Selective naphtha hydrodesulfurization with high temperature mercaptan decomposition

Abstract

A process for the selective hydrodesulfurization of olefinic naphtha streams containing a substantial amount of organically bound sulfur and olefins. The olefinic naphtha stream is selectively desulfurized in a first hydrodesulfurization reaction stage. This effluent stream is then contacted with a stripping agent in a H 2 S removal zone, such as steam or an amine solution, to remove H 2 S from the effluent stream, thereby reducing the H 2 S partial pressure of the process stream. The process stream is then subjected to a second desulfurization reaction stage followed by a mercaptan decomposition stage to reduce the content of mercaptan sulfur in the final product stream. In a second embodiment, the effluent stream from the first hydrodesulfurization reaction stage, after being subjected to the H 2 S removal zone, is fed directly to the mercaptan decomposition stage where total sulfur content and mercaptan sulfur content are reduced in the final product stream.

1 . A process for hydrodesulfurizing an olefinic naphtha feedstream and retaining a substantial amount of the olefins, which feedstream boils in the range of about 50° F. (10° C.) to about 450° F. (232° C.) and contains organically bound sulfur and an olefin content of at least about 5 wt. %, which process comprises: 
 a) hydrodesulfurizing said olefinic naphtha feedstream in a first reaction stage in the presence of a hydrogen-containing treat gas and a hydrodesulfurization catalyst, at first hydrodesulfurization reaction conditions including temperatures from about 450° F. (232° C.) to about 800° F. (427° C.), pressures of about 60 to about 800 psig, and hydrogen-containing treat gas rates of about 1000 to about 6000 standard cubic feet per barrel, to convert a portion of the elemental and organically bound sulfur in said olefinic naphtha feedstream to hydrogen sulfide to produce a first reactor effluent stream which has a total sulfur content lower than that of said olefinic naphtha feedstream;    b) conducting said first reactor effluent stream to an H 2 S removal zone wherein a stripping agent is utilized to remove substantially all of the H 2 S from said first reactor effluent stream to produce a stripped effluent stream;    c) conducting said stripped effluent stream to a second reaction stage in the presence of a hydrogen-containing treat gas and a hydrodesulfurization catalyst, at second hydrodesulfurization reaction conditions including temperatures from about 450° F. (232° C.) to about 800° F. (427° C.), pressures of about 60 to about 800 psig, and hydrogen-containing treat gas rates of about 1000 to about 6000 standard cubic feet per barrel, to convert at least a portion of the elemental and organically bound sulfur in said olefinic naphtha feedstream to hydrogen sulfide to produce a second reactor effluent stream which has a total sulfur content lower than that of said stripped effluent stream and some amount of mercaptan sulfur; and    d) conducting said second reactor effluent stream to a mercaptan decomposition reaction stage in the presence of a mercaptan decomposition catalyst, at mercaptan decomposition reaction conditions including temperatures from about 500° F. (260° C.) to about 800° F. (427° C.), and pressures of about 60 to about 800 psig, to decompose at least a portion of the mercaptan sulfur to produce a mercaptan decomposition reactor product stream with a mercaptan sulfur content lower than that of said second reactor effluent stream.    
   
   
       2 . The process of  claim 1 , wherein said olefinic naphtha feedstream, and the stripped effluent stream are in the vapor phase prior to contacting said first and second reaction stages.  
   
   
       3 . The process of  claim 2 , wherein said second reactor effluent stream is in the vapor phase prior to contacting said mercaptan decomposition reaction stage.  
   
   
       4 . The process of  claim 3 , wherein said stripping agent is selected from the group consisting of steam and an amine solution.  
   
   
       5 . The process of  claim 1 , wherein the total sulfur content of said mercaptan decomposition reactor product stream is less than about 1 wt % of the total sulfur content of said olefinic naphtha feedstream.  
   
   
       6 . The process of  claim 5 , wherein the mercaptan sulfur content of said mercaptan decomposition reactor product stream is less than about 10 wt. % of the mercaptan sulfur content of said first reactor effluent stream.  
   
