Vapor-Liquid Equilibrium Diagrams of Alcohol-Ketone Azeotropes as a Function of Pressure
MethanolAcetone
MethanolMethyl E t h y l Ketone
MethanolMethyl Propyl
Ketone
E. C. BRITI'ON, H. S. NUTTING, AND L. H. HORSLET The Dow Chemical Company, Midland, Mich.
P
RESSURE has a marked effect on the azeo-
tropic composition and vapor-liquid equilibrium diagrams of alcohol-ketone systems (1). This is due to the fact that the slopes of the vapor pressure curves of alcohols are appreciably greater than for ketones; it results in an unusually larger change in the relative boiling
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Vapor-Liquid Equilibrium Diagrams of Alcohol-Ketone Systems at Various Pressures Figure 1.
Weight Per Cent Alcohol
P
0 I 0
8 0
P
s 0
0
602
V O L U M E 19, NO. 8
points of the components of an alcohol-ketone system with change in pressure. As a result of the study of these systems, it has been found that the methanol-acetone azeotrope exhibits the unusual phenomenon of becoming nonazeotropic a t both low and high pressures-that is, below 200-mm. pressure the system is nonazeotropic with methanol as the more volatile product, while above 15,000 mm. the system is nonazrotropic with acetone the more volatile component. Some of the equilibrium data for this system and two other alc~ohol-k?tonrazeotropps ar? shown in Figures l and 2.
The similarity of the diagrams for the different systems at suitable pressures is of interest. For example, the diagram for methanol-acetone a t 10,000 mm. corresponds approximately to the diagram for methanol-methyl ethyl ketone a t 1000 mm. and for methanol-methyl propyl ketone a t 100 mm. LITERATURE CITED
(1) Britton, E. C., Nutting, H. S., and Horsley, L. H. (to Dow Chemical Co.), U. S.Patent 2,324,256 (July 13, 1943).
Graphical Method for Predicting Effect of Pressure on Azeotropic Systems H. S . NUTTING AND L. H. HORSLEY, The Dow Chemical Company, Midland, Mich.
4
manner and could obtain the curves only by detailed experimental work. I t has becn found that the vapor pressure curves of azeotropes are straight lines when plotted on a Cos chart which permits determination of the complete vapor pressure curve from data a t two pressures. Since an azeotrope by definition has either a higher or a lower vapor pressure than that of any of the components, the azeotropic vapor pressure curve will always lie above or below the
RAPID and easily applicable method has been found for
indicating the effect of pressure on the composition and Imiling point of an azeotropic system. The method is based on the w e of the Cox vapor pressure chart ( 1 ) on tvhich the log of vapor pressure is plotted as a function of l / ( t o C. 230) to give a straight line over a wide range of pressures. Lecat ( 2 ) has considered the use of the vapor pressure curves of azeotropes to indicate the pressure a t which a system would become nonazeotropic. However, he plotted in the conventional .i
+
10000
10000
e
e
6
6
4
4
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2
2
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LOO0 B 6 4 W
3
w 4
s
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2
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100 -20
-id
0
2
100 IO
20
30 4 0
60
80
DO
EO
160
200
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240
1
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o
IO
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30
40
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IX)
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-10
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20
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00
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1.000 8
a w
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a
4
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Hs
IO0
e 8 4
z 0
le0
I
[COX SCALE
TEMPERATURE
l/(T+230)]
C.
Figure 1. lzeotropic Vapor Pressure Curves of Methanol-Methyl Ethyl Ketone, Methanol-Acetone, Water-n-Propanol, and Water-Ethanol
