Sciencemadness Discussion Board - Purification of denatured ethanol

Purification of denatured ethanol

ZIGZIGLAR - 3-2-2014 at 15:20

Hi. I'm exploring cost effective means for preparing absolute ethanol for reactions without creating the rectified spirits myself (as this is considered moonshining and is illegal in my state).

Ironically, it seems the best option is purifying methylated/denatured spirits, as the cost per ml of the contained ethanol is extremely low as it bypasses the alcohol beverage tax laws here.

I have been reading Practical Organic Chemistry (pages 136-137) and Purification of Laboratory Chemicals (pages 166-170) and understand the processes described, however, I'm not clear as to which of them is appropriate in the comprehensive reliable separation of ethanol from methanol and other denaturing or bittering agents.

Can anyone clarify this for me? Many thanks in anticipation. Cheers

TheChemiKid - 3-2-2014 at 15:32

First off, this should have been posted in Beginnings.

UTFSE! Denatured alcohol can be fractionally distilled over activated carbon and sodium hydroxide. This may need to be repeated several times.

ZIGZIGLAR - 3-2-2014 at 15:38

Thanks, TheChemiKid. I'd never seen the abbreviation UTFSE before haha I have read through several threads resulting from my search efforts before posting. My apologies if I missed some relevant threads ... I'll try some new search parameters and see what they yield.

Looks like I may have been on a dead trail with the two books then, as there is no mention of this method as far as I recall. Many thanks for your assistance.

Cheers

subsecret - 3-2-2014 at 15:51

Remember that the methanol (bp: 65 C) has a lower boiling point than the ethanol (bp: 78 C), so remember to swap collection vessels after the methanol fraction has been purged from the apparatus. Bittering agents are usually large, higher-boiling organic molecules, so don't worry about carrying any of these over.

ZIGZIGLAR - 3-2-2014 at 16:54

Thanks, Awesomeness. I have a multi-fraction collection Cow to separate distillate fractions.

I re-searched the forum and read a number of threads and as far as I can tell, there appears to be a lot of theoretical debate on the reliability and comprehensiveness of any known method.

For many reactions, trace amounts of denaturants are of no consequence, but for others they are. If there was a method of proven conclusive separation, I'd prefer to use it so that the reagent is more versatile.

TheChemiKid - 3-2-2014 at 17:02

Just so you know, here at sciencemadness UTFSE is somewhat of a joke.
It is officially Use the Forum Search Engine, but many people think of it as Use the F***ing Search Engine

ZIGZIGLAR - 3-2-2014 at 17:10

Quote: Originally posted by TheChemiKid

First off, this should have been posted in Beginnings.

UTFSE! Denatured alcohol can be fractionally distilled over activated carbon and sodium hydroxide. This may need to be repeated several times.

When you say to distill it over activated carbon and sodium hydroxide, do you mean to introduce these to the boiling flask?

Oh I interpreted the abbreviation with the F*ing meaning,

TheChemiKid - 3-2-2014 at 17:17

Yes I do mean introduce these into the boiling flask.

ZIGZIGLAR - 3-2-2014 at 17:34

Thanks, I shall give it a go. However, I'm not sure how I can test for the possible denaturants. No manufacturer lists the specific denaturant/s or bittering agents, because they are not required to do so if they represent less than 1%.

Possible denaturants include but are not limited to: diethyl phthalate, tertiary butyl alcohol, brucine sulphate, denatonium benzoate, methyl isobutyl ketone, and fluorescein.

:/ any advice? What is your experience treating a denatured spirit with this method?

Would your method elliminate the denaturates in the following composition? (I found one that lists the denaturants):

NAME CAS RN %
ethanol 64-17-5 >95
methyl isobutyl ketone 108-10-1 0.25 ^
denatonium benzoate at 6.6 ppm
denatonium benzoate 3734-33-6 0.00066
fluorescein 0.0001
brucine sulfate 4845-99-2 Not spec^
water 7732-18-5 Balance

[Edited on 4-2-2014 by ZIGZIGLAR]

Bot0nist - 3-2-2014 at 18:06

By the time you get a suitable fraction that is free of denaturants and then go about drying it you will have invested a fair bit of time and energy. Why not start with 95% food grade ethanol (aka everclear or goldengrain liquor). It is more expensive, but then you can just proceed to the drying step.

