Author Topic: Distilling THF from pipe cement  (Read 20146 times)

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Chromic

  • Guest
Distilling THF from pipe cement
« on: June 25, 2002, 05:40:00 AM »
I've gone through the search engine, and haven't found any information on how to distill pipe cement to get the THF and the other solvents out. As Ab2 said in another thread, that if one was to use their glassware to distill this stuff, one would need all the recovered THF just to clean the flask...

I'm thinking about distilling it straight from the can using a water bath.

Has any one got experience doing this? What did you use? Did you do anything to prevent peroxide formation?

This is a 16 fluid oz can of a popular brand of gray PVC cement mentioned elsewhere on the Hive in other threads.

I'm thinking that it might be worthwhile to obtain another source of THF. This looks a lot worse than distilling the DCM-containing goop that's sold as paint stripper.

Elementary

  • Guest
Solvents
« Reply #1 on: June 25, 2002, 06:08:00 AM »
After looking at some MDMS data for various PVC cements these seem to be the solvents used :

Methyl Ethyl Ketone (40-55%) (BP = 79.6°C)
Tetrahydrofuran (25-40%)  (BP = 66°C) SEE NOTE
Cyclohexanone (5-10%)  (BP = 155.6°C)
Acetone (0-5%)  (BP = 56.5°C)
(PVC Resin (10-14%))

NOTE : Must be distilled with a reducing agent, as explosive peroxides may form (see Merck Index).

You may have a hard time seperating acetone, MEK and THF !



John Lennon - Working Class Hero

metwurst

  • Guest
H2O to start with
« Reply #2 on: June 25, 2002, 06:42:00 AM »
Perhaps a water wash is in order first. THF is soluble to 300g/L in water. The MEK and acetone are also soluble, but are both ketones, so saturating the resulting water/THF/MEK/acetone with bisulfite might crystallise them out leaving  THF in water.
Sound plausible?

Elementary

  • Guest
:-
« Reply #3 on: June 25, 2002, 07:19:00 AM »
The PVC resin may stop a lot of the solvents from going into the water.

You may still have to distill first, to get the solvents away from the resin.

But your bisuphite addition idear seems plausable, as long as the THF does not react with the bisulphite.

John Lennon - Working Class Hero

Ritter

  • Guest
WARNING!!!
« Reply #4 on: June 25, 2002, 08:50:00 AM »
Chromic:

I don't have the time to go through old posts to ref a post#, but I specifically remember one of the guys from back in the day (maybe Cheapskate?) distilling THF from PVC cement with near disasterous results.  The low grade ethers in those cement products are LOADED with peroxides.  There was at least one report here in the past which detailed a powerful explosion resulting from the distillation of THF from pipe cement.  BE CAREFUL!!  If you are going to do this, be sure to use a blast shield and have a good CO2 fire extinguisher at the ready in case the worst happens. 

Better yet, PM me and I'll hook you up with a company which sells THF cheap, no questions asked.

moo

  • Guest
According to my memory (which is not perfect) ...
« Reply #5 on: June 25, 2002, 01:03:00 PM »
According to my memory (which is not perfect) cheapskate had an accident while reluxing the stuff, not distilling it. It is  a little hard to believe that the THF used in glues would be unstabilised, after all it is intended to be used by non-chemists and has no warning labels about peroxide risk whatsoever (that would be obligatory wouldn't it?). The distillation has been performed straight from the can with a still fabricated from copper pipe, although only approximately half of the THF was distilled. Yes, there might be peroxides lurking in the can, but one could try to apply ferrous salts to the stuff to decompose them. I can't say I'm certain about this, so don't blame me if you get killed :P .

sYnThOmAtIc

  • Guest
peroxides
« Reply #6 on: June 25, 2002, 08:47:00 PM »
Well the glue is not sold to be distilled or refluxed for one. And as far as I know the peroxides are only dangerous when heated so plumbers ans plastic workers are in no danger as long as the product is being used as for what it is made for. Plus the cans do say that they contain flammable toxic solvents and to use only as directed in good ventilation. I highly doubt you could ever hold the company liable after an explosive reaction during a distillation of a product that has no place in your flask.

Chromic

  • Guest
Removing peroxides
« Reply #7 on: June 25, 2002, 11:53:00 PM »
What chemicals, besides FeSO4, can be used to remove the peroxides?

