Sciencemadness Discussion Board

Liquid Nitrogen generator

Gearhead_Shem_Tov - 28-12-2014 at 18:17

I came across this on Instructables today:

Home Made Liquid Nitrogen Generator

Enjoy.

-Bobby

[Edited on 29-12-2014 by Gearhead_Shem_Tov]

neptunium - 28-12-2014 at 18:59

have you seen this?

https://www.youtube.com/watch?v=4_bGkztd7t0

and that

https://www.youtube.com/watch?v=51a7X7lblMc


Bert - 28-12-2014 at 21:44

That's going to make amateur rocketry a lot more fun...

forgottenpassword - 29-12-2014 at 03:28

Very interesting. Being able to make liquid nitrogen on demand would meet any cooling requirements that a chemist could possibly have, I should think!
Personally I'd be more interested in buying one than making one. The fellow mentions making and selling them for $150, but whether he's made any to sell or not I have no idea. I wonder if there are any EXISTING commercial coolers that meet the same requirement of condensing nitrogen, that anyone is aware of? Hopefully more compact, too. Perhaps these are common in smaller laboratories? If not, they certainly should be! I've got all the parts together to make a Sprengel vacuum pump, so a source of liquid nitrogen could come in useful!


[Edited on 29-12-2014 by forgottenpassword]

careysub - 29-12-2014 at 05:14

I'm believe that the $150 product he references (if he does follow through) would be a kit-to-build kind of thing, certainly not with the compressor.

Here is also an NIST document about this technology for laboratory scale:


[Edited on 29-12-2014 by careysub]

Attachment: nbsscientificpaper419vol17p277_A2b.pdf (578kB)
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j_sum1 - 29-12-2014 at 05:40

Liquid air is not liquid nitrogen. Removal of the O2 is not insurmountable and may not be needed for some applications. However the tendency for oxygen to concentrate as the air evaporates presents a significant hazard.

forgottenpassword - 29-12-2014 at 05:53

Quote: Originally posted by careysub  

Here is also an NIST document about this technology for laboratory scale:

Interesting, thanks!
Quote: Originally posted by j_sum1  
However the tendency for oxygen to concentrate as the air evaporates presents a significant hazard.
What do you suggest practically doing about it?
Or are you just the person that says: "There is a significant hazard. I urge caution."

[Edited on 29-12-2014 by forgottenpassword]

HgDinis25 - 29-12-2014 at 06:15

Interesting, I'm planing to make a liquid air generator in a few days... And now I have one more topic filled with intel :D

http://gizmology.net/liquid_air.htm
What I plan to make is an adaptation of Carl von Linde's machine. I was able to get my hands on a fridge compressor and a dehumidifier compressor.

The theory is simples. When you take a pressurized gas and make it pass through a small opening, it decompresses and loses energy. The links posted above already explain this. However, when you compress a gas, its temperature increases.

I plan to put the two compressors inside an isolated box. The first one takes air from said box and compresses it through a tube going to a second isolated box (the collection vessel). There it passes through a small opening, decompresses, and loses energy. This box is conected to the first box through another tube. And the cycle repeats again.
So, air goes to the compressor, passes through small opening to the second box, returns to the first box and is compressed again.

Now, what about the second compressor, in the first box? That one is only going to compress air and pass it through a small opening INSIDE the first box. That way the increasing of temperature derived from both compressors working is compensated by the second compressor, while the first compressor makes the gas go to the second box.

I don't know if I'll be able to get this working or not. Even if it works, dry ice clogging the tubes will probably be a problem. Also, the boxes I mentioned need to have valves. One to allow more air to enter, should any gas condense, and other to remove said condensed gas.

Dr.Bob - 29-12-2014 at 06:43

That is a pretty interesting concept to make LN2 at home. I barely even use it at work now, mostly use dry ice a lot, but LN2 is very useful. And the LOX can be even more useful, especially for starting your charcoal fire, as I am sure many of you have seen. (if not, google "George LOX charcoal fire" or something like that.) I am always impressed by some of the home made apparatus I have seen made over the years. My favorite was a Van de Graf generator someone here made a few years back and was big enough to create quite a lightning storm.

