sense / nonsense of CO monitoring

[BRT]

The whole idea is well beyond my paygrade. I'm no chemist or anything similar, and I hope that one will give you an answer - here, or someplace else. You suggested idea is oversimplified I think.

For

At room temperature, this reaction must be catalyzed. Details at https://www.enotes.com/homework-help/when-carbon-monoxide-combines-oxygen-what-produced-655293

CO is a potential fuel so it could be burned with oxygen to produce carbon monoxide, but not in a Nitrox situation.

To produce carbon dioxide.

 

[JohnN]

mulling more over this, thought I'd throw this out as an open question if there are any chemists out there. (@DandyDon ?)

Supposing both were drawn from the same source with a high CO concentration (eg a dysfunctional compressor), would nitrox ultimately have a lower CO concentration than a regular air mix?

My thinking is that:

CO is converted to CO2 in the presence of O2 according to

2CO + O2 <=> 2CO2

if you increase the concentration of O2, then Le Chatelier's Principle should move the CO/CO2/O2 equilibrium to the right in the direction of decreasing CO which should decrease the CO concentration present in your tank.

Or am I missing something?

Having to dust off some chemistry from longer ago than I would like to remember. . .

Although the reaction of CO + O2 is exothermic (releases heat ~ 120 kcal/mole O2) , there is a considerable 'hump' prevents this from spontaneously happening. (by way of example, a mixture of H2 and O2 is quite stable until you introduce external energy or a catalyst). A 100 ft^3 tank is 2831 liters, assume 32% O2, so you have 2831*.32 = 905 liters of O2. @ 22.4 liters/mole that gives you ~ 40* 120 kcal of heat (if you could consume all of the O2)

An extreme example since you're not going to find a tank of 32% with that much CO, and if you could increase the temperature sufficiently to get over the thermodynamic 'hump'.

So yes, you're missing something. Stoichiometry ain't what happens in real life.

 

[UTscuba]

The whole idea is well beyond my paygrade. I'm no chemist or anything similar, and I hope that one will give you an answer - here, or someplace else. You suggested idea is oversimplified I think.

For

At room temperature, this reaction must be catalyzed. Details at https://www.enotes.com/homework-help/when-carbon-monoxide-combines-oxygen-what-produced-655293

CO is a potential fuel so it could be burned with oxygen to produce carbon monoxide, but not in a Nitrox situation.

*way* beyond mine too, I'm trying to remember a class I took more than 20 years ago

thanks @ catalysis, I've spent over an hour googling trying to find the thermodynamics of the reaction, but that would make sense.

Ah well it was a nice idea

 

[UTscuba]

Having to dust off some chemistry from longer ago than I would like to remember. . .

yep, I know the feeling

Although the reaction of CO + O2 is exothermic (releases heat ~ 120 kcal/mole O2) , there is a considerable 'hump' prevents this from spontaneously happening.

I agree, except I think my question's more about asking if the energy barrier can be sufficiently decreased by changing the proportion of O2 in the mix and compressing the gas: 40% nitrox has almost double the number of O2 molecules available compared to regular air, and referring back to @DandyDon's comment, although we're at room temperature we're not at 1atm pressure, and from Charles' law, compression is going to change the equilibrium point in the same way as adding heat to the system,

Just idle, covid quarantine triggered, speculation

 

[grf88]

yep, I know the feeling



I agree, except I think my question's more about asking if the energy barrier can be sufficiently decreased by changing the proportion of O2 in the mix and compressing the gas: 40% nitrox has almost double the number of O2 molecules available compared to regular air, and referring back to @DandyDon's comment, although we're at room temperature we're not at 1atm pressure, and from Charles' law, compression is going to change the equilibrium point in the same way as adding heat to the system,

Just idle, covid quarantine triggered, speculation

Without a catalyst the temperature required would probably far exceed those reached during compression in a scuba compressor.

 

[UTscuba]

Without a catalyst the temperature required would probably far exceed those reached during compression in a scuba compressor.

that's assuming pressure remains constant, which it doesn't during compression. Remember that from Charles' law/ideal gas law PV is proportional to T, and that's going to change the energetics pretty heavily. All the discussions online I've seen have assumed room temperature and 1atm pressure, but in a 3000psi fill you've increased the pressure to around 200 atmospheres.

So with a nitrox fill you've done two things, (1) doubled the number of O2 molecules present compared to CO, and (2) pushed the molecules closer together which will increase the frequency of them colliding and so the chances of them reacting. In contrast the effect of heating is to make the molecules move faster and collide more energetically which increases the chances of them reacting.

I agree you're probably correct, but I'd be interested to know for certain

 

[grf88]

Although you have high pressure this is only potential energy and probably doesn't factor in although I would be interested to know for certain. Based on what I am looking at you need a temperature of something like 1000 F or more which I don't want in my compressor. Like you I would be interested in information from somebody knowledgeable.

 

[DandyDon]

To produce carbon dioxide.

Right, thanks, edited. And I get so bothered when others get the names confused.

Ah well it was a nice idea

It was an interesting idea, but of no value, as I see it. First & foremost, keep CO out of your tanks.

 

[UTscuba]

It was an interesting idea, but of no value, as I see it. First & foremost, keep CO out of your tanks.

no disagreement there, but like I said, idle quarantine inspired speculation

 

[UTscuba]

Although you have high pressure this is only potential energy and probably doesn't factor in although I would be interested to know for certain. Based on what I am looking at you need a temperature of something like 1000 F or more which I don't want in my compressor. Like you I would be interested in information from somebody knowledgeable.

I'm still not completely convinced, the reaction rate's given by the Arrhenius equation

and I'm pretty sure that factor of RT can be replaced with PV (ideal gas law PV = nRT) to give the rate constant under a change in pressure rather than temperature.

edit: and that 'activation energy' is the height of the 'bump' mentioned above