gatewaycityca
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Oxygen mildly pressurized - safety?
I'm going to do an experiment soon where I would be mixing hydrogen peroxide and bleach (or possibly other chemicals) which release oxygen. The
oxygen would be mildly pressurized in a closed container and tubing, and the pressure would turn a very small fan (working as a turbine). Basically,
it
would be a very small kind of turbine engine, using a chemical reaction as the fuel. There wouldn't be much power, maybe just enough to turn a small
DC motor, having it work as a generator to recharge batteries or power a small radio, etc. I just thought it might be an interesting project to
build. The pressure wouldn't need to be that high, I'm thinking around 20 PSI at the very most. (I can blow on the fan and it spins pretty fast).
My concern though is would there be any safety issues with containing pure oxygen like that? After a short time, I'm guessing that there would only
be oxygen in the container and tubing, since air would be expelled when the valve is opened to release pressure and spin the turbine. The gas that
would be left would be the oxygen formed by the ongoing chemical reaction.
I would use other chemicals to work with CO2, but I want to leave oxygen as a possibility. Would it be safe to contain it and have it somewhat
pressurized like this?
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thesmug
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If you plan to directly run a motor with it (acting as a generator) be sure to use a brushless one since brushed motors can create sparks that can
ignite the oxygen.
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macckone
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Quote: Originally posted by thesmug  | | If you plan to directly run a motor with it (acting as a generator) be sure to use a brushless one since brushed motors can create sparks that can
ignite the oxygen. |
You won't generally get ignition with a motor and oxygen
although carbon brushes will make it possible. You need
something to oxidize and carbon oxidizes more readily than
most metal brushes.
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vmelkon
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20 psi isn't much. I've heard that wine bottles can handle 3 atm.
I don't know how much coca-cola 2 L bottles can handle but they are often rock hard full of pressure.
As for the DC motor, a long time ago, I was running a compressor in a O2 atmosphere in order to compress O2 into tanks. It was one of those cheap
compressors. The motor caught fire.
Signature ==== Is this my youtube page? https://www.youtube.com/watch?v=tA5PYtul5aU
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Metacelsus
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http://hypertextbook.com/facts/2000/SeemaMeraj.shtml
More than 30 psig.
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Zyklon-A
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Also, make sure that the motor is completely free of oil and grease.
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gatewaycityca
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Thanks for the help so far guys. 
I was looking at that table, and wow...some soda bottles and cans have a pressure of up to 55 PSI! I had no idea they would get that high. I
seriously doubt I would need to have pressures that high for my little "turbine engine."
Anyway, back to the oxygen question. As I understand, oxygen gas by itself isn't flammable. As an oxidizer, it will cause a flame to burn hotter and
faster, but it won't ignite by itself. So it's not like hydrogen, where a spark will cause it to ignite or explode like hydrogen can, right? The
motor I would use (to work as a small generator) would just be a small DC permanent magnet battery operated motor, like what would be in a toy car.
The turbine would spin it, generating a small electric current. So the only concern I might have is that the motor could catch fire if there's grease
on it? It wouldn't get hot, since I wouldn't be putting that much of an electric load on it anyway. The small turbine I'm using probably wouldn't
give enough torque to overcome that much back-EMF on the motor.
Now later on, who knows...maybe I'll build a bigger one to power a go-kart or something.  But that's much further down the road.
But my main question is, I don't have to worry about the containers themselves exploding or anything like that because of a reaction with the oxygen?
Maybe if I vent the O2 away from the motor after it passes through the turbine, that should make this reasonably safe?
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Zyklon-A
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I don't think oxygen is the best gas to use. Carbon dioxide is cheaper, and easier to make, and much less dangerous.
| Quote: |
As I understand, oxygen gas by itself isn't flammable. As an oxidizer, it will cause a flame to burn hotter and faster, but it won't ignite by itself
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Right, O2 isn't flammable by itself, only fluorine can oxidize oxygen.
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Because the process of oxidation is so widespread (fire, explosives, chemical synthesis, corrosion), the term oxidizing agent has acquired multiple
meanings. In one definition, an oxidizing agent accepts - or gains - electrons. |
This is actually the only true definition.
The better an oxidizer is at taking electrons, the more powerful it is. A element's ability to take electrons is expressed as it's
electronegativity.
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gatewaycityca
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Yeah, I would actually <i> prefer </i> not to use oxygen. CO2 is definitely what I would rather use since it would be a heck of a lot
safer. But since I already know of a fairly benign reaction that releases oxygen (hydrogen peroxide and bleach), I figured I would leave that as an
option. Bleach and H2O2 are dirt cheap too.
I would love to use carbon dioxide as the pressurizing gas, but so far the only chemicals I've worked with that release it are baking soda and vinegar
or lemon juice (citric acid). Using liquid chemicals would be much easier, since I could gravity feed them into the reaction container and use simple
valves to control the flow. If someone has any suggestions for liquid chemicals that I could mix to release CO2, that would be awesome. Again, I
would need something cheap, easy to find, and relatively non-toxic.
I wonder if I should ask this as a separate topic?
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Metacelsus
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Just dissolve the baking soda in a minimal amount of water. Also, you could use ammonium bicarbonate (sold in specialty baking stores), as it is more
soluble (216 g/L vs. 96 g/L).
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thesmug
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@gatewaycityca, sorry I phrased that wrong. What I meant is that with excess oxygen in the air there is a possibility of the various gasses (the ones
that make up air) mixing just right and creating a very dangerous situation. Even the tiniest sparks have been known to cause massive damage in these
kinds of situations and brushed motors create lots of these sparks.
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ZIGZIGLAR
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co2 is dirt cheap too ... I get a 6kg bottle refilled for $40. That's a lot of co2 right there.
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gatewaycityca
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Yeah, but I'm looking for cheap, simple ways of producing CO2 or O2 through a chemical reaction.
All things considered though, I think I will just work with CO2 for right now. It does seem safer, and I don't know how O2 would react with different
kinds of material, especially metal. If this experiment works and I can get this little turbine "engine" to work, I'll build a bigger one and then I
might try O2 at some point.
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subsecret
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As for a reaction vessel, you could buy a piece of PVC pipe at your local hardware store, add caps, and design a makeshift addition funnel. The
"addition funnel" portion of the apparatus should be pressure-equalizing, so as to prevent gas from bubbling back through the stopcock. Include a
pressure gauge and a hose barb if you choose to implement this design.
CO2 is definitely the cheaper alternative to O2.
Observed: Magnesium can burn in CO2. http://www.youtube.com/watch?v=NMZT2BAEtnc
Fear is what you get when caution wasn't enough.
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