Re: ORGLIST: Azeotropes

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From: Jacob Zabicky (zabicky$##$bgumail.bgu.ac.il)
Date: Wed Jan 10 2001 - 03:19:33 EST


Hello Wei Xing,

Aszeotropes are mixtures of compounds that at their boiling point have the
same composition in the liquid and vapor phases. In the rathr small table
of ternary azeotropes I have the ternary mixture you mentioned does not
appear; on the other hand acetonitrile-ethanol-water is mentioned. At 1 atm
it boils at 72.9 C, with a weight composition of 44.0-55.0-1.0%,
respectively.

Some remarks about your contention:

1. Azeotropes change composition with pressure, thus, if you realy have one
at ordinary pressure you break it if you go to a vacuum-assisted
evaporation;

2. I dont believe you have a water-rich azeotrope, so the more volatile
components will evaporate until at least one of them is depleted.

3. If your "aqueous solution" is not so strongly aqueous, then you may
reach a binary azeotrope composition as follows: Acetonitrile-water, 76.5
C, 83.7-16.3%, or, if you had only very little water to start with,
acetonitrile-methanol, 63.5 C, 81.0-19.0%. No methanol-water azeotrope is
known. If you get an azeotrope, just change the pressure at which you are
doing the job.

All the best,

Jacob

At 9:43 9/1/1, Kozak, Weixing wrote:
>Does anyone know the definition of Azeotropes ?
>I am trying to remove acetonitrile and methanol from an aqueous solution
>through distillation. I can remove them completely due the formation of
>Azeotropes. Thanks for your information in advance!
>
>Wei Xing
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