Sciencemadness Discussion Board - Quenching excess H2 in a reaction.

Quenching excess H2 in a reaction.

Monoamine - 30-7-2021 at 04:38

Following an earlier post for the catalytic preparation of NaH at room temperature.

The think is that since this reaction will likely take quite long, it means that a large amount of H_2\ gas will be generated.

Of course, doing this reaction out door should be relatively safe, but it it none theless make me feel more comfortable if there is a way to deal with it during the procedure.

For shame by collecting excess gas in a balloon where it can even be use for later experiments.

Alternatively the excess H₂ could be passed through a solution of and alkene solvent with a catalyst such as palladium on activated charcoal.

Finally (and probably the most dangerous of the approaches), would just let the H₂ bubble through a water solution (for safety) and then igniting the gas that comes out. This would ensure that the flame does does not flow into the reaction vessel.

Anyway, I'm curious to hear your thoughts about this and if you have any safer tips for dealing with H₂ gas.

Thank you.

teodor - 30-7-2021 at 05:21

Try to do an experiment of dissolving metals in HCl passing H2 into a balloon and then try to burn this balloon outside. Fill it not too much (in any case you couldn't) & use other possible precautions. This experiment will give you some idea about penetration ability of the gas with exceptionally small molecules, its mobility & flammability.
I personally think that attempts to safely collect it in this quantity and keep it on your table are always more dangerous than just bubbling it out. I could be wrong. But if you can invest in some air-flow / ventilation solution for your working place I think it will be the most right thing.

[Edited on 30-7-2021 by teodor]

Look: https://history.nasa.gov/SP-4404/ch8-6.htm

[Edited on 30-7-2021 by teodor]

[Edited on 30-7-2021 by teodor]

unionised - 30-7-2021 at 11:07

The easiest, and probably safest, way to dispose of it hydrogen is to vent it to atmosphere at the top of a pole The gas goes pretty much straight up and, as long as the birds don't smoke cigarettes, it will be dispersed harmlessly.

The trouble with reacting it with something in the presence of a Pd or Pt catalyst is that those may catalyse the reaction with air, causing a fire if things go wrong.

karlos³ - 30-7-2021 at 11:41

*boom*

How you're going to generate the H2 anyways?

Triflic Acid - 1-8-2021 at 07:28

Or, just light a match at the end of a long thin glass tube coming from the reaction vessel. Burns off the hydrogen in a steady stream.

Texium - 1-8-2021 at 07:35

Quote: Originally posted by Triflic Acid

Or, just light a match at the end of a long thin glass tube coming from the reaction vessel. Burns off the hydrogen in a steady stream.

Until there’s a slight change in pressure due to the hydrogen generator running low on reactants that causes the flame to be sucked into the reaction flask and… boom.

Don’t give such thoughtless advice. That’s how people get hurt.

Amos - 1-8-2021 at 08:19

I would have no problem simply venting it to the atmosphere outside, preferable through a single water bubbler and suckback trap. It's extremely light, quickly rises, and is easily moved by air currents.

unionised - 1-8-2021 at 08:48

Quote: Originally posted by Texium

Quote: Originally posted by Triflic Acid

Or, just light a match at the end of a long thin glass tube coming from the reaction vessel. Burns off the hydrogen in a steady stream.

If you haven't purged all the air out of the system first, you don't need to wait for a change in air pressure. The flame will flash back into the chamber anyway.

On the other hand, if you have purged all the air out with hydrogen, then just carry on using whatever stopped the stuff igniting so far.

Triflic Acid - 1-8-2021 at 09:11

Tom from tom's lab is still okay after lighting the excess hydrogen: https://www.youtube.com/watch?v=9lOBrKw6DrI&ab_channel=T...

j_sum1 - 1-8-2021 at 15:06

It takes a lot of pressure to fill a balloon. I would not attempt that.
In fact, I think any attempts to store it will be problematic. if you need H2 at a later date for something, just make it then.

I think the simplest and safest is simply to vent it. A long hose leading out the window should do the trick. That is unless your volumetric flow rate is enormous.