Vapor-Liquid Equilibrium in AcetoneBenzene-E thylene Dichloride Sy stern L. N. C,;LUJAR, E. C. HORSI, JH., .LSD R . R . ROTHFLS Carnegie Institute of Technology, P i t t s b u r g h 13, Pa.
S
the riltire raiigc of ~ ~ o ~ i i . ( , i i t r a itiii ( icw,h ~ i ~ case at a constant total pressure of 760 mm. of mcwury. The consistency of the himtry data \vas tested by meaiis of' thermodynamic a~ialysrs.
YSTESIS containing distinctly different types of compounds are especially suitable ones in which to observe the effect of component interactions on the vapor-liquid equilibrium. For the same reason, they are of particular interest in the study of heat and mass transfer pheiioinenn.
:to
Figure 1.
EXPERIllEYTAL &PI',\R.ilCS
Equilibrium Still. The principal piew of experimental e q u i p ment was an Othnier-type still purchased from the Emil Greiner Co. (8) The unit is illustrated in Figure 1 . The liquid in the bod:-, A ! of the still was heated b y means of a Sichrome element wrapped around the leg, B . The bypass tube, C, permitted a circulation of liquid through the leg. T h e vapors evolved from the boiling liquid passed upward through tubes 11 and E t o t h r condenser, F . There they were liquc4ed and dropped into the vapor trap, G, from ivhich they tvtlre rec*yclPdt o the body of the still through tube H . T h e temperature of the effluent vapors \vas determined by measuring the temperature of a drop of mercury a t the bottom of tube I . .in iron-plated, copper-constantan thermocouple was used for this purpose. Samples of the liquid and condensed vapor were drairn off through stoprocks J and K , respectively. I n order to minimize condensation a t the wall, the body of t h e still was completely covered by a layer of asbestos insulation approximately 1 inch thick.
a m
Schematic diagram of experimental equipment
Lquilibrium d a t a 011 the terriaq sg stem acetone-heiizerie~ethjlerie dichloiide have been obtained expeiimentallj in connection n ith a tian-fer rate studv being made a t this institution. The binar? niixtuies of these components foini faiil) regular solutions and the coirespondirig I elative \rol,rtilitiee vdi y f r o m rather high t o very lon valuee Considerable inteieat has been sliov 11 in the binar? equilibria, hut iin data on t h ~ ternar! s ~ s t e mhave been published Composition and temperature d a t a on the act~to1ie-heii7eiie system have been obtained by Soday and Bennett ( I d ) > Iteinders and De\Iinjer ( 1 2 ) ,Tallmadge and Canjar ( I 5 I , and Othmri (9). The acetone-ethj lerie diehloiide q s t c m has lieen studied by Fordyce and Sinionsen (5) and Pahlavouni ( I O ) D a t a on the benzene-ethylene dichloride qrstem have becn repoited by Rragg and Richards ( I ) , Rosanoff and Easley 113). Pahlavouni ( I O ) , Coulson, Hales, and Heiiiigton (3), ICireer and Skvortsovs ( T J , Zanidzhi ( 1 6 ) . and Kipling and Tester (6). I n the pirseiit inbestigation, the ternar) s j stern and the thiec binary combiiiations were stiidird sepni ately. D a t a n-ere obtained over
__
--
0 -
ACETONE
xn
Figure 2.
---
427
Ternar) \apor-liquid equilibria Mole yo acetone in vapor phase
BENZENE
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INDUSTRIAL AND ENGINEERING CHEMISTRY
E
ETHYLENE DICHLORIDE
Figure 3.
