Author Topic: PVC polymer extraction from THF  (Read 700 times)

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moo

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PVC polymer extraction from THF
« on: January 14, 2002, 01:07:00 PM »
0.5l of a plastic cold welding liquid was acquired (hereafter referred to as "THF/PVC mix"). The label indicated that the product was 90+% THF and 5-10% PVC polymer. The goal of the tests outlined below was to find out whether it is possible to get rid of the PVC without distilling the liquid.

It would be greatly appreciated if anyone has any insights into this problem as distilling THF is very tricky here for a number of reasons.

Also: Will Ca(OCl2) in a weak acetic acid solution do anything to PVC dissolved in THF? This would be a very useful piece of knowledege!

1) To the THF/PVC mix was slowly added a saturated NaCl water solution in a 1:1 ratio. Two clear, fully separate layers were obtained, the bottom one presumed to be the NaCl solution and upper the THF/PVC mix.

Upon heavy shaking, a large amount of PVC separated as white fibers and immediately three layers formed: a bottom water-clear NaCl solution layer, a middle, fairly thick layer consiting of a bunch of PVC fibres and a top, very cloudy layer of THF (obviously containing some PVC).

Following 30 minutes, around 50% of the fibres from the middle layer suprsingly dropped to the bottom of the flask. 2 hours later the top layer was still as cloudy as before but around 75% of the "fibres" and "flakes" had sedimented to the bottom of the NaCl solution.

Result: it was decided that this method was unsatisfactory in purifying the THF out of the THF/PVC mix.

2) Pure water and THF/PVC mix were mixed in a 1:1 ratio. The solution turned uniformly very cloudy, almost milky and a large bundle of PVC fibres floated to the top. The bundle was picked out and the solution was filtered. The result was still very cloudy (containing short-length PVC polymers) and is hereafter referred to as the "filtered water/THF/PVC solution".

3) To filtered water/THF/PVC solution was added a considerable amount of salt (enough to saturate the amount of water present). This result in two layers, lower one very cloud, upper clearer but its thickness was  1/2 the bottom one. In between was a VERY thin, and OILY emultion layer.

Result: It was very interesting to note that some of the PVC  moved into the the saturated NaCl solution layer, but the THF layer was still cloudy and it missed around 50% of the volumed of the THF. Unacceptable.

4) To filtered water/THF/PVC solution was added xylene in 1:1 ratio. To separate, but very cloudy layers formed with no emultion in between.

5) To filtered water/THF/PVC solution was added acetic acid (10%) so that the amount of pure acetic acid was 1/10th molar ratio of the THF. Following that was added Ca(OCl)2, 3/4th molar ratio of THF at the rate of 1-3 grams per minute  (some 20ml of THF were used). After each addition the temperature rose from 15 to 30-40 degrees Celsius.

After the addition was complete, there was a LOT of precipitate in the flask, probably excess Ca(OCl)2 but also CaCl2. The liquids were decanted and combined with xylene (couldn't find DCM of satisfactory quality). The xylene extract was water-clear but yellow and slightly greenish in color. After 8 hours of standing, the yellow colour disappeared.

Question: What was the yellow greenish color (chlorine?) and why is it gone (did xylene get chlorinated? what is there in the flask now?).

Can anyone suggest a better means of getting rid of the PVC (without distillation) ?

Evaporation of xylene will be undertaken when sufficient tools will be available  ::) .

foxy2

  • Guest
Re: PVC polymer extraction from THF
« Reply #1 on: January 14, 2002, 01:14:00 PM »
I know you said no distillations BUT

You really should distill it!!
Try doing it straight from the can it came in.

Beaware of peroxides if you are storeing THF!!
Look in the sticky thread in methods for a link about THF and using it safely.

I hate my government, does this mean I'm a terrorist??

Osmium

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Re: PVC polymer extraction from THF
« Reply #2 on: January 14, 2002, 01:49:00 PM »
You could try to precipitate the PVC by pouring the solution into an excess of well-stirred cold MeOH. But then you end up with a solution of THF in MeOH, and you have to distill that anyway for separation.

Another idea might be to add the THF dropwise to a well-stirred excess of cold (ice) water. Let the precipitated polymer settle, decant and filter the solution. Maybe this solution can be used in whatever reaction you are planning to do.

But distillation really is the best and easiest method to isolate pure THF.