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[*] posted on 29-5-2019 at 02:20
Chemistry behind RDX


Hello,
I'm interested in the chemistry behind explosives and their synthesis in general. In particular I want to know more about the synthesis of RDX from methenamine + HNO3 and the reasons behind all the temperature adjustments during its synthesis or how impurities affect the synthesis (eg NOx concentration, presence of sulfates or other salts, etc).

It's likely that there is already a thread with all this information, but looking for it proved to be difficult, considering the huge mole of forum posts on this subject. Most posts are about the procedure or cook recipes, without an in-depth explanation of the reasoning behind all those parameters or any "science" in general. So I want to know more about the "why"s rather than the "how"s.

1) Patent US2859215A on RDX synthesis gives a temperature range between -10 and +40°C. Some other recipes found in the web employ an ice-salt bath (-30°C). What changes with the temperature? The reaction is exothermic, so with lower T the theoretical yield increases at the expense of kinetics. In this sense, I assume the suggested 20-30°C operational temperature is a compromise between thermodynamics and kinetics. Is that correct? Or is it more of a safe temperature to avoid runaway or undesired reactions?

2) The addition of methenamine to WFNA has to be carried slowly. Is it because the reaction is dangerously exothermic and so it's necessary to let the mixture cool down a bit between each addition in order to easily maintain the temperature < 30°C?

3) After the two reactants are mixed, the temperature is quickly raised to 80°C. Is it to speed up the reaction? Why the temperature must be raised so quickly? What happens if it's raised gradually? Also why all that care to maintain it below 30°C in the first step if then you have to quickly raise the temperature? Or is the high temperature necessary to dissolve all the metenamine or rdx?

4) In order to precipitate the RDX crystals, the acid mixture is washed with cold water. Is it to counter the exothermic reaction between the leftover HNO3 and water? Or is it to more easily allow the precipitation of the crystals? Or both?

5) How do impurities affect the reaction? Especially NOx dissolved in HNO3 or the presence of sulfates or other salts: how do they influence the formation of unstable byproducts?

6) What is the most critical and dangerous step of this synthesis and why?

Mine is mostly scientific curiosity. Chemical reactions on the chart are often very simple but when you have to practically do it in reality, you have to take into account many things and make many adjustments, and so the actual procedure looks more complex. While for most industrial processes the reason behind each choice is justified, finding such info on topics like energetic materials production is more difficult.

It's ok even if you can redirect me to the related thread or link some textbook or paper or anything about it.

Thanks

[Edited on 29-5-2019 by Metallus]
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[*] posted on 29-5-2019 at 02:50


"Chemistry and Technology of Explosives", By T. Urbański has rather comprehensive information about the topic in nitramine related chapters. All the main production methods are discussed in satisfactory detail. It should at least give answers to some of your questions.

In general terms the cyclic nitramine formation takes place in a rather thick and complex "primordial soup" of the respective building blocks. There are countless ways these building blocks can stack themselves together forming a very wide array of products. The cyclic members are only one possible outcome from the reaction between nitration agents and the methenamine "fragments". Some of the byproducts are of linear configuration and these are sensitive end unstable.
The aim of the thermal and other control methods is to force the reaction towards the formation of the cyclic products and the breakup of the linear byproducts.
Especially the raising of temperature after the main synthesis is usually projected towards breaking up of the linear nitramine contaminants to yield a stable product. The nitration mixture is also diluted to some extent prior to rising of temperature so as to yield an oxydizing environment. In these conditions the linear nitramines are broken up and destroyed leaving the more stable cyclic products relatively unharmed as far as final yield goes.




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[*] posted on 29-5-2019 at 18:01


There is so much interesting details in the post above. Explosive chemistry is wonderful.

I heard an expert once talk about how using wet nitric acid causes the final product to be unstable. I believe the reason had to do with radicals.




