Sciencemadness Discussion Board - monopropellant project

monopropellant project

vaslop - 13-4-2011 at 09:46

Hi everyone,

I am at school (sixth form) doing an extended project in chemistry, looking at simple throttleable rocket propulsion, I have ruled out bipropellant rockets as they are too complex and dangerous.

I am basing my project on the efficiencies of polymers for hybrid rocket fuels. but would like to venture into simple (and relatively safe) monopropellants.

After doing some research, I have synthesized ethyl nitrate and nitrite, believing that they have desirable properties, as they are non-toxic and relatively stable.

This leads to my question, is their a practical way of initiating a decomposition of either of these? I've tried hot cobalt oxide catalyst, but I've reached the limit of my understanding.

Also, are there any other, more practical monopropellants that i have missed?

Thanks

Bot0nist - 13-4-2011 at 10:04

The nitrate salt of hydroxlamine, hydroxylammonium nitrate, is being researched as a rocket propellant, both in water solution as a monopropellant and in its solid form as a solid propellant. I believe it can be catalyzed with a noble metal.

Also H2O2 is a popular monopropellent in the right concentration and is easily decomposed. Almost too easily.

Neither of these is very safe though. Many accidents have occurred with hydrogen peroxide, and the hydroxlamine salt is corrosive, toxic and probably carcinogenic.

Why a monopropellent? What are the parameters of your project?

vaslop - 13-4-2011 at 10:14

yes, i looked at hydrogen peroxide, but its quite hard to get hold of, and seems to be a bit too 'reactive' for my liking.

I am just looking at the effectiveness of simple but practical rocket fuels, this has led me to hybrids, and possibly monopropellants.

I have seen the hydroxylammonium nitrate, and it looks interesting, shame about its toxicity.

Bot0nist - 13-4-2011 at 10:28

What about solid or casted propulsion mixes? Safe and tried and true. I like KNO3 and sugar myself. Not very high tech but I reliably achieve lift, and have never had a mishap.

Hydrogen peroxide is pretty easy to obtain here in the states from the 3-30 % concentrations. One can carefully distill it under a vacuum to approach 'high test" concentrations. Great care must be taken to prevent anything that would cause the peroxide to decompose while attempting this procedure though.

vaslop - 13-4-2011 at 10:39

I have 35% hydrogen peroxide, but really want to avoid distilling it. (don't like the idea of glass flying about in every direction)

I have made many solid rockets, of black powder, rcandy, (and the sugar and KNO3 as you described), ammonium nitrate composites and ammonium perchlorate composites (definitely my favorite) and will probably include these in my project. now you must think that I'm just another 'boomer' teenager, but im really interested in the chemistry, and learning the theory, and taking it further.

I just like the idea of doing some more complex work on something a bit new, (And whilst i have access to my schools equipment)

Bot0nist - 13-4-2011 at 10:49

I don't consider you a kewl at all. I also love amateur rocketry and pyrotechnics. It has been a great hobby and learning experience for me, and once I started to understand the actual chemistry behind it I really appreciated it. It has served as a kind of jumping off point to my current interest in amateur chemistry.

If you always post in an intelligent and scientifically meaningful way, and bring some information to the table with you to help spark discussion and to show a commitment to learning then you have nothing to worry about. In most cases almost any topic is OK for discussion here if the above mentioned rules are followed, I have noticed.

Also, did you check out hydrazine and 1,2-propylene glycol dinitrate? Neither is 'safe' though. I think the high energy required for a monopropellant to be useful would render it 'unsafe'

[Edited on 13-4-2011 by Bot0nist]

AndersHoveland - 13-4-2011 at 12:42

Nitroguanidine was once used as a propellent in model rocket motors. The exhaust gases were cooler than other typical compositions, which made for safer operation. Although nitroguanidine can also function as an explosive, it is fairly safe and will not explode when burned in a small rocket motor.

You might read more here:
http://reviews.ebay.com/About-JETEX-and-JET-X-rocket-engine-...

DADNE (FOX-7) can also be used as a propellent (it is very energetic for a monopropellent), although it is fairly difficult to prepare:
http://docs.google.com/viewer?a=v&q=cache:IPhyfBlkprQJ:w...

