Sciencemadness Discussion Board

making colorless ethanol

Jor - 1-4-2009 at 13:59

At supermarkets we can buy 85% ethanol (+3% methanol) for very low prices.

I am planning to use this a lot for cleaning, as it is much cheaper than acetone, wich I use at the moment. It is also less toxic to the environment.

But it has a strong blue color, and it stinks.
What is the easiest way to remove these? I know of the activated charcoal method, but that most of the time will make a very fine suspension of the carbon in the liquid. This is bothersome to filter, and besides, because I do not have vaccuum, filtering takes a long time for me.

Is there another way to remove the color and stench? I heard about adding a little acid. Maybe some hydrochloric acid? Or will there be nonvolatile residues left, wich don't evaporate, when you dry the glassware?

Ofcourse I can buy 5 liters of colorless, methylated spirit or 5 liters of technical acetone (technical grade, leaving almost no residue), form my supplier for very cheap, but I find that an unnecessary storage hazard. So I'd rather avoid it.

DJF90 - 1-4-2009 at 14:03

The smell is likely pyridine or another bittering agent. The colour is a dye. There are other threads that have discussed distillation of ethanol from methylated spirits. Go read them. Perhaps just a careful distillation at about 80C should leave you with colourless methylated spirits leaving the suspected pyridine and dye behind. But I'm just speculating.

Sedit - 1-4-2009 at 14:04

Why don't you think that simple distillation wont remove the color from the EtOH?

If simple distillation does not take care of it possibly try distilling over activated charcoal.

panziandi - 1-4-2009 at 14:09

You can use charcoal that has been previously washed with water to remove fine debris. This will remove the dye. Add a little acid to the Methylated this will neutralise the pyridine to a non-volatile salt, then fractionally distil the ethanol. Then you can redistil the ethanol more carefully and it should be high purity (low methanol). If desired it can be further dried with Mg turnings.

Jor - 1-4-2009 at 14:18

Yes, I have thought of all these methods already.

But it requires a lot of energy and time, for preparing WASH ethanol.

The problem is that I don't want to use the blue ethanol to wash with, as it will leave blue stains in beakers after EtOH evaporated.

Also, my largest flasks are 250mL, so I can only distill about 150mL a time, wich is simply not worth the effort for a cleaning agent.

I just read somewhere about adding some NaOH (a few prills to 1L) will remove the color. I will try that tomorrow. Problem is that I will have to neutralise it again with HCl, as a little bit of NaOH will prevent the remains of water from evaporating (NaOH is very hygroscopic), but when I add HCl, the pyridine-like compound (is it really pyridine, it smells very different?) will be formed as a non-volatile HCl salt.

DJF90 - 1-4-2009 at 15:18

The denaturants vary from country to country. You should be able to find an MSDS or formulation for this ethanol product. Here in the UK it is generally methanol, pyridine and methylene violet added to ethanol that makes our methylated spirits.

watson.fawkes - 1-4-2009 at 15:24

Quote: Originally posted by Jor  
Also, my largest flasks are 250mL, so I can only distill about 150mL a time, wich is simply not worth the effort for a cleaning agent.
You don't have to boil from a flask. A metal can (as is used to sell solvents in the US) works; what you would need is a way of introducing vapor from the can to your distillation head.

Sedit - 1-4-2009 at 18:15

I made something similar from a paint can and a piece of copper tubing soldered thru the top and bent at 90deg. Seal the edges with a thin piece of plastic and it works good for larger distilling jobs such as this. The condenser is nothing more then a long piece of plastic tubing (like 8 feet) from home depot that fit snugly with the copper tubing.

I understand what you mean though by not wanting to go thru all that hassle to purify what will become waste in the first place so I think your best bet would be to identify the dye that they used and then go from there on how to get rid of it.

Panache - 2-4-2009 at 01:26

Thinking laterally, how about getting some safety glasses that filter out the blue colour, that way it will appear colourless.

woelen - 2-4-2009 at 04:23

I do not believe that there is any other acceptable option besides distilling. Whatever method you use for removing the dye, you'll always be left with dissolved solid material, which will leave a residue after cleaning and evaporation of ethanol. Even if NaOH or HCl destroys the dye, a large-molecule compound remains in solution. Besides that, NaOH also dissolves somewhat in ethanol and this will lead to residues as well. HCl most likely forms a salt with the smelly compound (which probably has an N-atom with free electron pair and which can form RNH(+) ions) which certainly will remain in solution, at least to some extent. So, I would say, distill the material and do not go above 85 C and stop distilling when 90% or so has been collected in the receiver flask. This will give you a product, which is free from any non-volatile material and dyes, but you still will have some of the smell. This smell, however, is not a problem for cleaning. You'll have an alcohol, which leaves absolutely no residue on evaporation.

