Multibed Resin Electroregeneration Technology

Ion exchange water treatment technology has undergone over a century of development and has become the dominant water treatment method in softening and desalination. The advantage of this method is that ion exchange resins can be regenerated and reused using acid, alkali, and salt chemical agents after they become ineffective. However, the environmental pollution caused by resin regeneration urgently needs to be addressed.

During research on the electro-deionization (EDI) process, the authors discovered that in EDI water purification equipment, under the influence of a DC electric field, water is ionized into H+ and OH- ions, which are then used to regenerate the resin filling the bottom layer. Therefore, this portion of resin is continuously electro-regenerated with fresh resin, ensuring excellent effluent quality. This led to the invention of an electro-regeneration method and apparatus for ion exchange resins, pioneering a green regeneration process for ion exchange resins that is pollution-free.

Multi-bed Resin Electro-regeneration

Multi-bed refers to a system where cation and anion resins are placed in separate devices, one a cation bed and the other an anion bed, to distinguish it from a mixed bed where both types of resins are mixed in one device. Compared to mixed-bed resin, the difference in the external electroregeneration device for multi-bed resin 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 bed resin, besides adsorbing most of the Na+ 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.

A bipolar membrane consists of an anion exchange resin layer, a cation exchange resin layer, and a hydrophilic interfacial layer. Under the influence of a direct current electric field, it can directly ionize water into H+ and OH- ions, forming an ion flow of H+ and OH- ions in opposite directions. 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 separate regeneration of anion and cation exchange resins in a mixed-bed regeneration process.