.8311

0.5332 0.1659 0.3009 0.1101 0.0917 0.7982

T ¼ 318:15 K

0.8544 0.0624 0.0832 0.0554 0.0203 0.9243

0.8322 0.0818 0.0860 0.0580 0.0294 0.9126

0.7934 0.1110 0.0956 0.0738 0.0445 0.8817

0.7408 0.1349 0.1243 0.0854 0.0616 0.8530

0.6804 0.1704 0.1492 0.1163 0.0933 0.7904

0.6888 0.1729 0.1383 0.1177 0.0931 0.7892

FIGURE 1. Ternary diagram for experimental LLE of (water+ ethanol+ dimethyl glutarate) at

T ¼ 298:15 K. –n– Experimental tie-line data; –�– calculated (UNIFAC) tie-line data.


FIGURE 2. Ternary diagram for experimental LLE of (water+ ethanol + dimethyl glutarate) at


FIGURE 3. Ternary diagram for experimental LLE of (water+ ethanol + dimethyl glutarate) at



glutarate to separate ethanol from water. This quantity is found to be greater than 1

(separating factors varying between 2.57 and 6.16) for the system reported here,

which means that extraction of ethanol by dimethyl glutarate is possible.

The reliability of experimentally measured tie-line data can be ascertained by ap-plying the Othmer–Tobias correlation with equation 4 at each temperature [20].

lnð1� w33Þ=w33 ¼ aþ b � ln 1ð � w11Þ=w11; ð4Þ

TABLE 3

Distribution coefficients (Di ¼ wi3=wi1) of (water+ ethanol) and separation factors (S)

D1 D2 S

T ¼ 298:15 K

0.053 0.326 6.15

0.081 0.360 4.44

0.120 0.457 3.81

0.159 0.509 3.20

0.231 0.594 2.57

0.297 0.635 2.14

0.420 0.756 1.80

T ¼ 308:15 K

0.060 0.339 5.65

0.062 0.344 5.55

0.081 0.382 4.72

0.108 0.446 4.13

0.142 0.486 3.42

0.207 0.553 2.67

T ¼ 318:15 K

0.065 0.325 5.00

0.070 0.359 5.13

0.093 0.401 4.31

0.115 0.457 3.97

0.171 0.548 3.20

0.171 0.539 3.15

FIGURE 4. Distribution coefficient D2 of ethanol as a function of the mass fraction w21 of ethanol in

water-rich phase T ¼ (}; 298:15; �; 308:15; n; 318:15) K.


where w11, weight fraction of water in the water-rich phase; w33, weight fraction of

dimethyl glutarate in the solvent-rich phase; a and b are constants of the equation 4.

The linearity of the plot indicates the degree of consistency of the data. Othmer–

FIGURE 5. Othmer–Tobias plot of the (water+ ethanol+ dimethyl glutarate) ternary systems at

T ¼ 298:15 K.

TABLE 4

Constants of Othmer–Tobias equation for the (water+ ethanol + dimethyl glutarate) ternary system, (r2:regression coefficient)

T/K a b r2

298.15 0.135 0.697 0.998

308.15 0.909 1.007 0.972

318.15 0.425 0.870 0.993

FIGURE 6. Selectivity diagram at investigated temperatures (free-solvent basis) T ¼ ð}; 298:15;

�; 308:15; n; 318:15) K.


TABLE 5

UNIFAC group parameters for prediction tie-lines data [15]

–CH2– CH3COO– CH3– –OH H2O Rk Qk

–CH2– 0 114.8 0 156.4 300 0.6744 0.54

CH3COO– 232.1 0 232.1 101.1 72.87 1.9031 1.728

CH3– 0 114.8 0 156.4 300 0.9011 0.848

–OH 986.5 245.4 986.5 0 )229.1 1.00 1.20

H2O 1318 200.8 1318 353.5 0 0.92 1.40


Tobias plot is shown in figure 5 for only at T ¼ 298:15 K. The parameters of Oth-

mer–Tobias correlation are given in table 4. The approximation of the correlation

factor (r2) to 1 indicates the degree of consistency of related data.

Diagrams of selectivity on a solvent-free basis are plotted at each temperatures in

figure 6. The effect of temperature change on the selectivity values was found to beinsignificant.

4. Prediction of the LLE data by the UNIFAC method

The LLE data of the ternary mixture were predicted by UNIFAC method [15] us-

ing the interaction parameters between CH3, CH2, OH, CH3COO and H2O obtained

by Magnussen et al. [21]. The values of the UNIFAC parameters for LLE predic-tions are summarised in table 5. As shown in figures 1 to 3, LLE relations obtained

by the UNIFAC method cannot adequately fit the experimental LLE data. Because

the experimental and predicted data are practically independent of temperature, the

discrepancy between these values was observed not to change with temperature.

The root mean square deviations (rmsd) are calculated from the difference be-

tween the experimental data and the predictions of the UNIFAC method at each

temperature according to the following formula:

rmsd ¼XK

XJ

XI

ðXi;exp

"� Xi;calcdÞ2

!=6N

#1=2; ð5Þ

where I is water or ethanol, J is the solvent or aqueous phase, and K ¼ 1; 2; 3; . . . ;N(tie-lines). The UNIFAC method was used to correlate the experimental data at

T ¼ (298.15, 308.15 and 318.15) K with rmsd values of 0.2330, 0.3111 and 0.2487,

respectively.

5. Conclusion

LLE data of (water + ethanol + dimethyl glutarate) were determined experimen-

tally at each temperature. The temperature had practically no effect on the size of

immiscibility region at the temperatures studied. The tie-lines in figures 1 to 3 show,


that ethanol is more readily soluble in raffinate phase than in the solvent phase. Sep-

aration factors are decreased by increasing of ethanol concentration. The UNIFAC

method predictions did not fitted satisfactorily to the experimental data for the ter-

nary system but the same predictions agreed qualitatively with experimental data.

Acknowledgements

The authors would like to thank to Emel Keskinocak for GC analysis.

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AG 02/015

(liquid + liquid) equilibria of (water + ethanol + dimethyl glutarate) at several temperatures

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