Isopropyl nitrate, which can be fairly easily made, is safe enough for use as a rocket fuel, but not ethyl nitrate. Isopropyl nitrate, is nevertheless capable of detonation, but is very insensitve, having a detonation velocity of approximately 5400 m/sec. It is used as rocket fuel on some racing cars, known as "Thermolene". Isopropyl nitrate is still used as the liquid fuel component on some rockets in Azerbaijan, to reduce the quantity of oxidizer required.

Another version of "Thermolene" apparently used a combination of nitromethane and propane (instead of the isopropyl nitrate) burned with compressed oxygen.

Buy this for your children:
http://horsepowersports.com/turbonique-rocket-kart-for-sale/

The best propellent for your rocket may be nitrocellulose.
http://www.shadowrx.com/forums/showthread.php?t=1286

[Edited on 13-4-2011 by AndersHoveland]

497 - 13-4-2011 at 12:48

Methyl nitrate mixed with methanol forms an azeotrope at about 75:25 if i remember correctly. Methyl nitrate in its pure form is a relatively sensitive and powerful explosive, but when diluted it becomes fairly insensitive, and could be diluted further for an extra margin of safety. The germans used it in WWII. It does have the disadvantage of having a high vapor pressure which does not allow its use on a large scale, but for a smaller rocket I think it would work well.

It has the advantage of being easy to make from cheap materials (methanol, boiled down battery acid and a nitrate salt). If you have a layer of dichloromethane (distilled from paint stripper) above the mixed acid used to nitrate methanol, then pure methyl nitrate will never be formed since it dissolves into the DCM as it forms and is rendered insensitive if enough DCM is used. After separating and neutralizing the DCM/methyl nitrate mixture you could add methanol and distill off the DCM for reuse (just remember DCM forms an azeotrope with methanol so it will distill over with 6.3% methanol in it), so you are never exposing yourself to a sensitive explosive mixture. The nitration is super easy, I've done it. I believe you can nitrate it at higher temperatures than most things because there are no carbon-carbon bonds to be oxidized. Refluxing the DCM would probably be an effective way to cool the reaction.

I don't know the best way to ignite it in a rocket engine though. I bet a small electric arc would work well and be easy to build. Makes me want to try it myself..

12332123 - 13-4-2011 at 13:32

Ethyl nitrite is by no means stable - all nitrite esters will decompose giving NOx and this is likely autocatalysed; I would seriously recommend against them as propellants. How about a eutectic solution of ammonium nitrate in ethylammonium nitrate? This should be liquid at room temperature, and quite an energetic propellant.

vaslop - 13-4-2011 at 13:35

Bot0nist, thanks for the advice, and yes, I had looked at hydrazine, but after trying to synthesize hydrazine sulfate (resulting in 5g yield from hours of work and lots of ammonia fumes) it is an awful chemical to work with, and I really would like to avoid the danger associated with it.. but the PGDN looks good, maybe in need of some stabilising though?

I like the sound of the methyl nitrate, but yes, I'd refrained from making any due to its high sensitivity. but hopefully diluting with methanol would be good, (as a side note, could other liquid explosives be used in the same manner, for example EGDN or NG? or would that be way too dangerous?)

I would like to use nitrocellulose, but its too expensive and hard to regulate the nitration level, resulting in a wide variety of performance levels, a bit too dangerous for me thanks.

AndersHoveland, have you stated not to use ethyl nitrate? and also how would I go about practically decomposing the isopropyl nitrate?

I have already tried heating a cobalt oxide catalyst, and adding ethyl nitrate, this seems to work well, (a strange effect, where the oxide seems to glow, it might be that the cobalt is being reduced, but i dont know) but I have not taken it further yet.

AndersHoveland - 13-4-2011 at 14:04

n-propyl nitrate can be prepared through nitration on n-propanol. The nitric acid used should not have a density greater than 1.42g/cm3, otherwise a potentially dangerous runaway reaction will occur, since n-propanol is more vulnerable to oxidation than ethanol or glycerin.
However, preparing isopropyl nitrate is more difficult. One source states:
"The hydrogen atom which is attached to the carbon atom carrying the hydroxyl group is so easily oxidized that it is not feasible to prepare the compound by the action of nitric acid on the alcohol."

