Catalyst activation

Claim 1

IN A BATCH PROCESS FOR ACTIVATING PARTICULATE POLYMERIZATION CATALYST COMPRISING CHROMIUM OXIDE, A PORTION OF THE CHROMIUM BEING IN THE HEXAVALENT STATE IN AN ACTIVATED CONDITION WHEREIN SAID CATALYST IS FLUIDIZED IN AN ACTIVATION ZONE BY CONTACT WITH AIR, THE IMPROVEMENT WHICH COMPRISES PASSING A FLUIDIZING STREAM OF AIR THROUGH SAID ACTIVATION ZONE IN A CLOSED RECIRCULATING LOOP, HEATING SAID AIR STREAM AND THEREBY HEATING SAID CATALYST TO AN ACTIVATION TEMPERATURE IN THE RANGE OF 400 TO 1750* F., HOLDING SAID CATALYST AT ACTIVATION TEMPERATURE FOR A PERIOD OF TIME SUFFICIENT TO ACTIVATE SAID CATALYST AND AT LEAST UNTIL THE DEW POINT OF SAID AIR STREAM IS IN THE RANGE OF ABOUT 0*F. AND BELOW, THEREAFTER COOLING SAID AIR STREAM AND THEREBY COOLING SAID CATALYST TO BELOW 400* F., CONTINUOUSLY ADDING MAKE-UP AIR TO SAID RECIRCULATING AIR STREAM AT A SUBSTANTIALLY CONSTANT RATE DURING SAID HEATING, HOLDING, AND COOLING STEPS, SAID MAKE-UP AIR BEING MAINTAINED DRY AT LEAST DURING SAID HOLDING AND COOLING STEPS, AND MAINTAINING THE PRESSURE IN SAID LOOP SUBSTANTIALLY CONSTANT BY CONTINUOUSLY PURGING AIR FROM SAID AIR STREAM DURING SAID HEATING, HOLDING AND COOLING STEPS.