Xe/Kr separations. The noble gases xenon (Xe) and krypton (Kr) have many uses/applications (e.g. lighting, insulation in multi-pane windows, propellant for ion thrusters, anesthesia, and imaging). The majority of Xe and Kr production is via their isolation from air (abundance: Xe, 0.09 ppm, Kr, 1.1 ppm 66 ) via distillation at cryogenic temperatures. Particularly, the production of pure O 2 and N 2 from air via cryogenic distillation produces a byproduct stream enriched with both Xe and Kr; this mixture is then subject to an additional cryogenic distillation to obtain pure Xe and Kr. Note, distillation exploits the difference in boiling points of Xe and Kr, -108.