---
Ternary vapor-liquid eqiiilihria
Mule
5%
benrene i n v a p o r phase
Analytical Equipment. T h e rrfxwtive indives of the eaiiiple. withdrawii from the still were measured a t the sodium I ) line by nieaiis of a Bausch & 1,omb precision refrartometer, which was capable of indicating tlie refractive index to 1 3 x 10-5. T h e temaeratnre of the Drisni and sample was n i : i i r i t :rined :it the desired level by means of Tyater from a colistaiit temperature bath. T h e temper:tture oi the bath varied less than 0.02" C. T h e derisities of the samples were d e t e r m i n d b y means of a 25-ml. pycnometer and an analytical balance. T h e pycnometer and its contents were brought to constant tempe~,aturein a bath where the temperature varied less than 0.01" C. It was found t h a t the measured weiglits of the loaded pycnometer were reproducible to +0.5 mg., providing sufficient care wag tatlie~i in wiping and handling the piece. Equipment for Pressure Control. 111 order t o iiiaiiitaiii the system at a total pressure of iG0 mm. of mercury, i t was necessary t o impose u positive pressure a t the top of the condenser. FoI t h i j purpose, compressed air from a suppl>main was passed sucwssively tlirougll a pressure regulator, a surge tank, and a drying tube and then into a 1-liter pressure reservoir. T h e reservoir was connected t o a mercury U-tube manometer and then t o the top of the condenser. Another line from the reservoir was coiiiiected t o an Emil Greiner Cartesian mariostat, which maintained t h e reservoir pressure within 1 mm. of mercury of the desired level by controlling the rate a t which air u a s bled from the reservoir to the atmosphere. EXPERIMENTAL PROCEDURE
Purification of Components. ACETOXE. T h e acetone was ACS grade produced by Eimer and
Vol. 48,No. 3
Amend with a reported boiliiig range of 55.5' to 57.5' C. This material was further purified by distillation in a glass column 1 inch in diameter, pncke(1 t o a height of 5 feet with l/B-incti glass helires. The operation was performed at a reflux ratio of 5 to 1 and the first and last tenths of the distillate were discarded. Tablo I indicates t h a t the acetone purified in tlik manner exhibited properties which cornpar(' favorably with those reported by Dreisbach ( i ) . BESZESE. T h e benzene was produced by thcl Barrett Divisiori, Allied Chemical arid D y e Corp. Purification was accomplished by the same procedure as in the case of acetone. The properties of the purified material are shown iii Table I. ETIITLESEI~ICHI,ORIDE. T h e ethylene dichloride was the "piwified" grade produced by Eimer and .\mend. T h e material was distilled in tlie same manlier as the acetone and benzene, but in this case satisfactory purity was not attained. Consequently, a second distillatioil \vas performed using a reflux ratio of 10 to 1 and discarding the first and last tenths of the distillate as before. T h e ethylene dichloride thuv obtained had the properties listed in Table I. Analysis of Mixtures. T h e compositions of the binary mixtures were determined through density measurements alone. I n the case of t h r ternary system, both density and refractive index nieasurenie~its iwre used in establishing oonipo*itioris. The t y p r of analysis was favored by the fact that lines of coristaiit density and refractive index are almost perpendicular t o each other in all regions, when plotted :iytiinst composition on triangular coordinates. For the case a t Iimd, the estimated acc.uracy of the ternary ari:iIy& is tvitliiri 1 0 . 0 0 3 mole fraction.
ETHYLENE
DICHLORIDE
.A'O
Figure 1. Ternary vapor-liquid equilibria
---
Trnipernture,
'C .
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INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1956
Symbol-Reference
I
l
l
I * ----yo
e
0.02
0.04. m
2 0.03
I
~"
0.02
I
'
I I
I
I
.
;
-0.10
0.0 0.1 02 0.3 0 4 0.5 0.6 0.7 0.8 0.9 1.0
I ~
07 I +-
i1
l
i
-
Mol F r a c t i o n B e n z e n e
Figure 5 ,
Benzene-ethylene dichloride mixtures
Figure 6.
Relation of mole fraction of benzene in liquid to log y beazeney ethtlene dichloride
Sy m bo I-R e f e r ence CE
9
(3
12
8
14
i
2
0.30 %
0.25-
I C
ethylene
Symbol- R e f e r ence Table I.
15
0
P r e s e n t Worh
~ i l i l l 1 TIT
~
3Iaterial Acetone Benzene Ethylene dichloride
Properties of Purified Components
Normal ?oiling Point, C. Obsd. (3) 56.11 56.18 80.10 80.10
Refractive Index a t 30.0O C Obsd. (3) 1 . 3 5 3 9 8 1.38334 1.44405 1.49460
Density a t 30.0° C., G./III. Obsd. (5') 0.77939 0.77931 0.86837 0.86824
63.47
1.43930 1.43939
1 23839
83.47
1.23817
Operation of Still. A t the start of a run, approximately 400 mi. of liquid mixture n-as charged t o t h e body of the still aiid current was supplied t o t h e heater. After about a half hour of operation, the still was vented t o remove any air trapped in the hody. The total pressure on the system was then adjusted t o '760 nini. of mercurl-, absolute, by means of the Cartesian manostat. T h e rate of heating was adjusted y o as to boil off about 30 ml. per hour or, in other m-ords, completely replace the liquid holdup in the r a p o r t r a p each hour. The still was then left in undisturbed operation for approximately 24 hours, after which the temperature x a s recorded and samples \yere obtained. I n taking the samples, the contents of both the vapor trap and bod?of the still were completely drained into separate flasks immersed in a n ire bath t o minimize flashing.
