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M4D1NV3N70R
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Making Liquid Nitrogen
I'm wondering whether I could make my own liquid nitrogen using things available around the house, junkyard, or home improvement center. I'm
on an ultra tight budget - $20 max, so scrounging everything I can is going to be a requirement for me.
Compressing air to 3000 psi seems awefully expensive, and potentially dangerous (I've heard of pipe fittings going through skulls). Not only
that, It would seem to require fractional distillation after liquifying the air, which would really make it expensive.
Cascading refridgeration sounds more economical and less dangerous, but I can't find many details online (maybe I'm just looking in the
wrong places?), or even how much LN2 it generates.
Has anyone out there made their own LN2? How did you do it?
Change is good. Especially when it\'s more than you just paid.
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saps
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When you compress some air, you're putting energy in and it heats up. You can get it back to room temperature just by running it through some
coils which aren't special, they just have a lot of surface area to let heat flow out to the room. Now if you let that compressed gas expand
again, it does work, loses energy, and gets cold.
You can chain a few stages like that together. For example, the compressed air in the second stage can run through coild immersed in the cold air from
the first stage. It then starts off cold and gets even colder when it expands. But I dont believe that 3000 is enought presure. and you will NEVER be
able to produce LN2 with just 20 dollars.
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M4D1NV3N70R
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| Quote: | Originally posted by saps
When you compress some air, you're putting energy in and it heats up. You can get it back to room temperature just by running it through some
coils which aren't special, they just have a lot of surface area to let heat flow out to the room. Now if you let that compressed gas expand
again, it does work, loses energy, and gets cold.
You can chain a few stages like that together. For example, the compressed air in the second stage can run through coild immersed in the cold air from
the first stage. It then starts off cold and gets even colder when it expands. |
Yes, I'm familiar with
the basic principles, they are described quite well in the Refridgeration Technology thread on this forum. What I'm asking about are dirt cheap
inexpensive setups or even just ideas that others may have come up with. | Quote: | Originally posted by saps
But I dont believe that 3000 is enought presure. and you will NEVER be able to produce LN2 with just 20 dollars. |
Well, $20 is the max I can spend in addition to scrounging, elbow grease and ingenuity.
I was thinking maybe old air conditioners from the junk yard, jury rigged into a daisy chain using some piping from the home improvement center, and
possibly replacing the coolants with something more effective, building up to using methyl chloride in the unit just before the liquification stage.
But that cascading setup still leaves me with a need for fractional distillation to get pure LN2.
Change is good. Especially when it\'s more than you just paid.
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Fleaker
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What's wrong with purchasing some? It's not too expensive, and many places will loan you a dewar with a deposit on it. I'm lucky enough
to get free liquified gases (there's a cascade cooling plant right next door to the store that sells it)
Should be readily obtainable if you have any large welding store or medical supply.
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M4D1NV3N70R
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| Quote: | Originally posted by Fleaker
What's wrong with purchasing some? |
Because once it's gone it's gone. And I need an ongoing supply of reasonable quantities.
Change is good. Especially when it\'s more than you just paid.
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BromicAcid
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Refrigeration Technology
A thread with a similar angle to this one, the main purpose of that thread instead to make liquid air. Explosivo posted a nice picture of a liquid
air producing setup and there is some relevent discussion.
I invested some time into attempting some cascade cooling. Finding air conditioners that still work in peoples garbage was an easy task and I
collected four of them in two weeks. Simple tests involving measuring the temperature in the cooling coils with a thermometer of two different air
conditioners then putting the two together (cold side against hot side) did result in a lower temperature then either could acheive on their own. The
problem with cascade cooling as I saw it though was that the coolant in the systems would not have worked for the low temperature employed, Marvin
states that methyl chloride could be substitued into one of the systems and this used to cascade ethylene which could acheive temperatures to condense
air.
But how to change the coolant in these two air conditioners? Both methyl chloride and ethylene were employed at some time for these things, as a
matter of fact I managed to find a local shop that serived industrial machines that said they could put ethylene in an air conditioner (though they
didn't say they would do it for me).
