Nitric acid distillation

[Noxx]

Hello guys,
I'm currently trying to distillate some nitric acid. I would like to know what temperature I must get in order to evaporate the nitric. Currently, my solution is boiling and the vapours are at 110C. I made my nitric using KNO3, a bit of water and Sulfuric acid.

Thanks in advance.

 

[lazersteve]

Noxx,

68%/32% HNO3/water azeotrope boils at 120.5 C.

You should be using dry KNO3 and 98% H2SO4 for the reaction.

The receiving flask should be in an ice bath.

Be sure your glassware rig joints are tightly sealed and don't use any rubber stoppers or tubing. I teflon tape my joints when distilling.

Steve

 

[Noxx]

In the beginning, I tried with KNO3 + H2SO4 with no water and it gives a lot of NO2. So I added some water and it almost stopped.

I don't really mind if there is water in my nitric, I want to get about 40% nitric acid, but I want it Chlorine free !

Also, I'm using rubber stoppers for the moment... I know they aren't the best but they don't seem to be eaten that much by the acid.

I'm doing the distillation under a fume hood BTW.

Thanks

 

[lazersteve]

Noxx,

If you wrap the stoppers in a thin layer of teflon tape (plumbers type) you can prevent them from failing so fast. The rubber could fail and allow hot NOx or HNO3 fumes out!

Steve

 

[Lou]

Nitric of high strength will tear apart those stoppers, most of which are made from neoprene rubber. Also, the azeotrope will not distill over if you follow:
KNO3 + H2SO4 --> HNO3 + KHSO4. Instead you will get red fuming nitric acid, which is a pain to deal with giving your limited home setups. Unnecessary risk. Rather, distill with a small amount of water.


My suggestion to you is that you vacuum distill it in the dark; that is what I do and it prevents decomposition due to light and heat. This means your nitric, even if distilled to a high concentration, will be colourless and of good quality.

A vacuum pump that you should have, and that I highly recommend is that made by KNF Neuberger. It will resist nitric acid, aqua regia, chlorine fumes and serve you happily for many years. Use that to distill it, use the pump also for vacuum filtration. That is what I do; I have several pumps and I plan on getting more.

 

[Noxx]

I will try with the Teflon next time, thanks.

Lou, I'm looking for a vacuum pump since a while on eBay for my vacuum filtrations and possibly for vacuum distillation but they seem to be very expensive so I ended up with an hydro aspirator powered by a drill pump lol.

 

[Lou]

You can improvise your own aspirator with PVC tubing and a garden hose.

Those pumps cost about $300 on ebay, about 1/4 of what normally they sell for.