Infinite-dilution activity coefficients by comparative ebulliometry: the mixtures of freon 112 with oxygenated solvents and hydrocarbons

Fluid Phase Equilibria, 23 (1985) 303-313 Elsevier

Science

Publishers

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INFINITE-DILUTION ACTIVITY COEFFICIENTS BY COMPARATIVE EBULLIOMETRY: THE MIXTURES OF FREON 112 WITH OXYGENATED SOLVENTS AND HYDROCARBONS VLADIMiR

DOHNAL

and MARCELA

Department of PhysicaI Chemistry, (Czechoslovakia) (Received

December

NOVOTNA

Institute of Chemical Technolog)f, 16628 Prague 6

3, 1984; accepted

in final form April 29, 1985)

ABSTRACT Dohnal, V. and NovotnB, M., 1985. Infinite-dilution activity ebulliometry: the mixtures of Freon 112 with oxygenated

Fluid Phase Equilibria,

coefficients by comparative solvents and hydrocarbons.

23: 303-313.

Using the comparative ebulliometric technique; infinite-dilution activity coefficients were measured for 1.1,2,2-tetrachlorodifluoroethane (Freon 112) in 15 oxygenated solvents and hydrocarbons at several temperatures. A rather high melting temperature of Freon 112 prevents the activity coefficients from being determined at the opposite concentration limit. As a substitute, the total pressure was measured at one finite concentration for some of these systems to provide a data base for the group-contribution analysis. The UNIFAC and the ASOG parameters were calculated for the interactions of Freon 112 with aliphatic and aromatic hydrocarbons, ketones, alcohols and esters. The evaluation of reliable interaction parameters for Freon 112 with ethers proved unsuccessful. As demonstrated by comparing the experimental and the predicted yp”s for the systems not included in the data base, the UNIFAC method performs slightly better than the ASOG.

INTRODUCTION

In addition to a great variety of their other technological applications, freons are used as special solvents for washing and grease-removing purposes in the microelectronics industry. In many cases, their application in mixtures with oxygenated solvents may offer the increased washing ability even at lower costs. To judge the possibilities for regeneration of these mixtures, the corresponding vapour-liquid equilibrium data are required. The necessary experimental effort can greatly be reduced when infinite-dilution activity coefficients are measured instead and used for concentration and system extrapolations by a group-contribution method. In this work, the mixtures of 1,1,2,2-tetrachlorodifluoroethane (Freon 112) with oxygenated solvents and hydrocarbons are investigated by means of the 037X-3812/85/$03.30

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mentioned economical strategy. The infinite-dilution activity coefficients of Freon 112 were measured in a total of 15 selected alcohols, ketones, ethers, esters and hydrocarbons at several temperatures using the technique of comparative ebulliometry. At the opposite concentration limit, however, the activity coefficients could not be determined by this method because of a rather high melting temperature of Freon 112 (299 K) making it impossible to maintain the closed-system conditions during the experiment. To overcome this difficulty, we measured the total pressure at one finite concentration as a substitute. EXPERIMENTAL

Procedure The equipment and procedure used for the determination of infinite-dilution activity coefficients have been described in detail previously (Dohnal and Novotn&, 1985). Briefly, twin ebulliometers of the Swietoslawski type in the comparative arrangement are connected to a two-stage, on-off controlled manostatting system. Here, a Texas Instrument quartz pressure gauge (Model 145) serves as a measuring device as well as the sensor for the pressure control. The reproducibility of the pressure measurement and setting amounts to a few Pa. The absolute accuracy is assumed to be + 7 Pa. The boiling temperature differences are measured and monitored continuously by a Hewlett-Packard quartz thermometer (Model 2801A) with two 2850A sensing probes and recorded by a digital printer. The thermometer was recalibrated in situ by measuring the vapour pressures of several high purity, dry organic solvents, and its calibration was periodically rechecked. The reproducibility of the pure-component boiling point measurements usually amounted to a few mK, and the absolute accuracy is believed to be better than +0.02 K. In typical cases, the measurement of the boiling point differences is stable to + 1 mK. Both solvent and solute were loaded into the measuring ebulliometer gravimetrically using a gas-tight pipette and syringe, respectively. The limiting slopes (aT/axp)F were evaluated by the least squares method. Their standard deviations amount typically l-2%. To measure the total pressures ( PTxp), the same equipment was used. The overall composition xp of the mixture in the ebulliometer was determined gravimetrically. Materials All components used were commercially available substances whose source and initial purity grade is listed as follows, Cyclohexane, benzene, acetone,

