Sciencemadness Discussion Board

Dichloromethane Distillation/Azeotropes

MagicJigPipe - 4-4-2008 at 17:05

DCM is extremely expensive. Even more so when you must order it on the internet (the cheapest I have found is 11 dollars a liter plus shipping or about $19/L). Because of this I decided to do some OTC browsing today.

I found a product (I forgot the name so I can't check the MSDS but I did remember the ingredients) that claims to contain: Methylene chloride, isopropanol, ammonia and less than 4% MeOH.

A quick search turned up DCM forming a 98.5% azeotrope boiling at 38.1C with water (I believe). I know it forms an azeotrope with methanol but I can't seem to find the data. The ammonia shouldn't be a problem as it could just be boiled out or reacted with acid to create an ammonium salt. Does it form an azeotrope with 2-propanol? What about ternaries?

Is there a good way to seperate secondary and primary alcohols from DCM? Does DCM react with sulfuric acid? If not, could H2SO4 be used to dehydrate the alcohols to ethers and alkenes? Diisopropyl ether seems like it could be seperated with a good column and dimethyl ether is a gas at RT so it shouldn't be a problem.

I could have sworn this had been discussed but I can't seem to find it. And my references are temp. unavailable. I'm really not being lazy guys, I swear.

Magpie - 4-4-2008 at 17:22

http://sciencemadness.org/talk/viewthread.php?tid=1083&p...

not_important - 4-4-2008 at 17:58

Quote:
Originally posted by MagicJigPipe
...
Is there a good way to seperate secondary and primary alcohols from DCM? Does DCM react with sulfuric acid? ...


After a preliminary distillation to get a DMC-rich fraction, shake that with CaCl2 and filter. The lower alcohols form complexes with CaCl2, which will also grab any water in the mixture. A second distillation should give a fairly narrow boiling range around 39-40 C.

smuv - 4-4-2008 at 21:43

some azeotropes

Filter the CaCl2 before redistilling. If it is in a gel form as they usually are, absolutely do not fill the flask more than half full, it will really have a tendency to bump because of the gelling agent. If you are pushing too hard, and the gel is about to climb the column, take the flask out of the water/sand bath/heating mantle and swirl it to settle the bubbles.

It may be worthwhile to pop the flask in the refrigerator for a while before treatment with CaCl2.

Klute - 5-4-2008 at 08:04

Why don't you simply wash the alcohols off with water? Then dry and distill.

Damn, i pay 9E for 5L of >98% DCM......

PainKilla - 5-4-2008 at 08:51

DCM is definitely not hard to acquire OTC, however out of interest to keeping these sources secure, I will only say that a proper search will find you what you are looking for.

That said, it's easy to purify by washing with some water, acid, base, brine a few times, and that's it. It's a bit of work but there's not much you won't get out that way. Distill if you need to...

Or just buy it from a supplier.

As far as azeotropes are concerned, I translated some info out of a book... don't know how helpful it will be but here you go:

DCM azeotropes.JPG - 374kB

MagicJigPipe - 5-4-2008 at 10:57

I've searched pretty good. There don't seem to be any local sources that I can find. I called all places in the phone book that had to do with "plastic" and none of them had DCM.

Does washing with water really work well? Does it usually require a large amount of water. I'm pretty sure my DCM source is a clear liquid because it's for automotive paints.

Which complexes more alcohols gram for gram, MgSO4 or CaCl2? I have plenty of both.

Thanks for the azeotrope list Painkilla!

Klute - 5-4-2008 at 11:23

I would suggest washing with water, CaCl2 solution and drying with CaCl2 before distn. This is usually done when removing alcohols from esters. Water washes do a pretty good job at removing methanol and ethanol.

evil_lurker - 5-4-2008 at 13:04

Hey MJP, you should check out some of the fiberglass suppliers around memphis.

Been meaning to make a run there myself.

MagicJigPipe - 5-4-2008 at 16:31

Hey, good idea! If the price is right I wouldn't mind a 4 hour round trip to get some DCM. Of course I'd need to collect a 5 gallon bucket of it or something similar.

I haven't checked fiberglass places here. Damnit! It's too late on a Saturday.

leu - 5-4-2008 at 18:04

What you need to produce DCM from paint stripper most easily is a borosilicate glass adapter with a female ground glass joint that fits your distillation equipment on one end and a wide enough tube which is inserted into a one hole rubber stopper on the other end :P One then pours out a liter of the paint stripper and uses a salt water bath to distill the crude DCM until the temperature rises above 40ºC ;) One then removes the heat and after the metal can cools one adds the liter of paint stripper removed earlier back into the metal can and heats it back up and distills the rest of the crude DCM :D One then washes the crude DCM with tap water and then redistills it after drying it with anhydrous calcium chloride overnight :) One then has about thee liters of reasonably pure dichloromethane :cool:

Klute - 5-4-2008 at 18:08

Do you mean use the can as the still? Not a bad idea considering the gel/polymers left behind.. just need to throw it away :)

len1 - 5-4-2008 at 18:32

The can should be used as a still as else theres a lot of endless washing up. What he means by the pouring 1l out procedure is that there will be too much bumping if you use the full can - I think 1/2 full is better than 3/4 - and still you can get some gel carrying over. Its best to use glass wool plugged lightly inside joint to stop this. H2O removes some but not all CH3OH, complexing with CaCl2 does the rest as well as drying - but I think you save nothing that way and might as well form the CaCl2 adduct without washing. The CaCl2 needs decanting before 2nd distillation, else it will release some of its bound water.

