Group 18 elements Extraction

   In terms of commercial production, He and Ar are the two most important noble gases. Helium is extracted from natural gas by liquefaction of other gases present (He has the lowest boiling point of all the elements), leaving gaseous He which is removed by pumping. Neon is extracted as a byproduct when air is liquefied, being left behind as the only gas. Argon has almost the same boiling point as O₂ (Ar, 87K; O₂, 90K) and the two gases remain together during the fractionation of liquid air. The O₂/Ar mixture can be partially separated by further fractionation; the crude Ar is mixed with H₂ and sparked to removed O₂ as H₂O, excess H₂ being removed by passage over hot CuO. Krypton and xenon are usually separated from O₂ by selective absorption on charcoal.