m
5
Acetone-ethylene dichloride mivtiirea
Relation of mole fraction of acetone to log y acetone-, dichloride
0.05
0.00
- 0.05 -0.I O -0 15
RESULTS
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Mol F r a c t i o n A c e t o n e Figure 7 . Acetone-benzene mixtures Relation of mole fraction of acetone to log y acetone-? benzene
T h e esperimental results of the investigation are presented in Figures 2, 3, and 4 and in nine tables, which represent the actual d a t a and calibration curves obtained. As they are too voluminous for presentation here, they have been placed on file F i t h the .Imerican Documentation Institute ( 9 ) . I n the study of the ternary system, a fixed ratio of benzene and
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 48, No. 3
ethylene dichloride Tvas maintained in tlie liquid charged to the still throughout a given series of runs. This ratio ~ m essentially s unaltered bj- the vaporization process Imause of the vrry lox relative volatility ol henaene and ethylene dichloricle. C'onserluently the (lata were easily intcrpoluted to even values of !) and t for corist,ant benzene--ethylrne ciivhloricle ratio. T l i ~resultant ciuantitics are presented graphically in Figures 2, 3, and 4. I i n e ? of constant temperature : ~ n dmole fraction iii the rapor phase are Piion-n on triangular coordinates which rpprcseiit liquid conipositioiis. The vapor conipositioii corresponding to a particular liquid composition can be determined by intcqmlatiiig twtween adjacent lines of constant mole fr:iction in tlie vapoi' phase. The temperature can be obtained iii a siiiiilsr manner. Thermodynamic Analysis of Binary Data. Thc ;ic.tivit>' roefficients defined by the relationship Yi =
PY, px
\rere computed from the data obtained on the binary systems. Tlie pure component vapor pressures: P:, were obtained frnm t h e following equations: L I T E R A T U R E C ITEIJ
For acetone (S), logloPo = 1.14366 -
For benzene ( I I
1161.0 t 224.0
+
);
log,OPo
=
1.02484 -
1211.033 220.790 t
+ ~
For ethylene dichloride (31, logloPo = 1.30350
-
1358.46 232.2 t
+
I n each vase, the vapor pressure thus obtained was found to be consistent with the observed boiling point of the pure component. The logarithms of the activity coefficient ratios are shown in Figures 5. 6,and T as functions of the liquid compositions. .4ccording to Itedlich, Iiister. and Turnquist (If )> the area under each curve should be zero if the Gibhs-Duhem equation is obeyed by the data. Esperimrntal results which satisfy tlie criterion are not necessarily correc,t, b u t those which deviate from it contain thermodynamic inconsistencies. T h e area under the benzene-acetone curve is slightly lew than zero, hut seems t o agrre very closely with the work of moat other investigators. Some information obtained in this laboratory (161, using an apparatus that n-as not designed to obtain vaporliquid equilibrium data, seems t o be more consistent than that reported here, This difference, which seenu to depend on the type of apparatus used, is still unexplained. The area test ie
Uragg, L.B., liiclinrtls. A. I?.. ISD, ESG. CHEII.34, 1086 (1012). ('anjar. L. 1-., H o r n i . E. C., Jr., Rothfus, l t . I t . . .Xm. Doc. Irist., W a s h i n g t o n 25, El. C., D o c . 4771 (1956). ('onlson, E. A,, Ilale3, J . L., H e r i n g t o n , E. F.G , Trans. Faraday SOC. 44, 636 (1048). D r e i s h c h , Ilc!nentary to this article Ims been d e p o s i t r d as Document S o . 4 i i l \ n i l 1 [lie 1111 .-iiisiliars Publication- Project, I'Iiotodui,licat~on Service, Library of Congress, rT-asliinbzun 2 3 , n.C . A copy I n a s b e seciircd by citing tlic docoincnt nuniber and by r c i n i t t i w S3.i; for pilotoprints or I2.00 f o r 3 % ~ u t u .Inicroflm. .idranee p a y m e n t ii required. Xfake checks or money a r d e r s payable t o Chief, Photoduplication Seri-ice, Library of conal.r.is.
