Economic Cation-Exchange Membrane (Homogeneous vs. Heterogeneous) for Electrodialysis (ED), CEECEM

In Electrodialysis (ED), the Cation Exchange Membrane (CEM) is responsible for the selective transport of cations (e.g., Na+, Ca^{2+}, Li+) while blocking anions and water. Similar to anion membranes, the choice between homogeneous and heterogeneous structures determines the efficiency, lifespan, and cost-effectiveness of the water treatment or chemical process.

In a homogeneous CEM, the negatively charged functional groups (typically sulfonic acid groups, -SO3^-) are chemically bonded to a uniform polymer backbone. The membrane is a single-phase material. The polymer matrix and the ion-exchange groups are integrated at the molecular level, often created through polymerization of monomers or functionalization of a pre-formed film. It is suitable for high-purity applications, Lithium salt concentration, and energy-sensitive industrial processes.

Heterogeneous CEMs are composite materials. They are made by mixing finely ground cation-exchange resin (like those used in water softeners) with a thermoplastic binder (such as Polyethylene or Polypropylene). It is a "macro-composite" where the active resin particles are physically trapped within an inert plastic matrix. It is suitable for blackish water desalination, wastewater pre-treatment, and rugged environments where the stack might be disassembled and cleaned frequently.

Reference: 

1. M.A. Andreeva, et al., Effect of homogenization and hydrophobization of a cation-exchange membrane surface on its scaling in the presence of calcium and magnesium chlorides during electrodialysis, J. Membrane Sci., 2017, 540, 183-191.
2. László Koók, et al., László Koók, Functional stability of novel homogeneous and heterogeneous cation exchange membranes for abiotic and microbial electrochemical technologies, J. Membrane Sci., 2022, 658, 120705.