Recovery of finely divided solids

Claim 1

A PROCESS FOR THE CATALYTIC CONVERSION OF HYDROCARBONS IN THE PRODUCTION OF MOTOR FUELS WHICH INCLUDES THE IMPROVEMENT WHICH COMPRISES INTRODUCING HOT CARBONACEOUS CONTAMINATED FINELY DIVIDED CATALYST HAVING A PARTICLE SIZE BETWEEN ABOUT 0 AND ABOUT 150 MICRONS AND WITH AT LEAST ABOUT 10 PERCENT BY WEIGHT OF 10 TO 40 MICRON SIZE CATALYST PARTICLES INTO A REGENERATION ZONE, INTRODUCING AIR INTO THE BOTTOM PORTION OF SAID REGENERATION ZONE AT A VELOCITY TO PROVIDE A DENSE FLUIDIZED BED HAVING A DILUTE PHASE THEREABOVE OF A LESS DENSE GASEOUS FLUID SUSPENSION, MAINTAINING SAID REGENERATION ZONE AT A TEMPERATURE BETWEEN ABOUT 1000* F. AND 1200* F., SEPARATING ENTRAINED SOLID CATALYST PARTICLES FROM THE GASEOUS COMBUSTION PRODUCTS LEAVING SAID DENSE FLUIDIZED BED OF CATALYST PARTICLES AND EFFECTING SUCH SEPARATION IN A PLURALITY OF CENTRIFUGAL SEPARATION STAGES, RETURNING SEPARATED CATALYST PARTICLES TO SAID FLUIDIZED BED AND INCREASING THE INLET VELOCITY OF THE VAPOROUS REACTION PRODUCTS ENTERING SAID LAST SEPARATION STAGE BY AT LEAST 50% OVER THAT IN A PRIOR SEPARATION STAGE TO RECOVER 10 TO 40 MICRON CATALYST PARTICLES AND MAINTAIN THE DESIRED PERCENTAGE OF 10-40 MICRON CATALYST PARTICLES IN SAID DENSE FLUIDIZED BED IN SAID REGENERATION ZONE.