in preparation for the next purification step after the vessel 32 is cooled sufficiently it is slowly repressurized using a portion of the feed gas through the open valve 18 and the line 22 the vessel 30 continues to purify the feed gas during this time after repressurization of the vessel 32 the vessel 30 undergoes the steps of venting heating with purge gas and cooling with purge gas as described for the vessel 32 simultaneously the vessel 32 is purifying feed gas the process can run continuously in this manner the complete cycle time for the temperature swing process described in fig2 normally is from about 8 to 24 hours much longer than the cycle times for the pressure swing mode of operation a complete cycle for a two bed process operated in the temperature swing mode is given in table ii below table ii______________________________________ typical valves timestep open hours ______________________________________a pressurize vessel 30 with feed 16 18 60 0 25purify using vessel 32b purify using vessel 30 vent ves 16 26 58 0 25sel 32 to atmospherec purify using vessel 30 regenerate 16 26 52 2 5vessel 32 with hot purge gas 58d purify using vessel 30 cool ves 16 26 52 5 0sel 32 with purge gas 58e purify using vessel 30 pressurize 16 18 58 0 25vessel 32 with feedf purify using vessel 32 vent ves 18 24 60 0 25sel 30 to atmosphereg purify.