Good luck, and welcome.

Turner - 3-2-2014 at 18:19

Do you want to drink the ethanol that you are purifying?

ZIGZIGLAR - 3-2-2014 at 18:19

Quote: Originally posted by Bot0nist

By the time you get a suitable fraction that is free of denaturants and then go about drying it you will have invested a fair bit of time and energy. Why not start with 95% food grade ethanol (aka everclear or goldengrain liquor). It is more expensive, but then you can just proceed to the drying step.

Good luck, and welcome.

We don't get everclear here. The closest equivalent here is named Spirytus (self explanatory) and is $60 per 500ml. As such, I'm willing to invest a bit of time to produce my own!

The temptation to produce my own rectified spirits is increasing, but I will first continue to explore the possibility of using cheap household denatured ethanol. With the assistance of this forum

ZIGZIGLAR - 3-2-2014 at 18:29

Quote: Originally posted by Turner

Do you want to drink the ethanol that you are purifying?

Let's just say yes as I've already learnt how to extract a solution from denatured alcohol that adequately serves as an ethanol reagant for most reactions, but one of the main reasons I'm wanting to comprehensively elliminate all denaturants is because I may use it as a solvent in the process of making other consumables or topicals. (My wife employs my lab to further her own obsession with health and beauty.)

I won't actually drinking it (I prefer beer, if anything). I could invest in laboratory absolute ethanol and simply collect the distillate to stretch it out a while, but why not produce it cheaply if I can?

Bot0nist - 3-2-2014 at 18:36

Sorry, I assumed you were in the states. Im sorry. I personally use the everclear as a solvent and its not to pricy here. Anyways, good luck agian friend. Keep that attitude of gratitude, lol.

Crowfjord - 3-2-2014 at 18:55

I like to use Kleen Strip green denatured alcohol (green as in environmentally friendly); it is denatured only with small amounts of methanol, methyl isobutyl ketone and ethyl acetate. Do you have something similar where you live? I haven't tried yet, but I figure that one could make it fairly pure by distilling over sodium hydroxide, followed by a couple distillations. The ethyl acetate should cleave to ethanol and sodium acetate (or polymerize), and the ketones should polymerize and stay in the boiling flask, leaving you with methanol as the main impurity to deal with. I'm not sure how denatonium would behave under these conditions. Stevens or Sommelet rearrangement?

Bot0nist - 3-2-2014 at 19:09

What size fractionating column are you using?

ZIGZIGLAR - 3-2-2014 at 19:20

Quote: Originally posted by Bot0nist

What size fractionating column are you using?

I assume you're asking Crowfjord, but just in case you're asking me: the largest column I have is #24 400mm jacket length Vigreux. I have a smaller Hempel I could pack to probably achieve more theoretical plates though.

Fantasma4500 - 4-2-2014 at 04:56

methanol should react with Al2O3, which ive read alot about should be the main contaminant of denatured alcohol, however if you have found something stating that no methanol is added then you wouldnt be able to make aluminium methoxide from reacting the denatured alcohol with aluminium foil (in which has Al2O3 coating) followed by fractionally distilling it

denatonium benzoate remains after destillation as a solid that im not entire sure if i decided to taste, could be my mind totally just shut off the memory if i did?
i just used rubber plug with PVC hose to distill it, also you could potentially salt out other components, like water.. not sure if theres any limit to salting out's efficiency

hyfalcon - 4-2-2014 at 08:21

Salting out is not going to work. Not to break the azotrope of ethanol anyway. I would distill 3 times then take what came over the third time and fill my Hempel column with 3A molecular sieves and distill again. This should break your azotrope and get you where you want to be.

ZIGZIGLAR - 4-2-2014 at 14:12

The Denatured Spirits I found hasn't even got any methanol in it, strangely.

