Infinite-dilution activity coefficients by comparative ebulliometry: five systems containing ethyl formate

Fluid Phase Equilibria, 85 ( 1993) 17 1- 179 Elsevier Science Publishers B.V., Amsterdam

171

Infinite-dilution activity coefficients by comparative ebulliometry: five systems containing ethyl formate Ana S. Goncalves

and Eugenia

A. Macedo

*

Centro de Engenharia Quimica, Faculdade de Engenharia, 4099 Porto Code-x (Portugal) (Received

August

4, 1992; accepted

in final form September

21, 1992)

ABSTRACT GonGalves, A.S. and Macedo, E.A., 1993. Infinite-dilution activity coefficients by comparative ebulliometry: five systems containing ethyl formate. Fluid Phase Equilibria, 85: 171-179. Infinite-dilution activity coefficients were measured at both concentration limits and at two different temperatures for each of the systems ethyl formate/acetonitrile, ethyl formate/benzene, ethyl formate/methyl ethyl ketone, ethyl formate/chloroform and ethyl formate/tetrachloromethane, using the technique of comparative ebulliometry. The data obtained were used to estimate UNIFAC interaction parameters for the groups HCOO/CCN, HCOO/ ACH, HCOO/CH,CO. HCOO/CCl, and HCOO/CCl,, which are not available in the infinite-dilution specific parameter table or are not reliable. These parameters were used to predict vapor-liquid equilibrium data for systems containing the same groups and a comparison between experimental and predicted values is presented.

INTRODUCTION

Infinite-dilution activity coefficients play an important role in chemical technology, namely in qualitative and quantitative studies of separation processes such as azeotropic and extractive distillations or liquid-liquid extractions. A considerable amount of experimental information on these quantities is available in the literature and has been collected and published in a compilation by Tiegs et al. (1986). These infinite-dilution activity coefficients were used to estimate UNIFAC interaction parameters, and a parameter table based exclusively on such information was published by Bastos et al. (1988). The reliability of the UNIFAC predictions is therefore dependent on the accuracy and broadness of the experimental infinite-dilution activity coefficient database. For the estimation of the interaction between a ketone group ( CH2CO) and a formate group (HCOO), the available data are

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172

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and E.A. Macedo 1 Fluid Phase Equilibria

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scarce (Tiegs et al., 1986). Only data with 2-pentanone as solvent are available and not all of the data are consistent. In fact the standard deviation obtained with the parameters estimated by Bastos et al. (1988) for these data is 18.5%. Besides this, when using the HCOO/CH2C0 parameters from the table published by Bastos et al. (1988) in the prediction of the vapor-liquid equilibrium data for the system ethyl formate/methyl ethyl ketone at 40°C (Macedo et al., 1984), the deviations in pressure and vapor phase composition are rather high (APIP = 28; Ay = 0.06). This table also contains gaps, indicating the data needed for the evaluation of the missing parameters. Recently new data on infinite-dilution activity coefficients were published by Trampe and Eckert (1990) and Bergmann and Eckert (1991). However, there are still no experimental data for a considerable number of mixtures. In this work, infinite-dilution activity coefficients are given for mixtures of ethyl formate with acetonitrile, benzene, methyl ethyl ketone, chloroform and tetrachloromethane at both concentration limits. They were measured at two different temperatures, using the technique of comparative ebulliometry. The data obtained were used to estimate new group interaction parameters for the groups HCOO/CCN, HCOO/ACH, HCOO/CH2C0, HCOO/ CC& and HCOO/CCl,.

EXPERIMENTAL

Procedure The limiting activity coefficients were determined by comparative ebulliometry, i.e. by measuring isobaric changes in the boiling temperatures of a solvent, which result when small known amounts of solute are added. Measurements were made in a differential ebulliometer which consists of two glass boiling chambers connected through condensers to a common manifold. The change in boiling point is measured as the difference between the boiling point of the pure solvent (in the reference chamber) and the boiling point of the solute plus solvent (in the measuring chamber). The measuring and the reference ebulliometers are both of the Swietoslawski type. The design of the ebulliometers used in this work and the experimental procedure are similar to those described in detail by Eckert et al. (1981). For each experiment, five or six injections of either pure solute or a mixture of solute and solvent, approximately 1 ml each, were made. In order to obtain sufficiently low concentrations, the mole fraction regions studied were below 0.01. A Fischer Vakuum-Konstanthalter VKl instrument pressure gauge served as the sensor for the pressure control. In order to be able to measure the pressure with the desired accuracy, a mercury-filled U-tube manometer

