Method for preparing periodates via anodic oxidation in a steady state reactor

Abstract

The present invention relates to a method for preparing a metal para-periodate by anodic oxidation of an iodine compound with an oxidation state from −I to +V in an electrolysis cell under specific conditions, and to a device for carrying out this reaction.

1 . A method for preparing a metal para-periodate by anodic oxidation of an iodine compound with an oxidation state from −I to +V in an electrolysis cell, said electrolysis cell comprising an anodic compartment having one or more anodes, a cathodic compartment having one or more cathodes, and a separator arranged between said anodic and cathodic compartments, said method comprising
 recirculating a catholyte through a catholyte circuit into said cathodic compartment, 
 recirculating an anolyte through an anolyte circuit into said anodic compartment, said anolyte comprising a metal periodate and an iodine compound with an oxidation state from −I to +V selected from an iodine salt, elementary iodine, a mixture of different iodine salts or a mixture of iodine with one or more iodine salts, 
 carrying out said anodic oxidation of said iodine compound at a pH of at least 10, 
 wherein said anolyte circuit comprises at least one continuous stirred tank reactor operated in a steady-state mode with respect to the overall molar ratio of metal periodate to iodine compound with an oxidation state from −I to +V in said anolyte, wherein said continuous stirred tank reactor is operated in a steady-state mode by continuously or periodically feeding said iodine com-pound with an oxidation state from −I to +V into said continuous stirred tank reactor and continuously or periodically removing metal periodate from said continuous stirred tank reactor. 
 
     
     
         2 . The method according to  claim 1 , wherein said metal periodate comprised in said recirculated anolyte is predominantly a metal para-periodate. 
     
     
         3 . The method according to  claim 1 , wherein operating the continuous stirred tank reactor in a steady-state mode with respect to the overall molar ratio of metal periodate to iodine compounds with an oxidation state from −I to +V in said anolyte means that a predefined molar ratio or molar ratio range is selected and during operation, the actual molar ratio or molar ratio range of metal periodate to iodine compounds is kept at the predefined molar ratio or molar ratio range or in close vicinity of the preselected molar ratio or molar ratio range, wherein “close vicinity” means that the actual molar ratio or molar ratio range may deviate from the selected molar ratio or molar ratio range by at most ±20%, where the molar ratio is calculated on the basis of iodine atoms present in the metal periodate and the iodine compound. 
     
     
         4 . The method according to  claim 3 , wherein the predefined molar ratio or molar ratio range relates to the molar ratio or molar ratio range in the anolyte before entering the anodic compartment. 
     
     
         5 . The method according to  claim 1 , wherein in said recirculated anolyte the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from −I to +V is of from 1:>0 to 1:5; where in case that the iodine compound has an oxidation state from −I to +III, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from −I to +III is of from 1:0 to 8:1; and where in case that the iodine compound has an oxidation state of +V, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of +V is of from 1:0 to 1:5;
 where preferably the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from −I to +V is of from 1:>0 to 1:4; more preferably from 200:1 to 1:4; where in case that the iodine compound has an oxidation state from −I to +III, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from −I to +III is of from 1:0 to 10:1, and where in case that the iodine compound has an oxidation state of +V, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of +V is of from 1:0 to 1:4, preferably from 200:1 to 1:4. 
 
     
     
         6 . The method according to  claim 1 , wherein in said recirculated anolyte, when fed to the anodic compartment, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from −I to +V is of from 1:>0 to 1:5; where in case that the iodine compound has an oxidation state of from −I to +III, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of from −I to +III is of from 1:0 to 8:1; and where in case that the iodine compound has an oxidation state of +V, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of +V is of from 1:0 to 1:5;
 where preferably the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from −I to +V is of from 1:>0 to 1:4; more preferably from 200:1 to 1:4; where in case that the iodine compound has an oxidation state from −I to +III, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from −I to +III is of from 1:0 to 10:1, and where in case that the iodine compound has an oxidation state of +V, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of +V is of from 1:0 to 1:4, more preferably from 200:1 to 1:4. 
 
