[Corvettaholic]

You guys know how I have crazy ideas how to do things, so here's another one:

I want liquid nitrogen and I want a machine to make it for me. So all I gotta do is take some atmospheric air, and drop the temp to about -190C, right? Since there's so much nitrogen, I'm going to assume there's plenty for me to play with and that should be a liquid before any other gases in there.

Now how to do it. You guys heard of a peltier device before? Its a solid state active cooler, and works like a diode but transfers heat REALLY GOOD. The temp difference between the hot side and the cold side can be aroun 50C on average, and you can stack them on top of each other. More stacks doesn't improve cooling in a linear fashion however. These things run off of high current, low voltage DC power supplies. The power is not a problem, I can fab up a box that'll give me 50 amps at 12V for a decent amount of time before it blows up.

So if I take a big pyrex (enclosed) jar thing, full of air, and slap a peltier stack on it... should be able to get liquid N2, right? Now if you raise the pressure, things boil at higher temperatures, so if I pressurize the enclosure it should be easier. The things I worry about are the stability of glass/metal/whatever I use for the enclosure at extremely low temperatures. Can't use a thermos bottle, because I need to transfer heat to cool it off. So the structure has gotta be able to stand up to it. Also if I used compressed gas and liquify it, then the pressure in the chamber should go way down, right? If I kill the power and the temp rises, it'll go back to a vapor and there SHOULDN'T be an explosion hazard because its going to the original pressure, right?

Think this'll work guys?

[hmx9123]

Read in the Kirk-Othmer encyclopedia of chemical technology about the process for making liquid nitrogen.  It's more involved than you would expect.  In addition, even if you could get down to -190 deg C, you'd run into the problem of condensing dry ice, then argon, and then liquid oxygen first (oxygen being the biggest problem of these since it's in greatest abundance), because these other compounds have higher freezing/boiling points than liquid nitrogen.

[Corvettaholic]

Well thats even better! I just want ANY gas to liquify with my own invention. I did some more homework on peltier coolers though, and realistically they will only go down to -50C or so. I figured just increase the pressure, but that only works so far. Took a gander at some phase charts and there has to be a minimum temp regardless of pressure. Maybe a compressor method would work a lot better, but thats out of my price range. I'll take a look at the process though, and see if I can come up with a cheaper way.

[movies]

Condensing any amount of liquid oxygen is VERY dangerous because it is also a very, very powerful oxidant.  You might want to read up on how to deal with these things before you start trying them.

Just be careful.

[jdurg]

We always had fun in the science labs where we used liguid nitrogen.  We'd pour some into an aluminum cup and watch as the oxygen condensed on the outside.  I always was the geek who would laugh when people would think the liquid on the cup was water.    I think the coolest thing I ever saw was when the teacher had a LARGE aluminum container and poured liquid N2 in there and then took one of those oxygen tanks you get at a hardware store and released the O2 onto the side of the can.  He then collected the oxygen in a nice tall test tube.  It's pretty neat seeing liquid oxygen.  It has such a nice blue color to it.  The professor then poured the O2 between a magnet to show us how it is attracted to a magnet.  Pretty neat stuff.  He wound up disposing of the O2 by rapidly, and I mean RAPIDLY, rusting some iron.  

Speaking of condensing things, I've got something from my element collection that I really need to take few pictures of, or even a movie of.  With the brutally cold temperatures up here lately, it's cold enough for bromine to solidify later in the day once the sun has set.  (Bromine's freezing point is -7 degrees Celcius which is 19.4 degrees Fahrenheit).  What I'd like to do is put my bromine outside in the freezing cold and snow and let it solidify.  Then take a phot of it and perhaps a movie to see the yellow-brown solid melt into the dense liquid and then vaporize into the beautiful bromine vapor.  That'd be pretty neat to see.  

[Mitch]

One of my old professors took a big swig of liquid nitrogen in his mouth and then spat it out at us. Pretty cool, I have yet to attempt this.

[hmx9123]

I've done it, but it's not recommended.  It can crack your teeth, and if you accidentally swallow it, it's got about a 700 to 1 expansion ratio, so it can easily rupture your internal organs.
  And, Jdurg, the coldest part of the day is actually early morning once the earth has cooled off.  Get up just with the dawn and you'll have the coldest temp of the day.

[eugenedakin]

Hello Corvettaholic,

We would constantly make liquid nitrogen (5000 kg per day) by first purifying N2 from air (through a modified reverse osmosis unit).  Then, condense the 99.999 % nitrogen under pressure (at room temperature) to form liquid nitrogen.

The nitrogen MUST be pure prior to pressurizing, otherwise oxygen, moisture and other contaminants tend to be explosive at higher pressures.

Be careful,

Eugene Dakin Ph.D., P.Chem.