'i,
I'apor-Liquid Equilibria i n Binary S y s t e m s )
SYSTEMS INVOLVING cis- OR trans-DICHLOROETHYLENE AND AN ACETAL OR ETHER DONALD G. FLOJI', NORRIAS ALPERT, AND PHILIP J. ELVISG
T
HE binary systems were nelt inrestigated of czs- or transdichloroethylene with typical class I11 liquids; the latter
were methylal (dimethoxymethniie), tetrahydrofuran, and isopropyl ether. In calculating the isopiestic activity coefficients for evaluating and interpreting the equilibrium data, vapor pressure data were needed; although such data for czs-dichioroethylene, transdichloroethylene, and isopropyl ether were obtainable in the literature (19),it was found desirable t o redetermine the vapor pressures. A modified form of the Ramsay-Young dynamic method was used for this purpose. The vapor pressure data for tetrahydrofuran and methylal were kindly furnished by the Du Pont Co., the data for tetrahydrofuran subsequently being published ( 7 ) . EXPERIMENTAL
were purified by PREPARATION O B ~ ~ T E R I A -4 L11~ liquids . distillation through the 120-em. column described, a t a reflux ratio of about 20 to 1. The fraction of the boiled methylal (Paragon Testing Laborat,ories) used at 42.6" C. had a n%' of 1.3535. Tetrahydrofuran (East.man Kodak white label) was collected a t 66.1' C. (nao 1.4069), aft,er a considerable forerun. Isopropyl ether (Eastma11 Iiodak n-hite label) distilled a t 68.0" C. (n%O 3.3680).
=i wad of absorbent cotton is virapped around the bottom end of tube B and the hot junction of the copper-Constantan thermocouple. The thermocouple wires lead out through a small side arm on the joint, C. This arm is made vacuum-tight by sealing it with de Khotinsky wax. Tube B extends into the larger, vertical tube, A , 240 X 35 mm. in oiitside diamet'er, which is heated by means of a paraffin oil bath, the source of heat being a GlasCol hemisphere. A mercury thermomet'er is used to dekrmine the bath temperature. 4 reservoir fitted with a stopcock, F , is connected to the top end of tube R. A side tube leads from C to a receiver, H , 280 X 45 mm. in outside diameter. This receiver ir maintained a t a lox- temperature by means of a dry ice-trichloroethylene mixture in a Dewar flask. The exit of the receiver leads through a stopcock, I , to a 5-gallon bottle which serves as a surge tank; the latter, in turn, is connected to a manometer and to a vacuum pump. A capillary bleed with st'opcock, J , serves to admit air when necessary. Receiver H i s connected to the rest of the apparatus by 12/30 standard-taper joints. The cold junction of the thermocouple is placed in a distilled water and ice b:tth, and both junct.ions are connected to a high sensitivity potentiometer. D ETERN IN aTIO N O F V A P O R PRESSURES. The utilization of absorbent cott,on as the evaporating surface resulted in excellent vaporization, prevented superheating, and ensured that the liquid a t the thermocouple junction was in contact with its vapor onlv. The liquid to be examined was introduced into the reservoir and the apparatus was evacuated by means of a vacuum pump. Liquid was allonTed to enter from the reservoir and to saturat>ethe absorbent cotton around the thermocouple junction. Tube A was heated by means of the paraffin oil bath kept approximately 20" C. above the thermocouple temperature. When the system had reached equilibrium, and the temperature and pressure had become constant, a reading was taken. The pressure indicated by the manometer was read wit'h a cathetometer to +0.5 mm. of mercury. Air was then int,roduced through the bleed to changc the pressure and t,he procedure was repeated. The choice of stopcock grease was import.ant in obtaining a vacuum and in avoiding the dissolution of the grease by the organic liquids. Silicone high vacuum grease was unsatisfactory for a long-lasting seal. Cenco vacuum stopcock grease ( S o . 15522 il) was finally used in all the joints on the exit side of the receiver, H . -4grease compound of anhydrous glycerol, dextrin, and &mannitol (15) was used in all the joints to the left of H . DATA
/C Figure 4. Apparatus for Determination of Vapor Pressures
H
A d
Var~oizPRESSI-RE ,~PPARATI-S. The apparatus used (Figure 4) was similar in principle to tmhe Ramsay-Young apparatus (It?), the major changes being the introduction of standard-taper glasv joints and the substitution of a highly sensitive thermocouple for the mercury thermometer. A long glass tube of small diameter, B , 300 X 7 mm. in outside diameter, is connected by means of a ring seal through the center of an inner 50/30 semiball joint, C. 1
Present address, The Pennsylvania State College. State C o l l e g ~ ?a ,
VAPOR-LIQCID EQUILIBRIUM DATA. Equilibrium samples obtained from the Jones-Schoenborn-Colburn still were analyzed by refractive index measurements at 20" C., using the data of Table 1. The experimental results are presented in Tables VI1 to XI and shown graphically in Figure 5 ; the corresponding vaporliquid equilibrium diagrams are shown in Figure 6 . The apparent isopiestic activity coefficients for each component were calculated (Tables VI1 to XI) and plotted (Figure 7 ) . The compositions and boiling points of the azeotropes formed in and transthe systems, cis-dichloroethylene-tetrahydrofuran dichloroethylene-methylal, could not be checked by preparing mixtures approximating the azeotropic composition and fractionally distilling the mixtures, because the most efficient column available (60 theoretical plates) did not have sufficient resolving power. The vapor-liquid equilibrium relations are such that starting on either side of the azeotropic composition gave a residue that was richer than the azeotropic composition with respect to the component originally present in excess. As a result, azeotropic compositions and boiling points were determined from the smoothed vapor-liquid equilibrium data. Care was taken t o determine sufficient experimental points in the vicinity of the 1178
May 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
1179
Figure 6. Equilibrium Mole Fraction of Lower Boiling Component in Vapor, yl, US. Mole Fraction in Liquid, 21, at 760 Mm. of Mercury Pressure Roman numerals refer to same systems as in Figure 5
Figure 5.
