Sulfuric acid electrolysis method and sulfuric acid electrolysis apparatus

Abstract

An electrolysis apparatus comprising: an electrolytic cell in which a sulfuric acid solution is fed and discharged; a conductive anode and cathode electrode of diamond composition; a feeding unit for feeding the sulfuric acid solution to the electrolytic cell; a power supply unit for applying a voltage between the anode and cathode electrodes; and a power control unit for controlling the power supply unit such that a forward voltage is applied between the anode and cathode during normal electrolysis with the polarity applied between the anode and cathode inverted under predetermined conditions during intervals between normal operation to dissolve precipitates of sulfur generated in the electrolytic cell for stabilizing the electrolysis operation.

1 . A sulfuric acid electrolysis method of generating persulfuric acid by performing electrolysis in an electrolytic cell while flowing sulfuric acid solution of 70 mass % or more between an anode and an cathode among a plurality of electrodes which include at least the anode and cathode, each of which at least liquid contact surface is constructed with a conductive diamond, the method comprising:
 performing a normal operation of performing the electrolysis by applying a forward voltage between the anode and the cathode of the electrodes;   performing a polarity inversion operation of inverting the voltage applied between the anode and the cathode in an interval between the normal operations; and   dissolving precipitates of sulfur generated in the electrolytic cell during the normal operation into the sulfuric acid solution during the polarity inversion operation.   
     
     
         2 . The sulfuric acid electrolysis method according to  claim 1 , wherein the electrolysis is performed while introducing the sulfuric acid solution from an outside of the electrolytic cell into an inside of the electrolytic cell, and the electrolyzed sulfuric acid solution is discharged to the outside of the electrolytic cell. 
     
     
         3 . The sulfuric acid electrolysis method according to  claim 1 , wherein a retention portion where the flowing sulfuric acid solution is retained is included in the electrolytic cell. 
     
     
         4 . The sulfuric acid electrolysis method according to  claim 1 , wherein the electrolytic cell includes a narrow passage portion through which the flow of the sulfuric acid solution is confined. 
     
     
         5 . The sulfuric acid electrolysis method according to  claim 3 , wherein a spacer of securing a passage of the sulfuric acid solution is disposed between the electrodes, and the retention portion is formed with the spacer or with the spacer and other members. 
     
     
         6 . The sulfuric acid electrolysis method according to  claim 5 , wherein a sealing member is installed between the spacer and the electrode, and the retention portion is formed with at least the sealing member. 
     
     
         7 . The sulfuric acid electrolysis method according to  claim 5 , wherein the electrolytic cell has an outlet hole forming a narrow passage portion in the spacer through which the sulfuric acid solution passes. 
     
     
         8 . The sulfuric acid electrolysis method according to  claim 5 , wherein the electrolytic cell has an inlet hole forming a narrow passage portion in the spacer through which the sulfuric acid solution passes. 
     
     
         9 . The sulfuric acid electrolysis method according to  claim 1 , wherein a circulation line is installed to connect an outlet of the electrolytic cell and an inlet of the electrolytic cell, and a narrow passage portion is included in the circulation line and/or an upstream side of a retention portion of the electrolytic cell. 
     
     
         10 . The sulfuric acid electrolysis method according to  claim 1 , wherein the polarity inversion operation is performed after continuously performing the normal operation for a predetermined time. 
     
     
         11 . The sulfuric acid electrolysis method according to  claim 1 , wherein the polarity inversion operation is performed based on a result of determination of a precipitated state of the sulfur. 
     
     
         12 . The sulfuric acid electrolysis method according to  claim 1 , wherein at least one of the following conditions (a) to (c) is satisfied:
 (a) a concentration of sulfuric acid in the electrolytic cell is 85 mass % or more;   (b) a temperature of sulfuric acid at the inlet of the electrolytic cell is 70° C. or more; and   (c) a current density in the electrolysis is 50 A/dm2 or more.   
     
     
         13 . A sulfuric acid electrolysis apparatus comprising:
 an electrolytic cell which sulfuric acid solution can be fed to and discharged from;   a plurality of electrodes including at least an anode and a cathode in the electrolytic cell, which are disposed with a gap between the anode and cathode so that the sulfuric acid solution flows in the gap and each of which at least liquid contact surface is constructed with a conductive diamond;   a spacer which secures the gap of the electrodes;   a narrow passage portion formed in the spacer where the sulfuric acid solution flows;   a feeding unit which feeds the sulfuric acid solution to the electrolytic cell;   a power supply unit which applies a voltage between the anode and the cathode of the electrodes; and   a power control unit which controls the power supply unit to apply a forward voltage between the anode and the cathode during normal electrolysis and to perform polarity inversion of inverting the voltage applied between the anode and the cathode in a predefined condition.   
     
     
         14 . A sulfuric acid electrolysis apparatus comprising:
 an electrolytic cell which sulfuric acid solution can be fed to and discharged from;   a plurality of electrodes including at least an anode and a cathode in the electrolytic cell, which are disposed with a gap between the anode and cathode so that the sulfuric acid solution flows in the gap and each of which at least liquid contact surface is constructed with a conductive diamond;   a spacer which secures the gap of the electrodes;   a retention portion formed with the spacer or with the spacer and other members, where the sulfuric acid solution is retained;   a power supply unit which applies a voltage between the anode and the cathode of the electrodes; and   a power control unit which controls the power supply unit to perform polarity inversion of inverting a voltage applied between the anode and the cathode during normal electrolysis.   
     
     
         15 . The sulfuric acid electrolysis method according to  claim 2 , wherein the electrolytic cell includes a narrow passage portion through which the flow of the sulfuric acid solution is confined. 
     
     
         16 . The sulfuric acid electrolysis method according to  claim 3 , wherein the electrolytic cell includes a narrow passage portion through which the flow of the sulfuric acid solution is confined. 
     
     
         17 . The sulfuric acid electrolysis method according to  claim 6 , wherein the electrolytic cell has an outlet hole forming a narrow passage portion in the spacer through which the sulfuric acid solution passes.