Dehydrating agents(for concentrating HNO3)

[rikkitikkitavi]

Well, it is showing up in various threads in this section. So assuming we have a way of obtaining HNO3, how do we get it to 95+ %?

So what means of dehydrating do we have? Im refering to concentrating
68% , aezotropic HNO3. Trying to concentrate lower % acid is only a waste of dehydrating agent, since a simple distillation at atmospheric pressure can give 68 % HNO3 from lower conc.

First idea is H2SO4, which can be reused. This is well proven and might not need distillation under vacuum, if the extraction-route is taken. (se CH2Cl2-thread)

There is also the possibility of using solid dehydrating agents like
CaSO4, CaCl2, Mg(NO3)2 e t c.

I have experimented a bit with CaSO4, but gaining no success. Left was a mushy mix of HNO3-dreanced CaSO4 slowly solidfying. To much CaSO4 is needed to completely absorb all the water.

Industrially, Mg(NO3)2 is used in parallell to the H2SO4 method.

HNO3 of 68 % is mixed with 72 % Mg(NO3)2 and feed to a distillation tower. In the bottom 68 % Mg(NO3)2 is recovered and later reconcentrated under vacuum. At the top 100 % HNO3 is recovered.

This gives that for 100 grm HNO3 68 %, you need 544 grms 72 % solution, yielding 68 grams 100 % HNO3.
This is of course theoretical, losses come in to play in real life. The density of the Mg(NO3)2 solution is roughly 1,4 , so translates to rougly 400ml mixed with 70 ml HNO3.

Is this feasible to do in a labscale?

The Mg(NO3)2 solution will be thick in consistency, I have not a exact value, but a guestimate would be like syrup.

And more important, ideas to dehydrate HNO3 by other means? solids dehydration, extraction or whatever..

/rickard

[vulture]

Mg(NO3)2 could be possible, but using MgSO4 would be easier, since it's more easily available. How much water can Mg(NO3)2 take? I know that one mole MgSO4 can absorb up to 12 moles of water.
Also, does the Mg(NO3)2 dissolve? I'm asking this because when using MgSO4 and if it is added carefully and in excess, it won't dissolve but just fall out of the solution as the hydrate crystal. The nitric wouldn't need (as much) destillation then.

<small>[ August 23, 2002, 01:55 PM: Message edited by: vulture ]</small>

[xoo1246]

It occurs in nature as nitromagnesite( Mg(NO3)2.6H2O ).
I'm also interested in using MgSO4 to dehydrate HNO3 since it's easy to get and may be a good route for those who doesn't have distillation apparatus(?)

<small>[ August 23, 2002, 04:44 PM: Message edited by: xoo1246 ]</small>

[kingspaz]

wouldn't the HNO3 donate H+ to the sulphate ion present in the MgSO4 to some extent? i know it wouldn't very much since sulphate is a much weaker base but it would a little resulting in a minute amount of H2SO4 contamination...if that makes no sense sorry but i'm sooooo tired!

[Pu239 Stuchtiger]

Here's the problem.

MgSO4 + HNO3 ----&gt; MgHSO4(NO3)

MgHSO4(NO3) should be fairly soluble in HNO3. Problems like this are why HNO3 prepared from Ca(NO3)2 and H2SO4 by filtering out the precipitate is going to be heavily contaminated with Ca++ cations.

[Polverone]

Magnesium nitrate is easily prepared. Boil ammonium nitrate solution with magnesium carbonate or hydroxide. It does cling to water very tightly (hey, otherwise it wouldn't be of much use.) I've heated the molten hydrate up to 150 C and it just sat there, looking at me, apparently not doing anything. I'm not sure how hot it would have to get to give up all of its water. My Lange's handbook says that the hydrate decomposes at 129 C, but I don't know if they mean it starts giving up water at that temperature or what. In any case it doesn't give up the water very fast.

[rikkitikkitavi]

I think that anhydrous Mg(NO3)2 is hard to prepare, like anhydrous MgCl2, due to the fact that it has to be heated to such high temperatures that the NO3- ions decompose.

However, it is a solution of 72 % m/m that is used in the extractive distillation.

If you look up "dehydrating agents" in Lange (and CRC) , there is a table of how effective dehydrating agents are compare to each other.

Best is P2O5, H2SO4, CaSO4 e t c. This lead me to believe that
CaSO4 was efficent.

/rickard

[Madog555]

i am getting confused on this. i have read that you can boil down low concentrations up to 68%. can anyone confirm this? thats what a i need to know.

[rikkitikkitavi]

you cant "boil down" nitric acid to 68 % like you can with sulfuric acid.

If you have a HNO3/H2O mix with less than 68 % HNO3 and it boils the vapours will be richer in H2O % than the boiling liquid. But they still contain HNO3.

So the liquid slowly gets enriched in HNO3 until it reaches 68 %. Then the vapour also is 68 %.

So to do this properly , you need a distillation setup with a fractionating coulmn. Like in a still for home made alcohol.

This separates the HNO3/H2O more efficently, so that only H2O comes out at the top until the concentration in the botton reaches 68 % .

Counterwise , above 68 % the vapour given of is richer in HNO3 than the liquid until the concentration in the liquid has reached 68 %.