Boiling Point-Composition Diagrams
Temperature, O C., us. mole fraction of lower boiling component at 760 mm. of mercury pressure 1. cis-Dichloroethylene-methylal (lower boiling component) 11. trans-Dichloroethylene-methylal (lower boiling component) 111. cis-Dichloroethylene (lower boiling component)-tetrahydrofuran IV. trans-Dichloroethylene (lower boiling component)-tetrahydrofuran V. cis-Dichloroethylene (lower boiling component)-isopropyl ether VI. trans-Dichloroethylene (lowerhoiling aomponent)-isopropyl ether
azeotropes to permit drawing a good average curve. In the system, cis-dichloroethylene-tetrahydrofuran,a maximum boiling azeotrope, boiling a t 69.9" C. and containing 0.386 mole fraction cis-dichloroethylene, was found. In the system transdichloroethylene-methylal, a maximum boiling azeotrope, boiling a t 48.6" C. and containing 0.250 mole fraction methylal, was found. VAPORPRESSURE DATA.The vapor pressure-temperature relations for cis-dichloroethylene, trans-dichloroethylene, and isopropyl ether were determined over a range varying from approximately 15" C. to a temperature slightly greater than the boiling point of the compound in question (Table XII); the data for methylal and tetrahydrofuran were furnished by D u Pont. For the data obtained in this investigation, the plot of the logarithm of the pressure against the reciprocal of the absolute temperature A i shown in Figure 8.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1180
TABLE VII. VAPOR-IIIQUIU I’:QUILIBRIUM DATAA T 760.0 L h I . Temp., hlole Fraction xrethJ1al C. -Liquid, X I Vapor, vi
Activity Coefficients Methylal, Dlchloroethylene, YI
Y2
SYSTEM C~S-DICHLOROETHYLENE-~METHYL~L 0.0
60.3 60.1 69.9 59.4 58.3 57.0 55.3 54.0 52.4 50.9 49.4 47.5 48.9 43.8 42.8 42.6
0.020 0.048 0.104 0.180 0,267 0.366 0.437 0.513 0.581 0.653 0.737 0.810 0.918 0.983
1.000
0.0 0.025
0.062 0.130 0.237 0.349 0.481 0.567 0,652 0.727 0.790 0.859 0.909 0.967
0.998 1.000
0.630 0.662 0.686 0.682 0.740 0.766 0.814 0,844 0.874 0.906 0.932 0.952 0.969 0.991 0.989 1,000
1.000 0.988 0.983 0.994 0.982 0.978 0.953 0.942 0,926 0.890 0.879 0.836 0.782 0.717 0.217 0.600
Vol. 43, No. 5
TABLEIx. VAPOR-LIQCID EQUILIBRIUMD.4TA
FOR
t~UnS-DICHLOROETHYLESE-TETR.4HYDROFURAN AT
T$mp., C. 66.1 66.1 66.0 65.9 63.4 64.4 62.3 61 3 60 57 0 53 6 53.8 52 6 50. q 4 9 . .i 48 3
Mole Fraction tlans-Dichloroeth3’1ene Liquid, xi Vapor, vi 0 000 0.000 0 016 0.016 0 045 0.047 0.092 0 085 0,181 0 160 0.329 0 266 0.472 0 376 0 454 0.576 0.619 0 506 0.736 0 3 7 0.801 0 053 0 751 0.853 0 8’8 0 90.5 0 ‘201 0,948 0 367 0 078 I 000 1.000
SYSTEM
760.0 hIM.
