Process and apparatus using a plurality of catalytic beds in series for the production of gas oils with a low sulphur content

Abstract

A process for hydrotreating gas oils comprises: at least one first step a) for hydrodesulphurization in which said gas oil cut and hydrogen are passed over a catalyst disposed in a fixed bed; at least one subsequent second step b) in which a gas fraction containing at least a portion of the hydrogen sulphide contained in the total effluent from said first step is recovered along with an effluent that is depleted in hydrogen sulphide; and at least a third step c) in which at least a portion of the effluent depleted in hydrogen sulphide from step b) and hydrogen are passed over a catalyst disposed in a fixed bed that is identical to or different from that used in step a). The quantity of catalyst used in the first step is strictly more than 50% by weight of the total quantity of catalyst used in said process.

1 . A process for hydrodesulphurisation of a kerosine and/or gas oil cut comprising: 
 at least one first hydrodesulphurisation step a) in which said gas oil cut and hydrogen are passed over a catalyst disposed in a fixed bed comprising, on a mineral support, at least one metal or compound of a metal from group VIB of the periodic table in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.5% to 40%, and at least one non noble metal or compound of a non noble metal from group VIII of said periodic table in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0. 1% to 30%;    at least one subsequent second step b) in which a gas fraction containing at least a portion of the hydrogen sulphide contained in the total effluent from said first step is recovered along with an effluent that is depleted in hydrogen sulphide; and    at least one third step c) in which at least a portion of the effluent that is depleted in hydrogen sulphide from step b) and hydrogen are passed over a catalyst disposed in a fixed bed that is identical to or different from that used in step a) comprising, on a mineral support, at least one metal or compound of a metal from group VIB of the periodic table in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.5% to 40%, at least one non noble metal or compound of a non noble metal from group VIII of said periodic table in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.1% to 30%, said process being characterized in that the quantity of catalyst used in the first step is strictly greater than 50% by weight of the total quantity of catalyst used in said process.    
     
     
         2 . A process according to  claim 1 , in which the quantity of catalyst used in the first step is about 60% to about 90% of the total quantity of catalyst used in said process.  
     
     
         3 . A process according to  claim 1  or  claim 2 , in which in step b), recovery of a gas fraction containing at least a portion of the hydrogen sulphide contained in the total effluent from step a) is carried out by stripping using at least a hydrogen-containing gas at a pressure that is substantially identical to that prevailing in the first step and at a temperature of about 100° C. to about 450° C. under conditions for forming a gaseous stripping effluent containing hydrogen and hydrogen sulphide, along with a liquid feed that is depleted in hydrogen sulphide.  
     
     
         4 . A process according to  claim 1  or  claim 2 , in which in step b), recovery of a gas fraction containing at least a portion of the hydrogen sulphide contained in the total effluent from step a) is carried out by flashing the total effluent from step a).  
     
     
         5 . A process according to any one of  claims 1  to  4 , in which the operating conditions for step a) comprises a temperature of about 240° C. to about 420° C., a total pressure of about 2 MPa to about 20 MPa and an hourly space velocity of liquid feed of about 0.1 to about 5, and those of step c) comprise a temperature of about 240° C. to about 420° C., a total pressure of about 2 MPa to about 20 MPa and an hourly space velocity of liquid feed that is strictly higher than the hourly space velocity of the liquid feed in step a).  
     
     
         6 . A process according to any one of  claims 1  to  5 , in which the catalyst used in step a) and that used in step c) each comprise at least one metal or compound of a metal ftom group VIB selected from the group formed by molybdenum and tungsten and at least one metal or compound of a metal from group VIII selected from the group formed by nickel, cobalt and iron.  
     
     
         7 . A process according to any one of  claims 1  to  6 , in which the catalyst used in step a) and that used in step c) each comprise molybdenum or a compound of molybdenum in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 2% to 30%, and a metal or compound of a metal selected from the group formed by nickel and cobalt in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.5% to 15%.  
     
     
         8 . A process according to any one of  claims 1  to  7 , in which the catalyst used in step a) and that used in step c) each comprise nickel as the group VIII metal, and molybdenum as the group VIB metal.  
     
     
         9 . A process according to any one of  claims 1  to  8 , in which the catalyst used in step a) and that used in step c) each further comprise at least one element selected from the group formed by silicon, phosphorus and boron or one or more compounds of this element or elements.  
     
     
         10 . A process according to any one of  claims 1  to  9 , in which the catalyst support used in step a) and in step c) are selected independently of each other from the group formed by alumina, silica, silica-aluminas, zeolites, magnesia, titanium oxide TiO 2  and mixtures of at least two of these mineral compounds.  
     
     
         11 . A process according to any one of  claims 1  to  10 , in which the catalysts used in step a) and in step c) each comprise at least one halogen.  
     
     
         12 . A process according to any one of  claims 1  to  11 , in which the catalysts used in step a) and in step c) each comprise a quantity of halogen of about 0. 1% to about 15% by weight with respect to the weight of finished catalyst.  
     
     
         13 . A process according to any one of  claims 1  to  12 , in which the catalysts used in step a) and in step c) each comprise at least one halogen selected from the group formed by chlorine and fluorine.  
     
     
         14 . A process according to any one of  claims 1  to  13 , in which the catalysts used in step a) and in step c) each comprise chlorine and fluorine.  
     
     
         15 . A process according to any one of  claims 1  to  14 , in which the gas fraction recovered in step b) containing hydrogen sulphide is sent to a zone for at least partial elimination of the hydrogen sulphide it contains, from which purified hydrogen is recovered, at least a portion of which is recycled indifferently to the inlet to at least one of steps a), b) or c).