Selective desulfurization of fcc gasoline

Abstract

Processes for the desulfurization of high end point naphtha, such as naphtha fractions having an ASTM D-86 end point of greater than 450° F., greater than 500° F., or greater than 550° F., and containing hindered sulfur compounds, are disclosed.

What is claimed is: 
     
         1 . A process for the desulfurization of a full boiling range catalytically cracked naphtha comprising the steps of:
 (a) feeding (1) a full boiling range naphtha containing olefins, diolefins, mercaptans and other organic sulfur compounds and having an ASTM D86 end boiling point of at least 350° F., and (2) hydrogen to a first distillation column reactor;   (b) concurrently in the first distillation column reactor,
 (i) contacting the diolefins and the mercaptans in the full boiling range naphtha in the presence of a Group VIII metal catalyst in the rectification section of the first distillation column reactor thereby reacting:
 (A) a portion of the mercaptans with a portion of the diolefins to form thioethers, and/or 
 (B) a portion of the dienes with a portion of the hydrogen to form olefins; and 
 
 (ii) fractionating the full boiling range cracked naphtha into a distillate product containing C5 hydrocarbons and a first heavy naphtha containing sulfur compounds; 
   (c) recovering the first heavy naphtha from the first distillation column reactor as a first bottoms;   (d) feeding the first bottoms and hydrogen to a second distillation column reactor;   (e) concurrently in the second distillation column reactor,
 (i) reacting at least a portion of the organic sulfur compounds in the first bottoms with hydrogen in the presence of a hydrodesulfurization catalyst in the rectification section of the second distillation column reactor to convert a portion of the other organic sulfur compounds to hydrogen sulfide, and 
 (ii) separating the first heavy naphtha into a first intermediate naphtha having an ASTM D86 end point in the range from 270° F. to 400° F. and a second heavy naphtha; 
   (f) recovering the first intermediate naphtha, unreacted hydrogen, and hydrogen sulfide from the second distillation column reactor as a second overheads;   (g) recovering the second heavy naphtha containing hindered organic sulfur compounds from the second distillation column reactor as a second bottoms;   (h) feeding the second bottoms and hydrogen to a first fixed bed reactor containing a hydrodesulfurization catalyst;   (i) contacting the hindered organic sulfur compounds and hydrogen with the hydrodrodesulfurization catalyst in the first fixed bed reactor to convert at least a portion of the hindered organic sulfur compounds to hydrogen sulfide;   (j) recovering an effluent from the first fixed bed reactor.   
     
     
         2 . The process of  claim 1 , further comprising at least one of:
 (k) separating unreacted hydrogen and hydrogen sulfide from the effluent from the first fixed bed reactor;   (l) separating unreacted hydrogen and hydrogen sulfide from the second overheads;   (m) separating at least a portion of the hydrogen sulfide from the effluent from the second fixed bed reactor to form a naphtha fraction having a reduced sulfur content.   
     
     
         3 . The process of  claim 1 , further comprising admixing a diesel hydrocarbon fraction with the second bottoms prior to the contacting step (i). 
     
     
         4 . A process for the desulfurization of a full boiling range catalytically cracked naphtha comprising the steps of:
 (a) feeding (1) a full boiling range naphtha containing olefins, diolefins, mercaptans and other organic sulfur compounds and having an ASTM D86 end boiling point of at least 350° F., and (2) hydrogen to a first distillation column reactor;   (b) concurrently in the first distillation column reactor,
 (i) contacting the diolefins and the mercaptans in the full boiling range naphtha in the presence of a Group VIII metal catalyst in the rectification section of the first distillation column reactor thereby reacting:
 (A) a portion of the mercaptans with a portion of the diolefins to form thioethers, and/or 
 (B) a portion of the dienes with a portion of the hydrogen to form olefins; and 
 
