A paper pulp preparation device comprising: - a unit for cooking wood components, in which the wood components are separated into two fractions: ▪ paper pulp, and ▪ black liquor; the unit for cooking comprising a first inlet E 1a for introducing wood, a second inlet E 1b for discharging while liquor, a first outlet S 1a for discharging the paper pulp, and a second outlet S 1b for discharging the black liquor; - a hydrothermal liquefaction unit allowing the treatment of at least a part of the black liquor, and comprising: ▪ an inlet E 12 for the black liquor connected to second outlet S 1b of the cooking unit; ▪ a first outlet S 12a for an organic phase resulting from the hydrothermal liquefaction; ▪ a second outlet S 12b for an aqueous phase resulting from the hydrothermal liquefaction and containing organic molecules; - a connection line C 1-12 between outlet S 1b and inlet E 12; - a separation unit downstream of outlet S 12b of the hydrothermal liquefaction unit, the separation unit allowing the separation of organic molecules contained in the aqueous phase resulting from the hydrothermal liquefaction, and comprising: ▪ an inlet E 17 for the aqueous phase resulting from the hydrothermal liquefaction, connected to outlet S 12b of the hydrothermal liquefaction unit; ▪ a first outlet S 17a of organic molecules; ▪ a second outlet S 17b of aqueous phase; - a connection line C 12-17 between outlet S 12b and inlet E 17; - a causticizing unit comprising an inlet E 9 of the aqueous phase and an outlet S 9 for a white liquor, outlet S 9 being connected to second inlet E 1b of the cooking unit; - a connection line C 17-9 between outlet S 17b and inlet E 9; - a connection line C 9-1 between outlet S 9 and inlet E 1b. - a unit for cooking wood components, in which the wood components are separated into two fractions: ▪ paper pulp, and ▪ black liquor; the unit for cooking comprising a first inlet E 1a for introducing wood, a second inlet E 1b for discharging while liquor, a first outlet S 1a for discharging the paper pulp, and a second outlet S 1b for discharging the black liquor; ▪ paper pulp, and ▪ black liquor; the unit for cooking comprising a first inlet E 1a for introducing wood, a second inlet E 1b for discharging while liquor, a first outlet S 1a for discharging the paper pulp, and a second outlet S 1b for discharging the black liquor; - a hydrothermal liquefaction unit allowing the treatment of at least a part of the black liquor, and comprising: ▪ an inlet E 12 for the black liquor connected to second outlet S 1b of the cooking unit; ▪ a first outlet S 12a for an organic phase resulting from the hydrothermal liquefaction; ▪ a second outlet S 12b for an aqueous phase resulting from the hydrothermal liquefaction and containing organic molecules; ▪ an inlet E 12 for the black liquor connected to second outlet S 1b of the cooking unit; ▪ a first outlet S 12a for an organic phase resulting from the hydrothermal liquefaction; ▪ a second outlet S 12b for an aqueous phase resulting from the hydrothermal liquefaction and containing organic molecules; - a connection line C 1-12 between outlet S 1b and inlet E 12; - a separation unit downstream of outlet S 12b of the hydrothermal liquefaction unit, the separation unit allowing the separation of organic molecules contained in the aqueous phase resulting from the hydrothermal liquefaction, and comprising: ▪ an inlet E 17 for the aqueous phase resulting from the hydrothermal liquefaction, connected to outlet S 12b of the hydrothermal liquefaction unit; ▪ a first outlet S 17a of organic molecules; ▪ a second outlet S 17b of aqueous phase; ▪ an inlet E 17 for the aqueous phase resulting from the hydrothermal liquefaction, connected to outlet S 12b of the hydrothermal liquefaction unit; ▪ a first outlet S 17a of organic molecules; ▪ a second outlet S 17b of aqueous phase; - a connection line C 12-17 between outlet S 12b and inlet E 17; - a causticizing unit comprising an inlet E 9 of the aqueous phase and an outlet S 9 for a white liquor, outlet S 9 being connected to second inlet E 1b of the cooking unit; - a connection line C 17-9 between outlet S 17b and inlet E 9; - a connection line C 9-1 between outlet S 9 and inlet E 1b.