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G~n~alves and E.A. Laredo / Fluid Phase Equ~~~~ria85 (1993) 17i- 179

173

(inner diameter 20 mm) and a cathetometer were used. The accuracy of the measurements was within ltO.1 mmHg. The boiling point elevation was measured with a 2801 A Hewlett-Packard quartz thermometer and two 2850 A sensing probes. The accuracy of the measurements was within kO.01 K. Materials

Acetonitrile (Merck; spectroscopy grade, minimum purity 99.8%), benzene (Merck; special for chromatography, minimum assay 99.8%), methyl ethyl ketone (also known as 2-butanone) (British Drug Houses Ltd.; special for chromatography, minimum assay 99.7%), chloroform (Merck; special for chromatography, minimum purity 99.8%) and tetrachloromethane (Merck; special for chromatography, minimum purity 99.8%) were used as supplied. Analyses by gas chromatography showed purities greater than 998%. Ethyl formate (Merck-Schuchardt; minimum assay 98%) was purified in accordance with the method described by Riddick and Bunger (1970) and was stored over 4 A molecular sieve pellets. The purity assessed by gas-liquid chromatography was found to be better than 99.8%. The vapor pressures were determined for each pure component in the temperature range of interest. Reasonable agreement was obtained with the literature values, which provides an additional check of the purity of the materials used. RESULTS

The ebulliometric data were analyzed following the development of Gautreaux and Coates (1955) with additional terms to account for the vapor phase non-ideality. The infinite-dilution activity coefficients of a solute 1 diluted in a solvent 2 were calculated using the following equation (Bergmann and Eckert, 1991) :

where 4: is the fugacity coefficient of component i at pressure P, (bf is the fugacity coefficient of component i at its vapor pressure, 4, is the fugacity coeficient of component i in the vapor phase, v, is the liquid molar volume of pure component i, Pz is the vapor pressure of the component i at the equilibria temperature, X, is the equilib~um liquid mole fraction, T is the equilibria temperature and R is the ideal gas constant. The liquid molar volumes were calculated using the modified Rackett equation (Spencer and Danner, 1972). The fugacity coefficients and their

174

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and E.A. Macedo / Fkid

Phase Equilibriu

85 (1993) 171~ 179

derivatives with respect to pressure were determined using the virial equation of state, with virial coefficients estimated according to the method described by Hayden and O’Connell (1975). The pure component vapor pressures were calculated using the Antoine equation. The limiting composition derivative of the temperature, (aT/a.x, ) p”, is obtained from the ebulliometric data. The enrichment of the vapor above the boiling mixture with the more volatile component plus the hold-up of liquid condensate have been taken into account to estimate the true equilibrium liquid phase composition x1 from the gravimetrically determined composition of the mixture. This correction, usually less than 2%, was made by estimating the vapor and liquid condensate volumes, and solving the appropriate stoichiometric and thermodynamic relationships by an iterative method. The slopes were determined by fitting the data to the following analytical equations: AT = ax,

(2)

AT = ax, + bx:

(3)

AT=ax,

(4)

+b ln(1 +sl)

AT = ax1 + bx: + cx:

(5)

In each case the best fit was chosen, and usually expressions of type given in eqns. (3) and (4) gave the lower standard percentage deviation. Table 1 presents the limiting slopes, (aT/ax,)F, and the infinite-dilution activity coefficients calculated as described above for the systems studied. The errors in y X given in Table 1 were estimated by repeatedly calculating I”=, taking into account the maximum and minimum values in the limiting slopes due to fluctuations in the measured temperature, and the magnitude of the hold-up corrections. Using the measured infinite-dilution activity coefficients for the systems ethyl formate/acetonitrile, ethyl formate/benzene, ethyl formate/methyl ethyl ketone, ethyl formate/chloroform and ethyl formate/tetrachloromethane, UNIFAC interaction parameters for the group pairs HCOO/CCN, HCOO/ACH, HCOO/CH,CO, HCOO/CC13 and HCOO/ Ccl, were estimated using the following objective function: F m,n

=

where exp and talc UNIFAC method. components i. The listed in Table 2. combinatorial term suggestion of Kikic

(6) mean, respectively, experimental and calculated by the The summations were taken over all data points j and estimated group interaction UNIFAC parameters are The modification of the Flory-Huggins term in the of the UNIFAC equations was used, according to the et al. (1980). This modification was also used by Bastos

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Goncalves and E.A. Macedo 1 Fluid Phase Equilibria 85 (1993) I71 -179

TABLE

175

1

Infinite-dilution

activity

coefficients

for the systems

(2)