I really don't see a way to get just the liquid nitrogen without first taking out everything else from the air, Organikum made a post some time
ago on a setup to produce nitrogen from the air free of oxygen, maybe you should search for that for ideas, I believe that it used the passage of air
through hot copper turnings to acheive the removal of the oxygen.
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evil_lurker
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I'd say get the biggest damn thermos you can find for $20 and go to a welding shop.
A good thermos will keep Liquid N for 2-3 days.
Alternatively, a semen storage container would work too, but at a higher cost.
I can tell you right now that there practically is no way in hell your gonna scrounge up the equipment to freeze air down to its condensation temp.
Sadly this is the way it is with many chemical processes, its simply impossible/impractical to do it on a home scale.
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Fleaker
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A good quality dewar will hold it for weeks on end. I know that a 35L dewar takes about a month to go completely dry, but if you need a constant
supply, then you'd best save up :-\
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ChemicalBlackArts
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Or you could just go to a welding shop and buy it for 3 dollars per gallon. Just make sure you have a solid nalgene container to store it in.
--Chemistry in my veins--
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Fleaker
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3 dollars per gallon is a pretty good price, I called a large national distributor and they wanted 30 USD for 4 liters and they wanted a 70 dollar
deposit on the dewar. Needless to say, I found another supplier.
It's a shame that those Nalgene 'dewars' only hold LN2 for maybe 36 hours depending on their size. Good enough for a few distillations
or low temperature cryo research though :-)
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hdcwr0x2
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I've done quite a bit of research into this path myself. I was in the process of building a phase change cooler for my computer using propane for
a refrigerant (boils at -40something C) and I have all the parts I need although I'm a little lazy at the moment. Anyway, if you need more
information, I'd reccomend looking at these two sites.
http://www.xtremesystems.com/index.php
http://www.phase-change.com/
Also, if you search google there is a diagram of an enormous 3 stage cascade used by phillips to produce LN2. It uses propane for the first stage,
ethylene for the second, and methane for the third with a boiling in the -160s c. This is enough to liquify compressed air. All of this can be done
with standard refrigeration compressors, piping etc, although you'll want to change the oil in the compressor to be compatible with the
refrigerent that you will be using in each stage. Finally, if you're actually going to carry though with this, then this gas database from
airliquide should prove indispensible.
http://www.airliquide.com/en/business/products/gases/gasdata...
Good luck and PM me if you need any further info! Maybe someday I can attempt something like this if I get off my ass.
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Chris The Great
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Just an idea...
Could one liquify a gas, such as ethylene, and then lower the pressure below atmospheric to further drop the boiling point until it could liquify air?
Just popped into my head, it seems like a good idea....
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12AX7
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IIRC, refrigeration is a lot more efficient at elevated pressures. For sure, you'll be pumping a hell of a lot of evaporated gas volume for not
much actual mass if you do it like that.
A shame that you need so much cooling to get cryo... for a given power input at the lowest stage, you need that plus its refrigerator's power use
to be handled by the next stage, and so on. Nasty exponential growth there, a good reason to make the refrigerators as efficient as possible!
Tim
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Marvin
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In terms of working at all, the important values are the triple point of the refrigerent which determines the lowest temp you can achieve, and the
critical point of the gas you are trying to liquify. When they overlap it can work.
Practically things become more difficult. You have to worry about compression ratios, and otherwise trivial things like how cold a gas can become
before it freezes the pump trying to compress it.
There is of course the method using just air. Its been suggested by more compitant people than myself, that a fridge pump can do 30atm at least if
pushed, though not I suspect with reasonable life. If you can get 30atm then liquid air is just a matter of lots of metal tubing and insulation and
risk of explosion  Hampson's machine only ran at 50atm. It wont be cheaper
than buying LN2, but then neither would the cascade method I suspect.
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garage chemist
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Guess what I have been planning to do with my 40-Bar- producing fridge compressor even long before acquring it! 
Cascade cooling with several cooling systems using different refrigerants will never work. Period. Think of the heat the compressor motors produce-
100% of it are subtracted from the cooling performance of EACH STAGE. Only compressors that have motors cooled by separate systems and with insulated
pistons and cylinders can be used. Fridge comps rely on the residual coldness of the gas from the evaporator to cool the motors!
