Finding an Oxygen Absorber for Fast Gas Streams

[mrjeffy321]

I am looking for an Oxygen absorbing material which will absorb Oxygen fairly quickly.

Ideally, what I would like to do pass a stream of gas through a tube filled with this Oxygen absorber as well as a water absorbing material (possibly CaCl2) so as to remove as much Oxygen gas and water vapor as I can. Since the gas will be flowing through the tube, there will not be much time for it to react with whatever materials I use, but I want to “clean out” as much of the undesirable gasses as I can.

I think they use Iron Oxide (Fe₃O₄) as an Oxygen absorber for some foods [like beef jerky], but this would be much too slow for my needs I think.

The Oxygen absorber should not absorb any Hydrogen gas, but it can (optionally) absorb just about anything else like N₂, CO₂, …., but Oxygen gas is the priority.

 

[Gokul43201]

Take a look into pyrogallol.

 

[mrjeffy321]

I could not find much about it other than it is used in photography, it is a powerful reducing agent, and it is toxic, ...Oh yes, and it absorbs Oxygen.

I found a photography company selling it for $82 per pound + shipping + possible haz. mat. fee.

 

[Gokul43201]

I remember (from way back before the wheel was invented...no actually from high school) something about pyrogallol being used in the production of nitrogen from air. It was supposedly used to extract the oxygen, by bubbling the air through it - I got the impression it was a liquid. That's all I recall, and even that, I wouldn't bet on.

Edit : Yikes ! Looks like it produces tiny amounts of carbon monoxide -
http://nvl.nist.gov/pub/nistpubs/jres/045/1/V45.N01.A05.pdf

Further info : Scroll nearly half-way down this page and look at (e) under "Reagents".

Anyway, what's your budget for this ?

 

[Gokul43201]

Other than that, the only idea off the top of my head comes from working with high vacuum systems, where we use Ti (molten) as a getter for trace amounts of oxygen. Ba and Zr are also pretty good getters... but I strongly doubt these are any good for what you have in mind.

 

[mrjeffy321]

hmmmm, an expensive Oxygen absorber which produces Carbon Monoxide, so far, that stuff isn't looking too appealing.

I do not have a very big budget for this project. I don't have a set amount/limit of what to spend, but I'll know a good price when I see it.

Before posting this thread, I was doing a little bit of reseach on the subject. I found this thread,
https://www.physicsforums.com/showthread.php?referrerid=35074&t=78440
where you also suggested getters. But I believe in one of your links, it says that some getters also absorb Hydrogen gas, something I want to make sure not to do.
But anyway, yes, using molten metals isn't really an option for me on this project.

There are companies which sell pre-packaged Oxygen absorbers which are made for food. These might have been an option, if the time they took to absorb a relatively small amount of Oxygen was not measured in days, but rather in minutes or seconds.

Perhaps I am thinking in the wrong direction. Would there be another way to remove Oxygen from a gas mixture other than some type of Oxygen absorbing power or what-have-you?

 

[Gokul43201]

Oops, forgot to include the link for that last bit I wrote in post #4. For whatever it's worth, here it is. I think the pyrogallol is typically made up to an alkaline solution. It may take only a few grams (the link below speaks of an oxygen trap using 4.5 g of pyrogallol in KOH) of the stuff to make up the solution you need.

http://a257.g.akamaitech.net/7/257/2422/14mar20010800/edocket.access.gpo.gov/cfr_2002/aprqtr/21cfr101.108.htm

What is the typical composition of your gas mixture ? And how much of it (volume) do you have/use ?

 

[mrjeffy321]

You don't happen to have any idea on the rate at which it will absorb Oxygen or its Oxygen absorbing capacity, do you?
Perhaps if just a little bit is very effective, it may still be an option.

I don't know the exact composition of my gas mixture, but I do know that it will varry. The highest Oxygen concentration I would have to deal with would be 20% (normal air) and it could, in theory, drop to only a negligible amount.
What I want to do is take the output of my Hydrogen Generator and ensure that I clean out all the undesireable gasses possible, most importantly Oxygen. In the process of Hydrogen gas generation, the Hydrogen is collected in a chamber which will initially contain air from the outside atmosphere...air containing Oxygen [+ Nitrogen]. The Hydrogen and air should mix initially and both gasses would find their way into the output stream. As time passes and the air is depleted, the output will start to become purer and purer Hydrogen. But this takes time, time that I don't want to have to wait around, meanwhile letting my Hydrogen float away into the atmosphere.
What I could do, possibly, is actually try to measure the Oxygen concentration in the output gas as a function of the reaction time. Know any good methods of doing this? Or I could just assume that Oxygen is always there and just try to remove it somehow.

 

[wxrocks]

vacuum

Couldn't you get a vacuum chamber -- pump out the air and have your hydrogen generator output directly into the chamber. I know you can't get a perfect vacuum, but you'd have some pretty pure hydrogen (and please be careful!)

 

[mrjeffy321]

A vacuum would not work very well as a solution with my particular application.

