[The Tao]

Ok, so I have a limited knowledge of chemistry...one class in highschool...I'm currently enrolling in my first college class..but that's another story. What I want to do is make some liquid nitrogen.

What I know:

1. It dangerous.
2. You need  the correct container to hold it.
3. It doesn't last long.

Why I want to:

1. I'm bored
2. I want to experiment with it.
3. I love hours in my garage creating chemicals.

My chemistry teacher from highschool explained that his idea of making it, was to take nitrogen in the air, and run it through a tube of dry ice. Now...does anyone know of a synthesis book or something on the web I could look at to help me? I've searchd for hours, and all I could find was advertisements to buy machines that create liquid nitrogen.

[Borek]

You will not liquify nitrogen with solid ice. Google N₂ boling point and CO₂ freezing point.

[The Tao]

Not solid ice..."dry ice"

[Borek]

Not solid ice..."dry ice"

Call it a typo. Google what you were asked to google.

[billnotgatez]

I had the good fortune to have a chat with an engineer at an air liquefaction plant.  From what I remember, the process had many steps and involved high pressures. They removed the carbon dioxide and water early in the process so it would not interfere.

From the Nitrogen article
http://en.wikipedia.org/wiki/Nitrogen

Liquid nitrogen (liquid density at the triple point is 0.807 g/mL) is produced industrially in large quantities by fractional distillation of liquid air and is often referred to by the quasi-formula LN2 (but is more accurately written N2 (l)).

Also there is a liquid air article.
http://en.wikipedia.org/wiki/Liquid_air

Additionally there is a dry ice portion to the carbon dioxide article.
http://en.wikipedia.org/wiki/Dry_ice#Dry_ice

[The Tao]

You will not liquify nitrogen with solid ice. Google N₂ boling point and CO₂ freezing point.

Nitrogen condenses and turns to N₂ at -195.8 C....and CO₂ freezes at -78.5° C.

So I got your point. Well I guess I'll just ask the simple question: Is there any "do it yourself way" of making liquid nitrogen, or is it an expensive complicated process? I don't really mind the complication involved, as I would like it to be difficult, but I can't really afford to purchase machinery.

It makes me wonder why my teacher reccomended running it through dry ice however...

[jdurg]

Running gasses through dry ice is a good way to dry the gas as any water vapor will condense out and solidify at those temperatures.  However, there is no way to liquify any atmospheric gases by just passing them through dry ice.  Industrially, what they do is take a large sample of air and compress it.  Then they decompress it, and recompress it again.  The air sample goes through numerous cycles of compression and decompression which results in an intense drop in temperature.  (Any time you decompress a gas it cools down temperature wise.  If you have a can of condensed air and use it, you'll notice that it gets really cold as the high pressure gas escapes).

So by taking a sample of air and compressing it, then decompressing it, they drop the temperature of the air sample.  The air sample continues to cool down at each cycle and soon it begins to liquify.  More air is led into the tank and the procedure continues on indefinitely until there is so much liquid air inside that they can't compress any more.

Now, with all of the gases liquified, they slowly warm up the liquid air and as they do certain fractions boil off at certain points.  These fractions are collected and isolated in order to get the different components of air.

If you want to play with liquid nitrogen, and you want to use it frequently, I would suggest investing in a Dewar Transportation Flask.  These are specially designed for transferring liquid gasses and are the only equipment that gas companies like ABCO will legally put liquified gasses into.  Mind you they are expensive, but the liquid nitrogen itself is dirt cheap.

[Borek]

Industrially, what they do is take a large sample of air and compress it.  Then they decompress it, and recompress it again.  The air sample goes through numerous cycles of compression and decompression which results in an intense drop in temperature.  (Any time you decompress a gas it cools down temperature wise.  If you have a can of condensed air and use it, you'll notice that it gets really cold as the high pressure gas escapes).

Somehow you managed to evade the point of the whole process

It is not compression/decompression that is important, as adiabatic compression decompression cycle won't change a thing about gas - after decompression its temperature will be identical with the initial temp. What is important is that after the compression, when the gas temperature rises (V/T = const) is it cooled - so when it is decompressed it gets much colder than it was at the start. Even that will not help, as the maximum temperature drop in single compression-cooling-decompression cycle is a simple function of the initial pressure, pressure after compression and cooler temperature - just repeating the process will not get the gas colder. Thus in every next step you have to use much colder cooler if you are about to liquify the gas.

[The Tao]

Well considering I don't have a compressor, a friend of my suggested that I just use a standard thermus, and ask either my college, a hospital, or...lol..a strawberry freezing plant. Of course, I'll have to drill a hole at the top of the thermus to keep it from exploding, but what I'm curious about is, will the thermus hold N₂?

[billnotgatez]

One would wonder if a regular thermos would be able to handle the ultra-cold of liquid nitrogen.

[The Tao]

Well from what I've read on various websites, it is possible to hold N₂ in a standard thermos, but I havn't witnessed it in person. Does anyone know the anwser?

Edit: And when I say standard thermos, I mean the ones you use to go backpacking...not the plastic ones with Batman on them little kids carry their soup around with.

[AWK]

You can hold liquid nitrogen in standard thermos for a few hours

[constant thinker]

I've tried in the past to get liquid nitrogen. I failed miserably. The 2 local hospitals turned me down. I also spent god knows how many hours researching ways of making it. I've concluded either you have to get lucky and have a hospital/some other place that produces liquid air, or build yourself a liquefaction plant. 

Good luck with your quest to get liquid nitrogen.

[pantone159]

I've heard it can be had from some welding gas suppliers.  Have not tried this myself.

[jdurg]

I've heard it can be had from some welding gas suppliers.  Have not tried this myself.

Yes you can, and from welding gas suppliers it is by far the easiest, and probably cheapest, way to get it.  The thing is, they legally will NOT sell it to you unless you have a specific Dewar Type Flask designed for storage and transportation of liquid nitrogen.  These flasks typically cost around $1,000 if not more.  So the initial cost is sky-high, but if you use a lot of liquid N2, or other liquid gases, you really have no other choice.