Multi-step hydrodesulphurization process

A hydrodesulphurisation process for continuously effecting hydrodesulphurisation of a liquid sulphur-containing hydrocarbon feedstock which comprises:

• (a) providing a plurality of hydrodesulphurisation zones connected in series each having an inlet end and an exit end and containing a packed bed of a solid sulphided hydrodesulphurisation catalyst, said plurality of hydrodesulphurisation zones including a first hydrodesulphurisation zone and at least one other hydrodesulphurisation zone including a final hydrodesulphurisation zone;
• (b) maintaining hydrodesulphurisation temperature and pressure conditions in each hydrodesulphurisation zone effective for hydrodesulphurisation of the liquid feedstock;
• (c) supplying liquid sulphur-containing hydrocarbon feedstock to the inlet end of the hydrodesulphurisation zone;
• (d) passing the liquid feedstock through the plurality of hydrodesulphurisation zones in turn from the first hydrodesulphurisation zone to the final hydrodesulphurisation zone;
• (e) passing hydrogen-containing gas through the hydrodesulphurisation zones from one zone to another;
• (f) contacting the liquid feedstock with hydrogen under said hydrodesulphurisation temperature and pressure conditions in each hydrodesulphurisation zone in the presence of the respective charge of hydrodesulphurisation catalyst;
• and which further comprises:
• (i) recycling liquid material recovered from the exit and of the first hydrodesulphurisation zone to the inlet end of the first hydrodesulphurisation zone so as to provide diluent for admixture with the liquid feedstock;
• (ii) supplying make up hydrogen to the inlet end of a hydrodesulphurisation zone other than the first hydrodesulphurisation zone;
• (iii) recovering a hydrogen-containing gas from the exit end of each hydrodesulphurisation zone;
• (iv) supplying the first hydrodesulphurisation zone with hydrogen-containing gas recovered from a subsequent hydrodesulphurisation zone;
• (v) purging hydrogen-containing gas recovered from the exit end of the first hydrodesulphurisation zone;
• (vi) if there are three or more zones supplying any other hydrodesulphurisation zone other than the first hydrodesulphurisation zone and other than the hydrodesulphurisation zone of step (ii) with hydrogen-containing gas recovered from another hydrodesulphurisation zone;
• (vii) monitoring the sulphur content of the hydrogen-containing gas and of the mixture of diluent and liquid hydrocarbon feedstock supplied to the first hydrodesulphurisation zone;
• and
• (viii) supplying, when necessary, sulphur-containing material selected from H.sub.2 S and active sulphur-containing materials to the first hydrodesulphurisation zone so as to maintain the catalyst charge thereof in sulphided form.