Method for catalytic cracking with maximization of diesel base stocks

1. A method for catalytic cracking to maximize the production of diesel base stocks, comprising a first cracking reaction step in an upflow fluidized bed reactor, a step of separating the cracked hydrocarbons and coked catalyst, a step of fractionating the cracked hydrocarbons and a step of regenerating said coked catalyst, wherein the hydrocarbon feedstock is injected into the upflow reactor on a catalyst partially deactivated by prior coking of at least part thereof in the same upflow reactor, so that a reaction temperature of the effluents leaving said reactor varies from 470 to 600° C., this prior coking being carried out by injecting at least one hydrocarbon compound having a boiling point equal to or higher than 350° C., on at least part of the regenerated catalyst bounded by at least one zone defined by means of an internal device, the hydrocarbon feedstock to treat being injected downstream from the internal device in said reactor, and a second cracking reaction step in an upflow reactor, operating in parallel to the first cracking step, and in which hydrocarbon cuts having a boiling point equal to or lower than 160° C., and hydrocarbon cuts having a boiling point equal to or higher than 330° C. are recycled on the regenerated catalyst.

2. The method as claimed in claim 1 , wherein part of the coked catalyst, separated and then stripped during the separation step, is returned directly to the upflow reactor upstream, at and/or downstream of the hydrocarbon feedstock injection point, at a temperature equal to or lower than the reaction temperature.

3. The method as claimed in claim 2 , wherein 1 to 100% of at least one hydrocarbon compound having a boiling point equal to or higher than 350° C., produced at the outlet of the fractionation step, is recycled on 1 to 100% by weight of the regenerated catalyst introduced at the bottom of the upflow reactor.

4. The method as claimed in claim 1 , wherein part of the regenerated catalyst is coked upstream of the feedstock injection point by at least one hydrocarbon compound having a boiling point equal to or higher than 350° C. and wherein part of the coked and stripped catalyst, recovered in the separator, is also sent upstream, at and/or downstream of the feedstock injection point in the reactor.

5. The method as claimed in claim 1 , wherein 1 to 75% by weight of the coked and stripped catalyst recovered in the separation step is recycled to the upflow reactor upstream, at and/or downstream of the feedstock injection point.

6. The method as claimed in claim 1 , wherein at least one cut having a boiling point lower than 160° C. is injected on the regenerated catalyst in the upflow reactor upstream of the feedstock injection point.

7. The method as claimed in claim 1 , wherein hydrocarbon cuts having a boiling point equal to or lower than 145° C., and hydrocarbon cuts having a boiling point equal to or higher than 350° C., are recycled on the regenerated catalyst in the second cracking step.

8. The method as claimed in claim 7 , wherein the hydrocarbon cuts are selected from the effluents produced by the fractionation step, and from crude oil conversion and/or distillation units, including cuts derived from biomass.

9. The method as claimed in claim 7 , wherein operations in this second upflow reactor are carried out in severe cracking conditions with a C/O ranging from 4 to 20 for reaction temperatures between 470 and 650° C.