Production of Alkali Bicarbonate and Alkali Hydroxide From Alkali Carbonate in an Electrolyte Cell.

Abstract

Alkali bicarbonate is synthesized in an electrolytic cell from alkali carbonate. The electrolytic cell includes an alkali ion conductive membrane positioned between an anolyte compartment configured with an anode and a catholyte compartment configured with a cathode. The alkali conductive membrane selectively transports alkali ions and prevents the transport of anions produced in the catholyte compartment. An aqueous alkali carbonate solution is introduced into the anolyte compartment and electrolyzed at the anode to produce carbon dioxide and/or hydrogen ions which react with alkali carbonate to produce alkali bicarbonate. The alkali bicarbonate is recovered by filtration or other separation techniques. When the catholyte solution includes water, pure alkali hydroxide is produced. When the catholyte solution includes methanol, pure alkali methoxide is produced.

1 . A process for synthesizing alkali bicarbonate comprising:
 providing an electrolytic cell comprising an alkali ion conductive membrane positioned between an anolyte compartment configured with an anode and a catholyte compartment configured with a cathode, said alkali conductive membrane being configured to selectively transport alkali ions and prevent the transport of anions produced in the catholyte compartment;   introducing aqueous alkali carbonate into the anolyte compartment;   electrolyzing aqueous alkali carbonate at the anode according to one or both of the following reactions:
   H 2 O→2H + +2 e   − +½O 2  
 
   M 2 CO 3 →2M + +2 e   − +CO 2 +½O 2  
 
   
       wherein M is an alkali metal selected from Li, Na, and K;
 reacting either or both of the H +  or CO 2  produced above with aqueous alkali carbonate according to one or both of the following reactions:
   CO 2 +M 2 CO 3 +H 2 O→2MHCO 3 (precipitate)
 
   H + +M 2 CO 3 →M + +MHCO 3 (precipitate)
 
 
 
       and
 recovering the alkali bicarbonate produced. 
 
     
     
         2 . The process for synthesizing alkali bicarbonate according to  claim 1 , further comprising the step of maintaining the pH in the anolyte compartment at a pH in the range of about 7 to about 11. 
     
     
         3 . The process of  claim 2 , further comprising the step of maintaining the pH in the anolyte compartment at a pH in the range of about 7.5 to about 9.5. 
     
     
         4 . The process for synthesizing alkali bicarbonate according to  claim 2 , wherein the pH in the anolyte compartment is maintained by controlling the concentration of alkali carbonate introduced into the anolyte compartment and the cell operation temperature. 
     
     
         5 . The process for synthesizing alkali bicarbonate according to  claim 1 , further comprising the step of maintaining the temperature in the anolyte compartment at a temperature in the range of 20° C. to 70° C. 
     
     
         6 . The process for synthesizing alkali bicarbonate according to  claim 1 , further comprising:
 reacting CO 2  with aqueous alkali carbonate outside the anolyte compartment.   
     
     
         7 . The process for synthesizing alkali bicarbonate according to  claim 5 , further comprising:
 using the CO 2  recovered from the anolyte compartment; and   reacting that CO 2  with aqueous alkali carbonate outside the anolyte compartment.   
     
     
         8 . The process for synthesizing alkali bicarbonate according to  claim 1 , further comprising:
 introducing water and optionally a dilute alkali hydroxide solution into the catholyte compartment;   electrolyzing the water at the cathode according to the following reaction:
   2M + +2H 2 O+2 e   − →2MOH+H 2  
 
   
       and
 recovering the alkali hydroxide and hydrogen produced. 
 
     
     
         9 . The process for synthesizing alkali bicarbonate according to  claim 1 , further comprising:
 introducing methanol into the catholyte compartment;   electrolyzing the methanol solution at the cathode in the presence of alkali ions transported from the anolyte compartment across the alkali ion conductive membrane according to the following reaction:
   2M + +2CH 3 OH+2 e   − →2MOCH 3 +H 2  
 
   
       and
 recovering the alkali methoxide and hydrogen produced. 
 
     
     
         10 . The process for synthesizing alkali bicarbonate according to  claim 1 , wherein the alkali ion conductive membrane is an alkali ion super ion conductive membrane selected from NaSICON or NaSICON-type membranes, LiSICON or a LiSICON-type membranes, and KSICON or KSICON-type membranes. 
     
     
         11 . The process for synthesizing alkali bicarbonate according to  claim 1 , further comprising pressurizing the anolyte compartment to promote carbon dioxide dissolution and reaction to form bicarbonate. 
     
