Composition of Vapors from Boiling
Binarv Solutions J
A CE TONITRILE- F7A TER SYSTEM' Figure 1 .
Specific Grci\it?of A q u e o u h Solutionc of icetonitrile a t 20" C .
DOSALD F. OTH3IER AND S-43IUEL JOSEFOTITZ Polytechnic Institrctr, BrookZ.yn, \ . 1
l'he tapor-liquid compositions for the binnr) ' 1 steiii acetonitrile-water n ere determined a t atmospheric prescure, a t 300 mm., and a t 150 nim. pressure. I t was found that a t all of these pressures a minimum-boiling azeotrope w a s present. Extrapolation showed t h a t at about 10 nim. pressure this azeotrope would h a t e a composition of 95 mole 7~acetonitrile boiling a t approximately -12' C. The data were correlated by the methods of Othmer and Gilmont ( 8 ) and were further checked by the method of Carl-on and Colburn ( 1 ) .
T
HE use of acet,onitrile as a solvent and as a starting point in
i 20
.
10
/
'0
10
I
40 30
20 10
20
30
40
50
Liquid Composition
60 70 80 90 Mol % Acetonitrile
I00
the production of ethglamine, intermediates, and synthetic aromatics has expanded greatly during the last, few years. Users of acetonitrile have been confronted with the problem of separating this material, which is completely miscible with water, froni its aqueous solutioiis. The data on this system are sparse indeed. E v e r t ( 2 ) reported some vapor pressures of aqueous solutions of acetonitrile a t 20", 25', 30", 36', and 40" C. In reviewing the vapor pressures of binary solutions, Landsberg ( 4 ) calculated the composition of aqueous acetonitrile solutions a t 30" C . ThcJrefore, the vapor-liquid equilibriuni of aqueous solutions of acetonitrile \vas studied, and the effect of pressure on the azeotrope formed \\-as investigated. In this investigation C.P. acetonitrile was further purified by drying ivith calcium chloride and by redistilling. The fraction tloiling bctxeen 81.5' and 81.7' C. was used for these experiments. Thc, specific gravities of aqueous solutions 01 aeetonitrilc w r c ' .studied h>- a Kestphal balance a t 20' C . , and are givcn i n Table I and Figure 1. The analysis was made by measuring thc: sp3rifir gravity of solutions and reading off the compositions dirertly fi,oni Figure 1. The method and apparatus for determining the vapor-liquitl cquilibi,ia have been described previously (3,9). The temperature was observed directly with a thermometer calibrated 1 , ~thc. Sational Bureau of Standards within 0.1" C., and the prcssurts was read and maintained constant by a mercury manometer anti nt pressure device (3). The liyuid and vapor st:ttcs i n rium were detcrniirietl by gravimetric analysi. of samples of the liquid n-ithdrawn from the still and from the distillat(.
Figure 2. l-apor-Liquid Composition Equilibrium of Acetonitrile-Water System a t 760, 300, and 150 3lm. Pressure
1
Previous articles in thie series appeared in 1928 (page 7 4 3 ) , 1943 (page
614), 1944 ( p a g e 1061), 1945 ( p a g e 2 7 9 ) . a n d 1946 (page 7 5 1 ) : also in L Y T I C A L EDITIOS, 1932 ( p a g e 2 3 2 )
1175
Ah.4-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1176
Pressure
Firtire 3.
Vol. 39, No. 9
(mm.Hg)
Composition of Acetonitrile-Water izeotrope 1's. Pressure
* 20
3o0
40
60
80
I00
Composition Mol % Acetonitrile
Figure 3. Temperature-Composition Curbes for Icetonitrile-Water at 760, 300, and 150 RIm.
