Dry weight capacity

By way of example, a pH titration of a sulfonic acid resin (12% DVB) with sodium hydroxide solution gave the following results from which the dry weight capacity may be calculated ... 

Special applications or experimental studies may require values for dry weight capacity in non-standard ionic forms. In this case the usual method is one of column elution of the swollen resin of known water content, and subsequent analysis of the collected eluate for the exchanged ion. Where simple inorganic ionic forms are concerned the dry weight capacity may be calculated from the measured value in the standard form. 

Of course, should complete ion conversion of the resin be prevented for any reason the calculated capacity will be too high and actual measurement must be undertaken. Table 4.4 shows a comparison of measured and calculated dry weight capacities for different ionic forms of styrenesulfonic acid resins of different crosslinking. 

Table 4.4 Comparison of measured and calculated dry weight capacities of sulfonic acid cation exchange resins...

To estimate an apparent selectivity coelTicient K, p the total exchange capacity of the H form resin in mequiv. per swollen gram is required. This value may be obtained by titration of the swollen resin or from the dry weight capacity DWG (Box 4.5) and the resin water content IF% (Box 4.4), where ... 

The commercial resins have dry weight capacities of 5.0 0.1 eq/kg (typical wet-exchange capacity of Crt = 2.0 eq/L, although this number varies as the degree of swelling changes). These resins are very stable and commonly have 20 or more years of service [6]. 

For a cation exchanger the available capacity is determined by converting the resin to the hydrogen form, then using a neutral solution of a sodium salt to displace H" " ions which are then titrated as free acid by a standard solution of sodium hydroxide. Then if wt of dry resin = Wg NaOH titre = Tml molarity of NaOH = A dry weight capacity = T.A/Wm eq gm . ... 

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