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Petn1933
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My problem with pure fuming hno3
I got 2 liters of 95% nitric from one of my friends. To test it, I synthesized some petn, but after 4 tests, I failed each time for one reason, and
that was a sudden rise in temperature. I cooled 50 cc of nitric acid to -18 and placed it in an ice water bath. Then I added the dried and ground
pentaerythritol in a very small amount. But after adding 2-3 grams of pentaerythritol, the temperature of the acid rises and reaches from 2c to 15c
in 2 to 3 minutes. During this time no pentaerythritol is added and the whole acid is mixed by a magnetic stirrer. My pentaerythritol is 99% pure
and fresh, and nitric acid seems to have all the properties of 95% nitric acid (it burns latex gloves). What do you think is the problem? Why does
the temperature rise without the addition of pentaerythritol while being mixed by a magnetic stirrer?
Have any idea?
Thank you
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mackolol
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When making energetic materials especially nitrations, always cool them during the reaction.
Even if you cooled your HNO3 to -42C (at which I doubt that the reaction would be significant), the temperature will eventually rise, because they are
very exotermic. And the warmer the reaction is, the faster will it be and it will produce more heat.
You must cool it during the reaction for example in salted ice. And to be honest 2-3 grams pentaerythritol at once is quite much. If you don't cool
it good enough and don't wait between portions you can cause an explosion, resulting most probably in serious injuries.
There is no problem with your HNO3, rather with how you perform this reaction
[Edited on 9-5-2020 by mackolol]
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Petn1933
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Yes, it is important to keep the temperature as low as possible. But maybe I'm wrong, I didn't say add 2 grams of pentaerythritol at a time, I added
a maximum of 2_3 grams in a few steps in small sizes.
I have experienced a synthesis of petn by 95% nitric acid but this is the first time that despite all the conditions for cooling the acid mixture.
The temperature rises uncontrollably.
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Fulmen
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It's a bit counter-intuitive, but cooling components too far below the desired reaction temperature can cause this. The low temperature slow down the
reaction too much, so by the time it has risen enough for the reaction to take off you have already added far too much and the reaction goes runaway.
The proper method is to start closer to the desired rx-temperatue. This might even require pre-heating (told you it was counter-intuitive).
We're not banging rocks together here. We know how to put a man back together.
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Petn1933
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Quote: Originally posted by Fulmen  | It's a bit counter-intuitive, but cooling components too far below the desired reaction temperature can cause this. The low temperature slow down the
reaction too much, so by the time it has risen enough for the reaction to take off you have already added far too much and the reaction goes runaway.
The proper method is to start closer to the desired rx-temperatue. This might even require pre-heating (told you it was counter-intuitive).
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In your opinion. I have to start making petn at a temperature close to 0 to have more control over the temperature rise?
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Fulmen
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Correct. You could even start with room temperature acid and let it cool down in the cooling bath. This way you get a sense of how efficient your
cooling really is.
We're not banging rocks together here. We know how to put a man back together.
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Tsjerk
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You haven't been too clear about whether you are actually cooling the reaction, externally, while adding the PE. My guess is you are not.
And my second guess is that your guess about what Fulmen is saying is correct. I also think this is one of your problems. You can't expect a reaction
to stay below a certain temperature just by cooling the reactants while the reaction is exothermic.
Also have a look at the amount of energy it takes to get water from, example given, -18 to 0 degrees and the amount of energy it takes to get water
from -9 (frozen, ice-bath) to +9.
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Petn1933
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| Quote: Originally posted by Tsjerk | You haven't been too clear about whether you are actually cooling the reaction, externally, while adding the PE. My guess is you are not.
And my second guess is that your guess about what Fulmen is saying is correct. I also think this is one of your problems. You can't expect a reaction
to stay below a certain temperature just by cooling the reactants while the reaction is exothermic.
Also have a look at the amount of energy it takes to get water from, example given, -18 to 0 degrees and the amount of energy it takes to get water
from -9 (frozen, ice-bath) to +9. |
Your second guess is correct. I can't keep the acid temperature below the critical temperature.
After Fulmen said, I noticed that due to the low temperature at the beginning of the reaction a large proportion of pentaerythritol does not react.
perhaps the reason for this lack of attention is that I mostly use the second method for synthesis(hno3 65%-h2so4 98%), and in the second method I
start from a temperature below 0.
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Petn1933
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If the reaction is not caused by a failure to control the temperature, is it possible that the nitric acid is impure?
how to ensure its pure?
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Tsjerk
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For a start I would assume the nitric acid is pure (if colorless or only slightly yellow) and use proper cooling during the reaction.
Water and a lot of ice is standard in any nitration, using salt is optional.
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Petn1933
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| Quote: Originally posted by Tsjerk | For a start I would assume the nitric acid is pure (if colorless or only slightly yellow) and use proper cooling during the reaction.
Water and a lot of ice is standard in any nitration, using salt is optional. |
This is my hno3
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Tsjerk
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Ah, yes, of course... It is 95%+.
That will, most of the time, be yellow/orange. But again; did you cool the reaction while running it?
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Fulmen
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According to the first post he used an ice bath. That should be sufficient as long as one is patient and can tolerate temperatures up to say 3-5°C?
Trying to maintain a reaction at the cooling bath temp is hard, heat transfer requires a temperature difference and glass is a poor conductor. So I
would use a cooling medium at least 5° colder than the maximum allowable temp.
As for the acid, this synthesis is supposed to be sensitive to nitric oxides. I'm not sure what the problem is, but if it oxidizes the reagents or
product it could increase the heat output significantly. This might explain the different results with the 95%, was that acid clear?