 (ii) fractionating the full boiling range cracked naphtha into a distillate product containing C5 hydrocarbons and a first heavy naphtha containing sulfur compounds; 
   (c) recovering the first heavy naphtha from the first distillation column reactor as a first bottoms;   (d) feeding the first bottoms and hydrogen to a second distillation column reactor;   (e) concurrently in the second distillation column reactor,
 (i) reacting at least a portion of the organic sulfur compounds in the first bottoms with hydrogen in the presence of a hydrodesulfurization catalyst in the rectification section of the second distillation column reactor to convert a portion of the other organic sulfur compounds to hydrogen sulfide, and 
 (ii) separating the first heavy naphtha into a first intermediate naphtha having an ASTM D86 end point in the range from 270° F. to 400° F. and a second heavy naphtha; 
   (f) recovering the first intermediate naphtha, unreacted hydrogen, and hydrogen sulfide from the second distillation column reactor as a second overheads;   (g) recovering the second heavy naphtha containing hindered organic sulfur compounds from the second distillation column reactor as a second bottoms;   (h) feeding the second bottoms and hydrogen to a first fixed bed reactor containing a hydrodesulfurization catalyst;   (i) contacting the hindered organic sulfur compounds and hydrogen with the hydrodrodesulfurization catalyst in the first fixed bed reactor to convert at least a portion of the hindered organic sulfur compounds to hydrogen sulfide;   (j) recovering an effluent from the first fixed bed reactor;   (k) separating unreacted hydrogen and hydrogen sulfide from the effluent from the first fixed bed reactor;   (l) separating unreacted hydrogen and hydrogen sulfide from the second overheads;   (m) feeding at least a portion of the second overheads and hydrogen to a second fixed bed reactor containing a hydrodesulfurization catalyst to convert at least a portion of the sulfur compounds in the second overheads to hydrogen sulfide;   (n) recovering an effluent from the second fixed bed reactor;   (o) separating at least a portion of the hydrogen sulfide from the effluent from the second fixed bed reactor to form a naphtha fraction having a reduced sulfur content.   
     
     
         5 . The process of  claim 4 , wherein the full boiling range naphtha has an ASTM D86 end boiling point of at least 450° F. 
     
     
         6 . The process of  claim 4 , wherein the full boiling range naphtha has an ASTM D86 end boiling point of at least 500° F. 
     
     
         7 . The process of  claim 4 , further comprising at least one of:
 (p) feeding at least a portion of the separated effluent in (k) to the second fixed bed reactor; and   (q) fractionating the naphtha fraction having a reduced sulfur content to form a heavy naphtha fraction and a mid-range gasoline fraction, and recycling at least a portion of the heavy naphtha fraction to the second fixed bed reactor.   
     
     
         8 . The process of  claim 7 , wherein (p) comprises at least one of:
 conveying at least a portion of the effluent recovered in (j) to the separating (l); and   conveying at least a portion of the effluent recovered in (j) to the feeding (m).   
     
     
         9 . The process of  claim 4 , wherein a total sulfur content in the second overhead product is less than about 100 ppm S, by weight. 
     
     
         10 . The process of  claim 9 , further comprising forming a gasoline fraction from at least a portion of one or more of the distillate product, the naphtha fraction, and the effluent from the first fixed bed reactor, wherein the gasoline fraction has a total sulfur content of less than about 20 ppm S, by weight. 
     
     
         11 . The process of  claim 10 , wherein the gasoline fraction has a total sulfur content of less than about 10 ppm S, by weight. 
     
     
         12 . The process of  claim 9 , further comprising:
 reacting at least a portion of C5 and C6 olefins in the distillate product with an alcohol to form an ether.   
     
     
         13 . The process of  claim 12 , further comprising forming a gasoline fraction from at least a portion of one or more of the reacted distillate product, the naphtha fraction, and the effluent from the first fixed bed reactor, wherein the gasoline fraction has a total sulfur content of less than about 20 ppm S, by weight. 
     
     
         14 . The process of  claim 13 , wherein the gasoline fraction has a total sulfur content of less than about 10 ppm S, by weight. 
     
     
         15 . The process of  claim 4 , wherein the second distillation column reactor contains hydrodesulfurization catalyst only in the rectification section. 
     
