Ammonia Generator/Ammonia in Methanol

[Tweet]I'm getting board babysitting my ammonia generator, might as well post about it.[/Tweet]

In a very web 2.0 way, I will post about something as I am doing it .

I need a dry solution of NH3 in methanol, I can't think of any double displacement reactions that would conveniently produce this without also producing water (aside from resorting to alkoxides), so I setup a little ammonia generator and am bubbling the stuff through methanol. I am pleasantly surprised by how smoothly things are going. So far, my basement doesn't smell like ammonia.

Reagents:
350 mL MeOH (dissolves 3.3 mol NH3 @ 25c)
325g Ammonium Sulfate (~2.5 mol)
250g Sodium Hydroxide (~7 mol)
~7 mL 10% NH3(aq)



The setup, generating away

The setup is fairly self explanatory. The ammonia is generated in the left bottle, it passes through a cooled gas dryer (filled with KOH), it goes on to pass through an automotive PCV valve (check valve) and is bubbled through the cooled methanol using a pipette. Also, the right bottle looks capped, it is only loosely so (although I played with capping it, it does not build positive pressure...so long as the ammonia is dissolving...).

The reaction was setup by adding the ammonium sulfate and NaOH, but not mixing them, letting them layer (I did mine sulfate above NaOH. This is fine, but I think it would work even better the other way around). This mixture is metastable, it doesn't produce much ammonia as is. Next the aqueous ammonia was added and the generator bottle was quickly capped. At this point, not much ammonia is produced, but upon shaking the generator and mixing the reagents, it really gets going. The rate of ammonia production can be easily regulated by how frequently you shake it. Right now I have a good rate of production, I am shaking maybe every ~7 min as I hear the rate of production slacken.

Here are some more pictures of the different parts of the aparatus.



Production bottle (material HDPE)



Here is how a good seal is made using the original gasket (with a hole drilled through the center), the quarter is made of Nickel/copper, the tubing is 304 SS and the solder used was tin silver (the quarter and solder are probably susceptible to attack by ammonia).



This is the gas dryer, I was gonna make it out of PVC, but after pricing all the parts and fittings I found I could make it cheaper from iron pipe, I also use this piece as my vacuum drier/cold trap. The solder is 60/40 Sn/Pb and the tubing is 304 SS.



[Edited on 4-17-2011 by smuv]

It all went pretty well, except it took a long time, I think next time I will either add more water/aqua ammonia or even heat the generator bottle to ~40c to make sure that the sodium sulfate produced doesn't soak up all the water. No issues with suck-back, but this setup didn't really test the PCV valve. Tough I think the pcv valve does leak a little bit against flow (I tested a new one, it does the same), so it may only slow suck-back.

Somewhat related, I went to walmart today and was browsing their surprisingly well stocked aquarium department to see what I might be able to find. I ended up finding/buying a check valve (for air-stones apparently) and these really small ~1.5cm diamater 2cm tall airstones. One thing though, the check valve needs like 5psi to fully open (allows slow flow at ~0.5psi)...so if it were used in a gas generator it would definitly run at slightly elevated pressure.

Anyways, stay tuned for ammonia generator 2.0

Maverick + bbartlog, I'm glad you like my little ammonia generator. Feel free to ask questions.

now thats getto

when ive generated ammonia I have used a glass rig so hats off to ya.

the way ive done it is to have aqua caustic refluxing in a two neck flask with aqua ammonia salt
being dripped into the caustic.

the solution was stirred at all times.

there was a vacuum adapter with stopper put in the end of it slotted into the top of the condensor.

the vacuum nipple is then led to the KOH drying bottle like you have via a tube which is then
led to flask to gas or condense after being passed through a trap.

this pritty much does that except you are not refluxing a solution or dripping a solution.

I would personaly be a little scared of two solids like that being put in a flask then adding a liquid
to get gas.

when one refluxes caustic then drips in saturated ammonia salt solution into it you get a smooth
release of gas.

a final trap then hcl gas capture bottle will then guarentee you get no smells.

my setup looks like a district 9 reproduction shack compared to this. hamilton beach coffee makers use a one way check valve inside one of the brewing hoses and is exactly the same size as your tubing. is ammonia in methanol an old process?does it just smell like ammonia and not methanol or is it a totally different thing? is it ammonium hydroxide?flammable?what is it?.......interesting!

@Arthur: You're right, ball type check valves are usually better for liquids, reed valves are better for gases. I wouldn't worry too much about hose sizes, after all, aquarium air-stones use these small fittings, and that would probably be the best thing to use as a bubbler (probably way better than a pipette).

Erlenmeyer is fine, but I just wanted to avoid using another flask and having another set of leaks to deal with.

@Bot: I'll save that one for you to try. You would need to get the rate of generation up though before attempting this.

