Vapour-liquid equilibria in nonpolar mixtures

355

Fluid Phase Equilibria, 90 (1993) 355-364

Elsevier Science Publishers B.V., Amsterdam

Vapour - liquid equilibria in nonpolar mixtures. II. Carbon tetrachloride with alkylbenzenes and n -alkanes at 313.15 K M. G&al * and S. Zawadzki Warsaw University,

Department

of Chemistry,

Pasteura

1, 02-093 Warsaw (Poland)

(Received October 9, 1992; accepted in final form February

8, 1993)

ABSTRACT Got-al, M. and Zawadzki, S., 1993. Vapour-liquid equilibria in nonpolar mixtures. II. Carbon tetrachloride with alkylbenzenes and n-alkanes at 3 13.15 K. Fluid Phase Equilibria, 90: 355-364.

Total vapour pressure measurements using a modified static method at 313.15 K are reported for binary mixtures of Ccl, with benzene, toluene, o-xylene, p-xylene, hexane, heptane, octane, nonane and decane. The results were correlated with the generalized Redlich-Kister equation for excess Gibbs energy. A comparison with literature vapour-liquid equilibrium data and excess enthalpy was made. Consistency within homologous series was checked. Predictions made using the UNIFAC method and the Hildebrand-Scatchard equation were compared. Keywords: experiments, data, VLE low pressure, mixtures, benzene, toluene, p-xylene, hexane, heptane, octane, nonane, decane, carbon tetrachloride.

o-xylene,

INTRODUCTION

This work is part of a research project aimed at the determination of vapour-liquid equilibria (VLE) in mixtures of nonpolar solvents measured in a uniform way at 313.15 K. In Part I, VLE data for mixtures of 2,2,4_trimethylpentane with alkylbenzenes and, in Part III, VLE data for n-alkanes with alkylbenzenes are presented. The goal of this paper is to present experimental results for mixtures of Ccl, with n-alkanes and alkylbenzenes at 313.15 K. The data as supplemented by the literature will be used in Part IV to discuss local order in nonpolar mixtures due to geometrical factors, and the method of group contributions as applied to cubic equations of state will be presented in Part V.

* Corresponding

author.

0378-3812/93/$06.00 0 1993 - Elsevier Science Publishers B.V. All rights reserved.

356

M. G&al and S. Zawadzki

1 Fluid Phase Equilibria 90 (1993) 355-364

TABLE 1 Maximum mole fractions of impurities x, vapour pressure p and second virial coefficient /? Reagent

Carbon tetrachloride n-Hexane n-Heptane n-Octane n-Nonane n-Decane Benzene Toluene o-Xylene p-Xylene

100x

0.05 0.02 0.03 0.04 0.02 0.05 0.10 0.13 0.19 0.09

/I (dm3 mol-I)

P @Pa)

Lit. n

This work

28.444 37.255 12.327 4.145 1.402 0.475 24.367 7.887 2.051 2.644

24.363 37.257 12.336 4.161 1.417 0.488 24.363 7.886 2.069 2.668

-1.43 -1.66 -2.57 -3.80 - 5.39 - 7.52 -1.42 -2.32 -3.86 -3.63

a Calculated with Antoine’s constants (Boublik et al., 1973).

MATERIALS

CCL,, benzene, toluene, p-xylene and n-alkanes (except for nonane) were triply crystallized and then rectified on an SO-plate column; the fraction distilled within a 0.01 K interval was used for the measurements. Only nonane was fractionated on the same column. The o-xylene was obtained from The Institute of Physical Chemistry of The Polish Academy of Sciences and was used without further purification. Impurities were determined by gas chromatography. Water content was checked using Fischer’s reagent and was at the limit of detectability. Table 1 gives the results of the purity determination, the measured vapour pressures of the pure components and their reported values (Boublik et al., 1973)

METHOD

The vapour pressure over a liquid sample, prepared by weighing, was determined by a modified static method. Vapour concentration was not measured. The apparatus have been described previously (Janaszewski et al., 1982). The temperature measured with a Beckmann thermometer was constant to within 0.004 K and was controlled up to 0.002 K. The cathetometer readings contributed less than 0.004 kPa to the error of a single pressure measurement. The errors in the liquid mole fractions were less than 0.0005.

