Distilling pure anhydrous ammonia

when you hear the word ammonia you might think of this blue glass cleaner but actually this is mostly water with ammonia gas dissolved in it but for some future experiments I have planned I need the pure ammonia out of this damn hydrous ammonia meaning ammonia without water so in this video I'm going to talk about how to transform this into an hydrous ammonia and also how to store the product the material safety data sheet is a little sketchy but it's likely that this contains about five percent by mass pure ammonia and we could use that and that would work just fine however there's other chemicals in here too that might get in the way so you can also buy this on eBay and this is actually thirty percent by mass pure ammonia so think about that if you took a third of this entire jug you could actually extract that liquid and have pure anhydrous liquid ammonia of about a third of this entire jug so there's quite a lot dissolved in there the trick is that water loses its ability to hold ammonia as we raise the temperature so at room temperature thirty percent by mass is about as high as we can get but if we start to boil this or if we raise the temperature on the way to 100 degrees C all of the gas will start being emitted and by the time we reach 100 degrees C it'll just be pure water and all the ammonia will have been driven off the first part of the process is to put the ammonia solution into a vessel where we can easily raise the temperature I originally thought about using a sand bath or an oil bath to put this flask in or you know what would be even better as a heating mantle but I don't have any of that and since the temperatures aren't very high this flat bottom flask on a standard hot plate worked out just fine and then I stuck a temperature probe on the outside just to keep an eye on that and since we're going to be raising the temperature up to about a hundred C we're also going to be getting a lot of water vapor off of this and the problem is that we don't want that water vapor in our ammonia gas as this thing bubbles will be getting both off and we want to separate out the ammonia from the water vapor so the next stage is to put a condenser on top of the flask and here I just have very cold water at about five degrees C running through the coil so as the water vapor drifts upward through the condenser it condenses on the coils and drips back down at refluxes back into the flask whereas the ammonia gas that's been liberated from the solution continues upward through the apparatus I've used these Keck clamps to hold together the apparatus but there's a plug at the top here that purposefully doesn't have a clamp this is so that if the pressure increases high enough it'll just push this cork upward and vent the ammonia out instead of exploding the glassware and spraying ammonia everywhere which reminds me you'd have to be totally nuts not to do this in a fume hood I used silicone grease on all the ground glass seals to make sure that everything was gas tight so at this point in the system we have fairly dry ammonia gas but there's still a fair bit of water vapor mixed in and we'd like to remove that so that when we compress or chill our ammonia gas into a liquid we don't have lots of water contamination so what we want to do is pass this through a column of substance that will absorb the water basically it's a desiccant or a dehydrator and if you go to a hardware store you'll find a product called damp rid which you can't use for this application because damper it is actually calcium chloride and that would react with the ammonia gas I think silica gel also would actually react although I couldn't come up with a definitive answer for that from my research however there is a desiccant that works great and that is sodium hydroxide or lye 100% lye potassium hydroxide would be even better but that's harder to find the stuff you can get at the hardware store so I have this glass column and at the tip here I've put some glass wool just to keep the granules of sodium hydroxide from slipping through and then I dumped in you know about a handful just the amount is not too critical of sodium hydroxide and as the gas sort of diffuses through these NaOH pellets the water will be absorbed and the ammonia will pass right through so at this stage in the system we have fairly dry ammonia gasps at just over one atmosphere of pressure in order to store that gas we either have to compress it using a you know a mechanical compressor or we could chill it to the point where it condenses into a liquid and then we could pour the liquid into a vessel and that's that's the route that I chose to use this piece of equipment is a cryogenic freezer it has a well that's filled with alcohol in here and when it's running it can get all the way down to negative 100 degrees C so my plan originally was to get a small round bottom flask and get this hose adapter and then connect this hose up to the ammonia stream coming out of the glassware that we just saw and then put this down into the cold trap so as the ammonia gas went into the flask it would condense in here and I'd end up with a full flask of liquid ammonia this ended up not working probably because the thermal transfer through the glass wasn't very good and also when the system starts up there's a lot of air that has to be purged out of all that glassware and so you have to sit there for a long time with with this system open so that to get the air out and meanwhile there's you know tons of ammonia vapor coming coming out as well so ideally we'd have a condenser setup just like above the boiling flask where there's like a cold liquid flowing through and then as the ammonia drifts through it condenses on those coils so for a while I thought well maybe I could do like a submersible pumping here that would pump the cryogen up into a coil then the thing would drip down is that pump is a problem in priming it and the rubber is freeze and all that kind of stuff so eventually I came up with this system this is a stainless steel piece of apparatus in fact it was originally a nitrogen purification cartridge this is what the top of it looked like nitrogen purification now this wasn't a nitrogen separation membrane this thing requires that your gas already be 99% pure and then this will take you up to 99.999 or whatever and it was already spent so I cut it up and wanted it just for the fittings and the fact that it