Making Anhydrous Ethanol...

[kryfo]

I assume this topic goes here... if it doesn't, I apologize.

I was looking through the net trying to find ways, other than distillation, of concentrating ethanol, and specifically to concentrate it above 95.6% (highest concentration obtainable through distillation). I found the following two links that discuss that matter specifically:

http://journeytoforever.org/biofuel_library/eth_separate.html

http://journeytoforever.org/biofuel_library/ethanol_manual/manual12.html


The quicklime method from the second link, and the castor oil method from the first link seem the most promising to me, and I plan on testing them soon, but today I am leaving for a week's vacation :D (Eastern Orthodox Easter this weekend, and in my part of the world that's what is celebrated), and I won't be able to test it till I get back. Although I am not sure how I would be able to test the resulting ethanol for purity.

Anyway, I thought people would at least find the links interesting, and if anybody else tries any of those methods, a post of your results would be interesting...

[Marvin]

The whole first page on journey to forever seems flawwed, particulalay about the sulphur. It also fails to express why at the critical point, you need a differential solubility to seperate the supercritical ethanol from the liquid water. I suspect under these conditions what would be going on would be very complicated. I was also under the impression that the solubility of sulphur in ethanol was miniscule so I cant see this working usefully in the lab. Fundamentally these methods are only intended to produce burnable ethanol (possibly <15% water) directly from fermented material, not absolute or anhydrous ethanol.

Leaving the az ethanol in contact with quicklime for a day or two and then decanting or distilling should bring the water content down to below 0.5%, thats absolute ethanol, but its not anhydrous. The quicklime retains considerable ethanol and excessive atempts to remove it liberate the water as well.

Entraining is the standard industrial method for absolute ehtanol, it can be done in any good still (reflux type, not pot), you add a slight excess of the calculated amount of benzene, toluene or xylene (many others possible) as an entrainer, the trinary mixture comes off first, then the excess entrainer and ethanol as a binary mixture, then virtually anhydrous ethanol. The trinary mixture when condensed seperates into more than one layer, so the entrainer can be recycled if you know the composisiton. I dont have any of the numbers for these though, and a websearch will probably only produce the numbers for benzene.

The common lab method for anhydrous ethanol is to use magnesium ethoxide to remove water as insoluable magnesium hydroxide, and then distill from the resulting ethoxide/ethamnol solution. The ethoxide is made simply by adding magnesium turnings to a small portion of absolute ethanol with a small amount of a starter like carbon tet, or ethyl bromide and refl;uxing until the reaction starts. The success of this method usually depends on how well moisture is excluded from the aparatus, below 0.05% water should be easily possible. This method should ideally be tailered to the amount of water in the ethanol but example numbers from a lab book are,

5g magnesium,
60ml absolute ethanol, which must be absolute or better, or the reaction wont start.
a few drops a carbon tet
Reflux until reaction starts, then decant from excess magnesium and add to 900ml of absolute ethanol (below 0.5% water) then distill.

Ultimatly it depends what you want it for, how far you need to go.

[Mendeleev]

Wow, this thread has been dead a long while. There is a very easy method of making absolute alcohol, which involves bubbling equimolar amounts of ethylene through sulfuric acid. This forms an ethyl goup bonded to an oxygen of bisulfate. Adding an equimolar amount of water to this mix will yield an equimolar mix of ethanol and sulfuric acid. The products can be separated through distillation, and the sulfuric acid is not wasted at all. Basically just add water. Now that I think of it, would it be possible to just mix denatured ethanol, 95% with sufuric acid and distill it to get absolute ethanol? This would be more advantageous as I suspect ehtylene would be restricted due to its anasthetic properties, does anybody know how to get it? It work much like nitric acid distillation. The question is does it? As for the benzene synthesis a solution of about 18% ethanol, 7% water, and 75% benzene is used. Does anybody know where to get ethylene?

[Bert]

Now that I think of it, would it be possible to just mix denatured ethanol, 95% with sufuric acid and distill it to get absolute ethanol?

No, but it's a great way to make yourself some diethyl ether. First organic chem lab I remember doing in HS chemistry...

[Mumble]

With higher heating you could just get the ethylene wanted. This is the main way I know how to prepare it. It'd just go around in a circle. Breaking down ethanol to make more. Perhaps it would be one way to purify the Ethanol out of Denatured Spirits.

[tmp]

Kryfo, you're 2nd link describes the most practical method for dehydrating the
ethanol. I've used this method myself. To make sure you got all the water
out is easy. Use a hydrometer, or lacking that, put a drop of the ethanol on
your tongue and taste for salt. If you taste salt, it still has water in it.
Density of ethanol: 0.7893 @ 20 C(68 F) per CRC 52nd Edition 1971-1972.

