Sciencemadness Discussion Board - ETN - H2SO4 surplus + mixed charge

ETN - H2SO4 surplus + mixed charge

Swede - 5-7-2012 at 07:10

Objectives – Verify that a mixed Ammonium Nitrate / Erythritol charge, added to an excess of stirred H2SO4 would allow for a trouble-free and efficient nitration. Secondarily, determine what excess of H2SO4 was needed so as to allow the bath to both magnetically stir and pour with little fuss. The goal was to avoid pastes or slurries that are difficult to handle and heat unevenly.

Reagents were prepared as follows…

A PVC ball mill vessel was charged with Erythritol .and ceramic media. The Erythritol was milled for approximately 4 hours, reducing the sugar crystals to a state resembling wheat flower, perhaps finer. Tests had shown that Erythritol demonstrated little hygroscopicity; the moisture content was low. The milled Erythritol was stored in an airtight container.

Likewise, another ball mill vessel was charged with Ammonium Nitrate, AN. The AN was milled for approximately 4 hours until it too was reduced to a near talc-like consistency. The milled reagent was spread thinly on a degreased aluminum shallow pan and baked at 100 degrees for 3 hours. It was quickly gathered and stored in a 2 liter PTFE container that was absolutely moisture-proof.

The H2SO4 (lab-grade, 98%) was chilled in a refrigerator.

To prepare the charge, a quantity of the powdered reagents was weighed in a 4:1 ratio of AN to Er. Given the near identical consistencies of the powder, mixing them into a homogenous bulk was easily accomplished. This quantity was stored in a third moisture-proof container.

100 ml of chilled H2SO4 (184 grams of 98% acid) was measured into a 500ml beaker. A PTFE stir bar was added. The beaker was placed in an ice water bath and set upon a magnetic stirrer. A stand was equipped with an arm that supported a flexible, PTFE-coated thermocouple and digital meter so as to measure the temperature of the acid bath. The acid stabilized at 4 degrees.

Portion-wise, the 4:1 mixed charge was slowly added to the stirred acid. The size of each addition was approximately 200 to 400 milligrams. As the mixed powdered charge entered the acid, the stir bar did an excellent job of distributing the reagents. After perhaps a dozen portions was added over a few minutes, the temperature of the bath slowly rose to 20 C. Further additions of mixed reagents was then paced so as to maintain a bath temperature of 20 to 23 C. The color of the bath was a dirty white, slightly grey.

The nitration bath at 20 degrees had the consistency of pancake syrup, but could still be easily poured. There was little fuming and no noticeable evolution of NOx gasses. Overall, it was an easy and problem-free nitration.

I halted the addition of the mixed powders at an arbitrary point, where I was comfortable that the viscosity of the bath was still low enough so that it would remain completely uniform, thermally or otherwise, and would pour with ease.

After the last addition, the beaker was removed from the ice water bath, and the bath was stirred continuously for an additional 30 minutes. Temperature remained relatively stable, rising slowly to the ambient 25 C but no higher. There was never any indication of a thermal runaway or other problem.

After the 30 minute nitration/stir, the contents of the beaker were dumped into 750ml of cold, distilled water, and a wash bottle filled with cold water was easily able to cleanse clinging, syrupy remnants from the beaker into the dump water. A cloud of fluffy white precipitate formed, with a portion floating and another portion sinking.

This was filtered rapidly through a triple coffee filter. The retained solids were gently squeezed with a heavily gloved hand to remove excess liquid, and the solids were scraped/washed into a separate, clean 1 liter beaker. 500ml of cold distilled water was added and the ETN stirred. Small portions of a 5% Ammonium Carbonate solution were added, and the water with the ETN ppt tested via pH paper. CO2 gas evolved, but nothing problematic. The 5% Ammonium Carbonate was added in portions until the wash tested neutral or very slightly basic. The crude product was again filtered, washed one last time with a cold water after collection into the filter paper, and then gently spread to dry.

The precipitate was off-white, extremely fine. A minute sample was placed into a Melting Point apparatus, and the product sharply melted between 62 and 63 C. Another small sample dissolved easily in ethanol, further verifying that the collected precipitate was indeed ETN.

