Originally By Tony Ackland
Using Salt in DistillationMaurice advises ..
The "Household Cyclopedia" recommends ...
David cautions though ..
Bokakob advises ..
Ken recommends using Sodium Carbonate to reduce the amount of fusel oils present ..
Rob details the bicarb advantage too:
1. A well run column distillation will separate a mixture into fractions based on the boiling points of the components.
2. There will be some overlap in most real-life stills.
3. ethyl acetate can be smelled at very low concentrations
4. acetic acid cannot (it has a higher flavour threshold)
5. under neutral or acidic conditions acetic acid will esterify to some extent in the presence of ethanol.
6. sodium acetate is not volatile
7. sodium bicarbonate will neutralise acetic acid.
8. sodium bicarbonate may hydrolyse ethyl acetate to a greater or lesser extent.
9. Adding sodium bicarbonate at some point between a stripping run and final distillation has the effect of decreasing the volume of fractions collected which smell of ethyl acetate.
10. Adding sodium bicarbonate at some point between a stripping run and final distillation has the effect of making the main fraction "cleaner smelling"
11. without bicarb the main fraction _can_ smell of ethyl acetate (ymmv)
12. Sodium acetate is not esterified by ethanol.
1. Why is there ethyl acetate in the fractions after the heads? (no NaHCO3)
2. What does NaHCO3 addition do?
3. How do we best (read easiest) use it?
Rob's Answers/Opinions (currently!):
1. During distillation (after column stabilization) ethyl acetate is being formed in the boiler/column. This is why it continues to be present even after heads removal. (see assumptions 1, 5, 11)
2. Bicarb addition neuralises acetic acid, preventing ethyl acetate formation, distillation of acetic acid, and hence future esterification. (see assumptions 6, 7, 9, 10, 12)
3. Bicarb addition can hydrolyse ethyl acetate, thus decreasing it's quantity (see assumptions 8, 9)
4. There is actually a tiny amount of ethyl acetate about, but it is highly noticable (assumption 3). Using bicarb (as opposed to hydroxides) actually has a rather small effect on the amount of esters in the mix. What it does (primarily) is to prevent further formation, and hence allowing the still to do its job without the moving target of continually increasing ester concentrations in the boiler.
5. Based on this lot, adding bicarb at the start of the final distillation is sufficient, as neutralisation of acetic acid is instantaneous.
Why? Yeast and yeast nutrient both contain lots of ammonium salts (like DAP), which are very stable under acidic conditions, but which release lots of ammonia as the approach neutral conditions. Actually, you will start getting ammonia at about pH 5! Ammonia gas is very corrosive to copper, and you will find your condenser coil packed up with blue crystals after such a run (and blue alcohol too !)
Schweitzer's reagent is cuprammonium hydroxide, and is formed when copper hydroxide dissolves in a dilute ammonia solution). It is a deep blue colour, and is particularly known for its ability to dissolve cotton. The chemist who first discovered this property was Eduard Mathias Schweizer (1818 -1860), so it seems that it should really be called Schweizer's reagent.
It forms in stills when ammonia released from alkaline washes (nitrogen source may be plant material or yeasts) reacts with copper hydroxide formed by the action of steam on copper oxides coating the inside of copper columns or components. It may be avoided by ensuring that the liquid in the boiler is slightly acid (pH less than 7).