Techniques for production of chlorated products and prefabricated cathode structures

Abstract

Techniques for producing chlorinated products include an electrochemical process that includes the steps of providing an anode and a cathode in an electrolyte comprising impurities such as calcium ions, applying a voltage between the anode and the cathode under conditions to form an electrolysis product such as sodium chlorate in the electrolyte, and providing sufficient phosphate ions to form with at least a portion of the calcium ions a protective external layer including a calcium phosphate compound such as hydroxyapatite on the cathode, while preferably avoiding other phosphate precipitations. A pre-determined amount of phosphate ions may be added, for example, based on the surface area of the cathode in order to form the protective layer. Related uses and systems are also described. Prefabricated cathodes may include a substrate, a catalytic intermediate layer and a calcium phosphate protective layer.

1 . An electrochemical process comprising:
 providing an anode and a cathode in an electrolyte comprising impurities comprising calcium ions;   applying a voltage between the anode and the cathode under conditions to form an electrolysis product in the electrolyte; and   providing phosphate ions in the electrolyte in an amount sufficient to form with at least a portion of the calcium ions a protective external layer on the cathode, the protective external layer comprising a calcium phosphate compound, and to substantially avoid precipitation of calcium phosphate compounds in the electrolyte.   
     
     
         2 . The electrochemical process of  claim 1 , wherein the phosphate ions are added in an amount based on a surface area of the cathode that is in contact with the electrolyte. 
     
     
         3 . The electrochemical process of  claim 1 , further comprising applying the protective external layer on the catalytic intermediate layer prior to immersing the cathode into the electrolyte. 
     
     
         4 . The electrochemical process of  claim 3 , wherein the step of applying the protective external layer comprises sputter coating, dip coating, sol-gel, electrochemical deposition, biomimetic coating, hot isostatic coating, or plasma spraying. 
     
     
         5 . The electrochemical process of  claim 1 , further comprising forming the protective external layer on the catalytic intermediate layer after immersing the cathode into the electrolyte. 
     
     
         6 . (canceled) 
     
     
         7 . The electrochemical process of  claim 1 , wherein formation of the protective external layer comprises:
 reacting Ca(OH) 2  with H 3 PO 4  to produce Ca 3 (PO 4 ) 2  and water; and   reacting Ca(OH) 2  with Ca 3 (PO 4 ) 2  to produce Ca 10 (PO 4 ) 6 (OH) 2 , wherein the Ca 10 (PO 4 ) 6 (OH) 2  forms at least part of the protective external layer.   
     
     
         8 . The electrochemical process of  claim 1 , wherein the phosphate ions are provided in the electrolyte in a phosphate concentration up to about 75 ppm. 
     
     
         9 . (canceled) 
     
     
         10 . The electrochemical process of  claim 1 , wherein the phosphate concentration is sufficiently low to prevent formation of an iron phosphate compound or deposit on the anode. 
     
     
         11 . The electrochemical process of  claim 1 , wherein the phosphate concentration is sufficiently low to prevent an increase in O 2  levels in the electrolyte. 
     
     
         12 . The electrochemical process of  claim 1 , wherein the phosphate concentration is sufficiently low to prevent an increase in voltage requirements. 
     
     
         13 . The electrochemical process of  claim 1 , wherein the phosphate ions are at least partially provided by addition of H 3 PO 4 . 
     
     
         14 . The electrochemical process of  claim 1 , wherein the phosphate ions are at least partially provided by inherent presence in the electrolyte. 
     
     
         15 . The electrochemical process of  claim 1 , wherein the calcium ions are at least partially provided by inherent presence in the electrolyte. 
     
     
         16 . The electrochemical process of  claim 1 , wherein the electrolyte comprises a first portion of calcium ions for reacting with the phosphate ions to form the calcium phosphate compound on the cathode, and a second portion of calcium remaining unreacted in the electrolyte. 
     
     
         17 - 21 . (canceled) 
     
     
         22 . An electrochemical system comprising:
 an electrolysis chamber for containing an electrolyte, wherein the electrolyte comprises calcium ions and phosphate ions;   an anode located in the electrolysis chamber;   a cathode located in the electrolysis chamber; and   an ion adjuster configured to adjust ion levels in the electrolyte such that the electrolyte comprises an amount of phosphate ions sufficient to form with at least a portion of the calcium ions a protective external layer comprising a calcium phosphate compound on the cathode and to avoid precipitation of calcium phosphate compounds in the electrolyte.   
     