I may just look for another product for the THF, but I'm very interested in getting it OTC.

sYnThOmAtIc

  • Guest
Please
« Reply #8 on: June 26, 2002, 01:15:00 AM »
Chromic, Can you please post any info you have about removing peroxides from THF. If you have any info about nitroethane I'd appreciate it cause smiw believes he should distill it before its long life in the freezer.

starlight

  • Guest
peroxides
« Reply #9 on: June 26, 2002, 10:03:00 AM »
Vogel says you can remove peroxides from THF by:

a) passing through an alumina column
b) shaking with Iron II sulphate.

I'm afraid I'm not sure as to the practicality of these methods with regard to pipe cement as I have never seen it and am not sure of its consistency / viscosity / makeup

Osmium

  • Guest
Just add some motor oil and don't bother about ...
« Reply #10 on: June 26, 2002, 10:55:00 AM »
Just add some motor oil and don't bother about the peroxides. They aren't volatile and will stay behind, being safely diluted with the oil and other high-boiling stuff left in there.

I'm not fat just horizontally disproportionate.

Chromic

  • Guest
Excellent
« Reply #11 on: June 26, 2002, 10:58:00 AM »
Thanx for the ideas. I'll perform the distillation on a water bath as well to minimize my troubles... rigging a still head to the can is going to take some thought...

former_chemist

  • Guest
Use toluene or xylene
« Reply #12 on: June 26, 2002, 11:51:00 AM »
If the mix is too thick use toluene or xylene to thin it.  Both of these will be readily oxidized by any peroxides formed.  Xylene has the higher boiling point so separation should be cleaner.

Hansje

  • Guest
water and salt
« Reply #13 on: June 26, 2002, 01:57:00 PM »
I don't know what the pipe cement they sell around your place is like, but the stuff they sell here can be extracted like this:

1. Add about three quarters of the volume of water to the cement and stir. Be amazed to see that the PVC and all other non water miscible ingredients clot together in a big ball, that, believe it or not, isn't even sticky.

2. Filter everything through a piece of cloth. Wring out to catch as much liquid as possible.

3. Add 400g of table salt per liter of added water and stir. Presto: all organics float to the top.

4. Separate.

5. Distill top layer to get THF, MEK and whatever else is in there that you want.

Hansje high in proteine and fibre!

Cheapskate

  • Guest
Let me verify that
« Reply #14 on: June 26, 2002, 05:13:00 PM »
The procedure above that details adding water to remove the goop from pipe cement works quite well with the materials I have available also.  I never thought of using salt to separate it though, I just distilled the entire mess.

Water did a pretty good job of getting rid of the goop though.

Chromic

  • Guest
Hansje
« Reply #15 on: June 26, 2002, 11:50:00 PM »
Hansje, if this works with the O___y brand of gray cement... I will love you.

Thank you!!!

isop

  • Guest
HOW do you know it really works??
« Reply #16 on: June 27, 2002, 07:01:00 AM »
Hansje,
Have you actually CHECKED that your THF obtained by adding water to kick PVC out of the solution and then salting out the THF really works?

What I am concerned about is that the plastic you see coming out after adding water are only the longest polymers and the short PVC fibers still stay in the solution.

The obvious way to test this would be to vapourise on a glass plate some of the THF obtained in this manner to see if any residue is left.

Hansje

  • Guest
THF
« Reply #17 on: June 27, 2002, 09:39:00 AM »
Chromic: If you have any choice, go for the glue that is used to cement narrow-fitting hard-PVC pipes together. It will be highest in THF and lowest in polymers. Over here that is a clear, tannish, very viscous liquid. The gray stuff (again: over here) is used for wide fittings and has a lot more fillers in it.

isop: Sure, the liquid obtained by the separation is by no means pure THF. But the idea is that you distill it. Collect very little below 66°, a large fraction between 66° and 75°, have some polymeric crap fall out of solution at this point (so yes: you were right about that). Left in the flask is said crap and water, that only faintly smells of solvent. I know this is not scientific proof, but what would your guess be?

Hansje high in proteine and fibre!

isop

  • Guest
OK
« Reply #18 on: June 27, 2002, 11:20:00 AM »
Right, if you perform a distillation at the end of whatever you do, it should be OK. Didn't read your post very carefully  ::)

Chromic

  • Guest
Distilling THF
« Reply #19 on: June 27, 2002, 03:08:00 PM »
Thanks Hansje! Is storing the organic phase over aqueous sodium bisulfite good enough to inhibit peroxides?