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[*] posted on 30-5-2019 at 02:05


As markx writes above, the exact mechanisms of RDX/HMX formation from the nitrolysis of hexamine is poorly understood (AFAIK). Researchers have been tinkering with the reaction conditions to give the highest yield of the purest product (some of this research has been done right here on SM), but exactly what happens at the molecular level as a consequence of altering these parameters simply isn't known to science (to the best of my knowledge).
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[*] posted on 31-5-2019 at 00:49


Thank you marks for the reference and thank you guys for your answers.
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[*] posted on 15-6-2021 at 22:43


well these methods are valid for rdx type 1. Is it possible to produce type 2 rdx in an acetic anhydride free environment?
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[*] posted on 31-10-2022 at 22:31


Since I've finally made my first RDX synthesis. I do have some questions to ask about this as I found my yield to be really low (or is it supposed to be this low?) and I wonder if it is normal or not.

So what I did is this: The first thing I did was make HDN and use that as my starting nitration. as HDN is very hygroscopic, I first air dried it in order to remove all the acetone and any excess liquid before putting it in a container with calcium chloride to act as a dessicating agent. I did manage to successfully dry my HDN this way and using 20 grams of HDN and 98ml of WFNA (98%) that I had chilled in an icebath below -20C, I added the HDN slowly and stirred. The whole process took an hour and when the final addition of HDN was done, the temperature reached 0C, but never above. I continued to stir manually for almost 15 minutes before removing it from the ice bath and letting it rise to ambient temperature.

I then heated it in on my mantle to 50C and let it stay there for 5 minutes. I removed it from heat, but it didn't seem like the temp wanted to drop, so I placed the beaker in a room temperature water bath and the rising temp was brought under control. After this I let it cool down to room temp before dumping the liquid in ice cold distilled water and filtered off the RDX crystals and washed them with copious quantities of tap water to wash away all traces of acid. Once the water was acid free, I washed them still just in case.

After letting it dry and weighing everything, my final result was 10.38g of RDX. Is this supposed to happen? I know that it must be heated up to destroy any unwanted bits that could degrade it in long term storage (though I am unlikely to keep my RDX that long anyway. I just want to make the purest product that I can).

Was my yield really low? What is the best ratio of hexamine or HDN to WFNA? If anyone even has that ratio.
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[*] posted on 1-11-2022 at 08:57


I have made RDX a few times and from searching around here, these are the only details I could find:

http://www.sciencemadness.org/talk/viewthread.php?tid=63638

16 grams RDX from 25 grams dried HDN using 60 ml 99% WFNA.
Not the best but this was without adding anything else I have listed at bottom.

Your case is interesting as you have a large excess of acid which should maximise yield as the water by-product won't have as large a dilutent effect.

It is also strange that your reaction seemed like it was gaining exothermic momentum when taken off heat. The last heating step is there to push the reaction to completion but will result in a runaway if done too early. The fact that it "didn't seem like the temp wanted to drop" might be indicating that the nitrolysis wasn't entirely complete yet as heat energy is formed from making the bonds here.

I think maybe let it sit at room temperature (20-25°C) for a longer period of time after removing from ice when u attempt again. Then perform the heating step.

You could also try a small amount (a few grams) of ammonium nitrate dissolved in the nitric acid before chilling.
It works wonders for HMX yields and there is a couple of reasons. One is to do with deficiencies and the other is solely due to the ammonium ion. This has been proven in a paper where different nitrates (magnesium, copper, potassium, etc) were used in nitrolysis reactions and NH4 provided the highest product yields.

Another method is using nitric acid, ammonium nitrate, and acetic anhydride. This proves hard nowadays as the restriction status of acetic anhydride is extremely high due to illicit heroin manufacture.




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[*] posted on 1-11-2022 at 11:38


Quote: Originally posted by greenlight  
I have made RDX a few times and from searching around here, these are the only details I could find:

http://www.sciencemadness.org/talk/viewthread.php?tid=63638

16 grams RDX from 25 grams dried HDN using 60 ml 99% WFNA.
Not the best but this was without adding anything else I have listed at bottom.

Your case is interesting as you have a large excess of acid which should maximise yield as the water by-product won't have as large a dilutent effect.

It is also strange that your reaction seemed like it was gaining exothermic momentum when taken off heat. The last heating step is there to push the reaction to completion but will result in a runaway if done too early. The fact that it "didn't seem like the temp wanted to drop" might be indicating that the nitrolysis wasn't entirely complete yet as heat energy is formed from making the bonds here.

