Hey Buddy
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RDX K Method Temperature control
I have been attempting a preparation of RDX modifying the K method to use HDN rather than hexamine. This has resulted in dramatic runaways that
require dumping the reaction with loss of product. The runaway occurs on the heating of the reaction mixture.
97% nitric acid is cooled to 0 C.
2 molar equivalents NH4NO3 per hexamine is added to 8.6x w:w (HNO3:Hexamine) nitric acid with small exotherm and darkening of nitration solution.
HDN is added <15 C, working range of 5-10C.
Reaction is allowed to stabilize ~0C after addition of HDN.
Mixture becomes lighter colored and more transparent.
An 80 C water bath is prepared, time elapsed so far is over 1.5 Hrs.
Reaction vessel is transferred to hot water bath when it is ~70 C, reaction allowed to warm.
When the reaction gets to 60 C or so it begins the K type reaction that self sustains but loses control at around 4.5 minutes and begins to release
NO2 before totally going through full runaway.
My understanding is that the k reaction requires 80 C heating for 30 min. Im finding that this reaction appears to begin prior to reaching 80 C. But
then becomes self sustaining, losing control after a few minutes and decomposing around 90 C before running away.
I was wondering if anyone has experience with the heating during traditional K method and could recommend the heating regiment. Should I just slow it
down to 10C/5 min heating intervals to prevent the runaways?
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Sir_Gawain
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The heating step is to destroy any impurities from side reactions. The nitration must be complete before heating or it will run away. I allowed it to
slowly warm to room temperature before heating. Also, heating to 80C seems a bit extreme. I only heated to 50C and it worked fine. The problem could
also be with your nitric acid. Is it white or yellow?
“Alchemy is trying to turn things yellow; chemistry is trying to avoid things turning yellow.” -Tom deP.
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Hey Buddy
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Thank you for responding. I dont think I was clear in the first post.
Im familiar with the common classic methods, like what youre describing (british or hale or german method), destroying linear nitramines and
azododecanes etc with a high temperature.
K method (knoffler) has a secondary target reaction, rather than one as the traditional production methods. The second reaction is reported to only
activate at elevated temperature of 80 C. The reaction taking place in the 2nd half of K is a different reaction from classic methods.
C6H12N4 + 2NH4NO3 + 4HNO3 --> 2(CH2N.NO2)3 +6H2O
It involves interaction of NH4NO3 to provide additional amines to complete 2 units of cyclonite with high percent yield based on nitric acid and
hexamine.
The nitration in K does not complete until* it is activated by high temp. This is actually safe because of the reaction pathway of K method, as
opposed to the other methods that have some risks In elevating temps beyond 25 C (which they all require 30 C-75C with dilution) 80 C would not be an
appropriate temperature for traditional rdx preparation. There are some methods that do approach 75 C, but they involve significant dilution. Where as
knoffler method uses the high temp with concentrated acid.
I am using 97% nitric acid from low temp vacuum distillation. It does have some NO2 dissolved but it is very low. I also have used this batch of NA to
produce RDX a few times in the past, with the classic HDN route which is similar to what you recommend. So the acid concentration doent seem like an
issue.
Im actually attempting to reproduce the K method with HDN instead of hexamine for the purpose of comparing percent yield to literature and to compare
single distilled NA d 1.52 in k method versus hexamine method using the same acid batch to eliminate variation.
What im trying to understand at this point is simply how to achieve the K method with HDN, which has less than half the heat of reaction versus
straight hexamine. I dont see any reason that clean, dry HDN wouldnt be beneficial to K method.
What Im really wanting to know is if anyone has actually successfully completed the K method? And what they experience when achieving the 80 C
required? Im wondering if the HDN is activating the NH4NO3 reaction earlier at lower temp than the classic K method using hexamine?
I suppose the only sure way is to simply do both...
