Let’s say I wanted to make the purest Vodka ever. How would I do it?
Where do chemists who need pure ethanol get their stuff? Do commercial vodkas come close?
You can fractionally distill alcohol to about 95% ethanol. With the right equipment, this is pretty easy. Getting the rest of the water requires chemical treatment. I would use dried 4Å molecular seives for a small quantity. Anhydrous sodium sulfate or magnesium sulfate would do pretty well, but I think the seives would work best.
I think you’re answering the wrong question, or at least not all of it. Vodka distillation involves (1) repeated distillation to remove as much water and as many impurities as possible; (2) discarding the beginning and ending portions of the distillate to further reduce impurities; (3) filtration through charcoal or some other chemically purifying medium; (4) redilution to 80 proof, which is the usual drinking concentration – essentially replacing the “dirty” water removed during distillation with very pure water. It might also be the case that really pure alcohol can only be distilled in glass.
This is the same process used to produce the very purest alcohol found in laboratories; any difference would be found in the feedstock; alcohol can be produced by fermentation or from petroleum, and while most alcohol used in chemical production is synthesized, I think the stuff used for finicky analysis is fermented. I think.
I knew those chemistry classes would be good for something!
As posted above, you can only distill an ethanol/water mix to about 95% alcohol. (Wikipedia says 95.6%.) For purer alcohol, you can add some benzene and distill again. (That I remembered, but not the amount.) The linked article says benzene is carcinogenic, and some stays in the resulting alcohol, so it’s not good to drink. It also mentions some other methods of purification.
I’ll stick to beer, thanks.
This anecdote really has little to do with the OP, but I’ve been aching to share it, and there never seems to be a right thread for it:
Back when I worked for a Mom ‘n’ Pop herbalist place, we made all our tinctures in house. We had a big spreadsheet with the optimal ratio of herb to liquid, and the percentage of alcohol in that liquid which best extracted each particular herb. So you’d end up with something like (and I’m making these number up, because I’m too lazy to go look it up) Lemon balm 1:4; 70%, meaning one ounce (weight) of lemon balm leaf to 4 ounces (volume) of 70% alcohol.
Of course, then you need to figure out how to make 70% alcohol, right? Either you buy exactly 140 proof liquor (which doesn’t work for all those other plants that need something other than 70% alcohol) or you dilute what’s readily available off the shelf. In our case, we used Everclear. Ghastly stuff, but cheap and strong. (We also had to go to the suburbs to buy it, because Chicago’s banned the strongest stuff, but that’s another story.) Anyhow, we then need to calculate how much water to add to the 97% alcohol Everclear to get to the 70% liquid we need for how many ounces we have of our plant.
Are you tired of this yet? I sure was. So one day, while perusing a chemical supply company’s catalog, I spotted the 20 gallon drum of 99.9% pure ethyl alcohol. Brilliant! I thought. We can make our math so much easier, and it’s no more expensive than Everclear!
We had to provide my bosses’ acupuncture license number to get it. (The chem company would only sell to “licensed” people, but they didn’t seem too picky as to what that license was actually for. FTR, there’s no reason an acupuncturist would need pure alcohol in a normal practice.) We had to pay hazardous material shipping fees, and coordinate with the delivery guy so that he wouldn’t have to leave the drum outside or anything. I signed for it when it came.
The pharmacy director and I opened it together and nearly knocked ourselves out with the fumes.
As it turned out, the damn stuff evaporated so quickly that we lost an astounding amount every time we opened the drum. It did end up being more expensive than the Everclear after all, especially once the haz mat shipping fees were added in. So we didn’t do that again. Still, there’s nothing quite like a 20 gallon drum of almost pure alcohol.
So, um, I guess the moral is: be careful what you wish for. Unless you’re doing actual labwork, there’s probably no need for alcohol that pure, and it’s not without hazards!
Is the OP’s goal to make vodka or ethanol? Those are NOT the same thing.
I checked in the 4th edition (5th is the latest) of Purification of Laboratory Chemicals by Amarego and Chai for some extra info.
“Rectified spirit”* is the lowest water content you can get from normal distillation, as mentioned above, ~95%
“Absolute ethanol” (99.5%) can be obtained by refluxing the above over fresh CaO, followed by distillation.
To get it dryer, there are several methods that I’ve never heard of anyone trying:
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Heat with Mg turnings, treated with iodine. This will form magnesium ethoxide. Add more ethanol, reflux, then distill. I’m not sure what the iodine is for.
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Some nonsense with HgCl[sub]2[/sub]. No thanks.
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It gets weirder. I’m skipping to the next section.
4Å MS, Ca metal, CaH[sub]2[/sub] will all work
When we use sieves to dry something, we usually “activate” then by heating them to 300 °C at ~10 mtorr overnight. They’re then stored under a dry argon or nitrogen atmosphere.
Note that dry ethanol is super hygroscopic, so if you leave it exposed to air it will very rapidly absorb water from the atmosphere.
*I’d never heard this term
Somewhat unrelated, I’ve always been tempted to take some deuterated ethanol, dilute it to 80% with D[sub]2[/sub]O, and try a shot to see how it tastes. I’m not sure how deuterated ethanol is synthesized, so it’s probably got some crap in there that’s bad for me. Oh well.
Pure ethanol does not equal “the purest Vodka” - not that there is such a thing. It’s something of a “does not compute” scenario. The best vodkas aren’t the best because they’re all alcohol and nothing else.
Same as with a Grignard. It’s to activate the normally passive Magnesium surface.