305

2-butanone, methanol, ethanol, l-propanol, 1 -butanol, ethyl acetate and 1,4-dioxane were analytical grade produced by Lachema, Brno. Hexane was Lachema’s spectral grade. Freon 112 and methyl t-butylether were analytical grade produced by Spolchemie, Usti n-L. and KauCuk, Kralupy, respectively. Propyl acetate (pure reagent grade) was obtained from Reachim, U.S.S.R. Heptane (p.a.) and tetrahydrofuran (p.a.) were produced by Loba Chemie, Vienna, and Apolda, G.D.R., respectively. Each substance was fractionally distilled on a 1.5 m-long distillation column filled with stainless helices except for Freon 112 and 1,4-dioxane which were purified by repeated fractional crystallization on a 1 m-long Vigreux column. Acetone, methyl t-butylether, acetates and hydrocarbons were distilled without previous purification. Aldehyde impurities in 2-butanone were removed by boiling with KMnO, and CaO for several hours. Tetrahydrofuran was shaken with dehydrated FeSO, to remove peroxides and fractionally vacuum-distilled with sodium. The product was immediately used for measurements. Ethanol was partially dried with dehydrated CuSO, and then, like methanol and 1-propanol, refluxed with magnesium activated with iodine for several hours to remove the rest of water. 1-Butanol was dried by means of aluminium amalgam. All components (except for tetrahydrofuran) were finally dried and stored with Linde 4A molecular sieves. Water content as determined by the Fischer titration amounted typically to 0.01 g H,O/lOO ml and never exceeded 0.04 g H 20/ 100 ml. The purity of the final products was verified using gas-liquid chromatography. The purity was at least 99.9 or 99.8 mol.% except for n-heptane where almost 0.5 mol.% of close-boiling alkane isomers were found. Since the effect of such impurities on the infinite-dilution activity coefficients could be expected to be negligible no further purification was attempted. The vapour pressure was determined for each pure component in the range 25-95 kPa. Reasonable agreement was obtained with the literature values, which provides an additional check of purity of the materials used. To our knowledge, however, no reliable vapour pressure data are available in literature for Freon 112. Therefore, the data measured by us are listed along with the constants of the Antoine equation and the corresponding standard deviation of fit in Table 1. RESULTS

AND DISCUSSION

The limiting activity coefficients of Freon 112 were determined in 15 selected solvents including four alcohols, two ketones, two esters, three ethers and four hydrocarbons. For each system, the measurements were carried out at three or four temperatures to get some information on the temperature variation of yIw . The limiting activity coefficients were evaluated

306 TABLE

1

Vapour pressure of 1,1,2,2-tetrachlorodifluoroethane P’(kPa)

T(K)

363.453 94.459 360.516 86.660 357.898 79.993 355.100 73.327 Antoine equation constants a A = 6.02985 L? = 1271.82 S(W) = 0.0040 b a log P”(kPa) = A - B,/( T(K)+ b s(%) = [(l/(

n - 3)) c

T(K)

P’(kPa)

T(K)

P”(kPa)

352.093 348.841 346.025 342.976

66.661 59.995 54.662 49.329

339.652 335.993 331.899

43.996 38.663 33.331

C = -49.712

C).

(1 - P,&/P;exp)2]“2

x 100.

iE,

from the measured limiting slopes (aT/ax~)~ by means of the following equation accounting for the evapouration ratio, vapour and liquid phase holdups in the ebulliometer (Dohnal and Novotna, 1985) b. _ &rP; f+ 1 - p(aT/ax;),"(l Yl -p,” f+ i + p(a-r/axp),”

- N, + NJ)

(f+ N, - N,f)

where E? = exp

(B,, - Uk)( P; - P,“) + 6,,P;’ RT I

and I?,, - & RT

d In P; dT

The characteristic ebulliometer parameters ( f = 0.06, Nv = 0.02, N, = 0) determined previously (Dohnal and Novotna, 1985) were used for the calculations. Both the limiting slopes and the limiting activity coefficients are listed in Table 2. For the evaluation of y,“, the pure-component vapour pressures measured by us were used. The correlation due to Hayden and O’Connell (l975) was used to estimate the second virial coefficients. The association parameter for Freon 112 was assumed to be zero. The unknown solvatation parameters were estimated by those for the corresponding mixtures with Ccl, as given by Hayden and O’Connell (1975) and Prausnjtz et al, (1980). Densities of pure liquids were extracted from Riddick and Bunger (1970) and Timmermans (1950). Given in Table 2 are also the standard deviations of the measured limiting slopes, s(aZ”‘/ax~)~, and the standard