The standard fix for NOx is to add a little urea and pass dry air through the acid. But it might not be necessary with better temperature control.
We're not banging rocks together here. We know how to put a man back together.
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Petn1933
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| Quote: Originally posted by Tsjerk | Ah, yes, of course... It is 95%+.
That will, most of the time, be yellow/orange. But again; did you cool the reaction while running it? |
Yes . Throughout the reaction, the acid container inside the bath was ice water
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mackolol
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As far as I remember there is no need to use RFNA in pentaerythritol nitration and you can do it using regular 65% HNO3/ 90%< H2SO4 mix. I did so
when I performed this synthesis.
Especially if it is sensitive for Nitric Oxides. Do you have preparation of PETN that uses RFNA?
Good synthesis of energetic material that uses 95% HNO3 is synthesis of RDX.
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Petn1933
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| Quote: Originally posted by Fulmen | According to the first post he used an ice bath. That should be sufficient as long as one is patient and can tolerate temperatures up to say 3-5°C?
Trying to maintain a reaction at the cooling bath temp is hard, heat transfer requires a temperature difference and glass is a poor conductor. So I
would use a cooling medium at least 5° colder than the maximum allowable temp.
As for the acid, this synthesis is supposed to be sensitive to nitric oxides. I'm not sure what the problem is, but if it oxidizes the reagents or
product it could increase the heat output significantly. This might explain the different results with the 95%, was that acid clear?
The standard fix for NOx is to add a little urea and pass dry air through the acid. But it might not be necessary with better temperature control.
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maybe my words be funny
but
Is it possible for the reagent to be decomposed by acid?
That is, due to the presence of no2 gas, the pentaerythritol decomposes during acid entry?
This is the reason for my statement, When the temperature rose uncontrollably and I poured the acidic contents into the cold water There was no sign
of a small amount of petn in the water.
Anyway, I added some pentaerythritol to the acid, so at least some of it shouldn't have turned into petn?
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Petn1933
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| Quote: Originally posted by mackolol | As far as I remember there is no need to use RFNA in pentaerythritol nitration and you can do it using regular 65% HNO3/ 90%< H2SO4 mix. I did so
when I performed this synthesis.
Especially if it is sensitive for Nitric Oxides. Do you have preparation of PETN that uses RFNA?
Good synthesis of energetic material that uses 95% HNO3 is synthesis of RDX.
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Yes, you are absolutely right. But I want to fully understand the reason for this with your comments and those of other friends. Well, the way you
mentioned is more economical
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Microtek
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I would say that there is way too much NOx dissolved in the acid. You get too much oxidation that way. You should purge the acid by blowing DRY air
through it at ca. 50 C until it becomes almost colourless. You can also add urea (also at 50 C), but with the amount of NOx in your acid, the
byproduct water will dilute it appreciably.
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MineMan
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How do you blow dry air through it without spraying acid everywhere?
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mackolol
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I have done it with aquarium bubbling pump, in erlenmeyer flask.
It was splashing, but the flask was few times bigger than volume of the acid so acid drops were kept inside the flask.
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Petn1933
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| Quote: Originally posted by Microtek | | I would say that there is way too much NOx dissolved in the acid. You get too much oxidation that way. You should purge the acid by blowing DRY air
through it at ca. 50 C until it becomes almost colourless. You can also add urea (also at 50 C), but with the amount of NOx in your acid, the
byproduct water will dilute it appreciably. |
Should dry air be blown into acid? Or its optional
Because ican't make dry air now
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Microtek
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As I said, you can add urea instead of using dry air. The reaction is something like this:
4CO(NH2)2 + 6NO2 -> 4CO2 + 8H20 + 7N2
So, if you had 100 grams of nitric which contained 10% NO2, you would produce a little more than 5 grams of water, taking the concentration down to
below 95%. I don't know how much NOx is in your nitric, but looking at the colour of the gas above the liquid, I would say close to saturated (I don't
have exact numbers on what that is).
Dry air can be accomplished by using an aquarium air pump to pump air through a jam jar or tube with CaCl2, H2SO4 or other effective dessicant (I
prefer CaCl2 scale - it is cheap and not as messy as sulfuric acid). Then lead the air through a bubbler, into the acid. I use a polypropylene single
use pipette that I poke holes in with a needle, but numerous other methods could work as well.
The de-NOx-ing should be carried out at 50 C whether you choose the urea method (otherwise the reaction will be too slow) or the dry air method
(otherwise the solubility of NOx in the acid will be too high).
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DennyDevHE77
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Microtek, I have many times purified the distilled acid from nitrogen oxides with urea. But always cooled down to 10-15C. I used regular urea from the
fertilizer store, in 2-3mm granules. But the one time I tried to do it at room temperature, the nitric acid heated up quickly and the nitrogen oxides
only got bigger. As I guessed, the urea probably turned into urea nitrate. However, following your words, this could not be the case. Maybe I confused
urea with something else....
By the way, what do you think about removing nitrogen oxides with aminosulfamic acid (descaler), some people wrote that it is more effective than
urea.
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Etanol
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Use dry urea nitrate, not urea.
However, in my experience, neither urea nor nitrate ammonium nor hydrogen peroxide operates in acid more than 90%. They work only in the average
concentration HNO3.
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DennyDevHE77
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Well, that's how I clean 95% nitric acid. With urea. The nitric acid went from yellowish red to greenish. But it didn't turn clear as a teardrop.
Still, it was enough to comfortably make PETN. So it is probably necessary to always specify what is meant by cleaning.
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