Sulfur removal process

Abstract

A product of reduced sulfur content is produced from an olefin-containing hydrocarbon feedstock which includes sulfur-containing impurities. The feedstock is contacted with an olefin-modification catalyst in a reaction zone under conditions which are effective to produce an intermediate product which has a reduced amount of olefinic unsaturation relative to that of the feedstock as measured by bromine number. The intermediate product is then separated into at least three fractions of different volatility, and the lowest boiling first fraction is contacted with a hydrodesulfurization catalyst in the presence of hydrogen under conditions which are effective to convert at least a portion of its sulfur-containing impurities to hydrogen sulfide. The intermediate boiling fraction is contacted with a selective hydrotreating catalyst in the presence of hydrogen under conditions which are effective to convert at least a portion of its sulfur-containing impurities to hydrogen sulfide.

We claim:  
     
         1 . A process for producing a product of reduced sulfur content from a feedstock, wherein said feedstock contains sulfur-containing organic impurities and is comprised of a normally liquid mixture of hydrocarbons which includes olefins, said process comprising: 
 (a) contacting the feedstock with an olefin-modification catalyst in at least one olefin-modification reaction zone under conditions which are effective to produce a product having a bromine number which is lower than that of the feedstock and wherein the product contains refractive sulfur compounds;    (b) fractionating the product from said olefin-modification reaction zone to produce: 
 (i) a first fraction which comprises sulfur-containing organic impurities and has a distillation endpoint which less than about 140° C.;  
 (ii) a second fraction which is higher boiling than the first fraction which comprises sulfur-containing organic impurities and has a distillation endpoint which is less than about 240° C.; and  
 (iii) a third fraction which is higher boiling than the second fraction and comprises sulfur-containing organic impurities and refractive sulfur compounds;  
   (c) contacting said second fraction with a selective hydrotreating catalyst in the presence of hydrogen in a selective hydrotreating reaction zone under conditions which are effective to convert at least a portion of the sulfur as containing impurities in the second fraction to hydrogen sulfide; and    (d) contacting said third fraction with a hydrodesulfurization catalyst in the presence of hydrogen in a hydrodesulfurization reaction zone under conditions which are effective to convert at least a portion of the sulfur in said sulfur-containing impurities of the third fraction to hydrogen sulfide.    
     
     
         2 . The process of  claim 1  wherein the feedstock contains paraffins and wherein the conditions in said olefin-modification reaction zone are effective to produce a product having a bromine number which is lower than that of the feedstock and less than 10% of the paraffins in the feedstock are cracked.  
     
     
         3 . The process of  claim 1  which additionally comprises removing hydrogen sulfide from the effluent of said selective hydrotreating reaction zone to yield a desulfurized product which contains less than about 50 parts per million by weight of sulfur.  
     
     
         4 . The process of  claim 3  wherein the octane of the desulfurized product is at least 95% that of the feedstock to the olefin-modification reaction zone.  
     
     
         5 . The process of  claim 1  wherein the feedstock contains from about 0.05 wt. % to about 0.7 wt. % of sulfur in the form of organic sulfur compounds.  
     
     
         6 . The process of  claim 1  which additionally comprises removing hydrogen sulfide from the effluent of said hydrodesulfurization reaction zone to yield a desulfurized product which contains less than about 50 parts per million by weight sulfur.  
     
     
         7 . The process of  claim 6  wherein the octane of the desulfurized product is at least 90% that of the feedstock to the olefin-modification reaction zone.  
     
     
         8 . The process of  claim 1  wherein said feedstock contains basic nitrogen-containing impurities and said process additionally comprises removing said basic nitrogen-containing impurities from the feedstock before it is contacted with the olefin-modification catalyst.  
     
     
         9 . The process of  claim 8  wherein said feedstock is comprised of hydrocarbons from a catalytic cracking process.  
     
     
         10 . The process of  claim 1  wherein said feedstock is substantially free of basic nitrogen-containing impurities.  
     
     
         11 . The process of  claim 1  wherein said feedstock is comprised of a mixture of hydrocarbons which boils in the gasoline range.  
     
     
         12 . The process of  claim 1  wherein the feedstock is comprised of a treated naphtha which is prepared by removing basic nitrogen-containing impurities from a naphtha produced by a catalytic cracking process.  
     
     
         13 . The process of  claim 1  wherein the third fraction ranges from 2 to 10 vol % of the product from the olefin-modification reaction zone.  
     
     
         14 . The process of  claim 1  wherein the feedstock has an initial boiling point which is below about 79° C. and distillation endpoint which is not greater that about 345° C.  
     
     
         15 . A process for producing products of reduced sulfur content from a feedstock, wherein said feedstock contains sulfur-containing organic impurities and is comprised of a normally liquid mixture of hydrocarbons which includes olefins, said process comprising: 
 (a) contacting the feedstock with an olefin-modification catalyst in an olefin-modification reaction zone under conditions which are effective to produce a product which has a lower bromine number than that of the feedstock wherein the product contains refractive sulfur compounds, wherein said olefin-modification catalyst is selected from the group consisting of all solid acid catalysts;    (b) fractionating the product from said olefin-modification reaction zone to produce: 
 (i) a first fraction which comprises sulfur-containing organic impurities and has a distillation endpoint which is less than about 120° C.;  
 (ii) a second fraction which is higher boiling than the first fraction which comprises sulfur-containing organic impurities and has a distillation endpoint which is less than about 200° C.; and  
 (iii) a third fraction which is higher boiling than the second fraction and comprises sulfur-containing organic impurities and refractive sulfur compounds;  
   (c) contacting said second fraction with a selective hydrotreating catalyst in the presence of hydrogen in a selective hydrotreating reaction zone under conditions which are effective to convert at least a portion of the sulfur in said sulfur containing impurities in the second fraction to hydrogen sulfide;    (d) contacting said third fraction with a hydrodesulfurization catalyst in the presence of hydrogen in a hydrodesulfurization reaction zone under conditions which are effective to convert at least a portion of the sulfur in said sulfur-containing impurities of the third fraction to hydrogen sulfide.    
     
     
         16 . The process of  claim 15  which additionally comprises removing hydrogen sulfide from the effluent of said selective hydrotreating reaction zone to yield a desulfurized product having an octane which is at least 98% that of the feedstock to the olefin-modification reaction zone.  
     
     
         17 . The process of  claim 15  which additionally comprises removing hydrogen sulfide from the effluent of said hydrodesulfurization reaction zone to yield a desulfurized product having an octane which is at least 97% that of the feedstock to the olefin-modification reaction zone.  
     
     
         18 . The process of  claim 15  wherein said feedstock is comprised of hydrocarbons from a catalytic cracking process.  
     
     
         19 . The process of  claim 15  wherein the feedstock is comprised of a treated naphtha which is prepared by removing basic nitrogen-containing impurities from a naphtha produced by a catalytic cracking process.