3 58
C. G . DESZLER
L I QI-ID-L I (21-1D EQI-I LIl3R I L-14 D-%T;1 C ’ , C>. DESZLER Departineni of Chemical Engiiceerzriq, I-njverszty
os CirzciniiatL,
C ~ r i c z n n a t ~Ohio ,
12eceaied F e b r i i a i y 8 , 1945
In the course of a research problein. i t became neccs\ary to have data on the liquid-liquid equilibria 2nd refractiTre intlicca of the teinary systems benzene-lpropanol-water and carbon tetrachloride-l-propanol-~~ater, and refractive index data for the binar?- system carbon tctracliloridc~-l-propanol. A search of the literature up to the prcient yiclded inoufficient data (2, 5 ) . Therefore determinations were made on theqe
c FIG.1. Binodal curve for tlie ternary systeiii carbon tetrachloride-I-propanol-water a t 20°C. and atmospheric pressure.
BotEi oi the leinary \)stems c*ont:iin a .ingle pair of non-consolute liquids hoqe mutual solubilities increase upon addition of u third component, and theref ole their binodal curveq (figures 1 and 2 ) show the characteristic “hump”. Table- 1 and 2 present the data fioin nhich the binodul curves were drawn. The 1);nary iicm \\as one of complete mutual solubility. The iifpid-liquid equilibriuin curyes h a w been wpplemented with tie lines to i n c r c ~ ~the c ~usefulnesc: oi tlie data. TT
C
FIG.2. Binodal curve for t h e ternary system benzene-1-propanol-nater at 2 0 T . and atmospheric pressure. TABLE 1 T e r n a r y s y s t e m carbon tetrachloride-1 -propanol-water at 20°C. I
CiRBON TETRACHLORIDE
,
I
l-PRoPAsoL
zeigiil
per
C E N ~ ,
0.51 1.6 2.4 6.0 11.7 17.6 23.8
28.7 32.0
'
, '
1 j
~
~
i
1
I
I
IgE"x"G'?)
1-PROPAXOL
useight per cent
;ceiiht p e r ceizl
21.1 26.7 30.0 39.6 48.4 53.0 54.0 53.7 52.3
REFRACTIVE I m E X (25°C.)
~
I , ~
50.1 48.6 47.2 45.6 40.8 35.1 22.5 10.1 3.7
1.3509 1.3552 1.3578 1.3656 1.3743 1.3810 1.3866 1.3903 1.3928
1.3969 1.3991 1.4013 I.4022 1.4089 1.4130 1,4275 1.4411 1.4512
TABLE 2 T e m a r y system benzene-1 -propanol-water at 20°C. ~~
! BESZEXE
*
P PROPANOL
%eight p e r cent
.yeighl per cent
0.35 1.6 4.2 8.5 12.2 15.1 18.5 25.3 27.4
19.3 28.9 39.1 60.7 56.3 57.7 59.0 58.6 57.8
I
REFRACTIVE I N D E X (25'C.)