307 TABLE

2

Infinite-dilution

activity coefficients

Solvent (2)

T(K)

n-Hexane

340.15 330.15 320.15 369.15 359.15 349.15 347.15 337.15 327.15 316.40 351.05 340.23 328.40

n-Heptane

Cyclohexane

Benzene

Acetone

2-Butanone

Methanol

Ethanol

1 -Propanol

1-Butanol

Ethyl acetate

n-Propyl acetate

Methyl t-butylether

1,4-Dioxane

Tetrahydrofuran

316.58 327.15 317.15 307.15 350.15 340.15 330.15 336.15 326.15 316.15 349.15 339.15 329.15 368.15 358.15 348.15 381.93 371.80 358.51 348.15 338.15 328.15 372..15 362.15 352.15 326.19 313.14 301.68 372.15 362.15 352.15 337.15 327.15 317.15

of Freon 112 in oxygenated w/w% 13.97 13.25 12.73 - 14.05 - 14.28 - 13.86 3.92 3.60 3.50 3.55 3.24 2.51 2.19 1.84 11.56 11.33 10.63 - 2.21 - 2.31 - 2.30 - 78.83 - 76.60 - 75.99 - 60.03 - 64.25 - 65.10 - 80.54 - 87.95 - 91.56 - 119.0 - 121.3 - 134.1 5.72 5.25 4.98 - 16.15 - 16.34 - 15.82 22.60 21.90 20.62 - 37.62 - 37.78 - 37.13 18.04 16.62 15.98

0.08 0.15 0.13 0.20 0.09 0.18 0.08 0.07 0.08 0.03 0.03 0.05 0.01 0.07 0.24 0.16 0.09 0.01 0.06 0.01 1.73 1.89 1.72 0.28 0.62 0.32 1.14 1.01 0.61 0.5 1.4 4.5 0.03 0.03 0.05 0.33 0.17 0.18 0.06 0.15 0.12 1.40 0.66 0.64 0.10 0.19 0.09

solvents and hydrocarbons

Y;”

S(Y,“)

1.235 1.25’ 1.265 1.20 1.215 1.22 1.265 1.29 7.31 1.32 1.305 1.34s 1.37* 1.405 2.11 2.115 2.18 1.60 1.61 1.62 12.3 12.4 12.7 5.97 6.30 6.32 4.32 4.66 4.78 3.64 3.66 4.15 1.30 1.30 1.29 1.175 1.17 1.15 1.07 0.97 0.94 1.75 1.78 1 .785 1 .035 1.075 1.06

0.02 0.02 0.02 0.02 0.01 0.01 0.02 0.01 0.01 0.01 0.02 0.01 0.01 0.01 0.04 0.03 0.02 0.02 0.02 0.01 0.65 0.65 0.65 0.18 0.25 0.25 0.17 0.23 0.29 0.27 0.33 0.57 0.02 0.01 0.01 0.02 0.01 0.01 0.03 0.03 0.03 0.05 0.03 0.03 0.02 0.02 0.02

