Liquid Oxygen Synth

[Positive Electron]

This topic is about condensing gaseous oxygen into liquid oxygen.

The boiling point of oxygen is about -184 degrees, and at -184 it begins to condense into a pale blue liquid.

The materials you will need is an oxygen tank with the approiate valves, 2 metal jars, 2 clamps (one big enough for a jar, and one for a test tube), 4 feet of 1/4 inch copper tubing, a good epoxy, a test tube (size depends on how much you want to make) and enough liquid nitrogen to fill one of your jars three times over. It also helps to have a dowel to wrap your tubing around.

Take your tubing and wrap it around the dowel in a tight coil, leaving 5 inches on the top and bottom. cut to size.

drill a 1/4 inch hole in the bottom of one of your jars. slide the coil in, and secure and seal with epoxy. Attach this jar 8 inches off yiour working surface with a clamp.

beneath it, place the other jar on the work surface, and position the clamped test tube directly under the tubing.

begin to slowly fill the top jar with liquid nitrogen, adding it very slowly, and letting it boil off until the jar and pipe are -194 degrees. when it stops boiling, fill it to the top, and repeat the process in the bottom jar.

attach your oxygen tank to the top of the coil, and turn it on very low. the flow should be extremely low.

the oxygen will condense in the coil, and eventually your test tube will fill with liquid oxygen.

i don't know much of what you would do with it, most things burn in it explosivly, which is a good thing.

little fun note: hold two electromagnets about a quarter inch apart, on, and pour small amounts of the liquid o2 between them, adn notice how the oxygen is paramagnetic, and sticks. i had an idea about a fuel distribution system for a "potato gun" type gun, but it would be to expensive and unruly.

File: A diagram of the coil setup- <a href="http://www.angelfire.com/movies/nutsmeller234/chem/coildiagram.jpg" target="_blank">http://www.angelfire.com/movies/nutsmeller234/chem/coildiagram.jpg</a>

[Ctrl_C]

I'm not sure how well this would work in practice. You only have 10* to play with. It could be used to supersaturate a substance with oxygen though.

[Positive Electron]

it works quite well if you devoid the tubing and jars of all their kinetic energy. in about 22 minutes i have produced 100ml of liquid oxygen

[Mick]

basicly, exactly whats listed on this page... <a href="http://www.allatoms.com/LOXpage.htm" target="_blank">http://www.allatoms.com/LOXpage.htm</a>

[EP]

</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica"> i don't know much of what you would do with it </font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">I'd probably give LOX/sprengel explosives a shot if I had some liquid oxygen...

[xyz]

I've heard that pieces of charcoal or silicon wafers soaked in liquid oxygen explode violently, it was in the new scientist a while ago.

[Jhonbus]

The oxygen tank isn't really necessary, I wouldn't bother using one unless I already had the regulators etc. Normal air can be used, but the production will be slower, and you waste more of your..um, lack of heat.

[Marvin]

If you use air you will make liquid air or at the very best a nitrogen/oxygen mix slightly better than air. Useless for LOX explosives and requiring fractionation to seperate, essentially not possible without a lot of LN2 to waste and dedicated equipment. If you are going to the expense of getting liquid nitrogen (which is dirt cheap, but the containers are very pricey) youd get a source of pure oxygen.

[Jhonbus]

Separating a mix of LN2 and LOX is a simple matter of allowing the LN2 to evaporate.
Besides, I don't think much N2 would condense from the air anyway. You can think of it as an equilibrium between LN2 evaporating and N2(g) condensing. Since the surroundings are at a high relative temperature, LN2 will evaporate.

But yes you are right, Dewars are very expensive, so a bottle of O2 shouldn't be any trouble if you've got the LN2 side covered.