Solute (1)

Solvent

Ethyl formate

Acetonitrile

Acetonitrile

Ethyl formate

Ethyl formate

Benzene

Benzene

Ethyl formate

Ethyl formate

Methyl

Methyl

Ethyl formate

ethyl ketone

ethyl ketone

Ethyl formate

Chloroform

Chloroform

Ethyl formate

Ethyl formate

Tetrachloromethane

Tetrachloromethane

Ethyl formate

studied

T(K)

wiw;

Y;^

Uncertainty

323.22 326.43 323.16 325.90 313.48 323.86 312.96 323.67 314.24 325.00 313.43 324.45 312.48 322.58 313.25 322.65 320.85 327.93 317.59 326.29

- 64.24 -66.55 16.76 16.40 -46.27 -51.27 14.58 15.26 - 77.92 - 87.70 15.61 15.43 8.97 8.93 12.79 13.24 - 125.20 - 127.50 1.14 2.87

1.30 1.32 1.04 1.10 1.15 1.20 1.11 1.14

fO.O1 fO.O1 f 0.02 + 0.03 * 0.04 +0.08 fO.O1 kO.01 * 0.05 + 0.05 +0.02 fO.O1 +0.01 fO.O1 kO.01 kO.01 _t 0.05 +0.07 +0.05 * 0.03

1.66 1.72 1.05 1.13 0.53 0.55 0.65 0.68 2.65 2.60 2.02 1.87

et al. (1988) in the estimation of the interaction parameters for the y” parameter table. Since these parameters were evaluated from a limited database, their accuracy cannot be as high as that when calculating parameters from extensive databases. Nevertheless, good predictions were obtained for the vapor-liquid equilibrium data available in the literature for the systems ethyl for-mate/benzene at 50°C (Ohta and Nagata, 1980), ethyl formate/ methyl ethyl ketone at 40°C (Macedo et al., 1984) and ethyl formate/chloroform at 45°C (Ohta et al., 1980), as shown in Table 3. For the system ethyl

TABLE

2

UNIFAC Group ACH CH,CO CCN ccl, ccl,

group i

interaction

parameters

(K)

Group j

T(K)

a,

a11

HCOO HCOO HCOO HCOO HCOO

312.96-323.86 313.43-325.00 323.166326.43 312.48-322.65 317.59-327.93

275.00 811.88 270.86 165.83 438.22

-11.10 -212.13 - 149.00 - 37.27 193.73

A.S. Gongalves and E.A. Macedo / Fluid Phase Equilibria

176 TABLE

85 (1993) I71 -I 79

3

Comparison

of the UNIFAC

predictions

with the experimental

data

System

t (“C)

Number of data points

:(x100)

Ay

Ethyl formate( l)/benzene( 2)” Ethyl formate( 1) /chloroform( 2) b Ethyl formate( l)/methyl ethyl ketone(2)’

50.0 45.0 40.0

10 10 9

2.4 1.2 3.8

0.014 0.004 0.019

a Ohta and Nagata (1980). b Ohta et al. (1980). c Macedo et al. (1984).

for-mate/methyl ethyl ketone, it can be seen that the new parameters estimated in this work for the groups HCOO/CH2C0 give a satisfactory representation of the data, which it is not possible to obtain with the parameters published by Bastos et al. (1988). For the same systems, a comparison between experimental and calculated activity coefficients is presented in Figs. l-3. The errors obtained are smaller than or within the same order of magnitude as those calculated by Bastos et al. (1988), i.e. around 20%.

‘.O1 camp. 1

eonlp.2

l

0.6

In Y

0 0.4

i

I 0.2 -

.

m q

.

.

.

.

X 1

Fig. 1. Comparison of the UNIFAC predictions with the experimental activity coefficients for ethyl formate( l)/benzene(2) at 50°C. Experimental data: Ohta and Nagata (1980).

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GonGaloes and E.A. Macedo 1 Fluid Phase Equilibria

85 (1993) 171-l 79

177

1.0 -

q

camp. 1

0.6 A camp. 2 0.6

In Y

i

-

0.4 -

0.2 -

k

0.0 -

-0.2L u.0

.

0.2

0.4

0.6

X

0.0

1.0

1

Fig. 2. Comparison of the UNIFAC predictions with the experimental activity coefficients for ethyl formate(l)/methyl ethyl ketone(2) at 40°C. Experimental data: Macedo et al. (1984).

o.21

In r q

-0.6

0 camp. 1 l

-0.6

camp. 2

/

-,.,I

u.0

0.2

0.6

0.4

0.6

1 1

X 1

Fig. 3. Comparison of the UNIFAC predictions with the experimental activity coefficients for ethyl formate( l)/chloroform(2) at 45°C. Experimental data: Ohta et al. (1980).