Activity Coe5cients bichloroethylene, Tetrahydrofuran, Yl
YZ
SYSTEM t r a n s - D I C H L o H o l z T H Y L ~ s ~ - ~ ~ E T H Y L . 4 L
48.3 48.3 48.4 48.5 48 5 48.5 48.6 48.6 48 5 48.5 48.4 48.3 48.2 48.0 47.4 46.9 46.2 45.3 44.2 43.1 42.7 42.6
0.0 0.030 0.089 0.140 0.183 0.212 0.231 0.251 0.274 0.304 0.331 0 3\56 0.388 0,428 0.501 0.580 0.673 0.756 0.852 0.933 0.983 1,000
0.984 0.993 1,000
1,000 1.010 1.013 1,017 1.013 1.013 1.007 1,001 0.999 0.994 0.988 0.977 0.970 0.966 0.954 0.918 0.895 0.867 0.831 0.806 0.796 0.740
TABLE x. VAPOR-LIQTXDEQUILIBRIUM DATAFOR SYSTEM cis-DICHLOROETHYLENE-ISOPROPYL ETHER AT 760.0 AIM. blole Fraction Temp., C. 68 0 67.6 67.4 67.2 66.9 66.4 63.9 63.4
610 64.4 63.5 62.2 61.5 60.3
,
Activity Coefficients Ether,
cis-Dic’iloroethyiene Diohloroethylene,
Liquid, .rl 0.000 0.058 0.116 0.176 0.248 0.329 0,399 0.460 0.534 0.618 0.697 0.828 0.903 1,000
Vapor,
YZ
71
VI
o nno 0 063 0 129 0 198 0 270 0 378 0 450 0 521 o 604 0 684 0.767 0.877 0.932
1.000
TABLE VIII.
VAPOR-LIQUID EQUILIBRIUM D A T A FOR SYSTEU CZ‘S-DICHLOROETHYLEKE-TETR.4HYDROFURAN AT 760.0 AIM.
Mole Fraction Tzmp., cis-Dichloroethylene C. Liquid, zi Vapor, yi 66.1 0.000 0.000 66.4 0.018 0.010 60.9 0.045 0.030 67.1 0.083 0.055 0.096 67.8 0.136 0.150 68.A 0.185 0.203 68.9 0.232 0.259 69.3 0.281 0.297 69.7 0.313 0.350 69.7 0.357 69.8 0.373 0.368 0.395 69.8 0.392 0.427 69.7 0.421 0.466 69.4 0.447 0.526 68.9 0.497 0.609 68 0 0.552 0.697 67.0 0.627 0.768 66.3 0.695 0.851 64.9 0.775 63.6 0.843 0,907 0.943 62.4 0.909 61.6 0.981 0 945 60.3 1.000 1 000
Activity Coefficients Y1
-/a
the more volatile component in the liquid (linear scale) and comparing these plots with the van Laar and Margules equations which are integrated forms of the Gibbs-Duhem equation ( 5 ) . The clue as to which equation to use may be indicated by the molar volumes. The molar volume ratio of methylal to cis-dichloroethylene is 1.18 to 1. In this binary system, with A as -0.201 and B as -0.222, both the van Laar and Margules equations gave a good fit for the methylal curve-that is, within 1% over the entire range. The fit for the cis-dichloroethylene curve was Tithin 1%
1.0 .8 .6
The Clausius-Clapeyron equation was used to derive equations for the vapor pressure-temperature relations (6).
Figure 7. Activity C o e f f i c i e n t US. lMole Fraction Lower Boiling in Component Liquid, XI, a t 760 M m . of Mercury Pressure
Having calculated L, this equation can be used for moderately small temperature ranges between two points of the curve. The values of L based on Figure 8 are cis-Dichloroethylene
7510
trans-Dichloroethylene
7080
A.
* 5 cal./mole * 10 cal./mole
DISCUSSIOR
The thermodynamic consistency of the vapor-liquid equilibrium data was tested by plotting the activity coefficients (logarithmic scale) for each binary system against the mole fraction of
Activity
coeffi-
cient curve for
lower
B.
1.0 .8 .O
.2 .4 .6 .8 MOLE FRACTION - X,
1.0
boiling comonent Activity ooefficient curve for higher boiling c o m p onent.
R o m a n numerals r e f e r to s a m e SvstemS as i n Figure 5
May 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLEXI. VAPOR-LIQUIDEQUILIBRIUM DATAFOR .SYSTEM
800
760.0 M M . Activity Coefficients Diohloroethylene, Ether,
trans-DICHLOROETHYLENE-ISOPROPYL ETHERAT Mole Fraotion trans-Dichloroethylene~ Liauid. Vapor,
Temo.. 0
c-.