The denaturants have high boiling points. Unless any of them form azeotropes, shouldn't a simple distillation, carefully ceased as the temperature rises above 78~ be enough?

methyl isobutyl ketone : 117 bp
Methyl isobutyl ketone: ORAL (LD50): Acute: 1600 mg/kg [Guinea pig]. 2671 mg/kg
[Mouse]. 2080 mg/kg [Rat]. DERMAL (LD50): Acute: 20001 mg/kg [Rabbit]. VAPOR (LC50): Acute: 8000 ppm 4 hour(s) [Rat].

denatonium benzoate :163 ish bp
Denatonium benzoate: ORAL (LD50): Acute: 584 mg/kg [Rat].

fluorescein: 626c
No know health effects

brucine sulfate : 630bp

ZIGZIGLAR - 4-2-2014 at 14:18

Quote: Originally posted by hyfalcon

Salting out is not going to work. Not to break the azotrope of ethanol anyway. I would distill 3 times then take what came over the third time and fill my Hempel column with 3A molecular sieves and distill again. This should break your azotrope and get you where you want to be.

Refluxing the 95.6% ethanol/water azeotrope over anhydrous CaO is one of the most widely published methods of breaking the azeotrope to create the typical dry "absolute" 99.5% solution. I don't see why the this wouldn't work over 3A sieves, but I also don't see why packing a Hempel with them wouldn't work either.

subsecret - 4-2-2014 at 17:31

I've also heard of Crown "Next" denatured alcohol, which contains 90% ethanol and 10% isopropanol. Ethanol boils at about 78.4 C, and isopropanol boils at 82.5 C, and that's only a ~4 degree difference. Those would be rather hard to separate, even with a very good fractionating column. I haven't been able to find any in my local hardware stores, but try to see if yours provide it. Perhaps you could custom build a fractionating column by driving a long length of 1/2 inch copper tubing through a rubber stopper , and then sticking this into the neck of a flask. Adjust the size of the column as you wish, and add insulation if your column proves to be too much of an obstacle for the vapors. The other end of the copper pipe could be joined to a stillhead in a similar manner, or if you know how to solder, a turn could be made and the pipe could be fitted to a condenser with another stopper. (In the US, so-called "soft copper" pipe is available, and it can be bent more easily, provided you have a pipe-bending spring to slide over the section to be bent).The latter method could carry impurities from the copper into the ethanol, so a second distillation could be conducted, after the ethanol is dried. Chances are that you'd still have isopropanol in the distillate, but this volume would be significantly reduced be the long column.

As far as I know, this method has not been tested, and may not work as well as I think it will.

ZIGZIGLAR - 4-2-2014 at 20:51

Step 1. Add carefully concentrated sulfuric acid to the ethanol, and distill the ethanol.
The H, SO1 acts as an oxidizing agent for aldehydes, and this step also reduces the content
of amines.
Step 2. Redistill the ethanol from solid sodium hydroxide, to remove entrained sulfuric acid
and acidic impurities.
Step 3. Fractionally distill the ethanol with a good rectification column.

This combined treatment is said to reduce the content of aldehydes and ketones to <1 ppm, and
make the ethanol a solvent suitable for spectroscopic studies of solutes in the ultraviolet
region.

REFERENCE: B. Glabik and H. Sobczyk, Chem. Stosow, 18, 187 (1974); C.A., 81, 145492 m.

--------

This purification process is applicable to lab reagent ethanol, where typical impurities are other alcohols (methanol,
propanol) , acetone, and water.

---
I've not seen mention of activated carbon in any publications, so I am definitely curious to see where this stems from so I can do some more reading.

[Edited on 5-2-2014 by ZIGZIGLAR] copy/paste errors.

[Edited on 5-2-2014 by ZIGZIGLAR]

DJF90 - 5-2-2014 at 11:20

First off, whether you rectify your own mash or commercial denatured alcohol, you'll be breaking the law (as you're rendering the spirit drinkable and thus excise duty is due).

That being said, its useful to have pure ethanol in the lab where other lower alcohols and ketones are troublesome contaminants. The use of activated carbon is to remove the methyl violet dye they put in "methylated spirits" to provide a purple colouration.

The means of purification will depend upon the contaminants present. In the UK the main contaminants are pyridine and methanol, so a preliminary distillation from c. sulfuric acid is required to remove the former (and the purple dye). This distillate still has a funny smell (not sweet like lab grade ethanol), which I suspect is some form of hydrocarbon or something. When trying to fractionate is material, using a 40cm vigreux, the boiling point raises quite quickly to 75*C ish, and as the slow distillation proceeds, raises to 78*C. After collecting several fractions and analysing that passing over at 78 *C for methanol (1H-NMR) it was found to be present at 6%w/w (down from 12%w/w in the commercial material). No other organic material is found to be present but the smell is still there.

