Cyclic electrodialysis: Experimental results in a closed system

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Abstract
Experimental results are presented for cyclic reflux operation of an electrosorption — desorption separation process. Solute is alternately absorbed by, or desorbed from, a stack of multilayer ion‐selective membranes in a modified electrodialysis cell by periodically reversing the polarity of the applied electric field. Solution passes through a single set of flow channels parallel to the membrane sheets, and the flow alternates in direction synchronously with the electric current cycle. An axial concentration gradient is set up within the cell so that dialysate is produced at one end of the stack and concentrated solution at the other.Two cell designs are described, one containing a single stack of membranes, the other built in a modular arrangement with up to eight stacks in series. The effect of nine system parameters on the separation of aqueous NaCl solutions is reported for the first unit. Separation factors of up to 40 were obtained. For the second unit, the effect of channel length, displacement cycle, applied voltage and initial concentration on the rate of separation, the final separation factor, and the current consumption are reported. This unit has longer channels, more uniform flow distribution and less axial dispersion than the earlier design and gave separation factors > 103 with NaCl solution. Applications of the process to continuous separation in open systems are discussed.

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