If the smell really disturbs you, then you could add a ml or so of 50% H2SO4 to 1 liter of alcohol (not HCl, as this could cause vapor of HCl going into your cleaning alcohol, which makes it corrosive).

smuv - 2-4-2009 at 15:59

Acetone really isn't very bad for the environment relative to ethanol; if clean acetone is easier to obtain use that, it is a better solvent for cleaning glassware anyways.

Acetone is a natural product, and is a naturally in many animals' (including humans) urine.

unionised - 10-4-2009 at 12:35

You can strip the purple colour out of the meths in the UK using a cation exchange resin. However I think a still is more practical.

JohnWW - 12-4-2009 at 00:44

I understand that, besides pyridine, sucrose acetate (which is non-volatile) has been used as a bittering agent in denatured ethanol, also called "methylated spirits", to render it unpalatable. Removal of the methanol (especially) and any pyridine would be much more difficult than removing the other likely adulterants in it, because of the similarity of the boiling-points, ethanol 78.4ºC, methanol 64.7ºC, pyridine 115ºC, which would call for a fairly long distillation column. However, any pyridine can be made much less volatile and possibly crystallized out, by formation of the hydrochloride by adding HCl, but one would have to be careful not to add an excess of HCl. And then there is the matter of the constant-boiling azeotrope that ethanol (but not methanol) forms with water.

DJF90 - 27-3-2010 at 15:07

Putting methylated spirits through a column of activated carbon removes the purple dye, leaving it colourless like IMS, although I suspect it contains a little more methanol. The process is pretty slow; an evening yeilded only 100mls, so it would be much faster to distil it (to be attempted at a later date...) and distillation would also yeild pure ethanol with a decent column. I'll try and attach a before and after photo.


[Edited on 27-3-2010 by DJF90]

Skyjumper - 28-3-2010 at 13:54

It would still of course contain the methanol. Get one of those Britta water filter things, they can do about a liter at a time. Whats wrong with storing 5l of etOH? Its one large container. I keep a few 4l containers of anhydrous etOH under the hood, in my flammables cabinet, and in my organics locker. *shrugs*

DJF90 - 28-3-2010 at 17:25

I never said I had a problem with storing 5L EtOH, its just a matter of cleaning it up first. Brita filters also would not remove the methanol; I tried the experiment as a means to see if simple filtration through activated carbon would be enough to remove the dye and provide a product that more closely resembles IMS. My findings are thus: Use a coarse activated carbon, preferably granules. The stuff I used was far too fine, and ended up working its way through the sintered glass frit (through a 5mm layer of alumina first!) and into the decolourised spirits. Distillation was then the only reasonable way to clean it up, and doing so was quite challenging. The methylated spirits I had claimed to contain methanol, but upon distillation no fraction was collected around 65C - the temperature shot up from room temp. straight to 74-76C where it remained for a significant period of time. The temperature then shifted to 77-78C, at which point the recieving flask was changed. 400mls of "Ethanol" were subsequently collected.

The first fraction was poured away. The collected fraction still seemed to have that "pyridiny" odour that UK methylated spirits have. Distillation was undertaken slowly, a total 5 and a half hours to collect 400ml, through a 40cm long vigreux colum. The column was not lagged (there was no need to) and strangely, no reflux was seen from the points in the column. The heating mantle was set at the lowest setting that would allow distillate to pass over.

I have since learned that the first fraction, boiling between 74 and 76C, could be an azeotrope with methyl ethyl ketone (60% ethanol, bp 74.8C). MEK wasn't listed on the contents of the bottle but it is known that it is used in some formulations as a denaturant. This was the rationale for storing the "ethanol" over sodium hydroxide prills.

From here, what I plan to do is to decant the ethanol from any undissolved sodium hydroxide, acidifying to convert any pyridine possibly present to the less volatile hydrochloride salt, and distill the ethanol once again, perhaps this time through a better (Dufton) column. I was not very impressed by the vigreux. I'm open to any suggestions as to how you guys would proceed in the purification.


[Edited on 29-3-2010 by DJF90]

panziandi - 28-3-2010 at 18:07

Grossly distorting the images is a gross understatement there! LOL they are truly deformed :P

Anyway...

You can add what I call filter carbon, basically activated charcoal chips for aquarium filters etc, to the bottle of meths and leave to stand with some stirring from time to time.

MEK is not commonly found in the uk formulations but standing over NaOH should remove it.

If using mineralised methylated spirit, I would suggest acidifying with lets say 20% H2SO4 maybe, and then allowing to stand for a while (if indeed it does contain MEK) this will likely undergo a condensation, more importantly the pyridine will form a non-volatile salt, then distill out the ethanol, dry and redistil.