I do suspect the room temp standing and temp gradient to 80 C is probably too steep, causing runaway as the NH4NO3 reaction picks up with its own heat
of reaction.
[Edited on 24-10-2023 by Hey Buddy]
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Hey Buddy
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pale yellow, single distillation. I dont have issues with standard rdx from this acid. do you think it's NO2 comp percent?
I will work on pulling off this method and the regular k method and if I get a handle on it, i will report back
[Edited on 24-10-2023 by Hey Buddy]
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Hey Buddy
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I attempted to run the K method as reported in Urbanski Vol 3. Strict temperature control and hexamine were used along with 97% NA in 8.6x w:w
proportion to hexamine.
Duration was long, ~3 hours total. 30 min of nitrating after all the hexamine was added <15 C, which took awhile. Then the temperature was brought
to ~20 C for 10 min. Temperature was slowly raised to a target temperature of 80 C using a water bath. The increase was very slow, 2-3 degrees per
minute. As temp elevated, the in-solution RDX dissolved back into solution and the reaction became clear yellow.
At a temp somewhere around 70C or so I began to visually detect NO2 gas from reaction. Immediate action was taken to chill reaction on ice bath with a
target temp of 20 C.
The reaction was quickly brought under control and the reaction mixture became more opaque as temperature dropped. At 20C, RDX was precipitated in ~5x
volume cold water. Filtered. Washed with 5% NaHCO3. Still drying but next to a batch of RDX from HDN using the common procedure, the k method yield is
obviously a greater volume of RDX.
Will run some more tests between HDN and hexamine variations of K to target the high temperature problems and compare percent yield data. Dilution may
be required to reach and hold 80 C for 30 min. It appears not possible to achieve much above 70 C without triggering runaway.
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Hey Buddy
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HDN K method success
I just finished a semi-successful attempt at k method with HDN. The HDN is obviously much more controllable with less than half heat of reaction. I
run all comparative RDX batches at around .142 mol for hexamine or HDN so they can be easily compared.
This K method with HDN is by far the largest volume yield Ive seen yet on RDX. I was unable to hold 80 C for 30 min. 10 min was my max before I began
to see red fumes.
The development of NO2 slowly climbs the glass walls of beaker from about 70 C + and then after about 10 min at 80 C the NO2 spills over the beaker
and it's time to temp control. I also paused at 50 C for 10 minutes before allowing it to rise further. On runaway response I put the reaction into an
ice bath and drop it to below 20 C as fast as possible.
During initial temp incline, You can see the activation of the ammonium nitrate reaction, and it activates at a lower temp than claimed. I dont have
lab notes in front of me but it probably begins activation somewhere around 50-60 C with tiny bubbles appearing after a long period of no changes from
ambient to 50 C. Stirring has to be high powered in order to create quick response in temperature control. I was stirring with a ptfe paddle at
300-350 rpm and a mag stirrer would not be able to move the reaction mix at the same velocity. The stirring comes into play particularly when
immediate temp reduction is needed to neutralize run away.
I think the pausing shelves in temp elevation help in holding off decomp. 20, 30 and 50 C were all held for a few minutes before proceeding. From 60
to about 70 C it was a continuous climb, as I got impatient. but it would have probably been better to pause more frequently. I will keep working on
this.
The yield is quite good. I dont even have to weigh it to know that, because the precipitated volume is so great. It is clearly almost twice the
standard volume of product at .142 mol hexamine addition. Apparently, knoffler method works. Total time on this lab including bicarb wash and
filtering finished product was only 2 hrs 45 min. Much faster than hexamine version, and also 80 C was attained where as other attempts with hexamine
route have so far not been able to reach 80 C before runaway begins.
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Hey Buddy
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unfortunately the apparent volume was after dry weight, an efficiency of only 70%. At 70% there appears to be no benefit really over even nitrolysis
of hexamine. HDN is much more controllable than hexamine, will have to test some more...
[Edited on 28-10-2023 by Hey Buddy]
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