Production of gasoline by catalytic cracking

Claim 1

IN THE CATALYSTIC CRACKING OF A HYDROCARBON OIL BOILING ESSENTIALLY ABOVE GASOLINE TO PRODUCE CATALYTICALLY CRACKED MOTOR GASOLINE HAVING A SPECIFIED ASTM FINAL BOILING POINT WHEREIN THE OIL TO BE CRACKED IS CONTACTED IN SEPARATE AND DISTINCT CRACKING STAGES UNDER CRACKING CONDITIONS WITH A SOLID CRACKING CATALYST AND CRACKED PRODUCTS ARE REMOVED BY SEPARATE FRACTIONATION OF THE HYDROCARBON REACTION MIXTURES FROM THE SEPARATE STAGES, THE IMPROVEMENT WHICH COMPRISES EFFECTING THE FIRST STAGE CRACKING AT A TEMPERATURE BETWEEN ABOUT 900*F. AND ABOUT 1000*F. WITH THE CATALYST MAINTAINED DISPERSED IN THE OIL VAPORS, UNDER CONDITIONS OF SEVERITY GIVING ABOUT 35 TO 60% CONVERSION AND CLOSE TO 0.6 TIMES THE TOTAL CONVERSION FOR THE TWO CRACKING STAGES FRACTIONATING THE HYDROCARBON MIXTURE FROM THE FIRST STAGE OF CRACKING UNDER CONDITIONS TO REMOVE AS OVERHEAD PRODUCT A HYDROCARBON FRACTION HAVING A FINAL BOILING POINT ABOVE ABOUT 266*F. BUT AT LEAST 25*F. BELOW THE FINAL BOILING POINT OF THE MOTOR GASOLINE PRODUCT FROM A RESIDUUM FRACTION CONTAINING INSUFFICIENTLY CONVERTED OR UNCONVERTED OIL ALONG WITH A PART OF THE CATALYTICALLY CRACKED GASOLINE PRODUCED IN THE FIRST STAGE BOILING IN THE RANGE BETWEEN ABOUT 266*F. AND THE FINAL BOILING POINT OF THE MOTOR GASOLINE PRODUCT, SUBJECTING SAID RESIDUUM FRACTION, TO FURTHER CRACKING IN A SUBSEQUENT STAGE TO AN OVERALL CONVERSION OF AT LEAST 60%, FRACTIONATING THE HYDROCARBON REACTION MIXTURE FROM THE LAST STAGE OF CATALYTIC CRACKING UNDER CONDITIONS TO REMOVE AS OVERHEAD PRODUCT A CRACKED GASOLINE HAVING THE ASTM FINAL BOILING POINT OF SAID MOTOR GASOLINE PRODUCT AND BLENDING THE RESULTING GASOLINE WITH THE ABOVE SAID OVERHEAD PRODUCT TO PRODUCE SPECIFIED END POINT MOTOR GASOLINE.