Even the "professional" fluorination apparatus that I saw when I worked in a fluorochem lab was pretty much hand made and looked as much as something from an autoshop as from a chemical engineering lab. I think it was either Monel or some other nickel alloy, which might be a little pricey. I still have a nice piece of Monel pipe that is likely worth a lot as scrap if I could find a buyer. I used it as part of a pile driver type weight for a while before I knew what it was made from.

Bert - 29-12-2014 at 07:16

Quote: Originally posted by j_sum1  
the tendency for oxygen to concentrate as the air evaporates presents a significant hazard.


That's not a FLAW- that's a FEATURE!

careysub - 29-12-2014 at 11:15

Quote: Originally posted by forgottenpassword  

Quote: Originally posted by j_sum1  
However the tendency for oxygen to concentrate as the air evaporates presents a significant hazard.
What do you suggest practically doing about it?
Or are you just the person that says: "There is a significant hazard. I urge caution."

[Edited on 29-12-2014 by forgottenpassword]


I can volunteer for that one.

Short answer: you must treat it as if it was liquid oxygen, not that inert benign material liquid nitrogen.

It starts out as 20% LOX, bad enough itself, but the concentration only increases as nitrogen evaporates.

"Liquid oxygen contains 4,000 times more oxygen by volume than normal air. Materials that are usually considered non-combustible, (such as carbon and stainless steels, cast iron, aluminum, zinc and teflon (PTFE),) may burn in the presence of liquid oxygen. Many organic materials can react explosively, especially if a flammable mixture is produced. Clothing splashed or soaked with liquid oxygen can remain highly flammable for hours."
http://www.ccohs.ca/oshanswers/chemicals/cryogenic/cryogen1....

Bert - 29-12-2014 at 11:59

Liquid air is not to be trifled with, despite my previous tongue in cheek comment.

Oxyliquits:

http://www.sciencemadness.org/talk/viewthread.php?tid=16174&...

Note that some of these may detonate from fuse or exposure to fire without a detonator/booster needed.

Capable of quite high VOD too:

http://m.youtube.com/watch?v=iQKkctzGGUw

Vaguely recalled annecdote has it that spilling liquid O2 or nitrogen depleted liquid air on an asphalt runway surface has led to fatal explosions when people merely walked over the area of spill. Looking for a reference-

It is interesting to see these youtube videos at a time many areas are trying to prevent posession of various oxidizers. Access to air and electricity will be a bit harder to control?

j_sum1 - 29-12-2014 at 13:13

Yeah. I am just recommending caution. I can visualise some amateur with not quite enough knowledge accidently concentrating to 80% O2 and then pouring half a litre over his desk or clothes.

ValenceOctet - 30-12-2014 at 19:28

thx for the holiday reading :-)



[Edited on 31-12-2014 by ValenceOctet]

careysub - 31-12-2014 at 07:34

Quote: Originally posted by Bert  
Liquid air is not to be trifled with, despite my previous tongue in cheek comment.

Oxyliquits:

http://www.sciencemadness.org/talk/viewthread.php?tid=16174&...


Here is a particularly choice excerpt, from the hazard perspective:

"One of the most serious faults of liquid oxygen explosives is the ease with which they inflame and the rapidity with which they burn, amounting practically and in the majority of cases to their exploding from fire." (My emphasis).

And here is a NASA study of the hazard of LOX spills on asphalt (see attached).

Result of study - thick old asphalt was very sensitive to impact explosions. With a 10 kg-M impact they got explosions 100% of the time (20 test, 70% of them violent), with a 1 kg-M (!) impact they also got explosions 100% of the time, but "only" 1 out of the 3 tests was "violent".

Also a nice section showing in detail how they blew up their test stand.

