On 02-Oct-17 4:47 PM, Martin Brown wrote:
On 02/10/2017 12:54, NY wrote:
"Ade" wrote in message news
Ethanol bp is 78c which is why it isĀ* so easy to seperate from
Methanol at 64c when brewing.
And the boiling point of ethanol/water mixture at its 95/5% mixture is
fractionally *lower* than for pure ethanol (78.2 for the mixture, 78.4
for pure ethanol) so you can never get pure ethanol by simple
distillation. Apparently the way round this is add an "entrainer" such
as benzene or cyclohexane which preferentially binds with the water.
This triple mixture boils at 62 degrees and the water/benzene boils
off, leaving (in theory) pure ethanol as a residue.
Snag is you really don't want any benzene in drinking quality ethanol.
But don't you want 99%+ ethanol for drinking. The only reason to want
99.9% pure is for further chemical process or fuel.
Even the "rocket fuel" grades for consumption don't exceed 80% by
volume. Normal spirits on the shelf are around 40%-50% by volume.
Alternatively you add calcium oxide which binds chemically with the
water and the resulting calcium hydroxide can be filtered off,
allowing the filtrate to be re-distilled to extract pure ethanol.
Not sure they bother drying it aggressively for fuel grade ethanol since
it will quickly absorb water from the atmosphere again.
I'm not sure whether ethanol/water forms a similar azeotrope for
freezing, and whether you can separate them by freezing, since ethanol
and water (separately) freeze at different temperatures. I remember an
ice-cream van owner where we bought an ice cream telling my dad about
separating alcohol from water by freezing in a deep-freeze, and dad
strung him along by pretending to work for Customs and Excise :-)
It does in the sense that all the organics stay in the liquor and a
nearly pure water ice slush forms as it freezes. The bad news is that
the methanol and all the other bad organic impurities stay in the
alcohol phase so it is evil gut rot. It lacks the finesse of distilling.