One of the objectives of this experiment was to see how much of the mixed, powdered 4:1 charge could be added before the stir bar was unable to do its job adequately. During the nitration, I continued to add the small portions until the bath thickened to the point where additional powdered reagents would take it beyond a subjective viscosity I thought was acceptable. In the end, I halted additions to the 100ml acid after exactly 30.4 grams of NH4NO3 and 7.6 grams of Erythritol were in the bath. The ratio of reagents ended up as follows:

Reagent - Mass - Ratio - mMoles
100ml 98% H2SO4 - 180.3g - 23.7 - 1839.8
Erythritol - 7.6g - 1 - 62.2
NH4NO3 - 30.4g - 4 - 379.8

This is nearly twice as much sulfuric acid as the classic 12:4:1 ETN synthesis. Different countries have different issues with access to reagents, and in my location, at least, strong sulfuric acid is very common, and very cheap. From a procedural standpoint, the excess acid greatly eased the process of using sulfuric acid and a nitrate salt for this sort of process. Importantly, IMO, having a reasonably thin, magnetically stirrable bath also promotes a constant temperature, no hot spots, and an excellent homogenous mix that makes addition of the powders very easy.

Dry yield: 11.13g
Theoretical yield: 18.79g
Actual yield: 59.2%

Recrystallization: 11 grams of the crude ETN was placed in a 500ml beaker. The product was wetted with ethanol; a magnetic stirrer was added and the resulting slurry spun up to a moderate speed. Portions of room temperature ethanol were added until all of the solids were dissolved. The pH was checked with pH paper, and it was found that the fine crystals had trapped significant acidic remnants, which were neutralized by adding ammonium carbonate in tiny portions. When the solution showed a pH of ~7, diphenylamine wad added, 1% by weight (0.11g) relative to the crude ETN. Total ethanol to dissolve the 11 grams was approximately 100ml.

After several minutes of stirring, there were still some solids that showed no signs of dissolving. These were separated by another filtration and discarded.

A 250 ml buret was prepared and filled with a 2% solution of urea and a gram of sodium bicarbonate. This solution was added to the ETN solution dropwise with continuous stirring. The ETN began to fall out of solution after approximately 30ml had been added. Continued additions brought more ETN into its crystalline state. A simple process to determine when to stop the additions was devised… the magnetic stirrer was turned off, and the crystals allowed to settle. A 1ml plastic pipette was used to draw off the clear liquor above the crystals, and a small sample placed into a test tube. To this sample, a surplus of distilled water was added. Additional precipitation shows that the liquor still has dissolved ETN that can be extracted with continued water/urea additions. The sample is returned to the main batch, and water/urea additions continued.

When this test showed that no more ETN was going to separate from the solution, the beaker was covered and refrigerated for 2 hours. It was then filtered one last time. The solids were collected, washed with cold water, and collected for drying. The crystals were off-white platelets of satisfactory density, with a very faint yellow cast,

After drying, the batch massed 8.10 grams. 26.4% of the crude ETN was lost in the recrystallization process. The overall yield of 8.10 grams was 43.1%, but of a high purity and stability.

While this procedure might be considered wasteful of sulfuric acid, again, here at least, H2SO4 is inexpensive and widely available, and I believe the benefits are worthwhile. Further, the pre-mixed Er/AN powder is a convenient way to do the nitration. One must be confident that the powders are both anhydrous, AND of a consistency so that there is no mechanical separation during handling or storage.

A simplistic nose test on a closed bottle shows almost no odor, especially nothing resembling decomp products. An interesting experiment would be something like the Abel test done on a purified and stabilized product, vs. one with less care taken during collection and recrystallization.

[Edited on 5-7-2012 by Swede]

Swede - 5-7-2012 at 07:31

Pics:

[Edited on 5-7-2012 by Swede]

Leander - 16-7-2012 at 10:17

Thanks for your determination of the limits of sulfuric acid addition with respect to stirrability. This information can be helpfull in scaling up scenario's. For small batches though, thick nitration mixtures can be handled without much trouble when sufficient cooling/stirring is maintained. It's sad to see that even with a large surplus of sulfuric acid, the yield is still crappy.

From a thermodynamic point of view, adding all the ammonium nitrate to the acid at once, followed by cooling and finally portionwise addition of the erythritol seems favorable. In this case, the heat of dilution is dealt with first. This causes less temperature rise during erythritol addition. The start-off viscosity will be higher though, but with the acid ratio's you use, this doesn't seems problematic.

