Resins ionic form

Ion-exchange reactions are reversible. A regeneration procedure restores the resin to the ionic form it was in prior to the adsorption step. 

Separate ketdes and backwash towers are frequendy used to convert ion-exchange resins from one ionic form to another prior to packaging, and to cleanse the resin of chemicals used in the functionalization reactions. Excess water is removed from the resin prior to packaging by a vacuum drain. Both straight line filters and towers or columns are used for this purpose. 

Ton-exchange resins are used repeatedly in a cyclic manner over many years, and deterioration of both physical and chemical properties can be anticipated. Comparison of the properties of used resin with those of new resin is helpfiil to learning more about the nature and cause of deterioration (12). Corrective action frequendy extends the life of the resin. Comparison of properties must always be made with the resin in the same ionic form. 

Moisture and Water Content. Resins are thoroughly washed with water upon completion of manufacture and conversion (if necessary) to another ionic form. Excess water is removed by vacuum draining or filtration. Nevertheless, a significant quantity of water associated with the functional groups and adhering to the outer surface of the resin particles remains with the resin as it is discharged into shipping containers. No effort is made to dry the resin, except in a few appHcation areas, since the resins are used in aqueous processes in most installations. 

Silica fouling is the accumulation of insoluble silica on anion resins. It is caused by improper regeneration which allows the silicate (ionic form) to hydrolyze to soluble silicic acid which in turn polymerizes to form colloidal silicic acid with the beads. Silica fouling occurs in weak-base anion resins when they are regenerated with silica-laden waste caustic from the strongbase anion resin unless intermediate partial dumping is done. 

Every analysis performed on columns of this type (for example, carbohydrates, alcohols, organic acids, mixtures of these) can be improved with a column in the most suitable ionic form, even though solutions with compounds of differing types may impose the choice of a compromise. In analytical practice, however, it is not advisable to make an in-column conversion from one form to another, for the resin could shrink or even swell in relation to the type of cation linked. The effect of fixed-cation is made obvious when the compounds under analysis can coordinate with it, as in the case of carbohydrates. For example, the linkage of sugars with three adjacent hydroxyls may be more stable than those that have only two, with obvious effects in the resolution of the analytes. Finally, it is advisable to use a guard column to prolong the life of the... 

Columns are designed to have a larger internal volume than the quantity of resin they will contain. The extra space is to provide the necessary volume for a fluidized bed during backwash. Most units are designed for the space above the resin bed (free-board) to be between 50 and 100% of the packed resin bed. Small columns are, on occasion, designed for one-use applications. Since backwashing is of no importance, there is a tendency to fill the unit with as much resin as possible. That practice can be hazardous, especially if the resin swells as a result of oxidative attack or through conversion from one ionic form to another. 

---