Processes and apparatuses for removing mercaptans from a feed stream

Abstract

Processes and apparatuses for removing mercaptans from feed streams are provided. In one embodiment, a process for removing mercaptans from a feed stream includes extracting mercaptans and a polymeric precursor from the feed stream with a caustic solvent to form a polymeric precursor rich spent caustic solvent. The polymeric precursor rich spent caustic solvent is contacted with a polymeric precursor-deficient hydrocarbon stream in a multistage vessel and the polymeric precursor is extracted from the polymeric precursor rich spent caustic solvent to form a treated spent caustic solvent. The process contacts the treated spent caustic solvent with oxygen and oxidizes the mercaptans to disulfides to form an oxidized caustic solvent stream. The process includes separating the oxidized caustic solvent stream into an offgas stream, a disulfide stream, and a caustic solvent stream.

What is claimed is: 
     
         1 . A process for removing mercaptans from a feed stream comprising the steps of:
 extracting mercaptans and a polymeric precursor from the feed stream with a caustic solvent to form a polymeric precursor rich spent caustic solvent;   contacting the polymeric precursor rich spent caustic solvent with a polymeric precursor-deficient hydrocarbon stream in a multistage vessel and extracting the polymeric precursor from the polymeric precursor rich spent caustic solvent to form a treated spent caustic solvent;   contacting the treated spent caustic solvent with oxygen and oxidizing the mercaptans to disulfides to form an oxidized caustic solvent stream; and   separating the oxidized caustic solvent stream into an offgas stream, a disulfide stream, and a caustic solvent stream.   
     
     
         2 . The process of  claim 1  wherein the multistage vessel includes a plurality of contacting trays and wherein contacting the polymeric precursor rich spent caustic solvent with a polymeric precursor-deficient hydrocarbon stream comprises flowing the polymeric precursor rich spent caustic solvent and the polymeric precursor-deficient hydrocarbon stream countercurrently through the plurality of contacting trays. 
     
     
         3 . The process of  claim 1  wherein the multistage vessel includes packing and wherein contacting the polymeric precursor rich spent caustic solvent with a polymeric precursor-deficient hydrocarbon stream comprises flowing the polymeric precursor rich spent caustic solvent and the polymeric precursor-deficient hydrocarbon stream countercurrently through the packing. 
     
     
         4 . The process of  claim 1  further comprising the step of hydrotreating a naphtha stream to form the polymeric precursor-deficient hydrocarbon stream. 
     
     
         5 . The process of  claim 1  further comprising the step of extracting the polymeric precursor from a naphtha stream to form a raffinate, wherein the raffinate is the polymeric precursor-deficient hydrocarbon stream. 
     
     
         6 . The process of  claim 1  wherein contacting the polymeric precursor rich spent caustic solvent with a polymeric precursor-deficient hydrocarbon stream in a multistage vessel comprises introducing the polymeric precursor rich spent caustic solvent to the multistage vessel at a temperature of about 32° C. to about 49° C. 
     
     
         7 . The process of  claim 1  wherein contacting the polymeric precursor rich spent caustic solvent with a polymeric precursor-deficient hydrocarbon stream in a multistage vessel comprises introducing the polymeric precursor-deficient hydrocarbon stream to the multistage vessel with a boiling point of less than about 350° C. 
     
     
         8 . The process of  claim 1  wherein:
 extracting mercaptans and the polymeric precursor from the feed stream with a caustic solvent forms the polymeric precursor rich spent caustic solvent with a polymeric precursor content of about 0.5 wt % to about 3 wt %; and 
 contacting the polymeric precursor rich spent caustic solvent with a polymeric precursor-deficient hydrocarbon stream in a multistage vessel forms the treated spent caustic solvent with a polymeric precursor content of less than about 20 ppm. 
 
     
     
         9 . The process of  claim 1  further comprising the step of passing the disulfide stream through a disulfide sand filter and removing caustic and water from the disulfide stream. 
     
