Making some ethanol... [only for when you are reaaaaally bored !]

[John Cuthber]

5 minutes ago, dimreepr said:

What you can't do is ban it...

 

They did.

[dimreepr]

3 minutes ago, John Cuthber said:

They did.

They tried...

[John Cuthber]

The distillation ban is on the statute book.

[sethoflagos]

On 10/28/2022 at 3:45 AM, Sensei said:

When you distill something, you must slightly exceed the boiling point of the substance. Check the ethanol chart, and you will have the answer to your question..

I don't think it works quite like that.

Firstly for an ideal liquid mixture (methanol-ethanol mix is close to ideal) the partial pressures of each at any given temperature follow the simplest form of Raoult's Law (at pressures below 10 x atmospheric at least)

partial pressure of i (Pi) = partial pressure of pure i (P_i^*) x mole fraction of i (x_i)

So if x_i is small, the partial pressure is small even at the boiling point of the pure substance (in the case of the most volatile component). 

If you boil a methanol-ethanol mix, yes, there will be a significantly higher mole fraction of methanol in the vapour phase and x_i will fall a bit but for a single stage operation, the idea that what's left behind has a safe methanol level has made many, many people "mad, blind and dead - or was it blind, mad and dead" as my school chemistry teacher put it.

When you add water to the mix, things get a little more complicated. For both the methanol-water and ethanol-water systems, the alcohols are more attracted to themselves than to the water molecules. So these are non-ideal mixes and follow a modified version of Raoult's law that includes an activity coefficient a_i. 

                                          Pi = x_i a_i P_i^*

For these 'positive deviation' mixtures the activity coefficient >1.0 and offsets the effects of low mole fraction by increasing the alcohol's volatility.

a_i for methanol in its aqueous mix is typically around 2 but rises steeply in low concentrations to about 3.5. So a 50-50 methanol-water mix (x_i = 0.5) will actually boil close to the boiling point of pure methanol. 

a_i for ethanol in its aqueous mix is actually a bit higher, ~4 in low concentrations, which pushes its volatility even closer to that of methanol, making the separation even more challenging.

Now obviously I have no practical experience of distilling strong spirits for personal consumption and strongly advise against anyone even considering such a reckless practice. But if say I was in urgent need of quality surgical spirit for medical purposes, I think I'd consider starting off the separation with a very slow simmer, well below boiling point and let the vapour rich air currents rise by thermal convection into my condenser. 

Edited January 2, 2023 by sethoflagos
small clarification

[sethoflagos]

Having rekindled my interest in the topic I dug out Clausius-Clapeyron for P^* estimates (https://en.wikipedia.org/wiki/Clausius–Clapeyron_relation) and plugged it into Excel:

A bit rough and ready (I've used fixed latent heats) but it ties in with my gut feel. 

[mistermack]

I think the site I've linked below is really good and clear on the subject of methanol/ethanol separation, and also many of the other things that people have posted on this thread. There are some surprises too, espcially when you look at the allowed limits of methanol content in various products. 

I would have liked more detail on some things, like how exactly the ethanol that comes off first, with a high proportion of methanol, can be reclaimed, as they say it is.

https://www.barisonindustry.com/en/news/methanol-what-it-is-and-how-it-is-handled-in-distillation-processes

It does confirm what I posted earlier, that certain yeasts lead to higher concentrations of methanol in the mash. I don't get why there is such a disparity in the allowed proportions of methanol in the various drinks though. You would think that from a health point of view, the same levels would apply to any drinks. I must be missing something. 

[sethoflagos]

3 hours ago, mistermack said:

I don't get why there is such a disparity in the allowed proportions of methanol in the various drinks though. You would think that from a health point of view, the same levels would apply to any drinks. I must be missing something. 

To get methanol levels down to those of London Gin, you must use multiple stages of fractionation such as the Coffey Still (modern separation technology could effectively eliminate methanol from the product quite simply).

To enforce those levels across the drinks industry would effectively ban the use of pot stills. A lot of people would get upset about that. 

[mistermack]

Looking at the overall picture, I don't think there would be much danger involved in distilling spirits, so long as you took the obvious precautions. Like not using lead for soldering, not using old car radiators for a cooling tower, choosing the right yeast, and discarding a calculated portion of what comes off first. 

On that subject, I don't get why people would pour the first portion away. Methanol surely can be put to use in some way? Like as a fuel for the stove or added to petrol for the car or generator. Pouring it away seems a waste, and would probably leave a tell-tale smell. 

[John Cuthber]

10 hours ago, mistermack said:

It does confirm what I posted earlier, that certain yeasts lead to higher concentrations of methanol in the mash. I don't get why there is such a disparity in the allowed proportions of methanol in the various drinks though. You would think that from a health point of view, the same levels would apply to any drinks. I must be missing something. 

You are missing the fact that the levels are not set on grounds of health.

The methanol content is an indicator of what "good practice" achieves.

