Nano-technology in the context of Air-Separation Unit

How can nanotechnology be implemented in the context of air separation unit? (propellant generation) ?
What kind of air-separation unit with what tech specs and capabilities is possible with nano-assembly (given stable mature mnt) ?
How much propellant could such nano-assembled-ASU produce?
What could it enable in the context of instant reusability of a starship (s) ?
How could such nano-assembled-ASU be produced?
How could the operation of such nano-assembled-ASU look like?
How many such nano-assembled-ASUs could reliably supply instant reusability of how many Starships?