Hydrocracking process

A process for hydrocracking a petroleum hydrocarbon charge contaminated with nitrogenous compounds, in which said charge is treated in a first hydrocracking reaction zone at a temperature from about 300.degree. to 550.degree. C under a pressure from about 15 to 250 atmospheres, in the presence of hydrogen and of a catalyst containing at least one hydrogenating component selected from at least one metal of the groups VI B and VIII of the periodic table of the elements, in the form of the free metal or an oxide or sulfide thereof, said hydrogenating component being deposited on a solid carrier selected from a natural or a synthesis product, said process comprising the steps of feeding the effluent from the first hydrocracking reaction zone to a first separation zone whose pressure is the same as in the first hydrocracking reaction zone and whose temperature is from 200.degree. to 300.degree. C, separating in said separation zone (a), a vapor fraction containing, ammonia and the major part of the products converted in the first hydrocracking reaction zone and (b), a liquid effluent whose ammonia content is lower than about 50 parts by weight per million of parts of said effluent, adding to said effluent at least a portion of the liquid effluent from the bottom of a prefractionation zone as hereunder defined, feeding the resulting mixture of said liquid effluent of the first separation zone and said liquid effluent from the bottom of the prefractionation zone to a second hydrocracking reaction zone where it is heated in the presence of a catalyst containing at least one hydrogenating component selected from at least one metal of the groups VI B and VIII of the periodic table of the elements, in the form of the free metal or an oxide or sulfide thereof, said hydrogenating component being deposited on a solid carrier selected from a natural or a synthesis product, at a temperature from about 300.degree. to 550.degree. C under a pressure from about 15 to 250 atmospheres, admixing the new effluent obtained from the second hydrocracking reaction zone with the vapor fraction withdrawn from the first separation zone, feeding the resulting mixture of said effluent of said second hydrocracking reaction zone with said vapor fraction to a prefractionation zone operated under the same pressure as in the hydrocracking reaction zone from where said effluent has been withdrawn, separating in said prefractionation zone, by stripping with a gas as defined below, the liquid and gaseous phases of said effluent, so as to obtain, at the top of the prefractionation zone, a gaseous fraction containing mainly hydrogen and the major portion of the products converted in at least the hydrocracking reaction zone from where said effluent issues, and, at the bottom of the prefractionation zone, a fraction of heavy or uncoverted products, at least one part of which is recycled to at least the second hydrocracking reaction zone from where said effluent has been withdrawn, said gaseous fraction, withdrawn from the top of said prefractionation zone, being fed, after cooling, to a separation zone from wherein it is recovered, a gas of high hydrogen content and a new liquid effluent which is fed to a fractionation zone in order to separate the desired cuts as final products, in which process the gas used for the stripping step contains hydrogen, the said gas comprised of, at least partly, of the said gas of high hydrogen content obtained after cooling of the said gaseous fraction withdrawn from the top of the prefractionation zone of the said gas comprised of a mixture of fresh hydrogen with at least one portion of the said gas of high hydrogen content obtained after cooling of the said gaseous fraction withdrawn from the top of the prefractionation zone.