I think maybe let it sit at room temperature (20-25°C) for a longer period of time after removing from ice when u attempt again. Then perform the heating step.

You could also try a small amount (a few grams) of ammonium nitrate dissolved in the nitric acid before chilling.
It works wonders for HMX yields and there is a couple of reasons. One is to do with deficiencies and the other is solely due to the ammonium ion. This has been proven in a paper where different nitrates (magnesium, copper, potassium, etc) were used in nitrolysis reactions and NH4 provided the highest product yields.

Another method is using nitric acid, ammonium nitrate, and acetic anhydride. This proves hard nowadays as the restriction status of acetic anhydride is extremely high due to illicit heroin manufacture.


Acetic anhydride is not restricted in Canada (where I live) so I can get some but it seems like such an excess. I also have no access to ammonium nitrate (albeit I can make some with ammonia and nitric acid). I would rather use the fuming nitric and HDN method instead.

I used an excess of HNO3 because it is what Darian Ballard did. He did mention it was an excess of WFNA, but I wasn't sure how much. Since you said you put in 25g of HDN to 60ml WFNA, I will try that next time. we had similar yields, albeit you got slightly more than what I did (I got a little more than 50%, you seemed have gotten 64% of the starting HDN.

Quote:
It is also strange that your reaction seemed like it was gaining exothermic momentum when taken off heat. The last heating step is there to push the reaction to completion but will result in a runaway if done too early. The fact that it "didn't seem like the temp wanted to drop" might be indicating that the nitrolysis wasn't entirely complete yet as heat energy is formed from making the bonds here.

I think maybe let it sit at room temperature (20-25°C) for a longer period of time after removing from ice when u attempt again. Then perform the heating step.


Maybe I simply didn't let it cool on its own. This was my first real attempt at making RDX. I did make two attempts at making Keto-RDX, but the runaways I had really me think it wasn't worth it. I could have waited a few more minutes before putting the beaker in room temperature water. The fact that it started to cool down right away after I put the beaker in a cooler place very likely meant it that it was not a runaway.

I did let it stay at slightly below room temp for almost 20 minutes. Maybe the next time I will try to let it heat a little more before giving it the heat up.


Quote:
You could also try a small amount (a few grams) of ammonium nitrate dissolved in the nitric acid before chilling.
It works wonders for HMX yields and there is a couple of reasons. One is to do with deficiencies and the other is solely due to the ammonium ion. This has been proven in a paper where different nitrates (magnesium, copper, potassium, etc) were used in nitrolysis reactions and NH4 provided the highest product yields.


I can do that. As I don't have ammonium nitrate as i said, so I will use a little potassium nitrate instead. I know it won't get the highest yield, but if it can improve my RDX yields and add more HMX to the mix.
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[*] posted on 11-11-2022 at 06:56


Quote: Originally posted by greenlight  


Another method is using nitric acid, ammonium nitrate, and acetic anhydride. This proves hard nowadays as the restriction status of acetic anhydride is extremely high due to illicit heroin manufacture.


I have been prepping AN/NA nitrolysis agent this way for some time, however I have found it difficult to prep the nitrolysis reagent accurately each time. This method leads to the offgassing of NOx and can have varying degrees of dissolved NOx in the final solution. The solution can vary from a light yellow to red-orange color and my final RDX purity can vary based on this. Cooling the NA down before addition leads to a messy, viscous slurry.

Has anyone explored a way to stabilize this preparation and prevent the NOx gassing during addition of the AN to the nitric?
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[*] posted on 5-1-2023 at 22:47


So I appear to be having problem with having a pure nitrate salt. My synths of sodium and potassium nitrates are always haphazard and while I have been able to make excellent azeotropic nitric acid with my stuff, fuming nitric acid has been more challenging. While I did make WFNA with my old sodium nitrate batch, my newer one is not being very cooperative with my first attempt with it to make WFNA. I ended up making an azeotropic nitric acid (around 70 to 72%. Excellent and super clean, but not WFNA). It could be because of the cooling in my condenser, but I am thinking it is due to the impurites in my sodium nitrate. Since I went through the sodium bicarbonate to turn my CAN into NaNO3, I think I might have used an excess of bicarbonate that caused this problem and partially neutralized my product. I will need to experiment further to make sure I don't add an excess of bicarbonate that could cause this problem. I used 300 grams of calcium-ammonium nitrate dissolved in 650ml of water (to remove the insolubles) and to the cooled filtered solution I added 316 grams of bicarbonate. I think 50 grams less bicarbonate might be more appropriate since that is probably how much insolubles there are in the CAN.

