Regeneration of electrolytic ion exchange cells

Abstract

An apparatus and method to treat a solution comprising ions in an ion removal step and an ion rejection step are provided. The apparatus comprises an electrochemical cell comprising a housing comprising first and second electrodes and a solution channel. A variable voltage supply is capable of maintaining the first and second electrodes at a plurality of different voltages during an ion exchange stage and a flow control device is capable of controlling the flow of solution through the channel of the cell. A controller is provided to control the voltage supply and flow control device. The ion removal step can comprise, for example, a deionization step and the ion rejection step can comprise, for example, a cell regeneration step.

1 . An apparatus to treat a solution comprising ions, the apparatus comprising: 
 (a) an electrochemical cell comprising a housing with first and second electrodes, an ion exchange membrane between the electrodes, and a solution channel;    (b) a voltage supply to provide a voltage across the first and second electrodes;    (c) a flow control device to control the flow of solution through the solution channel of the cell; and    (d) a controller to control the voltage supply and flow control device to: 
 (i) in an ion removal step, maintain the first electrode as the positive electrode and the second electrode as the negative electrode relative to the first electrode, and flow solution through the solution channel; and  
 (ii) in an ion rejection step, maintain the first electrode as the negative electrode and the second electrode as the positive electrode relative to the first electrode, and reverse the flow direction of the solution through the solution channel.  
   
     
     
         2 . An apparatus according to  claim 1  wherein in the ion rejection step, the controller reverses the polarity of the first and second electrodes relative to the polarity of the electrodes in the ion removable step.  
     
     
         3 . An apparatus according to  claim 1  wherein the voltage supply applies a time modulated voltage to the first and second electrodes.  
     
     
         4 . An apparatus according to  claim 3  wherein in the ion removal step, the voltage supply applies a first time modulated voltage to the electrodes, and in the ion rejection step, the voltage supply applies a second time modulated voltage to the electrodes, and wherein the first time modulated voltage has a first magnitude and the second time modulated voltage has a different magnitude than the first magnitude.  
     
     
         5 . An apparatus according to  claim 1  wherein in the ion removal or rejection step, the voltage supply applies to the first and second electrodes a constant voltage level or a pulsed voltage level.  
     
     
         6 . An apparatus according to  claim 1  wherein the voltage supply applies a pulsed voltage level having one or more duty cycles.  
     
     
         7 . An apparatus according to  claim 1  wherein the voltage supply includes a polarity switch to switch the polarity of the voltage applied to the first and second electrodes.  
     
     
         8 . An apparatus according to  claim 7  wherein the voltage supply provides a variable DC voltage by half-wave or full-wave rectification of an AC voltage.  
     
     
         9 . An apparatus according to  claim 1  further comprising an ion sensor to (i) measure an ion concentration of the influent solution, at least partially treated solution, or effluent solution, and (ii) generate an ion concentration signal, and 
 wherein the controller receives the ion concentration signal and sends a control signal to the voltage supply to adjust the voltage applied to the electrodes in response to the ion concentration signal.    
     
     
         10 . An apparatus according to  claim 1  wherein the membrane comprises a cation exchange surface facing the first electrode and an anion exchange surface facing the second electrode, and the solution channel allows the solution to flow past both the anion and cation exchange surfaces of the ion exchange membrane.  
     
     
         11 . An apparatus according to  claim 1  wherein the electrochemical cell comprises an influent solution inlet abutting the first electrode and effluent solution outlet abutting the second electrode.  
     
     
         12 . An apparatus according to  claim 11  wherein in the ion removal step the controller operates the flow control device to supply the solution through the influent solution orifice, and in the ion rejection step the controller operates the flow control device to supply the solution through the effluent solution inlet.  
     
     
         13 . A method of treating a solution comprising ions in an electrochemical cell comprising a housing comprising first and second electrodes, an ion exchange membrane between the electrodes, and a solution channel, the method comprising: 
 (a) in an ion removal step, maintaining the first electrode as the positive electrode and the second electrode as the negative electrode relative to the first electrode, and flowing solution through the solution channel; and    (b) in an ion rejection step, maintaining the first electrode as the negative electrode and the second electrode as the positive electrode relative to the first electrode, and reversing the flow direction of the solution through the solution channel.    
     
     
         14 . A method according to  claim 13  wherein the ion rejection step comprises reversing the polarity of the first and second electrodes.  
     
     
         15 . A method according to  claim 13  comprising applying a time modulated voltage to the first and second electrodes.  
     
     
         16 . A method according to  claim 15  comprising measuring an ion concentration of the at least partially treated influent solution and varying the magnitude of the time modulated voltage in response to the measured ion concentration.  
     