Despite the relatively large difference in bp between ethanol and methanol, you need a very efficient column in order to separate the two, as there is little difference in composition between the vapor and liquid equilibrium curves. A more efficient column is required and a variable take-off stillhead would be really helpful in order to acheive a decent reflux ratio.

vmelkon - 5-2-2014 at 12:13

Quote: Originally posted by ZIGZIGLAR

Step 1. Add carefully concentrated sulfuric acid to the ethanol, and distill the ethanol.
[Edited on 5-2-2014 by ZIGZIGLAR]

That's the recipe for making diethyl ether.
And when someone says concentrated H2SO4, I imagine they mean 90 to 98% H2SO4.

ZIGZIGLAR - 5-2-2014 at 14:43

Quote: Originally posted by DJF90

First off, whether you rectify your own mash or commercial denatured alcohol, you'll be breaking the law (as you're rendering the spirit drinkable and thus excise duty is due).

I did not realise this, but it makes sense.

Quote: Originally posted by DJF90

That being said, its useful to have pure ethanol in the lab where other lower alcohols and ketones are troublesome contaminants. The use of activated carbon is to remove the methyl violet dye they put in "methylated spirits" to provide a purple colouration.

This I agree with; not only for reactions, but as a polar solvent as well. I have not seen a Methylated spirit with purple dye in it around for years and the use of methanol as a denaturant is slowly being phased out as many countries are outlawing it (making mass production for distbribution over multiple countries less economical).

The denaturants still posing a challenge to separate by the average small scale chemist are:

Code:

Chemical			BP		Azeotropic BP
isopropyl alcohol 		82.6°C		80.37°C/water
tertiary butyl alcohol		82.8°C		79.9°C/water
methyl ethyl ketone (butanone)	79.64 °C	74.8°C/ETHANOL

Quote: Originally posted by DJF90

The means of purification will depend upon the contaminants present. In the UK the main contaminants are pyridine and methanol, so a preliminary distillation from c. sulfuric acid is required to remove the former (and the purple dye). This distillate still has a funny smell (not sweet like lab grade ethanol), which I suspect is some form of hydrocarbon or something. When trying to fractionate is material, using a 40cm vigreux, the boiling point raises quite quickly to 75*C ish, and as the slow distillation proceeds, raises to 78*C. After collecting several fractions and analysing that passing over at 78 *C for methanol (1H-NMR) it was found to be present at 6%w/w (down from 12%w/w in the commercial material). No other organic material is found to be present but the smell is still there.

Despite the relatively large difference in bp between ethanol and methanol, you need a very efficient column in order to separate the two, as there is little difference in composition between the vapor and liquid equilibrium curves. A more efficient column is required and a variable take-off stillhead would be really helpful in order to acheive a decent reflux ratio.

From the conversations I've had with other consultant chemists, HPLC is the only reliable method to separate MeOH and EtOH. As you're indicating, it's certainly possible to reduce the MeOH, but so far I've not found any conclusive evidence suggesting fractionation alone is capable of a 99%+ separation.

I know how to anaylse ethanol for water content. What method do you use to test for MeOH in EtOH? Could I trouble you for a reference source?

Thanks a lot for all your responses. I greatly appreciate it.

ZIGZIGLAR - 5-2-2014 at 14:48

Quote: Originally posted by vmelkon

Quote: Originally posted by ZIGZIGLAR

Step 1. Add carefully concentrated sulfuric acid to the ethanol, and distill the ethanol.
[Edited on 5-2-2014 by ZIGZIGLAR]

That's the recipe for making diethyl ether.
And when someone says concentrated H2SO4, I imagine they mean 90 to 98% H2SO4.

