Preparation of olefins

Claim 1

A PROCESS FOR PREPARING OLEFINS BY CRACKING HIGH BOILING HYDROCARBONS WHILE SUPPRESSING SIDE REACTIONS WHICH COMPRISES PASSING A HIGH BOILING HYDROCARBON MIXTURE CONTAINING LESS THAN 25% BY WEIGHT OF AROMATICS TOGETHER WITH A MINOR PROPORTION OF COMBUSTION SUBSTAINING GAS THROUGH A RELATIVELY SMALL HEATING ZONE CONTAINING A BED OF PARTICULATE OXIDATION-PROMOTING SOLID UNDER CONDITIONS FOR ESSENTIALLY COMPLETE COMBUSTION OF A PORTION OF THE HYDROCARBON MIXTURE AND FOR QUICKLY RAISING THE TEMPERATURE THEREOF TO AT LEAST 500*C., AND IMMEDIATELY THEREAFTER PASSING THE RESULTING MIXTURE EFFLUENT FROM THE HEATING ZONE THROUGH AN UNOBSTRUCTED CRACKING ZONE WHOSE CAPACITY IS AT LEAST EIGHT TIMES THAT OF SAID HEATING ZONE FOR A SHORT RESIDENCE TIME THEREIN WHEREIN ESSENTIALLY ONLY THERMAL CRACKING CONDITIONS ARE MAINTAINED COOLING THE EFFLUENT CRACKED PRODUCTS FROM THE CRACKING ZONE BELOW CRACKING TEMPERATURE, AND RECOVERING OLEFINS FROM THE PRODUCT.