   
       7 . The process of  claim 1 , wherein said hydrodesulfurization catalysts utilized in said first and second reaction stages are comprised of at least one Group VIII metal oxide and at least one Group VI metal oxide.  
   
   
       8 . The process of  claim 7 , wherein said hydrodesulfurization catalysts utilized in said first and second reaction stages are comprised of at least one Group VIII metal oxide selected from Fe, Co and Ni, and at least one Group VI metal oxide, selected from Mo and W.  
   
   
       9 . The process of  claim 8 , wherein said metal oxides are deposited on a high surface area support material.  
   
   
       10 . The process of  claim 9 , wherein said high surface area support material is alumina.  
   
   
       11 . The process of  claim 1 , wherein said mercaptan decomposition catalyst is comprised of a refractory metal oxide in an effective amount to catalyze the decomposition of said mercaptan sulfur resistant to H 2 S.  
   
   
       12 . The process of  claim 11 , wherein said mercaptan decomposition catalyst is comprised of materials selected from alumina, silica, silica-alumina, aluminum phosphates, titania, magnesium oxide, alkali and alkaline earth metal oxides, alkaline metal oxides, magnesium oxide, faujasite that has been ion exchanged with sodium to remove the acidity, and ammonium ion treated aluminum phosphate.  
   
   
       13 . The process of  claim 12 , wherein said mercaptan decomposition catalyst is comprised of materials selected from alumina, silica, and silica-alumina.  
   
   
       14 . The process of  claim 13 , wherein said mercaptan decomposition catalyst possesses substantially no hydrogenation activity.  
   
   
       15 . The process of  claim 1 , wherein said first and second hydrodesulfurization reaction conditions include temperatures from about 500° F. (260° C.) to about 675° F. (357° C.), pressures of about 200 to about 500 psig, and hydrogen-containing treat gas rates of about 1000 to about 3000 standard cubic feet per barrel.  
   
   
       16 . The process of  claim 15 , wherein said first and second hydrodesulfurization reaction conditions include pressures of about 250 to about 400 psig.  
   
   
       17 . The process of  claim 16 , wherein said mercaptan decomposition reaction conditions include temperatures from about 550° F. (288° C.) to about 700° F. (371° C.), and pressures of about 150 to about 500 psig.  
   
   
       18 . The process of  claim 17 , wherein the total sulfur content of said third reactor product stream is less than about 1 wt. % of the total sulfur content of said olefinic naphtha feedstream.  
   
   
       19 . The process of  claim 18 , wherein the mercaptan sulfur content of said mercaptan decomposition reactor product stream is less than about 10 wt. % of the mercaptan sulfur content of said first reactor effluent stream.  
   
   
       20 . A process for hydrodesulfurizing an olefinic naphtha feedstream and retaining a substantial amount of the olefins, which feedstream boils in the range of about 50° F. (10° C.) to about 450° F. (232° C.) and contains organically bound sulfur and an olefin content of at least about 5 wt. %, which process comprises: 
 a) hydrodesulfurizing said olefinic naphtha feedstream in a first reaction stage in the presence of a hydrogen-containing treat gas and a hydrodesulfurization catalyst, at first hydrodesulfurization reaction conditions including temperatures from about 450° F. (232° C.) to about 800° F. (427° C.), pressures of about 60 to about 800 psig, and hydrogen-containing treat gas rates of about 1000 to about 6000 standard cubic feet per barrel, to convert at least a portion of the elemental and organically bound sulfur in said olefinic naphtha feedstream to hydrogen sulfide to produce a first reactor effluent stream which has a total sulfur content lower than that of said olefinic naphtha feedstream;    b) conducting said first reactor effluent stream to an H 2 S removal zone wherein a stripping agent is utilized to remove substantially all of the H 2 S from said first reactor effluent stream to produce a stripped effluent stream; and    c) conducting said stripped effluent stream to a mercaptan decomposition reaction stage in the presence of a hydrogen-containing treat gas and a mercaptan decomposition catalyst, at mercaptan decomposition reaction conditions including temperatures from about 500° F. (260° C.) to about 800° F. (427° C.), pressures of about 60 to about 800 psig, and hydrogen-containing treat gas rates of about 1000 to about 6000 standard cubic feet per barrel to decompose at least a portion of the mercaptan sulfur and convert at least a portion of the elemental and organically bound sulfur to produce a mercaptan decomposition reactor product stream with a mercaptan sulfur content less than that of said first reactor effluent stream.    
   