The source of the Oxygen impurities is the air which enters into the Hydrogen production chamber and sits above the water level. When the Hydrogen is produced, it bubbles up through the water and mixed with the gas above, then exists through a hole in the side and travels through a tube to be used/compressed/…
Outputting the Hydrogen gas into a vacuum does not solve the problem of the Oxygen in the Hydrogen stream….actually, it would introduce water vapor impurities into the stream since the water will boil away under the low pressure/vacuum.

There are a couple of solutions for this,

--Purge the entire Hydrogen generator with an inert gas, for example, Argon which is used in arc welding…or even Nitrogen gas would work. This however is not a very desirable solution for me since I don’t usually have a tank of inert gas just sitting around, and it would be tedious and time consuming to have to re-purge the container every time I open it (I do this, or at least want the ability to do this, a lot).

--Forget about absorbing the Oxygen gas from the gas stream, rather, just react it.
One could use a Platinum metal catalyst to recombine the Oxygen and Hydrogen gas together, forming water. Since Oxygen is, bar far, the limiting reactant, there will not be a significant impact on the overall Hydrogen concentrations in the gas stream and the water produced can be condensed and removed with relative ease. The problem with this is that platinum, or even platinum coated ___, is very expensive. Also, I have heard that if one intends to remove Oxygen gas in this manner, one needs to use a “Flash back arrestor” in case of a sudden explosive reaction between the O2 and H2. For my application, the flash back arrestor(s) should ideally be made of stainless steel (inside and out), but these don’t run cheap from what I have seen.

 

[PRDan4th]

The problem with reacting H2 with O2 to remove the O2 is you will release a lot of heat and may cause an explosion. You also remove two moles of H2 for each mole of O2, therefore have to generate a lot more H2 to achieve the same H2 concentration. There are a lot of ways of seperating H2 in commercial quantities (PSA, mol sieves, cryogenics etc) but your application sounds like a lab scale project.

 

[PRDan4th]

How about the way the lungs do it - hemoglobin, just a way-out idea.

 

[mrjeffy321]

Since the total amount of Oxygen in the Hydrogen stream will not be all that much, I can tolerate loosing 2 moles of Hydrogen for every mole of Oxygen removed.

Also, since the Hydrogen generating chemical reaction also releases quite a bit of heat, I already have a cooling system set up and it would not be overly difficult to modify it to further cool the "purified" gas.

 

[GCT]

I am looking for an Oxygen absorbing material which will absorb Oxygen fairly quickly.

Ideally, what I would like to do pass a stream of gas through a tube filled with this Oxygen absorber as well as a water absorbing material (possibly CaCl2) so as to remove as much Oxygen gas and water vapor as I can. Since the gas will be flowing through the tube, there will not be much time for it to react with whatever materials I use, but I want to “clean out” as much of the undesirable gasses as I can.

I think they use Iron Oxide (Fe₃O₄) as an Oxygen absorber for some foods [like beef jerky], but this would be much too slow for my needs I think.

The Oxygen absorber should not absorb any Hydrogen gas, but it can (optionally) absorb just about anything else like N₂, CO₂, …., but Oxygen gas is the priority.

There are other, perhaps better ways of removing oxygen from a reaction chamber, if that's what you intend to do. Passing inert gases such as N2 or Ar through the well sealed apparatus with a small adjustable outlet opening can do pretty well also. If it's a solution and you want to keep the oxygen out, you can employ an adequate sized degasser tube, with a large surface area tip (I don't recall the exact material at the moment). But the usual problem is in keeping the oxygen out and a good setup is to keep an constant input of the inert gas while letting the air out in a timely manner.

 

[mrjeffy321]

What I wanted to do was produce the Hydrogen in order to compress and store it in a tank.
I would think it would be a very bad idea to compress the Hydrogen gas while a small, but potentially significant, amount of Oxygen gas is mixed in.

The H2 producing react chamber is, by virtue of it producing so much Hydrogen, operated at an elevated pressure...so once the Oxygen gas is eliminated, it should not seep back in.
Thoroughly purging the container with an inert gas is probably the best solution in terms of effectiveness (and even possibly expense), but is awfully inconvenient for my needs.

I might be acting a little overly paranoid, I might not, but I just don’t like taking chances with this sort of stuff.
But that is OK, this project is not at the top of my 'to-do' list right now.

 

[ReefermanUK]

Oxygen removal from air

This may not be quite be what you are looking for but coincides with a similar problem I face obtaining nitrogen in non-commercial quantites. It should be able to provide a low quantity of gas which you can be throughput, continuously flushing your equipment.

It should be possible to electrolyse a quantity of distilled water to obtain & store hydrogen and then feed it slowly into a closed volume of air, via fine visible burner. On combustion the oxygen in the air should combine with the hydrogen creating water vapour while there is available oxygen. When the water vapour condenses on cooling, it can be run off. The remaining gas will be nitrogen & and an unavoidably small quantity of hydrogen. Hydrogen itself will escape through walls and seals over time as the molecules are so small.
Be warned however, that hydrogen and oxygen will explode in uncontrolled environments when ignited.

Like others, I recall school day experiments when air was run through a small fluid bath when the oxygen was absorbed, but unfortunately I cannot recall which chemical was used, nor can I trace it over the internet.