The Linde process using nothing else but "air and metal" is the only way that actually offers a CHANCE for success.
Marvin, you are absolutely right in stating that making liquid air is just a matter of lots of metal tubing and insulation when a suitable source of
pressurized air of at least 30 bar is available (well, the issue of air purification, especially removing the oil mist produced by the compressor is
also important but it can be done with lots of cotton wool stuffed into the metal pipe. Drying and removing CO2 from the air can be done
simultaneously by a single chemical: potassium hydroxide, employed in the ambient pressure suction line of the compressor).
My idea for producing pressure in excess of 60 bar (for increased efficiency) is to pressurize the inlet of the fridge comp to 8 bar using an ordinary
compressor. In theory, the comp multiplies this by 40 (in reality the motor will become blocked at maybe 80 bar due to the extreme overload which is
put on it and the parts- think of the pressure difference it has to overcome).
If this fails, a huge 200 Bar pressurized air bottle (maybe a scuba tank?) will be used as the pressure source.
I have read through Ullmann's section on "Cryogenic Technology" with great interest, everyone considering building an air liquefaction
apparatus must read this ( I really mean "must"!).
The importance of having a heat exchanger of extremely high efficiency (at least 99% for economic operation, every percent lacking from 100%
efficiency means a huge overall efficiency loss) is emphasized several times. Most normal exchanger technologies reach maybe 70%.
Put every bit of your skill and knowledge into the heat exchanger, everything relies on it.
The best approach to the heat exchanger would be to use Linde's original design as the material for it is the easiest to acquire (no huge rolls
of capillary copper tubing required like in other designs).
It consists of two coaxial copper tubes, the inner containing the high- pressure air and the outer the expanded air which precools the high- pressure
air. The arrangement is coiled up in order to save space and make insulation easier (also very important. I'll use self- expanding PU foam to
embed the whole exchanger. Linde used a wooden box filled with wool.).
I have already looked for the copper tubes and found that 8mm tubes fit nicely into 13mm tubes leaving maybe 2-5mm of air space between them, which is
perfect.
Cost will be the limiting factor for the length of the exchanger. It will be at least 5m long (coiled up of course). Using a low flow rate in the
exchanger also increases the efficiency a lot, but reduces the cooling capacity of the system and makes insulation even more important.
Overall, a low flow rate shifts the construction problems from the exchanger to the insulation.
The insulated vessel where the air will hopefully liquefy will be an all-steel thermos flask, tested for suitability by filling with bought liquid
nitrogen and observing the evaporation rate. I already tested a 0,5L- thermos flask and the outside didn't become noticeably cold, also no
boiling of the LN2 was observed inside it after the walls had become cold, which is a very good sign.
The connection of the exchanger to the flask will be made by a cork (only material suitable for getting it airtight without having to worry about
glassification at cryogenic temps, also the vessel will be very easy to remove from the connection in order to measure temperature inside it or look
for liquid air) with a 13mm hole in the middle.
The 13mm outer copper tube will be pushed through the hole in the cork, the inner high pressure line sticking out of it will end in the "Joule-
Thompson Valve".
The "Joule- Thompson Valve" will consist in the high- pressure line ending inside the thermos being hammered flat as to allow only a small
amount of air to escape and hoping that the 60 Bar won't push it open again. If it gets pushed open, soldering it and filing a tiny opening into
the pipe will be tried.
When I have succeeded in filling my gas flask with ammonia, I will work on this project. I can already see the entire thing before my eyes, I have
planned everything.
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watson.fawkes
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Bump for new kind of technique
http://benkrasnow.blogspot.com/2008/08/diy-liquid-nitrogen-generator.html
Precis: About 1 L / day output rate. Key components are a pre-built cryocooler and a nitrogen separation membrane. Parts acquired on eBay; project
cost under $500. Marginal cost of LN2 estimated at $1.15 / L.
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not_important
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Looks nice, certainly within hobbyist range, although obtaining the cryocooler at an acceptable cost appears to be a matter of luck. The membrane
separation units are slowly becoming more common, plus there's the possibility of cascading several surplussed portable oxygen supply units to give
oxygen enriched air and fairly pure nitrogen.
