HNO3 by desiccation

[Microtek]

Has anyoen tried this?
I'm running an experiment with desiccation of 62% HNO3 by CaCl2, but the container isn't entirely airtight.
I also considered using H2SO4. I can see that the CaCl2 has absorbed some moisture, but I don't know if this is from the HNO3.
Any thoughts ?

[tvs17]

This is possible. Although it is not as effective as the destillation with H2SO4.
And I am also doubting if CaCl2 is a strong enough dehydrator.
I've tried it in a dessicator under vaccuum with CuSO4 and Mg(NO3)2. This works fine. You could also just put some quantity of Mg(NO3)2 in HNO3 (if you have this offcourse), which also works fine, and then distilling the mixture.
But I do think you will have to make a well closed desscator else it is not very effictive as you say already..

[Anthony]

A while ago, I remember reading an idea about putting an insoluble dessicant into the HNO3 and then filtering it out. It might have been plaster, but my memory is like a sieve but without the solid material seperating the holeshttp://theforum.virtualave.net/ubb/smilies/smile.gif

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"Shit happens. Get a fucking helmet"

[Microtek]

Do you have any ideas on the concentration you can reach with, say, H2SO4?
The advantage is of course that you don't need an expensive vacuum-distillation setup, and the H2SO4 could simply be reconcentrated by boiling.

[mongo blongo]

What about sillica gel? I dont think it would react with the HNO3!

[a_bab]

I also saw a post wich indicate plaster as a dessicant for HNO3, but the plaster is somewhat porous after water absorbtion and this will cause a lose of nitric acid; I am thinking about some dehidrated copper sulfate; what about it ?

...Hmmm... is not the best idea. It will not react with the nitric acid, but it will be disolved by the acid...I guess that plaster (or silicagel) are the best ideas. I have the idea with copper sulfate from a month, but I realize only now that is not good at all (maybe because I'm EXTREMLY tired ?)
OK. Going to bed.


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Damn, I got a nitro-headache again...

[tvs17]

Why does everyone always say HNO3 has to be made with vaccuum destillation? Yes, I know, the HNO3 will decompose at temperatures around 80 dC. And that's why you lower the boiling point by reduced pressure, so it does not reach that point. This is also confirmed by the literature.
Previously I always made it under vaccuum. It worked just fine, except that my precious vaccuumpump is just being destroyed by this(yes, I do lead the gas to several neutralising washing bottles). So I decided to try without vacuum.
I start from 40% HNO3 which I mix with 2 parts conc H2SO4. I distill the HNO3 at a temperature between 80-100 dC. Then I distill it two more times with 1:1 HNO3/H2SO4. Last time with urea. The final product was always around 98% or more(confirmed by titration).

Decomposition of HNO3 is something like this:
HNO3 <---> H2O + NO2

And yes, there is more NO2 formed than compared with destillation under reduced pressure. But after the first 20 ml or so have come over the NO2 production also reduces(because the temperature is rised??).

Well, maybe the equibrillium comes more to the left when the temperature rises? But that sounds not extremely likely.
Or the formed H2O is immediately bonded by the H2SO4?

[tvs17]

Does no one has any thoughts or opinions in the method of HNO3 destillation I use?

[Microtek]

Dammit! I had just written at some length about my experiments with nitric acid destillation, but forgot to type in my PW before submitting. This erased the entire text, so here is a somewhat shorter version:

How to purge NOx gasses from the acid? I've tried adding a little urea and also bubbling air through it, and I can't seem to get these methods to work.

Did you know that aluminium is compatible with nitric acid ?
My destillation setup is made with Al tubing and foil and the only effect on the Al is that it forms a thin oxide layer ( and on most tubing this has already occurred).

[Nitro]

Microtek I ve read somewhere they bubel co2 in the nitric acid to bind or decompose the nox.(industrial methode)

[EventHorizon]

I thought that was pure aluminum and that alloys would not work. I could be wrong tho.

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-The world is a dangerous place to live, not because of the people who are evil, but because of the people who don't do anything about it.- Albert Einstein

PGP ID 0x147CEF54

[10fingers]

Aluminum is impervious to nitric acid at lower temperatures. I once tried to make a distillation condenser out of aluminum but the warm nitric acid vapors started to react with it.
I also tried the addition of calcium sulfate(gypsum) to try to remove water from nitric but it did not work.
I have seen bits of info around about using phosphorous pentoxide to remove the water. I'd like to get some more information on this to see if it is feasible.
I just bought one of those vacuum aspirators which connect to your water faucet. I'm quite surprised at how well it works. It's ideal for distilling acid since no vapor traps are required. Any vapors are mixed with water and sent down the drain. It will pull down to 28 inches of vacuum. Cost only $10.00.

