Ion-Exchange Heat

Fig. 39. High-resolution 29Si (at 79.80 MHz) and I7A1 (at 104.22 MHz) MAS NMR studies of the ultrastabilization of zeolite Y (163) (a) Parent zeolite NH4-Na-Y (b) after calcining in air for 1 hr at 400°C (c) after heating to 700°C for 1 hr in the presence of steam (d) after repeated ion exchange, heating, and prolonged leaching with nitric acid.

Zn, Pb, Bi Ion-exchange Heat resistance alloys, ferroalloys Photometry 2 ppm 146)... 

The recovery and purification of the desired product demands a further breakdown of exergy in the sense of mixing the aqueous feed with (pure) solvents (precipitation and extraction), salts (ion exchange), heat (evaporation and solvent recovery), electrical power (electrodialysis), pressure (filtration and membrane separations), or just extra water (gel filtration). This is shown schematically in Fig. 5. 

The ion-exchange heats in homoionic heulandite were measmed with a microcalorimeter [87R1]. In the case of K, NH4, Na, Mg, Ca, the selectivity of the zeolite was determined by the heat of hydratioa... 

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]. 

In open fibers the fiber wall may be a permselective membrane, and uses include dialysis, ultrafiltration, reverse osmosis, Dorman exchange (dialysis), osmotic pumping, pervaporation, gaseous separation, and stream filtration. Alternatively, the fiber wall may act as a catalytic reactor and immobilization of catalyst and enzyme in the wall entity may occur. Loaded fibers are used as sorbents, and in ion exchange and controlled release. Special uses of hoUow fibers include tissue-culture growth, heat exchangers, and others. 

One ion-exchange process, which was used for several years by Quebec Lithium Corp., is based on the reaction of P-spodumene with an aqueous sodium carbonate solution in an autoclave at 190—250°C (21). A slurry of lithium carbonate and ore residue results, and is cooled and treated with carbon dioxide to solubilize the lithium carbonate as the bicarbonate. The ore residue is separated by filtration. The filtrate is heated to drive off carbon dioxide resulting in the precipitation of the normal carbonate. 

Suspension Polymers. Methacrylate suspension polymers are characterized by thek composition and particle-size distribution. Screen analysis is the most common method for determining particle size. Melt-flow characteristics under various conditions of heat and pressure are important for polymers intended for extmsion or injection molding appHcations. Suspension polymers prepared as ion-exchange resins are characterized by thek ion-exchange capacity, density (apparent and wet), solvent sweUing, moisture holding capacity, porosity, and salt-spHtting characteristics (105). 

Another approach, the so-called seeding technique, provides preferential sites for the nucleation of scale, which permits the heat-transfer surfaces to remain clean of scale. Extensive studies of this technique have been conducted, and field use was reported ia the former USSR as early as the mid-1960s (42). The use of ion-exchange methods is another possible approach. Eor calcium, the exchange can be represented as... 

In order to produce high yields of ester in this manner it is necessary to remove the by-product ammonia (or amine) either by heating or combining with mineral acid, eg, H2SO4 or HCI. Recent work has shown that acidic ion-exchange resins can be used in place of mineral acids for converting sensitive unsubstituted amides (76). The stmctural relationships involved in esterification of amides are shown in Table 2 (77). 

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