Ethyl nitrate is much less sensitive than nitroglycerin or ethylene glycol dinitrate, but it is still soewhat of a sensitive explosive. Propyl nitrate is comparable to nitromethane in its resistance to impact.

vaslop - 14-4-2011 at 02:17

how would i go about initiating a decomposition of the propyl nitrate, id imagine, some kind of catalyst coated on a mesh screen? rather that just straight ignition?

Eclectic - 14-4-2011 at 04:31

Have you looked at N20 injected into cast solid fuel combustion chamber?
You wanted throttleable, yes?

http://en.wikipedia.org/wiki/Hybrid_rocket

[Edited on 4-14-2011 by Eclectic]

vaslop - 14-4-2011 at 04:48

That is in-fact what the main project is based on, I am using the nitrous oxide chargers from whipped cream suppliers (cheap and easily available) and different plastic fuels to determine their energy density and find the most effective fuel. (I have only tried polyester at the moment)

http://www.hpr.org.uk/mhybrid/gallery

and then scaling it to be throttleable.

I was thinking allong the lines of a liquid fuel tank, filled with monopropellant, pressurised with CO2 from a similar cylinder, that is then injected over a catalyst. This might be too simple, but just looks too interesting to give up on just yet.

simply RED - 14-4-2011 at 05:58

What about propane diol dinitrate? Has reasonable oxygen balance and energy output, extremely easy to synthesize. It has good stability on storage. Is it safe enough for monopropellant?

Bot0nist - 14-4-2011 at 06:18

Quote: Originally posted by vaslop

That is in-fact what the main project is based on, I am using the nitrous oxide chargers from whipped cream suppliers (cheap and easily available) and different plastic fuels to determine their energy density and find the most effective fuel. (I have only tried polyester at the moment)

http://www.hpr.org.uk/mhybrid/gallery

I think Mythbusters used a cored paraffin wax fuel with N2O injected through it. I don't think they got much lift though. Maybe with some tweaking and scaling down it would work though.

vaslop - 14-4-2011 at 06:27

I have looked at that, it seems perfect, cast-able, cheap and non toxic, but I think the fact that it has to melt and be vaporised limits it to the realms of huge motors, with long burn durations? but still something i will be testing, maybe as a composite with paper or wood pulp? (giving it a sort of wick).

Isnt propanediol dinitrate, PGDN?

Bot0nist - 14-4-2011 at 06:34

Yes, 1,2-propanediol dinitrate is PGDN.

With the wax, I think that modifying the core diameter and thickness could be a variable in scaling the project down and still getting the magic temperature. I think it may work, though I am no rocket scientist. It would be worthy of some testing though.

quicksilver - 14-4-2011 at 08:02

Here is a rather old original copy of the Hercules (explosives div.) reference manual for their nitro-cellulose. Specs / data, production, etc. A wealth of info; scanned from an original.

Attachment: herc_nitrocellulose.pdf (2MB)
This file has been downloaded 1025 times

Nitro-cellulose has SO much to offer from the stand-point of a propellant / explosive and is much easier to control & manipulate, it's really worth a look. From the standpoint of a mono-propellant, it has proven itself a wonderful starting point to research and development, that to by-pass it would be a shame.

[Edited on 14-4-2011 by quicksilver]

vaslop - 15-4-2011 at 03:04

I have come up with an idea, a combination of 35% H2O2 (in water) and ethanol, this can be injected over a platinum or silver catalyst and ignited simultaneously. It sounds dangerous to me, mixing an oxidiser and reducer like this, but it is a recognised monopropellant (using 50% H2O2) and i guess it must be stable until the catalyst is present. please tell me if what I plan to do is likely to kill me, or if I'm missing something important.

quicksilver, I have made some nitrocellulose, (via dissolving cotton in sulfuric acid and mixing with 70% nitric acid) but I'm struggling to get repeatable results, how would i be able to ensure that all my nitrocellulose is of a consistent nitration level?

gregkdc - 15-4-2011 at 05:56

I once saw a patent on the internet about using ammonium nitrate in solution as a replacement for hydrogen peroxide monopropellant. If I remember right the catalysts where various metals iron, copper, platinum as well as metal oxides that had to be heated to a certain temp before it would work. Considering that heat itself is probably the best catalyst for AN you maybe able to get it to decompose with some stainless steel mesh.

