Couldn't this also be done for the other reactive components (especially nitrogen and oxygen) before cooling the gas? Removing ~99% of the mass ahead of time would require that much less energy for cooling.
Liquid oxygen and nitrogen both have some commercial value.
The tricky but is the liquidation process only liquifies some small fraction of the gas. The rest remains as a gas, so you now have "helium enriched" air, but it is still a very small percentage helium.
