Electrochemical Process and Apparatus Therefor

Abstract

A process and apparatus are provided for the electrochemical reduction of carbon dioxide to formate. According one embodiment, an electrochemical process includes the catalytic electro-chemical reduction of carbon dioxide to formate utilizing a cathodic catalyst comprising tin and zinc, the zinc comprising between three and six weight percent of the catalyst. In a further embodiment, an electrochemical reactor for the electrochemical reduction of carbon dioxide to formate comprises a cathodic catalyst comprising tin and zinc, the zinc comprising between three and six weight percent of the catalyst.

We claim:  
     
         1 . A process, comprising:
 (a) introducing an anolyte into an anolyte compartment of an electrochemical reactor, the anolyte compartment at least partially containing an anode;   (b) introducing a catholyte into a catholyte compartment of the electrochemical reactor, the catholyte compartment separated from the anolyte compartment by a membrane, the catholyte compartment at least partially containing a cathode, the cathode comprising a cathodic catalyst, the catalyst comprising:
 tin; and 
 zinc, wherein the zinc comprises between three weight percent and six weight percent of the cathodic catalyst; 
   (c) introducing carbon dioxide into the catholyte compartment of the electrochemical reactor; and   (d) impressing a DC voltage across the anode and the cathode, whereby at least a portion of the carbon dioxide is converted to formate.   
     
     
         2 . The process of  claim 1 , the conversion of carbon dioxide to formate accomplished at a Faradaic Efficiency of between 65 percent and 68 percent. 
     
     
         3 . The process of  claim 2 , the Faradaic Efficiency accomplished at a potential of tween −1.70 V SCE  and −1.90 V SCE . 
     
     
         4 . The process of  claim 1 , wherein the catholyte is formulated for the electrochemical reduction of carbon dioxide to formate. 
     
     
         5 . The process of  claim 4 , wherein the catholyte comprises a solution selected from the group consisting of:
 2M potassium chloride at a pH of 5.5;   2M sodium chloride at a pH of 5.3;   0.5M potassium bicarbonate at a pH of 7.5;   2M potassium chloride at a pH of 2.5;   0.5M potassium sulfate at a pH of 6.5; and   0.5M sodium sulfate at a pH of 5.5.   
     
     
         6 . The process of  claim 1 , wherein the anolyte is formulated for the electrochemical reduction of carbon dioxide to formate. 
     
     
         7 . The process of  claim 6 , wherein the anolyte comprises a solution selected from the group consisting of:
 1M sodium hydroxide; and   0.5M sulfuric acid.   
     
     
         8 . The process of  claim 1 , wherein the cathode is porous, and further comprising:
 (a) introducing carbon dioxide from a gas compartment in fluid communication with the cathode into the cathode prior to introducing the carbon dioxide into the catholyte.   
     
     
         9 . The process of  claim 8 , the catholyte compartment containing a porous, absorbent nonconductive pad, the pad adjacent to the membrane side of the cathode. 
     
     
         10 . The process of  claim 9 , further comprising:
 (a) introducing at least a portion of the catholyte into the porous, absorbent nonconductive pad.   
     
     
         11 . The process of  claim 8 , further comprising:
 (a) introducing carbon dioxide from the gas compartment into a diffuser prior to introducing the carbon dioxide gas into the cathode, the diffuser adjacent to the gas compartment side of the cathode.   
     
     
         12 . The process of  claim 8 , wherein the catholyte is formulated for the electrochemical reduction of carbon dioxide to formate. 
     
     
         13 . The process of  claim 12 , wherein the catholyte comprises a solution selected from the group consisting of:
 2M potassium chloride at a pH of 5.5;   2M sodium chloride at a pH of 5.3;   0.5M potassium bicarbonate at a pH of 7.5;   2M potassium chloride at a pH of 2.5;   0.5M potassium sulfate at a pH of 6.5; and   0.5M sodium sulfate at a pH of 5.5.   
     
     
         14 . The process of  claim 8 , wherein the anolyte is formulated for the electrochemical reduction of carbon dioxide to formate. 
     
     
         15 . The process of  claim 14  wherein the anolyte comprises a solution selected from the group consisting of:
 1M sodium hydroxide; and 
 0.5M sulfuric acid. 
 
     
     
         16 . An apparatus, comprising:
 a container;   a membrane, the membrane positioned within the container, the membrane dividing the container into a catholyte compartment and an anolyte compartment;   a cathode, the cathode positioned at least partially within the catholyte compartment, the cathode comprising a cathodic catalyst, the cathodic catalyst comprising:
 tin; and 
 zinc, wherein the zinc comprises between three weight percent and six weight percent of the cathodic catalyst; and 
   an anode, the anode positioned at least partially within the anolyte compartment.   
     
     
         17 . The apparatus of  claim 16 , wherein the cathode is porous, and further comprising a gas compartment, the gas compartment in fluid communication with the cathode. 
     
     
         18 . The apparatus of  claim 17 , further comprising a porous, absorbent nonconductive pad, the pad adjacent to the membrane side of the cathode. 
     
     
         19 . The apparatus of  claim 17 , further comprising a diffuser adjacent to the gas compartment side of the cathode. 
     
     
         20 . A process, comprising:
 (a) introducing a catholyte into the catholyte compartment of  claim 16 ;   (b) introducing an anolyte into the anolyte compartment of  claim 16 ;   (c) impressing a DC voltage across the anode and the cathode of  claim 16 ; and   (d) withdrawing formate from the cathode compartment of  claim 16 .