Do you think grinding the erythritol has any effect on the yield? Since the powder doesn't really goes into solution, I've always believed that this specific reaction is mainly limited by the ability of the acid to penerate the polyol crystals to a sufficient depth to allow nitration to occur. Also, since the nitrated product is less soluble in acid, partial nitration could cause fresh erythritol to become 'encapsulated' by nitrated product, preventing further nitration. If this hypothesis is true, the only way to achieve proper ETN yields would be to employ a mixed acid system that is capable of fully dissolving both erythrytol and is nitrates. Any suggestions?

Rosco Bodine - 17-7-2012 at 01:18

Axt had found best results using potassium nitrate IIRC. Other nitrates may work better than the ammonium salt in terms of yield of ETN, but viscosity may be worse so it is a tradeoff. I suspect cyanoguanidine may be the best stabilizer as has been reported to be true for nitromannite. Freeform betaine is another candidate stabilizer. Welcome back Swede.

quicksilver - 17-7-2012 at 07:19

I had found that the stir-bar itself could make a difference. Some bars are designed to be substantially wide in the center (and an additionally larger bar). This allows a minimum of friction upon the heavy solution. It seems the "standard" shaped bar hugs the bottom of the beaker creating more contact at the heaviest point of spin. A somewhat "oval" bar still allows a reasonable spin, yet it seems less demanding to start with the whole of the weight and viscosity on start-up.

I couldn't find a quality picture but many have seen them. They look like a well fed snake.

[Edited on 17-7-2012 by quicksilver]

Swede - 17-7-2012 at 13:54

Quote:

Do you think grinding the erythritol has any effect on the yield?

Probably not much. The main reason I milled it was so as to match the consistency of the AN which I also milled and dried. If the two powders were not very close in consistency, they could mechanically separate.

This experiment was pretty much of a one-off, It is wasteful of sulfuric, no doubt. Mainly, I wanted to see how this nitration would take place from a thermal and rate POV, and it was definitely simple to regulate temperature . Each small addition of the mixed reagents would raise the temperature one or two degrees, and when it dropped down again, the addition was repeated. If anyone replicates this, be sure the AN is BONE dry, or it may overheat.

The yield would have been higher if my recovery technique was better. My handling of the product from end-of-nitration, to weighing of the crude ETN, was sloppy, in retrospect. More care would probably have raised the yield 10%

pjig - 17-7-2012 at 15:49

Is there a better option than ethanol, for the recrystallization process ? I know acetone is too strong of a solvent , but if I remember correctly, there was something in a patent other than those two solvents that was used with better results . That seems like a lot of loss in the recrystallization process IMO. You may be able to gain a few % better final yield as well with what Quicksilver suggested on the stirbar. The more exposure the erythritol has in the nitration bath the better the yield ( like Petn).

I believe it was PATR:
The ETN dissolved better in hot sol. of alcohol(not sure which would be the best choice) or glycerol .( not excluding acetone).

[Edited on 18-7-2012 by pjig]

Swede - 19-7-2012 at 14:09

I agree there is a bit of controversy surrounding the best way to reX ETN. I've heard methanol is another good option, maybe a bit stronger than ethanol, but not near acetone levels of dissolving power. Methanol is also supposedly able to deliver denser xtals. There's a lot of room for experimentation to get better yields, yet still retain a high purity and good stability.

I guess in retrospect, I'm not too disappointed with the yield, in the sense that erythritol is now available in kilogram bags, quite OTC, and not expensive. If it was pentaerythritol or some other harder-to-get reagent, it'd be far more important.

pjig - 19-7-2012 at 16:49

This is true.

Ahhhhh, it came to me..., it was nitro-methane that was suggested by someone on this site.... I had a hard time remembering. When you mentioned the crystal formation it reminded me . It was suggested that the nitro caused a higher yield and the crystal formation was denser and trapped less acids. It also altered the crystal formation , which must have been the reason it got someones attention. I'm pretty sure it was EtN that they did this with, and not some other H.E. salt.

CaliusOptimus - 23-7-2012 at 01:35

Swede,

I've had great success and 95%+ yields with a standard recrystallization scheme. Bring the ETN in EtOH to saturation @ 55-60c, then filter off the product after cooling to -10c. Rinse thoroughly with warm distilled water to claim a clean product that has stayed odorless for 6 months and counting.