     
         10 . The process of  claim 1  wherein the caustic solvent stream includes hydrocarbons and wherein the process further comprises the step of directing the caustic solvent stream to a disulfide scrubber to remove disulfide and to separate a regenerated caustic solvent and a regenerated hydrocarbon stream. 
     
     
         11 . The process of  claim 10  wherein extracting mercaptans and polymeric precursor from the feed stream with a caustic solvent comprises contacting the feed stream with the regenerated caustic solvent. 
     
     
         12 . The process of  claim 10  wherein contacting the polymeric precursor rich spent caustic solvent with a polymeric precursor-deficient hydrocarbon stream in a multistage vessel comprises contacting the polymeric precursor rich spent caustic solvent with the regenerated hydrocarbon stream. 
     
     
         13 . The process of  claim 1  wherein contacting the polymeric precursor rich spent caustic solvent with a polymeric precursor-deficient hydrocarbon stream in a multistage vessel forms a polymeric precursor rich hydrocarbon stream, and wherein the process further comprises:
 passing the disulfide stream and the polymeric precursor rich hydrocarbon stream through a disulfide sand filter. 
 
     
     
         14 . A process for removing mercaptans from a feed stream comprising the steps of:
 extracting mercaptans and butadiene from the feed stream with a solvent stream to form a product stream and a spent solvent stream;   contacting the spent solvent stream with a hydrocarbon stream in a multistage countercurrent liquid-liquid contacting vessel and extracting butadiene from the spent solvent stream to form a treated spent solvent stream;   converting the mercaptans to disulfides;   separating the treated spent solvent stream into a disulfide stream and a clean solvent stream; and   introducing the clean solvent stream and a fresh hydrocarbon stream to a contacting zone to remove remaining disulfide and to form the hydrocarbon stream and the solvent stream.   
     
     
         15 . The process of  claim 14  further comprising the step of hydrotreating a naphtha stream to form the fresh hydrocarbon stream. 
     
     
         16 . The process of  claim 14  further comprising the step of extracting butadiene from a naphtha stream to form a raffinate, wherein the raffinate is the fresh hydrocarbon stream. 
     
     
         17 . The process of  claim 14  wherein contacting the spent solvent stream with a hydrocarbon stream in a multistage countercurrent liquid-liquid contacting vessel comprises introducing the spent solvent stream to the multistage countercurrent liquid-liquid contacting vessel at a temperature of about 32° C. to about 49° C. and introducing the hydrocarbon stream with a boiling point of less than about 350° C. 
     
     
         18 . The process of  claim 14  wherein:
 extracting mercaptans and butadiene from the feed stream with a solvent stream to form a product stream and a spent solvent stream forms the spent solvent stream with a butadiene content of about 0.5 wt % to about 3 wt %; and 
 contacting the spent solvent stream with a hydrocarbon stream in a multistage countercurrent liquid-liquid contacting vessel forms the treated spent solvent stream with a butadiene content of less than about 20 ppm. 
 
     
     
         19 . The process of  claim 14  wherein contacting the spent solvent stream with a hydrocarbon stream in a multistage countercurrent liquid-liquid contacting vessel and extracting butadiene from the spent solvent stream forms a butadiene rich hydrocarbon stream, and wherein the process further comprises:
 passing the disulfide stream and the butadiene rich hydrocarbon stream through a disulfide sand filter. 
 
     
     
         20 . An apparatus for removing mercaptans from a feed stream comprising:
 a mercaptan extractor configured to remove mercaptans from the feed stream with a caustic solvent to form a product stream and a butadiene rich spent caustic solvent;   a multistage countercurrent liquid-liquid contacting vessel configured to contact the butadiene rich spent caustic solvent and a butadiene deficient hydrocarbon stream to extract butadiene from the butadiene rich spent caustic solvent to form a treated spent caustic solvent;   an oxidizer configured to receive the treated spent caustic solvent and to oxidize the mercaptans to disulfides to form an oxidized caustic solvent stream; and   a disulfide separator configured to separate the oxidized caustic solvent stream into an offgas stream, a disulfide stream, and a caustic solvent stream.