Resins capacity

Resin capacity is an extremely important parameter in ion chromatography. Details of the effect of capacity on the behavior of resins for ion chromatography are found in Chapter 5. Generally, resins of lower capacity will lower the eluent concentration needed to elute sample ions from the column. 

The capacity of a resin is usually given in milliequivalents of exchangeable ion per gram of resin. In some cases it is expressed as milliequivalents per milliliter of resin. High-capacity commercial cation resins contain approximately one functional group 

For anion chromatography, and especially for non-suppressed IC, it is necessary to have resins of low exchange capacity. Earlier work centered on functionalization of macroporous resins produced by Rohm and Haas. 

The resin substrate studied most often in anion chromatography is XAD-1. The substrate has the lowest surface area (100 m /g) and the largest average pore diameter (205 A) of the XAD series. The physical stability is excellent. XAD-1 can be converted to an anion exchanger very easily by chloromethylation, followed by amination with a tertiary amine. 

Anion-exchange resins of variable but low exchange capacities are produced under mild conditions and short reaction times in the chloromethylation reaction. Conditions for the amination are chosen to convert as much of the chloromethyl group as possible to the quaternary ammonium chloride, although experience indicates that some of the chloromethyl remains imreacted. 

The capacities of styrene-based anion exchangers are not so easily calculated because there may not be an anionic group on every benzene ring. Values of 2.5-4.0 meq/g are typical for strong anion resins. 

When the resin is incompletely ionised, its effective capacity will be less than the maximum. If equilibrium between resin and liquid is not achieved, a dynamic capacity may be quoted which will depend on the contact time. When equipment is designed to contain the resin, it is convenient to use unit volume of water-swollen resin as the basis for expressing the capacity. For fixed-bed equipment, the capacity at breakpoint is sometimes quoted. This is the capacity per unit mass of bed, averaged over the whole bed, including the ion exchange zone, when the breakpoint is reached. 

Freed of other restrictions, a mobile ion may be expected to diffuse down any concentration gradient that exists between porous solid and liquid. In the particular case of ion exchange, there is an additional requirement that the resin and liquid phases should remain electrically neutral. Any tendency for molecules to move in such a way as to disturb this neutrality will generate a large electrostatic potential opposing further movement, known as the Donnan potential. 

In considering ionic equilibria, it is convenient to write the exchange process in the form of a chemical equation. For example, a water-softening process designed to remove calcium ions from solution may be written as  

Including activity coefficients y, the thermodynamic equilibrium constant K becomes  

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Amberlite DP-1 2.5 1.17 Methacrylic acid-DVB high resin capacity. Use pH >5. 

Worldwide acetal resin capacity is ca 228,000 t/yr (47). Apphcations are tied to the consumer, apphance, constmction, and automotive markets and will probably grow only as fast as the world economy. Growth rates of 2—10% are projected for various areas (42). 

Companies produce alloys and blends in order to extend their existing resin capacity and product lines without high capital investment and to achieve property profiles required for specific appHcations. 

As we noted above, but a little differently, this step is known as regeneration. In general terms, the higher the preference a resin exhibits for a particular ion, the greater the exchange efficiency in terms of resin capacity for removal of that ion from solution. Greater preference for a particular ion, however, will result in increased consumption of chemicals for regeneration. 

Cross-linking function This adds strength to the resin, so that the higher the CL, the stronger the resin. Capacity drops proportionally as the IX sites are on the VB and are reduced with increased cross-linking. 

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). 

Resin Capacity (cycle 5) (g succinic acid/g resin) (g Capacity (cycle 10) succinic acid/g resin) Glucose capacity (g/g resin) Recovered in first step of base Combined recovery from base and hot water steps... 

In the particular case under examination here, using the flow rates in sections I to IV and the switching time as decision variables, the optimization yielded an optimal resin capacity of 4.3 mEq g-1, assuming a molar fraction of 100 % acetic acid in the feed stream, as shown in Fig. 6.17. 

For a stoichiometric feed concentration of acetic acid instead, the optimal resin capacity was calculated as 5 mEq g-1, which is the original Amberlyst 15 resin. Further optimization, including also the feed concentration of acetic acid as a decision variable, yielded an eluent requirement of ca. 3 mol methanol per mol methyl acetate for a 5 mEq g-1 resin and 60 40 acetic acid methanol feed stream (Fig. 6.17). 

The steep increase of the eluent requirement with decreasing resin capacity can be investigated in more detail by analyzing the key adsorptive and reaction parameters. 

While the selectivity of water/methanol is reduced slightly, and of methanol/ methyl acetate strongly, with decreasing resin capacity, the key selectivities of water/ methyl acetate and water/acetic acid decrease sharply as the resin capacity decreases. 

The positive impact of easier resin and solvent regeneration in sections I and IV at lower resin capacities is, according to Fig. 6.17, clearly dominated by the negative impact of the strongly decreasing key selectivities in sections II and III. 

Table 8.6 Hardness leakage and resin capacity as a function of regenerant salt dosage.

The resin capacity for americium was only a few percent of theoretical due to large concentrations of other polyvalent cations. The resin capacity was increased by adding one to two moles of oxalic acid per mole of iron in the feed. Less than 10% of the iron was retained by the resin. Addition of oxalic acid to both the feed and wash solution effectively separated 98% of the iron as well as >98% of the trace Zr, Nb, and Pu ions. 

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