I know I can further purify HNO3 by a 2nd distillation with a 1:1 ratio of nitric acid and sulfuric acid, but I am curious if I can make RDX via 70% HNO3 in the presence of sulfuric acid and using HDN.

I've seen PETN successfully made not with WFNA but with 68-70% HNO3 and 95% H2SO4. Can the same be done with RDX or is WFNA strictly required here?
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[*] posted on 6-1-2023 at 11:54



Quote:

I am curious if I can make RDX via 70% HNO3 in the presence of sulfuric acid and using HDN


No you cannot. When your HNO3 is below 98%, a slew of issues can arise. Low HNO3 can cause your RDX to have a heightened HMX content with a good amount of this HMX being alpha-variant, and heightened SEX/TAX impurities present. Due to the excess acetic anhydride present, the mixture will likely "gel" in your mixer. It will be a mess to clean up.

RDX's intermediates are also hydrolyzed by H2SO4. So I do not think using sulfuric acid is a good idea. WFNA or a 98% NA/NH4NO3 reagent is necessary.
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[*] posted on 6-1-2023 at 15:45


Sounds good.

Seems like my sodium nitrate synth right now is mostly not very good... I am going through a 2nd nitric acid pass and the way how the sulfuric acid I put in reacted with the sodium nitrate is telling me there is a lot of unreacted sodium bicarbonate in there. I am not sure why. But I will learn from it.
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[*] posted on 7-1-2023 at 06:52


Quote: Originally posted by ManyInterests  
Quote: Originally posted by greenlight  
I have made RDX a few times and from searching around here, these are the only details I could find:

http://www.sciencemadness.org/talk/viewthread.php?tid=63638

16 grams RDX from 25 grams dried HDN using 60 ml 99% WFNA.
Not the best but this was without adding anything else I have listed at bottom.

Your case is interesting as you have a large excess of acid which should maximise yield as the water by-product won't have as large a dilutent effect.

It is also strange that your reaction seemed like it was gaining exothermic momentum when taken off heat. The last heating step is there to push the reaction to completion but will result in a runaway if done too early. The fact that it "didn't seem like the temp wanted to drop" might be indicating that the nitrolysis wasn't entirely complete yet as heat energy is formed from making the bonds here.

I think maybe let it sit at room temperature (20-25°C) for a longer period of time after removing from ice when u attempt again. Then perform the heating step.

You could also try a small amount (a few grams) of ammonium nitrate dissolved in the nitric acid before chilling.
It works wonders for HMX yields and there is a couple of reasons. One is to do with deficiencies and the other is solely due to the ammonium ion. This has been proven in a paper where different nitrates (magnesium, copper, potassium, etc) were used in nitrolysis reactions and NH4 provided the highest product yields.

Another method is using nitric acid, ammonium nitrate, and acetic anhydride. This proves hard nowadays as the restriction status of acetic anhydride is extremely high due to illicit heroin manufacture.


Acetic anhydride is not restricted in Canada (where I live) so I can get some but it seems like such an excess. I also have no access to ammonium nitrate (albeit I can make some with ammonia and nitric acid). I would rather use the fuming nitric and HDN method instead.

I used an excess of HNO3 because it is what Darian Ballard did. He did mention it was an excess of WFNA, but I wasn't sure how much. Since you said you put in 25g of HDN to 60ml WFNA, I will try that next time. we had similar yields, albeit you got slightly more than what I did (I got a little more than 50%, you seemed have gotten 64% of the starting HDN.