It has as an appendix an NBS (NIST) report on LOX hazards, which mentions an (unsourced) incident of explosion caused by a man walking on a asphalt/gravel surface, and also has this useful bit of cautionary information relevant to the amateur chemist:

"Among the materials considered particularly hazardous in the presence of liquid oxygen are sulfur, hydrocarbons, alcohols, ethers, fuels of all kinds, oils, greases, waxes, tars, asphalt, starches, sugars, soaps, powdered metals, wood, cork, paper, textiles, rope, paints, and some plastics."

Also:
"A large number of materials may be placed in liquid oxygen for a few minutes and be detonated on impact."

Attachment: 19740002978.pdf (7.3MB)
This file has been downloaded 439 times


[Edited on 31-12-2014 by careysub]

HgDinis25 - 31-12-2014 at 13:00

Hum, interesting...

Oxygen has a b.p. of ~-183ºC while Nitrogen has a slightly inferior b.p. of ~-196ºC. CO2 solidifies at -78ºC. Therefore, if one tries to condense air without CO2, the first fraction that actually condenses will be the Oxygen one. At those "freezing" temperatures is there any risk of kaboom?

If so, the best method to avoid unwanted explosions would be to remove any oxygen from air prior to add the air to the machine...

jock88 - 31-12-2014 at 13:28


LOX + Carbon has been used in mines as a cheap explosive for years.
One advantage is that if it did not go off it became harmless if left for a few hours for all the O to go away.
It was static sensitive.

imsmooth - 14-3-2015 at 07:23

I guess I found this thread late. I made the liquid nitrogen generator using a compressor. Liquid air is an issue and I certainly don't want to be near a theromos full of LOX. If you read through my site you will see that I built a PSA nitrogen generator. This cost a few hundred dollars and is very reliable. I get 99% nitrogen out of it with one stage at about 30 L/min, maybe more.

Here is the link, which will hopefully solve the "liquid air" issue for those interested in pursuing LN2

careysub - 14-3-2015 at 17:19

Quite impressive project! Thanks!
Lots of amazing amateur projects show up on this site.

Could a commercial pressure swing oxygen concentrator be reworked to produce nitrogen?

Show us the nitrogen liquifier unit you have also.

imsmooth - 15-3-2015 at 08:38

A concentrator has to eject the waste gas in order to concentrate the other one. So, if one has an oxygen concentrator, the waste gas should be close-to-pure nitrogen. I've measured the waste gas on my system (N2 concentrator with O2 as waste) and it is over 40% oxygen. This is what I get from the stream coming out into the atmosphere. It is probably much purer, but I have not collected it.

The question is if the waste gas is coming out of a single tube that you can use for collection.

My project was listed above. The whole tutorial so others can copy it is right here.

Below is an image of the collection reservoir and terminal coil.

[img][/img]

inside cooling tower.jpg - 57kB

[Edited on 15-3-2015 by imsmooth]

[Edited on 15-3-2015 by imsmooth]

neptunium - 22-4-2015 at 20:32



finally got the last piece I needed for the sterling cooler to function properly...
0422152352.jpg - 510kB
the blue ish color is indeed O2
0422152353.jpg - 382kB
this things runs on 27 volt but consume quite a bit of juice!
the cable was hot !
0422152353a.jpg - 470kB
but it was worth it !

jock88 - 26-4-2015 at 13:44


Great project. Unfortunately the heart of the system, the compressor, is going to be a bit too expensive for most here. What are its specks.
It pumps to 200 atms (about 3000 psi) What would be the flow rate at this pressure.
Will fridge pumps give this sort of pressure (assuming you have a fridge pump that has the motor SEPARATE from the compressor.
Did you have to add special cryogenic oil to the compressor and was it specially designed to work a very low temperatures.