BENZESE
~
1
i
1
~
,
30.3 45.6 47.3 51.0 60.5 66.6 75.6 83.0
359
REFRACTIVE INDEX ( 2 5 T . )
zieisht per cent
weight per cenc
1.3501 1.3569 I.3678 1.3794 1.3872 1.3928 1,3970 1.4058 1.4085
1-PROPANOL
1 I
1
1
56.5 46.1 45.1 42.1 34.9 29.8 22.2 15.8
1.4121 1.4300 1.4321 1.4364 1.4474 1.4547 1.4654 1.4747
360
C . G. DEXZLER NATERISLS A S D BPPARATUS
All materials used were C.P. purified chemicals. The 1-propanol was dried for one week over calcium chloride and then subjected to three redistillations, a three-ball fractionating column being used. The first and last portions of each distillation were discarded. The values of the refractive indices of the materials a t 20°C. n-ere a? follon-s: benzene, 1.5010; carbon tetrachloride, 1.4604.;1-propanol, 1.3860; water, 1.3330. Refractive indices were taken with an Abbe refractometer with the temperature regulated to within &O.l"C. A 2-liter beaker, about tv-0-thirds filled with water, was used as n con>tanttemperature bath during end-point titrations. A small-sized bath of this type has the advantage of permitting close observation of the sample being titrated. It also allows the sample to be viewed from any desired angle, thus eliminating the necessity of looking directly into the source of illumination. The temperature during titration was controlled to &O.l"C. The buret used for titrations n-as modified by attaching to the tip oi i t , \ITmeans of rubber tubing, a piece of 5-nim. glass tubing about 4-5 in. long. The one end of the glass tubing Tvas drawn t o a fine capillary. Thi:, nttschment allowed constant shaking during titration and gave better control of the titration, since smaller drops formed from the capillary than from the buret. It n-a> found that a small piece of rubber tubing, $-in. in length, formed an air-tight stopper for the %ounce glass-stoppered bottleq which Tvere used in titrating the samples. This piece of tubing was placed just sbore the capillary u-hich extended into the bottles. PROCEDURE
I n determining a point on the binodal curve, two of the component- of a system, one of the non-consolutes and the homogenizer liquid, were mised in definite weighed amounts. The third component was then added from a buret until the mixture reached the state ]\-here the beginning of the formation of two liquid phases was indicated. The quantity of the third coniponent added n a i then determined gravimetrically. After titration '\vas finished the avprug'p ;ample weighed almost 20 g. The titrations were carried out a t 20°C. Since the samples were not clear a t this temperature, they \yere allowed to narm up and the refractii-e indes was then taken a t 25°C. After the binodal curves vere obtained, it v a s possible to obtain the tie lines by simply making up known mixtures in the tiyo-phase region, allowing them to come to equilibrium a t 20"C., and then measuring the refractive indes of the top layer. This gave the composition of one layer which, coupled with the overall composition of the mixturc, fixed a tie line. From the several tie line. deterniined experimentally for the systems (table 4), Bachnian charts (figiwe 4) Tverg constructed and more lines Tyere added by interpolation. For the binary system, appropriate portion.: of the components were lveighed
1.48OC
1.47OC
I .4 606
I .4
sa
I ,440C
1.430C
e' N
5 1.420C
2
sk
z2
1.4100
1.40x
1.3300
1.3800
I . 370G
/
*
\
I
I
I
~
1.3600
T E R N A R Y SYSTEMS
-
CO,, n - c j H g , HzO
I
1.3500
I BINARY S Y S T E M
I
I
1
CURVE-I ,SCALE-A
- CURVE-2 ,SCALE+
40
C&,n-t,H,O,
-
CCI,, n-cjHaO CURVE-3, SCALE-B
~
10
20
I 30
90
80
70
40 60
50 50 WEIGHT
80
60 40
30 70
x - 20%. (TERNARY
20
90 A 10 B
SYSTEMS)
FIG.3 . Graphical representation of refractive-index data. The composition of one of the components of each system is plotted against refractive index. Carbon tetrachloride and benzene are the components for the ternary systems. 361
362
- 70 CARBON TE T RACH L 0RID E SYSTEM LOWER SCALE
- 60
-
a
u b
-60
BENZENE SYSTEM U P P E R SCALE
9
- 2+
I
-40
u
N - w z m
-
-30 2 W 2 W
-
h(
-20
m
N
;;
Pt?= P L A I T P O I N T
- 10
Y = % WATER IN WATER-RICH LAYER
.I
I
.2
I
.3
I
P
I
!
.ti
.6
I
I
.7
.8
X -
I
.9
.
,
,
lo
,
1.0
Y
FIG.4. Bachman diagram for interpolation of tie lines TABLE 3 B i n a r y system carbon tetrachloride-1 -propanol REPBACTIYE INDEX
CARBON TETBACHLOBIDE
(25'c.)