M. G&al and S. Zawadzki

1 Fluid Phase Equilibria 90 (1993) 35.5-364

351

RESULTS: CORRELATION AND COMPARISON WITH LITERATURE

In Part I of this series, the van Laar equation for excess Gibbs energy (GE) with one adjustable parameter B was used for correlation of the VLE data: GE/RT = x+XjB/(X, + X,b,/bl)

(1)

where Xi, Xj are mole fractions of the ith and jth components respectively. As in the original equation of van Laar, bi, bi are equal to the excluded volumes of the van der Waals equation of state, and the ratio bj/bi is calculated using critical parameters: (14

bilbi = (T,i/P4I(T~~Ip~j) In contrast to data here do not correlate latter was generalized but using z-fractions GE/RT = bzizi i

presented in Part I, some of the mixtures investigated sufficiently accurately with eqn. (1). Therefore the to a form analogous to the Redlich-Kister equation, instead of mole fractions (RKz):

(2)

Kk(zi- Zj)"

k=O

where & are adjustable parameters, and ZipZj are fractions of the ith andjth components respectively, defined by b = xi + x,bjlbi;

zi = xi/b;

Zj =

1 -Zi

If the polynomial in eqn. (2) is truncated after the zeroth term, then eqns. ( 1) and (2) are equivalent. Equation (2) was used previously by Goral et al. (1988, 1990) with good results. For comparison, the Redlich-Kister equation (RI&) was also used: GE/RT=

XiXj i Kk(Xi-Xi)" k=O

The parameters of the above equations were determined using a modification of Barker’s method by minimizing the sum of the squares:

s = k=l 5 be -Pc)k2 where pe and pc are the experimental and calculated pressures respectively. The optimal number of parameters used in eqns. (2) and (3) was determined using Fisher’s distribution (G&al, 1977). The standard error of a single pressure measurement, C, was estimated using the equation 0 = [S&z - n)]

(5)

358

M. G&al and S. Zawadzki / Fluid Phase Equilibria 90 (1993) 355-364

TABLE 2 Comparison between correlating equations: Redlich-Kister equation with excluded volume fractions (RKz) and original Redlich-Kister equation with mole fractions (RKx), numbered in text as eqns. (2) and (3) respectively RKz n

a( Pa)

ccl, + hexane heptane octane nonane decane benzene toluene a-xylene p-xylene n = number of adjustable

RKx n

25 46 24 22 22 5 11 25 24 K-parameters;

4 Pa)

27 48 29 22 29 5 11 32 30 u = standard pressure error.

where m is the number of points, II is the number of parameters in correlating equations and S is defined by eqn. (4). The estimations of each variant of the correlation are given in Table 2, which shows that eqn.(2) needs less adjustable parameters than eqn. (3) to achieve the same accuracy of correlation. The data and results of the correlation with eqn. (2) are given in Table 3. Table 4 contains parameters for eqn. (2) as well as a comparison between the experimental values of equimolar GE/RT, and those calculated using the UNIFAC method by Fredenslund et al. (1977) and using the Hildebrand- Scatchard equation. Three of the CC& + n-alkane systems under consideration have been investigated by other authors, but under different conditions. Various VLE isotherms were correlated with eqn. (2) so they could be directly compared, yielding equimolar values of GE/RT (Q,,J which were plotted versus l/T in Figs. 1, 2 and 3. In each case, original values of the vapour pressures of the pure components reported by authors of the data were used for correlation of the data. This approach seems to reduce the effects caused by using chemicals of different purity. Our values of QO,swere extrapolated to other temperatures using literature data of heats of mixing HE (Harsted and Thomsen, 1974); the extrapolations are shown on the plots as solid lines. From comparison with four other data sources it can be concluded that the experimental error of the H& value used in this paper is less than 4 J mol-‘. This results in an error of extrapolated QO.s in the range of