Quote: Originally posted by Leander

Do you think grinding the erythritol has any effect on the yield? Since the powder doesn't really goes into solution, I've always believed that this specific reaction is mainly limited by the ability of the acid to penerate the polyol crystals to a sufficient depth to allow nitration to occur. Also, since the nitrated product is less soluble in acid, partial nitration could cause fresh erythritol to become 'encapsulated' by nitrated product, preventing further nitration. If this hypothesis is true, the only way to achieve proper ETN yields would be to employ a mixed acid system that is capable of fully dissolving both erythrytol and is nitrates. Any suggestions?

This has also been my assumption. From my experience: In a set of nitrations with all other factors being the same, one with coarse erythritol, the yield was around 25% of theoretical. With finely milled erythritol, the yield was around 60%. I've been pondering the use of an anti-caking agent, as milled erythritol will clump to some extent, and the small clumps may act like large crystals in the nitration.

Rosco Bodine - 24-7-2012 at 00:43

Erythritol can actually be sulfonated by dissolving it in the H2SO4 first if the temperature is kept moderate and the strength of the acid is 95% or less. The erythritol sulfate remains dissolved in the H2SO4 and can be converted to the nitrate ester by nitration with HNO3 or addition of a nitrate. With regards to use of a nitrate, postassium ion may be catalytic which would commend KNO3. A mixed nitrate basis by anhydous weights 65% Mg(NO3)2 - 35% KNO3 would be a probable good experiment. If precursor hydrated magnesium nitrate is calculated to form a dehydrated mixture at 65% with 35% KNO3 a eutectic melt will form from which the usually tenacious water of hydration of Mg(NO3)2 may be removed by heating, more readily still under vacuum. A similar dehydratable eutectic occurs with 51% Mg(NO3)2 - 49% NaNO3 (mp 135C) and such melts may provide a mixed nitrate having usefulness in other nitrate and sulfuric acid method nitrations. This is not something I have tried, but a review of the literature suggests that this would likely work. Difficulty of cooling and granulating anhydrous solidified eutectics is unknown. Because of the extreme hygroscopic nature of the Mg(NO3)2 special handling and storage of the prepared binary nitrate mixture would be a consideration. However such a scheme using magnesium nitrate has potential for maximizing the yields from nitrations based upon the solid nitrate plus H2SO4 method.

[Edited on 24-7-2012 by Rosco Bodine]

Swede - 25-7-2012 at 05:35

Quote:

I've had great success and 95%+ yields with a standard recrystallization scheme. Bring the ETN in EtOH to saturation @ 55-60c, then filter off the product after cooling to -10c. Rinse thoroughly with warm distilled water to claim a clean product that has stayed odorless for 6 months and counting.

I like this. Simple, straightforward, and high yield, taking advantage of ethanol's low freezing point. Do you feel that the alcohol does a good job retaining acidic byproducts and other garbage, i.e. no additions or neutralizations of the ethanolic solution? I ask this because my own ethanol solution was definitely acidic with nitration remnants, even after what I thought was a vigorous washing of the crude product.

Quote:

With regards to use of a nitrate, postassium ion may be catalytic which would commend KNO3

I believe this to be true, as procedures which use potassium nitrate tend to have higher yields, albeit a thicker nitration bath.

Quote:

Difficulty of cooling and granulating anhydrous solidified eutectics is unknown.

My guess would be it'd be tough but not impossible. A well-made ball mill jar with ceramic or zirconia media would do the job. Perhaps the hard part would be the melt itself, and the handling of the hot anhydrous mixture.

Rosco Bodine - 25-7-2012 at 09:38

Yeah, I have been thinking about that issue because I don't have a "shot tower" or prilling tower yet

Maybe streaming the melt onto a rapidly spinning disk like a teflon coated frying pan would granulate the solidifying melt, or break it up enough provide chunks for further milling. It could be convenient if there was phase separation with discrete crystallization of the components so the melt would just disintegrate to mixed anhydrous crystals, but that is probably too much to hope. With incorporation of something additional which is not phase stable, adding a high enough percentage to cause phase instability and deliberately cause segregation, it may be possible to engineer a nitrates mix that is "self milling" on temperature cycling. This would be the reverse idea of what fertilizer manufacturers try to accomplish with schemes that produce stable prilled mixtures, to create a mixture intended to segregate into loose crystals after cooling the melt.

