Principle of in Vitro Electroregeneration of Compound Bed Resin

Compared to mixed-bed resin regenerators, the difference in the external electroregenerator between multi-bed and mixed-bed resin regenerators lies in the addition of a bipolar membrane to the membrane pair structure. This is equivalent to inserting a bipolar membrane in the middle of the mixed-bed resin electroregeneration chamber, dividing it into two: one becomes the cation-bed resin electroregeneration chamber in the multi-bed system, and the other becomes the anion-bed resin electroregeneration chamber. Under the influence of a DC electric field, the H+ and OH- ions generated by water dissociation enter their respective cation and anion regeneration chambers, where they undergo exchange reactions with the corresponding exhausted resin, transforming the exhausted resin into H-form and OH-form, thus achieving electroregeneration. Simultaneously, it avoids harmful side reactions to the resin electroregeneration process. Because the mixed bed is located at the front end of the desalination system, the exhausted cation exchange resin, besides adsorbing most of the ions in the water, also adsorbs all the Ca2⁺ and Mg2⁺ ions. If this resin is sent to the original mixed bed electroregeneration chamber, the H⁺ ions generated by water ionization during electroregeneration can exchange with the Ca2⁺, Mg2⁺, and Na⁺ ions on the resin. The exchanged Ca2⁺ and Mg2⁺ ions may then react with the OH⁻ ions generated by water ionization, forming Ca(OH)2 or Mg(OH)2 precipitates. These precipitates cover the surface of the resin or membrane, clogging the pores and affecting subsequent ion migration, diffusion, and exchange processes, ultimately making it difficult to sustain resin electroregeneration.

The so-called bipolar membrane consists of an anion exchange resin layer, a cation exchange resin layer, and an intermediate hydrophilic layer. Under the action of a DC electric field, it can directly ionize water into H⁺ and OH⁻ ions, which, under the influence of the electric field, form opposing ion currents. Therefore, by inserting a bipolar membrane into the middle of a mixed-bed resin regeneration chamber, it can be divided into two electroregeneration chambers for the separate regeneration of anion and cation bed resins. By sending the failed cation bed resin and the failed anion bed resin into their respective external electroregeneration chambers for a certain regeneration time, fresh regenerated resin with a regeneration degree comparable to that of acid-base chemical regeneration can be obtained.