Weak Acid Cation Exchange Resins

Weak Acid Cation (WAC) exchange resins are a class of ion exchange resins .

The functional group of weak acid cation (WAC) exchange resins is typically the carboxyl group (–COOH). In acidic conditions, this group remains undissociated as –COOH; In alkaline conditions, the carboxyl group loses a proton (H⁺) and becomes a carboxylate ion (RCOO–), which is its ion exchange state.

Similar to Strong Acid Cation (SAC) exchange resins, WAC resins swap cations for hydrogen ions, leading to a mild increase in acidity within the treated solution. These resins are capable of exchanging with bases such as sodium hydroxide (NaOH) and weak acid salts like sodium bicarbonate (NaHCO₃).

WAC resins are typically classified into two categories according to the structure: gel type and macroporous type:

• In gel-type resins, the beads consist of a uniform gel structure, characterized by high ion exchange capacity, excellent chemical efficiency, robust mechanical stability, and a translucent, pseudocrystalline appearance.
• In contrast, macroporous resins, while offering a slightly lower ion exchange capacity, are distinguished by a bimodal pore size distribution, enhanced mechanical strength, superior resistance to oxidative environments and elevated temperatures, and an opaque, porous structure.

• MC270, Macroporous weak acid cation resin for industrial water deionization and softening

We provide WAC exchange resins for various applications, including water dealkalization, recovery of transition metals, and the purification of antibiotics and amino acids, among others.

• Weak acid cation resins are widely utilized in applications such as demineralization and dealkalization. Their strong affinity for divalent cations makes them particularly effective in removing hardness ions linked to alkalinity.
• Additionally, WAC resins exhibit a relatively high resistance to oxidation and offer mechanical durability, making them suitable for use in streams containing oxidizing agents like hydrogen peroxide and chlorine.

WAC resins with carboxyl groups (–COOH) are prepared through the copolymerization of acrylic or methacrylic acid with divinylbenzene (DVB). Iminodiacetic acid, which is prepared using a chloromethylated polystyrene/divinylbenzene (DVB) matrix, is one of the common functional groups in WAC resins. The iminodiacetic acid structure contains two carboxyl groups (–COOH) and one amine group (–NH), giving it weak acidity. Under appropriate pH conditions, the carboxyl groups can dissociate into carboxylate ions (RCOO–), allowing them to exchange cations in solution. Additionally, the amine group provides extra reactive sites, enhancing the ion exchange capacity of the resin.

The degree of dissociation of the functional groups is similar to that of acetic acid, meaning the ion exchange capacity of WAC resins decreases rapidly as the pH drops. Although WAC resins have a limited range of applications, they are easier to regenerate than SAC resins.