CONCLUSIONS

Infinite-dilution activity coefficients were determined acetonitrile, ethyl formate/benzene, ethyl formate/methyl

for ethyl formate/ ethyl ketone, ethyl

178

A.S. Goncalves and E.A. Macedo 1 Fluid Phase Equilibria

85 (1993) 171-l 79

formate/chloroform and ethyl formate/tetrachloromethane using the technique of comparative ebulliometry. New UNIFAC interaction parameters for the groups HCOO/CCN, HCOO/ACH, HCOO/CHICO, HCOO/CC13 and HCOO/CCl,, estimated from the experimental 1’” values, were used to predict binary vapor-liquid equilibrium data and, from the values obtained for the deviations in pressure and vapor phase mole fractions, it is possible to conclude that the 7% UNIFAC parameters are suitable for describing the vapor-liquid equilibrium behavior of the systems considered.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the financial support of this work by Instituto National de Investiga@o Cientifica (Portugal). In addition we thank Professor H. Knapp and Mr. T. Hauschild (Berlin, Germany) who have in different ways contributed to this work.

LIST OF SYMBOLS

parameter in eqns. (2) -( 5); UNIFAC parameter in eqns. (3) -( 5) parameter in eqn. (5) objective function pressure vapor pressure of component i gas constant temperature (“C) absolute temperature liquid molar volume liquid phase mole fraction vapor phase mole fraction

parameters

Greek letters YI

4, 4s

activity coefficient of component i vapor phase fugacity coefficient of component i fugacity coefficient of component i at saturation pressure

Subscripts 1 2 i j

component 1 (solute) component 2 (solvent) component i; group i data point j; group j

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85 (1993) 171-l 79

179

Superscripts talc exp s 00

calculated experimental saturation infinite dilution

REFERENCES Bastos, J.C., Soares, M.E. and Medina, A.G., 1988. Infinite dilution activity coefficients predicted by UNIFAC group contribution. Ind. Eng. Chem. Res.. 27: 1269-1277. Bergmann, D.L. and Eckert, CA., 1991. Measurement of limiting activity coefficients for aqueous systems by differential ebulliometry. Fluid Phase Equilibria, 63: 141- 150. Eckert, C.A., Newman, B.A., Nicolaides, G.L. and Long, T.C., 1981. Measurement and application of limiting activity coefficients. AIChE J., 27: 33-40. Gautreaux, M.F. and Coates, J., 1955. Activity coefficients at infinite dilution. AIChE J., 1: 496-500. Hayden, J.G. and O’Connell, J.P., 1975. A generalized method for predicting second virial coefficients. Ind. Eng. Chem. Process Des. Dev., 14: 209-216. Kikic, I., Alessi, P., Rasmussen, P. and Fredenslund, Aa., 1980. On the combinatorial part of the UNIFAC and UNIQUAC models. Can. J. Chem. Eng., 58: 2533258. Macedo. E.A., Mendonca, J.M. and Medina, A.G., 1984. Vapor-liquid equilibrium for the systems ethyl formate-methyl ethyl ketone, ethyl formate-toluene and ethyl formatemethyl ethyl ketone-toluene: new UNIFAC parameters for interactions between the groups ACH/HCOO, ACCH,/HCOO and CH,CO/HCOO. Fluid Phase Equilibria. 18: 197-210. Ohta, T. and Nagata, I., 1980. Thermodynamic properties of four ester-hydrocarbon mixtures. J. Chem. Eng. Data, 25: 283-286. Ohta, T., Hisashi, A. and Nagata, I., 1980. Thermodynamic study of complex formation in four binary liquid mixtures containing chloroform. Fluid Phase Equilibria. 4: 105- 114. Riddick, J.A. and Bunger, W.B., 1970. Organic Solvents, Wiley, New York. Spencer, C.F. and Danner, R.P., 1972. Improved equation for prediction of saturated liquid density. J. Chem. Eng. Data, 17: 236-241. Tiegs, D., Gmehling, J., Bastos, J.C., Soares, M.E., Medina, A.G., Alessi, P. and Kikic, I., 1986. Infinite Dilution Activity Coefficients. DECHEMA Chemistry Data Series, Vol. IX, Frankfurt am Main. Trampe, D.M. and Eckert, C.A., 1990. Limiting activity coefficients from an improved differential boiling point technique. J. Chem. Eng. Data, 35: 156-162.