Weak acid cation resins

The organic resin material is often a styrene divinylbenzene (DVB) copolymer in a network or matrix, to which are attached functional groups such as a sulfonic acid, carboxylic acid, and quaternary ammonium. The nature of these groups determines whether the resin is classified as a strong/weak acid (cation resin) or strong/weak base (anion resin) ion-exchanger. 

The benefit of WAC over SAC is the extremely high exchange capacity and lower (almost theoretical) regeneration efficiency. There is some additional cost in capital equipment and higher resin prices, but this is more than compensated for by lower operating costs. Weak acid cation resin capacity is flow-sensitive, so flows must match design criteria. The overall dealk/degasser/BX is the most popular IX process of its kind in the world today, followed by BX/SBA(C1). 

Weak acid cation resins Here, the ionic group is a carboxylic acid (—COOH) and these resins behave as if they were weak organic acids. They have a much higher affinity than strong acid resins for hydrogen ions. Therefore, fewer amounts of acids are required in... 

Ethylbenzene is not the only monomer that can be cross-linked with divinylbenzene to get a cross-linked polymer. By using the addition polymerization process, if methyl propionic acid (see Figure 7.20) and divinylbenzene are cross-linked, it is possible to obtain methacrylic divinylbenzene, a weakly acidic cationic resin (Figure 7.21) [118]. 

Theoretical advance (equilibrium, kinetics, mechanism) Acrylic weak acid cation resins Commercial uranium extraction by ion exchange First UK nuclear power station - Calder Hall Classical chromatography... 

Cation exchangers strong and weak-acidic cation resins... 

Both strong-acid cation and strong-base anion resins are high ionized in water thus, they can work in the entire pH range. The pH does not affect the ion-exchange performances. Conversely, weak-acid cation and weak-base anion resins are more like weak acid (base). For example, their ionization strongly depends on pH. When pH is below 6.0, weak-acid cation resin s performance will be significantly decreased. Similar phenomenon will occur to weak-base anion resin at pH above 7.0. 

The synthesis of weak acid cation resins has been described above. The ability of this type of resin to split neutral salts is very limited. The resin has the greatest affinity for alkaline earth metal ions in the presence of alkalinity. Only limited capacities for the alkali metals are obtained when alkalinity other than hydroxide is present. Effective use is limited to solutions above pH 4.0. 

In Table 9.9-1 both the dry and the wet capacity for some ion exchange resins are given. As can be seen there are no dramatic differences of the capacities dry for strongly or weakly acidic cation resins on the one hand and strongly or weakly basic anion resins on the other hand. The exact capacity is a function of maity parameters (cross-linking, homogeneous gel or macropore stracture, macroreticu-larity) and has to be measured for any resin. As a rule a variety of ions with the concentration in equiv./dm of the species i is present in a solution to be treated by ion exchange, for instance, the cations Na, , N7/4,, ... 

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