Please do find those papers! They may be describing a radical new chemistry that I'm not familiar with.
To be clear - methanol boils at 64C and ethanol boils at 78C. Are you suggesting that in standard distillation, there is still some non-trace methanol coming over at 78C? If I personally observed that in a laboratory setting, I'd quickly assume measurement error or external contamination.
It's not clear to me that simple distillation of a methanol/ethanol mixture can produce either pure ethanol or pure methanol at any point, just as it's impossible to distill ethanol and water to pure ethanol (absolute alcohol) if the water is above a small percentage of the mixture.
There is always some amount of vapor pressure, even below the boiling point of a substance. Otherwise, neither water nor alcohol would evaporate by themselves at room temperature! The temperature we call the "boiling point" is just the temperature at which the vapor pressure equals the ambient pressure.
This also matches what happens when distilling ethanol from water. You can't distill pure ethanol, but you csn distill ethanol-free water afterwards.
That's not what studies have shown. Methanol boils off in all phases of distillation, and remains in high concentration at least halfway through.
Right, normal commercial ethanol production is 95% EtOH, 5% H2O (the constant boiling mixture/azeotrope). That's good enough for most uses but not all. The only problem the average person would ever likely encounter from the residual H2O would be in the application of alcohol-based coatings such as shellac where it can cause whitish discoloration. Painters will occasionally use 99% EtOH which is substantially more expensive (removing that residual H2O requires an altogether different proxess).
From what I remember, the highest concentration of methanol is in the tails. That should tell you everything.
*EDIT* Found the paper
https://op.europa.eu/en/publication-detail/-/publication/0b9...
You can’t distill ethanol to higher than 95% because of the 95-5 ethanol-water azeotrope that boils at 78.2C, versus ethanol alone at 78.4C.
Methanol-water and methanol-ethanol don’t form an azeotrope so if properly done you can separate methanol via distillation.
Think of it this way: ethanol boils at 78.5. Water at 100. But when I’m distilling, the first stuff out of the still is coming out at like 80/20 ethanol to water, long before I’m near 100C. The later stuff still has some ethanol in it, even as I near 100C. (You can easily measure while distilling.)
So why would it be surprising that methanol behaved that way as well?
Temperature is just an average, the individual molecules can have a higher or lower temperature and can therefore evaporate already below boiling point.
It's probably pot still vs. reflux still. Chemists use fractionating columns to get better separation. Home distillers won't necessarily do so, so official advice has to assume they will not.
If you’re trying to get drunk cheaply, and without tasting liquor, you cannot beat the product and efficiency of a column still.
But I want my whiskey or apple brandy to have the characteristics of the mash I distill it from. A column still would reduce that.
So most home distilling is a pot still for sure.
It’s been a long time, but I thought there was a whole Raoult’s Law thing, about partial pressures in the vapor coming off the solution combining in proportion to each component’s molar fraction * its equilibrium vapor pressure (at that temperature, presumably). Or something.
Point being, if you’re starting with a bunch of volatiles in solution, there’d be quite a bit of smearing between fractions boiling off at any given temperature/pressure. And you’d be very unlikely to get clean fractions from a single distillation anywhere in that couple-dozen-degree range.
Probably mangled the description, but isn’t that why people do reflux columns?
If you are making brandy from clarified wine, it probably separates better than rotten grape mash.
It is still a continuum with some methanol molecules likely remaining even in the tails.
For all intents and purposes, the distiller's rule of thumb of throwing away the angels' share is still going to work because low methanol concentrations are never an issue —for the antidote for methanol is ethanol.
methanol and ethanol do not form an azeotrope with each other, they only (both, each) bind to water. that's why separation of methanol and ethanol by holding key temperatures works at all.
furthermore, the azeotrope effect only becomes relevant at concentrations beyond 90% alcohol. so when you're producing pure methanol and ethanol, then distillation won't cut it beyond 90+% as water+(m)ethanol then *at these high concentrations* boil and evaporate together. that's the grain of truth in your statement.
last not least going blind from methanol is _very_ real.
I don't think so https://en.wikipedia.org/wiki/Azeotrope_tables
But anyway, I don't think there's hazardous levels left after normal distillation+cutting, the reason for not buying booze from some guy behind a barn usually has more to do with lead contamination risks.