For use as fuel supplement, mix it with gasoline before putting it in the fuel
tank. That way the water separates out as layer.

[ordenblitz]

Molecular sieves are the easiest way to make absolute ethanol.
I think 4 angstrom, potassium aluminum zeolite are the best.

[Milamber]

I think you'll find that 4A sieves will absorb ethanol just as happily as they do water... 3A are the only option for drying the lower alcohols, if memory serves

[Dr_Pind]

I stumbled over this when I was working on making bio-diesel in a school project. Rather interesting procedures:
http://journeytoforever.org/biofuel_library/eth_separate.html

[Bugger]

(cut) Entraining is the standard industrial method for absolute ehtanol, it can be done in any good still (reflux type, not pot), you add a slight excess of the calculated amount of benzene, toluene or xylene (many others possible) as an entrainer, the trinary mixture comes off first, then the excess entrainer and ethanol as a binary mixture, then virtually anhydrous ethanol. The trinary mixture when condensed seperates into more than one layer, so the entrainer can be recycled if you know the composisiton. I dont have any of the numbers for these though, and a websearch will probably only produce the numbers for benzene.(cut).
As with water, ethanol also forms a minimum-boiling-point binary azeotrope with benzene. See Perrys Chemical Engineers Handbook, part 13. It contains 44.8% ethanol and boils at 68.24ºC at 1 standard atmosphere (760 mm Hg). The ethanol-water azeotrope has 10.57% water, and boils at 78.15ºC. This data is originally from the International Critical Tables (which are hard to get hold of as they have not, AFAIK, been released in electronic form, or issued in a revised edition for many years). As for the ternary water-ethanol-benzene system, Perry has only it boils at 64.48ºC, with 22.8% ethanol, 53.9% benzene, balance water. Unfortunately, the full data on the ternary water-ethanol-benzene system, in the form of a ternary phase diagram (triangular), which would be needed to design the apparatus, seems to be only in the International Critical Tables.

Virtually anhydrous ethanol prepared this way, with recycling of the excess benzene (or toluene) used as an entrainer, is supposed to contain a trace of benzene (or toluene), which is toxic. This would rule out its being used to make alcoholic liquors for consumption, e.g. ports or sherries, or liqueurs obtained by mixing with fruit juices etc. or steeping/macerating fruit in it.

Bugger.

[FrankRizzo]

I stumbled over this when I was working on making bio-diesel in a school project. Rather interesting procedures:
http://journeytoforever.org/biofuel_library/eth_separate.html


Yeah...so I was, like, doing this school project on biodiesel, and just happened to run across this link. Seriously, WTF?!? This is the same damn link that Kyfo started this thread with.

[Marvin]

Thankyou John, those numbers differ somewhat from mine and after an hour of calculator bashing I think most of the difference is due to your numbers being in molar percent. Everything else on this forum is in mass % unless otherwise indicated maybe chemical engineers have different assumptions. Going by the CRC values,

Ethanol water is 96% Ethanol boiling at 78.17C.

Benzene ethanol is 68.3% Benzene boiling at 67.9C

The trinary azeotrope is 7.4% Water, 18.5% Ethanol and 74.1% Benzene boiling at 64.86C.

You cant drink the alcohol produced by this process but then its not normal to demand more than 96% Ethanol content for drinks or making tinctures.

We dont need anymore information to actually use this process, but aside from benzene being carcinogenic and not widely available if we cant recycle the entrainer we may as well just use a throw away dehydrating agent. The trinary azeotrope is positive 2 phase heterogenious. So when you condense the vapour it forms 2 layers. One layer is rich in water, the other is rich is benzene. If we knew the composition of these layers, we'd be able to recycle the benzene (and probably most of the wasted ethanol) for furthur dehydrations.

We can look up data for other useful azeotropes to use something safer than benzene but we'd still lack the information on the way the trinary splits. I'd have to agree with later posters that if you can get 3A molecular sieves, this has to be the easiest way to absolute ethanol. Does anyone know how well (ie % water remaining) these work?

[Bugger]

The percentages of components given in Perrys Chemical Engineers Handbook, part 13, are all in MOLE %.

Perry also has the mole % and boiling-point particulars (but not the full ternary phase diagrams) of the following further ternary azeotropes, which may constitute other dehydration methods: Water-CCl4-ethanol, Water-trichloroethylene-ethanol, water-ethylacetate-ethanol.

Bugger.

[FrankRizzo]

Here's a few links that may be of use:

Liquid-Liquid extraction process for acetic acid/benzene azeotrope. A similar process could be adapted for ethanol.
http://www.ddpsinc.com/ProcessProfiles/pp50.html

Drying Agent Selection Guide
http://www.rhodium.ws/chemistry/equipment/dryingagent.html

Drying Agent Data
http://www.rhodium.ws/chemistry/equipment/dryingagent.data.html