Radioactive krypton gas separation

A method for the separation of radioactive krypton from a feed gas mixture comprising nitrogen and trace amounts of carbon dioxide and said radioactive krypton, comprising the steps of:

• a. providing said feed gas mixture at superatmospheric pressure and ambient temperature and passing same from the feed inlet end through the first of at least two crystalline zeolite molecular sieve adsorption zones for preferential adsorption of carbon dioxide, and coadsorption of a minor part of said krypton;
• b. discharging non-adsorbed prepurified gas from the feed discharge end of said first adsorption zone of (a) and cooling same to cryogenic temperature;
• c. distilling the cryogenically cooled prepurified gas from (b) against nitrogen liquid to produce a krypton bottoms concentrate liquid and purified nitrogen overhead gas;
• d. partially rewarming said purified nitrogen overhead gas of (c) to about ambient temperature by heat exchange with said nonadsorbed prepurified gas for said cooling of (b);
• e. passing a first part of said partially rewarmed purified nitrogen overhead gas as cool purge gas at low pressure into the feed discharge end and through the second of said crystalline zeolite molecular sieve adsorption zones having previously been at least partially loaded with carbon dioxide and krypton by passage of said feed gas mixture therethrough, thereby desorbing substantially all of said krypton and only a minor part of said carbon dioxide from such second zone and discharging the krypton-containing first part of cool purge gas from the feed inlet end of said second zone;
• f. joining said first part of purge gas from (e) with said feed gas mixture for said passing through the first zone of (a);
• g. further warming to at least 350.degree.F. a second part of said rewarmed purified nitrogen overhead gas as hot purge gas and passing same into the feed discharge end and through an other-than-first said crystalline zeolite molecular sieve adsorption zone having previously been at least partially loaded with carbon dioxide and coadsorbed krypton by passage of said feed gas mixture therethrough and thereafter only completely desorbed of said krypton by passage of said first part of purge gas therethrough, thereby desorbing carbon dioxide from such other-than-first zone and discharging the carbon dioxide-containing second part of hot purge gas from the feed inlet end of said other-than-first zone;
• and
• h. passing a third part of said partially rewarmed purified nitrogen overhead gas into the feed discharge end and through said other-than-first adsorption zone after the hot purge gas flow for recooling of such zone.