Thermally regenerable resins

Comparison of Thermally Regenerable Resins Prepared by Various Routes 111... 

The incorporation of a weak-acid and a weak-base resin into a crosslinked inert matrix or adjustment of the polymerization procedure of a mixture of weak-acid and weak-base monomers (or their derivatives) so that discrete acidic and basic domains would be formed has led to the development of a new class of ion-exchange resins known as thermally regenerable resins which will be discussed in the next section. 

Bolto et al. > have constructed normal-sized beads by including both the required types of groups within one particle so that the diffusion paths for proton transfer are much shorter. Amphoteric resins and snake-cage resins can be considered for use as thermally regenerable resins for the reason stated above, however, their practical disadvantage is their lower performance due to the interaction between carboxyl and amino groups which are in very close proximity to one another. 

Table 10. The influence of the overall plum pudding bead rize on adsorption rates of thermally regenerable resins ...

No-matrix resins, i.e., resins devoid of inert matrix as described by Bolto et al. constitute a novel way of enhancing the capacity of thermally regenerable resins. In the idealized structure of a no-matrix resin, active groups of one type are grouped into domains of size 0.01-5 pm, adjacent to domains of opposite character in porous particles of the conventional size 300-1200 pm. Thermally regenerable capacities up to 2.1 meq/g should be possible in the absence of any diluent. 

In the literature, thermally regenerable resins have also been referred to as composite resins. However, the thermally regenerable resins are dealt with in a separate section as the developments in this new field are quite significant. Mainly, the systematic approach on the manipulation of polymerization procedures to obtain resins having the maximum thermally regenerable capacity is discussed. The Section on composite resins deals with resin systems which incorporate inert materials and magnetic particles. 

As the thermally regenerable resin capacity is strongly dependent on solution pH and, thus, on any water, the pH of the raw feed water must be closely controlled at a particular level, near neutrality. This is particularly important when the raw water has a high concentration of carbonate or bicarbonate alkalinity which act as a competing buffer with the dual weak-acid/weak-base resin. It can therefore be advantageous to remove the alkalinity prior to contacting the resin 223). 

J. Weiss Thermally regenerable ion-exchange resins and water desalination based on them. 1964... 

Parrish, F. W., Sharpies, P. M., Hoagland, P. D. and Woychik, J. H. 1979, Demineralization of cheddar whey ultrafiltrate with thermally regenerable ion-exchange resins Improved yield of a-lactose monohydrate. J. Dairy Sci. 44, 555-557. 

It may be mentioned that some ion-exchange resins having a poly(4-vinylpyridine) matrix partly quaternized with oa-aminoalkyl groups have been prepared and studied with interesting results, as far as their thermal regenerability is concerned 87). This is apparently a recent development of a wide research project on thermally regenerable ion-exchange resins 88>. 

Bolto, B. A. The role of polyamine resins in thermally regenerable ion exchange, in Polymeric amines and ammonium salts, (ed.) Goethals, E. J., p. 365, New York, Pergamon Press 1980... 

Thermally regenerable ion-exchange resins or Sirotherm resins refer to a novel ion-exchange process which makes use of hot water as regenerant A comprehensive... 

Sirotherm is the ICI Australia Limited Trade Mark for thermally regenerable ion-exchange resins and associated plant... 

The research effort in perfecting a resin system capable of efficient performance in a thermally regenerable ion-exchange process can be divided into two distinct phases (j) selection of mixtures of weakly basic and weakly acidic resins as... 

Since the salt uptake process takes place at near neutral pH levels where the proton concentration is very low, the rate of salt adsorption by the resin system is extremely slow The rate-limiting step in thermally regenerable ion-exchange resins is the transfer of protons from the acidic to the basic sites. Rapid reaction rates in these resins have been achieved through the use of different methods. 

Table 8. The influence of the amount and type of polysalt matrix on the rate of salt uptake by thermally regenerable plum pudding resins...

In no-matrix resins, triallylamine is used as the self-crosslinking monomer with methacrylic or acrylic acid as the acidic monomer. The crosslinked resin obtained by polymerizing a mixture of triallylamine and an acidic monomer would be expected to have the sites arranged so that maximum interaction occurs between amine and carboxylic acid groups as shown in Fig. 9 Indeed, such particles have no thermally regenerable capacity and electron micrographs of these products show a uniform gel phase with no segragation of sites into domains. Obviously, measures are necessary to prevent such interactions. Several approaches have been made to minimize the internal salt formation in no-matrix resins these are discussed below. 

Synthetic Ion-Exchange Resins Table 11. The influence of counter-ions on of resins" the thermally regenerable capacity... 

Table 12. Thermally regenerable capacity of resins" prepared by the precipitation approach...

The electron micrographs of no-matrix resins prepared by the precursor method show that there are discrete acidic and basic domains in which the acidic groups are in effect, embedded in a matrix of the polyamine. A possible mode of polymerization is one in which block copolymers are formed as a result of the formation, initially, of a macroradical. The marked dependence of the thermally regenerable capacity of a resin on the solvent suggests that a macroradical may be involved, since their formation and stability are also greatly dependent on the solvent. However, a study of some linear analogues suggests that this is an oversimplified picture. 

The yield of TAA-grafted MA-ABME copolymer depends on (a) total concentration of TAA HCl and MA-ABME copolymer, (b) suspending medium (paraffin oil better than hexane), (c) solvent (dimethylformamide superior to tetrahydrofuran or acetone), and (d) ABME amount in copolymer The best resins prepared by this method using MA-ABME copolymer and TAA have a thermally regenerable capacity of about 0.7 meq/g and an acid-to-base ratio of 1.4. 

Table 13, Thermally regenerable capacity of resins made from heterogeneous emulsion of mono-...

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