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Author: Subject: Separating waxy crap from methylene chloride
Quince
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[*] posted on 6-12-2006 at 07:44
Separating waxy crap from methylene chloride


After distillation through a vigreux into ice water, I realized that even though I did not let the head go above 40*C, a good deal of the gelling agent/thickener came over... after some hardcore stirring with the water, some of it separates from the methylene chloride, forming a sticky white mess. Seems suspiciously similar to paraffin (and the brush scrubbed it off the glassware easily without solvents or pirahna solution), but I don't understand how it could have come over at such a low temperature...could it form something akin to an azeotrope? In that case even fractioning would not separate all of it out. I removed the water and floating wax bubbles with a separatory funnel and swirled in some sulfuric acid. It became yellow and gathered up some more wax. Still not gone... Another washing with ice water. More wax comes out. What the fuck? How do I finish this process? I don't have any other source for methylene chloride, as the pure one sold as acrylic solvent is five to ten times more expensive.

[Edited on 6-12-2006 by Quince]




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[*] posted on 6-12-2006 at 09:33


Just a thought......how about putting it in the freezer and let the wax harden and just peel off the wax and recover your wax -free dichloromethane................solo



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[*] posted on 6-12-2006 at 09:38


I can think of better reagents to do this, but since it seems you would probably have limited or no access to them.

Steam distill your DCM/wax. You should end up with fairly pure DCM/H20 in your reciever.

As for the wax left behind in your distillation flask, boil some heptane rinse your flask with it, and while you're at it pull it through your clogged fritted funnel.

Heptane can be had from most car starter sprays. It is the higher boiling fraction. I'm sure you would probably end up keeping the lower boiling fraction as well.

Make sure to do the heptane/ether seperation first in a clean distillation setup, since waxes are known to sparingly dissolve in both.
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[*] posted on 6-12-2006 at 11:19


How about buying pure DCM instead of that crap that obviously cannot be separated into its constituents?
And no, I don't mean the overpriced acrylic solvent.
I mean DCM.

And don't even start complaining that you can't find a supplier. Maybe no supplier will ship to individuals, but nearly all suppliers will ship to pharmacies.




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[*] posted on 6-12-2006 at 14:27


I do not know if your mixture has azeotrope or not but separating substances with fractional distillation is not always fast and easy. I also do not know how you did this process but to get good separation one should distill very slowly. Most of liquid must flow back from column to boiling flask and if you get output of one drop per secund you will probably get rather weak separation (at least if your column is not >60cm hempel wth HQ filling).

Shortly, you may want distill it with much higher reflux ratio, collecting 10 drops per minute or even less. This may or may not help in your case. What i know for sure is that slower distilation (even if no column is used) gives usually much better separation than fast bulk distillation.


[Edited on 6-12-2006 by chromium]




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[*] posted on 6-12-2006 at 23:52


Quote:
Originally posted by garage chemist
nearly all suppliers will ship to pharmacies.

Not in Canada. I've asked several pharmacies here for a variety of substances, and the only thing I managed to get was citric acid. And for DCM specifically, what possible reason could I give the pharmacy for wanting it?

[Edited on 7-12-2006 by Quince]




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[*] posted on 7-12-2006 at 00:02


Quote:
Originally posted by XxDaTxX
Steam distill your DCM/wax. You should end up with fairly pure DCM/H20 in your reciever.

Is this what you mean?
http://upload.wikimedia.org/wikipedia/en/3/35/Steam_Distilla...
I don't know much about this procedure. So this works even if the DCM is fairly insoluble in water? What temperatures would be appropriate for the flask containing the impure DCM?

BTW, I managed to remove the wax from the flask by adding a bit of lye solution which turned it all white and less sticky, and then came off with just light scrubbing with a standard brush. The funnel I cleaned with piranha solution.

[Edited on 7-12-2006 by Quince]




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[*] posted on 7-12-2006 at 00:32


Quote:
Originally posted by chromium
I also do not know how you did this process but to get good separation one should distill very slowly. Most of liquid must flow back from column to boiling flask and if you get output of one drop per secund you will probably get rather weak separation (at least if your column is not >60cm hempel wth HQ filling).

I distilled 800 mL over about two hours, but the problem is not only do I have just a simple Vigreux instead of a proper fractioning column, but I had no way to cool the column so I ran very low heat on the flask, resulting in not just slow distillation but also very slow reflux back into the flask. The problem is the low 40*C temperature. Even a fan doesn't help much. Does anyone have a good way to cool the Vigreux? Doing this outside has the advantage that the air is cold. Doing this outside has the disadvantage that my skinny body can't handle the cold. Any other way?

Also, I want to add that I've accidentally become a guinea pig on the effects of inhaling large amounts of DCM, and I'll say other than a very short-lived, mild vertigo, there's no lingering malaise.

