I believe OP is asking how different gases are extracted to fill a tank.
At least, that’s what I gather.
I don’t know how an oxygen generator works to pull O2 from the air, but I assume the same type of process would work for helium (I assume it’s somehow extracted from the breathing air vs. Things like natural gas, which come from underground)
Noble gasses (helium, neon, argon, etc) are found pure in nature, usually as a byproduct of natural gas and oil extraction.
Hydrogen and oxygen is made via hydrolysis. The process involves running an electrical current through water to separate hydrogen and oxygen. It’s an expensive process, and hydrogen is extremely difficult to store for long periods of time.
Helium is a special case. Basically all the helium we use is extracted along side natural gas and separated out using [Fractional Distillation](https://en.wikipedia.org/wiki/Fractional_distillation) to separate the helium from the other components of natural gas
Less rare gasses like Nitrogen and Oxygen can be gathered from the atmosphere using either membranes or adsorption.
For the membrane approach you use a specially crafted membrane and ram air through it, the gas you want will scoot through the membrane while the others won’t and it gives you a decently pure supply.
For adsorption, you take a material which grabs onto the gas you want and load a chamber up with it. Pressurize the chamber with normal air for a bit and you’re desired gas will get stuck the the adsorbent like a sponge, then you dump the air and reseal the chamber, the adsorbent will give up the gas and you can suck the gas out of there and put it in a pressurized chamber. You can repeat this to get whatever purity of the gas you need (99.9995% nitrogen is made this way)
In some cases you can use a selective membrane to separate gases. I did a lab in school where we fed compressed air through a membrane and (i believe) nitrogen permeated out the shell-side since it’s smaller, and oxygen went straight through the tube.
From [wikipedia](https://en.wikipedia.org/wiki/Membrane_gas_separation#Uses) other membrane separations include:
* The separation of nitrogen or oxygen from air (generally only up to 99.5%)
* Separation of hydrogen from gases like nitrogen and methane
* SO2, CO2, H2S, H2O, NH3 separations from other components
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