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mr.crow
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Thanks for the link, I never knew such a thing existed!
If you want liquid nitrogen dress like a student or professor and go to a university. They will give it to you for free because its not worth charging
a few dollars to a credit card. They even had liquid helium but you need a better flask for that.
Edit: Video from Maker Faire
[Edited on 9-6-2010 by mr.crow]
Double, double toil and trouble; Fire burn, and caldron bubble
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densest
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In the US, welding supply stores are usually gas supply stores as well. I bought a good quality dewar (expensive) and get LN2 for (IIRC) $0.50 a
liter. The dewar keeps it for weeks.
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JohnWW
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What do you want to use the liquid N2 for, MadInventor? Surely not as a cooling drink on a hot summer day.
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watson.fawkes
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Quote: Originally posted by not_important  | | Looks nice, certainly within hobbyist range, although obtaining the cryocooler at an acceptable cost appears to be a matter of luck. The membrane
separation units are slowly becoming more common, plus there's the possibility of cascading several surplussed portable oxygen supply units to give
oxygen enriched air and fairly pure nitrogen. |
Luck: yes, the guy got really lucky in scoring his cryocooler.
And now that his device has gotten so much web attention, the remaining once-a-year deals will be even harder to get. It's too bad that these are just
not a DIY kind of part, what with all the machining tolerances required for helium as a working fluid. Perhaps the thermoacoustic devices currently in
research will prove to be, given that the moving part is typically a piezoelectric transducer.
Nitrogen supply: The home medical units that have become so common recently are pressure-swing adsorption (PSA) units. The zeolite packing inside them
preferentially adsorbs oxygen (and argon). There are other zeolites that preferentially adsorb nitrogen. Packing the columns with this other material
yields quite pure nitrogen, > 99% as I recall, in a single stage. The raffinate (waste) gas is oxygen enriched (? 30-40%), but not pure. These
devices should be considered extraction devices, not separation ones. Cascading them will work, but at rather much larger costs. The raffinate gas
from an oxygen concentrator is still something like 10% O2, so you need quite a number of stages.
Incidentally: Last year I scored a batch of three-way solenoid valves (the key expensive part in a PSA system) on the cheap from a surplus vendor.
I'll know more about sourcing these zeolites when I get to building a unit, as I'm planning to make the columns swappable for three outputs: O2, N2,
dry air (with silica gel packing).
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elementcollector1
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Does anyone know of a very small model of portable LN2 generator? This is important to me for a possible college research project.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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Zyklon-A
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I'm not sure if you already saw this, as it was posted earlier in this thread, anyway, there's this:
http://www.elan2.com/
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elementcollector1
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Saw it. It's small, but not quite as small as I was hoping. I guess I'll lay out my requirements, and then see if it's even mechanically possible:
-Portable! I don't really want to plug this in, unless that 'charges' it. The 27V DC to run the version below is doable (perhaps with 2 12V lead-acid
batteries instead), but this would add a lot of size for just battery storage. Ideally, this would be powered by a series of 9V's - but that's just
silly in terms of amp-hours.
-Small. As in, really small. Looking at the setup outlined here (http://benkrasnow.blogspot.com/2008/08/diy-liquid-nitrogen-g...), I could probably get rid of the nitrogen tank, and the dewar itself (as any
liquid nitrogen produced will immediately be used, and then possibly sent back to the cooling unit as either gas or slightly-warmer liquid). I could
also theoretically get rid of the nitrogen separation procedures, but then I'd have to deal with liquid oxygen. While colder than LN2, it's also more
reactive, so I'm hesitant to introduce a safety risk. Also, I could probably stand to scale down whatever I can, as I won't need a high output.
This is for the purpose of cooling superconducting materials (to complement my recent interest), so once the pump starts flowing it could probably
stand to recycle liquid nitrogen that has been warmed by the superconductor and pathway tubing.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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Zyklon-A
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By the way, How do you buy that LN2 generator? (the one I linked) I couldn't find anywhere on the site or any links posted on actually
purchasing the thing. Am I missing something obvious?
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