Process for desulphurizing a hydrocarbon cut in a simulated moving bed

Abstract

The invention describes a process for desulphurizing a gas oil type hydrocarbon cut by adsorption to obtain a desulphurized effluent containing less than 10 ppm by weight in a yield of more than 95% by weight. Said process comprises a step for simulated moving bed adsorption of sulphur-containing compounds in the feed, a raffinate distillation step and an extract distillation step.

1 . A process for deep desulphurization of a hydrocarbon feed with a distillation range in the range 150° C. to 450° C. containing up to 3% of sulphur, the process comprising the following steps in succession: 
 a step for adsorbing sulphur-containing compounds from the feed ( 1 ) carried out in at least one first adsorption column ( 2 ) functioning as a simulated moving bed and containing a plurality of beds of an adsorbent having a selectivity which is different for sulphur-containing hydrocarbons and non sulphur-containing hydrocarbons, said column comprising at least four functional zones; a first zone between the point for introducing desorbant ( 9   b ) and the point for withdrawing extract ( 4 ); a second zone between the point for withdrawing extract ( 4 ) and the point for introducing feed ( 1 ); a third zone between the point for introducing feed ( 1 ) and the point for withdrawing raffinate ( 3 ); and a fourth zone between the point for withdrawing raffmate ( 3 ) and the point for introducing desorbant ( 9   b ), the ratio of the desorbant to the feed being in the range 0.5 to 2.5 by volume;    a step for distilling raffinate ( 3 ) carried out in at least one distillation column ( 5 ), from which a desulphurized gas oil effluent ( 8 ) is extracted as well as a stream of desorbant ( 9 ) at least part of which is recycled to the first adsorption column ( 2 );    a step for distilling extract ( 4 ) carried out in at least one distillation column ( 6 ), from which an effluent ( 10 ) containing sulphur-containing impurities is withdrawn along with a practically pure stream ( 11 ) of desorbant at least part of which is recycled to the first adsorption column.    
   
   
       2 . A deep desulphurization process according to  claim 1 , wherein the sulphur content in the desulphurized gas oil ( 8 ) is less than 10 ppm by weight, with a yield with respect to the inlet feed which is generally more than 97% by weight.  
   
   
       3 . A deep desulphurization process according to  claim 1 , wherein the solid adsorbent used in the adsorption unit is activated charcoal with a specific surface area of more than 1200 m 2 /g and a total pore volume of more than 0.5 cm 3 /gram.  
   
   
       4 . A deep desulphurization process according to  claim 1 , wherein the pore volume fraction in the microporosity of said adsorbent is more than 0.2 cm 3 /gram.  
   
   
       5 . A deep desulphurization process according to  claim 1 , wherein the operating temperature of the adsorbent unit is in the range 50° C. to 350° C.  
   
   
       6 . A deep desulphurization process according to  claim 1 , wherein the simulated moving bed adsorption unit comprises at most 24 beds, preferably at most 15 beds.  
   
   
       7 . A deep desulphurization process according to  claim 1 , wherein the simulated moving bed adsorption unit has a ratio of desorbant to feed in the range 0.7 to 2.0 by volume.  
   
   
       8 . A deep desulphurization process according to  claim 1 , wherein the feed to be treated is sent in advance to a distillation column located upstream of the simulated moving bed adsorption unit, from which an overhead stream ( 1   a ) is withdrawn at least part of which is used as desorbant, and a bottom stream ( 1   b ) is withdrawn which is introduced as the feed to the simulated moving bed adsorption unit ( 2 ).  
   
   
       9 . A deep desulphurization process according to  claim 1 , wherein the stream ( 10 ) of sulphur-containing impurities is sent as a mixture to a fuel oil cut (fuel).  
   
   
       10 . A deep desulphurization process according to  claim 1 , wherein the effluent containing sulphur-containing impurities ( 10 ) is recycled to a hydrodesulphurization unit.  
   
   
       11 . A deep desulphurization process according to  claim 8 , wherein the stream ( 10 ) of sulphur-containing impurities is sent as a mixture to a fuel oil cut (fuel).  
   
   
       12 . A deep desulphurization process according to  claim 8 , wherein the effluent containing sulphur-containing impurities ( 10 ) is recycled to a hydrodesulphurization unit.  
   
   
       13 . A process according to  claim 2 , wherein the sulphur content in the desulphurized gas oil is less than 5 ppm by weight.  
   
   
       14 . A process according to  claim 2 , wherein the sulphur content in the desulphurized gas oil is less than 1 ppm by weight.  
   
   
       15 . A process according to  claim 2 , wherein said yield is more than 99% by weight.  
   
   
       16 . A process according to  claim 5 , wherein said operating temperature is in the range of 50° to 250° C.  
   
   
       17 . A process according to  claim 6 , wherein the adsorption unit comprises at most 15 beds.  
   
   
       18 . A deep desulphurization process according to  claim 2 , wherein the solid adsorbent used in the adsorption unit is activated charcoal with a specific surface area of more than 1200 m 2 /g and a total pore volume of more than 0.5 cm 3 /gram.  
   
   
       19 . A deep desulphurization process according to  claim 2 , wherein the pore volume fraction in the microporosity of said adsorbent is more than 0.2 cm 3 /gram.  
   
   
       20 . A deep desulphurization process according to  claim 3 , wherein the simulated moving bed adsorption unit has a ratio of desorbant to feed in the range 0.7 to 2.0 by volume.