Process for sulfur reduction in naphtha streams

Abstract

A process for fractionating and treating of a full range naphtha stream. The full boiling range naphtha stream is first split into a light boiling range naphtha, an intermediate boiling range naphtha and a heavy boiling range naphtha. The bottoms are subjected to hydrodesulfurization and the effluent combined with the intermediate boiling range naphtha containing thiophene and thiophene boiling range mercaptans and subjected to a second hydrodesulfurization. The effluent from the polishing reactor may be combined with the light boiling range naphtha to produce a new full boiling range naphtha containing substantially less total sulfur than the original feed. The mercaptans in the light naphtha may be removed by thioetherification prior to splitting or by wet caustic wash afterwards. The object being to meet higher standards for sulfur removal, by treating the components of the naphtha feed with the process that preserves the olefinic while most expediently removing the sulfur compounds.

The invention claimed is:  
     
         1 . A process for reducing the organic sulfur content of a full boiling range cracked naphtha stream containing olefins, diolefins, mercaptans, thiophenes, and other organic sulfur compounds, comprising the steps of: 
 (a) separating the full boiling range cracked naphtha stream into three fractions comprising a light cracked naphtha fraction, an intermediate cracked naphtha fraction and a heavy cracked naphtha;    (b) subjecting the heavy cracked naphtha to hydrodesulfurization in a first hydrodesulfurization reactor containing a hydrodesulfurization catalyst; and    (c) combining the effluent from the first hydrodesulfurization reactor with the intermediate cracked naphtha and subjecting the combined stream to hydrodesulfurization in a second hydrodesulfurization reactor.    
     
     
         2 . The process according to  claim 1  wherein said light cracked naphtha contains substantially all of the mercaptans and is subjected to a wet caustic wash process wherein the mercaptans contained therein are converted to sulfides and said sulfides are removed.  
     
     
         3 . The process according to  claim 1  wherein said intermediate cracked naphtha contains mercaptans and substantially all of the thiophenes and substantially all of said mercaptans and thiophenes are converted to hydrogen sulfide in said second hydrodesulfurization reactor.  
     
     
         4 . The process according to  claim 1  wherein said heavy cracked naphtha contains thiophenes and substantially all of said other organic sulfur compounds and a portion of said thiophenes and other organic sulfur compounds are converted to hydrogen sulfide in said first hydrodesulfurization reactor.  
     
     
         5 . The process according to  claim 4  wherein substantially all of the remaining thiophenes and other organic sulfur compounds are converted to hydrogen sulfide in said second hydrodesulfurization reactor.  
     
     
         6 . The process according to  claim 1  wherein said full boiling range cracked naphtha stream is first subjected to thioetherification in a thioetherification reactor prior to separating the full boiling range cracked naphtha stream into said three fractions, wherein substantially all of said mercaptans are reacted with a portion of said diolefins to form sulfides.  
     
     
         7 . The process according to  claim 6  wherein said sulfides are removed in said heavy cracked naphtha and substantially all of said sulfides are converted to hydrogen sulfide in said first hydrodesulfurization reactor.  
     
     
         8 . The process according to  claim 7  wherein the remaining sulfides are converted to hydrogen sulfide in said second hydrodesulfurization reactor.  
     
     
         9 . The process according to  claim 1  wherein said light cracked naphtha fraction boils in the range of C 5  to about 150° F., said intermediate cracked naphtha fraction boils in the range of about 150 to about 250° F. and said heavy cracked naphtha boils in the range of about 250 to 450° F.  
     
     
         10 . A process for reducing the organic sulfur content of a full boiling range cracked naphtha stream containing olefins, diolefins, mercaptans, thiophenes, and other organic sulfur compounds, comprising the steps of: 
 (a) subjecting the full boiling range naphtha to thioetherification in a thioetherification reactor wherein substantially all of said mercaptans are reacted with a portion of said diolefins to form sulfides;    (b) separating the effluent from the thioetherification reactor into three fractions comprising a light cracked naphtha fraction boiling in the range of C 5  to about 150° F, an intermediate cracked naphtha fraction boiling in the range of about 150 to about 250° F. and a heavy cracked naphtha boiling in the range of about 250 to 450° F.;    (b) subjecting the heaving cracked naphtha to hydrodesulfurization in a first hydrodesulfurization reactor containing a hydrodesulfurization catalyst; and    (c) combining the effluent from the first hydrodesulfurization reactor with the intermediate cracked naphtha and subjecting the combined stream to hydrodesulfurization in a second hydrodesulfurization reactor.    
     
     
         11 . A process for reducing the organic sulfur content of a full boiling range cracked naphtha stream containing olefins, diolefins, mercaptans, thiophenes, and other organic sulfur compounds, comprising the steps of: 
 (a) separating the full boiling range cracked naphtha stream into three fractions comprising a light cracked naphtha fraction boiling in the range of C 5  to about 150° F., an intermediate cracked naphtha fraction boiling in the range of about 150 to about 250° F. and a heavy cracked naphtha boiling in the range of about 250 to 450° F.;    (b) subjecting the heaving cracked naphtha to hydrodesulfurization in a first hydrodesulfurization reactor containing a hydrodesulfurization catalyst;    (c) combining the effluent from the first hydrodesulfurization reactor with the intermediate cracked naphtha and subjecting the combined stream to hydrodesulfurization in a second hydrodesulfurization reactor and    (d) subjecting said light cracked naphtha to a wet caustic wash wherein substantially all of the mercaptans contained therein are converted to sulfides.