1
weight p e r cent
weight per cent
0.0 6.0
10.1 16.3 20.9 26.0 32.6 34.8 40.8 47'9 51.8
REFRACTIVE I N D E X
CARBON TETRACHLORIDE
1
1.3839 1.3859 1.3879 1.3906 1.3926 1.3953 1.3988 1.4004 1.4033 1.4076 1.4101
55.8 60.2
1.4126 1.4160 1.4199 1.4237 1.4215 1.4325 1.4375 1.4433 1.4490 1.4574
65.6
I
1 I1
70.4 75.1 80.0 84.9 89.1 94.6 100.0 I I
(Z5"c.)
LIQUID-LIQUID
E Q U I L I B R I U M D.1T.k
363
and mixed and the refractive index measured a t 25°C. The total weight of a sample n-as about 10 g. Table 3 gives the data for this system. E K D - P O I S T CH.\R.ICTERISTICS
Since the “cloud point” method n-as used in the determination of the liquidliquid equilibrium data, accurate attainment of this end point became of primary importance. There is little material in the literature on the appearance of this point. Bonner (2), Cline and Dunn (3), and Curtis and Titus (4) describe it as the appearance of a haze which becomes opaque on further titration and then separates into tu-o layers. For the tn-o systems investigated in this case, the end point was not found to be such. The appearance of the end point varied 11-ith concentration. For small concentrations of one of the non-con3olutes (concentration here referring to the final value) up to approximately 1 per cent, the end point was a blue haze which appeared slowly. I n spite of the gradual appearance, the end point could still be obtained accurately since, as the end point n-as approached, a drop of titrant became cloudy immediately upon striking the solution. Therefore it v a s possible to tit,-ate rapidly until the titrant began to cloud upon entering the solution. It follom that each additional drop cleared more slowly, and when the complete dispersion of a drop became very slon-, the end point n-as near and the blue haze n-as watched for closely. -4s the concentration of one of the non-consolutes increased over the range 1-10 per cent, or it might be said as the concentrations of the non-consolutes approached each other, the appearance cf the endpoint gradually changed to that of a grey mist. The mist appeared much more sharply than did the haze and little indication n a s given of its approach. For this type of end point, titration could be made rapidly only after familiarity n-ith the end point had been attained. This point, however, was more easily identified than the first. Aboye the 10 per cent concentration of one of the non-consolutes, neither the blue haze nor the grey mist appeared. The end point was indicated by a suspension of fine globules of a second layer in the solution. The point n-a< taken at the first permanent, but not dense, suspension. This end point had to be identified with care since, as it was approached, the suspension of globules formed by each additional drop disappeared more slam-ly and sometimes a suspension which seemed to be permanent actually disappeared after a while. Here again, familiarity with the end point is required to make rapid titrations. All three kinds of end point actually consisted of a suspension of a second layer, the particles of each type of suspension differing in size. The blue haze was a suspension of extremely fine particles, undetectable with the eye. The grey mist was also a fine suspension but detectable 1vith the eye if observed closely enough. The particles of the third type of suspension Tvere of such a size that reflected light made them plainly visible to the eye. Further titration past the end point rendered the first and second type- opaque. The second formed t T T - 0 layer5 and eventually cleared, while the first merely remained opaque. The third type formed two layers immediately upon further titration and could be rendered opaque only by agitation.
364
C. G . DESZLER PL.1IT POISTS
The plait points or critical points of the tn-o ternary systems v,-ere determined by extrapolation of the lines on the Bachman charts t o intersect with the equilibriuni curve. The actiial procedure is one of trial and error. Its application depends upon the accuracy of the data and lion- closely the data run to the TABLE 4 Tie-line data f o r the system carbon tetrachloride-1-propanol-water at 20°C. LOWER LAYER
UPPER LAYER
CzHiOH
CCl4
CzHiOH
w i g h t per cent
weight per cent
weight per cent
='eight per cent
12.7 19.2" 1.7 0.72" 0.43* 0.38" 0.30* 0.28* 0.26* 0.2 0.2
49.4 53.7 24.9 21.5 20.2 19.5 19.0 18.7 18.5 16.9 16.4
3.6 2.2 23.0 28.5 35.0 39.8 44.1 51.8 63.2 68.2 75.0
32.6 27.6 53.4 53.6 51.4 49.0 46.4 41.3 32.9 28.8 23.0
CCh
-
1
Tie-line data f o r the system benzene-1-propanol-water at 20°C.
