Two-step hydrocracking method using a partitioned distillation column

A two-step process for the hydrocracking of hydrocarbon feedstocks containing at least 20% by volume and preferably at least 80% by volume of compounds boiling above 340° C., said process comprising at least the following steps:

• a) a step of hydrotreating said feedstocks in the presence of hydrogen and at least one hydrotreating catalyst, at a temperature of between 200° C. and 400° C., under a pressure of between 2 and 16 MPa, at a space velocity of between 0.2 and 5 h−1 and with an amount of hydrogen introduced such that the liter of hydrogen/liter of hydrocarbon ratio by volume is between 100 and 2000 l/l,
• b) a step of hydrocracking at least one portion of the effluent from step a), the hydrocracking step b) taking place, in the presence of hydrogen and at least one hydrocracking catalyst, at a temperature of between 250° C. and 480° C., under a pressure of between 2 and 25 MPa, at a space velocity of between 0.1 and 6 h−1 and with an amount of hydrogen introduced such that the liter of hydrogen/liter of hydrocarbon ratio by volume is between 80 and 5000 l/l,
• c) a step of separating at high pressure the effluent from the hydrocracking step b) to produce at least a gaseous effluent and a liquid hydrocarbon effluent,
• d) a step of distilling at least one portion of the liquid hydrocarbon effluent from step c) carried out in at least one distillation column comprising a vertical dividing wall in the bottom of said column, dividing the bottom of said column into two separate compartments, the first compartment and the second compartment, by introducing said effluent into the first compartment, at a level lower than or equal to the upper end of said dividing wall, from which step the following are withdrawn:
• optionally a gaseous fraction,
• optionally at least one gasoline fraction boiling at a temperature below 150° C.,
• a middle distillates fraction having a boiling point between 150° C. and 370° C., preferably between 150° C. and 350° C. and preferably between 150° C. and 340° C.,
• an unconverted liquid fraction having a boiling point greater than 340° C., withdrawn at the level of the lower end of said first compartment, and
• an unconverted heavy liquid fraction containing HPNAs, having a boiling point greater than 340° C., withdrawn at the level of the lower end of said second compartment delimited by said dividing wall,
• e) the purge of at least one portion of said unconverted heavy liquid fraction containing HPNAs, having a boiling point greater than 340° C., is withdrawn via the line 13 at the lower end of said second compartment of the distillation column of step d),
• f) a second step of hydrocracking at least one portion of the unconverted liquid fraction having a boiling point greater than 340° C. from step d) withdrawn from the lower end of said first compartment of the distillation column, mixed with the unpurged portion of the unconverted heavy liquid fraction containing HPNAs, having a boiling point greater than 340° C. from step d), withdrawn at the lower end of said second compartment, said step f) operating in the presence of hydrogen and of at least a second hydrocracking catalyst, at a temperature of between 250 and 480° C., under a pressure of between 2 and 25 MPa, at a space velocity between 0.1 and 6 h−1 and with an amount of hydrogen introduced such that the liter of hydrogen/liter of hydrocarbon ratio by volume is between 100 and 2000 l/l,
• g) a step of separating at high pressure the effluent from the second hydrocracking step f) to produce at least a gaseous effluent and a liquid hydrocarbon effluent,
• h) recycling into the second compartment delimited by the dividing wall of said distillation step d), at least one portion of said liquid hydrocarbon effluent from step g), at a level below the upper end of said dividing wall.