I've purchased a PTFE thermometer adapter for experiments invoving distilling concentrated Nitric Acid. The adapter contains a rubber ring to secure
the thermometer and create a seal. Will the Nitric acid not attack this ring and cause me a problem of having the thermometer fall into the round
bottom possibly cracking the flask and spilling the contents into my mantle?Magpie - 29-4-2010 at 11:43
I have one of these and use it for making 68% nitric acid. I've had no problems and the rubber O-ring seems to be holding up well.rrkss - 29-4-2010 at 22:18
I'm gonna give it a shot when the rain stops and I can do the work outside. I will use a claisen adapter so if the ring fails, the thermometer falls
into the adapter and not into the reaction flask. Thanks for giving me some peace of mind.Bikemaster - 30-4-2010 at 06:26
I made at least 3 distillation of 96% nitric acide of over an hour and an half with this adapter and I never have problem. It is sure that it will
slowly get ruin, but not in a time of one distillation. And even there, I think that it will only "dry" and the thermometer will fall into the flask.
It will definitely lost some seal over time but it is very easy to change that part if destroyed.Lambda-Eyde - 30-4-2010 at 06:27
The ring is probably made of some sort of elastic fluoropolymer that will resist nitric acid.densest - 30-4-2010 at 11:54
When I distilled sulfuric acid I replaced the o-ring with a teflon (well, some white fluoropolymer) and that ring has lasted for years doing all sorts
of distillations. See http://www.mcmaster.com for an amazing array of parts & tools. Often one can get individual things cheaper elsewhere but the convenience of
having it all there and getting everything in one box with one shipping charge usually wins. Magpie - 30-4-2010 at 20:24
The black O-ring that came with my Ace Glass PTFE thermometer adaptor shows no sign of detioration after making several batches of 68% nitric acid.
In another instance the black O-ring that came with my non-name brand PTFE shaft bearing showed small cracks around the whole periphery after exposing
it to hot bromine/S2Br2/Ac2O several times. I replaced it with a black O-ring from my local hardware store. I'll be surprised if it holds up for
long.
I don't know the composition of any of these O-rings. I think the best overall material would be DuPont's Kalrez (or equivalent). This is a
perfluoroelastomer. DuPont's Viton might also have good overall resistance, but probably not as good as Kalrez. The cost difference of these
materials is very large, however.
I'm gonna give it a shot when the rain stops and I can do the work outside. I will use a claisen adapter so if the ring fails, the thermometer falls
into the adapter and not into the reaction flask. Thanks for giving me some peace of mind.
I had something remarkably similar happen. Same kind of adaptor and, on undoing it to adjust the position, the darn thermometer dropped down a 600mm
vigreux column, snapping a spike off the wall and ruining a nice piece of glass. I wasn't pleased. The claisen head is a good plan.
[Edited on 1-5-2010 by peach]rrkss - 1-5-2010 at 20:39
Well did a distillation of Nitric acid using only H2SO4 and KNO3. The distillation was a failure as the salt slurry foamed so much I could not get
any liquid past the condenser before having to shut down to prevent a problem. The HNO3 did not do any visible damage to the O-ring so that is a good
thing.
One bad thing is I got a drop of concentrated HNO3 on my skin that got past my gloves. Surprisingly, I did not feel a thing and only noticed the HNO3
on my skin due to the yellow color of my skin. Washed it off with water and put on a bicarbonate paste.
Anybody know how long my skin will remain yellow?Magpie - 1-5-2010 at 22:07
Well did a distillation of Nitric acid using only H2SO4 and KNO3. The distillation was a failure as the salt slurry foamed so much I could not get
any liquid past the condenser before having to shut down to prevent a problem.
One bad thing is I got a drop of concentrated HNO3 on my skin that got past my gloves.
Anybody know how long my skin will remain yellow?
For foam control I found it useful to attach a Claisen adaptor to the pot then attach the distillation adaptor. This provides some surge capacity for
the foam. Using a good grade of KNO3 (I use pottery grade) and a decent H2SO4 (like Rooto) also helps.
I believe that yellow will be gone in 3-4 days, IIRC. peach - 2-5-2010 at 15:51
If you're having problems with foam, buy a long distillation column (preferably a vigreux), you can find 600mm columns for $40. A vigreux would be
handy since it'd be more prone to popping the bubbles.
You might also want to consider a 'bump head' for the column, which is basically a bulb shaped thing with the column connecting at the base and a
nozzle from the column pointing downwards in the bulb. There is a vent at the top that the vapors pass out through. Any big bumps, or foam, will then
end up trapped in the bulb before they can get through to the condenser.
A further suggestion on that note would be to fit some form of wash bottle arrangement between the column and condenser, filled with something that'll
allow the vapors to pass by that'll catch the foam. Basically, a bump head. May as well go straight for the latter.
You could also consider adding something to the distillation flask to knock the bubbles on the head. Foaming is a problem in chrome plating baths.
They drop a whole load of things that are essentially ping pong balls into the bath to kill the bubbles. Obviously, ping pong balls might not be a
good choice for what you're up to, but you might be able to apply some innovation and come up with something fitting. If I could suggest an
alternative I would, but I can't.
[EDIT] Yes I can, try packing the column with broken glass. Anti-bumping smashed up glass, which is essentially finely broken glass, may work even
better. If you can't buy it, put some normal broken glass in a coffee grinder. Loosely plug the ends of the column with something inert, like glass
wool. You could use the same packing in a bump head, perhaps even glass wool alone.
[Edited on 3-5-2010 by peach]Chainhit222 - 3-5-2010 at 13:43
I have a threaded Teflon thermometer adapter from united glass tech with a o-ring (also I assume this to be Teflon). It experienced no sign of
deterioration from distilling nitric acid under a vacuum. However, I believe when I was trying to distill sulfuric acid under vacuum it got too hot
and started to sag (it is slightly bent out of shape). It still holds an airtight seal, but it is worth noting. Fleaker - 3-5-2010 at 14:26
What's wrong with teflon tape?Panache - 6-5-2010 at 09:07
loosely packing teflon wool (made from drilling/machining teflon) into the entire flask, claisen head and stilhead does an excellent job generally of
reducing foaming and bumping. If there is a commercial plastic CNC mob around your area call and ask them for some teflon swarf (don't know if this
spelling is correct, it's just how its pronounced), they often happily accumulate and give it away. Polypropylene would also work fine but the
additives might be problematic.
I have never distilled nitric so i am just suggesting what i would try, not that i know this works. Silicon oil from an oil bath often does a good job
as an antifoam at around 1%.
As for the original question i believe most of the rubber rings in thermometer adaptors are silicon rubber, fairly inert and high temperature. They
also have a teflon sleeve that minimises contact.
Not to be annoying but an o-ring is not an o-shaped ring (this would be a tautology), rather the o refers to the cross-section. The rings on
thermometer adapators would thus be called square-rings.