M. G&al and S. Zawadzki TABLE

359

/ Fluid Phase Equilibria 90 (1993) 355-364

3

Liquid mole fraction x,, calculated vapour fraction y,, experimental total vapour pressure p, and differences between experimental pressure and those calculated using eqn. (2), dp, at 313.15 K P @Pa)

XlZ

dp WV

Carbon 0.0000 0.0799 0.1533 0.2061 0.2667 0.3296 0.4067 0.4468

tetrachloride(a) 0.0000 0.0725 0.1376 0.1837 0.2362 0.2904 0.3568 0.3916

+ n-hexane(b) 37.257 37.001 0.015 36.710 0.022 36.476 0.031 36.153 0.018 35.818 0.042 35.284 -0.001 34.988 -0.016

Carbon 0.0000 0.0770 0.1343 0.1850 0.2530 0.3138 0.3710 0.4328

tetrachloride(a) 0.0000 0.1770 0.2835 0.3642 0.4571 0.5283 0.5874 0.6441

+ n-heptane(b) 12.336 13.864 0.000 14.972 0.005 15.924 0.004 17.229 0.067 18.242 0.004 19.212 -0.011 20.233 -0.021

Carbon 0.0000 0.1150 0.1559 0.2053 0.2690 0.3190 0.4348 0.4902

tetrachloride(a) 0.0000 0.4861 0.5721 0.6500 0.7237 0.7678 0.8416 0.8678

Carbon 0.0000 0.2027 0.2437 0.2982 0.3532 0.4212 0.4601 0.5169

tetrachloride(a) 0.0000 0.8385 0.8679 0.8962 0.9171 0.9362 0.9448 0.9552

P

x,

WW

dp WV

0.5087 0.5557 0.6847 0.7454 0.8007 0.8582 0.9313 1.oooo

0.4460 0.4881 0.6094 0.6711 0.7310 0.7985 0.8946 1.oooo

34.554 34.089 32.917 32.249 31.573 30.819 29.691 28.452

0.019 - 0.060 -0.012 -0.011 -0.012 0.010 0.007

0.4842 0.5460 0.6138 0.6738 0.7325 0.7929 0.8678 0.9357 1.oooo

0.6868 0.7335 0.7802 0.8184 0.8535 0.8878 0.9288 0.9652 1.OOoo

21.082 22.042 23.109 24.001 24.869 25.532 26.752 27.631 28.452

- 0.006 -0.020 0.012 0.016 0.040 -0.143 0.053 0.025

+ n-octane(b) 4.161 7.182 -0.017 8.239 -0.024 9.506 - 0.030 11.178 0.020 12.392 - 0.023 15.251 - 0.022 16.599 -0.014

0.5532 0.6220 0.6769 0.7256 0.7832 0.8508 0.9184 1.OOoo

0.8928 0.9157 0.9315 0.9441 0.9576 0.9720 0.985 1 1.oooo

18.108 19.756 21.042 22.175 23.483 25.018 26.551 28.452

- 0.008 0.021 0.031 0.042 0.030 0.021 0.004

+ n-nonane(b) 1.417 7.083 0.020 8.226 0.021 9.733 0.012 11.246 -0.001 13.103 -0.022 14.175 -0.019 15.724 - 0.022

0.5754 0.6410 0.6947 0.7431 0.8068 0.8742 0.9348 1JO00

0.9640 0.9722 0.9778 0.9822 0.9873 0.9921 0.9960 1.oOOo

17.357 19.070 20.500 21.785 23.457 25.197 26.759 28.452

0.026 -0.019 -0.012 0.004 0.024 0.03 1 0.031

360 TABLE XC7

M. G&al and S. Zawadzki

1 Fluid Phase Equilibria 90 (1993) 355-364

3 (continued) Y,

P MO

Q WW

x,

Yll

P @Pa)

