Selective hydroprocessing and mercaptan removal

Abstract

A process for the production of naphtha streams from cracked naphthas having sulfur levels which help meet future EPA gasoline sulfur standards (30 ppm range and below).

What is claimed:  
     
         1 . A method for producing a gasoline blendstock having a decreased amount of sulfur comprising the steps of: 
 (a) selectively hydroprocessing a petroleum feedstream comprising cracked naphtha and sulfur-containing species to produce a first naphtha product comprising mercaptan sulfur having more than 5 carbon atoms, olefins, non-mercaptan sulfur, and hydrogen gas;    (b) removing at least a portion of said hydrogen sulfide and at least a portion of said hydrogen gas from said first naphtha product to obtain a second naphtha product having a decreased amount of hydrogen sulfide and hydrogen gas;    (c) contacting said second naphtha product with a liquid extractant and removing or converting at least a portion of said mercaptan sulfur from said second naphtha product to obtain a third naphtha product having a decreased amount of said mercaptan sulfur; and    (d) fractionating said third naphtha product to obtain at least one higher boiling point product comprising at least a portion of said converted mercaptan sulfur and at least one lighter boiling point product.    
     
     
         2 . The method of  claim 1  wherein said lighter boiling point product has a boiling point below about 480° F., and said higher boiling point product has a boiling point above about 480° F.  
     
     
         3 . The method of  claim 1  wherein said first naphtha product contains less than 50 ppm non-mercaptan sulfur.  
     
     
         4 . The method of  claim 1  wherein said first product contains less than 30 wppm non-mercaptan sulfur.  
     
     
         5 . The method of  claim 1  wherein said removal step (c) is accomplished by a process selected from the group consisting of extraction, adsorption, fractionation, sweetening followed by fractionation, thermal decomposition and membrane separation.  
     
     
         6 . The method according to  claim 5  wherein said mercaptan sulfur is removed or converted by sweetening in the sweetening unit already existing with the base hydrotreating unit.  
     
     
         7 . The method according to  claim 1  wherein about 1% to about 100% of said hydrogen gas is removed from said first naphtha product.  
     
     
         8 . The method according to  claim 1  wherein step (d) is conducted in a disulfide fractionator.  
     
     
         9 . The method according to  claim 1  wherein step (d) is conducted in the existing stripper of the base hydrotreating unit.  
     
     
         10 . The method of  claim 2  wherein step (b) of  claim 1  comprises: 
 (a) separating from said first naphtha product at least a portion of hydrogen gas and at least a portion of hydrogen sulfide in a separation drum to produce a naphtha product having reduced levels of hydrogen sulfide and hydrogen gas;  
 (b) passing said naphtha product having reduced levels of hydrogen sulfide and hydrogen gas to a monoethanolamine scrubber to produce a naphtha product having reduced levels of non-mercaptan sulfur; and,  
 (c) regenerating said monoethanol amine.  
 
     
     
         11 . The method of  claim 8  or  9  wherein a hydrocarbon stream is injected into said existing stripper such that the flow of said hydrocarbon stream is countercurrent or co-current to the flow of the product stream from the mercaptan conversion reactor.  
     
     
         12 . The method according to  claim 11  wherein said hydrocarbon stream is diesel oil.