Two-stage hydrocracking process comprising a hydrogenation stage upstream of the second hydrocracking stage, for the production of middle distillates

A process producing middle distillates from hydrocarbon feedstocks containing at least 20% by volume of compounds boiling above 340° C., said process comprising at least the following:

• a) hydrotreating said feedstocks in the presence of hydrogen and at least one hydrotreating catalyst, at a temperature of 200° C. to 450° C., under a pressure of 2 to 25 MPa, at a space velocity of 0.1 to 6 h−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is 100 to 2000 Nl/l,
• b) hydrocracking at least one portion of the effluent resulting from a), hydrocracking b) taking place, in the presence of hydrogen and at least one hydrocracking catalyst, at a temperature of 250° C. to 480° C., under a pressure of 2 to 25 MPa, at a space velocity of 0.1 to 6 h−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is 80 to 2000 Nl/l,
• c) high-pressure separation of effluent resulting from hydrocracking b) to produce at least a gaseous effluent and a liquid hydrocarbon effluent,
• d) distilling at least one portion of the liquid hydrocarbon effluent resulting from c) carried out in at least one distillation column, from which the following are drawn off:
• a gaseous fraction,
• at least one petroleum fraction having at least 80% by volume of products boiling at a temperature below 150° C.,
• at least one middle distillates fraction having at least 80% by volume of products having a boiling point 150° C. to 380° C.,
• an unconverted heavy liquid fraction having at least 80% by volume of products having a boiling point above 350° C.,
• e) optionally purging of at least one portion of said unconverted heavy liquid fraction containing HPNAs, having at least 80% by volume of products having a boiling point above 350° C., before the introduction thereof into f),
• f) hydrogenating at least one portion of the unconverted heavy liquid fraction having at least 80% by volume of products having a boiling point above 350° C. resulting from d) and optionally purged, f) taking place, in the presence of hydrogen and a hydrogenation catalyst, at a temperature TR1 of 150° C. to 470° C., under a pressure of 2 to 25 MPa, at a space velocity of 0.1 to 50 h−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is 100 to 4000 Nl/l, said hydrogenation catalyst comprising at least one non-noble metal from group VIII of the Periodic Table that is nickel, cobalt, iron, or a mixture thereof, and not comprising any noble metal from group VIII or metal from group VIB, and a refractory oxide support,
• g) a second hydrocracking at least one portion of effluent resulting from f), g) taking place, in the presence of hydrogen and at least one second hydrocracking catalyst, at a temperature TR2 of 250° C. to 480° C., under a pressure of 2 to 25 MPa, at a space velocity of 0.1 to 6 h−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is 80 to 2000 Nl/l, and in which the temperature TR2 is at least 10° C. higher than the temperature TR1,
• h) high-pressure separation of effluent resulting from the hydrocracking g) to produce at least a gaseous effluent and a liquid hydrocarbon effluent,
• i) recycling, to distillation d), at least one portion of the liquid hydrocarbon effluent resulting from h).