Extraction of Mercaptans in the Absence of Oxidation Catalyst

Abstract

Processes for the extractive removal of mercaptan compounds from hydrocarbon feeds, in which the contact between oxidation catalyst with oxygen and mercaptan in the feed is reduced or eliminated, are described. Oxidation of mercaptan compounds to disulfides in the extraction zone is prevented, thereby overcoming separation inefficiencies associated with the inability to extract disulfides in this zone. The invention advantageously relies on the use of a fixed bed of catalyst in the oxidation or regeneration zone, which is coupled to the extraction zone.

1 . A process for treating a hydrocarbon feed comprising mercaptan compounds and oxygen, the process comprising:
 (a) contacting the hydrocarbon feed with a lean aqueous extraction medium to provide a treated hydrocarbon product and a rich aqueous extraction medium comprising extracted mercaptide compounds   (b) passing the rich aqueous extraction medium and an oxygen-containing reactant to a catalytic oxidation zone comprising a fixed bed of solid oxidation catalyst, to convert at least a portion of the extracted mercaptide compounds to disulfide compounds, contained in an oxidation zone effluent.   wherein the lean aqueous extraction medium is essentially free of circulating oxidation catalyst   
     
     
         2 . The process of  claim 1 , further comprising:
 (c) separating, from the oxidation zone effluent, a regenerated aqueous extraction medium, a disulfide rich organic product, and an off gas, and   (d) recycling at least a portion of the regenerated aqueous extraction medium to provide at least a portion of the lean aqueous extraction medium.   
     
     
         3 . The process of  claim 1 , wherein the wherein the treated hydrocarbon product is essentially free of disulfide compounds. 
     
     
         4 . The process of  claim 3 , wherein treated hydrocarbon product comprises disulfide sulfur in an amount of less than about 5 ppm by weight. 
     
     
         5 . The process of  claim 1 , wherein the hydrocarbon feed comprises fuel gas or a hydrocarbon fraction having a distillation end point temperature from about 138° C. (280° F.) to about 216° C. (420° F.). 
     
     
         6 . The process of  claim 5 , wherein the hydrocarbon fraction is obtained from a fluid catalytic cracking (FCC) process. 
     
     
         7 . The process of  claim 1 , wherein the hydrocarbon feed comprises dissolved oxygen in an amount from about 1 ppm to about 100 ppm by weight. 
     
     
         8 . The process of  claim 1 , wherein the hydrocarbon feed comprises mercaptan sulfur in an amount from about 20 ppm by weight to about 500 ppm by weight. 
     
     
         9 . The process of  claim 1 , wherein the treated hydrocarbon product comprises mercaptan sulfur in an amount of less than about 5 ppm by weight. 
     
     
         10 . The process of  claim 1 , wherein step (a) occurs in a counter-current extraction column. 
     
     
         11 . The process of  claim 10 , wherein step (a) is carried out under extraction conditions including a temperature from about 20° C. (68° F.) to about 121° C. (250° F.) and a pressure from about 3.4 barg (50 psig) to about 10 barg (150 psig). 
     
     
         12 . The process of  claim 1 , wherein, in step (a), is carried out at a lean aqueous extraction medium:hydrocarbon feed volumetric ratio from about 1:20 to about 1:4. 
     
     
         13 . The process of  claim 1 , wherein the lean aqueous extraction medium comprises sodium hydroxide having a concentration from about 5% to about 20% by weight. 
     
     
         14 . The process of  claim 1 , wherein the oxygen-containing reactant comprises oxygen in an amount from about 100% to about 200% of a required stoichiometric amount for oxidation of the extracted mercaptan compounds. 
     
     
         15 . The process of  claim 1 , wherein the oxygen-containing reactant comprises air. 
     
     
         16 . The process of  claim 1  the catalytic oxidation zone is maintained at a temperature from about 20° C. (68° F.) to about 121° C. (250° F.) and a pressure from about 0 barg (0 psig) to about 21 barg (300 psig) for converting at least the portion of the extracted mercaptan compounds to disulfide compounds. 
     
     
         17 . The process of  claim 1 , wherein the rich aqueous extraction medium is combined with a wash oil, prior to being passed to the catalytic oxidation zone. 
     
     
         18 . The process of  claim 2 , wherein the oxidation effluent is combined with a wash oil, prior to separating, from the oxidation zone effluent, a regenerated extraction medium, a disulfide rich organic product, and an off gas. 
     
     
         19 . A process for treating a hydrocarbon feed comprising mercaptan compounds and oxygen, the process comprising:
 (a) extracting at least a portion of the mercaptan compounds in a rich aqueous extraction medium essentially free of circulating oxidation catalyst.   
     
     
         20 . The process of  claim 19 , wherein the hydrocarbon feed comprises fuel gas or a hydrocarbon fraction obtained from a fluid catalytic cracking (FCC) process and the extracting step comprises contacting the hydrocarbon feed with a lean aqueous extraction medium comprising sodium hydroxide having a concentration from about 5% to about 20% by weight to provide a treated hydrocarbon product that is essentially free of disulfide compounds.