EDIT Sorry about all the questions. On further reading of the page they are answered.
What sort of a pump did the old timers use. Oil free? Or do you just need oil free for high purity liquids gases at the output. If you could produce 'dirty' liquid gasses they you could use a simply heat exchanger (or cold exchanger if ya like!) to give you high purity liquid gasses.



J88

[Edited on 26-4-2015 by jock88]

Fulmen - 25-7-2015 at 01:14

Impressive project indeed. And the physics is quite interesting for those inclined to do the math.

One question: Rather than using a N2-concentrator, wouldn't it be possible to incorporate two throttles to separate N2 and O2?

neptunium - 15-12-2015 at 16:57

I know some people use a membrane that separate O2 and N2 from a fridge compressor

annaandherdad - 15-12-2015 at 19:04

Here's another liquid N2 generator on youtube. Applied Science has some very good videos on a variety of topics.

https://www.youtube.com/watch?v=7PWESWqhD8s

kt5000 - 16-1-2016 at 11:46

Quote: Originally posted by forgottenpassword  
Very interesting. Being able to make liquid nitrogen on demand would meet any cooling requirements that a chemist could possibly have, I should think!
Personally I'd be more interested in buying one than making one. The fellow mentions making and selling them for $150, but whether he's made any to sell or not I have no idea. I wonder if there are any EXISTING commercial coolers that meet the same requirement of condensing nitrogen, that anyone is aware of? Hopefully more compact, too. Perhaps these are common in smaller laboratories? If not, they certainly should be! I've got all the parts together to make a Sprengel vacuum pump, so a source of liquid nitrogen could come in useful!


[Edited on 29-12-2014 by forgottenpassword]


I think the $150 was for the RTD temperature probe and display only.

halogen - 16-1-2016 at 14:10

PTFE burns in liquid oxygen?! :o

teodor - 2-11-2020 at 02:13

So, what is the most affordable method to produce small quantities of liquid air or nitrogen in a home lab? Is anything available commercially today, let say, for the price not more than several hundreds euros? Tutorials to build a home-made compressor looks a bit complex for one who has no experience in building such kind of devices, I suspect most of them also are not "entry level" ones.

Ubya - 2-11-2020 at 10:11

Quote: Originally posted by teodor  
So, what is the most affordable method to produce small quantities of liquid air or nitrogen in a home lab? Is anything available commercially today, let say, for the price not more than several hundreds euros? Tutorials to build a home-made compressor looks a bit complex for one who has no experience in building such kind of devices, I suspect most of them also are not "entry level" ones.



if you can find a used cryo cooler vacuum pump you can turn that into a liquid air/nitrogen generator, i've seen them sold for $200-500.
Liquid air is easier to make, you don't need any purifying process before the liquefation stage.


teodor - 2-11-2020 at 10:37

Thanks Ubya, I will definitely follow offers for a used lab equipment, I think a chance to buy something like that in 200-400 bucks range should be a good deal. But I think I still need few other components to make complete system.

I saw some ready-to-use device presented in this video: https://youtu.be/dCXkaQa53QQ?t=39 . But I have an impression that it is more like a toy.

Ubya - 3-11-2020 at 10:29

Quote: Originally posted by teodor  
Thanks Ubya, I will definitely follow offers for a used lab equipment, I think a chance to buy something like that in 200-400 bucks range should be a good deal. But I think I still need few other components to make complete system.

I saw some ready-to-use device presented in this video: https://youtu.be/dCXkaQa53QQ?t=39 . But I have an impression that it is more like a toy.


there are 2 "kinds" of cryo pumps, the one in the video you sent has everything in the same cylinder, then there are pumps where the helium compressor is separated from the cold head and connected via helium lines.
They both can liquefy air/nitrogen but ofc the rate is different. The compact version can't make you liters of nitrogen everyday but in general they both are pretty slow systems.
Grant Thompson made 3 years ago a video about his setup, https://youtu.be/I_qKVyQ1ry0?t=130
as you can see he used the "split" kind of pump, and to fill his dewer he still needed 1 week