@cyanureeves: haha, Ephoton calls it ghetto you call it Hamilton beach. Ammonia and methanol is just like ammonia in water, simply a solution. Ammonia in water contains very little "NH4OH" and is 99% just NH3 dissolved in water. Likewise ammonia in methanol is 99% dissolved NH3 with a small amount of "NH4OMe". But to be honest, I hate how even in literature NH3(aq) is referred to as NH4OH; this only confuses people. Yes it smells like ammonia and methanol, but mostly ammonia.

@Ephoton: Damn E, next time I'll just have to make it out of platinum and unicorns to please you.

I have all the glassware to do this (except the gas drier wouldn't have been pretty), but I didn't want to muck up my glass with the caustic in the generator and drier; so plastic and steel are the way to go IMO. I heavily considered the aqua ammonia route, but I only can get 10% ammonia at prices reasonable for generation, so I was worried that it wouldn't be concentrated enough.

Anyways, thanks for the positive feedback, stay tuned I need to make more ammonia so I'll definitely refine the process and my apparatus a little.

Ammonia Generator 2.0

Hate to double post, but I AM SO PLEASED WITH MY AMMONIA GENERATOR!

The changes are:

Aquarium check valve: I used an air compressor to compare it to the pcv valve, reverse flow, this thing doesn't leak at all. The pcv valve...leaks, even a new one. Although, the aquarium check valve does cause the system to run at a bit of a positive pressure...BE WARNED.

Switched generator bottle: I did a rigorous pressure test of my old bottle, it leaked a little, really not much, but still a little. This one is made from plastic tubing glued through the cap of the bottle (with JB Weld...essentially epoxy).

Aquarium Airstone + stirring the reciever: Much more efficient gas capture, nuff said.

Modified reagent quantities/procedure:

To the generator bottle, 475 g (3.5 mol) ammonium sulfate were added followed by 50 mL NH3(aq). Next, 225 g (5.63 mol) of NaOH was added and the bottle was capped. In this state the generator did not produce much ammonia. The reagents were mixed by shaking. The rate of production could be regulated by how well the reagents were mixed.

With the new procedure the rate of ammonia production is much faster; the generator can be pushed to overwhelm the gas absorption setup, even though gas absorption is more efficient than the previously. Anyways, I am happy.



The setup. Don't get confused by the vac filtration going on nearby


This is the gas receiver, notice I use an insulated wire to prop up the airstone away from the stirbar, while still achieving good immersion. Bare wire CANNOT be used, copper is attacked by ammonia...

Sorry for my post-whoreyness, but this is just cool; look at the volume change after saturation! This started as 350mL of MeOH! I gotta keep this in the freezer, this thing is gonna blow up if I let it come to room temp.




@Mav: One thing to keep in mind is you setup the gas drier like this.

I believe he posted a link to a pic of the drying tube. In the pic it seems to use a glass apparatus. I'm sure that could be improvised though. My understanding is that the wet gas flows to the bottom of the drying tube and is then forced though the drying agent (KOH) and is then collected out of the top. The key is to get the gas to flow through as much KOH as possible before collecting.



[Edited on 20-4-2011 by Bot0nist]

[Edited on 20-4-2011 by Bot0nist]

check my set up :D

I'm about to have a go at this tomorrow, before I do I'd like a thumbs up or a thumbs down on my set-up . It's probably hard to see but in the graduated cylinder there is a small pipet for a nozzle. It may not disperse perfectly but I am checking for a weight increase and a bit of excess is no problem.



Now I've done this before in a mason jar but with a large excess of reactants, a small amount of water to solvate it, and no requirement for dry gas. This time when I try this, of course I will have the receiving vessel in a salt/ice-bath and it will be done OUTDOORS.

This time around I am bubbling it into 95% ethanol for an attempt to synthesize triethylamine(and friends ).

I'm mostly worried about the drying chamber. I have CaCl2 granules in there(the center vessel), if they get wet won't they clog the tube? Maybe I should put a very light and fluffy layer of cotton balls underneath the outlet to prevent this? I'd use NaOH, but it's quite costly, even if it means CaCl2 will yoink some of the gas.

Also worried about suck-back(which did happen last time).

[Edited on 7-11-2011 by smaerd]

Quote: Originally posted by smaerd

I'm mostly worried about the drying chamber. I have CaCl2 granules in there...I'd use NaOH, but it's quite costly, CaCl2 will yoink some of the gas.

Yea I guess I should have looked more into the literature rather then threads here on S.M. where someone mentioned using CaCl2(iirc). Now I have found a paper stating that CaCl2 adsorbs ammonia at room temperature. Good catch, thanks for that . I'll have to look out for soda-lime(primarily CaOH), but if I can't find it I'll just use NaOH, it's really not that expensive and I have ~400 grams on hand.

Yea I should read some more books, I have only taken gen. chem and currently in org. chem 1. So I'm experimenting a little above my knowledge base. Thanks.

are you being witty and implying I will be asphyxiated by NH3 fumes and will need a re-breather? hahaha. Do recall in my original post I said this will be done out-side, and on 1 mole scale. I'll be okay . I guess experimentation is the best teacher I'll report back some-time tomorrow.