Yl
Y1
XI
68.0 66.9 65.9 65.0 63.1 61.1 59.5 58.0 56.1 55.6 53.4 53.3 51.6 50.7 49.4 48.3
700
600 '
YY
1 * 000 1.006 0.998 0.995 1.000 1.022 1.016 1.001 0.970 0.986 0.919 0.853 0,891 0.924 0.957 0.950
0.000 0.099 0.172 0.242 0.358 0.464 0.560 0.624 0.725 0.734 0.836 0.881 0.902 0.928 0.971 1.000
0.000 0.063 0,110 0.160 0.248 0.341 0.417 0.474 0.576 0.588 0,706 0.769 0.805 0.857 0.942 1.000
1181
500 (j 400 I
I I 300 [r
3
m
(0
w
TABLE XII. VAPORPRESSURE-TEMPERATURE RELATIONS transDichloroethylene
CiS-
Dichloroethylene Pressure,
TEmz.,
mm.
PresTEmg.,
Hg
mm.
196.0 264.1 322.2 381.3 463.8 536.9 594.8 648.9 713.3 766.3 833.7
200
Isopropyl Ether Pressure,
Tzmz.,
mm.
13.3 26.8 35.1 42.4 47.9 53.0 56.7 59-8 63.0 66.3 69.5 70.6
86.0 161.5 228.7 303.2 377.7 450.5 514.1 572.1 640.4 719.0 781.6 821.1
Hg
13.5 20.5 25.3 29.7 34.7 38.6 41.6 44.1 46.8 49.1 51.6
19.2 26.9 34.1 39.3 44.4 47.8 52.1 55.0 58.4 60.4 62.0
sure,
a a
Hg
1001
.
265 587 760
15 25 35 45 55 65
I
'
30
I
I
31 I/T
' 32' x
I
'
33
I
'
34
I
I
35
104
Figure 8. Vapor Pressure-Temperature Relations for Isopropyl Ether, cis-Dichloroethylene, and trans-Dichloroeth ylene
TetraMethylal hydrofuran PresPressure, sure, Tgrnz., mm. Ttrnz., mm. Hg Hg
16.3 35.2 42.3
'
29
A . Isopropyl ether S. cis-Diohloroethylene C. trans-Dichloroethylene
114 176 263 385 550 760
from 0.0 to 0.3 mole fraction methylal, but beyond this the fit dropped off to within 3 to 7'30. Using other values of A and B did not improve the fit. The molar volume ratio of methylal to trans-dichloroethylene is 1.16 to 1. Using a value of A equal to -0.194 and B equal to -0.131, both the van Laar and Margules equations gave poor fits t o the experimental data. Values of A and B calculated from data on the maximum boiling azeotrope found in this binary system did not give a better fit. The molar volume ratio of tetrahydrofuran to cis-dichloroethylene is 1.08 to 1, and of tetrahydrofuran to trans-dichloroethylene 1.06 to 1. The vapor pressure data for tetrahydrofuran furnished by Du Pont were used to obtain the slope of the curve, log vapor pressure us. reciprocal of absolute temperature; the vapor pressures were then adjusted to the observed boiling point (66.1' (3.). Both binary systems gave a poor fit to both the van Laar and Margules equations. In the system cis-dichloroethylene-tetrahydrofuran the A and B values tried were -0.319 and -0.174, respectively. Values of A and B calculated from the
data on the maximum boiling azeotrope in this system did not improve the fit. I n the system trans-dichloroethylene-tetrahydrofuran, the A value was -0.252 and the B values tried were -0.071, -0.046, and -0.036. The molar volume ratio of isopropyl ether to cis-dichloroethylene is 1.88 to 1, and of isopropyl ether to trans-dichloroethylene 1.84 to 1. Both binary systems gave a fair to poor fit to both the van Laar and Margules equations. In the system cis-dichloroethylene-isopropyl ether, the A and B values were -0.097 and -0.036, respectively; in the system trans-dichloroethylene-isopropyl ether, the A and B values were -0.046 and -0.022, respectively. SUMMARY
Vapor-liquid equilibrium data a t atmospheric pressure are presented for the binary systems formed by cis- or trans-dichloroethylene with methylal, tctrahydrofuran, and isopropyl ether. Refractive index-composition, boiling point-composition, vaporliquid equilibrium, and activity coefficient-composition relationships are presented for the above systems. Maximum boiling azeotropes have been observed in the binary systems, transdichloroethylene-methylal and cis-dichloroethylene-tetrahydrofuran. The data did not fit entirely satisfactorily either the van Laar or Margules equations. The vapor pressure-temperature relations for isopropyl ether, cis-dichloroethylene, and trans-dichloroethylene were determined.
* * * *