     
         23 - 27 . (canceled) 
     
     
         28 . An electrochemical process comprising:
 providing an anode and a cathode in an electrolyte impurities comprising calcium ions and ferric ions;   applying a voltage between the anode and the cathode under conditions to form electrolysis product in the electrolyte; and   providing phosphate ions in the electrolyte in an amount sufficient to form with at least a portion of the calcium ions a protective external layer on the cathode, the protective external layer comprising a calcium phosphate compound, and to substantially avoid precipitation of iron phosphate compounds in the electrolyte.   
     
     
         29 - 36 . (canceled) 
     
     
         37 . The electrochemical process of  claim 28 , wherein the phosphate concentration is sufficiently low to prevent formation of an iron phosphate compound or deposit on the anode, to prevent an increase in O 2  levels in the electrolyte, or to prevent an increase in voltage requirements. 
     
     
         38 - 53 . (canceled) 
     
     
         54 . The electrochemical process of  claim 1 , wherein a pre-determined amount of phosphate ions is between about 0.025 mg per cm 2  of the cathode and about 0.2 mg per cm 2  of the cathode. 
     
     
         55 - 73 . (canceled) 
     
     
         74 . The electrochemical process of  claim 54 , wherein the pre-determined amount of phosphate ions are calculated based on a target thickness of the protective external layer to obtain. 
     
     
         75 - 80 . (canceled) 
     
     
         81 . A prefabricated cathode comprising:
 a substrate;   a catalytic intermediate layer; and   an protective external layer comprising a calcium phosphate compound.   
     
     
         82 - 84 . (canceled) 
     
     
         85 . The prefabricated cathode of  claim 81 , wherein the catalytic intermediate layer is contiguous with an outer surface of the substrate, and the catalytic intermediate layer comprises a metal matrix doped with a catalytic compound. 
     
     
         86 - 88 . (canceled) 
     
     
         89 . The prefabricated cathode of  claim 81 , wherein the calcium phosphate compound comprises a hydroxy calcium phosphate compound. 
     
     
         90 - 91 . (canceled) 
     
     
         92 . The prefabricated cathode of  claim 81 , wherein the protective external layer has a thickness between about 0.25 micron and about 1.5 microns. 
     
     
         93 . (canceled) 
     
     
         94 . The prefabricated cathode of  claim 81 , wherein the protective external layer covers an entire outer surface of the catalytic intermediate layer to prevent direct contact of the catalytic intermediate layer with calcium impurities in the electrolyte. 
     
     
         95 . (canceled) 
     
     
         96 . The prefabricated cathode of  claim 81 , wherein the protective external layer has a reticulum structure, honeycomb structure, a structure enabling the hydrogen evolution reaction to take place there-under while preventing calcium impurities from poisoning the intermediate catalytic layer, or a structure enabling blocking of chlorate and hypochlorite ions from reaching a surface of the intermediate catalytic layer to reduce or avoid the following reactions:
   ClO − +H 2 O+2 e=>Cl   − +2OH − ; or     ClO 3   − +3H 2 O+6 e   − =>Cl − +6OH − .   
     
     
         97 - 112 . (canceled) 
     
     
         113 . The electrochemical process of  claim 1 , wherein:
 wherein the cathode comprises:   a substrate composed of a corrosion resistant material; and   a catalytic intermediate layer;   and the process further comprises:   performing electrolysis for electrolysis periods, comprising applying a voltage between the anode and the cathode under conditions to form an electrolysis product in the electrolyte; and   periodically shutting down the electrolysis for shutdown periods, comprising terminating the voltage, wherein the corrosion resistant material of the substrate prevents release of ferric ions into the electrolyte during each of the shutdown periods;   wherein the providing the phosphate ions in the electrolyte is sufficient such that, during each electrolysis period, the phosphate ions form or re-form with at least a portion of the calcium ions the protective external layer on the catalytic intermediate layer of the cathode, the protective external layer comprising the calcium phosphate compound.   
     
     
         114 . (canceled)