Ion exchanger swelling

The application of ion-exchange dynamics for the determination of HETP or HTU values should be studied in ion-exchange systems characterized by invariable static and kinetic parameters such as ion-exchanger swelling, electrolyte sorption, separation coefficient, and interdiffusion coefficients in solution and resin phases over experimentally investigated ranges of component variation. 

Changes in ion-exchanger swelling in the course of the exchange process affects the efficiency of countercurrent columns with an alternating mode of phase transfer. If the resin beads increase in size as a result of exchange the efficiency reduces while contraction increases the efficiency of operation. 

J. R. Millar, D. G. Smith, and W. E. Marr, Interpenetrating Polymer Networks. Part II. Kinetics and Equilibria in a Sulphonated Secondary Intermeshed Copolymer, J. Chem. Soc., 1789 (1962). IPNs as ion exchange resins. Kinetics of ion exchange. Swelling behavior in water. 

The first group includes studies of intCTcalation, ion exchange, swelling, and grafting reactions [11,17,42,43], Ha-e the stracture of the silicate layer is considered unknown and is recorded ma-ely in toms of a specified thickness. The detailed structure plays a secondary role to reaction chemistry. 

A tremendous variety of structures is known, and some of the three-dimensional network ones are porous enough to show the same type of swelling phenomena as the layer structures—and also ion exchange behavior. The zeolites fall in this last category and have been studied extensively, both as ion exchangers and as gas adsorbents (e.g.. Refs. 185 and 186). As an example, Goulding and Talibudeen have reported on isotherms and calorimetric heats of Ca -K exchange for several aluminosilicates [187]. 

The degree of swelling and shrinking is important for design of ion-exchange columns, especiaUy for the location of the distributors used to disperse incoming fluids, and coUect outgoing ones, evenly over the cross-sectional area of the resin bed. Once placed, these distributors are not adjustable. The upper distributor should be above (the lower one below) the resin bed, even in the bed s swoUen form. 

Ion-exchange resins swell in water to an extent which depends on the amount of crosslinking in the polymer, so that columns should be prepared from the wet material by adding it as a suspension in water to a tube already partially filled with water. (This also avoids trapping air bubbles.) The exchange capacity of a resin is commonly expressed as mg equiv./mL of wet resin. This quantity is pH-dependent for weak-acid or weak-base resins but is constant at about 0.6-2 for most strong-acid or strong-base types. 

Sephadex. Other carbohydrate matrices such as Sephadex (based on dextran) have more uniform particle sizes. Their advantages over the celluloses include faster and more reproducible flow rates and they can be used directly without removal of fines . Sephadex, which can also be obtained in a variety of ion-exchange forms (see Table 15) consists of beads of a cross-linked dextran gel which swells in water and aqueous salt solutions. The smaller the bead size, the higher the resolution that is possible but the slower the flow rate. Typical applications of Sephadex gels are the fractionation of mixtures of polypeptides, proteins, nucleic acids, polysaccharides and for desalting solutions. 

Swelling The expansion of an ion-exchange W which occurs when the re- active groups on the resin are converted from one form to another. 

As already indicated, ion exchange resins are osmotic systems which swell owing to solvent being drawn into the resin. Where mixed solvent systems are used the possibility of preferential osmosis occurs and it has been shown that strongly acid cation and strongly basic anion resin phases tend to be predominantly aqueous with the ambient solution predominantly organic. This effect (preferential water sorption by the resin) increases as the dielectric constant of the organic solvent decreases. 

Swelling water uptake, electric conductivity, and transport number of the membranes are measured as a function of the ion-exchange capacity (lEC). lEC has been estimated in terms of... 

Pectins is a general term for a group of natural polymers based on polymerized galacturonic acid partly esterified with methanol. In addition these polymers must be considered as copolymers due to existence of neutral sugar branched zones. [1]. Some uronic acid units may also be esterified on 0-2 or 0-3 position with acetic acid. The pectins occur in the cell wall of higher plants and control at least partly the mechanical properties, the ion exchange properties and the swelling of the cell walls. 

Bentonite is an impure clay that is formed by weathering of volcanic tuffs. It contains a high content of montmorillonite. Bentonites exhibit properties such as ability to swell, ion exchange, and thixotropy. Properties can be modified by ion exchange, for example, exchange of earth alkali metals to alkali metals. The specific surface can be modified with acid treatment. Organophilic properties can be increased by treatment with quaternary ammonia compounds. 

The stability of shales is governed by a complicated relationship between transport processes in shales (e.g., hydraulic flow, osmosis, diffusion of ions, pressure) and chemical changes (e.g., ion exchange, alteration of water content, swelling pressure). 

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