Process for the production of a light gasoline with a low sulphur content

Abstract

A process for the treatment of a gasoline comprising diolefins, olefins and sulphur-containing compounds including mercaptans: a) demercaptanization by addition of at least a portion of the mercaptans onto the olefins by bringing the gasoline into contact with at least one first catalyst; b) treatment of the gasoline obtained from a) with hydrogen in a distillation column comprising at least one reaction zone including at least one second catalyst. The operating conditions and the second catalyst of b) are selected such that in the distillation column, separation of the gasoline obtained from a) into a light gasoline fraction and a heavy gasoline fraction is carried out simultaneously with a reaction for thioetherification and selective hydrogenation of the diolefins of a gasoline fraction obtained from a) by contact with the second catalyst.

1 . A process for the treatment of a gasoline comprising diolefins, olefins and sulphur-containing compounds including mercaptans, said process comprising the following steps:
 a) carrying out a step for demercaptanization by addition of at least a portion of the mercaptans onto the olefins by bringing gasoline into contact with at least one first catalyst, at a temperature in the range 50° C. to 250° C., at a pressure in the range 0.4 to 5 MPa and with a liquid hourly space velocity (LHSV) in the range 0.5 to 10 h −1 , the first catalyst being in the sulphide form and comprising a first support, at least one metal selected from group VET and at least one metal selected from group VIb of the periodic classification of the elements, the % by weight, expressed as the oxide equivalent of the metal selected from group VIII with respect to the total catalyst weight, being in the range 1% to 30% by weight and the % by weight, expressed as the oxide equivalent of the metal selected from group VIb, being in the range 1% to 30% with respect to the total catalyst weight;   b) carrying out a step for treating the gasoline obtained from step a) with hydrogen in a distillation column comprising at least one reaction zone comprising at least one second catalyst comprising a second support and at least one metal from group VIII, the conditions of step b) being selected such that the following operations are carried out simultaneously in said distillation column:   I) distillation in order to separate the gasoline obtained from step a) into a light gasoline fraction which is depleted in sulphur-containing compounds and into a heavy gasoline fraction with a boiling point which is higher than that of the light gasoline and comprising the majority of the sulphur-containing compounds, the light gasoline fraction being evacuated at a point located above the reaction zone and the heavy gasoline fraction being evacuated at a point below the reaction zone;   II) bringing a fraction of the gasoline obtained from step a) into contact with the second catalyst in order to carry out the following reactions:   i) thioetherification, by addition of a portion of the mercaptans onto a portion of the diolefins to form thioethers;   i) selective hydrogenation of a portion of the diolefins to olefins; and optionally   iii) isomerization of the olefins.   
     
     
         2 . The process according to  claim 1 , in which step b) is carried out at a pressure in the range 0.4 to 5 MPa, preferably in the range 0.6 to 2 MPa, and at a temperature in the range 50° C. to 150° C., preferably in the range 80° C. to 130° C., in the reaction zone. 
     
     
         3 . The process according to  claim 1 , in which the first catalyst comprises nickel and molybdenum, with a % by weight of nickel with respect to the total catalyst weight, expressed as the oxide, in the range 1% to 30%, preferably in the range 4% to 12%, and a % by weight of molybdenum with respect to the total catalyst weight, expressed as the oxide, in the range 1% to 30%, preferably in the range 6% to 18%. 
     
     
         4 . The process according to  claim 1 , in which the second catalyst comprises nickel with a % by weight of nickel with respect to the total catalyst weight, expressed as the oxide, in the range 10% to 60%. 
     
     
         5 . The process according to  claim 1 , in which the second catalyst comprises palladium with a % by weight of palladium metal with respect to the total catalyst weight in the range 0.1% to 2%. 
     
     
         6 . The process according to  claim 1 , in which the H 2 /HC ratio in step a) is in the range 0 to 25 Nm 3  of hydrogen per m 3  of feed, preferably in the range 0.5 to 2 Nm 3  of hydrogen per m 3  of feed. 
     
     
         7 . The process according to  claim 1 , in which the gasoline is a catalytically cracked gasoline or any cracked gasoline containing olefins, diolefins and mercaptans, pure or as a mixture with straight run gasolines. 
     
     
         8 . The process according to  claim 1 , in which the distillation column is configured to function as a depentanizer or dehexanizer. 
     
     
         9 . The process according to  claim 1 , in which an intermediate gasoline cut is withdrawn as a side stream. 
     
     
         10 . The process according to  claim 1 , in which the pressure employed in the distillation column of step b) is equal to the pressure employed in the reactor for step a) apart from the pressure drop in the hydraulic circuit. 
     
     
         11 . The process according to  claim 1 , in which a step for condensation and separation is carried out on the light gasoline in order to recover unconsumed hydrogen. 
     
     
         12 . The process according to  claim 11 , in which unconsumed hydrogen is recycled to step a) or b). 
     
     
         13 . The process according to  claim 1 , in which in step a), addition of the H 2 S present in the gasoline to be treated onto the olefins is carried out concomitantly. 
     
     
         14 . The process according to  claim 1 , in which the heavy gasoline fraction obtained from step b) is treated in a hydrodesulphurization unit.