Process for the production of hydrocarbons with low sulfur and mercaptan content

Abstract

Process for desulfurization of a cut containing hydrocarbons comprising sulfur compounds and olefinic compounds comprising at least the following successive steps: a first desulfurization in the presence of hydrogen and a hydrodesulfurization catalyst under conditions leading to a desulfurization rate of said cut strictly higher than 90%; separation of most of the hydrogen sulfide from the effluents resulting from the first desulfurization; a second desulfurization of the effluents, with the hydrogen sulfide removed, resulting from the separation step, in the presence of hydrogen and a hydrodesulfurization catalyst, and under conditions leading to a desulfurization rate of said effluents less than that of the first desulfurization.

1 . Desulfurization process for a cut containing hydrocarbons comprising sulfur and olefinic compounds and having at least the following successive steps: 
 a first desulfurization in the presence of hydrogen and a hydrodesulfurization catalyst under conditions leading to a desulfurization rate of said cut strictly higher than 90%,    separation of most of the hydrogen sulfide (H 2 S) from the effluents resulting from the first desulfurization,    a second desulfurization of the effluents, with the hydrogen sulfide removed, resulting from the separation step, in the presence of hydrogen and of a hydrodesulfurization catalyst and under conditions leading to a desulfurization rate of said effluents less than that of the first desulfurization.    
     
     
         2 . Process according to  claim 1 , wherein at least one of the hydrodesulfurization catalysts has at least one element from group VIII of the periodic table.  
     
     
         3 . Process according to  claim 2 , wherein at least one of the catalysts further has at least one element from group VIB of the periodic table.  
     
     
         4 . Process according to  claim 1 , comprising at least one element from group VIII of the periodic table selected from the group consisting of nickel and cobalt and at least one element from group VIB from the periodic table selected from the group consisting of molybdenum and tungsten.  
     
     
         5 . Process according to one of the preceding claims, wherein the first desulfurization is performed at a temperature between 250° C. and 350° C., under pressure between 1 and 3 MPa, at an hourly spatial liquid speed between 1 h −1  and 10 h −1 , and with an H 2 /HC ratio between 50 l/l and 500 l/l.  
     
     
         6 . Process according to one of the preceding claims, wherein the second desulfurization is performed at a temperature between 200° C. and 300° C., under pressure between 1 and 3 MPa, at an hourly spatial liquid speed between 1 h −1  and 10 h −1  and with an H 2 /HC ratio between 50 l/l and 500 l/l.  
     
     
         7 . Process according to one of the preceding claims, wherein the desulfurization rate of the second desulfurization is strictly greater than 80%.  
     
     
         8 . Process according to one of the preceding claims, wherein the difference between the desulfurization rates of the first and the second desulfurization is at least one percent in absolute value.  
     
     
         9 . Process according to one of the preceding claims, further comprising a supplementary step of selective hydrogenation of the diolefins contained in the cut, said step being performed before the first desulfurization.  
     
     
         10 . Process according to one of the preceding claims, further comprising a supplementary step of making the light sulfurous compounds heavy, said step being performed before the first desulfurization.  
     
     
         11 . Process according to one of the preceding claims, further comprising at least one supplementary separation step for said cut into at least two fractions: 
 a light fraction containing a small amount of the sulfurous compounds,    a heavy fraction containing most of the sulfurous compounds, at least said heavy fraction then being processed according to the first desulfurization step.    
     
     
         12 . Application of the process according to the preceding claims to gasolines resulting from catalytic cracking or coking of a heavy batch containing hydrocarbons or steam cracking.