     
         12 . The process for synthesizing alkali bicarbonate according to  claim 1 , wherein the alkali metal is sodium. 
     
     
         13 . A process for synthesizing pure alkali hydroxide from alkali carbonate comprising:
 providing an electrolytic cell comprising an alkali ion conductive membrane positioned between an anolyte compartment configured with an anode and a catholyte compartment configured with a cathode, said alkali conductive membrane being configured to selectively transport alkali ions and prevent the transport of anions produced in the catholyte compartment;   introducing aqueous alkali carbonate into the anolyte compartment;   electrolyzing aqueous alkali carbonate at the anode according to one or both of the following reactions:
   H 2 O→2H + +2 e   − +½O 2  
 
   M 2 CO 3 →2M + +2 e   − +CO 2   +½O   2  
 
   
       wherein M is an alkali metal selected from Li, Na, and K;
 introducing water and optionally a dilute alkali hydroxide solution into the catholyte compartment; 
 electrolyzing the water at the cathode according to the following reaction:
   2M + +2H 2 O+2 e   − →2MOH+H 2  
 
 
 
       and
 recovering the pure alkali hydroxide produced. 
 
     
     
         14 . The process for synthesizing pure alkali hydroxide from alkali carbonate according to  claim 13 , further comprising recovering the hydrogen produced. 
     
     
         15 . The process for synthesizing pure alkali hydroxide from alkali carbonate according to  claim 13 , further comprising:
 reacting either or both of the H +  or CO 2  produced above with aqueous alkali carbonate according to one or both of the following reactions:
   CO 2 +M 2 CO 3 +H 2 O→2 MHCO 3 (precipitate)
 
   H + +M 2 CO 3 →M + +MHCO 3 (precipitate)
 
   
       and
 recovering the alkali bicarbonate produced. 
 
     
     
         16 . The process for synthesizing pure alkali hydroxide from alkali carbonate according to  claim 13 , wherein the alkali ion conductive membrane is an alkali ion super ion conductive membrane selected from NaSICON or NaSICON-type membranes, LiSICON or a LiSICON-type membranes, and KSICON or KSICON-type membranes. 
     
     
         17 . The process for synthesizing alkali bicarbonate according to  claim 13 , wherein the alkali metal is sodium. 
     
     
         18 . A process for synthesizing pure alkali methoxide from alkali carbonate and methanol comprising:
 providing an electrolytic cell comprising an alkali ion conductive membrane positioned between an anolyte compartment configured with an anode and a catholyte compartment configured with a cathode, said alkali conductive membrane being configured to selectively transport alkali ions and prevent the transport of anions produced in the catholyte compartment;   introducing aqueous alkali carbonate into the anolyte compartment;   electrolyzing aqueous alkali carbonate at the anode according to one or both of the following reactions:
   H 2 O→2H + +2 e   − +½O 2  
 
   M 2 CO 3 →2M + +2 e   − +CO 2 +½O 2  
 
   
       wherein M is an alkali metal selected from Li, Na, and K;
 introducing methanol into the catholyte compartment; 
 electrolyzing the methanol solution at the cathode in the presence of alkali ions transported from the anolyte compartment across the alkali ion conductive membrane according to the following reaction:
   2M + +2CH 3 OH+2 e   − →2MOCH 3 +H 2  
 
 
 
       and
 recovering the pure alkali methoxide produced. 
 
     
     
         19 . The process for synthesizing pure alkali methoxide from alkali carbonate and methanol according to  claim 18 , further comprising recovering the hydrogen produced. 
     
     
         20 . The process for synthesizing pure alkali methoxide from alkali carbonate and methanol according to  claim 18 , further comprising:
 reacting either or both of the H +  or CO 2  produced above with aqueous alkali carbonate according to one or both of the following reactions:
   CO 2 +M 2 CO 3 +H 2 O→2MHCO 3 (precipitate)
 
   H + +M 2 CO 3 →M + +MHCO 3 (precipitate)
 
   
       and
 recovering the alkali bicarbonate produced. 
 
     
     
         21 . The process for synthesizing pure alkali methoxide from alkali carbonate and methanol according to  claim 18 , wherein the alkali ion conductive membrane is an alkali ion super ion conductive membrane selected from NaSICON or NaSICON-type membranes, LiSICON or a LiSICON-type membranes, and KSICON or KSICON-type membranes. 
     
     
         22 . The process for synthesizing pure alkali methoxide from alkali carbonate and methanol according to  claim 18 , wherein the alkali metal is sodium.