Process for the selective desulphurization of olefinic gasolines, comprising a hydrogen purification step

Abstract

The invention concerns a process for selective hydrodesulphurization of an olefinic gasoline, in which makeup hydrogen and/or the overall feed at the inlet to the catalytic reactor has a CO content of less than 50 ppmv of even less, but a CO x (═CO+½CO 2 ) content of more than 120 ppmv. The invention allows diversification as regards the sources of makeup hydrogen and/or can simplify the purification treatment for said hydrogen, and/or can reduce the purge of hydrogen from the hydrodesulphurization unit.

1 . A process for hydrodesulphurization of a hydrocarbon cut HC comprising at least 5% by weight of olefins, in which said hydrocarbon cut, a stream HYD of makeup hydrogen and optionally a stream REC of recycle hydrogen are mixed to form an overall feed which is supplied to the inlet to at least one reactor comprising a desulphurization catalyst, under operating conditions that can transform the organic sulphur-containing compounds of the HC cut into H 2 S, in which the source or sources of hydrogen forming the stream HYD is selected, and optionally at least one hydrogen purification treatment is carried out on HYD, REC or a mixture thereof such that said overall feed comprises at most 50 ppmv of CO and at least 120 ppmv of CO x , where CO x ═CO+½CO 2 .  
   
   
       2 . A process according to  claim 1 , in which the source or sources of hydrogen forming the stream HYD is selected and at least one hydrogen purification treatment is carried out on at least a portion of HYD so that HYD comprises at most 50 ppmv of CO and at least 120 ppmv of CO x .  
   
   
       3 . A process according to  claim 1 , comprising at least one hydrogen purification treatment T1 carried out on HYD, REC or a mixture thereof, said treatment T1 comprising carrying out limited CO 2  elimination to obtain at least 200 ppmv of CO 2  in the overall feed.  
   
   
       4 . A process according to  claim 1 , comprising at least one treatment T2 for the purification of hydrogen carried out on HYD, REC or a mixture thereof, said treatment T2 comprising carrying out catalytic oxidation of CO by O 2  and/or H 2 O to obtain at most 50 ppmv of CO in the overall feed.  
   
   
       5 . A process according to  claim 1 , comprising at least one treatment T3 for the purification of hydrogen carried out on HYD, REC or a mixture thereof, said treatment T3 comprising carrying out catalytic methanation of CO by H 2  to obtain at most 50 ppmv of CO in the overall feed.  
   
   
       6 . A process according to  claim 4 , comprising a hydrogen purification treatment carried out on HYD, and optionally on REC or a mixture thereof, said treatment comprising a treatment T2 of carrying out catalytic oxidation of CO by O 2  followed directly, and with no secondary elimination of CO 2 , by desulphurization of the HC cut in the presence of a stream of the purified hydrogen.  
   
   
       7 . A process according to  claim 5 , comprising a hydrogen purification treatment carried out on HYD, and optionally on REC or a mixture thereof, said treatment T3 comprising carrying out methanation of CO by H 2  followed directly, and with no secondary elimination of CO 2 , by desulphurization of the HC cut in the presence of a stream of the purified hydrogen.  
   
   
       8 . A process according to  claim 6 , comprising a conducting said treatment T1 for eliminating CO 2  on HYD upstream of T2 or T3.  
   
   
       9 . A process according to  claim 1 , comprising a hydrogen recycle REC ard a purge of recycled hydrogen WGAS in which the flow rate of the purge WGAS is controlled so that the CO content in the overall feed is less than 50 ppmv but that the COX content in the overall feed is more than 120 ppmv.  
   
   
       10 . A process according to  claim 1 , for hydrodesulphurization of an olefinic gasoline cut, carried out on a catalyst which comprises at least one element from group VIII and optionally an element from group VIB, the element from group VIII being selected from the group constituted by nickel, cobalt and iron, the optional group VIB element is molybdenum or tungsten, in which the reactor pressure is in the range 0.5 MPa to 5 MPa, the ratio of the flow rate of hydrogen in normal litres of hydrogen per hour to the flow rate of hydrocarbons in litres per hour is in the range 50 to 800, and the temperature is in the range 200° C. to 400° C.  
   
   
       11 . A process according to  claim 10 , in which the catalyst comprises cobalt and molybdenum.  
   
   
       12 . A process according to  claim 2 , comprising at least one treatment T2 for the purification of hydrogen carried out on HYD, REC or a mixture thereof, said treatment T2 comprising carrying out catalytic oxidation of CO by O 2  and/or H 2 O to obtain at most 50 ppmv of CO in the overall feed.  
   
   
       13 . A process according to  claim 3 , comprising at least one treatment T2 for the purification of hydrogen carried out on HYD, REC or a mixture thereof, said treatment T2 comprising carrying out catalytic oxidation of CO by O 2  and/or H 2 O to obtain at most 50 ppmv of CO in the overall feed.  
   
   
       14 . A process according to  claim 2 , comprising at least one treatment T3 for the purification of hydrogen carried out on HYD, REC or a mixture thereof, said treatment T3 comprising carrying out catalytic methanation of CO by H 2  to obtain at most 50 ppmv of CO in the overall feed.  
   
   
       15 . A process according to  claim 3 , comprising at least one treatment T3 for the purification of hydrogen carried out on HYD, REC or a mixture thereof, said treatment T3 comprising carrying out catalytic methanation of CO by H 2  to obtain at most 50 ppmv of CO in the overall feed.  
   
   
       16 . A process according to  claim 12 , comprising a hydrogen purification treatment carried out on HYD, and optionally on REC or a mixture thereof, said treatment comprising a treatment T2 of carrying out catalytic oxidation of CO by O 2  followed directly, and with no secondary elimination of CO 2 , by desulphurization of the HC cut in the presence of a stream of the purified hydrogen.  
   
   
       17 . A process according to  claim 13 , comprising a hydrogen purification treatment carried out on HYD, and optionally on REC or a mixture thereof, said treatment comprising a treatment T2 of carrying out catalytic oxidation of CO by O 2  followed directly, and with no secondary elimination of CO 2 , by desulphurization of the HC cut in the presence of a stream of the purified hydrogen.  
   
   
       18 . A process according to  claim 14 , comprising a hydrogen purification treatment carried out on HYD, and optionally on REC or a mixture thereof, said treatment T3 comprising carrying out methanation of CO by H 2  followed directly, and with no secondary elimination of CO 2 , by desulphurization of the HC cut in the presence of a stream of the purified hydrogen.  
   
   
       19 . A process according to  claim 15 , comprising a hydrogen purification treatment carried out on HYD, and optionally on REC or a mixture thereof, said treatment T3 comprising carrying out methanation of CO by H 2  followed directly, and with no secondary elimination of CO 2 , by desulphurization of the HC cut in the presence of a stream of the purified hydrogen.