[EventHorizon]

How long does it take you to distill your acid, its been a while but as I recall it takes quite some time, like an hour or two, and running water for that long may be a problem or would be costly for someone on a municipal system.

Anyone had success by using an aspirator and a recirculating pump. I made a condensor coolant pump from a 5gal bucket and a bildgepump that works great and I've been thinking about attaching some sort of water pump to a 12V source and rigging the aspirator into a closed loop system but I don't know if it would deliver the kind of pressure and volume of water required by an aspirator.

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-The world is a dangerous place to live, not because of the people who are evil, but because of the people who don't do anything about it.- Albert Einstein

PGP ID 0x147CEF54

[10fingers]

That's a good idea. I was thinking of something similar to that. You could take a cooler and fill it with ice and water and put your pump in it. Then take the output of your aspirator and run it through the condenser and back into the cooler. I could do it out in the garage then, my wife doesn't appreciate my chemistry work in "her" kitchen.
It usually takes a couple hours to distill 2 or 3 hundred ml's. I like to do it at low temp to cut down on the NOx.
If your only criteria is cost, the cost of water is cheap, it would cost more to run a small electric motor for the same time period.




[This message has been edited by 10fingers (edited September 27, 2001).]

[tvs17]

Why are you ignoring my post? As I've said, I distill my HNO3 *WITHOUT* vaccuum. After two to three destillations starting with 40% HNO3 mixed with conc H2SO4, I always obtain 96-98% HNO3.
I know in literature is stated that you should use vaccuum for reasons I would believe also, but the method I use DOES work.
I use it for RDX, DNU and other nitrations who require highly conc. HNO3, and it just works...
Removing NO2 with urea works perfectly, you just have to shake a little or maybe heat it up a bit.
Dehydratation of HNO3 with P2O5 is a frequently used method for the synthesis of N2O5, which is also a nitrating agent.

[10fingers]

Well for one thing you can distill faster with vacuum.
And believe it or not you're not the only one on this thread that has information to share.

[tvs17]

I'm sorry if I did come over a little...(don't know the word).

But I just find it very strange that many people are trying to find all kind of ways for constructing vaccuum systems or protections for the pump while it just perfectly works without vaccuum!
And I also find it strange that this point is just being ignored by everyone.

Well, for the destillation speed I would not say this is a very large difference. In fact I did not see a significant change in speed in my experience.

[EventHorizon]

I'd rather obtain high conc. HNO3 from one distillation and preferably in less time then from 2-3 distillations.

No one is doubting you tvs17 nor ignoring your post, just offering suggestions on ways to improve the process.


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-The world is a dangerous place to live, not because of the people who are evil, but because of the people who don't do anything about it.- Albert Einstein

PGP ID 0x147CEF54

[tvs17]

I'm starting from 38-40% HNO3, so that needs more destillations. If you start from high percentages like 68% you need less destillations. Some time ago I always made my HNO3 by the same method starting with 68%.. One destillation with H2SO4 is sufficient then for things like RDX. For synths where products are easily hydrolized you maybe need to distill one more time...

And it isn't a bad idea anyway to distill twice even when you're using vaccuum. For example you can often read in journals that they redestil their commercial 98% HNO3 one more time before using it..

Glad I'm not being ignored http://theforum.virtualave.net/ubb/smilies/smile.gif. But I was just a bit perplex that just nobody said anything. I would think this is quite important for some people here since not everyone has a pump...

[10fingers]

No TVS17, you have a good point. It does work without vacuum if you keep the temp low. I've found it takes two distillations from H2SO4 to get a reasonably water free nitric acid. With vacuum I can do it in one. The reason I mentioned the aspirator in this thread is because there has been a lot of discussion on this forum about different types of vacuum pumps for distilling acid. Many people have said that the aspirator did not work very well. I also did not think that for the cost that it would work very well. After trying one I must say that it is ideal for distilling acid. And for the cost anyone can obtain one.
I'm interested in trying the phosphorous pentoxide method too. I have to get some phosphorous to make it though.

[Microtek]

Tvs17: How much urea do you add, and what colour does the acid end up?

I don't use vacuum either and have quite little NOx evolution. I distil on an ethylene glycol bath placed on an inverted iron ( the household appliance ). The heat is only just sufficient to let the nitric get into the Al pipe which is cool to the touch 15 cm from the flask. I get about 35 g nitric from 60 g AN and 50 mL H2SO4.
This acid is concentrated enough to yield 4.6 g MHN from 2.0 g mannitol.

[tvs17]

Microtek,
Well I don't know exactly how much I add.. I just throw in some, heat a little and shake. It should be just colourless or close to it.

Why don't you try to find out the concentration? Well, if you have a buret.. And if you have an accurate scale and some volumetric glassware you could also measure density.