X 1 ,j 79.2 78.8 77 9 7i.l ib 3 76 0 i6.3 iS.2 78.4 i9.3 8 0 . $4
85.2
!)I) , ,1 91
,
95 0 n7.8 9!1 0 In0 0
0
50
60
80 100 200 Vapor Pressure Of Water (mm.Hq)
300
6
Figure 4. Total Vapor Pressure of tqueous Solutions of icetonitrile TS. Vapor Pressure of Water at Same Temperature
100.0 97.1 90 3 33.0
0 787 0.794 0 804 11.822
73.7 50 0 26.3
0.844 I 1 899 ti 955
22.8
8.1 3.7 0.0
.WU
,>$
4
a3.2 5'' 3 i1 (i i1 1 i1. 1 .il, il.I .74, u Ii4 i i3.5 i5 8
4
0.990
36 7 :36 6 36.0 3 4 . ti 34.; 34 0 36.7 44.8
0.994 1 000
60 '2
0.965
58.7
0 787 0.78U 0.790 0 793 0.79; 0.807 1) 816 0.835 0.886 0.906 0.935 0.9ti; 0 9% 0.995 0.998 0 999 1.000 1. on0 I 000 0.i 8 7
787.5 0 788 I ) . 793 li
0.i Y ! I 0 . sici 0 849 0 896 0 . 960
0.99(1 0.998 1 OO(1
0 78i 0 788 0.790 0 . 795 0 810 0.850 0.042 0.984 0.998 1 000
1U0.0 96.0 95.0 91.4 88 0 79.5 72 6 .59 7 34.9
0.787 0 797 0 . e00
27.9 18.8 9.9 :3 9 1 ,5 06 0 2 0.0
0 810
0.802
0.807 0.814 0.816 i).820
0.827
0 .0
0.83i 0.843 0 864 0.894 0.906 0.938 0.974 0.991 1 0110
100 0 9:4. (1
0 787 i l 790
0.0
98 0 91.4
86.0 7 0 il 5" 0 31.1 11 8 3.0 0.8
0 0
IUO.O 98.0 95.5
".a I ,
.2
51.3 16.8 5.2 0.3 0.0
793 0 802 11
0.804
0.810 0.813 0.814 0.821 0 876 U.964 1.000.
0.787 0,790 0.704 0 79'j 0.802 0,806 0.814 0.851 0.979 1.000
100.0 8i.9 85.1 61.5 79 S 74.0
72.6 6!l. 3 64.5 02.7 58 2 .i5.O
44.7 32 0
27.9 18.0
7.9
2 ti 0.I1 11)O.U
9%;.:I 91.4 83.2 80.8 7; I 7 4 , ti i3 2 68.6 42.2 lo., 0.u 100.0
95.5 91.0 86.0 83.5 81.0 i3.2 j0.7 6.4
0.0
September 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 6 ( T o p ) . Partial Pressures of icetonitrile rh. \ apor Pressure of R ater at Same Temperature
40
"C.
Tempercture
70
60
80
Vaporpressure Of Water (mrn.)
out previously 18). Figure 7 sho\vs further correlations oi the activity coefficients of hot h components against liquid roiiipo~itioii a t coilstant pressure. E s c ~ ~ l l ccorrelations nt were thus obtaintd which, as pointed out by ( ' a i ~ l m iand Colburn ( I ) , may give HIIOthti~evaluation of the accuracy ot' this type of data. By plotting thtl activity coefficients a t constant c.oiii~iitrationagainst a temperature sc*:ilt* cdibrated from the vapor pressure of water (Figure s), straight linea are obtained which permit easy extrapolation arid shon- the effect 011 thcl aotivity coefficients of changes in prcwure. T h r excellent correlatiori 011 this plot and on the direct logarithiiiic plot against pressure, prcvioualy described ( 8 ) ,is probably the btxst indication of t h r reliability [ I f thl, data.
coYcLusIoss Because of the t'orniation of azcorropcs, it i, not p i c t i c a l t o separate the aqueous solution:: o i ac~btoiiiti.ile by a straight distillation process. It is, h o ~ , possible to purify this material to a dcgrw sufficient for most of its present applicatioii.~ hv using Ion. pres>ure tli.stillatioiis iii ordc~r t o incre tht, pc~rri~ntiige of this imiti~i~ial i n the. :izc~~tropc,.
1117
Temperature 50 60
40
"C.
70
80
90
E4
>o c
c
.a, 3
0 .-
c Le a,
g2 + -
2
c
2 I
30
50
70
100
Vapor Pressure Of Water
200
(mrn3
400
600
Figure 8. Activity Coenicierits of .icetonilrile 2's. \ apor Pressure of T%ater a t Same Temperature
