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

A process for producing middle distillates from hydrocarbon feedstocks, said process comprising:

• a) hydrotreating a hydrocarbon feedstock containing at least 20% by volume of compounds boiling above 340° C. 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 volume ratio of liter of hydrogen/liter of hydrocarbon is between 100 and 2000 Nl/l,
• b) hydrocracking at least one portion of effluent resulting from a), 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 volume ratio of liter of hydrogen/liter of hydrocarbon is between 80 and 2000 Nl/l,
• c) subjecting effluent resulting from hydrocracking b) to high pressure separation 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) in at least one distillation column, from which distilling 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 between 150° C. and 380° C., and
• an unconverted heavy liquid fraction having at least 80% by volume of products having a boiling point above 350° C.,
• e) optionally purging at least one portion of said unconverted heavy liquid fraction having at least 80% by volume of products having a boiling point above 350° C., before the introduction thereof into f),
• f) hydrocracking at least one portion of the unconverted heavy liquid fraction having at least 80% by volume of products with a boiling point above 350° C., resulting from d) and optionally purged, wherein hydrocracking f) is 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 volume ratio of liter of hydrogen/liter of hydrocarbon is between 80 and 2000 Nl/l,
• g) 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 volume ratio or liter of hydrogen/liter of hydrocarbon is between 100 and 4000 Nl/l, 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) subjecting effluent resulting from the hydrogenation g) to high-pressure separation to produce at least a gaseous effluent and a liquid hydrocarbon effluent, and
• i) recycling, into distilling d), at least one portion of the liquid hydrocarbon effluent resulting from h).