     
         16 . The process of  claim 4 , wherein the second distillation column reactor contains hydrodesulfurization catalyst in both the rectification section and in the stripping section. 
     
     
         17 . The process of  claim 4 , further comprising forming a diesel fraction from at least a portion of the effluent from the first fixed bed reactor. 
     
     
         18 . The process of  claim 7 , further comprising forming a diesel fraction from at least one of at least a portion of the effluent from the first fixed bed reactor and at least a portion of the heavy naphtha fraction. 
     
     
         19 . The process of  claim 4 , wherein hydrodesulfurization catalyst in the first fixed bed reactor comprises a supported cobalt-molybdenum catalyst. 
     
     
         20 . The process of  claim 19 , wherein the supported cobalt-molybdenum catalyst comprises from 2 to 5 wt % cobalt and from 5 to 20 wt % molybdenum. 
     
     
         21 . The process of  claim 19 , wherein the hydrodesulfurization catalyst in the first fixed bed reactor further comprises a supported nickel-molybdenum catalyst. 
     
     
         22 . A process for the desulfurization of a full boiling range catalytically cracked naphtha comprising the steps of:
 (a) feeding (1) a full boiling range naphtha containing olefins, diolefins, mercaptans and other organic sulfur compounds and having an ASTM D86 end boiling point of at least 350° F., and (2) hydrogen to a first distillation column reactor;   (b) concurrently in the first distillation column reactor,
 (i) contacting the diolefins and the mercaptans in the full boiling range naphtha in the presence of a Group VIII metal catalyst in the rectification section of the first distillation column reactor thereby reacting:
 (A) a portion of the mercaptans with a portion of the diolefins to form thioethers, and/or 
 (B) a portion of the dienes with a portion of the hydrogen to form olefins; and 
 
 (ii) fractionating the full boiling range cracked naphtha into a distillate product containing C5 hydrocarbons and a first heavy naphtha containing sulfur compounds; 
   (c) recovering the first heavy naphtha from the first distillation column reactor as a first bottoms;   (d) feeding the first bottoms and hydrogen to a second distillation column reactor;   (e) concurrently in the second distillation column reactor,
 (i) reacting at least a portion of the organic sulfur compounds in the first bottoms with hydrogen in the presence of a hydrodesulfurization catalyst in the rectification section of the second distillation column reactor to convert a portion of the other organic sulfur compounds to hydrogen sulfide, and 
 (ii) separating the first heavy naphtha into a first intermediate naphtha having an ASTM D86 end point in the range from 270° F. to 400° F. and a second heavy naphtha; 
   (f) recovering the first intermediate naphtha, unreacted hydrogen, and hydrogen sulfide from the second distillation column reactor as a second overheads;   (g) recovering the second heavy naphtha containing hindered organic sulfur compounds from the second distillation column reactor as a second bottoms;   (h) feeding the second bottoms and hydrogen to a first fixed bed reactor containing a hydrodesulfurization catalyst;   (i) contacting the hindered organic sulfur compounds and hydrogen with the hydrodrodesulfurization catalyst in the first fixed bed reactor to convert at least a portion of the hindered organic sulfur compounds to hydrogen sulfide;   (j) recovering an effluent from the first fixed bed reactor;   (k) separating unreacted hydrogen and hydrogen sulfide from the effluent from the first fixed bed reactor;   (l) partially condensing the second overheads and separating the uncondensed portion of the second overheads including unreacted hydrogen and hydrogen sulfide from the condensed portion of the second overheads;   (m) feeding at least a portion of the condensed portion of the second overheads to the second distillation column reactor as reflux;   (n) feeding the separated effluent (k), the uncondensed portion of the second overheads, and at least a portion of the condensed second overheads to a fractionation column for separating unreacted hydrogen and hydrogen sulfide and to recover a bottoms hydrocarbon fraction;   (o) feeding the bottoms hydrocarbon fraction and hydrogen to a second fixed bed reactor containing a hydrodesulfurization catalyst to convert at least a portion of the sulfur compounds in the bottoms hydrocarbon fraction to hydrogen sulfide;   (p) recovering an effluent from the second fixed bed reactor;   (q) separating at least a portion of the hydrogen sulfide from the effluent from the second fixed bed reactor to form a naphtha fraction having a reduced sulfur content; and   (r) forming a gasoline from one or more of (i) at least a portion of the naphtha fraction and (ii) at least a portion of the distillate fraction, wherein the gasoline has a total sulfur content of less than about 20 ppm S, by weight.   
     
