497
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Destroying carbon monoxide in a gas stream
If I had a gas stream that contains a small amount of CO, what would be the best way to purify it? The amount of gas would be fairly small and have
only a small amount of CO if any, but I need to sure its free of it. The only other gases in the mix would be N2, CO2, O2 and possibly a little bit of
propane and NOx (combustion exhaust).
I saw mention of copper sulfonate compounds, but I was hoping for something a little simpler (and hopefully OTC/cheap). I don't think a chunk of
catalytic converter would useful but I suppose its possible.
[Edited on 21-4-2008 by 497]
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not_important
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If it's combustion exhaust, and you don't really care about the rest of the stream, just add a little air and run over a catalyst, the catalytic
converter just might do the job. Use the exit flow from that to pre-heat the additional air.
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12AX7
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I recall reading on here bubbling through copper sulfate either complexes or oxidizes it.
I can breathe combustion products from my propane burner all day, it produces very little CO at neutral mixture. If this is an indoor thing, don't
worry about it, plenty of people have indoor gas stoves. Just open a window.
Tim
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497
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| Quote: |
I can breathe combustion products from my propane burner all day, it produces very little CO at neutral mixture. |
I know, but the circumstances are a little different.
I will (fortunately) not be breathing it, but some fairly valuable and sensitive organisms will.
Also its not going to burn in open air, it will be in a closed combustion chamber with premixed propane/air. If the ratios are right everything should
be fine, but on the off chance something screws up, I can't have it pumping out CO.
All this keeping in mind the amount of propane burned will be quite small, on the order of a 20-50 grams per day continuously.
I saw mention of I2O5, it is supposed to work good... not quite the easiest method. The water vapor would pose a problem for that. Hmmm.
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BromicAcid
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Aqueous iron compounds should complex it or at least it seems like it should considering irons affinity for it. Failing that I would purge the system
with nitrogen to the inlet of a torch however that seems a little extream for such a small amount of carbon monoxide. Could you explain a little
better about these valuble sensitive organisms you mention? Are the organisms present where this combustion is taking place or are they just in
contact with the effluent gasses?
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Xenoid
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A material called hopcalite (try Google) is/was used in gas masks to remove CO. It comprises a mixture of oxides which catalyse the oxidation of CO to
CO2.
Hopcalite: Manganese dioxide (50%), copper oxide (30%), cobaltic oxide (15%) and silver oxide (5%). Works at room temperature. It may be possible to
obtain an appropriate gas filter from a "safety supplies" shop that sells respirators.
Many metal oxides when heated are reduced to metals by CO, with the CO oxidised to CO2.
In the "old style" gas analysers, an ammoniacal or HCl solution of cuprous chloride was often used to quantitatively absorb CO.
For truly OTC and if you are really desperate, you could bubble the gasses through a solution of blood. Haemoglobin
combines with CO to form cherry-red carbonyl haemoglobin .... 
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not_important
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| Quote: |
Also its not going to burn in open air, it will be in a closed combustion chamber with premixed propane/air. If the ratios are right everything should
be fine, but on the off chance something screws up, I can't have it pumping out CO.
All this keeping in mind the amount of propane burned will be quite small, on the order of a 20-50 grams per day continuously.
I saw mention of I2O5, it is supposed to work good... not quite the easiest method. The water vapor would pose a problem for that. Hmmm.
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I can't see who you need to burn a fuel in this case. The amount of heat released is low, as is the amount of H2O and CO2 formed. Depending on what
you are after you should be able to supply it - heat, CO2, H2O, by some means that will not form carbon monoxide (and small amounts of NOx, which are
likely to be damaging as well).
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497
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Yes the alternative is a canister of CO2... unfortunately that will run me several hundreds of dollars for solenoids and regulators.
The alternative is supplying it through combustion, although more complicated, is much cheaper.
I think I'll just end up setting it up to run with excess air and hope there's no CO produced. I see now that capturing the CO will not be worth the
effort.
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not_important
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| Quote: | Originally posted by 497
Yes the alternative is a canister of CO2... unfortunately that will run me several hundreds of dollars for solenoids and regulators.
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If I made the apparatus for you, it would cost you several hundred dollars. If I made it for me, it would cost a lot less. It seems to be that if
you need to switch the gas on and off, you'll need the valving for propane or CO2.
http://www.labx.com/v2/newad.cfm?catid=173
http://www.electronicsurplus.com/ccc2131-valves.htm
(for instance http://www.electronicsurplus.com/ccp75746-3-way-valve-24vac-... http://www.electronicsurplus.com/ccp86840-valve-5-8inch-orif... both around $25)
http://www.herbach.com/Merchant2/merchant.mv?Screen=CTGY&...
http://www.herbach.com/Merchant2/merchant.mv?Screen=CTGY&...
http://www.sciplus.com/search.cfm and search for valve turns up | Quote: | | This take-out device features a trio of Norgren air regulator valves mounted on a 9-3/4" x 7-3/4" black steel door with (2) pressure switches. (1)
switch is rated for 125"/H2O, the other for 220"/H2O. The (3) valves are unmarked but appear to be good for at least 150psi, and are connected to each
other and to the switches by a labyrinth of 1/4" OD tubing. The switches are N/O and wired in parallel. |
And there are other ways. Consider storing CO2 in water solution, dropping a measured amount into a heated cup and boiling it off to give CO2+H2O.