I
UPPER LAYER
LOWER LAYER
I
CsH;OH
i
CzHiOH
CBHU
i e e i g i t p e r cent
weight per cent
weiaht per cent
weight per cent
11.0 15.6* 19.0" 21.6 25.0 27.9* 34.0
55.0 57.8 58.6 58.6 58.2 57.3 54.4 50.1 46.3 43.6 39.8
1.9 1.7
28.1 25.3 23.6 21.2 20.0 19.2 18.3 18.1 17.2 16.7 16.3
40.8*
47.2* 50.0 54.8*
* Experimentally
1.4 1.2 1.1 1.o 0.9 0.8 0.7 0.6 0.4
8
determined values.
plait point. If the data do not fit u straight line closely or are taken over a range remoyed irom the plait point, large errors n-odd probably result in the values a t the plait point. In this case, the data are satisfactory for the use of the method. The procedure is the same as that for obtaining an interpolated tie line, with the special condition in mind that the composition of the two phases must be the
365
LIQUID-LIQVID E Q C I L I B R I L X DAT.1
same. Since the approaimate location of the point is knoivn from the phaie diagram, usually not inore than three or four trials are required. The values obtained here for the ternary systemq inve>tigated are a.; tollon-:
1, . . . . . . .. ,
........ ............
percenl by weight
56.0 39.8 4.2
li
per
ieicl
by
;,eighl
11 Water. ........................ 1 1-Propanol.. . . . . . . . . . . . . . . . . ..~ 1, Carbon tetrachloride.. . . . . . . . . I ~
32.3 40.9
6.8
RESULTS
The carbon tetrachloride ternary system exhibited an interesting c!i:t:.acateristic, in that, during the determination of the tie lines, there v a s a reversal of phase relationships. Table 4 shon-s that for lon-er percentages of carbon tetrachloride, the carbon tetrachloride-rich layer is the upper layer Tdiile :it higher percentages it beconies the lon-er layer. K i t h regard t o the accuracy of the data, coiisiderjng the binary compositicn i d u e is accurate to 0.3 per cent. This figure takes into account the limiting 1,efractive index values of the system (table 3 ) , and also the fact that the Abbe refractometer is readable to k0.0002. Upon analysis of the tPrnary systems in the same m y , the accuracy of a single composition figure liecomes 0.14 per cent and 0.12 per cent as applied to the carbon tetrachloride znd the benzene, reqiectively. These latter figures are average values and include the difference in accuracy of the readings over different ranges of composition. Figure 3 bears out’ the variation of accuracy in the ternary system>. SLXAIART
The binodal curves for the tn-o ternary systems benzene-1-propanol-nater and carbon tetrachloride-1 -propanol-ivater have been determined at 20°C’. Refractive-index data for these systems and for the binary system carlmn tetrnchloride-1-propanol are presented in tabular form. Characteriqtics of end points in lLcloudpoint” titrations are described :tnd :I method for determining plait points by the use of Rachnian charts is e\;plained. REFERESCES (1) BACHMAS, I.. Ind Eng. Cheni , Anal. Ed. 12, 38 (1940). (2) BONSER.JV D . : J. P h j s . Chem. 14, 738 (1910). ( 3 ) CLISC, C., .4ND D v s s , J. IT: Thesis (p. 13), University of Cincinnati, 1933. (4) CUR TI^. H.h.,AND TITCS,E . Y.. J. Phys. Chem 19, 739 (1915). (5’1 SmTii, J C: Ind. Eng. Chem 34, 234 (1943).