I’m suprised that CaO won’t get it to 100% ethanol. That is definitively one of the most useful books in any chemistry lab.
ETA: Actually I’m suprised Calcium doesn’t result in an explosion, but I’ve never worked with Calcium so I have no idea. I should have thought of Calcium Hydride, because I’ve used it for exactly that.
sorry, sorry, I wasn’t meaning to get the water out. The water can stay. But every other molecule and ion has to go.
Really? You could find Polish rectified alcohol (spirytus) at pretty much any local Polish store, and that’s 192 proof (96%). It’s even imported into Chicago by Stawski imports. Is this a relatively new law? Or does only apply to Everclear? I’m wondering what the fundamental difference is between the two.
Alex - You still haven’t answered the question. Are you trying to make ethanol or vodka?
Vodka is a lot more than ethanol. So you can’t want to remove “every other molecule and ion” if you’re trying to make vodka.
And if you’re trying to make ethanol, why did you mention vodka at all? There are a lot of ways to make pure ethanol that have nothing to do vodka. Starting with a heavily polluted ethanol mixture, which is what vodka is, then trying to remove the impurities is silly.
Think for a couple minutes before writing, then write a decent question and I’m sure we can get you a good answer.
Or is your question really: "I want to start with vodka, and end up with pure ethanol (plus a little water if necessary). How do I remove all the impurities from vodka so as to have just ethanol & H2O left over?
I can only answer what the guys at Binny’s told us: anything over…151? maybe?..can’t be sold in Chicago. Something about it being used in the production of crack cocaine.
Everclear has a lesser version that you can still find in the city limits, but the chest scorching 191-proof (which is 95%, not 97%, sorry) we had to purchase and pick up or have delivered from their Skokie store.
What must be in vodka besides ethanol? I’m under the impression that if you make the purest ethanol/water mixture, it will have the smoothest, most pleasant taste. Am I mistaken?
That’s not necessary.
Interesting. It does seem Chicago has had a ban since 1994. Looks like the Polish delis are flying under the radar, then.
I’ve not drunk pure aqueous ethanol - I’ve heard it said anecdotally that it is tasteless but I could well be wrong on that. What it does have, however, is a foul smell - the nose of such a mixture would be grim indeed.
Lay off Alex, guys; you’re all answering the wrong questions, and apparently don’t know enough to answer the right one.
Vodka produced in the US and the EU is required to be flavorless*, so yes, the goal of most producers is to produce essentially pure aqueous ethanol.
*In the US, “(1) “Vodka” is neutral spirits so distilled, or so treated after distillation with charcoal or other materials, as to be without distinctive character, aroma, taste, or color.” A similar, but less bold-faced requirement applies in EU. This is one reason why traditional vodka-producing countries are exchanging some furious rhetoric with the rest of the EU – they want to maintain the characteristic flavors of traditional vodka, as well as restrict the starting stock to grain or potatoes.
Busy Scissors, pure aqueous alcohol, if diluted to proper drinking range (40% v/v) does NOT have a “foul smell” – maybe you mean “anhydrous,” or maybe you were sniffing at a much higher concentration, or maybe you don’t drink?
I think ethanol has a pleasant, sweet aroma. Maybe that’s just because so many of the other solvents I work with smell bad. I’ve never tasted our anhydrous ethanol, since it might have nasty impurities.
As for removing everything but ethanol and water, multiple fractional distillations will get you there. I really don’t know what the major impurities in vodka are; it would be interesting to shoot some on the GC/MS and see what’s in there. Some of the impurities are going to volatile substances that come over with the distillate. Wikipedia says there’s ethyl acetate and lactate, and “fusel oils” (another new term for me), which are mostly longer-chain aliphatic alcohols.
There can also be impurities in the water that’s added to dilute the ethanol to 80%. It’s hard to get ultra-pure water, as even super-distilled/filtered/dionized (18.2 Mohm-cm) will pick up stuff from the atmosphere. How much any of this affects taste, I don’t know.
But I imagine that super-pure 80% ethanol would taste similar to one or more of the higher-end vodkas that are commercially available. Since I can’t tell plastic-jug vodka from Grey Goose (or Coke from Pepsi), I probably wouldn’t notice the difference!
Ok, now we’re getting somewhere.
So say we wanted to produce our own ultra-premium neutral spirit, the Straight Dopé ®. What could we use to get at those last impurities that neither distillation or charcoal will catch? Can we bioengineer enzymes that catch or decompose those specific buggers? Or maybe apply some ordinary chemistry? Say we can afford to spend $50 a liter making the stuff. (We’ll sell it for $400, but the distributors will want a cut too).
Well first, remember that nothing is ever “pure”*. While the word “pure” is an absolute–something is either pure or it isn’t–in reality (and how the word is used), purity is a relative thing. We have several limits to look at. Is the impurity detectable by human senses? Animal senses? Modern analytical techniques?
Fractional distillation really can do a lot to remove impurities. There isn’t too much added cost in simply using a longer column; when I do that I just have to apply more heat. Hook up our still to the waste heat generated by the SDMB hamsters, and that’s free.
I don’t think chromatographic separation techniques would be appropriate in this situation.
I don’t know of any membranes that would block out these impurities.
That leaves chemical and (as you suggested) biological degradation. I don’t know of any bugs that would live happily in a high-EtOH environment. The acetate and lactate can be hydrolyzed to ethanol and acetic or lactic acid by adding some acid or base and heating. There’s not really any good way to separate the “oils”.
I think the best bet would simply to do a more careful fractional distillation. Keep less of the distillate (discard more of the beginning and end fractions), and repeat a few times.