     
         17 . A method according to  claim 13  comprising applying to the first and second electrodes a constant voltage level or a pulsed voltage level.  
     
     
         18 . A method according to  claim 17  comprising applying a pulsed voltage level having one or more duty cycles.  
     
     
         19 . An apparatus to treat a solution comprising ions, the apparatus comprising: 
 (a) an electrochemical cell comprising a housing with first and second electrodes, an ion exchange membrane between the electrodes, and a solution channel;    (b) a variable voltage supply to provide a voltage across the first and second electrodes; and    (c) a controller to control the variable voltage supply and flow control device to: 
 (i) in an ion removal step, flow solution through the solution channel while applying a voltage to the first and second electrodes to deionize the solution; and  
 (ii) in an ion rejection step, regenerate the ion exchange membrane by flowing solution through the solution channel while (1) in a first regeneration step, supply a first voltage to the electrodes of the cell for a time period, and (2) in a second regeneration step, supply a second voltage to the electrodes of the cell for a time period, the second voltage being a different voltage than the first voltage.  
   
     
     
         20 . An apparatus according to  claim 19  wherein the first and second voltages have different magnitudes.  
     
     
         21 . An apparatus according to  claim 20  wherein the first and second voltages have negative values relative to the voltage applied in the ion removal step.  
     
     
         22 . An apparatus according to  claim 19  wherein the first and second voltages are each a fixed constant voltage level or fixed pulsed voltage level.  
     
     
         23 . An apparatus according to  claim 19  wherein the first voltage comprises a pulsed voltage having a first duty cycle and the second voltage comprises a pulsed voltage having a second duty cycle.  
     
     
         24 . An apparatus according to  claim 23  wherein the first voltage is provided over a first time period and the second voltage is provided over a second time period that is a different time period than the first time period.  
     
     
         25 . An apparatus according to  claim 23  wherein in the ion rejection step, the controller further controls the variable voltage supply to provide a third voltage over a time period.  
     
     
         26 . An apparatus according to  claim 19  wherein the voltage supply includes a polarity switch to switch the polarity of the voltage applied to the first and second electrodes in the ion rejection stage relative to the polarity applied in the ion removal stage.  
     
     
         27 . An apparatus according to  claim 19  further comprising a flow control device to control the flow of solution, and wherein in the ion rejection stage, the controller controls the flow control device to reverse the flow direction of the solution through the solution channel relative to the flow direction in the ion removal stage.  
     
     
         28 . An apparatus according to  claim 19  further comprising an ion sensor to measure an ion concentration of the regenerated waste solution and generate an ion concentration signal, and wherein the controller receives the ion concentration signal and sends a control signal to the variable voltage supply to adjust the voltage applied to the first and second electrodes in response to the ion concentration signal.  
     
     
         29 . A method of treating a solution comprising ions in an electrochemical cell comprising an ion exchange membrane between electrodes, the method comprising: 
 (a) in an ion removal step, flowing solution into the cell while applying a voltage to the first and second electrodes to deionize the solution; and    (b) in an ion rejection step, regenerating the ion exchange membrane by flowing solution through the cell while (1) in a first regeneration step, supplying a first voltage to the electrodes for a time period, and (2) in a second regeneration step, supply a second voltage to the electrodes for a time period, the second voltage being a different voltage than the first voltage.    
     
     
         30 . A method according to  claim 29  comprising supplying first and second voltages having different magnitudes.  
     
     
         31 . A method according to  claim 29  comprising supplying first and second voltages having negative values relative to the voltage applied in the ion removal step.  
     
     
         32 . A method according to  claim 29  comprising supplying first and second voltages that are each a fixed constant voltage level or fixed pulsed voltage level.  
     
     
         33 . A method according to  claim 29  comprising supplying a first voltage comprising a pulsed voltage having a first duty cycle and the second voltage comprising a pulsed voltage having a second duty cycle.  
     
     
         34 . A method according to  claim 29  comprising supplying a first voltage over a first time period and a second voltage over a second time period that is a different time period than the first time period.  
     
     
         35 . A method according to  claim 29  comprising supplying a third voltage over a time period.  
     
     
         36 . A method according to  claim 29  comprising switching the polarity of the voltage applied to the first and second electrodes in the ion rejection stage relative to the polarity applied in the ion removal stage.  
     
     
         37 . A method according to  claim 29  comprising reversing the flow direction of the solution in the cell in the ion rejection stage relative to the flow direction in the ion removal stage.  
     
     
         38 . A method according to  claim 29  comprising measuring an ion concentration of the regenerated waste solution, generating an ion concentration signal, and adjusting the first or second voltages supplied to the first and second electrodes in response to the ion concentration signal.