Process for the treatment of a gasoline by separation into three cuts

A process for the desulphurization of a gasoline containing sulphur-containing compounds, olefins and diolefins, the process comprising at least the following:

• a) fractionating the gasoline in order to recover a light gasoline cut LCN and a first heavy gasoline cut HCN;
• b) carrying out a first desulphurization of the first heavy gasoline cut HCN in the presence of a hydrodesulphurization catalyst and hydrogen, at a temperature in the range 160° C. to 450° C., at a pressure in the range 0.5 to 8 MPa, with a liquid velocity in the range 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, in the range 50 Nm3/m3 to 1000 Nm3/m3 in a manner such as to produce a first desulphurization effluent;
• c) partially condensing the first desulphurization effluent obtained from b) in a manner such as to produce a gaseous phase of hydrogen and H2S and a liquid hydrocarbon phase HCN′ comprising dissolved H2S;
• d) separating the liquid hydrocarbon phase HCN′ into an intermediate gasoline cut MCN and a second heavy gasoline cut HHCN;
• e) carrying out a second desulphurization of the second heavy gasoline cut HHCN in the presence of a hydrodesulphurization catalyst and hydrogen, at a temperature in the range 160° C. to 450° C., at a pressure in the range 0.5 to 8 MPa, with a liquid velocity in the range 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, in the range 50 Nm3/m3 to 1000 Nm3/m3 in a manner such as to produce a desulphurized second heavy gasoline cut HHCN, the process comprising:
• c′) in which the dissolved H2S of the liquid hydrocarbon phase HCN′ obtained from step c) is separated in order to produce a liquid hydrocarbon phase HCN″ with a reduced dissolved H2S content and said liquid hydrocarbon phase HCN″ with a reduced dissolved H2S content being treated in d), or
• d′) in which the dissolved H2S of the intermediate gasoline cut MCN obtained from d) is separated in order to produce an intermediate gasoline cut MCN with a reduced dissolved H2S content.