[Edited on 7-12-2006 by Quince]




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[*] posted on 7-12-2006 at 03:59


Quote:
Originally posted by solo
Just a thought......how about putting it in the freezer and let the wax harden and just peel off the wax and recover your wax -free dichloromethane................solo

OK, I froze it, but now it just looks milky in color, nothing separating out...




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[*] posted on 7-12-2006 at 05:40


Quote:
Originally posted by XxDaTxX
Steam distill your DCM/wax. You should end up with fairly pure DCM/H20 in your reciever.

And what, pray tell, is the point of steam distilling something with a bp < 100°C?
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[*] posted on 7-12-2006 at 06:28


Steam distillation doesn't necessarily reach 100*C as the mixture can have a lower boiling point. The water vapor can remain vapor at much lower temperatures.

[Edited on 7-12-2006 by Quince]




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[*] posted on 7-12-2006 at 11:38


There may be a point to steam distilling things that boil below 100C but I don't see any point to steam distilling DCM.
To a good aproximation what will happen is that steam will condense to water in the distilling flask and the DCM will boil. This is just a complicated way of heating the flask.
I find it hard to believe that any wax distilled over; fobbing or spraying seem much more likely to me.
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[*] posted on 7-12-2006 at 12:23


Quote:
Originally posted by unionised
There may be a point to steam distilling things that boil below 100C but I don't see any point to steam distilling DCM.
To a good aproximation what will happen is that steam will condense to water in the distilling flask and the DCM will boil. This is just a complicated way of heating the flask.
I find it hard to believe that any wax distilled over; fobbing or spraying seem much more likely to me.


Your oversimplification holds true in many cases depending on the components being distilled, but multicomponent systems are are far from the "ideal" model of distillation you have in mind if their constituents are extremely dissimilar. I will spare you the ramblings about Raoult's/Dalton's law and the magnificent 3D vapor pressure graphs that follow. Just know that it works.

Steam distillation using an external source of steam may not be necessary. Steam distillation by merely adding water to your flask, heating, and distilling is common practice. Some sort of mixing should be employed, presumably a magnetic stirrer. Please don't ask why you have to mix it. Its finals week and these engineering classes are kicking my arse.

But yes, an external source of steam would be most efficient as it would increase the water vapor pressure inside the distillation column.

Alternatively if you have an addition funnel you can drip your methylene chloride/wax solution into a moderately heated flask of water w/mag stirring and collect the distillate. But it would not have a higher efficiency than the previously mentioned method.

[Edited on 7-12-2006 by XxDaTxX]
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[*] posted on 7-12-2006 at 14:54


What's fobbing?

Also, there was no spray as all was caught by the Vigreux, whereas the stuff was in pretty heavy amounts. I found it strange that, although the head never exceeded 40*C, the flask itself was quite hot when I pulled it out, and it wasn't just the glass.

I may try the steam distillation. I can't use a rubber cork for the incoming steam tube as the DCM will destroy it, but I'll try to squeeze the one I have through the thermometer adapter; unfortunately, then I won't be able to use the thermometer...

[Edited on 7-12-2006 by Quince]




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[*] posted on 8-12-2006 at 01:37


Good luck. And please post a video.
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[*] posted on 8-12-2006 at 02:54


LOL, I don't even have a digital camera to take stills. I occasionally scan my film photos at university. I'll buy something when I get a job.



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[*] posted on 8-12-2006 at 08:12


I have to add that traditionally one would chill and centrifuge first, but it seems you chilled and filtered already, and are still getting waxes, and I assume you have no access to a centrifuge so steam away....

Use a pipet, and make sure your water flask has a stopcock or something to vent/control flow rate to your DCM/wax flask.

Hvap of DCM:water is something like 3:4 so start with the vent open, heat, then clamp down on vent to control steam flow into the DCM.

[Edited on 8-12-2006 by XxDaTxX]
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[*] posted on 9-12-2006 at 08:49


Do I need to chill the DCM flask during the process to prevent it from boiling? I'm not sure when you talk about control, what I'm watching for that I would adjust when I see it.



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[*] posted on 9-12-2006 at 15:11


In steam distillations one can usually crank up the heat on the generator to achieve fairly high velocities through a condenser, however using a refrigerant like (DCM) changes that quite extensively.

For 1 mol of DCM that you want to vaporize, you only need .75 mol of water, assuming no thermal losses.

This translates into 85g of DCM for every 13.5g of water condensed. You see what I mean now? How good of a condenser do you have? =]

Unless you have a good chiller, you should take it slow. Generator /w two outlets, one to a stopcock/adjustable "vent" ... and the other to your still. Use a pipet, or something with an appropriately small diameter tip or else you will not be able to maintain low steam flow. Don't ask me why, its too long of an answer.

