Conversion process comprising at least one step for fixed bed hydrotreatment and a step for hydrocracking in by-passable reactors

A continuous process for the treatment of a hydrocarbon feed containing at least one hydrocarbon fraction with a sulphur content of at least 0.1% by weight, an initial boiling temperature of at least 340° C. and a final boiling temperature of at least 440° C., the process comprising:

• a) hydrodemetallization in which at least two permutable reactors are operated at a temperature in the range 300° C. to 500° C., and under an absolute pressure in the range 5 MPa to 35 MPa, in the presence of the hydrocarbon feed and hydrogen, and a hydrodemetallization catalyst,
• b) fixed bed hydrotreatment, in at least one reactor in which the effluent obtained from a) when is brought into contact with at least one hydrotreatment catalyst at a temperature in the range 300° C. to 500° C. and under an absolute pressure in the range 5 MPa to 35 MPa,
• c) fixed bed hydrocracking, in at least one by-passable reactor under an absolute pressure in the range 5 MPa to 35 MPa, in the presence of effluent obtained from b), and a hydrocracking catalyst, in which said by-passable reactor for the fixed bed hydrocracking is stopped as soon as the temperature of said by-passable reactor is between 390° C. and 430° C.,
• d) separating effluent obtained from hydrocracking in c) in order to obtain at least one gaseous fraction and at least one heavy liquid fraction, said heavy liquid fraction being sent to an atmospheric distillation producing at least one atmospheric distillate and an atmospheric residue, a portion or the entirety of said atmospheric residue being sent to a vacuum distillation producing a vacuum residue, said atmospheric and vacuum residues optionally being sent to a catalytic cracking process or being used as a fuel oil or fuel oil base.