Polarity reversal electrodes
First Claim
1. An electrodialysis stack comprising ion-permeable membranes spaced from each other to form fluid treatment chambers with a polarity reversing electrode unit positioned at each terminal end of said stack, each electrode unit comprising an anode portion and a cathode portion electrically separated from each other, means for supplying current to the electrode units with switching means for connecting the anode portion of said first electrode to the positive pole of said current supply means while disconnecting the cathode portion thereof, and means for connecting the cathode portion of said second electrode to the negative pole of said current supply means while disconnecting the anode portion thereof, further means for connecting the active anode of said first electrode unit to the inactive anode of said second electrode unit and means to maintain a trickle of positive current to said inactive anode which is substantially less than the current to said active anode, and in the other position of said switch means, the anode portion of said first unit is made passive by being disconnected and the cathode portion being made cathodically active by connection to the negative pole of said current supply means and connecting the anode portion of said second electrode unit to the positive pole of said current supply means while disconnecting the cathode portion, with further means for connecting the active anode of said second electrode unit to supply and maintain a trickle of positive current to said inactive or passive anode portion of said first electrode unit, which current is substantially less than the current to said active anode.
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Accused Products
Abstract
A polarity reversing electrodialysis membrane stack containing a composite electrode at each end of the stack with each electrode having anode and cathode portions electrically insulated from each other. Current is supplied to the anode portion of one electrode and to the cathode portion of the other electrode with means for maintaining a trickle of current from the active anode of one electrode to the inactive anode of the other electrode. Upon reversal of stack polarity the electrodes change their polarities and the trickle currents runs to the other electrode. The invention also is directed to the use of noble metal coated electrodes wherein the coating covers substantially less than the total electrode surface which is in contact with electrolytic solution during use.
22 Citations
11 Claims
- 1. An electrodialysis stack comprising ion-permeable membranes spaced from each other to form fluid treatment chambers with a polarity reversing electrode unit positioned at each terminal end of said stack, each electrode unit comprising an anode portion and a cathode portion electrically separated from each other, means for supplying current to the electrode units with switching means for connecting the anode portion of said first electrode to the positive pole of said current supply means while disconnecting the cathode portion thereof, and means for connecting the cathode portion of said second electrode to the negative pole of said current supply means while disconnecting the anode portion thereof, further means for connecting the active anode of said first electrode unit to the inactive anode of said second electrode unit and means to maintain a trickle of positive current to said inactive anode which is substantially less than the current to said active anode, and in the other position of said switch means, the anode portion of said first unit is made passive by being disconnected and the cathode portion being made cathodically active by connection to the negative pole of said current supply means and connecting the anode portion of said second electrode unit to the positive pole of said current supply means while disconnecting the cathode portion, with further means for connecting the active anode of said second electrode unit to supply and maintain a trickle of positive current to said inactive or passive anode portion of said first electrode unit, which current is substantially less than the current to said active anode.
- 4. In an electrodialysis apparatus, a stack comprising ion-permeable membranes spaced from each other to form fluid treatment chambers with at least one polarity reversing, substantially planar electrode unit positioned at each terminal end of said stack, each electrode unit comprising a plurality of first regions comprising titanium alloys which are substantially corrosion resistant under reducing, acid conditions, coated at least in part with a coating selected from the group consisting of iridium, rhodium and platinum, their oxides and mixtures thereof, the anodically active area of such first region being substantially less than the electrolytically conducting active area of the majority of the ion-permeable membranes in said stack and means for making such first regions, working anodes for a substantial fraction of the time working current is carried by such membranes, such first regions being substantially uniformly distributed over the surface of said electrode unit.
Specification