garage chemist - 30-10-2004 at 11:27
When doing nitrations, do you always water down the acid, extract the product and pour the dilute acids down the drain?
I don't want to waste sulfuric acid, so I'm thinking about how to recover it from spent nitration mix.
With NC, it seems simple: squeeze the acid out of the nitrated cotton, distill remaining dilute nitric acid from it and then boil it down to get conc.
H2SO4 again. The problem here lies in squeezing out the cotton: the fibers hold the acid very tight and it's much harder to squeeze out than
squeezing water out of cotton. You also need an apparatus to squeeze it out. I have a perforated ceramic plate which is perfect for this. The
squeezing is done with the bottom of a jam- jar.
I once tried to squeeze out the NC with my hands wearing gloves: the gloves turned into yellow goo in a few seconds. My bare hands are more resistant
to acid!
With NG, it is also possible to recover all of the H2SO4. When the nitration is finished (all glycerine added and reaction finished) the NG slowly
floats to the top. It takes long, but if you let the mix stand for a few days, the acid and NG separate completely. Just draw off the upper layer (NG)
with a pipette and recycle the acid as described before (NG is insoluble in the acid, so don't worry when you heat it).
These procedures of course only work if HNO3 + H2SO4 is used. With xnitrate + H2SO4, the H2SO4 is lost.
Now, does anybody have an idea about how to recover the H2SO4 from a batch of TNP? The watering down of the acid seems necessary to precipitate the
TNP. But I think that the industrial method of TNP production recovers the H2SO4 somehow. Does someone know how this is done?
JohnWW - 30-10-2004 at 11:47
Just off the top of my head, I think there may be something about it in Ullman's or Othmer's.
budullewraagh - 30-10-2004 at 12:46
you could precipitate barium nitrate then filter out the sulfuric
JohnWW - 30-10-2004 at 13:08
Wrong; adding a soluble Ba salt would result in precipitation of BaSO4 as a highly insoluble powder.
John W.
budullewraagh - 30-10-2004 at 13:43
right. sorry, i was (and still am) really tired and was incorrect. my most sincere apologies are extended unto you
The_Davster - 30-10-2004 at 15:27
That depends, was the TNP made by phenol+sulfuric+nitric or ASA+nitric +sulfuric or ASA + xnitrate+sulfuric. Any of the ASA methods will also have
acetic acid as a contaminant.
unionised - 31-10-2004 at 02:48
" (NG is insoluble in the acid, so don't worry when you heat it). "
OK, but can I worry about the side products instead please?
I havn't tried this but I suspect that ther would be enough other trash present that, at best, you would end up with a lot of nitrous fumes to
deal with .
neutrino - 31-10-2004 at 05:11
Why not just add a nitrate and extract nitric acid? This way, nothing but the H<sub>2</sub>SO<sub>4</sub> should matter.