was made of stainless steel all the fittings are stainless including the sealing ferrule that's inside there and I bent the tube around so that when this thing sits down into the cold the cold alcohol in there the ammonia will have more than enough chance to condense and it will flow up in here as a liquid and then this thing will you know hold all the liquid until I'm ready to put it in the storage container and this ended up working quite well the storage tank for the anhydrous ammonia must have all steel or stainless steel construction because the ammonia will corrode brass and other copper containing alloys the tank must also be about you know this big to hold the quantity that I needed and also have a small enough diameter to fit down into the cryogenic freezer and must also have a working pressure of a few hundred psi so this tank is pretty much perfect this is a liquid propane tank that you can get at the store for just a few dollars really and I set about converting it for use with ammonia I used a really coarse screw to yank out this plastic collar that's on the inside of the neck and then used a Schrader valve tool to remove both the main valve that's in the the neck of the cylinder and also the safety relief valve I found a 1/8 to 3/8 pipe fitting that had an outer diameter almost exactly the same as the propane cylinder neck and I TIG welded this on after the weld was cool I hooked up the cylinder to a pressure manifold and then used an old refrigeration compressor to just pump air into the cylinder as a pressure test and one thing that I found interesting is that the safety valve doesn't have a hard stop it's not like you screw in the safety valve and it has a preset pressure it actually the set pressure goes up as you screw the valve in further and further and there's no definitive stop in there which I found kind of weird so I used my AC this high pressure gage on the AC manifold to check the pressure while I screwed the valve in further and set it to a relief pressure of just over 300 psi so here's the whole system running we've got the ammonia solution bubbling away we've got the cold water circulating and condensing the water vapor which we don't want and then the gas the ammonia being dried and passing down into the cryogenic freezer where it's being liquefied and then every half hour or so my little stainless condenser would be filled up and I would manually tip it out and pour the ammonia into the storage container and I had to remove the emergency expansion valve off of the container to provide a vent path the neck is still very small diameter inside there and so even using a funnel the boiling vapor would just cause the ammonia to splatter everywhere and if you're wondering yes the smell was terrible in fact the the vapor that this thing puts off is you know ridiculously strong actually and I did in fact use this when I was doing the ammonia transfers I really couldn't endorse it since this is kind of more of a you know a novelty almost at this point it's it is actually a real gas mask but this cartridge is old however despite all that using this made it such that I could almost not even smell the ammonia inside the mask so I was very happy to have this today another problem I had is that the cryogenic freezer has only an on/off switch it's meant as a cold trap device and as soon as you switch it on it tries to get down to negative 100 C as quickly as it can however the melting point of ammonia is negative 78 C so if the cold trap got all the way down to negative 100 instead of condensing it actually freeze the ammonia solid and I actually found this out the hard way too so in that narrow passageway at the bottom of the condenser this this will become solid ammonia and then nothing passes through and the system pressure builds up until that glass cork pops off and sprays ammonia out so I don't have a temperature controller for this so I was just switching the freezer on and off manually anyway after getting all these kinks worked out after about half a day today I built up quite a bit of liquid ammonia and I took the storage container out of the freezer and screwed in this steel valve so that now the thing you can hear the liquid sloshing around in there but now I can control it very easily through this steel needle valve here's an interesting demonstration we can do with some of the anhydrous ammonia that I just created so I have a beaker filled with some of the chilled alcohol and then inside the test tube is the anhydrous M and I have a little stir bar sitting at the bottom there and this whole thing is on a stir plate and the idea with using this beaker of cold ammonia or cold alcohol is just to give this more thermal mass so that the ammonia doesn't boil away so I'll start the stir bar spinning a little bit and to it I'm going to add lithium metal I just put in a flake about the side let's do another one and you can hear a slight amount of boiling right as the lithium goes in and hits the cold ammonia this is called the birch reduction and the color actually comes from free solvated electrons so what you're looking at is an extremely good electrical conductor because it has free electrons as you can see after I add more lithium metal these solution changes from a dark blue color to this very metallic bronze color it's really a beautiful color ammonia gas is technically flammable but not really I hooked it up to my manifold and made a primitive torch and then sprayed pure ammonia over an alcohol flame as you can see it actually puts the flame out it's it doesn't catch at all in that sort of circumstance so I decided to up the ante and I mixed the ammonia with pure oxygen and then shot that out of the makeshift torch and as you can see it still doesn't even sustain a flame I tried different mixtures I probably could have dialed it a little bit more carefully but needless to say it's not really much of a fire hazard since it's just so difficult to get started I believe the ignition temperature is even higher than the flame temperature which you know it means it doesn't self-sustained okay stay tuned to see what I have plans next for this see you next time bye

Channel: Applied Science

Views: 293,844

Keywords: ammonia, anhydrous, anhydrous ammonia, krasnow, applied science, distillation, drying, cryogenic, ammonia tank, distill, glass cleaner, birch reduction, lithium

Id: I_DD2_7QkRk

Length: 13min 41sec (821 seconds)

Published: Sun Apr 19 2015