308

deviations of the determined infinite-dilution activity coefficients. The latter w&-e calculated by means of the error propagation formula assuming the same error levels in the input quantities as those given previously (Dohnal and NovotnB, 1985). The inaccuracy of the determined yl”s correlates quite well with the infinite-dilution relative volatility, cyg, being enhanced for higher (YE mainly by the uncertainty in the ebulliometer parameters. Rather narrow t.emperature range of our measurements enables us to draw typically not more than qualitative conclusions on partial molar excess enthalpies at infinite dilution. For most systems studied, h:OO is positive. Only the systems with acetates or methyl t-butylether exhibit the exothermic mixing, which is consistent with the excess enthalpy data for the polychloroalkane + ester (or ether) mixtures (Christensen et al., 1982). It is probably the higher temperature level of the ebulliometric measurements which accounts for the slightly endothermic mixing inferred for Freon with cyclic ethers since a strongly positive c: is expected for these mixtures. To apply group-contribution methods, several systems were selected as a data base so as these systems comprised all the functional groups forming the compounds involved in the present study. For the chosen systems the datum on yp” was supplemented by one PTxp measurement at a finite X: as the substitute of y2” (see Table 3). Using the yp” and PTxT measurements, interaction parameters of the group-contribution methods UNIFAC and ASOG were evaluated. The calculation consists in solving simultaneously a system of four nonlinear equations comprising two equilibrium equations, the relation for yl” given by the group-contribution model, and the material balance equation (eqn. 6, Dohnal and NovotnB, 1985). For details concerning the solution procedure see Appendix. The parameters currently recommended for the interactions of CH, with the oxygen-containing groups (Gmehling et al., 1982; Kojima and Tochigi, 1979) were used in our calculations. Freon 112 was treated as a single group designated F112. Its volume parameter, R F112= 4.457, and surface parameter, &II2 = 3.832, were calculated for the UNIFAC method from the van der Waals’ group volumes and surfaces given by Bondi (1968). To reduce the number of adjusted parameters per group interaction to two for the ASOG method, we set mij = mjj = 0 for all group interactions with F112. The calculated interaction parameters are listed in Tables 4 and 5 for the UNIFAC and the ASOG method, respectively. Naturally, the reliability of the calculated parameters cannot be as high as that when evaluating these parameters from extensive data bases. Thus, longer extrapolations using our parameters should be avoided. However, even though the calculated parameters are based on as little data as possible, quite good predictions were achieved (except for the mixtures with ethers) for closely related systems, as illustrated in Table 6. Except for alcohols, the UNIFAC method performed somewhat better than the ASOG one.

309 TABLE

3

TPxp data for the basal systems Freon 112 (l)+ n-Hexane Benzene Acetone Methanol 1 -Propanol n-Propyl acetate Methyl t-butylether 1,4-Dioxane

T

P

w

WW

330.15 328.40 327.15

42.866 38.570 58.207 76.314 93.492 87.303 47.604 66.789

326.15 358.15 362.15 326.19 352.15

0 Xl

0.7512 0.5446 0.7167 0.4571 0.1933 0.7211 0.6559 0.6857

As may be seen from Tables 4 and 5, the economy in the characterization of basal systems may lead to certain difficulties in determining the group-interaction parameters. The narrower the effective group-concentration range, the more probable that the calculated parameters are unreliable, multiple or even do not exist. Owing to experimental limitations, the group-concentration range encountered is prohibitively small for Freon + esters and Freon + methyl t-butylether, i.e., for the systems where the mentioned difficulties occurred. Let us note that no problems with solution existence or multiplicity were found when using common correlating equations such as Wilson (see Table 7), Margules, -etc. Hence, we conclude that the economical procedure used for the group-contribution description can be successful only

TABLE

4

UNIFAC

group-interaction

F112(i)+

parameters

a ‘J

aJi

Data base: Freon 112 +

a group( j )

CH,

ACH CH,CO OH(I) a OH(I1) b COOC ’ (A) (B) CH,O

d

45.60 104.5 369.4 502.7 587.0 179.0 - 37.03 - 167.8

- 22.95 - 70.67 - 61.64 237.1 286.8 - 6.452 310.5 559.2

a Recommended for methanol and ethanol. b Recommended for propanol and higher alcohols. ’ Double solution. d Unreliable predictions.

n-hexane benzene acetone methanol I-propanol n-propyl acetate 1 ,Cdioxane

310 TABLE

5

ASOG

group-interaction

parameters

n

F112(i)+

a

‘J

n /’

Data base:

- 101.6 - 20.99 - 411.0 - 1129.0 - 1125.0 13.68 _ _

n-hexane benzene acetone methanol 1 -propanol n-propyl acetate 1,4-dioxane methyl t-butylether

Freon

112+

a group( i)

CH,

76.19

ArCH C=O OH(I) h OH(II) ’ coo Od

a b ’ d

5.405 103.8 - 453.6 - 589.8 - 484.5 _ _

m,, = m,, = 0. Recommended Recommended No solution.

TABLE Sample

for methanol for propanol

and ethanol. and higher alcohols.

6 predictions

of v,= for systems

not included

in the data

base

Predicted system: Freon 112 (l)+

T(K)

UP exptl.

