Please forgive me if I misunderstood you. But AIR (70% n2, 21% o2 + others ELEMENTS) can be liquid. ONE more time: compress the air, remove the heat of compression and you get liquid air of the same mixture that you started with. You only get the purified elements after fractionation. End of discussion. You are welcome to live in your world and I’ll live very well in mine.
Miles.