Sciencemadness Discussion Board

Disposal of (old) THF Still

dapper - 12-5-2009 at 22:03

I want to dismantle a THF still that has been sitting with sodium without much use for more than a year. The side-arm part where it would be when volatile is covered with aluminum foil, the still-pot is not.

I was thinking about dropping in isopropyl alcohol slowly w/ cooling in a hood...with a blast shield?

Need any more precautions betaken?

Panache - 12-5-2009 at 23:35

If those precautions are all taken this will be a perfectly safe method. Using methylated/denatured spirits (~4% water) is recommended by Vogel but i'm always nervous when disposing of small pieces of sodium into wet primary alcohol. A dry secondary alcohol will be quite benign.

Klute - 13-5-2009 at 00:50

Just take your time adding IPA at first, beware as it takes quite long until bubbling stops completly, I usually take a day or two to completly neutralize a large still, dropping IPA slowly, then H2O/IPA mixture, then water, the flask sitting in a ice bath at first.

Nicodem - 13-5-2009 at 01:25

Just never trust that all sodium is quenched based on lack of hydrogen bubbles. Particularly when using isopropanol pieces of sodium can get occluded in the slurry and if you just throw the whole crap into water you may be doing a big mistake resulting in a scary fire (or maybe just the sink blowing up :P ). Rather do like Klute suggested and add some more isopropanol/water when no more bubbling, but leave it standing for a couple of days before dismantling. No hurry, no accidents.

But then... you ain't a real chemist unless you experience a sodium fire. :cool:
... and survive intact.

Hydragyrum - 13-5-2009 at 01:36

Quote: Originally posted by dapper  
I want to dismantle a THF still that has been sitting with sodium without much use for more than a year.

Well... the sodium has had ample time to oxidise a very thick crust. Beware, beware - you'll think it's finished, and then potentially large pieces of Na will be exposed, and if you've already switched to ethanol and/or water and/or acid* you be in for a nasty surprise. :o

* You may be tempted to use acid to clean the crud from the flask after 'all' the sodium has been quenched; just make sure it has been.

[Edited on 13-5-2009 by Hydragyrum]

dapper - 13-5-2009 at 02:14

Thank you all for the excellent replies. Am I in any danger from peroxide formation of the THF?

Hydragyrum - 13-5-2009 at 02:53

Peroxides could be a problem, but if it were me I'd wait until all was dissolved (and I knew the Na was all quenched) and then treat the solution with Na2SO3 or SO2, something like this.

Do not go poking around with a metal spatula when there might be peroxides present in the crusty material - this can trigger an explosion. It is safest to just let it dissolve, no matter how long it takes (you've waited a year already, so don't rush it).

There's probably not too much point adding the reducing agent when there is still more Na present. Hope this helps.

S.C. Wack - 13-5-2009 at 10:54

I've used 70-100% IPA to decompose excess sodium many times, the reaction is very mild at STP for me. I'd just pour a bunch in and let it sit, but then it's not like I've done this on kg scale.

panziandi - 13-5-2009 at 11:21

I usually use IPA instead of IMS. Its cheaper and I feel safer disposing of waste sodium in that over IMS. Then I just waste to drain with plenty of water. Your plan sounds fine to me, Though I would just add the IPA in small portions rather than dripping it in.