Process for hydrodesulphurizing an olefinic gasoline

A process for the treatment of a gasoline containing sulphur-containing compounds, olefins and diolefins, comprising:

• a) fractionating the gasoline into at least:
• a light gasoline cut LCN;
• a primary intermediate gasoline cut, MCN;
• and
• a primary heavy gasoline cut HHCN;
• b) desulphurizing the primary intermediate gasoline cut MCN alone and in the presence of a hydrodesulphurization catalyst and hydrogen, at a temperature of 160° C. to 450° C., at a pressure of 0.5 to 8 MPa, with a liquid space velocity of 0.5 to 20 h−1 and with a ratio between the flow rate of hydrogen, expressed in normal m3 per hour, and the flow rate of feed to be treated, expressed in m3 per hour under standard conditions, of 50 Nm3/m3 to 1000 Nm3/m3 to produce an at least partially desulphurized primary intermediate gasoline cut MCN;
• c) desulphurizing the primary heavy gasoline cut HHCN alone in the presence of a hydrodesulphurization catalyst and hydrogen, at a temperature of 200° C. to 450° C., at a pressure of 0.5 to 8 MPa, with a liquid space velocity of 0.5 to 20 h−1 and with a ratio between the flow rate of hydrogen, expressed in normal m3 per hour, and the flow rate of feed to be treated, expressed in m3 per hour under standard conditions, of 50 Nm3/m3 to 1000 Nm3/m3 to produce an at least partially desulphurized primary heavy gasoline cut HHCN;
• d) sending, as a mixture, the partially desulphurized primary intermediate gasoline cut MCN which has not undergone treatment following b) and the partially desulphurized primary heavy cut HHCN which has not undergone treatment following c) to a separation column in order to separate a gaseous stream containing hydrogen and H2S, a secondary intermediate gasoline cut MCN and a secondary heavy gasoline cut HHCN containing sulphur-containing compounds including recombinant mercaptans, wherein the secondary intermediate gasoline cut MCN has a sulphur and mercaptans content less than the secondary heavy gasoline cut HHCN;
• and
• e) desulphurizing the secondary heavy gasoline cut HHCN obtained from d) containing sulphur-containing compounds including recombinant mercaptans in the presence of a hydrodesulphurization catalyst and hydrogen, at a temperature of 200° C. to 450° C., at a pressure of 0.5 to 8 MPa, with a liquid space velocity of 0.5 to 20 h−1 and with a ratio between the flow rate of hydrogen, expressed in normal m3 per hour, and the flow rate of feed to be treated, expressed in m3 per hour under standard conditions, of 50 Nm3/m3 to 1000 Nm3/m3.