Cracking with short contact time and high temperatures

Claim 1

In a fluidized catalytic hydrocarbon conversion process wherein hydrocarbon conversion is carried out in a transport type reaction zone in the presence of hot freshly regenerated catalyst, spent catalyst from said reaction zone is stripped of volatile hydrocarbons in a catalyst stripping zone in admixture with hot freshly regenerated catalyst, and stripped catalyst is regenerated with an oxygen-containing gas in a catalyst regeneration zone, the improvement which comprises contacting freshly regenerated cracking catalyst with vaporized hydrocarbon feedstock in a substantially horizontal transport reaction zone maintained at an elevated cracking temperature in the range of 1150° to 1350° F. and passing said catalyst and vaporized hydrocarbon through said reaction zone with an average contact time in the range of 0.1 to 1 second, discharging reaction products and spent catalyst from said reaction zone into a separation zone effecting substantially complete separation of hydrocarbon conversion products from spent catalyst, passing spent catalyst to a stripping zone into admixture with freshly regenerated catalyst at a temperature in the range of 1275° to 1450° F., stripping said spent catalyst with steam at a temperature in the range of 1200° to 1400° F., passing stripped catalyst from said stripping zone to a first catalyst regeneration zone, maintaining a dense phase fluidized bed of catalyst in said first regeneration zone by the introduction of primary regeneration air into the lower portion of said zone at a rate sufficient to cause fluidization of said catalyst particles and regeneration of said catalyst, passing partially regenerated catalyst particles from said dense phase fluidized bed regeneration zone into a dilute phase entrained catalyst riser regeneration zone, supplying secondary regeneration air to said riser regeneration zone in an amount sufficient to provide an excess of oxygen over that required for complete combustion of coke from said catalyst to carbon dioxide, discharging regenerated catalyst and flue gases resulting from the burning of coke from spent catalyst from the riser regneration zone into the lower portion of a second dense phase fluidized bed regenerator zone, discharging resulting flue gases containing 2 to 5 mole percent oxygen and less than 500 ppm carbon monoxide from said second regeneration zone, withdrawing regenerated catalyst at a temperature in a range of 1250° to 1450° F. from said second dense phase regeneration zone into said reaction zone, and withdrawing a separate portion of said regenerated catalyst from said second dense phase fluid bed catalyst regeneration zone to said stripping zone.