Cryogenic process for the production of methane-free, krypton/xenon product

Claim 1

In a process for separating a feed gas containing krypton, xenon, oxygen and methane in a cryogenic distillation column wherein the feed gas is fed to an intermediate location of the distillation column for fractionation into a methane-free, krypton and xenon bottoms liquid and a methane-rich waste overhead, wherein liquid reflux for the column is provided by introducing a liquid feed to an upper location in the column above the intermediate feed location, and wherein vapor reflux is provided to the column by introducing a gaseous bottom feed to an lower location in the column below the intermediate feed location, the improvement for increasing recovery of krypton and xenon and producing a krypton and xenon product containing less than 1 ppm methane comprises using a gaseous stream containing at least 2% oxygen and less than 1 ppm methane as the gaseous bottom feed and operating the column so that the vapor to liquid flow ratio in the column is less than 0.15.