/rickard

[jimwig]

i haven't tried this yet but sulphuric will suck water like the tijuana whores
will suck the chrome off a bumber hitch. (or so I have been told)

sounds reasonable. mixture of "HNO and HSO" and distill. should be some pretty strong
stuff. don't spill any on your bumber hitch. using vacuum wouldn't hurt. lowers distillation
temperature i figure. clean high test - rrroooooommm!!!

[rikkitikkitavi]

gee, jimwig, that was some useful info ./irony
If I ever go to Tijuana...

/rickad

[simply RED]

You can distil a mixture of Pb(NO3)2 and H2SO4(96%H2SO45, anhydridous lead nitrate) to get 96%HNO3 good enough for hexogen. I made a distiller using a construction similar to "iodine chrystalizer" the nitric acid condenses on the cool test tube and leaks in a beher glass below the test tube.
i'm gonna describe the device when have time...
yu can make the device with a glass jar and polyethylene v shaped "cap' in the jar is put another jar or beher glass to collect the acid
one ay i made 400 ml almost anhydride HNO3...

<small>[ October 18, 2002, 07:19 AM: Message edited by: simply RED ]</small>

[Marvin]

That method will certainly work, and the low solubility of lead sulphate will aid it, but to me it seems something of a waste of lead nitrate. I'm sure I dont have to mention its toxic, but it will decompose to 'nitrous gasses' essentially a mix of NO2 and NO on heating, this would contaminate the acid but can be very useful. The temperature affects the ratio and with the right ratio pure sodium nitrite can be produced from hydroxide or carbonate, and more interestingly ammonium nitrite can be produced. Ammonium nitrite resists most other attempts to produce it, eg a mixture of a nitrite and an ammonium compound generally decomposes to nitrogen and water.

A dehydrating agent for nitric acid that may or may not have been discussed allready is metaphosphoric acid, it can be made easily and its *just* possible a mixture can be obtained consisting of more than one phase. Potentially removing the requirement for distillation.

I will search to see if either of these has been discussed before, and what information I have on the subjects.

[Polverone]

</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica">Ammonium nitrite resists most other attempts to produce it, eg a mixture of a nitrite and an ammonium compound generally decomposes to nitrogen and water.</font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">Truly? That's kind of disappointing. I'd always thought that if I ever wanted ammonium nitrite I'd just mix potassium nitrite and ammonium perchlorate.

[vulture]

Just a side note: Most ammoniumsalts with non metal oxides as the negative polyatomic group are only stable if the non metal has the highest valence to oxygen. Examples: Ammoniumperchlorate is very stable, while chlorate is not, the same goes for bromate/perbromate.
I think this has something to do with the stronger oxidizing properties of the chlorate/bromate versus perchlorate/perbromate.

[simply RED]

"Pb(NO3)2 will decompose in my distilation system"

lead nitrate decomposes in very very high temperature, at that temperatures H2SO4 boils and ecomposes too! The ditilator works on water bath, this is 100 degrees and none of the products decompose, of course some HNO3 turns to nitrous oxides and oxigen but the ditilator is colosed and they form hno3 again... Pb(NO3)2 is not poisonous if not taken very long time, or in very, very high dose, look in its data in the net!!!

Ca(NO3)2 - 1dolar per kilo
H2SO4 96% 2 dolars per kilo
hexamine 2 dolars per kilo
~20 kilos Ca(NO3)2 plus ~15 kilos H2SO4 will produce ~15 kilos 96% nitric acid - 50$
15kilos HNO3 + 2 kilo hexamine = 2 kilo RDX
2 dolars for the silicone paste and you have 2kg PBX... for ~60$
Period of production 3 days (if you work untouched)!!!
(at the same price everyoune can make 5kg plasticized PETN)
I'm gonna prove it if have enough time
:)

<small>[ October 21, 2002, 09:51 AM: Message edited by: simply RED ]</small>

[Marvin]

("Pb(NO3)2 will decompose in my distilation system")

Dont paraphrase with quotes simply RED, use brackets or something else.

You are quite right about the decomposition, I assumed since it could be done in glass containers that it was less than about 350C, its actually about 450C. If your distillation is at 100C then you are doing very well, when I was using sodium nitrate and sulphuric acid my distillation ended somewhere over 250C. If you are willing to have lower yeilds based on sulphuric acid you can reduce these temperatures.

"Pb(NO3)2 is not poisonous if not taken very long time, or in very, very high dose"

Lead nitrate is downright toxic and the MSDS supports this. Though the acute exposure, LD50 is somewhat unimpressive, this is becuase its not commonly relavent, exactly why MSDS sheets dont just rely on these values and in the case of this specific salt often dont contain them. Lead is a cumulative toxin with a very long biological half life, of the order of 20 years. Hydrogen cyanide for example has a biological half life of about 1 hour. This explains why the long term exposure values (eg TLV/TWA) for lead nitrate are lower (by a factor of 20) than cyanide salts.

This doesnt mean that lead nitrite is more toxic than cyanide, but it does mean safe levels of exposure in the long term (even if the actual exposure is acute) is lower for lead nitrate than it is for cyanides.