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ManyInterests
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I don't have a heating cabinet. I will find something. Maybe preheat the oven to only 75C before switching off? The temperature would be a bit too low
to damage it. I will test it with a bit.
Right now I am having issues with my new setup for nitric acid. The adapter that I thought I could use was no good and I needed to use a Clairsen
adapter with another 3-way on one side. I think I didn't put my thermoproble (I am using one of those small tiny ones for this) at the absolute bottom
of the adapter, which I guess meant that once it got to 90 and started to climb, it condensed back into the flask. I was told that it needed to be
higher up. Which I will do next time.
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Microtek
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The longer the distillation path, the more you will need to heat it to collect anything. This can be a problem with compounds that suffer from thermal
instability (such as nitric acid). You can mitigate the problem by insulating the upper parts of you setup (wrap it with a cloth and use Al foil or a
clothes pin to keep it in place). You can also shorten the path as much as possible by eliminating any extra joints between the boiling flask and the
condenser. There really is no need for a thermometer (or probe) for this distillation.
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ManyInterests
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Quote: Originally posted by Microtek  | | The longer the distillation path, the more you will need to heat it to collect anything. This can be a problem with compounds that suffer from thermal
instability (such as nitric acid). You can mitigate the problem by insulating the upper parts of you setup (wrap it with a cloth and use Al foil or a
clothes pin to keep it in place). You can also shorten the path as much as possible by eliminating any extra joints between the boiling flask and the
condenser. There really is no need for a thermometer (or probe) for this distillation. |
OK so once again I would direct you to my thread in Beginnings.
I found a workaround that uses my old setup, but since I have a smaller thermoprobe, I was able to insert it in the small thermometer adapter hole. I
wrapped it with copious amounts of teflon tape to protect it and seal the hole at the top. I did not see any gasses escape and after the distillation
I washed it and removed the tape. It was intact. So I know this way I can measure the temperature while keeping a short path.
The only problem is, I got 75% nitric acid. Maybe it was because of the mishap yesterday (probably that) But I did see that nothing came over until
the temperature reached 113. Maybe I kept the the small thermoprobe a little too high?
If you look at the picture, that little white thing in the adapter is the probe head. What do you think of the setup?
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Microtek
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The setup looks fine, but add insulation as described above and preferably some vacuum if possible. Vacuum is obviously NOT possible with the
improvised thermocouple adapter, but you could just replace that with a stopper (if you have one). PTFE tape is not great for vacuum seals, I would
replace with grease (or old school conc H2SO4 if you don't have grease). Ideally you shouldn't see red NOx fumes in your boiling flask since these are
a sign that your HNO3 is decomposing (though I have heard that a little is unavoidable if using nitrate salt and sulfuric - another reason I prefer to
use 65% HNO3 instead of a salt).
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ManyInterests
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I wish I could use a stopper, but the joint that I have doesn't allow for it. I will see what I can do to make a small vacuum filter. I have a small
tiny little air pump. It isn't much and is very weak, but it is cheap and I don't mind losing it if the acid vapors destroy it.
The thing is, I've ALWAYS seen red fumes when I power up my mantle. I think what I am going to do now is to gradually increase the temperature. Like
start to make it go to 50C and gradually raise the temp until I set it to 85 or so.
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Hey Buddy
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| Quote: Originally posted by Hey Buddy | | I love nitric acid and I love PTFE. Here is one of those neat tricks. If you make some HNO3 and put it in a small mouth Erlenmeyer, you can lightly
stretch PTFE tape over the opening and tape the circumference with electrical tape to hold it in place. You can heat the HNO3 and it drives water off
through the PTFE and will bring HNO3 beyond azeotrope. A diaphragm concentrator. This is sort of a red neck engineering thing, so you have to play
with a few types of PTFE and stretching and the temperature to get a good system. I havent measured the resulting HNO3 concentration because I havent
taken a serious effort at it, but it works. Also works with concentrating H2SO4. |
I must have been smoking crack when I wrote this. I somehow have a memory of doing this but recently I tried it and it doesnt work at all with HNO3.
It does work with H2SO4. I dont know why I thought it worked on HNO3. Anyways, on standard ptfe, when its stretched NO2 goes right through tape so
dont waste your time. I did however notice the NO2 slips through the PTFE with ease, like its not there. NO2 I believe is smaller than H2O. Not sure
of HNO3 molecular size... it may be possible to pull H2O out in a reduced pressure distillation with PTFE membrane... need to experiment
[Edited on 16-10-2023 by Hey Buddy]
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