Quote:
It is also strange that your reaction seemed like it was gaining exothermic momentum when taken off heat. The last heating step is there to push the reaction to completion but will result in a runaway if done too early. The fact that it "didn't seem like the temp wanted to drop" might be indicating that the nitrolysis wasn't entirely complete yet as heat energy is formed from making the bonds here.

I think maybe let it sit at room temperature (20-25°C) for a longer period of time after removing from ice when u attempt again. Then perform the heating step.


Maybe I simply didn't let it cool on its own. This was my first real attempt at making RDX. I did make two attempts at making Keto-RDX, but the runaways I had really me think it wasn't worth it. I could have waited a few more minutes before putting the beaker in room temperature water. The fact that it started to cool down right away after I put the beaker in a cooler place very likely meant it that it was not a runaway.

I did let it stay at slightly below room temp for almost 20 minutes. Maybe the next time I will try to let it heat a little more before giving it the heat up.


Quote:
You could also try a small amount (a few grams) of ammonium nitrate dissolved in the nitric acid before chilling.
It works wonders for HMX yields and there is a couple of reasons. One is to do with deficiencies and the other is solely due to the ammonium ion. This has been proven in a paper where different nitrates (magnesium, copper, potassium, etc) were used in nitrolysis reactions and NH4 provided the highest product yields.


I can do that. As I don't have ammonium nitrate as i said, so I will use a little potassium nitrate instead. I know it won't get the highest yield, but if it can improve my RDX yields and add more HMX to the mix.


Magnesium Nitrate was recommended from my research.
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[*] posted on 7-1-2023 at 21:40


Well the company that formerly sold chemicals to anyone has changed their policy that they won't be shipping to residential addresses anymore. This means I would need to make my own magnesium nitrate to do that.

At any rate, I do have some ammonium nitrate now, I will be using that in my next synth. I actually forgot about that!
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[*] posted on 8-1-2023 at 03:27


Quote: Originally posted by ManyInterests  
I would need to make my own magnesium nitrate to do that!

Making anhydrous magnesium nitrate is difficult and the normal hydrated form isn't a desiccant.




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[*] posted on 8-1-2023 at 16:22


So ammonium nitrate then.

At any rate, I am having some difficulties that I wasn't sure I had previously with making sodium nitrate (and possibly the potassium nitrate that I have made last summer. But I am more worried about the sodium nitrate). It was using them as the nitrate salt in reactions. I am making nitric acid with what I believe is highly impure sodium nitrate. I am making good nitric acid with it, albeit despite my best attempts at making WFNA, the specific gravity only 1.4954 or so despite my best attempts. I realize it does need to be at least around 1.51 for it to be WFNA (I didn't take the temperature, but it is very cold).

I am thinking of starting another thread on the whole thing, but I want to do my own research first and some other experimentation.

But just one quick question here. To further concentrate nitric acid, the less than WFNA must be added with magnesium nitrate (which I don't have) or (more cheaply and easily that I can get) sulfuric acid to redistill and distill over the nitric acid while leaving the sulfuric behind, am I correct in this assumption?

Nurdrage uses a 1:1 of azeotropic nitric acid to sulfuric acid (albeit nurdrage said that an excess of nitric acid is fine). Most of my yields are on the upper end of RFNA, would a 1:1 still be good or a less amount of sulfuric acid is acceptable?

[Edited on 9-1-2023 by ManyInterests]
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[*] posted on 9-1-2023 at 10:19


Quote: Originally posted by ShotBored  
Quote: Originally posted by greenlight  


Another method is using nitric acid, ammonium nitrate, and acetic anhydride. This proves hard nowadays as the restriction status of acetic anhydride is extremely high due to illicit heroin manufacture.


I have been prepping AN/NA nitrolysis agent this way for some time, however I have found it difficult to prep the nitrolysis reagent accurately each time. This method leads to the offgassing of NOx and can have varying degrees of dissolved NOx in the final solution. The solution can vary from a light yellow to red-orange color and my final RDX purity can vary based on this. Cooling the NA down before addition leads to a messy, viscous slurry.

Has anyone explored a way to stabilize this preparation and prevent the NOx gassing during addition of the AN to the nitric?