Q WW

Carbon 0.0000 0.1854 0.2317 0.2895 0.3345 0.3990 0.4577 0.5095

tetrachloride(a) + n-decane(b) 0.0000 0.488 0.9288 5.642 0.004 0.9454 6.915 - 0.026 0.9590 8.591 0.016 0.9665 9.838 -0.015 0.9744 11.708 0.019 0.9798 13.360 - 0.005 0.9835 14.847 0.003

0.5641 0.6300 0.6780 0.7414 0.8003 0.8633 0.9309 1.oooo

0.9867 0.9898 0.9917 0.9938 0.9955 0.997 1 0.9986 1.oooo

16.403 18.296 19.616 21.348 23.006 24.743 26.594 28.452

0.003 0.027 -0.006 - 0.043 - 0.007 0.018 0.044

Carbon 0.0000 0.1390 0.1882 0.2411 0.2986 0.3577 0.4105 0.4675

tetrachloride(a) 0.0000 0.1709 0.226 1 0.283 1 0.3427 0.3998 0.4531 0.5073

+ benzene(b) 24.363 25.378 -0.004 25.703 0.005 26.016 0.001 26.324 - 0.009 26.628 0.004 26.883 0.001 27.132 0.004

0.5181 0.5950 0.6406 0.7046 0.7707 0.8268 0.9085 1.ooOO

0.5545 0.6253 0.6669 0.725 1 0.7853 0.8368 0.9127 1.oOOo

27.324 27.602 27.739 27.927 28.096 28.218 28.343 28.452

- 0.004 0.000 -0.007 -0.001 0.006 0.010 -0.003

Carbon 0.0000 0.0807 0.1524 0.1958 0.3143 0.3735 0.4241

tetrachloride(a) 0.0000 0.2507 0.4019 0.4738 0.6237 0.6812 0.7240

+ toluene(b) 7.886 9.699 - 0.000 11.238 -0.006 12.172 0.015 14.593 -0.010 15.803 -0.009 16.849 0.007

0.4897 0.5371 0.6122 0.6686 0.7171 0.7902 0.9156 1.oooo

0.7725 0.8034 0.8468 0.8754 0.8979 0.9283 0.9733 1.oooo

18.170 19.152 20.664 21.825 22.775 24.249 26.778 28.452

- 0.006 0.012 - 0.002 0.016 -0.014 -0.012 0.012

Carbon 0.0000 0.0839 0.1937 0.2836 0.3579 0.4212 0.5040 0.5683

tetrachloride(a) 0.0000 0.5560 0.7639 0.8411 0.8814 0.9065 0.9314 0.9463

+ o-xylene(b) 2.069 4.269 -0.015 7.106 -0.023 9.459 0.009 11.410 0.030 13.055 0.016 15.231 -0.002 16.924 -0.028

0.6241 0.6905 0.7429 0.8011 0.8860 0.9328 0.9658 1.oooo

0.9571 0.9678 0.9750 0.9819 0.9905 0.9946 0.9973 1.oooo

18.429 20.246 21.645 23.198 25.483 26.719 27.583 28.452

- 0.022 0.007 -0.002 -0.003 0.036 0.042 0.037

Carbon 0.0000 0.2066 0.2679 0.3152 0.3836 0.4404 0.5013

tetrachloride(a) 0.0000 0.7311 0.7914 0.8263 0.8652 0.8904 0.9124

+ p-xylene(b) 2.668 7.934 -0.019 9.498 0.007 10.700 0.018 12.431 0.010 13.885 0.001 15.419 -0.054

0.5626 0.6334 0.6844 0.7516 0.8045 0.8614 0.9399 1.OOoo

0.9305 0.9477 0.9580 0.9696 0.9775 0.9848 0.9937 1.oooo

17.124 18.981 20.326 22.083 23.483 24.942 26.948 28.452

0.034 0.010 -0.001 -0.019 0.003 0.002 0.026

M. G&al and S. Zawadzki

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/ Fluid Phase Equilibria 90 (1993) 355-364