<small>[ October 06, 2002, 11:47 AM: Message edited by: Jhonbus ]</small>

[Marvin]

I can see why you would think oxygen would condense fairly pure from the air, and why any LN2 would evaporate first from a mixture, unfortunatly it isnt that simple. Its tempting to think that the boiling point of a liquid is the temperature at which molecules leave the solution and enter the gas phase. This isnt true though, its the temperature at which the pressure of the gas phase of the liquid exceeds atmospheric pressure. Below this point there is a partial pressure of gas phase less than atmospheric pressure, but still present. Ok, mixtures. Lets assume that the mixture of 2 liquids is "ideal", that is, there is no interaction between the molecules of the two liquids. The consiquence of this is that there will be no eutectic in the vapour phase diagram, which makes the thought experiment easier. The total pressure of gas exerted by the liquid will be the *sum* of the partial pressures from both componants. (While this is always true, one partial pressure is only said not to affect the other if the liquids are not miscable, a state you end up from if there really is no interaction between the molecules of the two phases). If you boil the liquid, the gas phase you get will be in molecular proportion to the partial pressures of the gasses over the liquid at the temperature its boiling at. Which in real mixtures, does not have to bear much relation to the boiling points of either one of the componants as its the sum of the partial pressures of both componants exceeding atmospheric pressure that matters. If a mixture is ideal, you can make your own VLE diagram based on tables of partial pressures for both componants.

Ok, what does this boil down to. Chemistry humor, my apologies. A mixture (even an ideal one) of liquids will only seperate a pure compound by single plate distillation if the partial pressure of all the other componants is zero.

If you leave liquid air to evaporate, the mixture will enrich, becuase the partial pressure of the oxygen in the gas phase will be lower due to its higher boiling point. You wont get oxygen moving back from gas into the liquid in preference to nitrogen however, as they are both in equilibrium. Blowing atomospheric air over the solution will give you a small degree of oxygen going into solution, up until the point the partial pressure of oxygen in the gas phase at equilibrium exceeds the content of normal air, at the expense of a much greater loss of liquid air, unless you have a heat exchanger to swap the energy of the air going in with the slightly oxygen reduced boiloff going out. This would be one step closer to the dedicated equipment for seperating I talked about. The result of all this is you need to let boil a *lot* of liquid air to end up with a liquid phase that is over half oxygen, unless you have a refinary setup.

Since condensing is just the reverse equilibrium of boiling exactly the same argument applies to explain why you cant condense pure oxygen from the air. The definations are simply turned on their heads, and condensing becomes the point at which the *sum* of the partial pressures in the gas falls below atmospheric pressure, and you get the same choice, simply feed in the air and get liquid air, or let it circulate without a heat exchanger and get a much smaller amount of slightly enriched oxygen in liquid air.

Ordinary 'glass' thermos bottles of the type you keep tea hot in usually work very well for liquid nitrogen. The pyrex they are made from handles LN2 with no problems, my university used these for students. They are vastly cheaper than dedicated dewars but you are usually limited to types under 2 litres simply becuase noone seems to sell bigger thermos bottles. 2 litres is far too small for any real experiments but you can use these to handle it from the main dewar.

[Jhonbus]

Thanks for correcting me. As you can tell, physical chem isn't exactly my forte... ugh. :cool:

I don't have any experience buying cryogenic gases, will companies sell to you even if you don't have the "proper" equipment? If so, perhaps a discussion on insulating containers for the purposes of containing largish volumes (say 25 litres) of LN2 is in order.
Would ordinary solid foams such as styrofoam or polyurethane foam insulate well enough? If so a rough and ready container could be made from two thinwalled containers, one inside the other, and a layer of foam between them.

<small>[ October 06, 2002, 02:15 PM: Message edited by: Jhonbus ]</small>

[PYRO500]

The best containers to keep LN2 are vacuum flasks, mainly beacuse the liquid nitrogen is going to cool and freeze anything it touches. I have herd of people taking those coffee flasks that are vacuum bottles and having them filled although I don't have experience in doing so. One thing you have to keep in mind is that your flask will need to vent the nitrogen gas to keep from exploding. so drill a hole in the cap of your container if it's air tight.

<small>[ October 06, 2002, 04:01 PM: Message edited by: PYRO500 ]</small>

[a_bab]

Those flasks will be always air tight because you don't want to spill the hot tee, and are called "Dewar" flasks.