10fingers, I wouldn't spill any precious phosphorus on making P2O5 for HNO3 dehydration except if you want to make N2O5.. But N2O5 isn't really an extremely powerful nitration agent and as far as I know it is mostly used in very selective nitration reactions.
BTW, I'm working on a method for synthesizing nitroniumtetrafluoroborate(NO2BF4), this is a very powerfull nitrating agent as you may know..

[cutefix]

Nitrogen pentoxide is a powerful oxidizing agent,it is more practical to use and had been used longer if compared to nitronium tetrafluoroborate which is good only for laboratory use in pioneering work for synthesizing new products.NO2BF4 is a respectable material,and it was due to it that HNIW, bicyclo HMX and other exotic materials came to existence,but when practicality was the concern, such as in large scale synthesis nothing beats the N2O5 which is easier to prepare and cheaper than the fluoroborate material.I think nitrogen pentoxide enriched HNO3 is used in high efficiency synthesis of HMX,TNGU, and even CL-20. and a lot of other energetic materials.
It is more easier to prepare the N2O5 than the NO2BF4 in the lab.Just add P2O5 to HNO3 and you have it,while these fluoroborate will need a lot of ingredients such a boron trifluoride,anhydrous hydrogen fluoride or fluorine,nitromethane or ethyl nitrate(depending on what process you use).It is a complicated process which include intensive reagent purification(removal of SiF4,moisture) more complex equipment such as high vacuum etc and other special apparatus in its preparation.If I am working in the lab and would need it, I would rather buy it.There are many suppliers like Acros,Alkemi and Interchem,that can provide reagent quantities.
On the other side it is interesting to know about new developments related to its synthesis and other potential application.I hear that it is useful also for pharmaceutical synthesis ,but I think it does not concern us here.

[EventHorizon]

I'll..umm...post this stupid question. Would molecular seives work. I know nothing about them, only that I've read somewhere that they work for pulling water out of solutions. I could be completely wrong tho.

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-The world is a dangerous place to live, not because of the people who are evil, but because of the people who don't do anything about it.- Albert Einstein

PGP ID 0x147CEF54

[tvs17]

Well, it all depends on the use you have in mind.
As you say NO2BF4 is an interesting compound for research in preparation of novel compounds but not really interesting for the "production" or something like that.
N2O5 has its advantages but also disadvantages. For example the reactionmechanism for nitration reactions with N2O5 is stronly dependent on temperature, solvent etc. Slight changes in these factors can easily change the obtained product. An advantage could be for N2O5 that you can use many polar and apolar solvents. For compounds who are not resistant against acids this could be very useful.
But I think mixed acid is in most "standard" nitrations just the best reagent if possible.
I agree with you that N2O5/HNO3 mixtures are particulary interesting while N2O5 is completely converted to the nitronium ion.
In my previous post I was not really comparing NO2BF4 and N2O5.. Sure, N2O5 has many advantages above NO2BF4, but the NO2BF4 can be very interesting for prepararion of some novel compounds..
Regarding to NO2BF4, yes it's nasty, very nasty. I have an article of NO2BF4 synthesis. They lead anhydr. HF and BF3 in an solution of HNO3 in DCM. The reaction is not complicated, but the dangers involved with HF and BF3 are not very nice. No need for vaccuum in this synthesis. Also a reasonably pure product is obtained from this reacton, free of NOBF4. If I could order it I would, but I am not in the position of working in a lab. Just high school..
(Edit: some typing errors..)

[This message has been edited by tvs17 (edited September 30, 2001).]

[Microtek]

I read in alt.engr.explosives that you need 1 g urea per 200 mL nitric. BTW, I tried adding urea to a small sample of my nitric and then bubbled air that had been dried with CaCl2 through it. It only got slightly less yellow, but I decided to try it anyway, figuring that the yellow colour could be some other substance. So I used the rdx procedure from mega's site, and upon addition of water to the solution, a white powdery precipitate instantly appeared in the beaker. After washing, neutralizing and drying it weighed 1.0 g. I had used 0.5 g hexamine for the experiment, and some excess of acid. The product behaved exactly as rdx is supposed to.

[tvs17]

For RDX it is not really necessary to remove nitric oxides.. Maybe the yield is a bit reduced by this, but I did notice this.

[10fingers]

Microtek, it takes me about 1/2 hour of bubbling dry air through the nitric acid to get it to clear up. I take about 200 ml's and warm it up to about 50 C, add a pinch of urea at a time, bubble dry air for a couple of minutes, if not clear add another pinch, etc. until it clears.
How much urea you have to add and how long it takes depends on how much NOx you have in the acid to begin with. I have noticed that you cannot tell by how orange the acid is at room temp, if there is lots of NOx it will darken upon warming.
I have seen conflicting info on whether or not NOx is a problem for RDX.