As for chilling the DCM, the thermal losses would induce the same effect that an adjustable vent would do. Either that or just turn down the generator. If you have a problem with patience then yes, keep an ice bath handy, while your at it pick up a scuba tank. =]

[Edited on 9-12-2006 by XxDaTxX]
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[*] posted on 10-12-2006 at 02:47


This is a slightly weird steam distillation. Normally we talk about steam distilling something relatively involatile like nitrobenzene. The large volume of steam carries over a small amount of nitrobenzene vapour at a temperature (just below 100C) well below the boiling point of nitrobenzene (211C).
In this case we are talking about the very volatile DCM. It would be better to think of this as dichloromethane vapour- distilling water. The DCM vapour will carry over a little water and lets you distill water at the azeotrope temperature for mixture.
Having the dcm vapour carry a little water with it at a slightly lower temperature than just distilling it doesn't seemlikly to serve any real purpose.
You still need to separate the water later- not difficult, but why bother?
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[*] posted on 10-12-2006 at 03:05


Is it safe for the DCM to add lye? I find that when I was cleaning the wax from the flasks, lye turned it it from a thick, greasy, clear gel into an almost solid white, slimy-instead-of-greasy plastic-like stuff. I'm thinking it may precipitate it out of the DCM, and I can just filter it out and then wash the DCM with water to remove any soapy residue if that's what's the lye is doing.

[Edited on 10-12-2006 by Quince]




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[*] posted on 10-12-2006 at 08:11


The alkali can abstract the protons from the CH2Cl2 leading to dichlorocarbene (:CCl2).

Good luck,

O3




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[*] posted on 10-12-2006 at 08:12


Quote:
Originally posted by unionised
This is a slightly weird steam distillation. Normally we talk about steam distilling something relatively involatile like nitrobenzene. The large volume of steam carries over a small amount of nitrobenzene vapour at a temperature (just below 100C) well below the boiling point of nitrobenzene (211C).
In this case we are talking about the very volatile DCM. It would be better to think of this as dichloromethane vapour- distilling water. The DCM vapour will carry over a little water and lets you distill water at the azeotrope temperature for mixture.
Having the dcm vapour carry a little water with it at a slightly lower temperature than just distilling it doesn't seemlikly to serve any real purpose.
You still need to separate the water later- not difficult, but why bother?


There is no DCM/Water azeotrope. Technically it is more though of as "Stripping" DCM away from high boiling components, as opposed to "vaporizing" or traditional "distillation". But I don't want to get into those technicalities. It can be done correctly the way I said it, or one can use heated air into a DCM:Wax:Water mixture. Which is infact better as far as controlling the rate of condensate, but requires one to have a source of said air ~70oC or so.

Quote:
Originally posted by Quince
Is it safe for the DCM to add lye? I find that when I was cleaning the wax from the flasks, lye turned it it from a thick, greasy, clear gel into an almost solid white, slimy-instead-of-greasy plastic-like stuff. I'm thinking it may precipitate it out of the DCM, and I can just filter it out and then wash the DCM with water to remove any soapy residue if that's what's the lye is doing.


Some n-alkanes are cheap solvents, whether you have access to them I am not sure. Heat some it in your flask, swirl, decant, repeat. Rinse again with water, then tell yourself "I will never again extract essential oils with DCM. I will do as XxDaTxX says and steam distill before partitioning in DCM."

[Edited on 10-12-2006 by XxDaTxX]
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[*] posted on 10-12-2006 at 08:28


Quote:
Originally posted by XxDaTxX
There is no DCM/Water azeotrope.

All immiscible liquids distill an azeotrope mixture since such mixtures boil at the sum of the partial pressures of the two liquids. Hence the boiling point of such mixtures are always lower than the boiling point of the most volatile component. According to Table of Azeotropes and Nonazeotropes (Horsley, 1947 – available for download somewhere on this forum) the CH2Cl2/H2O azeotrope boils at 38.1°C and contains 1.5% water and 98.5% dichloromethane. The author of the table refers to Bakowski and Treszczanouicz, Przemsyl. Chem., 22, 211 as his source.




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[*] posted on 10-12-2006 at 08:41


Quote:
Originally posted by Nicodem
Quote:
Originally posted by XxDaTxX
There is no DCM/Water azeotrope.

All immiscible liquids distill an azeotrope mixture since such mixtures boil at the sum of the partial pressures of the two liquids. Hence the boiling point of such mixtures are always lower than the boiling point of the most volatile component. According to Table of Azeotropes and Nonazeotropes (Horsley, 1947 – available for download somewhere on this forum) the CH2Cl2/H2O azeotrope boils at 38.1°C and contains 1.5% water and 98.5% dichloromethane. The author of the table refers to Bakowski and Treszczanouicz, Przemsyl. Chem., 22, 211 as his source.


If you want to get technical, then yes, but when one speaks of azeotropes it is usually in respect to an appreciable ratio of components. Do you really think I assume a partial pressure of 0 for water. Heheheh.
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