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Author: Subject: Vacuum pump for vacuum distillation.
FranzAnton
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[*] posted on 13-5-2020 at 14:30


Sorry my stupid question, but if you only want to do the preparation of that ester (for historical interest) you can use H2SO4 in excess so you will get it anyway in smaller amounts but it's possible. So if the glycerol is at leat 80% you will make it without pump and equipment.
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TLutman
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[*] posted on 14-5-2020 at 16:18


As a beginner into organic chemistry, I'm just trying to weigh the pro's/cons of different methods. My first few things to synthesize were things experienced chemists would just go buy, and I might get there one day myself.
I decided to make some HNO3, which is what sparked my curiosity to begin with (thanks Nurdrage), but wanted to avoid any NO gas. I just used a $16 12V vac pump from Adafruit (electronics site), which pulled almost 30inHg IIRC. Yep, the BP was lowered. Nope, no NO. But also I could drop the vapor column back into the boiling flask and immediately stop the boiling by breaking the vacuum at the vac adapter.

I figure the cheap pump would last a little while, and is cheap enough to just replace when it goes belly up. I might get a pump down the road that isn't so annoying, but for now, it will do.
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FranzAnton
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[*] posted on 15-5-2020 at 06:54


If you want to concentrate the HNO3 only by destillation (vacuum or not) you will not get much higher than approx. 68-70% because the aceotropic concentration do not differ significantly with pressure.

So you need somethin in addition to remove water. Mg(NO3)2 or H2SO4 can help. A destillation under reduced pressure helps only to recuce decomposing during destillation. (Intense Light speeds up the decomposing)
The higher the concentration of HNO3 the faster it will decompose. So for long therm storage a 68% solution is much more stable under the same storage conditions that a 98%.
By the way in this forum library there is a book which will help you to get a detailed view of nitric acid (Mellor_ACTITC_v08_1931) It's old, but really packed of information.


[Edited on 15-5-2020 by FranzAnton]
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Mateo_swe
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[*] posted on 19-5-2020 at 10:22


Thanks for that Nitric acid reading tip, i will read it.

Im just a beginner when it comes to chemistry but i will eventually try make some nitric acid and try to get as good % i can get.
I thought aspirators was the only way to do a vacuum destillation of nitric acid as it ruins any diafragm pump very quickly.
Thats what i have read at least.
Im not even considering cold trap pumps due to cost.
I have looked into making some nitric using NaHSO4 + KNO3.
What will the strength of the nitric be using this method?
I know the temps are little to high using this procedure resulting in some nasty fumes that requires it to be done outside.
I do have a DIY fumehood but this one i will be doing outside anyway.
Can aspirator vacuum be applied in this procedure to try lower the temps and reduce the decomposition of the nitric acid?
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Fyndium
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[*] posted on 26-7-2020 at 11:24


My pump is getting alarmingly low on oil. I looked for vacuum pump oil everywhere but can't find other but one supplier that sells €50 per liter + 20€ shipping. I tried to look for alternatives and the composition of vacuum pump oil is a close resemblance of liquid paraffin oil, which is essentially a mineral oil. It has similar density, vapor pressure and cst value and both share the fact that they lack any additives.

To be real, what would happen if I were to just load the pump with liquid paraffin oil? I happen to have a bottle on my hand. The pump wasn't very expensive and worst that could happen is maybe an oil mist, so would I be stupid to try it out?

I'm speaking of the european type paraffin oil that is viscous as normal lubricating oil and is used for all kinds of things, from treating woods to skin, never as a fuel.

[Edited on 26-7-2020 by Fyndium]
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monolithic
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[*] posted on 26-7-2020 at 13:49


Quote: Originally posted by Fyndium  
My pump is getting alarmingly low on oil. I looked for vacuum pump oil everywhere but can't find other but one supplier that sells €50 per liter + 20€ shipping. I tried to look for alternatives and the composition of vacuum pump oil is a close resemblance of liquid paraffin oil, which is essentially a mineral oil. It has similar density, vapor pressure and cst value and both share the fact that they lack any additives.

To be real, what would happen if I were to just load the pump with liquid paraffin oil? I happen to have a bottle on my hand. The pump wasn't very expensive and worst that could happen is maybe an oil mist, so would I be stupid to try it out?

I'm speaking of the european type paraffin oil that is viscous as normal lubricating oil and is used for all kinds of things, from treating woods to skin, never as a fuel.

[Edited on 26-7-2020 by Fyndium]


I think it would work just fine. Most "purpose made" vacuum pump oils are just mineral oils which are fractionated and maybe mixed with a rust inhibitor. This webpage explains it in a little detail: http://www.hyvac.com/Products/Oil/vac_oils.htm (They're a good source for materials on vacuum pump maintenance, too.)

Try it, I don't think it poses any risk to your pump.

[Edited on 7-26-2020 by monolithic]
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Fyndium
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[*] posted on 11-11-2020 at 04:08


For the record, I successfully used paraffin oil. I've also used it as joint grease.

How to cool vacuum pump?

Mine gets very hot, above 90C when running for a longer period and too hot to touch. It would be trivial to cool down with water, but that'd be more difficult to carry out. One crazy idea that came in mind is to put the pump in a thick plastic bag and immerse it in water bath so the pump exhaust and other necessary accessories are not blocked.
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wg48temp9
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[*] posted on 11-11-2020 at 05:00


Quote: Originally posted by Fyndium  
F
How to cool vacuum pump?

Mine gets very hot, above 90C when running for a longer period and too hot to touch. It would be trivial to cool down with water, but that'd be more difficult to carry out. One crazy idea that came in mind is to put the pump in a thick plastic bag and immerse it in water bath so the pump exhaust and other necessary accessories are not blocked.


Thats a terrible idea. Most pump motors are cooled by a fan at one end so they should be operated with access to air. If you still want to cool the pump body (not the motor) down attach a 6in fan to it to blow air over it.




I am wg48 but not on my usual pc hence the temp handle.
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[*] posted on 11-11-2020 at 07:46


Fyndium:
My 2-stages vacuum pump is allowed to run 20 minutes without extra cooling, but for every run longer than 20 minutes it requires to add an extra fan to blow air to its side(s). This is written exactly in its manual and also its seller told me the same. According the oil (few months old question) - my bottle with oil (which I got together with my pump from the seller to replace the pump oil) states it is hydraulic oil, such oils are used in cars, machinery etc.




If there is a heaven, it seems not to be materially based. Does chemistry exist there and if yes, how does it look like? Are there good souls well supplied with laboratory equipment, glass, chemicals and information?
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Fyndium
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[*] posted on 11-11-2020 at 08:00


This is 1-phase pump.

My logic was that cold water, even through plastic membrane, is many times better conductor of heat than air.

Only good thing about running the pump hot yesterday was that the slight water emulsion contamination cleared up due to water just simply evaporating away.
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