TABLE 4 Excluded volume of hydrocarbons divided by excluded volume of Ccl,, b, lb,, and adjustable parameters K,,, K,, K2 in eqn. (2); equimolar excess Gibbs free energy, Gz,, difference between the experimental value of GE, and those calculated by the UNIFAC method, A,; deviation between the G&, value and those calculated with the Hildebrandt-Scatchard equation A2

ccl, + n-hexane n-heptane n-octane n-nonane n -decane benzene toluene 0 -xylene p -xylene

bilb,

K,

1.37 1.62 1.88 2.11 2.40 0.94 1.18 1.39 1.44

0.1814 0.1352 0.0905 0.0598 0.0241 0.1295 0.0580 -0.0030 -0.0003

K,

K2

0.0204 0.0271 0.0211 -0.0131 0.0257 -0.0019 0.0039 0.0440

G& (J mol-‘)

A, (J mol-I)

AZ(J mol-‘)

137 109 77 46 12 82 42 -2 0

76 73 72 17 80 19 37 72 72

-63 -50 -48 -53 -64 46 26 -29 -8

313 + 20 K, less than 1 x 10 -4, which is far below the experimental error of Q,,5. Therefore the plots are useful for checking the agreement of VLE data measured at different temperatures. Scattering of the QO,svalues shown in the Figures can be related to relative deviations of vapour pressure, indicated in each Figure by a marked sector. Each sector shows the shift of QO,s corresponding to a 1% error in the equimolar pressure. The plots show clearly that the temperature dependence of the data of Jain et al. (1970) for all three

3.14

3.26 3.38 1000/T

3.0

3.2

3.4

Fig. 1 (left). CC& +n-hexane. Comparison of equimolar GE/RT (&) obtained from different VLE data: 0, this work; 0, Jain et al. (1970); A, Bissel and Wiliamson (1975). Fig. 2 (right). Ccl, + n-heptane. Comparison of equimolar GE/RT (Qo,J obtained from different VLE data: q, this work; 0, Jain et al. (1970); A, Bissel and Wiliamson (1975).

362

M. Gbral and S. Zawadzki 1 Fluid Phase Equilibria PO (1993) 3.55-364

1000/T

Fig. 3. CCl,+n-octane. Comparison of equimolar VLE data: El, this work; 0, Jain et al. ( 1970).

GE/RT (&)

obtained

from different

systems shown in Figs. 1, 2 and 3 is not quite correct. Agreement between the literature and our data is fairly good, but it is difficult to say which is better. Figure 4 is more helpful, where values of QO.Sat 313.15 K for mixtures of CCL, with consecutive n-alkanes are plotted versus the number of carbon atoms of the corresponding n-alkanes. Literature values of Q,,S at 313.15 K were obtained by interpolation or extrapolation with the help of HE. The Figure shows good consistency of our data; the literature data are more scattered. Literature VLE data exist for the mixtures Ccl, + benzene and CC& + toluene measured at 313.15 K. They are compared directly with our measurements by plotting excess experimental pressure versus mole fraction in Figs. 5 and 6. Excess pressure (p”) is defined as the deviation of pressure from Raoult’s law. Figure 5 shows good agreement between our data set and the two literature ones. Figure 6 for Ccl, + toluene shows that our vapour pressure is higher than the literature value. Comparison of our values of QO,s,given in Table 4 for the series of mixtures CC& + benzene,

-I“:I: LO

I1%

0

n

i

30

8

20

6

8 N

10

Fig. 4. Mixtures of Ccl, with n-alkanes at 313.15 K. Equimolar GE/RT (Q& plotted versus number of carbon atoms of the corresponding n-alkane: 0, this work; 0, Jain et al. (1970); A, Bissel and Wiliamson (1975).