VladimirLem - 3-8-2012 at 11:21

Hi guys

im going to make some ETN but ive got some question...

Is it possible to make ETN the way like PETN with, let's say; 400ml nitric acid and 100g Erythritol without using H2SO4 ?

Wiki said so :-/

...AND...is the ratio of 400/100 at ETN okay, or have i to use more NA ?

CaliusOptimus - 4-8-2012 at 15:27

Quote: Originally posted by Swede

Do you feel that the alcohol does a good job retaining acidic byproducts and other garbage, i.e. no additions or neutralizations of the ethanolic solution? I ask this because my own ethanol solution was definitely acidic with nitration remnants, even after what I thought was a vigorous washing of the crude product.

The ethanol does carry a lot of impurities, though the crystals that form from it seem to be quite pure. Rinsing with warm water is an absolute necessity, and removes most of the acid. It wouldn't hurt to add a few mg of NaBicarb to the final rinse. Or better yet, recrystallize twice. Once provides a useful product, twice should be enough for just about any use short of an analytical reagent.

Swede - 9-8-2012 at 17:59

Quote:

Thanks, that does make sense. The very nature of crystallization precludes most impurities INSIDE the xtals, and a solid wash with warm water would carry away clinging ethanol + impurities.

Vikascoder - 24-11-2012 at 08:20

can ETN be made in the same way we make nitrocellulose and nitroglycerine.by this I mean that can we first make nitrating mix with 70%HNO3 and 98%H2SO4 then add erythritol slowly and stir for half and hour keeping temperature low and the filter out the ETN . Please tell can we make ETN in this way

gnitseretni - 24-11-2012 at 10:23

Yes, you can.

Swede - 24-11-2012 at 17:02

There are several methods which provide decent yields of ETN. The one I presented here simply varies the classic 12:4:1 mass ratios of 96 to 98% sulfuric, 4 Ammonium Nitrate, 1 Erythritol.

Like many, if good yields are possible with sulfuric acid and a nitrate salt, I'd rather preserve my stocks of nitric acid. And apparently, KNO3 is the nitrate salt of choice.

I believe the goal for ALL amateur syntheses of energetics should be a pure and stable product, with an emphasis on creating a clean material that will not decompose.

Accidents with nitrated esters, when they happen, is often caused by decomp due to residual acids and impurities.

Not saying impurity was the cause, but there was a guy here who ended up in the hospital due to melting ETN in a test tube. Please be warned and careful. We have an audience reading these threads from the kewlwst of the kewl, to real professionals, and the former can be scary at times.

Vikascoder - 24-11-2012 at 20:52

Basically for me acquiring nitric acid is cheaper then acquiring nitrate salt . So that's why i want to know the procedure of synthesizing ETN from nitric acid and sulphuric acid will anyone please give a light on that procedure

Kalium - 25-11-2012 at 03:44

Quote: Originally posted by Vikascoder

Basically for me acquiring nitric acid is cheaper then acquiring nitrate salt . So that's why i want to know the procedure of synthesizing ETN from nitric acid and sulphuric acid will anyone please give a light on that procedure

I believe the ratios are interchangeable with PETN. PowerLabs has a method for PETN synthesis that has been used successfully by members of this site.

Motherload - 3-8-2013 at 19:26

The ratios are NOT interchangeable with PETN.
Erythritol is a linear polyol as opposed to pentaerythritol which is a tertiary polyol.
There is more interference from fellow -O-NO2 groups in a linear setup .... Requiring more dehydration/H2SO4.
I have tried to replace Pentaerythritol with Erythritol and ended up with a clear solution at the end when the mix was poured in water.

I have used 1 gm Erythritol for every 4 ml HNO3(68%) and 6 ml H2SO4 (95%)

To overcome the viscosity problem .... Would filtering out the K2SO4 crystals, out of the nitrating mix, through a sintered glass frit work ?
I read that only 7.4 gm of K2SO4 is soluble in 100 ml of water @ 0*C.
http://en.wikipedia.org/wiki/Solubility_table
So I would think even less would dissolve in 95% HNO3 @ -5*C (freezer temp)

This may also help with cleanup (less Sulfate to wash out) during WFNA distillation.

Or can K2SO4 made to precipitate completely at a low enough temperature skipping distillation ?

[Edited on 4-8-2013 by Motherload]