Combined co2 capture and conversion method and system

Abstract

Systems and methods are described that utilize mixed conductive membranes in conjunction with solid oxide electrolysis in a single unit operation. The mixed conductive membranes of the systems are high-flux electrochemical separation membranes that can selectively and efficiently capture CO 2 from a source gas, e.g., a flue gas or fuel gas, by transporting the CO 2 across the membrane in the form of carbonate ions followed by oxidation of the carbonate-ions at the second side of the membrane to reform CO 2 in a capture stream. The solid oxide electrolysis can be immediately downstream of the capture system to convert the CO 2 into CO and H 2 O into H 2 , for example thereby forming syngas thereby capturing CO 2 and converting it to a more useful form.

What is claimed is: 
     
         1 . A method for selective capture and conversion of carbon dioxide from a gaseous stream comprising:
 contacting a feed stream with a mixed carbonate ion conducting membrane, the mixed carbonate ion conducting membrane having a first side and a second opposite side, the feed stream contacting the first side, the feed stream including carbon dioxide, the carbon dioxide being reduced to form carbonate ion upon contact between the feed stream and the first side, the carbonate ion migrating across the mixed carbonate ion conducting membrane to the second side;   contacting the second side of the mixed carbonate ion conducting membrane with a capture gas stream, the carbonate ion being oxidized at the second side of the mixed carbonate ion conducting membrane to form carbon dioxide, the carbon dioxide being collected by the capture gas stream;   immediately downstream of the second side of the mixed carbonate ion conducting membrane, contacting the capture gas stream with an electrode of a solid oxide electrolysis cell, the capture gas stream containing the carbon dioxide and steam, the carbon dioxide and steam of the capture gas stream being reduced at the electrode to form carbon monoxide and hydrogen and oxide ion, the oxide ion migrating across an electrolyte of the solid oxide electrolysis cell.   
     
     
         2 . The method of  claim 1 , wherein the feed stream is a precombustion gaseous stream. 
     
     
         3 . The method of  claim 1 , wherein the feed stream comprises hydrogen (H 2 ). 
     
     
         4 . The method of  claim 1 , wherein the feed stream is a post-combustion flue gas stream. 
     
     
         5 . The method of  claim 1 , wherein the feed stream comprises oxygen (O 2 ) and/or nitrogen (N 2 ). 
     
     
         6 . The method of  claim 1 , wherein the mixed carbonate ion conducting membrane conducts oxide ion in addition to the carbonate ion. 
     
     
         7 . The method of  claim 1 , wherein the mixed carbonate ion conducting membrane conducts electrons in addition to the carbonate ion. 
     
     
         8 . The method of  claim 1 , wherein the capture gas stream comprises water. 
     
     
         9 . The method of  claim 1 , wherein the capture gas stream comprises carbon monoxide and hydrogen (H 2 ). 
     
     
         10 . The method of  claim 9 , wherein the capture gas stream comprises syngas. 
     
     
         11 . A carbon dioxide capture and conversion system comprising:
 a feed stream;   a mixed carbonate ion conducting membrane comprising a first side and a second side, the first side of the mixed carbonate ion conducting membrane having a first side and a second opposite side, the first side being in fluid communication with the feed stream;   a capture gas stream, the capture gas stream being in fluid communication with the second side of the mixed carbonate ion conducting membrane;   a solid oxide electrolysis cell immediately downstream of the mixed carbonate ion conducting membrane, the solid oxide electrolysis cell comprising a first electrode, an electrolyte, and a second electrode, the first electrode being in fluid communication with the capture gas stream.   
     
     
         12 . The system of  claim 11 , wherein the mixed carbonate ion conducting membrane also conducts oxide ions. 
     
     
         13 . The system of  claim 12 , wherein the mixed carbonate ion conducting membrane comprises a doped cerium oxide. 
     
     
         14 . The system of  claim 13 , wherein the dopant comprises Sm 2 O 3 . 
     
     
         15 . The system of  claim 11 , wherein the mixed carbonate ion conducting membrane also conducts electrons. 
     
     
         16 . The system of  claim 15 , wherein the mixed carbonate ion conducting membrane comprises silver. 
     
     
         17 . The system of  claim 11 , wherein the mixed carbonate ion conducting membrane comprises an alkali metal or an alkaline earth metal salt, or a mixture of such salts. 
     
     
         18 . The system of  claim 11 , wherein the solid oxide electrolysis cell comprises an electrolyte that conducts oxide ions. 
     
     
         19 . The system of  claim 11 , the second electrode of the solid oxide electrolysis cell being in fluid communication of the feed stream. 
     
     
         20 . The system of  claim 11 , wherein the system is a unit operation of a syngas formation process. 
     
     
         21 . The system of  claim 11 , wherein the system is a unit operation of a steam reforming process. 
     
     
         22 . The system of  claim 11 , wherein the system is a unit operation that is downstream of a water-gas shift reaction.