Or heating NaHCO3 or "magnesium carbonate", just need an electric heater that can reach 250-500 C.
Or use 5A or 13X molecular sieves to store dry CO2, heat them to release it. Or set up a container of yeast fermenting sugar, although that will
release a little ethanol as well.
There is a tendency for people come up with a solution and then ask how they can make it work, with way too little information on the
application, rather than stating the actual problem needed a solution:
"I need to have a CO2 supply/stream of X liters per day at Y pressure, and it should be pure CO2 or CO2 plus water vapour. How might I do this?"
[Edited on 24-4-2008 by not_important]
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497
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I have plenty of knowledge of the application. Here's your formula:
I need to have a CO2 stream of 5 liters per day at standard pressure, and it can have any contaminant as long as it is not toxic to aquatic life, and
the CO2 is over 10% by volume. How might I do this?
The cost of the setup is probably the most important factor right now. It has to be able to run continuously for a long time with minimal maintenance.
Preferably it could be controlled by a timer or controller although this is not critical.
Obviously a canister is ideal for this. And I might end up going that route, but I would much rather avoid it. And maybe have fun building something
while I'm at it.
Yeast is an option that I have tried, and it does work although it is much harder to control, inconsistent and high maintenance. It is fairly cheap
though.
Reaction of an acid with a carbonate is possible if the acid can be found cheap enough. This might be viable, although will need more maintenance than
I'd like. A 20 dollar 5 gallon container of battery acid would give me 200 liters of CO2. 15 bucks a month plus the carbonate is pretty spendy. And
thats not including the required pumps, etc.
The only other viable thing I can think of off hand is combustion. The cost of running it would be amazingly cheap, 110 grams (50-25 cents) of propane
would be equivalent to that 25 dollars worth of H2SO4/carbonate. One problem is the CO2 will only be 10-14% and a little more will have to be made to
compensate. For my applications that will not be of much consequence. The main problem with this comes from the more challenging apparatus
construction, the possibilities of CO production, propane leaks and things (my house  ) catching fire. I think the construction issues could be resolved with some ingenuity. The cost of the apparatus would be minimal too, simply a
screw on propane valve, an aquarium pump, and some tubing and glass. I'll attach my design when I can.
Maybe there's something I'm forgetting? What do you think?
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497
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I just found a simple OTC mixture that will destroy CO at room temperature. I found it in "The War Gases" as an addition to gas mask filters to remove
CO. It is called "Hopcalite" and is a powder that consists of 60% MnO2 and 40% CuO. From what I can gather, it is actually a catalyst and does not get
consumed. This is a useful thing to know if you ever needed to destroy some CO.
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Xenoid
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@ 497
What is the point of people replying to posts if they are obviously never read... 
I suggested and described "Hopcalite" 6 posts from the start of this thread.....!
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497
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Hmm sorry about that, I did read the thread, I don't know how I missed yours.
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Klute
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I used to be an aquariophile myself, and tried a few application for supplying CO2 to the aquarium. Like you, i started off with yeast
Very cheap indeed, but messy and hard to control to flow. The bottle was depleted in a couple days... On the second hand, i was advised to not
supply a continous flow of CO2, but rather alterning periods (1day on, 2days off, etc etc).
I tried the CaCO3 + dilute H2SO4, both very cheap, and gives off a rather consatnt flow if controlled well enough. I just had to empty the sludge
evry now and then. Not having much chemsitry equipment back then, I did have a addition funnel So iused on of those little tap for the air pumps. i used two bottles, on with the acid on top, a hole in the bottom
where a little aquarium tubing was sealed in, the tap, and more tubing attached to the lid of the second bottle, with a wide neck. In the lid there
was attached a piece of tubing going half way down the bottle, to which the air pump was attached, and a third hole with the tubing going to the
aquarium. I used a little in-line activated carbon on that tubing, although it might not have been very necessary.
The whole system worked pretty well, but after a while the connection started to leak a bit (acid!), and the whole thing started to be a pain to
maintain, so I finished by buying a CO2 cartridge at the aquarium shop, with on of those cool adsorption sytems where CO2 bubbles stay in contact with
the water for a long time. The initial cost was relatively high although I don't remember the exact price, and I latter discovered CO2 gas was much
cheaper at the ice-factory, so got a rechargeable bottle from them. I needed to swap the detender (?), the new one was less precise and it was tricky
to get a good setting.
If you are ready to put alittle money in it, I would sugest this kind of system, but DIY would come out much cheaper than what the aquarium people
try to sell it. And get a rechargeable cartridge
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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MagicJigPipe
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IMO, using a refillable CO2 cylinder would be much cheaper and be much less of a hassle (in the long wrong) than anything I can think of. What is
your aversion to doing this? Cost of the CO2? It's incredibley cheap. Go check up on it.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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not_important
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I suggest you read up on Hopcalite a bit more. It is most effective at low moisture levels, below 5% although it can tolerate higher amounts of
moisture when warm. Also, many suppliers of breathing apparatus using Hopcalite suggest replacing the Hopcalite cartridge after 8 to 10 hours use.
http://de.scientificcommons.org/18786257
http://www.freshpatents.com/Heterogeneous-composite-carbonac...
Attachment: Cobalt promoted copper manganese oxide catalysts for ambient temperature carbon monoxide oxidation.pdf (361kB)
This file has been downloaded 1719 times
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