I would certainly assume 98%+ H2SO4. A concentration level that requires lock and key precautions. How long does it take for H2SO4 at this concentration to permanently scar a human body? I don't know, and I don't want to find out haha
ether

BromicAcid - 5-2-2014 at 15:34

It all depends on what you have to distill with that determines if you can perform the separation between methanol and ethanol. At my work we have used different solutions to determine the efficiency of our distillation columns. Methanol/Ethanol has been used before. I was always told 5 theoretical plates but doing a search gave the reference:

Recommended Test Mixtures for Distillation Columns which has a nice table in it (able to be viewed on google book, at least the table) giving a number of mixtures and how many theoretical plates you need for good separation. Methanol / Ethanol is listed as needing 4-8 theoretical plates. Nowhere near as bad as p-xylene vs. m-xylene (50-250 theoretical plates) and still more than a vigreux (2.5 theoretical plates for a 20 cm column by one source but probably lower in practice because you're usually not fractionating with it just distilling through it) but still something you could accomplish with decent equipment. But it's not just a simple short-path distillation like some might think.

ZIGZIGLAR - 5-2-2014 at 16:36

Quote: Originally posted by BromicAcid

It all depends on what you have to distill with that determines if you can perform the separation between methanol and ethanol. At my work we have used different solutions to determine the efficiency of our distillation columns. Methanol/Ethanol has been used before. I was always told 5 theoretical plates but doing a search gave the reference:

Recommended Test Mixtures for Distillation Columns which has a nice table in it (able to be viewed on google book, at least the table) giving a number of mixtures and how many theoretical plates you need for good separation. Methanol / Ethanol is listed as needing 4-8 theoretical plates. Nowhere near as bad as p-xylene vs. m-xylene (50-250 theoretical plates) and still more than a vigreux (2.5 theoretical plates for a 20 cm column by one source but probably lower in practice because you're usually not fractionating with it just distilling through it) but still something you could accomplish with decent equipment. But it's not just a simple short-path distillation like some might think.

Thanks for chiming in.

I don't think my Vigreux is 4-8 theoretical plates, but I could easily exceed this with a rachig packed Hempel, I suppose.

If fractionation is a possiblity, the next step is finding a reliable method to test for methanol contamination within the ethanol distillate. I don't have the means nor skill to use GC or HPLC ...

How reliable is the use of Red Litmus papers (PH 6.8 - 8.1)?

Cheers,

BromicAcid - 5-2-2014 at 17:34

Also helping the odds is the you might be aiming for 99.9% EtOH but just a little bit of MeOH isn't the end of the world.

http://www.ncbi.nlm.nih.gov/pubmed/11926610

Defines the acceptable level as <0.4% by the EU, also says absolute maximum in one study was <2 grams MeOH / Day to stay safe. Of course best course would not drink any MeOH.

ZIGZIGLAR - 5-2-2014 at 21:27

Quote: Originally posted by BromicAcid

Also helping the odds is the you might be aiming for 99.9% EtOH but just a little bit of MeOH isn't the end of the world.

http://www.ncbi.nlm.nih.gov/pubmed/11926610

Defines the acceptable level as <0.4% by the EU, also says absolute maximum in one study was <2 grams MeOH / Day to stay safe. Of course best course would not drink any MeOH.

I'd be happy with 0.4%, but I would need a way to quantify a test solution to confirm this...

I've read people suggesting adding potassium permanganate to a diluted solution and adding sulphuric acid ... and if the solution turns red, it indicates the presence of methanol. I'm not sure if they're trolling or if they are aware of the dangerousness of their advice, but it has made me rather persistent and cautious when finding suggestions on the Internet haha

People have said that red ph papers will reveal the presence of methanol, but I have no idea what threshold this is accurate to in order for this test to be useful.

Any ideas?

ZIGZIGLAR - 6-2-2014 at 14:58

Code:

1) Measure the specific gravity of the solution
 
Let  X = unknown volume of methanol

Let (1-X) = unknown volume of ethanol

Then   X + (1-X) = 1 Litre

Specific Gravity of methanol = 0.7915
Specific Gravity of ethanol = 0.7905
(X) 0.7915) + (1-X) (0.7905) = Sp. G of solution
 
Solve for X

(X) (100%) = the concentration of methanol
(1-X) (100%) = the concentration of ethanol

I could use a 0.8-0.9 Hydrometer and this formula if I had an anhydrous solution, but I am not sure how to calculate the concentration of a 3 part solution. Any advice from the more mathematically inclined?

