Asymmetric Polarity Reversal for an Electrolytic - Cation Exchange Module (E-CEM)

Abstract

An electrochemical system includes a first electrode disposed in a first electrode compartment, a second electrode disposed in a second electrode compartment, a center compartment disposed between and separated from the first electrode compartment and the second electrode compartment by cation exchange membranes, an electrical power source electrically coupled to the first electrode and to the second electrode, and a control system configured to perform repeating cycles of causing the electrical power source to apply a positive voltage to the first electrode and a negative voltage to the second electrode for a first amount of time, reverse polarities of the voltages applied to the electrodes after the first amount of time, and maintain the reversed polarities for a second amount of time, the second amount of time being different from the first amount of time.

What is claimed is: 
     
         1 . An electrochemical system comprising:
 a first electrode disposed in a first electrode compartment;   a second electrode disposed in a second electrode compartment;   a center compartment disposed between and separated from the first electrode compartment and the second electrode compartment by cation exchange membranes;   an electrical power source electrically coupled to the first electrode and to the second electrode; and   a control system configured to perform repeating cycles of causing the electrical power source to:
 apply a positive voltage to the first electrode and a negative voltage to the second electrode for a first amount of time, 
 reverse polarities of the voltages applied to the electrodes after the first amount of time, and 
 maintain the reversed polarities for a second amount of time, the second amount of time being different from the first amount of time. 
   
     
     
         2 . The electrochemical system of  claim 1 , wherein the first amount of time is greater than the second amount of time. 
     
     
         3 . The electrochemical system of  claim 1 , wherein the first electrode is formed of a valve metal core with a with a platinum (Pt), iridium (Ir), or ruthenium (Ru) mixed metal oxide (MMO) coating or a Pt/Ir coating. 
     
     
         4 . The electrochemical system of  claim 1 , wherein the first electrode is formed of a corrosion-resistant nickel-based alloy. 
     
     
         5 . The electrochemical system of  claim 2 , further comprising a source of seawater fluidically couplable to the center compartment. 
     
     
         6 . The electrochemical system of  claim 5 , wherein the second amount of time is sufficient to generate an amount of dissolved hydrogen ions at the second electrode to dissolve scale from the second electrode during operation of the electrochemical system with the switched polarities. 
     
     
         7 . The electrochemical system of  claim 5 , wherein the second amount of time is sufficient to cause a pH of electrolyte in the second compartment to be at or less than about 4. 
     
     
         8 . The electrochemical system of  claim 5 , wherein the first amount of time is sufficient to cause a pH of seawater in the center compartment to be at about 4. 
     
     
         9 . The electrochemical system of  claim 1 , configured as an electrolytic-cation exchange module. 
     
     
         10 . The electrochemical system of  claim 1 , further comprising a source of electrolyte fluidly connectable to the first electrode compartment and to the second electrode compartment. 
     
     
         11 . A method of operating an electrochemical system including a first electrode disposed in a first electrode compartment, a second electrode disposed in a second electrode compartment, a center compartment disposed between and separated from the first compartment and the second compartment by cation exchange membranes, the method comprising performing repeated cycles of:
 applying a first current through the electrodes for a first period of time;   reversing the applied current after the first period of time; and   applying the reversed current through the electrodes for a second period of time.   
     
     
         12 . The method of  claim 11 , wherein the first amount of time is greater than the second amount of time. 
     
     
         13 . The method of  claim 11 , further comprising flowing electrolyte with a conductivity of less than about 250 μS/cm through each of the first electrode compartment and the second electrode compartment. 
     
     
         14 . The method of  claim 11 , further comprising flowing seawater through the center compartment. 
     
     
         15 . The method of  claim 14 , wherein the second amount of time is sufficient to generate an amount of dissolved hydrogen ions at the second electrode to dissolve scale from the second electrode during operation of the module with the switched polarities. 
     
     
         16 . The method of  claim 14 , wherein the second amount of time is sufficient to change a pH of electrolyte in the second compartment to about 4. 
     
     
         17 . The method of any one of  claims 11-16 , wherein the first amount of time is sufficient to change a pH of seawater in the center compartment to about 4. 
     
     
         18 . A method of retrofitting an electrochemical system including a first electrode disposed in a first electrode compartment, a second electrode disposed in a second electrode compartment, a center compartment disposed between and separated from the first electrode compartment and the second electrode compartment by cation exchange membranes, an electrical power source electrically coupled to the first electrode and to the second electrode, and a control system, the method comprising reprogramming the control system to perform repeating cycles of applying a first current through the electrodes for a first period of time, reversing the applied current after the first period of time, and applying the reversed current through the electrodes for a second period of time, the second period of time having a different duration than the first period of time. 
     
     
         19 . The method of  claim 18 , further comprising replacing the first electrode with an electrode formed of a metal core with a coating of one of ruthenium oxide, iridium oxide, or a mixed metal oxide. 
     
     
         20 . A non-transitory computer readable medium having instructions encoded thereon which when executed by a computerized control system of an electrochemical system including a first electrode disposed in a first electrode compartment, a second electrode disposed in a second electrode compartment, a source of electrolyte fluidly connected to the first electrode compartment and to the second electrode compartment, a center compartment disposed between and separated from the first electrode compartment and the second electrode compartment by cation exchange membranes, causes the computerized control system to perform repeating cycles of applying a first current through the electrodes for a first period of time, reversing the applied current after the first period of time, and applying the reversed current through the electrodes for a second period of time, the second period of time having a different duration than the first period of time.