Device and method for the flexible use of electricity

Abstract

An electrolysis cell for chlor-alkali electrolysis, having an anode half-cell, a cathode half-cell and a cation exchange membrane that separates the anode half-cell and the cathode half-cell from one another, an anode arranged in the anode half-cell for evolution of chlorine, an oxygen-consuming electrode arranged in the cathode half-cell as the cathode, a catholyte space which is formed between the cation exchange membrane and the oxygen-consuming cathode, and through which electrolyte flows, a gas space adjoining the oxygen-consuming electrode at a surface facing away from the catholyte space, a conduit for supply of gaseous oxygen to this gas space, a second cathode for generation of hydrogen arranged within the catholyte space and at least one conduit for purging of the gas space with inert gas, enables flexible use of power in a method in which, when power supply is low, the oxygen-consuming electrode is supplied with gaseous oxygen and oxygen is reduced at the oxygen-consuming electrode at a first cell voltage, and when power supply is high, the oxygen-consuming electrode is not supplied with oxygen and hydrogen is generated at the second cathode at a second cell voltage which is higher than the first cell voltage.

1 - 15 . (canceled) 
     
     
         16 . A device for flexible use of electrical power, comprising:
 a) an electrolysis cell for chlor-alkali electrolysis having an anode half-cell, a cathode half-cell and a cation exchange membrane that separates the anode half-cell and the cathode half-cell from one another;   b) an anode arranged in the anode half-cell for evolution of chlorine;   c) an oxygen-consuming electrode arranged in the cathode half-cell as a first cathode;   d) a catholyte space which is formed between the cation exchange membrane and the oxygen-consuming electrode, through which catholyte space electrolyte flows;   e) a gas space adjoining the oxygen-consuming electrode at a surface facing away from the catholyte space, and a conduit for supply of gaseous oxygen to this gas space;   f) a second cathode for generation of hydrogen arranged within the catholyte space; and   g) at least one conduit for purging of the gas space with inert gas.   
     
     
         17 . The device of  claim 16 , wherein the oxygen-consuming electrode and the second cathode have separate power connections. 
     
     
         18 . The device of  claim 16 , further comprising a conduit for withdrawing inert gas from the gas space, and a sensor arranged at this conduit for measuring the content of oxygen in the inert gas. 
     
     
         19 . The device of  claim 16 , further comprising at least one conduit for purging the catholyte space with inert gas. 
     
     
         20 . The device of  claim 16 , wherein the second cathode abuts the cation exchange membrane. 
     
     
         21 . The device of  claim 16 , wherein the oxygen-consuming electrode has a porous hydrophobic gas diffusion layer containing metallic silver and a fluorinated polymer. 
     
     
         22 . The device of  claim 16 , comprising a plurality of electrolysers arranged in parallel, each of the electrolysers comprising a plurality of electrolysis cells each having a gas space, and a common conduit for supply of gaseous oxygen to the gas spaces of the electrolysis cells of the electrolyser and a common conduit for purging of the gas spaces of the electrolysis cells of the electrolyser with inert gas, wherein the device comprises separate conduits for supply of oxygen to the electrolysers and separate conduits for supply of inert gas to the electrolysers. 
     
     
         23 . A method for flexible use of electrical power, wherein chlorine is produced by chlor-alkali electrolysis in a device according to  claim 16 , and wherein:
 a) when power supply is low, the oxygen-consuming electrode is supplied with gaseous oxygen, and oxygen is reduced at the oxygen-consuming electrode at a first cell voltage; and   b) when power supply is high, the oxygen-consuming electrode is not supplied with oxygen, and hydrogen is generated at the second cathode at a second cell voltage which is higher than the first cell voltage.   
     
     
         24 . The method of  claim 23 , wherein, when changing from hydrogen generation at the second cell voltage to oxygen reduction at the first cell voltage, the cell voltage is reduced until essentially no current flows, and the gas space is purged with an inert gas, before gaseous oxygen is supplied to the oxygen-consuming electrode. 
     
     
         25 . The method of  claim 23 , wherein, when changing from oxygen reduction at the first cell voltage to hydrogen generation at the second cell voltage, the cell voltage is reduced until essentially no current flows, and the gas space is purged with an inert gas, before hydrogen is generated at the second cathode. 
     
     
         26 . The method of  claim 23 , comprising the steps of:
 a) defining a threshold value for a power supply;   b) determining the power supply;   c) operating the electrolysis cell with the first cell voltage with supply of gaseous oxygen to the oxygen-consuming electrode when the power supply is below the threshold value and operating the electrolysis cell with the second cell voltage without supply of oxygen to the oxygen-consuming electrode when the power supply is above the threshold value; and   d) repeating steps b) and c).   
     
     
         27 . The method of  claim 23 , wherein nitrogen is used as the inert gas. 
     
     
         28 . The method of  claim 23 , wherein, after a switchover from oxygen reduction at the first cell voltage to hydrogen generation at the second cell voltage, a gas mixture comprising hydrogen and inert gas is withdrawn from the cathode half-cell and hydrogen is separated from this gas mixture through a membrane. 
     
     
         29 . The method of  claim 23 , wherein the device has a plurality of electrolysis cells and the proportion of the electrolysis cells to which no oxygen is supplied and in which hydrogen is generated at the second cathode is altered as a function of the power supply; and wherein each electrolysis cell comprises:
 a) an anode half-cell, a cathode half-cell and a cation exchange membrane that separates the anode half-cell and the cathode half-cell from one another;   b) an anode arranged in the anode half-cell for evolution of chlorine;   c) an oxygen-consuming electrode arranged in the cathode half-cell as a first cathode;   d) a catholyte space which is formed between the cation exchange membrane and the oxygen-consuming electrode, through which catholyte space electrolyte flows;   e) a gas space adjoining the oxygen-consuming electrode at a surface facing away from the catholyte space, and a conduit for supply of gaseous oxygen to this gas space;   f) a second cathode for generation of hydrogen arranged within the catholyte space; and   g) at least one conduit for purging of the gas space with inert gas.   
     
     
         30 . The method of  claim 23 , wherein a prediction of the expected power supply is made, a minimum duration for operation with the first and with the second cell voltage is set, and a switchover between operation with the first cell voltage with supply of gaseous oxygen to operation with the second cell voltage without supply of oxygen is performed only when the predicted duration of a low or high power supply is longer than the minimum duration set. 
     
     
         31 . The method of  claim 23 , wherein, in said device, the oxygen-consuming electrode and the second cathode have separate power connections. 
     
     
         32 . The method of  claim 23 , wherein the device of  claim 16  further comprises a conduit for withdrawing inert gas from the gas space, and a sensor arranged at this conduit for measuring the content of oxygen in the inert gas. 
     
     
         33 . The method of  claim 23 , wherein said device further comprises at least one conduit for purging the catholyte space with inert gas. 
     
     
         34 . The method of  claim 23 , wherein, in said device, the second cathode abuts the cation exchange membrane. 
     
     
         35 . The method of  claim 23 , wherein, in said device, the oxygen-consuming electrode has a porous hydrophobic gas diffusion layer containing metallic silver and a fluorinated polymer.