Because there's a lot more pectin in some of the substrates than in others, the methanol levels will be higher.

 

4 minutes ago, mistermack said:

On that subject, I don't get why people would pour the first portion away. Methanol surely can be put to use in some way? Like as a fuel for the stove or added to petrol for the car or generator. Pouring it away seems a waste, and would probably leave a tell-tale smell. 

The light fraction is full of acetaldehyde which makes engines knock like hell.
Also, there are miscibility issues with methanol and saturated hydrocarbons.

 

[mistermack]

39 minutes ago, John Cuthber said:

You are missing the fact that the levels are not set on grounds of health.

The methanol content is an indicator of what "good practice" achieves.

I'm not sure I see the logic of that. Good practice is surely enforced on health grounds? Why else? I'm not sure if those limits are legal limits, the website calls them 'maximum limits', which isn't 100 percent clear. I can't see why the legal limit for gin would be set at half that of vodka, or forty times less than brandy, just to encourage good practice. Gin is pretty much vodka with aromatics added anyway, so why have a different methanol limit?

The good practice explantion might be right, but it's not immediately obvious at first sight.

Edit : Wikipedia seems to clear that one up. The critical wording is "London" Gin. To be classed as London gin it must have no more than 5g methanol and be produced by re-distilling using the flavouring ingredients. So it's a catagory limit, as opposed to a health limit. 

Edited January 3, 2023 by mistermack

[John Cuthber]

What do you think a reasonable "health based" limit would be?

[mistermack]

I don't know, but I suspect in reality it's fairly hard to hit that limit with sensible precautions making moonshine. There are deaths around the world, but the suspicion has to be that most of them occur due to adding the methanol, rather than directly from brewing. 

I read that permanent visual damage may occur with minimum ingestion of 30 mL of methanol. But if it's taken with ethanol, the figure's likely to be higher because ethanol works against the methanol toxicity.

Then it depends on your body weight etc. If you take the highest number on the chart, 1500 g per hectolitre, you would have to drink about 80 litres of spirit to damage your eyesight. You'd be dead long before your eyes started to suffer. 

Edited January 3, 2023 by mistermack

[John Cuthber]

1 hour ago, mistermack said:

Then it depends on your body weight etc. If you take the highest number on the chart, 1500 g per hectolitre, you would have to drink about 80 litres of spirit to damage your eyesight. You'd be dead long before your eyes started to suffer. 

OK.
So, without the protective effects of ethanol 30 g of methanol will cause harm.
But a litre of ethanol would probably kill you.
So, as long as the methanol content is less than about 30 grams per litre or 3% the ethanol will kill you before the methanol does any harm.
30 grams per litre 
3000 grams per hectolitre or roughly 2 times higher than the highest figure in the table will be "safe" because of the antidote also being present.

OK, so the table can not be anything to do with health- let's face it, the healthy option doesn't include drinking much hooch.
The reason is that they don't want people adding industrial meths to the authentic product.

You could, realistically get away with adding a bit of meths to something like fruit brandy and blame the methanol of pectin.
You can't do that with gin.
So it's a practical measure of how much methanol indicates that the product has been adulterated.
A quality control issue, rather than a health issue.

 

Edited January 3, 2023 by John Cuthber

[CharonY]

16 minutes ago, John Cuthber said:

So it's a practical measure of how much methanol indicates that the product has been adulterated.
A quality control issue, rather than a health issue.

I found it interesting that in Europe there are varying limits (as indicated above), quite likely due to the range of methanol generated in the various traditional production processes. Spirits from a selected list of fruit species have an allowable methanol content that is higher than the general limit for fruit spirits, for example (see European Parliament and of the Council (EU). 2019/787 Definition, description, presentation and labelling of spirit drinks, the use of the names of spirit drinks in the presentation and labelling of other foodstuff. Off. J. Eur. Union 2019, L 130, 1–54)

Conversely, other countries, such as US and Australia have a flat limit for all spirits, which is higher than the EU limit for wine spirit and brandy, but lower than the EU limit for fruit spirits. So in these countries it appears to be more a simple balance of safety vs process probably with less consideration for adulteration.

[mistermack]

I just noticed that I got hectolitres wrong. I had to look it up, and did clock it as 100 litres, but when I worked out my dose estimate, I somehow remembered it as 1,000 litres. So I guess my estimated figure should have been 8 x 1 litre bottles, not 80.  ( bottles of 50% abv ) 

8 would kill you just as dead as 80 though. 

The reason I'm interested is that I've drunk Irish Poteen on many occasions, only sipping it, and it ranged from absolutely foul to really nice. I don't think I'd drink it now though, unless I made it myself.

My brother keeps threatening to start distilling. I told him he would need a licence and he absolutely won't have it. He seem to think that if it's legal for the shops to sell you the distilling equipment, it's legal to use it, and he won't have it any other way. He does brew a lot of beer and wine.