[Edited on 6-2-2014 by ZIGZIGLAR] corrected SG to 20c

[Edited on 7-2-2014 by ZIGZIGLAR]

ZIGZIGLAR - 10-2-2014 at 14:49

So, taking a closer look at a readily available denatured spirit:

<CODE>

NAME CAS RN %
Ethanol 64-17-5 >95
Methyl isobutyl ketone 108-10-1 0.25
Denatonium Benzoate at 6.6 ppm, i.e
Denatonium Benzoate 3734-33-6 0.00066
Fluorescein 0.0001
Brucine Sulfate 4845-99-2 Not spec
Water 7732-18-5 Balance

</CODE>

I can't see any reason why this can't be purified rather easily by a fractional distillation over activated carbon. The carbon will adsorb the fluorescein and the other compounds will be left behind due to their higher boiling points.

I haven't found any information suggesting Methyl Isobutyl Ketone forms any azeotropes with water or ethanol, so I can't see why this would be difficult to separate, even by simple distillation as the boiling point is 30c higher than ethanol.

Any observations? Am I missing anything?

testimento - 10-2-2014 at 17:04

I checked the denatured ethanol product and it contains isopropanol, methyl ethyl ketone and methyl isobutyl ketone and also some extent of tert-butyl alcohol. The question arises: does any of these react with something that ethanol doesn't? The azeotrope could be broken with CaO as said before to get 99.9% anhydrous(?) and therefore make the difference of few degrees C to get them separated. I have 2000mm fractionation column available, though it's diameter is 80mm so it would be economically feasible to distill only larger batches, like 10-100 liters a time. But the cost of otc denatured ethanol is very high compared to self-made(about 2 a liter), which is at least half less expensive so if I'd need any amounts of high purity ethanol, I'd make it myself.

How about ethanol fuel? It certainly contains all kind of stuff:

Ethanol 75% (78)
Gasoline hydrocarbons 15-20% (benzene(80), toluene(110, 1/100) and hexane(69))
MTBE (55, 2.6/100)
ETBE (71. 1.2/100)
TAME (86, 1.7/100)
TAEE (? ?)
Isobutanol (107, 8.7/100)

Ethanol readily goes into water, but so does some of the ethers and butanol. I'd add water so the layers separate, take the watery layer and pre-distill it to remove the ethers and then take the ethanol and possibly distill it again to gain more pure product and dry it with CaO. Some of the solvents, like hexane, isobutanol and why not the ethers and toluene too, would be viable to recover.

ZIGZIGLAR - 10-2-2014 at 17:35

I won't dispute that it is likely cheaper (especially in smaller batch sizes) to make your own rectified spirit by fermenting a sugar wash. 2.5L 95% ethanol could be yielded from a 5kg wash, costing approximately $15-20 to produce. A 2.5L bottle of methylated spirits with the ingredient base as above (ie minimum 95% ethanol) is around $15-$25, depending on source.

The price gap narrows as the quantity of methylated spirits increases as the intended customer base becomes more industrial. The CaO and activated carbon would be necessary in either application, so I've not factored in those costs for comparative purposes. One can skip the wash preparation and fermentation process (and save on set up costs if they are a factor too) by simply pouring the denatured alcohol directly into the distillation apparatus.

Purifying ethanol from ethanol fuel seems like a much more involved process, assuming my calculations are correct as far as the ease of purify the above listed denatured alcohol product goes. I'm fairly tempted to give it a go just to satisfy the chemist in me.

I will also admit that, initially, I didn't realise that the purification of denatured alcohol was illegal, so that is another reason why I hadn't considered moonshining as a viable pathway, yet pursued this instead. As usual for myself, the academic process has taken over and I feel obliged to find the answers even if in practice I will not pursue them.

ZIGZIGLAR - 17-2-2014 at 14:49

I found some information on the government legislation for poisons on ingredients for denaturing spirits and it states that Methylated Spirits are to be denatured with: denatonium benzoate, methyl isobutyl ketone and
fluorescein.

There must be something we don't know about how these ingredients incorporate, as in theory it just seems too easy to purify the ethanol (even a simple distillation over activated carbon should work).