Sciencemadness Discussion Board

Filling old gas canisters

Terran - 24-6-2019 at 17:37

Luck has blessed me with two full canisters of oxygen and a full canister of nitrous. Does anyone here know about a system for refilling these canisters with other gasses produced in the lab? Chlorine, hydrogen, ect.

Sulaiman - 24-6-2019 at 19:14

Both oxygen and nitrous are oxidisers,
so you would need to use a vacuum pump to evacuate a cylinder before introducing hydrogen.
Chlorine plus a tiny ammount of moisture will eat most metals.

Overall I recommend not bottling either hydrogen or chlorine but either
buy your gasses ready bottled
or
produce your required gasses on demand ... much safer

Metacelsus - 24-6-2019 at 23:34

Furthermore, hydrogen will cause metal embrittlement, so hydrogen canisters have to be specially designed for hydrogen. It is quite unsafe to put hydrogen in a canister not designed for it.

Terran - 25-6-2019 at 03:53

Thank you for the information

RogueRose - 25-6-2019 at 12:16

Maybe you could purge the cannisters with CO2, N2 or argon, not to a high pressure, just enough to ensure there is no oxidizer left in the bottle. I've heard of people doing something similar with water as well, like in propane tanks but IDK how you would get all the moisture and air out of it afterwards, maybe heat it with the valve open, but you'd still have to get the air out afterwards.

Ubya - 25-6-2019 at 13:50

Quote: Originally posted by RogueRose  
Maybe you could purge the cannisters with CO2, N2 or argon, not to a high pressure, just enough to ensure there is no oxidizer left in the bottle. I've heard of people doing something similar with water as well, like in propane tanks but IDK how you would get all the moisture and air out of it afterwards, maybe heat it with the valve open, but you'd still have to get the air out afterwards.

Vacuum pump, instead of purging with an inert gas and then purging again with your gas pump down the cylinder, fill it with your gas, vacuum it again, add your gas now (you need to get to the lowest possible pressure or cycle vacuum/filling more times)

XeonTheMGPony - 25-6-2019 at 14:42

Quote: Originally posted by Metacelsus  
Furthermore, hydrogen will cause metal embrittlement, so hydrogen canisters have to be specially designed for hydrogen. It is quite unsafe to put hydrogen in a canister not designed for it.


you all so need a heat component, the worst issue is diffusion through the metal.

Terran - 25-6-2019 at 17:46

Quote: Originally posted by Ubya  
Quote: Originally posted by RogueRose  
Maybe you could purge the cannisters with CO2, N2 or argon, not to a high pressure, just enough to ensure there is no oxidizer left in the bottle. I've heard of people doing something similar with water as well, like in propane tanks but IDK how you would get all the moisture and air out of it afterwards, maybe heat it with the valve open, but you'd still have to get the air out afterwards.

Vacuum pump, instead of purging with an inert gas and then purging again with your gas pump down the cylinder, fill it with your gas, vacuum it again, add your gas now (you need to get to the lowest possible pressure or cycle vacuum/filling more times)

So it would be empty canister, vacuum remainder out, then vacuum gas in. Correct?

Ubya - 25-6-2019 at 18:19

Quote: Originally posted by Terran  
Quote: Originally posted by Ubya  
Quote: Originally posted by RogueRose  
Maybe you could purge the cannisters with CO2, N2 or argon, not to a high pressure, just enough to ensure there is no oxidizer left in the bottle. I've heard of people doing something similar with water as well, like in propane tanks but IDK how you would get all the moisture and air out of it afterwards, maybe heat it with the valve open, but you'd still have to get the air out afterwards.

Vacuum pump, instead of purging with an inert gas and then purging again with your gas pump down the cylinder, fill it with your gas, vacuum it again, add your gas now (you need to get to the lowest possible pressure or cycle vacuum/filling more times)

So it would be empty canister, vacuum remainder out, then vacuum gas in. Correct?

Empty canister, vacuum it, fill it with your gas (atmospheric pressure or less), vacuum it again, fill it to the desired pressure

unionised - 26-6-2019 at 09:52

You may have missed out one or more steps there.
If the container has air in it then you evacuate it, then fill it with something "inert" (N2 or CO2 or Ar...) then evacuate it again before adding anything flammable.
Similarly, if you go from a flammable material to an oxidant you fill it with something inert in between.

If youare unlucky...
Empty canister.
Connect to vacuum pump
Discover vac pump isn't suitable for flammable gas.
Extinguish fire.
Learn that you aren't meant to refill disposable gas bottles.


Ubya - 26-6-2019 at 10:22

Quote: Originally posted by unionised  
You may have missed out one or more steps there.
If the container has air in it then you evacuate it, then fill it with something "inert" (N2 or CO2 or Ar...) then evacuate it again before adding anything flammable.
Similarly, if you go from a flammable material to an oxidant you fill it with something inert in between.


the purging with an inert gas is necessary if you have a crappy vacuum pump, if you get thr canister to 1 torr (pretty reasonable) the percentage of air after filling the canister with gas is already 1/760, repeating the process one more time and the air is pretty much non existent, but yea if the vacuum pump can get only to 20kPa, inert gas purging is mandatory

unionised - 26-6-2019 at 10:43

The big problem is the gas mixture you make in the pump.
It starts off full of air, and then you add some flammable gas...
(or vice versa)

Ubya - 26-6-2019 at 11:33

Quote: Originally posted by unionised  
The big problem is the gas mixture you make in the pump.
It starts off full of air, and then you add some flammable gas...
(or vice versa)


rotary vane vacuum pumps are commonly used in HVAC applications, where refrigerants can be flammable gases (r600a, r290 etc) so they must be safe

[Edited on 26-6-2019 by Ubya]

Terran - 26-6-2019 at 16:33

Thank you all, you've all been great