| Pages:
1
2 |
ZIGZIGLAR
Hazard to Self
Posts: 79
Registered: 3-2-2014
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Self
Posts: 79
Registered: 3-2-2014
Member Is Offline
Mood: No Mood
|
|
| 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
International Hazard
Posts: 3247
Registered: 13-7-2003
Location: Wisconsin
Member Is Offline
Mood: Rock n' Roll
|
|
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
Hazard to Self
Posts: 79
Registered: 3-2-2014
Member Is Offline
Mood: No Mood
|
|
| 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
International Hazard
Posts: 3247
Registered: 13-7-2003
Location: Wisconsin
Member Is Offline
Mood: Rock n' Roll
|
|
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
Hazard to Self
Posts: 79
Registered: 3-2-2014
Member Is Offline
Mood: No Mood
|
|
| 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
Hazard to Self
Posts: 79
Registered: 3-2-2014
Member Is Offline
Mood: No Mood
|
|
| 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
Hazard to Self
Posts: 79
Registered: 3-2-2014
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Others
Posts: 351
Registered: 10-6-2013
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Self
Posts: 79
Registered: 3-2-2014
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Self
Posts: 79
Registered: 3-2-2014
Member Is Offline
Mood: No Mood
|
|
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).
|
|
|
| Pages:
1
2 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