     
     
         7 . The method according to  claim 1 , wherein for operating the continuous stirred tank reactor in a steady-state mode with respect to the overall molar ratio of metal periodate to iodine compounds with an oxidation state from −I to +V, for the anolyte before entering the anodic compartment a predefined molar ratio or molar ratio range is selected, and during operation, the actual molar ratio of metal periodate to iodine compounds in the anolyte before entering the anodic compartment is kept at the predefined molar ratio or molar ratio range±20%;
 wherein said predefined molar ratio or molar ratio range is selected thusly that in said anolyte, before entering the anodic compartment (i.e. when fed to the anodic compartment), the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from −I to +V is of from 1:>0 to 1:5; where in case that the iodine compound has an oxidation state of from −I to +III, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of from −I to +III is of from 1:0 to 8:1; and where in case that the iodine compound has an oxidation state of +V, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of +V is of from 1:0 to 1:5; 
 where the molar ratio is calculated on the basis of iodine atoms present in the metal periodate and the iodine compound. 
 
     
     
         8 . The method according to  claim 1 , for preparing an alkali metal para-periodate, preferably sodium or potassium para-periodate, where the iodine compound with an oxidation state from −I to +V is an alkali metal iodide, alkali metal iodate, iodine or a mixture thereof, preferably sodium iodide, potassium iodide, sodium iodate, potassium iodate, iodine or a mixture thereof. 
     
     
         9 . The method according to  claim 1 , where the anodic oxidation is carried out at a pH of at least 11. 
     
     
         10 . The method according to  claim 1 , where the anodic oxidation is carried out in the presence of a base, where the base is selected from the group consisting of metal hydroxides, metal oxides and metal carbonates. 
     
     
         11 . The method according to  claim 10 , where the anodic oxidation is carried out in the presence of a metal hydroxide, where in case that said iodine compound with an oxidation state from −I to +V is an alkali metal iodine salt, the metal of the base corresponds to the metal in the metal iodine salt. 
     
     
         12 . The method according to  claim 1 , where the catholyte comprises an aqueous medium with a pH of at least 10, preferably of at least 11. 
     
     
         13 . The method according to  claim 1 , where the anodic oxidation is carried out at a current density in the range of from 10 to 1000 mA/cm2, preferably from 100 to 750 mA/cm2, in particular from 250 to 500 mA/cm2 and specifically of 400 to 430 mA/cm2. 
     
     
         14 . The method according to  claim 1 , where said separator arranged between said cathodic and anodic compartments is selected from semipermeable membranes, diaphragms and frits, and is in particular an ion-exchange membrane. 
     
     
         15 . The method according to  claim 1 , where the one or more anodes comprise a carbon-based active layer. 
     
     
         16 . The method according to  claim 15 , where the one or more anodes comprise a diamond layer doped with one or more IUPAC group 13, 15 or 16 elements of the periodic table. 
     
     
         17 . The method according to  claim 16 , where the one or more anodes comprise a boron-doped diamond layer. 
     
     
         18 . The method according to  claim 1 , where said iodine com-pound with an oxidation state from −I to +V is fed into said continuous stirred tank reactor in form of an aqueous solution, aqueous suspension or in solid form. 
     
     
         19 . A device configured for preparing a metal para-periodate by the method of  claim 1 , the device comprising
 said electrolysis cell comprising an anodic compartment having one or more anodes, a cathodic compartment having one or more cathodes, and a separator arranged between said anodic and cathodic compartments,   said catholyte circuit for recirculating catholyte through said cathodic compartment, said catholyte circuit comprising a catholyte reservoir,   said anolyte circuit for circulating anolyte through said anodic compartment, said anolyte circuit comprising at least one continuous stirred tank reactor, said at least one continuous stirred tank reactor being provided with feeding means for feeding said iodine compound with an oxidation state from −I to +V selected from an iodine salt, elementary iodine, a mixture of different io-dine salts or a mixture of iodine with one or more iodine salts into said at least one continuous stirred tank reactor and withdrawing means for withdrawing said metal periodate reaction product from said at least one continuous stirred tank reactor.