Two-stage hydrocracking process for producing naphtha, comprising a hydrogenation stage implemented downstream of the second hydrocracking stage

Process for producing naphtha from hydrocarbon feedstocks containing at least 20% by volume and preferably at least 80% by volume of compounds boiling above 340° C., said process comprising and preferably consisting of 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 450° 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 litre of hydrogen/litre of hydrocarbon volume ratio is between 100 and 2000 NI/I,
• b) a step of hydrocracking at least one portion of the effluent resulting 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 litre of hydrogen/litre of hydrocarbon volume ratio is between 80 and 2000 NI/I,
• c) a step of high-pressure separation of the effluent resulting 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 resulting from step c) performed in at least one distillation column, from which step the following are drawn off:
• a gaseous fraction,
• at least one fraction comprising the converted hydrocarbon products having at least 80% by volume of products boiling at a temperature below 250° C., preferably below 220° C., preferably below 190° C. and more preferably below 175° C., and
• an unconverted liquid fraction having at least 80% by volume of products having a boiling point above 175° C., preferably above 190° C., preferably
• above 220° C. and more preferably above 250° C.,
• e) optionally a purging of at least one portion of said unconverted liquid fraction containing HPNAs, having at least 80% by volume of products having a boiling point above 175° C., before the introduction thereof into step f),
• f) a second step of hydrocracking at least one portion of the unconverted liquid fraction having at least 80% by volume of products with a boiling point above 175° C., resulting from step d) and optionally purged, said step f) being performed in the presence of hydrogen and of at least one second hydrocracking catalyst, at a temperature TR1 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 litre of hydrogen/litre of hydrocarbon volume ratio is between 80 and 2000 NI/I,
• g) a step of hydrogenating at least one portion of the effluent resulting from step f) performed in the presence of hydrogen and of a hydrogenation catalyst, at a temperature TR2 between 150° C. and 470° C., under a pressure of between 2 and 25 MPa, at a space velocity of between 0.1 and 50 h−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is between 100 and 4000 NI/I, said hydrogenation catalyst comprising at least one metal from group VIII chosen from nickel, cobalt, iron, palladium, platinum, rhodium, ruthenium, osmium and iridium alone or as a mixture and not containing any metal from group VIB and a support chosen from refractory oxide supports, and in which the temperature TR2 is at least 10° C. below the temperature TR1,
• h) a step of high-pressure separation of the effluent resulting from the hydrogenation step g) to produce at least a gaseous effluent and a liquid hydrocarbon effluent,
• i) recycling, into said distillation step d), at least one portion of the liquid hydrocarbon effluent resulting from step h).