Reflux Still Design
| Summary
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To increase the purity of the alcohol, and hence reduce the amount of
"off-flavours" in it, you need to use a taller column, packed with something
which has a large surface area (scrubbers are best), and have some of the vapour condensing
and being returned back down over the packing as a liquid (reflux).
For a certain height of packing (called the HETP), the purity will
improve - roughly 1x = approx 85% purity, 3x = 90%, 5x = 93%, and 7-9xfor 95%+.
Just make it as high as what you want pure. For scrubbers the HETP is about
10cm (4 inches), whereas it is 24-38 cm (10-16 inches) for raschig rings or marbles.
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See my
Detail of the Equations used
if you want to get into the detail of this.
Purity is improved during distillation by allowing the rising vapour
to mingle with some liquid at a slightly cooler temperature. In doing
so, some of the water rich vapour will condense, supplying
a bit of energy to allow some alcohol rich vapour to form from the liquid
, and join the existing vapour. Each time this "mingling" is sufficient
to reach equilibrium, the purity takes a "step" on the graph
below:
