[Stoves] News: Methanol cooking fuel for india...

[Crispin Pemberton-Pigott]

Dear Andrew and Distillers

>>The % purity of ethanol has to do with the cost of purification. A standard industrial fractional distillation tower can produce 95% ethanol in one pass.

>Yes

>>That's it. Anything above that needs a second or third pass,

>>No. Cannot be done, the 95% alcohol:5% water mixture boils at a lower temperature than pure ethanol and will always remain 95%:5% at each distillation. To make anhydrous alcohol needs a separate process like passing it through oven dried cracked wheat. Search on positive azeotropic mixture

The attached paper<https://chemeng.queensu.ca/courses/CHEE332/files/distillation.pdf> explains how to use a second pass through a distillation system to greatly reduce the water content of the ethanol in spite of the fact it is bound to the water as an azeotrope. See Fig 13 for the principles and Fig 14 for the method used in Canada to create 99.5% pure ethanol with only distillation towers.

The method (patented in 1980) uses a recycled additive that that also wants to create a three-component azeotrope. This boils at a lower temperature (if you choose carefully) and leaves the ethanol free to condense in the tower without the ethanol-water azeotrope. The reasons why there is still 0.5% water is explained in detail in the paper.

Regards
Crispin
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