Method for producing a light petrol fraction having a low sulphur content

A process for the production of a light gasoline comprising a sulfur content of less than 10 ppm by weight, with respect to the total weight of said light gasoline, starting from a gasoline containing sulfur compounds, olefins and diolefins, the process comprising at least the following stages:

• a) a stage of selective hydrogenation so as to hydrogenate the diolefins and to carry out a reaction for increasing the molecular weight of a part of the sulfur compounds, in which process the gasoline and the hydrogen are brought into contact with a selective hydrogenation catalyst at a temperature of between 100° C. and 220° C., with a liquid space velocity of between 1 h−1 and 7 h−1 and a pressure of between 0.5 MPa and 5 MPa, and with a molar ratio of the hydrogen to the diolefins to be hydrogenated of greater than 1 mol/mol and less than 100 mol/mol, with a ratio of the hydrogen flow rate, expressed in standard m3 per hour, to the flow rate of feedstock to be treated, expressed in m3 per hour at standard conditions, of between 2 Sm3/m3 and 100 Sm3/m3, said selective hydrogenation catalyst comprising an active phase containing at least one metal from group VIB and at least one metal from group VIII and a porous support containing at least alumina, said catalyst comprising a specific surface of between 100 m2/g and 400 m2/g;
• b) a stage of separation of the effluent obtained on conclusion of stage a) into a gaseous fraction, a light gasoline cut and a heavy gasoline cut, said stage b) being carried out in a fractionation column comprising n plates, n being an integer of greater than or equal to 20, the first plate being the reboiler and the plate “n” being the condenser, it being understood that the light gasoline cut is withdrawn from said fractionation column at the plate “n-i”, with i of between 1 and 10;
• c) a stage of hydrodesulfurization of the heavy gasoline HCN cut obtained on conclusion of stage b) in the presence of hydrogen and of a hydrodesulfurization catalyst comprising an oxide support and an active phase comprising a metal from group VIB and a metal from group VIII, at a temperature of between 210° C. and 320° C., at a pressure of between 1 MPa and 4 MPa, with a space velocity of between 1 h−1 and 10 h−1 and a ratio of the hydrogen flow rate, expressed in standard m3 per hour, to the flow rate of feedstock to be treated, expressed in m3 per hour at standard conditions, of between 100 Sm3/m3 and 600 Sm3/m3, so as to convert at least a part of the sulfur compounds into H2S.