Methods and apparatuses for removing sulfur compounds from a hydrocarbon stream

Abstract

Methods and apparatuses are provided for removing sulfur compounds from a hydrocarbon stream. A method includes contacting a hydrocarbon feed stream with a basic aqueous solution in an extractor to produce a sweetened hydrocarbon stream and a rich stream, where the rich stream includes a mercaptan salt. The rich stream is contacted with oxygen in an oxidizer to convert the mercaptan salt into a disulfide and to produce an oxidizer effluent stream. The oxidizer effluent stream is separated into a gas recycle stream and a mixed disulfide stream, and the gas recycle stream is combined with the rich stream.

What is claimed is: 
     
         1 . A method for removing sulfur compounds from a hydrocarbon stream comprising:
 contacting a hydrocarbon feed stream with a basic aqueous solution in an extractor to produce a sweetened hydrocarbon stream and a rich stream, wherein the rich stream comprises a mercaptan salt;   contacting the rich stream with oxygen in an oxidizer to convert the mercaptan salt into a disulfide and to produce an oxidizer effluent stream comprising the disulfide;   separating the oxidizer effluent stream into a gas recycle stream and a mixed disulfide stream; and   combining the gas recycle stream with the rich stream, wherein the gas recycle stream comprises oxygen.   
     
     
         2 . The method of  claim 1  further comprising:
 pressurizing the oxidizer effluent stream prior to separating the oxidizer effluent stream, wherein the oxidizer effluent stream is pressurized to a pressure in the oxidizer effluent greater than a pressure in the oxidizer. 
 
     
     
         3 . The method of  claim 1  further comprising:
 measuring an oxygen concentration in the gas recycle stream; and 
 controlling the oxygen concentration in the gas recycle stream to within a desired gas recycle oxygen concentration. 
 
     
     
         4 . The method of  claim 3  wherein controlling the oxygen concentration in the gas recycle stream comprises adding oxygen to the gas recycle stream. 
     
     
         5 . The method of  claim 3  wherein controlling the oxygen concentration in the gas recycle stream comprises adding nitrogen to the gas recycle stream. 
     
     
         6 . The method of  claim 1  wherein contacting the hydrocarbon feed stream with the basic aqueous solution comprises contacting the hydrocarbon feed stream with the basic aqueous solution wherein the basic aqueous solution comprises a caustic solution. 
     
     
         7 . The method of  claim 1  wherein:
 contacting the rich stream with oxygen in the oxidizer comprises contacting the rich stream with oxygen in the oxidizer in the presence of a catalyst. 
 
     
     
         8 . The method of  claim 7  wherein contacting the rich stream with oxygen in the oxidizer comprises contacting the rich stream with oxygen in the oxidizer in the presence of the catalyst, wherein the catalyst comprises a metal chelate, and wherein the metal chelate comprises one or more of iron, cobalt, manganese, molybdenum, and vanadium. 
     
     
         9 . The method of  claim 1  further comprising:
 separating the mixed disulfide stream into a disulfide stream and the basic aqueous solution in a disulfide separator. 
 
     
     
         10 . The method of  claim 9  further comprising:
 limiting vented gases from the disulfide separator to zero emissions for a period of about 24 hours or greater while contacting the hydrocarbon feed stream with the basic aqueous solution. 
 
     
     
         11 . The method of  claim 1  wherein contacting the hydrocarbon feed stream with the basic aqueous solution comprises contacting the hydrocarbon feed stream with the basic aqueous solution wherein the hydrocarbon feed stream comprises about 90 volume percent or more hydrocarbons having either 3 or 4 carbon atoms. 
     
     
         12 . The method of  claim 1  wherein separating the oxidizer effluent stream into the gas recycle stream and the mixed disulfide stream comprises separating the oxidizer effluent stream in an oxidizer effluent separator, the method further comprising:
 controlling a liquid level in the oxidizer effluent separator to within a desired liquid level range. 
 
     
     
         13 . A method for removing sulfur compounds from a hydrocarbon stream comprising:
 converting a mercaptan in a hydrocarbon feed stream into a disulfide in a sulfur compound removal unit;   discharging a sweetened hydrocarbon stream from the sulfur compound removal unit, wherein the concentration of sulfur containing compounds in the sweetened hydrocarbon stream is lower than in the hydrocarbon feed stream; and   recycling a gas recycle stream such that intentionally vented gaseous discharges from the sulfur compound removal unit are controlled to about 1 volume percent or less of a volume of the sweetened hydrocarbon stream during a time period of about 24 hours or more.   
     
     
         14 . The method of  claim 13  wherein converting the mercaptan in the hydrocarbon feed stream into the disulfide further comprises:
 contacting the hydrocarbon feed stream with a basic aqueous solution to form the sweetened hydrocarbon stream and a rich stream, wherein the rich stream comprises a mercaptan salt; and 
 oxidizing the mercaptan salt in the rich stream with oxygen in the gas recycle stream to produce the disulfide in an oxidizer effluent stream. 
 
     
     
         15 . The method of  claim 14  further comprising:
 separating the oxidizer effluent stream into the gas recycle stream and a mixed disulfide stream. 
 
     
     
         16 . The method of  claim 15  further comprising:
 separating the mixed disulfide stream into a disulfide stream and the basic aqueous solution in a disulfide separator; and 
 discharging the disulfide stream. 
 
     
     
         17 . The method of  claim 16  further comprising:
 limiting vented gases from the disulfide separator to zero emissions for about 24 hours or more while converting the mercaptan in the hydrocarbon feed stream into the disulfide. 
 
     
     
         18 . The method of  claim 13  further comprising:
 measuring a gas recycle oxygen concentration; and 
 controlling the gas recycle oxygen concentration to within a desired gas recycle oxygen concentration. 
 
     
     
         19 . The method of  claim 18  wherein controlling the gas recycle oxygen concentration comprises adding oxygen to the gas recycle stream. 
     
     
         20 . An apparatus for removing sulfur compounds from a hydrocarbon stream comprising:
 an extractor;   an oxidizer coupled to the extractor;   an oxidizer effluent separator coupled to the oxidizer, where the oxidizer effluent separator in configured to produce a gas recycle stream and a mixed disulfide stream, and wherein the gas recycle stream is coupled to the oxidizer; and   a disulfide separator coupled to the mixed disulfide stream.