[Positive Electron]

i was thinking of some sort of application to sabatoge a combustion engine or some sort of application where it would be combined magnesium to ignite thermite

[Anthony]

Igniting thermite? Even something like KNO3/sucrose will do that? Why deal with the complexity of producing, storing, handling, transporting LOX needlessly?

How would you sabbotage a car with LOX? If you pour it in the "gas" tank all it's going to do is boil off as it touches the comparitevly "hot" contents of the tank. In fact you'd probbaly burst the tank with the sudden expansion of gas, or shoot the contents out of the filler tube and all over yourself...

Simplify :)

[Jhonbus]

If you pour LOX into petrol, it will instanty ignite, probably quite explosively. Not a good idea.

[Marvin]

If I'm not careful Jhonbus will think I have something against him personally, which I assure you isnt the case. I'm not conviced LOX and petrol is a hypergolic mixture though. Pure oxygen at room temp and petrol doesnt ignite automatically, so I fail to see why pure oxygen at around 100K would ignite it. You wont get the two liquids 'touching' in any real sense. Pure oxygen gas and petrol vapour would ignite very easily and spectaculaly, so the slightest spark is all thats needed.

If its present for a prolonged period, Id expect the petrol to be cooled below its flashpoint (which will be lower with pure oxygen than air), and become very difficult to ignite. The petrol would freeze before the temp drops far enough to let the two phases mix. How to sabatage a car with LOX? Tell the owner if he feeds pure oxygen into the engine it will go faster, and wait.

[Jhonbus]

I was making my assumption based on reports of petroleum jelly spontaneously igniting in 100% O₂ atmospheres. Perhaps petrol wouldn't spontaneously ignite, but I would expect it to, and I certainly wouldn't want to pour them together. Boiling oxygen will raise the petrol into a very fine mist, creating an even more hazardous situation.

[Jackotrades]

Exposing a combustible material to pure oxygen only lowers its flash-point (the temperature at which the material will spontaneously ignite without flame) so it is safe to assume that a mixture of LOX and petroleum fuel at cryogenic temperatures would not spontaneously ignite. The flash point of most petroleum based products can, however, be lowered to room temperature in a pure-oxygen environment (gaseous oxygen, also at room temperature).

[Marvin]

Your definition of flash point is wrong. Its the point a fuel can be ignited by a spark or a flame. That is to say its burning will self sustain. You are thinking of the autoignition point, but I'm not convinces this will change much with pure oxygen at room temp anyway.

[Jacks Complete]

Hmmm. Not tried with LOX, but for storing LN, I always used a Thermos flask. A two liter one was good, with a pouring spout that could be left open. If you drill a small hole, it might ice up if it is damp, causing a pressure build-up. I found it would last for about 4 days if you just left it, mostly. Leave it outside in the shade.

Also, don't let some spastic "friend" drop anything in the flask. It is *not* cool.

[MightyQuinn®]

Those flasks will be always air tight because you don't want to spill the hot tee, and are called "Dewar" flasks.

I belive you are wrong (or kidding) Dewars are never 'air tight.'

1 cubic foot of liquid nitrogen will expand to 696 cubic feet of gaseous nitrogen at 70° F. Any air-tight container containing liquid nitrogen would surely explode in due time.

I believe most dewars use something akin to a styrofoam lid to cap the container.

[Anthony]

You don't keep hot tea in a dewar, do you? He's talking about vacuum flasks used to keep hot drinks (Thermos flasks), and saying that they are usually sealed (to keep the drink from spilling), and so would be unsuitable for storing cryogenic liquified gases.

[Mumble]

At the lab I worked at over the summer there were two types of LN containers we used. One was this plastic container with a styrofoam lid. I assume it was a styrofoam between the inner and outer walls, it didn't seem to top of the line. It has a pressure release notch to keep it from pressurising. The other was a 4L dewar with a tapered neck, down to about 1 1/2". Metal construction with a vacuum between the inner and outer. The lid was basically oversized by about 1/4" all around with 3 crimps in to hold it on the top of the container. It didn't press all the way down and allowed pressure to escape pretty easily.