I like the idea that 12332123 of using a mix of AN and ethyl AN. The thermal decomp at the mesh should be enough to keep the reaction going; you would just need to devise a way to preheat the catalyst.

quicksilver - 15-4-2011 at 11:57

Quote: Originally posted by vaslop

quicksilver, I have made some nitrocellulose, (via dissolving cotton in sulfuric acid and mixing with 70% nitric acid) but I'm struggling to get repeatable results, how would i be able to ensure that all my nitrocellulose is of a consistent nitration level?

Repeatability in a nitration is similar to most any other synthesis with multiple variables. You would need to make note of the time (within contact nitration), temperature, volume (of both acids and precursor), weight, strength, purity levels, & purification agenda.
You would be in a better position to take very fine notes of a productive synthesis where all variables are mapped out before-hand and make sure you could provide a repeat of all conditions & materials.

It's actually not as easy as it would appear because subtle changes such as temperature rise or lower time, container (of the volumetric mass), & precursor elements must be maintained. Nitration (to maintain consistency) is often done on a large scale because of all these variables. In plant conditions it's found that issues such as sourcing (of the cellulose in this case) can bring about differences. Acids are generally obtained in very large supply for repeat-ability sake as well.
In something as direct as nitration with technical grade HNO3 it's important to remember that HNO3 can have a strength alteration of at least 2% if left standing exposed to air for a period of time. Often 70% acid is found to be 65% acid when tested and for this reason, large amounts are frequently obtained. This becomes much more significant with higher purity levels.
The volume of the container vessel has an influence as does (sometimes) slight alterations in temperature. Cooling rate alteration in some nitrations has a significant impact as would precursor purity or form.

[Edited on 15-4-2011 by quicksilver]

aquaregia - 9-5-2011 at 23:35

Vaslop,
I am catching the train running...
What comes to mind, if your sole purpose is having a throtable motor, is an N2O/Rubber hybrid. I know it's not exotic, but that works... By controlling the flow of N2O being injected into the combustion chamber, thrust is controlled. Of course, the problem might be re-ignition of the motor after a long shutdown when the chamber has cooled down. I guess a way to achieve re-ignition would be to inject a strong oxydiser (fuming NO3H?) to get some rubber burning prior to reopening N2O valve... You can also imagine having a grain of special compound at the top of the chamber dedicated to ignition? permanganate? I am just throwing ideas...
It's just that all "practical"' propellants have been explored, believe you me. Also, apart from ease of operation, one of the most important parameter to keep in mind is Specific impulse... What is a point to have a throtable monopropellant motor with a poor Isp? Finally, small hybrid motors are readily available and a good starting point.

vaslop - 12-5-2011 at 13:15

I've decided to expand the parameters of my experiment, I'm now looking at the most practical rockets for amateur 'enthusiasts.'

However i believe that 'throttleability' (assuming that this is a word) is an advantage.

i guess that with solely an oxidiser like fuming HNO3, a kind of hypergol could be created, is this possible with a solid state fuel? I don't know, but with both N2O and HNO3 injectors could be too complex for small motors.

Also the means of storing, injecting and avoiding the toxic and potentially corrosive by-products, could be an issue, without the whole device dissolving.

I might look into ammonium dinitramate, but that would require dry ice, which is like gold dust and I cant find any anywhere in the UK.

[Edited on 12-5-2011 by vaslop]

hissingnoise - 13-5-2011 at 04:50

Quote:

I might look into ammonium dinitramate, but that would require dry ice, which is like gold dust and I cant find any anywhere in the UK.

If you can get a cylinder of CO2 you can make dry ice using a dry ice maker . . .