Process for hydrotreatment of a heavy hydrocarbon fraction using permutable reactors and introduction of a middle distillate

Abstract

A hydrotreatment process is carried out in at least two steps to hydrotreat a heavy hydrocarbon fraction containing asphaltenes, sulphur-containing impurities and metallic impurities, comprising a first hydrodemetallization step and a subsequent second hydrodesulphurization step, in which the hydrodemetallization step comprises one or more hydrodemetallization zones with fixed beds preceded by at least two hydrodemetallization guard zones (A) and (B), also with fixed beds, disposed in series for cyclic use consisting of successive repetition of steps b) and c) defined below. The process comprises the following steps: a) a step in which the guard zones are used together for a period of at most equal to the deactivation time and/or clogging time of one thereof, b) a step during which the deactivated and/or clogged guard zone is short-circuited and the catalyst it contains is regenerated and/or replaced by fresh catalyst, and c) a step during which the guard zones (A) and (B) are used together, the guard zone where the catalyst has been regenerated during the preceding step being reconnected and said step being carried out for a period at most equal to the deactivation and/or clogging time of one of the guard zones. The process is characterized by introducing a quantity of middle distillate, particularly a gas oil, with the feed representing 0.5% to 80% by weight with respect to the feed. The process can comprise a prior hydrovisbreaking step and optionally a final deasphalting step using a solvent.