Chilling the nitric acid right down in a salt ice bath in a small round bottom flask and adding the ammonium nitrate in very small portions with stirring seems to minimise the off gassing for me.

Yes, it is quite viscous and light yellow, but still works as a nitrolysis bath. You can always thin it out a little with a small extra portion of nitric acid as this won't cause any harm.

[Edited on 9-1-2023 by greenlight]




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[*] posted on 9-1-2023 at 10:35


Quote: Originally posted by ManyInterests  
So ammonium nitrate then.

At any rate, I am having some difficulties that I wasn't sure I had previously with making sodium nitrate (and possibly the potassium nitrate that I have made last summer. But I am more worried about the sodium nitrate). It was using them as the nitrate salt in reactions. I am making nitric acid with what I believe is highly impure sodium nitrate. I am making good nitric acid with it, albeit despite my best attempts at making WFNA, the specific gravity only 1.4954 or so despite my best attempts. I realize it does need to be at least around 1.51 for it to be WFNA (I didn't take the temperature, but it is very cold).

I am thinking of starting another thread on the whole thing, but I want to do my own research first and some other experimentation.

But just one quick question here. To further concentrate nitric acid, the less than WFNA must be added with magnesium nitrate (which I don't have) or (more cheaply and easily that I can get) sulfuric acid to redistill and distill over the nitric acid while leaving the sulfuric behind, am I correct in this assumption?

Nurdrage uses a 1:1 of azeotropic nitric acid to sulfuric acid (albeit nurdrage said that an excess of nitric acid is fine). Most of my yields are on the upper end of RFNA, would a 1:1 still be good or a less amount of sulfuric acid is acceptable?

[Edited on 9-1-2023 by ManyInterests]


I start with 62% nitric acid and use double its volume of concentrated sulfuric acid when distilling for higher purity.

The resulting yellow ~85-90% nitric acid can then be either vacuum distilled or dry air bubbled through it.

Vacuum distilling requires very gentle heat and is definitely not the best thing to expose pumps to, even with a base trap in between the rig and pump. I have used this method before though to obtain WFNA.

A better method to WFNA is by bubbling dry air through it to remove the trapped nitrogen (di)oxides. The air must be dry though otherwise it will result in dilution.
I usually fully submerge a fish pond air pump underneath fresh calcium chloride im a small container so the air is pulled through it first. An in-line drying tube could be rigged up alternatively which would be more cost efficient.
Warming the acid on a hotplate with stirring and dry air bubbling results in some nasty fumes during the process and some water white highly fuming acid at the end.
Thankfully, it doesn't take too long to perform.

The acid is good to use for any nitrolysis after.

Make it to use soon after, cause damn that stuff is a bitch to store.
It has turned one of my schott duran GL 45 blue lids completely white around where it was contacting the fumes inside the bottle.




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[*] posted on 9-1-2023 at 13:35


The blue caps are just PP so it's not surprising ;)
It's a bitch to store even with the better PFA caps !




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[*] posted on 9-1-2023 at 19:17


Quote:

A better method to WFNA is by bubbling dry air through it to remove the trapped nitrogen (di)oxides. The air must be dry though otherwise it will result in dilution.
I usually fully submerge a fish pond air pump underneath fresh calcium chloride im a small container so the air is pulled through it first. An in-line drying tube could be rigged up alternatively which would be more cost efficient.
Warming the acid on a hotplate with stirring and dry air bubbling results in some nasty fumes during the process and some water white highly fuming acid at the end.
Thankfully, it doesn't take too long to perform.


Yes! I actually remembered that method. I don't have a strong air pump, but a very small pump (pictured below). It works for my vacuum filter and I did bubble through azeotropic nitric acid to clean it up (it worked fine) though when I did the method of putting it in calcium chloride I must have done it improperly because while it did nicely clean up my acid, it did result in a dilution.