   
       21 . The process of  claim 20 , wherein said olefinic naphtha feedstream is in the vapor phase prior to contacting said first reaction stage.  
   
   
       22 . The process of  claim 21 , wherein said stripped effluent stream is in the vapor phase prior to contacting said mercaptan decomposition stage.  
   
   
       23 . The process of  claim 22 , wherein said stripping agent is selected from the group consisting of steam and an amine solution.  
   
   
       24 . The process of  claim 20 , wherein the total sulfur content of said mercaptan decomposition reactor product stream is less than about 1 wt % of the total sulfur content of said olefinic naphtha feedstream.  
   
   
       25 . The process of  claim 24 , wherein the mercaptan sulfur content of said mercaptan decomposition reactor product stream is less than about 10 wt. % of the mercaptan sulfur content of said first reactor effluent stream.  
   
   
       26 . The process of  claim 20 , wherein said hydrodesulfurization catalyst utilized in said first reaction stage is comprised of at least one Group VIII metal oxide and at least one Group VI metal oxide.  
   
   
       27 . The process of  claim 26 , wherein said hydrodesulfurization catalyst utilized in said first reaction stage is comprised of at least one Group VIII metal oxide selected from Fe, Co and Ni, and at least one Group VI metal oxide, selected from Mo and W.  
   
   
       28 . The process of  claim 27 , wherein said metal oxides are deposited on a high surface area support material.  
   
   
       29 . The process of  claim 28 , wherein said high surface area support material is alumina.  
   
   
       30 . The process of  claim 20 , wherein said mercaptan decomposition catalyst is comprised of a refractory metal oxide in an effective amount to catalyze the decomposition of said mercaptan sulfur resistant to H 2 S.  
   
   
       31 . The process of  claim 30 , wherein said mercaptan decomposition catalyst is comprised materials selected from alumina, silica, silica-alumina, aluminum phosphates, titania, magnesium oxide, alkali and alkaline earth metal oxides, alkaline metal oxides, magnesium oxide, faujasite that has been ion exchanged with sodium to remove the acidity, and ammonium ion treated aluminum phosphate.  
   
   
       32 . The process of  claim 31 , wherein said mercaptan decomposition catalyst is comprised of materials selected from alumina, silica, and silica-alumina.  
   
   
       33 . The process of  claim 32 , wherein said mercaptan decomposition catalyst possesses substantially no hydrogenation activity.  
   
   
       34 . The process of  claim 20 , wherein said first hydrodesulfurization reaction conditions include temperatures from about 500° F. (260° C.) to about 675° F. (357° C.), pressures of about 200 to about 500 psig, and hydrogen-containing treat gas rates of about 1000 to about 3000 standard cubic feet per barrel.  
   
   
       35 . The process of  claim 34 , wherein said first hydrodesulfurization reaction conditions include pressures of about 250 to about 400 psig.  
   
   
       36 . The process of  claim 35 , wherein said mercaptan decomposition reaction conditions include temperatures from about 550° F. (288° C.) to about 700° F. (371° C.), and pressures of about 150 to about 500 psig.  
   
   
       37 . The process of  claim 36 , wherein the total sulfur content of said mercaptan decomposition reactor product stream is less than about 1 wt. % of the total sulfur content of said olefinic naphtha feedstream.  
   
   
       38 . The process of  claim 37 , wherein the mercaptan sulfur content of said mercaptan decomposition reactor product stream is less than about 10 wt. % of the mercaptan sulfur content of said first reactor effluent stream.