DJF90 - 28-3-2010 at 18:12

The pictures were taken with a 5MP camera... who could have known! Filter carbon is what I had in mind for the task, and its what I would have used but the finer stuff was at hand. As you say, MEK is not common in UK formulations (typically ethanol, wood naptha or substitute, pyridine, and crystal/methylene violet) but it's presence is possible I guess. Acidifying with H2SO4 is definately a good idea (as woelen mentions up-thread HCl is not suitable) although I would use 50% myself.

JohnWW - 28-3-2010 at 19:20

That is a good try, DJF90 - but is the stuff now safe for drinking, at least in liqueurs or cocktails? Have you analyzed it for the CH3OH content?

chemrox - 28-3-2010 at 19:30

How cheap are you trying to be? If acetone is too expensive for cleanup buy bulk MeOH. I bought a 10 gallon can for $38 US from a fuel depot. I prefer tech MeOH for drying glassware and washing up counters anyway. If ventilation is an issue maybe you should re-consider doing whatever it is you're up to.

DJF90 - 29-3-2010 at 06:19

JohnWW; I wouldnt drink it even if I were desperate. The residual pyridine smell is far too off-putting. Hopefully once I've continued purification it will approach LRG, but I can only be hopeful. Any idea how to test for methanol qualitatively or quantitatively?

JohnWW - 29-3-2010 at 07:14

Quote: Originally posted by DJF90  
JohnWW; I wouldnt drink it even if I were desperate. The residual pyridine smell is far too off-putting. Hopefully once I've continued purification it will approach LRG, but I can only be hopeful. Any idea how to test for methanol qualitatively or quantitatively?

To test for CH3OH in the presence of CH3CH2OH and H2O could be done by gas-liquid chromatography, although to do it quantitatively a calibration plot for the relative elution peak sizes would have to be constructed using a series of standards of known composition.

Also, an IR spectrometric analysis could be attempted, using the fact that CH3CH2OH has a C-C bond that CH3OH and H2O does not have. To use the intensity of the C-C stretching absorption frequency to measure the content of ethanol, a calibration plot made using a series of standards of known composition would be needed. However, this would not accurately give the CH3OH content by simple subtraction, due to the presence of H2O.

Skyjumper - 29-3-2010 at 15:48

Why not just Isopropyl alcohol? I have seen IPA used as a denaturant for etOH before without problems? Stuffs cheap and can be bought in a store. or hell if you really wanted you could distill cheap vodka to get a pure etOH

DJF90 - 29-3-2010 at 23:49

Why not just Isopropyl alcohol? Because its not Ethanol. I know the OP's intention was to use the alcohol for washing, but my motivation is purification for use as a reagent. Cheap vodka is still significantly more expensive than Methylated spirits, which I can get for just over £5/2L, and contains far less alcohol (~40% vs. perhaps 80-90%).

Testing for methanol by chemical means would be far more accessible; surely there must be one or two (at least qualitative) reactions where methanol reacts differently to the other alcohols, inherent of its one carbon skeleton (if it can be called a skeleton!).

Skyjumper - 30-3-2010 at 15:49

Well if your planning on small scale reagent use, you shouldn't even have to deal with the mass scale hes looking at. A simple distillation should suffice?

Come to think of it my etOH has IPA as an additive. Maybe I will distill off the IPA, for a purer product, that could hypothetically fudge with my ester preparations.

Lambda-Eyde - 30-3-2010 at 16:25

Quote: Originally posted by Jor  

But it has a strong blue color, and it stinks.
What is the easiest way to remove these? I know of the activated charcoal method, but that most of the time will make a very fine suspension of the carbon in the liquid. This is bothersome to filter, and besides, because I do not have vaccuum, filtering takes a long time for me.


I have used activated charcoal to render blue isopropanol colorless. The way I did it was that I used a plastic tube with 1-hole stoppers in each end, with ~2 cm cotton plugs at bottom and top and activated charcoal in between. A funnel was inserted in one end, while the other end pointed down in a graduated cylinder. The alcohol was completely colorless after the treatment, and contained no suspended particles at all. There is some loss of alcohol because some is retained in the charcoal, but in a 1L run this was less than 30 mL. I used less than 10 cm of activated charcoal (ID of the plastic tube was approx. 2 cm). I don't know how effective it is at removing methanol, pyridine, etc however. Probably not.

Sure, it takes a while, but why don't you read a good chemistry book while you're waiting? ;)

Runningbear - 6-4-2010 at 20:37

Why not just make your own reflux still and brew your own. Make the still once and you've got ethanol for life.