I saw a youtube video where someone used a gas washing bottle filled with calcium chloride in order to bubble something. I tried to make my own gas washer out of a coke bottle but the pump wasn't strong enough, or my makeshift gas wash bottle was too big. I ordered a gas washing bottle (a small one) that I hope will work. I need to make sure it'll do the trick when it arrives. I will cover the pump and the gas wash bottle with calcium chloride and I hope that it will both clean everything up and dry up the 95% or so HNO3 and bring it up to 99%.

Quote:
The blue caps are just PP so it's not surprising ;)
It's a bitch to store even with the better PFA caps !


I will use the acid immediately after. Right now I am storing 255ml or so of my 95% nitric acid in a 375ml liquor bottle. The cap is made of plastic and is NOT screwed on. I put it in a plastic bag with sodium carbonate in it to neutralize the fumes coming out. It is in a corner where I cannot easily knock it down by accident.

my gas wash bottle cannot come fast enough!

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[*] posted on 9-1-2023 at 20:12


I use air from a cylinder to clean up my nitric acid.
I scuba dive so have access to cheap, clean and dry air, not an option for everyone obviously.
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[*] posted on 10-1-2023 at 10:38


Quote: Originally posted by Herr Haber  
The blue caps are just PP so it's not surprising ;)
It's a bitch to store even with the better PFA caps !


Oh wow, I thought they were made of something tougher than that haha. No wonder I've had to replace a few.




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[*] posted on 10-1-2023 at 10:43


Quote: Originally posted by ManyInterests  
Quote:

A better method to WFNA is by bubbling dry air through it to remove the trapped nitrogen (di)oxides. The air must be dry though otherwise it will result in dilution.
I usually fully submerge a fish pond air pump underneath fresh calcium chloride im a small container so the air is pulled through it first. An in-line drying tube could be rigged up alternatively which would be more cost efficient.
Warming the acid on a hotplate with stirring and dry air bubbling results in some nasty fumes during the process and some water white highly fuming acid at the end.
Thankfully, it doesn't take too long to perform.


Yes! I actually remembered that method. I don't have a strong air pump, but a very small pump (pictured below). It works for my vacuum filter and I did bubble through azeotropic nitric acid to clean it up (it worked fine) though when I did the method of putting it in calcium chloride I must have done it improperly because while it did nicely clean up my acid, it did result in a dilution.

I saw a youtube video where someone used a gas washing bottle filled with calcium chloride in order to bubble something. I tried to make my own gas washer out of a coke bottle but the pump wasn't strong enough, or my makeshift gas wash bottle was too big. I ordered a gas washing bottle (a small one) that I hope will work. I need to make sure it'll do the trick when it arrives. I will cover the pump and the gas wash bottle with calcium chloride and I hope that it will both clean everything up and dry up the 95% or so HNO3 and bring it up to 99%.

Quote:
The blue caps are just PP so it's not surprising ;)
It's a bitch to store even with the better PFA caps !


I will use the acid immediately after. Right now I am storing 255ml or so of my 95% nitric acid in a 375ml liquor bottle. The cap is made of plastic and is NOT screwed on. I put it in a plastic bag with sodium carbonate in it to neutralize the fumes coming out. It is in a corner where I cannot easily knock it down by accident.

my gas wash bottle cannot come fast enough!


A gas washing bottle will be even better than what I had set up. As long as the air is passing though a decent length cylinder of anhydrous calcium chloride you should be able to get away with just the bottle. You can cover the pump as well for extra measure if you want to of course. Calcium chloride is cheap and easy to get, 99% nitric acid not so much

Another way is to find the inlet of the pump and attach a tube packed with some calcium chloride to it.





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[*] posted on 10-1-2023 at 19:22


My gas wash bottle is quite small, so I will need to do extra of filling the bottle AND covering my upcoming air pump (it's an air mattress and pool/beach toy pump with both vacuum and pump. It should work very well for anything I need pumping for.). I have a 450 gram unopened bag of calcium chloride that I bought and I will be filling the bottle up as much as I can and cover the air in-take section of the pump completely with calcium chloride. I will need to make an improvised setup to make sure that I have as dry of a setup as possible.

Heat the acid to 50C (with a water bath) and keep pumping dry into it. I pray that this will succeed. I might make more nitric acid tomorrow and practice on making clean, concentrated WFNA and make it well.
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