Rhadon - 7-3-2003 at 11:57
One short question: What do you think would be the cheapest way to ~90%+ pure oxygen, preferrably free from reactive byproducts?
a_bab - 7-3-2003 at 13:04
Obviously from decomposing chlorates or perchlorates is not a cheap option. From water (via electrolysis) is out of question aswell. I would say that
decomposing the H2O2 with MnO2 could be a cheap alternative, assuming that you can get technical cheap 30 % H2O2 (I can get about 3 litters of 30%
with 1 buck. That's roughly speaking around 175 grams (~122 litters) of pure O2/buck)
[Edited on 7-3-2003 by a_bab]
Rhadon - 7-3-2003 at 13:24
Yes, getting H2O2 is not a problem. I knew this method, but I thought that there could be a cheaper way, since H2O2 (30%) costs about 8 Euros / litre
for me. Anyway, thanks for helping!
BASF - 7-3-2003 at 13:25
Gentle heating of KNO3 would yield nitrite and O2, i think.
I doubt it would be possible to get one´s hands on industrial 30% H2O2 as a private person here...
Another disadvantage would be to get only very moist O2...
I can´t remember where i have seen it, nor if it was on this forum, or on E&W, but somebody described some experiences with liquifying air, using
a small compressor....fractional distillation of air seems far too complicated for backyard experimentation on first sight, but it is still the best
method for mass production....
a_bab - 8-3-2003 at 01:12
I always dreamed about such a thing as making liquid air. The good news are that the nitrogen will boil first, leaving a very oxigen rich liquid. So
it'd be the cheapest method presuming that you are able to build such a device. It requires ALOT of tubing, that's for sure. IIRC, Linde
used a tower 10 m high and 200 atm presure. The most modern devices (Frankl) are using 6-7 atm pressure only.
Mongo Blongo - 8-3-2003 at 08:07
You can buy it for welding. I can't remember the price but it's quite cheap. It is practically pure and dry. It should be sold at almost any
hardware store. I will get some sometime (for purging NOx out of HNO3) and I will post the price if you want.
Rhadon - 8-3-2003 at 08:11
Although prices differ greatly between the US and the EU sometimes, it'd be nice if you could tell me what it costs. Thanks in advance!
Haggis - 8-3-2003 at 08:55
In a local hardware store, they sell Oxygen tanks next the the MAPP gas, propane and I believe butane. They are around a foot tall and cost 7.99.
There is no liquid in them so they feel empty. These tanks are very high pressure and you would probably need a regulator of some sort.
I am a fish - 8-3-2003 at 12:43
Once you have the equipment (in particular, a suitable power supply), electrolysis of water is cheap. Liberating 1kg of oxygen from water requires
3.7 kilowatt hours of energy (assuming 100% effciency). Even allowing for a lousy efficiency, this is cheaper than decomposing H2O2.
Chris
Rhadon - 8-3-2003 at 12:58
But then you have a mixture of oxygen and hydrogen, which you won't be able to separate the easy way.
Aaron-V2.0 - 8-3-2003 at 20:33
IIRC in electrolysis the H2 is released at the negative terminal and the O2 is released at the positive terminal? Possibly the other way around. So
knowing that simply use a cell that's U shaped with the anode/cathode on each side so the gas is not mixed.
I think.
Blind Angel - 8-3-2003 at 21:40
make your electrode hooked and put two tube over them. (Maybe my electrode are inverted)
Mongo Blongo - 9-3-2003 at 09:55
They cost 6.99 from a chain store called Halfords. It sounds like they are exactly like the same ones that Haggis described and they do need a
regulator. The regulator I got was 11.99. They got oxygen, CO2, propane, acetylene, argon and other useful gases that I can't remember, all pure
and dry to boot.
Rhadon - 9-3-2003 at 10:53
Sounds nice, maybe I might take a look at it. Thanks for informing me Mongo, also for the electrolysis hint from Blind Angel and Aaron-V2.0 
!
hodges - 27-6-2006 at 13:45
What an old thread! Recently I ran across a mechanical device that separates the nitrogen and oxygen in the air. I think the concept is simple
enough that it could be done at home.
http://www.casi-ne.com/nitrogen.html
Hodges
Mr. Wizard - 27-6-2006 at 18:49
Check the obituaries for some old geezer who was on a 'concentrator' ;-) The things can easily produce 4+ liters per minute of O2. My mother is on
one and the thing puts out lots of O2 from room air and electricity. It works by selective adsorption of O2 or removal of the N2, I don't know which.
I've seen commercial ones at second hand machine part warehouses that were used to supply welders and cutters.
Twospoons - 27-6-2006 at 21:50
The hard part is getting the adsorber, the rest is just a compressor and a couple of valves. I did see a patent once that used an adsorber based on
burnt coconut shells, modified with ethene(?) to reduce the pore size. Just another form of activated carbon I suppose.
As a bonus to your O2 supply you also get a nice stream of fairly pure Nitrogen.
There's another system that uses reverse osmosis, but the cartridges are really expensive ($2000 for a small one!).
hodges - 28-6-2006 at 13:51
I'm seeing oxygen concentrators as low as $70 on E-Bay (Buy-it-now for a 3 liter per minute used unit).
I don't have much need for generating large amounts of oxygen at the moment but I needed to generate a lot I think this would be the way to do it.
They all seem to consume 300 to 400 watts so that is going to cost only a nickel or so an hour to operate. That's about 1 penny per 40 liters of
oxygen!
Hodges