While sounding complicated this method of Nitrogen generation is all in the name.
This method of nitrogen generation is achieved by taking advantage of the different condensing points of gasses, with cryogenic separation, the main difference between cryogenic separation and pressure swing adsorption technologies is price and practicality.
How it works:
Cryogenic separation functions similarly to distillation but in reverse, instead of using heat to raise the temperature to a specific point between the boiling point of two mixed substances, cryogenic separation reduces the temperature to between the boiling point of the mixed gaseous substances.
The process of generating nitrogen through this process requires that air be inserted to the apparatus, whereupon it is subsequently supercooled to below the boiling point of nitrogen. Below this point nitrogen can no longer remain a gas and is now liquid nitrogen. Liquid nitrogen (now heavier than the surrounding air) falls under gravity in the container commonly an industrial-sized Dewar flask. Once at the bottom a regular flow of pure nitrogen can be siphoned out from the lower portion of the container assuming a regular flow of supercooled fluid coming in. All the oxygen and other trace elements that were in the input air are still in gas form as their transition temperature has not been reached and therefore “float” on the surface of the liquid Nitrogen.
This process is highly energy-intensive and requires very specialist equipment while providing unparalleled levels of purity there are very few processes that can appropriately use or are suited to that level of purity.
The main use of this technique is for industrial-scale production of Argon having the nitrogen as a side product and as a separation technique for other highly valuable gasses (natural gas, hydrogen, biogas, carbon monoxide).
Small scale systems could be technically possible but are financially prohibitive as well as overly complicated for the desired/required outputs namely nitrogen at a purity of 99.9%.
For all scientific laboratories needs pressure swing adsorption is capable of producing the purity greater than needed and for a fraction of the capital and maintenance cost of a small scale cryoseparater.