Sciencemadness Discussion Board

NaHSO4 from nitric distill

Dre_co - 29-6-2011 at 19:51

I've heard (from a few sources) that it is easier to distill HNO3 with a 1:1-1.5 ratio of h2so4 and NaNO4 (everything remains fluid)


Two questions:

1. What is the best method to check when the reaction is completed?
I will be distilling 70%HNO3 around 120C, will the temp raise as it completes? Or must I observe an irregular dripping of distillate?

2. How to best deal with waste?
I believe I'll be left with a mix of unreacted H2SO4 and Na2SO4.
Is there any way to easily separate the two? Or best to neutralize with baking soda. I don't think I want to flush it down the drain as is.

edit: i beliveve i would be left with sodium bisulfate...correct?


I'll post a complete thread (incl photos) of my process when I begin in the next couple of weeks (if there is any intrest)

Thanks guys.


[Edited on 30-6-2011 by Dre_co]

[Edited on 30-6-2011 by Dre_co]

Mailinmypocket - 30-6-2011 at 04:58

Actually you will be distilling near pure nitric acid (fuming) which usually will be at least 95%, are you adding water to dilute it down to 70%? As for telling when the reaction is complete watch for a reduction of the distillate and also keep an eye for a yellowish/brown gas being formed in the reaction vessel which indicates nitrogen oxides and the end of HNO3 production. I unfortunately don't have a thermometer for my glass set up, so I need to rely on eyeballing it, others may have different suggestions.

Cleaning the residue from the vessel is relatively simple, prepare a large beaker half full of NaHSO4 solution (cold), and allow the reaction vessel to cool. I usually end up with a tough cake of Na/K sulfate to which I add water quickly, and slosh it around to break up the cake, and then proceed to pour into the bicarbonate solution which results in a lot of foaming. Repeat this until all the cake is gone.

As for separating the end products, I am not sure... The mix of acids in it may complicate the process also...

Hope this helps!

Dre_co - 30-6-2011 at 06:43

Thanks, yea, it does help a bit.
Any input is appreciated.

As for distilling 70% I have diluted my H2SO4 down around 70%. This way water will pass across, saving me the trouble of handling RFNA.

I have the exact numbers in my lab, but I also think magpie wrote publication on it somewhere on this forum. I have printed it out, but again it's in my lab.

Rogeryermaw - 30-6-2011 at 07:17

if you add water to the reaction the you are correct, you will distill the azeotropic max which is ~70%. as for the formation of NOx, this is related to the heat used, as HNO3 will decompose under strong heating to give off NOx. on my first attempt to distill nitric acid i used a sidearm flask leading a hose into another flask in ice water. this gave very red, dirty acid. on my second attempt i used an all glass distillation setup with condenser and the coldest, salted ice water i could manage and the formation of NOx was minimal, but still present. there are techniques posted on this site for turning your RFNA into WFNA. not trying to change your mind, but that last 20-25 percent of acid concentration opens up some chemistry not available to azeotropic HNO3. if you do not feel comfortable handling such chemicals, then you should not put yourself at risk.

Dre_co - 30-6-2011 at 16:27

Thanks Rogeryermaw ,

I am wanting to obtain 70%, to further dilute (when needed) for refining silver. at this point i have no need for R-WFNA, although, should the need occur, im just a vacuum pump away from having the full setup needed.

yes ive read this forum from cover to cover (and a few others) and found allot on the nitric distillation process. Because everyones setup is slightly different, i just wanted to check some finer points before starting.

Magpies publication reads as follows:
"As the system heats up it will first fill with brown NO2 gas. This will escape through the vacuum adapter port"
"After a few minutes the generation of NO2 will cease. The vapor temperature at the stillhead will reach and hold solid at 120°C."

"A steady generation of 68% nitric acid will follow. Very little attention is needed until near the end of the distillation. At this time the Claisen adapter will begin to fill with foam. Terminate the distillation at this time."

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

This is the first time i have heard of foaming as a shut of point. is this because of the added water? Magpie was using KNO3, Will it also happen with NaNO3?

Vacuum???

albqbrian - 30-6-2011 at 23:33

Shouldn't this distillation be done under vacuum? And isn't salted dry ice the preferred coolant for the receiving flask?

hkparker - 30-6-2011 at 23:41

How does salting dry ice lower the temperature? Thought that only worked on water as salt is soluble, changes the colligative properties, etc...

Vacuum is good for reducing nitrogen oxide contaminates but isnt nessicary if your making RFNA.

Doesn't matter weather you use Na or K, should behave the same way. Do not use ammonium nitrate however as it will decompose.

hissingnoise - 1-7-2011 at 03:24

Who needs vacuum when you can decolourise RFNA by warming and blowing dry air through it?


Dre_co - 1-7-2011 at 16:04

Good point.
Any one have confirmation that 120C is the correct for distilling 70% HNO3? I would have thought it would be closer to 100C

Rogeryermaw - 1-7-2011 at 19:59

Quote: Originally posted by hkparker  
How does salting dry ice lower the temperature? Thought that only worked on water as salt is soluble, changes the colligative properties, etc...

Vacuum is good for reducing nitrogen oxide contaminates but isnt nessicary if your making RFNA.

Doesn't matter weather you use Na or K, should behave the same way. Do not use ammonium nitrate however as it will decompose.


i have used NH4NO3 with great success making HNO3.

hkparker - 2-7-2011 at 00:43

I have heard mixed results. Some people say it works well, others say it works but has low yields, and some claim disastrous results. I think its all about how you heat it. But because of that I just avoid it.

Dre_co - 3-7-2011 at 20:34

Quote: Originally posted by Mailinmypocket  


Cleaning the residue from the vessel is relatively simple, prepare a large beaker half full of NaHSO4 solution (cold), and allow the reaction vessel to cool. I usually end up with a tough cake of Na/K sulfate to which I add water quickly, and slosh it around to break up the cake, and then proceed to pour into the bicarbonate solution which results in a lot of foaming. Repeat this until all the cake is gone.



Would a CHNaO3 solution work instead of NaHSO4?

Here in Japan, NaHSO4 is a little hard to come by.

Rogeryermaw - 3-7-2011 at 23:31

you can also neutralize with baking soda solution. that is how i dispose of my waste when distilling nitric. also many other processes using strong acids.

Mailinmypocket - 4-7-2011 at 11:42

CRAP, my bad, I meant to say NaHCO3, not NaHSO4

Dre_co - 4-7-2011 at 21:39

Quote: Originally posted by Mailinmypocket  
CRAP, my bad, I meant to say NaHCO3, not NaHSO4


no worries.

thanks :)