Low NOx carbon monoxide combustion promoter

Abstract

The amount of NOx formed during regeneration of a cracking catalyst in the presence of a metallic carbon monoxide combustion catalyst is decreased by utilizing as the carbon monoxide combustion catalyst rhodium and/or iridium on an oxide support such as alumina.

1 . A process for cracking hydrocarbons comprising: 
 (1) cycling particulate cracking catalyst between a cracking zone and a catalyst regeneration zone, in a catalytic cracking system;    (2) cracking said hydrocarbons in contact with said catalyst at cracking conditions in said cracking zone whereby coke is formed on said catalyst;    (3) burning coke off said catalyst with an oxygen-containing gas at regeneration, and, wherein a flue gas from said catalyst regeneration zone includes carbon monoxide    (4) combusting said carbon monoxide in said regeneration zone by contacting said flue gas with a CO oxidation promoter consisting essentially of rhodium and/or iridium supported on a particulate, non-zeolitic oxide solid.    
     
     
         2 . A process according to  claim 1  wherein said CO oxidation promoter consists essentially of rhodium.  
     
     
         3 . A process according to  claim 1  wherein said CO oxidation promoter consists essentially of iridium.  
     
     
         4 . A process according to  claim 1  wherein said CO oxidation promoter consists essentially of rhodium and iridium.  
     
     
         5 . A process according to  claim 1  wherein said particulate oxide solid includes at least one of alumina and silica.  
     
     
         6 . A process according to  claim 1  wherein said particulate oxide solid includes alumina.  
     
     
         7 . A process according to  claim 1  wherein said CO oxidation promoter is a particulate solid separate from said particulate cracking catalyst.  
     
     
         8 . The process of  claim 7  wherein said CO oxidation promoter circulates between the cracking zone and regeneration zone.  
     
     
         9 . A process according to  claim 7  wherein said CO oxidation promoter is maintained in said regeneration zone.  
     
     
         10 . A process according to  claim 8  wherein said CO oxidation promoter is added in the fresh state to the inventory of particulate cracking catalyst.  
     
     
         11 . A process according to  claim 9  wherein said CO oxidation promoter is added in the fresh state to said regeneration zone.  
     
     
         12 . A process according to  claim 1  wherein the concentration of rhodium and/or iridium on said particulate oxide solid ranges from 0.01 to 1% by weight.  
     
     
         13 . A process according to  claim 12  wherein said rhodium and\or iridium is present on said particulate oxide solid in amounts of 0.02 to 0.5% by weight.  
     
     
         14 . A process according to  claim 1  wherein said rhodium and/or iridium is present in the form of free metal, or the oxides, sulfides, or sulfates thereof.  
     
     
         15 . A process according to  claim 1  wherein said cracking is performed in the absence of externally-supplied hydrogen.  
     
     
         16 . A process according to  claim 1  wherein said hydrocarbons contain nitrogen-containing compounds.  
     
     
         17 . A process according to  claim 2  wherein said particulate oxide solid is alumina.  
     
     
         18 . A process according to  claim 3  wherein said particulate oxide solid is alumina.  
     
     
         19 . A process according to  claim 18  wherein said CO oxidation promoter further includes an alkaline earth oxide.  
     
     
         20 . A process according to  claim 19  wherein said alkaline earth oxide is BaO.  
     
     
         21 . A process according to  claim 6  wherein the said support is substantially α-alumina.