     
         23 . A process for the desulfurization of a full boiling range naphtha comprising the steps of:
 (a) feeding (1) a full boiling range naphtha containing olefins, diolefins, mercaptans and other organic sulfur compounds and having an ASTM D86 end boiling point of at least 350° F., and (2) hydrogen to a first distillation column reactor;   (b) concurrently in the first distillation column reactor,
 (i) contacting the diolefins and the mercaptans in the full boiling range naphtha in the presence of a Group VIII metal catalyst in the rectification section of the first distillation column reactor thereby reacting:
 (A) a portion of the mercaptans with a portion of the diolefins to form thioethers, and/or 
 (B) a portion of the dienes with a portion of the hydrogen to form olefins; and 
 
 (ii) fractionating the full boiling range cracked naphtha into a distillate product containing C5 hydrocarbons and a first heavy naphtha containing sulfur compounds; 
   (c) recovering the first heavy naphtha from the first distillation column reactor as a first bottoms;   (d) feeding the first bottoms and hydrogen to a second distillation column reactor;   (e) concurrently in the second distillation column reactor,
 (i) reacting at least a portion of the organic sulfur compounds in the first bottoms with hydrogen in the presence of a hydrodesulfurization catalyst in the rectification section of the second distillation column reactor to convert a portion of the other organic sulfur compounds to hydrogen sulfide, and 
 (ii) separating the first heavy naphtha into a first intermediate naphtha having an ASTM D86 end point in the range from 270° F. to 400° F. and a second heavy naphtha; 
   (f) recovering the first intermediate naphtha, unreacted hydrogen, and hydrogen sulfide from the second distillation column reactor as a second overheads;   (g) recovering the second heavy naphtha containing hindered organic sulfur compounds from the second distillation column reactor as a second bottoms;   (h) feeding the second bottoms and hydrogen to a first fixed bed reactor containing a hydrodesulfurization catalyst;   (i) contacting the hindered organic sulfur compounds and hydrogen with the hydrodrodesulfurization catalyst in the first fixed bed reactor to convert at least a portion of the hindered organic sulfur compounds to hydrogen sulfide;   (j) recovering an effluent from the first fixed bed reactor;   (k) separating unreacted hydrogen and hydrogen sulfide from the effluent from the first fixed bed reactor;   (l) separating unreacted hydrogen and hydrogen sulfide from the second overheads;   (m) feeding at least a portion of the second overheads and hydrogen to a second fixed bed reactor containing a hydrodesulfurization catalyst to convert at least a portion of the sulfur compounds in the second overheads to hydrogen sulfide;   (n) recovering an effluent from the second fixed bed reactor;   (o) separating at least a portion of the hydrogen sulfide from the effluent from the second fixed bed reactor to form a H 2 S separated naphtha fraction;   (p) fractionating the H 2 S separated naphtha fraction to form a heavy naphtha fraction and a mid-range gasoline fraction; and   (q) recycling at least a portion of the heavy naphtha fraction to the second fixed bed reactor; and   (r) forming a gasoline from one or more of (i) at least a portion of the distillate product, (ii) at least a portion of the naphtha fraction, and (iii) at least a portion of the effluent from the first fixed bed reactor, wherein the gasoline has a total sulfur content of less than about 20 ppm S, by weight.   
     
     
         24 . The process of  claim 23 , further comprising feeding at least a portion of the separated effluent in (k) to the second fixed bed reactor. 
     
     
         25 . The process of  claim 23 , further comprising reacting at least a portion of C5 and C6 olefins in the distillate product with an alcohol to form an ether prior to the forming a gasoline (r).