Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: Question about PTFE Thermometer Adapter
rrkss
Hazard to Others
***




Posts: 193
Registered: 18-12-2009
Member Is Offline

Mood: No Mood

[*] posted on 29-4-2010 at 11:02
Question about PTFE Thermometer Adapter


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?
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 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.



The single most important condition for a successful synthesis is good mixing - Nicodem
View user's profile View All Posts By User
rrkss
Hazard to Others
***




Posts: 193
Registered: 18-12-2009
Member Is Offline

Mood: No Mood

[*] posted on 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.
View user's profile View All Posts By User
Bikemaster
Hazard to Others
***




Posts: 120
Registered: 8-10-2008
Member Is Offline

Mood: No Mood

[*] posted on 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.
View user's profile View All Posts By User
Lambda-Eyde
International Hazard
*****




Posts: 856
Registered: 20-11-2008
Location: Norway
Member Is Offline

Mood: Cleaved

[*] posted on 30-4-2010 at 06:27


The ring is probably made of some sort of elastic fluoropolymer that will resist nitric acid.
View user's profile View All Posts By User
densest
National Hazard
****




Posts: 359
Registered: 1-10-2005
Location: in the lehr
Member Is Offline

Mood: slowly warming to strain point

[*] posted on 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.
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 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.

For purchasing individual Viton or Kalrez O-rings:
http://www.sisweb.com/vacuum/o-rings/viton.htm

[Edited on 1-5-2010 by Magpie]

[Edited on 2-5-2010 by Magpie]




The single most important condition for a successful synthesis is good mixing - Nicodem
View user's profile View All Posts By User
peach
Bon Vivant
*****




Posts: 1428
Registered: 14-11-2008
Member Is Offline

Mood: No Mood

[*] posted on 1-5-2010 at 06:24


Quote: Originally posted by rrkss  
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]
View user's profile View All Posts By User
rrkss
Hazard to Others
***




Posts: 193
Registered: 18-12-2009
Member Is Offline

Mood: No Mood

[*] posted on 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?
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 1-5-2010 at 22:07


Quote: Originally posted by rrkss  
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.

http://www.sciencemadness.org/talk/viewthread.php?tid=13090

I believe that yellow will be gone in 3-4 days, IIRC.




The single most important condition for a successful synthesis is good mixing - Nicodem
View user's profile View All Posts By User
peach
Bon Vivant
*****




Posts: 1428
Registered: 14-11-2008
Member Is Offline

Mood: No Mood

[*] posted on 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]
View user's profile View All Posts By User
Chainhit222
Hazard to Others
***




Posts: 138
Registered: 22-8-2009
Location: peach's mailbox
Member Is Offline

Mood: grignard failing to start

[*] posted on 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.



The practice of storing bottles of milk or beer in laboratory refrigerators is to be strongly condemned encouraged
-Vogels Textbook of Practical Organic Chemistry
View user's profile View All Posts By User
Fleaker
International Hazard
*****




Posts: 1242
Registered: 19-6-2005
Member Is Offline

Mood: nucleophilic

[*] posted on 3-5-2010 at 14:26


What's wrong with teflon tape?



Neither flask nor beaker.


"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
View user's profile View All Posts By User
Panache
International Hazard
*****




Posts: 1290
Registered: 18-10-2007
Member Is Offline

Mood: Instead of being my deliverance, she had a resemblance to a Kat named Frankenstein

[*] posted on 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.


SO GET IT RIGHT NEXT TIME YOU IMBECILES, GOD!!




View user's profile View All Posts By User

  Go To Top