M. Gtiraf and S. Zawad~k~ [ Fluid Phase E~~iiibria 90 (1993) 355-364

0.2 OA 0.6 0.8 &

0.2 t.l4 a6 X,

363

0.8

Fig. 5 (left). Ccl, + benzene at 313.15 K. Excess vapour pressure (pE) plotted versus liquid mole fraction of Ccl, (x,): Cl, this work; 0, Scatchard et al. (1940); x , Steinbrecher and Bittrich (1963); + , Fowler and Lim (1956). (1 hPa = 100 Pa). Fig. 6 (right). Ccl, + toluene at 313.15 K. Excess vapour pressure (pE) plotted versus liquid mole fraction of Ccl, (x,): 0, this work; x , Kind et al. (1968); 0, Wang et al. (1970). (1 hPa = 100 Pa).

CC& + toluene and CC& + xylene, seems to indicate consistency of our data. It can be concluded that comparison with literature data and within the homologous series shows a high degree of accuracy of our data. ACKNOWLEDGEMENT

Support of this work by research grant BST-412/16/92 is acknowledged. All the data for the Figures were taken from the Warsaw data bank. LIST OF SYMBOLS

b I.3

excluded volume used in eqns. (I), ( la) and (2) parameter used in eqn. ( 1) GE excess Gibbs energy HE excess enthalpy of mixing parameters of eqns. (2) and (3) Kk experimental pressure PC calculated pressure PC excess pressure PE critical pressure used in eqn. ( la) PC equimolar value of GE/RT Q0.S R gas constant s sum of least squares defined by eqn.(5) T temperature (K) critical tem~rature used in eqn. (la) TC

364

M. Gciral and S. Zawadzki / Fluid Phase Equilibria 90 (1993) 355-364

xbxi liquid mole fractions of the ith and jth component respectively calculated vapour fraction of component a zi,zj excluded volume fractions of the ith and jth component respectively

YC2

Greek symbols /3 virial coefficient

CT standard error of experimental pressure REFERENCES Bissel, T.G. and Wiliamson, A.G., 1975. J. Chem. Thermodyn., 7: 13 1. Boublik, T., Fried, V. and Hala, E., 1973. The Vapour Pressures of Pure Substances. Elsevier, Amsterdam. Fowler, R.T. and Lim, SC., 1956. J. Appl. Chem., 6: 74. Fredenslund, A., Gmehling, J. and Rasmussen, P., 1977. Vapor-Liquid Equilibria using UNIFAC. Elsevier, Amsterdam. Goral M., 1977. Error analysis in Barker’s method of vapour pressure isotherm data processing. Z. Phys. Chem., 258: 1040. G&al, M., Oracz, P. and Warycha, S., 1988. The ternary system carbon tetrachloridemethanol-chloroform at 293.15 K. Fluid Phase Equilibria, 44: 77. Goral, M., Oracz, P. and Warycha, S., 1990. The ternary system carbon tetrachloridemethanol-chloroform at 303.15 K. Fluid Phase Equilibria, 55: 337. Harsted B.S. and Thomsen E.S., 1974. Excess enthalpies from flow microcalorimetry. J. Chem. Thermodyn., 6: 557-563. Jain, D.V.S., Gupta, V.K. and Lark, B.S., 1970. Indian J. Chem., 8: 815. Janaszewski, B., Oracz, P., G&al, M. and Warycha, S., 1982. Vapour-liquid equilibria. I. An apparatus for isothermal total vapour pressure measurements: binary mixtures of ethanol and t-butanol with n-hexane, n-heptane and n-octane at 313.15 K. Fluid Phase Equilibria, 9: 295-310. Kind, R., Kahnt, G., Schmidt, D., Schumann, J. and Bittrich, H.J., 1968. Z. Phys. Chem., 238: 277. Scatchard, G., Wood, S.E. and Mochel, J.M., 1940. J. Am. Chem. Sot., 62: 712. Steinbrecher, M. and Bittrich, H.J., 1963. Z. Phys. Chem., 224: 1963. Wang, J.L.H., Boublikova, L. and Lu, B.C.Y., 1970. J. Appl. Chem., 20: 172.