Carbon dioxide/carbon monoxide electroreduction system with gas-liquid recirculation

Abstract

Systems and processes designed for gas and liquid recirculation for continuous carbon dioxide reduction to different target products are disclosed. The systems and processes include gas regeneration through the anodic oxidation of carbon monoxide and hydrogen gas. Advantageously, the target chemical products produced using said systems and processes are substantially pure without requiring any separation processes to remove unreacted reactants or unwanted byproducts.

1 .- 44 . (canceled) 
     
     
         45 . A continuous process to convert carbon dioxide to target product without requiring any separation processes to remove unreacted reactants or unwanted byproducts, said process comprising:
 (a) producing target product from carbon dioxide at a cathode with simultaneous anodic oxidation of water for a time T1 using a flow-cell electrolyzer comprising three compartments, wherein a first compartment and a second compartment are separated by a gas diffusion electrode (GDE) coated with cathodic electrocatalyst material and the second compartment and a third compartment are separated by an anion exchange membrane (AEM), and wherein the third compartment is in direct contact with an anode, wherein the first compartment is in fluid communication with a gas recirculation system, the third compartment via a gas-liquid separator, or both, wherein the second compartment is in fluid communication with a catholyte recirculation system comprising a catholyte, and the third compartment is in fluid communication with an anolyte recirculation system comprising an anolyte and the gas-liquid separator,   wherein the producing comprises:
 adjusting a first valve so that a gas comprising carbon dioxide from the gas recirculation system is introduced to the first compartment for contact with the GDE; 
 applying a voltage across the GDE and the anode of the flow-cell electrolyzer, 
   wherein carbon dioxide in the gas that is in contact with the GDE in the first compartment electrochemically reacts and produces target product in the catholyte, and water is oxidized at the anode;
 removing a mixture of gas from the first compartment and flowing same to the gas recirculation system, wherein the mixture of gas comprises CO 2 , H 2  and CO and is quantitatively compensated with additional carbon dioxide, and is reintroduced to the first compartment following carbon dioxide concentration adjustment for multi-pass electroreduction to produce additional target product in the catholyte, 
   wherein over time T1, the percent of H 2  and CO increases and the percent CO 2  decreases in the mixture of gas, relative to the total amount of gas;   (b) regenerating the mixture of gas for a time T2 to decrease the percent H 2  and CO and increase the percent CO 2  in the mixture of gas from (a), relative to the total amount of gas, wherein the regenerating comprises:
 adjusting the first valve so that the mixture of gas from the gas recirculation system is introduced to the third compartment for contact with the anode; 
 oxidizing, at the anode, hydrogen gas and/or carbon monoxide gas present in the mixture of gas to CO 2  and H 2 O, wherein the anodic potential during step (b) oxidation is decreased to be less than that during step (a) oxidation; 
 flowing the anolyte comprising the mixture of gas out of the third compartment and separating the mixture of gas from the anolyte using the gas-liquid separator; 
 directing the mixture of gas from the gas-liquid separator to the first compartment for an electrochemical reaction at the GDE to produce target product in the catholyte; 
 removing the mixture of gas from the first compartment and passing same through the gas recirculation system, wherein the mixture of gas comprising CO 2 , H 2  and CO is quantitatively compensated with additional carbon dioxide for reintroduction to the third compartment; and 
   (c) repeating step (a) and step (b) for continuous CO 2  to target product conversion.   
     
     
         46 . The process of  claim 45 , wherein an applied cell voltage during step (a) is in a range of about 1.5 V to about 10V. 
     
     
         47 . The process of  claim 45 , wherein a current density during step (a) is about 1 mA/cm 2  to about 5 A/cm 2 . 
     
     
         48 . The process of  claim 45 , wherein carbon dioxide is reduced at the GDE and H 2  (g) and/or CO(g) is oxidized at the anode in step (b) at a cell voltage of about 0.5V to about 2.3V. 
     
     
         49 . The process of  claim 45 , wherein an anodic potential in step (b) is not greater than 1.23 V. 
     
     
         50 . The process of  claim 45 , wherein a stabilized current density in step (b) is about 1 mA/cm 2  to about 3 A/cm 2 , depending on the voltage applied. 
     
     
         51 . The process of  claim 45 , wherein the gas recirculation system comprises at least one of at least one mass flow controller, at least one pressure controller, a source of carbon dioxide for quantitative compensation, a pressure-buffering reservoir for storage, a gas pump, a moisture trap, at least one valve, and a vent. 
     
     
         52 . The process of  claim 45 , wherein the catholyte recirculation system further comprises a container comprising catholyte electrolyte solution, at least one pumping means, and a product container for target product produced during the electrochemical reaction. 
     
     
         53 . The process of  claim 45 , wherein the anolyte recirculation system further comprises a container comprising anolyte electrolyte solution and at least one pumping means. 
     
     
         54 . The process of  claim 45 , wherein the GDE is coated with tin oxide or bismuth nanopowders. 
     
     
         55 . The process of  claim 45 , wherein the anode is a dimensionally stable anode (DSA). 
     
     
         56 . The process of  claim 45 , wherein the catholyte electrolyte solution comprises at least one species selected from the group consisting of sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, cesium bicarbonate, lithium bicarbonate, sodium carbonate, potassium carbonate, lithium carbonate, calcium carbonate, ammonium carbonate, sodium sulfate, potassium sulfate, lithium sulfate, and ammonium sulfate. 
     
     
         57 . The process of  claim 45 , wherein the catholyte and the anolyte comprise the same electrolytic component or the catholyte and the anolyte comprise different electrolytic components. 
     
     
         58 . The process of  claim 45 , wherein the catholyte and the anolyte both comprise a bicarbonate solution. 
     
     
         59 . The process of  claim 45 , wherein the target product is selected from the group consisting of formaldehyde, formate salts, formic acid, acetaldehyde, methanol, ethanol, n-propanol, isopropanol, butanol, acetate ions, and acetone. 
     
     
         60 . The process of  claim 45 , wherein the target product comprises the formate ion. 
     
     
         61 . The process of  claim 45 , wherein the catholyte comprising target product is recirculated through the catholyte recirculation system and accumulated until reaching a targeted concentration, wherein thereafter the target product is sent to a target product container. 
     
     
         62 . The process of  claim 61 , wherein the targeted concentration is greater than 100 mmol/L. 
     
     
         63 . A system comprising:
 a flow-cell electrolyzer comprising three compartments, wherein a first compartment and a second compartment are separated by a gas diffusion electrode (GDE) coated with cathodic electrocatalyst material and the second compartment and a third compartment are separated by an anion exchange membrane (AEM), and wherein the third compartment is in direct contact with an anode,   a gas recirculation system in fluid communication with a first outlet of the first compartment and, using a first valve, either a first inlet of the first compartment or a third inlet of the third compartment;   a catholyte container in fluid communication with a second inlet and a second outlet of the second compartment;   an gas-liquid separator communicatively connected to a third outlet of the third compartment, wherein liquid from the gas-liquid separator is communicatively connected to the third inlet of the third compartment and wherein gas from the gas-liquid separator is communicatively connected to a second valve, wherein the second valve can be adjusted such that the gas can be introduced to the first inlet of the first compartment.