[Edited on 6-4-2008 by len1]

not_important - 5-4-2008 at 19:20

I'm going with Len here, skip the water wash. DMC dissolves a bit in water, 13 g/l or so, the alcohols will increase the solubility. Just distill the crude DMC out, complex with CaCl2, filter that out, repeat with a bit of CaCl2 to insure you've got it all, fractionate the filtered DMC. You can recover the alcohol from the CaCl2 by heating (I've done it in a resin kettle which makes removal of the CaCl2 easy) or by dissolving the complex in water then distilling the alcohol off (may be better if you just have ordinary flasks).

497 - 5-4-2008 at 23:27

Has anyone here concentrated nitric with DCM? I've heard of it and read the patent on it and it looks good, just wondering if anyone has actually done it. It should be able to be replaced by chloroform too, just less effective. I am also interested in the possibility of nitrating things (glycerin, toluene, etc.) directly in the DCM. The patent mentions that it can nitrate toluene, but says nothing more on that. What do you think?

MagicJigPipe - 6-4-2008 at 09:49

I always thought you could just nitrate glycerin with mixed acids and then just seperate with a separatory funnel. Why would you want to use DCM?

Also, IMO, distillation of nitric acid would be much easier than having to worry about getting an electrode that is unreactive towards it.

497 - 6-4-2008 at 10:25

Electrode? I'm not sure what you're talking about.

I'm talking about taking something like ammonium nitrate, adding sulfuric, mixing with DCM, then decanting the DCM that has absorbed about 10 or 15% its weight in pure anhydrous nitric acid, excluding all the salts and sulfuric. You could then simply evaporate it off and get the pure nitric, or as I was thinking, use it as is.

I think the advantages would be: absolutely no chance of detonation, less chance of a runaway because the DCM would probably boil and cool it before that happened. Also there would be much less contamination with various other chemicals, the DCM/NG could be decanted, neutralized and distilled at low temp to leave you with very pure nitroglycerin. Yes it would be a little extra work, but if it keeps my hand from getting blown off, I'm all for it.

leu - 6-4-2008 at 18:31

The posted procedure is based on JACS 48 562 (1926) which has been a standard method of purification for dichloromethane for many years :) One doesn't apply much heat when distilling a 3/4 full can, then one has no problem with bumping :D The chart posted above states that there is an azeotrope of dichloromethane and methanol so a water wash is needed to completely get rid of the methanol :P

not_important - 6-4-2008 at 19:01

In 1926 they weren't concerned with pouring halocarbons into the sewer system, often weren't too concerned with wasting a few percent of a then cheap solvent. A lot of those older methods are useful but require updating.

And while there is an azeotrope, CaCl2 removes the alcohol too.

MagicJigPipe - 6-4-2008 at 19:05

What is DCM used for in the fiberglass "industry"?

497, I could have sworn that I saw something about electrolysis in your post. Maybe that was another thread. Sorry.

Now that I think about it. The DCM/Nitric does sound interesting.

not_important - 6-4-2008 at 20:00

Fiberglass outlets often sell DMC as a solvent, useful in cleaning up.

There was a thread that had a good deal on DMC+HNO3, however I failed at trying to find it quickly.

MagicJigPipe - 7-4-2008 at 10:03

I called around to some fiberglass "outlets" today. After the first 3 or so had no idea what I was talking about I just got aggravated (and pissed off at the situation) and gave up. This is rediculous. DCM then NH4NO3... What's next? My guess is sulfuric acid OTC. And H2SO4 any other way is basically pointless because of the HAZMAT fees.

smuv - 7-4-2008 at 10:44

Products containing ca 90% methylene chloride are readily available in the united states. A brand called klean strip has a lot of products containing methylene chloride. Go to walmart, look at the strippers they carry, and then cross refrence their products w/ the msds. I have seen a certain product made by this company everywhere from home depot, to walmart, to lowes, to ace/truevalue, I guarantee if you actually go out and look you will find it.

MagicJigPipe - 7-4-2008 at 10:47

Yes, I know there are products that contain methylene chloride. The reason I was looking was to obtain a 100% DCM product so I would only have to distill once to purify it.

evil_lurker - 10-4-2008 at 15:50

HA!

Found me some DCM at Advanced Plastics in Nashville (they got several branches all over the southeast US).

Got 5 gallons of DCM for $68 plus some change... the shipping alone would have probably ran at least that much.

Will Calls are the way to go when it comes to chems!