Twospoons
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Removing ozone from a low pressure gas stream?
I'm looking for a quick, cheap way to remove ozone from a gas stream at low pressure ( 1 torr or so). This is the exhaust gas from a plasma cleaner I
built to do some tests at work - just a crude lash-up, using air.
I'm a little concerned the ozone may be damaging the vacuum pump, given the discoloration of the plastic tubing running from plasma chamber to pump.
Flow rate is low, so I don't have to deal with kg of O3, buts its enough you can smell it easily (currently I vent the exhaust outside).
Quick hunt on google yields some commercially made catalysts using CuO + MnO2. Not sure if I could obtain small quantity, or make some perhaps (how
would I make a usable structure for column packing?).
Wikipedia suggests ozone reacts with lots of things - I noted carbon and urea, and maybe hydrogen as possible candidates - would prefer a solid
reactant that I can load into a packed column, but a gas feed would be OK.
Wanting low cost, easily obtainable materials, works under vacuum. Regular replacement is OK, as the plasma cleaner on runs from time to time.
Any suggestions?
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Adas
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The urea would be your best choice, IMO. One molecule of O3 oxidizes one molecule of urea (CH4N2O + O3
----> CO2 + 2 H2O + N2)
Rest In Pieces!
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watson.fawkes
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Quote: Originally posted by Twospoons  | | Quick hunt on google yields some commercially made catalysts using CuO + MnO2. Not sure if I could obtain small quantity, or make some perhaps (how
would I make a usable structure for column packing?). |
Two concerns: Pumping rate through a packed column and
catalyst fabrication.
If you use a packed column, you'll reduce the outflow rate to the pump. The effect will be that the gas pressure inside the chamber will rise. It may
not rise enough to cause problems, but it's something to be aware of. If the catalyst bed offers too much resistance, you can always change the pump
for something with higher intrinsic capacity.
At 1 torr and ordinary tubing diameters, you're in the viscous flow region, where you can use ordinary fluid flow equations for modelling. Flow
through a porous medium can be modeled with Darcy's law, ordinary used for groundwater. The permeability of the medium is proportional to the square of the pore size, so if you use a small
catalyst support, you have much more resistance to flow. Overall geometry has series and parallel flow, just like electrical resistance networks. The
upshot is that you want a shorter, wider column rather than a longer, thinner one. Think something shaped like a desiccant cartridge rather than a
distillation column. Consider integrating it into the chamber itself.
As for catalyst composition, many of these kind of oxide catalysts are active because they are co-deposited with low melting salts (such as
chlorides), you that you actually have a surface-liquid-film/gas interaction rather than a solid/gas interaction. You may have to heat the catalyst to
activate it; check the commercial products to see if they do this. (I don't know anything specifically about the activity of ozone catalysts.)
As for catalyst support, given the relatively small scale I suspect you could just use glass wool. Ceramic beads could also work..
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ScienceSquirrel
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I would suggest a heated quartz tube packed with silver wool.
http://www.google.com/patents/US6054098
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unionised
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At the risk of being a bit late in the day, activated charcoal is used for this.
The NOx detector we used at work had the same issue- killing the ozone before the ozone killed the pump and they used a charcoal trap.
the problem is that you may still need to vent the gas outside because one of the products is carbon monoxide.
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Twospoons
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Its never too late. As it happens activated carbon is what I am trying first - its so cheap and easy to buy. And I found several references to it
being used to remove ozone.
So I'm currently fitting out a preserving ('Mason') jar with a new acrylic lid, pneumatic fittings, and a plastic overwrap in case of breakage and I
have 2kg of carbon pellets.
Thanks for all the replies!
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ScienceSquirrel
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| Quote: Originally posted by unionised | At the risk of being a bit late in the day, activated charcoal is used for this.
The NOx detector we used at work had the same issue- killing the ozone before the ozone killed the pump and they used a charcoal trap.
the problem is that you may still need to vent the gas outside because one of the products is carbon monoxide. |
That sounds like the best idea to me.
A glass tube packed with charcoal chips might solve your problem.
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