Y;” UNIFAC

UP ASOG

Basal system: Freon 112 (l)+

n-Heptane Cyclohexane 2-Butanone Ethanol I-Butanol Ethyl acetate Methyl t-butylether

359.15 337.15 350.15 339.15 371.80 338.15 313.14

1.215 1.29 1.60 6.30 3.66 1.30 0.97

1.23 1.30 1.72 5.72 3.25 1.32 0.36

1.30 1.26 2.12 5.78 3.51 1.56 _

n-hexane n-hexane acetone methanol I-propanol n-propyl acetate 1 ,Cdioxane

TABLE Wilson Freon

7 parameters 112 (l)+

n-Hexane Benzene Acetone Methanol 1 -Propanol n-Propyl acetate Methyl t-butyLether 1,4-Dioxane

aa,, = (X8, -

A,,)/R.

for the basal

systems

’

.

a,,(R)

a,,(K)

u4/u:

25.28 28.36 - 55.55 201.2 128.4 - 44.21 397.2 105.5

59.12 77.49 337.9 888.9 590.5 110.6 - 244.8 99.90

1.06779 0.72072 0.60117 0.33458 0.60870 0.93585 0.97337 0.68765

311

if a sufficiently large group-concentration concerning the ether-containing systems, involved in this study are rather atypical trend.

range is involved. Moreover, we must admit that the ethers and not following a homologous

LIST OF SYMBOLS

ai; *,iy

Bi,

CP

f: i;

mi; nij

w_ NV

P P; Qk R

R/c s

T V,fxi

xy Yi

group-interaction parameter (UNIFAC); binary interaction eter for any two-parameter gE-model second virial coefficients excess heat capacity evapouration ratio excess Gibbs energy partial molar excess enthalpy of component i group-interaction parameter (ASOG) group-interaction parameter (ASOG) relative liquid-phase holdup relative vapour-phase holdup total pressure saturation vapour pressure of component i surface parameter of group k gas constant volume parameter of group k standard deviation absolute temperature liquid molar volume of component i (298.15 K) liquid-phase mole fraction of component i overall mole fraction of component i vapour-phase mole fraction of component i

param-

Greek letters a12

P Y; 6 12 Ei Xi j - Xii

relative volatility of component 1 with respect a function defined in the text activity coefficient of component i = 2B,, - B,, - B,, vapour-phase nonideality correction Wilson parameter

Superscript 00

at infinite

dilution

to component

2

312 APPENDIX

The system of equations to be solved for the unknowns aji, aji, x1 and y, is XIYI(XIY

P=

Yl

a;j,

aji)PIs+ (l -

EdYI >

=

x~Y~(x,,

Yl"=v*(

%(Y,)

a,,, a&T

4YM XI =

0, a,,,

xI)Y2(xl,

a,;,

a.ji)P2S

(Al) 69

aj;)

Since ajj can be expressed from eqn. (A3) explicitly, the system of equations treated simultaneously can be reduced to (A5)

and eqn. (A4). With the first approximation x, = xp and &r= Ed= 1, eqn. (A5) is solved for aji by the NewtonRaphson method. Then, y, is calculated from eqn. (A6). Having evaluated E, and Ed, the calculation returns to eqn. (A5). The number of iterations required in this loop is typically 2-3. Once the vapour composition corresponding to the current value of x1 is obtained, a new estimate of x1 is calculated from the balance equation (A4). The whole calculation scheme is repeated with the new value of x1_ The procedure continues until, for two successive iterations, the values of x1 are essentially the same. Thus, all four equations, (Al-4) are satisfied. REFERENCES Bondi, A., 1968. Physical Properties of Molecular Crystals, Liquids, and Glasses. Wiley, New York, pp. 450-469. Christensen, J.J.. Hanks, R.W. and Izatt, R.M., 1982. Handbook of Heats of Mixing, Wiley, New York. Dohnal, V. and Novotna, M., 1985. Infinite-dilution activity coefficients by comparative ebulliometry: A model of ebulliometer and the experimental equipment and procedure. Collect. Czech. Chem. Commun. (in-press). Gmehling, J., Rasmussen, P. and Fredenslund, A., 1982. Vapor-liquid equilibria by UNIFAC group contribution, Revision and extension. 2. Ind. Eng. Chem. Process Des. Dev., 21: 118-127.

313 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. Kojima, K. and Tochigi, K., 1979. Prediction of Vapor-Liquid Equilibria by the ASOG Method. Elsevier, Amsterdam, pp. 15-22. Prausnitz, J.M., Anderson, T.F., Grens, E.A., Eckert, C.A., Hsieh, R. and O’Connell, J.P., 1980. Computer Calculations for Multicomponent Vapor-Liquid and Liquid-Liquid Equilibria. Prentice Hall, Inc., Englewood Cliffs, pp. 160-178. Riddick, J.A. and Bunger, W.B., 1970. Organic Solvents. Wiley, New York. Timmermans, J., 1950. Physico-chemical constants of pure organic compounds. Elsevier, Amsterdam.