Graphical Method for Predicting Effect of Pressure on Azeotropic

tropes to indicate the pressure at which a system would become nonazeo tropic. .... tropic below 200 mm. of mercury and above 15,000 mm. compared to...
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Graphical Method for Predicting Effect of Pressure on Azeotropic Systems H. S. NUTTING and L. H. HORSLEY

Downloaded by UNIV OF BATH on October 30, 2014 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0116.ch004

The Dow Chemical Co., Midland, Mich.

A rapid and easily applicable method has been found for indicating the effect of pressure on the composition and boiling point of an azeo­ tropic system. The method is based on the use of the Cox vapor pressure chart (1) on which the log of vapor pressure is plotted as a function of 1/(t° 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 azeo­ tropes to indicate the pressure at which a system would become nonazeo­ tropic. However, he plotted in the conventional manner and could obtain the curves only by detailed experimental work. It has been found that the vapor pressure curves of azeotropes are straight lines when plotted on a Cox chart which permits determination of the complete vapor pressure curve from the data at 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 pres­ sure curve will always lie above or below the curves of the components. This is indicated schematically in Figure 1 where A and Β are vapor

AZEOTROPE DISAPPEARS AT Ρ AND P

1

AZEOTROPIC AT ALL PRESSURES

COX SCALE l / ( T ° C . + 230)

Figure 1.

Schematic of vapor pressure curves of binary azeotropes 626

In Azeotropic Data—III; Horsley, L.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.

627

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