Catalytic adsorbents for mercury removal from flue gas and methods of manufacture therefor

Abstract

The present invention provides catalytic adsorbents formed from doping activated carbon with a dispersed halide salt. The catalytic adsorbents provided herein are stable and harmless at room temperature, yet allow for chemical adsorption at elevated temperatures typical of those for flue gas streams. The present invention also provides methods of manufacturing the doped activated carbon adsorbents.

1 . A catalytic adsorbent composition for removing mercury from a flue gas stream at elevated temperatures, comprising: 
 an activated carbon having a halide salt dispersed thereon, the halide salt having a cation and an anion.    
   
   
       2 . The composition of  claim 1 , wherein the cation is selected from the group comprising: an alkaline metal, an alkaline earth metal, and a transition metal.  
   
   
       3 . The composition of  claim 2 , wherein the cation is selected from the group consisting of: Na, Mg, Ca, Cu and K.  
   
   
       4 . The composition of  claim 1 , wherein the anion is selected from the group comprising: bromide and chloride.  
   
   
       5 . The composition of  claim 1 , wherein the halide salt is selected from the group consisting of: NaCl, KCl, CaCl 2 , CuCl 2 , CuBr 2 , NaBr, KBr, CaBr 2 , MgBr 2  and mixtures thereof.  
   
   
       6 . The composition of  claim 5 , wherein the halide salt is NaBr, KBr or mixtures thereof.  
   
   
       7 . A method of making a catalytic adsorbent for use in the adsorption of mercury from flue gas streams at elevated temperatures, comprising: 
 placing a powder activated carbon in an aqueous solution containing a halide salt having a cation and an anion to form a mixture;    stirring the mixture until a homogeneous slurry is formed;    drying the powder activated carbon such that water from the aqueous solution evaporates and the halide salt is dispersed on the surface of the powder activated carbon.    
   
   
       8 . The method of  claim 7 , wherein the cation is selected from the group comprising: an alkaline metal, an alkaline earth metal, and a transition metal.  
   
   
       9 . The method of  claim 8 , wherein the cation is selected from the group consisting of: Na, Mg, Ca, Cu and K.  
   
   
       10 . The method of  claim 7 , wherein the anion is selected from the group comprising: bromide and chloride.  
   
   
       11 . The method of  claim 7 , wherein the halide salt is selected from the group consisting of: NaCl, CaCl 2 , CuCl 2 , CuBr 2 , NaBr, KBr, CaBr 2 , MgBr 2  and mixtures thereof.  
   
   
       12 . The method of  claim 11 , wherein the halide salt is NaBr, KBr or mixtures thereof.  
   
   
       13 . A method of making catalytic adsorbent for use in the adsorption of mercury from flue gas streams at elevated temperatures, comprising: 
 injecting a presoaked carbonaceous feedstock into a reaction chamber; and    injecting at least one oxidizing gas into the reaction chamber;    injecting steam into the reaction chamber,    wherein the carbonaceous feedstock, the air and the steam are injected into the reaction chamber under conditions and for a residence time sufficient to form an activated carbon having a halide salt having a cation and an anion dispersed on the surface of the activated carbon.    
   
   
       14 . The method of  claim 13 , wherein the oxidizing gas comprises: air, oxygen, steam, nitrogen or combinations thereof.  
   
   
       15 . The method of  claim 13 , wherein the reaction chamber is a tube furnace.  
   
   
       16 . The method of  claim 13 , wherein the reaction chamber is a fluidized bed reactor.  
   
   
       17 . The method of  claim 13 , wherein the cation is selected from the group comprising: an alkaline metal, an alkaline earth metal, and a transition metal.  
   
   
       18 . The method of  claim 17 , wherein the cation is selected from the group consisting of: Na, Ca, Cu and K.  
   
   
       19 . The method of  claim 13 , wherein the anion is selected from the group comprising: bromide and chloride.  
   
   
       20 . The method of  claim 13 , wherein the halide salt is selected from the group consisting of: NaCl, KCl, CaCl 2 , CuCl 2 , CuBr 2 , NaBr, KBr, CaBr 2 , MgBr 2  or mixtures thereof.  
   
   
       21 . The method of  claim 19 , wherein the halide salt is NaBr, KBr or mixtures thereof.  
   
   
       22 . A method for removing mercury from a gas stream at an elevated temperature, the method comprising: 
 injecting a catalytic adsorbent containing an activated carbon and a dopant, the dopant having a cation and an anion into the gas stream;    adsorbing mercury onto the catalytic adsorbent; and    removing the mercury containing catalytic adsorbent from the gas stream.    
   
   
       23 . The method of  claim 22 , wherein the gas stream contains oxidative gas, acidic gas or a combination thereof.  
   
   
       24 . The method of  claim 22 , wherein the gas stream contains an inert gas.  
   
   
       25 . The method of  claim 24 , wherein the inert gas comprises nitrogen.